SIST EN 12499:2003
(Main)Internal cathodic protection of metallic structures
Internal cathodic protection of metallic structures
This standard specifies the structures, electrolytes, metals, surfaces which can be protected against corrosion by application of internal cathodic protection - specifies the conditions necessary to the application of internal cathodic protection - give guidances on realisation and operation of an efficient cathodic protection system of specific structures, namely - Domestic water heaters, appliances for heating and storage, feed tank with variable level, filtering tanks, internal surface of wells casing, internal surface of pipes, tubular heat exchangers.
Kathodischer Korrosionsschutz für die Innenflächen von metallischen Anlagen
Diese Europäische Norm legt die Anlagen, die Metalle und Oberflächen, die durch Anwenden des inneren kathodischen Schutzes gegen Korrosion geschützt werden können, die Elektrolytlösungen und die für einen kathodischen Innenschutz erforderlichen Bedingungen fest. Ferner gibt sie Anleitungen für die Installation und für den Betrieb eines wirksamen kathodischen Schutzsystems.
Diese Norm betrifft die Anwendung des inneren kathodischen Schutzes von häuslichen Wassererwärmern, Warm- und Kaltwasserbehältern, Wasserzirkulationsleitungen, Kondensatoren, Wärmetauschern sowie ganz allgemein Anlagen, die eine Elektrolytlösung enthalten, so dass der kathodische Schutz technisch möglich ist. Diese Norm gilt für metallische Anlagen, die gespeichertes oder fließendes Wasser enthalten, das stagnierend oder ausgetauscht sowie kalt oder warm sein kann. Sie gilt für Trinkwasser oder Betriebswässer und selbst für wässrige Suspension.
ANMERKUNG Es wird davon ausgegangen, dass die Elektrolytlösungen eine Leitfähigkeit über 10-3 S m-1 und einen pH Wert über 4,5 haben. Falls der pH-Wert unter 5,5 oder die Leitfähigkeit unter 10-2 S m-1 sinkt, sollten 5.4 und 6.9.2.2 beachtet werden.
Diese Norm gilt für metallische Anlagen, die aus einem Werkstoff oder zusammen mit weiteren Werkstoffen hergestellt sind. Diese Werkstoffe sind:
Eisen und niedriglegierte Stähle;
schmelztauchverzinkter Stahl;
Kupfer und Kupferlegierungen;
Blei;
Zinn;
nichtrostende Stähle;
Aluminium und Zink;
Titan.
Diese Norm gilt sowohl für unbeschichtete Metalle als auch für solche, die bereits mit nieder- oder hochohmigen Beschichtungen versehen sind.
Protection cathodique interne des structures métalliques
La présente Norme européenne spécifie les structures, les métaux et les surfaces susceptibles d'etre protégés contre la corrosion par l'application d'une protection cathodique interne, ainsi que les solutions d'électrolytes et les conditions nécessaires pour l'application d'une protection cathodique interne, et donne des indications sur l'application et le fonctionnement d'un systeme de protection cathodique interne efficace.
La présente norme s'applique a la protection cathodique interne des chauffe-eau domestiques, des réservoirs d'eau chaude et d'eau froide, des canalisations de circulation d'eau, des condensateurs, des échangeurs de chaleur et, de façon générale, de toute structure contenant une solution d'électrolytes qu'il est possible, du point de vue technique, de protéger cathodiquement. La présente norme s'applique aux structures métalliques qui contiennent de l'eau accumulée ou en circulation, dormante ou renouvelée, chaude ou froide, de l'eau potable ou de l'eau industrielle, ainsi que des suspensions aqueuses.
NOTE Les solutions d'électrolytes ont, par hypothese, une conductivité > 10-3 Siemens m-1, et un pH > 4,5. Lorsque le pH < 5,5 ou lorsque la conductivité est < 10-2 Siemens m-1, voir 5.4 et 6.9.2.2.
La présente norme est applicable aux structures métalliques composées des métaux suivants, isolément ou en combinaison :
fonte et acier faiblement allié ;
acier galvanisé ;
cuivre et alliages de cuivre ;
plomb ;
étain ;
aciers inoxydables ;
aluminium et zinc ;
titane.
La présente norme est applicable a la protection cathodique des métaux non revetus et des métaux munis de revetements a résistance d'isolement faible ou élevée.
Notranja katodna zaščita kovinskih konstrukcij
General Information
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Kathodischer Korrosionsschutz für die Innenflächen von metallischen AnlagenProtection cathodique interne des structures métalliquesInternal cathodic protection of metallic structures91.080.10Kovinske konstrukcijeMetal structures25.220.40Kovinske prevlekeMetallic coatingsICS:Ta slovenski standard je istoveten z:EN 12499:2003SIST EN 12499:2003en01-december-2003SIST EN 12499:2003SLOVENSKI
STANDARD
SIST EN 12499:2003
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 12499January 2003ICS 77.060English versionInternal cathodic protection of metallic structuresProtection cathodique interne des structures métalliquesKathodischer Korrosionsschutz für die Innenflächen vonmetallischen AnlagenThis European Standard was approved by CEN on 7 November 2002.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the officialversions.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.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2003 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12499:2003 ESIST EN 12499:2003
EN 12499:2003 (E)2ContentspageForeword.31Scope.42Normative references.43Symbols, terms and definitions.44Principle and criteria for internal cathodic protection.95Factors affecting design and application.116Design and application of internal cathodic protection.137Measurements.188Commissioning.199Operation and maintenance.2010Cathodic protection of domestic water heater.2111Cathodic protection of appliances for heating and storage of hot water.2612Cathodic protection of structures with variable level feed tanks — condensates and similarappliances.2813Cathodic protection of filtering tanks.2914Internal cathodic protection of wells.3115Internal cathodic protection of pipes.3216Cathodic protection of tubular heat exchangers.33Annex A (normative)
Test of the electrode potential of galvanic anodes.36Annex B (informative)
Protection potential ranges for low alloy steel compared with Ag/AgClelectrodes in different types of water.38Bibliography.39SIST EN 12499:2003
EN 12499:2003 (E)3ForewordThis document (EN 12499:2002) has been prepared by Technical Committee CEN/TC 219 "Cathodic protection",the secretariat of which is held by BSI.This European Standard shall be given the status of a national standard, either by publication of an identical text orby endorsement, at the latest by July 2003, and conflicting national standards shall be withdrawn at the latest byJuly 2003.Annex A is normative. Annex B is informative.According to the CEN/CENELEC Internal Regulations, the national standards organisations of the followingcountries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal,Slovakia, Spain, Sweden, Switzerland and the United Kingdom.SIST EN 12499:2003
EN 12499:2003 (E)41 ScopeThis European Standard specifies the structures, metals and surfaces which can be protected against corrosion bythe application of internal cathodic protection, the electrolytic solutions and the conditions necessary for theapplication of internal cathodic protection and gives guidance on the application and operation of an effectiveinternal cathodic protection system.This standard applies to the internal cathodic protection of domestic water heaters, hot and cold water tanks,circulating water pipes, condensers, heat exchangers and, generally speaking, to every structure containing anelectrolytic solution that it is technically possible to cathodically protect. This standard applies to metallic structureswhich contain stored or circulating water, which can be stagnant or renewed, cold or hot, drinking water or industrialwater and also to aqueous suspension.NOTEElectrolytic solutions are assumed to have a conductivity > 10-3 Siemens m-1, and a pH > 4,5. Where the pH < 5,5or the conductivity less than10-2 Siemens m-1 see 5.4 and 6.9.2.2.This standard is applicable to metallic structures made from the following on their own or with others:¾ iron and low alloy steel;¾ galvanised steel;¾ copper and copper alloys;¾ lead;¾ tin;¾ stainless steels;¾ aluminium and zinc;¾ titanium.This standard is applicable to the cathodic protection of uncoated metals, and of metals already coated with low orhigh insulation resistance coatings.2 Normative referencesThis European Standard incorporates by dated or undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text, and the publications are listed hereafter. Fordated references, subsequent amendments to or revisions of any of these publications apply to this EuropeanStandard only when incorporated in it by amendment or revision. For undated references the latest edition of thepublication referred to applies (including amendments).EN 50014, Electrical apparatus for potentially explosive atmospheres – General requirements.EN 60335-2-21, Safety of household and similar electrical appliances - Part 2: Particular requirements for storagewater heaters (IEC 60335-2-21:1997 + Corrigendum 1998, modified).EN ISO 8044:1999, Corrosion of metals and alloys - Basic terms and definitions (ISO 8044:1999).3 Symbols, terms and definitionsFor the purposes of this standard the symbols, terms and definitions of EN ISO 8044:1999 and the following apply.SIST EN 12499:2003
EN 12499:2003 (E)53.1 SymbolsICurrentRResistanceJCurrent densityUVoltageaYearEAgMetal-to-electrolytic solution potential with respect to a silver/silver chloride reference electrodeElLimiting critical potentialEnFree corrosion potentialEoffInstantaneous off potentialEonOn potentialEpProtection potentialEHMetal-to-electrolytic solution potential with respect to a standard hydrogen electrodeEZnMetal-to-electrolytic solution potential with respect to a zinc electrodeIaAnode current outputIpProtection currentJpProtection current density (A/m2)rcSpecific coating resistance (×m2)TTemperaturetTimerResistivity (×m)3.2
Terms and definitions3.2.1anaerobicwithout free oxygen in the electrolytic solution adjacent to a metallic structure3.2.2anodic areapart of a structure surface which acts as an anode3.2.3cathodic areapart of a structure surface which acts as a cathodeSIST EN 12499:2003
EN 12499:2003 (E)63.2.4cathodic protection systementire installation, including passive and active elements, that provides cathodic protection to a structure3.2.5coating defectdiscontinuity in the protective coating3.2.6coating resistanceelectrical resistance between a coated metal and the electrolytic solutionNOTEIt is determined largely by the size and number of coating defects and coating pores and is therefore indicative ofthe condition of the coating (see also specific coating resistance).3.2.7continuity bondbond designed and installed specifically to ensure electrical continuity3.2.8continuous anodelong flexible anode3.2.9couponrepresentative metal sample of known weight and dimensions used to quantify the extent of corrosion or theeffectiveness of applied cathodic protection3.2.10drinking waterwater in conformity with European directive 98/83/CE from November 3, 19983.2.11electrical continuitystate within a protected structure in which the circulating current does not produce a significant voltage drop3.2.12electrical isolationstate in which there is no metallic electrical path between structures or components3.2.13electrical shieldingintervening objects that prevent the flow of the current through the electrolytic solution to a structure3.2.14equalising currentcurrent that flows between two separate points after interruption of the protection currentNOTEEqualising currents can flow, for example, as a result of removing cathodic protection current from a structure withcomponents exposed to different depolarisation conditions.3.2.15foreign cathodemetal part fitted in the protected structure which has a more positive free corrosion potential than the protectedstructure and which requires a greater current density than the protected structure to achieve cathodic polarisationNOTEForeign cathodes can seriously impair the cathodic protection of the rest of the structure.3.2.16impressed current anodeanode in an impressed current stationSIST EN 12499:2003
EN 12499:2003 (E)7NOTEImpressed current anodes can be permanent anodes or soluble anodes.3.2.17impressed current stationequipment and materials required to provide cathodic protection by impressed currentNOTESuch materials and equipment will include impressed current anodes, cables, sensing electrodes, and transformerrectifiers.3.2.18off potentialstructure to electrolytic solution potential measured immediately after synchronous interruption of all sources ofapplied cathodic protection current3.2.19IR dropvoltage developed across a resistance, or resistive path, in accordance with Ohm’s Law (U = I × R
V)3.2.20IR -free potentialpotential measured without the voltage error caused by the IR drop (EIR FREE)3.2.21isolating jointelectrically discontinuous joint or coupling between two lengths of pipe, inserted in order to provide electricaldiscontinuity between them3.2.22measuring pointpoint at which the actual measurement takes placeNOTEIn the case of structure to electrolytic solution potentials this refers to the location of the reference electrode.3.2.23on potentialstructure to electrolytic solution potential measured with the structure cathodic protection current flowing3.2.24overprotectionstate in which the structure to electrolytic solution potentials are more negative than those recommended forsatisfactory cathodic protectionNOTEOverprotection provides no useful function and can cause damage to the structure by excessive production of gaseswhich can constitute an explosion hazard, embrittlement of metals, or protective coating damage.3.2.25permanent anodesimpressed current anodes for which the rate of corrosion is much smaller than the rate calculated in accordancewith Faraday’s Law3.2.26permanent reference electrodepermanent installed reference electrode designed for a long life3.2.27potential gradientdifference in potential between two separate points in the same electrolytic solutionSIST EN 12499:2003
EN 12499:2003 (E)83.2.28potentiostatprotection current device by means of which the structure/electrolytic solution potential is brought and maintained toa prescribed level despite variations in polarisation conditionsNOTE
The current delivered by the generator, the protection current, is controlled by the structure potential measured by areference electrode.3.2.29protected structurestructure to which cathodic protection is effectively applied3.2.30protection current (Ip)current made to flow into a metallic structure from its electrolytic environment in order to effect cathodic protectionof the structure3.2.31resistance bondbond with significant resistance to limit the flow of current to within prescribed limitsNOTEResistance can be achieved by the insertion of resistors into the bond connection.3.2.32soluble anodeimpressed current anode which is consumed in accordance with Faraday’s Law by the impressed anodic currentNOTEThe adjectives soluble and sacrificial used alone do not specify if anodes are working by galvanic action or byimpressed current. To avoid confusion it is proposed to apply the following convention: "galvanic anode" for sacrificial galvanicanode; "soluble anode" for soluble impressed current anode.3.2.33standard reference electrodereference electrode whose potential does not depend on the concentrations of various elements in the electrolyticsolution of the corrosion system3.2.34sensing electrodepermanently installed reference electrode used to measure the structure to electrolytic solution potential and toprovide a signal to control the protection current of an automatic impressed current system3.2.35silver/silver chloride reference electrodeAg/AgCl reference electrodeelectrode consisting of silver, coated with silver chloride, in an electrolytic solution containing chloride ionsNOTEThe potential of this electrode changes when the electrolytic solution concentration of the chloride ions changes(see annex B).3.2.36silver/silver chloride standard electrodeAg/AgCl standard electrodereference electrode consisting of silver, coated with silver chloride, in an electrolytic solution containing a fixedconcentration of chloride ions3.2.37specific coating resistancemeasurement derived from the variation of potential induced by a variation of the protection current i.e. the absolutevalue of the variation of potential divided by the corresponding variation of current density (see 7.4)NOTEThis is expressed in ×m2.SIST EN 12499:2003
EN 12499:2003 (E)93.2.38standard hydrogen electrodereference electrode consisting of platinum, in an electrolytic solution containing hydrogen ions at unit activity andsaturated with hydrogen gas at one standard atmosphere3.2.39structure (to electrolytic solution) potentialcorrosion potential of a structure in a given corrosion systemNOTEThe contact of the reference electrode with the electrolytic solution must be close to the structure to minimise errorsdue to the voltage drop associated with any current flowing in the electrolytic solution.3.2.40sulphate reducing bacteriabacteria which reduce sulphates in their environment, producing sulfides which accelerate the corrosion ofstructural materialsNOTE
This group of bacteria is found in most soils and natural waters, but is active only under anaerobic conditions of nearneutrality and free of oxygen.3.2.41transformer-rectifierdevice that transforms the alternating voltage and then rectifies it to direct currentNOTEDirect current derived in this way is used as a power source for impressed current cathodic protection systems.3.2.42utilisation factorproportion of a galvanic anode that may be consumed before the anode ceases to provide a current output inaccordance with the cathodic protection design4 Principle and criteria for internal cathodic protection4.1 PrincipleThe decrease of the corrosion rate is achieved by lowering the corrosion potential to reach the protection potentialrange. Cathodic protection is achieved when all the metallic surfaces to be protected have reached the protectionpotential range.The lowering of the potential is achieved by means of a protection current passing from the electrolytic solution tothe metal surface. This current enters the electrolytic solution from the surface of an anode.Throughout clause 4 all electrode potentials are IR-free potentials.4.2 CriteriaThe protection potential depends on the physical and chemical conditions at the interface between the metal andthe electrolytic solution. The coverage of the metal by calcareous deposits and the rate of diffusion of ions issuingfrom metal are different according to the medium.Protection potential values are determined by practical experience.One single potential criterion cannot cover the range of different situations that arise in internal cathodic protectionapplications.The only criterion that cannot be disputed is a lack of corrosion established by inspection.Some practical values are listed in Table 1. Precautions additional to those listed may need to be taken to protectagainst
effects caused by the simultaneous presence of different metals or by the precipitation of some ions.SIST EN 12499:2003
EN 12499:2003 (E)10Overprotection needs to be avoided on internal cathodic protection. Overprotection will result in the formation ofgases. Some metal may be subject to specific damages at very negative potentials. It is essential that theirpotential is not brought to values lower than the limiting critical potential given in Table 1.Table 1 — Guidance values of protection potential range with respect to the standard hydrogen electrodeProtection potential, EHMetalElectrolytic solutionVLimiting criticalpotentialNeutral cold water - 0,55Hot water - 0,65Iron and low alloy steelAcid water or presenceof bacteria - 0,65Low alloy steel coupledwith stainless steelCold or hot water - 0,55See footnote aStainless steelCold or hot water
-0,1See footnote aCopper and copperalloyCold or hot water - 0,20TinCold or hot water - 0,35- 1,0ZincCold or hot water - 0,90 - 1,0 bLeadNeutral cold water - 0,33 - 0,65Cold or hot water- 0,45 - 0,80 bAluminium and alloyswith Magnesium orManganeseSea water - 0,55 - 0,80 bCold or hot water - 0,60 - 0,80Aluminium zinc alloysSea water - 0,70 - 0,90TitaniumSea water-0,75aProtection potentials shall be determined by testing in each case as well as the limiting critical potentials forferritic and martensitic steel. There is no limiting critical potential for austenitic steel.bAluminium and zinc cannot be polarised to such a negative potential that the anodic reaction rate becomesnegligible. These metals are self protected by their oxidation products. Cathodic polarisation can regularise thisinitial oxidation.When the metal potential is measured between the metal and a reference electrode other than a standardhydrogen electrode, the EH metal potential with respect to the standard hydrogen electrode is calculated as follows:EH = EM + ER; orEM = EH - ER (see annex B)whereEMis the measured algebraic value of the potential difference between the metal and the reference electrode;ERis the measured algebraic value of the potential difference between the reference electrode and astandard hydrogen electrode.SIST EN 12499:2003
EN 12499:2003 (E)11Table 2 — Potentials of some electrodes with respect to the standard hydrogen electrodeElectrode potential,ERElectrode typeElectrolytic solutionVField of useStandard electrodeCopper/coppersulphateSaturated coppersulphate+ 0,32SoilSilver/silver chloride(saturated)Saturated potassiumchloride+ 0,20Sea water – FreshwaterThallium/thalliumchloride3.5 M potassiumchloride- 0,57Hot waterPermanent reference electrodeZinc/sea waterSea water- 0,77 approx.Sea waterSea water+ 0,25 approx. aSea waterSilver/silver chlorideFresh water+ 0,35 approx. aFresh water containingchloridesaThese potentials change with chloride concentration; the variation is about 60 mV at 30 oC for each ten-foldchange in concentration (see annex B).5 Factors affecting design and application5.1 Different metalsIt is necessary to consider all the possible operating conditions and then determine whether or not a range ofprotection criteria can be established.If different metals are protected by cathodic protection, then the least noble metal needs to reach its protectionpotential. It is essential that the protection potential ranges of the various metals are not incompatible.5.2 Electrolytic solution conductivityThere needs to be a continuous electrolytic contact between the surfaces of the protected structure and theprotective anodes ensuring a sufficient distribution of current. Internal cathodic protection is not possible when theliquid on the whole is non-conductive.5.3 Electrical continuityThe structure to be protected needs to be electrically continuous. Individual components of the structure need to beconnected with low resistance metallic bonds.5.4 Current distributionThe current distribution needs to be able to achieve the protection potential range on each point of the entirestructure.The factors improving current distribution are the following:¾ high electrolytic solution conductivity;¾ high polarisation resistance (the polarisation resistance can be improved by coating);¾ surface and positioning of the anodes;¾ design of the structure to be protected.SIST EN 12499:2003
EN 12499:2003 (E)12Very low conductivities, e.g. in de-ionised water, can result in such an inadequate distribution of current thatcathodic protection cannot be achieved at all points and need specific and wide distribution of anodes.5.5 Current densityThe current density necessary for the protection of metallic surfaces is dependent upon the following parameters:¾ composition of the electrolytic solutions;¾ service conditions (e.g. flow rate, temperature);¾ coating properties including the permeability of the coating to water, ions and oxygen and its electricalconductivity;¾ characteristics of the structure.In general the necessary initial current density is greater than the current density in a polarised stable operatingstate.5.6 Coating propertiesWhen, coatings are applied, it is necessary to examine whether the coating presents the required properties for asufficiently long time under service conditions.Possible impairments of the coating are the following:¾ disbonding;¾ cathodic disbonding at coating defects;¾ blistering in the coating;¾ alkaline saponification.When cathodic protection is to be applied to an existing coating the design shall make provision for the futuredeterioration of the coating.Resistance to deterioration depends upon the kind of coating and the kind of the surface preparation.Experience gained from the external cathodic protection of structures cannot be applied to internal cathodicprotection of coated or lined structures.5.7 Side effectsElectrochemical reactions may produce the following conditions:¾ evolution of gases;¾ corrosion products from anodes;¾ deoxygenation;¾ cathodic products on the protected structure.SIST EN 12499:2003
EN 12499:2003 (E)13It is necessary to examine which electrolytic reactions occur on the protected structure and on the anodes and towhat extent these reactions interfere with the function of the protected item, e.g. with respect to the following:¾ a contamination of the medium by reaction products of the electrode materials;¾ an electrochemical reaction of constituents of the medium;¾ an interfering accumulation of gases, in particular hydrogen.The changes in the electrolytic solution caused by the electrochemical reactions shall not alter certain properties ofthe electrolytic solution (e.g. drinkability, metal-ionic concentration).For example, oxygen consumption on the cathode can cause anaerobic conditions to develop in drinking waterwhich, in combination with sulphate reducing bacteria, results in a bad odour from hydrogen sulfide.Depending on the extent of these possible impairments, the following are to be taken into consideration in thedesign:¾ type and surface of the anodes;¾ reduction of current density requirements by use of a coating;¾ gas venting;¾ anodic current density.5.8 LifetimeAs far as type, number, geometry and lifetime of the anodes are concerned, it is necessary when designing acathodic protection system to take the lifetime of the protected structure into consideration. If necessary, adequatemaintenance intervals are to be prescribed.6 Design and application of internal cathodic protection6.1 DesignThe following documents shall be made available for the design:¾ construction drawing of the structure to be protected with details of the materials used;¾ chemical composition of the medium with details on its possible fluctuations;¾ details on the service conditions with details on their fluctuations: height of the medium, temperature, velocity,pressure.The design shall be undertaken by competent personnel having sufficient knowledge and experience in theapplication of internal cathodic protection systems. At this stage it is necessary to consider whether or not theapplication of cathodic protection will have any effect on the function or operation of the structure to be protected.The selection of coating should take into account the compatibility with the proposed cathodic protection system.6.2 Design of the structure to be protectedThe following measures shall be undertaken in the design of the structure to be protected:a) the equipotential bonding of components by means of metallic electrical connections;b) where high resistance insulating coatings are used, the electrical isolation of certain components;c) the use of insulated flanges and bushings for cable, anodes and reference electrodes;SIST EN 12499:2003
EN 12499:2003 (E)14d) the provision of connection points for anodes and, if necessary, cathodes;e) the elimination or special coating of parts of the structure that are exposed to air and cannot be cathodicallyprotected;f) the installation of manholes, covering boxes, fixing devices and cables;g) the provision of electrical safety measures and protection against electrical contact;h) where there is any risk of gas build up, the installation of gas venting systems.6.3 Influence of foreign cathodesIn the presence of foreign cathodes caused by multiple metals the provisions of 5.1 shall be applied.If the cathodic protection of the structure is adversely affected by such cathodes then one or both of the followingmeasures
shall be taken to ensure effective cathodic protection:¾ adjust the number and location of cathodic protection anodes;¾ electrically isolate parts of the structure.When it is necessary to electrically isolate parts it may be useful to introduce resistive bonds between these partsand cathodes to ensure that unacceptable anodic corrosion is avoided on the isolated part.Non-metallic electron conducting materials such as charcoal can impair current distribution on the structure to beprotected. In this case it is essential that electrical insulation of the structure from conducting materials is achieved.6.4 Isolating jointsWherever possible, interruptions to the electrical continuity of the structure to be protected should be avoided. Ifisolating joints are nevertheless used they can introduce a risk of corrosion by concentrating current flow from theisolated part or foreign cathode to the main part of the structure at the isolating joint itself (see Figures 1 and 2).This risk is determined mainly by the level of d.c. current, the conductivity of the electrolytic solution, and the lengthof the isolation joint, but not by the corrosiveness of the electrolytic solution.The distance between parts separated by the isolating piece shall be designed in such a way that the currentflowing from the isolated part to the main part of the structure causes only negligible corrosion damage.It is essential that the insulated pieces and insulating components withstand the electrical, mechanical, thermal andcorrosive chemical stresses which develop in the installation and during service.The isolating materials used shall not contain any electron conducting filling materials.Isolating pieces in areas where there is a danger of explosion shall conform to the requirements of EN 50014.6.5 Anode6.5.1 GeneralThe selection of the anode will depend of the electrolytic solution and such service conditions as:¾ no evolution of hydrogen gas;¾ no evolution of oxygen gas;¾ no decrease of oxygen concentration;SIST EN 12499:2003
EN 12499:2003 (E)15¾ no addition to the electrolytic solution of com
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