ASTM E797 E797M-2010 8125 Standard Practice for Measuring Thickness by Manual Ultrasonic Pulse-Echo Contact Method《手动超声波脉冲-回声接触法测定厚度的标准实施规程》.pdf

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1、Designation: E797/E797M 10Standard Practice forMeasuring Thickness by Manual Ultrasonic Pulse-EchoContact Method1This standard is issued under the fixed designation E797/E797M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the ye

2、ar of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice2provides guidelines for measuring thethickness of materials using the contact pulse-echo method at

3、temperatures not to exceed 93C (200F).1.2 This practice is applicable to any material in whichultrasonic waves will propagate at a constant velocity through-out the part, and from which back reflections can be obtainedand resolved.1.3 UnitsThe values stated in either SI units or inch-pound units are

4、 to be regarded separately as standard. Thevalues stated in each system may not be exact equivalents;therefore, each system shall be used independently of the other.Combining values from the two systems may result in non-conformance with the standard1.4 This standard does not purport to address all

5、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 limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E317 Practice for Eval

6、uating Performance Characteristicsof Ultrasonic Pulse-Echo Testing Instruments and Systemswithout the Use of Electronic Measurement InstrumentsE494 Practice for Measuring Ultrasonic Velocity in Mate-rialsE543 Specification for Agencies Performing Nondestruc-tive TestingE1316 Terminology for Nondestr

7、uctive Examinations2.2 ASNT Documents:4Nondestructive Testing Handbook, 2nd Edition, Vol 7SNT-TC-1A Recommended Practice for Personnel Qualifi-cation and Certification in Nondestructive TestingANSI/ASNT CP-189 Standard for Qualification and Certi-fication of Nondestructive Testing Personnel2.3 Aeros

8、pace Industries Association Document:NAS-410 Certification and Qualification of NondestructiveTesting Personnel53. Terminology3.1 DefinitionsFor definitions of terms used in thispractice, refer to Terminology E1316.4. Summary of Practice4.1 Thickness (T), when measured by the pulse-echo ultra-sonic

9、method, is a product of the velocity of sound in thematerial and one half the transit time (round trip) through thematerial.T 5Vt2where:T = thickness,V = velocity, andt = transit time.4.2 The pulse-echo ultrasonic instrument measures the tran-sit time of the ultrasonic pulse through the part.4.3 The

10、 velocity in the material being examined is afunction of the physical properties of the material. It is usuallyassumed to be a constant for a given class of materials. Itsapproximate value can be obtained from Table X3.1 in PracticeE494 or from the Nondestructive Testing Handbook,oritcanbe determine

11、d empirically.4.4 One or more reference blocks are required havingknown velocity, or of the same material to be examined, andhaving thicknesses accurately measured and in the range of1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsib

12、ility of Subcommittee E07.06 onUltrasonic Method.Current edition approved June 1, 2010. Published July 2010. Originally approvedin 1981. Last previous edition approved in 2005 as E797 - 05. DOI: 10.1520/E0797-10.2For ASME Boiler and Pressure Vessel Code applications, see related PracticeSE-797 in Se

13、ction II of that Code.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available fromAmerican Society for Non

14、destructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.5Available from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerospace.org.1Copyright ASTM International, 100 Bar

15、r Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.thicknesses to be measured. It is generally desirable that thethicknesses be “round numbers” rather than miscellaneous oddvalues. One block should have a thickness value near themaximum of the range of interest and another

16、block near theminimum thickness.4.5 The display element (A-scan display, meter, or digitaldisplay) of the instrument must be adjusted to present conve-nient values of thickness dependent on the range being used.The control for this function may have different names ondifferent instruments, including

17、 range, sweep, material stan-dardize,orvelocity.4.6 The timing circuits in different instruments use variousconversion schemes. A common method is the so-calledtime/analog conversion in which the time measured by theinstrument is converted into a proportional d-c voltage which isthen applied to the

18、readout device. Another technique uses avery high-frequency oscillator that is modulated or gated by theappropriate echo indications, the output being used eitherdirectly to suitable digital readouts or converted to a voltage forother presentation. A relationship of transit time versus thick-ness is

19、 shown graphically in Fig. 1.5. Significance and Use5.1 The techniques described provide indirect measurementof thickness of sections of materials not exceeding tempera-tures of 93C (200F). Measurements are made from one sideof the object, without requiring access to the rear surface.5.2 Ultrasonic

20、thickness measurements are used extensivelyon basic shapes and products of many materials, on precisionmachined parts, and to determine wall thinning in processequipment caused by corrosion and erosion.5.3 Recommendations for determining the capabilities andlimitations of ultrasonic thickness gages

21、for specific applica-tions can be found in the cited references.6,76. Basis of Application6.1 The following items are subject to contractual agree-ment between the parties using or referencing this practice.6.2 Personnel Qualification:6.2.1 If specified in the contractual agreement, personnelperform

22、ing examinations to this standard shall be qualified inaccordance with a nationally or internationally recognizedNDT personnel qualification 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 pr

23、actice or standard used and its applicablerevision shall be identified in the contractual agreement be-tween the using parties.6.3 Qualification of Nondestructive AgenciesIf specifiedin the contractual agreement, NDT agencies shall be qualified6Bosselaar, H., and Goosens, J.C.J., “Method to Evaluate

24、 Direct-ReadingUltrasonic Pulse-Echo Thickness Meters,” Materials Evaluation, March 1971, pp.4550.7Fowler, K.A., Elfbaum, G.M., Husarek, V., and Castel, J., “Applications ofPrecision Ultrasonic Thickness Gaging,” Proceedings of the Eighth World Confer-ence on Nondestructive Testing, Cannes, France,

25、Sept. 611, 1976, Paper 3F.5.NOTE 1Slope of velocity conversion line is approximately that of steel.FIG. 1 Transit Time/Thickness RelationshipE797/E797M 102and evaluated as described in Specification E543. The appli-cable edition of Specification E543 shall be specified in thecontractual agreement.6.

26、4 Procedures and TechniquesThe procedures and tech-niques to be utilized shall be as specified in the contractualagreement.6.5 Surface PreparationThe pre-examination surfacepreparation criteria shall be specified in the contractual agree-ment.7. Apparatus7.1 InstrumentsThickness-measurement instrume

27、nts aredivided into three groups: (1) Flaw detectors with an A-scandisplay readout, (2) Flaw detectors with an A-scan display anddirect thickness readout, and (3) Direct thickness readout.7.1.1 Flaw detectors with A-scan display readouts displaytime/amplitude information. Thickness determinations ar

28、emade by reading the distance between the zero-corrected initialpulse and first-returned echo (back reflection), or betweenmultiple-back reflection echoes, on a standardized base line ofthe A-scan display. The base line of the A-scan display shouldbe adjusted for the desired thickness increments.7.1

29、.2 Flaw detectors with numeric readout are a combina-tion pulse ultrasound flaw detection instrument with an A-scandisplay and additional circuitry that provides digital thicknessinformation. The material thickness can be electronicallymeasured and presented on a digital readout. The A-scandisplay p

30、rovides a check on the validity of the electronicmeasurement by revealing measurement variables, such asinternal discontinuities, or echo-strength variations, whichmight result in inaccurate readings.7.1.3 Thickness readout instruments are modified versionsof the pulse-echo instrument. The elapsed t

31、ime between theinitial pulse and the first echo or between multiple echoes isconverted into a meter or digital readout. The instruments aredesigned for measurement and direct numerical readout ofspecific ranges of thickness and materials.7.2 Search UnitsMost pulse-echo type search units(straight-bea

32、m contact, delay line, and dual element) areapplicable if flaw detector instruments are used. If a thicknessreadout instrument has the capability to read thin sections, ahighly damped, high-frequency search unit is generally used.High-frequency (10 MHz or higher) delay line search units aregenerally

33、 required for thicknesses less than about 0.6 mm(0.025 in.). Measurements of materials at high temperaturesrequire search units specially designed for the application.When dual element search units are used, their inherentnonlinearity usually requires special corrections for thin sec-tions. (See Fig

34、. 2.) For optimum performance, it is oftennecessary that the instrument and search units be matched.7.3 Standardization BlocksThe general requirements forappropriate standardization blocks are given in 4.4, 8.1.3,8.2.2.1, 8.3.2, and 8.4.3. Multi-step blocks that may be usefulfor these standardizatio

35、n procedures are described in AppendixX1 (Figs. X1.1 and X1.2).8. Standardization of Apparatus8.1 Case IDirect Contact, Single-Element Search Unit:8.1.1 ConditionsThe display start is synchronized to theinitial pulse. All display elements are linear. Full thickness isdisplayed on the A-scan display.

36、8.1.2 Under these conditions, we can assume that thevelocity conversion line effectively pivots about the origin(Fig. 1). It may be necessary to subtract the wear-plate time,requiring minor use of delay control. It is recommended thatstandardization blocks providing a minimum of two thick-nesses tha

37、t span the thickness range be used to check thefull-range accuracy.8.1.3 Place the search unit on a standardization block ofknown thickness with suitable couplant and adjust the instru-ment controls (material standardization, range, sweep, orvelocity) until the display presents the appropriate thick

38、nessreading.8.1.4 The readings should then be checked and adjusted onstandardization blocks with thickness of lesser value to im-prove the overall accuracy of the system.8.2 Case IIDelay Line Single-Element Search Unit:8.2.1 ConditionsWhen using this search unit, it is neces-sary that the equipment

39、be capable of correcting for the timeduring which the sound passes through the delay line so thatthe end of the delay can be made to coincide with zerothickness. This requires a so-called “delay” control in theinstrument or automatic electronic sensing of zero thickness.8.2.2 In most instruments, if

40、 the material standardize circuitwas previously adjusted for a given material velocity, the delaycontrol should be adjusted until a correct thickness reading isobtained on the instrument. However, if the instrument must becompletely standardized with the delay line search unit, thefollowing techniqu

41、e is recommended:8.2.2.1 Use at least two standardization blocks. One shouldhave a thickness near the maximum of the range to bemeasured and the other block near the minimum thickness. Forconvenience, it is desirable that the thickness should be “roundnumbers” so that the difference between them als

42、o has aconvenient “round number” value.8.2.2.2 Place the search unit sequentially on one and thenthe other block, and obtain both readings. The differencebetween these two readings should be calculated. If the readingthickness difference is less than the actual thickness difference,place the search

43、unit on the thicker specimen, and adjust thematerial standardize control to expand the thickness range. Ifthe reading thickness difference is greater than the actualthickness difference, place the search unit on the thickerspecimen, and adjust the material standardize control to de-crease the thickn

44、ess range. A certain amount of over correctionis usually recommended. Reposition the search unit sequen-tially on both blocks, and note the reading differences whilemaking additional appropriate corrections. When the readingthickness differential equals the actual thickness differential,the material

45、 thickness range is correctly adjusted. A singleadjustment of the delay control should then permit correctreadings at both the high and low end of the thickness range.8.2.3 An alternative technique for delay line search units isa variation of that described in 8.2.2. A series of sequentialadjustment

46、s are made, using the “delay” control to providecorrect readings on the thinner standardization block and theE797/E797M 103“range” control to correct the readings on the thicker block.Moderate over-correction is sometimes useful. When bothreadings are “correct” the instrument is adjusted properly.8.

47、3 Case IIIDual Search Units:8.3.1 The method described in 8.2 (Case II) is also suitablefor equipment using dual search units in the thicker ranges,above 3 mm (0.125 in.). However, below those values there isan inherent error due to the Vee path that the sound beamtravels. The transit time is no lon

48、ger linearly proportional tothickness, and the condition deteriorates toward the lowthickness end of the range. The variation is also shownschematically in Fig. 2(a). Typical error values are shown inFig. 2(b).8.3.2 If measurements are to be made over a very limitedrange near the thin end of the sca

49、le, it is possible to standardizethe instrument with the technique in Case II using appropriatethin standardization blocks. This will produce a correctioncurve that is approximately correct over that limited range.Note that it will be substantially in error at thicker measure-ments.8.3.3 If a wide range of thicknesses is to be measured, itmay be more suitable to standardize as in Case II usingstandardization blocks at the high end of the range and perhapshalfway toward the low end. Following this, empirical correc-tions can be established for the very thin end