ASTM G82-1998(2003) Standard Guide for Development and Use of a Galvanic Series for Predicting Galvanic Corrosion Performance《预测电流腐蚀特性用电流系列的制定和使用标准指南》.pdf-资源下载-麦多课文库

ASTM G82-1998(2003) Standard Guide for Development and Use of a Galvanic Series for Predicting Galvanic Corrosion Performance《预测电流腐蚀特性用电流系列的制定和使用标准指南》.pdf

1、Designation: G 82 98 (Reapproved 2003)Standard Guide forDevelopment and Use of a Galvanic Series for PredictingGalvanic Corrosion Performance1This standard is issued under the fixed designation G 82; the number immediately following the designation indicates the year of originaladoption or, in the c

2、ase 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.1. Scope1.1 This guide covers the development of a galvanic seriesand its subsequent use as a method of

3、predicting the effect thatone metal can have upon another metal can when they are inelectrical contact while immersed in an electrolyte. Sugges-tions for avoiding known pitfalls are included.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It

4、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. Specific precau-tionary statements are given in Section 5.2. Referenced Documents2.1 ASTM Standards:G3 Practice for Convent

5、ionsApplicable to ElectrochemicalMeasurements in Corrosion Testing2G15 Terminology Relating to Corrosion and CorrosionTesting2G16 Guide forApplying Statistics toAnalysis of CorrosionData2G71 Guide for Conducting and Evaluating Galvanic Cor-rosion Tests in Electrolytes23. Terminology3.1 Definitions o

6、f terms used in this guide are from Termi-nology G15.3.2 activethe negative (decreasingly oxidizing) directionof electrode potential.3.3 corrosion potentialthe potential of a corroding surfacein an electrolyte relative to a reference electrode measuredunder open-circuit conditions.3.4 galvanic corro

7、sionaccelerated corrosion of a metalbecause of an electrical contact with a more noble metal ornonmetallic conductor in a corrosive electrolyte.3.5 galvanic seriesa list of metals and alloys arrangedaccording to their relative corrosion potentials in a givenenvironment.3.6 noblethe positive (increas

8、ingly oxidizing) direction ofelectrode potential.3.7 passivethe state of the metal surface characterized bylow corrosion rates in a potential region that is stronglyoxidizing for the metal.3.8 polarizationthe change from the open-circuit elec-trode potential as the result of the passage of current.4

9、. Significance and Use4.1 When two dissimilar metals in electrical contact areexposed to a common electrolyte, one of the metals canundergo increased corrosion while the other can show de-creased corrosion.This type of accelerated corrosion is referredto as galvanic corrosion. Because galvanic corro

10、sion can occurat a high rate, it is important that a means be available to alertthe user of products or equipment that involve the use ofdissimilar metal combinations in an electrolyte of the possibleeffects of galvanic corrosion.4.2 One method that is used to predict the effects of galvaniccorrosio

11、n is to develop a galvanic series by arranging a list ofthe materials of interest in order of observed corrosion poten-tials in the environment and conditions of interest. The metalthat will suffer increased corrosion in a galvanic couple in thatenvironment can then be predicted from the relative po

12、sition ofthe two metals in the series.4.3 Types of Galvanic Series:4.3.1 One type of Galvanic Series lists the metals of interestin order of their corrosion potentials, starting with the mostactive (electronegative) and proceeding in order to the mostnoble (electropositive). The potentials themselve

13、s (versus anappropriate reference half-cell) are listed so that the potentialdifference between metals in the series can be determined. Thistype of Galvanic Series has been put in graphical form as aseries of bars displaying the range of potentials exhibited bythe metal listed opposite each bar. Suc

14、h a series is illustrated inFig. 1.4.3.2 The second type of galvanic series is similar to the firstin that it lists the metals of interest in order of their corrosionpotentials. The actual potentials themselves are not specified,1This guide is under the jurisdiction of ASTM Committee G01 on Corrosio

15、n ofMetals and is the direct responsibility of Subcommittee G01.11 on ElectrochemicalMeasurements in Corrosion Testing.Current edition approved October 1, 2003. Published October 2003. Originallyapproved in 1983. Last previous edition approved in 1998 as G 8298.2Annual Book of ASTM Standards, Vol 03

16、.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.however. Thus, only the relative position of materials in theseries is known and not the magnitude of their potentialdifference. Such a series is shown in Fig. 2.4.4 Use of a Galvan

17、ic Series:4.4.1 Generally, upon coupling two metals in the GalvanicSeries, the more active (electronegative) metal will have atendency to undergo increased corrosion while the more noble(electropositive) metal will have a tendency to undergo re-duced corrosion.4.4.2 Usually, the further apart two me

18、tals are in the series,and thus the greater the potential difference between them, thegreater is the driving force for galvanic corrosion. All otherNOTEDark boxes indicate active behavior of active-passive alloys.FIG. 1 Galvanic Series of Various Metals in Flowing Seawater at 2.4 to 4.0 m/s for 5 to

19、 15 Days at 5 to 30C (Redrawn from Original)5G 82 98 (2003)2factors being equal, and subject to the precautions in Section 5,this increased driving force frequently, although not always,results in a greater degree of galvanic corrosion.5. Precautions in the Use of a Galvanic Series5.1 The galvanic s

20、eries should not be confused with theelectromotive force series, which, although of a similar appear-ance to the galvanic series, is based on standard electrodepo-tentials of elements and not on corrosion potentials of metals.The electromotive force series should not be used for galvaniccorrosion pr

21、ediction.5.2 Each series is specific to the environment for which itwas compiled. For example, a series developed in a flowingambient temperature seawater should not be used to predict theperformance of galvanic couples in fresh water or in heatedseawater.5.3 Corrosion potentials can change with tim

22、e and theenvironment. These changes can affect the potential differencebetween the metals of interest and, in some cases, can reverserelative positions. It is thus imperative that the series used forthe prediction be obtained under similar conditions of exposureduration and electrolyte composition a

23、s the situation beingpredicted.5.4 Galvanic corrosion can occur between two identicalmaterials in different environments. The galvanic series gen-erated herein cannot be applied to this situation.5.5 Use of a galvanic series provides qualitative predictionof galvanic corrosion. It should not be used

24、 for quantitativepredictions of galvanic corrosion rate. A more precise determi-nation of the effect of galvanic coupling can be obtained by themeasurement of the corrosion currents involved as outlined inGuide G 71.3,45.6 Some published Galvanic Series, such as those in Fig. 15and 2, consider the p

25、ossibility of there being more than onepotential range for the same material, depending on whetherthe material is in the active or the passive state. Knowledge ofconditions affecting passivity of these materials is necessary todetermine which potential range to use in a particular applica-tion.5.7 G

26、alvanic corrosion behavior is affected by many factorsbesides corrosion potentials. These factors must also be con-sidered in judging the performance of a galvanic couple. Theyinclude, but are not limited to, the following:5.7.1 Anode-to-cathode area ratio,5.7.2 Electrolyte conductivity,5.7.3 Distan

27、ce between coupled metals,5.7.4 Shielding of metal surfaces by marine growth, sedi-ments, and so forth,5.7.5 Localized electrolyte concentration changes inshielded areas, and5.7.6 Polarization characteristics of the metals involved.5.8 Some materials that are subject to chemical attack inalkaline so

28、lutions may suffer increased attack when made thecathode in a galvanic couple due to generation of hydroxyl ionsby the cathodic reaction. Use of a galvanic series will notpredict this behavior.5.9 A more detailed discussion of the theory of galvaniccorrosion prediction is presented inAppendix X1 and

29、 inASTMSTP 576.46. Development of a Galvanic Series6.1 The development of a Galvanic Series may be dividedinto several steps. First is the selection of the environment andconditions of interest. During the exposures, the environmentand conditions should be as close as possible to serviceconditions.

30、A list of environmental factors and conditions that3Brasunas, A., Editor, NACE Basic Corrosion Course, Chapter 3, NACE,Houston, TX, 1970.4Baboian, R., “Electrochemical Techniques for Predicting Galvanic Corrosion,”Galvanic and Pitting Corrosion-Field and Laboratory Studies, ASTM STP 576,Am.Soc. Test

34、sive)| 18-12-3 Stainless Steel Type 316 (Passive)(+) SilverNOBLE or GraphitePASSIVE END GoldPlatinumFIG. 2 Galvanic Series of Various Metals Exposed to Sea Water3G 82 98 (2003)3could affect open-circuit potentials follows. This is not in-tended to be a complete listing, but it should serve as a guid

35、eto the types of factors that require consideration:6.1.1 Temperature,6.1.2 Flow velocity, and6.1.3 Electrolyte composition:6.1.3.1 Dissolved oxygen,6.1.3.2 Salinity,6.1.3.3 Heavy-metal ions,6.1.3.4 Organic matter, including bacteria and marinegrowth,6.1.3.5 Soluble corrosion products,6.1.3.6 pH,6.1

36、.3.7 Conductivity,6.1.3.8 Corrodents not part of the original environment (forexample, de-icing salts, fertilizers, and industrial effluents), and6.1.3.9 Waterline effects.6.2 The metals of interest are to be obtained and preparedfor exposure. The processing and surface condition of thesemetals shou

37、ld be as close as possible to the expected conditionof the metals used in service. A list of factors that could affectthe potentials of the metals follows. This is not intended to bea complete listing, but it should serve as a guide to the types offactors that require consideration:6.2.1 Bulk compos

38、ition,6.2.2 Casting or wrought processing method,6.2.3 Heat treatment, and6.2.4 Surface condition:6.2.4.1 Mill finish,6.2.4.2 Degree of cold-work from surface preparation,6.2.4.3 Corrosion product films,6.2.4.4 Prior electrochemical history-passive versus active,and6.2.4.5 Pits or shielded (crevice)

39、 areas.6.3 Panels of the materials of interest should have electricalwires attached, with the attachment points protected from theelectrolyte by coating of an appropriate nonconductive materialor by the panels being mounted such that the point of electricalconnection is not in contact with the elect

40、rolyte. A referencehalf-cell, which is stable in the environment of interest over theanticipated duration of exposure, should be selected. Duringexposure of the panels, their corrosion potential relative to thereference half-cell will be measured periodically, using avoltmeter.6.3.1 The size of the

41、panels, wire connections, and voltme-ter input resistance should be selected to preclude errors causedby polarization of the panel material, any voltage drop in thewire, and polarization of the reference half-cell during thepotential measurement procedure.6.3.2 Exposure duration should be sufficient

42、ly long to beindicative of the anticipated service condition.6.3.3 Potentials should be measured frequently enough toprovide good indications of potential variability during expo-sure, as well as systematic potential shifts that may occur.6.3.4 If the intent is to simulate long-term service, thepote

43、ntial readings should show no systematic variation over thelatter portion of the exposures which would preclude theaccurate extrapolation of the data to the service times ofinterest.6.4 Information relevant to selecting environment and ma-terials, as well as to the mounting of specimens and taking d

44、ata,may be found in Practice G71.7. Report7.1 The report concerning the development of the galvanicseries should include as much detailed information as possible,such as the following:7.1.1 The metallurgical history of the metals tested, includ-ing the factors listed in 6.2,7.1.2 The size, shape, an

45、d surface preparation of panelsbefore exposure, and the method used to hold the panels,7.1.3 The environment and conditions, including thoseitems listed in 6.1,7.1.4 The equipment and procedure used for potential mea-surements,7.1.5 The exposure duration and potential measurementfrequency,7.1.6 The

46、condition of panels after exposure, and type ofcorrosion, and7.1.7 A listing of the materials arranged in order of averageor steady-state corrosion potential over the time of interest.This list should follow the guidelines set forth in Practice G3.7.1.7.1 The measured corrosion potential for each ma

47、terialmay be listed beside that material in the form of an average orsteady-state value with or without a standard deviation or othererror band as calculated by procedures in Practice G16,orinthe form of a total range of potentials. This information may beplotted in bar graph form.7.1.7.2 The final

48、listing or graph should contain an indica-tion of the noble and active directions, and sufficient informa-tion about the conditions under which the series was obtainedto prevent misuse of the series for other environments andconditions.8. Keywords8.1 active; corrosion potential; galvanic corrosion;

49、GalvanicSeries; noble; passiveG 82 98 (2003)4APPENDIX(Nonmandatory Information)X1. THEORY OF GALVANIC CORROSIONX1.1 The difference in electrochemical potential betweentwo or more dissimilar metals in electrical contact and in thesame electrolyte causes electron flow between them. Attack ofthe more noble metal or metals is usually decreased, andcorrosion of the more active metal is usually increased.X1.2 Under the influence of galvanic coupling, appreciablepolarization of the metals may occur, which may produce aprotective film on the metal surface or which may causebrea

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