ASTM_G_100_-_89_2015.pdf

Designation:G10089(Reapproved 2015)Standard Test Method forConducting Cyclic Galvanostaircase Polarization1This standard is issued under the fixed designation G100;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers a procedure for conductingcyclic galvanostaircase polarization(GSCP)to determine rela-tive susceptibility to localized corrosion(pitting and crevicecorrosion)for aluminum alloy 3003-H14(UNS A93003)(1).2It may serve as guide for examination of other alloys(2-5).This test method also describes a procedure that can be used asa check for ones experimental technique and instrumentation.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in 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.2.Referenced Documents2.1 ASTM Standards:3D1193 Specification for Reagent WaterG1 Practice for Preparing,Cleaning,and Evaluating Corro-sion Test SpecimensG5 Reference Test Method for Making PotentiodynamicAnodic Polarization MeasurementsG59 Test Method for Conducting Potentiodynamic Polariza-tion Resistance MeasurementsG69 Test Method for Measurement of Corrosion Potentialsof Aluminum Alloys3.Significance and Use3.1 In this test method,susceptibility to localized corrosionof aluminum is indicated by a protection potential(Eprot)determined by cyclic galvanostaircase polarization(1).Themore noble this potential,the less susceptible is the alloy toinitiation of localized corrosion.The results of this test methodare not intended to correlate in a quantitative manner with therate of propagation of localized corrosion that one mightobserve in service.3.2 The breakdown(Eb),and protection potentials(Eprot)determined by the cyclic GSCP method correlate with theconstant potential corrosion test(immersion-glassware)resultfor aluminum(1,6,7).When the applied potential was morenegative than the GSCP Eprot,no pit initiation was observed.When the applied potential was more positive than the GSCPEprot,pitting occurred even when the applied potential was lessnegative than Eb.3.2.1 Severe crevice corrosion occurred when the separationof Eband Eprotwas 500 mV or greater and Eprotwas lessthan 400 mV Vs.SCE(in 100 ppm NaCl)(1,6,8).Foraluminum,Eprotdetermined by cyclic GSCP agrees with therepassivation potential determined by the scratch potentiostaticmethod(1,9).Both the scratch potentiostatic method and theconstant potential technique for determination of Eprotrequiremuch longer test times and are more involved techniques thanthe GSCP method.3.3 DeBerry and Viebeck(3-5)found that the breakdownpotentials(Eb)(galvanodynamic polarization,similar to GSCPbut no kinetic information)had a good correlation with theinhibition of localized corrosion of 304L stainless steel bysurface active compounds.They attained accuracy and preci-sion by avoiding the strong induction effect which theyobserved by the potentiodynamic technique.3.4 If this test method is followed using the specific alloydiscussed it will provide(GSCP)measurements that willreproduce data developed at other times in other laboratories.3.5 Eband Eprotobtained are based on the results from eightdifferent laboratories that followed the standard procedureusing aluminum alloy 3003-H14(UNS A93003).Eband Eprotare included with statistical analysis to indicate the acceptablerange.4.Apparatus4.1 CellThe cell should be constructed of inert materialssuch as borosilicate glass and PTFE fluorocarbon.It shouldhave ports for the insertion of a working electrode(1 cm2flat1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.11 onElectrochemical Measurements in Corrosion Testing.Current edition approved Nov.1,2015.Published December 2015.Originallyapproved in 1989.Last previous edition approved in 2010 as G10089(2010)1.DOI:10.1520/G0100-89R15.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 specimen holder(Note 1)is very convenient),two auxiliaryelectrodes,salt bridge for reference electrode,and a thermom-eter or a thermostat probe for temperature control.The figure