1、Designation: E2479 11Standard Practice forMeasuring the Ultrasonic Velocity in Polyethylene TankWalls Using Lateral Longitudinal (LCR) Waves1This standard is issued under the fixed designation E2479; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers a procedure for measuring theultrasonic velocities in the outer wal
3、l 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 corrected
4、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 o
5、utersurfaces 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.1.4 The values stated in SI units are to be regarded asstandard. The values g
8、iven in parentheses are mathematicalconversions to inch-pound units that are provided for informa-tion only and are not considered standard.1.5 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 t
9、o establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E494 Practice for Measuring Ultrasonic Velocity in Mate-rialsE543 Specification for Agencies Performing Nondestruc-tive TestingE1316
10、 Terminology for Nondestructive ExaminationsE2373 Practice for Use of the Ultrasonic Time of FlightDiffraction (TOFD) Technique2.2 ASNT Documents:3SNT-TC-1A Recommended Practice for NondestructiveTesting Personnel Qualification and CertificationANSI/ASNT CP-189 ASNT Standard for Qualification andCer
11、tification of Nondestructive Testing Personnel2.3 AIA Document:4AIA/NAS-410 Nondestructive Testing Personnel Certifica-tion and Qualification3. Terminology3.1 DefinitionsFor definitions of terms used in this prac-tice, see Terminology E1316.4. Summary of Practice4.1 The lateral longitudinal wave (he
12、nceforth 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 indications comingthrough the tank wall. The typical setup is shown in Fig. 1where the sending and recei
13、ving transducers are connectedwith a link through a pivot joint. The frequency selected is suchthat the wavelength is short compared to the wall thickness,1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.06
14、 onUltrasonic Method.Current edition approved July 1, 2011. Published July 2011. Last previousedition approved in 2006 as E2479 - 06. DOI: 10.1520/E2479-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of AST
15、MStandards 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.4Available from Aerospace Industries Association of America
16、, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerospace.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.assuring bulk wave velo
17、city. Moreover, since 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. Significance and Use5.1 Me
18、asuring the velocity of ultrasound in materials is aunique method for determining nondestructively the physicalproperties, which can vary due to both manufacturing pro-cesses and environmental attack. Velocity is directly related tothe elastic moduli, which can vary based on environmentalexposure an
19、d manufacturing process, The LCRmethod de-scribed herein is able to measure the velocity between twoadjacent points on a surface and therefore is independent of theconditions on the opposite wall. Applications of the methodbeyond polymer tanks will undoubtedly be developed andexamination may occur i
20、n the production line as well as in thein-service mode.6. Basis of Application6.1 The following items are subject to contractual agree-ment between the parties using or referencing this standard.6.1.1 Personnel QualificationPersonnel performing ex-aminations to this standard shall be qualified in ac
21、cordancewith a nationally or internationally recognized NDT personnelqualification practice or standard such asANSI/ASNT CP-189,SNT-TC-1A, NAS-410, or a similar document and certified bythe employer or certifying agency, as applicable. The exami-nation should be supervised by a person holding Level
22、IIIASNT certification, or equivalent. The practice or standardused and its applicable revision shall be identified in thecontractual agreement between the using parties.6.2 Qualification of Nondestructive AgenciesIf specifiedin the contractual agreement, NDT agencies shall be qualifiedand evaluated
23、as described in E543. The applicable edition ofE543 shall be specified in the contractual agreement.6.3 Practices and TechniquesThe practices and tech-niques to be utilized shall be as specified in the contractualagreement.7. Apparatus7.1 The ultrasonic system to be used in this practice shallinclud
24、e the following:7.1.1 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 requiredfeature is the ability to freeze the signal an
25、d manipulate andzoom the gate so that the appropriate peak 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 exp
26、ected velocity in a referencestandard. Further, the instrument 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 incor
27、porated in a single unit.The receiving amplifier must be capable of displaying at fullscreen height the signals arriving at the receiver search unit forall tank conditions.7.1.2 Search UnitThe dual longitudinal angle beam (LCR)search unit propagates waves across the chord of the tank wall.The LCRwav
28、e is excited at an incident angle slightly past thefirst 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 ma
29、tch with the polyethylene tank wall. Typicaltransducer frequencies 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 bl
30、ock and must be such that the longitudinalFIG. 1 Dual Search Unit Examination Setup Using LCRWaves on Tank WallE2479 112wave travels across 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-
31、nation in moderate and low loss polymers and different tankwall thicknesses.7.1.3 CouplantStandard ultrasonic gel type couplants arepreferred. 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 significa
32、nt residue. Itmust be fully compatible with the polyethylene tank material.7.1.4 ComputerThe computer supporting this examina-tion should 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. I
33、t should be able tocalculate expected velocity at the wall temperature during thetest. The difference between the expected speed for newmaterial at the test temperature and the observed speed is theparameter used to evaluate tank wall condition. Manual dataentry in a spreadsheet must be possible if
34、the computer is notavailable, or its use is inconvenient. The calculations describedabove may be accomplished in the spreadsheet or by handcalculations.7.1.5 Reference BlocksA small section of material is usedfor standardization. This section should be the same typematerial as the tank being examine
35、d, and should be flat.Initially, it should have experienced no significant UV expo-sure and it should be protected from long-term exposure duringits use. First, the search units need to be checked to assure theintegrity of the travel path in the wedge, and that a strong LCRsignal is being generated.
36、 Secondly, the standardization of thezero offset on the ultrasonic unit requires that the arrival timebe adjusted to give an observed velocity equal to the expectedvelocity for the sample being examined. The procedure forstandardization is given in more detail in the following and inAppendix X2.8. P
37、ractice8.1 Standard practice is to take readings at locations ap-proximately 30 cm (1 ft) and 90 cm (3 ft) from the base(bottom) of the tank. These readings should be taken at aminimum of two different N-E-S-W directions on the tank.Their relation to some notable location on the tank, forexample, th
38、e tank manhole, should be recorded since tanksmay be moved and turned during their life. The surface shouldbe clean and not have undue surface fluctuations. The impor-tant thing is that a spot gives good readings and that the samelocation is investigated from year to year. The location shouldbe mark
39、ed on the tank or designated on the record so that futuredata are collected at the same place.8.1.1 For a typical examination, connect the sending trans-ducer to the BNC OUT terminal and the receiving transducer tothe BNC IN terminal.8.1.2 Place a generous amount of couplant on both of thesearch uni
40、t faces (a dollop about 25 mm (1 in.) in diameter). Itis required since there is some initial priming of the surfaceneeded for full transmission into the material. Place the searchunit on the area of the tank to be examined. When looking atthe dual search unit, the two search units should be in acir
41、cumferential arrangement. The dual search unit assembly isspring loaded. Manipulate the search unit assembly until agood signal is visible on the screen. Repeat couplant applica-tion if needed for additional surface priming. Once a goodsignal has been found, the signal should be frozen with theultra
42、sonic unit for further analysis. The gate may be moved tothe appropriate point on the wave as discussed above. The tankwall velocity may then be calculated.8.1.3 For maximum confidence, the practice of full removal,wiping and reapplication of the couplant should be repeatedseveral times at each sear
43、ch unit position. Since there willalways be some scatter in the data, a minimum of three valuesshould be obtained at each location of interest.8.1.4 The LCRwave traversing the chord of the tank wallshould appear as the first arriving signal on the flaw detectorscreen after the initial pulse. A short
44、 gate (time less than onewavelength) is used to identify the arrival time of the LCRwave. Fig. 2 shows a typical signal identified by the gatesetting. Here the cursor is on the first peak of the wave. Theultrasonic unit should be set to display the time associated withFIG. 2 Typical Signal with LCRP
45、eak Located Within the GateE2479 113the zero crossing of the earliest peak in the gate. It is easilydistinguishable from the preceding portions and from thefollowing wave that goes through the interior of the material.Since the refracted beams of the two search units are approxi-mately parallel to t
46、he surface of the tank wall, there is no beamintersection point as defined by Practice E2373.8.1.5 Velocity values based on previously measured tanks inthe field are available as an aid in isolating the LCRwave(Appendix X3). Using the prediction curve based on the yearsof service for the tank being
47、examined can narrow down theapproximate location of the LCRwave arrival.8.1.6 Occasionally, a complex waveform will occur makingthe LCRdifficult to isolate. This is often due to a combinationof conditions such as incomplete contact, high instrument gainused in these lossy materials and the parallel
48、sound paths(crosstalk) that occur in the search units and in the air. In thewave shown in Fig. 3, the LCRwave is less distinguishable.This arrival was taken from the same location as the wave inFig. 2. There appears to be a wave that looks similar to the LCRwave in front of the cursor. This, however
49、, comes from parallelsignal transmission in the higher speed wedge material andshould not be evaluated. In addition, the wave behind the LCRwave is commingled. Without experience and the predictedvelocity table, one could easily take the wrong reading in thiscase.8.1.7 The characteristics to look for in finding the LCRwaves are: a sharply rising peak immediately after a significanttrough and a slight separation between the wave and thefollowing wave. This appearance may depend on the specifictransducer properties. The height of the wave may be similar tothe amplitude of
