1、Designation: E2261/E2261M 12Standard Practice forExamination of Welds Using the Alternating Current FieldMeasurement Technique1This standard is issued under the fixed designation E2261/E2261M; the number immediately following the designation indicates the yearof original adoption or, in the case of
2、revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice describes procedures to be followed duringalternating current field measurement e
3、xamination of 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 UnitsThe values stated in either inch-pound units orSI units are to be regard
4、ed separately as standard. The valuesstated in each system might not be exact equivalents; therefore,each system shall be used independently of the other. Combin-ing values from the two systems may result in nonconformancewith the standard.1.5 This standard does not purport to address all of thesafe
5、ty 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 applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E543 Specification for Agencies
6、Performing NondestructiveTestingE1316 Terminology for Nondestructive Examinations2.2 ASNT Standard:3SNT-TC-1A Personnel Qualification and Certification inNondestructive TestingANSI/ASNT-CP-189 Standard for Qualification and Certifi-cation of Nondestructive Testing Personnel3. Terminology3.1 Definiti
7、onsFor definitions of terms relating to thispractice refer to Terminology E1316, Section A, CommonNDT terms, and Section C, Electromagnetic testing. Thefollowing definitions are specific to the alternating current fieldmeasurement technique:3.2 Definitions:3.2.1 excitera device that generates a time
8、 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 receiver.3.2.3 uniform fieldas applied to nondestructive testingwith magnetic fiel
9、ds, 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 couplingof the exciting coil.3.2.4 graduated fieldas applied to nondestructive testing
10、with 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 instrumentation, software, probes, and all associatedcomponents and cables required for performing we
11、ld exami-nation using the alternating current field measurement tech-nique.3.3.2 operational reference standarda reference standardwith specified artificial slots, used to confirm the operation ofthe system.3.3.3 Bxthe x component of the magnetic field, parallel tothe weld toe, the magnitude of whic
12、h 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/heat affected zone surface, the mag-nitude of which is proportional to the lateral deflection of theinduced currents in the plane of that surface.3.3.5
13、 X-Y Plotan X-Y graph with two orthogonal compo-nents of magnetic field plotted against each other.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 Nov.
14、1, 2012. Published November 2012. Originallyapproved in 2003. Last previous edition approved in 2007 as E2261 - 07. DOI:10.1520/E2261_E2261M-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards v
15、olume 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM Internatio
16、nal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.3.6 time base plotsthese plot the relationship betweenBx or Bz values with time.3.3.7 surface plotfor use with array probes. This type ofplot has one component of the magnetic field plotted over anarea, typica
17、lly 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 datastandardization data and instru-mentation settings for a particular probe stored in a computerfile.3.3.10 twin fiel
18、dsmagnetic fields generated in two or-thogonal directions by use of two excitersNOTE 1Different 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 curre
19、nt field measurement system,a small probe is moved along the toe of a weld. The probecontains an 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 t
20、his current varies with material typeand frequency but is typically 0.004 in. 0.1 mm deep inmagnetic 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 distu
21、rb the flow of the alternatingcurrent. The maximum distance from the scan line to a targetdiscontinuity, 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 com
22、ponents of the surface magneticfields (Bx and Bz) determines the severity of the disturbance(see 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
23、data and instrument settings from eachindividual probe. This discontinuity sizing can be performedautomatically using system software. Discontinuities essen-tially perpendicular to the weld may be detected (in ferriticmetals only) by the flux leakage effect. However confirmationof such transverse di
24、scontinuities (and detection of the same innon-ferritic metals) requires scans with the induced magneticfield perpendicular to the direction of the weld.4.2 Configuration data is loaded at the start of the exami-nation. System sensitivity and operation is verified using anoperation reference standar
25、d. System operation is checked andrecorded prior to and at regular intervals during the examina-tion. Note that when a unidirectional input current is used, anydecay in strength of the input field with probe lift-off or thincoating is relatively small so that variations of output signal (asmay be as
26、sociated with a discontinuity) are reduced. If a thickcoating is present, then the discontinuity size estimation mustcompensate for the coating thickness. The coating thicknessrequiring compensation is probe dependent. This can beaccomplished using discontinuity-sizing tables in the systemsoftware a
27、nd an operator-entered coating thickness or auto-matically if the equipment measures the coating thickness orstand-off distance during the scanning process. Using thewrong coating thickness would have a negative effect on depthsizing accuracy if the coating thickness discrepancy is toolarge. Data is
28、 recorded in a manner that allows archiving andsubsequent recall for each weld location. Evaluation of exami-nation results may be conducted at the time of examination orat a later date. The examiner generates an examination reportdetailing complete results of the examination.5. Significance and Use
29、5.1 The purpose of the alternating current field measure-ment method is to evaluate welds for surface breaking discon-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
30、(beyond the scope of this practice). This practice is notintended for the examination of welds for non-surface breakingdiscontinuities.6. Basis of Application6.1 Personnel Qualification:6.1.1 If specified in the contractual agreement, personnelperforming examinations to this practice shall be qualif
31、ied inaccordance with a nationally or internationally recognizedNDT personnel qualification practice or standard such asANSI/ASNT-CP-189 or SNT-TC-1A or a similar documentand certified by the employer or certifying agent, as applicable.FIG. 1 Example Bx and Bz Traces as a Probe Passes Over aCrack(Th
32、e orientation of the traces may differ depending upon theinstrumentation.)E2261/E2261M 122The practice or standard used and its applicable revision shallbe identified in the contractual agreement between the usingparties.6.2 Qualification of Nondestructive Evaluation Agenciesifspecified in the contr
33、actual agreement, NDT agencies shall bequalified and evaluated as described in Practice E543, withreference to sections on electromagnetic examination. Theapplicable edition of Practice E543 shall be specified in thecontractual agreement.7. Job Scope and Requirements7.1 The following items may requi
34、re 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 beexamined, design specifications, degradation history, previousnondestructive examination results, maintenance history, pro-cess conditions
35、, and specific types of discontinuities that arerequired 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, or cleaning of surface, or both, which will affectproductivity.)7.1.3 Size, material grade and
36、type, and configuration ofwelds to be examined. If required by type of equipment chosen,thickness of coating and variation of coating thickness.7.1.4 A weld numbering or identification system.7.1.5 Extent of examination, for example: complete orpartial coverage, which welds and to what length, wheth
37、erstraight 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 alternating current field measurement instru-ment and probe; and description of operations referece stan-dard used, including such details as dimensions an
38、d material.7.1.8 Required operator qualifications and certification.7.1.9 Required 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 t
39、echniques may be usedto obtain additional information.7.1.12 Acceptance criteria 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
40、 conditions, which maycompromise the alternating current field measurement tech-nique.8.2 Material Properties:8.2.1 Although there are permeability differences in a fer-romagnetic material between weld metal, heat affected zoneand parent plate, the probe is normally scanned along a weldtoe and so pa
41、sses along a line of relatively constant permeabil-ity. If a probe is scanned across a weld then the permeabilitychanges may produce indications, which could be similar tothose from a discontinuity. Differentiation between a transversediscontinuity signal and the weld signal can be achieved bytaking
42、 further scans parallel to the indication, or using an arrayprobe. The signal from a discontinuity will die away quickly. Ifthere is no significant change in indication amplitude at 0.8 in.20 mm distance from the weld then the indication is likelydue to the permeability changes in the weld.8.3 Magne
43、tic State:8.3.1 DemagnetizationIt must be ensured that the surfacebeing examined is in the 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
44、 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 Grinding marksmagnetic permeability can also beaffected by surface treatments such as grinding. These cancause localized areas of altered
45、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 strong indications in both Bx and Bz, whichmay be confused with a discontinuity indication. If a discon-tinuity is suspected in a r
46、egion of grinding, further scans shouldbe taken parallel but away from the weld toe and perpendicularacross the region of grinding. The indication from a lineardiscontinuity will die away quickly away from the location ofthe discontinuity so that the scan away from the weld toe willbe flatter. If th
47、ere is no significant change in indicationamplitude at 0.80 in. 20 mm distance from the weld then theindication is likely due to the effect of the grinding. Theindication from a region of grinding will be the same for theperpendicular scan.8.4 Residual stress, with accompanying permeabilityvariation
48、s, 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 for
49、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 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 mistaken for discontinu
