1、Designation: E 2261 07Standard 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:2E 543 Specification for Agencies Performing Nondestruc-tive TestingE 1316 Terminology for Nondestructive Examinations2.2 ASNT Standard:
6、3SNT-TC-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
7、 C, Electromagnetic 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
8、as a receiver.3.2.3 uniform fieldas applied to nondestructive testingwith magnetic fields, the area of uniform magnetic field overthe surface of the material under examination produced by aparallel induced alternating current, which has been passedthrough the weld and is observable beyond the direct
9、 couplingof the exciting coil.3.2.4 graduated fieldas applied to nondestructive testingwith magnetic fields, a magnetic field having a controlledgradient in its intensity.3.3 Definitions of Terms Specific to This Standard:3.3.1 alternating current field measurement systemtheelectronic instrumentatio
10、n, 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 blocka reference stan-dard with specified artificial slots, used to confirm the opera-tion of the system
11、.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 the electric field.3.3.4 Bzthe z component of the magnetic field normal tothe inspected base metal/hear affected zone surface, the mag-nitude of which is pr
12、oportional to the lateral deflection of theinduced currents in the plane of that surface.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 plotsthese plot the relationship betweenBx or Bz values with time.3.3.7 surface plotfor use
13、 with array probes. This type ofplot has one component of the magnetic field plotted over anarea, typically as a color contour plot or 3-D wire frame plot.3.3.8 data sample ratethe rate at which data is digitizedfor display and recording, in data points per second.3.3.9 configuration datastandardiza
14、tion data and instru-mentation settings for a particular probe stored in a computerfile.1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.07 onElectromagnetic Method.Current edition approved Dec. 1, 2007. Pu
15、blished January 2008. Originallyapproved in 2003. Last previous edition approved in 2003 as E 2261 - 03.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standard
16、s 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.NOTE 1Different
17、 equipment manufacturers may use slightly differentterminology. Reference should be made to the equipment manufacturersdocumentation for clarification.4. Summary of Practice4.1 In a basic alternating current field measurement system,a small probe is moved along the toe of a weld. The probecontains a
18、n exciter coil, which induces anAC magnetic field inthe material surface aligned to the direction of the weld. This,in turn, causes alternating current to flow across the weld. Thedepth of penetration of this current varies with material typeand frequency but is typically 0.004 in. 0.1 mm deep inmag
19、netic materials and 0.08 - 0.3 in. 2 - 7 mm deep innon-ferrous materials. Any surface breaking discontinuitieswithin a short distance of either side of the scan line at thislocation will interrupt or disturb the flow of the alternatingcurrent. The maximum distance from the scan line to a targetdisco
20、ntinuity, potentially detectable at a specified probabilityof detection, is determined by the probe assembly size, but istypically 0.4 in 10 mm. Measurement of the absolute quan-tities of the two major components of the surface magneticfields (Bx and Bz) determines the severity of the disturbance(se
21、e Fig. 1) and thus the severity of the discontinuity. Discon-tinuity sizes, such as crack length and depth, can be estimatedfrom key points selected from the Bx and Bz traces along withthe standardization data and instrument settings from eachindividual probe. This discontinuity sizing can be perfor
22、medautomatically using system software.4.2 Configuration data is loaded at the start of the exami-nation. System sensitivity and operation is verified using anoperation standardization block. System operation is checkedand recorded prior to and at regular intervals during theexamination. Note that w
23、hen a unidirectional input current isused, any decay in strength of the input field with probe lift-offor thin coating is relatively small so that variations of outputsignal (as may be associated with a discontinuity) are reduced.If a thick coating is present, then the discontinuity sizeestimation m
24、ust compensate for the coating thickness. Thecoating thickness requiring compensation is probe dependent.This can be accomplished using discontinuity-sizing tables inthe system software and an operator-entered coating thicknessor automatically if the equipment measures the coating thick-ness or stan
25、d-off distance during the scanning process. Usingthe wrong coating thickness would have a negative effect ondepth sizing accuracy if the coating thickness discrepancy istoo large. Data is recorded in a manner that allows archivingand subsequent recall for each weld location. Evaluation ofexamination
26、 results may be conducted at the time of examina-tion or at a later date. The examiner generates an examinationreport detailing complete results of the examination.5. Significance and Use5.1 The purpose of the alternating current field measure-ment method is to evaluate welds for surface breaking di
27、scon-tinuities such as fabrication and fatigue cracks. The examina-tion results may then be used by qualified organizations toassess weld service life or other engineering characteristics(beyond the scope of this practice). This practice is notintended for the examination of welds for non-surface br
28、eakingdiscontinuities.6. Basis of Application6.1 Personnel Qualification:6.1.1 If specified in the contractual agreement, personnelperforming examinations to this practice shall be qualified inaccordance with a nationally or internationally recognizedNDT personnel qualification practice or standard
29、such asANSI/ASNT-CP-189 or SNT-TC-1A or a similar documentand certified by the employer or certifying agent, as applicable.The practice or standard used and its applicable revision shallbe identified in the contractual agreement between the usingparties.6.2 Qualification of Nondestructive Evaluation
30、Agenciesif specified in the contractual agreement, NDTagencies 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 Requiremen
31、ts7.1 The following items may require agreement by theexamining 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, m
32、aintenance history, processconditions, and specific types of discontinuities that are re-quired to be detected, if known.FIG. 1 Example Bx and Bz Traces as a Probe Passes Over aCrack(The orientation of the traces may differ depending upon theinstrumentation.)E22610727.1.2 The maximum window of oppor
33、tunity 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. If required by type of equipment chosen,thickness of coating and variation of coating thickness.7.1
34、.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 access to welds, and areas where access maybe restricted.7.1.7 Type of al
35、ternating 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 Required weld cleanliness.7.1.10 Environmental conditions, equipment an
36、d 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 criteria to be used in evaluating discon-tinuities.7.1.13 Disposition of
37、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 tech-nique.8.2 Material Properties:8.2.1 Although there are permeabili
38、ty differences in a fer-romagnetic material between weld metal, heat affected zoneand parent plate, the probe is normally scanned along a weldtoe and so passes along a line of relatively constant permeabil-ity. If a probe is scanned across a weld then the permeabilitychanges may produce indications,
39、 which could be similar tothose from a discontinuity. Differentiation between a transversediscontinuity signal and the weld signal can be achieved bytaking further scans parallel to the indication. The signal froma discontinuity will die away quickly. If there is no significantchange in indication a
40、mplitude at 0.8 in. 20 mm distancefrom the weld then the indication is likely due to the perme-ability changes in the weld.8.3 Magnetic State:8.3.1 DemagnetizationIt must be ensured that the surfacebeing examined is in the non-magnetized state. Therefore theprocedure followed with any previous magne
41、tic 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 plot, which may sometimes beconfused with a discontinuity indication.8.3.2 Grindi
42、ng 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 marksshould always be reported by the probe operator, since thesecan give rise to
43、 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 indicationfrom a linear discontinuity will die away quickly away fromthe locati
44、on 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 effect of thegrinding.8.4 Residual stress, with accompanying permeability varia-ti
45、ons, may be present with effects similar to those due togrinding, but are much smaller.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, with a discontinuity indication. Thesame procedure is used as fo
46、r 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 because of objects near the weldthat are ferromagnetic or condu
47、ctive 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 mistaken for discontinuities. (See8.5.)8.8 Weld Geometry:8.8.1
48、 When a probe scans into a tight angle between twosurfaces the Bx indication value will increase with little changein the Bz value. In the representative plot of Fig. 2, this appearsas a rise in the X-Y plot. If the equipment is capable ofmeasuring lift-off, the lift-off will also change.FIG. 2 Exam
49、ple X-Y Plot Produced by Plotting the Bx (vertical)and Bz (horizontal) Together(The orientation of the plot may differ depending upon theinstrumentation.)E22610738.9 Crack Geometry Effects:8.9.1 A discontinuity at an angle to the scana discontinu-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 anasymmetric X-Y plot. Additional scans may be made along theweld or parent plate to determine the position of the other endof the discontinu
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