DNVRPB401 Cathodic Protection Design.docx

DNVRPB401 Cathodic Protection Design.docx

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DNVRPB401CathodicProtectionDesign

DNV-RP-B401CathodicProtectionDesign

1.General

1.1Introduction

1.1.1 'Cathodicprotection'（CP）canbedefinedase.g."electrochemicalprotectionbydecreasingthecorrosionpotentialtoalevelatwhichthecorrosionrateofthemetalissignificantlyreduced"（ISO8044）or"atechniquetoreducecorrosionofametalsurfacebymakingthatsurfacethecathodeofanelectrochemicalcell"（NACERP0176）.Theprocessofsuppressingthecorrosionpotentialtoamorenegativepotentialisreferredtoas'cathodicpolarization'.

1.1.2 ForgalvanicanodeCPsystems,theanodeoftheelectrochemicalcellisacastingofanelectrochemicallyactivealloy（normallyaluminium,zincormagnesiumbased）.ThisanodeisalsothecurrentsourcefortheCPsystemandwillbeconsumed.Accordingly,itisoftenreferredtoasa'sacrificialanode',asalternativetotheterm'galvanicanode'consistentlyusedinthisRecommendedPractice（RP）.For'impressedcurrent'CP,aninert（non-consuming）anodeisusedandthecurrentissuppliedbyarectifier.InthisRP,thecathodeoftheelectrochemicalcell（i.e.thestructure,sub-systemorcomponenttoreceiveCP）isreferredtoasthe'protectionobject'.

1.1.3 Forpermanentlyinstalledoffshorestructures,galvanicanodesareusuallypreferred.Thedesignissimple,thesystemismechanicallyrobustandnoexternalcurrentsourceisneeded.Inaddition,inspectionandmaintenanceduringoperationcanlargelybelimitedtoperiodicvisualinspectionofanodeconsumptionandabsenceofvisualcorrosivedegradation.However,duetoweightanddragforcescausedbygalvanicanodes,impressedcurrentCPsystemsaresometimeschosenforpermanentlyinstalledfloatingstructures.

1.1.4 Cathodicprotectionisapplicableforalltypesofmetalsandalloyscommonlyusedforsubseaapplications.Itpreventslocalisedformsofcorrosionaswellasuniformcorrosionattack,andeliminatesthepossibilityforgalvaniccorrosionwhenmetallicmaterialswithdifferentelectrochemicalcharacteristicsarecombined.However,CPmayhavecertaindetrimentaleffects,forexamplehydrogenrelatedcrackingofcertainhigh-strengthalloysandcoatingdisbondmentasdescribedin5.5.

1.1.5 Cathodicprotectionisprimarilyintendedformetalsurfacespermanentlyexposedtoseawaterormarinesediments.Still,CPisoftenfullyeffectiveinpreventinganyseverecorrosioninatidalzoneandhasacorrosionreducingeffectonsurfacesintermittentlywettedbyseawater.

1.2Scope

1.2.1 ThisRecommendedPractice（RP）hasbeenpreparedtofacilitatetheexecutionofconceptualanddetailedCPdesignusingaluminiumorzincbasedgalvanicanodes,andspecificationofmanufactureandinstallationofsuchanodes.Whilsttherequirementsandrecommendationsaregeneral,thisdocumentcontainsadviceonhowamendmentscanbemadetoincludeprojectspecificrequirements.TheRPcanalsoeasilybeamendedtoincluderequirementsorguidelinesbyaregulatingauthority,ortoreflectowner'sgeneralphilosophyoncorrosioncontrolbyCP.

1.2.2 SomeofthedesignrecommendationsandmethodsinSections5,6and7arealsovalidforCPsystemsusingothercurrentsourcessuchasmagnesiumanodesandrectifiers（i.e.impressedcurrent）.

1.2.3 ThisRPisprimarilyintendedforCPofpermanentlyinstalledoffshorestructuresassociatedwiththeproductionofoilandgas.Mobileinstallationsforoilandgasproductionlikesemi-submersibles,jack-upsandmono-hullvesselsarenotincludedinthescopeofthisdocument.However,tothediscretionoftheuser,relevantpartsofthisRPmaybeusedforgalvanicanodeCPofsuchstructuresaswell.

1.2.4 DetaileddesignofanodefasteningdevicesforstructuralintegrityisnotincludedinthescopeofthisRP.Considerationsrelatedtosafetyandenvironmentalhazardsassociatedwithgalvanicanodemanufactureandinstallationarealsobeyonditsscope.

1.2.5 Comparedtothe1993editionofDNV-RP-B401,designconsiderationsforimpressedcurrentCPhavebeendeletedfromthescopeofthe2004revisionwhilstthesectionsonanodemanufactureandinstallationaremademorecomprehensive.CPofsubmarinepipelinesisfurtherexcludedfromthescope（see1.5）.However,thisRPisapplicableforCPofcomponentsofapipelinesysteminstalledontemplatemanifolds,riserbasesandothersubseastructureswhensuchcomponentsareelectricallyconnectedtomajorsurfacesofstructuralC-steel.

Inthisrevision,guidanceandexplanatorynotesarecontainedina'Guidancenote'totheapplicableparagraphinSections6,7,8andinAnnexBandC.（MostoftheGuidancenotesarebasedonqueriesonthe1993revisionofDNV-RP-B401andotherexperiencefromitsuse.Furthermore,someinformativetextintheoldrevisionhasbeencontainedinsuchnotes）.

AlltablesandfiguresassociatedwithSec.6arecontainedinAnnexA.ThedocumenthasfurtherbeenrevisedtofacilitatespecificationofPurchaserinformationtoContractor,andoptionalrequirementsassociatedwithCPdesign,manufactureandinstallationofanodes（see1.3）.Additionalcommentsonrevisionsinthis2004issuearemadeintheIntroduction（lastparagraph）ofSections6,7,8andAnnexBandC.

1.3ObjectivesandUse

1.3.1 ThisRPhastwomajorobjectives.ItmaybeusedasaguidelinetoOwner'sortheircontractors'executionofconceptualordetailedCPdesign,andtothespecificationofgalvanicanodemanufactureandinstallation.Itmayalsobeusedasanattachmenttoaninquiryorpurchaseorderspecificationforsuchwork.IfPurchaserhaschosentorefertothisRPinapurchasedocument,thenContractorshallconsiderallrequirementsinSections6-9ofthisdocumentasmandatory,unlesssupersededbyamendmentsanddeviationsinthespecificcontract.Referringtothisdocumentinapurchasedocument,referenceshallalsobemadetotheactivitiesforwhichDNV-RP-B401shallapply,i.e.CPdesigninSections6and7,anodemanufactureinSec.8and/oranodeinstallationinSec.9.

1.3.2 CPdesign,anodemanufactureandanodeinstallationaretypicallycarriedoutbythreedifferentparties（allreferredtoas'Contractor'）.Differentpartiesissuingacontract（i.e.'Purchaser'）mayalsoapply.Thelatterincludes'Owner',e.g.forCPdesignandqualificationofgalvanicanodematerials.Fordefinitionofcontractingpartiesandassociatedterminology,seeSec.3.

1.3.3 SpecificationofprojectspecificinformationandoptionalrequirementsforCPdetaileddesign,anodemanufactureandanodeinstallationaredescribedin7.1.2,8.1.2and9.1.3,respectively.

1.4DocumentStructure

1.4.1 GuidelinesandrequirementsassociatedwithconceptualanddetailedCPdesignarecontainedinSections5,6and7,whilstgalvanicanodemanufactureandinstallationarecoveredinSec.8andSec.9,respectively.TabulateddataforCPdesignarecompiledinAnnexA.AnnexBandCcontainrecommendedproceduresforlaboratorytestingofanodematerialsforproductionqualitycontrolandfordocumentationoflong-termelectrochemicalperformance,respectively.

1.5RelationtoOtherDNVDocuments

1.5.1 CathodicprotectionofsubmarinepipelinesiscoveredinDNV-RP-F103.

2.References

2.1General

Thefollowingstandards（2.2-2.7）arereferredtointhisRP.Thelatesteditionsapply.

2.2ASTM（AmericanSocietyforTestingand

Materials）

ASTMG8 

TestMethodforCathodicDisbondingofPipelineCoating 

ASTMD1141 

SpecificationforSubstituteOcean

Seawater 

2.3DNV（DetNorskeVeritas）

DNV-RP-F103 

CathodicProtectionofSubmarine

PipelinesbyGalvanicAnodes 

2.4EN（EuropeanStandards）

EN10204 

MetallicProducts-TypesofInspectionDocuments 

2.5NORSOK

NORSOKM-501 

StandardforSurfacePreparationandProtectiveCoating 

2.6ISO（InternationalOrganizationfor

Standardisation）

ISO3506 

MechanicalPropertiesof

Corrosion-ResistantStainlessSteel

Fasteners 

ISO8044 

CorrosionofMetalsandAlloys;BasicTermsandDefinitions 

ISO8501-1 

PreparationofSteelSubstratesfor

ApplicationofPaintandRelated

Products-VisualAssessmentofSurfaceCleanliness.

Part1:

RustGradesandPreparationGradesofUncoatedSteelSubstrates. 

ISO10005 

QualityManagement-GuidelinesforQualityPlans 

ISO10474 

SteelandSteelProducts-InspectionDocuments 

2.7NACEInternational

NACERP0176 

CorrosionControlofSteelFixedOffshoreStructuresAssociatedwithPetroleumProduction 

NACERP0387 

MetallurgicalandInspectionRequirementsforCastSacrificialAnodesforOffshoreApplications 

3.TerminologyandDefinitions

3.1Terminology

Owner 

Partylegallyresponsiblefordesign,constructionandoperationoftheobjecttoreceiveCP. 

Purchaser 

Party（Ownerormaincontractor）issuinginquiryorcontractforCPdesign,anodemanufactureoranodeinstallationwork,ornominatedrepresentative. 

Contractor 

Partytowhomthework（i.e.CPdesign,anodemanufactureoranodeinstallation）hasbeencontracted. 

shall 

indicatesamandatoryrequirement. 

should 

indicatesapreferredcourseofaction. 

may 

indicatesapermissiblecourseofaction. 

agreed/agreement 

referstoawrittenarrangementbetweenPurchaserandContractor（e.g.asstatedinacontract）. 

reportandnotify 

referstoanactionbyContractorinwriting. 

accepted

acceptance 

referstoaconfirmationbyPurchaserinwriting. 

certificate

certified 

referstotheconfirmationofspecifiedpropertiesissuedbyContractororsupplierofmetallicmaterialsaccordingtoEN10204:

3.1.B,ISO10474:

5.1-Borequivalent. 

purchase

document（s） 

referstoaninquiry/tenderorpurchase/contractspecification,asrelevant. 

3.2Definitions

F