ASTM G82-1998(2009) 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的标准指南》.pdf-资源下载-麦多课文库

ASTM G82-1998(2009) 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的标准指南》.pdf

1、Designation: G 82 98 (Reapproved 2009)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 () 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 p

3、redicting 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 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in

4、 thisstandard.1.3 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-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.

5、Specific precau-tionary statements are given in Section 5.2. Referenced Documents2.1 ASTM Standards:2G3 Practice for ConventionsApplicable to ElectrochemicalMeasurements in Corrosion TestingG15 Terminology Relating to Corrosion and CorrosionTestingG16 Guide forApplying Statistics toAnalysis of Corro

6、sionDataG71 Guide for Conducting and Evaluating Galvanic Cor-rosion Tests in Electrolytes3. Terminology3.1 Definitions of 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 corro

7、ding surfacein an electrolyte relative to a reference electrode measuredunder open-circuit conditions.3.4 galvanic corrosionaccelerated 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

8、and alloys arrangedaccording to their relative corrosion potentials in a givenenvironment.3.6 noblethe positive (increasingly oxidizing) direction ofelectrode potential.3.7 passivethe state of the metal surface characterized bylow corrosion rates in a potential region that is stronglyoxidizing for t

9、he metal.3.8 polarizationthe change from the open-circuit elec-trode potential as the result of the passage of current.4. 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

10、show de-creased corrosion.This type of accelerated corrosion is referredto as galvanic corrosion. Because galvanic corrosion 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 electro

11、lyte of the possibleeffects of galvanic corrosion.4.2 One method that is used to predict the effects of galvaniccorrosion 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 meta

12、lthat will suffer increased corrosion in a galvanic couple in thatenvironment can then be predicted from the relative position 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 wi

13、th the mostactive (electronegative) and proceeding in order to the mostnoble (electropositive). The potentials themselves (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

14、graphical form as a1This guide is under the jurisdiction of ASTM Committee G01 on Corrosion ofMetals and is the direct responsibility of Subcommittee G01.11 on ElectrochemicalMeasurements in Corrosion Testing.Current edition approved May 1, 2009. Published May 2009. Originallyapproved in 1983. Last

15、previous edition approved in 2003 as G 8298(2003).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.1Copyright

16、ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.series of bars displaying the range of potentials exhibited bythe metal listed opposite each bar. Such a series is illustrated inFig. 1.4.3.2 The second type of galvanic series is similar to the f

17、irstin that it lists the metals of interest in order of their corrosionpotentials. The actual potentials themselves are not specified,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

18、Use of a Galvanic Series:NOTEDark 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 15 Days at 5 to 30C (Redrawn from Original)(see Footnote 5)G 82 98 (2009)24.4.1 Generally, upon coupling two metals in the

19、 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 metals are in the series,and thus the greater the potential

20、difference between them, thegreater is the driving force for galvanic corrosion. All otherfactors 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 Gal

21、vanic Series5.1 The galvanic series 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

22、 used for galvaniccorrosion prediction.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

23、potentials can change with time 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

24、 and electrolyte composition as 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 co

25、rrosion. It should not be used for quantitativepredictions of galvanic corrosion rate. A more precise deter-mination of the effect of galvanic coupling can be obtained bythe measurement of the corrosion currents involved as outlinedin Guide G71.3,45.6 Some published Galvanic Series, such as those in

26、 Fig. 15and Fig. 2, consider the possibility of there being more thanone potential range for the same material, depending onwhether the material is in the active or the passive state.Knowledge of conditions affecting passivity of these materialsis necessary to determine which potential range to use

27、in aparticular application.5.7 Galvanic 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 Elect

28、rolyte conductivity,5.7.3 Distance 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

29、to chemical attack inalkaline solutions 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 predictio

30、n is presented inAppendix X1 and inASTMSTP 576.43Brasunas, 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. Testin

34、ve)| 18-12-3 Stainless Steel Type 316 (Passive)(+) SilverNOBLE or GraphitePASSIVE END GoldPlatinumFIG. 2 Galvanic Series of Various Metals Exposed to Seawater(see Footnote 3)G 82 98 (2009)36. Development of a Galvanic Series6.1 The development of a Galvanic Series may be dividedinto several steps. F

35、irst is the selection of the environment andconditions of interest. During the exposures, the environmentand conditions should be as close as possible to serviceconditions. A list of environmental factors and conditions thatcould affect open-circuit potentials follows. This is not in-tended to be a

36、complete listing, but it should serve as a guideto 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.

37、1.3.5 Soluble corrosion products,6.1.3.6 pH,6.1.3.7 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 proce

38、ssing and surface condition of thesemetals should 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 offacto

39、rs that require consideration:6.2.1 Bulk composition,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 vers

40、us active,and6.2.4.5 Pits or shielded (crevice) 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 electr

41、icalconnection is not in contact with the electrolyte. 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 period

42、ically, using avoltmeter.6.3.1 The size of the 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 procedu

43、re.6.3.2 Exposure duration should be sufficiently 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 i

44、ntent is to simulate long-term service, thepotential 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 we

45、ll as to the mounting of specimens and taking data,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

46、factors listed in 6.2,7.1.2 The size, shape, and 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 duratio

47、n and potential measurementfrequency,7.1.6 The 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

48、.1 The measured corrosion potential for each materialmay 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

49、 beplotted in bar graph form.7.1.7.2 The final 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; GalvanicSeries; noble; passiveG 82 98 (2009)4APPENDIX(Nonmandatory Information)X1. THEORY OF GALVANIC CORROSIONX1.1 The difference in electrochemical potential betweentwo or more dissimilar metals in electrical contact and in

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