1、Designation: E 1962 09Standard Practice forUltrasonic Surface Testing Using Electromagnetic AcousticTransducer (EMAT) Techniques1This standard is issued under the fixed designation E 1962; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, 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. Scope1.1 This practice covers guidelines for utilizing EMATtechniques for detecting material discontinuities
3、that are pri-marily open to the surface (for example, cracks, seams, laps,cold shuts, laminations, through leaks, lack of fusion). Thistechnique can also be sensitive to flaws and discontinuities thatare not surface-breaking, provided their proximity to thesurface is less than or equal to the Raylei
4、gh wave length.1.2 This practice covers procedures for the non-contactcoupling of surface waves into a material via electromagneticfields.1.3 The procedures of this practice are applicable to anymaterial in which acoustic waves can be introduced electro-magnetically. This includes any material that
5、is either electri-cally conductive or ferromagnetic, or both.1.4 This practice is intended to provide examination capa-bilities for in-process, final, and maintenance applications.1.5 This practice does not provide standards for the evalu-ation of derived indications. Interpretation, classification,
6、 andultimate evaluation of indications, albeit necessary, are beyondthe scope of this practice. Separate specifications or agreementwill be necessary to define the type, size, location, anddirection of indications considered acceptable or non-acceptable.1.6 The values stated in inch-pound units are
7、to be regardedas the standards. The SI units given in parentheses are forinformation only.1.7 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 practic
8、es and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 543 Specification for Agencies Performing Nondestruc-tive TestingE 587 Practice for Ultrasonic Angle-Beam Examination bythe Contact MethodE 1316 Terminology for Nondestructive Exam
9、inationsE 1774 Guide for Electromagnetic Acoustic Transducers(EMATs)E 1816 Practice for Ultrasonic Testing Using Electromag-netic Acoustic Transducer (EMAT) Techniques2.2 ANSI/ASNT Standards:Recommended Practice SNT-TC-1A Personnel Qualifica-tion and Certification in Nondestructive Testing3ANSI/ASNT
10、 CP-189 Standard for Qualification and Certi-fication of Nondestructive Testing Personnel32.3 Military Standard:MIL-STD-410 Nondestructive Testing Personnel Qualifica-tion and Certification43. Terminology3.1 Definitions:3.1.1 Additional related terminology is defined in Terminol-ogy E 1316.3.2 Defin
11、itions of Terms Specific to This Standard:3.2.1 electromagnetic acoustic transducer (EMAT)anelectromagnetic device for converting electrical energy intoacoustical energy in the presence of a magnetic field.3.2.2 Lorentz forcesapplied to electric currents whenplaced in a magnetic field. Lorentz force
12、s are perpendicular toboth the direction of the magnetic field and the currentdirection. Lorentz forces are the forces responsible behind theprinciple of electric motors.1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subc
13、ommittee E07.06 onUltrasonic Method.Current edition approved June 1, 2009. Published July 2009. Originally approvedin 1998. Last previous edition approved in 2004 as E 1962 - 04.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org.
14、For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Available from U.S. Government Printing Office Superint
15、endent of Documents,732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.3 magnetostrictive forcesforces arising from magneticdomain wall movements within a magnetic materia
16、l duringmagnetization.3.2.4 meander coilan EMAT coil consisting of periodic,winding, non-intersecting, and usually evenly-spaced conduc-tors.4. Summary of Practice4.1 The techniques outlined in this practice address theelectromagnetic generation of Rayleigh acoustic wave modesfor sensitivity to surf
17、ace or near-surface flaws or discontinui-ties. Flaws are detected by reflection or attenuation of acousticwaves from interactions at discontinuity interfaces.4.2 Fig. 1 shows one typical EMAT setup for the generationof Rayleigh waves. An external magnetic induction Bo parallelto the surface is appli
18、cable on ferromagnetic material. Themagnetic field may be generated by a permanent magnet, apulsed magnet, or a DC electromagnet. A meander RF coil isoriented in the plane of and near the surface of the object to betested. The magnetic field lines are tangential to the coil andperpendicular to the c
19、onductor. The coil is excited by an RFtoneburst pulse produced by a specialized EMAT pulser. Asurface current is induced in the test sample by transformeraction. The surface current interacts with the external magneticfield by means of the Lorentz force. This disturbance istransferred to the lattice
20、 of the solid and is thus the ultrasonicsource responsible for producing the surface acoustic waves.As shown in Fig. 1, an ordinary meander coil producesbidirectional waves. In practice, specially designed meandercoils can be designed to produce unidirectional waves.4.3 Fig. 2 illustrates a typical
21、meander coil for generation ofsurface waves. The following relationship must be valid forRayleigh wave generation with a meander coil:VR5 2Df (1)where:VR= Rayleigh wave velocity,D = separation of adjacent conductors, andf = frequency.4.4 Surface flaws or discontinuities lead to reflection orattenuat
22、ion of the surface waves. Either pulse-echo or pitch-catch modes can be used. Upon approaching the receiverEMAT, the reflected or attenuated ultrasonic waves produceoscillations within the conductor in the presence of themagnetic field and thus induce a voltage in the receiver coil(similar to an ele
23、ctric generator) allowing detection.5. Significance and Use5.1 EMAT techniques show benefits and advantages overconventional piezoelectric ultrasonic techniques in specialapplications where flexibility in the type of wave modegeneration is desired. EMATs are highly efficient in thegeneration of surf
24、ace waves.5.2 Since EMATs are highly efficient in the generation ofsurface waves, and since acoustic techniques utilizing surfacewaves are proven effective for detecting surface and near-surface discontinuities, they should be considered for anyapplications where conventional penetrant testing and m
25、ag-netic particle NDT techniques are effective but undesirable.5.3 Since EMAT techniques are non-contacting, they shouldbe considered for ultrasonic testing where applications involveautomation, high-speed inspections, moving objects, applica-tions in remote or hazardous locations, applications to o
26、bjectsat elevated temperatures, or objects with rough surfaces.5.4 The purpose of this practice is to promote the EMATtechnique of the ultrasonic method as a viable alternative toconventional PT and MPT methods for detecting the presenceof surface and near-surface material discontinuities.5.5 The us
27、e of EMATs and the selection of appropriateoperating parameters presuppose a knowledge of the geometryof the component; the probable location, size, orientation, andreflectivity of the expected flaws; the allowable range of EMATlift-off; and the laws of physics governing the propagation ofultrasonic
28、 waves. This procedure pertains to a specific EMATsurface inspection application.FIG. 1 Typical EMAT Configuration for Rayleigh Wave GenerationFIG. 2 Typical EMAT Meander Coil for Generation of SurfaceWavesE19620926. Basis of Application6.1 The following items are subject to contractual agree-ment b
29、etween the parties using or referencing the standard:6.1.1 Personnel Qualification6.1.1.1 If specified in the contractual agreement, personnelperforming examination to this practice shall be qualified inaccordance with a nationally or internationally recognizedNDT personnel qualification practice or
30、 standard such asANSI/ASNT-CP-189, SNT-TC-1A, MIL STD-410, or a similardocument and certified by the employer or certifying agency,as applicable. The practice or standard used and its applicablerevision shall be indentified in the contractual agreementbetween the using parties.6.1.2 Qualification of
31、 Nondestructive AgenciesIf speci-fied in the contractual agreement, NDT agencies shall bequalified and evaluated as described in Practice E 543. Theapplicable edition of Practice E 543 shall be specified in thecontractual agreement.6.1.3 Procedures and TechniquesThe procedures andtechniques to be ut
32、ilized shall be as specified in the contractualagreement.6.1.4 Surface PreparationThe pre-examination surfacepreparation criteria shall be in accordance with 10.2.2 unlessotherwise specified.6.1.5 Timing and Extent of ExaminationShall be specifiedin the contractual agreement6.1.6 Reporting Criteria/
33、Acceptance CriteriaReportingcriteria for the examination results shall be in accordance withSection 12 unless otherwise specified.Acceptance criteria shallbe specified in the contractual agreement.6.1.7 Reexamination of Repaired/Re-Worked ItemsReexamination of repaired/re-worked items is not address
34、ed inthis practice and, if required, shall be specified in the contrac-tual agreement.7. Techniques7.1 This practice describes three separate techniques forEMAT surface wave examination. The first involves pulse-echo or pitch-catch techniques for the detection of reflectedsurface waves. The second t
35、echnique involves a pitch-catchmethod sensitive to the attenuation of surface waves. The thirdtechnique involves surface wave diffraction with focusedmeander coils.7.2 Pulse-Echo or Pitch-Catch Reflected Surface WaveTechniqueThese techniques are analogous to conventionalultrasonic techniques. The te
36、chniques use either one (pulse-echo) or two (pitch-catch) EMAT sensors and rely upon thereception of reflected surface waves from the flaw. Theadvantage of these techniques is simplicity. One disadvantageis the difficulty in detecting all flaw orientations withoutelaborate scanning routines. Also, w
37、hen these techniques areused for weld applications, a problem arises in that the root andcrown of the weld can produce reflections that are prominentenough to interfere with and even obscure flaw signals. Whensuch interferences are apparent, it is recommended that one ofthe other two techniques desc
38、ribed herein be utilized to avoidthese problems.7.3 Pitch-Catch Attenuation TechniqueThe attenuationtechnique is most effectively applied using the arrangement ofsensors illustrated in Fig. 3. The technique indicates thepresence of a flaw by noting attenuation of the UT signal. Thesensors use small
39、permanent magnets to generate narrowsurface wave beams that cross at right angles. The preferredtechnique requires two channels of EMAT instrumentationalthough it may be modified for one-channel operation. Toimplement one-channel operation, the distance between onetransmitter receiver pair is increa
40、sed slightly to displace thetwo received signals in time. The transmitter coils are thenwired in series and the receiver coils are wired in series. Thisarrangement allows both pairs of EMAT coils to be used withone channel of EMAT instrumentation. One advantage to theattenuation technique is sensiti
41、vity to all flaw orientations.Another advantage to using the attenuation technique is theability to scan both sides of a weld simultaneously. It also scanslarge areas of the material in one scan. A disadvantage relatesto the beam width, which must be narrow or focused in orderto achieve a minimum of
42、 6 dB of attenuation.7.4 Diffraction TechniqueThe basis of the diffractiontechnique is illustrated in Fig. 4. Two collinear focused EMATs(transmitter and receiver) or one pulse-echo EMAT are posi-tioned at an angle (the diffraction angle) with respect to thenormal to the weld centerline. The weld ro
43、ot and crown act asa specular reflector whose signals are reflected away from theEMAT receiver. The flaw is, however, detected over a wideangular range by means of diffraction. Depending upon the sizeof the flaw relative to the ultrasonic wavelength, it acts aseither a point diffractor or a series o
44、f point diffractors.Anaturalflaw such as a fatigue crack has a series of facets and branchesthat act as point diffractors. Therefore, it is typically possible todetect the presence of a natural flaw several inches long withthis technique. Surface waves can be focused to a regionapproximating a point
45、 focus (a region approaching a wave-length as a limit). It is frequently advantageous to have areasonable focal depth to increase the area covered with eachlinear scan. For many welds, it is possible to scan one half ofthe weld crown from each side of the weld. A single EMATsensor is sensitive to al
46、l orientations except possibly a crackFIG. 3 Attenuation TechniqueE1962093parallel to the incident beam. Therefore, two sensors withpositive and negative diffraction angles will be sensitive to allflaw orientations.8. Apparatus8.1 The apparatus may be considered to consist of theEMAT sensor and the
47、EMAT instrumentation. The sensorconsists of an RF coil and a source of magnetic field. Theinstrumentation consists of a tone burst pulser/receiver, a dataacquisition system or display device such as an oscilloscope,an impedance matching network, a preamplifier (preferred),and a well shielded cable f
48、rom the pulser/receiver to the sensor.8.2 Coil Design:8.2.1 A meander coil is used to produce surface waves. Coildesign and conductor spacing required to produce a givenfrequency has been discussed in 4.3. The coil may be focusedor nonfocused depending upon the technique being used andthe desired re
49、solution and sensitivity. Fig. 5 gives an exampleof typical design parameters for a focused coil, similar to thatused for the diffraction technique. Many EMAT coils areflexible printed circuits produced by photoetching on a polya-mide substrate. The surface of the coil can be backed with athin layer of foam and covered with a thin (0.001 to 0.005 in.(0.025 to 0.127 mm) wearplate of high molecular weightpolyethylene or titanium. The purpose of the wearplate is tomaintain a constant liftoff for the EMAT coil. The wearplateshould be pliable and conform to irregular or curv
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