1、Designation:G401(Reapproved 2008)Standard 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.
2、 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 guide covers procedures for conducting corrosiontests in plant equipment or systems under operating conditionsto evaluate the
3、corrosion resistance 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 andori
4、entation of the test 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. I
5、t 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. See also 10.4.2.2. Referenced Documents2.1 ASTM Standards:2A 262 Practices for Detecting Susceptibility to Intergranu-lar
6、 Attack in Austenitic Stainless SteelsE3 Guide for Preparation of Metallographic SpecimensG1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test SpecimensG15 Terminology Relating to Corrosion and CorrosionTestingG16 Guide for Applying Statistics to Analysis of CorrosionDataG30 Practice
7、for Making and Using U-Bend Stress-Corrosion Test SpecimensG36 Practice for Evaluating Stress-Corrosion-CrackingResistance of Metals and Alloys in a Boiling MagnesiumChloride SolutionG37 Practice for Use of Mattssons Solution of pH toEvaluate the Stress-Corrosion Cracking Susceptibility ofCopper-Zin
8、c AlloysG41 Practice for Determining Cracking Susceptibility ofMetals Exposed Under Stress to a Hot Salt EnvironmentG44 Practice for Exposure of Metals and Alloys by Alter-nate Immersion in Neutral 3.5 % Sodium Chloride Solu-tionG46 Guide for Examination and Evaluation of PittingCorrosionG47 Test Me
9、thod for Determining Susceptibility to Stress-Corrosion Cracking of 2XXX and 7XXXAluminumAlloyProductsG58 Practice for Preparation of Stress-Corrosion TestSpecimens for WeldmentsG78 Guide for Crevice Corrosion Testing of Iron-Base andNickel-Base Stainless Alloys in Seawater and OtherChloride-Contain
10、ing Aqueous Environments2.2 NACE Standard:3RP0497 Field Corrosion Evaluation Using Metallic TestSpecimens3. Significance and UseNOTE 1This guide is consistent with NACE Standard RP0497.3.1 Observations and data derived from corrosion testingare used to determine the average rate of corrosion or othe
11、rtypes of attack, or both (see Terminology G15), that occurduring the exposure interval. The data may be used as part ofan evaluation of candidate 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 a
12、lso be usedas guide lines to the behavior of existing plant materials for thepurpose of scheduling maintenance and repairs.3.3 Corrosion rate data derived from a single exposuregenerally do not provide information on corrosion rate changeversus time. Corrosion rates may increase, decrease, or remain
13、1This guide is under the jurisdiction of ASTM Committee G01 on Corrosion ofMetals and is the direct responsibility of Subcommittee G01.14 on Corrosion ofMetals in Construction Materials.Current edition approved May 1, 2008. Published May 2008. Originallyapproved in 1968. Last previous edition approv
14、ed in 2001 as G 401.2For 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.3Available from NACE International (NACE)
15、, 1440 South Creek Dr., Houston,TX 77084-4906, http:/www.nace.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.constant, depending on the nature of the corrosion products andthe effects of incubation time required at the onset of
16、pitting orcrevice corrosion.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 orcooling the liquid. In certain services, the corrosion of heat-exchanger tub
17、es 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 designand interpretation of plant tests.4.2 Effects caused by high velocity,
18、 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 of dissolved oxygen. Itis essential that the test specimens be placed in lo
19、cationsrepresentative 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 Corrosion products from the plant equipment mayinfluence the corrosion of one
20、 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 specimens may have their corrosion resistanceenhanced by the presence of the oxidi
21、zing 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 concentration in the acid increases.4.7 Tests covered by this guide are pre
22、dominantly 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. It should be observed, however, that galvanic corro-sion can be greatly affe
23、cted 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 corrosionproducts between specimens can promote localized corrosionof some alloys or aff
24、ect 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 readily observable in mass loss measure-ments and often requires microscopic e
25、xamination 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.Close attention and a more sophisticated evaluation than asimple mass loss meas
26、urement 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 astatistical phenomenon and its incidence can be directly relatedto the area
27、 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 confirm this mechanism ofattack. SCC usually occurs with no significant loss in
28、 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, there is noacceptable method to remove the film without removingsignificant un
29、corroded 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 testspecimens may not adequately cover this region.5. Test Specimen Design5
30、.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 duration, cost, confidencelevel, and expected results affect the choice of the sh
31、ape, 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 normally made by one of three methods: (1)by punching from sheet material, (2) by
32、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) the surface area can be minimized wherethere is restricted space, such as
33、 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) disks are very costly to fabricate if a ground finishand machined edges a
34、re 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 bar isundesirable unless end-grain effects are to be evaluated.5.2 Rectangula
35、r 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-effective forrectangular specimens than for disks when ground finished andmachi
36、ned sides are required, and they can be made using veryfew shop tools. In some cases, rectangular specimens are moreawkward to mount.G401(2008)25.3 Material availability and machinability also affect thecost of producing all types of specimens. Before the shape andsize are specified, the corrosion e
37、ngineer should determine thecharacteristics of the proposed materials.6. Test Specimens6.1 The size and shape of test specimens are influenced byseveral factors and cannot be rigidly defined. Sufficient thick-ness should be employed to minimize the possibility ofperforation of the specimen during th
38、e 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 equipment.6.2 A convenient size for a standard corrosion disk shapedspecimen
39、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 38mm nozzle. However, it is also convenient for larger sizenozzle ent
40、ries 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 in.) or 55 by 1.5 mm (2 by 0.062 in.) is sometimesemployed. These la
41、st 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 to a few in number in preliminary tests; special designsshould be emp
42、loyed 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 fabricatingequipment, welded specimens should be included as much aspossible in the tes
43、t 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 can alsobe evaluated. The weld and heat affected zone regions arerel
44、atively small; therefore, welded specimens should be madeslightly larger than the normal non-welded specimens whenpossible, for example, 50 by 75 mm (2 by 3 in.). The optimummethod of welding corrosion test specimens is to join the twohalves using a single vee or double vee groove with fullpenetrati
45、on 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 process and number of passes influencethe heat input and, consequently, the wi
46、dth 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 Test Specimens7.1 Controversy exists as to whether the test specimen edgesshou
47、ld 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 differentmaterials can be affected by the amount of cold work per-formed on t
48、he 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 andshearing operations typically extends back from the cut edge toa distance e
49、qual 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 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 shear
