1、Designation: E 749 07Standard Practice forAcoustic Emission Monitoring During Continuous Welding1This standard is issued under the fixed designation E 749; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、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 provides recommended guidelines foracoustic emission (AE) monitoring of weldments during andimmediately following thei
3、r fabrication by continuous weldingprocesses.1.2 The procedure described in this practice is applicable tothe detection and location of AE sources in weldments and intheir heat-affected zone during fabrication, particularly in thosecases where the time duration of welding is such that fusionand soli
4、dification take place while welding is still in progress.1.3 The effectiveness of acoustic emission to detect discon-tinuities in the weldment and the heat-affected zone is depen-dent on the design of theAE system, theAE system verificationprocedure, the weld process, and the material type. Material
5、sthat have been monitored include low-carbon steels, low-alloysteels, stainless steels, and some aluminum alloys. The systemperformance must be verified for each application by demon-strating that the defects of concern can be detected with thedesired reliability.1.4 This standard does not purport t
6、o 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 applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 543 Sp
7、ecification for Agencies Performing Nondestruc-tive TestingE 569 Practice for Acoustic Emission Monitoring of Struc-tures During Controlled StimulationE 650 Guide for Mounting Piezoelectric Acoustic EmissionSensorsE 1316 Terminology for Nondestructive Examinations2.2 ASNT Standards:3SNT-TC-1A Recomm
8、ended Practice for NondestructiveTesting Personnel Qualification and CertificationANSI/ASNT CP-189 Standard for Qualification and Certi-fication of Nondestructive Testing Personnel2.3 AIA Standard:4NAS-410 Certification and Qualification of NondestructivePersonnel (Quality Assurance Committee)3. Ter
9、minology3.1 DefinitionsFor definitions of terms relating to acousticemission testing, see Section B of Terminology E 1316.4. Significance and Use4.1 Detection and location of AE sources in weldmentsduring fabrication may provide information related to theintegrity of the weld. Such information may b
10、e used to directrepair procedures on the weld or as a guide for application ofother nondestructive evaluation (NDE) methods. A majorattribute of applying AE for in-process monitoring of welds isthe ability of the method to provide immediate real-timeinformation on weld integrity. This feature makes
11、the methoduseful to lower weld costs by repairing defects at the mostconvenient point in the production process. The AE activityfrom discontinuities in the weldment is stimulated by thethermal stresses from the welding process. The AE activityresulting from this stimulation is detected by AE sensors
12、 in thevicinity of the weldment, which convert the acoustic wavesinto electronic signals. The AE instrumentation processessignals and provides means for immediate display or indicationof AE activity and for permanent recordings of the data.4.2 Items to be considered in preparation and planning formo
13、nitoring should include but not be limited to the following:1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.04 onAcoustic Emission Method.Current edition approved Feb. 15, 2007. Published March 2007. Origi
14、nallyapproved in 1980. Last previous edition approved in 2001 as E 749 - 01.2For 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 standards Document Summary page onth
15、e ASTM website.3Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4Available from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.ai
16、a-aerospace.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2.1 Description of the system or object to be monitored orexamined,4.2.2 Extent of monitoring, that is, entire weld, cover passesonly, and so forth,4.2.3 Limitations o
17、r restrictions on the sensor mountingprocedures, if applicable,4.2.4 Performance parameters to be established and main-tained during theAE system verification procedure (sensitivity,location accuracy, and so forth),4.2.5 Maximum time interval between AE system verifica-tion checks,4.2.6 Performance
18、criteria for purchased equipment,4.2.7 Requirements for permanent records of the AE re-sponse, if applicable,4.2.8 Content and format of test report, if required, and4.2.9 Operator qualification and certification, if required.5. Basis of Application5.1 The following items are subject to contractual
19、agree-ment between the parties using or referencing this practice.5.2 Personnel Qualification:5.2.1 If specified in the contractual agreement, personnelperforming examinations to this standard shall be qualified inaccordance with a nationally or internationally recognizedNDT personnel qualification
20、practice or standard such asANSI/ASNT CP-189, SNT-TC-1A, NAS-410, or a similardocument and certified by the employer or certifying agency,as applicable. The practice or standard used and its applicablerevision shall be identified in the contractual agreement be-tween the using parties.5.3 Qualificat
21、ion of Nondestructive AgenciesIf specifiedin the contractual agreement, NDT agencies shall be qualifiedand evaluated as described in Practice E 543. The applicableedition of Practice E 543 shall be specified in the contractualagreement.5.4 Procedures and TechniquesThe procedures and tech-niques to b
22、e utilized shall be as specified in the contractualagreement.6. Examination Preparation6.1 The following preparatory procedures should be com-pleted before initiating AE monitoring:6.1.1 Select the location(s) where the sensor(s) will beacoustically coupled. The sensor(s) should be centrally located
23、near the weldment to provide for optimal AE response from allportions of the weld. If the sensor(s) are piezoelectric, thislocation should be such that the maximum temperature stayssubstantially below the Curie temperature of the sensor(s).Take care in selecting the sensor mounting locations to avoi
24、dcontact or disturbance, or both, of the sensor by any of thewelding or structural positioning equipment. Typical distancesfrom 6 in. to 1 ft (150 to 300 mm) from the heat-affected zoneof the weld are usually satisfactory. Typical fixed sensorplacement patterns that have been successfully used are s
25、hownin Figs. 1-3.6.1.1.1 If a fixed contact sensor(s) is used, clean the area(s)where attachment will be made to eliminate loose scale,welding flux, or other debris, and attach the sensor in accor-dance with Guide E 650.6.1.1.2 If moving sensors are used, clean the coupling pathso that uniform sensi
26、tivity is maintained as the sensor moves.Fig. 4 shows side and top views of a typical configuration formoving sensors.6.1.2 Position and route the signal cables connecting thesensor(s) to the AE instrumentation to avoid contacting the hotweld bead or entangling the welding and positioning equip-ment
27、.6.1.3 Adjustment of Apparatus:6.1.3.1 After all sensors are mounted, connected, and op-erational (without objectionable background noise), the AEmonitoring system can then be adjusted using an AE simulator.6.1.3.2 Gain AdjustmentTo set the gain for a channel (ifnecessary), locate the acoustic emiss
28、ion simulator at a selecteddistance adjacent to the sensor. Monitor the response to thesimulated emission, and adjust the channel gain to a specifiedamplitude level. Repeat this procedure two times, placing thesimulator at the same distance from the sensor but at differentazimuthal positions relativ
29、e to the original simulator positions(see Fig. 5). Record the average gain for the three simulatorpositions. Repeat the entire procedure for each AE sensor onthe structure, and adjust the gains. The average gains for allchannels should give responses to the simulator that have peakvoltages identical
30、 to within 63 dB.6.1.4 Determination of Source-Location AccuracyCheckthe operation of the AE source-location function by analyzingsimulated AE signals from several random locations in theweld and on the structure, as well as from any specific criticalFIG. 1 Typical Sensor Placement for Single Channe
31、l AEMonitoring of a Linear WeldFIG. 2 Typical Sensor Placement for Two-Channel AE Monitoringof a Linear WeldFIG. 3 Typical Sensor Placement for Three-Channel AEMonitoring of a Circular WeldE749072locations. For each placement of the simulator, determine andrecord the precision and accuracy of the AE
32、 location function.It should be noted that the accuracy of locating the simulatorsource will not necessarily be the same as for locating a realAEsource. During trial welding in multipass configurations, itshould be verified that location accuracy is maintained duringweld buildup. Experiments indicat
33、e that location accuracydepends on the percentage completion of multipass welds.6.2 Check the integrity of the welding ground return systemto eliminate the possibility of diverting the weld currents to theAE instrumentation ground.7. Apparatus7.1 The AE apparatus normally consists of sensors, pream-
34、plifiers, and electronic instrumentation with display and re-cording capabilities. Acoustic emission monitoring duringwelding places many specialized requirements on AE appara-tus due to severe environmental factors and interfering noisesources. The following criteria provide guidelines to aid inmin
35、imizing these interfering factors, and maximizing theeffectiveness of the monitoring process:7.1.1 Sensors should be used that are capable of operatingin the temperature range to be encountered. Use of “high-temperature” sensors or waveguides to isolate conventionalsensors may be necessary for multi
36、pass, high heat input welds,or welds maintained at elevated preheat temperatures. Thesensors should be electrically insulated from the structureunder test to ensure that the weld current or welder ground isnot coupled into the AE instrumentation. If the weld current ispulsed or has a significant tra
37、nsient component, differentialsensors may aid in suppressing interference.7.1.2 Frequency Bandpass Filters are recommended tominimize background noise interference during AE monitoringof welding. A low-frequency limit to the passband in thevicinity of 100 kHz will aid in minimizing background noised
38、ue to mechanical noise sources such as grinding, chipping,FIG. 4 Moving Sensor Configuration with Sensor Position Fixed Relative to Weld HeadFIG. 5 AE Simulator Positions During Sensor CalibrationE749073and manipulation of the structure under test. Radio frequencyinterference due to contactors and h
39、eavy electrical machinery,as well as the welding arc, may be minimized by use of ahigh-frequency limit to the passband ranging from 100 kHz to1 MHz. The sensor operating frequency range should becompatible with the above considerations.7.2 The Welding Arc is a low-level continuous source ofAE.To min
40、imize interference from the welding arc, the sensitivityof the AE monitoring apparatus should be adjusted so that arcnoise is below the trigger threshold. This sensitivity is themaximum usableAE sensitivity for weld monitoring and varieswith different welding methods. Table 1 indicates overall gainf
41、or a particular system monitoring welding methods and usingtypical commercial piezoelectric transducers. This table is forgeneral guideline purposes and not for direct reference.7.3 Single-Channel AE Instrumentation employing a singlesensor may provide information on the presence of disconti-nuities
42、 in a weld. For low-heat input welds, where the delaytime between fusion and AE activity is short, discontinuitiesmay also be located in the weld by noting the presence ofunusual AE activity and recording the position of the weldinghead when such activity occurs. As the weld heat inputincreases, the
43、 delay time between fusion and AE activityusually increases, thus making use of multichannel arrival timeinterval measurements necessary for AE source location.7.4 TheAE apparatus should be capable of providing outputsignals that are proportional to overall acoustic activity (suchas RMS or Average S
44、ignal Level, ASL) and acoustic emissionenergy or count rate. In addition, AE counts, energy or peakamplitude for each AE event plotted versus time is useful forAE monitoring of welds. The latter are particularly useful foracoustically active weld processes such as submerged-arcwelding where the pres
45、ence of solid flux cracking contributesgreatly to the AE activity. Experience has shown that for thesetypes of welds, the AE activity from flaws and from normalslag bead cracking may have similar peak amplitudes andenergies. To prevent false alarms from acceptable slag beadactivity, gated rate monit
46、ors can sometimes be used to identifyflaw activity which generally consists of groups of AE eventsoccurring at much higher rates than the rate of slag beadevents.8. Examination Procedures8.1 Acoustic emission data may be accumulated during thewelding process. Due to the delay between weld fusion(sol
47、idification) and AE activity, monitoring must continue for atime period following welding to acquire all significant AEdata. The AE monitoring time after welding increases withincreasing weld heat input, ranging from 10 seconds formanual gas tungsten (approximately 100 A) to more than 2minutes for s
48、ubmerged arc welding (600 to 800 A). Thedesirable time should be established during developmentalmonitoring of trial welds.8.2 For AE systems with gain controls, the gain-settingprocedure should be reapplied at the completion of a weld. Forheavy section welds that may take many days to complete, the
49、gain-setting procedure should be reapplied at least once duringevery work shift (for example, 8 hours). All changes in systemgain or source location accuracy should be recorded and thesystem readjusted as necessary.8.3 Observable conditions that occur in conjunction withunusual AE activity should be recorded to aid in later interpre-tation of the data. This would include cleanup or chipping andgrinding by the welder, for example.9. Examination Records9.1 The examination records should contain the followinginformation:9.1.1 AE system verification data and instrument adjust-ments
