ASTM E2479-2006 Standard Practice for Measuring the Ultrasonic Velocity in Polyethylene Tank Walls Using Lateral Longitudinal (LCR) Waves《利用侧向纵波(L)测定聚乙烯容器壁中超声波速度的标准实施规程》.pdf
《ASTM E2479-2006 Standard Practice for Measuring the Ultrasonic Velocity in Polyethylene Tank Walls Using Lateral Longitudinal (LCR) Waves《利用侧向纵波(L)测定聚乙烯容器壁中超声波速度的标准实施规程》.pdf》由会员分享,可在线阅读,更多相关《ASTM E2479-2006 Standard Practice for Measuring the Ultrasonic Velocity in Polyethylene Tank Walls Using Lateral Longitudinal (LCR) Waves《利用侧向纵波(L)测定聚乙烯容器壁中超声波速度的标准实施规程》.pdf(7页珍藏版)》请在麦多课文档分享上搜索。
1、Designation: E 2479 06Standard Practice forMeasuring the Ultrasonic Velocity in Polyethylene TankWalls Using Lateral Longitudinal (LCR) Waves1This standard is issued under the fixed designation E 2479; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、 case of revision, the year 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 covers a procedure for measuring theultrasonic velocities in the outer w
3、all of polyethylene storagetanks.An angle beam lateral longitudinal (LCR) wave is excitedwith wedges along a circumferential chord of the tank wall. Adigital ultrasonic flaw detector is used with sending-receivingsearch units in through transmission mode. The observedvelocity is temperature correcte
4、d and compared to the expectedvelocity for a new, unexposed sample of material which is thesame as the material being evaluated. The difference betweenthe observed and temperature corrected velocities determinesthe degree of UV exposure of the tank.1.2 The practice is intended for application to the
5、 outersurfaces of the wall of polyethylene tanks. Degradation typi-cally occurs in an outer layer approximately 3.2-mm 0.125-in. thick. Since the technique does not interrogate the insidewall of the tank, wall thickness is not a consideration other thanto be aware of possible guided (Lamb) wave effe
6、cts orreflections off of the inner tank wall. No special surfacepreparation is necessary beyond wiping the area with a cleanrag. Inside wall properties are not important since the longitu-dinal wave does not strike this surface. The excitation of Lambwaves must be avoided by choosing an excitation f
7、requencysuch that the ratio of wavelength to wall thickness is one fifthor less.1.3 UV degradation on the outer surface causes a stiffeningof the material and an increase in Youngs modulus and thelongitudinal wave velocity.2. Referenced Documents2.1 ASTM Standards:2E 494 Practice for Measuring Ultra
8、sonic Velocity in Mate-rialsE 543 Specification for Agencies Performing Nondestruc-tive TestingE 1316 Terminology for Nondestructive ExaminationsE 2373 Practice for Use of the Ultrasonic Time of FlightDiffraction (TOFD) Technique2.2 ASNT Documents:3SNT-TC-1A Recommended Practice for NondestructiveTe
9、sting Personnel Qualification and CertificationANSI/ASNT CP-189 ASNT Standard for Qualification andCertification of Nondestructive Testing Personnel2.3 AIA Document:4NAS-410 Certification and Qualification of NondestructiveTesting Personnel3. Terminology3.1 DefinitionsFor definitions of terms used i
10、n this prac-tice, see Terminology E 1316.4. Summary of Practice4.1 The lateral longitudinal wave (henceforth called the LCRwave) used in this practice is selected because it is the fastestwave in the tank wall, and, therefore its arrival at the receiverlocation is free from surrounding spurious indi
11、cations comingthrough the tank wall. The typical setup is shown in Fig. 1where the sending and receiving transducers are connectedwith a link through a pivot joint. The frequency selected is suchthat the wavelength is short compared to the wall thickness,assuring bulk wave velocity. Moreover, since
12、it is a bulk wavethe propagation is not affected by variations in the inside tankwall. Therefore, the velocity measured in the outer tank wall isindicative of the material properties of that region, and notaffected by the inner tank wall conditions.5. Apparatus5.1 The ultrasonic system to be used in
13、 this practice shallinclude the following:5.1.1 Test InstrumentAn ultrasonic instrument comprisinga time base, pulser and receiver and A-scan display showingfull wave (RF) signals with gates such that arrival times can bedetermined with a resolution of 10 ns or better. A required1This practice is un
14、der the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.06 onUltrasonic Method.Current edition approved Feb. 15, 2006. Published March 2006.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
15、 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 43228-0518.4Available from Aerospace In
16、dustries Association of America, Inc. (AIA), 1250Eye St., NW, Washington, DC 20005.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.feature is the ability to freeze the signal and manipulate andzoom the gate so that the appropriate pe
17、ak or zero crossing maybe identified with satisfactory resolution. The proper arrivaltime is either the first significant peak or the preceding positive(upward) zero crossing. Zero offset is used to standardize theobserved velocity with the expected velocity in a referencestandard. Further, the inst
18、rument must be capable of commu-nicating with a laptop computer or other digital signal-processing device and sending arrival waveforms as well asother pertinent data for processing and storage. The ultrasonicand computer functions may be incorporated in a single unit.The receiving amplifier must be
19、 capable of displaying at fullscreen height the signals arriving at the receiver search unit forall tank conditions.5.1.2 Search UnitThe dual longitudinal angle beam (LCR)search unit propagates waves across the chord of the tank wall.The LCRwave is excited at an incident angle slightly past thefirst
20、 critical angle. A typical transducer has a 25-mm 1-in.diameter element, with low damping and narrow bandwidth inorder to maximize the signal strength. The wedge has a lowspeed material column for energy transmission to provide aSnells law match with the polyethylene tank wall. Typicaltransducer fre
21、quencies range from 0.5 MHz to 2.25 MHz, Thefrequency must be high enough to assure that no Lamb wavesare excited in the tank wall. Search unit separation must begreater than the near field estimated experimentally using thestandardization block and must be such that the longitudinalwave travels acr
22、oss the chord of the tank wall and does notstrike the inside wall. A typical distance is 47 mm 1.85 in.,but may be adjusted to other spacing to accommodate exami-nation in moderate and low loss polymers and different tankwall thicknesses.5.1.3 CouplantStandard ultrasonic gel type couplants areprefer
23、red. The couplant must adhere to the sidewall of the tankand not run off, yet it must be easily wiped off when theexaminations are completed, leaving no significant residue. Itmust be fully compatible with the polyethylene tank material.5.1.4 ComputerThe computer supporting this examina-tion should
24、be able to store full site and tank detail information.Further, it should be able to calculate the true travel path basedon probe separation and tank curvature. It should be able tocalculate expected velocity at the wall temperature during thetest. The difference between the expected speed for newma
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