1、Designation: E 1211 07Standard Practice forLeak Detection and Location Using Surface-MountedAcoustic Emission Sensors1This standard is issued under the fixed designation E 1211; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the y
2、ear 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 a passive method for detectingand locating the steady state source of gas and liquid l
3、eakingout of a pressurized system. The method employs surface-mounted acoustic emission sensors (for non-contact sensorssee Test Method E 1002), or sensors attached to the system viaacoustic waveguides (for additional information, see Terminol-ogy E 1316), and may be used for continuous in-servicemo
4、nitoring and hydrotest monitoring of piping and pressurevessel systems. High sensitivities may be achieved, althoughthe values obtainable depend on sensor spacing, backgroundnoise level, system pressure, and type of leak.1.2 The values stated in inch-pound units are to be regardedas the standard. SI
5、 units are provided for information only.1.3 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory
6、 limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 543 Specification for Agencies Performing Nondestruc-tive TestingE 650 Guide for Mounting Piezoelectric Acoustic EmissionSensorsE 750 Practice for CharacterizingAcoustic Emission Instru-mentationE 976 Guide for Determining the Re
7、producibility of Acous-tic Emission Sensor ResponseE 1002 Test Method for Leaks Using UltrasonicsE 1316 Terminology for Nondestructive ExaminationsE 2374 Guide for Acoustic Emission System PerformanceVerification2.2 ASNT Documents:3SNT-TC-1A Recommended Practice for NondestructiveTesting Personnel Q
8、ualification and CertificationANSI/ASNT CP-189 Standard for Qualification and Certi-fication of Nondestructive Testing Personnel2.3 AIA Document:NAS 410 Certification and Qualification of NondestructiveTesting Personnel43. Summary of Practice3.1 This practice requires the use of contact sensors, amp
9、li-fier electronics, and equipment to measure their output signallevels. The sensors may be mounted before or during theexamination period and are normally left in place oncemounted rather than being moved from point to point.3.2 Detection of a steady-state leak is based on detection ofthe continuou
10、s, broadband signal generated by the leak flow.Signal detection is accomplished through measurement ofsome input signal level, such as its root-mean-square (RMS)amplitude or average signal level.3.3 The simplest leak test procedure involves only detectionof leaks, treating each sensor channel indivi
11、dually. A morecomplex examination requires processing the signal levelsfrom two or more sensors together to allow computation of theapproximate leak location, based on the principle that the leaksignal amplitude decreases as a function of distance from thesource.4. Significance and Use4.1 Leakage of
12、 gas or liquid from a pressurized system,whether through a crack, orifice, seal break, or other opening,may involve turbulent or cavitational flow, which generatesacoustic energy in both the external atmosphere and the systempressure boundary. Acoustic energy transmitted through thepressure boundary
13、 can be detected at a distance by using asuitable acoustic emission sensor.4.2 With proper selection of frequency passband, sensitivityto leak signals can be maximized by eliminating background1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct
14、 responsibility of Subcommittee E07.04 onAcoustic Emission Method.Current edition approved July 1, 2007. Published July 2007. Originally approvedin 1987. Last previous edition approved in 2002 as E 1211 - 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Custome
15、r Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4Availa
16、ble from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerospace.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.noise. At low frequencies, generally
17、below 100 kHz, it ispossible for a leak to excite mechanical resonances within thestructure that may enhance the acoustic signals used to detectleakage.4.3 This practice is not intended to provide a quantitativemeasure of leak rates.5. Basis of Application5.1 The following items are subject to contr
18、actual agree-ment between parties using or referencing this practice.5.2 Personnel Qualification5.2.1 If specified in the contractual agreement, personnelperforming examinations to this practice shall be qualified inaccordance with a nationally or internationally recognizedNDT personnel qualificatio
19、n 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 Qualific
20、ation 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 Timing of ExaminationThe timing of examinationshall be in
21、accordance with 7.1.7 unless otherwise specified.5.5 Extent of ExaminationThe extent of examination shallbe in accordance with 7.1.4 and 10.1.1.1 unless otherwisespecified.5.6 Reporting Criteria/Acceptance CriteriaReporting cri-teria for the examination results shall be in accordance with10.2.2 and
22、Section 11 unless otherwise specified. Since accep-tance criteria are not specified in this practice, they shall bespecified in the contractual agreement.5.7 Reexamination of Repaired/Reworked ItemsReexamination of repaired/reworked items is not addressed inthis practice and if required shall be spe
23、cified in the contractualagreement.6. Interferences6.1 External or internal noise sources can affect the sensi-tivity of an acoustic emission leak detection system. Examplesof interfering noise sources are:6.1.1 Turbulent flow or cavitation of the internal fluid,6.1.2 Noise from grinding or machinin
24、g on the system,6.1.3 Airborne acoustic noise, in the frequency range of themeasuring system,6.1.4 Metal impacts against, or loose parts frequently strik-ing the pressure boundary, and6.1.5 Electrical noise pick-up by the sensor channels.6.2 Stability or constancy of background noise can alsoaffect
25、the maximum allowable sensitivity, since fluctuation inbackground noise determines the smallest change in level thatcan be detected.6.3 The acoustic emission sensors must have stable charac-teristics over time and as a function of both the monitoringstructure and the instrumentation system examinati
26、on param-eters, such as temperature.6.4 Improper sensor mounting, electronic signal conditionernoise, or improper amplifier gain levels can decrease sensitiv-ity.7. Basic Information7.1 The following items must be considered in preparationand planning for monitoring:7.1.1 Known existing leaks and th
27、eir distance from the areasto be monitored should be noted so that their influence on thecapabilities of the method can be evaluated.7.1.2 Type of vessel, pipeline, or installation to be exam-ined, together with assembly, or layout drawings, or both,giving sufficient detail to establish dimensions,
28、changes ofshape likely to affect flow characteristics, positions of welds,and the location of components such as valves or flanges, andattachments to the vessel or pipe such as pipe hangers whereleaks are most likely to arise. Regions with restricted accessi-bility due to walls, the existence or loc
29、ation of cladding,insulation, or below surface components must be specified.7.1.3 When location of the peak is of primary interest,quantitative information regarding the leakage rates of interestand whenever possible the type of leak is necessary.7.1.4 Extent of monitoring, for example, entire volum
30、e ofpressure boundary, weld areas only, etc.7.1.5 Material specifications and type of surface covering(for example paint or other coating) to allow the acousticpropagation characteristics of the structure to be evaluated.7.1.6 Proposed program of pressure application or process-pressure schedule, sp
31、ecifying the pressurization schedule to-gether with a layout or sketch of the pressure-applicationsystem and specifying the type of fluid used during theexamination, for example, gas, water, or oil.7.1.7 Time of monitoring, that is, the point(s) in the manu-facturing process, or service life at whic
32、h the system will bemonitored, or both.7.1.8 Frequency range to be used in the monitoring equip-ment.7.1.9 Environmental conditions during examination thatmay affect instrumentation and interpretation of results; forexample, temperature, moisture, radioactivity, vibration, pres-sure, and electromagn
33、etic interference.7.1.10 Limitations or restrictions on the sensor mountingprocedure, if applicable, including restrictions on couplantmaterials.7.1.11 The location of sensors or waveguides and prepara-tion for their installation to provide adequate coverage of theareas specified in 7.1.3. Where par
34、ticular sections are to beexamined with particular sensors, the coverage of the vessel orsystem by sensor subgroups shall be specified. The sensorlocations must be given as soon as possible, to allow position-ing difficulties to be identified.7.1.12 The communications procedure between the acoustice
35、mission staff and the control staff, the time intervals at whichpressure readings are to be taken, and the procedure for givingwarning of unexpected variations in the pressure system.7.1.13 Requirements for permanent records, if applicable.7.1.14 Content and format of examination report, if re-quire
36、d.E12110727.1.15 Acoustic Emission Examiner qualifications and cer-tification, if required.8. Apparatus8.1 SensorsThe acoustic emission sensors are generallypiezoelectric devices and should be mounted in accordancewith Practice E 650 to ensure proper signal coupling. Thefrequency range of the sensor
37、s may be as high as 1 MHz, andeither wideband or resonant sensors may be employed. Thehigher frequencies can be used to achieve greater discrimina-tion against airborne or mechanical background noise.8.2 AmplifiersAmplifiers/preamplifiers should have suffi-cient gain to allow the signal processing e
38、quipment to detectthe level of acoustic background noise on the pressurizedsystem. The sensor/amplifier bandwidth should be selected tominimize background noise.8.3 Signal ProcessorThe signal processor measures theRMS level, the acoustic emission signal power, the averagesignal level, or any other s
39、imilar parameters of the continuoussignal. A leak location processor to compute the sourcelocation from signal levels and attenuation data may beincluded. Alarm setpoints may also be included as a processorfunction.8.4 Leak Signal Simulator:8.4.1 A device for simulating leaks should be included toev
40、aluate the effectiveness of the monitoring system. Thefollowing could be considered: a sensor on the pressureboundary driven from a random-noise generator, a small waterjet, or a gas jet.8.4.2 When leak location processing is to be performed,leak simulation should be carried out initially over a suf
41、fi-ciently large number of diverse points to verify proper opera-tion of the location algorithm.9. System Performance Verification9.1 System performance verification consists of two stages.The first stage concerns periodic calibration and verification ofthe equipment under laboratory conditions. Thi
42、s procedure isbeyond the scope of this practice (see Practice E 750) but theresults must be made available to the system owners ifrequested. The second stage concerns in-situ verification tocheck the sensitivities of all channels and the satisfactoryoperation of the detection equipment. For every ve
43、rificationoperation, a written procedure shall be prepared.9.2 In-situ sensitivity check of all sensors should be per-formed by placing a leak signal simulator (see Guide E 976)ata specified distance from each sensor and recording theresulting output level from the amplifier, as referred to theampli
44、fier input terminal. Amplifier gains may also be adjustedas appropriate to correct for sensitivity variations.9.3 Periodic system verification checks shall be made priorto the examination and during long examinations (days) or ifany environmental changes occur. The relative verificationcheck is acco
45、mplished by driving various sensors or activatingvarious leak simulation devices such as water or gas jets (seeGuide E 2374) and measuring the outputs of the receivingsensors. The ratio of the outputs of two receiving sensors for agiven injection point should remain constant over time. Anychange in
46、the ratio indicates a deviation in performance. In thisway, all sensors on a system may be compared to one or severalreference signals and proper adjustments made (see GuideE 976).9.4 When leak location calculations are to be performed, theacoustic attenuation between sensors should be characterized
47、over the frequency band of interest, especially if the presenceof discontinuities, such as pipe joints, may be suspected toaffect the uniformity of attenuation. The measurements shouldthen be factored into the source location algorithm.10. Procedure10.1 Pre-Examination Requirements:10.1.1 Before beg
48、inning the acoustic emission monitoring,ensure that the following requirements are met:10.1.1.1 Evaluate attenuation effects, that is, the change insignal amplitude with sound-propagation distance, so as todefine the effective area covered by each individual sensor; andin the case of sensor sub-grou
49、ps, the maximum distancebetween sensing points.10.1.1.2 Ensure that sensors are placed at the predeterminedpositions. If it is necessary to modify these positions duringinstallation, record the new sensor locations. Record themethod of attachment of the sensors and the couplant used.10.1.1.3 Review the operating schedule to identify all po-tential sources of extraneous acoustic noise such as nozzle-plugmovement, pump vibration, valve stroking, personnel move-ment, fluid flow, and turbulence. Such sources may requireacoustic isolation or control so that they will not mask relev
