1、Designation: E2479 11E2479 16Standard 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,
2、in the case 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 the ultrasonic velocities in the
3、outer wall of polyethylene storage tanks. Anangle beam lateral longitudinal (LCR) wave is excited with wedges along a circumferential chord of the tank wall. A digitalultrasonic flaw detector is used with sending-receiving search units in through transmission mode. The observed velocity istemperatur
4、e corrected and compared to the expected velocity for a new, unexposed sample of material which is the same as thematerial being evaluated. The difference between the observed and temperature corrected velocities determines the degree of UVexposure of the tank.1.2 The practice is intended for applic
5、ation to the outer surfaces of the wall of polyethylene tanks. Degradation typically occursin an outer layer approximately 3.2-mm (0.125-in.) 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 than to be aware of
6、 possible guided (Lamb) wave effects or reflectionsoff of the inner tank wall. No special surface preparation is necessary beyond wiping the area with a clean rag. Inside wallproperties are not important since the longitudinal wave does not strike this surface.The excitation of Lamb waves must be av
7、oidedby choosing an excitation frequency such that the ratio of wavelength to wall thickness is one fifth or less.1.3 UV degradation on the outer surface causes a stiffening of the material and an increase in Youngs modulus and thelongitudinal wave velocity.1.4 The values stated in SI units are to b
8、e regarded as standard. The values given in parentheses are mathematical conversionsto inch-pound units that are provided for information only and are not considered standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsi
9、bilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E494 Practice for Measuring Ultrasonic Velocity in MaterialsE543 Specification for Agencies Perform
10、ing Nondestructive TestingE1316 Terminology for Nondestructive ExaminationsE2373 Practice for Use of the Ultrasonic Time of Flight Diffraction (TOFD) Technique2.2 ASNT Documents:3SNT-TC-1A Recommended Practice for Nondestructive Testing Personnel Qualification and CertificationANSI/ASNT CP-189 ASNT
11、Standard for Qualification and Certification of Nondestructive Testing Personnel2.3 AIA Document:4AIA/NAS-410 Nondestructive Testing Personnel Certification and Qualification2.4 ISO Standard5ISO 9712 Non-Destructive TestingQualification and Certification of NDT Personnel1 This practice is under the
12、jurisdiction ofASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.06 on Ultrasonic Method.Current edition approved July 1, 2011June 1, 2016. Published July 2011June 2016. Originally approved in 2006. Last previous edition approved in 20062011 asE2479 -
13、06.E2479 - 11. DOI: 10.1520/E2479-11.10.1520/E2479-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Avail
14、able from American Society for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4 Available from Aerospace Industries Association of America, Inc. (AIA), 1000 Wilson Blvd., Suite 1700, Arlington, VA 22209-3928, http:/www.aia-aerospace.org
15、.5 Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,Switzerland, http:/www.iso.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indicati
16、on of what changes have been made to the previous version. 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 consi
17、dered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 DefinitionsFor definitions of terms used in this practice, see Terminology
18、E1316.4. Summary of Practice4.1 The lateral longitudinal wave (henceforth called the LCR wave) used in this practice is selected because it is the fastest wavein the tank wall, and, therefore its arrival at the receiver location is free from surrounding spurious indications coming through thetank wa
19、ll. The typical setup is shown in Fig. 1 where the sending and receiving transducers are connected with a link through apivot joint.The frequency selected is such that the wavelength is short compared to the wall thickness, assuring bulk wave velocity.Moreover, since it is a bulk wave the propagatio
20、n is not affected by variations in the inside tank wall. Therefore, the velocitymeasured in the outer tank wall is indicative of the material properties of that region, and not affected by the inner tank wallconditions.5. Significance and Use5.1 Measuring the velocity of ultrasound in materials is a
21、 unique method for determining nondestructively the physicalproperties, which can vary due to both manufacturing processes and environmental attack. Velocity is directly related to the elasticmoduli, which can vary based on environmental exposure and manufacturing process, The LCR method described h
22、erein is ableto measure the velocity between two adjacent points on a surface and therefore is independent of the conditions on the oppositewall. Applications of the method beyond polymer tanks will undoubtedly be developed and examination may occur in theproduction line as well as in the in-service
23、 mode.6. Basis of Application6.1 The following items are subject to contractual agreement between the parties using or referencing this standard.6.1.1 Personnel QualificationPersonnel performing examinations to this standard shall be qualified in accordance with anationally or internationally recogn
24、ized NDT personnel qualification practice or standard such as ANSI/ASNT CP-189,SNT-TC-1A, ISO 9712, NAS-410, or a similar document and certified by the employer or certifying agency, as applicable. Theexamination should be supervised by a person holding Level III ASNT certification, or equivalent. T
25、he practice or standard usedand its applicable revision shall be identified in the contractual agreement between the using parties.6.2 Qualification of Nondestructive AgenciesIf specified in the contractual agreement, NDT agencies shall be qualified andevaluated as described in E543. The applicable
26、edition of E543 shall be specified in the contractual agreement.6.3 Practices and TechniquesThe practices and techniques to be utilized shall be as specified in the contractual agreement.7. Apparatus7.1 The ultrasonic system to be used in this practice shall include the following:7.1.1 Test Instrume
27、ntAn ultrasonic instrument comprising a time base, pulser and receiver and A-scan display showing fullwave (RF) signals with gates such that arrival times can be determined with a resolution of 10 ns or better. A required feature isthe ability to freeze the signal and manipulate and zoom the gate so
28、 that the appropriate peak or zero crossing may be identifiedwith satisfactory resolution. The proper arrival time is either the first significant peak or the preceding positive (upward) zerocrossing. Zero offset is used to standardize the observed velocity with the expected velocity in a reference
29、standard. Further, theinstrument must be capable of communicating with a laptop computer or other digital signal-processing device and sending arrivalFIG. 1 Dual Search Unit Examination Setup Using LCR Waves on Tank WallE2479 162waveforms as well as other pertinent data for processing and storage. T
30、he ultrasonic and computer functions may be incorporatedin a single unit.The receiving amplifier must be capable of displaying at full screen height the signals arriving at the receiver searchunit for all tank conditions.7.1.2 Search UnitThe dual longitudinal angle beam (LCR) search unit propagates
31、waves across the chord of the tank wall. TheLCR wave is excited at an incident angle slightly past the first critical angle. A typical transducer has a 25-mm (1-in.) diameterelement, with low damping and narrow bandwidth in order to maximize the signal strength. The wedge has a low speed materialcol
32、umn for energy transmission to provide a Snells law match with the polyethylene tank wall. Typical transducer frequenciesrange from 0.5 MHz to 2.25 MHz, The frequency must be high enough to assure that no Lamb waves are excited in the tank wall.Search unit separation must be greater than the near fi
33、eld estimated experimentally using the standardization block and must besuch that the longitudinal wave travels across the chord of the tank wall and does not strike the inside wall. A typical distance is47 mm (1.85 in.), but may be adjusted to other spacing to accommodate examination in moderate an
34、d low loss polymers anddifferent tank wall thicknesses.7.1.3 CouplantStandard ultrasonic gel type couplants are preferred. The couplant must adhere to the sidewall of the tank andnot run off, yet it must be easily wiped off when the examinations are completed, leaving no significant residue. It must
35、 be fullycompatible with the polyethylene tank material.7.1.4 ComputerThe computer supporting this examination should be able to store full site and tank detail information. Further,it should be able to calculate the true travel path based on probe separation and tank curvature. It should be able to
36、 calculateexpected velocity at the wall temperature during the test. The difference between the expected speed for new material at the testtemperature and the observed speed is the parameter used to evaluate tank wall condition. Manual data entry in a spreadsheet mustbe possible if the computer is n
37、ot available, or its use is inconvenient. The calculations described above may be accomplished inthe spreadsheet or by hand calculations.7.1.5 Reference BlocksA small section of material is used for standardization. This section should be the same type materialas the tank being examined, and should
38、be flat. Initially, it should have experienced no significant UV exposure and it should beprotected from long-term exposure during its use. First, the search units need to be checked to assure the integrity of the travelpath in the wedge, and that a strong LCR signal is being generated. Secondly, th
39、e standardization of the zero offset on the ultrasonicunit requires that the arrival time be adjusted to give an observed velocity equal to the expected velocity for the sample beingexamined. The procedure for standardization is given in more detail in the following and in Appendix X2.8. Practice8.1
40、 Standard practice is to take readings at locations approximately 30 cm (1 ft) and 90 cm (3 ft) from the base (bottom) of thetank. These readings should be taken at a minimum of two different N-E-S-W directions on the tank. Their relation to some notablelocation on the tank, for example, the tank ma
41、nhole, should be recorded since tanks may be moved and turned during their life.The surface should be clean and not have undue surface fluctuations. The important thing is that a spot gives good readings andthat the same location is investigated from year to year. The location should be marked on th
42、e tank or designated on the recordso that future data are collected at the same place.8.1.1 For a typical examination, connect the sending transducer to the BNC OUT terminal and the receiving transducer to theBNC IN terminal.8.1.2 Place a generous amount of couplant on both of the search unit faces
43、(a dollop about 25 mm (1 in.) in diameter). It isrequired since there is some initial priming of the surface needed for full transmission into the material. Place the search unit onthe area of the tank to be examined. When looking at the dual search unit, the two search units should be in a circumfe
44、rentialarrangement. The dual search unit assembly is spring loaded. Manipulate the search unit assembly until a good signal is visibleon the screen. Repeat couplant application if needed for additional surface priming. Once a good signal has been found, the signalshould be frozen with the ultrasonic
45、 unit for further analysis. The gate may be moved to the appropriate point on the wave asdiscussed above. The tank wall velocity may then be calculated.8.1.3 For maximum confidence, the practice of full removal, wiping and reapplication of the couplant should be repeated severaltimes at each search
46、unit position. Since there will always be some scatter in the data, a minimum of three values should beobtained at each location of interest.8.1.4 The LCR wave traversing the chord of the tank wall should appear as the first arriving signal on the flaw detector screenafter the initial pulse.Ashort g
47、ate (time less than one wavelength) is used to identify the arrival time of the LCR wave. Fig. 2 showsa typical signal identified by the gate setting. Here the cursor is on the first peak of the wave. The ultrasonic unit should be setto display the time associated with the zero crossing of the earli
48、est peak in the gate. It is easily distinguishable from the precedingportions and from the following wave that goes through the interior of the material. Since the refracted beams of the two searchunits are approximately parallel to the surface of the tank wall, there is no beam intersection point a
49、s defined by Practice E2373.8.1.5 Velocity values based on previously measured tanks in the field are available as an aid in isolating the LCR wave(Appendix X3). Using the prediction curve based on the years of service for the tank being examined can narrow down theapproximate location of the LCR wave arrival.8.1.6 Occasionally, a complex waveform will occur making the LCR difficult to isolate. This is often due to a combination ofconditions such as incomplete contact, high instrument gain used in these lossy highly attenuative materials and the parallel soundE2479
