ASTM_G_148_-_97_2011.pdf

Designation:G14897(Reapproved 2011)Standard Practice forEvaluation of Hydrogen Uptake,Permeation,and Transportin Metals by an Electrochemical Technique1This standard is issued under the fixed designation G148;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 practice gives a procedure for the evaluation ofhydrogen uptake,permeation,and transport in metals using anelectrochemical technique which was developed by Devana-than and Stachurski.2While this practice is primarily intendedfor laboratory use,such measurements have been conducted infield or plant applications.Therefore,with proper adaptations,this practice can also be applied to such situations.1.2 This practice describes calculation of an effective diffu-sivity of hydrogen atoms in a metal and for distinguishingreversible and irreversible trapping.1.3 This practice specifies the method for evaluating hydro-gen uptake in metals based on the steady-state hydrogen flux.1.4 This practice gives guidance on preparation of speci-mens,control and monitoring of the environmental variables,test procedures,and possible analyses of results.1.5 This practice can be applied in principle to all metalsand alloys which have a high solubility for hydrogen,and forwhich the hydrogen permeation is measurable.This methodcan be used to rank the relative aggressivity of differentenvironments in terms of the hydrogen uptake of the exposedmetal.1.6 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:3G96 Guide for Online Monitoring of Corrosion in PlantEquipment(Electrical and Electrochemical Methods)3.Terminology3.1 Definitions:3.1.1 charging,nmethod of introducing atomic hydrogeninto the metal by galvanostatic charging(constant chargingcurrent),potentiostatic charging(constant electrode potential),free corrosion,or gaseous exposure.3.1.2 charging cell,ncompartment in which hydrogenatoms are generated on the specimen surface.This includesboth aqueous and gaseous charging.3.1.3 decay current,ndecay of the hydrogen atom oxida-tion current due to a decrease in charging current.3.1.4 Ficks second law,nsecond order differential equa-tion describing the concentration of diffusing specie as afunction of position and time.The equation is of the formCx,t!/t5/xD1/xCx,t!#for lattice diffusion in one di-mension where diffusivity is independent of concentration.See3.2 for symbols.3.1.5 hydrogen flux,nthe amount of hydrogen passingthrough the metal specimen per unit area as a function of time.The units are typically concentration per unit area per unittime.3.1.6 hydrogen uptake,nthe concentration of hydrogenabsorbed into the metal(for example,g/cm3or mol/cm3).3.1.7 irreversible trap,nmicrostructural site at which ahydrogen atom has a infinite or extremely long residence timecompared to the time-scale for permeation testing at therelevant temperature,as a result of a binding energy which islarge relative to the migration energy for diffusion.3.1.8 mobile hydrogen atoms,nhydrogen atoms that areassociated with sites within the lattice.3.1.9 oxidation cell,ncompartment in which hydrogenatoms exiting from the metal specimen are oxidized.3.1.10 permeation current,ncurrent measured in oxida-tion cell associated with oxidation of hydrogen atoms.3.1.11 permeation transient,nthe increase of the perme-ation current with time from commencement of charging to the1This practice is under the jurisdiction of ASTM Committee G01 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.11 on Electrochemi-cal Measurements in Corrosion Testing.Current edition approved May 1,2011.Published May 2011.Last previousedition approved in 2003 as G149-97(2003).DOI:10.1520/G0148-97R11.2Devanathan,M.A.V.,and Stachurski,Z.,Proceedings of Royal Society,A270,90102,1962.3For 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 attainment of steady state,or modification of charging condi-tions(that is,rise transient).The decrease of the permeationcurrent with time resulting from a decrease in charging current(that is,decay transient).3.1.12 recombination poison,nchemical specie presentwithin the test environment in the charging cell which en-hances hydrogen absorption by retarding the recombination ofhydrogen at