涂装基本知识之Corrosion-foundamental

JotunProtectivePaintingknowledgeofcorrosionJotunKoreaCoatingsCo.,Ltd.Coatingadvisor:Danny(DanGuo-qiang)2015-07JotunProtectiveContents1.Thedefinitionofcorrosion2.Fundamentalsofcorrosion3.5keyfactorsofcorrosion4.Generaltypesofcorrosion5.Methodsofcorrosioncontrol6.ICCPJotunProtectiveWhatiscorrosion?•Corrosion,asdefinedintheNACEis“thedestructionofasubstance(usuallyametal)oritspropertiesbecauseofareactionwithitsenvironment”JotunProtectiveFundamentalsofcorrosion•ThetendthematerialgobacktoitsnaturalstateHumanusemassiveamountofenergytochangetheoreintousefulmetal.Themoreenergyitisabsorbedbythemetal,theeasierittendstocorrodeEx:FeFe3+•ElectromotiveforceTheoneswhichrequirethegreatestamountofenergyinputinordertomakethemetalitselfarealsotheoneswiththehighestelectromotiveforceJotunProtectiveElectromotiveforce•Becauseoftheelectromotiveforce,metalshaveagreattendencytogointosolutionandformironsZnSO4ZnJotunProtectiveElectromotiveforceJotunProtectiveElectromotiveforceseries•Asthechartshowed,hydrogenisusedasaarbitraryreferenceelement.Theelementslistedabove“H”areincreasinglymoreactive,whiletheelementslistedbelow“H”becomeincreasinglyinertwithlesstendencytoionizeJotunProtective5keyfactorsofcorrosion1.Anode2.Cathode3.Electrolyte4.Externalcircuit5.OxygenFournecessaryelementstomakeacorrosioncellOxygencanbeconsideredasthefifthelementJotunProtectivecorrosioncell•Anode:ZnZn→Zn2++2e•Cathode:Cu2H++2e→H2↑H2SO4H2↑ZnCuH2SO4ZnCuAKZn2+H2↑JotunProtectiveOxygenandPolarization•Oxygencanbeconsideredthefifthelementinacorrosioncell.Whilethecorrosionmaybeginwiththepresenceoftheabovefourfactors,withoutoxygen,theprocesssoonslowdownorstopaltogether.•Oxygenisextremelyimportantinmostallcorrosionreactionsinordertoremovethehydrogenionfromthecathodeandtoallowadditionalelectronstobeneutralized•Whenhydrogenaccumulatesonthesurfaceofcathodeasafilm,theelectronscannolongerbeeasilyneutralizedandthecorrosioncellissaidtobepolarizedJotunProtectiveElectrochemicalcorrosioneZnZn22OHeOHO22212222)(2OHZnOHZn222)(21OHZnOHOZnAnode：Cathode：•CorrosionoccursinneutraloralkalinesolutionJotunProtectiveOtherchemicalcorrosion•OxideetchEx:Sodiumhypochlorite,sodiumperborate•SulfidescorrosionItreactswiththemetalanddoesnotrequireanelectrolyteforthecorrosion.Itcontainsinnaturalgasandcrudeoil•DisplacementcorrosionZnOOZn22122HFeSFeSHCuFeFeCu22JotunProtectiveMethodsofcorrosioncontrol•Selectingandusingcorrosion-resistantmaterials•Changingoralteringtheenvironment•Usingabarrierbetweenthestructuralmaterialandtheenvironment•Usingcathodicprotection•GooddesignforcoatingJotunProtectiveICCP•Generaldescriptions•Impressedcurrentanode•Impressedcurrentreferenceelectrode•Bonding•Powersupplyunit•Operationsystem•Hydrogenevolution•Putty•DrydockingJotunProtectiveGeneraldescriptionsAmetalalsocanbemadecathodicbyelectricallyconnectingittoanothermetalliccomponentinthesameelectrolytethroughasourceofdirectelectriccurrentanddirectingthecurrentflowtooccuroffthesurfaceofaddedmetalliccomponent(anode),intotheelectrolytetothesimplecellandassumingyetanotherrefcellwithapowersourceisintroducedandthatthecurrentflowfromthisrefcellissufficienttoovercomethenaturalcorrosioncurrent.Becauseanexternalcurrentsourceisemployed,thistypeofprotectionistermed“IMPRESSEDCURRENTCATHODICPROTECTION”JotunProtectiveGeneraldescriptionsJotunProtectiveGeneraldescriptionsJotunProtectiveGeneraldescriptionsJotunProtectiveImpressedcurrentanodeThefunctionofanodeistoconducttheD.CprotectivecurrentintotheseawaterJotunProtectiveImpressedcurrentanodeThefunctionofanodeistoconducttheD.CprotectivecurrentintotheseawaterJotunProtectiveImpressedcurrentreferenceelectrodeNormally,thehighpurity,highstability,zincrefcellaredesignedtogiveastablereferenceagainstwhichthehull/seapotentialscanbemeasuredandasmallcurrentflowthatisusedintheclosedloopcircuittomaintainthepresetlevelsofprotectionJotunProtectiveBondingToenabletheruddertoreceiveprotectionitisprovidedwithadedicatedelectricalbondintheformofaflexiblecablefromthetopoftherudderstocktothemainshipstructure.Inthesamewayanystabilisersarebondedtoallowprotectivecurrenttothesesurfaces.Toallowprotectionofthebarepropellerandanyexposedshaftingandtopreventelectricalarcingbetweenshaftandbearingsthepropellershaftisfittedwithaslipringassembly.Asetofbrushesprovidethecompletionofalowresistancepathtoallowcurrenttoflowtothepropellerbladesalongtheshaftandbacktothehull.JotunProtectivePowersupplyunitSupplypowertomeetthecorrosionneed,convertAC220Vor440VintoDC24VJotunProtectiveOperationsystemJotunProtectiveOperationsystemCircleblisteringsJotunProtectivePuttyjobPuttyistomakethecurrentdistributionmoreevenlyJotunProtectiveHydrogenevolutionHydrogenevolutionpotentialAsthecurrentonthecathodeincrease，cathodicpotentialalsowillbemorenegative，whenthepotentialreachEH，thenhydrogenwillbeformed，thepotentialEHisHydrogenevolutionpotential.e.HEiEHEJotunProtectiveHydrogenevolutionReactionincreases,reactionproductsmakethedisbondmenthappenJotunProtectiveDrydockingInordertoavoidlargepercentageofpillingofforblisteringoradhesionfailurebet