ASTM_G_217_-_16.pdf

Designation:G21716Standard Guide forCorrosion Monitoring in Laboratories and Plants withCoupled Multielectrode Array Sensor Method1This standard is issued under the fixed designation G217;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 guide outlines the procedure for conducting corro-sion monitoring in laboratories and plants by use of the coupledmultielectrode array sensor(CMAS)technique.1.2 For plant applications,this technique can be used toassess the instantaneous non-uniform corrosion rate,includinglocalized corrosion rate,on a continuous basis,without re-moval of the monitoring probes,from the plant.1.3 For laboratory applications,this technique can be usedto study the effects of various testing conditions and inhibitorson non-uniform corrosion,including pitting corrosion andcrevice corrosion.1.4 UnitsThe values stated in SI units are to be regardedas the standard.No other units of measurement are included inthis standard.1.5 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:2G1 Practice for Preparing,Cleaning,and Evaluating Corro-sion Test SpecimensG4 Guide for Conducting Corrosion Tests in Field Applica-tionsG16 Guide for Applying Statistics to Analysis of CorrosionDataG46 Guide for Examination and Evaluation of Pitting Cor-rosionG48 Test Methods for Pitting and Crevice Corrosion Resis-tance of Stainless Steels and Related Alloys by Use ofFerric Chloride SolutionG96 Guide for Online Monitoring of Corrosion in PlantEquipment(Electrical and Electrochemical Methods)G102 Practice for Calculation of Corrosion Rates and Re-lated Information from Electrochemical MeasurementsG193 Terminology and Acronyms Relating to CorrosionG199 Guide for Electrochemical Noise Measurement3.Terminology3.1 DefinitionsThe terminology used herein,if not spe-cifically defined otherwise,shall be in accordance with Termi-nology G193.Definitions provided herein and not given inTerminology G193 are limited only to this guide.3.2 Definitions of Terms Specific to This Standard:3.2.1 coupledmultielectrodearraysensor,CMAS,ndevice with multiple working electrodes that are coupledthrough an external circuit such that all the electrodes operateat the same electrode potential to simulate the electrochemicalbehavior of a single-piece metal.3.2.2 non-uniform corrosion,ncorrosion that occurs atvarious rates across the metal surface,with some locationsexhibiting higher anodic rates while others have higher ca-thodic rates,thereby requiring that the electron transfer occursbetween these sites within the metal.3.2.2.1 DiscussionNon-uniform corrosion includes bothlocalized corrosion and uneven general corrosion(1).3Non-uniform corrosion also includes the type of general corrosionthat produces even surfaces at the end of a large time interval,but uneven surfaces during small time intervals.3.2.3 uneven general corrosion,ncorrosion that occursover the whole exposed surface or a large area at different rates.3.2.3.1 DiscussionIn this guide,general corrosion is fur-ther divided into even general corrosion,or uniform corrosion,which is defined as the corrosion that proceeds at exactly thesame rate over the surface of a material(see TerminologyG193)and uneven general corrosion.Uneven general corro-sion is defined as the general corrosion that produces uneven1This 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 Nov.1,2016.Published November 2016.DOI:10.1520/G0217-16.2For 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 a 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 surface or wave-like surface on a metal that has an even surfacebefore the corrosion(2,3).3.2.4 zero-voltage ammeter,ZVA,ndevice that imposes anegligibly low voltage drop when inserted into a circuit formeasurement of current.3.2.4.1 DiscussionThe ZVA defined in this guide alsomeets the definition of the zero-resistance ammeter(ZRA)inGuide G199.A typical ZRA is built with inverting operationalamplifiers to limit the voltage drop in the current-measuringcircuit to a low value.Both ZRA