1、Designation: E 2373 04Standard Practice forUse of the Ultrasonic Time of Flight Diffraction (TOFD)Technique1This standard is issued under the fixed designation E 2373; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice establishes the requirements for develop-ing ultrasonic examination procedures using the ultrasonictechniq
3、ue known as Time-of-Flight Diffraction (TOFD).1.2 The values stated in SI units are to be regarded asstandard. Inch-pound units are provided for information.1.3 Consistent with ASTM Policy, TOFD may be regardedas an ultrasonic test method whereby the qualities and charac-teristics of the item tested
4、 are evaluated, measured and in somecases identified. Measurements may be subject to precision andbias that may be determined statistically or as a function ofsome parameter(s) such as wavelength. This practice may beused for applications that would be qualitative and properlyaddressed as examinatio
5、ns as well as quantitative and moreproperly addressed as tests.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 and health practices and determine the applic
6、a-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 164 Practice for Ultrasonic Contact Examination ofWeld-mentsE 1065 Guide for Evaluating Characteristics of UltrasonicSearch UnitsE 1316 Terminology for Nondestructive ExaminationsE 1324 Guide for Measuring S
7、ome Electronic Characteris-tics of Ultrasonic Examination Instruments2.2 Other Documents:BS 7706 (1993) Guide to Calibration and Setting-up of theUltrasonic Time-of-Flight Diffraction (TOFD) Techniquefor Detection , Location and Sizing of Flaws, BritishStandards Institute, 19933Code Case 2235 ASME B
8、oiler and Pressure Vessel Code43. Terminology3.1 DefinitionsRelated terminology is defined in Termi-nology E 1316.3.2 Definitions of Terms Specific to This Standard:3.2.1 B-scan displaya sectional view of the plotted in-spection data formed by the stacking of A-scans. (Some usersrefer to stacked A-s
9、cans from non-parallel scans as D-scansand reserve those used with parallel scans as B-scans.)3.2.2 back-wall echoa specular reflection from the back-wall of the component being examined (usually assumed to bea plate).3.2.3 lateral wavea compression wave that travels by themost direct route from the
10、 transmitting probe to the receivingprobe in a TOFD configuration.3.2.4 parallel scana scan whereby the probe pair motionis parallel to the ultrasonic beam axis. Also called a B-scan bysome users.3.2.5 PCSabbreviation for probe center spacing. Refers tothe distance between the marked exit points of
11、a pair of TOFDprobes for a specific application.3.2.6 non-parallel or longitudinal scana scan wherebythe probe pair motion is perpendicular to the ultrasonic beamaxis.3.2.7 RF waveformsthe non-rectified A-scan.4. Significance and Use4.1 This practice provides general principles for the appli-cation
12、of the Time-of-Flight Diffraction Technique as a tool fordetection and sizing of discontinuities.4.2 TOFD is a nondestructive ultrasonic examination tech-nique that is not based on amplitude response. However,sufficient sensitivity is required to identify indications forevaluation.1This practice is
13、under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.06 onUltrasonic Method.Current edition approved July 1, 2004. Published July 2004.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
14、 Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from BSI Management Systems, 12110 Sunset Hills Road, Suite 140,Reston VA 20190.4Available from the American Society of Mechanical Engineers, A
15、SME Inter-national, 22 Law Drive, Box 2900, Fairfield, NJ 07007-2900.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.3 Techniques used are typically applied to welded joints incarbon steel but the principles may be applicable to ot
16、herapplications including other materials with suitable validationprocedures agreeable to the contracting parties.4.4 In addition to a stand-alone ultrasonic detection tech-nique TOFD may be used in conjunction with weld examina-tions such as those described in Practices E 164 and E 1961where it may
17、 be used to improve sizing estimates of flawsdetected by the manual or mechanized pulse-echo techniquesand help discriminate between flaws and geometric reflectors.4.5 The technique has proven effective on thicknesses from9 to 300 mm 0.375 to 12 in. TOFD has been used onthicknesses outside of this r
18、ange but special considerations arenecessary. Techniques developed outside of this range ofthickness shall be demonstrated as capable of meeting therequired detection and sizing requirements of the specificationused.5. Procedures5.1 Introduction:5.1.1 TOFD is an ultrasonic examination technique that
19、 canprovide improved detection and sizing capabilities of discon-tinuities compared to standard ultrasonic pulse-echo tech-niques. It uses forward scattered tip diffraction and reflection oftransmitted ultrasonic pulses. This document describes therequirements for TOFD equipment and procedures on fl
20、at platesurfaces. Guidance for more complex geometries is provided intheAppendix. General guidance on TOFD can also be found inBritish Standards BS 7706. Acceptance criteria typical andperformance demonstration requirements that may be usedwith TOFD techniques are found in ASME Code Case 22355.5.1.2
21、 Because phase inversions of signals play an importantrole in the evaluation of TOFD results, all procedures devel-oped using this practice shall require that the equipmentpresentation use and store RF waveforms.5.1.3 Whether motorized or manually-operated, probe mo-tion must be encoded for position
22、 and probes held in a fixturethat maintains correct PCS during scanning. Time basedsampling of data collection is not acceptable.5.1.4 Fig. 1 illustrates the typical probe configuration for aTOFD examination. The figure uses a weld for convenience ofreferences; however, TOFD need not be restricted t
23、o just weldexaminations.5.1.5 The lateral wave and back-wall echo signals provideconvenient references. For most applications mode convertedsignals from flaws are not used and therefore flaw indicationsare usually recognized as occurring between the lateral waveand back-wall echo signals. Although i
24、t is more often the caseto use refracted compression mode in the examination piece,some applications may produce better results when the incidentangle is greater than the first critical angle, thereby providing arefracted transverse shear mode in the examination piece.When using a refracted compress
25、ion mode in the examinationpiece the direct shear and head waves also are generated;however, due to their lower acoustic velocities, shear wavesarrive later in time than the back-wall signal.5.1.6 Fig. 2 is a sketch of a typical presentation for anon-parallel scan of a butt weld in a plate with an i
26、mbeddedflaw. The right side of Fig. 2 illustrates a waveform extractedfrom a B-scan display showing the lateral wave, upper tipdiffracted, lower tip diffracted and the back-wall echo signals.The left side of Fig. 2 indicates the probe placement withrespect to the weld (upper left) and relative motio
27、n of theprobes (a non-parallel scan is indicated).5.1.7 Fig. 3 illustrates an actual TOFD scan with fiveindications (identified on the left) and an extractedA-scan fromone of the indications.5.2 Written ProcedureA documented examination strat-egy or scan plan shall be provided showing probe placemen
28、t,movement, and component coverage that provides a standard-ized and repeatable methodology for component acceptance.The scan plan shall also include ultrasonic beam angle(s) used,beam directions with respect to some reference such as a weldcenterline, and volume examined.5.3 Examination Materials a
29、nd Surface Preparation:5.3.1 TOFD technique can be applied to both metals andnonmetals. Best results are had on fine-grained isotropicmaterials with low attenuation including some finer grainedaustenitic alloys and aluminum. With suitable validation pro-cedures, agreeable to the contracting parties,
30、 coarser-grainedand anisotropic materials may also be examined using TOFD.These usually require additional modifications to frequenciesand digital signal processing.5.3.2 The scanning area shall be clear of weld spatter andother conditions which may interfere with the movement of theprobes, the coup
31、ling liquid, or the transmission of acousticenergy into the material. Any surface condition such asgeometry, coating, and so forth, impeding the ultrasonicexamination shall be noted for corrective action prior toscanning.5Reference to ASME CC2235 is made only as an example of an existing codewhere t
32、he mutually agreed upon acceptance criteria allowsTOFD to be applied.Thisdoes not suggest that application of ASME CC2235 would be appropriate in allcases. It should be recognized that the high sensitivity of the TOFD technique couldresult in indications from reflectors in plate materials that meet
33、all plate ultrasonicspecification requirements. Such indications should not be considered unacceptableunless they fail to meet the acceptance criteria agreed upon in 7.1.FIG. 1E23730425.3.3 The TOFD technique may be used with immersion,contact or gap techniques. Single element or phased arraypiezoel
34、ectric probes may be used. EMAT or other non-standardprobes may also be used with suitable validation proceduresagreeable to the contracting parties.5.3.4 The acoustic coupling shall be obtained by using amedium suitable for the purpose and compatible with thematerial being examined. Water, coupling
35、 gels or pastes,greases and oils are typically used. Water additives such asenvironmentally-safe wetting agent and corrosion inhibitorsmay be used to enhance acoustic coupling and protect theexamination piece. For examination where ambient tempera-tures are below 0C 32F methyl alcohol or similar med
36、iamay be used. For examination at elevated temperatures theexamination surface or probes may require cool-down orspecially designed high-temperature couplants. The couplingmedium selected shall provide uniform and reliable examina-tion in the temperature range of intended use. Couplant andscanning c
37、onditions, including temperature, used for standard-ization shall be the same as that used in the examination.5.4 Qualification and Certification of PersonnelIf speci-fied in the contractual agreement, personnel performing exami-nations to this practice shall be qualified in accordance with anationa
38、lly-recognized NDT personnel qualification standardand certified by the employer or certifying agency as appli-cable. The practice or standard used and its applicable versionshall be identified in the contractual agreement between theusing parties and should include a requirement for trainingspecifi
39、c to TOFD.5.5 Equipment RequirementsAn ultrasonic system forTOFD shall provide a means of transmitting, receiving, stor-ing, displaying and analyzing ultrasonic signals. As well, itshall provide a fixed spacing between the transmitting andreceiving probes and ensure that probe motion is encoded andi
40、ts position maintained within prescribed tolerances with re-spect to a reference position such as the weld centerline.5.5.1 Electronics:5.5.1.1 The instrument shall provide a linear “A” scanpresentation for both setting up scan parameters and for signalanalysis. Instrument linearity may be determine
41、d in accordanceFIG. 2FIG. 3E2373043with the procedures detailed in Guide E 1324, within sixmonths of the intended end use date. For digital-based instru-ments alternative calibration methods may be used to verifyamplitude and time-base output linearity. A copy of thecalibration certificate shall be
42、kept on file by the user of theequipment. Instrument linearity shall be such that the accuracyof indicated amplitude or time is within 65 % of the actualfull-scale amplitude or time.5.5.1.2 The ultrasonic pulser may provide excitation voltageby tone burst, uni-polar or bi-polar square wave. Pulse wi
43、dthshall be tunable to allow optimization of pulse amplitude andduration.5.5.1.3 The bandwidth of the ultrasonic receiver shall be atleast equal to that of the nominal probe frequency and such thatthe 6 dB bandwidth of the probe does not fall outside of the6 dB bandwidth of the receiver.5.5.1.4 Rece
44、iver gain control shall be available to adjustsignal amplitude in increments of 1 dB or less. Since diffractedsignal amplitudes may be significantly lower than for pulse-echo techniques it may be necessary to incorporate a pre-amplifier in the system.5.5.1.5 Analogue to digital conversion of wavefor
45、ms shallhave sampling rates at least four times that of the nominalfrequency of the probe. When digital signal processing is to becarried out on the raw data this shall be increased to eight timesthe nominal frequency of the probe.5.5.2 Data Display and Recording:5.5.2.1 The data display used for TO
46、FD shall allow theoperator to view the un-rectified A-scan and position the startand length of a gate that determines the extent of the A-scantime-base that is collected.5.5.2.2 Data collection equipment shall permit storage of allgated A-scans to a magnetic or optical storage medium.Equipment used
47、for TOFD shall require computer software thatprovides a B-scan display of the collected waveforms (asillustrated in Fig. 2). The B-scan display shall have a minimumof 64 gray-scale or color levels. (Storage of just B-scan imageswithout the underlying A-scan waveforms is not an acceptableform of data
48、 recording.)5.5.2.3 Computer software for TOFD displays shall includealgorithms to linearize cursors or the waveform time-base topermit depth and vertical extent estimations.5.5.2.4 In addition to storage of waveform data includingamplitude and time-base details, the TOFD equipment shallalso store p
49、ositional information indicating the relative positionof the waveform with respect to the adjacent waveform(s); thatis, encoded position.5.5.3 ProbesUltrasonic probes used for TOFD techniquesshall conform to the following minimum requirements:5.5.3.1 Two probes shall be used in a pitch-catch arrange-ment (TOFD pair).5.5.3.2 Each probe in the TOFD pair shall have the samenominal frequency.5.5.3.3 The TOFD pair shall have the same element dimen-sions.5.5.3.4 The pulse duration of the probe shall not exceed twocycles as measured to the 20 dB level below the peak respo
