1、Designation: E376 11Standard Practice forMeasuring Coating Thickness by Magnetic-Field or Eddy-Current (Electromagnetic) Testing Methods1This standard is issued under the fixed designation E376; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f 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 Department of Defense.1. Scope*1.1 This practic
3、e covers the use of magnetic- and eddy-current-type thickness instruments (gauges) for nondestructivethickness measurement of a coating on a metal substrate.1.2 More specific uses of these instruments are covered byPractice D7091 and the following test methods issued byASTM: Test Methods B244, B499,
4、 B530, and G12.1.3 UnitsThe values stated in SI units are to be regardedas standard. The values given in parentheses are mathematicalconversions to inch-pound units that are provided for informa-tion only and are not considered standard.1.4 Measurements made in accordance with this practicewill be i
5、n compliance with the requirements of ISO 2178 asprinted in 1982.1.5 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 appl
6、ica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B244 Test Method for Measurement of Thickness ofAnodicCoatings on Aluminum and of Other Nonconductive Coat-ings on Nonmagnetic Basis Metals with Eddy-CurrentInstrumentsB499 Test Method for Measurement of Coa
7、ting Thick-nesses by the Magnetic Method: Nonmagnetic Coatings onMagnetic Basis MetalsB530 Test Method for Measurement of Coating Thick-nesses by the Magnetic Method: Electrodeposited NickelCoatings on Magnetic and Nonmagnetic SubstratesD7091 Practice for Nondestructive Measurement of DryFilm Thickn
8、ess of Nonmagnetic Coatings Applied toFerrous Metals and Nonmagnetic, Nonconductive Coat-ings Applied to Non-Ferrous MetalsE543 Specification for Agencies Performing Nondestruc-tive TestingE1316 Terminology for Nondestructive ExaminationsG12 Test Method for Nondestructive Measurement of FilmThicknes
9、s of Pipeline Coatings on Steel2.2 ASNT Standards:3SNT-TC-1A Recommended Practice for Personnel Qualifi-cation and Certification in Nondestructive TestingANSI/ASNT-CP-189 Standard for Qualification and Certi-fication of NDT Personnel2.3 AIA Standard:NAS-410 Certification and Qualification of Nondest
10、ructiveTesting Personnel42.4 International Standard:ISO 2178 Nonmagnetic Coatings on Magnetic SubstrateMeasurement of Coating ThicknessMagneticMethod5NOTE 1See Appendix X1.3. Terminology3.1 DefinitionsFor definitions of terms relating to thispractice, refer to Terminology E1316.4. Significance and U
11、se4.1 GeneralNo presently available thickness gauge isapplicable to all combinations of coating-substrate thicknessesand materials. The limitations of a particular instrument aregenerally delineated by its manufacturer.4.2 MagneticMagnetic-type gauges measure either mag-netic attraction between a ma
12、gnet and a coating or its substrate,1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.07 onElectromagnetic Method.Current edition approved July 1, 2011. Published July 2011. Originally approvedin 1989. Last
13、previous edition approved in 2006 as E376 06. DOI: 10.1520/E0376-11.2For 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 w
14、ebsite.3Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4Available from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerosp
15、ace.org.(Replacement standard for MIL-STD-410.)5Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box
16、 C700, West Conshohocken, PA 19428-2959, United States.or reluctance of a magnetic flux path passing through thecoating and substrate. These gauges are designed to measurethickness of a nonmagnetic coating on a magnetic substrate.Some of them will also measure thickness of nickel coatings ona magnet
17、ic or nonmagnetic substrate.64.3 Eddy CurrentEddy-current-type thickness gauges areelectronic instruments that measure variations in impedance ofan eddy-current inducing coil caused by coating thicknessvariations. They can only be used if the electrical conductivityof the coating differs significant
18、ly from that of the substrate.4.4 AccuracyThe accuracy of a measurement depends onthe instrument, its calibration and standardization, and itsoperating conditions. The accuracy is also affected by theinterferences listed in Section 5, such as part geometry (cur-vature), magnetic permeability, and su
19、rface roughness.NOTE 2This practice allows the coating thickness to be determinedwithin 610 % of its true thickness or to within 62.5 m (or 60.0001-in.),whichever is the greater. (See exceptions in Appendix X2.)5. Interferences5.1 Thickness of CoatingThe precision of a measurementchanges with coatin
20、g thickness depending on method used andinstrument design. Generally, the precision is a percentage ofthe coating thickness except at the lower end of the rangeswhere it is a fixed thickness.5.2 Magnetic Properties of Basis MetalMagnetic thick-ness gauges are affected by variations of the magnetic p
21、roper-ties of the basis metal. For practical purposes, magneticvariations in low-carbon AISI 1005-1020 steels may be con-sidered to be insignificant. To avoid the influences of severe orlocalized heat treatments and cold working, the instrumentshould be standardized using a reference standard having
22、 abase metal with the same magnetic properties as that of the testspecimen or, preferably and if available, with a sample of thepart to be examined before application of the coating.5.3 Thickness of SubstrateFor each method there is aneffective depth of penetration of field created by the instrument
23、probe. This is the critical depth or thickness beyond which theinstrument will no longer be affected by increase of substratethickness. Since it depends on the instrument probe andsubstrate, it should be determined experimentally.5.4 Structure and Composition of Coating and SubstrateEddy-current ins
24、truments are sensitive to variations of struc-ture, composition, and other factors affecting electrical con-ductivity and magnetic permeability of the coating andsubstrate. For example, such instruments are sensitive todifferences between: (1) aluminum alloys, (2) chromium coat-ings deposited at dif
25、ferent temperatures, and (3) organiccoatings containing variable amounts of metallic pigments.5.5 Edge EffectAll examination methods are sensitive toabrupt surface changes of test specimens; therefore, measure-ments made too near an edge or inside corner will not be validunless the instrument is spe
26、cifically standardized for such ameasurement. The effect usually extends 3 to 13 mm (18 to12in.) from the discontinuity, depending on method probe con-figuration, and instrument. Edge effect is usually a function ofcoil diameter.5.6 Curvature of Examination SurfaceThickness mea-surements are sensiti
27、ve to curvature of the specimen. Thissensitivity varies considerably between instruments and be-comes more pronounced with increasing curvature.5.7 Smoothness of Surface, Including That of Base MetalSince a rough surface may make single measurements inaccu-rate, a greater number of measurements will
28、 provide anaverage value that is more truly representative of the overallcoating thickness. Roughness also may cause certain instru-ments to read high since their probes may rest on peaks.5.8 Direction of Rolling of Base MetalInstruments withtwo pole pieces may be sensitive to direction of rolling o
29、f thebase metal; that is, gauge readings may change depending onalignment of pole pieces with surface of specimen or part underexamination.5.9 Residual Magnetism in Base MetalResidual magne-tism in base metal may affect readings of magnetic- andeddy-current-type instruments.5.10 Stray Magnetic Field
30、sStrong magnetic fields, asfrom arc welding, can seriously interfere with operations ofcertain thickness gauges.5.11 Cleanness of Probe and Test SurfaceMeasurementsare sensitive to foreign material that prevents intimate contactbetween probe and coating surface.5.12 Pressure of ProbeInstrument readi
31、ngs can be sensi-tive to pressure with which probe is applied to test surface.5.13 Probe PositionSome magnetic-type gauges are sen-sitive to position of probe relative to the earth. For example,operation of gauge in a horizontal or upside-down position mayrequire a new standardization or may be impo
32、ssible.5.14 TemperatureEddy-current instruments may be af-fected by temperature variations.6. Basis of Application6.1 The following items are subject to contractual agree-ment between the parties using or referencing this standard.6.2 Personnel Qualification6.2.1 If specified in the contractual agre
33、ement, personnelperforming examinations to this standard shall be qualified inaccordance with a nationally or internationally recognizedNDT personnel qualification practice or standard such asANSI/ASNT-CP-189, SNT-TC-1A, NAS-410, or a similardocument and certified by the employer or certifying agenc
34、y,as applicable. The practice or standard used and its applicablerevision shall be identified in the contractual agreement be-tween the using parties.6.3 Qualification of Nondestructive Testing AgenciesIfspecified in the contractual agreement, NDT agencies shall bequalified and evaluated as specifie
35、d in Specification E543. Theapplicable edition of Specification E543 shall be specified inthe contractual agreement.6.4 Procedures and TechniquesThe procedures and tech-niques to be utilized shall be as specified in the contractualagreement.6Autocatalytically deposited nickel-phosphorus alloys conta
36、ining more than 8 %phosphorus are sufficiently nonmagnetic to be measured by this method, as long asthe measurement is made prior to any heat treatment.E376 1126.5 Surface PreparationThe pre-examination surfacepreparation criteria shall be in accordance with 5.11 andrequirements specified in the con
37、tractual agreement.6.6 Timing of ExaminationThe timing of examinationshall be in accordance with the applicable contractual agree-ment.6.7 Extent of ExaminationThe extent of examination shallbe in accordance with the applicable contractual agreement.6.8 Reporting Criteria/Acceptance CriteriaReportin
38、g cri-teria for the examination results shall be in accordance withSection 9 unless otherwise specified. Since acceptance criteriaare not specified in this standard, they shall be specified in thecontractual agreement.6.9 Reexamination of Repaired/Reworked ItemsReexamination of repaired/reworked ite
39、ms is not addressed inthis standard and if required shall be specified in the contrac-tual agreement.7. Calibration and Standardization7.1 Each instrument should be calibrated in accordance withthe manufacturers instructions and standardized before use byemploying suitable thickness standards. Stand
40、ardization shouldbe checked at frequent intervals during use. Attention shouldbe given to Section 5 and Section 8.7.2 Reference standards of uniform thickness are availablein either of two types, foil or coated substrate, as supplied orrecommended by the manufacturer of the instrument. There areinst
41、ances, however, where reference standards are made byother than instrument manufacturers.7.2.1 Standardization Foils (Shims)Standardization foil isplaced on the surface of uncoated base metal when standard-izing the instrument. Foils are advantageous for standardizingon curved surfaces and are often
42、 more readily available than acoated standard. To prevent measurement errors due to poorcontact between foil and substrate, make sure of intimatecontact between them. Foils are subject to indentation andshould, therefore, be replaced when damaged.7.2.1.1 Nonmagnetic foils may be used to standardize
43、mag-netic thickness gauges for measurement of nonmagnetic coat-ings. Nonconductive plastic foils can be used to standardizeeddy-current instruments for measurement of nonconductivecoatings.7.2.1.2 Resilient foils should not be used if there is possi-bility that the instrument probe will cause a chan
44、ge in thicknessreading. Use of two or more foils on top of each other shouldbe avoided unless flexibility of thin foils is required for acurved surface.7.2.2 Coated reference standards consist of coatings ofknown thickness permanently bonded to the substrate material.7.3 Thicknesses of reference sta
45、ndards should bracket andbe as close as possible to the coating thickness being measured.7.4 For magnetic instruments, reference standards shouldhave the same magnetic properties as the coated specimen.7.5 For eddy-current instruments, the reference standardshould have the same electrical and magnet
46、ic properties asthose of coated specimen being measured (see 5.4).7.6 To determine standardization validity, a reading on abare specimen identical in magnetic and electrical properties tothat of the test specimen substrate is recommended.7.7 If the coating process is changed, the standardizationmay
47、no longer be valid, especially for magnetic coatings andeddy-current gauges (see 5.4).7.8 In some cases, standardization of instruments withtwo-pole probes should be checked with the poles rotated 0, 90,180, and 270 (see 5.8 and 5.9).7.9 The substrate thickness for examination/measurementand standar
48、dization should be the same if the depth ofpenetration referred to in 5.3 is not exceeded. Very often it ispossible to back up the substrates of standard and examinationspecimens with sufficient thickness of the same material (toexceed the critical thickness) and make readings independentof substrat
49、e thickness.77.10 If the curvature of the coating to be measured is soarched as to preclude standardization on a flat surface, then thecurvature of the coated standard or of the substrate on whichthe foil is placed should have the same contour.8. Procedure8.1 Operate each instrument in accordance with the manu-facturers instructions giving appropriate attention to factorslisted in Section 5.8.2 Check the instrument calibration at the site each time theinstrument is put into service and at frequent intervals duringuse to assure proper performa
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