ASTM_G_149_-_97.pdf

Designation:G 149 97Standard Practice forConducting the Washer Test for Atmopsheric GalvanicCorrosion1This standard is issued under the fixed designation G 149;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(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers the evaluation of atmosphericgalvanic corrosion of any materials that can be made intowashers.1.2 The washer,or disk,test was used by H.O.Teeple in19492for a series of exposures for ASTM Committee B 03.08on Corrosion of Non-Ferrous Metals and Alloys.Since thattime,ASTM has refined the test and conducted other investi-gations using this practice.3,4,51.3 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:G 1 Practice for Preparing,Cleaning,and Evaluating Cor-rosion Test Specimens6G 3 Practice for ConventionsApplicable to ElectrochemicalMeasurements in Corrosion Testing6G 15 Terminology Relating to Corrosion and CorrosionTesting6G 16 Guide forApplying Statistics toAnalysis of CorrosionData6G 50 Practice for Conducting Atmospheric Corrosion Testson Metals6G 82 Guide for Development and Use of a Galvanic Seriesfor Predicting Galvanic Corrosion Performance6G 84 Practice for Measurement of Time-of-Wetness onSurfaces Exposed to Wetting Conditions as inAtmosphericCorrosion Testing6G 91 Practice for Monitoring Atmopsheric SO2Using theSulfation Plate Technique6G 92 Practice for Characterization of Atmospheric TestSites6G 104 Test Method for Assessing Galvanic CorrosionCaused by the Atmosphere6G 116 Practice for Conducting Wire-on-Bolt Test for Atmo-spheric Galvanic Corrosion63.Terminology3.1 For definitions of terms used in this practice,refer toTerminology G 15.For conventions related to this practice,refer to Practice G 3.4.Summary of Practice4.1 The practice consists of atmospheric exposure of speci-men assemblies,each consisting of a set of four washers,graduated in size with alternating anode and cathode materials,bolted together through center holes.Only the center twowashers are used for the analysis,the outer washers being usedonly to establish the proper environment on the inner washers.Mass loss of the washers is determined after the exposure.Reference assemblies of the anode material are exposedconcurrently to allow for separation of general and crevicecorrosion effects from galvanic corrosion effects.5.Significance and Use5.1 The arrangement of the washers gives close to a 1:1cathode-to-anode area ratio,making this test less severe thanthe wire-on-bolt test described in Practice G 116 and similar inseverity to the plate test described in Test Method G 104.As inthe plate test,typical exposure periods range from 1 to 20years.5.2 The major advantage of this test over other atmosphericgalvanic corrosion tests standardized by ASTM is that materialfor this test may be easier to obtain than material for the othertests,in that only small pieces of thin sheet are required.Inaddition,the washer test is probably the easiest of the threetests standardized by ASTM to setup and evaluate.5.3 The anode/cathode relationship of the materials in-volved need not be known beforehand,so information such asthat in Guide G 82 is not required.5.4 Unlike the plate test,the washer test yields only corro-sion rate information,and it is difficult to determine corrosionmorphology visually due to the shape of the components.It is1This practice is under the jurisdiction of ASTM Committee G-1 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.04 on AtmosphericCorrosion.Current edition approved Apr.10,1997.Published November 1997.2Teeple,H.O.,Symposium on Atmospheric Corrosion of Non-Ferrous Metals,ASTM STP 175,ASTM,1955,pp.89113.3Baboian,R.,“Final Report on the ASTM Study:Atmospheric GalvanicCorrosion of Magnesium Coupled to Other Metals,”Atmospheric Factors Affectingthe Corrosion of Engineering Materials,ASTM STP 646,Coburn,S.Ed.,ASTM1978,pp.1724.4Blum,W.,Symposium on Properties,Tests and Performance of Electrodepos-ited Metallic Coatings,ASTM STP 197,ASTM,1956,p.49.5ASTM Proceedings,Vol 41,No.170,1941.6Annual Book of ASTM Standards,Vol 03.02.1AMERICAN SOCIETY FOR TESTING AND MATERIALS100 Barr Harbor Dr.,West Conshohocken,PA 19428Reprinted from the Annual Book of ASTM Standards.Copyright ASTMalso difficult to determine changes in mechanical propertieswith this test.Test Method G 104 is preferable for determiningmorphology and mechanical property changes.6.Interferences6.1 The manufacturing process used to make the sheet mayaffect corrosion potentials and polarization behavi