ASTM_G_96_-_90_2013.pdf

Designation:G9690(Reapproved 2013)Standard Guide forOnline Monitoring of Corrosion in Plant Equipment(Electrical and Electrochemical Methods)1This standard is issued under the fixed designation G96;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 guide covers the procedure for conducting onlinecorrosion monitoring of metals in plant equipment underoperating conditions by the use of electrical or electrochemicalmethods.Within the limitations described,these test methodscan be used to determine cumulative metal loss or instanta-neous corrosion rate,intermittently or on a continuous basis,without removal of the monitoring probes from the plant.1.2 The following test methods are included:Test MethodAfor electrical resistance,and Test Method B for polarizationresistance.1.2.1 Test Method A provides information on cumulativemetal loss,and corrosion rate is inferred.This test methodresponds to the remaining metal thickness except as describedin Section 5.1.2.2 Test Method B is based on electrochemical measure-ments for determination of instantaneous corrosion rate butmay require calibration with other techniques to obtain truecorrosion rates.Its primary value is the rapid detection ofchanges in the corrosion rate that may be indicative ofundesirable changes in the process environment.1.3 The values stated in SI units are to be consideredstandard.The values in parentheses are for information only.1.4 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.Specific precau-tionary statements are given in 5.6.2.Referenced Documents2.1 ASTM Standards:2D1125 Test Methods for Electrical Conductivity and Resis-tivity of WaterG1 Practice for Preparing,Cleaning,and Evaluating Corro-sion Test SpecimensG3 Practice for Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG4 Guide for Conducting Corrosion Tests in Field Applica-tionsG15 Terminology Relating to Corrosion and Corrosion Test-ing(Withdrawn 2010)3G59 Test Method for Conducting Potentiodynamic Polariza-tion Resistance MeasurementsG102 Practice for Calculation of Corrosion Rates and Re-lated Information from Electrochemical Measurements3.Terminology3.1 DefinitionsSee Terminology G15 for definitions ofterms used in this guide.4.Summary of Guide4.1 Test Method AElectrical ResistanceThe electricalresistance test method operates on the principle that theelectrical resistance of a measuring element(wire,strip,or tubeof metal)increases as its cross-sectional area decreases:R 5 lA(1)where:R=resistance,=resistivity of metal(temperature dependent),l=length,andA=cross-section area.In practice,the resistance ratio between the measuringelement exposed to corrosion and the resistance of a similarreference element protected from corrosion is measured,tocompensate for resistivity changes due to temperature.Basedon the initial cross-sectional area of the measurement element,the cumulative metal loss at the time of reading is determined.Metal loss measurements are taken periodically and manually1This guide is under the jurisdiction of ASTM Committee G01 on Corrosion ofMetals and is the direct responsibility of ASTM Subcommittee G01.11 onElectrochemical Measurements in Corrosion Testing.Current edition approved Aug.1,2013.Published August 2013.Originallyapproved in 1990.Last previous edition approved in 2008 as G9690(2008).DOI:10.1520/G0096-90R13.2For 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 last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 or automatically recorded against a time base.The slope of thecurve of metal loss against time at any point is the correctionrate at that point.The more frequently measurements are taken,the better is the resolution of the curve from which thecorrosion rate is derived.4.1.1 The electrical resistance of the metal elements beingmeasured is very low(typically 2 to 10 m).Consequently,special measurement techniques and cables are required tominimize the effect of cable resistance and electrical noise.4.1.2 Various probe element cross-sectional areas are nec-essary so that a wide range of corrosion rates can be monitoredwith acceptable resolution.4.2 Test Method BPolarization Resistance:4.2.1 The polarization resistance test method involv