ASTM E114-20

Standard Practice for Ultrasonic Pulse-Echo Straight-Beam Contact Testing

SIGNIFICANCE AND USE
5.1 This practice employs the use of normal-incident, or straight beam, longitudinal wave ultrasound for the detection and evaluation of discontinuities in materials requiring volumetric examination.  
5.2 Although not all requirements of this practice can be applied universally to all inspection situations and materials, it does provide the basis for establishing contractual criteria between suppliers and purchasers of materials for performing contact longitudinal wave pulse-echo examination and may be used as a guide for writing detailed procedures for particular applications.  
5.3 Types of information that may be obtained from the pulsed-echo straight-beam practice are as follows:  
5.3.1 Apparent discontinuity size (see Note 1) by comparison of the signal amplitudes from the test piece to the amplitudes obtained from a reference standard.  
5.3.2 Depth location of discontinuities by calibrating the horizontal scale of the A-scan display.  
5.3.3 Material properties as indicated by the relative sound attenuation or velocity changes of compared items.  
5.3.4 The extent of bond and unbond (or fusion and lack of fusion) between two ultrasonic conducting materials if geometry and materials permit.
Note 1: The term “apparent” is emphasized since true size depends on orientation, composition, and geometry of the discontinuity and equipment limitations.
SCOPE
1.1 This practice2 covers ultrasonic examination of materials using the conventional pulse-echo method using straight-beam longitudinal waves introduced by direct contact of the search unit with the material being examined.  
1.2 This practice shall be applicable to development of an examination procedure agreed upon by the users of the document.  
1.3 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 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.

General Information

• Status: Published
• Publication Date: 30-Nov-2020
• ICS: 19.100 - Non-destructive testing
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.06 - Ultrasonic Method

Relations

• Refers: ASTM E1316-24 - Standard Terminology for <?Pub Dtl?>Nondestructive Examinations
• Effective Date: 01-Feb-2024
• Refers: ASTM E1316-19b - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2019
• Refers: ASTM E1316-19 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Mar-2019
• Refers: ASTM E1316-18 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jan-2018
• Refers: ASTM E1316-17a - Standard Terminology for Nondestructive Examinations
• Effective Date: 15-Jun-2017
• Refers: ASTM E1316-17 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Feb-2017
• Refers: ASTM E1316-16a - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Aug-2016
• Refers: ASTM E1316-16 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Feb-2016
• Refers: ASTM E1316-15a - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2015
• Refers: ASTM E1316-15 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Sep-2015
• Refers: ASTM E1316-14 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jun-2014
• Refers: ASTM E1316-14e1 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jun-2014
• Refers: ASTM E1316-13d - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2013
• Refers: ASTM E1316-13c - Standard Terminology for Nondestructive Examinations
• Effective Date: 15-Jun-2013
• Refers: ASTM E1316-13b - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jun-2013

Overview

ASTM E114-20: Standard Practice for Ultrasonic Pulse-Echo Straight-Beam Contact Testing provides a comprehensive methodology for using ultrasonic pulse-echo testing with straight-beam, longitudinal waves. Administered by ASTM International, this standard outlines best practices for the nondestructive volumetric examination of materials, helping to detect and evaluate internal discontinuities such as inclusions, cracks, and voids. This standard is widely referenced by suppliers and purchasers for establishing inspection agreements and developing procedures for quality assurance in manufacturing and construction.

Key Topics

• Ultrasonic Pulse-Echo Testing: Focuses on using straight-beam, normal-incident ultrasonic waves introduced through direct contact between the transducer (search unit) and the test material.
• Detection of Discontinuities: Allows for identification of flaws such as cracks and bonding defects by observing changes in reflected ultrasonic signals.
• Measurement Techniques:
  • Apparent Discontinuity Size - Determined by comparing signal amplitude with reference standards.
  • Depth Location - Achieved through horizontal scale calibration of the A-scan display.
  • Material Properties - Inferred from variations in sound attenuation or velocity.
• Standardization and Calibration: Emphasizes the need to standardize equipment and reference blocks to match the test material and geometry, ensuring accurate signal interpretation.
• Procedure Requirements: Outlines procedures for surface preparation, search unit selection, scanning techniques (manual and automated), and documentation of results.
• Purchaser-Supplier Agreements: Encourages clear agreements on extent of examination, timing, qualification of personnel, and acceptance criteria.

Applications

ASTM E114-20 is essential across industries where internal material integrity is critical. Key application areas include:

• Manufacturing Quality Control: Ensures product reliability by detecting internal flaws in components before shipment.
• Energy and Utilities: Used for inspection of pipes, pressure vessels, and structural components to prevent failures.
• Aerospace and Automotive: Validates the integrity of high-stress and safety-critical parts.
• Construction and Infrastructure: Checks steel beams, welds, and structural elements for discontinuities that could compromise strength and safety.
• Material Development: Assists in characterizing new materials by evaluating internal features without causing damage.

The standard's adaptability allows organizations to define detailed procedures suitable for their specific materials, configurations, and operational needs.

Related Standards

The following standards are commonly referenced in conjunction with ASTM E114-20 for ultrasonic testing and nondestructive evaluation:

• ASTM E317: Practice for Evaluating Performance Characteristics of Ultrasonic Pulse-Echo Testing Instruments and Systems.
• ASTM E543: Specification for Agencies Performing Nondestructive Testing.
• ASTM E1316: Terminology for Nondestructive Examinations.
• ASNT SNT-TC-1A / ANSI/ASNT CP-189: Recommended practices and standards for qualification and certification of nondestructive testing personnel.
• NAS-410: Certification and Qualification of Nondestructive Test Personnel for aerospace applications.
• ISO 9712: International standard for qualification and certification of nondestructive testing personnel.

Practical Value

By adhering to ASTM E114-20, organizations can:

• Improve product quality by reliably identifying subsurface discontinuities.
• Ensure compliance with regulatory and contractual requirements.
• Reduce the risk of structural failures through early detection.
• Establish clear inspection procedures and documentation for repeatability and audit purposes.
• Facilitate effective communication between suppliers and purchasers through standardized terminology and criteria.

Keywords: ultrasonic testing, pulse-echo, straight-beam, nondestructive testing (NDT), ASTM E114-20, material inspection, quality control, discontinuity detection

Standards Content (Sample)

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.
Designation: E114 − 20
Standard Practice for
Ultrasonic Pulse-Echo Straight-Beam Contact Testing
This standard is issued under the fixed designation E114; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* E1316 Terminology for Nondestructive Examinations
2.2 ASNT Standards:
1.1 This practice covers ultrasonic examination of materi-
SNT-TC-1A Recommended Practice for Personnel Qualifi-
als using the conventional pulse-echo method using straight-
cation and Certification in Nondestructive Testing
beam longitudinal waves introduced by direct contact of the
ANSI/ASNT CP-189 ASNT Standard for Qualification and
search unit with the material being examined.
Certification of Nondestructive Testing Personnel
1.2 This practice shall be applicable to development of an
2.3 Other Documents:
examination procedure agreed upon by the users of the
NAS-410 Certification and Qualification of Nondestructive
document.
Test Personnel
1.3 Units—The values stated in inch-pound units are to be
2.4 ISO Standard:
regarded as standard. The values given in parentheses are
ISO 9712 Non-Destructive Testing—Qualification and Cer-
mathematical conversions to SI units that are provided for
tification of NDT Personnel
information only and are not considered standard.
3. Terminology
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3.1 Refer to Terminology E1316 for definitions of terms
responsibility of the user of this standard to establish appro-
used in this practice.
priate safety, health, and environmental practices and deter-
4. Basis of Application
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor-
4.1 Purchaser-Supplier Agreements—The following items
dance with internationally recognized principles on standard-
require agreement between the using parties for this practice to
ization established in the Decision on Principles for the
be used effectively:
Development of International Standards, Guides and Recom-
4.1.1 Qualification of Nondestructive Testing Agencies—
mendations issued by the World Trade Organization Technical
Agreement is required as to whether the nondestructive testing
Barriers to Trade (TBT) Committee.
agency, as defined in Specification E543, must be formally
evaluated and qualified to perform the examination. If such
2. Referenced Documents
evaluation and qualification is specified, a documented proce-
2.1 ASTM Standards:
dure such as Specification E543 shall be used as the basis for
E317 Practice for Evaluating Performance Characteristics of
evaluation.
Ultrasonic Pulse-Echo Testing Instruments and Systems
4.1.2 Personnel Qualification—Nondestructive testing
without the Use of Electronic Measurement Instruments
(NDT) personnel shall be qualified in accordance with a
E543 Specification for Agencies Performing Nondestructive
nationally recognized NDT personnel qualification practice or
Testing
standardsuchasANSI/ASNTCP-189,SNT-TC-1A,NAS-410,
ISO9712,orasimilardocument.Thepracticeorstandardused
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
and its applicable revision shall be specified in the contractual
structive Testing and is the direct responsibility of Subcommittee E07.06 on
agreement between the using parties.
Ultrasonic Method.
Current edition approved Dec. 1, 2020. Published January 2021. Originally
approved in 1955. Last previous edition approved in 2015 as E114 – 15. DOI:
10.1520/E0114-20. AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
For ASME Boiler and Pressure Vessel Code applications, see related Practice 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
SE-114 in Section II of that Code. Available fromAerospace IndustriesAssociation ofAmerica, Inc. (AIA), 1000
For referenced ASTM standards, visit the ASTM website, www.astm.org, or WilsonBlvd.,Suite1700,Arlington,VA22209-3928,http://www.aia-aerospace.org.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Available from International Organization for Standardization (ISO), ISO
Standards volume information, refer to the standard’s Document Summary page on Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
the ASTM website. Geneva, Switzerland, http://www.iso.org.
*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
E114 − 20
4.1.3 Extent of Examination—The extent of the examination ultrasound from the search unit into the material under test.
shall be determined by agreement of the using parties. Typical couplants include water, cellulose gel, oil, and grease.
4.1.4 Time of Examination—The time of examination shall Corrosion inhibitors or wetting agents, or both, may be used.
be determined by agreement of the using parties. Couplants must be selected that are not detrimental to the
4.1.5 Interpretation Criteria—The criteria by which the product or the process. The couplant used in standardization
ultrasonic signals and part acceptability will be evaluated and should be used for the examination. During the performance of
shall be determined by agreement of the using parties. a contact ultrasonic examination, the couplant layer between
search unit and examination material must be maintained such
5. Significance and Use
that the contact area is held constant while maintaining
5.1 This practice employs the use of normal-incident, or adequate couplant thickness. Lack of couplant reducing the
effective contact area or excess couplant thickness will reduce
straight beam, longitudinal wave ultrasound for the detection
and evaluation of discontinuities in materials requiring volu- the amount of energy transferred between the search unit and
the examination piece. These couplant variations in turn result
metric examination.
in examination sensitivity variations.
5.2 Although not all requirements of this practice can be
6.1.3.1 The couplant should be selected so that its viscosity
applied universally to all inspection situations and materials, it
is appropriate for the surface finish of the material to be
does provide the basis for establishing contractual criteria
examined. The examination of rough surfaces generally re-
between suppliers and purchasers of materials for performing
quires a high-viscosity couplant. The temperature of the
contact longitudinal wave pulse-echo examination and may be
material’s surface can change the couplant’s viscosity. As an
used as a guide for writing detailed procedures for particular
example, in the case of oil and greases, see Table 1.
applications.
6.1.3.2 At elevated temperatures as conditions warrant,
5.3 Types of information that may be obtained from the
heat-resistant coupling materials such as silicone oils, gels, or
pulsed-echo straight-beam practice are as follows:
greases should be used. Further, intermittent contact of the
5.3.1 Apparent discontinuity size (see Note 1) by compari-
search unit with the surface or auxiliary cooling of the search
son of the signal amplitudes from the test piece to the
unit may be necessary to avoid temperature changes that affect
amplitudes obtained from a reference standard.
the ultrasonic wave characteristics of the search unit.At higher
5.3.2 Depth location of discontinuities by calibrating the
temperatures, certain couplants based on inorganic salts or
horizontal scale of the A-scan display.
thermoplastic organic materials, high-temperature delay
5.3.3 Material properties as indicated by the relative sound
materials, and search units that are not damaged by high
attenuation or velocity changes of compared items.
temperatures may be required.
5.3.4 The extent of bond and unbond (or fusion and lack of
6.1.3.3 Where constant coupling over large areas is needed,
fusion) between two ultrasonic conducting materials if geom-
as in automated examination, or where severe changes in
etry and materials permit.
surface roughness are found, other couplants such as liquid gap
couplingwillusuallyprovideabetterexamination.Inthiscase,
NOTE 1—The term “apparent” is emphasized since true size depends on
the search unit does not contact the examination surface but is
orientation, composition, and geometry of the discontinuity and equip-
ment limitations.
separated by a short distance which is filled with couplant.
Liquid flowing through the search unit fills the gap. The
6. Apparatus
flowing liquid provides the coupling path and has the addi-
6.1 Complete ultrasonic apparatus shall include the follow-
tional advantage of cooling the search unit if the examination
ing:
surface is hot.
6.1.1 Instrumentation—The ultrasonic instrument shall be
6.1.3.4 An alternative means of direct contact coupling is
capable of generating, receiving, and amplifying high-
provided by the wheel search unit. The search unit is mounted
frequency electrical pulses at such frequencies and energy
at the required angle to a stationary axle about which rotates a
levels required to perform a meaningful examination and to
liquid-filled flexible tire. A minimum amount of couplant
provide a suitable readout.
provides ultrasonic transmission into the examination surface
6.1.2 Search Units—The ultrasonic search units shall be
capableoftransmittingandreceivingultrasoundinthematerial
at the required frequencies and energy levels necessary for
TABLE 1 Suggested Viscosities—Oil Couplants
discontinuity detection. Typical search unit sizes usually range
1 1
from ⁄8 in. (3.2 mm) in diameter to 1 ⁄8 in. (28.6 mm) in NOTE 1—The table is a guide only and is not meant to exclude the use
of a particular couplant that is found to work satisfactorily on a particular
diameter with both smaller and larger sizes available for
surface.
specific applications. Search units may be fitted with special
Approximate Surface Roughness Average Equivalent Couplant
shoes for appropriate applications. Special search units encom-
(Ra), µin. (µm) Viscosity, Weight Motor
passing both a transmitter and a receiver as separate piezoelec-
Oil
tric elements can be utilized to provide some degree of
5–100 (0.1–2.5) SAE 10
improved resolution near the examination surface. 50–200 (1.3–5.1) SAE 20
100–400 (2.5–10.2) SAE 30
6.1.3 Couplant—Acouplant, usually a liquid or semi-liquid,
250–700 (6.4–17.8) SAE 40
is required between the face of the search unit and the
Over 700 (18–) cup grease
examination surface to permit or improve the transmittance of
E114 − 20
since the elastic tire material is in rolling contact and conforms scanning is indicative of poor coupling, increased attenuation,
closely to the surface. or sound scattering discontinuities provided that front and back
6.1.4 Reference Standards—The production item itself may surface roughness and parallelism of the production piece are
be an adequate standard using the height of the back wall echo approximately the same as that of the standard. For non-
for reference. For more quantitative information, machined parallel surfaces, the time trace of the display shall be
artificial reflectors (discontinuities) or charts representing standardized by using standards that include the maximum
distance-amplitude relationships of known reflector sizes for a thickness of the production item being examined.
particular search unit and material may be used for standard-
7.6 Forbond/unbond(fusion/lackoffusion)examinations,a
ization. These artificial reflectors may be in the form of
reference standard should be used similar to the production
flat-bottom holes, side-drilled holes, or slots. An alternate
item being examined containing areas representing both
method of fabricating a reference standard may be the intro-
bonded (fused) and unbonded (lack of fusion) conditions, if
ductionofknowndiscontinuitiesduringthefabricationprocess
geometry and material permit.
of a production item or other convenient configuration. The
7.7 Standardization with respect to reference
...

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: E114 − 15 E114 − 20
Standard Practice for
Ultrasonic Pulse-Echo Straight-Beam Contact Testing
This standard is issued under the fixed designation E114; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This practice covers ultrasonic examination of materials byusing the conventional pulse-echo method using straight-beam
longitudinal waves introduced by direct contact of the search unit with the material being examined.
1.2 This practice shall be applicable to development of an examination procedure agreed upon by the users of the document.
1.3 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.4 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.
1.5 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
E543 Specification for Agencies Performing Nondestructive Testing
E1316 Terminology for Nondestructive Examinations
2.2 ASNT Standards:
SNT-TC-1A Recommended Practice for Personnel Qualification and Certification in Nondestructive Testing
ANSI/ASNT CP-189 ASNT Standard for Qualification and Certification of Nondestructive Testing Personnel
2.3 Other Documents:
NAS-410 Certification and Qualification of Nondestructive Test Personnel
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, 2015Dec. 1, 2020. Published December 2015January 2021. Originally approved in 1955. Last previous edition approved in 20102015
as E114 - 10.E114 – 15. DOI: 10.1520/E0114-15.10.1520/E0114-20.
For ASME Boiler and Pressure Vessel Code applications, see related Practice SE-114 in Section II of that Code.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
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.
*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
E114 − 20
2.4 ISO Standard:
ISO 9712 Non-Destructive Testing—QualificaitonTesting—Qualification and Certification of NDT Personnel
3. Terminology
3.1 Refer to Terminology E1316 for definitions of terms used in this practice.
4. Basis of Application
4.1 Purchaser-Supplier Agreements: Agreements—The following items require agreement between the using parties for this
practice to be used effectively:
4.1.1 Qualification of Nondestructive Testing Agencies—Agreement is required as to whether the nondestructive testing agency,
as defined in Specification E543, must be formally evaluated and qualified to perform the examination. If such evaluation and
qualification is specified, a documented procedure such as Specification E543 shall be used as the basis for evaluation.
4.1.2 Personnel Qualification—Nondestructive testing (NDT) personnel shall be qualified in accordance with a nationally
recognized NDT personnel qualification practice or standard such as ANSI/ASNT CP-189, SNT-TC-1A, NAS-410, ISO 9712, or
a similar document. The practice or standard used and its applicable revision shall be specified in the contractual agreement
between the using parties.
4.1.3 Extent of Examination—The extent of the examination shall be determined by agreement of the using parties.
4.1.4 Time of Examination—The time of examination shall be determined by agreement of the using parties.
4.1.5 Interpretation Criteria—The criteria by which the ultrasonic signals and part acceptability will be evaluated and shall be
determined by agreement of the using parties.
5. Significance and Use
5.1 This practice employs the use of normal-incident, or straight beam, longitudinal wave ultrasound for the detection and
evaluation of discontinuities in materials requiring volumetric examination.
5.2 Although not all requirements of this practice can be applied universally to all inspection situations and materials, it does
provide the basis for establishing contractual criteria between suppliers and purchasers of materials for performing contact
longitudinal wave pulse-echo examination and may be used as a guide for writing detailed procedures for particular applications.
5.3 Types of information that may be obtained from the pulsed-echo straight-beam practice are as follows:
5.3.1 Apparent discontinuity size (see Note 1) by comparison of the signal amplitudes from the test piece to the amplitudes
obtained from a reference standard.
5.3.2 Depth location of discontinuities by calibrating the horizontal scale of the A-scan display.
5.3.3 Material properties as indicated by the relative sound attenuation or velocity changes of compared items.
5.3.4 The extent of bond and unbond (or fusion and lack of fusion) between two ultrasonic conducting materials if geometry and
materials permit.
NOTE 1—The term “apparent” is emphasized since true size depends on orientation, composition, and geometry of the discontinuity and equipment
limitations.
6. Apparatus
6.1 Complete ultrasonic apparatus shall include the following:
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.
E114 − 20
6.1.1 Instrumentation—The ultrasonic instrument shall be capable of generating, receiving, and amplifying high-frequency
electrical pulses at such frequencies and energy levels required to perform a meaningful examination and to provide a suitable
readout.
6.1.2 Search Units—The ultrasonic search units shall be capable of transmitting and receiving ultrasound in the material at the
required frequencies and energy levels necessary for discontinuity detection. Typical search unit sizes usually range from ⁄8 in.
(3.2 mm) in diameter to 1 ⁄8 in. (28.6 mm) in diameter with both smaller and larger sizes available for specific applications. Search
units may be fitted with special shoes for appropriate applications. Special search units encompassing both a transmitter and a
receiver as separate piezoelectric elements can be utilized to provide some degree of improved resolution near the examination
surface.
6.1.3 Couplant—A couplant, usually a liquid or semi-liquid, is required between the face of the search unit and the examination
surface to permit or improve the transmittance of ultrasound from the search unit into the material under test. Typical couplants
include water, cellulose gel, oil, and grease. Corrosion inhibitors or wetting agents, or both, may be used. Couplants must be
selected that are not detrimental to the product or the process. The couplant used in standardization should be used for the
examination. During the performance of a contact ultrasonic examination, the couplant layer between search unit and examination
material must be maintained such that the contact area is held constant while maintaining adequate couplant thickness. Lack of
couplant reducing the effective contact area or excess couplant thickness will reduce the amount of energy transferred between the
search unit and the examination piece. These couplant variations in turn result in examination sensitivity variations.
6.1.3.1 The couplant should be selected so that its viscosity is appropriate for the surface finish of the material to be examined.
The examination of rough surfaces generally requires a high-viscosity couplant. The temperature of the material’s surface can
change the couplant’s viscosity. As an example, in the case of oil and greases, see Table 1.
6.1.3.2 At elevated temperatures as conditions warrant, heat-resistant coupling materials such as silicone oils, gels, or greases
should be used. Further, intermittent contact of the search unit with the surface or auxiliary cooling of the search unit may be
necessary to avoid temperature changes that affect the ultrasonic wave characteristics of the search unit. At higher temperatures,
certain couplants based on inorganic salts or thermoplastic organic materials, high-temperature delay materials, and search units
that are not damaged by high temperatures may be required.
6.1.3.3 Where constant coupling over large areas is needed, as in automated examination, or where severe changes in surface
roughness are found, other couplants such as liquid gap coupling will usually provide a better examination. In this case, the search
unit does not contact the examination surface but is separated by a distance of about 0.2 in. (5.1 mm) short distance which is filled
with couplant. Liquid flowing through the search unit fills the gap. The flowing liquid provides the coupling path and has the
additional advantage of cooling the search unit if the examination surface is hot.
6.1.3.4 An alternative means of direct contact coupling is provided by the wheel search unit. The search unit is mounted at the
required angle to a stationary axle about which rotates a liquid-filled flexible tire. A minimum amount of couplant provides
ultrasonic transmission into the examination surface since the elastic tire material is in rolling contact and conforms closely to the
surface.
6.1.4 Reference Standards—The production item itself may be an adequate standard using the height of the back wall echo for
reference. For more quantitative information, machined artificial reflectors (discontinuities) or charts representing distance-
amplitude relationships of known reflector sizes for a particular search unit and material may be used for standardization. These
artificial reflectors may be in the form of flat-bottom holes, side-drilled holes, or slots. An alternate method of fabricating a
TABLE 1 Suggested Viscosities—Oil Couplants
NOTE 1—The table is a guide only and is not meant to exclude the use
of a particular couplant that is found to work satisfactorily on a particular
surface.
Approximate Surface Roughness Average Equivalent Couplant
(Ra), μin. (μm) Viscosity, Weight Motor
Oil
5–100 (0.1–2.5) SAE 10
50–200 (1.3–5.1) SAE 20
100–400 (2.5–10.2) SAE 30
250–700 (6.4–17.8) SAE 40
Over 700 (18–) cup grease
E114 − 20
reference standard may be the introduction of known discontinuities during the fabrication process of a production item or other
convenient configuration. The surface finish of the reference standard should be similar to the surface finish of the production item
(or corrected; see 7.3). The reference standard material and the production material should be acoustically similar (in velocity and
attenuation). The reference standard selected shall be used by the examiner as the basis for signal comparisons.
7. Standardization of Apparatus
7.1 If quantitative information is to be obtained, vertical or horizontal linearity, or both, should be checked in accordance with
Practice E317 or another procedure approved by the users of the document. An acceptable linearity performance may be agreed
upon by the users of the document.
7.2 Prior to examination, standar
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