1、Designation: E1962 09E1962 14Standard Practice forUltrasonic Surface Testing Using Electromagnetic AcousticTransducer (EMAT) Techniques1This standard is issued under the fixed designation E1962; 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.1. Scope Scope*1.1 This practice covers guidelines for utilizing EMAT techniques for detecting material di
3、scontinuities that are primarily opento the surface (for example, cracks, seams, laps, cold shuts, laminations, through leaks, lack of fusion). This technique can alsobe sensitive to flaws and discontinuities that are not surface-breaking, provided their proximity to the surface is less than or equa
4、lto the Rayleigh wave length.1.2 This practice covers procedures for the non-contact coupling of surface waves into a material via electromagnetic fields.1.3 The procedures of this practice are applicable to any material in which acoustic waves can be introduced electromagneti-cally. This includes a
5、ny material that is either electrically conductive or ferromagnetic, or both.1.4 This practice is intended to provide examination capabilities for in-process, final, and maintenance applications.1.5 This practice does not provide standards for the evaluation of derived indications. Interpretation, c
6、lassification, and ultimateevaluation of indications, albeit necessary, are beyond the scope of this practice. Separate specifications or agreement will benecessary to define the type, size, location, and direction of indications considered acceptable or non-acceptable.1.6 The values stated in inch-
7、pound units are to be regarded as the standards. The SI units given in parentheses are forinformation only.1.7 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 a
8、nd health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E543 Specification for Agencies Performing Nondestructive TestingE587 Practice for Ultrasonic Angle-Beam Contact TestingE1316 Terminology for Nondestructive Examinatio
9、nsE1774 Guide for Electromagnetic Acoustic Transducers (EMATs)E1816 Practice for Ultrasonic Testing Using Electromagnetic Acoustic Transducer (EMAT) Techniques2.2 ANSI/ASNT Standards:Recommended Practice SNT-TC-1A Personnel Qualification and Certification in Nondestructive Testing3ANSI/ASNT CP-189 S
10、tandard for Qualification and Certification of Nondestructive Testing Personnel32.3 Military Standard:MIL-STD-410 Nondestructive Testing Personnel Qualification and Certification43. Terminology3.1 Definitions:3.1.1 Additional related terminology is defined in Terminology E1316.1 This practice is und
11、er the jurisdiction ofASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.06 on Ultrasonic Method.Current edition approved June 1, 2009Oct. 1, 2014. Published July 2009October 2014. Originally approved in 1998. Last previous edition approved in 20042009
12、asE1962 - 04.E1962 - 09. DOI: 10.1520/E1962-09.10.1520/E1962-14.2 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 websi
13、te.3 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.4 Available from U.S. Government Printing Office Superintendent of Documents, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.This document is not an ASTM
14、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 may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all
15、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 the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2 Definiti
16、ons of Terms Specific to This Standard:3.2.1 electromagnetic acoustic transducer (EMAT)an electromagnetic device for converting electrical energy into acousticalenergy in the presence of a magnetic field.3.2.2 Lorentz forcesapplied to electric currents when placed in a magnetic field. Lorentz forces
17、 are perpendicular to both thedirection of the magnetic field and the current direction. Lorentz forces are the forces responsible behind the principle of electricmotors.3.2.3 magnetostrictive forcesforces arising from magnetic domain wall movements within a magnetic material duringmagnetization.mag
18、netization, where magnetostrictive materials will undergo a strain in the presence of a magnetic field.3.2.4 meander coilan EMAT coil consisting of periodic, winding, non-intersecting, and usually evenly-spaced conductors.4. Summary of Practice4.1 The techniques outlined in this practice address the
19、 electromagnetic generation of Rayleigh acoustic wave modes forsensitivity to surface or near-surface flaws or discontinuities. Flaws are detected by reflection or attenuation of acoustic waves frominteractions at discontinuity interfaces.4.2 Fig. 1 shows one typical EMAT setup for the generation of
20、 Rayleigh waves. An external magnetic induction Bo parallel tothe surface is applicable on ferromagnetic material. Other applications where B0 is perpendicular to the surface can also be usedif the coil design is appropriate. The magnetic field may be generated by a permanent magnet, a pulsed magnet
21、, or a DCelectromagnet. A meander RF coil is oriented in the plane of and near the surface of the object to be tested. The magnetic fieldlines are tangential to the coil and perpendicular to the conductor. The coil is excited by an RF toneburst pulse produced by aspecialized EMAT pulser. A surface c
22、urrent is induced in the test sample by transformer action. The surface current interacts withthe external magnetic field by means of the Lorentz force. The time varying magnetic field will also interact with the ferromagneticmaterial to generate vibrations via magnetostriction. This disturbance is
23、transferred to the lattice of the solid and is thus theultrasonic source responsible for producing the surface acoustic waves. As shown in Fig. 1, an ordinary meander coil producesbidirectional waves. In practice, specially designed meander coils can be designed to produce unidirectional waves.4.3 F
24、ig. 2 illustrates a typical meander coil for generation of surface waves. The following relationship must be valid forRayleigh wave generation with a meander coil:VR 52Df (1)where:VR = Rayleigh wave velocity,D = separation of adjacent conductors, andf = frequency.4.4 Surface flaws or discontinuities
25、 lead to reflection or attenuation of the surface waves. Either pulse-echo or pitch-catch modescan be used. Upon approaching the receiver EMAT, the reflected or attenuated ultrasonic waves produce oscillations within theconductor in the presence of the magnetic field and thus induce a voltage in the
26、 receiver coil (similar to an electric generator)allowing detection.5. Significance and Use5.1 EMAT techniques show benefits and advantages over conventional piezoelectric ultrasonic techniques in specialapplications where flexibility in the type of wave mode generation and where no fluid coupling i
27、s desired. EMATs are highlyefficient in the generation of surface waves.FIG. 1 Typical EMAT Configuration for Rayleigh Wave GenerationE1962 1425.2 Since EMATs are highly efficient in the generation of surface waves, and since acoustic techniques utilizing surface wavesare proven effective for detect
28、ing surface and near-surface discontinuities, they should be considered for any applications whereconventional penetrant testing and magnetic particle NDT techniques are effective but undesirable.5.3 Since EMAT techniques are non-contacting, they should be considered for ultrasonic testing where app
29、lications involveautomation, high-speed inspections,examinations, moving objects, applications in remote or hazardous locations, applications toobjects at elevated temperatures, or objects with rough surfaces.5.4 The purpose of this practice is to promote the EMAT technique of the ultrasonic method
30、as a viable alternative toconventional PT and MPT methods for detecting the presence of surface and near-surface material discontinuities.5.5 The use of EMATs and the selection of appropriate operating parameters presuppose a knowledge of the geometry of thecomponent; the probable location, size, or
31、ientation, and reflectivity of the expected flaws; the allowable range of EMAT lift-off;and the laws of physics governing the propagation of ultrasonic waves. This procedure pertains to a specific EMAT surfaceinspection application.6. Basis of Application6.1 The following items are subject to contra
32、ctual agreement between the parties using or referencing the standard:6.1.1 Personnel Qualification6.1.1.1 If specified in the contractual agreement, personnel performing examination to this practice shall be qualified inaccordance with a nationally or internationally recognized NDT personnel qualif
33、ication practice or standard such as ANSI/ASNT-CP-189, SNT-TC-1A, MIL STD-410, or a similar document and certified by the employer or certifying agency, as applicable. Thepractice or standard used and its applicable revision shall be indentifiedidentified in the contractual agreement between the usi
34、ngparties.6.1.2 Qualification of Nondestructive AgenciesIf specified in the contractual agreement, NDT agencies shall be qualified andevaluated as described in Practice E543. The applicable edition of Practice E543 shall be specified in the contractual agreement.6.1.3 Procedures and TechniquesThe pr
35、ocedures and techniques to be utilized shall be as specified in the contractualagreement.6.1.4 Surface PreparationThe pre-examination surface preparation criteria shall be in accordance with 10.2.2 unlessotherwise specified.6.1.5 Timing and Extent of ExaminationShall be specified in the contractual
36、agreement6.1.6 Reporting Criteria/Acceptance CriteriaReporting criteria for the examination results shall be in accordance with Section12 unless otherwise specified. Acceptance criteria shall be specified in the contractual agreement.6.1.7 Reexamination of Repaired/Re-Worked ItemsReexamination of re
37、paired/re-worked items is not addressed in thispractice and, if required, shall be specified in the contractual agreement.7. Techniques7.1 This practice describes three separate techniques for EMAT surface wave examination. The first involves pulse-echo orpitch-catch techniques for the detection of
38、reflected surface waves. The second technique involves a pitch-catch method sensitiveto the attenuation of surface waves. The third technique involves surface wave diffraction with focused meander coils.7.2 Pulse-Echo or Pitch-Catch Reflected Surface Wave TechniqueThese techniques are analogous to c
39、onventional ultrasonictechniques. The techniques use either one (pulse-echo) or two (pitch-catch) EMAT sensors and rely upon the reception of reflectedsurface waves from the flaw. The advantage of these techniques is simplicity. One disadvantage is the difficulty in detecting allflaw orientations wi
40、thout elaborate scanning routines.Also, when these techniques are used for weld applications, a problem arisesin that the root and crown of the weld can produce reflections that are prominent enough to interfere with and even obscure flawsignals. When such interferences are apparent, it is recommend
41、ed that one of the other two techniques described herein be utilizedto avoid these problems.7.3 Pitch-Catch Attenuation TechniqueThe attenuation technique is most effectively applied using the arrangement of sensorsillustrated in Fig. 3. The technique indicates the presence of a flaw by noting atten
42、uation of the UT signal. The sensors use smallpermanent magnets to generate narrow surface wave beams that cross at right angles. The preferred technique requires twochannels of EMAT instrumentation although it may be modified for one-channel operation. To implement one-channel operation,the distanc
43、e between one transmitter receiver pair is increased slightly to displace the two received signals in time. The transmittercoils are then wired in series and the receiver coils are wired in series. This arrangement allows both pairs of EMAT coils to beFIG. 2 Typical EMAT Meander Coil for Generation
44、of Surface WavesE1962 143used with one channel of EMAT instrumentation. One advantage to the attenuation technique is sensitivity to all flaw orientations.Another advantage to using the attenuation technique is the ability to scan both sides of a weld simultaneously. It also scans largeareas of the
45、material in one scan. A disadvantage relates to the beam width, which must be narrow or focused in order to achievea minimum of 6 dB of attenuation.7.4 Diffraction TechniqueThe basis of the diffraction technique is illustrated in Fig. 4. Two collinear focused EMATs(transmitter and receiver) or one p
46、ulse-echo EMAT are positioned at an angle (the diffraction angle) with respect to the normal tothe weld centerline. The weld root and crown act as a specular reflector whose signals are reflected away from the EMAT receiver.The flaw is, however, detected over a wide angular range by means of diffrac
47、tion. Depending upon the size of the flaw relativeto the ultrasonic wavelength, it acts as either a point diffractor or a series of point diffractors.Anatural flaw such as a fatigue crackhas a series of facets and branches that act as point diffractors. Therefore, it is typically possible to detect
48、the presence of a naturalflaw several inches long with this technique. Surface waves can be focused to a region approximating a point focus (a regionapproaching a wavelength as a limit). It is frequently advantageous to have a reasonable focal depth to increase the area coveredFIG. 3 Attenuation Tec
49、hniqueFIG. 4 The Diffraction TechniqueE1962 144with each linear scan. For many welds, it is possible to scan one half of the weld crown from each side of the weld.Asingle EMATsensor is sensitive to all orientations except possibly a crack parallel to the incident beam. Therefore, two sensors with positiveand negative diffraction angles will be sensitive to all flaw orientations.8. Apparatus8.1 The apparatus may be considered to consist of the EMAT sensor and the EMAT instrumentation. The sensor consists of anRF coil and a source of magnetic field. The instrumentati
