1、Designation:C74387(Reapproved 2014)1Standard 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
2、number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1NOTEIntroduction was added and minor units abbreviations corrected editorially in June 2014.INTRODUCTIONThis test provides a means to evaluate a porc
3、elain 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 per
4、mits 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 s
5、tated 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 problems,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and heal
6、th practices and determine the applica-bility of regulatory limitations prior to use.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 Equipm
7、ent 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 voltagean
8、d 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.A
9、pparatus4.1 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 indicat
10、ed 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 th
11、e 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
12、 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.6.Conditioning6.1 Before testing,wash the specimens with a 1 weight%,solution of tris
13、odium phosphate on a soft cellulose sponge,1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatingsand is the direct responsibility of Subcommittee B08.12 onMaterials for Porcelain Enamel and Ceramic-Metal Systems.Current edition approved May 1,2014.Publishe
14、d June 2014.Originallyapproved in 1973.Last previous edition approved in 2009 as C743 87(2009).DOI:10.1520/C0743-87R14E1.2For 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
15、the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 rinse with tap water,and then rinse with distilled water.Thendry the specimens thoroughly in air.7.Procedure7.1 Measuring the Enamel Th
16、icknessMeasure the enamelthickness at a minimum of three locations on the specimen.Make these measurements to the nearest 0.03 mm(1.0 mil)inaccordance with the operating instructions for the thicknessgage.Use the maximum value obtained as the enamel thick-ness.7.2 Selecting the Test VoltageThe test voltage to be useddepends upon the purpose for conducting the test.The test canbe used to determine(1)the presence of defects open to boththe enamel surface and the base metal,(2)the location of areas