ASTM E797/E797M-21

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. Because
it 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 version
of the standard as published by ASTM is to be considered the official document.
Designation: E797/E797M − 15 E797/E797M − 21
Standard Practice for
Measuring Thickness by Manual Ultrasonic Pulse-Echo
Contact Method
This standard is issued under the fixed designation E797/E797M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, 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*
1.1 This practice provides guidelines for measuring the thickness of materials using the contact pulse-echo method at
temperatures not to exceed 93°C [200°F].93 °C [200 °F].
1.2 This practice is applicable to any material in which ultrasonic waves will propagate at a constant velocity throughout the part,
and from which back wall reflections can be obtained and resolved.
1.3 This practice is primarily for flat components with parallel surfaces and has limited applicability for components with
non-parallel or concentric surfaces per 1.2.
1.4 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in
each system mayare not benecessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be
used independently of the other. Combiningother, and values from the two systems may result in non-conformance with the
standard.shall not be combined.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E317 Practice for Evaluating Performance Characteristics of Ultrasonic Pulse-Echo Testing Instruments and Systems without the
Use of Electronic Measurement Instruments
E494 Practice for Measuring Ultrasonic Velocity in Materials by Comparative Pulse-Echo Method
E543 Specification for Agencies Performing Nondestructive Testing
E1316 Terminology for Nondestructive Examinations
This practice is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.06 on Ultrasonic Method.
Current edition approved Dec. 1, 2015June 1, 2021. Published December 2015September 2021. Originally approved in 1981. Last previous edition approved in 20102015
as E797 - 10.E797/E797M – 15. DOI: 10.1520/E0797_E0797M-15.10.1520/E0797_E0797M-21.
For ASME Boiler and Pressure Vessel Code applications, see related Practice SE-797 in Section II of that Code.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*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
E797/E797M − 21
2.2 ASNT Documents:
Nondestructive Testing Handbook, 2nd Edition, Vol 7
SNT-TC-1A Recommended Practice for Personnel Qualification and Certification in Nondestructive Testing
ANSI/ASNT CP-189 Standard for Qualification and Certification of Nondestructive Testing Personnel
2.3 Aerospace Industries Association AIA Document:
NAS-410 Certification and Qualification of Nondestructive Testing Personnel
2.4 ISO Standard:
ISO 9712 Non-Destructive Testing—Qualification and Certification of NDT Personnel
3. Terminology
3.1 Definitions: Definitions—For definitions of terms used in this practice, refer to Terminology E1316.
3.1 Definitions—For definitions of terms used in this practice, refer to Terminology E1316.
4. Summary of Practice
4.1 Thickness (T), when measured by the pulse-echo ultrasonic method, is a product of the velocity of sound in the material and
one half the transit time (round trip) through the material.
Vt
T 5
where:
T = thickness,
V = velocity, and
t = transit time.
T = Component thickness,
V = Sound velocity in the material, and
t = Sound path 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. It is usually assumed to
be a constant for a given class of materials. Its approximate value can be obtained from Table X3.1 in Practice E494 or from the
Nondestructive Testing Handbook, or it can be determined empirically.
4.4 One or more reference blocks are required having known velocity, or of the same material to be examined, and having
thicknesses 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 range
of interest 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 convenient values
of thickness dependent on the range being used. The control for this function may have different names on different instruments,
including range, sweep, material standardize, or velocity.
4.6 The timing circuits in different instruments use various conversion schemes. A common method is the so-called time/analog
conversion in which the time measured by the instrument is converted into a proportional d-c voltage which is then applied to the
readout device. Another technique uses a very high-frequency oscillator that is modulated or gated by the appropriate echo
indications, the output being used either directly to suitable digital readouts or converted to a voltage for other presentation. A
relationship of transit time versus thickness is shown graphically in Fig. 1.
Available from American Society for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
Available from Aerospace Industries Association of America, Inc. (AIA), 1000 Wilson Blvd., Suite 1700, Arlington, VA 22209-3928, http://www.aia-aerospace.org.
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.
E797/E797M − 21
NOTE 1—Slope of velocity conversion line is approximately that of steel.
FIG. 1 Transit Time/Thickness Relationship
5. Significance and Use
5.1 The techniques described provide indirect measurement of thickness of sections of materials not exceeding temperatures of
93°C [200°F].93 °C [200 °F]. 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 precision
machined parts, and to determine wall thinning in process equipment caused by corrosion and erosion.
5.3 Recommendations for determining the capabilities and limitations of ultrasonic thickness gages for specific applications can
7,8
be found in the cited references.
6. Basis of Application
6.1 The following items are subject to contractual agreement between 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 in accordance
with a nationally or internationally recognized NDT personnel qualification practice or standard such as ANSI/ASNT CP-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 of Nondestructive Agencies—If specified in the contractual agreement, NDT agencies shall be qualified and
evaluated as described in Specification E543. The applicable edition of Specification E543 shall be specified in the contractual
agreement.
Bosselaar, H., and Goosens, J.C.J., J. C. J., “Method to Evaluate Direct-Reading Ultrasonic Pulse-Echo Thickness Meters,” Materials Evaluation, March 1971, pp. 45–50.
Fowler, K.A., Elfbaum, G.M., G. M., Husarek, V., and Castel, J., “Applications of Precision Ultrasonic Thickness Gaging,” Proceedings of the Eighth World Conference
on Nondestructive Testing, Cannes, France, Sept. 6–11, 1976, Paper 3F.5.
E797/E797M − 21
6.4 Procedures and Techniques—The procedures and techniques to be utilized shall be as specified in the contractual agreement.
6.5 Surface Preparation—The pre-examination surface preparation criteria shall be specified in the contractual agreement.
7. Apparatus
7.1 Instruments—Thickness-measurement instruments are divided into three groups: (1) Flawflaw detectors with an A-scan
display readout, (2) Flawflaw detectors with an A-scan display and direct thickness readout, and (3) Directdirect thickness readout.
7.1.1 Flaw detectors with A-scan display readouts display time/amplitude information. Thickness determinations are made by
reading the distance between the zero-corrected (pulse triggered or delay controlled) initial pulse and first-returned echo (back wall
reflection), or between multiple-back reflection echoes,wall reflections, on a standardized base line of the A-scan display. The base
line of the A-scan display should be adjusted for the desired thickness increments.
7.1.2 Flaw detectors with numeric readout are a combination pulse ultrasound flaw detection instrument with an A-scan display
and additional circuitry that provides digital thickness information. The material thickness can be electronically measured and
presented on a digital readout. The A-scan display provides a check on the validity of the electronic measurement by revealing
measurement 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 initial pulse
and the first echo or between multiple echoes is converted into a meter or digital readout. The instruments are designed for
measurement and direct numerical readout of specific ranges of thickness and materials.
7.1.4 Time-base linearity is required so that a change in the thickness of material will produce a corresponding change of indicated
thickness. If an A-Scan display is used as a readout, its horizontal linearity can be checked by using Practice E317.
7.2 Search Units—Most pulse-echo type search units (straight-beam contact, delay line, and dual element) are applicable if flaw
detector 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 required
for thicknesses less than about 0.6 mm [0.025 in.]. Measurements of materials at high temperatures require search units specially
designed for the application. When dual element search units are used, their inherent nonlinearity usually requires special
corrections for thin sections. (See Fig. 2 and Fig. X2.1.) For optimum performance, it is often necessary that the instrument and
search units be matched.
7.3 Standardization Blocks—The 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 (Figs. X1.1 and
X1.2).
8. Standardization of Apparatus
8.1 Case I—Direct Contact, Single-Element Search Unit:
8.1.1 Conditions—The display start is synchronized to the initial pulse. All display elements are linear. Full thickness is displayed
on the A-scan display.
8.1.2 Under these conditions, we can assume that the velocity 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 that standardization blocks
providing 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 instrument controls
(material standardization, range, sweep, 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 improveverify
the overall accuracy of the system.
8.2 Case II—Delay Line Single-Element Search Unit:
E797/E797M − 21
(a) Proportional sound path increases with decrease in thickness.
(b) Typical reading error values.
FIG. 2 Dual Transducer Nonlinearity
8.2.1 Conditions—When using this search unit, it is necessary that the equipment be capable of correcting for the time during
which the sound passes through the delay line so that the end of the delay can be made to coincide with zero thickness. This
requires a so-called “delay” control in the instrument or automatic electronic sensing of zero thickness.
8.2.2 In most instruments, if the material standardize circuit was previously adjusted for a given material velocity, the delay
control should be adjusted until a correct thickness reading is obtained on the instrument. However, if the instrument must be
completely standardized 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 measured and
the other block near the minimum thickness. For convenience, it is desirable that the thickness 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 between these
two readings should be calculated. If the reading thickness difference is less than the actual thickness difference, place the search
unit on the thicker specimen, and adjust the material standardize control to expand the thickness range. If the reading thickness
difference is greater than the actual thickness difference, place the search unit on the thicker specimen, and adjust the material
standardize control to decrease the thickness range. A certain amount of over correction is usually recommended. Reposition the
search unit sequentially on both blocks,blocks and note the reading differences while making additional appropriate corrections.
When the reading thickness differential equals the actual thickness differential, the material
...