挪威表面处理检验员培训资料

1、- -前言（preface）FROSIO（挪威表面处理检验员培训认证专业委员会），成立于1986年，目标是培训和认证表面处理检验员。为了达到这个目标，将有一个建立于挪威标准NS476的课程和80小时的培训，油漆和涂料，表面处理检验员的承认和证明。这本书是挪威“OverflatebehandlingmotKorrosjon”英语翻译版本，这本书在挪威使用了很多年，很多希望成为FROSIO认证的检验员的考生用它来帮助课程的培训。这本书包括了FROSIO课程全部项目，并且它是一个获得需要通过理论考试和实践考试方面知识的好的帮手。FROSIO也极力推荐这本书，用来培训以获得FROSIONS467证书。

2、FROSIOBoardFROSKJ目录（contents）第一章腐蚀(corrosion)目标(objective)当你在学习(gothrough)本章的时候，你应该能：解释腐蚀是怎么(how)影响金属材料的解释什么因素影响腐蚀过程用电解序位表(galvanicseries)判断当金属(metals)连接在一起时发生电解腐蚀的危险不同种类腐蚀的区别，并且描述它们的特有的特点(characteristicfeature)引言(introduction)每年腐蚀浪费了巨大的社会资源。在西方世界，估计(estimated)达到将近国民生产总值(grossnationalproduct)的3-4%。一

3、个主要的原因是缺乏腐蚀和产生腐蚀条件方面的知识。如果选择材料没有足够的考虑，结果可能会扩大腐蚀的毁坏程度。据估计，提高腐蚀和腐蚀保护方面的知识能够减少接近15%的损失。提起腐蚀保护，意味着油漆涂料的施工员和检验员都很重要。为了确保工作执行的正确性，他们必需对诸如腐蚀(corrosion)、表面处理(surfacepreparation)和腐蚀保护(protectionagainstcorrosion)方面课题有一个良好的理解。在本书的后面这些课题将被很详细的讨论到。什么是腐蚀？(whatiscorrosion?)有一个普遍的观点是腐蚀就是和锈(rust)是一样的，这是不完全对的。锈(rust)

4、是铁(iron)和钢(steel)腐蚀产生的腐蚀产物。但是很多其他的金属也会遭到侵蚀。其中总所周知的例子是，铜(copper)上的铜绿(patina)和锌(zinc)上的白锈(whiterust)。这些都是腐蚀产物。综上所述，腐蚀(corrasion)是材料(materials)与环境产生反应，使得材料退化(deterioration)或衰退(breakdown)。除了对金属的破坏，腐蚀还会发生在混泥土(concrete)和塑料(plastic)材料。为什么(why),在我们的周围很多建筑物材料(constructionmaterials)被毁坏，它们是怎么(how)发生的呢？如果我们仔细观察

5、这些金属，很多金属的生产是施加大量的能量在原材料(rawmaterials)，就是矿石(ore)。在这样的状态(state)中，在自然中找到的金属是最稳定的状态或形式(form)。作为矿石,金属经常是和氧(oxygen)、碳(carbon)，硫(sulphur)和其他元素(elements)。Sheetspipes:薄片管子Energymanufacture：能量提炼Wateroxygen:水分氧气Rawmaterial：原材料Ironore：铁矿石Rust:锈图示1.1铁或钢的腐蚀产物和退化过程在提炼金属的时候，能量注入到原材料矿石中去。在这个过程，矿石融化，金属从矿渣中分离出来，在金属红热

6、的状态时候，金属可以压扎成型。在热压扎的过程中，钢与空气接触表面形成很薄的一层膜。这层膜通常称为氧化皮(rn辺scale)，氧化皮是容易粹的(brittle)，只是在其未受破坏的时候(itisintact)对钢板有保护作用。如果钢板是处于户外，氧化皮最后会有裂痕(crack)并且使得钢板开始生锈。对于这样的破坏，腐蚀，钢板变成了锈。从化学的角度来看(chemicallyspeaking)，锈和矿石的组成成分几乎是一样的。这个过程到此就结束了。它从矿石开始，结束与锈。铁元素又处于更低dower)的和更“自然稳定的(naturalandstable)”能量形式。金属的生产可以比喻成一个足球放在山的

7、脚下，加入能量，我们把球带到了山顶上，当球放在比较高水平位置上时，它就开始往下滚，直到滚到最底的水平位置才停止。Moisture(0SWecondt;onInnature:在自然状态下Puremetal：纯金属Energy：能量Oxygen：氧Moisture:湿气Stablecondition：稳定条件图示1.2InnatureFigure1.21hisiswhathappens：rIliebalkwhichw嚮llIastablelevel,transferredioanojvstabli?level.Duetophysicalreasonstheballrollsdownlhehilla

8、ndfinallycomestoahahuitheftKrtofthebill.Theballwillagainbeatitsmoststablelevel.Inprinciple,thisjsalsowhathappensduringtheproduciiorofmcuLToextractthtmetal,foundonlyinlimitedquantitiesintheore,energyisrequire!Duetotheenergyexpended,themetalinTheoreistraRsferreilfromitswLabletv亡1loanunstablelevel.Tlie

9、metalhasnowbeenextFiCledfrirnlftk：ort,butJXtertYiil-oaditionslikertioistiiieandoxygencauseTlieconosionprocesstosun.Thecomion卩roc-cssisiinaturalpr(?cesswhichundertherightcircumstances(i.e.oxygensupplyandhighhumidity)triestocoiiventhemetalbacktoitsmoststablestate,whichisoreThechemicalcompositionsofocc

10、andthecorrosionproductarevermuchalike,Ifwewanttopreservt:ltiesoiiiGthingmustbedone.Intndtrwprevent(h#corrosionprocessfrorn尺uning、weusepaints,coaungfe:indlining附orotherbarriersrostupanydirectcontactbetweenrhemetalandtheenvironmentfiure/.?Ev-e/ituallymillscakwillcrackandlheEM加警Mtoc&rrdcCorrosiontheory

11、Inorderfoijlareexamplesofelectrolytes-.Pollutioninth&airmaydissolveinwaierandmakeilconducti.ve.Metalshaveatendency(oreleaseeleutricullychargedatomsCioriSi)whenincontactwithwater.Folsomemeialsthistindencyisweak,forexampleinthecaseof卩kidnumandgold.Suchnietalsarccallednoblemetak.Othermetalsreleasealarg

12、enumberofinnsinuontaciwithwwr,G)rexamplealuiniTiiuiiiandzinc.SuchmetalsarecalledignobleIfwiimmerseiwodiffcrentmetakinaconducriveliquid(狂口clectrolyLe)withoutnyelectricalconnecdorjbetweenthem.,bothmetalsconodeatacertainmic.BuiifthemetalsarejoinedtogethertherateafC-OnOiQnmCte&seztldielenoblernetal.Howf

13、althecorpusit)nukesplacedependsonanumberoffactors,includingthetneLaltypes,forliowlonghumidiiyhpresent,poHudnon(hesurface,etc.labk1.1giver,thecurrosiotirale由pni/ycai(thQusniijThmillimetreperyear)forthemetalssteel,aluminLunicopperandzincaftertwo,fiveandtenycars,exposureatatestingfitutjononthewestcoast

14、ofSwedenTheC)rrOsionof由亡metalslakes,placedtverydiffewntrateshwhichismainlydueto(heformationofoxidefilmsandcorrosionproducesonthemetalsurfaces.Itcanalsobenotedthataporoutcorrosionproductlikew吠10extetitrcsultfiinareducedcorrosionrateoverLime(giveninpin/year).TtbfeI.JRatcorrosioninjm/yea)ft)rdifferentm

15、eliilxuj亦7,、Emeofexp&sureinamarineenvinmmenfJ2years5years10yejrsSteelBIA32-20.7Aluminium0.480.760.35Copper1.81A071ZincIiiordertoexplainihistnmoredeiail+thinkofanexamplewhereironincuiiijciwilhcopperinanelectrolyte.WhenanironaU)mieavesthemctisufilivleases(wqelectronsaridbecomesanmmion.Theitew

16、licrt(histakeplucciircalledanodes.Theano-dciscoriiuincdbycorrosion.Theelecironspsthrunsjiilmirontotheco卩per-thetathodtAtihccathoriehydroxylion、arcforrtteci,wliuhcombinewithdieirojiinnjAfterthi2reactiontakes:placewithoxygeninjiiIdproducerust,whichmaybecalledwater-containngironoxide.Figure1.4Corrosumn

17、ofthecorrosionprocessisprovidedbytheactivitywithinadrycellbatten.ThedrycellbatteryconsistsofdcarbonorgrapliiterodinasubsUnceabletoconductelectricity(牺clectj-oLyteXThisubaianceisenclosedbyaLinecase.Thecarbonorgraphite-rodismorenoblethantheincc-ase.Ifasmalllighfbulbisinsertedbetweenthepolesofthebatter

18、y,ilwilllighup,Iheb3iter?supplierthepoer.Wheninuse,thebtnieryisbeingdlischurged.Tlnslsbcciiiisethezinccae(theanode)corrodes.Iftlicprocess15dlovvcdtocontirmelongenough,thehauery1willeventuallystopworkjnt;andconleistantoleak.Tliccorrosionprocesshasccrroded山亡2inccasesurroundingtheelectroyie.Consequentl

19、y.thetessuobJeothtbVOmeidlSinCO：n,Cth陽b怕kendowniint3,beingtheanode,zinchasdeliveredtheenergytothecattiode.Howeverinordertorcorrosiontocakeplace,itnotneccissaiydialdiiniilLirmclalsarejoined皿inthise?caiiiple.Il丄iwell-knownfactrhatsfcclmstbifexposedoLildoorKinwindandweatherThereasonGthat冨notmicroscopic

20、allyunifortn.kcontainsnnuinberofsmallareelswithnobleandbaseparticles.OjIunpaiutedstlmillscale.Iaphiicgrains,riothernobleparticleslendTobe-enmecathcxles；.whilehobulkmaterialOhesteel)becomestheanode.TheseartAsformiUT谕!ngthtnselvcorrodtiiibatteriesTheiiorrosionStucksignoblearcaonthesieel(anodes.Attheca

21、th.uJcthereisnobreakdownolhemetalMbutthe;uklUorarovdtbccaihodhccciineiilkaline.+(CaWouts)Fignrc/,6Asieelsurfaceofnumerouswi他an(fbnsprri-存氏化“片t盘科gihetrts&lvestheseareasformnuillcbailerInsimpletenns,thecorrosionprocesscanbedescribedasfollows:iron+oxygen+water-ironions+hydroxyionsturonhydroxide(rust)Th

22、Ei门打ionsandthe-hydroxylicinsreactwithoneu.noiherandformrust.AttheckLthiheir&ictinrihiintheiormationofhydroxyions.Inaci-die(acids)hydrogengasisformed.De卩osii.ofnoblepaniclesfromasolutionatthesurfaceofdiemetalmayalsobeacathodereaction.It疋iwpyrUnttonote(hatifweeanpreventthemetals；urfacefiomeuinintocnni

23、actwithkiir(oxygut0andanelectralyie(water),weareaciuallyableiopievcTKcorrosionThisisioareatextentuiilizedinpractice.JustLhinkofclosedw;iicr-fillcdsylwv/hcrethereihlinleexehLingeofthewater,forexampleincentralJieafinesystems(radiittors)inblocksafhousesandofllccbaiklings.Jhclimitedquantityofoxygenprese

24、ntinthewaterwhenhesystemistakenintouseiiquicklyconsumeddueegcorrosion.Whentheoxygenhaslcnconsumed,rhecornelunattackwithin?heysEctuerases.TherareinanyavsmwhichwecainpreventmetalsutihiLCsfromcitingintocontactwHhmoistLirc.For&xanlpk-sSUfacSaah亡pointedorappliedwithother(ypesc(coatings.itis31sopracticall

25、ypossibletoremovereducefiuniidatyindosed-inconslructionstoLsuchinextentthatthefonnatio-iiof;iLtxrdactivewaterfilmisnotpossible.Thisprincipleisusedworld-widecnbridgesmadeassteelbox:girderconslruciions.Outside,thesicdconstructioncanbeappliedwithllduplex,systemintheformofthermallysprayedzinccoatingandp

26、ainlbutm$idetheueeiisonlypinled.AdehurnidifyingsystemensuresihallherelativehurtlidicyinsidetheEnictureisconsianrlyapproximaieh40%TheideaisChat肝suchIawrel-ativehumiditytheformaligtiofancleetRilyt已insiid巳isnorpossible.Thispreventsxnyinternalcoirosior.EiectrochemicalseriesTliccorrosimtranceoftmetalindi

27、catestheabilityofthunietltoresistcor-msidninad-efinedeiivlronnientHowlesisiLLntmetalsoralloysare.dependsonfactorssuchasthetypeofmetalandtheenvironmenttowhichitisexposed.In削11nietlsoralloysmixturesolmetals)制certainamaentofeaergvissEorcd.Tlhisamountofenergycunbetncasuredinvoir.Thesemeasurinenhartusual

28、lycalledpoientialormeasremrr.ThedifferenceinpotenlialbciwetntwomettLlscunbeuieastireriby(Lvokmetcr.Htiwevekinordertomeasurethepottnliatofthemetals,either4oncortogether,areferenceelectrodemustbeusedAreference：electrodeserves;ts-aklnilolzeropoint.Suchareferencedoctrodeiscalledthestandardhydmg别诚弋刖如ofte

29、nabbreviatedSHEIthasaputentialof0Vinadefinedsolutional25C.-.:-:0VullrrioterReferenceclectrodp/.7wtHiameasuremen!withreferencelectrodt?Forpotentialmeasuremenisinseawalerthereferenceelectrodeslistedbelowir七used.Whenacenainreferenceelectrodeisreferredtotthechemicalnamesortheabbreviationsintheparenthese

30、sareoccasionallyused.rhble1.2Potentialsfi)rdifferentreferenceelectrodesmrelationfothestandardhydrogenelectrodeSHE)ReferenceetectrodeElectrolytePotentialversusSHE(V)ZincSeawaterapproximately-078vSilvor/silverchlorideSSC)Seawaterapproximately*0.25VCopper/coppersulphate(CSE)Saawaterapproxinnately+0.32V

31、Calomel(SCE)KCIapproximate!/+0.245VItcanbeseenthatareferenceelectrod已ofzincisnegativecomparedtothestandardhydrogenelectrode,zmdthatth.totherthreeaieinOiepOsi(ivtTMetalsandalloyscLinberanked111elecxrocheinicillseriesaccortliiigtotheircorrosionrcsisU.nct.SuchelectrGhcmicaIseriesatecsiaHisheclbylYasuri

32、ngtheporentialofnmtaluranalloyinadefinedeiivironnient.Themostwiiielyknownandusedseriesisthegalvanicseriesinseawater.Acloserloo-knlth.6-ilvaiiicseriesquicklyrevealswhiclioftwojoinedmemL1；willcorrode.Ttiblc1.3showsthatboth齐incandaluminiumandlli-cirall&ysarcle讣nobletlianisteel.Iftwometalsareplacedinele

33、ctroch-emicalconuct,iheIck.snoblemeudwillsufferincreasedcorrosion.Thiscircumstanceisofgreatpracticalimportance,farexampleinuonneciionwithcorrosionprotecLied,AluminiunnalloysimHsteellLny&donixcorrodelaanygreatestcutwhtnexposedinurbanorindustrialal-mosphcrc,However,theattackmaybeimportantiftheamcalloy

34、sareCXpOd!forexampleseawairr.Inthegalvanicseriesafewmetalsoralloysarelistedtwice.Thisisduetothefactthatsomemetalsarecoveredbynrkinandprotectiveoxidefilm.Aslongasthisoxidefilm忑inLctithelpsthemetaltcremainpassive.IflhefiImhasbeenremovedordamaged,forexamplethroughabrasion.,thepositioninthegalvankseries

35、changesThemetalnowahighertendencytoCOnfOKiMcuhwiths,uchanoxidefilmincludestiiinlcsssteel,nickelalloysantialu-inmuinalloysIf(hereispkhlufulsupplyo-fandcxygcnTthtse叮id亡filmsareself-repaiiing.Underlayersofdinandpollutantsthesupplyofoxygenmabecomelotlow.Ininchsitesliltoxidefilmisnotrepaired,andcorrosion

36、occur.UndersuchcondiIlors,stjueprocessindustiieshaveexpcrjcnccdproblemswithcriceandpiningmrrosionofordinary*stainlesssteel.ThishasresultedinachangerohighergradelesssieeltypcsfurcxdniplcASTMS31254.TcibleL3Galvanicseriesinflawingse/rwater(2.5-4m/sKtenipcratureraneJi-3()2C.Poientiaharemensuredversussai

37、Lmitedctihmelrerenteelectrode(SCE)Crcvitcandpiningcoirosion粗“typesofcorrasiotiwhichtuiuslocalizedturro-sionattacksonmetals,lheattackoftenstartswherethereisapoo匚exchangeofelectrolyteinnarrowertvLgjsorinpitsThistypeofattackoftentakersplactiveryquickly3nilmayresultiniheicKialcorrodingcompletelyElwough.

38、Galvaniccorrosion話alsof(?undiftheexternalconditionsbetweentwoequallynoblemetalsresultinadifferenceinpotential.SuchadifferencemayoccurduetoadifferenceinoxygenciinceiilrLition,forexampleoilpilessubmergedinseawatr.Galvaniccorrosion曲alyprroHionbecausethtreisnocontinuouselectrolytebeingformedontlicsurfac

39、e.Inthecaseottwidoorexposure.ecorrosionattack,(hej?ivalueoftliesoluiitjnivmeasured.ThepHvalueisusuallymeasuredwithinaraneiwmCto14.PurewaterhasThepHvalueof7,whichisaneutralsolutiou.If目卩Ivaluedilessthan7ismejsurd,itisanacidicsolution.Thelloserlo0,ihcmoracidn：rliesolution.RdinWitteroftenhi巧npHYaln(?aro

40、und5becausenhasuiken,门卩utidicpollution.ThepHsaleislgarilhmiG.Thi&rncanthat.IforeverysinglepointabovebelowapHvalueot7fthesolutionwillbetentimesmorecocicentL-ated.,AsoluiionwithapHvalueof5isconsequentlylOx10=100timesmoreconcentratedthananeutralsolutionwithpHvalueLAcrdic”i1-AlkEiineNeutraI厂r1j11ILIT1!1

41、1rL-11OF234567S9W111213UFigure77irpH.raMAlkalinesubstnncchavepHvaluesfrom7to14.Exain卩俺呂ofsuchsubstancesaresodiumhydroxide(caustic!sodahlye),ammoniaandcement.Acidic.nibstiinc&shavepHvaluesfromQto7-ExamplesofsuehMil)s(inces;uchydrochloricacidandauI卩huricacidTheirareaofuseincludespretreciinienr(picklin

42、g)ofsteelbeforehotdipgaivauizing.Thec-oiTOsionattackonmetals用oltertintensifiedinacidicandalkalinesolu-tinns.Bottialuminimnnntlzincsustainverysetre刖笛cksiticontactwithHowever,ifsteeltsimmersedinanalkalinesolution,thesteelispassivated.Athill3runuxtdcfilmisformedontheurJucewhichoffersgoodprotectionugain

43、stcorro-si&ti,Andtherateofuorroicnisreducedconsiderably.ReinforcingsteelbarsarewellprotectedandkeptpassivatedbythealkalineenviTonnientiticoncrete.rhedecisivefactorforchi?cxn*i(hiprocessiswhetherwaicrfromraiiLdewqlcondensationclue10酋highrdiidvi;humidityoftheairisprcsculontheiiLtuilsuriace.However,the

44、Consequencesmayvarymn对ck叮:HyWhenitrains,conllimimaneslikesaltsanddirtcollectedoilthesurfacewillbewiMhpdiwtiv：Butin.tliighhunudityorcondenauri“計Ehek：elfsuchcontaminantsarenotwashedoff.Contaminantsineformofdusiandsaltattractmoisture(theyarehygroscopic),andthisprolongsthetiirueofwetnessLForthisreason,s

45、tructuresinLinenvironmentofhi莒hhuniiilitybutliideprecipitationnayslainse-verucorrosiondiL：k匚A.uminiumHiiHSteelIronoxideAlkalineso.utionFigureF.9ConranwithstrongalkaliswiilcausaanackmhathJnrandaluminium,butnotc)f)stelCorrosiontypesSofarlheckterlorationof卫亂代bhbytheprocessofcprrcsianhasbeendcscribCAlin

46、verygnerl【enns-.Inthecaseofcorros-iononmetals,theattacksareusuallygivenamoredetailedcharacferitKin,primarilybusedontheappearancechanic-tcfiftiesoftheattach.Amoredetai1-eddescriptioriwtFnowbegivvnofsinefihumosTconimonrypeiofcorroxiodloimdctimeoE.Uniformcorrosion(generalcorrosion)WhencunosLOndevelops;

47、U“卩proxinmtclythes.amrateovertheeniirckikLis-ur-facc,itiscalleduniformcorrosion.Thistypeofcorrosionresultsinafairlyevenbreakdownof(hemeta.AnattackJikcthiscauseslwt!iEinodcitxlcathodereactions(ooccuronthesamemetalAresofdiffereiirnoblenesscanbefounddutoparticlfbrei呂口inuiatstingpreseminthemetalsurfaceo

48、rintheelectrolytestechnicallyspeaking.Chis(yp&orcorrosionisntitveryprobSematic.IKehfe-timeotviiciisalloysinvariousnvirunimcnts匚日dbecalciiiatedxIltheattacktakesplace自israteotapproximatelyOJnunAre；ir,inwilltaki?2()yearsbeforeainetalthicknessof2mmhascorroded4waycomplexly.Normallyrequirememsrabathstreng

49、thandlifetimearetakenintoconsiderationandthemetalthicknessincreasedbyacorronionallowance.FiguTeLIOUniformAnoldgalvanizedroofwheretheinchascorrodedawayisancxainplcofunifornicoiTOSiaii-Attacksonlowalloyandweatheringsteelsareofienofthistype.ThiscorrosiontypecanbeseenunmoSTmetallicniciItrials.Uniformcor

50、rosionanbereducedbyselectingth亡rightnjaterialaddinginhibitor(tosystetnscarrringliquid)us-ingcathodicprotecticnusingcoatings/LiningsGalvaniccorrosion(birnet创liecorrosion)Ontofthemostwidelyobs亡vedc-o-rrOLOntype爲andoftenthemosfdangeroiaslypetisgalvaniccorrosion.Tinstypeofconosionoccurswhentherei%nietal

51、liccontactbetweentwometalsinacorrosivecnvirynment,Thec-orrosionisatceleratedonthebasemetalandisreducedonthenoblemetal.tThodcAnodeFigufTLIIGalvaniccorrosianllicattackonthemetal,theSnadc,ismoilseverecloa中打加】anodeoitenleadstoafasterandmoresevereconosionaitaukthanin(liecaseofasimldifferenceinurea.Theoff

52、shereoilindustryhasexperiencedproblemswi(hsometypes)fweldingelectrodesusedforweldingofcarbonslcel.Byacci-denlinsutficicntlyalloyedclcctrodecomparedioiliepipeswereused.ThisresultedincoinpleieenrrasionoftheweldedjouHsinrecordrimewildsiensivcdamagetothemateria.Thereastm小galvaniccorrosioncannedbyh1irgec

53、athodearea(hepipes)andasniatlanod-eirea(thewelds).Hiegalvanicscriesinseawater(seeJbk】-3)wasinetnionedabove.Toacertainexternthissenesprovidesapossibilityforpredictingtheriskofgalvaniccorrosion.BeloA1someexamplesofvariouslypcsolattackcausedbyLfalviinicconta.ctbetweendissimilarmeialswillbediscussed.The

54、StatusofLibertyinNewYorkCitywascompletedin1886.Th.ecoppersraiiiewjssupportedinternallybyaframeworkofironandsteel.Thecepperskinanddiesteelwereoriginallyiisulat&Jlronie()chotherbymeansofasbestosfabricinipregiuitcdwithshellac.Overtheyearslheasbestosfabrichaddeterioraitriiandstartedtnworkitsawickbetween

55、themetLils.IntheearlythesleclrantuwOkhadbecomecxiensivelydamagedduetvgalViinickOrrosiotl,11kigrnxi门门atraclonthsteelandcrackitiofiheii(uhudcauseddefoiniarJiinofchetopperskinina口umberofplaces.Duringtherestorationameffortwasmadetopreventgalvaniccorrasion.Mostof(hesteelwasreplacedbystanksHsteelandthewer

56、einsuEatcdfromeachcitherbymeansotTeflonuskeis/inscrts,口AnunibcrofwheelhollonareofLiJimtiniiiin.Thishas.Tesuldingalvaniccorrosionintheimcrfacc1)clwcceisteelandaluiEiinLLiiiL,buttheproblemshavenewbeenreducedbycbginthejoiningwchni屮h怡amlhyii珥门芸Linticorrnsionpaints.GctlvLtniccorroNioncanbereducedby-using

57、fillermetalsf&rweldingwhicharenoblerthantheparentmaterialchangingthemateriatsllsciIinordertoitvoklhanTifnl心ontacfbtweinnbleandbatematerialsinsnhdngmaterialsfrofneachother，usingmetacoatingsorpaintcnjtingsavoiding!hedeposit:flblc-rirttUliotiunthesurfacerCrevfcecorrosionNarrowerevicesexposedtoalrqunl,t

58、ypicWywatcr-conUmingsolutions.Jiiiybeopenenoughiiullowtheliquii!topenetrate,butstillnarrowthatlheliquidbccumtsxiag.runtwithinihem.Ifthisisthecase.crevicecorrosionmayoccur.Thedrivingforceforthistypeofcorrosiuti.isadifferenceinoxygancontentinsideandemtsideecrevice.ThemDStpronulincedcrcvigcorrs.ionoccu

59、rsonmetalswhich上心卩jssiveoreasilypassiVciled,sutlijsskinlesssteelhaluminium-jn-d.steelinpredontjiiantlyalkahtLetuyironments.Forexampitmseawaterthepasivcj己kiyeroilsemeneialsmaybebrokendownbyaggressivechlorideions.CrevicecomosjonoccursinHangedjoints,underrivetheadsandscrewheads,inoverlapsandwhenthemctL

60、iliscuveredbylorexampledirr,anil.coiTosionproductsormarinegrowth_|島712J斗亠ni.wp.jj*iL起尹7t+_Watermorerichi，.-becomcisntheeathiicregiorifigureL12CricecorrosionCathodicreader；O3+H0+2e=2OH-厂!lherofpracticalprecautions;Useweldingitisteadoftlanged(niitsandboltedihiiewhciiEUE卩05切hM.Mujjmjicclhenumberofsharp