1、Designation: G 31 72 (Reapproved 2004)Standard Practice forLaboratory Immersion Corrosion Testing of Metals1This standard is issued under the fixed designation G 31; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last
2、revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice2describes accepted procedures for andfactors that influence laboratory immersion corrosion tests,particularl
3、y mass loss tests. These factors include specimenpreparation, apparatus, test conditions, methods of cleaningspecimens, evaluation of results, and calculation and reportingof corrosion rates. This practice also emphasizes the impor-tance of recording all pertinent data and provides a checklistfor re
4、porting test data. Other ASTM procedures for laboratorycorrosion tests are tabulated in the Appendix. (WarningInmany cases the corrosion product on the reactive metalstitanium and zirconium is a hard and tightly bonded oxide thatdefies removal by chemical or ordinary mechanical means. Inmany such ca
5、ses, corrosion rates are established by mass gainrather than mass loss.)1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its us
6、e. 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.2. Referenced Documents2.1 ASTM Standards:3A 262 Practices for Detecting Susceptibility to Intergranu-lar Attack in Au
7、stenitic Stainless SteelsE 8 Test Methods for Tension Testing of Metallic MaterialsG 1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test SpecimensG 4 Guide for Conducting Corrosion Coupon Tests in FieldApplicationsG 16 Guide for Applying Statistics to Analysis of CorrosionDataG 46 Gui
8、de for Examination and Evaluation of PittingCorrosion3. Significance and Use3.1 Corrosion testing by its very nature precludes completestandardization. This practice, rather than a standardized pro-cedure, is presented as a guide so that some of the pitfalls ofsuch testing may be avoided.3.2 Experie
9、nce has shown that all metals and alloys do notrespond alike to the many factors that affect corrosion and that“accelerated” corrosion tests give indicative results only, ormay even be entirely misleading. It is impractical to propose aninflexible standard laboratory corrosion testing procedure forg
10、eneral use, except for material qualification tests wherestandardization is obviously required.3.3 In designing any corrosion test, consideration must begiven to the various factors discussed in this practice, becausethese factors have been found to affect greatly the resultsobtained.4. Interference
11、s4.1 The methods and procedures described herein representthe best current practices for conducting laboratory corrosiontests as developed by corrosion specialists in the processindustries. For proper interpretation of the results obtained, thespecific influence of certain variables must be consider
12、ed.These include:4.1.1 Metal specimens immersed in a specific hot liquidmay not corrode at the same rate or in the same manner as inequipment where the metal acts as a heat transfer medium inheating or cooling the liquid. If the influence of heat transfereffects is specifically of interest, speciali
13、zed procedures (inwhich the corrosion specimen serves as a heat transfer agent)must be employed (1).44.1.2 In laboratory tests, the velocity of the environmentrelative to the specimens will normally be determined byconvection currents or the effects induced by aeration orboiling or both. If the spec
14、ific effects of high velocity are to bestudied, special techniques must be employed to transfer the1This practice is under the jurisdiction of ASTM Committee G01 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.05 on LaboratoryCorrosion Tests.Current edition approved May 1,
15、 2004. Published May 2004. Originallyapproved in 1972. Last previous edition approved in 1998 as G 31 72 (1998).2This practice is based upon NACE Standard TM-01-69, “Test Method-Laboratory Corrosion Testing of Metals for the Process Industries,” with modifica-tions to relate more directly to Practic
16、es G 1 and G 31 and Guide G 4.3For 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.4The boldface numbers in parent
17、heses refer to the list of references at the end ofthis practice.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.environment through tubular specimens or to move it rapidlypast the plane face of a corrosion coupon (2). Alternatively,
18、 thecoupon may be rotated through the environment, although it isthen difficult to evaluate the velocity quantitatively because ofthe stirring effects incurred.4.1.3 The behavior of certain metals and alloys may beprofoundly influenced by the presence of dissolved oxygen. Ifthis is a factor to be co
19、nsidered in a specific test, the solutionshould be completely aerated or deaerated in accordance with8.7.4.1.4 In some cases, the rate of corrosion may be governedby other minor constituents in the solution, in which case theywill have to be continually or intermittently replenished bychanging the s
20、olution in the test.4.1.5 Corrosion products may have undesirable effects on achemical product. The amount of possible contamination canbe estimated from the loss in mass of the specimen, with properapplication of the expected relationships among (1) the area ofcorroding surface, (2) the mass of the
21、 chemical producthandled, and (3) the duration of contact of a unit of mass of thechemical product with the corroding surface.4.1.6 Corrosion products from the coupon may influence thecorrosion rate of the metal itself or of different metals exposedat the same time. For example, the accumulation of
22、cupric ionsin the testing of copper alloys in intermediate strengths ofsulfuric acid will accelerate the corrosion of copper alloys, ascompared to the rates that would be obtained if the corrosionproducts were continually removed. Cupric ions may alsoexhibit a passivating effect upon stainless steel
23、 coupons ex-posed at the same time. In practice, only alloys of the samegeneral type should be exposed in the testing apparatus.4.1.7 Coupon corrosion testing is predominantly designedto investigate general corrosion. There are a number of otherspecial types of phenomena of which one must be aware i
24、n thedesign and interpretation of corrosion tests.4.1.7.1 Galvanic corrosion may be investigated by specialdevices which couple one coupon to another in electricalcontact. The behavior of the specimens in this galvanic coupleare compared with that of insulated specimens exposed on thesame holder and
25、 the galvanic effects noted. It should beobserved, however, that galvanic corrosion can be greatlyaffected by the area ratios of the respective metals, the distancebetween the metals and the resistivity of the electrolyte. Thecoupling of corrosion coupons then yields only qualitativeresults, as a pa
26、rticular coupon reflects only the relationshipbetween these two metals at the particular area ratio involved.4.1.7.2 Crevice corrosion or concentration cell corrosionmay occur where the metal surface is partially blocked fromthe corroding liquid as under a spacer or supporting hook. It isnecessary t
27、o evaluate this localized corrosion separately fromthe overall mass loss.4.1.7.3 Selective corrosion at the grain boundaries (forexample, intergranular corrosion of sensitized austenitic stain-less steels) will not be readily observable in mass lossmeasurements unless the attack is severe enough to
28、cause graindropping, and often requires microscopic examination of thecoupons after exposure.4.1.7.4 Dealloying or “parting” corrosion is a condition inwhich one constituent is selectively removed from an alloy, asin the dezincification of brass or the graphitization of cast iron.Close attention and
29、 a more sophisticated evaluation than asimple mass loss measurement are required to detect thisphenomenon.4.1.7.5 Certain metals and alloys are subject to a highlylocalized type of attack called pitting corrosion. This cannot beevaluated by mass loss alone. The reporting of nonuniformcorrosion is di
30、scussed below. It should be appreciated thatpitting is a statistical phenomenon and that the incidence ofpitting may be directly related to the area of metal exposed. Forexample, a small coupon is not as prone to exhibit pitting as alarge one and it is possible to miss the phenomenon altogetherin th
31、e corrosion testing of certain alloys, such as the AISI Type300 series stainless steels in chloride contaminated environ-ments.4.1.7.6 All metals and alloys are subject to stress-corrosioncracking under some circumstances. This cracking occursunder conditions of applied or residual tensile stress, a
32、nd itmay or may not be visible to the unaided eye or upon casualinspection. A metallographic examination may confirm thepresence of stress-corrosion cracking. It is imperative to notethat this usually occurs with no significant loss in mass of thetest coupon, although certain refractory metals are a
33、n exceptionto these observations. Generally, if cracking is observed on thecoupon, it can be taken as positive indication of susceptibility,whereas failure to effect this phenomenon simply means that itdid not occur under the duration and specific conditions of thetest. Separate and special techniqu
34、es are employed for thespecific evaluation of the susceptibility of metals and alloys tostress corrosion cracking (see Ref. (3).5. Apparatus5.1 A versatile and convenient apparatus should be used,consisting of a kettle or flask of suitable size (usually 500 to5000 mL), a reflux condenser with atmosp
35、heric seal, a spargerfor controlling atmosphere or aeration, a thermowell andtemperature-regulating device, a heating device (mantle, hotplate, or bath), and a specimen support system. If agitation isrequired, the apparatus can be modified to accept a suitablestirring mechanism, such as a magnetic s
36、tirrer. A typical resinflask setup for this type test is shown in Fig. 1.5.2 The suggested components can be modified, simplified,or made more sophisticated to fit the needs of a particularinvestigation. The suggested apparatus is basic and the appa-ratus is limited only by the judgment and ingenuit
37、y of theinvestigator.5.2.1 A glass reaction kettle can be used where the configu-ration and size of the specimen will permit entry through thenarrow kettle neck (for example, 45/50 ground-glass joint). Forsolutions corrosive to glass, suitable metallic or plastic kettlesmay be employed.5.2.2 In some
38、 cases a wide-mouth jar with a suitable closureis sufficient when simple immersion tests at ambient tempera-tures are to be investigated.5.2.3 Open-beaker tests should not be used because ofevaporation and contamination.G 31 72 (2004)25.2.4 In more complex tests, provisions might be needed forcontin
39、uous flow or replenishment of the corrosive liquid, whilesimultaneously maintaining a controlled atmosphere.6. Sampling6.1 The bulk sampling of products is outside the scope ofthis practice.7. Test Specimen7.1 In laboratory tests, uniform corrosion rates of duplicatespecimens are usually within 610
40、% under the same testconditions. Occasional exceptions, in which a large differenceis observed, can occur under conditions of borderline passivityof metals or alloys that depend on a passive film for theirresistance to corrosion. Therefore, at least duplicate specimensshould normally be exposed in e
41、ach test.7.2 If the effects of corrosion are to be determined bychanges in mechanical properties, untested duplicate speci-mens should be preserved in a noncorrosive environment at thesame temperature as the test environment for comparison withthe corroded specimens. The mechanical property commonly
42、used for comparison is the tensile strength. Measurement ofpercent elongation is a useful index of embrittlement. Theprocedures for determining these values are shown in detail inTest Methods E 8.7.3 The size and shape of specimens will vary with thepurpose of the test, nature of the materials, and
43、apparatus used.A large surface-to-mass ratio and a small ratio of edge area tototal area are desirable. These ratios can be achieved throughthe use of square or circular specimens of minimum thickness.Masking may also be used to achieve the desired area ratios butmay cause crevice corrosion problems
44、. Circular specimensshould preferably be cut from sheet and not bar stock, tominimize the exposed end grain. Special coupons (for example,sections of welded tubing) may be employed for specificpurposes.7.3.1 A circular specimen of about 38-mm (1.5-in.) diam-eter is a convenient shape for laboratory
45、corrosion tests. Witha thickness of approximately 3 mm (0.125-in.) and an 8-mm(516-in.) or 11-mm (716-in.) diameter hole for mounting, thesespecimens will readily pass through a 45/50 ground-glass jointof a distillation kettle. The total surface area of a circularspecimen is given by the following e
46、quation:A 5p/2D22 d2! 1 tpD 1 tpd (1)where:t = thickness,D = diameter of the specimen, andd = diameter of the mounting hole.7.3.1.1 If the hole is completely covered by the mountingsupport, the last term (tpd) in the equation is omitted.7.3.2 Strip coupons 50 by 25 by 1.6 or 3 mm (2 by 1 by116or18 i
47、n.) may be preferred as corrosion specimens, particularlyif interface or liquid line effects are to be studied by thelaboratory tests (see Fig. 1), but the evaluation of such specificeffects are beyond the scope of this practice.7.3.3 All specimens should be measured carefully to permitaccurate calc
48、ulation of the exposed areas. A geometric areacalculation accurate to 61 % is usually adequate.7.4 More uniform results may be expected if a substantiallayer of metal is removed from the specimens to eliminatevariations in condition of the original metallic surface. This canbe done by chemical treat
49、ment (pickling), electrolytic removal,or by grinding with a coarse abrasive paper or cloth such as No.50, using care not to work harden the surface (see section 5.7).At least 0.0025 mm (0.0001 in.) or 0.0155 to 0.0233 mg/mm2(10 to 15 mg/in.2) should be removed. (If clad alloy specimensare to be used, special attention must be given to ensure thatexcessive metal is not removed.) After final preparation of thespecimen surface, the specimens should be stored in a desic-cator until exposure, if they are not used immediately. Inspecial cases (for example, for aluminum and certain c
