1、Designation: E2338 11E2338 17Standard Practice forCharacterization of Coatings Using Conformable Eddy-Current Eddy Current Sensors without Coating ReferenceStandards1This standard is issued under the fixed designation E2338; the number immediately following the designation indicates the year oforigi
2、nal 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.1. Scope*1.1 This practice covers the use of conformable eddy-current eddy c
3、urrent sensors for nondestructive characterization ofcoatings without standardization on coated reference parts. It includes the following: (1) thickness measurement of a conductivecoating on a conductive substrate, (2) detection and characterization of local regions of increased porosity of a condu
4、ctive coating,and (3) measurement of thickness for nonconductive coatings on a conductive substrate or on a conductive coating. This practiceincludes only nonmagnetic coatings on either magnetic ( 0) or nonmagnetic ( = 0) substrates. This practice can also be usedto measure the effective thickness o
5、f a process-affected zone (for example, shot peened layer for aluminum alloys, alpha case fortitanium alloys). For specific types of coated parts, the user may need a more specific procedure tailored to a specific application.1.2 Specific uses of conventional eddy-current eddy current sensors are co
6、vered by Practices D7091 and E376 and the followingtest methods issued byASTM: B244, and E1004, and . Guidance for the use of conformable eddy current sensor arrays is providedin G12E2884.1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematic
7、al conversionsto inch-pound units that are provided for information only and are not considered standard.1.4 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 saf
8、ety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development
9、of International Standards, Guides and Recommendations issuedby the World Trade Organization 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 onNonma
10、gnetic Basis Metals with Eddy-Current InstrumentsD7091 Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metalsand Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous MetalsE376 Practice for Measuring Coating Thickness by Magnetic-Field o
11、r Eddy Current (Electromagnetic) Testing MethodsE543 Specification for Agencies Performing Nondestructive TestingE1004 Test Method for Determining Electrical Conductivity Using the Electromagnetic (Eddy Current) MethodE1316 Terminology for Nondestructive ExaminationsG12E2884 Test Method for Nondestr
12、uctive Measurement of Film Thickness of Pipeline Coatings on SteelGuide for EddyCurrent Testing of Electrically Conducting Materials Using Conformable Sensor Arrays (Withdrawn 2013)2.2 ASNT Documents:3SNT-TC-1A Recommended Practice for Personnel Qualification and Certification In Nondestructive Test
13、ingANSI/ASNT-CP-189 Standard for Qualification and Certification of NDT Personnel1 This practice is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.07 on ElectromagneticMethod.Current edition approved Feb. 15, 2011Nov. 1, 20
14、17. Published March 2011November 2017. Originally approved in 2004. Last previous edition approved in 20062011as E2338 - 06.E2338 - 11. DOI: 10.1520/E2338-11.10.1520/E2338-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For
15、Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from American Society 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
16、 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 may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases on
17、ly the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at 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
18、 410 Certification and Qualification of Nondestructive Testing Personnel4NOTE 1See Appendix X1.2.4 ISO Standards:5ISO 9712 Non-destructive TestingQualification and Certification of NDT Personnel3. Terminology3.1 DefinitionsFor definitions of terms relating to this practice, refer to Terminology E131
19、6. The following definitions arespecific to the conformable sensors:3.1.1 conformablerefers to an ability of sensors or sensor arrays to conform to nonplanar surfaces without any significanteffects on the measurement results.3.1.2 lift-offnormal distance from the conformable sensor winding plane to
20、the top of the first conducting layer of the partunder examination.3.1.3 model for sensor responsea relation between the response of the sensor (for example, transimpedance magnitude andphase or real and imaginary parts) to properties of interest, for example, electrical conductivity, magnetic perme
21、ability, lift-off, andconductive coating thickness, etc. These model responses may be obtained from database tables and may be analysis-based orempirical.3.1.4 depth of sensitivitydepth to which sensor response to features or properties of interest, for example, coating thicknessvariations, exceeds
22、a noise threshold.3.1.5 spatial half-wavelengthspacing between the center of adjacent primary (drive) winding segments with current flow inopposite directions; this spacing affects the depth of sensitivity. Spatial wavelength equals two times this spacing. A single turnconformable circular coil has
23、an approximate spatial wavelength of twice the coil diameter.3.1.6 insulating shimsconformable insulating foils used to measure effects of small lift-off excursions on sensor response.3.1.7 air standardizationan adjustment of the instrument with the sensor in air, that is, at least one spatial wavel
24、ength awayfrom any conductive or magnetic objects, to match the model for the sensor response. Measurements on conductive materials afterair standardization should provide absolute electrical properties and lift-off values. The performance can be verified on certifiedreference standards over the fre
25、quency range of interest.3.1.8 reference substrate standardizationan adjustment of the instrument to an appropriate reference substrate standard. Theadjustment is to remove offsets between the model for the sensor response and at least two reference substrate measurements (forexample, two measuremen
26、ts with different lift-offs at the same position on the standard). These standards should have a knownelectrical conductivity that is essentially uniform with depth and should have essentially the same electrical conductivity andmagnetic permeability as the substrate in the components being characte
27、rized.3.1.9 performance verification, uncoated parta measurement of electrical conductivity performed on a reference part withknown properties to confirm that the electrical conductivity variation with frequency is within specified tolerances for theapplication. When a reference standardization is p
28、erformed, reference parts used for standardization should not be used forperformance verification.These variations should be documented in the report (see Section 9). Performance verification is a qualitycontrol procedure recommended prior to or during measurements after standardization.3.1.10 perfo
29、rmance verification, coated parta measurement of coating electrical conductivity and/or thickness on a coatedreference part with known properties to confirm that the coating electrical conductivity and/or thickness are within specifiedtolerances for the application. Performance verification is a qua
30、lity control procedure that does not represent standardization andshould be documented in the report (see Section 9).3.1.11 process-affected zonea region near the surface with depth less than the half wavelength that can be represented by aconductivity that is different than that of the base materia
31、l, that is, substrate.3.1.12 sensor footprintarea of the sensor face placed against the material under examination.4. Significance and Use4.1 Conformable Eddy-Current Eddy Current SensorsConformable, eddy-current eddy current sensors can be used on bothflat and curved surfaces, including fillets, cy
32、lindrical surfaces, etc. When used with models for predicting the sensor response andappropriate algorithms, these sensors can measure variations in physical properties, such as electrical conductivity and/or magneticpermeability, as well as thickness of conductive coatings on any substrate and nonc
33、onductive coatings on conductive substrates4 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 International Organization for Standardiza
34、tion (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,Switzerland, http:/www.iso.org.E2338 172or on a conducting coating. These property variations can be used to detect and characterize heterogeneous regions within theconductive coatings, for example, re
35、gions of locally higher porosity.4.2 Sensors and Sensor ArraysDepending on the application, either a single-sensing element sensor or a sensor array can beused for coating characterization. A sensor array would provide a better capability to map spatial variations in coating thicknessand/or conducti
36、vity (reflecting, for example, porosity variations) and provide better throughput for scanning large areas. The sizeof the sensor footprint and the size and number of sensing elements within an array depend on the application requirements andconstraints, and the nonconductive (for example, ceramic)
37、coating thickness.4.3 Coating Thickness RangeThe conductive coating thickness range over which a sensor performs best depends on thedifference between the electrical conductivity of the substrate and conductive coating and available frequency range. For example,a specific sensor geometry with a spec
38、ific frequency range for impedance measurements may provide acceptable performance foran MCrAlY coating over a nickel-alloy substrate for a relatively wide range of conductive coating thickness, for example, from75 to 400 m (0.003 to 0.016 in.). Yet, for another conductive coating-substrate combinat
39、ion, this range may be 10 to 100 m(0.0004 to 0.004 in.). The coating characterization performance may also depend on the thickness of a nonconductive topcoat. Forany coating system, performance verification on representative coated specimens is critical to establishing the range of optimumperformanc
40、e. For nonconductive, for example, ceramic, coatings nonconductive coatings, such as ceramic coatings, the thicknessmeasurement range increases with an increase of the spatial wavelength of the sensor (for example, thicker coatings can bemeasured with larger sensor winding spatial wavelength). For n
41、onconductive coatings, when roughness of the coating may havea significant effect on the thickness measurement, independent measurements of the nonconductive coating roughness, forexample, by profilometry may provide a correction for the roughness effects.4.4 Process-Affected ZoneFor some processes,
42、 for example, shot peening, the process-affected zone can be represented by aneffective layer thickness and conductivity. These values can in turn be used to assess process quality. A strong correlation must bedemonstrated between these “effective coating” properties and process quality.4.5 Three-Un
43、known AlgorithmUse of multi-frequency impedance measurements and a three-unknown algorithm permitsindependent determination of three unknowns: (1) thickness of conductive nonmagnetic coatings, (2) conductivity of conductivenonmagnetic coatings, and (3) lift-off that provides a measure of the noncond
44、uctive coating thickness.4.6 AccuracyDepending on the material properties and frequency range, there is an optimal measurement performance rangefor each coating system. The instrument, its air standardization and/or reference substrate standardization, and its operation permitthe coating thickness t
45、o be determined within615 % of its true thickness for coating thickness within the optimal range and within630 % outside the optimal range. Better performance may be required for some applications.5. Interferences5.1 Thickness of CoatingThe precision of a measurement can change with coating thicknes
46、s.The thickness of a coating shouldbe less than the maximum depth of sensitivity. Ideally, the depth of sensitivity at the highest frequency should be less than theconductive coating thickness, while the depth of sensitivity at the lowest frequency should be significantly greater than theconductive
47、coating thickness. The number of frequencies used in the selected frequency range should be sufficient to provide areliable representation of the frequency-response shape.5.2 Thickness of SubstrateThe thickness of the substrate should be larger than the depth of sensitivity at the lowest frequency.O
48、therwise, this thickness must be known and accounted for in the model for the sensor response.5.3 Magnetic Permeability and Electrical Conductivity of Base Metal (Substrate)The magnetic permeability and electricalconductivity of the substrate can affect the measurement and must be known prior to coa
49、ting characterization unless they can bedetermined independently on a coated part. When the substrate properties vary spatially, this variation must be determined as partof the coating characterization on a noncoated part that preferably has the same thermal history as the coated parts. Originaluncoated parts may have significantly different microstructure than heat treated coated substrates. Uncoated colder regions ofotherwise coated parts may have different properties than the coated substrate due to changes during coating and heat treatment,and,
