1、Designation: E797/E797M 10E797/E797M 15Standard 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 rev
2、ision, the year 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. Scope Scope*1.1 This practice2 provides guidelines for measuring the thickness of materials using the contac
3、t pulse-echo method attemperatures not to exceed 93C 200F.1.2 This practice is applicable to any material in which ultrasonic waves will propagate at a constant velocity throughout thepart, and from which back reflections can be obtained and resolved.1.3 UnitsThe values stated in either SI units or
4、inch-pound units are to be regarded separately as standard. The values statedin each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining valuesfrom the two systems may result in non-conformance with the standardstandard.1.4 This standard do
5、es not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof 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 Stand
6、ards:3E317 Practice for Evaluating Performance Characteristics of Ultrasonic Pulse-EchoTesting Instruments and Systems without theUse of Electronic Measurement InstrumentsE494 Practice for Measuring Ultrasonic Velocity in MaterialsE543 Specification for Agencies Performing Nondestructive TestingE131
7、6 Terminology for Nondestructive Examinations2.2 ASNT Documents:4Nondestructive Testing Handbook, 2nd Edition, Vol 7SNT-TC-1A Recommended Practice for Personnel Qualification and Certification in Nondestructive TestingANSI/ASNT CP-189 Standard for Qualification and Certification of Nondestructive Te
8、sting Personnel2.3 Aerospace Industries Association Document:5NAS-410 Certification and Qualification of Nondestructive Testing Personnel2.4 ISO Standard:6ISO 9712 Non-Destructive TestingQualification and Certification of NDT Personnel3. Terminology3.1 Definitions: DefinitionsFor definitions of term
9、s used in this practice, refer to Terminology E1316.1 This practice is under the jurisdiction ofASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.06 on Ultrasonic Method.Current edition approved June 1, 2010Dec. 1, 2015. Published July 2010December 201
10、5. Originally approved in 1981. Last previous edition approved in 20052010 asE797 - 05.E797 - 10. DOI: 10.1520/E0797_E0797M-10.10.1520/E0797_E0797M-15.2 For ASME Boiler and Pressure Vessel Code applications, see related Practice SE-797 in Section II of that Code.3 For referencedASTM standards, visit
11、 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.4 Available from American Society for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingat
12、e Ln., Columbus, OH 43228-0518, http:/www.asnt.org.5 Available from Aerospace Industries Association of America, Inc. (AIA), 1000 Wilson Blvd., Suite 1700, Arlington, VA 22209-3928, http:/www.aia-aerospace.org.6 Available from International Organization for Standardization (ISO), ISO Central Secreta
13、riat, 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 indication of what changes have been made to the previous version. Becauseit may not be technically
14、 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 considered the official document.*A Summary of Changes section appears at the end of this standa
15、rdCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Practice4.1 Thickness (T), when measured by the pulse-echo ultrasonic method, is a product of the velocity of sound in the materialand one half the transit time (round tr
16、ip) through the material.T 5Vt2where:T = thickness,V = velocity, andt = transit time.4.2 The pulse-echo ultrasonic instrument measures the transit time of the ultrasonic pulse through the part.4.3 The velocity in the material being examined is a function of the physical properties of the material. I
17、t is usually assumedto be a constant for a given class of materials. Its approximate value can be obtained from Table X3.1 in Practice E494 or fromthe Nondestructive Testing Handbook, or it can be determined empirically.4.4 One or more reference blocks are required having known velocity, or of the s
18、ame material to be examined, and havingthicknesses accurately measured and in the range of thicknesses to be measured. It is generally desirable that the thicknesses be“round numbers” rather than miscellaneous odd values. One block should have a thickness value near the maximum of the rangeof intere
19、st and another block near the minimum thickness.4.5 The display element (A-scan display, meter, or digital display) of the instrument must be adjusted to present convenientvalues of thickness dependent on the range being used. The control for this function may have different names on differentinstru
20、ments, including range, sweep, material standardize, or velocity.4.6 The timing circuits in different instruments use various conversion schemes.Acommon method is the so-called time/analogconversion in which the time measured by the instrument is converted into a proportional d-c voltage which is th
21、en applied to thereadout device. Another technique uses a very high-frequency oscillator that is modulated or gated by the appropriate echoindications, the output being used either directly to suitable digital readouts or converted to a voltage for other presentation. Arelationship of transit time v
22、ersus thickness is shown graphically in Fig. 1.NOTE 1Slope of velocity conversion line is approximately that of steel.FIG. 1 Transit Time/Thickness RelationshipE797/E797M 1525. Significance and Use5.1 The techniques described provide indirect measurement of thickness of sections of materials not exc
23、eeding temperatures of93C 200F. Measurements are made from one side of the object, without requiring access to the rear surface.5.2 Ultrasonic thickness measurements are used extensively on basic shapes and products of many materials, on precisionmachined parts, and to determine wall thinning in pro
24、cess equipment caused by corrosion and erosion.5.3 Recommendations for determining the capabilities and limitations of ultrasonic thickness gages for specific applications canbe found in the cited references.7,86. Basis of Application6.1 The following items are subject to contractual agreement betwe
25、en the parties using or referencing this practice.6.2 Personnel Qualification:6.2.1 If specified in the contractual agreement, personnel performing examinations to this standard shall be qualified inaccordance with a nationally or internationally recognized NDT personnel qualification practice or st
26、andard such as ANSI/ASNTCP-189, SNT-TC-1A, NAS-410, ISO 9712, or a similar document and certified by the employer or certifying agency, as applicable.The practice or standard used and its applicable revision shall be identified in the contractual agreement between the using parties.6.3 Qualification
27、 of Nondestructive AgenciesIf specified in the contractual agreement, NDT agencies shall be qualified andevaluated as described in Specification E543. The applicable edition of Specification E543 shall be specified in the contractualagreement.6.4 Procedures and TechniquesThe procedures and technique
28、s to be utilized shall be as specified in the contractual agreement.6.5 Surface PreparationThe pre-examination surface preparation criteria shall be specified in the contractual agreement.7. Apparatus7.1 InstrumentsThickness-measurement instruments are divided into three groups: (1) Flaw detectors w
29、ith an A-scan displayreadout, (2) Flaw detectors with an A-scan display and direct thickness readout, and (3) Direct thickness readout.7.1.1 Flaw detectors with A-scan display readouts display time/amplitude information. Thickness determinations are made byreading the distance between the zero-corre
30、cted initial pulse and first-returned echo (back reflection), or between multiple-backreflection echoes, on a standardized base line of the A-scan display. The base line of the A-scan display should be adjusted for thedesired thickness increments.7.1.2 Flaw detectors with numeric readout are a combi
31、nation pulse ultrasound flaw detection instrument with anA-scan displayand additional circuitry that provides digital thickness information. The material thickness can be electronically measured andpresented on a digital readout. The A-scan display provides a check on the validity of the electronic
32、measurement by revealingmeasurement variables, such as internal discontinuities, or echo-strength variations, which might result in inaccurate readings.7.1.3 Thickness readout instruments are modified versions of the pulse-echo instrument. The elapsed time between the initialpulse and the first echo
33、 or between multiple echoes is converted into a meter or digital readout. The instruments are designed formeasurement and direct numerical readout of specific ranges of thickness and materials.7.2 Search UnitsMost pulse-echo type search units (straight-beam contact, delay line, and dual element) are
34、 applicable if flawdetector instruments are used. If a thickness readout instrument has the capability to read thin sections, a highly damped,high-frequency search unit is generally used. High-frequency (10 MHz or higher) delay line search units are generally requiredfor thicknesses less than about
35、0.6 mm 0.025 in. Measurements of materials at high temperatures require search units speciallydesigned for the application. When dual element search units are used, their inherent nonlinearity usually requires specialcorrections for thin sections. (See Fig. 2.) For optimum performance, it is often n
36、ecessary that the instrument and search units bematched.7.3 Standardization BlocksThe general requirements for appropriate 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 useful for these standardization procedures are described in Appendix X1
37、(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 the initial pulse. All display elements are linear. Full thickness isdisplayed on the A-scan display.7 Bosselaar, H., and Goosens, J.C.J., “Me
38、thod to Evaluate Direct-Reading Ultrasonic Pulse-Echo Thickness Meters,” Materials Evaluation, March 1971, pp. 4550.8 Fowler, K.A., Elfbaum, G.M., Husarek, V., and Castel, J., “Applications of Precision Ultrasonic Thickness Gaging,” Proceedings of the Eighth World Conference onNondestructive Testing
39、, Cannes, France, Sept. 611, 1976, Paper 3F.5.E797/E797M 1538.1.2 Under these conditions, we can assume that the velocity conversion line effectively pivots about the origin (Fig. 1). It maybe necessary to subtract the wear-plate time, requiring minor use of delay control. It is recommended that sta
40、ndardization blocksproviding a minimum of two thicknesses that span the thickness range be used to check the full-range accuracy.8.1.3 Place the search unit on a standardization block of known thickness with suitable couplant and adjust the instrumentcontrols (material standardization, range, sweep,
41、 or velocity) until the display presents the appropriate thickness reading.8.1.4 The readings should then be checked and adjusted on standardization blocks with thickness of lesser value to improve theoverall accuracy of the system.8.2 Case IIDelay Line Single-Element Search Unit:8.2.1 ConditionsWhe
42、n using this search unit, it is necessary that the equipment be capable of correcting for the time duringwhich the sound passes through the delay line so that the end of the delay can be made to coincide with zero thickness. Thisrequires a so-called “delay” control in the instrument or automatic ele
43、ctronic sensing of zero thickness.8.2.2 In most instruments, if the material standardize circuit was previously adjusted for a given material velocity, the delaycontrol should be adjusted until a correct thickness reading is obtained on the instrument. However, if the instrument must becompletely st
44、andardized with the delay line search unit, the following technique is recommended:8.2.2.1 Use at least two standardization blocks. One should have a thickness near the maximum of the range to be measuredand the other block near the minimum thickness. For convenience, it is desirable that the thickn
45、ess should be “round numbers”so that the difference between them also has a convenient “round number” value.8.2.2.2 Place the search unit sequentially on one and then the other block, and obtain both readings. The difference betweenthese two readings should be calculated. If the reading thickness di
46、fference is less than the actual thickness difference, place thesearch unit on the thicker specimen, and adjust the material standardize control to expand the thickness range. If the readingthickness difference is greater than the actual thickness difference, place the search unit on the thicker spe
47、cimen, and adjust thematerial standardize control to decrease the thickness range. A certain amount of over correction is usually recommended.(a) Proportional sound path increases with decrease in thickness.(b) Typical reading error values.FIG. 2 Dual Transducer NonlinearityE797/E797M 154Reposition
48、the search unit sequentially on both blocks, and note the reading differences while making additional appropriatecorrections. When the reading thickness differential equals the actual thickness differential, the material thickness range is correctlyadjusted.Asingle adjustment of the delay control sh
49、ould then permit correct readings at both the high and low end of the thicknessrange.8.2.3 An alternative technique for delay line search units is a variation of that described in 8.2.2. A series of sequentialadjustments are made, using the “delay” control to provide correct readings on the thinner standardization block and the “range”control to correct the readings on the thicker block. Moderate over-correction is sometimes useful. When both readings are“correct” the instrument is adjusted properly.8.3 Case IIIDual Search Units:8.3.1 The method de
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1