ASTM G78-2001(2007) Standard Guide for Crevice Corrosion Testing of Iron-Base and Nickel-Base Stainless Alloys in Seawater and Other Chloride-Containing Aqueous Environments《海水及其它含.pdf

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1、Designation: G 78 01 (Reapproved 2007)Standard 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 G 78; the number immediately following the designation indi

2、cates 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 (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONCrevice corrosion of iron-base and nickel-bas

3、e 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

4、 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 servi

5、ce. 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 dimens

6、ions 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 an

7、d 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.

8、3 The values stated in SI units are to be regarded as thestandard. 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

9、-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For a specificwarning statement, see 7.1.1.2. Referenced Documents2.1 ASTM Standards:2G1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test SpecimensG4 Guide for Conducting Corr

10、osion Tests in Field Appli-cationsG15 Terminology Relating to Corrosion and CorrosionTestingG46 Guide for Examination and Evaluation of PittingCorrosionG48 Test Methods for Pitting and Crevice Corrosion Re-sistance of Stainless Steels and Related Alloys by Use ofFerric Chloride Solution1This guide i

11、s 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 May 1, 2007. Published May 2007. Originallyapproved in 1983. Last previous edition approved in 2001 as G 7801.2For refer

12、enced 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West

13、 Conshohocken, PA 19428-2959, United States.3. Terminology3.1 Definitions of related terms can be found in Terminol-ogy G15.4. 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

14、be applicable to crevicecor-rosion testing in other chloride containing natural waters andvarious laboratory prepared aqueous chloride environments.4.2 This guide describes the use of a variety of creviceformers including the nonmetallic, segmented washer designreferred to as the multiple crevice as

15、sembly (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

16、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 genera

17、lly 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 or will not occurunder other cond

18、itions. Because of the many interrelatedmetallurgical, environmental, and geometric factors known toaffect crevice corrosion, results from any given test may ormay not be indicative of actual performance in service appli-cations where the conditions may be different from those of thetest.5. Apparatu

19、s5.1 Laboratory tests utilizing filtered, natural seawater, orother chloride containing aqueous environments are frequentlyconducted in tanks or troughs under low velocity (for example,;0.5 m/s (1.64 ft/s) or less) or quiescent conditions. Contain-ers should be resistant to the test media.5.2 Fig. 1

20、 shows a typical test apparatus for conductingcrevice-corrosion tests under controlled temperature conditionswith provisions for recirculation or refreshment of the aqueousenvironment, or both, at a constant level.5.3 The apparatus should be suitably sized to providecomplete immersion of the test pa

21、nel. Vertical positioning ofthe crevice-corrosion specimens facilitates visual inspectionwithout the need to remove them from the environments.6. Test Specimens6.1 Because of the number of variables which may affect thetest results, a minimum of three specimens are suggested foreach set of environme

22、ntal, metallurgical, or geometric condi-tions to be evaluated. If reproducibility is unsatisfactory,additional specimens should be tested.6.2 Dimensions of both the test specimen and creviceformer should be determined and recorded.6.3 Variations in the boldly exposed (crevice-free) toshielded (crevi

23、ce) area ratio of the test specimen may influencecrevice corrosion.All specimens in a test series should have thesame nominal surface area. While no specific specimen dimen-sions are recommended, test panels measuring up to 300 by300 mm (11.81 by 11.81 in.) have been used in seawater testswith both

24、naturally occurring and man-made crevice formers.For laboratory studies, the actual size of the specimen may belimited by the dimensions of the test apparatus and this shouldbe taken into consideration in making comparisons.6.3.1 A test program may be expanded to assess any effectof boldly exposed t

25、o shielded area ratio.6.3.2 If crevice geometry aspects, such as crevice depth, areto be studied, the adoption of a constant boldly exposed toshielded area ratio is recommended to minimize the number oftest variables.6.4 When specimens are cut by shearing, it is recommendedthat the deformed material

26、 be removed by machining orgrinding. Test pieces that are warped or otherwise distortedshould not be used. The need to provide parallel surfacesbetween the crevice former and the test specimen is animportant consideration in providing maximum consistency inthe application of the crevice former.6.5 A

27、ppropriate holes should be drilled (and deburred) inthe test specimen to facilitate attachment of the crevice former.Punched holes are not recommended since the punchingprocess may contribute to specimen distortion or work hard-ening, or both. The diameter of the holes should be largeenough to allow

28、 clearance of the fastener (and insulator)otherwise additional crevice sites may be introduced.6.6 Specimens should be identified by alloy and replication.Mechanical stenciling or engraving are generally suitable,provided that the coding is on surfaces away from the intendedcrevice sites. Identifica

29、tion markings should be applied prior tothe final specimen cleaning before test. Marking the samplesmay affect the test results. See the Identification of TestSpecimens section of Guide G4.6.7 Depending on the test objectives, mill-produced sur-faces may be left intact or specimens may be prepared b

30、yproviding a surface definable in terms of a given preparationprocess.6.7.1 Because of the possible variations between “as-produced” alloy surface finishes, the adoption of a givensurface finish is recommended if various alloys are to becompared. This will tend to minimize the variability of crevice

31、geometry in contact areas.6.7.2 While some specific alloys may have proprietarysurface conditioning, some uncertainty may exist with regardto the actual end use surface finish. It is recommended thatmore than one surface condition be examined to assess anyeffect of surface finish on an individual al

32、loys crevice corro-sion behavior.6.7.3 Surface grinding with 120-grit SiC abrasive paper is asuitable method for preparing laboratory test specimens. Wetgrinding is preferred to avoid any heating. Depending on thesurface roughness of the mill product, machining may berequired prior to final grinding

33、.G 78 01 (2007)26.8 Cut lengths of pipe and tubing can be used as specimensto test the crevice corrosion resistance of these product formsin the as-manufactured or surface treated condition. Othercylindrical products can be tested in the as-produced orfinished condition.6.8.1 The selection of cylind

34、rical sample sizes should bemade with the knowledge of the availability of appropriatelysized crevice formers, as described in 9.5.6.8.2 The type of crevice former selected may dictate thelength of the cylindrical test specimens. Lengths of 4 to 12 in.(10 to 30 cm) and longer have been used.7. Clean

35、ing7.1 Pre-Test Cleaning:7.1.1 Cleaning procedures shall be consistent with PracticeG1. Typically, this may include degreasing with a suitablesolvent, followed by vigorous brush scrubbing with pumicepowder, followed by water rinse, clean solvent rinse, and airdrying. (WarningSolvent safety and compa

36、tibility with thetest material should be investigated and safe practices fol-lowed).7.1.2 For the most part, commercially produced stainlessalloys and surface ground materials do not require a pre-exposure pickling treatment. The use of acid cleaning orpretreatments shall be considered only when the

37、 crevice-corrosion test is designed to provide guidance for a specificapplication.7.1.3 Any use of chemical pretreatments shall be thoroughlydocumented and appropriate safety measures followed.8. Mass Loss Determinations8.1 Mass loss data calculated from specimen weighingbefore and after testing may

38、 provide some useful informationin specific cases. However, comparisons of alloy performancebased solely on mass loss may be misleading because highlylocalized corrosion, which is typical of crevice corrosion, canoften result in relatively small mass losses.9. Crevice Formers9.1 General Comments:9.1

39、.1 The severity of a crevice-corrosion test in a givenenvironment can be influenced by the size and physicalproperties of the crevice former.9.1.2 Both metal-to-metal and nonmetal-to-metal crevicecomponents are frequently used in laboratory and field studies.9.1.3 Nonmetallic crevice formers often h

40、ave the capacityfor greater elastic deformation and may produce tighter crev-ices which are generally considered to more readily promotecrevice-corrosion initiation. Acrylic plastic, nylon, polyethyl-ene, PTFE-fluorocarbons, and acetal resin are a few of thecommonly used nonmetallics.9.1.4 The prope

41、rties of the nonmetallic crevice former mustbe compatible with the physical and environmental demands ofthe test.9.1.5 Regardless of the material or type of crevice former,contacting surfaces should be kept as flat as possible toenhance reproducibility of crevice geometry.9.2 Various Designs for Fla

42、t Specimens:9.2.1 Fig. 2 shows the shapes of a few popular creviceformer designs, such as coupons, strips, O-rings, blocks,continuous and segmented washers. In many cases, two creviceformers are fastened to a flat specimen, that is, one on eachside.9.2.2 Multiple crevice assemblies (MCA) consist of

43、twononmetallic segmented washers, each having a number ofgrooves and plateaus.The design shown in Figs. 3 and 4 is onlyone of a number of variations of the multiple crevice assemblywhich are in use. Each plateau, in contact with the metalsurface, provides a possible site for initiation of crevicecor

44、rosion. Multiple crevice assemblies fabricated of acetalresin have been shown to be suitable for seawater exposures.Other nonmetallics, such as PTFE-fluorocarbon and ceramic,have also been used (see 9.1.4).9.2.3 For metal-to-metal crevice-corrosion tests, flat wash-ers or coupons are often fastened

45、to a larger test specimen. Allcomponents should be of the same material and prepared forexposure in the same manner.9.2.3.1 Crevice testing with metal to metal componentsassembled with either nonmetal or metal fasteners (withinsulator) will necessarily result in the formation of secondarycrevice sit

46、es where the fastener contacts the metallic creviceformer. In some cases, the geometry of these secondary sitesmay be more severe than the intended primary crevice site.9.3 Method of Attachment:9.3.1 Either metallic or nonmetallic fasteners, for example,nut- and bolt-type, can be used to secure the

47、crevice formers tothe test panel.NOTE 1While it is recognized that rubber bands may be used in the 72h ferric chloride test method covered by Test Methods G48, rubber bandsare not recommended for long-term tests. Potential crevice sites formed byrubber bands on specimen edges may not be desirous for

48、 tests beyond thescope of Test Methods G48.9.3.2 Metallic fasteners are often preferable because of theirgreater strength advantage over nonmetallics. Corrosion resis-tant alloys should be selected for the fastener material. Tita-nium, Alloy 625 (UNS No. N06625) and Alloy C-276 (UNSNo. N10276) have

49、proven corrosion resistance in marineenvironments and are frequently utilized for crevice-corrosiontests.9.3.3 When metallic fasteners are used, they should beelectrically insulated from the test specimen.9.3.4 The use of a torque wrench is recommended to helpprovide consistency in tightening. All crevice assemblies in agiven series should be tightened to the same torque, preferablyby the same individual in order to minimize variability.9.3.4.1 A torque of 8.5 Nm (75 in.-lb) on an acetal resinMCA (using a14-20 metallic fastener) for example, willroutinely result in crevice corro