ASTM_G_59_-_97_2014.pdf

Designation:G5997(Reapproved 2014)Standard Test Method forConducting Potentiodynamic Polarization ResistanceMeasurements1This standard is issued under the fixed designation G59;the number immediately following the designation indicates the year of originaladoption or,in the case 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 test method covers an experimental procedure forpolarization resistance measurements which can be used for thecalibration of equipment and verification of experimentaltechnique.The test method can provide reproducible corrosionpotentials and potentiodynamic polarization resistance mea-surements.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:2G3 Practice for Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG5 Reference Test Method for Making PotentiodynamicAnodic Polarization MeasurementsG102 Practice for Calculation of Corrosion Rates and Re-lated Information from Electrochemical Measurements3.Significance and Use3.1 This test method can be utilized to verify the perfor-mance of polarization resistance measurement equipment in-cludingreferenceelectrodes,electrochemicalcells,potentiostats,scan generators,measuring and recording de-vices.The test method is also useful for training operators insample preparation and experimental techniques for polariza-tion resistance measurements.3.2 Polarization resistance can be related to the rate ofgeneral corrosion for metals at or near their corrosion potential,Ecorr.Polarization resistance measurements are an accurate andrapid way to measure the general corrosion rate.Real timecorrosion monitoring is a common application.The techniquecan also be used as a way to rank alloys,inhibitors,and so forthin order of resistance to general corrosion.3.3 In this test method,a small potential scan,E(t),definedwith respect to the corrosion potential(E=E Ecorr),isapplied to a metal sample.The resultant currents are recorded.The polarization resistance,RP,of a corroding electrode isdefined from Eq 1 as the slope of a potential versus currentdensity plot at i=0(1-4):3Rp5S E iDi50,dE/dt0(1)The current density is given by i.The corrosion currentdensity,icorr,is related to the polarization resistance by theStern-Geary coefficient,B.(3),icorr5 106BRp(2)The dimension of Rpis ohm-cm2,icorris muA/cm2,and B isin V.The Stern-Geary coefficient is related to the anodic,ba,and cathodic,bc,Tafel slopes as per Eq 3.B 5babc2.303ba1bc!(3)The units of the Tafel slopes are V.The corrosion rate,CR,in mm per year can be determined from Eq 4 in which EW isthe equivalent weight of the corroding species in grams and is the density of the corroding material in g/cm3.CR5 3.2731023icorrEW(4)Refer to Practice G102 for derivations of the above equa-tions and methods for estimating Tafel slopes.1This 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 May 1,2014.Published May 2014.Originallyapproved in 1978.Last previous edition approved in 2009 as G59-97(2009).DOI:10.1520/G0059-97R14.2For 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.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.4 The test method may not be appropriate to measurepolarization resistance on all materials or in all environments.See 8.2 for a discussion of method biases arising from solutionresistance and electrode capacitance.4.Apparatus4.1 The apparatus is described in Test Method G5.Itincludes a 1 L round bottom flask modified to permit theaddition of inert gas,thermometer,and electrodes.This stan-dard cell or an equivalent cell can be used.An equivalent cellmust be constructed of inert materials and be able to reproducethe standard curve in Test Method G5.4.2 A potentiostat capable of varying potential at a constantscan rate and measuring the current is needed.4.3 A method of recording the varying potential and result-ing current is needed.5.Test of Electrical Equipment5.1 Before the polarization resistance measurement is made,the instrument system(potentio