1、Designation: E 2261 03Standard Practice forExamination of Welds Using the Alternating Current FieldMeasurement Technique1This standard is issued under the fixed designation E 2261; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e year of last 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 describes procedures to be followed duringalternating current field measurement examination o
3、f welds forbaseline and service-induced surface breaking discontinuities.1.2 This practice is intended for use on welds in anymetallic material.1.3 This practice does not establish weld acceptance crite-ria.1.4 The values stated in either inch-pound units or SI unitsare to be regarded separately as
4、standard. The values stated ineach system might not be exact equivalents; therefore, eachsystem shall be used independently of the other.1.5 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 e
5、stablish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 543 Practice for Agencies Performing NondestructiveTesting2E 1316 Terminology for Nondestructive Examinations22.2 ASNT Standard:3SNT-T
6、C-1A Personnel Qualification in NondestructiveTestingANSI/ASNT-CP-189 Standard for Qualification and Certi-fication of Nondestructive Testing Personnel3. Terminology3.1 General definitions of terms used in this practice can befound in Terminology E 1316, Section A, Common NDTterms, and Section C, El
7、ectromagnetic testing.3.2 Definitions:3.2.1 excitera device that generates a time varying elec-tromagnetic field, usually a coil energized with alternatingcurrent (AC); also known as a transmitter.3.2.2 detectorone or more coils or elements used to senseor measure a magnetic field; also known as a r
8、eceiver.3.2.3 uniform fieldas applied to nondestructive testing,the area of uniform magnetic field over the surface of thematerial under examination produced by a parallel inducedalternating current, which has been passed through the weldand is observable beyond the direct coupling of the excitingco
9、il. The field is uniform on the surface but the strength decaysexponentially with depth.3.2.4 alternating current field measurementa nondestruc-tive examination technique that measures changes in an appliedAC uniform magnetic field to detect and characterize discon-tinuities.3.3 Definitions of Terms
10、 Specific to This Standard:3.3.1 alternating current field measurement systemtheelectronic instrumentation, software, probes, and all associatedcomponents and cables required for performing weld exami-nation using the alternating current field measurement tech-nique.3.3.2 operational standardization
11、 blocka reference stan-dard with specified artificial slots, used to confirm the opera-tional parameters and to indicate discontinuity detection sen-sitivity.3.3.3 Bxthe x component of the magnetic field, parallel tothe weld toe, the magnitude of which is proportional to thecurrent density set up by
12、 the electric field.3.3.4 Bzthe z component of the magnetic field normal tothe weld toe, the magnitude of which is proportional to thecurvature of the current in the x-y plane.3.3.5 X-Y Plotan X-Y graph with two orthogonal compo-nents of magnetic field plotted against each other.3.3.6 time base plot
13、sthese plot the relationship betweenBx or Bz values with time.3.3.7 surface plotfor use with array probes. These plotone component of magnetic field over an area, typically as acolor contour plot or 3-D wire frame plot.1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive
14、 Testing and is the direct responsibility of Subcommittee E07.07 onElectromagnetic Methods.Current edition approved February 10, 2003. Published April 2003.2Annual Book of ASTM Standards,Vol03.03.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 100
15、36.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.3.8 data sample ratethe rate at which data is digitizedfor display and recording, in data points per second.4. Summary of Practice4.1 In a basic alternating current field measureme
16、nt system,a small probe is moved along the toe of a weld. The probecontains an exciter coil, which induces an AC magnetic field inthe material surface aligned to the direction of the weld. This,in turn, causes uniform alternating current to flow across theweld, orthogonal to the toe. The depth of pe
17、netration of thiscurrent varies with material type and frequency but is typically0.004 in. 0.1 mm deep in magnetic materials and 0.08 - 0.3 in.2 - 7 mm deep in non-ferrous materials. Any surface breakingdiscontinuities within 0.4 in. 10 mm of either side of the scanline at this location will interru
18、pt or disturb the flow of theotherwise uniform electromagnetic field. Measurement of theabsolute quantities of the two major components of the surfacemagnetic fields (Bx and Bz) determines the severity of thedisturbance (see Fig. 1) and thus the severity of the disconti-nuity. Discontinuity sizes, s
19、uch as crack length and depth, canbe predicted from key points selected from the Bx and Bztraces along with the standardization data and instrumentsettings from each individual probe. This discontinuity sizingcan be performed automatically using system software.4.2 Standardization data and instrumen
20、t settings for eachindividual probe are determined at the factory and stored in acomputer file, which is loaded at the start of the examination.System sensitivity is verified using an operation standardiza-tion block. System sensitivity is checked and recorded prior toand at regular intervals during
21、 the examination. Note that whena unidirectional input current is used, any decay in strength ofthe input field with probe lift-off or thin coating is relativelysmall so that variations of output signal (as may be associatedwith a discontinuity) are reduced. If a thick coating, that is,greater than
22、0.04 in. 1 mm is present then the discontinuitysize prediction must compensate for the coating thickness. Thiscan be accomplished using discontinuity-sizing tables in thesystem software. Using the wrong coating thickness wouldhave a negative effect on depth sizing accuracy if the discrep-ancy was 0.
23、04 in. 1 mm or more. As the current flow isarranged normal to the weld toe there is no perturbation in thatdirection so that no indication occurs at the interface due tochanges in permeability. Data is recorded in a manner thatallows archiving and subsequent recall for each weld location.Evaluation
24、of examination results may be conducted at the timeof examination or at a later date. The examiner generates anexamination report detailing complete results of the examina-tion.5. Significance and Use5.1 The purpose of the alternating current field measure-ment method is to evaluate welds in the are
25、a of the toe forsurface breaking discontinuities such as fatigue cracks. Theexamination results may then be used by qualified organiza-tions to assess weld service life or other engineering charac-teristics (beyond the scope of this practice).5.2 Comparison with Conventional Eddy CurrentExaminationc
26、onventional eddy current coils are typicallyconfigured to sense the field from the weld in the immediatevicinity of the emitting element, whereas alternating currentfield measurement probes are typically designed to sense themagnetic field from the weld distant from the exciter.6. Basis of Applicati
27、on6.1 Personnel Qualification:6.1.1 If specified in the contractual agreement, personnelperforming examinations to this practice shall be qualified inaccordance with a nationally recognized NDT personnel quali-fication practice or standard such as ANSI/ASNT-CP-189 orSNT-TC-1A or a similar document a
28、nd certified by the em-ployer or certifying agent, as applicable. The practice orstandard used and its applicable revision shall be identified inthe contractual agreement between the using parties.6.2 Qualification of Nondestructive EvaluationAgenciesif specified in the contractual agreement, NDTage
29、ncies shall be qualified and evaluated as described inPractice E 543, with reference to sections on electromagneticexamination. The applicable edition of Practice E 543 shall bespecified in the contractual agreement.7. Job Scope and Requirements7.1 The following items may require agreement by theexa
30、mining party and their client and should be specified in thepurchase document or elsewhere:7.1.1 Location and type of welded component to be exam-ined, design specifications, degradation history, previous non-destructive examination results, maintenance history, processconditions, and specific types
31、 of discontinuities that are re-quired to be detected, if known.7.1.2 The maximum window of opportunity for work.(Detection of small discontinuities may require a slower probescan speed, which will affect productivity.)7.1.3 Size, material grade and type, and configuration ofwelds to be examined.FIG
32、. 1 Typical Bx and Bz Traces as a Probe Passes Over a CrackE22610327.1.4 A weld numbering or identification system.7.1.5 Extent of examination, for example: complete orpartial coverage, which welds and to what length, whetherstraight sections only and the minimum surface curvature.7.1.6 Means of acc
33、ess to welds, and areas where access maybe restricted.7.1.7 Type of alternating current field measurement instru-ment and probe; and description of operations standardizationblock used, including such details as dimensions and material.7.1.8 Required operator qualifications and certification.7.1.9 R
34、equired weld cleanliness.7.1.10 Environmental conditions, equipment and prepara-tions that are the responsibility of the client; common sourcesof noise that may interfere with the examination.7.1.11 Complementary methods or techniques may be usedto obtain additional information.7.1.12 Acceptance cri
35、teria to be used in evaluating discon-tinuities.7.1.13 Disposition of examination records and referencestandards.7.1.14 Format and outline contents of the examinationreport.8. Interferences8.1 This section describes items and conditions, which maycompromise the alternating current field measurement
36、tech-nique.8.2 Material Properties:8.2.1 Although there are permeability differences in a fer-romagnetic material between weld metal, heat affected zonematerial and parent plate, the probe is normally scanned alonga weld toe and so passes along a line of relatively constantpermeability. If a probe i
37、s scanned across a weld then thepermeability changes may produce indications, which could besimilar to those from a discontinuity. Differentiation between atransverse discontinuity signal and the weld signal can beachieved by taking further scans parallel to the discontinuity.The signal from a disco
38、ntinuity will die away quickly. If thereis no significant change in indication amplitude at 0.8 in. 20mm distance from the weld then the indication is likely due tothe permeability changes in the weld.8.3 Magnetic State:8.3.1 DemagnetizationIt must be ensured that the surfacebeing examined is in the
39、 non-magnetized state. Therefore theprocedure followed with any previous magnetic techniquedeployed must include demagnetization of the surface. This isbecause areas of remnant magnetization, particularly where theleg of a magnetic particle examination yoke was sited, canproduce loops in the X-Y plo
40、t, which may sometimes beconfused with a discontinuity indication.8.3.2 Grinding marksmagnetic permeability can also beaffected by surface treatments such as grinding. These cancause localized areas of altered permeability across the line ofscan direction. The extent and pressure of any grinding mar
41、ksshould always be reported by the probe operator, since thesecan give rise to strong indications in both Bx and Bz, whichmay be confused with a discontinuity indication. If a discon-tinuity is suspected in a region of grinding, further scans shouldbe taken parallel but away from the weld toe. The i
42、ndicationfrom a linear discontinuity will die away quickly away fromthe location of the discontinuity so that the scan away from theweld toe will be flatter. If there is no significant change inindication amplitude at 0.80 in. 20 mm distance from theweld then the indication is likely due to the effe
43、ct of thegrinding.8.4 Residual stress, with accompanying permeability varia-tions, may be present with similar, but much smaller, effects togrinding.8.5 Seam Welds:8.5.1 Seam welds running across the line of scanning alsoproduce strong indications in the Bx and Bz, which cansometimes be confused, wi
44、th a discontinuity indication. Thesame procedure is used as for grinding marks with furtherscans being taken away from the affected area. If the indicationremains constant then it will not have been produced by alinear discontinuity.8.6 Ferromagnetic and Conductive Objects:8.6.1 Problems may arise b
45、ecause of objects near the weldthat are ferromagnetic or conductive which may reduce thesensitivity and accuracy of discontinuity characterization whenthey are in the immediate vicinity of the weld.8.7 Neighboring Welds:8.7.1 In areas where welds cross each other, there areindications, which may be
46、mistaken for discontinuities. (See8.5.)8.8 Weld Geometry:8.8.1 When a probe scans into a tight angle between twosurfaces the Bx indication value will increase with little changein the Bz. This will cause the X-Y plot to rise.8.9 Crack Geometry Effects:8.9.1 A discontinuity at an angle to the scana d
47、iscontinu-ity at an angle to the scan will reduce either the peak or thetrough of the Bz as the sensor probe only passes through theedge of one end of the discontinuity. This produces an un-equalsided X-Y plot. Additional scans may be made along the weldor parent plate to determine the position of t
48、he other end of thediscontinuity.8.9.2 A discontinuity at an angle to the surfacethe effectof a discontinuity at a non-vertical angle to the probe isgenerally to reduce the value of the Bz signal. The value of theBx signal will not be reduced. This has the effect of reducingthe width of the X-Y plot
49、.8.9.3 Line contact or multiple discontinuitieswhen con-tacts occur across a discontinuity then minor loops occurwithin the main X-Y plot loop produced by the discontinuity. Ifmore than one discontinuity occurs in the scan then there willbe a number of loops returning to the background.8.9.4 Transverse discontinuitiesif a transverse discontinu-ity occurs during the scan for longitudinal discontinuities thenthe Bx will rise instead of falling and the Bz signal will remainthe same as for a short longitudinal discontinuity. The X-Y plotwill then go upwards i
