1、Designation: E376 11E376 17Standard Practice forMeasuring Coating Thickness by Magnetic-Field or Eddy-Current Eddy Current (Electromagnetic) Testing Methods1This standard is issued under the fixed designation E376; the number immediately following the designation indicates the year oforiginal adopti
2、on 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.
3、1. Scope*1.1 This practice covers the use of magnetic- and eddy-current-type eddy current-type thickness instruments (gauges) fornondestructive thickness measurement of a coating on a metal substrate.(i.e. electrically conducting) substrate. The substrate maybe ferrous or nonferrous. The coating or
4、plating being measured may be electrically conducting or insulating as well as ferrousor non-ferrous.1.2 More specific uses of these instruments are covered by Practice D7091 and the following test methods issued by ASTM:Test Methods B244, B499, B530, and and G12B530.1.3 UnitsThe values stated in SI
5、 units are to be regarded as standard. The values given in parentheses are mathematicalconversions to inch-pound units that are provided for information only and are not considered standard.1.4 Measurements made in accordance with this practice will be in compliance with the requirements of ISO 2178
6、 as printedin 1982.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regul
7、atory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organi
8、zation Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2B244 Test Method for Measurement of Thickness of Anodic Coatings on Aluminum and of Other Nonconductive Coatings onNonmagnetic Basis Metals with Eddy-Current InstrumentsB499 Test Method for Measurement of C
9、oatingThicknesses by the Magnetic Method: Nonmagnetic Coatings on Magnetic BasisMetalsB530 Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Electrodeposited Nickel Coatings onMagnetic and Nonmagnetic SubstratesD7091 Practice for Nondestructive Measurement of Dry Film Thickn
10、ess of Nonmagnetic Coatings Applied to Ferrous Metalsand Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous MetalsE543 Specification for Agencies Performing Nondestructive TestingE1316 Terminology for Nondestructive ExaminationsG12 Test Method for Nondestructive Measurement of Film Thickness
11、 of Pipeline Coatings on Steel (Withdrawn 2013)32.2 ASNT Standards:3SNT-TC-1A Recommended Practice for Personnel Qualification and Certification in Nondestructive TestingANSI/ASNT-CP-189 Standard for Qualification and Certification of NDT Personnel1 This practice is under the jurisdiction of ASTM Co
12、mmittee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.07 on ElectromagneticMethod.Current edition approved July 1, 2011Nov. 1, 2017. Published July 2011December 2017. Originally approved in 1989. Last previous edition approved in 20062011 asE376 06.E376 11. DOI:
13、10.1520/E0376-11.10.1520/E0376-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from American S
14、ociety for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit
15、 may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at
16、 the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States12.3 AIA Standard:NAS-410 Certification and Qualification of Nondestructive Testing Personnel42.4 International Standard:Standards:5ISO 2178 Nonmagnetic Coatings
17、on Magnetic SubstrateMeasurement of Coating ThicknessMagneticMethodNOTE 1See Appendix X1.ISO 9712 Non-destructive TestingQualification and Certification of NDT PersonnelNOTE 1See Appendix X1.3. Terminology3.1 DefinitionsFor definitions of terms relating to this practice, refer to Terminology E1316.4
18、. Significance and Use4.1 GeneralNo presently available thickness gauge is Most thickness gages are not applicable to all combinations ofcoating-substrate thicknesses and materials. The limitations of a particular instrument are generally delineated by its manufacturer.The substrate material and coa
19、ting combination to be measured as well as the inherent variations in the substrate and coating shallbe reviewed prior to selecting the instrument to be used and the measurement accuracy required.4.2 MagneticMagnetic-type gauges measure either magnetic attraction between a magnet and a coating or it
20、s substrate, orreluctance of a magnetic flux path passing through the coating and substrate. These gauges are designed to measure thickness ofa nonmagnetic coating on a magnetic substrate. Some of them will also measure thickness of nickel coatings on a magnetic ornonmagnetic substrate.64.3 Eddy Cur
21、rentEddy-current-type Eddy current-type thickness gauges are electronic instruments that measure variations inimpedance of an eddy-current eddy current inducing coil caused by coating thickness variations. They can only be used if theelectrical conductivity of the coating differs significantly from
22、that of the substrate.4.4 AccuracyThe accuracy of a measurement depends on the instrument, the foils, its calibration and standardization, and itsoperating conditions. The accuracy is also affected by the interferences listed in Section 5, such as part geometry (curvature),magnetic permeability, ele
23、ctrical conductivity, and surface roughness.NOTE 2This practice allows under ideal conditions may allow the coating thickness to be determined within 610 % of its true thickness or to within62.5 m (or 60.0001-in.), whichever is the greater. (See exceptions in Appendix X2.)5. Interferences5.1 Thickne
24、ss of CoatingThe precision of a measurement changes with coating thickness depending on method used andinstrument design. Generally, the precision is a percentage of the coating thickness except at the lower end of the ranges whereit is a fixed thickness.5.2 Magnetic Properties of Basis MetalMagneti
25、c thickness gauges are affected by variations of the magnetic properties of thebasis metal. For practical purposes, magnetic variations in low-carbonAISI 1005-1020 steels may be considered to be insignificant.To avoid the influences of severe or localized heat treatments and cold working, the instru
26、ment should be standardized using areference standard having a base metal with the same magnetic properties as that of the test specimen or, preferably and ifavailable, with a sample of the part to be examined before application of the coating.5.3 Thickness of SubstrateFor each method there is an ef
27、fective depth of penetration of field created by the instrument probe.This is the critical depth or thickness beyond which the instrument will no longer be affected by increase of substrate thickness.Since it depends on the instrument probe and substrate, it should be determined experimentally.5.4 S
28、tructure and Composition of Coating and SubstrateEddy-current Eddy current instruments are sensitive to variations ofstructure, composition, and other factors affecting electrical conductivity and magnetic permeability of the coating and substrate.For example, such instruments are sensitive to diffe
29、rences between: (1) aluminum alloys, (2) chromium coatings deposited atdifferent temperatures, and (3) organic coatings containing variable amounts of metallic pigments.5.5 Edge EffectAll examination methods are sensitive to abrupt surface changes of test specimens; therefore, measurementsmade too n
30、ear an edge or inside corner will not be valid unless the instrument is specifically standardized for such a measurement.The effect usually extends 3 to 13 mm (18 to 12 in.) from the discontinuity, depending on method probe configuration, andinstrument. Edge effect is usually a function of coil diam
31、eter.4 Available from Aerospace Industries Association of America, Inc. (AIA), 1000 Wilson Blvd., Suite 1700, Arlington, VA 22209-3928, http:/www.aia-aerospace.org.(Replacement standard for MIL-STD-410.)5 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New Yor
32、k, NY 10036, http:/www.ansi.org.6 Autocatalytically deposited nickel-phosphorus alloys containing more than 8 % phosphorus are sufficiently nonmagnetic to be measured by this method, as long as themeasurement is made prior to any heat treatment.E376 1725.6 Curvature of Examination SurfaceThickness m
33、easurements are sensitive to curvature of the specimen. This sensitivityvaries considerably between instruments and becomes more pronounced with increasing curvature.5.7 Smoothness of Surface, Including That of Base MetalSince a rough surface may make single measurements inaccurate,a greater number
34、of measurements will provide an average value that is more truly representative of the overall coating thickness.Roughness also may cause certain instruments to read high since their probes may rest on peaks.5.8 Direction of Rolling of Base MetalInstruments with two pole pieces may be sensitive to d
35、irection of rolling of the basemetal; that is, gauge readings may change depending on alignment of pole pieces with surface of specimen or part underexamination.5.9 Residual Magnetism in Base MetalResidual magnetism in base metal may affect readings of magnetic- and eddy-current-type eddy current-ty
36、pe instruments.5.10 Stray Magnetic FieldsStrong magnetic fields, as from arc welding, can seriously interfere with operations of certainthickness gauges.5.11 Cleanness of Probe and Test SurfaceMeasurements are sensitive to foreign material that prevents intimate contactbetween probe and coating surf
37、ace.5.12 Pressure of ProbeInstrument readings can be sensitive to pressure with which probe is applied to test surface.5.13 Probe PositionSome magnetic-type gauges are sensitive to position of probe relative to the earth. For example, operationof gauge in a horizontal or upside-down position may req
38、uire a new standardization or may be impossible.5.14 TemperatureEddy-current Eddy current instruments may be affected by temperature variations.6. Basis of Application6.1 The following items are subject to contractual agreement between the parties using or referencing this standard.6.2 Personnel Qua
39、lification6.2.1 If For direct reading instruments or if specified in the contractual agreement, personnel performing examinations to thisstandard shall be qualified in accordance with a nationally or internationally recognized NDT personnel qualification practice orstandard such as ANSI/ASNT-CP-189,
40、 SNT-TC-1A, NAS-410, ISO 9712, or a similar document and certified by the employer orcertifying agency, as applicable. The practice or standard used and its applicable revision shall be identified in the contractualagreement between the using parties.6.3 Qualification of Nondestructive Testing Agenc
41、iesIf specified in the contractual agreement, NDTagencies shall be qualifiedand evaluated as specified in Specification E543. The applicable edition of Specification E543 shall be specified in the contractualagreement.6.4 Procedures and TechniquesThe procedures and techniques to be utilized shall be
42、 as specified in the contractual agreement.6.5 Surface PreparationThe pre-examination surface preparation criteria shall be in accordance with 5.11 and requirementsspecified in the contractual agreement.6.6 Timing of ExaminationThe timing of examination shall be in accordance with the applicable con
43、tractual agreement.6.7 Extent of ExaminationThe extent of examination shall be in accordance with the applicable contractual agreement.6.8 Reporting Criteria/Acceptance CriteriaReporting criteria for the examination results shall be in accordance with Section9 unless otherwise specified. Since accep
44、tance criteria are not specified in this standard, they shall be specified in the contractualagreement.6.9 Reexamination of Repaired/Reworked ItemsReexamination of repaired/reworked items is not addressed in this standardand if required shall be specified in the contractual agreement.7. Calibration
45、and Standardization7.1 Each instrument should be calibrated in accordance with the manufacturers instructions and standardized before use byemploying suitable thickness standards. Standardization should be checked at frequent intervals during use. Attention should begiven to Section 5 and Section 8.
46、7.2 Reference standards of uniform thickness are available in either of two types, foil or coated substrate, as supplied orrecommended by the manufacturer of the instrument. There are instances, however, where reference standards are made by otherthan instrument manufacturers.7.2.1 Standardization F
47、oils (Shims)Standardization foil is placed on the surface of uncoated base metal when standardizingthe instrument. Foils are advantageous for standardizing on curved surfaces and are often more readily available than a coatedstandard. To prevent measurement errors due to poor contact between foil an
48、d substrate, make sure of intimate contact betweenthem. Foils are subject to indentation and should, therefore, be replaced when damaged.E376 1737.2.1.1 Nonmagnetic foils may be used to standardize magnetic thickness gauges for measurement of nonmagnetic coatings.Nonconductive plastic foils can be u
49、sed to standardize eddy-current eddy current instruments for measurement of nonconductivecoatings.7.2.1.2 Resilient foils should not be used if there is possibility that the instrument probe will cause a change in thickness reading.Use of two or more foils on top of each other should be avoided unless flexibility of thin foils is required for a curved surface.7.2.2 Coated reference standards consist of coatings of known thickness permanently bonded to the substrate material.7.3 Thicknesses of reference standards should bracket and be as
