ASTM_B_244_-_09_2014.pdf

Designation:B24409(Reapproved 2014)Endorsed by AmericanElectroplaters SocietyEndorsed by NationalAssociation of Metal FinishersStandard Test Method forMeasurement of Thickness of Anodic Coatings onAluminum and of Other Nonconductive Coatings onNonmagnetic Basis Metals with Eddy-Current Instruments1This standard is issued under the fixed designation B244;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.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This test method covers the use of eddy-current instru-ments for the nondestructive measurement of the thickness ofa nonconductive coating on a nonmagnetic basis metal.It isintended to supplement manufacturers instructions for theoperation of the instruments and is not intended to replacethem.1.2 This test method is particularly useful for measuring thethickness of an anodic coating on aluminum alloys.Chemicalconversion coatings are too thin to be measured by this testmethod.1.3 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.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.2.Referenced Documents2.1 ASTM Standards:2B499 Test Method for Measurement of Coating Thicknessesby the Magnetic Method:Nonmagnetic Coatings onMagnetic Basis Metals3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 accuracy,nthe measure of the magnitude of errorbetween the result of a measurement and the true thickness ofthe item being measured.3.1.2 adjustment,nthe physical act of aligning a instru-ments thickness readings to match those of a known thicknesssample(removal of bias),in order to improve the accuracy ofthe instrument on a specific surface or within a specific portionof its measurement range.An adjustment will affect theoutcome of subsequent readings.3.1.3 calibration,nthe high-level,controlled and docu-mented process of obtaining measurements on traceable cali-bration standards over the full operating range of theinstrument,then making the necessary instrument adjustments(as required)to correct any out-of-tolerance conditions.3.1.3.1 DiscussionCalibration of coating thickness instru-ments is performed by the equipment manufacturer,an autho-rized agent,or by an authorized,trained calibration laboratoryin a controlled environment using a documented process.Theoutcome of the calibration process is to restore/realign theinstrument to meet/exceed the manufacturers stated accuracy.3.1.4 reference standard,na specimen of known thicknessused to verify the accuracy of a coating thickness measuringinstrument.3.1.5 verification of accuracy,nobtaining measurementson a reference standard prior to instrument use for the purposeof determining the ability of the coating thickness instrument toproduce reliable values,compared to the combined instrumentmanufacturers stated accuracy and the stated accuracy of thereference standard.4.Summary of Test Method4.1 Instruments complying with this test method measurecoating thickness by the use of eddy currents.Aprobe is placeddirectly on the coated surface in a perpendicular position andelectronic circuitry is used to convert a reference signal into acoating thickness measurement.1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 onTest Methods.Current edition approved May 1,2014.Published May 2014.Originallyapproved in 1949.Last previous edition approved in 2009 as B244 09.DOI:10.1520/B0244-09R14.2For 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 States1 4.2 The instrument probe coil is energized by alternatingcurrent that induces eddy currents in the metal substrate.Theeddy currents in turn create a secondary magnetic field withinthe substrate.The characteristics of this secondary field aredependent upon the distance between the probe and the basismetal.This distance(gap)is measured by the instrument probeand shown on the instrument display as the thickness(micronsor mils)of the intervening coating.5.Significance and Use5.1 The thickness of a coating is often critical to itsperformance.This eddy-current method is nondestructive andis suitable for measuring the thickne