ASTM_C_743_-_87_2018.pdf

Designation:C74387(Reapproved 2018)Standard Test Method forContinuity of Porcelain Enamel Coatings1This standard is issued under the fixed designation C743;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.INTRODUCTIONThis test provides a means to evaluate a porcelain enamel coating for pinholes,discontinuities,andinsufficient application to better assess the ability of the coating to protect the substrate.1.Scope1.1 Porcelain enamel coatings are applied to metals toprovide protection from corrosion as well as to enhance theirappearance.This test method permits the easy detection ofdiscontinuities and areas of light coverage,not readily seen byvisual inspection,which limit the protection to the substrate.Somewhat similar tests applicable to the thicker glass coatingsused for chemical reaction vessels are found in Test MethodsC536 and C537.1.2 Values stated in SI units are to be regarded as thestandard.Inch-pound units are provided for information only.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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2C536 Test Method for Continuity of Coatings in GlassedSteel Equipment by Electrical TestingC537 Test Method for Reliability of Glass Coatings onGlassed Steel Reaction Equipment by High Voltage3.Terminology3.1 air-gap voltagevoltage needed to arc through a defectthat is open to both the surface of the porcelain enamel and themetal substrate.The length of the air gap is estimated bymeasuring the enamel thickness.3.2 overvoltagedifference between an applied test voltageand the air-gap voltage for the porcelain enamel being tested.3.3 RMS voltageroot mean square voltage,or“average”voltage,shown on ac test meters.3.4 peak voltagefor ac meters,the voltage that willdischarge across the air gap or across a defect.The peakvoltage is the RMS voltage multiplied by 1.414.4.Apparatus4.1 A nondestructive coating thickness gage with a range ofat least 0 to 0.5 mm in 0.03 mm increments(0 to 20 mils in 1.0mil increments).4.2 Either an ac or a dc high-voltage discharge test instru-ment with a continuously variable output voltage over therange of at least 0 to 4 kV as indicated on a built-in voltmeter.The instrument shall be capable of being set to 0.1 kV and shallhave an insulated cable and probe and a means for indicating(light,meter,or bell)a voltage discharge.Before use in thistest,the high-voltage discharge test instrument shall be cali-brated in accordance with the procedure set forth in AnnexA1.4.3 A test probe constructed of 100 mesh wire gauze asillustrated in Fig.1.5.Test Specimens5.1 Porcelain enameled specimens of any size may be usedin this test.The enamel shall be removed from an edge or theback of the specimen to provide an electrical ground for the testinstrument.If the probe is wider than the specimen,the edgesof the specimen shall be masked with electrical insulating tapeto prevent discharges from occurring at the edges whereporcelain coverage may be light.1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.12 onMaterials for Porcelain Enamel and Ceramic-Metal Systems.Current edition approved Oct.1,2018.Published October 2018.Originallyapproved in 1973.Last previous edition approved in 2014 as C743 87(2014)1.DOI:10.1520/C0743-87R18.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.1 6.Conditioning6.1 Before testing,wash the specimens with a 1 weight%,solution of trisodium phosphate on a soft cellulose sponge,rinse with tap water,and then rinse with distilled water.Thendry the specimens