1、Designation: E 797 05Standard Practice forMeasuring Thickness by Manual Ultrasonic Pulse-EchoContact Method1This standard is issued under the fixed designation E 797; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 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 practice2provides guidelines for measuring thethickness of materials using the contact pulse-echo method attemperatu
3、res not to exceed 200F 93C.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 The values stated in either inch-pound or SI units are tobe regarded as stan
4、dard. The values given in brackets are forinformation only.1.4 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 to establish appro-priate safety and health practices and determine the applica-bi
5、lity of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E 317 Practice for Evaluating Performance Characteristicsof Ultrasonic Pulse-Echo Examination Systems Withoutthe Use of Electronic Measurement InstrumentsE 494 Practice for Measuring Ultrasonic Velocity in Mate-ri
6、alsE 1316 Terminology for Nondestructive Testing2.2 ASNT Document:Nondestructive Testing Handbook, 2nd Edition, Vol 743. Terminology3.1 DefinitionsFor definitions of terms used in thispractice, refer to Terminology E 1316.4. Summary of Practice4.1 Thickness (T), when measured by the pulse-echo ultra
7、-sonic 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.
8、4.3 The 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 PracticeE 494 or from the Nondestructive Testing Handbook,oritcanbe d
9、etermined 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 ofthicknesses to be measured. It is generally desirable that thethicknesses be “round numbers” rather than misc
10、ellaneous oddvalues. One block should have a thickness value near themaximum of the range of interest and another 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
11、 on the range being used.The control for this function may have different names ondifferent instruments, including 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
12、which the time measured by theinstrument is converted into a proportional d-c voltage which isthen applied to the 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 dig
13、ital readouts or converted to a voltage for1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.06 onUltrasonic Testing Procedure.Current edition approved Dec. 1, 2005. Published December 2005. Originallyapprov
14、ed in 1981. Last previous edition approved in 2001 as E 797 - 95(2001).2For ASME Boiler and Pressure Vessel Code applications, see related PracticeSE-797 in Section II of that Code.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.or
15、g. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518.1Copyright ASTM International, 100 Barr Harbor Drive,
16、PO Box C700, West Conshohocken, PA 19428-2959, United States.other presentation. A relationship of transit time versus thick-ness is shown graphically in Fig. 1.5. Significance and Use5.1 The techniques described provide indirect measurementof thickness of sections of materials not exceeding tempera
17、-tures of 200F 93C. Measurements are made from one sideof the object, without requiring access to the rear surface.5.2 Ultrasonic thickness measurements are used extensivelyon basic shapes and products of many materials, on precisionmachined parts, and to determine wall thinning in processequipment
18、caused by corrosion and erosion.5.3 Recommendations for determining the capabilities andlimitations of ultrasonic thickness gages for specific applica-tions can be found in the cited references.5,66. Apparatus6.1 InstrumentsThickness-measurement instruments aredivided into three groups: (1) Flaw det
19、ectors with an A-scandisplay readout, (2) Flaw detectors with an A-scan display anddirect thickness readout, and (3) Direct thickness readout.6.1.1 Flaw detectors with A-scan display readouts displaytime/amplitude information. Thickness determinations aremade by reading the distance between the zero
20、-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.6.1.2 Flaw detectors with numeric readout are a c
21、ombina-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 provides a check on the validity of the electro
22、nicmeasurement by revealing measurement variables, such asinternal discontinuities, or echo-strength variations, whichmight result in inaccurate readings.6.1.3 Thickness readout instruments are modified versionsof the pulse-echo instrument. The elapsed time between theinitial pulse and the first ech
23、o 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.6.2 Search UnitsMost pulse-echo type search units(straight-beam contact, delay line, and dual element) areap
24、plicable 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 are5Bosselaar, H., and Goosens, J.C.J., “Method to Evaluat
25、e Direct-ReadingUltrasonic Pulse-Echo Thickness Meters,” Materials Evaluation, March 1971, pp.4550.6Fowler, 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,
26、 Sept. 611, 1976, Paper 3F.5.NOTE 1Slope of velocity conversion line is approximately that of steel.FIG. 1 Transit Time/Thickness RelationshipE797052generally required for thicknesses less than about 0.6 mm0.025 in. Measurements of materials at high temperaturesrequire search units specially designe
27、d for the application.When dual element search units are used, their inherentnonlinearity usually requires special corrections for thin sec-tions. (See Fig. 2.) For optimum performance, it is oftennecessary that the instrument and search units be matched.6.3 Standardization BlocksThe general require
28、ments forappropriate standardization blocks are given in 4.4, 7.1.3,7.2.2.1, 7.3.2, and 7.4.3. Multi-step blocks that may be usefulfor these standardization procedures are described in AppendixX1 (Figs. X1.1 and X1.2).7. Standardization of Apparatus7.1 Case IDirect Contact, Single-Element Search Uni
29、t:7.1.1 ConditionsThe display start is synchronized to theinitial pulse. All display elements are linear. Full thickness isdisplayed on the A-scan display.7.1.2 Under these conditions, we can assume that thevelocity conversion line effectively pivots about the origin(Fig. 1). It may be necessary to
30、subtract the wear-plate time,requiring minor use of delay control. It is recommended that(a) Proportional sound path increases with decrease in thickness.(b) Typical reading error valuesFIG. 2 Dual Transducer NonlinearityE797053standardization blocks providing a minimum of two thick-nesses that span
31、 the thickness range be used to check thefull-range accuracy.7.1.3 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 thicknessre
32、ading.7.1.4 The readings should then be checked and adjusted onstandardization blocks with thickness of lesser value to im-prove the overall accuracy of the system.7.2 Case IIDelay Line Single-Element Search Unit:7.2.1 ConditionsWhen using this search unit, it is neces-sary that the equipment be cap
33、able 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.7.2.2 In most instruments, if the m
34、aterial 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 technique is r
35、ecommended:7.2.2.1 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 also has
36、aconvenient “round number” value.7.2.2.2 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 unit o
37、n 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 thickness ra
38、nge. 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 thick
39、ness 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.7.2.3 An alternative technique for delay line search units isa variation of that described in 7.2.2. A series of sequentialadjustments are
40、made, using the “delay” control to providecorrect 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 bothreadings are “correct” the instrument is adjusted properly.7.3 Case IIIDual Searc
41、h Units:7.3.1 The method described in 7.2 (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 longer linearly proportion
42、al 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).7.3.2 If measurements are to be made over a very limitedrange near the thin end of the scale, it is possible to s
43、tandardizethe 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.7.3.3 If a wide range of thicknesses is
44、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 of the range.7.3.4 For a direct-reading panel-type meter
45、 display, it isconvenient to build these corrections into the display as anonlinear function.7.4 Case IVThick Sections:7.4.1 ConditionsFor use when a high degree of accuracyis required for thick sections.7.4.2 Direct contact search unit and initial pulse synchroni-zation are used. The display start
46、is delayed as described in7.4.4. All display elements should be linear. Incrementalthickness is displayed on the A-scan display.7.4.3 Basic standardization of the sweep will be made asdescribed in Case I. The standardization block chosen for thisstandardization should have a thickness that will perm
47、it stan-dardizing the full-sweep distance to adequate accuracy, that is,about 10 mm 0.4 in. or 25 mm 1.0 in. full scale.7.4.4 After basic standardization, the sweep must be de-layed. For instance, if the nominal part thickness is expected tobe from 50 to 60 mm 2.0 to 2.4 in., and the basic standard-
48、ization block is 10 mm 0.4 in., and the incremental thicknessdisplayed will also be from 50 to 60 mm 2.0 to 2.4 in., thefollowing steps are required. Adjust the delay control so thatthe fifth back echo of the basic standardization block, equiva-lent to 50 mm 2.0 in., is aligned with the 0 reference
49、on theA-scan display. The sixth back echo should then occur at theright edge of the standardized sweep.7.4.5 This standardization can be checked on a known blockof the approximate total thickness.7.4.6 The reading obtained on the unknown specimen mustbe added to the value delayed off screen. For example, if thereading is 4 mm 0.16 in., the total thickness will be 54 mm2.16 in.8. Technical Hazards8.1 Dual search units may also be used effectively withrough surface conditions. In this case, only the first returnedecho, such as from the bottom
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