Surface preparation

Marine, Protective, Yacht and Aerospace Coatings

For internal use only, not to be circulated outside AkzoNobel

Surface Preparation

IPJ Training Modules, 10th~13th May, 2004

For internal use only. Not to be circulated outside Akzo Nobel.

1. Removing contamination and increasing surface roughness will allow maximum bond strength and adhesion to develop between coating & substrate.

2. This is CRITICAL because of the great demands on Heavy-Duty coatings (such as abrasion, impact, moisture, salt etc).

3. If the coating is applied to a well prepared substrate, they will have strong adhesion to that substrate and may be able to withstand these conditions.

4. Coating performance is directly related to the quality of Surface Preparation.

Introduction of Surface Preparation


Objectives for Surface Preparation

-, Section 1 : Coating Adhesion and Substrate Contamination

-, Section 2 : Methods of Surface Preparation

-, Section 3 : Abrasive Materials and Surface Profile

-, Section 4 : Surface Preparation and Blasting Standards


1. Adhesive Bonds

Chemical Bonding

- Primary Valence Bonding

- Polar or Secondary Bonding

Mechanical Adhesion due to surface roughness or profile.

- Prevention of Slumping

- Increasing Surface Area

2. Substrate Contamination

- Millscale, Rust, Salt, Dust, Grit

- Oil / Grease, Water / Moisture, Salt

- Steel Defects

Section 1: Coating Adhesion and Substrate Contamination


Chemical Bonding -Primary Valence Bonding

Coating chemically bonded to surface

Inorganic Zinc Silicate Coating


All types of primary and polar bonds require close contact between the coating and substrate to be effective.(Hydroxyl molecule)

O O O

H H H+ + +

Resin

Positive dipole

on ion

_ _Negative site on

steel surface

_

Chemical Bonding-Polar or Secondary Bonding


Steel Substrate

Mechanical and Chemical Adhesion

Profile Height

50 - 75µ

Coating

Metal reactive sites for valence and polar bonding

Mechanical and Chemical

Adhesion increased by Surface Profile


• Contaminants which must be removed:-Contaminants which must be removed:-

• Soluble SaltsSoluble Salts

• RustRust

• WaterWater

• MillscaleMillscale

• Dust &GritDust &Grit

• Oil & GreaseOil & Grease

• Old Loose PaintOld Loose Paint

• Steel Defects Steel Defects

Removal of Contamination


Chlorides (Marine environment)• On steel surfaces the chlorine ion and water form a ferrous chloride solution which is conductive (so helps the corrosion process) AND is a strong corrodant itself.• Ferrous chloride oxidises to Ferric Chloride (a hygroscopic salt) which draws moisture from humidity in the air, creating ferric chloride solution on the steel surface.• It takes very little ferrous or ferric chloride to lead to corrosion of steel. Dark Green -> Light Yellow-> Brown -> Black• If this happens after several blasts, HPFWW again to remove the salt.

Sulphates (Industrial Environment)• Not as aggressive as chlorides but can still cause problems.• Found on ship decks, downwind of funnels.

Removal of Contamination - Soluble Salts


Water is drawn through the paint film by osmosis

Salt dissolves in the water...

Paint applied

Coating

Substrate

Soluble Salt

Soluble salt left on surface

The pressure forces the paint

film to stretch out creating a blister

…..and expands

Do not just paint over salt contamination!Do not just paint over salt contamination!



Soluble Salts - Measurement

• Specific procedures for blasting abrasive and surfaces.

• Technical Service Training Module 8 – “Salt Contamination”

< 5 ug/cm2 - Permissible

5-10 ug/cm2 - May be acceptable

> 10 ug/cm2 - Probably harmful



Rust• Can vary from thick, heavy scale to light gingering• This is the most common contaminant on steel• Ferric Oxide Fe2O3 (light brown) is inert & must be removed if loose - but will not cause further reaction with the steel or coating• BUT most rust on ships is hydrated iron oxide, often contaminated with salts - and often found deep in pits!

Oil & Grease• Impossible to paint over successfully• Difficult to “wet” the steel surface because of lowered surface energy.

Dust & Grit• From blasting, dry-spray or other work• From natural build-up of dust on horizontal surfaces

Removal of Contamination - Rust, Oil & Grease, Dust & Grit


Water & Moisture

• We would not paint over a puddle or pool of water - BUT IT IS NOT ALWAYS SO OBVIOUS

• Care is taken to check the risk of condensation on surfaces, by measuring the Relative Humidity (and hence Dew Point) and the Surface Temperature.

• Surface Temperature should be 3oC or more above the Dew Point for painting to be carried out

Removal of Contamination - Water


• Loose paint is easily removed - taking newly applied paint with it!

• High film build-up may cause detachment &/or cracking as stresses build up within the film. Failure may only occur later with temperature changes etc

• Compatibility of paints is important. Painting 1-pack paints over 2-pack paints (or vice versa) can lead to problems and it is always safer to remove the underlying paint - if practical!

Removal of Contamination - Old loose paint


Millscale is is the upper oxide layer formed on new, hot rolled steel and can be up to 250um thick. It is not uniform in consistency, and the lowest layer (scale binder) is the most difficult to remove.

Ferric Oxide Fe2O3 - 28% O2

Steel

Scale Binder FeO + Fe

Ferrous Oxide FeO - 22% O2

Magnetite Fe3O4 - 28% O2

Removal of Contamination - Millscale


Millscale

Steel

Millscale in good condition

Damage to millscale (impact, weathering...)

Pitting corrosion of steel!

STEEL IS ANODIC TO MILLSCALE!!!

•Although it appears to be well adhered, temperature cycling will cause detachment - taking paint with it.• Steel is ANODIC to millscale, and so if the millscale is damaged, a corrosion cell is created leading to rapid pitting corrosion of the steel.

Removal of Contamination - Millscale


Not strictly contaminants, but affect paint in a similar way, and may lead to coating failure.

• Surface Laminations and Shelling• Cracks and Deep Crevices• Sharp Edges• Weld Spatter, Weld Porosity, Weld Undercut• Jagged Manual Welding Seams• Missed Welds and Stitch Welding• Weld Slag and Weld Flux Residues• Etc.

All must be repaired (filled, ground down etc) before coating application

Removal of Contamination – Defects in steel work


Section 2: Method of Surface Preparation

1. High Pressure Fresh Water Washing

2. Solvent Cleaning or Degreasing

3. Manual Methods of Surface Preparation

4. Power Tool Methods of Surface Preparation

5. Dry Abrasive Blasting

6. Rotary or Wheelabrator Blasting

7. Surry Blasting

8. Hydroblasting


Functions:- • To remove salts from surface.• To remove salt from pitted steel after blasting.• To remove fouling on drydocking (Marine).• To remove antifouling leached layers (Marine).• To remove dust.

General Guidelines:-•MUST be Fresh (at least for last wash) otherwise new contamination is applied to the surface (salt, oil etc).• Hosing (low pressure) is normally OK to wash down a surface during general OBM.• High Pressure Fresh Water Wash (HPFWW) is required for hull outside shell or Ballast Tanks, and here normal pressures are 1,000-10,000psi (70-700kg/cm2).

High Pressure Fresh Water Washing


Fouling Growth on vessels entering Dry-dock

Green/Brown weed Fouling in Drydock


CDP CROSS SECTION

Leached Layer = 75 µm

Anticorrosive

CDP

Leached Layer – Cross Section


Fouling Growth on vessels entering Dry-dock

High Pressure Fresh Water Washing (HPFWW)



High Pressure Fresh Water Washing (HPFWW)

Topsides to remove salt

UW to remove leach layer, salt and fouling

U/W to remove reached layer & salt

Side Bottom to remove foulings & salt



Solvent Cleaning or Degreasing

Removal of oil and grease from the surface

Solvent or thinner degreasing should only be used for small areas only

Water rinsable degreasing fluids are most efficient for large areas


Removal of soluble salts deposited from sea water, polluted environments or formations from rusted steel

Removal of emulsified degreasing fluid

Removal of loose dirt and dust

Degreasing & HP Water Washing


Degreasing •Very slow and hard work.• Work methodically!• Do not just spread the grease - Use plenty of clean solvent and clean rags.

SSPC-SP1 is the recognized standard.Remove Heavy Oil/Grease by scraper, then ......• Wipe/scrub with rags wetted with solvent.• Spray surface with solvent.• Vapour degrease.• Immerse in solvent• Use emulsion/alkaline cleaners (& fresh water wash)• Steam clean

Degreasing and SSPC SP1


Manual Methods of Surface Preparation

Hard Scraping / Slicing

Chipping Hammers or Chisels

Wire Brushing

Power Tool Methods of Surface Preparation

Rotary Wire Brushing

Rotary Discing

Impact Cleaning – Needle Guns

Manual and Power Tool Methods of Surface Preparation


• Only effective for small areas• Leaves a layer of rust / millscale on the surface so the chance of coating failure is high.

Scrapers - OK for loose material, but ineffective on tightly adhered corrosion or rust.

Chipping hammers / Chisels - slow and laborious. OK for heavy scale, loose corrosion products and paint. Best followed by 2ary surface preparation (eg wire brushing).



Wire brushing - good for loose contamination, but ineffective for scale and deep seated corrosion. Take care not to polish residual scale (with rust still underneath).

Scraper / Wire BrushCombination



Better than hand tools….

• Less laborious

• Possible to use for larger areas.

• More effective

……BUT still does not produce a truly clean surface.

2 main types - Rotary & Impact



Rotary Wire Brushing• OK for loose contamination but not tightly adherent scale - watch out for polishing effect.

• Radial brushes - awkward areas• Cup brushes - larger areas

• Polished steel looks nice – but does not help adhesion!

• Bad for spreading oil & grease



Rotary Discing• Abrasive discs attached to angle grinders or abrasive flap wheels on straight or in-line tools.

• Can remove loose & tightly adherent rust & scale.

• Feathering back of spot blasted areas - but can get clogged with soft paints.

• Can remove base metal so care must be taken.

• A viable alternative when blasting not possible.



• Dependent on cutting blade/point pounding at surface and breaking away the contaminants.

• Good at removing brittle substances but only effective at the point of impact, leaving contamination in bottom of pits - so follow with rotary wire brushing.

• eg Scaling hammers, Chisels & Needle Guns

• Because they cut the steel surface, they can produce a sharp profile, which can lead to flash rusting if painted without further preparation.

Impact Power Tools



Power tool preparation using Needle guns

Needle Gun

Power Tool Methods of Surface Preparation-Impact Power Tool


Power tooling with discers and needle gunsNoisy and slow progress



Ballast Spaces - Surface Preparation by Power Tooling

Power Tool Methods of Surface Preparation-Block(Inside)


Dry abrasive Blasting

- Blasting Machine

- Types of Abrasive

- Spot Blasting

- Sweep Blasting

- Vacuum Blasting

Dry Abrasive Blasting of Surface Preparation


Dry Abrasive Blasting – Blasting Machine


Blasting set-up using large silos

Dry Abrasive Blasting – Compressed Air Blasting Machine


Dry Abrasive Blasting – Type of Blasting Nozzles


Dry Abrasive Blasting – Correct Coupling & Blasting Nozzle


• Undercutting of adjacent areas.

• Discing recommended, but very rarely done.

• Undercut film may curl up when softened by new paint and corrosion may follow.

• Surrounding area damaged so further touch up.

• Abrasive stream is played across surface, (difficult to switch on & off), so more touch-up is needed.

• More corrosion becomes apparent as work proceeds.

Dry Abrasive Blasting – Spot Blasting


Premature Breakdown of Coatings

due to Overblast Damage



Spot blasted area with reasonablefeathering but note the over blast



Spot blasting with a new micro unit



• Specified to repair patch corrosion.

• The idea is to blast corroded spots to the specified standard, and move the stream onto the next area of corrosion without damaging the intermediate intact paint.

BUT…...



Spot blasting with a lot more control but still could be improved by taking larger blocks.



This is simply “sweeping” a jet of abrasive across a surface to “roughen” it up.

Light Sweeping (Fine Grit 0.2-0.5mm)

• To make a profile on existing hard coating (eg Epoxy).

• To remove loose coatings or corrosion products.

Heavy Sweeping

• To remove old paints to shop primer or bare steel, but only to an “acceptable” surface for some paints.

• To remove of old coatings (upgrade) or shop primer.

Dry Abrasive Blasting – Sweep Blasting


Dry Abrasive Blasting – Sweep Blasting


• Cleans surface by throwing abrasive from impeller wheels or rotors.

• Used in enclosed environments (Shop Primer plants).

• Similar impact speeds to Compressed Air systems.

Rotary / Wheelabrator Blasting


Vacuum Blasting


Water + Abrasive = Slurry

2 methods

“Pressurised Water

Abrasive Blasting”

“Air Abrasive

Wet Blasting”

Abrasive added to

High Pressure Water

Water added to

Compressed Air & Abrasive

Slurry Blasting


Advantages Disadvantages

Dust Reduction Rate of Cleaning

Salt Removal Costs & reliability

Surface Profile Awkward areas

Reduced Abrasive Use (40%) Poor visibility

Removal of wet abrasive

Washing down blasted surfaces

Flash Rusting

Chemical Corrosion Inhibitors - IF USED, MUST BE WASHED OFF

BEFORE APPLYING PAINT

Slurry Blasting


• ONLY water is used - there is NO abrasive.

• Pressures are EXTREMELY high

......this is NOT just HPFWW with the tap on FULL!

• We must be careful with definitions, but…

“Hydroblasting” = “Hydrojetting” = “Water Jetting”

Hydro Blasting


Low Pressure WW - 1,000psi

High Pressure WW - 1,000 - 10,000psi

Hydroblasting - >10,000psi

High Pressure Hydroblasting - 10,000 - 25,000psi

Ultra High Pressure Hydroblasting - 30,000 - 36,000psi

Hydro Blasting


Advantages Disadvantages

Dust Reduction Does NOT create profile

Pollution Reduction Costs & reliability

Salt Removal Awkward areas

Safer Working Poor visibility

Established Standards Flash Rusting

Chemical Corrosion Inhibitors - IF USED, MUST BE WASHED OFF

BEFORE APPLYING PAINT

Hydro Blasting


Hydroblasting Flow Diagram

Hydro Blasting


Hydro Blasting


“Pacific Teal”, BNFL – Condition After Hydroblasting

Hydro Blasting


3 different types

Natural Materials Manufactured

Bi-products Silica Sand

Olivine Sand

Garnet

Calcium Carbonate

Metal Slags

Coal Slags

Silicon Carbide

Aluminium Oxide

Glass Beads

Sodium Bicarbonate

Frozen CO2

Section 3 : Abrasive Materials and Surface Profile


Wood Aluminium StainlessSteel

Steel Fibreglass

Copper Refinery Slag N/A X X X

Coal Furnace Slag N/A X X X

Nickel Refinery Slag N/A X X X

Iron Furnace Slag N/A X X X

Fused Aluminium Oxide

N/A

Olivine Sand N/A

Garnet N/A

Type of Abrasive


Most commonly used are:-

• Cast Steel

• Malleable Iron

• Chilled Cast Iron

Abrasives


Key factors:-

• Strength & hardness of surface (thickness - no effect).

• Velocity of abrasive (E=1/2mv2).

• Hardness & SG of abrasive.

• Size/mass of abrasive.

• Angle of impact.

• Time of exposure to blasting.

Surface Profile


1) Sand & Mineral Abrasive

• Scouring (abrasive fractures as it hits the surface)

• Fractured pieces speed away from point of impact parallel to metal surface, scouring and removing contamination as they go.

• Better at cleaning rusty surfaces than steel shots & grits, but poor at removing heavy rust and millscale.

Surface Profile & Abrasive Type


1) Sand & Mineral Abrasive



2) Steel Shot

• Cleans by Impact damage, giving a “peened” effect.

• Profile is smaller than with steel grit.

• Good at breaking and removing brittle deposits such as heavy rust, scale & millscale, BUT not so good at removing thin surface residues which may be pounded into the surface.

• The surface of the substrate may be warped by the impact which may be a problem for thin plates.



2) Steel Shot



3) Steel Grit

• New Grit is angular and has a greater cutting action than either sand or shot.

• As it ages and becomes rounded off, it will produce a more peened profile.

• The cutting action tends to open up the surface and increase the number of surface sites for coating adhesion.

• Must be careful of rogue peaks with new grit.



3) Steel Grit



Surface Profile

• Measured from peak to valley - average value.

• Too shallow - reduced coating adhesion

• Too deep, excessive paint use and peaks may show.

• Specific requirements may be stated for products.

• Can be controlled using Abrasive/Profile tables.

Surface Profile


Abrasive Size Range

(mm)

Profile Range

(um)Minimum Maximum Minimum Maximum

1.00 3.1 ~200

1.5 2.5 100 150

0.25 2.0 85 130

0.25 1.5 75 100

0.25 1.4 70 100

0.20 0.7 25 75

0.10 0.4 10 15

Surface Profile & Abrasive Size


Section 4 : Surface Preparation and Blasting Standards

1. Primary Surface Preparation Standards

1-1, ISO Standard 8501-1:1988(Swedish Standard SIS 05 59 00)

1-2, Steel Structures Painting Council Standards(SSPC-SP)

1-3, NACE Standards(National Association of Corrosion Engineers)

1-4, JSRA Standards(Shipbuilding Research Association of Japan)

1-5, Major Local Shipyard Standards

2. Secondary Surface Preparation Standards

2-1, Pictorial Abrasive Sweep Blasting Standards

2-2, JSRA Secondary Surface Preparation Standards

2-3, Major Local Shipyard Standards

3. Hydro Blast Standards


4 Initial Rust Grades :- for millscaled, rusted or previously coated steel.

• “A” - mainly adhering millscale, but little rust.

• “B” - rusting and flaking of millscale has begun.

• “C” - Millscale is rusting away, with slight pitting.

• “D” - Millscale has rusted away, with general pitting.

Rust Grades – ISO Standards 8501-1:1988


Blast Cleaning Sa Standards

• Sa1 - “Light Blast Cleaning”.• Sa2 - “Thorough Blast Cleaning”.• Sa2.5 - “Very thorough Blast Cleaning”• Sa3 - “Blast Cleaning to Visually Clean Steel”.

Hand and Power Tool Cleaning St Standards

• St1 - Exists but not suitable for painting.(not included in ISO STD)• St2 - “Thorough Hand & Power Tool Cleaning”.• St3 - “Very thorough Hand & Power Tool Cleaning”

ISO Standards 8501-1:1988(Swedish Standard SIS 05 59 00)


Description SSPC ISO NACE JSRA

Extremely thorough White Metal Blast SP5 Sa3 No 1 Sh(d)3

Very thorough White Metal Blast SP10 Sa2½ No 2 Sh(d)2

Thorough White Metal Blast SP6 Sa2 No 3 Sh(d)1

Light Brush-off Blast SP7 Sa1 No 4

Extremely thorough Power Tool Cleaning

SP11 - - Pt3

Very thorough Power Tool Cleaning SP3 St3 - Pt2

Thorough Power Tool Cleaning SP2 St2 - -

Solvent Cleaning SP1 - - -

Corresponding Table of Surface Preparation Standards


Rust Grade, SSPC –VIS 1-89


Blast Cleaning Standards – SIS 05 59 00

Thorough Blast Cleaning

Very Thorough Blast Cleaning

Blast Cleaning to Visually Clean Steel

Light Blast Cleaning


Sweep blasting `

Pictorial Abrasive Sweep Blast Cleaning Standards


Pt 2

Pt 0 Pt 1

Pt 3

Hand & Power Tool Cleaning Standards(Burnt Damage) - JSRA


Pt 2

Pt 0 Pt 1

Pt 3

Hand & Power Tool Cleaning Standards(Welds) - JSRA


Hydroblasting Standards are based on the Grit Blasting Standards such as Sa2, Sa2.5 etc, but are taken to a further level because as soon as this blast is achieved, it will start to corrode because of the warm clean and bright metal surface.

We therefore note:-

1) The degree of blast achieved.

2) The degree of flash rusting that has occurred.

Hydro Blasting Standards


C - HB2.5C - HB2

Rust Grade C

Initial Conditionof Steel



C HB2.5 L C HB2.5 M C HB2.5 H

C HB2.5

Initial blast achieved

Effect of Flash Rusting with time



Any Question ?

Surface Preparation

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