1、Designation: E 1139 02Standard Practice forContinuous Monitoring of Acoustic Emission from MetalPressure Boundaries1This standard is issued under the fixed designation E 1139; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r 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 provides guidelines for continuous moni-toring of acoustic emission (AE) from metal pressure bound
3、-aries in industrial systems during operation. Examples arepressure vessels, piping, and other system components whichserve to contain system pressure. Pressure boundaries otherthan metal, such as composites, are specifically not covered bythis document.1.2 The functions of AE monitoring are to dete
4、ct, locate,and characterize AE sources to provide data to evaluate theirsignificance relative to pressure boundary integrity. Thesesources are those activated during system operation, that is, nospecial stimulus is applied to produce AE. Other methods ofnondestructive testing (NDT) may be used, when
5、 the pressureboundary is accessible, to further evaluate or substantiate thesignificance of detected AE sources.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 saf
6、ety and health practices and determine the applica-bility of regulatory limitations prior to use. For specificprecautionary statements, see Section 6.2. Referenced Documents2.1 ASTM Standards:E 543 Practice for Evaluating Agencies that Perform Non-destructive Testing2E 569 Practice for Acoustic Emis
7、sion Monitoring of Struc-tures During Controlled Stimulation2E 650 Guide for Mounting Piezoelectric Acoustic EmissionSensors2E 750 Practice for Characterizing Acoustic Emission Instru-mentation2E 976 Guide for Determining the Reproducibility of Acous-tic Emission Sensor Response2E 1316 Terminology f
8、or Nondestructive Examinations22.2 Aerospace Industries AssociationNAS-410 Certification and Qualification of NondestructiveTesting Personnel2.3 Other Documents:SNT-TC-1A Recommended Practice for NondestructiveTesting Personnel Qualification and Certification3ANSI/ASNT CP-189 ASNT Standard for Quali
9、fication andCertification of Nondestructive Testing Personnel33. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this practice, refer toTerminology E 1316.3.2 Definitions of Terms Specific to This Standard:3.2.1 continuous monitoringthe process of monitoring apressure boundary cont
10、inuously to detect acoustic emissionduring system operation and also during system shut-downtesting such as hydrostatic testing.3.2.2 raw datadata values determined directly from mea-surement of analog inputs. These could include emission countor emission event count, or both, relative time of signa
11、l arrivalat different sensors (delta time), signal rise time, peak signalamplitude, RMS signal level, pressure system pressure andtemperature, and the like.3.2.3 processed datadata resulting from analysis of rawdata. Included would be AE source location coordinates, AEversus time from a given source
12、 area, AE signal amplitudeversus time, and the like.4. Summary of Practice4.1 This practice describes the use of a passive monitoringsystem to detect, locate, and characterize AE sources, in orderto evaluate their significance to the integrity of metal pressureboundaries.4.2 The practice provides gu
13、idelines for selection, qualifi-cation, verification, and installation of the AE monitoringsystem. Qualification of personnel is also addressed.4.3 The practice provides guidelines for using the AEinformation to estimate the significance of a detected AEsource with respect to continued pressure syst
14、em operation.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.Current edition approved June 10, 2002. Published August 2002. Originallypublished as E 1139 87. Last previous edition E
15、1139 97.2Annual Book of ASTM Standards, Vol 03.03.3Available from American Society for Nondestructive Testing, 1711 ArlingatePlaza, PO Box 28518, Columbus, Ohio 43228-0518.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Significan
16、ce and Use5.1 Acoustic emission examination of a structure requiresapplication of a mechanical or thermal stimulus. In this case,the system operating conditions provide the stimulation. Dur-ing operation of the pressurized system, AE from activediscontinuities such as cracks or from other acoustic s
17、ourcessuch as leakage of high-pressure, high-temperature fluids canbe detected by an instrumentation system using sensorsmounted on the structure. The sensors are acoustically coupledto the surface of the structure by means of a couplant materialor pressure on the interface between the sensing devic
18、e and thestructure. This facilitates the transmission of acoustic energy tothe sensor. When the sensors are excited by acoustic emissionenergy, they transform the mechanical excitations into electri-cal signals. The signals from a detected AE source areelectronically conditioned and processed to pro
19、duce informa-tion relative to source location and other parameters needed forAE source characterization and evaluation.5.2 AE monitoring on a continuous basis is a currentlyavailable method for continuous surveillance of a structure toassess its continued integrity. The use of AE monitoring in thisc
20、ontext is to identify the existence and location of AE sources.Also, information is provided to facilitate estimating thesignificance of the detected AE source relative to continuedpressure system operation.5.3 In addition to immediate evaluation of the AE sources,a permanent record of the total dat
21、a collected (AE plus pressuresystem parameters measured) provides an archival recordwhich can be re-evaluated.6. Hazards6.1 WarningApplication of this practice will inherentlyinvolve work in an operating plant. This may involve potentialexposure to hazardous materials and equipment and, in the caseo
22、f nuclear power plants, exposure to nuclear radiation. Awritten safety plan shall be prepared for each monitoringinstallation which defines requirements to be observed toprotect personnel safety, safety of the plant system, and to meetadministrative and legal needs. This plan shall be approved byall
23、 parties prior to start of work on the plant.7. Basis of Application7.1 Personnel Qualification7.1.1 If specified in the contractual agreement, personnelperforming examinations to this standard shall be qualified inaccordance with a nationally recognized NDT personnel quali-fication practice or stan
24、dard such as ANSI/ASNT-CP-189,SNT-TC-1A, NAS-410, or a similar document and certified bythe employer or certifying agency, as applicable. The practiceor standard used and its applicable revision shall be identifiedin the contractual agreement between the using parties.7.2 Qualification of Nondestruc
25、tive Agencies7.2.1 If specified in the contractual agreement, NDT agen-cies shall be qualified and evaluated as described in PracticeE 543. The applicable edition of Practice E 543 shall bespecified in the contractual agreement.7.3 Timing of Examination7.3.1 The timing of examination shall be contin
26、uous, inaccordance with 1.1 unless otherwise specified.7.4 Extent of Examination7.4.1 The extent of examination shall be that part of thepressure boundary in the coverage range of the mountedacoustic emission sensors, unless otherwise specified.7.5 Reporting Criteria/Acceptance Criteria7.5.1 Reporti
27、ng criteria for the examination results shall bein accordance with Section 15 unless otherwise specified.Since acceptance criteria (for example, for reference radio-graphs) are not specified in this standard, they shall bespecified in the contractual agreement.7.6 Reexamination of Repaired/Reworked
28、Items7.6.1 Reexamination of repaired/reworked items is not ad-dressed in this standard and if required shall be specified in thecontractual agreement.7.7 Routine operation of the acoustic emission system forcollection and interpretation of the data may be performed bya competent plant engineer not n
29、ecessarily specialized inacoustic emission. However, acoustic emission system opera-tion and data interpretation should be verified by a qualifiedacoustic emission specialist on approximately six-month inter-vals or sooner if the system appears to be malfunctioning or thedata appear unusual.8. Monit
30、oring System Functional Requirements andQualification8.1 Functional Requirements:8.1.1 The monitoring system must include the functionalcapabilities shown in Fig. 1 which also shows a suggestedsequence of monitoring system functions.8.1.2 Signal DetectionThe AE sensor together with theacoustic coupl
31、ing to the structure must have sensitivity suffi-cient to detect AE signals while the pressure system isoperating. In most cases, this determination must be performedwhen the pressure system is not operating. AE system responseto normal operational noise, which must be considered here, isdiscussed i
32、n 9.1. One method of performing the requiredevaluation is to use a pencil lead break as a signal source. WithFIG. 1 Functional Flow DiagramContinuous AE MonitoringSystemE1139022the sensor in place and connected to the amplifier(s), theresponse at the amplifier output to fracturing a 0.3-mm pencillea
33、d against the surface being monitored, at a distance of 150to 300 mm (6 to 12 in.) from the sensor should show aminimum signal-to-noise (electronic plus process noise) ratioof 4 to 1 in a frequency range suitable for the plannedmonitoring environment. A differential sensor should be con-sidered to m
34、inimize interference from electronic transients.The sensor must be capable of withstanding the monitoringenvironment (temperature, moisture, nuclear radiation, me-chanical vibration, and the like) for an extended period ofcontinuous exposure. The minimum length of this period willbe dictated by acce
35、ssibility to the location to change sensors,and by economic considerations.8.1.3 Signal AmplificationA total signal amplification of80 to 90 dB is usually required to achieve an adequate AEsignal level for measurement of signal parameters. Due to thevery small magnitude of energy involved in an AE s
36、ource, it isdesirable to locate the first stage of signal amplification as nearas possible to the output of the sensor. This is beneficial incontrolling noise interference and AE signal transmission loss.The amplifiers must have low inherent electronic backgroundnoise. This should not exceed 20 V pe
37、ak (Note 1) referred tothe input. Resistance of the amplifier circuits to the environ-ment (temperature, moisture, nuclear radiation, mechanicalvibration, and the like) must be considered and appropriatesteps taken to protect them.NOTE 1When used herein, peak means zero to peak voltage.8.1.4 Monitor
38、ing Frequency BandThe frequency re-sponse of the sensor or amplifier combination must be selectedfor the given application. The AE signal being a transient pulseis detectable over a broad range of frequencies. Because theacoustic attenuation in engineering materials is frequencydependent, it is desi
39、rable to use a low monitoring frequency(50 to 100 kHz) to maximize the distance from the AE sourceover which the AE event can be detected. The low end of themonitoring frequency will usually be controlled by the back-ground noise present in the monitoring environment. In someapplications such as ope
40、rating nuclear reactors, the backgroundnoise may require a low frequency cut-off point of 400 to 500kHz. In cases of severe continuous background noise, inductivetuning of the sensor at the preamplifier input may be effective.The high end of the frequency response band may be limited to1.0 MHz to he
41、lp reduce amplifier electronic noise.8.1.5 Signal Measurement:8.1.5.1 The signal measurement section will receive thefully-amplified analog signal. Generally its operation will becontrolled by a voltage threshold circuit which will limitaccepted data to that exceeding the voltage amplitude thresh-ol
42、d. AE parameters measured may include AE count, AE eventcount, signal amplitude, time from threshold crossing to signalpeak, signal duration, difference in time of signal arrival atvarious sensors making up a source location array, clock time,data, and the value of any process system parameters (tem
43、-perature, pressure, strain, and the like) available to the AEmonitoring system. If the AE monitoring system is to performdetection of pressure system leaks, it must measure the averagesignal level or AE rms voltage for each sensing channel.8.1.5.2 It is desirable that the signal measurements includ
44、e afunction to assess the characteristics of an acoustic emissionsignal to determine if it matches those originating from crackgrowth. The function should provide a “flag” for those signalswhich have characteristics similar to those known to originatefrom crack growth as determined by an AE speciali
45、st.8.1.5.3 The output from the signal measurement subsystemshould be in digital form to facilitate storage of large quantitiesof data.8.1.6 Raw Data StorageThe AE monitoring system mustinclude a raw digital data storage feature to facilitate retentionof the output from the signal measurement subsyst
46、em. Thisserves as a backup in the event that the data analysis processmalfunctions, for example, incorrect operation of the dataanalyzer or loss of power which might destroy data in acomputer memory. The raw data storage device must becompact with a high capacity and be nonvolatile. The dataretentio
47、n period will be governed by the operating character-istics of the pressure system and by plant procedures. Thestorage device should include provision to play back therecorded information directly to the data analysis subsystem orto a peripheral computer.8.1.7 Data Analysis:8.1.7.1 One of the major
48、functions of the data analysissection is to determine the source of AE signals. There are twoprimary methods used to locate discrete AE signals:(a) Calculate the source point using the difference in timeof signal arrival at the sensors (Dt) in a given source locationarray.(b) Utilize the Dt informat
49、ion to enter a “look-up” tablewhich will define an area including the specific Dt location.Either approach is acceptable. The “look-up” table area reso-lution must be examined in light of the accuracy requirementsof the application. Neither approach can be expected to yieldlocation accuracies closer than 6 one wall thickness of thepressure system component being monitored.8.1.7.2 A third method used largely for processing “continu-ous” signals produced by a pressure system leak to approxi-mate the source of AE is to compare the amplitude of responsefrom various sensors. Thi
