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CHAPTER 1.............................................................................................................................10CORROSION.......................................................................................................................10

Electrical Circuit..............................................................................................................10The Chemical Reaction....................................................................................................11

CHAPTER 2.............................................................................................................................14SURFACE PREPARATION METHODS & STANDARDS..............................................14

Dry abrasive blast cleaning..............................................................................................14Abrasives......................................................................................................................15Sizing of abrasives.......................................................................................................17Adhesion and Profile....................................................................................................17Profile...........................................................................................................................18Shot blasted profile......................................................................................................18Profile measurement.....................................................................................................19Assessing a profile to BS 7079 Pt C ISO 8503.1.........................................................23Use of the comparators.................................................................................................23Using the comparators..................................................................................................24Preparation of steel substrate before application of paints and related products.........24Abrasive Blasting Grades.............................................................................................25Equipment....................................................................................................................26Considerations..............................................................................................................26Air Blasting..................................................................................................................27

Water Blasting..................................................................................................................29High pressure water blasting up to 30 000 psi (water jetting).....................................29High pressure water plus abrasive injection.................................................................30Low pressure water plus abrasive injection.................................................................30Steam Cleaning............................................................................................................30Air blasting with water injection..................................................................................30

Hand and power tool cleaning. 7079 Pt A, ISO 8501, SS 05 59 00...............................30Flame cleaning.................................................................................................................31

Method.........................................................................................................................32Pickling............................................................................................................................32Vapour degreasing...........................................................................................................33Weathering.......................................................................................................................33

CHAPTER 3.............................................................................................................................34SURFACE CONTAMINANTS AND TESTS FOR DETECTION....................................34

Test for soluble iron salts.................................................................................................34Test to detect soluble chlorides........................................................................................34Other tests for salts...........................................................................................................35Test to detect the presence of millscale............................................................................35Test to detect the presence of dust on a substrate............................................................36Test to detect the presence of moisture on a substrate.....................................................36Test to detect the presence of oil or grease......................................................................36

CHAPTER 4.............................................................................................................................37SOLUTIONS AND DISPERSIONS....................................................................................37

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Solutions...........................................................................................................................37Dispersions.......................................................................................................................37A suspension....................................................................................................................37An emulsion.....................................................................................................................37

CHAPTER 5.............................................................................................................................38APPRECIATION OF PAINT TECHNOLOGY..................................................................38

1 Binder...........................................................................................................................39Oils...............................................................................................................................39Resins...........................................................................................................................39Linear Polymer.............................................................................................................40Branched polymers.......................................................................................................41Crosslinked polymers...................................................................................................41

2 Pigments.......................................................................................................................413 Solvents........................................................................................................................42Other additives.................................................................................................................42Drying and curing of paint films......................................................................................42Methods used to protect against corrosion.......................................................................45

CHAPTER 6.............................................................................................................................46STAGES OF PIPELINE CONSTRUCTION......................................................................46

Planning............................................................................................................................46Pre construction drainage.................................................................................................46R.O.W clearance..............................................................................................................46Topsoil strip.....................................................................................................................46Pipe storage......................................................................................................................46Stringing...........................................................................................................................47Bending............................................................................................................................47Front end welding............................................................................................................48Back end welding.............................................................................................................48NDT..................................................................................................................................48Coating and wrapping......................................................................................................48Ditching............................................................................................................................48Backfill.............................................................................................................................49Reinstatement...................................................................................................................49Numbering system for pipeline welds..............................................................................49

CHAPTER 7.............................................................................................................................50COAL TAR AND BITUMEN COATINGS TO.................................................................50BGC PS CW AND BGC PS CS3........................................................................................50

Coal Tar, enamel source BS 4164. BGC PS CW1..........................................................51Bitumen enamel source. BS4147 BGC PS CW3............................................................51

Test for bitumen and coal tar.......................................................................................52Using enamels..................................................................................................................52

Brief synopsis of factory coating.................................................................................52Coating with enamels on site.......................................................................................53Procedure for wrapping a butt......................................................................................53

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Considerations for materials........................................................................................54Inspection criteria for attached coatings..........................................................................54

D.F.T............................................................................................................................54Adhesion......................................................................................................................54

Bond test...................................................................................................................54Procedure..................................................................................................................55

Holiday detection.........................................................................................................55Visual checks...............................................................................................................55Repairs..........................................................................................................................55Safety............................................................................................................................56Toxicity........................................................................................................................56

CHAPTER 8.............................................................................................................................57HOT APPLIED TAPES.......................................................................................................57

Use of hot applied tapes...................................................................................................57Factory application.......................................................................................................57Site application.............................................................................................................57Procedure for wrapping a butt......................................................................................57Procedure for wrapping full pipe lengths (mechanical damage).................................58Considerations for materials........................................................................................58

Inspection criteria for attached coatings..........................................................................59D.F.T............................................................................................................................59Adhesion......................................................................................................................59Holiday detection.........................................................................................................59Visual checks...............................................................................................................59Checks on detached film..............................................................................................59Repairs..........................................................................................................................59Safety............................................................................................................................60Toxicity........................................................................................................................60

CHAPTER 9.............................................................................................................................61COLD APPLIED LAMINATE TAPE.................................................................................61

Use of cold applied laminate tapes...................................................................................62Factory application.......................................................................................................62Site application.............................................................................................................62Typical procedure for wrapping a butt.........................................................................62Repairs to existing coating using C.A.L.T...................................................................63Considerations for materials........................................................................................63

Inspection criteria for attached coatings..........................................................................63D.F.T............................................................................................................................63Adhesion......................................................................................................................63Holiday detection.........................................................................................................63Visual checks...............................................................................................................64Checks on detached film..............................................................................................64Repair of C.A.L.T........................................................................................................64Safety............................................................................................................................64

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Toxicity........................................................................................................................64CHAPTER 10...........................................................................................................................65

GREASED BASED TAPES................................................................................................65Factory application...........................................................................................................65Site application.................................................................................................................65

A typical procedure would be......................................................................................65Considerations for materials........................................................................................66

Inspection criteria for attached coating............................................................................66D.F.T............................................................................................................................66Adhesion......................................................................................................................66Holiday detection.........................................................................................................66Visual checks...............................................................................................................67Checks on detached film..............................................................................................67Repairs..........................................................................................................................67Safety............................................................................................................................67Toxicity........................................................................................................................67

CHAPTER 11...........................................................................................................................68COLD APPLIED SELF ADHESIVE OVERWRAP TAPES.............................................68

Factory application...........................................................................................................68Site application.................................................................................................................68

Considerations for materials........................................................................................68Inspection criteria for attached coating............................................................................69

D.F.T............................................................................................................................69Adhesion......................................................................................................................69Holiday detection.........................................................................................................69Visual checks...............................................................................................................69Checks on detached film..............................................................................................69Repairs..........................................................................................................................69Safety............................................................................................................................69Toxicity........................................................................................................................69

CHAPTER 12...........................................................................................................................70POLETHYLENE CLADDING...........................................................................................70




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CHAPTER 13...........................................................................................................................72FILLERS, MASTICS AND PUTTIES................................................................................72




CHAPTER 14...........................................................................................................................74HEAT SHRINKABLE PLASTICS.....................................................................................74




CHAPTER 15...........................................................................................................................76BRUSHING MASTICS.......................................................................................................76




CHAPTER 16...........................................................................................................................78FUSION BONDED EPOXY...............................................................................................78

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Factory application of F.B.E’s.........................................................................................78Site application.................................................................................................................79


D.F.T............................................................................................................................81Adhesion......................................................................................................................81Holiday detection.........................................................................................................82Tests on raw materials (powders)................................................................................82

The gel time test.......................................................................................................82Visual checks...............................................................................................................83Checks on detached film..............................................................................................83

Cure checks..............................................................................................................83Sampling..................................................................................................................83D.S.C........................................................................................................................84Quick methods of cure check...................................................................................85

Repairs..........................................................................................................................86Brush or trowel applied M.C.L’s.............................................................................86Cold applied laminate tape.......................................................................................88Repairs using meltstick............................................................................................88

Safety............................................................................................................................88Toxicity........................................................................................................................88

CHAPTER 17...........................................................................................................................89M.C.L’s URETHANES.......................................................................................................89

Factory application...........................................................................................................89Method.........................................................................................................................90Plural spray pumps.......................................................................................................90

Site application.................................................................................................................90Tie-ins on F.B.E coated lines.......................................................................................90Coal tar enamel............................................................................................................91Considerations for materials........................................................................................91

Inspection criteria for attached coating............................................................................92D.F.T............................................................................................................................92Adhesion......................................................................................................................92Holiday detection.........................................................................................................92Visual checks...............................................................................................................92Checks on detached film..............................................................................................92Repairs..........................................................................................................................92Safety............................................................................................................................92Toxicity........................................................................................................................93

CHAPTER 18...........................................................................................................................94SPECIAL SITUATIONS.....................................................................................................94

CHAPTER 19...........................................................................................................................95INTERNAL COATINGS FOR FITTINGS AND LINEPIPE.............................................95

CHAPTER 20...........................................................................................................................96

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HOLIDAY DETECTION....................................................................................................96Use of the holiday detector..............................................................................................96

CHAPTER 21...........................................................................................................................98HANDLING TRANSPORT AND STORAGE...................................................................98

Handling of pipes.............................................................................................................98Stacking of pipes..............................................................................................................99

CHAPTER 22.........................................................................................................................101CONCRETE COATINGS.................................................................................................101

Considerations for Materials..........................................................................................101Application.....................................................................................................................101

Moulding....................................................................................................................101Impingement..............................................................................................................102Guniting......................................................................................................................102

Inspection considerations...............................................................................................102CHAPTER 23.........................................................................................................................103

DITCHING AND BACKFILLING...................................................................................103Ditching the pipe............................................................................................................103Backfilling of the trench.................................................................................................103

CHAPTER 24.........................................................................................................................104PEARSONS SURVEY......................................................................................................104

CHAPTER 25.........................................................................................................................105TESTING OF PAINT FOR PROPERTIS AND PERFORMANCE.................................105

Viscosity.........................................................................................................................105Kinematic viscosity........................................................................................................106Flow viscometers (Flow cups).......................................................................................107

CHAPTER 26.........................................................................................................................109FILM THICKNESSES.......................................................................................................109

Wet film thickness measurement...................................................................................109Tests done on dry paint films.........................................................................................111

Dry film thickness......................................................................................................111Test panels..............................................................................................................112Calculations............................................................................................................112Destructive test gauges...........................................................................................112Non destructive test gauges....................................................................................113

Adhesion........................................................................................................................116‘V’ cut test......................................................................................................................117Cross cut (cross hatch test).............................................................................................117Dolly test........................................................................................................................117Hydraulic adhesion test equipment................................................................................118

CHAPTER 27.........................................................................................................................119SPECIFIED COATING CONDITIONS............................................................................119

Relative Humidity..........................................................................................................119Dew Point.......................................................................................................................119The Whirling Hygrometer, Aspirated Hygrometer or Psychrometer.............................120

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Steel temperature measurement.....................................................................................120CHAPTER 28.........................................................................................................................121

CATHODIC PROTECTION.............................................................................................121Sacrificial anode systems...............................................................................................121Impressed current system...............................................................................................122Interference....................................................................................................................123Monitoring CP................................................................................................................123Cathodic disbondment....................................................................................................124

CHAPTER 29.........................................................................................................................126HEALTH AND SAFETY..................................................................................................126

Hazard warning symbols................................................................................................126Responsibilities..............................................................................................................127Dräger tube and Dräger bellows....................................................................................128Using the tubes and bellows...........................................................................................129

CHAPTER 30.........................................................................................................................131DUTIES OF AN INSPECTOR..........................................................................................131

CHAPTER 31.........................................................................................................................135LIST OF SPECIFICATIONS AND BS NUMBERS.........................................................135

CHAPTER 32.........................................................................................................................137QUALITY..........................................................................................................................137

Quality assurance...........................................................................................................137Quality control...............................................................................................................137Quality related standards................................................................................................137Quality related definitions (from the above)..................................................................138

CHAPTER 33.........................................................................................................................139REVISION QUESTIONS..................................................................................................139

Paint technology revision questions...............................................................................139Enamels revision questions............................................................................................141Sleeves, tapes and mastics revision questions................................................................143Epoxy resin powder coatings revision questions...........................................................145Urethane coatings revision questions.............................................................................147Revision paper operations other than coating................................................................148Testing of coatings revision questions...........................................................................150Weather conditions revision questions...........................................................................152Corrosion OP revision questions....................................................................................153Surface preparation revision question............................................................................154Surface preparation 2 revision questions.......................................................................155RH and DP exercise.......................................................................................................157

Appendix A............................................................................................................................158Tables.................................................................................................................................158

Table 1 – Preferred methods for the removal of anti-corrosion coatings......................158Table 2 – Surface preparation quality............................................................................159Table 3 – Recommended field applied coatings for the protection of pipewirk and fittings............................................................................................................................160

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Table 4 – Preferred materials for protection of weld joints...........................................161Table 5 – Systems for overwrapping existing pipe coatings..........................................162Table 6 – Systems for coating exposed pipe..................................................................162Table 7 – Repair systems for dry surfaces.....................................................................163Table 8 – Repair systems for damp surfaces..................................................................164

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CHAPTER 1

CORROSION

Corrosion can be generally defined as “Degradation of a metal by chemical or Electro-chemical means”.

From this definition it is obvious that two mechanisms are involved, firstly an electrical circuit and secondly a chemical reaction.

Electrical Circuit

In a corrosion circuit the current is always D.C. (Direct Current). It is conventionally thought that a current passes from positive + to negative -, i.e. from anode to cathode. In fact electrons are flowing in exactly the opposite direction, from cathode to anode. For corrosion circuit to exist three things are needed:

a) Anode

An anode is a positively charged area. It becomes positively charged because the atoms release two electrons each, thus causing an imbalance between protons and electrons, positive and negatively charged units. In it’s passive state, the iron atom has 26 of each, protons and electrons, when the two electrons are released the atom still has it’s 26 protons, but now only 24 electrons. In this state the atom is now an ion, overall positively charged by two units and written as Fe++. (An ion is a charged particle, and can be positive or negative, a single atom or a group of atoms, known as a molecule.) This losing of electrons can be shown as: - Fe Fe++ + 2e. The Fe++ is called a positive iron ion. An ion can be positive or negative and is a charged particle, an atom or a group of atoms.

A passive iron atom Fe 26 protons and 26 electrons.

An iron ion Fe++, 26 protons and only 24 electrons

Figure 1.1 iron atoms

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b) Cathode

A cathode is a negatively charged area where there are more electrons than needed in its passive state. These are electrons released from the anode. At the cathode the electrons enter into the electrolyte to pass back to the anode.

c) Electrolyte

An electrolyte is a substance, which will conduct a current and be broken down by it, (dissociate into ions). Water is the most abundant electrolyte and also very efficient. Acids, alkalis and salts in solution are also very efficient electrolytes. As the electrons pass into the electrolyte it is dissociated into positive and negative ions, as shown by the formula: -2H2O2H+ + 2OĦ. Simultaneously the electrons couple back with the Hydrogen ions to form two full Hydrogen atoms, which join together diatomically to form Hydrogen gas. This is termed as being evolved, or given off from the cathode. The hydroxyl ions return to the anode through the electrolyte carrying the electrons.

The corrosion triangle, as shown below, can illustrate the electrical circuit. The electron circuit can be seen to be from anode A, to cathode C, through the electrolyte E, back to A.

Figure 1.2 The corrosion triangle

The Chemical Reaction

From the above we can see that no chemical reaction, (combination of elements) has occurred at the cathode, or in the electrolyte. The chemical reaction, the formation of corrosion products, only occurs at the anode. The positive iron ions, Fe++, receive the returning hydroxyl ions and ionically bond together to form iron hydroxide, which is hydrous iron oxide, rust, and is shown by the formula: Fe++ + 2OĦ Fe (OH)2 It is now apparent that corrosion only occurs at the anode, never at the cathode. Hence the term cathodic protection. If a structure can be made to be the cathode in a circuit, it will not corrode.

The corrosion triangle shows the three elements needed for corrosion to occur, anode, cathode and electrolyte. If any one of these three is removed from the triangle, corrosion cannot occur. The one most commonly eliminated is the electrolyte. Placing a barrier

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between the electrolyte and the anodic and cathodic areas, in the form of a coating or paint system does this. If electrolyte is not in direct contact with anode and cathode, there can be no circuit, and so no corrosion.

The basic corrosion reaction, as explained above, occurs fairly slowly at ambient temperatures. In common with all chemical reactions certain factors can increase the reaction rate, listed below are some of these.

1 Temperature. Steel, in common with most metals, is thermodynamically unstable. The hotter the steel is the faster the corrosion will occur.

2 Hygroscopic Salts. An hygroscopic salt is one, which will attract water and dissolve in it. When salts are present on a substrate and a coating is applied over them, water will be drawn through the film and the resulting solution builds up a pressure under the film. Eventually the film is forced up to form blisters. These blisters are called osmotic or hygroscopic blisters, and are defined as ‘pinhead sized water filled blisters’. Sulphates and Chlorides are the two most common salts, chlorides predominant in marine environments, and sulphates in industrial areas and sometimes agricultural.

3 Aerobic conditions, (presence of oxygen). By introducing oxygen into the cathodic reaction the number of Hydroxyl ions doubles. This means that double the number of iron ions will be passivated and therefore double the corrosion rate. Shown by :- 2H2O + O2 + 4e 4OH-

4 Presence of some types of bacteria on the metal surface, for example Sulphur Reducing Bacteria, better known as SRB’s, or MEM’s, Metal Eating Microbes.

5 Bi-metallic contact. Otherwise known as Bi-Metallic Corrosion.

Metals can be listed in order of nobility. A noble metal is one, which will not corrode. In descending order, the further down the list the metal is, the more reactive it is, and so, the more anodic it is, the metal loses its electrons to become reactive ions. The degree of activity can be expressed as potential, in volts. The list can be called a Galvanic List, but when the free potentials of the metals are known it can also be called the Electro Motive forces series or the Electro-Chemical series. Below is a list of some metals in order of nobility with potentials as measured using a copper/copper sulphate half cell reference electrode, in seawater at 25oc.

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MATERIAL KNOWN POTENTIAL AV. VALUESGraphite + 0.25 vTitanium 0.0 vSilver - 0.1 vNickel 200 - 0.15 vLead - 0.2 vAdmiralty Brass - 0.3 vCopper - 0.35 vTin - 0.35 vMill Scale - 0.4 vLow Alloy Steel - 0.7 vMild Steel - 0.7 vAluminium Alloys - 0.9 vZinc - 1.0 vMagnesium - 1.6 v

From the list above it can be seen that millscale is immediately above steel on the galvanic list. This means that millscale is cathodic to steel, and if left on the surface of steel will accelerate the corrosion of the steel substrate.

Millscale is formed during the rolling operation of steel sections e.g. RSC, RSA, RSJ. The oxides of iron form very quickly at temperatures in excess of 580c. The first oxide formed is FeO, iron oxide, the next is Fe3O4 and last of all Fe2O3. Common names in order are Wustite, Magnetite and Haematite. These oxides are compressed during the rolling operation to produce blue millscale. The thickness of millscale varies from 25 to 100 um. Because millscale is only produced during rolling, when it has been removed by any surface preparation method, it can never re-cur.

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CHAPTER 2

SURFACE PREPARATION METHODS & STANDARDS

If the products of the corrosion reactions, and other contaminants, were left on a substrate and paint applied over them, the adhesion of the coating and thus the coatings life would be far from satisfactory. Surface preparation involves removing these contaminants, and in some instances increasing the area available for adhesion by roughening up the substrate. A good surface preparation grade (degree of cleanliness) along with a suitable surface profile can give 10 years life from a typical four coat paint system. The same system applied over a substrate with little or no profile and contaminant remaining might give four to six years, or even less.

Therefore two factors need to be considered when inspecting a surface preparation.

1. Degree of cleanliness2. Surface Profile (degree of roughness)

If a specification gives criteria for both of these factors, then quality is not achieved until both criteria are satisfied.

Surfaces can be prepared for paint application in several different ways, each one varies in cost, efficiency, ease and suitability.

a) Dry Abrasive Blast Cleaningb) Water Blastingc) Hand and Power Tool Cleaningd) Flame Cleaninge) Picklingf) Vapour Degreasingg) Weathering

Dry abrasive blast cleaning

Dry abrasive blast cleaning involves compressing air and forcing it along a hose and out of a small aperture called a nozzle. A pressure of 100 PSI results in the air exiting the nozzle at approximately 450 mph. If abrasive particles are mixed in with the air and travel at the same speed, they will carry a lot of work energy. This energy is used in chipping away millscale and other detritus from the substrate. With some abrasives part of the energy is used in shattering into small pieces and with others all the energy is used in impinging into the steel

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surface, roughening the surface and increasing the surface area to increase adhesion properties.

Because all standards refer to the amount of contamination remaining on the surface, the longer the time spent on this operation, the higher the degree of cleanliness.

Abrasives

Abrasives come in many forms and can be classified in several different ways, as shown below.

None metallic (Mineral) expendable

Metallic (Recyclable) Agricultural by-product

Copper SlagNickel SlagBoiler SlagGlass BeadAquamarine (Olivine)GarnetSand

ACI (Angular Chilled Iron)Steel GritSteel ShotGrit and Shot MixGarnet

Walnut ShellCoconut ShellEggshellCorn Cob HuskPeach Husk

It can be seen that the recyclable abrasives are the more costly, and therefore justify a cleansing operation before re-use.

In the context of this course we are considering the following: -

a) Sand

It is not permitted to use sand. SI 1657 states that any mineral used as an abrasive must release less than 1% free silica on impact. (Silica causes preumonicosis or silicosis). COSHH REGS does not allow the use of sand containing silica for dry blasting. Sand itself is perfectly safe, but shattering on impact releases silica which can be inhaled.

b) Copper Slag

Although the name implies metallic content the amount of copper in the structure is extremely minute. Minerals smelted with the copper, liquefy and form a protective cover over the molten copper to prevent reaction with the atmosphere like slag on a weld. When the copper metal is run off the slag is rapidly cooled in cold running water, which causes it to shatter.

The material is supplied in grit form (random, sharp edges, amorphous) and is very brittle,

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shatters into smaller pieces on impact, and should be used only once and then discarded and so classed as expendable.

c) Garnet

A natural mineral classed as being “of a diamond type hardness” can be either expendable or recyclable. If the situation justifies, cleansing units are available to extract contamination so that the material can be reused, usually up to three times. Doesn’t shatter on impact but does suffer some “wear”. Supplied in Grit form.

d) Metallic Grit

In this context, steel and iron are both metallic. Cast steel grit being the softer of the two tends to round off on impact and loses its sharp edges. Angular Chilled Iron chips off small slivers on impact to produce sharp cutting surfaces on its next cycle. The finings so produced are extremely abrasive and cause extreme wear on moving parts of the recovery systems.

Metallic abrasives are recyclable because the particles reduce in size slowly. Hence it can be re-used many times and still perform a useful function in a '‘working mix’. A working mix is an accepted ratio of large and small particles, where the large particles cut the profile and the smaller particles clean out the troughs.

e) Metallic Shot

Shot is spherical and doesn’t shatter (otherwise it would form grit). When supplied the particles are virtually uniform in size and shape, (not a working mix) but like the grit they wear down slowly in size. Regular addition of new abrasive as with grit, will then maintain a working mix. The particles are worn down eventually to finings, and are drawn out of the system during cleansing.

f) Metallic Shot and Grit Mixed

A mix of shot and grit results in a more uniform profile. The grit cuts the profile and the shot, being unable to enter the troughs produced, controls the peak height and so greatly reduces the number of ‘rogue peaks.’ A rogue peak is one, which is well proud of the acceptable profile range, and if painted over due to contraction of the paint, will leave bare metal in contact with the atmosphere, thus allowing corrosion to occur. When rogue peaks are in concentrated area the effect is of a rash, hence rust rashing or rust spotting.

A typical mix ratio of Shot to Grit as used in a pipe coating mill would be 70 – 80 % shot to 20 –30 % grit.

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Other properties of an abrasive have an effect on the resulting substrate also, these being.

Size of the particlesHardness of the materialDensity of the materialShape of the particle

For example steel has a density of approximately 7.6 gm/cc and copper slag, depending on composition, approximately 4.2 gm/cc. If one particle of each material, of identical size, hit a steel substrate, then it would be logical to say that the steel would impinge further into the substrate, resulting in a deeper trough. A spherical particle would not impinge as deeply because the large smooth surface area would use its energy up in peening or work hardening the surface rather than cutting into it. So a shot blasted surface is different in appearance and texture to that of a grit blasted surface.

Sizing of abrasives

G Prefix = Grit amorphous, points and cutting edges, irregular profile.S Prefix = Shot spherical, smoother profile.

The G or S notation is followed by a number, which denotes the particle size. E.g. G24 or S330. From system to system the number can represent vastly different values, e.g. with the now defunct BS 2451 the 24 means nominally 24 thousandths of an inch where as in the SAE system it represents 1/24

" = approximately 40 thou. The new BS ref. 7079 pt E uses a different method again, in metric units. G140 would mean a nominal particle size of 1.4mm

Adhesion and Profile

A commonly used definition of adhesion is: - The force required to separate two surfaces in touch.

A newly rolled plate, perfectly smooth, 1m x 1m has an apparent surface area of 1m2 and an actual area of 1m2. Abrasive blasting roughens the surface and increases the actual area, (the apparent area is still 1m2), thus increasing the adhesion. Two theories of adhesion are: -

1 Molecular Interference. Because the surface is rough and uneven the paint wets, and locks into the profile, analogy Velcro. Physical.

2 Molecular Attraction. Negatively charged particles attracted to positive areas, and vice versa. Analogy Magnet (sometimes called Ionic Bonding). Chemical.

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Profile

Surface profile, anchor pattern, key, peak to trough height and amplitude are all expression meaning the cross section of a blasted area, as measured from the top of the peaks to the bottom of the troughs. The surface profile requirements are given on the specification for the job, e.g. for B. Gas 30 – 75 microns.

Shot blasted profile

Also amplitude, key, anchor pattern, surface profile.

Figure 2.1 Terms relating to preparing surfaces

Other terms relating to preparing surfaces are illustrated below.

Figure 2.2 Shot blasted profile

Hackle – A small surface lamination, which stands upright like a needle after blasting. Approximately ≤ 13 mm. Easily removed.

Lamination – Appears to be a longitudinal ‘crack’, one lip curling back, any laminations (slivers) found must be referred to engineer for ultrasonic check.

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Peak to trough

HackleRogue Peak

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Profile measurement

If a profile requirement is specified, it is the inspector’s duty to ensure that the specification requirements are met. This can be done in two ways.

a) By measuring – using gauges with and without replica tape.b) By assessing – using surface comparators.

a) Measuring

Digital gauges are common nowadays, but refineries, gas plants etc have stringent safety requirements and batteries can produce sparks, so the dial gauges are still very often used. The dial gauges fall into two categories, Surface Profile Needle Gauge and Dial Micrometers and Replica Tape.

i Surface Profile Needle Gauge.

The gauge is applied to the blasted substrate and the needle can be felt to locate a trough. Then by applying a slight pressure to allow the flat ‘foot’ of the gauge to sit firmly on the peaks of the blasted substrate, the needle will pass into the trough as far as it can.

Figure 2.3 Surface profile needle gauge

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Foot

Plane for zero

Distance travelled by needle from zero = profile depth

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In order to measure the difference from peak to trough we need to zero the gauge when the point of the needle is on the same plane as the flat foot, i.e. on a smooth piece of glass.

This is done by applying slight pressure to the foot to ensure that it is perfectly flat on the glass. By loosening the locking screw, the bezel can now be moved easily in any direction. Still applying the slight pressure, the bezel should be moved so that the zero on the gauge is immediately behind the needle, then tighten the locking screw and the gauge is ready for use. When using this type of gauge it is normal to work to an average figure. Several readings are taken, usually more than ten, in random positions over the substrate, and the average calculated. This type of gauge is not ideally suited for curved areas such as pipes.

ii Dial Micrometer and Replica Tape

Replica tape, more often referred to by its trade name “Testex”, is also sometimes called ‘cornplaster method’. Although more costly than the needle gauge this method provides a permanent record and the traceability required from quality systems. The tapes are supplied in two grades: - Coarse Grade and Extra Coarse Grade, to cover two different ranges of blasted profiles.

Coarse Grade for measuring profiles 0.8 to 2 Thou". 20-50umExtra Coarse Grade for measuring profiles 1.5 to 4.5 Thou" 37-115um

The correct tape should be selected otherwise the readings will not be accurate.

Figure 2.4 Cross section of a replica tape

The procedure for using replica tape is as follows

1 Zero the dial micrometer. Clean the anvils (paper or fingers) an d allow the contacts to come together, release the locking screws and adjust the bezel so that the zero is immediately behind the large needle.

2 Remove the backing paper from the replica tape, ensure that the small white disc with the black ring is detached also. Stick the replica tape to the area to be measured.

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Mylar tough transparent Polyester plastic

Testex PastePaper

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3 Using a pen or pencil end, or the specially provided plastic stick, rub firmly and evenly all over the area of the mylar. This causes the testex paste to pass into the troughs and the peaks of the blast will butt up to the transparent mylar.

4 Remove the replica tape and check. The mylar area should no longer be white (now grey), and pinpricks of light should be visible through the mylar when held up to the light.

5 Place the testex paste area between the anvils of the micrometer and allow them too gently close together. From the final reading on the gauge deduct two thou if using an imperial gauge or 50um if using a metric gauge. The balance figure is the peak to trough height of the profile.

Figure 2.5 Metric micrometer for testex measurement in microns

1 mm = 1000 um25.4 um = 0.001" (1 Thou.)40 Thou" = 1 mm25.4 mm = 1 inch

Micrometer is reading 93 um, subtract 50 um for testex plastic backing. The surface amplitude is therefore 43 um

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Figure 2.6 Metric micrometer for testex measurement in microns

Figure 2.7 Imperial micrometer for testex measurement in 1000 of an inch

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1100 mm

10 microns

100 microns

0.10 mm

Micrometer is reading 80 microns (0.080 mm) subtract 50 microns (0.050 mm) for testex plastic backing, the surface amplitude is therefore 30 microns.

Micrometer is reading 4.6 Thou (0.0046"), subtract 2 thou (0.002") for testex plastic backing, the surface amplitude is therefore 2.6 thou (0.0026")

1 10 Thou

0.0001"

1 Thou

0.001"

Testex(allow 2 Thou (0.002") for plastic backing

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Reading the gauges.

There are four common scales for dial micrometers, one of which, the 2um scale is also used on the needle gauge.

The common scales are: -

0.01 mm = 10 microns / small division0.002 mm = 2 microns / small division0.001” = 1 thou / small division0.0001” = 1/10 thou / small division

With all four scales the value given represents the smallest increment on the periphery of the large scale. The small dial at 11 or 1 o-clock position gives the number of complete revolutions of the needle on the main scale. Typically the 2 um scale is 200 um per full revolution. Most profiles are around 75 – 100 um. Therefore the small dial can be virtually ignored for normal use.

Useful conversion factors are: -

1 mm = 1000 um1 thou = 25.4 um

25.4 mm = 1 inch2.54 cm = 1 inch

Assessing a profile to BS 7079 Pt C ISO 8503.1

Grit and shot abrasives produce different surface profiles, therefore two comparators are specified. One for grit blasted profiles, G. and one for shot blasted profiles, S. When a mix has been used then the reference comparator should be G. In all instances the entire area should be blasted to SA21/2 or SA3 grade. (discussed later)

Use of the comparators

There are three methods which can be employed to assess the roughness characteristics of blast cleaned steel.

1 Naked Eye2 Visual Aid, not exceeding 7x magnification3 Tactile(N.B. the comparators are not for assessing cleanliness.)

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The comparators to BS 7079 are approximately 8 cm square with a 2 cm diameter hole in the middle, and are divided into four segments, by smooth strips. On each strip is an arrow indicating the segment number. Segment one is the smoothest and the degree of roughness progressively increases up to segment four.

Using the comparators

With all three methods it is important to remember that the prepared surface should not be touched (contamination). For the tactile method the fingernail or a clean wooden stylus may be used.

The principle is to compare the surface profile of the blasted steel with the segments on the ISO/BS comparator, looking for two segments between whose profile the test surface lies.

The grading used is: -Fine - Profiles equal to segment one and up to, but excluding segment two.Medium - Profiles equal to segment two and up to, but excluding segment three.Coarse - Profiles equal to segment three and up to, but excluding segment four.

Any profile below the lower limit for ‘Fine’ grading is referred to as finer than fine.Any profile above the upper limit for ‘Coarse’ grading is referred to as coarser than coarse.

Because the blasted surface is considered to be a secondary profile, the primary profile is the surface of the steel prior to abrasive blasting. The primary profile is therefore going to have an effect on the secondary profile. It is customary to report on the condition of the substrate before preparation in the following manner.

Preparation of steel substrate before application of paints and related products

Rust Grades. BS 7079 Pt A, ISO 8501, SS 05 59 00

The numbers given all refer to the same book, which gives high quality pictorial standards for condition and cleanliness before and after surface preparation, by abrasive blasting, hand and power tool cleaning and flame cleaning. The steel can then be graded. E.g. B. SA 3, from the definitions below.Rust Grade A - Steel surface largely covered with adherent millscale with little if any

rust.Rust Grade B - Steel surface, which has begun to rust and from which the millscale has

begun to flake.Rust Grade C - Steel surface on which the millscale has rusted away or from which it

can be scraped, but with slight pitting visible under normal vision.Rust Grade D - Steel surface on which the millscale has rusted away and on which

general pitting is visible under normal vision.

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The original rust grade is then given a degree of cleanliness, i.e. a grading relating to how much contaminant is left on the surface after preparation. The degree of cleanliness is mainly dependent on the time spent on the area and the velocity of the particles.

Abrasive Blasting Grades

Before surface preparation commences any oil or grease should be removed (by specified solvent or proprietary degreaser) and heavy rust and scale removed by chipping. After preparation the surface should be free from dust and debris.

Sa 1 - Light Blast Cleaning. When viewed without magnification, the surface shall be free from visible oil grease and dirt and from poorly adhering mill scale, rust, paint coatings and foreign matter.

Sa 2 - Thorough Blast Cleaning. When viewed without magnification, the surface shall be free from visible oil grease and dirt and most of the millscale, rust, paint coatings and foreign matter. Any residual contamination shall be firmly adhering.

Sa 21/2 - Very Thorough Blast Cleaning. When viewed without magnification, the surface shall be free from visible oil grease and dirt and from millscale, rust, paint coatings and foreign matter. Any remaining traces of contamination shall show only as slight stains in the form of spots or stripes.

Sa 3 - Blast Cleaning to Visually Clean Steel. When viewed without magnification the surface shall be free from visible oil grease and dirt, and shall be free from millscale, rust, paint coatings and foreign matter. It shall have a uniform metallic colour.

From the above definitions it can be seen that Sa 1 and Sa 2 are not achievable on rust grade A and consequently there are no photographs for the grades.

The American SSPC and NACE (Steel Structures Painting Council and National Association of Corrosion Engineers) have their own systems and compare as below.

BS 7079 PtA SSPC NACESa 3 White Metal SP5 Grade 1Sa 21/2 Near White Metal SP10 Grade 2Sa 2 Commercial Finish SA6 Grade 3Sa 1 Light Blast and Brush of SP7 Grade 4

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Equipment

1 Wheelabrators

Wheelabrators, sometimes known as centrifugal blast units are a mechanised way of preparing components for coating. They are ideal for long production runs on similar section components such as pipes in a pipe coating mill, or bridge steelwork. They are usually referred to by the number of ‘wheels’ which they operate e.g. 6 wheel. Special machines are designed for special circumstances e.g. flat steel plated for fabrication yards or ship yards, pneumatically driven operator controlled machines for blasting decks or internal tanks, magnetic crawlers for tank externals.

The operators of these machines prefer shot as an abrasive, grit cuts the impellers and entails large amounts of downtime, but when the specification demands, it must be used.

The abrasive is gravity fed into the centre of the wheel. Centrifugal forces carry it to the end of the impeller where it is impelled at the component to be cleaned at a speed of 220 mph app. in a fan pattern. The fast moving metallic abrasive shatters millscale, cuts a profile etc., ricochets and eventually, its kinetic energy spent, drops. The floor of the unit is open grating over a ‘V’ shaped pit, in the bottom of which is a rotating screw which carries the spent abrasive plus detritus into a hopper. A conveyer system then carries the abrasives to the top of the machine, dispenses it, to start a gravity fed path back to be re-used. As an integral part of the system the abrasive passes aver a tilted plated, known as a weir plate. As the abrasive and detritus cascades over the edge of the weir plate, a current of air is drawn through it. This draws out low density materials such as rust, millscale, flakes of paint etc., and finings, abrasive worn so small that it is no longer useful. This is known as an Air Wash Separator, the same principle is used in enclosed grit blasting pens. Meanwhile the cleansed abrasive is fed back into a common hopper with feed lined to all the wheels, to be re-used. As mentioned previously new abrasives need to be added periodically to maintain an adequate working mix.

Considerations

The quality can be controlled by adjusting the feed roller speeds and therefore is more consistent. Because the system is totally enclosed there is efficient use of abrasives.

More operator safety because the operator is not involved.

The systems can be far more productive (dependent on supply of components) than open blasting.

One major problem is access to bolt pockets, gussets and stiffeners etc. Because the wheels are fixed, there is no manoeuvrability, and thus shadow areas arise. One way to avoid this is manually blast difficult areas prior to machine blasting.

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Air Blasting

Site blasting is normally carried out using expendable abrasives and open blasting systems. Open blasting systems operate using.

a) A compressor.b) A pot containing the abrasives.c) Vapour Traps for oil and water (knock out pots).d) A hose, usually carbon impregnated.e) A nozzlef) A dead mans handle for operator safety.

a) Compressor

Compressors are rated by two factors.

i Air pressure – measured in Psi, pounds per square inch.ii Capacity, the amount of air it can deliver at the pressure required, in cubic feet per min

cfm, or litres/min.

It is normal in the UK for portable compressors to be set at 100 psi, which is considered to be the ultimate pressure for open blasting. Air abrasive mix and stand off being constant it is considered that blasting at 100 psi gives 100% efficiency. Using pressures over the 100 psi uses more abrasives, more fuel, more effort from the operator, more work by the compressor, without a proportionate increase in area blasted, where as every 1 psi drop in pressure results in an efficiency drop of 11/2%. 80 psi blasting pressure results in 70% efficiency. Although this is not a responsibility of the inspector it is required information.

It is far better to have a large capacity compressor working below its capacity than to have a smaller rated compressor working to full capacity.

b) Blast Pot

For site work the most common is the pressurised blasting pot. These are supplied in various sizes and are selected according to purpose. E.g. it would not be economical to recharge the pot every 5 minutes when blasting a large crude oil tank. The pots are charged with abrasives and when pressurised, seal, rubber to rubber, by means of a mushroom shaped cap. The abrasive is blown by air pressure into the air stream feeding the nozzle. The abrasive flow can be adjusted by means of a metering valve on the conical base of the pot. This is sometimes called a ‘miser’ valve.

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c) Vapour Traps

Air contains water vapour and when air is compressed the water vapour in the air is compressed.

Compression produces heat and as the air heats up its capacity to hold water increases, every 110C rise in temperature the airs capacity to hold water doubles. Conversely when the air cools rapidly on expansion, exiting the nozzle, water droplets are formed. Should this water contact the substrate, corrosion would result. Also atomised oil (from the cylinder lubricants) needs to be extracted, otherwise low surface energy material, oil, on the substrate will adversely affect adhesion. The knockout pots are on the main airline and are inverted transparent glass domes. A small cock on the bottom allows them to be emptied, and usually are kept slightly open. In the UK climate it is not unusual to blow dowstream 20 gallons of water in an eight-hour working day.

d) Carbon impregnated Hose

Because pressure drops along the length of the hose, line lengths are better restricted to around seven to eight metres. Internal couplings reduce the hose diameter and act as pressure reducers, cause turbulence and wear, so external couplings should be used. Hose diameter is related to nozzle size and should have an internal diameter at least three to four times the nozzle diameter. Any specified blasting pressure refers to pressure as taken at the nozzle. This can be measured using a hypodermic needle gauge. The needle is placed through the hose near the nozzle with the needle facing towards the nozzle.

e) Nozzles

The air consumption and air speed are directly related to the nozzle aperture size. The larger the nozzle size the more air will be needed to maintain pressure. Typically a ¼" nozzle will need 103 cfm to maintain 100 psi, where as a ½" nozzle needs 413 cfm. Therefore big nozzle, large bore hose, needs high capacity compressor. Sometimes the nozzles are lined with tungsten carbide or ceramics to reduce wear.

Various types of nozzles exist including angled nozzles straight bore and venturi. The venturi shaped nozzle give a larger blast pattern with a more even spread of abrasives and higher velocity of the particles at approximately 450 mph. The straight bore nozzle gives a small concentrated area of abrasive contact with a fringe area of lower concentration and particle speed of around 200 mph. The stand off distance for both types varies according to hose size and nozzle aperture size, but an average figure is around 450mm.

f) Safety to 1GE SR 21

With enclosed systems like wheel abrators, personnel passing the equipment are far safer than in site situations, abrasives are confined in a small area. When abrasive blasting is taking

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place on a construction site or pipeline, access is not restricted and vehicles and personnel can be within close proximity of the equipment. It is therefore necessary to have warning signs advising that abrasive blasting is in progress, along with warning buntings segregating the area.

Other safety considerations are.

i The hose should be carbon impregnated to reduce the chance of the operator getting electric shock from static.

ii A dead mans handle should be under direct operator control for his/her own safety.iii Hoses should be kept as straight and as short as possible to avoid kinks, and blowouts

and to maintain pressure at the nozzle.iv Use reinforced hoses if possible.v Use external bayonet type couplings, continually bonded.vi Maintain operating pressure at 100 psi.vii Correct protective clothing should be worn by the operator, including direct air fed

helmet, with adequate visors, leather aprons and gloves, boots and ear protectors.

Water Blasting

Surface preparation methods using water are more environmentally friendly than open blasting and also, from the safety aspect, spark free. They are ideal for removal of soluble salts, sulphates and chlorides, (the hygroscopics) although complete removal needs high pressure ranges. Wet blasting methods are also ideal for removing layers of toxic materials, e.g. read lead, calcium plumbate, and zinc chromate primers. These materials are safe during application but removal by abrasion results in fine particulate matter passing into the air, which can then be inhaled and passed into the bloodstream.

There are certain disadvantages related to wet blasting e.g. supply of large amounts of water and disposal of the resulting slurry (water and detritus as an entity) and also mixing substrate inhibitors if the specification demands it. (Substrate inhibitors are substances usually sodium compounds, added to the water, to retard the formation of corrosion products) Some organisations, including B G do not allow the use of inhibitors, in which case wet blasting is followed by dry blasting, to remove light oxidation.

High pressure water blasting up to 30 000 psi (water jetting)

Using pure water, usually out of a rotating head giving alternating pencil and fan jets. Water usage is about 60 litres per minute. To work efficiently the head must be near to the surface, within 25 to 35 mm, and as the distance increases the efficiency reduces, until at approximately 250 mm only loose and flaking material will be removed.. The principle of operation is simple and flexible, but operator fatigue is a problem. This system will remove

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soluble contamination and millscale at the higher pressure ranges but will not cut a profile. It will only clean up the original profile on rework areas.

High pressure water plus abrasive injection

This system operates at about 20,000 p.s.i. and uses abrasives, either gravity fed into the system, suction fed or mixed as a slurry. Marine growths e.g. barnacles, are easily removed with this system and it us often used in dry-docks on ship hulls. Because of the abrasives a profile is cut using this method.

Low pressure water plus abrasive injection

Uses normal blasting pressures of 100 p.s.i. but with water as a propellant rather than air. The abrasive content is semi-soluble e.g. Sodium Bicarbonate crystals, talc, chalk, and ideal for use on non-ferrous metals and G. R. P. Sodium Bicarbonate is excellent for acidic or greasy situations. This method is very slow and controllable and can if needed, remove one coat of paint. The abrasives have a very gentle action but leave masses of problematic slurry.

Steam Cleaning

Ideal for oily and greasy situations, but steam production requires a heat source, which is not conducive with the oil and gas industry.

Air blasting with water injection

Water is injected, with or without an inhibitor into the air/abrasive stream, either immediately after it exits the nozzle or immediately before it enters the nozzle. Water usage with this method is approximately one to one and a half litres per minute, which is sufficient to control dust.

Hand and power tool cleaning. 7079 Pt A, ISO 8501, SS 05 59 00

Any hand operated or power tools, including needle guns, wire brushes, emery cloth and grinders can be used to achieve these standards.

Hand and power tool cleaning methods are tried and tested over many years, but are now considered to be far less efficient than other modern methods. Limited access or environmental considerations may be factors which influence the choice of methods. Hand and power tool cleaning is often specified for short term maintenance programmes. One major disadvantage of this method is the lack of surface profile. Wire brushing will not produce a profile and in most cases will actually reduce an existing profile, sometimes

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resulting in burnishing, which is polishing, and a smooth shiny area does not provide good adhesion. Burnishing needs to be treated by abrading with coarse emery.

As with abrasive blasting heavy rust, oil and grease need to be removed prior to preparation of the substrate.

St2 – Thorough hand and power tool cleaning. When viewed without magnification the surface shall be free from visible oil, grease and dirt and from poorly adhering millscale rust, paint coating and foreign matter.

St3 – Very thorough hand and power tool cleaning. As for St2 but the surface shall be treated much more thoroughly to give a metallic sheen arising from the metallic substrate.

There are no wire brushing grades for Rust Grade A as the millscale is much harder than the bristles on the brushes, which are of non sparking alloys such as phosphor bronze and beryllium bronze.

If needle guns, jasons hammers, are used they tend to leave a very coarse profile which invariably needs to be reduced by abrading with emery, or grinding.

Flame cleaning

Not likely to be used on oil and gas plants, but it is an approved method of surface preparation, with photographic standards. The BS 7079, ISO 8501 (SS 05 5900) contains four photographs showing flame cleaning standards from the original rust grades A, B, C, D. The designation given is AFl, BFl, CFl, and DFl. There is only one flame cleaning standard for each rust grade.

Three factors contribute to how flame cleaning works.

1. Expansion

All materials have different co-efficient of expansion. I.e. all expand and contract at different rates per degree centigrade rise or fall in temperature. Millscale is chemically bonded to the steel and applied heat causes the materials to expand at different rates, thus breaking the chemical bond.

2. Dehydration

Water in the corrosion products and in the fissures etc. is evaporated away, facilitating the removal of the corrosion products.

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3. Heat penetration

The heat is conducted efficiently into the substrate aiding the drying of the steel and removal of penetrated oil or grease. It is not wise to use this method of surface preparation on any fasteners relying on tension, e.g. rivets, screws, nuts and bolts.

Method

The operator slowly passes an oxygen/HC gas flame (Butane, Propane, Acetylene) over the area to be cleaned, (weld preheat torches or specially adapted lances) to burn and de oxidise the corrosion products and other contaminants. This leaves a grey coloured ash deposit.

A second operator follows on with a power brush to remove the now loose, ash deposits.

The primer can now be applied over the warm steel, reducing the need for addition of thinners. Other benefits are that the heat reduces the viscosity of the paint and gives better flow properties. The paint can then 'wet out' better and pass into tiny cavities and irregularities on the surface. The heat also accelerates the drying process and keeps the steel above dew point temperature.

Pickling

Pickling is a general term relating to the chemical removal of oxides (rust), from a metal substrate. The metals can be either dipped (totally immersed) in the pickling fluid or sprayed with it. Usually aqueous solutions of acids are used for steel, they convert the oxides into soluble salts e.g. Sulphuric Acid produces Iron Sulphate salts. Sulphuric is the most common acid used for economic and safety reasons.

Footners Duplex System involves the pickling process followed by a passivation process using Phosphoric or Chromic acid along with a small percentage of iron filings, which produces Iron Chromate or Iron Phosphate salts, which are not soluble.

These form a rust inhibitive layer, which passivates the surface and increases the adhesion properties. They are also extremely resistant to cathodic disbondment.

A typical process would be: -

1. Any oil or grease needs to be removed by using a suitable solvent e.g. xylene or as specified. Oil and grease show up as fluorescent yellow/green under an ultra violet light.

2. Totally immerse in a bath of Sulphuric Acid, 5 – 10% concentration at a temperature of 65 – 70oc. Time can vary from 5 to 25 minutes depending on degree of contamination but is invariably at the lower end.

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3. Rinse using clean warm water to remove the layer of soluble salts formed. If required the component could be coated after pickling. Likewise components can be blast cleaned and sent on for phosphating/chromating, but the patented process is only called “Footners” when pickled then phosphated/chromated.

4. Immerse in a bath of phosphoric/chromic acid, 2% solution at 80oc for approximately one to two minutes with iron filing (0.5%) (and an inhibitor to prevent embrittlement). This leaves a very thin layer of iron phosphate/chromate, which acts as a rust preventative for a limited time.

5. Rinse in clean water, and check for pH values.

pH is a measure of acidity or alkalinity of a substance and is measured using pH indicator strips. An indicator such as litmus will only tell if a substance is an acid or an alkali. Indicator strips give a measure of acidity or alkalinity, based upon the scale below.

Figure 2.8 pH scale

This is a logarithmic scale and seven is neutral, the pH value of distilled water. From 7 to 0 the acidity increases, and from 7 to 14 the alkalinity increases. A typical requirement after rinsing will be in the region of pH 4.5 to 7.0, slightly less acidic than household vinegar.

Vapour degreasing

Fumes from a solvent bath condense on a component suspended over the bath and dissolve any oil or grease, which then drips back into the bath. Very rarely used because of modern regulations regarding strong hydrocarbon solvents.

Weathering

Weathering relies on co-efficient of expansion properties as mentioned in Flame Cleaning. When left in a stockyard, open to temperature changes, day and night, the millscale sheds. This can now leave the steel open to atmospheric corrosion, which produces such as Sulphate salts.

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CHAPTER 3

SURFACE CONTAMINANTS AND TESTS FOR DETECTION

Any contaminants left on a prepared substrate will effect the adhesion of a coating to that substrate, and therefore specifications often request that certain tests are done to ensure that contamination is within set criteria. Some tests are qualitative and some are quantitative. A qualitative test is one, which give a result as accept/reject, pass/fail, go/no go, whereas a quantitative test is one, which gives a result in known units e.g. milligrams/m2.

Test for soluble iron salts

This is a qualitative test, it will not even differentiate between the salts. It will detect the presence of either Sulphates or Chlorides.

This test is known as the Potassium Ferricyanide test, although it is now under a new universal naming system, known as Potassium Hexa-cyanoferrate, a name more descriptive of its formula.

Test papers, usually Whatman No3 laboratory filter papers are soaked in a 5 – 10% solution of potassium ferricyanide and distilled water, and left to dry. The result is a lime green paper, fringed with an orange brim.

The area of blast to be tested is sprayed with a fine mist of distilled water, (any other water is likely to contain dissolved salts), and left a few seconds to allow the salts, if present, to dissolve and form a solution.

A potassium ferricyanide test paper is then applied to the area and by capillary action draws up the solution like blotting paper.

If there are any dissolved salts they react with the potassium ferricyanide to form potassium ferrocyanide. The ferrocyanide is prussian blue and shows as blue spots on a lime green background.

Test to detect soluble chlorides

The test for detecting chloride salts is known as the Silver Nitrate Test.

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As with the previous test a solution of silver nitrate, 2% with distilled water, is made and the Whatman papers cut into strips.

The strips are then soaked in the solution and pressed onto the area under test for about 20 seconds, then washed in distilled water.

The reaction between silver nitrate and any chloride salts present produces silver chloride, which remains on the strip after washing.

If the strip is then dipped into photographic developer the chlorides show up as black/brown.

Other tests for salts

1 Merkoquant

A salts/water solution is made by swabbing an area of 150 mm x 150 mm with distilled water, 22.5 ml. Merkoquant strips are then dipped into the solution and the resulting colour change is compared to a master chart on the container. The concentration is read off from the chart.

2 Bresle sample patch

Reported as being 95% accurate. An adhesive patch with a rubber diaphragm is stuck onto the surface and distilled water injected and extracted several times to produce a solution of any salts present. By a process of Mercuric Nitrate Titration concentrations of 15 mg/m2 can be detected. A quantitative test.

3 Salt contamination meters

Salt contamination meters measure the resistivity or conductivity of a given sample and convert this value into a concentration (mg/m2).

With any of the above tests, if the amount of salts present is greater than specified, the area should be washed down with copious amounts of clean water, reblasted and retested.

Test to detect the presence of millscale

Millscale being cathodic in relation to steel can cause corrosion cells under a paint film and subsequent early disbondment. Millscale in small quantities is permitted on a SA 2½ blast standard, but not on an SA3. Therefore the test needs to be carried out only if the specification requires an SA3.

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Blasted steel is dark grey in colour and millscale is dark blue, so by naked eye the contrast is difficult. However, if the surface is sprayed with a fine mist of slightly acidic copper sulphate solution, the solution ionises and tints the steel copper colour and blackens the millscale, if present, thus providing a better contrast.

If this test indicates millscale presence then it should be reblasted and then retested.

Test to detect the presence of dust on a substrate

Any dust on a blasted substrate will adversely effect the adhesion of a paint film. In conditions of low relative humidity, dust and finings passing down a blast hose become electro statically charged and stick onto the substrate. Brushing or air blowing the surface will not remove them, self adhesive tape however, will.

If a piece of self adhesive tape is stuck onto the surface and snatched off, the dust/finings sticks to the tape. By then sticking the tape onto white paper the dust can easily be seen.

Test to detect the presence of moisture on a substrate

Presence of moisture, even in the teeniest amount, can affect the choice of paints and if work can be done or otherwise.

A very simple test for the presence of moisture is to sprinkle with talc or powdered chalk and then lightly blow away. The powder will stick to areas where moisture is.

Test to detect the presence of oil or grease

Other than ultra violet light, oil and grease can be detected by dropping solvent onto the suspect area, and absorbing the solution on Whatman or blotting paper. The solvent will evaporate and oil or grease will give a darker appearance.

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CHAPTER 4

SOLUTIONS AND DISPERSIONS

Solutions

A solvent is a liquid, which will dissolve another material, liquid or solid.

A solute is the material dissolved by the solvent.

A solution is the resulting liquid. Salt and water, sugar and water are solutions, a binder and solvent are also a solution.

Dispersions

A paint consists of solid particles suspended in the vehicle, where there is no solubility, so a paint is a dispersion. A dispersion can be either a solid or liquid dispersed within another liquid, where there is no solubility.

A suspension

A suspension is when fine particulate solids, e.g. pigment and extenders are dispersed within a liquid, the vehicle. Ideally after the manufacturing process, each particle should be completely wetted by the vehicle. However because the pigment particles are so small, they cluster together to form agglomerates or aggregates. In some paints, especially gloss, the size of these aggregates is a very important factor and so has to be checked. The aggregate size is known as Degree of Dispersion of Fineness of Grind.

An emulsion

An emulsion is a liquid dispersed in another liquid when there is no solubility. In vinyl or acrylic emulsion, very tiny droplets of resin are suspended within water, which can now be seen to be a non solvent. In an emulsion water is a carrier, not a solvent. Water is called the continuous phase, and oil/resin is called the dispersed phase.

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CHAPTER 5

APPRECIATION OF PAINT TECHNOLOGY

Some aspects of paint technology apply equally to pipeline coatings and site painting. Some coatings commonly used on pipelines specify primers. Some repair systems are based on two pack epoxies and urethanes. Some materials are not suitable for use over others, solvents in a material may have adverse effects on an underlying coating.

It is important, therefore, to have an understanding of the basic concepts of paint technology.

Paints can be divided into three categories.

1 Liquid paints containing solvents

Primers for enamels and tapes fall under this category. By definition a solvent is a liquid that will dissolve another substance, and so water borne materials also fall under this category, but in the context of pipeline coatings the solvents referred to are Hydrocarbon.

2 Solvent free liquid paints

Generally referred to as M.C.L’s, (Multi-Component Liquids). Used widely on pipelines for repairs and, in special circumstances, as a primary system.

3 Powder paints

First used in 1976 and since that, adopted the main coating system for BG Lines. Principally the same concept as solvent free paints, but at room temperatures are particles of solid materials. Powdered materials can be either thermoplastic or thermosetting. Thermoplastic means the material will soften when heat is applied and thermosetting means it will cure when heat is applied.

Paints are formulated to suit various situations and environments, but consist of three main components with minor additives to control or enhance certain properties.

The three main constituents are Binder, Pigment and Solvent.

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1 Binder

The main constituent of the paint or coating, usually chosen for its suitability to resist degradation in certain environments, and its ability to resist the permeation of water, especially for pipeline coatings. Other considerations are ease of application, its ability to provide adhesion to the substrate, to hold the other constituents together in a cohesive film for as long as the system is designed to last. (To provide adhesion the binder must wet out thoroughly over the complete prepared surface, not a problem for liquid paints, but powder paints need to be melted to perform this function). To satisfy the other requirements the material must be able to change from a liquid into a solid coating. Some such materials are Epoxies, Urethanes, Vinyls, Acrylics, Alkyds, Phenolics, Silicones, Natural Oils and Natural Resins and many more. The binder often lends its name to the paint type e.g. Oil paint, epoxy paint etc. All the binder types above are either oils or resins.

Oils

Oils come from the seeds of plants, e.g. linseed, rape seed, olive oil, and because of the mechanism used to change from a liquid into a solid, are totally unsuitable for subterranean or subsea use. These use oxygen from the environment in order to undergo a chemical change and have a relatively short life. Natural oils are slow drying and flexible and are used to modify properties of natural resins.

Resins

Resins can be subdivided into two categories.

1 Natural Resins

Resins derived from trees and plants, e.g. copals, dammars, and coumarones, lac and amber. These materials are fast drying and very brittle and are modified using oils to make oleoresinous paints (a mixture of oil and resin). Natural resins cure by combination with oxygen from the environment, and are not suitable for pipeline work.

2 Synthetic Resins

Some synthetic resins, e.g. Phenolics and Alkyds are made to mimic the properties of natural resins in paint, and by the same token are just as unsuitable for pipeline coatings.

Epoxies and Urethanes however are synthetic resins which will only cure by chemical means, not by Oxygen in the atmosphere. These two materials are ideally suited to a pipeline environment because they provide all the qualities required, especially impermeability.

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All binders which change from a liquid to a solid do so by polymerisation. I.e. they form polymers. A polymer can be described as “a string or structure of repeated units”. The units being mers or monomers, which can be single atoms or groups of atoms called molecules. Polymerisation therefore is the joining together of the string or structure of repeated units. The main elements involved in organic polymers are Carbon, Hydrogen, Nitrogen, Chlorine and Oxygen.

In coating terms there are three main types of polymer, Linear, Branched and Crosslinked.

Linear Polymer

Figure 5.1 Linear polymer

Where each circle is a monomer joined to the next by a single line to form a line (in actual fact many thousands long) of monomers. The line joining each monomer represents an electron bond. Only one line joining the mers together depicts a “saturated bond”. More than one line depicts a double, a triple or unsaturated bond, which incidentally does not occur in a linear polymer when formed, but is essential in the formation of the polymer.

H|

H – C – H|

H

H H| |

H – C – C – H| |

H H

H H| |

C = C| |

H H

CH4

METHANESATURATEDSINGLEBOND

C2H6

ETHANESATURATEDSINGLEBOND

C2H4

ETHYLENEUNSATURATEDDOUBLEBOND

Figure 5.2 Saturated and unsaturated bonds

When the unsaturated molecules are together in correct conditions of temperature and pressure etc. the secondary valency bond (the weaker of the two) releases and joins to another molecule. This reaction repeats until the chain is many thousands of molecules long.

Figure 5.3 Ethylene molecules polymerise

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H H| |C C| |

H H

H H| |C C| |

H H

H H| |C C| |

H H

H H| |C C| |

H H

H H| |C C| |

H H

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When each end closes of with a Hydrogen atom the polymer then has no activity points for further chemical reaction, and so retains this form until destroyed.

Linear polymers in liquid form e.g. primers for enamels and tapes are reversible or non-convertible, which means that when dry, if the solvent is re-added the film will return to its original liquid form. Linear polymers in materials, which are solid at ambient temperature, are thermoplastic, i.e. they soften when heat is applied. Materials in this category are vinyl tapes and polyethylene tapes, polyethylene and polypropylene cladding and neoprene and many more.

Branched polymers

Materials using the polymerisation mechanism are not used in pipeline coating systems but the principle is the same. A linear molecule has two or three double bonds situated near the centre of the line of carbons, so when joining (this time to Oxygen in the atmosphere) the reaction forms a ‘branch’.

Crosslinked polymers

A crosslinked polymer is formed as the result of a chemical reaction and is a three dimensional polymer formation resulting in a strong resilient coating. Chemically curing materials are Epoxies and Urethanes, widely used as repair systems and as principal systems.

Figure 5.4 Crosslinked polymer

2 Pigments

Pigments are added into coating materials for several reasons. They can contribute to film properties in various ways, e.g. aid cohesion, and the durability of the film. Pigments are solid particles, which must be inert and insoluble in the binder and solvent, if a solvent is present. A typical particle size for a pigment is less than 1 um.

There are several pigment classifications but not all are relevant to pipeline materials.

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a) Pigments which provide colour only i.e. Opaque Pigments are employed on pipeline coatings e.g. carbon (black), titanium dioxide (white).

b) Extender Pigments, filler materials such as talc, chalk kaolin and slate dust. Used in binders to aid with inter-coat adhesion and cohesion.

c) Metallic pigments in coatings e.g. zinc and aluminium provide cathodic protection.d) Rust inhibitive pigments, added into primers to provide anticorrosion properties.e) Laminar Pigmentation, leafing pigments, platelets which lie parallel to the substrate and

provide a degree of impermeability.

3 Solvents

Solvent in a coating material improves its application and levelling properties, reduces the viscosity and allows better wetting of the substrate, which in turn will improve adhesion. However, low viscosity materials will not provide high build films.

Other properties of a solvent are rate of evaporation, toxicity, solvent power and flash point.

Other additives

To modify or enhance certain properties of a coating material, other constituents can be added. Among these are driers and anti-skinning agents, used in oils and resins, thixotropes as an aid to storage, antifoaming agents and flow control agents used in powders, and many more.

Drying and curing of paint films

During the drying/curing process a paint changes from a liquid into a solid. It does this by various mechanisms and combinations of mechanisms. The time it takes to undergo this physical change is governed by several factors including temperature. Generally three terms are used to refer to drying/curing temperatures.

a) Air Drying

This refers to normal ambient temperatures.

b) Forced Drying

When heat is needed to effect a cure or accelerate the reaction it is called forced drying, but the temperature range for forced drying is ambient to 65oc.

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c) Stoving

When temperatures above 65oc are used, using ovens or infra red, the term used is stoving.

Industrial paints, with a few exceptions e.g. intumescents, are generally in the air drying category, and the liquid to solid transition is dependant on one of the four drying mechanisms as follows.

1 Solvent Evaporation

Paints employing this drying mechanism are linear polymer materials, sometimes referred to as solution polymers. Solution polymers dissolve in the solvent, when the paint is applied the solvent evaporates away allowing the fully formed linear polymers, saturated, with no activity points, to come out of solution and form a film on the substrate. The polymers lie in a random interlocking pattern, similar to cooked spaghetti or noodles and loosely bond together by “ secondary Hydrogen bonds”. The solvents used by these materials are strong solvents and, when reapplied onto the paints, easily penetrate between the polymers and split the secondary bond, allowing the polymer to go back into solution. Materials, which can do this are, called reversible or non-convertible. Chlorinated rubber, vinyl’s, acrylics, cellulosic materials and laquers fall into this category.

2 Oxidation

Paints using this mechanism form a film by “oxidative cross linking” (polymerisation) using atmospheric oxygen, and in some cases, the oxygen contained in the driers. First of all if a solvent is present, the solvent evaporates away, allowing the oxidation to begin. Oxygen then combines with the unsaturated bonds on the fatty acid esters, progressively linking them together, to form the film. Once the oxygen has reacted with the binder, it has changed the chemical structure of the binder and cannot be removed. These materials are therefore convertible or non-reversible. Because oxygen is in abundance in the atmosphere the reactions continue, ad infinitum, until the materials crack and peel, having formed a very complex cross-linked matrix. Alkyds, Phenolics, natural oils and resins are materials from this category.

3 Chemical Curing

Chemical curing paints need addition of a second material, (in some cases as in moisture curing, water from the atmosphere) but generally the second material, the activator, is supplied in a can, hence the term 2 pack or Multi Component Liquid. In order to obtain the desired film the whole of the contents of both cans should be thoroughly mixed together and instructions on the materials data sheet should be strictly observed. Some materials will require an induction period and most data sheets will state the 'pot life'.

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An induction period is “The length of time after mixing which the paint should stand before use”. Induction time is also called stand time or lead time, and is recommended to allow thorough wetting of the solids. During the induction period the chemical reaction will commence and will be either: -

a) An exothermic reaction. Giving off heat, the container will warm upb) An endothermic reaction. Taking in heat, the container will cool forming condensation.

A typical induction period is 20 – 30 minutes.

Pot life is the period of time after mixing in which the paint must be used, and with industrial paints, dependant on temperature is usually 6 – 8 hours. After the recommended pot life the material becomes very user unfriendly and if in bulk, is quite often subject to spontaneous combustion.

2 pack materials curing agents

Amides – Epoxy curing agents, usually quote seven days to full cross linking at 20 oc.Amines – Epoxy curing agents, three days to full cross linking at 20oc.Isocyanates – Mainly used for urethanes but also for some epoxies where low temperature application is unavoidable, -10oc being typical. Ambient temperature urethanes, especially for pipeline use, quote 16 hours to full cure.

NB. Isocyanates are very toxic and need great care during use.

Chemically curing materials are convertible or non-reversible.

4 Coalescence

Coalescence means to physically join together. In an emulsion the resin droplets are dispersed in the continuous phase, water. Upon application the water evaporates away allowing the resin droplets to come close together until they are touching. At this stage small amounts of high boiling point solvents are concentrated in the voids between the spheres, from where they migrate into the spheres, plasticise them and allow them to fuse together. In so doing they also reduce the Tg of the material (Tg = Glass Transition and is the temperature at which the material changes from a rubbery to a glassy solid, and vice versa). If the Tg wasn’t changed, the resulting film would stay as a liquid and be easily wiped away.

These materials e.g. acrylics and vinyl’s are reversible. It is important to remember in this case that water is not a solvent, but if the true hydrocarbon solvent was used the material would form a solution.

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Methods used to protect against corrosion

A steel substrate needs to be protected against corrosion. Protection can be provided by employing one or more of the systems listed below.

1 Barrier principle. Ideally a thick, impermeable layer of a high electrical resistance.2 The Passivation principle. The surface is passivated by chemical means e.g. by the use

of rust inhibitive pigmentation.3 Cathodic protection. The use of less noble metals as pigmentation in a coating, any

electrolyte permeation, e.g. water, allows a circuit to join so that the pigmentation corrodes preferentially to the substrate.

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CHAPTER 6

STAGES OF PIPELINE CONSTRUCTION

Planning

During the planning stage the route of the pipeline is determined, and access rights are purchased, linepipe ordered and other contractual details dealt with.

Pre construction drainage

Pre construction drainage is often required to keep the area of the right of way reasonably dry and help to prevent the pipeline from becoming in itself, a drain. The engineer and farmer, land owner/agent meet and prepare a pre entry record, with photographs of condition of the land, fences, hedges, walls etc. and if possible a plan of any existing drainage (aslaids). The pre construction drainage is installed on the upside of the planned line, (sometimes both) with the drain three metres inside the demarcation fence line on the subsoil side of the R.O.W or under the topsoil area on the topsoil side of the R.O.W.

R.O.W clearance

Any existing field boundaries are noted and photographed, dry stone walls are manually stripped and stacked to one side, hedges uprooted and flumes laid in ditches, any existing crops are cut and disposed of and suitable stock proof fencing erected, with appropriate gates for access. Typical R.O.W 50 m wide.

Topsoil strip

The topsoil is bulldozed into piles on the East side, (North is always the direction to the end of the proposed line, South is the beginning), leaving a running track for men and vehicles, and room for the trench.

Pipe storage

As the coated pipes are delivered, ready for the construction stage, to the pipe dump, we have the first input from a site coatings inspector. A full record of pipe numbers, lengths, heat

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numbers and existing damages is taken and the pipes stacked in accordance with the specifications.

Stringing

The linepipe is loaded out from the pipe dump and taken out to the spread, easement or right of way are alternative expressions, where the pipes are laid out in readiness for welding together. The inspector should again record all possible information and note where each linepipe is positioned for full traceability. Specification requirements regarding handling and stacking should be rigidly enforced to avoid damage to coating and weld preparation areas.

The pipes are placed on skids (stacks of wooden blocks) and padded and chocked to avoid contact damage and possible rolling off. Longitudinal submerged arc welds should be placed on the top position, alternating between 10 and 2 o’clock.

Each linepipe is strung at an angle of approximately 300 to the intended pipeline to enable access between them. Linepipe would not be placed across farm access track but instead laid parallel to the linepipe on either side.

Figure 6.1 Stringing

Bending

Geographical factors, e.g. hills and valleys may necessitate the bending of a linepipe. An inspector should be present to ensure minimum damage to the coating is incurred. A bending machine is used to perform this operation. This entails a hydraulic ram being used to apply pressure to slightly bend the pipe. The pipe is then moved along and the ram engaged again to extend the bend. An internal mandrel can be used to check the degree of bend. To minimise coating damage, all pipe to shoe contact point should be padded with at least 12 mm of rubber. An aluminium pull through plate can be used to check for ovality. The plate should be 95% of the nominal internal diameter of the pipe. No bending should take place within two metres of the ends of the pipe.

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The pipes are then appropriately marked as Sag bends, Over bends, Left or right bends according to in line position. Pipes can be bent up to about 22.50.

Front end welding

This operation is covered by a welding inspector, not a coatings inspector. The pipes are lifted from the skids by side booms, checked for alignment and a root pass deposited, followed by a hot pass and a first filler, if MMA is being employed. If mechanised M.A.G process is used then two weld passes are deposited. This procedure is repeated until many pipes are welded together, called a string. Each weld is allocated a number in sequence of welding by the front end inspector. Everyone then uses that number for reference.

Back end welding

Again, not the coatings inspectors duty. The back end welders fill in the remaining weld prep area and apply the final cap.

NDT

After the welding operation is completed all butts are subjected 100% to Non Destructive Testing in the form of X-Radiography. Pipes of 750 mm diameter and above are also subjected to M.P.I on internal roots 11 o’clock to 1 and 5 o’clock to 7, top and bottom.

Coating and wrapping

All welds are coated with specified systems after acceptance of welds/repairs by NDT, under inspection by the site coating inspector.

Ditching

The pipe strings are lowered into the trench by side booms. When two strings need welding together, it may be that there is overlap of the two, in which case the excess is cut off, re bevelled and welded. If there is a gap between the two string ends then a P.U.P (Pick-up-piece) is inserted to specified requirements and two welds performed. In both cases the welding would be facilitated by digging a “bell hole”. These welds are called “tie in welds”, in the case of the latter situation the second weld would be the “final tie in weld”. Tie in welds would also be found at RDX’s, RVX’s and RLX’s (Road, River and Rail crossings), as well as in the middle of long sections, typically were two front end crews have been working. A section is the area between two RDX’s.

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Backfill

The areas above and around the pipe are filled and compacted with selected material from the spoil. An inspector should be present at all times.

Reinstatement

After ripping and subsoiling, the breaking up of the compacted “panning” caused by heavy traffic along the running track, the topsoil is replaced. All hedges and walls, gates and fences are replaced or replanted so that the land is, or soon will be, back to its original condition. This is part of the duties of the Agricultural Inspector.

Numbering system for pipeline welds

Two methods of allocating section numbers can be employed.

1 The section from the start AG1 to the first RDX is Section 02 The section from the start AG1 to the first RDX is Section 1

In either situation the welds are numbered in sequence of welding the front end butts, starting at W1.

If crossing a railway or river the first number allocated after the crossing follows in sequence to the last number allocated before the crossing.

The fabrication used to go over or under at the crossing is then numbered as RLX no W1 or RVX no W1. A special fabrication (SF) normally has fittings e.g. forged bends or block valves incorporated and will include more than two welds. These welds are numbered SF1 etc. Repairs are allocated a suffix R e.g. WIR. Re welds are allocated a prefix RW e.g. RWI. A repair on a reweld would then become RWI R. Only a road crossing will alter the section number, then the weld numbers will start again at W1.

The welding inspector records which pipe numbers are welded to which others and the weld number allocated. All pipeline personnel then use that allocated number as a reference.

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CHAPTER 7

COAL TAR AND BITUMEN COATINGS TOBGC PS CW1 AND BGC PS CW3

Coal tar, as a barrier coating, has been in use since before 1680. The first patent on the material was taken out in 1681, re the use of coal tarre and pitch, No 214. Originally the materials used were unplaticised, brittle, and cracked and disbonded at temperatures below 00c. Later, additions of plasticisers meant that better temperature flexibility could be achieved and softening points and penetration resistance could be controlled. When synthetic primers were introduced, adhesion and overcoating properties were greatly improved (original coal tar primers oxidised, went dead and provided no adhesion).

Around the same period of time nearly a century ago the Americans discovered that naturally occurring Bitumen in Trinidad had equally good anticorrosion properties and started using it for coating iron and steel pipes, becoming widely used for transporting oil gas and water subterranean and subsea. Further advancement in technology resulted in the materials further development and subsequently a major coating system for pipelines, and were only superseded as the major system in the mid seventies.

B Gas Transco no longer use the systems but there are many many miles of pipeline, still in service coated with these systems, and an inspector will need to be aware of compatibility aspects if ever they are encountered in tie-in operations etc.

Coal Tar Enamel and Bitumen enamel are covered in different B Gas Specifications and have different BS reference numbers because they are utterly and completely incompatible, and come from completely different sources. Any one will not stick to the other and if mixed when molten, will curdle.

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Coal Tar, enamel source BS 4164. BGC PS CW1

The source of coal tar is coal, a vegetable product. If coal oil (plasticiser) is re-added to coal tar the result is coal tar enamel.

Figure 7.1 Coal Tar, enamel source BS 4164. BGC PS CW1

Bitumen enamel source. BS4147 BGC PS CW3

Bitumen is the end of the distillation chain in crude oil, an animal source.

Figure 7.2 Distillation chain in crude oil

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Coal Tar

Coal oil

Sulphur

CoalHeat Coke

PhenolsTown gas

BenzeneTolueneXylene

Coal Tar Enamel

Heat

Lube oils

Crude oil

Gases

Chemical feed stock

Gasolines

KeroseneDiesels & Oils

Paraffin waxes

Heavy fuel oils

Bitumen (Asphalt)

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The bitumen is oxidised (air blown), paraffin waxes added as plasticisers, result is bitumen enamel.

Extenders in the form of slate flour are added to give bulk to both products. Pulverised coal is sometimes digested into coal tar to give the same effect as “blowing” the bitumen.

Because both materials are incompatible it is necessary to have a test to differentiate between the two, as they are identical in appearance.

Test for bitumen and coal tar

Allow a few drops of strong solvent, preferably Xylene, but toluene or acetone will work equally well, to fall onto a sliver or ball of the enamel placed on white blotting paper or Whatman filter paper or similar. The solvent will dissolve some of the enamel and carry it onto the paper. Bitumen will leave a heavy brown stain. Coat tar will leave a lightly stained Yellow area.

Using enamels

Brief synopsis of factory coating

Larger pipe coating mills would use a production line system whereas smaller units would coat linepipe as individual items. Specifications and dimensions are the same in either case.

1 Prepare the surface by grit blasting to Sa 2½, remove dust etc. by vacuum, clean compressed air or brush. Profile 50.75 um.

2 Apply synthetic, type B, fast drying primer for coal tar enamels and synthetic or bitumen based primer for bitumen enamels.

3 When the primer is dry apply hot enamel at approximately 200 – 205 0c through a flood box onto the 12 o’clock position on the pipe. (The pipe would be slowly rotating and moving forward with plastic spacers separating and protecting the weld preparation area, overwrapped with wax or silicone paper).

4 Simultaneously as the enamel wets the whole of the pipe diameter a reinforcement of fibre glass bandage is fed in at the 6 o’clock position from a creel, tensioned so that the reinforcement embeds approximately half way into the total enamel thickness. As the fibreglass bandage approaches the 12 o’clock position again, further enamel is poured on which fuses with the first layer through the wetted reinforcing bandage.

5 Just outside the flood box area the final wrap of thermoglass is applied (a mineral impregnated outer wrap bandage of the same base material as the enamel. Thermoglass is a trade name but is widely used for this generic material). The base material of the outer wrap fuses with the molten enamel to form a complete homogenous layer.

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Note. All reinforcements and outer wraps our applied in a spiral fashion with a minimum of 25 mm overlap.

6 The spacers and silicone paper is removed and the enamel coating is bevelled back by at least 25 mm, leaving 150 mm at both ends of the pipe uncoated.

7 A colour coded solar protective coating is applied, white for coal tar enamel and blue for bitumen. 300 mm of enamel at each end should be left uncoated.

Figure 7.3 Cross section of coated end

Primer D.F.T = 19± 6 umEnamel D.F.T = 4 to 7 um. 2.4 mm over weldsInner reinforcing to be not within 1 mm of pipe surface

Coating with enamels on site

After the pipes have been welded together on site there will be a certain amount of damage from heat transfer from the weld, and the pipe cannot be rotated. The enamel is melted in a melting pot with a thermocouple build into it for temperature control. The enamel is melted by flame from butane/propane bottled gas and transported by bucket to the butt to be coated.

Procedure for wrapping a butt

1 Blast clean to Sa 2½ removing any damaged or extraneous material over the entire butt. Blast onto sound existing coating 100 mm on either side to provide a key. Profile over the blast cleaned area to be 50 – 75 um.

2 Remove dust and detritus by blowing with clean dry compressed air or by vacuum or brushing.

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15025Solar

reflectiveEnamel

Primer

Reinforcing bandage

Weld prepPipe

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3 Apply appropriate primer by brush to give a D.F.T of 19± 6 um overlapping onto existing coating by 100 mm.

4 As soon as the primer is dry apply one flood coat of hot enamel at the 12 o’clock position overlapping onto primed area by at least 75mm.

5 Apply inner reinforcing in a spiral fashion 25mm overlap, overlapping 75 um minimum onto existing coating.

6 Apply further flood coats.7 Apply outer wrap in a spiral fashion 25mm overlap, overlapping onto existing coating

to provide a neat seal.

Considerations for materials

1 Primers, enamel and substrate should be compatible.2 Enamels will not stick to any plastic e.g. vinyl or polyethylene.3 Temperature of material is critical. Coal tar should not exceed 2600c and bitumen 2400c.

If these temperatures are exceeded the material should be discarded.4 Ideal application temperature range 240 – 2550c for coal tar and 2300c for bitumen.5 In any situation requiring stoppage of work, the heat should be reduced and the material

maintained at approximately 2000c.6 The enamel should be agitated at intervals of less than one hour.7 Coal tar is now known to be carcinogenic. Every conceivable precaution should be

taken to avoid skin contact. Barrier creams, masks and goggles should be worn at all times. It is not practical to erect shelters in the event of inclement weather.

8 Herbicides should be incorporated into bitumen enamels.

Inspection criteria for attached coatings

D.F.T

To be checked using a correctly calibrated ‘banana’ gauge (Magnetic Thickness Gauge). The D.F.T should be a minimum of 2.4mm over welds, a nominal of 4mm over general plate areas, and should not exceed 7mm at any position.

Adhesion

Bond test

The bond test should not be conducted within 24 hours of application of the enamel and is done “at a frequency specified by the engineer”, or when the inspector, having done a tapping test, suspects inherent adhesion faults.

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Procedure

1 Ensure that the enamel temperature is within the range of 50c to 250c.2 Circumferentially, cut two parallel lines through to the substrate 100mm long and

30mm apart, heating the knife blade if necessary.3 Make a longitudinal cut at the lower end to join the two circumferential.4 Insert a flat blade into the longitudinal cut and apply a levering motion downwards.5 The enamel should chip cohesively at the edge and not lift from the substrate nor split

along any layer.

Holiday detection

All areas are subject to 100% holiday detection. The holiday detection should be carried out using DC holiday detector set at 15kv. The maximum voltage setting permitted is 15kv, and BGC PS CW5 recommends 5v per micron, but enamels are an exception.

Visual checks

1 Blisters. Dome shaped projections in the enamel.2 Holes. Caused by escaping vapours, or by impact.3 Bleed through. Bleed through is not a fault, it is an indication that fusion has occurred

between the enamel and the outer wrap. It manifests as small shiny areas where the enamel in the outer wrap has melted.

4 Icicles. Occurs at the six o’clock position on a pipe. It is where excess enamel runs off forming drips, which solidify. Icicles can be incorporated back into hot enamel by operating a canvas or leather sling back and forth on the enamel.

5 Carbonising (coking). Carbonising or coking occurs when enamel is over heated. It appears as a protrusion from the film and when firmly scratched reveals tiny bubbles in a closed cell structure.

6 Cracks. Usually on aged coatings and mainly due to soil stressing. Soil stressing occurs due to variation in temperature and backfill compression etc. leaving a pipe room to expand. Enamels and hot applied tapes (discussed later) are brittle at low temperatures and form a random zig zag crack, usually along the top of the pipe. A typical situation where soil stressing would be expected is the outlet side of a compressor station.

Repairs

Small holes and pinholes can be repaired by moulding in a small plug of enamel, using a heated blade, or by softening adjacent areas and mould to fill the hole.

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Larger areas would now be repaired using more modern technology, such as urethane pitch, to be discussed later.

Safety

Naked flames and other sources of ignition including smoking, should not be permitted near hot material, especially in enclosed areas.

Toxicity

Bitumen and coal tar enamels, when heated, give of fumes, which are now known (especially coal tar) to be carcinogenic. It is therefore necessary to observe recommended safety precautions which may include.

i) Avoid skin contact.ii) Wear protective clothing.iii) Use barrier creams on exposed areas of skin.iv) Maintain good personal hygiene (wash hands, before and after toilet).v) Seek medical advice if warts are found.vi) Avoid, if possible, inhaling fumes.

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CHAPTER 8

HOT APPLIED TAPES

Hot applied tapes consist of a plasticised coal tar or bitumen enveloping a carrier tape of woven nylon or similar synthetic material with an open mesh of approximately 20 x 20. The tapes are approximately 2mm thick, shiny black and flexible enough to form a roll. One side of the tape usually has a thicker deposit of plasicised enamel. This thicker side is placed against the pipe surface to be coated. Hot applied tapes are covered in two BGC specifications.

BGC PS CW2 - cold applied wrapping tapes and tape systems, which covers the technical requirements.BGC PS CW5 – code of practice for selection and application of field applied external pipework coatings.

Like enamels, these materials are no longer used by BG but they are likely to be encountered on tie ins and maintenance work on existing lines.

Use of hot applied tapes

Factory application

These materials are not used for coating full pipe lengths as a principle system.

Site application

Hot applied tapes can be used in two situations on site.

1 Wrapping a butt when two adjoining pipes are coated with the same enamel system.2 Overwrapping an existing enamel coated pipe for extra resistance to mechanical

damage, for example, thrust boring, or at the interface of above/below ground on a riser.

Procedure for wrapping a butt

1 Blast clean the area to Sa 2½, profile 50.75 um using an expendable abrasive. The existing coating should be bevelled back 50mm with the blast pattern overlapping the coating to provide a key.

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2 Apply appropriate primer, synthetic type B for coal tar enamel or a synthetic or bitumen based primer for bitumen enamel, to a D.F.T of 19± 6 um, overlapping onto sound existing coating by 100mm.

3 When the primer is dry apply the tape in a spiral fashion with 55% overlap to give double tape thickness over the area.

4 Overlap the existing coating by at least 75mm ensuring that both the start and finish of the tape is facing in a downward direction to avoid water traps.

Procedure for wrapping full pipe lengths (mechanical damage)

1 Remove any solar protective coating by power wire brushing.2 Remove any oil or grease contamination by swabbing with a solvent. (Care needs to be

exercised during this operation, as the enamels are reversible and extremely sensitive to solvents).

3 Apply the appropriate primer to the full pipe length.4 When the primer is dry apply the tape in a spiral fashion with a 55% overlap to give a

minimum of two tape thicknesses for the length of the pipe.5 On a riser the wrapping should commence at the lower end of the pipe so that the

overlap is facing in a downward direction (like roof tiles).

In all cases the tape is applied by using a blow torch or hot air torch, or any device which will melt the enamel. This is a two man job, one man maintaining tension and the spiral of the wrapping, the other operating the heat source.

The tape is maintained at a tangent to the pipe and the heat applied into the interface angle. As the tape melts it is fused onto the pipe enamel by the spiralling motion applied by the wrapper.


1 Primers, enamels and substrates should all be compatible.2 Neither hot applied tape material will stick to any plastic.3 Lack of attention by the operator can result in the material catching fire or alternatively

not being melted to allow fusion. The main area for this being 6 o’clock and 12 o’clock. Flames are easily extinguished by dousing with water. Under heating remedied by reapplication of heat externally. Fully treated tapes are hard and brittle like enamels. Under treated tapes retain the plasticisers and remain soft and flexible.

4 Because of its brittle nature, like enamels, hot applied tapes are susceptible to soil stressing.

5 The tapes when heated produce irritant and acrid fumes and every conceivable precaution taken to avoid skin contact. Barrier creams, masks and goggles should be worn at all times. It is not practical to erect shelters in the event of inclement weather.

6 Herbicides should be incorporated into bitumen enamels.

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D.F.T

No specified D.F.T requirement.

Adhesion

Usually ‘V’ cut test on butts, at a frequency agreed by the engineer, two per day, or if the inspector has reason to believe that there is a fault.

Holiday detection

Fixed voltage requirement of 15kv as per enamels. 15kv is maximum permitted voltage on site.

Visual checks

1 Blisters. Dome shaped projections in the wrapping.2 Holes. Caused by escaping vapours or impact damage.3 Carbonising. Overheating and burning of the enamel tapes.4 Creases. Caused by incorrect tensioning or wrong angle of spiral, or tape too wide for

pipe diameter.5 Cracks. Usually on aged coatings due to soil stressing.6 55% overlap. Check for correct overlap to ensure two thicknesses.7 Start and finish. Check start and finish to ensure downward facing direction (where

applicable).

Checks on detached film

None specified.

Repairs

Small holes and pinholes can be repaired by moulding in with a hot knife.

Larger areas, overwrap with further layer of tape.

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Safety

Naked flames and other sources of ignition, including smoking should not be permitted, especially in enclosed areas.

Toxicity

Bitumen and coal tar enamels when heated, give off fumes, which are now known (especially coal tar) to be carcinogenic. It is therefore necessary to observe recommended safety precautions, which may include.

i) Avoid skin contact.ii) Wear protective clothing.iii) Use barrier creams on exposed areas of skin.iv) Maintain good personal hygiene (wash hands, before and after toilet).v) Seek medical advice if warts are found.vi) Avoid, if possible, inhaling fumes.

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CHAPTER 9

COLD APPLIED LAMINATE TAPE

Cold applied laminate tapes, C.A.L.T, consist of a plastic carrier tape of P.E (polyethylene) or P.V.C (poly vinyl chloride) one side of which is coated with a layer of sticky mastic. The mastic can be either synthetic rubber or rubber modified bitumen. The superb adhesive properties of the mastics provide an excellent bond to the carrier tape, and to enable it to be rolled it is essential to incorporate a layer of waxed or silicone paper on top of the mastic, to avoid adhesion to the next layer.

Cold applied laminate tapes can be subdivided into two categories, light and heavy duty tapes. There is no set criteria for light or heavy duty and tape manufacturers have freedom of choice. Tape thickness can vary immensely from 0.2mm to 1.0mm with subsequent effect on the performance properties of the tape. Both the mastics and the carrier tape material are thermoplastic in nature and low temperature application renders the tape systems user unfriendly. The minimum application temperature is specified at 50c, and maximum handling temperatures 270c, because the materials are too soft over this temperature. It is common practice to heat up the tapes prior to application in cooler weather.

The BGC Specification numbers which apply to this wrapping system are: -

BGC PS CW2 - cold applied wrapping tapes and tape systems, covering technical requirements.BGC PS CW5 – code of practice for selection and application of field applied external pipework coatings.

Cold applied laminate tapes currently approved for use on a BG Transco pipeline are: -

Light duty tapes

Maflowrap 40/15, Serviwrap –R 15A and Densopol 60

Heavy duty tapes

Maflowrap 50/40 Serviwrap 50/40Maflowrap 65/75 Densopol 80

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Use of cold applied laminate tapes

Factory application

Not a specified system for BG but can be applied by rolling rig. Extra large rolls are supplied, approximately 12m, are correctly tensioned on a creel and geared to traverse along the slowly rotating pipe, to achieve a neat even overlap and constant tensioning.

Site application

Cold applied laminate tapes can be used in most situations on a pipeline. The only limitation is coal tar/bitumen compatibility factors with the rubberised bitumen mastic types.

C.A.L.T are commonly specified for repairing damaged areas on Polyethylene Clad lines, FBE coated lines and lines previously wrapped with C.A.L.T and also on C.T.E coated lines, (compatibility considered).

Cold applied laminate tapes are specified as a preferred system for coating butts on many pipe to pipe coating systems. Ref. table four CW5. E.g.

Polyethylene to F.B.E, M.C.L, C.T.E, Polyethylene.C.A.L.T to F.B.E, M.C.L, C.A.L.T, Polyethylene.

Also specified as a second option on the following systems.

M.C.L to F.B.E, M.C.L.C.T.E to F.B.E, M.C.L, C.T.E.

The materials suitability for use in this wide range of situations stems partially from its tolerance of substrate surface preparation standards. BGC PS CW5 supplement CA/13 states surface preparation to either Sa 2½ grit blast, or wire brush to St2 or St3, according to the preference of the engineer.

Typical procedure for wrapping a butt

1 Prepare the area (according to specified method and standard), overlapping onto existing sound coatings to provide a key.

2 Remove dust and detritus by brushing or blowing with clean dry compressed air.3 Apply primer (as supplied by the tape manufacturer) by brush to recommended

thickness, overlapping onto existing coatings by 100mm.4 Apply the tape in a spiral fashion with 55% overlap to ensure two tape thicknesses over

the area, starting and finishing in a downwards facing direction, overlapping onto existing coating by 75mm minimum.

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Note. When wrapping a butt where polyethylene cladding is involved, due regard should be paid to the following. When the butt is welded, heat conducts through the pipe steel and melts the end of the polyethylene, causing the tensioned polymers to pull in and “pucker”. This forms a raised, hard ring around the pipe diameter. Before any surface preparation commences the “puckering” should be removed by cutting with a sharp knife. The cut should be done neatly, evenly, circumferentially, leaving an even chamfer.

Repairs to existing coating using C.A.L.T

Surface preparation as specified, prime using material supplied by the tape manufacturer. When the primer is dry apply the C.A.L.T in a spiral fashion with 55% overlap. According to the size of the repair, a minimum of one and a half turns is required to ensure starting and finishing in a downward facing direction.

Note. Patches of C.A.L.T are not recommended for repairs.


1 There are no incompatibility problems other than bitumen enamel.2 Because of their thermoplasticity they are prone to damage in warmer temperatures.3 They have little resistance to mechanical damage (thrust boring).4 Rubberised bitumen mastics are susceptible to microbiological attack and should

incorporate appropriate biocides.5 The materials should preferably be stored in cool conditions to avoid flow of mastic,

but may benefit from warming prior to application.


D.F.T

No specified D.F.T but will be required in order to set correct voltage for holiday detection.

Adhesion

Not before 24 hours have elapsed. Done by V cut test. Two per day specified by the engineer, one a.m., one p.m. Random or “if the inspector has reason to believe”.

Holiday detection

Voltage set according to thickness, using the formula 5v per micron, to a maximum of 15kv.

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Visual checks

1 Blisters. Dome shaped projections in the film.2 Creases and folds. Bad application techniques or incorrect tape width.3 Over tensioning. Will result in ‘necking’, a narrowing of the tape, usually accompanied

by blue or grey longitudinal streaks and excess mastic squeezed from the tape edge.4 Surface preparation. Light abrasion should be visible at primer edge.5 Primer. Primer should be visible at tape edges.6 55% overlap. Should show as a regular slightly raised ridge at the edge of the tape.


None specified.

Repair of C.A.L.T

Overwrap (sometimes contra wrap) with further layer of C.A.L.T, 55% overlap with a minimum of one and a half turns, starting and finishing in a downward facing direction

Safety

Operators should wear gloves and other precautions as per site requirements.

Toxicity

No known significant hazards.

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CHAPTER 10

GREASE BASED TAPES

Application to BGC PS CW5, technical requirements to BGC PS CW2

Grease based tapes consist of a woven synthetic bandage coated with petrolatum grease, with other minor additives e.g. inhibitors and some times moisture displacing additives.

Grease based tapes are chemically compatible with all coatings in current use and are tolerant of very low standards of surface preparation. Unfortunately grease based tapes do not provide a stand alone system of pipeline protection, and need to be used in conjunction with self adhesive overwrap tapes. Grease based tapes, because of their mouldability, are often used to coat areas of difficult access, e.g. on small service pipes, but still give better performance if overwrapped.

Because this type of material is compatible with all known pipe coating it is one of a few which is suitable for coating a butt when the two adjoining pipes are, one bitumen and the other coal tar enamel.

Grease based tapes currently approved for use are: -

Denso tape, PAM 105 and Serviwrap G45A

Factory application

Not applied in a factory.

Site application

BGC PS CW5, table four refers to grease based tapes, as an option (not preferred method) for Polyethylene to F.B.E, M.C.L, C.T.E and Polyethylene. The tape can be folded and moulded to give a chamfer on polyethylene cladding and likewise on old enamels. Other uses include valves, flanges and items of complex shape where advantage can be taken of the mouldability of the material.

A typical procedure would be

1 Remove any loose rust and dirt by specified method to the required standard (any firmly adhering paint in good condition is not a problem).

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2 Remove dust and any moisture by compressed air or swabbing.3 Apply by brush, paste type primer, overlapping existing coating by 100mm.4 Apply grease based tape in a spiral fashion with 55% overlap, overlapping onto existing

coating by 75mm minimum. (Assuming easy access, in other situations the tape would be moulded from small patches).

If a coating of pipeline quality was required e.g. Bitumen to Coat Tar Enamel coated pipe butt, then a further clause would be added.

5 Apply an overwrap of P.E or P.V.C self adhesive tape overlapping onto sound existing coating by a further 50mm, in a spiral fashion with an overlap of 25mm or 55%, at the discretion of the engineer. The overwrap to be terminated by one full turn back on itself.

Note. When the last clause is applicable, using the grease based primer would leave only 25mm of the original coating at each end for the overwrap tape to adhere to.


1 At normal temperatures the grease is non drying, but at elevated temperatures will form a crust due to slow distillation.

2 It has no mechanical strength and needs overwrapping to stop migration.3 High standards of surface preparation are unnecessary.4 The material is tolerant of damp or moist surfaces.5 Very simple to apply

Inspection criteria for attached coating

D.F.T

No specified requirements

Adhesion

No specified requirements

Holiday detection

Not done unless the tape is overwrapped.

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Visual checks

Check for adequate, even coverage.


None specified.

Repairs

Easily affected by addition of further material.

Safety

No hazards known

Toxicity

No hazards known.

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CHAPTER 11

COLD APPLIED SELF ADHESIVE OVERWRAP TAPES

Application to BGC PS CW5, technical requirements to BGC PS CW5

This classification of tapes is supplied in a wide variety of tape widths and colours. The main tape is of P.E or P.V.C coated with a very thin layer of pressure sensitive adhesive. (Pressure sensitive means the tighter the tension, the better the adhesion). These tapes have the appearance of insulating tapes, nothing like cold applied laminate tapes, which have the interleafing wax paper. They are not a stand alone system and are used to stop migration of, for example, fillers mastics, putties and grease based tapes.

Materials currently having approval for use include: -

Scotchwrap No 50 Sellotape 1408 Rotunda Allweather 2901Denso P.V.C Sellotape 1408 Maflowrap 20/10

Factory application

Not applicable

Site application

Surface preparation is not required because the tapes are used for overwrapping other systems. Primers are usually recommended except when applying over grease based tapes. The tapes are applied neatly, spirally 55% or 25mm overlap (at the discretion of the engineer) terminating the wrap with one full turn back on itself.


1 No problems of compatibility with any coating used.2 Best suited for use on smooth surfaces such as F.B.E, Polyethylene and M.C.L’s. Will

not bond efficiently to roughened surfaces with pits and imperfections e.g. enamels. In this case for the overwrapping of a grease based tape wrapped joint, it is far better to use it than not.

3 The tapes are sufficiently flexible for easy application and are less likely than other tape types to be affected by soil stressing.

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D.F.T

No specified requirements. Done for Holiday detection setting.

Adhesion

No requirement. (No adhesion over greased based tapes)

Holiday detection

Voltage set at 5kv per mm of coating thickness to a maximum of 15kv.

Visual checks

Check for neat business-like appearance of completed job.


None specified.

Repairs

Apply further layer of self adhesive tape.

Safety

No hazards known

Toxicity

No hazards known.

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CHAPTER 12

POLETHYLENE CLADDING

Factory application to PS CW4 – Polyethylene cladding on steel pipe, dealing with steel pipes up to 450mm nominal bore.

Polyethylene cladding cannot be applied on site to butt joints. A medium to high density yellow polyethylene (dependant on polymer length) is applied over a mastic by extrusion.

Nominal thickness for the polyethylene is 1.3mm and for the mastic 0.15mm, the tolerances allow an absolute minimum dimension of 12½% below this nominal figure.

Factory application

Pipes are prepared by specified method, usually grit blasting and flood coated with hot mastic at approximately 2000c. Immediately following this operation the pipe is passed through a circular die (a cross head extrusion die) which is extruding a continual sheath of polyethylene. The pipe is not rotating as in enamel coating. Immediately after the die cold water is sprayed onto the polyethylene, which contracts and tightly envelopes the mastic. Profiled rollers push back any entrapped air pockets.

Site application

Not applicable


1 The material is thermoplastic and ‘puckers’ when heated to near melting point.2 The linear polymers are stretched during application and tend to line up in one

direction. Damages tend to split longitudinally.


D.F.T

Not applicable, done at factory.

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Adhesion

Having the mastic undercoat adhesion is not a problem.

Holiday detection

Special voltage of 10kv

Visual checks

1 Blisters. Dome shaped projections usually air filled.2 Damages. Usually seen as areas of exposed black mastic.


Not applicable.

Repairs

BGC PS CW5, table seven recommends in order of preference.1 Cold applied laminate tape.2 Heat shrinkable plastics.3 Grease based tapes (overwrapped with self adhesive overwrap tapes).

Safety

No hazards (in its solid form).

Toxicity

No hazards.

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CHAPTER 13

FILLERS, MASTICS AND PUTTIES

Field application procedures to BGC PS CW5Technical requirements to BGC PS CW2

Fillers, mastics and putties are used for modifying contours to facilitate the use of wrapping tapes, typically on valves and flanges and ‘T’ pieces.

Usually supplied in a variation of mediums e.g. cans, bags and specially designed extrusion devices they can be easily matched for compatibility with existing coating and tapes to be applied over them.

Materials currently approve are: -Denso Mastic Servicised Moulding PuttyDensyl Mastic Servicised G45A Mastic

Factory application

Not applicable

Site application

Surface preparation carried out as specified, apply primer, when primer is dry, apply mastic/putty by gloved hand, moulding to the required contour. Knives and trowels can be used but the material is better moulded by hand. The whole is then overwrapped with the specified tape system.


1 Compatibility with existing coating and overwrapping tape to be used to be considered.2 Where bitumen is involved the materials should contain biocides.3 Working temperature of the component should be considered.


D.F.T

Only for Holiday detection setting.

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Adhesion

No requirements, materials will migrate under pressure.

Holiday detection

Voltage settings according to formula specified in CW5, 5v per micron up to a maximum of 15kv.

Visual checks

Check for smooth contour to facilitate overwrapping.


Not applicable.

Repairs

Repair using same material.

Safety

No hazards known, usual precautions e.g. gloves.

Toxicity

No hazards known

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CHAPTER 14

HEAT SHRINKABLE PLASTICS

Application as per BGC PS CW5

Heat shrinkable plastics have worldwide applications both onshore and offshore. In terms of BG Transco, heat shrinkables are mentioned in only one context, for the repair of polyethylene cladding and even then, only as a first option, not the preferred method. Ref. CW5, table seven.

Heat shrinkable materials can be supplied in many forms, as wraparounds or tapes and pre expanded sleeves. Pre formed sections are supplied for flanges, bends, weld on tees and many more. Other variations include soft mastic lining with interleaving polythene and grafted co polymer adhesive, which melts when heat is applied.

Approved currently as suppliers are: -1 Raychem2 Canusa

Factory application

Not applicable

Site application

Because of the wide ranging materials and variations available, a single procedure would not suffice but typically assuming a wraparound sleeve with a closure strip.

1 Clean the area to be coated as specified.2 Remove any dust/detritus as specified.3 Preheat the area using e.g. a propane torch, until above the dew point or warm to the

touch.4 Remove the plastic cover and wrap the sleeve loosely around the pipe. (Printed arrows

or logo line will indicate direction of shrink). Position the overlap to facilitate easy access for the closure strip. E.g. 12 o’clock.

5 Use the yellow flame to heat the closure strip evenly and apply to the overlap neatly. No bubbles or creases.

6 Beginning from the centre of the sleeve apply heat circumferentially using a constant uniform motion.

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1 If using tapes ensure correct direction of shrink.2 Apply primers only if recommended.


D.F.T

Not specified

Adhesion

V cut in the event of suspicion.

Holiday detection

Special voltage setting of 15kv

Visual checks

1 Blisters.2 Burnt or puckered areas.3 Ensure firm edges with overlap onto sound coating.


Not specified.

Repairs

No method specified, dependant on specification.

Safety

Leather gloves, goggles, hard hat (local government regulations)

Toxicity

No hazards stated

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CHAPTER 15

BRUSHING MASTICS

This category of materials used to be called brush applied compounds and fall under BGC PS CW5 field application procedures, BGC PS CW2 for technical requirements. The products are not mentioned on CW5 T4 (protection of welded joints), but do appear as table six (exposed pipe) and table seven, repairs for dry surfaces.

After primer application two coats of the high viscosity mastics will normally be needed to build to a specified minimum D.F.T of approximately 500 um. The primer and the main mastic coating will be of different colours e.g. reddy brown and black.

Materials of this category currently approved for use are: -

1 Plasgard 2001 & Longcote 300 (primer)2 Denso Metrosol Mastic & Denso 1340 (primer)

Factory application

Not applicable

Site application

Brushing mastics are specified for use in a variety of situations, typically valves and flanges, on risers to protect above/below ground interface from damage due to lime stone chippings, and in valve pits.

Surface preparation will be as specified according to the situation. Primer application by brush over the entire prepared area to give a specified D.F.T of approximately 25 um, the primer overlapping onto sound existing coating by 100mm. A typical drying time at 200c is approximately one hour. After appropriate drying time the mastic is applied by brush, evenly, overlapping onto existing coating by 75 mm. After recommended drying time of approximately four hours apply a further coat of mastic to build up to the minimum specified D.F.T of approximately 500 um.

Recommended drying times for the materials are for the Metrosol mastic a minimum of 24 hours, for the Plasgard a minimum of 48 hours. If the coated component is to be buried, then it is recommended that a drying time of seven days be allowed for Plasgard material.

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1 The mastics will not adhere to plastic tapes and polyethylene cladding.2 The dried material is fairly brittle but is easily repaired using the same material.3 Tapes will adhere to mastic surfaces.


D.F.T

Use correctly calibrated magnetic gauge to check for minimum D.F.T, no area to be below specified minimum.

Adhesion

No specified requirements but if necessary, V cut test.

Holiday detection

Set to minimum specified D.F.T using the formula 5v per micron. 500 um = 2.5kv.

Visual checks

Check for misses, voids, correct overlap etc.


None specified.

Repairs

Apply further material after abrasion.

Safety

Site regulations apply.

Toxicity

No known hazards.

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CHAPTER 16

FUSION BONDED EPOXY

Fusion bonded epoxy (F.B.E) sometimes called R.P.C, resin powder coatings, are used in the field on butts, when both adjoining pipes are coated with F.B.E. Fusion bonded epoxy powder is virtually a premixed two pack epoxy which is solid at room temperature, in powder form. Each particle in theory contains all components necessary to effect a full cure when the powder is melted into a liquid. Two B. Gas Transco specifications deal with powder coatings.

BGC PS CW6, specification for the external protection of steel pipelines and fittings, using resin powder and associated coating systems.Pt 1 – Requirements for materials and methods of test.Pt 2 – Factory applied coatings.

BGC PS CW5, code of practice for the selection and application of field applied external pipework coatings.

One material which is approved for use on all parts of a pipeline is Scotchkote 206 N, made by 3M (Minnesota Mining & Manufacturing) and an applicator of the materials approved by BG Transco is P.I.H, Pipeline Induction Heat.

Factory application of F.B.E’s

Linepipe and fittings are coated in the factory prior to despatch to site. Different application techniques are used dependant upon the steel thickness variations. Linepipe is even wall thickness for the 12m length, whilst a blockvalve will have several areas of the casting with a quite substantial thickness of steel which will result in irregular temperatures if the same method of heating is employed.

Fittings, e.g. valves and bends and ‘T’ pieces are therefore heated in an oven over a longer period of time before coating.

Any oil or grease present is removed by swabbing with a solvent, usually xylene, or as otherwise specified, e.g. proprietry degreasers.

The components are then blast cleaned to Sa 2½ with a profile of 50 – 100 um using grit shot mix of metallic abrasives (factory). The surface is inspected for slivers and any found are reported to the engineer for Ultrasonic Testing. If sufficient wall thickness remains the engineer will give permission to remove the sliver by grinding and the area is then reblasted.

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Linepipe sections will then progress through a series of induction coils (very rare occasions gas flames) to heat up the steel. Any weld preparation areas are masked off to leave an uncoated area of 40 ± 15 mm back from the root face at each end of the pipe. The pipe then passes into the coating area where it is coated electrostatically. The powder is sprayed through an area of ionised air, which charges the powder positively. The pipe is earthed into the circuit by means of a wheel on the internal surface of the pipe. The pipe then becomes negatively charged and attracts the positively charge powder particles onto its surface. The powder melts instantaneously and starts its cure reaction. As the thickness builds it insulates against the attraction of further particles, which are then attracted to other areas. The epoxy thickness can be controlled by the voltage potential of the system, and the speed of the pipe passing through the coating area.

Components such as bends etc. can be coated in various ways after removal from the ovens. Some components are suspended from a rotating hook and manually sprayed with powder, giving extremely irregular thicknesses, 1500 um being not uncommon.

Another method for coating these components is called the Fluidised bed. By passing air through powder in a container, the particles separate and achieve freedom similar to the molecules in a liquid, giving the appearance of a liquid, hence fluidised. The components are then immersed into this container, sometimes electrostatically, charged and coated.

The specified D.F.T should be 350 – 500 um with a nominal thickness of 400 um, for factory application.

Site application

F.B.E application on site is only done on the welded joint between two pipes when both of the pipes are factory coated with epoxy powder. The process is done in three stages, one immediately following on from the previous stage, i.e. preparation by blast cleaning, followed immediately by heating with an induction coil, and finally the powder application.

It is customary for the equipment needed for all three operations to be carried on one vehicle, this enables immediate access to the previously treated butt in its ideal condition. E.g. the induction coil can move onto a grit blasted butt within minutes of completion. As soon as the butt reaches the required temperature the rig moves on a further butt allowing access for the coating equipment.

Each individual operation is carried out as follows.

1 Preparation of the butt

If necessary the area is degreased by using a suitable solvent, typically xylene. An area of 250mm on either side of the weld, should be degreased in this way. Any burnt and damaged

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epoxy from the welding process should be removed and the bare steel area of the butt should be blasted to Sa 2½ with a profile of 50 to 100 um, using an expendable abrasive. The blast pattern should encroach onto 30mm of sound coating on either side of the butt, to provide a key, and the edge of the existing coating should be chamfered.

The area should be inspected for slivers and loose and disbonded areas of coating. Slivers to be ground and reblasted (with the engineers approval). Loose and jagged areas removed, reblasted and re chamfered by approximately 15mm.

2 Heating the butt

The blast cleaned area of the butt must be at Sa 2½ quality with no rust blooming or degradation when the induction coil is started. The induction coil is clipped in place and started. Operating at site voltage of 110v the induction coil runs on AC supply. The copper strips which constitute the coil do not heat up and radiate heat onto the butt, they conduct the AC current which sets up a field causing the molecules in the pipe steel to agitate, and their friction causes the heat. The time taken depends upon factors such as the starting temperature of the steel, the pipe wall thickness, and the pipe diameter, and can result in times of one to eight minutes, but would typically be four to five minutes.

The butt will be heated to a temperature above the powder application temperature to allow for a “heat decay”, the temperature drop before the powder application starts. A typical temperature, as specified by the engineer would be 2530c, measured by tempil stick or contact thermometer. Tempil sticks would be the preferred method. (Tempil sticks are temperature indicating crayons which melt when a specified temperature is reached, guaranteed to be within ± 1% of temperature indicated on the crayon).

Prior to heating a small mark is made on the steel with the tempil stick approximately 10mm. When the wax mark melts the temperature required has been reached and the coil should be stopped. The operator should then ensure that the molten mark is removed (by wire brushing) before the coating operation commences. The butt temperature should never be allowed to reach the blue temper stage, 3000c, when the mechanical properties of the steel can be affected. Exceeding the 3000c would result in a “cut out”. Therefore the inspector should also be in possession of a tempil stick which should not melt at a temperature below 3000c. Ideally warning notices should be displayed to warn personnel that the pipes are hot.

3 Powder Application

When the butt temperature drops to the specified powder application temperature range, the powder application can commence by using either a manual or semi automatic method. The specified temperatures will be stated on the materials data sheet and would be in the region of 2180c to 2460c. The steel temperature, would be taken at 12 o’clock and 6 o’clock positions, the latter being the coolest place on the line.

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Semi automatic systems usually consist of two application heads, manually operated through just over 1800 on either side of the pipe, with the application positions being diametrically opposed. The powder is fed through flexible lines and ejected onto the hot pipe, where it melts and cures in approximately three minutes. Because the pipe is continually cooling and chemical cure rates are temperature dependent the powder needs to be applied in as few passes as is possible to avoid differential curing. A typical number of passes would be six and a typical butt coating time approximately two to three minutes.

The operators should check that sufficient powder is available to coat a butt before the operation commences, and some equipment has a suction reclaim facility. The reclaimed material should not exceed 25% of material in the application container.

The CW5 supplement, CA8 gives a minimum specified D.F.T requirement of 400 um, over the entire blast cleaned area of the butt. No maximum is given but economics will dictate.


1 F.B.E cannot be applied over any other coating material, nothing else can stand the temperature.

2 If the finished product is to be exposed to UV it will require solar protective coating.3 Raw Material Storage. The powder needs to be stored in dry conditions. Containers

should not be damaged and material exposed to sunlight or water. The material has a stated shelf life which should not be exceeded so batches should be used in date order or first in first out (FIFO). The powder is also susceptible to compaction sintering so boxes should not be damaged. It is also advisable to have a quarantine area.


D.F.T

Minimum D.F.T requirements are specified on both pipe lengths and butts. D.F.T’s on butts should be done at ambient temperatures using correctly calibrated magnetic thickness gauges. Six readings to be taken spaced equidistantly around the butt. Any areas found to be under thick are repaired by approved methods or by recoating.

Adhesion

At a frequency agreed by the engineer, usually two per day, one on a morning and one in the afternoon. ‘V’ cut test allowing no peeling.

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Holiday detection

Done 100% at ambient temperature using the formula, 5v per micron. Holiday detector needs only to be set a minimum D.F.T stated = 400 um = 2kv.

Tests on raw materials (powders)

F.B.E’s are thermosetting materials and in common with all thermosetting materials the cure rate is temperature dependent, the higher the temperature the faster the cure to final crosslinking.

The curing graph follows an exponential curve, i.e. every 100c rise in temperature, the chemical cure rate doubles from the previous 100c, hence the “differential cure” in powder application.

During its transition from powder to solid film the material passes through four stages.

1 Flow time, from powder to semi liquid, less than one second.2 Wetting time, from powder to liquid, approximately one second.3 Gel time, from powder to start of solidification, approximately 46 seconds.4 Cure time, from powder to completion of crosslinking, approximately three minutes.

From these four stages, the gel time is a very important property of a powder paint. After the stated gel time the material can no longer wet out over the surface to provide adhesion, so if a material deteriorates in any way and the gel time shortens then the performance can be severely adversely affected. If a gel time test indicates that the gel time is below the time specified on the data sheet, then the material should not be used on the pipe.

The test is conducted as follows: -

The gel time test

1 Heat up a hotplate to stated temperature, usually 2040c.2 Apply ½ to 1gm of powder to cover an area 3 – 5 cm2.3 Simultaneously start a stopwatch when powder strikes the plate.4 Stir the epoxy (which should now be liquid) with the spatula and keep lifting from the

wet film. After a few lifts the liquid will retain its peak, at this point stop the watch. This is the gel time.

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Visual checks

1 Pinholes, could be escaping gas or water vapour.2 Contamination. Specks of foreign matter in the film.3 Orange peeling. Usually under thick, viscosity problem.4 Over cure. Brown cast to material.5 Under cure. Sickly green appearance.6 Staining. Could be non-removal of tempil stick mark.7 Detachment. Lack of surface preparation.8 Lack of chamfer. Original coating should be adequately feathered.9 Weld toes. Undercut and cold lap will have uncoated areas.10 Excess weld cap height. The vertical face will have little or no cover.

Note. Weld defects (the last two) cannot be dealt with by the coatings inspector and should be reported to senior personnel.


Cure checks

Checks to ascertain the degree of cure of the epoxy coating are carried out on all procedure butts, (first ten on a pipeline), and then one per day, or one per 100 butts, whichever is the most frequent.

The quantitative test used by BG Transco is the D.S.C, the Differential Scanning Calorimeter, a laboratory test used to determine the degree of cure of a coating applied onto a butt.

The test determines the Tg, the glass transition temperature which can be defined as “the temperature at which the material changes from a glassy solid to a rubbery solid”. Tg is a “thermal characteristic” of the cured epoxy.

Sampling

The inspector or engineer selects a butt and takes a sample from the 6 o’clock position, on the parent plate area of the coated butt. The sample size should be no more than 10mm x 10mm = 1cm2, and should be taken by use of a small hammer and chisel, ensuring no damage is done to the pipe steel. Any indentation is a possible crack propagation point. Ideally a colleague should hold a clean tissue or linen handkerchief under the sample area to collect the slivers of epoxy (material falling onto the spread will be contaminated). The sample should then be put into a small sealable polythene bag and labelled with the following information.

1 Epoxy batch number.2 Section number.3 Correct butt number.

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4 Pipe number.5 Position of sample.6 Date of sample.

The sample area should then be repaired (see repairs later) as specified, and holiday detected after the time lapse recommended by the manufacturer of the repair material.

D.S.C

The manufacturer of the powder provides a trace of the D.S.C’s done under ideal conditions. The D.S.C’s traces obtained from the samples from the pipe butts are then compared to the manufacturers.

Under ideal laboratory conditions the Tg of the cured powder should be at 100% cure, if the Tg of the raw, uncured powder is known then the temperature difference between the two can be apportioned into a percentage value. E.g. raw powder Tg = 1000c, cured epoxy Tg = 1050c, sample from pipe Tg = 1040c would represent 80 cure.

The sample taken from the pipe is micronised and a sample size of 10 –15 milligrams is placed into a reference cup and heated prior to the test, to dispel any moisture present. The heat source is then activated giving a known heat input to raise the temperature by 200c per minute, and a trace is activated to record the reaction temperature in the cup. A line passing in an upward direction represents an exothermic reaction and a downward line represents an endothermic reaction. (Exothermic = giving off heat, Endothermic = taking in heat).

A trace from a sample taken from a pipe should not show an exothermic reaction, this would represent an uncured coating.

Two runs are done on each sample, Run 1 and Run 2, providing two Tg values, i.e. Tg1 and Tg2.

On each run the material is given the chance to cure further and so theoretically the Tg2 should be on, or nearer to, the ideal laboratory Tg, than is Tg1. So the criteria is given as Tg2 should be within –2 and +50c of Tg1.

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Figure 16.1 Typical powder manufacturers graph

Tg’s shown as shift in baseline due to temperature density changes.

Figure 16.2 Powder sample not cured

Quick methods of cure check

1 M.I.B.K swab test

Soak a lint free swab in M.I.B.K (Methly-Iso-Butyl-Ketone) and rub for 30 seconds on material to be assessed for cure. If there is no colour transfer from the epoxy onto the swab the epoxy is deemed to be cured.

2 Buchholz indentor and microscope

The buchholz indentor is a block of steel weighing one kilogram. Approximately 25mm thick x 100mm x 50mm. A slot cut into the front houses a ‘glass cutter’ shaped wheel 30mm

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Temperature heating rate 200c/minute

End

othe

rmic

Exo

ther

mic

H

Tg raw powder

Tg post cure run

Original powder trace

Post cure trace

Temperature

H

Residual exotherm

Temperature

Run 1

Run 2 H

Tg2

Tg1

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diameter. Two small feet are on the underside of the block spaced so that when the block is placed in position there is 500gm point load on the wheel contact.

Figure 16.3 Buchholz indentor

Method

i) Apply the buchholz onto the surface and leave for 30 seconds.ii) Remove and measure the indent length using the microscope (in the kit).iii) Convert indent length to hardness figure from tables in BS 3900 E6.iv) Apply an M.I.B.K swab to immediately adjacent area. Leave for one hour.v) Apply buchholz to the swabbed area and leave for 30 seconds.vi) Remove the buchholz and measure the second indent length.vii) Obtain a second hardness value from E6.

Criteria

If hardness value two is 85% or more of hardness value one then the material is deemed to be sufficiently cured.

Repairs

Repairs on resin powder coatings (for dry surfaces) can be done in several ways. Table seven from CW5 gives, in order of preference.

1 Brush or trowel applied M.C.L’s.2 Light or heavy duty C.A.L.T’s

Brush or trowel applied M.C.L’s

M.C.L’s can be either epoxy or urethane. Both products come supplied in a variety of forms, cans, tubes and blister packs, but always involve mixing the components together in correct

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ratios. Some of the materials are designed to cure quicker than others and so have very short pot lives with very exothermic reactions, and so are only used on small areas.

Repairs on areas up to 1cm2 (10mm x 10mm)

Abrade using coarse grade emery or wire brush.Remove dust and detritus by wiping or blowing (clean dry air).Repair using quickset materials.Holiday detect after recommended time lapse.

A typical quickset material for this category of repair would be a blister pack urethane or interpon quickset epoxy (tubes). Blister packs are two components separated by a plastic sealing strip. The strip is removed and the components worked together by squeezing. When thoroughly mixed (no colour streaks) a corner is cut from the pack leaving a very small aperture through which the urethane can be dispensed by squeezing onto the repair area.

Interpon quickset is supplied in tubes the contents of one being white and the other yellow. Equal amounts from each tube are mixed thoroughly until no streaking is evident and the material is of a uniform consistency, and then applied onto the repair area using a scraper of filing knife or similar to give a smooth raised area of approximately 600 um D.F.T. The manufacturer of this material quotes: -

Base resin pack A – Yellow contentsActivator resin pack B – White contentsMixing ratio 1:1 V:VPot life 5 minutes @ 200c

Hard dry 1 hour @ 200c

Full crosslinking 7 days @ 200c

Repairs on areas over 1cm2

Blast clean to Sa2½ removing a further 10mm of sound coating from around the area.Clean the area by blowing with clean dry compressed air.Repair by using two pack repair material.Holiday detect.

This type of repair is done using either epoxy or urethane, as specified, supplied in cans. Pack A, base resin and pack B activator resin are mixed together thoroughly, by emptying the total contents (scrape out using a spatula or similar) of pack B into the space left in pack A. The total contents are then thoroughly mixed, mechanically preferably, or by a flat, square ended stirrer until a homogenous liquid (no streaks) is achieved. It is then applied by brush or trowel onto the repair area.

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A typical material in this category is Interpon Repair Compound and the manufacturer quotes: -

Base resin pack A - 500ml can containing 200ml yellowActivator resin pack B - 250ml can containing 200ml whiteMixing ratio 1:1 V:VPot life 1 hour @ 200c

Hard dry 12 hours @ 200c

Full crosslinking 7 days @ 200c

All the repair material M.C.L’s are solvent free, and solvent should never be added to them. Solvents are permitted for cleaning tools and equipment only.

Cold applied laminate tape

Repairs on F.B.E Lines can be done using C.A.L.T, but only, by specification, of full circumferential repairs. (It may be worthy of not that C.A.L.T can be used on the butts of an F.B.E coated line when grit blasting cannot be done, and wire brushing is the alternative).

Repairs using C.A.L.T are performed in the standard way, by abrasion (onto existing coating) and primer application, the tape is applied in a spiral fashion with a 55% overlap, starting and finishing in a downward facing direction.

Repairs using meltstick

Meltsticks are not specified and not used for repairs now, but it is considered that an inspector should be aware of them.

Meltsticks are in the form of an oval cross section approximately 10 x 6mm of varying lengths, quire flexible and of thermoplastic type material. By applying a lighted match, cigarette lighter to the end of the stick, it melts and then can be rubbed onto the repair area. Some other specifications allow their use on polyethylene and polypropylene and other polyols.

Safety

When working with the powder form it is advisable to avoid inhalation, (wear masks), and refrain from smoking. When mixed with area the powder is inflammable. Site safety regulations would apply.

Toxicity

No known hazards in its solid form.

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CHAPTER 17

M.C.L’s URETHANES

Urethane M.C.L’s have two specified uses on a pipeline. Firstly for coating tie in welds on a pipeline when the powder coating machinery may have difficulty accessing, and secondly for patch repairing of damaged areas on coal tar enamel. CW5 T7, repair for dry surfaces, gives M.C.L’s as the preferred method with grease based tapes as first option.

Urethane M.C.L’s are two pack components consisting of a base material of urethane or polyurethane, and coal tar or pitch, and a curing agent of isocyanates modified in various ways. The modification give different properties e.g. some materials can cure at very low temperatures –200c slowly but effectively, some will cure underwater with no adverse effect, some cure by using moisture from the atmosphere. However the ones used on BG Transco pipelines are extremely moisture sensitive.

These two pack urethanes have a very high viscosity base material and very low viscosity isocyanate curing agent, and should be mixed mechanically, sometimes preheating may be required to slightly lower the viscosity. It is advisable with some materials to mix at approximately 400 r.p.m to avoid air entrapment and mixing should be done as quickly as possible as the material has a very short pot life, about 10 minutes at 200c. Both components are blackish in colour and therefore homogeneity is the only sign of adequate mixing. Because isocyanates are extremely toxic, urethanes are supplied in two grades, brushing and spraying. Protegol 32-10 is a common spray grade urethane and Protegol 32-10L designed for brush trowel application.

All these materials are solvent free and solvent should never be added, for any reason, without written consent from the manufacturer.

They should comply with BGC PS CW6 Pt1. Some materials currently approved for use by BG Transco are: -

Protegol 32-10 Acothane DebrathaneProtegol 32-10L Durathane Versathane

Factory application

In a factory the urethanes would normally be spray applied using typically Protegol 32-10 spraying grade. The application conditions applicable to this material are very strict, regarding both its sensitivity to moisture and the toxicity of the urethanes curing agent, isocyanates, (spraying is not allowed in the open due to atomised isocyanates passing into the atmosphere).

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Application constraints will require that urethanes cannot by applied (this applies to factory and site with brushing grades) during fog, mist, rain or snow or when the surface is wet. The air or metal temperature must not be within 30c of the calculated dew point temperature, and the air or metal temperature must not be below 100c. a typical R.H constraint would be not more than 80%, although some manufacturers say 70%.

It is permissible to erect shelters and use dehumidifiers and heaters to ensure these constraints can be met, and maintained for the required period.

Method

Grit blast to Sa 2½ with a surface profile of 75 – 100 um (no primers are used so a coarser profile is needed for adhesion). Apply urethane tar using a plural pump system to a minimum thickness of 1mm, unless BG Transco specify otherwise. Chemical cure time is temperature dependant but will be around eight hours at 200c, (heating the pipe would accelerate this time but must not be done without engineers permission). The newly coated piece should not be handled if damage is likely to occur and the coating must not be allowed to be in contact with water within this cure period, which, regardless of the manufacturers recommendations is 24 hours for BG Transco.

Plural spray pumps

Two or more airless spray pumps are metered to pump fixed ratios of base and activator into a mixing baffle. The containers are heated (in jackets) to facilitate the flow and accelerate the cure. In the mixing baffle the components thoroughly mix and pass along a short line to the spray gun, for application. Before the baffle the components are stable, but upon mixing the cure starts. If for any reason spraying has to stop, the pumps are stopped and a solvent pumped into the baffle to clear the system from the baffle onwards. If this is not done and the material starts to gel, the baffle, line and spray gun are rendered useless. Before spraying can recommence the solvent supply must be shut off and the system flushed through to remove all traces of solvent.

Site application

It is normal to use the brush/trowel grade for site work Protegol 32 10L, although spraying can be carried out subject to constraints of the previous paragraph.

Tie-ins on F.B.E coated lines

Blast clean to Sa 2½ using expendable abrasives, with a surface profile of 75 – 100 um, providing a key on existing coating either side.

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Remove dust and detritus by blowing with clean dry compressed air or brushing.

Apply a first coat by brush/trowel commencing at the underside of the pipe and spreading circumferentially, with excess material directed towards the weld. Overlap 75mm minimum onto sound existing coating on each side of the weld.

Allow the recommended drying time, typically one hour, before the application of a further coat.

Apply a second coat of the urethane in a longitudinal direction with excess material conducted towards the weld area overlapping 75mm minimum onto existing coating either side of the weld.

Apply any further coats as above, at 900 to the application direction of the previous coat, until the required thickness of 1mm is achieved. Ensure that the final application is smooth and professional looking

Coal tar enamel

Urethane tar materials are specified on CW5 T7 for coating C.T.E to C.T.E pipe butts and for repairs to C.T.E, dry damaged areas. They are not compatible with bitumen enamel.

The specification for the coating of butts using U.T requires that the existing enamel be bevelled back by 100mm. The area should be grit blasted to Sa 2½, profile 75 – 100 um blown down and cleaned as previous.

The urethane tar should then be applied circumferentially then longitudinally to build to the required 1mm D.F.T, overlapping onto sound existing coating by not less than 150mm.

The specification requires that the two interface areas be then overwrapped with heavy duty C.A.L.T. Nowadays however it is not considered to be necessary as the manufacturers of Protegol guarantee the bond.


1 Urethane tars are not suitable for use over plastics.2 Urethane tars are not compatible with any bitumen based material.3 The materials are only toxic in liquid form.4 They are extremely moisture sensitive and due regard should be given to application

constraints.5 The materials should not be exposed to temperatures above 1450c as they release

various cyanide gasses.

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D.F.T

Six reading to be taken on butts, equidistant on random areas using a correctly calibrated banana gauge, minimum thickness 1mm. Any areas under thick to be recoated.

Adhesion

‘V’ cut test. It may be found necessary to use a mini-hacksaw rather than a craft knife.

Holiday detection

100% of area to be holiday detected using voltage settings to minimum D.F.T requirements, formula 5v per micron = 5kv.

Visual checks

Check for blisters, pinholes etc. usual defects.


None specified.

Repairs

For areas of less than 1cm2, surface preparation by abrading with coarse emery. Areas greater than 1cm2 by blast cleaning. The prepared areas are then coated using the same material as the existing parent coating.

Safety

Recommended safety precautions must be observed, and the liquid material should not be allowed to contact any bare areas of skin. If this occurs then the affected area must be washed immediately with soap and water. In the event of U.T having to be removed from a surface, it must be done using prolonged blasting (CW5 table 1), with no heat application.

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Toxicity

The isocyanate curing agents employed in curing urethanes are very toxic and have an M.E.L of 0.02 milligrams per cubic metre (see health and safety unit). During spray application of these materials the applicators should wear as a minimum, a positive air supply mask, total body coverage sealed at the wrists and ankles, over gloves and adequate footwear. Extraction units should be operating.

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CHAPTER 18

SPECIAL SITUATIONS

A situation may arise when it is not possible to use the specified material. One such instance would be for the repair of coal tar enamel subjected to soil stressing on a live line.

In a situation such as this, the line would have been exposed by excavation, and in all probability the base of the trench would be in standing water. The operating temperature of the gas in the line would be below dew point temperature and so the enamel would be wet with condensation. Therefore repairs using urethane tar would be out of the question, as would repairs on bitumen enamel with urethane tar. Laminate tapes would also be out of the question, firstly the damp surfaces and secondly because of the room under the pipe, (full circumferential repairs).

In situations such as these a material called Plasgard 410 would be used. Plasgard 410 is a solvent free, two pack epoxy, which is moisture tolerant and compatible with all coating materials (being solvent free).

The soil stressing would be wire brushed along the length using a disc brush to clean all debris out of the zig-zag longitudinal crack, and solar protective materials and other debris from a band approximately 300 – 400mm wide centred on the crack. The area would then be swabbed to remove as much moisture as possible and progressively swabbed and brush coated with Plasgard along the length of the damage. Any condensation will then form on the outer surface of the Plasgard, and can be easily swabbed away prior to subsequent coats. Specified minimum D.F.T would be 500 um but ideally the damage would be filled to be flush with the surface. After an appropriate time lapse the pipe would be subjected to holiday detection, and if satisfactory, the trench refilled.

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CHAPTER 19

INTERNAL COATINGS FOR FITTINGS AND LINEPIPE

Coatings applied to the internal surfaces of linepipe and fittings are not a consideration for the site coatings inspector, in fact once the linepipe has left the coating plant there is no procedure for repairing damages to internal coatings. It is however considered to be essential for the inspector to understand the reasons for applying internal coatings, which are: -

1 To help to reduce noise.2 To ease the gas flow by reducing friction.3 To reduce turbulence and thus vibration.4 To prevent corrosion during pipe storage.5 To reduce fatigue stress

The materials used are usually two pack polyamide cured epoxy applied over an Sa 2½ blast to a D.F.T of approximately 50 um.

The BG specifications dealing with internal coatings are: -

BGC PS CM1 - Procedure for internal coating operations for steel linepipe and fittings.BGC PS CM2 - Specification for internal coating materials for steel linepipe and fittings.BGC PS PA8 - Specification for internal coatings for steel small bore pipes (below

100mm nominal size)

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CHAPTER 20

HOLIDAY DETECTION

Holiday detection is an operation carried out by a coatings inspector in order to find any voids, misses or uncoated areas, which may be present on a pipeline. This operation can also detect areas of low film build, but is not a substitute for any other inspection function, it is done in conjunction with all other inspection functions. High voltage holiday detectors, sometimes called “spark detectors” all work on the same principle.

All coating materials used on pipelines (polymer based) have a known resistance to the passage of a current, measured in ohms per cm, ranging from 108 to 1015 Ω/cm. Air and water have extremely low resistances compared to this. If a substrate is made into a cathode Θ in a circuit and the anode is passed over the coating, where there is sufficient resistance in the coating it will not allow the passage of the current. If however the anode is passed over a pinhole in the coating, the resistance of the air in the pinhole is far far less and will allow the passage of the current. Where a coating is under thick the resistance will be reduced and the current will pass. It should be noted however that there will be no indication as to why the circuit has been joined, but only a signal that it has been joined.

D.F.T’s and visual inspection are therefore still very important. There are several types of holiday detector, AC, DC and high frequency and pulsed, but for pipeline work the most common is the DC detector, powered by a 6v rechargeable battery.

For F.B.E coated lines a 5kv model is quite adequate and the scales are usually set in 25v increments for accuracy.

For C.T.E and polyethylene a much larger model capable of providing 15kv would be required.

For using within the auspices of a quality system the machines should be calibrated and checked.

For obvious reasons this type of equipment should not be used on wet surfaces, or in the rain.

Use of the holiday detector

Prior to actual use it is necessary to set the voltage to a predetermined value, as specification or to a formula. BG Transco use the formula 5v per micron = 5kv per mm. Special voltage setting are specified for some coatings e.g. C.T.E at 15kv, others such as C.A.L.T require a D.F.T and then setting as per the formula.

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It is essential to have the voltage setting correct as too low a voltage setting will result in holiday not being detected and too high a voltage setting will cause holidays.

The structure to be holiday detected must be earthed into the circuit by means of a crocodile clip onto the structure (bare steel) wired up to a spike driven into electrolyte level in the ground, or wired direct to the holiday detector. If using the spike method (advantageous for working some distance away, above the length of the earth wire provided), a spike with a connection to the holiday detector must be used similarly at the station of work. The holiday detector is then switched on and the circuit tested by contacting a known pinhole with the anode, or striking the earth clip. If the circuit is OK then the operation can commence.

The anode, which is now preferably a wire or copper bristled brush, (spring and carbon impregnated neoprene are not now permitted by BG Transco) is passed over the coating at a speed of not more than 300 mm/sec. The brushes can be of the drum brush type or in some cases over 15” long copper bristled brushes, sometimes curved to suit the pipe contour. Flat brushes should be traversed circumferentially and ‘T’ pieces should be done by circumferential action on both the carrier pipe and the branch, with the weld done as an entity using the corner of the brush, on both sides of the pipe.

On contacting a holiday the following will indicate its presence.

1 Needle on the kv dial will drop to zero.2 A bleeper will sound.3 Lights will flash on the control box or anode handle.4 Blue sparks will crackle from anode to cathode.

When dismantling the holiday detector the earth should be the last disconnection.

Holidays should be marked by circling with a waterproof marker, with the holiday in the centre of the circle, so as not to interfere with the adhesion of the repair.

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CHAPTER 21

HANDLING TRANSPORT AND STORAGE

It is an inspector’s duty to ensure that all handling, transport and storage is conducted according to IGE TD 1.

Materials control requirements are that an inspector should report and record the following during receiving, loading and stringing.

a) Location/section number (loading out)b) Operation type.c) Pipe number, heat number and pipe length.d) Coating type.e) Any coating damage and repair details.f) Any damages or dents to weld preparation area.g) Destination (on load out operations).h) If stringing the direction of travel, normal for low to high section number reverse

when stringing to next low number section

Handling of pipes

In order to minimise coating damage, certain precautions are specified for handling transport and storage.

When pipes are to be lifted the preferred method is a spreader beam with slings. When a spreader beam is not practicable then brothers shall be used, (two leg chains fitted with profiled hooks, fined with material which will not damage the weld preparation area e.g. nylon). A guide rope is fitted to each leg for operator safety. It is not permitted to use chains, padded or otherwise around a pipe.

When transporting pipes from mill to pipe store or out to the spread they can be stacked either pyramidal or on specially profiled cradles, dependant on size. It is essential that every contact point be padded with at least 12mm of rubber, pipe to pipe, pipe to cradle or batten, pipe to stanchion and pipe to straps.

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Stacking of pipes

Pipes shall be stacked, according to specification, in pyramid fashion on hard or soft standings. Tables in the specification give details, according to pipe diameter and coating type, as to how many tiers may be used.

On soft standing two parallel rows of sand (berms) approximately three metres apart are deposited, covered with polyethylene, and the pipes lain across the sand rows, allowing a fall of approximately 150mm for drainage of water from the inside of the pipe.

Hard standings consist of the specified number of bearers (skids or sleepers), in rows, padded with wood wool pads underneath the bottom layer of pipes. Further tiers can be laid according to conditions specified.

Table 21.1 Stacking details for 12 m random length resin coated pipe

Pipe nominal

size

mm

In ground 3 m proximity 30% stress In station

Wall thickness

mm

Number of tiers (maxi-mum)

Wall thickness

mm


Wall thickness

mm


Wall thickness

mm


80 5.49 30 - - - - 5.49 30

100 4.49 28 11.91 20 11.91 20 6.02 28

150 5.56 22 11.91 17. 11.91 17 7.11 22

200 6.35 18 12.70 14 12.70 14 8.18 18

250 6.35 16 12.70 12 12.70 12 8.74 16

300 7.14 14 12.70 11 12.70 11 9.52 14

400 8.74 12 14.27 8 14.27 8 10.31 11

450 9.52 9 15.88 7 15.88 7 11.91 9

600 9.52 7 17.48 5 17.48 5 14.27 6

750 11.91 5 19.05 4 22.22 4 15.88 5

900 12.70 5 19.05 3 25.40 2 15.88 4

1050 14.27 4 19.05 3 28.71 2 17.48 4

1200 12.70 4 - - - - - -

1400 14.27 4 - - - - - -

Note – Numbers of tiers based on the following conditions:1. Coating stress limited to 20% of manufacturers published compressive strength.2. Maximum rubber compression of 40%.3. Three equally spaced separators fitted to each linepipe section.4. Separator width of 100mm and thickness of 5mm.5. Separators manufactured from rubber with 60 to 70 IRHD.6. Three additional supporters of the same dimensions and material being placed beneath the bottom row on

hard standings.

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Table 21.2 Stacking details for 12m random length coal tar coated pipe

Pipe nominal size

mm

Standard* 3 m proximity**

Wall thickness

mm

Number of tiers (maximum)

Wall thickness

mm

Number of tiers (maximum)

80 5.49 27 - -

100 4.49 21 11.91 13

150 5.56 14 11.91 11

200 6.35 11 12.70 9

250 6.35 8 12.70 8

300 7.14 7 12.70 7

400 8.74 6 14.27 5

450 9.52 5 15.88 5

600 9.52 3 17.48 3

750 11.91 2 19.05 2

900 12.70 2 19.05 2

1050 14.27 2 19.05 2

1200 12.70 2 - -

1400 14.27 2 - -

Notes

* The number of tiers given is based on 4 equally spaced separations between pipe layers and 7 bearers and pads beneath the bottom layer.

** The number of tiers given is based on 6 equally spaced separations between pipe layers and 11 bearers and pads beneath the bottom layers.

It is also a requirement that the weld preparation areas are not damaged during transport and storage. There are three specified methods of protection.

1 Plastic end caps (night caps) taped in position over the ends of the pipe.2 Specially profiled metal caps which bolt in position.3 Wax-oil, a preparation which is painted on or dipped. This is regarded as a temporary

measure and would preferably be covered with an end cap.

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CHAPTER 22

CONCRETE COATINGS

Concrete is applied to the external surfaces of pipes in certain, situations. The specification BGC PS CW9, concrete coating of pipes is a three part specification.

Part 1 - Negative Buoyancy Coatings (plus supplement notes for guidance)Part 2 - Security CoatingsPart 3 - Thrust Bore Coatings

During the planning stage of the pipeline it can be determined how many linepipe sections will be needed for each eventuality, and so, much of the coating is done as a factory. There are occasions however when concrete may have to be applied at site.

Considerations for Materials

1 The cement used can be either Portland, Blast Furnace, or Sulphate resisting cement.2 The aggregates and sand used should be clean (potable).3 The reinforcements used should be concentric and rigid.4 Plastic (non conductive) spacers should be used to hold the reinforcement from contact

with the pipe.

Application

Application of the concrete can be by any of three methods.

a) Mouldingb) Impingementc) Guniting

Moulding

Female moulds are made from timber or similar, filled with concrete and allowed to set.

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Impingement

The concrete is passed under a roller with rubber blades, rotating and flicking the concrete onto the pipe. The pipe generally traverses across the application area giving a corrugated appearance.

Guniting

Spray application of concrete. The mixed concrete is compressed by means of a rotating screw and forced along a hose. Upon exiting the hose the concrete is carried by high pressure water, and/or compressed air onto the substrate.

In all cases, concrete is applied over existing anti-corrosion coatings. Because F.B.E is relatively thin, there is a strong likelihood that during impingement or guniting, the coating could suffer impact damage. In order to avoid this the mill coating will be applied to an extra thickness of 650 – 700 um.

Inspection considerations

1 The concrete thickness should be 75mm 10%.2 The concrete should be applied to within 400 25mm from the pipe ends.3 The anti-corrosion coating should be inspected and holiday detected, (on the uncoated

area) and any damages repaired.4 There should be no continuity between pipe and reinforcing. This is tested using a 6 or

12v battery circuit with a bulb wired in. One end connected to the reinforcing, the other to the pipe end. For acceptance the bulb should not light.

5 Ambient conditions should be recorded.6 Visual checks cracks, voids, spalling, and compaction.7 Ringing test using a 2lb hammer, similar to enamels.8 Check for ovality

Note. Security coating can be done by using concurrent sleeving, with thinsulators to hold the carrier pipe dead centre of the sleeving, sealing off the ends with forged steel caps. The internal pipe space between the security pipe and the carrier pipe is called the annular space.

This space can be filled with grout (concrete) or alternatively by using nitrogen gas to a pressure of 1½ bar.

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CHAPTER 23

DITCHING AND BACKFILLING

Ditching the pipe

When the pipe has been successfully coated, holiday detected, and repairs completed, the next operation is the ditching of the pipe. This is done to the general pipeline specification BGC PS P10. This specification deals with the civil engineering requirements on a pipeline such as trench depth and width, fencing requirements etc.

Ditching means the placing of the completed sections of pipe into the ditch, and is done by means of a number of side booms progressively lifting the pipe from the skids, moving it over the ditch and lowering into the ditch. Ideally the jibs should be padded with old car tyres to prevent damage if the suspended pipe should swing back and strike the jib.

The inspector should walk the length of ditch and inspect for electrodes or protruding rocks etc. which might damage the pipe coating during ditching operations. If the trench is excavated in rocky ground it may be required to line the ditch with 150mm layer of imported sand/gravel to provide a level surface and avoid unnecessarily stressing the pipe. As the pipe is lifted from the skids, the contact area, previously inaccessible, should be holiday detected (and repaired if needed).

Note. Where thermoplastic coatings are used, handling must not take place if the temperature exceeds 270c, as migration of the material may occur.

Backfilling of the trench

When the pipe is laid in the bottom of the trench, sometimes it may be deemed necessary to pad around the pipe with further imported backfill, but otherwise stone free layers of 300mm deep, from the best of the excavated material would be used, and compacted with hand rammers or mechanical devices. The layers should be of the same material as the layers evident on the sides of the excavation, e.g. yellow clay to yellow clay. The stone free layers, 300mm deep should be deposited until there is 300mm of cover over the pipe. The remaining backfill may then be replaced, in 300mm layers, providing stones and lumps of vegetation over 200mm are discarded, up to the top of the subsoil level. The total cover over the top of the pipe to the top of the topsoil (when replaced) should be 1.2m, minimum.

The backfill compaction can be checked by either a C.B.R, Californian Bearing Ratio, or a penetrometer.

Impact damage on the pipe coating can be minimised by using Rockguard, a plastic mesh, which is strapped around the pipe.

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CHAPTER 24

PEARSONS SURVEY

After backfill, when the electrolyte has been allowed sufficient time to permeate through to the pipe coating, a persons survey can be done. From the persons survey the following can be detected.

i) The presence of coating damage.ii) Metallic objects near the pipe.iii) By triangulation, the depth of the pipe.iv) The pipe position and direction.

Two operators walk along the line of the buried pipe. Both are wearing clampon type fittings on their boots. The spiked boots are connected by wire to their belts, which in turn are connected together by an eight metre long conductive cable. At any time a circuit can be joined between the two men, to earth.

A battery is coupled to a CP test point and a current passed into the pipe. The battery is earthed by driving a pin into the ground, wired to the negative pole.

Wherever bare steel on the pipe is in direct contact with electrolyte in the soil, (damaged areas), current will be released into the electrolyte.

The lead man of the two carries an instrument, which amplifies the signal of the current release. As he passes directly over the top of a damage he will receive his strongest signal. The signal will diminish as he gets further away. Through his earphones the second man will know when he is approaching, when the signal is equal for both men, the damage is half way between them. When the second man receives peak signal, he stops and marks the spot by hammering a small peg into the ground.

The repair team then investigates by excavating manually to find the problem.

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CHAPTER 25

TESTING OF PAINT FOR PROPERTIES AND PERFORMANCE

Viscosity

Viscosity is a very important property for paint, it affects the manufacturing process and application and levelling properties.

Viscosity is defined as being a fluids resistance to flow. Therefore a liquid described as being of a high viscosity is one which has a high resistance to flow, it will not run easily, and conversely, a low viscosity fluid runs very easily.

An increase in temperature (or decrease) can have a severe effect on a fluid’s viscosity and therefore comparative tests should be done at the same temperature. As the temperature increases the molecules within the paint gain more molecular freedom, move more easily and thus reduce viscosity. A typical recommended temperature is standard laboratory temperature of 20oc 0.5oc.

There are several types of equipment available for measuring viscosity but they mainly fall into two categories.

1 Rotational Viscometers & 2 Flow Viscometers

1 Rotational viscometers

Rotational viscometers rely on a paddle, disc or ball rotating in a liquid to measure the viscosity. The rotation can be driven by an electric motor, which gives Dynamic Viscosity measurements, or by falling weights which gives Kinematic Viscosity measurements.

a) Dynamic viscosity

For dynamic viscosity measurements a rotothinner can be used

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Poises

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Figure 25.1 Rotothinner

The rotothinner, a flat circular disc with four holes drilled transversely through it, is fixed into the chuck of the rotational viscometer (not unlike a pillar drill) and lowered into a 250 millilitre can containing the fluid under test. The can is magnetically attached to a spring loaded conical shaped base. When the disc enters the can, a micro-switch engages the motor and starts the disc rotating. When the rotating disc enters into the paint the frictional forces between the disc and the paint molecules and the can cause the can to rotate, which in turn tensions a spring in the base. When the two equalise the can will stop rotating and a reading can be taken from the pointer on the scale on the conical base.

The systems international (SI) units for dynamic viscosity are, newton-second per square metre (N.s/m2) although on many machines the poise is still used (c.g.s. unit). A poise has ten subdivision called centi-poise.

Water has a viscosity of approximately one centi-poise. One poise is equal to one dyne second per cm2.

b) Kinematic viscosity

Figure 25.2 Krebs stormer viscometer

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Weight

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Kinematic viscosity is measured using a Krebs Stormer Viscometer. The weight is allowed to fall, which in turn causes the paddle to rotate in the paint. More weight added results in a higher rotation speed. Weights are added until the rotation speed is 200 r.p.m as measured either with a stroboscope or digital display counter. A viscosity unit frequently used for kinematic viscosity is the stoke and centi stoke. A fluid having a viscosity of one poise and a density of 1 gm/cc has a viscosity density ratio of one stoke. (Krebs units or poise can also be used.)

Flow viscometers (Flow cups)

There are various types of flow cups e.g. Zahn and Frikmar, used for hot fluids, Ford, I.S.O and DIN used for ambient temperature materials. The ford cup being the most widely used for industrial paints.

The flow cup is machined from Aluminium, has a capacity of 100cc, and is fitted with a stainless steel nozzle at the bottom with various orifice sizes, in millimetres. For use with industrial paints a 4mm hole size is standard, and known as A Ford Flow Cup No4. The cup is mounted on a special stand, and has a lid with a bubble spirit level. The triangular base of the stand has one fixed foot and two screw adjustable feet, to facilitate the levelling of the stand and cup.

A typical procedure for use would be: -1 Ensure that the equipment and paint temperatures are at 20oc 0.5oc.2 Level off the equipment using the bubble level and adjustable screw legs.3 Put the lid to one side when levelling is complete.4 Place a suitably sized receptacle under the orifice (greater than 100cc).5 Place a finger over the nozzle orifice and fill with the paint to be tested, up to the brim,

leaving a convex meniscus.6 Using a straight edge (a ruler) quickly scrape excess material into the overflow rim on

the top of the cup.7 Simultaneously start a stopwatch (or use sweep second hand) and remove finger from

the nozzle.8 The paint will run from the orifice in a continual stream. At the first distinctive break

in the stream i.e. when it drips, stop the watch. The time in seconds is recorded as the viscosity, at the measured temperature.

Thinners added to paint over and above recommended quantities could also be determined by viscosity. To do this a sample containing maximum amount permitted (by manufacturers TDS) is prepared, and compared to samples taken from the operators at the point of application. Using the flow cup, if the operators sample runs through the cup faster than the reference sample, then more thinners than allowed has been added. To find the exact percentage added, small amounts can be added to the reference sample until operator’s sample and reference sample run through in the same time. Should the operator’s sample

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take longer than the reference sample, then there is no problem. Thixotropic paints cannot be measured using a flow cup.

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CHAPTER 26

FILM THICKNESSES

Wet film thickness measurement

From information given on a specification and the technical data sheets (T.D.S) correct application thickness can be calculated. If regular checks of wet film thickness (W.F.T) are carried out, and found to be adequate, it gives added confidence that upon checking the following day, the dry film thickness (D.F.T) should meet specification requirements and hopefully eliminate major rectification.

Wet film readings should be taken immediately after application, in order to obtain true readings (solvent starts to evaporate away as it exits the spray tip). W.F.T’s can be measured by using either an eccentric wheel, or comb gauges.

1 Eccentric wheel

An eccentric wheel is a steel disc, machined to cut two grooves leaving three rims. The centre rim is machined smaller than and eccentric to the two outer rims. The inner rim is called the Eccentric Rim and the two outer, the Concentric Rims.

Figure 26.1 Eccentric wheel

A scale is engraved on the outer surface of one side of the wheel giving degree of eccentricity at any point.

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Degree of eccentricity, 250 um normal

0

125

250

125

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To use the wheel it should be placed on the surface with the zero at the six o’clock position, rolled through 180o in one direction, back to the zero and then 180o in the opposite direction, back to zero. The concentric outer rims will be wet for the full circumference, but the inner rim, the eccentric rim, will only be wet for part of the circumference, having left and re-entered the film on two occasions. The wet film thickness value is taken by transferring (mentally) the interface between wet and dry on both sides of the eccentric rim into a value from the scale. The average of the two values is the W.F.T of the paint film.

It should be noted that the eccentric wheel can only be used on flat plate. On a pipe, for example it would be used circumferentially.

2 Comb gauges

Comb gauges are supplied in many forms, square, rectangular, and triangular, in metal and in plastic. Disposable plastic gauges will be supplied in small boxes containing several hundred. Stainless Steel gauges are supplied in sets of four in a leather wallet. However all comb gauges are used in a similar manner.

Assuming use of the SS gauges, four gauges will each have two working ends covering eight different W.F.T ranges. Above each tooth is engraved a value ‘thou’ on one side and its equivalent in microns on the other side. This represents the value of the gap from tooth end to substrate when the gauge is place firmly, perpendicularly onto the substrate.

When the gap under the tooth is full of paint it will wet the tooth. When not full it will not wet the tooth.

A procedure for this operation would be: -

a) Select the appropriate gauge with the smallest increment rise tooth to tooth.b) Apply the gauge firmly, perpendicular to the substrate into the paint film ensuring that

the two end lands are firmly on the substrate.c) Withdraw the comb gauge and look at the teeth.d) Two values should be recorded. The number above the last tooth wetted by the paint

and the value of the next highest not wetted.

The WF.T is not an absolute value but ‘in between’. NB Comb gauges should be used longitudinally on curved surfaces e.g. pipes.

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Figure 26.2Comb gauge

W.F.T’s can be calculated by using the following formulae, according to information given.

WFT = 100 x DFTVS

WFT = V = VolumeA Area

Figure 26.3 Contraction from evaporation

Tests done on dry paint films

Dry film thickness

The specification for a painting contract will state a D.F.T criteria for each coat of paint applied. As it is the inspector’s main function to ensure that work is carried out to specification, he/she should perform as many checks as needed to ensure that the specification criteria is met. The D.F.T value can be determined by one of four methods.

1 Test panels2 Calculations3 Destructive test gauges4 Non destructive test gauges

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SolventWFTSolvent

Binder

Pigment, Extenders and others

DFTVolumeSolids %

Solvent %

Paint

Substrate

25 50 75Wet

Wet

Not wetRecorded as 50/75

Wet

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Test panels

Test panels are usually 150mm square plates of the same material as the component being processed. The plates undergo the same operations at the same time as the main components. Mainly used for destructive tests e.g. adhesion, they can also be used for D.F. T checks.

Calculations

Using certain formulae and information given on a materials data sheet, in conjunction with values determined from W.F.T’s for example, calculations can give us the ‘unknown’ values. Four formulae can be used according to information provided.

1 WFT = VA

3 DFT = WFT x VS1 100

2 WFT = 100 x DFTVS 1

4 VS% = DFT x 100WFT 1

Destructive test gauges

As the name implies these types of gauges cause damage to the film which then needs to be repaired. If a specification required a magnetic gauge to be used to measure a coating including M.I.O (Micaceous Iron Oxide), in theory it can't be done, M.I.O is magnetic and would cause error in the reading. In this instance a destructive test gauge might be specified or it may be required to monitor closely the WFT and calculate (as above) the DFT.

A P.I.G, paint inspectors gauge is a type of destructive gauge. A reference line of a contrasting colour is drawn on the painted surface to be tested. A blade is tightened into a special slot in the P.I.G, pressure applied to force the blade through the paint to the substrate and then cut across the reference line, leaving a damage about ⅜" it is then possible to examine the damage through a focusable microscope. Measurements can be taken by means of a graticule scale engraved on one of the lenses.

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Figure 26.4 Destructive test gauge

The dimensions taken from the graticule scale at this point are not in any units, as the angle of the cutter used alters, so will the representations of the graticule.

A chart is supplied with each gauge, and blades of different angles. If for example the chart indicates Blade No3 will be ground to x angle, can be used on thickness less than 500 um, multiply graticule reading by 1.8, 20 unit of graticule scale would then convert to 20 x 1.8 = 36 um.

Other commonly used destructive gauges are the Ericson Test Drill and Saberg Thickness Drill. The damage caused with this is circular.

Non destructive test gauges

This category of gauges is the most widely used and can be subdivided into Electronic and Magnetic.

a) Electronic

The electronic gauges work mainly on two principles. Electro Magnetic Induction and Eddy Current. The Electro Magnetic Induction is suitable for ferro-magnetic substrates and the Eddy Current is suitable for non ferro-magnetic substrates.

Modern electronic gauges are sometimes supplied with probes suitable for both situations, and the gauges automatically change function according to the fitted probe. Both types are for measuring non-ferro magnetic coatings. Accuracy ½ %.

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Blade

View

Damage

Reference line

View through lens with graticule scale

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b) Magnetic

This classification of gauges works with permanent magnets, no batteries. The simplest of these is: -The Tinsley Pencil or Pull of Gauge. Sometimes called a foreman's gauge is suitable for spot checks and is not very accurate, even on modern gauges of this type 15 % accuracy is quoted. It looks very much like a pen and indeed is sometimes fitted with a pocket clip. It has a permanent magnet attached to a spring. The tension of the spring can be adjusted so that the gauge can be calibrated to work over a variety of thicknesses.

Figure 26.5Cross section of Tinsley pencil

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Screw to adjust tension

Spring

Cursor line

Permanent magnet

Scale

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Figure 26.6 Magnetic horseshoe gauge

The Magnetic Horseshoe gauge is a very old type of gauge still favoured for measuring hot surfaces such as metal spray. Accuracy often quoted as better than 10% and as for all magnetic gauges, it is suitable for use in hazardous areas. This gauge works by measuring the change in magnetic flux between two magnetic poles at the bottom of the gauge. The flux change is brought about by the thickness of the non-magnetic coating. The gauges are supplied in a wide variety of scales and are calibrated like all magnetic gauges.

The Magnetic Coating Thickness gauge, known colloquially as the 'banana gauge', measures non-ferromagnetic coatings over ferromagnetic substrates and can, according to the manufacturer even be used under water. This type of gauge relies on spring tension to break the magnetic attraction of a permanent magnet to a ferromagnetic substrate. Because spring tension doesn't have a linear function the scales on the gauges are in logarithmic increments. When calibrating for use it is therefore of paramount importance to calibrate using a shim as near as possible to the paint thickness. Modern gauges of this type often quote 5 % accuracy.

Procedure for calibration to BS 3900 PT C5 (now ISO 2808)(BG Transco specify calibration on a prepared surface, therefore a plate with the same substrate surface finish as that to which the paint is applied, should be used).

It is extremely important to remember that should the gauge be calibrated on a flat plate, the reading on a blasted surface would take from approximately ⅔ of the depth of the profile, giving values of up to 50 um more than the actual 'over the peak' value.

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Lock/unlock

Knurled wheel for calibration

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1. Select a plastic shim (magnetically insulated) as near as possible in thickness to that of the paint to be measured.

2. Place the shim centrally on the calibration plate, as detailed above.3. Locate the magnet in the gauge onto the shim, apply a light pressure to ensure that the

heel doesn't wobble or rock, and wind the scale wheel on the gauge fully forward to release all tension on the spring allowing the magnet to attach to the substrate.

4. Wind the wheel slowly back, clockwise, tensioning the spring until the magnet detaches. At this point the movable cursor on the gauge is adjusted so that the red line on top of the cursor is in line with the thickness value of the shim as shown on the scale wheel.

The gauge is now ready to use.

Some 'banana' gauges do not have a movable cursor. Instead these have a fixed cursor, moulded into the case, and a movable scale, and to calibrate these gauges, the value of the shim on the scale wheel has to be moved to the cursor.

Adhesion

Inspection is defined as “Examining, testing, gauging, one or more characteristics etc.” One of the properties required of a paint film is to ‘provide adhesion to the substrate’, therefore an inspector is expected to test to ensure the paint is performing this function. There are three main areas for adhesive failure within a paint system.

a) Primer to substrate failureb) Inter-coat adhesion (between films)c) Cohesive failure (within a paint film)

a) Primer to substrate failure

Primer to substrate failure is the most serious. Failure here means no protection at all. This is a surface contamination problem mainly. Lack of adequate surface preparation, grease, oil, dirt, dust are the usual causes.

b) Inter-coat adhesion

Caused by the problems above and others. Lack of observance of recommended over-coating limits and expansion/contraction differences between materials.

c) Cohesive failure

Over thickness of a layer can entrap solvent during the drying process and thus stop polymerisation and the correct formation of the film, reducing cohesive strength. The main

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reason for cohesive failure is solvent entrapment but incorrect ratio mix of a two pack can have exactly the same effect.

These failure points can be detected in several ways, some costly, requiring equipment costing several hundred pounds and some requiring an outlay of a few pounds only.

‘V’ cut test

A craft knife is all that is required to perform this test. Cut through the paint, to the steel substrate, with two cuts forming an inclusive angle of approximately 30o, with leg length of approximately 13 mm. Insert the tip of the blade into the tip of the ‘V’ and try to lever off. The paint should chip across the tip of the ‘V’ clearly and cohesive without following the line of any of the faults described. It should not expose any of the substrate.

Cross cut (cross hatch test)

Cut through the paint using six horizontal and six vertical cuts approximately 2 mm spaces giving a 25 squared grid. Special profile cutters can be purchased for this, or a craft knife can be used. Apply an agreed tape to the area (different tapes have different degrees of stickiness and would give different results), rub smoothly onto the hatched area and then snatch off. The resulting areas of disbondment are then compared to diagrams shown in BS 3900 Pt E6 and classified according to percentage area of disbondment.

Dolly test

The dolly test is more expensive to use, but unlike the above gives an answer in units of p.s.i or newtons/um square, etc and so is classed as a quantitative test.

A typical procedure for the test would be: -

Ensure the test area is clean and oil/grease free, lightly abrade the area and apply mixed two pack heavy duty adhesive. Firmly place the aluminium alloy dolly in position onto the adhesive ensuring that the skirted flange is to the adhesive. Leave for manufacturers recommended cure time. Place the core drill supplied around the dolly and cut through the coating to the substrate (this ensures that only the area of the dolly flange receives the pull off forces). Apply the pull off gauge and apply pull off force, (some models use a ratcheted lever, others a knurled wheel) until failure occurs. This will usually involve a loud bang and the instrument will ‘jump’ from the substrate. Examine the face of the dolly and apportion adhesive failure according to areas exposed, at the pull off force indicated on the scale.

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For example with an aluminium metal spray, single coat, there could be: -

1. Adhesive to dolly failure.2. Adhesive to aluminium failure.3. Cohesive failure within the aluminium.4. Aluminium to substrate failure.

Hydraulic adhesion test equipment

This is a much quicker test with a higher degree of accuracy. The H.A.T.E use cyano-acrylic impact adhesives and can usually be done approximately two hours after dolly/adhesive application, the dolly’s are mild steel and reusable because they are heated up to destroy the adhesive after use. Big downside for this test is initial cost and usually high maintenance.

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CHAPTER 27

SPECIFIED COATING CONDITIONS

A manufacturers product data sheet will indicate under which ambient conditions a paint/coating can or cannot be applied. The clients specification may sometimes be a little stricter. However, in all cases, it is the specification which takes precedence, (it is common practice nowadays to include a phrase such as “when these conditions do not prevail” or similar, to allow coating to continue using special products).

A typical specification used to be: -

“It is not permissible to apply paints

1. During rain, snow, or high winds”. This clause would be sensible even in modern specifications.

2. When the air or metal temperature is down to within 3oc above the dew point temperature”. Still common in specification now, but can be overridden by giving alternate systems.

3. When the air or metal temperature is below 5oc”. Solvent evaporates very slowly at low temperatures and chemical cure rates used to be static.

4. When the relative humidity is more than 90%”. Still a very common restraint, and sometimes the benchmark for using moisture curing polyurethane’s.

From the above, two very important phrases arise, Relative Humidity and Dew Point.

Relative Humidity

Defined as being “The amount of water vapour in the air expressed as a percentage of the amount of water vapour which could be in the air at that same temperature”. 100% humidity, saturation, is measured as being taken within 1" of the surface of a fast flowing river.

Dew Point

This is the temperature at which water vapour in the air will condense. Condensation cannot occur unless the relative humidity is 100%. Recalling that every 11oc drop in temperature results in the airs capacity to hold water halving, even the smallest drop in temperature results in water being released from the air, in the form of condensation. So at 100% humidity the air temperature and dew point temperature, and wet bulb temperature on the whirling hygrometer are all the same value.

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The Whirling Hygrometer, Aspirated Hygrometer or Psychrometer

Commonly called the whirling hygrometer, this piece of equipment is widely used by coating inspectors to determine wet and dry bulb temperature readings, from which, using calculators or hygrometric tables, relative humidities and dew points can be calculated.

Two thermometers are mounted in a plastic frame, fitted with a handle so that the frame can be rotated through the air. One of the thermometers is fitted with a wick around the bulb. The wick passes through a hole in the end of the frame and into a small container with a screw lid, into which is put distilled water or clean rainwater i.e. de-ionised water. The water is drawn by capillary action all along the wick out the area enveloping the thermometer bulb. This is referred to as the wet bulb and the second thermometer is the dry bulb.

The frame with the thermometers mounted should be rotated quickly about a horizontal axis. (The BS 2482 states in front of and to windward of the operator) so that the bulbs pass through the air at 4m/sec. If there is a wind the operator should face into the wind, if no wind then walk slowly into a clean air current.

The frame should be rotated for 30 – 40 seconds, or as otherwise specified, as fast as possible (to meet requirement as above) and then read the values on the thermometer, always the wet bulb first, immediately on ceasing rotation. The water on the wet bulb uses heat energy from the air to change into water vapour, so the wet bulb will give a lower temperature reading than the dry bulb. When rotation stops, the aspiration rate slows and so the wet bulb temperature will slowly start to rise towards that of the dry bulb.

This operation should be repeated as many times as is necessary until the following criteria is met. On two consecutive spins the readings should be within 0.2oc, wet bulb to wet bulb and dry bulb to dry bulb.

The wet bulb and dry bulb temperatures recorded can then be used to determine the R.H and D.P from scales or tables.

This operation should be carried out as near as possible to where the work is being done. Big difference in temperature can occur from N side to S side of a tank or down a trench and topside.

Steel temperature measurement

The air temperature (ambient) is the temperature recorded from the dry bulb thermometer. To measure the steel substrate temperature a magnetic gauge, known commonly as a limpet gauge is used, or a digital thermometer, thermocouple, sometimes called a touch pyrometer.

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CHAPTER 28

CATHODIC PROTECTION

Cathodic protection is a secondary line of defence against corrosion, the primary defence being the coating. When damage to the coating occurs e.g. through impact on the coating during back filling on a pipeline, sling damage during the lowering in operation, or flotsam impact on an offshore platform leg, the underlying steel can then be in contact with electrolyte and corrosion can occur. But if these areas can become cathodic i.e. receive current, corrosion can be avoided. In order for cathodic protection to be applied, an electrolyte must be present. For example the external surface of a tank cannot have cathodic protection, but internal surfaces can if the tank is holding an electrolytic medium, but only up to the level of medium, not above. Underground and subsea pipelines can be protected, but steelwork above ground in an AGI needs painting. Cathodic protection can be applied in one of two ways.

a) Sacrificial Anodes Systems.b) Impressed Current Systems.

Sacrificial anode systems

This system sometimes called, Galvanic Anode System, works on the principle of bimetallic corrosion, the natural potential between metals. Any metal which is more electronegative (less noble) or below steel on the galvanic list can be used as an anode. The choice of metal used would depend upon the potential required to protect the prescribed area. Sacrificial systems only protect small areas and the anodes need changing regularly as they corrode away.

Figure 28.1 Sacrificial system

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Approximately 50 m maximum Connecting wire of

copper. Minimum resistance

+

Aluminium zinc or magnesium or alloys of these

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Impressed current system

The impressed current system is used to protect long lengths of pipeline from one installation, a distance of approximately 10 miles. The current needed to run the system comes from the national grid and is connected through a transformer rectifier (TR). The national grid is very high voltage and very high amperage and also AC. Anti-corrosion currents need to be DC. The TR rectifies the current to DC and transforms it to low voltage and amperage. The positive side of the TR is connected to a ground bed (anode system) and the negative to the pipe, making the pipe the cathode.

The current is released into the electrolyte at the ground bed, passes through the electrolyte and is received at areas of coating damage on the pipe.

A typical ground bed will be approximately 50 m in length, at the same depth as, and running parallel to the pipe. The cables carrying the current are of a substantial diameter and pure copper to produce a circuit of little or no resistance at the anode. The resistance encountered comes in the soil/clay/rock bearing the electrolyte and this will govern the driving voltage required, and the number of anodes required to maintain negative potential on the buried pipe.

The voltage required varies but is usually within the range of 10v to 50v at an amperage of around 0.15 amps. A CP system does not eliminate corrosion, it controls where corrosion occurs.

Figure 28.2 Impressed current system

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Ground bed releases current into electrolyte

To national grid supply

Current received at cathode. Protected.

TR. Transformer rectifier

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Interference

When a buried steel structure is near to, or in the case of another pipeline, passes over or below a pipeline which is cathodically protected, problems can occur. This is “interference” but the term can be misleading. The offending structure does not adversely affect the CP system, but instead is affected by it.

The “interference” structure picks up current released from the anode bed and conducts the current through a circuit of minimal resistance and releases the current again into the electrolyte near to the protected line. The interference therefore becomes a secondary anode and can suffer severe corrosion.

If there is a possibility of a structure becoming interference then precautions need to be taken to avoid this eventuality. With the permission of the owner of the offending structure, three main methods can be employed.

1 Attach isolation joints one pipe length either side of the nearest point of the offending line to the protected line. Join the two pipe lengths to the protected line with insulated wire and doubler plates, thus making them the same potential.

2 Attach isolation joints to both lines, one pipe length either side of the nearest point. Join the two isolated sections together and install a sacrificial anode to protect both sections.

3 Double wrap and contra-wrap the protected line giving four tape thicknesses with Cold Applied Laminate Tape for one pipe length either side of the nearest point.

The method chosen would be at the discretion of the engineer.

Monitoring CP

It is considered that –850 mv will maintain a pipeline in a passive state but most CP engineers will require a more negative value, -1 to –2v being typical. To ensure that the required potential is being maintained, checks need to be carried out at regular intervals. One method of monitoring is known as half-cell reference electrode. The most commonly used half-cell electrode is the copper/copper sulphate half-cell electrode. It is used for measuring the pipe to earth potential, i.e. cathode to earth, the other half of the circuit being anode to earth.

Periodically along the line, CP monitoring posts are installed, with a direct wire connection to the pipe, accessed from a stud on the CP post panel. A voltmeter is connected to the stud and to the copper/copper sulphate half-cell, which is then pushed into the earth directly above the pipe. This provides a circuit for electrons from the pipe, into the electrolyte, back to the anode bed.

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Figure 28.3 Monitoring CP

Cathodic disbondment

Part of the electrical circuit of the corrosion reaction is the evolvement of Hydrogen gas from the cathode. Hydrogen is a very powerful gas and can cause cracking in steel, (HICC). If Hydrogen gas can penetrate underneath a coating it can easily disbond it. This is known as Cathodic or Hydrogen Disbondment. Over protection of damaged areas on a pipe, results in over production of Hydrogen and subsequent disbondment of more of the coating, resulting in a bigger area to protect, needing more current.

All material used on a pipeline have to undergo tests to determine their resistance to cathodic disbondment. The test is done in the following manner.

A 6 mm diameter hole is drilled into a plate coated with the material to be tested, through the coating and into but not through the underlying steel. A short length, approximately 50 mm of plastic tube approximately 50 mm diameter is fixed in position, using typically araldite epoxy or elastomeric sealant with the drilled hole central to the tube. This is then part filled with 3% solution of common salt, sodium chloride, and a lid fitted. The lid can be machined from a block of polyethylene with a suitable diameter hole drilled through. The plate is connected to the negative pole of a battery, an anode is connected to the positive pole and inserted through the hole in the lid into the salt solution.

When the circuit is switched on the plate is the cathode and Hydrogen (and Chlorine) will be evolved from the steel, and also at the interface of steel/coating. This enables Hydrogen to penetrate under the coating, simulating areas of coating damage.

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Pipe

CP postVoltmeter

Half cell reference electrode filled with copper sulphate solution

Porous plug

Ground level

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The circuit is stopped after 28 days stripped down, dried off, and using a craft knife, two cuts are made at an inclusive angle of approximately 30o radiating from the centre of the hole, through the coating to the substrate. Where disbondment has occurred the coating will chip of as the cuts are being made. The distance from the edge of the hole to the extent of the disbondment is measured and should not exceed the stated requirements. For example FBE maximum 5mm after 28 days.

Figure 28.4 Cathodic disbondment

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6 mm diameter hole

Elastomeric sealant

Coating

LidPlastic ring

Salt solution

Battery

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CHAPTER 29

HEALTH AND SAFETY

Control of substance hazardous to health regulations 1988 generally abbreviated to C.O.S.H.H regulations.

These regulations provide a framework to help to protect personnel at the workplace against health risks from substances, which are hazardous.

For the purpose of COSHH regulations, substances hazardous to health include.

a) Substances or preparations listed as being toxic, very toxic, harmful, corrosive or irritant in part 1A of Chemicals (Hazard Information for Packaging) Supply.

b) Substances with M.E.L or O.E.S as detailed in schedule one of COSHH or if Health and Safety Commission has approved an O.E.L.

c) Harmful micro-organisms.d) Dust of any kind in substantial concentrations.e) Any other substance creating comparable hazards to peoples health such as pesticides

and other chemicals used on farms.

Hazard warning symbols

- Black symbol of skull and crossbones on an orange square with the words Toxic or Very Toxic printed below

- Black diagonal cross on an orange square with the words Harmful or Irritant printed below.

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- Black symbol showing a tilted test-tube dripping onto a hand with a chunk out, adjacent to a test tube dripping onto a stone flag. Orange background with the word corrosive printed below.

Responsibilities

It is the employer’s duty to assess the risk to employees on his/her premises and any other premises, which might be visited during the execution of duties. Training establishments are responsible for trainees.

It is an employers duty to prevent, where ever possible, exposure to hazardous substances, but if it is not reasonably practical to totally prevent exposure then protective clothing, masks etc. should be issued to minimise exposure.

COSHH regulations require that regular monitoring should be carried out and records kept, particularly in situations where there could be serious risk to health if control measures were to fail or deteriorate.

Guidance note EH 40 (occupational exposure limits), is a document published by the HSE, which lists all substances known to be hazardous to mankind. It gives details in table form of common names, chemical formulae and chemical names of hazardous substances.

The Hydrocarbon solvents used in modern paint formulations are hazardous to health and are listed in EH 40.

Xylene is one such solvent and has an Occupational Exposure Limit (O.E.L) of 100 ppm (parts per million). This means that air containing more than 100 ppm would be considered to be a hazard to the health of personnel exposed to it. There are two categories of O.E.L.

1 Maximum Exposure Limit (M.E.L).

“The maximum concentration of an airborne substance, averaged over a reference period, to which employees may be exposed by inhalation under any circumstances and is specified, together with the appropriate reference period, in Schedule one of COSHH.”

2 Occupations Exposure Standard (O.E.S).

“The concentration of an airborne substance, averaged over a reference period, at which, according to current knowledge, there is no evidence that it is likely to be injurious to

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employees if they are exposed to inhalation, day after day, to that concentration, and which is specified in a list approved by H.S.E.”

When referring to reference periods above, long term exposure limits are averaged over an eight hour reference period and short term exposures over ten minute reference periods.

If the EH 40 specifies that a substance has an M.E.L then the quoted figure must not be exceeded at any time, but kept as low as is reasonably practical.

With an O.E.S it is permissible to exceed the stated figure provided that the average over a reference period is below the stated figure. Exposures above should result in measures being taken to reduce the value to below the stated O.E.S.

O.E.L examples of some solventsSolvent Name O.E.L in ppmAlcohol’s Methanol

Ethanol200

1000Ethers Ethyl Ether

Isopropyl Ether400250

Esters Methyl AcetateEthyl Acetate

200400

Ketones AcetoneMethyl Ethyl Ketone

750200

Aromatics XyleneToluene

10050

Aliphatics White SpiritHexane

100500

Chlorinated Hydrocarbons 1.1.1 TrichloroethaneTrichloroethylene

350 ab100 ac

Dräger tube and Dräger bellows

Figure 29.1 Dräger tube

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N =

5

Dräger

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One way of monitoring the toxicity of the air is by dräger tube and dräger bellows.

The dräger tube is a glass tube about 110 mm long with moulded nipples at each end. One half of the tube is filled with chemical crystals (sensitive to the material testing for) and are held in position by fine wire mesh plugs. A cellophane sleeve, incorporating a scale in ppm is wrapped around the tube. There is also an arrow on the sleeve indicating the way in which the tube is to be inserted into the bellows.

The bellows are hand operated and are a one way air system, as the bellows are depressed, air is expelled from a slot at the back, when released, air is drawn in through a small rubber grommet like aperture at the front. The bellows incorporate two compression springs and stops, and two retaining chains, so that every depression and release exchanges an air volume of 100 cc exactly.

Figure 29.2 Cross-section of dräger bellows

Using the tubes and bellows

Using a special fitting situated on the bellows, the nipples are snapped off both ends of the tube, which is then inserted into the aperture on the bellows in the direction indicated by the arrow. The crystals should be adjacent to the bellows. The bellows are then depressed and released according to the number expressed as n =, as written circumferentially around the centre of the tube. Each depression and release slowly draws 100 cc of air through the open end of the tube, through the crystals and into the bellows. As the air containing the hazardous

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material passes into the crystals, a chemical reaction takes place, resulting in a colour change in the crystals. The extent of the colour change along the scale is recorded in ppm.

NB. Many variation of crystal combinations exist for monitoring a variety of different toxicants, all have a different requirement for number of depressions and different colour changes. The tube for monitoring the concentrations of Xylene needs five depressions and the colour change is from white to reddish brown.

Some materials in common use in the coatings industry do not evaporate into gas or fumes, they remain instead as tiny particles of solids suspended in the atmosphere. Materials of this nature cannot therefore be detected by Dräger Tube. They are quantified by the units milligrams per cubic metre rather than p.p.m.

Three materials, which fall into this category, are Asphalt, Coal Tar and Isocyanates. Asphalt is considered to be fairly safe with an O.E.L of 5 m/gm per m3. Isocyanates are very toxic with an M.E.L of 0.02 m gm/m3.

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CHAPTER 30

DUTIES OF AN INSPECTOR

BS 4778 Pt1 (EN 28402, ISO 8402) Quality Vocabulary – International Terms, defines inspection as “Activities such as measuring, examining, testing, gauging, one or more characteristics of a product or service and comparing these with specified requirements, to determine conformity”.

Documents available to an inspector could include, but not be limited to.

a) Job Specification.b) Data Sheets for the paints/coatings.c) Procedures.d) Quality Plans.e) Plant Drawings.f) Site Plans.g) BS’s e.g. 7079 Pt A.h) Waste Management, Duty of Care Document.i) Relevant Local Regulations.

The job specification is the main tool of the inspector and should be observed at all times. It is not the inspector’s responsibility to rewrite the specification and permission for any deviation should be given in writing and retained by the inspector.

An inspector should keep adequate and accurate records of all stages of the work being carried out, materials used, ambient conditions etc. so that in the event of illness or any other situation requiring a replacement, the new inspector will be in full possession of all relevant information.

Paint/Coatings Inspectors Daily Report Sheets need to be completed, and passed on to the engineer, containing all information requested, and a copy retained by the inspector.

The format of Daily Report Sheets varies but in general will require the following information.

1 Details about the contract and contractor, including plant on site and number of personnel.

2 Ambient conditions applicable during the work period, to be monitored as near as possible to the task location.

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3 For surface preparation activities the information required will include, method used, original substrate condition, abrasive type, degree of cleanliness achieved, profile achieved, identity of plant and times of starting and completion.

4 For materials, the information required will include manufacturer, product reference number, expiry date, batch number, colour, reference number of thinners, W.F.T and resulting D.F.T, time of application and identity of plant. In the case of labour only contracts it will be required to record quantity used.

5 The comment part is a space left for the inspector to report on any irregularities, non-conformance or deviation from specification.

In addition to the daily reports it may also be a requirement to complete a weekly summary, detailing progress and any other information, such as repeated deviation from specification, for the engineer.

Typical examples of situations to report would be.

1 Substituting approved products with unapproved products.2 Substituting new materials with out of date materials.3 Using solvents other than those approved by the manufacturer.4 Not observing induction times when specified.5 Using untrained personnel.6 Re-using expendable abrasives.7 Not observing recommended over coating times.8 Continuing with the next stage of operations without inspection of the substrate and

approval.9 Painting/coating over areas of inadequate surface preparation.10 Working in conditions outside of specified requirements.

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Job: Report No.Contractor: Date:Location: Specification:No.of men: Start time: Finish time:

Weather a.m. p.m.

TimeAmbien

t temp.oC

Relative

humidity%

Dew point oC

Steel temp oC

Time Ambient

temp.oC

Relative

humidity%

Dew point oC

Steel temp oC

Surface preparation: Initial condition:Blast clean Abrasive: Type:Profile Sa2 Sa2½ Sa3Hand clean

Method St2 St3

Paint application:Manufacturer’s name:Coat No. Manufacturer’s

descriptionRef. No. Colour W.f.t D.f.t Quantity

used-ltrs.

Item coated Coat No. Ref. No. Batch No.

Time interval

W.f.t Total D.f.t

Comments:

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Transmission DepartmentPAINTING INSPECTION FORM

WALES GASNWY CYMRU

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Signature:

EXAMPLE

PAINTINGCONTRACTOR

PAINTSUPPLIER

ABRASIVE SUPPLIER

AREAS TREATED SURFACEPREPARATION

PAINTSAPPLIED

METHOD OF APPLICATION

WFT DFT

TIMEDRY

BULB TEMP

WET BULB TEMP

RELHUM

DEW POINT

STEEL TEMP

TYPE OF

WORKTIME

DRY BULB TEMP

WET BULB TEMP

RELHUM

DEW POINT

STEEL TEMP

TYPE OF

WORK

WEATHERNo OF MENON SITE

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PAINTING INSPECTION REPORT

CUSTOMER REF NO

CONTRACT REF No

CLIENT

LOCATION

REPORTNo

DATE

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COMMENTS

INSPECTOR PRINT SIGNEDINSPECTOR SIGNED ENGINEER

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CHAPTER 31

LIST OF SPECIFICATIONS AND BS NUMBERS

BS 410 - Specification for test sieves.

BS 2451 - Specification for chilled iron, shot and grit (now defunct).

BS 3900 - Methods of test for paints.

BS 7079 - Preparation of steel substrates before application of paints and related products.

BS 7079 Group A - Visual assessment of surface cleanliness.

BS 7079 Group B - Methods of assessment of surface cleanliness.

BS 7079 Group C - Surface roughness characteristics of blast cleaned steel substrates.

BS 7079 Group D - Methods for surface preparation.

ISO 8501 - As group “A” as above.

ISO 8502 - As group “B” as above.

ISO 8503 - As group “C” as above.

ISO 8504 - As group “D” as above.

SIS 055900 - Pictorial surface preparation standards for painting steel surfaces.

BGC PS CW1 - External wrap operations for steel linepipe (using coal tar).

BGC PS CW2 - Cold applied wrapping tapes and tape systems.

BGC PS CW3 - External wrap operations for steel linepipe (hot applied bitumen).

BGC PS CW4 - Specifications for polyethylene cladding on steel pipe.

BGC PS CW5 - Code of practice for the selection and application of field applied external pipework coatings.

BGC PS CW6 - Specification for external protection of steel pipelines and fittings using resin powder and associated coating systems.

BGC PS CW6 Pt1 - Requirements for coating materials.

BGC PS CW6 Pt2 - Factory applied coatings.

BGC PS CW9 - Concrete coating of pipes.

BGC PS CW9 part 1 - Negative buoyancy coatings.

BGC PS CW9 part 2 - Security coatings.

BGC PS CW9 part 3 - Thrust bore coatings.

BGC PS PA8 - Internal coatings for steel small bore pipes.

BGC PS P10 - General pipeline specification.

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IGE SR 21 - Code of practice for safety during blast cleaning operations.

IGE TD 1 -

BGC PS CM1 - Procedure for internal coatings operations for steel linepipe and fittings.

BGC PS CM2 - Specification for internal coating material for steel linepipe and fittings.

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CHAPTER 32

QUALITY

Quality assurance

The definition of quality assurance in BS 4778 Pt1, Quality Vocabulary is “All those planned and systematic actions necessary to provide adequate confidence that a product or service will satisfy given requirements for quality”.

Quality assurance is regarded as being a management tool, a method of maintaining and improving quality whilst controlling costs. A quality system operates on the theory that if there is time and budget allocation to rectify mistakes within a process, then it is preferable to allow a little time to “get it right first time” at reasonable cost. (By using mathematical tools like Pareto Analysis on a production line, eliminate the most frequent fault and reparation is often halved, then eliminate the next most frequent.)

Companies employing quality systems produce procedures for every task performed, if everyone works in a formalised way to achieve the requirements of the specification, then consistency of quality should automatically follow. If quality is improved and costs reduced than a company can be more competitive and consequently improve its position in the market place. Quality assurance is not solely operated by production, but is throughout an organisation, and deals with every aspect of a companies operations from planning and design and training through to packing the final product, transport and marketing.

Quality control

BS 4778 Pt1 definition “Operation techniques and activities that are used to fulfil requirements for quality”.

The inspection function provides information in order that quality control can be maintained by adjusting the process to eliminate any deficiency.

Quality related standards

BS EN I.S.O 9000 series Quality systems.BS 4778 Quality vocabulary (EN 28402 ISO 8402).BS 7229 Quality systems auditing.BS EN 30011 Guidelines for auditing quality systems.

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Quality related definitions (from the above)

1 Code of practice - Document that recommends practices or procedures for the design, manufacture, installation maintenance or utilisation of equipment, structures or products.

2 Instruction - Provision that conveys an action to be performed.

3 Normative document - A document that provides rules guidelines or characteristics for activities or their results.

4 Procedure - A specified way to perform an activity.

5 Regulation - A document providing binding legislative rules that is adopted by an authority.

6 Specification - The document that prescribes the requirements with which the product or service has to conform. NB. A specification should refer to or include drawings, patterns or other relevant documents and should also indicate the means and the criteria where by conformity can be checked.

7 Standard - Document, established by consensus, and approved by a recognised body, that provides, for common and repeated use, rules, guidelines or characteristics for activities or their results, aimed at the achievement of the optimum degree of order in a given content.

8 Technical specification - A document that prescribes technical requirements to be fulfilled by a product, process or service. NB. A technical specification should indicate, where ever appropriate, the procedure(s) by means of which it may be determined whether the requirements given are fulfilled.

A technical specification may be a standard, a part of a standard or independent of a standard.

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CHAPTER 33

REVISION QUESTIONS

Paint technology revision questions

1 What are the three main constituents in a paint?2 What are the three main groups of paint?3 Where do oils com from?4 Where do resins come from?5 Name three oils.6 Name three resins.7 How do binders change from liquid to solid?8 What is meant by the term monomer?9 What is a polymer?10 Is a linear polymer reversible or convertible?11 Is a thermosetting material reversible or non reversible?12 What is meant by thermoplastic?13 What is meant by thermosetting?14 Are oxidising binders used on a pipeline?15 What is meant by polymerisation?16 Name three elements likely to be found in an organic polymer?17 What type of polymer does F.B.E form?18 Are polyethylene and polypropylene thermoplastic or thermosetting?19 Is urethane thermoplastic?20 Are thermoplastic materials crosslinked or linear polymers?21 What purposes do pigments serve?22 What is a typical pigment particle size?23 If carbon was added to a paint what colour would it be?24 If titanium dioxide was added to a paint what would be the colour?25 What are the properties of a solvent?26 Name three additives in a paint other than binder, pigment and solvent.27 Name the three corrosion protection methods.28 Which metallic pigments are used in the cathodic protection method?29 What are the four drying mechanisms?30 Which of the four drying mechanisms apply to pipeline coatings?31 What is meant by pot life?32 What is a typical pot life for pipeline materials?33 What is meant by induction period?34 Do pipeline materials have an induction period?35 Name two materials, which cure chemically.

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36 Which type of polymer dries by solvent evaporation only?37 What is meant by “barrier principle”?38 If a material has a short pot life, will it have an induction period?39 Are chemically curing paints convertible or non convertible?40 Are thermoplastic materials reversible or non reversible?

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Enamels revision questions

1 What is the recommended application temperature for hot enamels?2 Which primer would be used with coal tar enamel?3 Why is solar protective coating applied?4 How far from the end of the pipe should solar protection finish?5 Which solvent would ideally be used to identify an enamel?6 How much overlap is recommended on the inner wrap?7 Which primer would be used for bitumen enamel?8 What would be the colour of solar protection applied to coal tar?9 What is the BG specification for coal tar coated pipes?10 At what temperature should coal tar enamel be discarded on site?11 What colour does coal tar bleed in the solvent test?12 What is the minimum distance from the pipe surface for inner reinforcements?13 What preparation standard would apply to coal tar enamel?14 What is meant by bleed through?15 What would be the colour of solar protection applied to bitumen enamel?16 What would be a typical D.F.T for primers?17 What colour does bitumen bleed in the solvent test?18 What is the BG specification for bitumen enamel coated pipes?19 At what temperature should bitumen enamel be discarded in a factory?20 What is meant by disbonded thermoglass?21 What is the dimension of the uncoated area at the end of a pipe?22 What is the minimum enamel thickness allowed over a weld?23 By how much must a coating be bevelled back?24 What is another name for carbonising?25 Over general plate areas what thickness is specified as a minimum?26 What preparation standard would apply to bitumen enamel?27 Will the enamels stick to plastics?28 What is meant by flood coating?29 Which voltage setting is recommended for holiday detecting enamels?30 What is the maximum enamel thickness allowed?31 What should be the temperature of the enamels to conduct a bond test?32 How long must elapse before a bond test is conducted?33 What length and width is the strip cut for the bond test?34 How could pinholes be repaired in enamels?35 What is another name for disbonded outer wrap?36 What is meant by ‘icicles’ in pipeline terminology?37 What do you understand from the term ‘stringing’?38 Would C.T.E be an ideal coating for a pipe to be bent?39 What dimension would a pull through plate be?40 Why would a pull through plate be used?41 Why would it be necessary to bend a pipe?

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42 During stringing why would wood-wool pads be used?43 What are skids?44 Why is a herbicide incorporated into bitumens?45 What is a particular hazard associated with coal tar?46 How would coking appear on an enamel coupon?47 Why would bitumen enamel be discarded when heated to 2500c?48 Would it be satisfactory to use enamels without the inner reinforcing?49 How would a lamination appear on an enamel coupon?50 How could laminations be detected on a full pipe length?

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Sleeves, tapes and mastics revision questions

1 Which BG specification covers application of hot applied tapes?2 Can cold applied laminate tapes be used to repair C.T.E?3 Can grease based tapes be used on polyethylene?4 Name two materials from which self adhesive overwrap tapes are made.5 What is the nominal thickness of PE cladding?6 Can C.A.L.T be used to repair polyethylene cladding?7 How could the risk of soil stressing be reduced on C.A.L.T?8 Which tape system can be used to wrap a butt joining bitumen to C.T.E?9 Which BG specification covers technical requirements for hot applied tapes?10 What are the carrier tapes made of for hot applied tapes?11 What is the main purpose of using self adhesive overwrap tapes?12 Can polyethylene cladding be field applied?13 How do heat shrinkable plastics adhere?14 Are primers required for hot applied tapes?15 How are grease based tapes constituted?16 Can heat shrinkables be used to repair C.T.E?17 Are primers used with self adhesive overwrap tapes?18 Name three situations where hot applied tapes might be used.19 What is the thickness of mastic for PE cladding?20 What voltage would be selected to holiday detect heat shrinkable plastic?21 Which specification covers application of grease based tapes?22 Can heat shrinkable plastics be used to repair F.B.E?23 Do heat shrinkables require a primer?24 When applying hot applied tapes to a butt, what bevel is specified?25 Over which material can we not use grease based tapes?26 What voltage setting would be used when holiday detecting hot applied tapes?27 How are hot applied tapes heated for application?28 Which voltage would be used to holiday detect grease based tapes?29 Which specification covers application of self adhesive overwrap tapes?30 Name three types of heat shrinkable materials.31 Which voltage setting would be used to holiday detect PE cladding?32 What is the minimum temperature for application of C.A.L.T?33 With C.A.L.T how is over tensioning evident?34 Why is interleaving paper incorporated with C.A.L.T?35 What is “puckering” of PE and how is it treated?36 What surface preparation standards apply to C.A.L.T?37 How would an adhesion test be carried out on C.A.L.T?38 What can be used to even the contour of a ‘T’ piece?39 Which primer should be used with C.A.L.T?40 With cold applied self adhesive overwrap tapes, what is meant by pressure sensitive?41 What degree of surface preparation is required for grease based tapes?

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42 Is a primer used with grease based tapes?43 Are primers used with mastics and fillers?44 How are mastics and fillers applied?45 What is a typical total D.F.T for a brushing mastic?46 How many coats will be required to give the recommended D.F.T?47 What holiday detection voltage would be used on brushing mastics?48 Name two situations when brushing mastic might be used.49 Are primers used with brushing mastics?50 How can one tell if C.A.L.T has been over tensioned?

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Epoxy resin powder coatings revision questions

1 What is the specified band width for degreasing on F.B.E?2 Why is it specified to blast 30mm onto sound existing coating?3 How are the butts heated for powder application?4 What is the dimension specified for feathering after reblasting?5 What does BGC PS CW6 cover?6 What voltage is used on an induction coil?7 What is the surface preparations standard for F.B.E?8 What would be a typical specified preheat, temperature?9 Other than epoxy powder, what does BGC PS CW5 cover?10 What temperature is considered to be critical when heating a butt?11 What profile is specified for F.B.E?12 How is the temperature measured when heating a butt?13 Name five constituents of F.B.E powder.14 What action should be taken if laminations are evident after blasting?15 Are F.B.E’s convertible or non convertible?16 Which solvent could be used for degreasing?17 What is the specified application temperature range for F.B.E?18 How many passes would be typically used to apply the powder?19 What is a tempil stick?20 Can F.B.E be applied to a butt joining F.B.E coating to PE cladding?21 What is the specified minimum D.F.T for a coated butt?22 Where should the temperature be measured prior to application of powder?23 What are the three stages of operations for powder applications?24 Are F.B.E’s thermoplastic or thermosetting?25 What percentage of reclaimed powder is permitted in the application container?26 What is meant by the gel time?27 Which curing mechanism is employed by F.B.E’s?28 What is meant by differential cure?29 What are the four stages from powder to cured coating?30 What safety precautions should be taken during powder applications?31 What are the considerations of storing F.B.E’s?32 Which adhesion check is done of F.B.E’s?33 How many D.F.T readings should be taken around a butt?34 If a low area is found during D.F.T checks, what action should be taken?35 What voltage would be selected for holiday detecting F.B.E butts?36 What is the criteria for acceptance for adhesion test on F.B.E?37 Name three cure checks.38 What does the abbreviation D.S.C mean?39 Why is a gel time test done?40 Where should a cure check sample be taken from?41 What is the frequency of taking D.F.T’s on butts?

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42 Where could an inspector find reference to the gel time?43 What should be done immediately following the D.S.C sample?44 What size should a D.S.C sample be?45 What is the frequency of adhesion testing?46 What is meant by Tg?47 What is a typical gel time for F.B.E?48 What are the criteria for acceptance on a D.S.C sample?49 Why is a D.S.C sample taken from 6 o’clock position?50 What information is required on a D.S.C sample bag?51 What is a melt stick?52 How long should elapse before holiday detection of a repair of less than 1cm2?53 What surface preparation standard and method applies to repair over 1cm2?54 What is meant by the term fluidised bed?55 How can F.B.E be repaired?56 How is powder applied in a factory?57 What is the dimension of the uncoated area on the pipe end of F.B.E/?58 What is a typical pot life of a quickset repair compound?59 What is the specified D.F.T for factory applied coating?60 What heating methods can be employed in a factory, other than induction?61 How can the D.F.T be controlled on straight pipe lengths in a factory?62 What is a melt stick?63 Can C.A.L.T be used on F.B.E?64 When can solvents be used with M.C.L repair materials?65 If a material has 5 minutes pot life, what would be a typical induction period?

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Urethane coatings revision questions

1 What is meant by the abbreviation U.T?2 What is the minimum specified D.F.T for urethanes?3 What overlap is specified for urethane application onto existing coating?4 Which protegol product is for brush application?5 Which protegol product is for spray application?6 Is it permissible to spray urethanes in the open?7 Which BG specification covers urethanes?8 What cure time is specified by BG?9 What is the minimum specified overlap when repairing C.T.E with U.T?10 How much bevel is required on existing coating when using U.T to repair C.T.E?11 What is a typical specified use for urethanes?12 How many layers of urethane would be applied to achieve 1mm D.F.T?13 What are the specified application conditions for urethanes?14 How are the contents of the two containers mixed together?15 Which surface preparation standard applies to urethanes?16 What is the required profile for urethane application?17 What is the curing agent used with urethanes?18 Urethane is applied in two grades, what are they?19 Is it permissible to brush apply urethanes in the open?20 What is a typical pot life at 200c for urethanes?21 What would be the major differences on reports for spray and brush applied U.T?22 Are thinners permitted to be used in urethanes?23 What is the approved method for removal of urethane coatings?24 How would an area of less than 1cm2 be repaired?25 How would an area of greater than 1cm2 be repaired?26 Which adhesion check is employed on urethanes?27 Is it permissible to weld a butt near to urethane coatings?28 How many D.F.T checks are done on a coated butt?29 If under thick areas are found on urethanes, how are they built up?30 Which holiday detection voltage would be used on urethane coatings?

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Revision paper operations other than coating

1 What does BGC PS CM2 refer to?2 Why are pipes coated internally?3 What is a spreader beam?4 Which material could be used to repair soil stressing on damp C.T.E?5 Describe repair procedures for the above?6 What would be a typical D.F.T for an internal coating?7 Is Plasgard 410 an epoxy or a urethane?8 What does BGC PS CM1 refer to?9 If a damaged internal coating was seen on a pipe dump, how would it be repaired?10 What are “brothers”?11 Is it permissible to use chains slung around pipes?12 Which solvent is used with Plasgard 410?13 Which BG specification applies to internal coating of small bore pipes?14 What is meant by “berm”?15 What would be the minimum ‘fall’ for drainage during storage?16 Is Plasgard 410 a single pack or a two pack material?17 What is meant by “hard standing” for stacking pipes?18 Name three methods of protecting weld preparation bevels during transport.19 Why are sand berms covered with polythene sheeting?20 Why do the profiled hooks need to be lined for handling?21 What is the purpose of non-metallic spacers?22 How thick is a concrete coating?23 How much of the pipe end is left uncoated with concrete?24 What is meant by impingement of concrete?25 What are the three parts of BGC PS CW9?26 What could be used, other than grout, to fill the annular space on a sleeved pipe?27 Why would the original coating on a concreted pipe need H.D?28 What is meant by moulding of concrete?29 What would be the thickness of F.B.E for concrete coating?30 What do you understand from the term continuity check?31 What is meant by guniting of concrete?32 Would a 3mm crack be permitted in concrete?33 Why should the reinforcing not contact the pipe surface?34 What is a side boom?35 What is meant by imported backfill?36 Why should the booms be padded?37 What is the number for the general pipeline specification?38 What is the minimum cover over the top of the ditched pipe?39 What is the maximum temperature recommended for handling thermoplastics?40 What is meant by ditching?41 How deep should each layer of soil be for compacting?

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42 What is the maximum size of stone or clump of vegetation permitted for backfill?43 Why should the ditch be evenly bedded?44 Name two methods of checking compaction.45 What is rockgard and why is it used?46 How soon after ditching is the pearsons survey done?47 How many men are needed to do a pearsons survey?48 What can be determined from a pearsons survey?49 Name two methods of cathodically protecting a pipeline?50 What is a C.P post?51 What is a copper/copper sulphate half cell reference electrode used for?52 Why is cathodic protection necessary?53 What is a ground bed?54 Does cathodic protection eliminate corrosion?55 What is meant by interference?56 What does a transformer rectifier do?57 Which metals are commonly used as sacrificial anodes?58 What does a cathodic disbondment test determine?59 How is a cathodic disbondment test done?60 Name two methods of avoiding interference?61 What is meant by double wrap and contrawrap?62 What is meant by half-cell, as in reference electrode?63 Is under protection or over protection the cause of cathodic disbondment?64 In the hydrogen disbondment test is the steel plate anode or cathode?65 What is the percentage strength of salt solution used in the disbondment test?66 What are the symbols for toxic, very toxic, harmful, corrosive and irritant?67 What are the units of quantity on a dräger tube?68 Five depressions of the dräger bellows would draw through how much air?69 What are the abbreviations M.E.L, O.E.L and O.E.S?70 What units are used for toxicity measurements of coal tar, bitumen and isocyanates?71 What are the abbreviations R.A.Q, U.E.L and L.E.L?72 What are the C.H.I.P.S regulations?73 What is the E.H 40?74 How many depressions of the bellows are needed for a dräger tube for xylene?75 What would be the colour change in a dräger tube for xylene?76 Are five depressions the standard number for all tubes?77 What is the occupational exposure limit for xylene?78 What is meant by ‘reference period’?79 Which solvent is the least toxic, xylene or acetone?80 Describe how a dräger tube is used.

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Testing of coatings revision questions

1 What is a Tinsley Pencil?2 Does an eddy current gauge measure on magnetic substrates?3 Name four non-destructive test gauges.4 What is a horseshoe gauge?5 Does an electromagnet gauge measure on non-ferromagnetic substrates?6 What is the stated accuracy of 111 and 211 banana gauges?7 What can a holiday detector detect? 8 How is a banana gauge calibrated?9 Name four methods of determining D.F.T’s?10 What is an eddy current gauge?11 Why is it vital to set a high voltage holiday detector at the correct voltage?12 What is the common size of rechargeable battery in a holiday detector?13 What is special about springs and carbon impregnated neoprene pads?14 When setting up for holiday detection which connection is made first?15 If a pipe is wet on the surface is it possible to holiday detect?16 Can lack of thickness be detected using a holiday detector?17 What is the BG formula for setting a holiday detector?18 What indications will an operator have that a circuit has been joined?19 What is the maximum travel spec permitted for brushes whilst holiday detecting?20 Name two ways by which earthing could be achieved on a pipeline?21 If it is raining can we holiday detect a pipeline?22 How would a ‘T’ piece be holiday detected?23 How would a holiday be marked for repair?24 What equipment is used to measure flashpoint?25 At what point during the test is the flashpoint recorded?26 What happens if an orange flame is seen?27 What is meant by ‘flashpoint’?28 Would a high flashpoint solvent be safer or otherwise, than a low flashpoint?29 At what frequency is the spark activated?30 Define viscosity?31 What is a rotational viscometer?32 What is a flow viscometer?33 Why is temperature important when checking viscosity?34 Name two flow cups.35 Name two rotational viscometers.36 What is meant by high viscosity and give an example.37 Give two units for Dynamic viscosity?38 What unit is used with the flow cup?39 What is meant by low viscosity and give an example.40 In the expression Ford Flow Cup No 4, what does the 4 represent?41 Name two units of kinematic viscosity.

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42 What is the capacity of a flow cup?43 Briefly describe the operation of a ford flow cup?44 What is an eccentric wheel gauge?45 Briefly describe the operation of an eccentric wheel gauge.46 On what type of surface could you not use an eccentric wheel gauge?47 What would be recorded as the W.F.T using an eccentric wheel gauge?48 Name two methods of checking W.F.T’s?49 On which type of surface could you not use a comb gauge?50 Which units are used on a comb gauge?51 How would the W.F.T be recorded using comb gauges?52 Name four adhesion tests.53 Which is the most common adhesion test on a pipeline?54 Name two quantitative adhesion tests.55 What is a dolly?56 Briefly describe a dolly test?57 What is the main advantage of a H.A.T.E over a dolly test?58 For how long is a cathodic disbondment test run?59 Why are two tests done together?60 What is the test criteria for F.B.E?61 Which of the two connections becomes the anode?62 Why is a cathodic disbondment test done?63 What size of hole is drilled into the plate?64 What can be used to seal the bottom of the container?65 Is the circuit used AC or DC?

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Weather conditions revision questions

1 What is meant by aspiration?2 At what speed should the hygrometer be rotated?3 Give two other names for a whirling hygrometer.4 Define Dewpoint.5 Which temperature should be read first?6 Why should the above be read first?7 Define Relative Humidity.8 On two consecutive spins, wet to wet and dry to dry should be within what?9 What is the maximum possible R.H.?10 What should be used to wet the wick on a hygrometer?11 If the wet bulb temperature was 100c and the dry bulb was 100c, what would be the R.H?12 How is the steel temperature determined?13 Where should R.H and D.P readings be taken?14 What should the operator do to take readings when there is no wind?15 Why use de-ionised water to wet the wick?16 Is it permissible to use a hygrometer with a dirty wick?17 If a dry wick was used what results would ensue?18 If there is very little difference between wet and dry bulbs what does this indicate?19 Is it possible for the wet bulb temperature to be higher than that of the dry?20 What should be check about the mercury in the thermometers before use?

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Corrosion OP revision questions

1 Is the electrical circuit in a corrosion reaction AC or DC?2 Does corrosion occur at the cathode or at the anode?3 Name the three factors needed for corrosion to occur.4 What is meant by the term electrolyte?5 What is corrosion?6 In the corrosion circuit do electrons flow from anode to cathode?7 Which gas is released at the cathode when the electrolyte is water?8 Which is the more noble metal, steel or Aluminium?9 Which is more electronegative, steel or Aluminium?10 If steel and copper were in contact in an electrolyte which would corrode?11 Name two common Hygroscopic salts.12 Name three metals used as sacrificial anodes on a steel pipeline.13 What is the approximate thickness of millscale?14 Which of the two metals would corrode if steel and zinc were coupled?15 Which other names relate to the Galvanic List?16 In which environment are you likely to encounter chloride salts?17 Which three compounds together form millscale?18 If magnesium was coupled with zinc, which would corrode?19 In which environment would sulphate salts be found?20 What is an osmotic blister?21 What is an ion?22 What is meant by polarisation?23 Is an anode positive or negative?24 Can corrosion occur without an electrolyte?25 Name a sub atomic particle.26 What is millscale and when and where does it occur?27 Name three factors, which can accelerate corrosion reactions.28 Why is it considered essential to remove millscale prior to painting?29 Why does an un-coated steel plate corrode?30 If corrosion occurs at anodic areas, why does steel corrode evenly all over the surface?

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Surface preparation revision question

1 Which British standard would be used in determining the size of copper slag abrasive?2 Which British standard would be used in determining the size of metallic abrasives?3 Which regulations prohibit the use of sand for blasting steel?4 What is meant by the term ‘key’?5 Why is it important to have good surface preparation?6 What is meant by the term sliver?7 What is a hackle?8 Name two other terms that could be used for ‘anchor pattern’?9 What are the main advantages of using ‘Testex papers’ for measuring profiles?10 What is meant by the term grade, relating to a blast finish?11 What are the main factors governing the grade of a blast finish?12 Can the grade of a blast finish be determined by using the surface comparators to BS

7079 Pt C3?13 What profile range can be measured using X coarse Testex?14 What profile range can be measured using coarse grade Testex?15 What are the two theories of adhesion?16 Briefly describe the mechanisms of the two theories of adhesion.17 How many microns are in 1um?18 Give three different names for the cross section of a blast.19 What is the approximate speed of abrasives leaving a venturi nozzle?20 What is the most common cause of flash rusting on a blasted substrate?21 What would be considered to be an ideal shot grit mix?22 What is the purpose of mixing shot and grit?23 Which abrasive would have the effect of work hardening a substrate?24 Name three methods of measuring or assessing a profile.25 What is the most common cause of rogue peaks on a substrate?26 In what situation would it be better to use steel grit in preference to copper slag

abrasives?27 If cracks or laminations are found on a substrate after blasting what steps should be

taken?28 Using comparators to ISO 8503, what are the three main profile assessments?29 What are the other two assessments when the above three are not appropriate?30 What would be size of copper slag needed to give a profile of 50 to 75 um?

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Surface preparation 2 revision questions

1 What is the title of the BS 7079?2 What are the four characteristics of an abrasive?3 Why are blast hoses carbon impregnated?4 Name the gauge used for measuring pressure at the blast nozzle?5 Name four advantages of centrifugal blasting over open blasting.6 According to BS 7079 is it possible to blast clean to an A Sa1?7 Is there any difference between an A Sa1 and B Sa1?8 Could you tell the difference between rust grades A and B blasted to Sa3?9 Could you tell the difference between rust grades C and D blasted to Sa3?10 What would be a typical speed of abrasives leaving a wheel abrator?11 What is considered to be the most efficient blasting pressure?12 What is meant by the term “burnishing”?13 What would be the equivalent to St2 in the Sa grades?14 What is the neutral figure on the pH scale?15 How is pH measured?16 Why are inhibitors sometimes added to water in wet blasting?17 Name two typical areas where needle guns might be used?18 What is the Duplex Process of surface preparation?19 Which pH range covers acids?20 Which pH range covers alkalies?21 What is the meaning of pH?22 Name three disadvantages of wet blasting.23 Name two areas on a structure where flame cleaning cannot be done.24 Which three basic operations are performed during flame cleaning?25 How does BS 7079 define Flame Cleaning standards?26 What is a ‘Jasons Hammer’?27 What is meant by St2 and St3?28 Two alloys are used to render wire brushes spark free, what are they?29 Why should ‘Burnishing’ be avoided?30 Name two major disadvantages of using a needle gun.31 After phosphating, what would be a typical pH requirement prior to coating?32 What is understood by the term ‘knock out pot’?33 If an operator was blasting with a nozzle pressure of 80 p.s.i. What would be his

approximate efficiency?34 Which solvents are commonly used for degreasing?35 What is a ‘dead mans handle’?36 Why is carbon impregnated into blast hoses?37 How is abrasive cleansed in a wheel abrator system?38 What is the main disadvantage of high pressure jetting compared to other systems?39 Name five methods of wet blasting.

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40 What would be the typical temperature and concentration of Sulphuric Acid in the pickling process?

41 Describe the ‘Duplex Process’.42 What would be a maximum pressure for high pressure water jetting?43 What are the disadvantages of wet blasting over dry blasting?44 Describe the phosphating process.45 What would be considered to be advantages of wet blasting over dry blasting?46 Why is the phosphating or chromating of steel done?47 What would be an acceptable remedy for burnished areas?48 Would burnishing be expected on areas of St2 preparation?49 How many photographs of blast cleaning standards are shown in BS 7079 Pt A?50 Do the plates shown in Bs 7079 Pt A relate to grit blasting or shot blasting?

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RH and DP exercise

W.B D.B D.P R.H Steel Temp. Y/N1 10 12 132 9 10 113 4 6 64 5 7 6.55 11 12 126 14.5 15.5 167 9.5 10.5 118 12 16 179 12 13 1310 13 13.5 1411 17.5 21 2312 14 17.5 1713 11 11 11.514 7.5 8.5 815 7 6 716 6.5 8 1117 2 3 318 13 15 1619 8 8 820 16 18.5 1921 17 18 1822 8 9.5 1023 22 24.5 24.524 16 16.5 1925 3 4 526 7 8 927 19 18 2028 12 12.5 1329 14 16.5 16.530 8.5 11 11

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Appendix A

Tables

Table 1 – Preferred methods for the removal of anti-corrosion coatings

Type of coating

Method of removal (see Note 1)(method ‘a’ is preferred to method ‘b’

HeatingScraping followed by blast cleaning

Prolonged blast cleaning

Power wire brushing

Resin powder a (see Note2) b a N/A

Multi-component liquid

N/A (see Note 3) N/A (see Note 3) a N/A

Coal tar enamel N/A a b b

Polyethylene b (see Note 3) a N/A N/A

Wrapping tape b (see Note 3) a N/A N/A

Notes1. Any method that risks damaging the pipe is unacceptable.2. The metal temperature shall not exceed 3000C.3. The use of heat should be limited since some of these materials may release toxic

particles or fumes.

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Table 2 – Surface preparation quality

Field applied coating group Minimum preparation standard

Ref. No.

Description SIS 05 59 00 BS 4232

1 Cold applied self adhesive tapes Overwrap only Overwrap only

2 Cold applied laminate tapes St 2/Sa 1# N/A

3Heavy duty cold applied laminate tapes

St 2/Sa 1# N/A

4 Grease based tapes St 2 N/A

5 Fillers St 2/Sa 1# N/A

6 Mastics St 2/Sa 1# N/A

7 Heat shrink materials St 2/Sa 1# N/A

8 Resin powders Sa s½ 2nd quality

9Spray applied multi-component liquids

Sa 2½ 2nd quality

10Brush/trowel applied multi-component liquids

Sa 2½ 2nd quality

11Multi-component liquid repair materials

Sa 2½ 2nd quality

12Moisture tolerant multi-component liquids

Sa 2½* 2nd quality*

* This surface will flash rust due to the continued presence of surface moisture.# Better than St2 with loose millscale, rust and foreign matter removed and dust finally removed with a clean brush.

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Table 3 – Recommended field applied coatings for the protection of pipewirk and fittings

Description of component

Preferred coating 1st option 2nd option

Product group Product group Product group

Long pipe lengths, tees and bends

Spray or brush/trowel applied multi-

component liquids

Light duty or heavy duty cold applied

laminate tapes

#Grease based tapes

Valves, flanges, cast iron couplings and similar components

Spray or brush/trowel applied multi-

component liquids

#*Grease based tapes Light and heavy duty cold applied laminate

tapes

Service pipe and fittings (up to 50mm) including non-ferrous metals

#Grease based tapes Spray or brush/trowel applied multi-

component liquids

Light and heavy duty cold applied laminate

tapes

* complicated shapes must be evenly contoured by the use of the mastic fillers or putties prior to wrapping.# Grease based tapes to be over wrapped with group 1 cold applied self adhesive overwrap tape.

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Table 4 – Preferred materials for protection of weld joints

Possible components of differing types of coating on each side of a weld

Choice of weld joint coating

Preferred Option

Product group Product group

Resin powder Resin powder

Resin powder

#Spray or brush/trowel applied

multi-component liquid


Resin powderSpray or brush/trowel

applied multi-component liquid

Light or heavy duty cold applied laminate

tape



Coal tar enamel Resin powder *Spray or brush/trowel applied

multi component liquid

Coal tar enamel Multi-component liquid

Coal tar enamel Coal tar enamel

Polyethylene Resin powder


tape

Grease based tape overwrapped with

Group 1 cold applied self adhesive overwrap tape

Polyethylene Multi-component liquid

Polyethylene Coal tar enamel

Polyethylene Polyethylene

Cold laminate tape Resin powder


tape-

Cold laminate tape Multi-component liquid

Cold laminate tape Polyethylene

Cold laminate tape Cold laminate tape

*The junction of coal tar enamel and multi component liquids shall be overwrapped with light or heavy cold applied laminate tape.#A second option is the use of light or heavy duty cold applied laminate tape.

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Table 5 – Systems for overwrapping existing pipe coatings

Existing factory/field applied coating

Recommended overwrap systems

Preferred Option


Resin powderSpray or brush/trowel applied

multi-component liquidsLight or heavy duty cold applied laminate tapes

Polyethylene Light or heavy duty cold applied laminate tapes

*Grease based tapesCoal tar enamel

Multi-component liquidSpray or brush/trowel applied

multi-component liquidsLight or heavy duty cold applied laminate tapes

*Grease based tapes shall be overwrapped with Group 1 cold applied self adhesive overwrap tape at the discretion of the engineer.

Table 6 – Systems for coating exposed pipe

*Existing factory/field applied coating

Recommended overwrap systems

Preferred Option


Resin powder Spray or brush/trowel applied multi-component liquid

Brushing masticMulti-component liquid

Polyethylene Light or heavy duty cold applied laminate tape

-Cold laminate tape

Coal tar enamelLight or heavy duty cold

applied laminate tapeBrushing mastic

Brushing mastic Brushing masticLight or heavy duty cold applied laminate tapes

*For paint coatings refer to BG/PS/PA10

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Table 7 – Repair systems for dry surfaces

Existing factory/field applied coatings

Repair systems

Preferred Option1 Option 2

Product group Product group Product group

Resin powderBrush/trowel applied multi-

component liquids

Light or heavy duty cold applied

laminate tapesN/A

PolyethyleneLight or heavy

duty cold applied laminate tapes

Heat shrinkable materials

*Grease based tapes

Coal tar enamel #Spray or brush/trowel

applied multi-component liquids

*Grease based tapes

N/AMulti-component liquids

Cold laminate tapesLight or heavy

duty cold applied laminate tapes

N/A N/A

Brush mastic Brush mastic N/A N/A

* Grease based tapes shall be overwrapped with group 1 cold applied self adhesive overwrap tape at the discretion of the Engineer.# Multi-component liquid repairs shall be overwrapped with a light or heavy cold applied laminate tape.

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Table 8 – Repair systems for damp surfaces

Existing factory/field applied coatings

Repair systems

Preferred Option


Resin powderMoisture tolerant multi-

component liquid*Grease based tapes

Polyethylene *Grease based tapes -

Coal tar enamelMoisture tolerant multi-


Cold laminate tapes *Grease based tapes -

Multi-component liquidsMoisture tolerant multi-


Brush mastic *Grease based tapes -

* Grease based tapes shall be overwrapped with group 1 cold applied self adhesive overwrap tape at the discretion of the Engineer.

Strain polarisation

In certain situations on site, coated pipes have to undergo cold bending, and it is important that the coating can withstand the stresses imposed.

When the pipe is bent the steel and coating is stressed. After bending the result of the stress is strain. In operation the pipe will be polarised negative (cathodically protected) hence the strain polarisation test to ensure that the coating will work under those conditions.

A coated strip is bent by means of a mandrel, with the coating on the outside of the bend. A cup is placed in position on the minimum radius of the bend (the area most strained) and a test done as per Cathodic Disbondment Test as above, except that no holes are drilled. It is run for twenty-eight days. The area, after twenty-eight days, should not show any cracks or pinholes and should undergo a pinhole detection test.

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