ASTM G4-2001 Standard Guide for Conducting Corrosion Tests in Field Applications《用现场设备进行腐蚀试验的标准指南》.pdf

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1、Designation:G401Standard Guide forConducting Corrosion Tests in Field Applications1This standard is issued under the fixed designation G 4; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision. A number in pare

2、ntheses indicates the year of last reapproval. A superscriptepsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers procedures for conducting corrosiontests in plant equipment or systems under operating conditionsto evaluate the corrosion resista

3、nce of engineering materials. Itdoes not cover electrochemical methods for determining cor-rosion rates.1.1.1 While intended primarily for immersion tests, generalguidelines provided can be applicable for exposure of testspecimens in plant atmospheres, provided that placement andorientation of the t

4、est specimens is non-restrictive to aircirculation.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 use. It is theresponsib

5、ility 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. See also 10.4.2.2. Referenced Documents2.1 ASTM Standards:A 262 Practices for Detecting Susceptibility to Intergranu-lar Attack in Austeni

6、tic Stainless Steels2E3 Practice for Preparation of Metallographic Specimens3G1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test Specimens4G15 Terminology Relating to Corrosion and CorrosionTesting4G16 Guide for Applying Statistics to Analysis of CorrosionData4G30 Practice for Making

7、 and Using U-Bend Stress Corro-sion Test Specimens4G36 Practice for Evaluating Stress-Corrosion-CrackingResistance of Metals and Alloys in a Boiling MagnesiumChloride Solution4G37 Practice for Use of Mattssons Solution of pH 7.2 toEvaluate the Stress-Corrosion Cracking Susceptibility ofCopper-Zinc A

8、lloys4G41 Practice for Determining Cracking Susceptibility ofMetals Exposed Under Stress to a Hot Salt Environment4G44 Practice for Exposure of Metals and Alloys by Alter-nate Immersion in Neutral 3.5 % Sodium Chloride Solu-tion4G46 Guide for Examination and Evaluation of PittingCorrosion4G47 Test M

9、ethod for Determining Susceptibility to Stress-Corrosion Cracking of 2XXX and 7XXXAluminumAlloyProducts4G 58 Practice for Preparation of Stress-Corrosion TestSpecimens for Weldments4G78 Guide for Crevice Corrosion Testing of Iron-Base andNickel-Base Stainless Alloys in Seawater and OtherChloride-Con

10、taining Aqueous Environments43. Significance and Use53.1 Observations and data derived from corrosion testingare used to determine the average rate of corrosion and/or othertypes of attack (see Terminology G15) that occur during theexposure interval. The data may be used as part of anevaluation of c

11、andidate materials of construction for use insimilar service or for replacement materials in existing facili-ties.3.2 The data developed from in-plant tests may also be usedas guide lines to the behavior of existing plant materials for thepurpose of scheduling maintenance and repairs.3.3 Corrosion r

12、ate data derived from a single exposuregenerally do not provide information on corrosion rate changeversus time. Corrosion rates may increase, decrease, or remainconstant, depending on the nature of the corrosion products andthe effects of incubation time required at the onset of pitting orcrevice c

13、orrosion.4. Limitations4.1 Metal specimens immersed in a specific liquid may notcorrode at the same rate or in the same manner as in equipmentin which the metal acts as a heat transfer medium in heating or1This guide is under the jurisdiction of ASTM Committee G01 on Corrosion ofMetals and is the di

14、rect responsibility of Subcommittee G01.14 on Corrosion ofMetals in Construction Materials.Current edition approved Oct. 10, 2001. Published December 2001. Originallyissued as A 224-39. Last previous edition G 4-95.2Annual Book of ASTM Standards, Vol 01.03.3Annual Book of ASTM Standards, Vol 03.01.4

15、Annual Book of ASTM Standards, Vol 03.02.5This guide is consistent with NACE document RP0497, Standard Recom-mended Practice “Field Corrosion Evaluation Using Metallic Test Specimens”.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.c

16、ooling the liquid. In certain services, the corrosion of heat-exchanger tubes may be quite different from that of the shell orheads. This phenomenon also occurs on specimens exposed ingas streams from which water or other corrodents condense oncool surfaces. Such factors must be considered in both d

17、esignand interpretation of plant tests.4.2 Effects caused by high velocity, abrasive ingredients,etc. (which may be emphasized in pipe elbows, pumps, etc.)may not be easily reproduced in simple corrosion tests.4.3 The behavior of certain metals and alloys may beprofoundly influenced by the presence

18、of dissolved oxygen. Itis essential that the test specimens be placed in locationsrepresentative of the degree of aeration normally encounteredin the process.4.4 Corrosion products from the test specimens may haveundesirable effects on the process stream and should beevaluated before the test.4.5 Co

19、rrosion products from the plant equipment mayinfluence the corrosion of one or more of the test metals. Forexample, when aluminum specimens are exposed in copper-containing systems, corroding copper will exert an adverseeffect on the corrosion of the aluminum. On the contrary,stainless steel specime

20、ns may have their corrosion resistanceenhanced by the presence of the oxidizing cupric ions.4.6 The accumulation of corrosion products can sometimeshave harmful effects. For example, copper corroding in inter-mediate strengths of sulfuric acid will have its corrosion rateincreased as the cupric ion

21、concentration in the acid increases.4.7 Tests covered by this guide are predominantly designedto investigate general corrosion; however, other forms ofcorrosion may be evaluated.4.7.1 Galvanic corrosion may be investigated by specialdevices that couple one specimen to another in electricalcontact. I

22、t should be observed, however, that galvanic corro-sion can be greatly affected by the area ratios of the respectivemetals.4.7.2 Crevice or concentration cell corrosion may occurwhen the metal surface is partially blocked from the bulkliquid, as under a spacer. An accumulation of bulky corrosionprod

23、ucts between specimens can promote localized corrosionof some alloys or affect the general corrosion rates of others.Such accumulation should be reported.4.7.3 Selective corrosion at the grain boundaries (for ex-ample, intergranular corrosion of sensitized austenitic stainlesssteels) will not be rea

24、dily observable in mass loss measure-ments and often requires microscopic examination of thespecimens after exposure.4.7.4 Parting or dealloying is a condition in which oneconstituent is selectively removed from an alloy, as in thedezincification of brass or the graphitic corrosion of cast iron.Clos

25、e attention and a more sophisticated evaluation than asimple mass loss measurement are required to detect thisphenomenon.4.7.5 Pitting corrosion cannot be evaluated by mass loss. Itis possible to miss the phenomenon altogether when usingsmall test specimens since the occurrence of pitting is often a

26、statistical phenomenon and its incidence can be directly relatedto the area of metal exposed.4.7.6 Stress-corrosion cracking (SCC) may occur underconditions of tensile stress and it may or may not be visible tothe naked eye or on casual inspection. A metallographicexamination (Practice E3) will conf

27、irm this mechanism ofattack. SCC usually occurs with no significant loss in mass ofthe test specimen, except in some refractory metals.4.7.7 A number of reactive metals, most notably titaniumand zirconium, develop strongly adherent corrosion productfilms in corrosive environments. In many cases, the

28、re is noacceptable method to remove the film without removingsignificant uncorroded metal. In these cases, the extent ofcorrosion can best be measured as a mass gain rather than massloss.4.7.8 Some materials may suffer accelerated corrosion atliquid to atmospheric transition zones. The use of small

29、testspecimens may not adequately cover this region.5. Test Specimen Design5.1 Before the size, shape, and finish of test specimens arespecified, the objectives of the test program should be deter-mined, taking into consideration any restrictions that mightdictate fabrication requirements. The durati

30、on, cost, confidencelevel, and expected results affect the choice of the shape, finish,and cost of the specimen.5.1.1 Test specimens are generally fabricated into disks orrectangular shapes. Other shapes such as balls, cylinders, andtubes are used, but to a much lesser extent.5.1.2 Disks are normall

31、y made by one of three methods: (1)by punching from sheet material, (2) by slicing from a bar, or(3) by trepanning by a lathe or mill. Punched disks are by farthe least expensive and should be considered if materialthickness is not a limitation. Some of the positive characteris-tics of disks are: (1

32、) the surface area can be minimized wherethere is restricted space, such as in pipeline applications, (2)disks can be made inexpensively if a polished or machinedsurface finish is not required, and (3) edge effects are mini-mized for a given total surface area. Some negative character-istics are: (1

33、) disks are very costly to fabricate if a ground finishand machined edges are required, (2) disks fabricated fromsheet material result in a considerable amount of scrap mate-rial, and (3) disks sliced from a bar present a surface orienta-tion that can result in extensive end-grain attack. Using a ba

34、r isundesirable unless end-grain effects are to be evaluated.5.2 Rectangular specimens are fabricated by either punch-ing, shearing, or saw cutting. Punched disk shaped specimensare the most economical if the quantity is sufficiently high tojustify the initial die cost. Fabrication is more cost-effe

35、ctive forrectangular specimens than for disks when ground finished andmachined sides are required, and they can be made using veryfew shop tools. In some cases, rectangular specimens are moreawkward to mount.5.3 Material availability and machinability also affect thecost of producing all types of sp

36、ecimens. Before the shape andsize are specified, the corrosion engineer should determine thecharacteristics of the proposed materials.G40126. Test Specimens6.1 The size and shape of test specimens are influenced byseveral factors and cannot be rigidly defined. Sufficient thick-ness should be employe

37、d to minimize the possibility ofperforation of the specimen during the test exposure. The sizeof the specimen should be as large as can be convenientlyhandled, the limitation being imposed by the capacity of theavailable analytical balance and by the problem of effectingentry into operating equipmen

38、t.6.2 A convenient size for a standard corrosion disk shapedspecimen is 38 mm (1.5 in.) in diameter and 3 mm (0.125 in.)in thickness with an 11 mm (0.438 in.) hole in the center of theround specimen. This size was arrived at as being the maxi-mum size that could easily effect entry through a normal

39、38mm nozzle. However, it is also convenient for larger sizenozzle entries as well as for laboratory corrosion testing. Aconvenient standard specimen for spool-type racks measures25 by 50 by 3 mm (1 by 2 by 0.125 in.) or 50 by 50 by 3 mm(2 by 2 by 0.125 in.). A round specimen of 53 by 3 mm (2 by0.125

40、 in.) or 55 by 1.5 mm (2 by 0.062 in.) is sometimesemployed. These last three measure about 0.005 dm2in surfacearea.6.3 Other sizes, shapes, and thicknesses of specimens can beused for special purposes or to comply with the design of aspecial type of corrosion rack. Special designs should bereduced

41、to a few in number in preliminary tests; special designsshould be employed to consider the effect of such factors ofequipment construction and assembly as heat treatment, weld-ing, soldering, and cold-working or other mechanical stressing.6.4 Since welding is a principal method of fabricatingequipme

42、nt, welded specimens should be included as much aspossible in the test programs.6.4.1 Aside from the effects of residual stresses, the mainitems of interest in a welded specimen are the corrosionresistance of the weld bead and the heat affected zone.Galvanic effects between weld metal and base metal

43、 can alsobe evaluated. The weld and heat affected zone regions arerelatively small; therefore, welded specimens should be madeslightly larger than the normal non-welded specimens whenpossible, for example, 50 mm by 75 mm (2 in. by 3 in.). Theoptimum method of welding corrosion test specimens is to j

44、ointhe two halves using a single vee or double vee groove with fullpenetration and multiple passes. Double vee joint preparationis used for very thick samples. Machining the weld flush isoptional, depending on how closely the sample will be exam-ined afterward (see practice G58).6.4.2 The welding pr

45、ocess and number of passes influencethe heat input and, consequently, the width and location of theheat affected zone. For example, gas tungsten arc welding haslower heat input than oxygen fuel welding and causes anarrower heat affected zone, which is also closer to the weldbead.7. Preparation of Te

46、st Specimens7.1 Controversy exists as to whether the test specimen edgesshould be machined. The cold-worked area caused by shearingor punching operations can provide valuable information onalloy susceptibility to stress corrosion cracking. Also, theability to compare information among specimens of d

47、ifferentmaterials can be affected by the amount of cold work per-formed on the material. Therefore, the decision to machine andto test specimens with/without the residual stresses associatedwith cold work should be made on a case-to-case basis.7.1.1 The depth of cold work associated with punching an

48、dshearing operations typically extends back from the cut edge toa distance equal to the specimen thickness. Removal of thecold worked areas can be performed by grinding or carefulmachining the specimen edges.7.1.2 Ideally, the surface finish of the specimen shouldreplicate that of the surface finish

49、 of the material to be used forequipment fabrication. However, this is often difficult becausethe finish on materials varies between mills, between sheet andplate and even between heat treatments. The mill scale and theamount of oxides on the surface can vary as well. Also, surfacefinishes are difficult to apply to edges that have been distortedby punching or shearing. Since the primary requirement isusually to determine the corrosion resistance of the materialitself, a clean metal surface is most often used. The purpose ofthe test dictates the required finish of the specimen. Forinstance