1、Designation:E74907 Designation: E749/E749M 12Standard Practice forAcoustic Emission Monitoring During Continuous Welding1This standard is issued under the fixed designation E749/E749M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision
2、, 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 provides recommended guidelines for acoustic emission (AE) monitoring of weldments during
3、 andimmediately following their fabrication by continuous welding processes.1.2 The procedure described in this practice is applicable to the detection and location of AE sources in weldments and in theirheat-affected zone during fabrication, particularly in those cases where the time duration of we
4、lding is such that fusion andsolidification take place while welding is still in progress.1.3 The effectiveness of acoustic emission to detect discontinuities in the weldment and the heat-affected zone is dependent onthe design of the AE system, the AE system verification procedure, the weld process
5、, and the material type. Materials that havebeen monitored include low-carbon steels, low-alloy steels, stainless steels, and some aluminum alloys. The system performancemust be verified for each application by demonstrating that the defects of concern can be detected with the desired reliability.1.
6、41.4 UnitsThe values stated in either SI units or inch-pound units are to be regarded separately as standard. The values statedin each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining valuesfrom the two systems may result in non-conforma
7、nce with the standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to
8、 use.2. Referenced Documents2.1 ASTM Standards:2E543 Specification for Agencies Performing Nondestructive TestingE569 Practice for Acoustic Emission Monitoring of Structures During Controlled StimulationE650 Guide for Mounting Piezoelectric Acoustic Emission SensorsE1316 Terminology for Nondestructi
9、ve Examinations2.2 ASNT Standards:3SNT-TC-1A Recommended Practice for Nondestructive Testing Personnel Qualification and CertificationANSI/ASNT CP-189 Standard for Qualification and Certification of Nondestructive Testing Personnel2.3 AIA Standard:4NAS-410 Certification and Qualification of Nondestr
10、uctive Personnel (Quality Assurance Committee)3. Terminology3.1 DefinitionsFor definitions of terms relating to acoustic emission testing, see Section B of Terminology E1316.4. Significance and Use4.1 Detection and location of AE sources in weldments during fabrication may provide information relate
11、d to the integrity ofthe weld. Such information may be used to direct repair procedures on the weld or as a guide for application of other nondestructiveevaluation (NDE) methods. A major attribute of applying AE for in-process monitoring of welds is the ability of the method toprovide immediate real
12、-time information on weld integrity. This feature makes the method useful to lower weld costs by repairing1This practice is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.04 on Acoustic EmissionMethod.Current edition approv
13、ed Feb.June 15, 2007.2012. Published March 2007.July 2012. Originally approved in 1980. Last previous edition approved in 20012007 asE749 - 017. DOI: 10.1520/E0749-07.10.1520/E0749-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceast
14、m.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3Available from American Society for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4Available from Aerospace I
15、ndustries Association of America, Inc. (AIA), 1000 Wilson Blvd., Suite 1700, Arlington, VA 22209-3928, http:/www.aia-aerospace.org.1This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version.
16、 Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section
17、appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.defects at the most convenient point in the production process. The AE activity from discontinuities in the weldment is stimulatedby the thermal stres
18、ses from the welding process. The AE activity resulting from this stimulation is detected by AE sensors in thevicinity of the weldment, which convert the acoustic waves into electronic signals. The AE instrumentation processes signals andprovides means for immediate display or indication of AE activ
19、ity and for permanent recordings of the data.4.2 Items to be considered in preparation and planning for monitoring should include but not be limited to the following:4.2.1 Description of the system or object to be monitored or examined,4.2.2 Extent of monitoring, that is, entire weld, cover passes o
20、nly, and so forth,4.2.3 Limitations or restrictions on the sensor mounting procedures, if applicable,4.2.4 Performance parameters to be established and maintained during the AE system verification procedure (sensitivity,location accuracy, and so forth),4.2.5 Maximum time interval between AE system v
21、erification checks,4.2.6 Performance criteria for purchased equipment,4.2.7 Requirements for permanent records of the AE response, 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 followi
22、ng items are subject to contractual agreement between the parties using or referencing this practice.5.2 Personnel Qualification:5.2.1 If specified in the contractual agreement, personnel performing examinations to this standard shall be qualified inaccordance with a nationally or internationally re
23、cognized NDT personnel qualification practice or standard such as ANSI/ASNTCP-189, SNT-TC-1A, NAS-410, or a similar document and certified by the employer or certifying agency, as applicable. Thepractice or standard used and its applicable revision shall be identified in the contractual agreement be
24、tween the using parties.5.3 Qualification of Nondestructive AgenciesIf specified in the contractual agreement, NDT agencies shall be qualified andevaluated as described in Practice E543. The applicable edition of Practice E543 shall be specified in the contractual agreement.5.4 Procedures and Techni
25、quesThe procedures and techniques to be utilized shall be as specified in the contractual agreement.6. Examination Preparation6.1 The following preparatory procedures should be completed before initiating AE monitoring:6.1.1 Select the location(s) where the sensor(s) will be acoustically coupled. Th
26、e sensor(s) should be centrally located near theweldment to provide for optimal AE response from all portions of the weld. If the sensor(s) are piezoelectric, this location shouldbe such that the maximum temperature stays substantially below the Curie temperature manufacturers specifications of thes
27、ensor(s). Take care in selecting the sensor mounting locations to avoid contact or disturbance, or both, of the sensor by any ofthe welding or structural positioning equipment. Typical distances from 6 in. 150 to 1 ft (150300 mm 6 to 300 mm)12 in. fromthe heat-affected zone of the weld are usually s
28、atisfactory. Typical fixed sensor placement patterns that have been successfully usedare shown in 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, weldingflux, or other debris, and attach the sensor in accordance with G
29、uide E650.6.1.1.2 If moving sensors are used, clean the coupling path so that uniform sensitivity is maintained as the sensor moves. Fig.4 shows side and top views of a typical configuration for moving sensors.6.1.2 Position and route the signal cables connecting the sensor(s) to the AE instrumentat
30、ion to avoid contacting the hot weldbead or entangling the welding and positioning equipment.6.1.3 Adjustment of Apparatus:6.1.3.1 After all sensors are mounted, connected, and operational (without objectionable background noise), the AE monitoringsystem can then be adjusted using an AE simulator.6.
31、1.3.2 Gain AdjustmentTo set or select the overall gain for a channel (if necessary), locate the acoustic emission simulatorat a selected distance adjacent to the sensor. Monitor the response to the simulated emission, and adjust the overall channel gainto a specified amplitude level. Repeat this pro
32、cedure two times, placing the simulator at the same distance from the sensor but atdifferent azimuthal positions relative to the original simulator positions (see Fig. 5). Record the average gain for the three simulatorFIG. 1 Typical Sensor Placement for Single Channel AEMonitoring of a Linear WeldE
33、749/E749M 122positions. Repeat the entire procedure for each AE sensor on the structure, and adjust the gains. The average gains for all channelsshould give responses to the simulator that have peak voltages identical to within 63 dB.6.1.4 Determination of Source-Location AccuracyCheck the operation
34、 of the AE source-location function by analyzingsimulatedAE signals from several random locations in the weld and on the structure, as well as from any specific critical locations.For each placement of the simulator, determine and record the precision and accuracy of the AE location function. It sho
35、uld beFIG. 2 Typical Sensor Placement for Two-Channel AE Monitoringof a Linear WeldFIG. 3 Typical Sensor Placement for Three-Channel AEMonitoring of a Circular WeldFIG. 4 Moving Sensor Configuration with Sensor Position Fixed Relative to Weld HeadE749/E749M 123noted that the accuracy of locating the
36、 simulator source will not necessarily be the same as for locating a real AE source. Duringtrial welding in multipass configurations, it should be verified that location accuracy is maintained during weld buildup.Experiments indicate that location accuracy depends on the percentage completion of mul
37、tipass welds.6.2 Check the integrity of the welding ground return system to eliminate the possibility of diverting the weld currents to the AEinstrumentation ground.7. Apparatus7.1 The AE apparatus normally consists of sensors, preamplifiers, and electronic instrumentation with display and recording
38、capabilities. Acoustic emission monitoring during welding places many specialized requirements on AE apparatus due to severeenvironmental factors and interfering noise sources. The following criteria provide guidelines to aid in minimizing these interferingfactors, and maximizing the effectiveness o
39、f the monitoring process:7.1.1 Sensors should be used that are capable of operating in the temperature range to be encountered. Use of “high-temperature” sensors or waveguides to isolate conventional sensors may be necessary for multipass, high heat input welds, orwelds maintained at elevated prehea
40、t temperatures. The sensors should be electrically insulated from the structure under test toensure that the weld current or welder ground is not coupled into the AE instrumentation. If the weld current is pulsed or has asignificant transient component, differential sensors may aid in suppressing in
41、terference.7.1.2 Frequency Bandpass Filters are recommended to minimize background noise interference during AE monitoring ofwelding. A low-frequency limit to the passband in the vicinity of 100 kHz will aid in minimizing background noise due tomechanical noise sources such as grinding, chipping, an
42、d manipulation of the structure under test. Radio frequency interferencedue to contactors and heavy electrical machinery, as well as the welding arc, may be minimized by use of a high-frequency limitto the passband ranging from 100 kHz to 1 MHz. The sensor operating frequency range should be compati
43、ble with the aboveconsiderations.7.2 The Welding Arc is a low-level continuous source of AE. To minimize interference from the welding arc, the sensitivity ofthe AE monitoring apparatus should be adjusted so that arc noise is below the trigger threshold. This sensitivity is the maximumusable AE sens
44、itivity for weld monitoring and varies with different welding methods. Table 1 indicates overall gain for a particularsystem monitoring welding methods and using typical commercial piezoelectric transducers. This table is for general guidelinepurposes and not for direct reference.7.3 Single-Channel
45、AE Instrumentation employing a single sensor may provide information on the presence of discontinuitiesin a weld. For low-heat input welds, where the delay time between fusion and AE activity is short, discontinuities may also belocated in the weld by noting the presence of unusualAE activity and re
46、cording the position of the welding head when such activityoccurs. As the weld heat input increases, the delay time between fusion and AE activity usually increases, thus making use ofmultichannel arrival time interval measurements necessary for AE source location.7.4 The AE apparatus should be capa
47、ble of providing output signals that are proportional to overall acoustic activity (such asRMS or Average Signal Level, ASL) and acoustic emission energy or count rate. In addition, AE counts, energy or peak amplitudefor eachAE event plotted versus time is useful forAE monitoring of welds. The latte
48、r are particularly useful for acoustically activeFIG. 5 AE Simulator Positions During Sensor CalibrationTABLE 1 Gain For AE System Utilizing Typical CommerciallyAvailable Piezoelectric Sensors Monitoring Typical Weld MethodsWeld MethodAE System GainRange, dBSubmerged arc (single or tandem wire 800 t
49、o 1000 A) 35 to 45Submerged arc (single wire 400 to 500 A) 45 to 55Submerged arc (single wire 200 to 400 A) 55 to 65Gas shielded metal arc (MIG or short arc 150 to 400 A) 50 to 70Gas shielded tungsten arc (TIG 75 to 250 A) 60 to 80E749/E749M 124weld processes such as submerged-arc welding where the presence of solid flux cracking contributes greatly to the AE activity.Experience has shown that for these types of welds, the AE activity from flaws and from normal slag bead cracking may havesimilar peak amplitudes and energies. To prevent false alarms from acceptable slag
