ASTM_G_78_-_15.pdf

Designation:G7815Standard Guide forCrevice Corrosion Testing of Iron-Base and Nickel-BaseStainless Alloys in Seawater and Other Chloride-ContainingAqueous Environments1This standard is issued under the fixed designation G78;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONCrevice corrosion of iron-base and nickel-base stainless alloys can occur when an occlusion orcrevice limits access of the bulk environment to a localized area of the metal surface.Localizedenvironmental changes in this stagnant area can result in the formation of acidic/high chlorideconditions that may result in initiation and propagation of crevice corrosion of susceptible alloys.In practice,crevices can generally be classified into two categories:(1)naturally occurring,that is,those created by biofouling,sediment,debris,deposits,etc.and(2)man-made,that is,those createdduring manufacturing,fabrication,assembly,or service.Crevice formers utilized in laboratory andfield studies can represent actual geometric conditions encountered in some service applications.Useof such crevice formers in service-type environments are not considered accelerated test methods.The geometry of a crevice can be described by the dimensions of crevice gap and crevice depth.Crevice gap is identified as the width or space between the metal surface and the crevice former.Crevice depth is the distance from the mouth to the center or base of the crevice.1.Scope1.1 This guide covers information for conducting crevice-corrosion tests and identifies factors that may affect results andinfluence conclusions.1.2 These procedures can be used to identify conditionsmost likely to result in crevice corrosion and provide a basis forassessing the relative resistance of various alloys to crevicecorrosion under certain specified conditions.1.3 The values stated in SI units are to be regarded asstandard.The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.For a specificwarning statement,see 7.1.2.Referenced Documents2.1 ASTM Standards:2G1 Practice for Preparing,Cleaning,and Evaluating Corro-sion Test SpecimensG4 Guide for Conducting Corrosion Tests in Field Applica-tionsG46 Guide for Examination and Evaluation of Pitting Cor-rosionG48 Test Methods for Pitting and Crevice Corrosion Resis-tance of Stainless Steels and Related Alloys by Use ofFerric Chloride SolutionG193 Terminology and Acronyms Relating to Corrosion3.Terminology3.1 Definitions of related terms can be found in Terminol-ogy G193.4.Significance and Use4.1 This guide covers procedures for crevice-corrosion test-ing of iron-base and nickel-base stainless alloys in seawater.The guidance provided may also be applicable to crevice1This guide is under the jurisdiction of ASTM Committee G01 on Corrosion ofMetals and is the direct responsibility of Subcommittee G01.09 on Corrosion inNatural Waters.Current edition approved June 1,2015.Published July 2015.Originally approvedin 1983.Last previous edition approved in 2012 as G7801(2012).DOI:10.1520/G0078-15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 corrosion testing in other chloride containing natural watersand various laboratory prepared aqueous chloride environ-ments.4.2 This guide describes the use of a variety of creviceformers including the nonmetallic,segmented washer designreferred to as the multiple crevice assembly(MCA)as de-scribed in 9.2.2.4.3 In-service performance data provide the most reliabledetermination of whether a material would be satisfactory fora particular end use.Translation of laboratory data from asingle test program to predict service performance under avariety of conditions should be avoided.Terms,such asimmunity,superior resistance,etc.,provide only a general andrelatively qualitative description of an alloys corrosion per-formance.The limitations of such terms in describing resis-tance to crevice corrosion should be recognized.4.4 While the guidance provided is generally for the pur-pose of evaluating sheet and plate materials,it is also appli-cable for crevice-corrosion testing of other product forms,suchas tubing and bars.4.5 The presence or absence of crevice corrosion under oneset of conditions is no guarantee that it will