详细介绍清理之前，我们需要考虑不锈钢的表面。当轧钢厂的不锈钢出酸洗池用清水清洗时，同时有一层很薄的粘性氧化膜在表面形成(图1)。这层膜厚大约8～10埃，是一层含有铁和镍的透明铬氧化物。这是我们能看到的和环境接触的表面。如果该膜形成完好而且干净．它在大多数环境条件下都不活跃。因此，常常说不锈钢是钝化了的随后进行的“钝化处理主要是清洁过程，它不会进一步钝化，但是可以对膜上的缺陷进行修补，去除可能导致保护膜损A380-06StandardPracticeforCleaning,Descaling,andPassivationofStainlessSteelParts,Equipment,andSystems1.Scope1.1Thispracticecoversrecommendationsandprecautionsforcleaning,descaling,andpassivatingofnewstainlesssteelparts,assemblies,equipment,andinstalledsystems.Theserecommendationsarepresentedasproceduresforguidancewhenitisrecognizedthatforaparticularserviceitisdesiredtoremovesurfacecontaminantsthatmayimpairthenormalcorrosionresistance,orresultinthelatercontaminationoftheparticularstainlesssteelgrade,orcauseproductcontamination.Forcertainexceptionalapplications,additionalrequirementswhicharenotcoveredbythispracticemaybespecifieduponagreementbetweenthemanufacturerandthepurchaser.Althoughtheyapplyprimarilytomaterialsinthecompositionrangesoftheaustenitic,ferritic,andmartensiticstainlesssteels,thepracticesdescribedmayalsobeusefulforcleaningothermetalsifdueconsiderationisgiventocorrosionandpossiblemetallurgicaleffects.1.1.1Thetermpassivationiscommonlyappliedtoseveraldistinctlydifferentoperationsorprocessesrelatingtostainlesssteels.Inordertoavoidambiguityinthesettingofrequirements,itmaybenecessaryforthepurchasertodefinepreciselytheintendedmeaningofpassivation.Someofthevariousmeaningsassociatedwiththetermpassivationthatareincommonusageincludethefollowing:Passivationistheprocessbywhichastainlesssteelwillspontaneouslyformachemicallyinactivesurfacewhenexposedtoairorotheroxygen-containingenvironments.Itwasatonetimeconsideredthatanoxidizingtreatmentwasnecessarytoestablishthispassivefilm,butitisnowacceptedthatthisfilmwillformspontaneouslyinanoxygen-containingenvironmentprovidingthatthesurfacehasbeenthoroughlycleanedordescaled.Passivationisremovalofexogenousironorironcompoundsfromthesurfaceofastainlesssteelbymeansofachemicaldissolution,mosttypicallybyatreatmentwithanacidsolutionthatwillremovethesurfacecontaminationbutwillnotsignificantlyaffectthestainleessteelitself.ThisprocessisdescribedinageneralwayinanddefinedpreciselyinwithfurtherreferencetotherequirementsofandPartIIofthetableonacidcleaningofsteel.Unlessotherwisespecified,itisthisdefinitionofpassivationthatistakenasthemeaningofaspecifiedrequirementforpassivation.Passivationisthechemicaltreatmentofastainlesssteelwithamildoxidant,suchasanitricacidsolution,forthepurposeofenhancingthespontaneousformationoftheprotectivepassivefilm.Suchchemicaltreatmentisgenerallynotnecessaryfortheformationofthepassivefilm.PassivationdoesnotindicatetheseparateprocessofdescalingasdescribedinSection,althoughdescalingmaybenecessarybeforepassivationcanbeeffective.1.2Thispracticedoesnotcoverdecontaminationorcleaningofequipmentorsystemsthathavebeeninservice,nordoesitcoverdescalingandcleaningofmaterialsatthemill.Ontheotherhand,someofthepracticesmaybeapplicableforthesepurposes.Whilethepracticeprovidesrecommendationsandinformationconcerningtheuseofacidsandothercleaninganddescalingagents,itcannotencompassdetailedcleaningproceduresforspecifictypesofequipmentorinstallations...