1、Designation: E1816 18Standard Practice forMeasuring thickness by Pulse-Echo ElectromagneticAcoustic Transducer (EMAT) Methods1This standard is issued under the fixed designation E1816; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, 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 provides guidelines for measuring thethickness of materials using Electromagnetic Acousti
3、c Trans-ducers (EMAT), a non-contact pulse-echo method, at tempera-tures not to exceed 1200F 650C.1.2 This practice is applicable to any electrically conductiveor ferromagnetic material, or both, in which ultrasonic waveswill propagate at a constant velocity throughout the part, andfrom which back r
4、eflections can be obtained and resolved.1.3 UnitsThe values stated in either SI units or inch-pound units are to be regarded separately as standard. Thevalues stated in each system may not be exact equivalents;therefore, each system shall be used independently of the other.Combining values from the
5、two systems may result in noncon-formance with the standard.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, health, and environmental practices and deter-m
6、ine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendation
7、s issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E114 Practice for Ultrasonic Pulse-Echo Straight-BeamContact TestingE494 Practice for Measuring Ultrasonic Velocity in Materi-alsE543 Specification for Agencies Performing N
8、ondestructiveTestingE587 Practice for Ultrasonic Angle-Beam Contact TestingE797 Practice for Measuring Thickness by Manual Ultra-sonic Pulse-Echo Contact MethodE1316 Terminology for Nondestructive ExaminationsE1774 Guide for Electromagnetic Acoustic Transducers(EMATs)2.2 ASNT Standards:3SNT-TC-1A Re
9、commended Practice for Personnel Qualifi-cations and Certification in Nondestructive TestingANSI/ASNT CP-189 Standard for Qualification and Certifi-cation of Nondestructive Testing Personnel2.3 Aerospace Industries Association Standard:NAS 410 Certification and Qualification of NondestructiveTest Pe
10、rsonnel42.4 International Standards Organization (ISO):5ISO 9712 Qualification and Certification of NDT Personnel3. Terminology3.1 Definitions: Related terminology is defined in Terminol-ogy E1316.3.2 Definitions of Terms Specific to This Standard:3.2.1 bulk wavean ultrasonic wave, either longitudin
11、al orshear horizontal mode, used in nondestructive testing tointerrogate the volume of a material.3.2.2 butterfly (double elongated racetrack) coilan EMATcoil consisting of two coils wound on an elongated racetrackshape, placed side by side, and connected so the current on theconductors in the middl
12、e section flows in only one direction.3.2.3 electromagnetic acoustic transducer (EMAT)anelectromagnetic device for converting electrical energy intoacoustical energy in the presence of a magnetic field.1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is t
13、he direct responsibility of Subcommittee E07.06 onUltrasonic Method.Current edition approved July 1, 2018. Published July 2018. Originally approvedin 1996. Last previous edition approved in 2012 as E1816 - 12. DOI: 10.1520/E1816-18.2For referenced ASTM standards, visit the ASTM website, www.astm.org
14、, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, ht
15、tp:/www.asnt.org.4Available from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerospace.org.5Available from International Organization for Standardization (ISO), ISOCentral Secretariat, BIBC II, Chemin de Blandonnet 8, C
16、P 401, 1214 Vernier,Geneva, Switzerland, http:/www.iso.org.*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 StatesThis international standard was developed in accordance with in
17、ternationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.4 Lorentz forcesforces exerted on a charg
18、ed particleby electric currents when placed in a magnetic field. Lorentzforces are perpendicular to both the direction of the magneticfield and the current direction. Lorentz forces are the forcesresponsible behind the principle of electric motors.3.2.5 magnetostrictive forcesforces arising from mag
19、neticdomain wall movements within a magnetic material duringmagnetization.3.2.6 meander coilan EMAT coil consisting of periodic,winding, nonintersecting, and usually evenly spaced conduc-tors.4. Summary of Practice4.1 Determining the thickness (T) of a material, whenmeasured by the pulse-echo ultras
20、onic method, is a product ofthe velocity of sound in the material (V) and the transit time (t)divided by two due to round trip through the material.T 5 Vt2 (1)4.2 The pulse-echo ultrasonic instrument measures the tran-sit time of the ultrasonic pulse travelling through the part.4.3 The velocity in t
21、he material being measured is afunction of the material physical properties. It is usuallyassumed to be uniform for a given class of materials and itsapproximate value can be obtained from Table X3.1 in PracticeE494, from other references, or can be estimated experimen-tally. Different alloys of ste
22、el, aluminum, or other metals canhave differences in velocity enough to make your readingoutside of its accuracy requirements. Extreme care must betaken when selecting calibration block materials.4.4 One or more reference blocks are required havingknown velocity or, preferably, being of the same all
23、oy materialas that being examined, and having thicknesses accuratelymeasured, and which are in the range of thicknesses to bemeasured. It is generally desirable that the thicknesses be“round numbers” rather than miscellaneous odd values. Oneblock should have a thickness value near the maximumthickne
24、ss of the range of interest and another block near theminimum thickness.4.5 Thickness measurements of materials at high-temperature can be performed with specially designed searchunits with high temperature compensation. Normalization ofapparent thickness readings for elevated temperatures is re-qui
25、red. A rule of thumb mentioned in Practice E797 and oftenused is as follows: The apparent thickness reading obtainedfrom steel walls having elevated temperatures is high (toothick) by a factor of about 1 % per 100F (55C). Thus, if theinstrument was standardized on a piece of similar material at68F (
26、20C), and if the reading was obtained with a surfacetemperature of 860F (460C), the apparent reading should bereduced by 8 %. This correction is an average one for manytypes of steel. Other corrections would have to be determinedempirically for other materials.4.6 The display element (A-scan display
27、, meter, or digitaldisplay) of the instrument must be adjusted to present conve-nient values of thickness dependent on the range being used.The control for this function may have different names ondifferent instruments, including range, sweep, materialstandardize, or velocity.4.7 The timing circuits
28、 in different instruments use variousconversion schemes. A common method is the so-calledtime/analog conversion in which the time measured by theinstrument is converted into a proportional d-c voltage which isthen applied to the readout device. Another technique uses avery high-frequency oscillator
29、that is modulated or gated by theappropriate echo indications, the output being used eitherdirectly to suitable digital readouts or converted to a voltage forother presentation.5. Significance and Use5.1 The methods described provide indirect measurement ofthe thickness of sections of materials not
30、exceeding tempera-tures of 1200F 650C. Measurements are made from oneside of the object, without requiring access to the rear surface.5.2 Ultrasonic thickness measurements are used extensivelyon basic shapes and products of many materials, on precisionmachined parts, and to determine wall thinning i
31、n processequipment caused by corrosion and erosion.5.3 Recommendations for determining the capabilities andlimitations of ultrasonic thickness gages for specific applica-tions can be found in the cited references (1,2).66. Basis of Application6.1 The following items are subject to contractual agree-
32、ment between the parties using or referencing this standard.6.2 Personnel Qualification:6.2.1 If specified in the contractual agreement, personnelperforming examinations to this standard shall be qualified inaccordance with a nationally- or internationally-recognizedNDT personnel qualification pract
33、ice or standard such asANSI/ASNT-CP-189, SNT-TC-1A, NAS-410, ISO 9712, or asimilar document and certified by the employer or certifyingagency, as applicable. The practice or standard used and itsapplicable revision shall be identified in the contractual agree-ment between the using parties. Instrume
34、nts with direct readthickness displays, including automated thicknessmeasurement, may be used by personnel only trained in thethickness measurement procedure if initial programing of theinstrument is done by personnel trained in accordance with oneof the standards mentioned above.6.3 Qualification o
35、f Nondestructive AgenciesIf specifiedin the contractual agreement, NDT agencies shall be qualifiedand evaluated as described in Specification E543. The appli-cable edition of Specification E543 shall be specified in thecontractual agreement.6.4 Procedures and TechniquesThe procedures and tech-niques
36、 to be used shall be as described in this practice unlessotherwise specified. Specific techniques may be specified in thecontractual agreement.6The boldface numbers in parentheses refer to a list of references at the end ofthis standard.E1816 1827. Apparatus7.1 InstrumentsMost instruments capable of
37、 thickness-measurement using EMATs are flaw detectors with an A-scandisplay and direct thickness readout.7.1.1 Flaw detectors with A-scan display readouts displaytime/amplitude information. Thickness determinations aremade by reading the distance between the zero-corrected initialpulse and first-ret
38、urned echo (back reflection), or betweenmultiple-back reflection echoes, on a standardized baseline ofthe A-scan display. The baseline of the A-scan display shouldbe adjusted for the desired thickness increments.7.1.2 Some flaw detectors have thermocouple inputs inorder to acquire the materials temp
39、erature, which is then usedto apply a temperature correction algorithm (See PracticeE797).7.1.3 Automated EMAT thickness measurement systemsmay have a variety of displays including direct read, colorcoded mapping, line scans, point maps, etc.8. Standardization8.1 EMAT transducers and instrumentation
40、 are availablefrom several manufacturers. In addition to custom designs forspecific applications, there are off-the-shelf SH and L waveEMAT transducers offered for the most common ultrasonicfrequencies (typically 1.5 MHz, 2.5 MHz, 5 MHz, 7.5 MHz)and transducer dimensions (ranging from 0.25 to 2 in.
41、(6 to 50mm). The characteristics of the different transducers(dimensions, center frequency, bandwidth, beam profile)should be made available by the transducer manufacturer.8.2 Prior to examination, the EMAT system should bestandardized by means of appropriate reference blocks, de-scribed in 4.4, 8.9
42、.1, or as specified in the contractual specifi-cation. If the instrument is capable of storing different veloci-ties based on Alloy programs, a program for a specific alloycan be loaded and a verification step performed instead of astandardization. If the verification step shows that the instru-ment
43、 reads outside of tolerance a standardization must beperformed before use.8.3 Reference standards should have ultrasonic characteris-tics similar to the material being examined.8.4 As in conventional ultrasonic application, attenuationcorrection should be completed if the amplitude of a referenceref
44、lector (for example, backwall) in the reference standard doesnot match that of the sample.8.5 Reference standards should be rechecked following anysystem or operator changes to maintain standardization.8.6 If the EMATs are being operated in a scan mode ofoperation, it should be verified that the sca
45、n rates are optimumto ensure ultrasonic resolution adequate to the specified con-tract.8.7 Unless otherwise specified, the EMAT system shouldalways provide an A-scan display. As a minimum, the initialpulse and one back wall reflection should be present on theoscilloscope trace. The total number of v
46、isible reflectionsdepends on operator preference.8.8 Specific standardization procedures should be generatedfor specific applications. Generic procedures for thicknessapplications are outlined as follows.8.9 Thickness Applications:8.9.1 Reference Block SelectionThe requirements for ap-propriate refe
47、rence blocks are given in 4.4, Appendix XI inPractice E797. It is recommended that reference blocks also beavailable representing thicknesses between the maximum andminimum values. The EMATs are placed on the selectedreference block and the instrumentation parameters adjusteduntil appropriate thickn
48、esses are displayed.8.9.2 Since the major difference between examinations withEMATs and those with conventional ultrasonics lies in thecoupling mechanism, standardization guidance from conven-tional ultrasonic thickness procedures should be used, asappropriate (for example, Practice E797).8.9.3 Back
49、 Reflection AmplitudeThe amplitude of theback wall reflection should be monitored to ensure thatadequate signal strength is available for accurate thicknessmeasurements and to ensure that adequate electromagneticcoupling is being maintained.8.9.4 Back Reflection GatingGating for the back wallreflection should be verified prior to examining and periodi-cally thereafter to ensure that the proper gating location andlength are being maintained to ensure the accuracy of exami-nation.9. Procedure9.1 Case I Magnetic Materials (Spiral coil Radiallypolarize
