FINAL DRAFT prEN 13636 - CORRPOLcorrpol.com.pl/pkeopk-sep/pren13636.pdfProtection cathodique des...
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EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM FINAL DRAFT prEN 13636 June 2003 ICS 23.020.10; 77.060 English version Cathodic protection of buried metallic tanks and related piping Protection cathodique des réservoirs métalliques enterrés et conduites associées Kathodischer Korrosionsschutz von unterirdischen metallenen Tankanlagen und zugehörigen Rohrleitungen This draft European Standard is submitted to CEN members for formal vote. It has been drawn up by the Technical Committee CEN/TC 219. If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom. Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and shall not be referred to as a European Standard. EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG Management Centre: rue de Stassart, 36 B-1050 Brussels © 2003 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. prEN 13636:2003 E
Transcript of FINAL DRAFT prEN 13636 - CORRPOLcorrpol.com.pl/pkeopk-sep/pren13636.pdfProtection cathodique des...
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
FINAL DRAFTprEN 13636
June 2003
ICS 23.020.10; 77.060
English version
Cathodic protection of buried metallic tanks and related piping
Protection cathodique des réservoirs métalliques enterréset conduites associées
Kathodischer Korrosionsschutz von unterirdischenmetallenen Tankanlagen und zugehörigen Rohrleitungen
This draft European Standard is submitted to CEN members for formal vote. It has been drawn up by the Technical Committee CEN/TC219.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations whichstipulate the conditions for giving this European Standard the status of a national standard without any alteration.
This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other languagemade by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the samestatus as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and UnitedKingdom.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice andshall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATIONC OM ITÉ EUR OP ÉEN DE NOR M ALIS AT IONEUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2003 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.
Ref. No. prEN 13636:2003 E
prEN 13636:2003 (E)
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Contents Page
Foreword ....................................................................................................................... ...................................... 4
1 Scope......................................................................................................................... ............................. 5
2 Normative references.......................................................................................................... .................. 5
3 Terms and definitions......................................................................................................... .................. 6
4 Criteria for cathodic protection .............................................................................................. ............. 7
5 Prerequisites for the application of cathodic protection .................................................................. 85.1 General ..................................................................................................................... .............................. 85.2 Electrical continuity ....................................................................................................... ....................... 85.3 Electrical separation ....................................................................................................... ...................... 85.4 External coating ............................................................................................................ ........................ 8
6 Base data for design.......................................................................................................... ................... 96.1 General ..................................................................................................................... .............................. 96.2 Neighbouring structures ..................................................................................................... ................. 96.3 Soil environment ............................................................................................................ ....................... 96.4 Tank and piping data ........................................................................................................ .................. 106.4.1 General ................................................................................................................... .............................. 106.4.2 Stored medium ............................................................................................................. ....................... 10
7 Design and prerequisites ...................................................................................................... ............. 107.1 Structure materials......................................................................................................... ..................... 107.2 Electrical separation ....................................................................................................... .................... 117.2.1 General ................................................................................................................... .............................. 117.2.2 Isolating devices ......................................................................................................... ........................ 117.2.3 Temporary connections ..................................................................................................... ................ 117.2.4 Permanently connected electrical equipment................................................................................ .. 117.3 Explosion hazard prevention ................................................................................................. ............ 127.3.1 General ................................................................................................................... .............................. 127.3.2 Electrical equipment installation ......................................................................................... .............. 127.3.3 Isolating joints .......................................................................................................... ........................... 127.4 Other equipment............................................................................................................. ..................... 137.4.1 Test stations ............................................................................................................. ........................... 137.4.2 Coupons................................................................................................................... ............................ 147.4.3 Mechanical connections including flanges.................................................................................. .... 147.4.4 Sleeve pipe............................................................................................................... ............................ 147.4.5 Wall entries .............................................................................................................. ............................ 147.4.6 Drainage station .......................................................................................................... ........................ 147.4.7 Local earthing systems .................................................................................................... .................. 147.5 Galvanic anode systems ...................................................................................................... .............. 147.5.1 General ................................................................................................................... .............................. 147.5.2 Materials................................................................................................................. .............................. 157.5.3 Location .................................................................................................................. ............................. 157.5.4 Connection of anodes to the structure ..................................................................................... ........ 157.6 Impressed current systems ................................................................................................... ............ 157.6.1 General ................................................................................................................... .............................. 157.6.2 Components ................................................................................................................ ........................ 157.7 Cables...................................................................................................................... ............................. 167.8 Interference................................................................................................................ .......................... 17
8 Installation of cathodic protection systems................................................................................... .. 178.1 General ..................................................................................................................... ............................ 17
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8.2 Installation of cables...................................................................................................... ..................... 188.2.1 General ................................................................................................................... .............................. 188.2.2 Cable connections to structures ........................................................................................... ............ 198.3 Installation of structures to be protected .................................................................................. ....... 198.3.1 Buried structures ......................................................................................................... ....................... 198.3.2 Above-ground structures ................................................................................................... ................ 198.3.3 Isolating joints .......................................................................................................... ........................... 198.4 Anodes ...................................................................................................................... ........................... 208.4.1 General ................................................................................................................... .............................. 208.4.2 Galvanic anodes........................................................................................................... ....................... 208.4.3 Impressed current anodes .................................................................................................. ............... 208.5 Impressed current stations .................................................................................................. .............. 218.5.1 Location .................................................................................................................. ............................. 218.5.2 Electrical installation ................................................................................................... ....................... 218.6 Test stations, measuring points and coupons ................................................................................ 2 18.7 Bondings and drainage stations .............................................................................................. ......... 218.8 Labelling................................................................................................................... ............................ 218.9 Installation checks ......................................................................................................... ..................... 228.10 As-built documentation ..................................................................................................... ................. 22
9 Commissioning ................................................................................................................. .................. 229.1 Preliminary checking ........................................................................................................ .................. 229.2 Start-up.................................................................................................................... ............................. 239.3 Verification of the cathodic protection effectiveness ..................................................................... 239.4 Determination of relevant measuring points.................................................................................. .. 239.5 Commissioning documents ..................................................................................................... .......... 24
10 Inspection and maintenance................................................................................................... ........... 2410.1 General .................................................................................................................... ............................. 2410.2 Inspection ................................................................................................................. ........................... 2410.2.1 General .................................................................................................................. ............................... 2410.2.2 Functional checks of Equipment........................................................................................... ............ 2510.2.3 Structure measurements................................................................................................... ................. 2510.2.4 Inspection intervals..................................................................................................... ........................ 2510.2.5 Inspection Report........................................................................................................ ........................ 2710.3 Maintenance................................................................................................................ ......................... 2710.3.1 Cathodic protection equipment ............................................................................................ ............. 2710.3.2 Instrumentation .......................................................................................................... ......................... 27
Annex A (informative) Tank and associated piping with cathodic protection ........................................... 28A.1 Isolation of electrical equipment ........................................................................................... ............ 29A.2 Electrical equipment of protection class II or III (double isolation) ............................................... 30A.3 Fault current breaker with local earthing system............................................................................ 31A.4 Isolating transformer ....................................................................................................... ................... 32A.5 Example with d.c. decoupling unit ........................................................................................... ......... 33
Annex B (informative) Groundbed data.......................................................................................................... 34B.1 General considerations ...................................................................................................... ................ 34B.2 Type of groundbed........................................................................................................... ................... 34B.2.1 General ................................................................................................................... .............................. 34B.2.2 Remote located groundbeds................................................................................................. ............. 34B.2.3 Close located groundbed ................................................................................................... ................ 34B.3 Anodes types................................................................................................................ ....................... 35B.3.1 General ................................................................................................................... .............................. 35B.3.2 High silicon chromium cast iron anodes.................................................................................... ...... 35B.3.3 Mixed-metal oxide anodes (DSA anodes)..................................................................................... .... 35
Annex C (informative) Extract of pr EN 50162 ............................................................................................... 37
Annex D (informative) Determination of inspection interval ........................................................................ 38
Bibliography ................................................................................................................... .................................. 41
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Foreword
This document (prEN13636:2003) has been prepared by Technical Committee CEN/TC219 “CathodicProtection”, the secretariat of which is held by BSI.
Annexes A, B, C and D are informative.
The following countries have participated in the drafting process:
Austria
Belgium
Czech Republic
France, Convenor and Secretariat
Germany
Italy
Netherlands
Spain
Sweden
Switzerland
United Kingdom
The work of CEN TC 219/WG1 concerning cathodic protection against corrosion of buried orimmersed metallic structures, the standard EN 12954 is the basic document giving general principlesapplicable to the protection of all types of such structures.
The present standard, which deals with buried metallic tanks and associated piping takes into accountthe specific features of buried tanks in terms of construction, electrical equipment and safetyconsiderations.
This standard only covers the technical aspects of corrosion protection of tanks and associatedpiping. The application of cathodic protection depends on national requirements and the factorsoutlined in EN 12954:2001, clause 5.
In the case of existing structures the standard should be applied as far as possible. If there arerestrictions given by the existing construction, these have to be taken in account for the design.
Cathodic protection is a technique based on the application of electrochemical principles and covers awide variety of materials and equipment together with a variety of measurement techniques. In orderto achieve effective and efficient cathodic protection, the design, installation, commissioning,inspection and maintenance should be performed by adequately trained, experienced, competent andreliable personnel.
This standard aims to ensure effective cathodic protection and is therefore directed primarily to theabove personnel.
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1 Scope
This European Standard specifies the principles for the implementation of a system of cathodicprotection against corrosive attacks on buried metal tanks and associated piping.
This standard indicates conditions and parameters that should be met to achieve cathodic protectionas well as rules and procedures that should be followed for design, installation, commissioning andmaintenance for the protection of buried metal tanks and associated piping.
This standard is applicable to the external surfaces of buried metallic tanks and associated buriedpiping.
NOTE The protection of internal surfaces is the subject of EN 12499.
This standard is applicable to buried tanks and associated piping which are separated from anygeneral earthing systems and other buried structures.
Therefore tanks which are covered by the present standard include:
industrial storage tanks, irrespective of their dimensions and the nature of the stored medium(liquid or gas, flammable or not, toxic or non-toxic, polluting or not);
tanks used at petrol stations and on domestic or commercial premises, which contain flammableliquids or gases or polluting substances.
This standard is not applicable to:
above-ground storage tank floors in contact with the ground;
reinforced concrete containers;
buried storage tanks that are electrically connected to the whole or a part of an industrialcomplex;
buried storage tanks electrically connected to any general earthing systems.
NOTE Cathodic protection of the last two types of tanks is subject of prEN 14505 (Cathodic Protection ofcomplex structure).
Measurement techniques are described in detail in prEN 13509.
2 Normative references
This European Standard incorporates, by dated or undated reference, provisions from otherpublications. These normative references are cited at the appropriate places in the text and thepublications are listed hereafter. For dated references, subsequent amendments to or revisions of anyof these publications apply to this European Standard only when incorporated in it by amendment orrevision. For undated references the latest edition of the publication referred to applies (includingamendments).
EN 12 954:2001 Cathodic protection of buried or immersed metallic structures- General principles and application for pipelines
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prEN 14505 2002 Cathodic protection of complex structures
EN ISO 8044:1999 Corrosion of metals and alloys - Basic terms and definitions(ISO 8044:1999)
EN 50014 Electrical apparatus for potentially explosive atmospheres -General requirements
EN 50020 Electrical apparatus for potentially explosive atmospheres -Intrinsic safety "i"
EN 50018 Electrical apparatus for potentially explosive atmospheres -Flameproof enclosures "d"
EN 50017 Electrical apparatus for potentially explosive atmospheres -Powder filling "q"
EN 50016 Electrical apparatus for potentially explosive atmospheres -Pressurized apparatus "p"
EN 50019 Electrical apparatus for potentially explosive atmospheres -Increased safety 'e'
EN 50028 Electrical apparatus for potentially explosive atmospheres;encapsulation m
EN 50039 Electrical apparatus for potentially explosive atmospheres.Intrinsic safety "i" Systems
prEN 50-162 Protection against corrosion by stray current from DCsystems
EN 60742 Isolating transformers and safety isolating transformers -Requirements (IEC 60742:1983 + A1:1992, modified)
EN 61140 Protection against electric shock - Common aspects forinstallation and equipment (IEC 61140:2001)
EN 60079-10 Electrical apparatus for explosive gas atmospheres - Part 10:Classification of hazardous areas (IEC 60079-10:1995)
IEC 60587 Test methods for evaluating resistance to tracking anderosion of electrical insulating materials used under severeambient conditions
3 Terms and definitions
For the purposes of this European Standard, the terms and definitions given in EN 12954:2001 andEN ISO 8044:1999 apply.
3.1hazardous areaarea in which local or process conditions can cause the atmosphere to become explosive(classifiedas zones 0, 1 or 2 as per EN 60079-10 for gas atmospheres)
3.2electrical connection (electrically connected)means that current can flow via electrons between two different metallic structures
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3.3electrical separation (electrically separated)means that current cannot flow via electrons between two different metallic structures
3.4associated Pipingall metallic process piping that is electrically connected to a buried tank and can be protected by thecathodic protection system of the tank
3.5local earthing systemlocal earthing system for the structure under consideration which is electrically separated from anyother general earthing
3.6shieldconductive or non conductive structure or object, which modifies the protection current distribution on astructure to be protected
4 Criteria for cathodic protection
The metal to electrolyte potential at which the corrosion rate is < 0,01 mm per year is the protectionpotential, Ep. This corrosion rate is sufficiently low so that during the design life time corrosiondamage cannot occur. The criterion for cathodic protection is therefore:
E ≤ Ep
For carbon steel in soils with resistivities of ρ < 100 Ωm and in the absence of sulphate reducingbacteria, the protection potential versus a Cu/CuSO4 saturated reference electrode, Ep,, is -0.85 V.Special measures (see EN 12954:2001 Table 1) shall be taken for steel with higher yield strengths toavoid hydrogen-induced cracking.
e.g. welding
metallic bond or cable
Structure 1 Structure 2
Structure 1 Structure 2Structure 1 Structure 2
Structure 1 Structure 2
Structure 1 Structure 2
Isolating material
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Full details of the principle and criteria of cathodic protection are given in EN 12954:2001, clause 4.
NOTE On well insulated tanks where the potential criterion is difficult to verify, the effectiveness of cathodicprotection may be checked by measurement via a coupon (see 7.4.2).
5 Prerequisites for the application of cathodic protection
5.1 General
The design of cathodic protection for tank systems depends on the location and the extent of thestructure, the kind of embedding material, the soil resistivity, the coating (type, coating resistance etc.)and also on general safety requirements.
The different elements of the structure to be cathodically protected need to be separated from eachother. The separation distance will depend on the diameter, the length and above all the averagecoating resistance of the tanks. It depends also on the location (close or remote) of the groundbed inrelation to the structure. As a minimum for well-coated tanks this distance should be 0,40 m betweentanks.
The protected structure needs to be also sufficiently remote from any other buried structure so thatthese foreign structures do not act as a shield for the structure to be cathodically protected and do notsuffer from interference effects. For well coated tanks, the distance between protected and foreignstructures should be as a minimum 1,0 m.
Where the tanks being protected are enclosed within steel reinforced concrete retaining walls, specialattention shall be given to avoid:
detrimental effects of CP currents upon the rebar;
metallic contact between the steel reinforcement and the tank, because this contact would reducethe current entering the tank.
For applying cathodic protection the prerequisites given in 5.2 to 5.4 need to be met.
5.2 Electrical continuity
The structure, or a section of the whole structure, to be protected must be electrically continuous. Thecontinuity needs to achieve a low longitudinal resistance and the components which may increase thelongitudinal resistance of the structure must be short-circuited, e.g. by using cables with a suitablecross section area as recommended in 7.7.
It is recommended that bonds are capable of being disconnected for measuring purposes.
5.3 Electrical separation
Tanks to be protected shall have no metallic contact with parts of structures which are not to beprotected, with earthed structures (e.g. reinforcing steel) or with general earthing system even madeof galvanised steel.
If earthing is necessary for safety reasons (e.g. for electrical equipment, lightning and explosionprotection) special measures need to be taken (see 7.2.3, 7.2.4 and 7.4.7).
5.4 External coating
The structures to be protected should normally be provided with a suitable external coating.
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NOTE This coating should provide sufficient corrosion protection, be compatible with cathodic protectionand be resistant to the stored fluid.
A good external coating reduces protection current demand, improves current distribution andreduces interference to other foreign structures.
On structures which are bare or poorly coated, e.g. existing tank, cathodic protection needs to beapplied with care to avoid electrical interference.
6 Base data for design
6.1 General
The design of effective cathodic protection systems is highly dependent upon correct informationconcerning the proposed structure to be protected.
Structure details, local soil conditions, service conditions and the chosen design lifetime for thecathodic protection system need to be known to establish the correct method of protection and thecorrect materials to achieve and sustain effective cathodic protection.
6.2 Neighbouring structures
Details of neighbouring buried structures should be obtained. Such information should include as aminimum :
location (e.g. maps, detailed site layout);
principle dimensions and characteristics;
coating details, type and location of any earthing system;
type and location of isolating devices;
details of foreign cathodic protection systems and/or other possible sources of stray current.
The use of such information can help to prevent adverse effects on the structure and on neighbouringstructures.
6.3 Soil environment
Environmental conditions can have a major impact on the application of cathodic protection andtherefore need to be fully considered during the design phase.
For widely dispersed structures, differences in environmental conditions should be taken into account.These may include:
soil resistivities at suitable depths and locations;
presence of stray currents;
probability of sulphate reducing bacteria activity;
ground water level.
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6.4 Tank and piping data
6.4.1 General
For the design of the cathodic protection of tanks and associated piping the following informationshould be available:
location of the structure;
structure materials and dimensions including surface area;
tank design (number of manholes, pits, etc.);
coating characteristics;
bedding details (method and materials);
earthing systems;
stored medium;
location and details of isolating devices;
location and details of sleeve pipes;
location and details of wall entries;
electrical equipment connected to the structures;
hazardous area classification;
existence of paved ground surface.
For existing tanks the design may be based on the above information in conjunction with informationgathered in field tests.
6.4.2 Stored medium
The physical and chemical characteristics of the medium in the tank and piping should be taken intoaccount for the design and the selection of materials of the cathodic protection system.
Isolating joints used in the piping shall be selected with due consideration for the stored medium(corrosivity, conductivity, pressure, temperature etc.; see EN 12954:2001, 7.2).
7 Design and prerequisites
7.1 Structure materials
The structure material will determine the protection potential Ep required (see EN 12954:2001, 4.2).
If parts of the structure are made of different materials, the determination of the protection potentialsneed to take account of the metals used. In this case, special measures may need to be taken in thedesign of the cathodic protection system.
Such measures may be:
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increasing the resistance to earth by applying a suitable coating material to the metal with themore positive free corrosion potential, e.g. stainless steel, copper;
installing permanent reference electrodes, coupons or external potential test probes close to themetal with the more negative free corrosion potential near its contact with the other metal.
7.2 Electrical separation
7.2.1 General
Cathodically protected structures shall not be electrically connected directly to the general earthingsystem of the plant (see 5.3). Otherwise, such structures are relevant of the prEN 14505
7.2.2 Isolating devices
Electrical separation between the structure to be protected and structures which are connecteddirectly to the general earthing system is obtained by means of isolating devices (e.g. isolating joints).
These should be installed in such a way that accidental contacts of the isolated parts of the structureto the general earthing systems are avoided.
They have to be protected against damages caused by atmospherical and mechanical influences.
All isolating joints should preferably be installed above ground and, for measurement purposes,should be easily accessible from both sides. If buried, they shall be coated (see 8.3.3).
The requirements for isolating joints in hazardous areas are given in 7.3.
7.2.3 Temporary connections
The electrical separation and consequently the cathodic protection can be disturbed due to temporaryconnections between the structure to be protected and trains, trucks, ships. The CP system shall bedesigned in such a way that it still functions properly after the disconnection.
7.2.4 Permanently connected electrical equipment
The installation of electrical equipment (e.g. pumps, electrically controlled valves, telemetricmeasuring devices...) in the structure to be protected can affect the electrical separation between thisstructure and the general earthing system.
Depending on national regulations, separation can be achieved by:
a) the isolation of electrical equipment from the cathodically protected structure. In this case theequipment is not protected by the cathodic protection system of the tank (see A.1);
b) the use of electrical equipment of protection classes II or III defined in EN 61 140 (see A.2);
c) the installation of a fault current breaker, if necessary in conjunction with a local earthing system(see A.3);
d) the use of an isolating transformer (safe isolation, see EN 60 742 ) (see A.4);
e) the installation of d.c. decoupling devices between the electrical equipment and the generalearthing system (see A.5).
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7.3 Explosion hazard prevention
7.3.1 General
Cathodic protection equipment and its installation in explosive gas atmospheres conform toEN 50014.
For the purposes of this sub-clause, the classification of the hazardous area (zones 0, 1 and 2)conforms to EN 60079-10.
7.3.2 Electrical equipment installation
Installation of electrical equipment in zone 0 should be avoided. If installed in zone 0, it is essentialthat the equipment conforms to EN 50020 and that it is of type ia.
In zone 1, it is essential that explosion-proof electrical equipment or systems conforming to one of thefollowing standards is used:
EN 50020, Intrinsic safety type ‘i’;
EN 50018, Flame-proof enclosure type ‘d’;
EN 50017, Sand-filled type ‘q’;
EN 50016, Pressurisation type ‘p’;
EN 50019, Increased safety type ‘e’;
EN 50028, Enclosure type ‘m’;
EN 50039, Intrinsically safe system type ‘SYST’.
In zone 2, the equipment shall comply with requirements of EN 50021 dealing with “Non sparkingtype ‘n’.
7.3.3 Isolating joints
Isolating joints between cathodically protected and non-protected parts of the installation should notbe placed in hazardous areas.
NOTE Attention is drawn to safety regulation covering hazardous areas
Installation of isolating joints is not permitted in zone 0, except if the zone 0 is located inside the pipe.In this case an isolating joint may be installed only in combination with additional explosion hazardmeasures (e.g. flame arrestor).
If isolating joints are installed in zone 1 and 2, they have to meet the requirement for use in therespective zone.
The design shall be such that accidental bonding is avoided.
To avoid sparks or flashover at isolating joints in zones 1 and 2, the installation of explosion-proofspark gaps should be considered.
Spark gaps are not required across isolating joints located inside petrol pump housings at servicestations.
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Isolating joints in a loading/unloading installation for flammable fluids shall only be installed on thefixed part of the piping installation.
7.4 Other equipment
7.4.1 Test stations
A minimum of one test station shall be installed for each electrically isolated tank. Provisions shall bemade for permanent cathodic protection measuring points. This is particularly important:
if the tank is placed under buildings;
if the tank is buried under isolating layers, e.g. asphalt, sealed concrete;
if the tank is installed at ground level and subsequently covered with a mound of earth (moundedvessel);
if several tanks are closely parallel;
if the tank has a large surface area.
In cases where isolating layers are provided for groundwater or soil protection, the design of themeasuring point needs to be such that ingress of polluting substances is avoided.
The number and location of fixed measuring points with or without a permanent reference electrodeshould be sufficient to ensure that the cathodic protection potentials measured are representative ofthe entire structure.
The different sizes and configurations of tank installations preclude firm recommendations on thenumber and location of measuring points. As an indication there should be:
at least one measuring point for each tank,
at least two measuring points for each tank with a surface area of more than 20 m2 and less than100 m2;
one additional measuring point for every 100 m2 up to 500 m2;
one additional measuring point for every 500 m2 thereafter;
for measurement purposes, all isolating joints should be easily accessible from both sides. If they arenot accessible, they shall be provided with a test station.
Measuring points and if necessary test stations, shall be defined along the piping, at least at the endsand near critical points (e.g. sleeve pipe).
The number of test stations to be installed on the pipework will depend on the length and geometricalarrangement of the piping.
To facilitate fault location, it is recommended that the installation of the structure and the cathodicprotection system be carried out in such a way that each part of the structure (tank, pipes, localearthing devices, etc.) can be electrically separated. Bonds, which are to be temporarily opened formeasurement reason shall be placed above ground.
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7.4.2 Coupons
Where the quality of the coating is very high and there is no metal in contact with the electrolyte,polarisation cannot occur. In such cases, a 1 cm2 to 10 cm2 steel coupon should be connected to thestructure. In this way conventional cathodic protection measurements can be made on the coupons toshow whether the respective size of a possible coating defect on the tank can be cathodicallyprotected.
Coupons should be connected via a test station.
7.4.3 Mechanical connections including flanges
Mechanical connections, other than isolating joints, which could cause an unacceptable increase inthe longitudinal resistance of the structure shall be electrically bonded.
7.4.4 Sleeve pipe
Sleeve pipe should be avoided where possible. If sleeve pipe are required by regulations, specialprecautions should be taken in accordance with EN 12954:2001, 7.5.
7.4.5 Wall entries
Where entries are made through concrete structures, metallic contact between reinforcing steel andthe protected structure shall be avoided (see EN 12954:2001, 7.6.)
A flawless coating shall be applied to the structure and special care shall be taken to avoid coatingdefects.
7.4.6 Drainage station
The need for installing drainage station should be taken into account (see also prEN 50162).
7.4.7 Local earthing systems
Where earthing is required for safety reasons, a local earthing system (see 3.5) should be installed.
This system should be made of a metal with a more negative free corrosion potential than the metal tobe protected. For carbon steel tanks, local earthing material of zinc, galvanised steel and magnesiumcan be used.
For a carbon steel tank, it is highly recommended not to use copper, stainless steel, or reinforcingsteel in concrete as a local earthing material.
To enable accurate measurements (current, earthing resistance, and potential measurements) to bemade, it should be possible to temporarily disconnect this local earth connection.
NOTE Attention is drawn to safety regulations regarding earth connections.
7.5 Galvanic anode systems
7.5.1 General
Cathodic protection using galvanic anodes can be obtained economically if.
the current requirement is low;
the soil has a low resistivity.
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Galvanic anodes are usually installed in a low-resistivity and non-carbonaceous backfill.
To meet the cathodic protection criteria, the following should also be considered:
use of an efficient protective coating on the tank and piping;
maintain a good isolation between the structure to be protected and the neighbouring structuressuch as sleeve pipes, wall entries and foreign structures;
avoid the use of bare buried wires (e.g. for making connections to the earthing system).
7.5.2 Materials
Magnesium and zinc can be used as galvanic anode materials.
Zinc anodes have a lower capacity and a smaller driving voltage against carbon steel thanmagnesium anodes.
The choice between magnesium and zinc also depends on design life requirements and economicconsiderations.
7.5.3 Location
The location of the galvanic anodes depends on the structure to soil resistance and should beselected such that the desired current distribution can be achieved. A low structure to soil resistancerequires a larger distance between galvanic anode and structure.
Additional measures may be necessary to prevent accidental contact between the anodes and thestructure to be protected.
In general, anodes are located at a distance of at least 1 m from the structure.
7.5.4 Connection of anodes to the structure
To check the efficiency of the galvanic anode system, it shall be connected to the structure via a teststation.
For functional checks, each anode should be connected separately to the test station.
7.6 Impressed current systems
7.6.1 General
Impressed current cathodic protection can be applied to buried metallic tanks and associated piping.
7.6.2 Components
7.6.2.1 Anode materials
Anode materials commonly used are:
silicon iron alloys;
graphite;
metallic oxides;
prEN 13636:2003 (E)
16
conductive polymers;
steel.
The selection of the anode material will depend on the individual application (see annex B).
7.6.2.2 Transformer rectifiers
The transformer rectifiers shall be rated for the anticipated current output until the end of the chosendesign lifetime of the cathodic protection system and in accordance with safety rules (see EN 60742)and operating conditions (see EN 50014).
The transformer rectifier specification should take account of monitoring requirements (e.g. remotecontrol, output control) and the site location.
NOTE Attention is drawn to local regulations.
7.6.2.3 Groundbeds
The number, size and position of the anodes and the extent of the groundbeds should be selected sothat:
they correspond to the chosen design lifetime for the cathodic protection system;
the desired current distribution can be achieved without adverse interference on foreignstructures.
For deep well and shallow groundbeds located remote from the tank (see annex B and EN 12954).
For a distributed anode system on buried cylindrical tanks and associated piping the anodes shouldbe installed at or below the axis of the tank.
Tanks originally constructed above ground and subsequently covered with a layer of earth will requireanodes to be distributed to achieve full cathodic protection for all soil conditions.
The anodes should be placed in a suitable low resistive backfill, e.g. electrically conductive coke.
The distance between the anodes and the protected structure should be at least 1 m. Between theanodes and foreign structures, the distance depends on the driving voltage and the soil resistivity, butshould be large and at least 2 m.
7.7 Cables
NOTE Attention is drawn to electrical and safety regulations governing cables.
Insulated cables should be used.
Minimum cable cross sections should be as follows (see EN 12954:2001, 7.11.3)
Impressed current system:
cable to protected structure: 10 mm2 Cu
cable to groundbed: 4 x 2,5 mm² or 10 mm2 Cu
Galvanic anode system:
prEN 13636:2003 (E)
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cable to protected structure: 4 mm2 Cu
cable to single anode: 2,5 mm2 Cu
Test station:
cable for potential measurement: 2 x 2,5 mm2 or 6 mm2 Cu
cable for continuity bond : 4 x 2,5 mm2 or 10 mm2 Cu
In general, the cable size will be determined by the permissible IR drop in the specific cable run.However, where current requirements are very small, selection of the conductor cross section may bebased upon mechanical strength rather than electrical resistance.
Therefore this cable with smaller cross sections than those recommended may be used if the cablesand their connections have adequate mechanical protection.
7.8 Interference
Any possible interference on the structure to be protected will depend on the extent of the structureand the proximity of possible sources of stray current, e. g. d.c. traction systems, neighbouringcathodic protection systems. The adverse effects of stray d.c. current interference and measures toreduce this interference are detailed in prEN 50162 (see extract in annex C)
The level of interference on foreign structures caused by a cathodically protected structure willdepend mainly on the output current of the anodes and on the distance between the anodes and theforeign structures To minimise the risk of interference on foreign structures, one or more of thefollowing measures may be taken :
the rectifier output voltage and the anode current output should be minimized;
the distance between the foreign structure and the nearest anode should be increased.
The measures listed above only cover the anodic part of the protection system. Interference can alsooccur on nearby foreign structures close to bare parts of the protected structure (e.g. coating defects)where a significant voltage gradient may appear. In this case other measures should be taken inaccordance with prEN 50162.
8 Installation of cathodic protection systems
8.1 General
This clause concerns main aspects that should be considered during the installation of cathodicprotection components.
Installation of the cathodic protection system shall be carried out in accordance with the design basedon the prerequisites detailed in clause 7. This includes the location and installation of test stations andgalvanic anodes or impressed current systems, or drainage stations.
The other equipment determined by the design, such as isolating joints, coatings, sleeve pipes andlocal earthing devices, are integral parts of the structure to be protected and are therefore installed atthe same time as the main structure to be protected.
The cathodic protection system should be installed as soon as possible preferably during the burial ofthe tanks and the pipework.
prEN 13636:2003 (E)
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As a general rule, the following points shall be considered:
a) Before the beginning of the work, it shall be verified that:
the equipment and the materials to be installed are in conformity with those indicated in thedesign;
the local conditions are the same as those used for the design.
b) During the work, it is necessary to verify that the installation and materials are in conformity withthe appropriate regulations, including safety.
c) Deviations from the design shall be justified for approval, then documented and later reported onas-built documentation.
d) The explosion hazard prevention measures mentioned in 7.3 should be taken.
If there is a risk that tanks may come into metallic contact with other structures (e.g. reinforcing steel,anchors) it is recommended that permanent electrical isolation is ensured before backfilling.
8.2 Installation of cables
8.2.1 General
In all cathodic protection installations cables shall be installed with great care to avoid damage to theinsulation. They should be run through non conductive ducts and be protected with sufficient depth ofcover (e.g. 80 cm) and have warning tapes.
If cables in ducts pass through hazardous areas, the ducts shall be sealed by adequate means toprevent flammable liquids and gases from being carried into non-hazardous areas.
As far as possible cable joints in the ground should be avoided.
Cable should be long enough to deal with ground settlements.
All cables should be run to above-ground junction boxes preferably installed outside hazardous areas.Junction boxes in hazardous areas e.g. valve pits and dome shafts should be flameproof.
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The cables shall be clearly identified, either by using different colours or by identification marks.
NOTE Attention is drawn to the electrical and safety regulations governing cables.
8.2.2 Cable connections to structures
Cables bonding different parts of the structure to be protected should be accessible and allowdisconnection. Cable connections to foreign structures shall be agreed with the owners of thosestructures.
The cables should be connected to the structure at points where they are unlikely to be damagedduring operation or maintenance.
Cable connections to the structure to be protected should be made by welding, brazing, bolts orconductive adhesives and shall be protected against corrosion (e.g. by coating). Conductive epoxyshould not be used for current carrying connections on impressed current systems.
For screwed connections and cable lugs, bolts of at least size M8 which are protected against self-loosening shall be used. All cable connections shall be high conductive.
The cable connecting procedure used should be such that it does not affect the mechanical propertiesof the structure.
It is recommended that conductors used for measuring purposes be kept separate from thosecarrying protection current.
8.3 Installation of structures to be protected
8.3.1 Buried structures
Tanks and pipes should preferably be embedded in a material that does not damage the coating (e.g.sand). This material shall be free from electronically conducting constituents (metals, carbonaceousmaterials, metal oxides such as magnetite, etc.).
A homogeneous bedding material ensures good current distribution and avoids shielding.
8.3.2 Above-ground structures
Where an above-ground structure including any associated local earthing system cannot beseparated from the protected structure, it shall be protected against accidental contact with structuresconnected to the main earthing system. Vent pipes, for example, should be protected by placing themin a plastic sleeve or by applying a plastic coating.
Pipes leaving the ground shall be protected by a coating at the air/soil area. If applicable, this part ofthe structure should be coated up to a height of 0,5 m.
8.3.3 Isolating joints
Isolating joints shall be designed for electrical, mechanical and chemical operating conditions andbefore installation be able to withstand a testing alternating voltage of 5 kV according to IEC 60587over a period of one minute.
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To allow inspection, isolating joints, particularly of the insulated flange type, should preferably not beburied. However, joints of all types, when buried, shall be coated with materials compatible with thestructure coating and shall be fitted with test cables.
NOTE Above-ground isolating joints installed in hazardous areas are covered by national safety regulations,which require special safety measures to be taken, e.g. the application of a protective coating to preventaccidental contact and the fitting of explosion-proof spark gaps to prevent flashover.
If there are several isolating joints in a confined area (e.g. in a dome shaft), measures should betaken to avoid accidental contact, e.g. by installing joints at the same level. If water enters a domeshaft containing isolating joints, electrolytic short-circuiting can occur, causing corrosion. This can beavoided by, for example, mounting the isolating joints at a high level or providing adequate waterdrainage to the shaft or pit.
8.4 Anodes
8.4.1 General
At the time of anode installation, the following shall be ascertained by reference to the designdocuments:
that the anodes are located in accordance with the design and the recommendations given in 7.5and 7.6, particularly those referring to the condition of the soil and its resistivity;
that there is no shielding between the anodes and the structure to be protected;
that there is no risk of unacceptable interference to other buried metallic structures (see 7.8).
The electrical circuit between the anodes and the structure should in general be left disconnected untilthe free corrosion potential has been measured (see 9,1).
8.4.2 Galvanic anodes
At the time of installation of galvanic anodes, checks should be carried out to ascertain, by referenceto the design file (plans, specifications and procedures) whether or not the following points arecovered:
the electrolyte condition and resistivity where the anodes are to be located corresponds to thedesign;
there is isolating shielding between the anode and the structure to be protected;
if there is any risk of interference, corrective measures have been taken, anodes conform to thespecifications;
for buried anodes, the anode backfill material used is the correct type for the anodes concerned,and that the homogeneous backfill mixture is evenly distributed around the anode;
the pre-package anodes have been thoroughly wetted before burial;
the electrical circuit between the anode and the structure has been left open at the test stationuntil the commissioning (see clause 9).
8.4.3 Impressed current anodes
The dimensions of the anodic mass should be checked to see if they correspond to those indicated inthe design. The backfill, if any, should be checked to verify if it is suitable and that it has been
prEN 13636:2003 (E)
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correctly prepared. It is particularly important to check that the backfill is both sufficient in quantity andhomogeneous, and meets the requirements of the project specification.
8.5 Impressed current stations
8.5.1 Location
The impressed current stations should be easily accessible and be protected against the effects of theenvironment and mechanical damage. It should be located outside hazardous areas or, alternatively,be of a type suitable for use in such areas (e.g. with a flameproof, pressurised or ventilatedenclosure).
8.5.2 Electrical installation
The electrical equipment and its installation should ensure continuous operation (e.g. with anindicator).
NOTE Attention is drawn to electrical and safety regulations.
8.6 Test stations, measuring points and coupons
Test stations should be located in easily accessible places in accordance with 7.4.1, protected againstthe risk of damage (e.g. shocks) and set up in such a way as to make them easy to find. They shouldpreferably be located outside hazardous areas.
The number and location of fixed measuring points and coupons shall be verified according to thedesign.
8.7 Bondings and drainage stations
Connection devices between cathodically protected and foreign structures shall be easily accessibleto all concerned parties and should be protected against damage by environmental effects.
8.8 Labelling
For information and safety reasons appropriate labels should be attached to the main components ofthe systems, such as impressed current stations, drainage stations and test stations and the structureto be protected.
Depending on the place of installation and the type of structure protected, these labels should:
include safety signs concerning the dangers of electricity;
include hazardous area signs;
describe measures to be taken in case of failure;
give the name of the owner/operator of the system;
indicate that the cathodic protection system must continuously be on, unless work is beingcarried out on the protected structure;
include circuit diagrams.
All cables within test stations shall be clearly identified.
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8.9 Installation checks
During the work, it is necessary to verify that the installation and materials are in conformity with thedesign and appropriate regulations, including safety.
Underground components, including connections, shall be checked before covering with soil.
Deviations from the design shall be justified for approval, then documented and later reported on as-built documentation.
Checks may include:
installation of the galvanic anodes;
installation of the transformer/rectifier (design, anode and cathode cable connections and electricfunction);
installation of the groundbed with backfill;
cable laying, cable connections, cable marking, integrity of cable ducts;
installation of permanent measurement coupons;
installation of fixed measuring points;
test stations (placing, design and marking of measurement sockets).
8.10 As-built documentation
Electrical diagrams and site layout drawings shall be made for the cathodic protection system,showing the structure with its main components, the location and type of galvanic and impressedcurrent anodes, the impressed current stations, test stations and isolating joints as well as nearbyforeign structures.
9 Commissioning
9.1 Preliminary checking
Before a cathodic protection system is activated, care should be taken to check that all installationsare in accordance with the design. In particular, cable connections and safety measures (contactprotection, lightning protection, explosion proofing,) where necessary shall be checked.
D.c. connections to the transformer rectifier shall be checked for correct polarity.
Further, the following measurements may be made and the readings compared with the designrequirements:
a) Resistance measurements
Resistance against remote earth of the groundbed or the galvanic anodes.
Resistance between the structure to be protected and the groundbed or the galvanic anodes.
b) Electrical separation of the structure
At isolating joints.
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At metal sleeve pipes.
From the general earthing system (see 5.3).
c) Potential measurements
Free corrosion potential, En, of the structure.
Interference due to suspected stray currents.
Anode to electrolyte potential of galvanic anodes.
Structure to electrolyte potential of nearby structures.
d) Measurement to determine the extent of any interference from or on foreign structures.
9.2 Start-up
Switch on the cathodic protection station and confirm that it is functioning correctly.
Adjust station settings to conform to the potential requirements in the design. If major deviationsoccur, the causes should be ascertained by measurement.
When necessary, connect galvanic anodes to the protected structure via a variable resistor forcurrent limitation.
Next make the following measurements :
rectifier output voltage on the impressed current station,
protection current output,
on and off potential at all measuring points,
on potential and current of foreign electrodes,
possible a.c. or d.c. interference (See pr EN 50162).
If stray currents are present, make measurements to determine the interference level in order toachieve the effectiveness of cathodic protection. These measurements shall be made with andwithout the cathodic protection stations in operation.
In addition, make measurements on any nearby foreign structures to ensure that they are notadversely affected by the cathodic protection system installed (see pr EN 50162).
9.3 Verification of the cathodic protection effectiveness
Once the protected structure has sufficient electrical ground contact and after a suitable polarisationperiod , the effectiveness of cathodic protection needs to be checked in accordance with clause 4.
9.4 Determination of relevant measuring points
At the end of the commissioning measuring points that are relevant for further periodic structuremeasurements may be determined.
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9.5 Commissioning documents
After the successful commissioning of the cathodic protection installations, the following shall beprepared:
as-built drawings of the structure and it's geographical position and those of all neighbouringstructures likely to be affected by the cathodic protection system (see 8.10);
cathodic protection design with as-built drawings and all details pertaining to the cathodicprotection of the structure;
results of interference tests carried out on neighbouring structures;
details of equipment operation and adjustment and the results of all measurements carried outbefore and after commissioning;
a summary of the installation records with references to any materials used and/or installationwork that were not covered by the design.
NOTE The final data are the bases for subsequent system checks to be performed on the structure andtherefore need to be filed and retained.
10 Inspection and maintenance
10.1 General
The aim of inspection and maintenance is to ensure the effectiveness of cathodic protectionthroughout the life of the structure. For this to be achieved, the required structure to electrolytepotential shall be maintained within the limits stated in the design by continuous operation andmaintenance of the cathodic protection system.
Subsequent to commissioning (see clause 9), regular inspection is necessary according to : approvedprocedures.
The procedures should be subject to review to reflect operating experience and new technology.
Instrumentation used for measurements shall be kept in good working order and shall be subject toperiodical calibration and safety checks.
10.2 Inspection
10.2.1 General
The inspection of the effectiveness of applied cathodic protection can be conveniently divided into twoareas: equipment function checks and structure measurements.
The measuring results and all other findings shall be recorded.
The procedures used and the results obtained shall be reviewed and approved by cathodic protectionpersonnel with adequate theoretical and practical knowledge.
If any abnormalities are observed, the causes shall be investigated and appropriate action shall betaken.
NOTE Attention is drawn to national regulations regarding the checking of electrical safety.
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10.2.2 Functional checks of Equipment
Regular visual inspections of the installation (e.g. functioning of the rectifier, readings of indicators,accessibility of test stations, connections,) should be made to check the functioning and the goodworking conditions of the cathodic protection equipment.
10.2.3 Structure measurements
The cathodic protection effectiveness is assessed by comparing measurement values with theprotection criterion or reference values.
Measured values established at the time of commissioning as well as in subsequent years are usedas reference values.
Depending on the structure (type, size…) and the cathodic protection system, the followingmeasurements should be carried out:
rectifier output voltage of impressed current station;
protective current;
on and off potential at relevant measuring points and coupons;
on potential and current requirements of foreign electrodes;
d.c. interference to or from foreign structures, if found to be necessary following modification orreadjustment of the cathodic protection system (see prEN 50162).
Measurements listed in 9.1 may be also carried out to gather information on variations occurred onthe cathodic protection system. They concerned:
resistance measurements;
electrical separation of the structures.
All measurements should be made by adequately qualified cathodic protection personnel.
If there are indications that the cathodic protection is not fully effective throughout the structure,investigations should be carried out and appropriate corrective action taken to restore effectivecathodic protection. The measured values obtained are then be used as the new reference values.
10.2.4 Inspection intervals
10.2.4.1 Frequency of equipment functional checks
Unless telemetric methods are used and regularly verified, function checks should be carried out atthe typical following frequencies:
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Table 1 — Frequency and nature of functional checks
Galvanic anode stations According to the frequency of the structuremeasurements (c.f. 10.2.4.2) or more frequently ifrequired by operational conditions.
Impressed current stations Every 3months or more frequently if required byoperational conditions.
Connections to foreign structures Annually or more frequently if required byoperational conditions.
Safety and protection devices Annually or more frequently if required byoperational conditions.
Test stations According to the frequency of the structuremeasurements (c.f. 10.2.4.2) or more frequently ifrequired by operational conditions.
10.2.4.2 Frequency of structure measurements
The period of time between two successive assessments of cathodic protection effectiveness istypically one year.
Nevertheless according to the type and location of tanks, and the consequences of a leak, thisinspection interval may be reduced or increased to a maximum period of time that shall not exceedthree years.
This inspection interval may be reduced to accommodate requirements imposed by nationalauthorities.
The effectiveness of cathodic protection should also be checked when changes are observed in thestructure or the environment and in particular after construction work on or in the vicinity of thestructure.
Adequately trained, experienced, competent and reliable personnel shall determine the inspectionfrequency.
To determine the suitable inspection frequency Table 2 and Table 3 shall be used.
Table 2 — Selection of Weight factors
Weight factors (*)Items
Low Medium High
1. Complexity of cathodic protection system 0 3 6
2. Coating imperfections 0 2 4
3. Environmental conditions e.g. d.c. Interferences 0 2 4
4. Susceptibility to damage by lightning ormechanical impacts
0 1 2
5. Risk of personal injury or risk of environmentalpollution or damage to property that could becaused by leakage of stored medium
0 3 6
(*) Intermediate values are not allowed.
Additional information concerning each item is given in annex D
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Table 3 — Selection of Inspection frequency
Total weight of items Inspection frequency
9 - 22 One year
5 - 8 Two years
0 - 4 Three years
10.2.5 Inspection Report
The results of inspections shall be recorded and evaluated.
These records shall be kept for a sufficient period of time to provide detailed information on thecathodic protection effectiveness and to allow comparative checks to be carried out.
In addition, it is recommended that the records and the cathodic protection history are kept forreference purposes for the lifetime of the structure.
10.3 Maintenance
10.3.1 Cathodic protection equipment
Routine maintenance shall be carried out in a way to ensure that the cathodic protection systemcontinues to operate in the manner intended by the design.
Transformer rectifiers shall be maintained in accordance with the manufacturer’s recommendations.
Maintenance on cathodic protection equipment should also be carried out when necessary during oras soon as possible after functional checks or structure measurements.
10.3.2 Instrumentation
Instrumentation (e.g. permanent reference electrodes, measuring and regulating devices, telemetry)shall be kept in good working order and shall be subjected to periodical calibration and safety checks.
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Annex A(informative)
Tank and associated piping with cathodic protection
prEN 13636:2003 (E)
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A.1 Isolation of electrical equipment
1
23
4
56
7 98
10
Key
1. Phases 6. Cable bonds
2. Neutral 7. Electrical pump. Fixation of the pump must be isolated from rebar and
3. Protective cable all structures connected to the principal earth.
4. Rebar 8. Isolating flanges
Metallic structure without cathodic protection 9. Electrical valve
equipotential system 10. Tank
5. Motor
Figure A.1 Tank and associated piping with cathodic protection - Isolation of electrical equipment
prEN 13636:2003 (E)
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A.2 Electrical equipment of protection class II or III (double isolation)
Tank and associated piping with cathodic protection
1
23
4
5 6
78 9
10
Key
1. Phases 6. Motor with class ll or lll isolation
2. Neutral 7. Electrical pump with class ll or lll isolation
3. Protective cable 8. Flanges
4. Rebar. Metallic structure without cathodict ti
9. Electrical valve
equipotential system 10. Tank
5. Cable bonds
Figure A.2 Tank and associated piping with cathodic protection Electrical equipment of protection class II or III (double isola tion)
prEN 13636:2003 (E)
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A.3 Fault current breaker with local earthing system
1
23
4
56
7
8
910
11
12
Key
1. Phases 5. Fault current breaker 9. Electrical pump. Fixation of the pump must be isolated fromb d2. Neutral 6. Cable bond all structures connected to the principal earth.
3. Protective cable 7. Motor 10. Flange
4. Rebar. Metallic structure without cathodict ti
8. Local earth * (zinc, galvanised steel) 11. Electrical valve
equipotential system 12. Tank
* Re local earth <safety voltage/fault current,
e.g. Safety voltage = 50 V, Fl = 300 mA, Re < 165 Ω ; e.g. Safety voltage = 24 V, Fl = 300 mA, Re < 80 Ω
Figure A.3 Tank and associated piping with cathodic protection - Fault current breaker with local earthing system
prEN 13636:2003 (E)
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A.4 Isolating transformer
Tank and associated pipe with cathodic protection
1
4
6
2
3
5
7
9
1011
8
12
Key
1. Isolating transformer 6. Rebar. Metallic structure without cathodic protection equipotential system 10. Flanges
2. Phase 7. Cable bond 11. Electrical valve
3. Neutral 8. Motor 12. Tank
4. Isolation survey 9. Electrical pump. Fixation of the pump must be isolated from all structures
5. PA (isolated cable for Equipotential purposes) connected to the principal earth.
Figure A.4 Isolating transformer - Tank and associated pipe with cathodic protection
prEN 13636:2003 (E)
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A.5 Example with d.c. decoupling unitTank and associated pipe with cathodic protection
1
23
45a
6
7
8
9 10
11
Key
1. Phases 5a. d.c. decoupling device 10. Electrical valve
2. Neutral 6. Cable bond 11. Tank
3. Protective cable 7. Motor
4. Rebar 8. Electrical pump. Fixation of the pump must be isolated from all structures
Metallic structure without cathodic protection connected to the principal earth.
Equipotential system 9. Flangea For safety reasons, in case of failure of the d.c. decoupling device, it must ensure current flowing to the earths.
Figure A.5 Example with d.c. decoupling unit - Tank and associated pipe with cathodic protection
prEN
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Annex B
(informative)
Groundbed data
B.1 G
eneral considerations
The application of cathodic protection to com
plex structures, as described in this standard, usually needsparticular configurations of the groundbeds. S
ometim
es a configuration with a rem
ote located groundbedcan be used, but m
ore often a close located groundbed system is necessary.
In order to ensure suitable current and voltage outputs, the earthing resistance of the anodes must be
carefully calculated and, where necessary, techniques m
ust be used to lower the groundbed resistance
to earth.
When designing a groundbed system
, it is important to take into consideration all factors that can affect
the groundbed lifetime. In selecting groundbed sites and voltage output, care needs to be exercised to
avoid interference to other structures. The presence of electrical shielding betw
een the groundbed andthe structure to be protected should be avoided.
B.2 T
ype of groundbed
B.2.1 G
eneral
For general description and characteristics of shallow
and deep groundbed refer to EN
12954.
B.2.2 R
emote located groundbeds
A cathodic protection installation equipped w
ith a remote located groundbed provides a w
ide distributionof the current all over the structure to be protected.
Generally, a deep w
ell groundbed is often preferred over shallow groundbeds to provide better current
distribution over the tank installation.
B.2.3 C
lose located groundbed
When a close located groundbed system
is used, the anodes are placed close along the structure to beprotected.
Close located groundbed are of tw
o types :
Distributed groundbed m
ade of anodes that are generally placed throughout or along the major
dimensions of the structure to be protected at short intervals.
Continuous groundbed can be m
ade using flexible wire anodes or anodes placed in a continuous
carbonaceous backfill at suitable intervals.
With this configuration an uniform
current distribution along the structure is provided, less overallcurrent and voltage output is needed and shielding and interference problem
s are generally avoided.
Shallow
groundbeds, both horizontal and vertical, are generally used.
Horizontal groundbeds are, if possible, installed as deep as the structure to be protected.
prEN
13636:2003 (E)35
B.3 A
nodes types
B.3.1 G
eneral
In this paragraph the most com
monly used in local cathodic protection current im
pressed anode materials
are described.
B.3.2 H
igh silicon chromium
cast iron anodes.
A typical m
aterial composition is :
Silicon
14.20-14.75 %
Chrom
ium3.25-5.00 %
Carbon
0.70-1.10 %
Manganese
1.50 %-m
ax
Copper
0.50 %-m
ax
Molybdenum
0.20 %-m
ax
Balance Iron
……
……
…..
The perform
ance of this material as m
aterial for cathodic protection anodes depends on the formation of
a thin layer of silicon dioxide on the surface of the anode. This film
is partially protective and its formation
is not fully developed if the alloy contains less than 14.2 % of silicon and, in environm
ents containinghalides, less than about 4 %
of chromium
.
High silicon cast iron anodes w
ithout chromium
may be used in halide-free environm
ents.
The m
ost comm
on anode shapes are cylindrical rods and tubes. These anodes are available both bare
and pre-packaged with carbonaceous backfill inside steel canisters.
High silicon chrom
ium cast iron anodes are suitable for applications in soil, in w
ater (both sea-water and
fresh-water) and in sea m
ud.
Underground applications include deep vertical, shallow
vertical, or horizontal bed with or w
ithout backfill.
The consum
ption rates vary from 0.1 kg A
-Y to 0.5 kg A
-Y and depend on the environm
ent and the max.
current density applied, that can range from 10 to 50 A
/m².
B.3.3 M
ixed-metal oxide anodes (D
SA
anodes)
Mixed-m
etal oxide anodes consist of electrocatalytic active coatings on a high-purity titanium substrate.
The coatings usually consist of a m
ixture of highly conductive oxides. The titanium
serves as a supportfor the oxides and is protected by a thin adherent film
witch resists the passage of current in the anodic
direction. The oxide coating is the anode m
aterial.
The follow
ing anode shapes are mostly used:
tubular, both bare and pre-packaged in steel canisters filled with carbonaceous backfill;
wires and rods, usually in steel canisters w
ith carbonaceous backfill;
mesh;
prEN
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36
strips.
DS
A anodes are suitable for applications in seaw
ater, in freshwater, in m
ud and in soil, preferably incarbonaceous backfill.
The m
aximum
current density ranges from 35 A
/m2 - 50 A
/m2 in freshw
ater to 100 A/m
2 in soil incarbonaceous backfill and to 500 A
/m2 in seaw
ater.
prEN
13636:2003 (E)37
Annex C
(informative)
Extract of pr E
N 50162
7.8.2A
dju
stment of tran
sformer rectifier output
The cu
rrent output of th
e rectifier installe
d on
an
interferin
g structure sh
all be adjusted to the
minim
um leve
l providin
g cath
od
ic protection. In particu
lar case
s, the possibility of distributin
g the
tota
l curre
nt b
y ad
ditio
na
l rectifie
rs an
d g
rou
nd
be
ds co
uld
be
con
side
red
.
7.8.3Increasing co
ating resistance
Structures w
ith high quality coatings require less cathodic protection current and hence minim
ize stray
current interference. Coating defects on a cathodically protected structure m
ay need to be locatedand repaired if the level of interference to nearb
y structures needs to be reduced.
7.8.4G
roundbed location
The
interference from
im
pressed current
anodes depends
on the
current output,
distance to
neighbouring structures, and the environment resistivity of the surrounding m
edium.
The interference can be reduced b
y ensuring that the neighbouring structures are not within the area
of the anode field where the potential gradient causes the potential to shift outside the lim
its detailed(see prE
N 50162). T
his can be achieved by:
increasing the
distance from
the
anode to
neighbouring structures
(either horizontally
orvertically). T
his is the most effective m
ethod;
reducing the voltage gradient around the groundbed by enlarging the groundbed geometry or by
reducing the current output (see 7.8.2);
locating distributed anodes close to the structure to be protected.
prEN
13636:2003 (E)
38
Annex D
(informative)
Determ
ination of inspection interval
To determ
ine an inspection interval each aspect as mentioned in 10.2.4.2 should be w
eighted as“low
”, “medium
” or “high”.
In case of unclear identification the higher weight factor should be chosen.
Com
plexity of the cathodic protection system
Depending the extent of a cathodic protection system
and the object(s) to be protected a weight factor
has to be specified.
The w
eight factor is related to the number of tanks, geom
etry of object, surface to be protected, typeof cathodic protection system
(galvanic-anode or impressed current system
), number of anodes,
length of underground piping to be protect, etc.)
Weight factor
Typical exam
ples
Low•
2 galvanic anodes or impressed current system
for one single tankand short piping
Medium
• A
petrol station with three tanks and short piping
High
• A
large mounded vessel
• A
tank with large surface, or high num
ber of tanks
• Long piping
• A
tank enclosed within a steel reinforced concrete retaining w
alls
• S
everal tanks and piping coated with different coatings
Coating im
perfections
Weight factor
Typical exam
ples
Low•
A coating w
ithout defect and fine embedding m
aterial (e.g. sand)
Medium
A coating in good condition on the tank w
ith poorly applied field coatingon piping and spare parts
High
• A
coating with large and num
erous defects (e.g. bitumen, jute).
• Inappropriate em
bedding material (e.g. soil w
ith stones)
prEN
13636:2003 (E)39
Environm
ental conditions
Weight factor
Typical exam
ples
Low•
A hom
o geneous soil, no interfering d.c. source, no lower pit w
hererainw
ater is
stored and
more
cathodic protection
current is
required.
1
23
4
Key
1. Ground level
2. Level measuring point in a pit
3. Water
4. Tank
Figure D
.1 Hom
ogenous soil
Total length of the structure under consideration is low
er than 10 m.
Medium
• D
ifferent soil resistivities (clay/sand),
• A
partly submerged tank in groundw
ater,
• T
he ground level is polluted with de-icing salts,
• T
he distance from interferin g d.c. sources is sm
all (approximately
30 m
or
even less)
with
a total
length of
the structure
underconsideration greater than 10 m
.
High
• C
ombination of tw
o “medium
weight” exam
ples
• T
he distance
from
interferin g d.c.
sources is
very sm
all(approxim
ately 10 m) or the total len gth of the structure under
consideration is much higher than 10 m
.
prEN
13636:2003 (E)
40 Susceptibility to dam
age by lightning or mechanical im
pact.
Weight factor
Typical exam
ples
Low•
A location w
ithout above ground piping
• A
location with a low
probability of excavation
Medium
• A
location with extended above ground piping
High
• A
location with a high probability of excavation
Risk of personal injury, environm
ental pollution or damage to property that could be
caused by leakage of stored medium
Weight factor
Typical exam
ples
Low•
One sm
all LPG
tank located in a rural area
Medium
• A
petrol station in a rural area
High
• A
petrol station in an urban area or along an highwa
y.
• A
petrol station in a shopping area .
• A
tank filled w
ith a
pollutin g product
in an
extraction area
forpotable w
ater
SM
-R/E
S030123
prEN
13636:2003 (E)41
Bibliography
EN
12499Internal cathodic protection of m
etallic structures
EN
12501-1P
rotection of metallic m
aterials against corrosion - Corrosion
likelihood in soil - Part 1: G
eneral
EN
13509C
athodic protection measurem
ent techniques
prEN
12696-1C
athodic protection
of steel
in concrete
- P
art 1:
Atm
ospherically exposed concrete
EN
50122-2R
ailway applications - F
ixed installations - Part 2: P
rotectiveprovisions against the effects of stray currents caused byd.c.
traction
systems
/ N
ote: Includes
C
orrigendum
ofA
ugust 2001
