ASTM E1901-23

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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: E1901 − 18 E1901 − 23
Standard Guide for
Detection and Evaluation of Discontinuities by Contact
Pulse-Echo Straight-Beam Ultrasonic Methods
This standard is issued under the fixed designation E1901; 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 guide covers procedures for the contact ultrasonic examination of bulk materials or parts by transmitting pulsed ultrasonic
waves into the material and observing the indications of reflected waves. This guide covers only examinations in which one search
unit is used as both transmitter and receiver (pulse-echo). This guide includes general requirements and procedures that may be
used for detecting discontinuities, locating depth and distance from a point of reference and for making a relative or approximate
evaluation of the size of discontinuities as compared to a reference standard.
1.2 This guide complements Practice E114 by providing more detailed procedures for the selection and standardization of the
examination system and for evaluation of the indications obtained.
1.3 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 guide 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 guide to establish the 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.
2. Referenced Documents
2.1 ASTM Standards:
E114 Practice for Ultrasonic Pulse-Echo Straight-Beam Contact Testing
E127 Practice for Fabrication and Control of Flat Bottomed Hole Ultrasonic Standard Reference Blocks
E317 Practice for Evaluating Performance Characteristics of Ultrasonic Pulse-Echo Testing Instruments and Systems without the
Use of Electronic Measurement Instruments
E428 Practice for Fabrication and Control of Metal, Other than Aluminum, Reference Blocks Used in Ultrasonic Testing
(Withdrawn 2019)
E543 Specification for Agencies Performing Nondestructive Testing
E1158 Guide for Material Selection and Fabrication of Reference Blocks for the Pulsed Longitudinal Wave Ultrasonic Testing
of Metal and Metal Alloy Production Material (Withdrawn 2019)
This guide 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 July 1, 2018July 1, 2023. Published July 2018July 2023. Originally approved in 1997. Last previous edition approved in 20132018 as
E1901 - 13.E1901 – 18. DOI: 10.1520/E1901-18.10.1520/E1901-23.
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
E1901 − 23
E1316 Terminology for Nondestructive Examinations
2.2 ASNT Standard:
SNT-TC-1A Recommended Practice for Personnel Qualification and Certification in Nondestructive Testing Personnel
2.3 ANSI/ASNT Standard:
ANSI/ASNT CP-189 ASNT Standard for Qualification and Certification of Nondestructive Testing Personnel
2.4 Aerospace Industries Association Document:
NAS-410 NAS Certification and Qualification of Nondestructive Test Personnel
2.5 ISO StandardStandard:
ISO 9712 Non-destructive testing — Qualification and certification of NDT personnel
3. Terminology
3.1 Definitions—For definitions of terms used in this guide, see Terminology E1316.
4. Basis for Application
4.1 Contractual Agreement—The using parties cognizant engineering organization and the suppliers should agree on the
applicable procedural requirements, as listed herein,requirements listed in 4.1.1 through 4.1.12, prior to the examination of any
material.
4.1.1 Materials, sizes, and shapes examined,examined.
4.1.2 Stage of manufacture when examined (time of examination), examination).
4.1.3 Surface finish requirements,requirements.
4.1.4 Minimum equipment requirements, as in Table 1 herein,
4.1.4 Search unit size, frequency and type,type.
4.1.5 Couplant,
4.1.6 Automated turning, fixturing or scanning, or both, as applicable,applicable.
TABLE 1 Minimum Equipment Requirements (Longitudinal Wave)
Ultrasonic
Test
Instrument Characteristics Frequency
MHZ
(Record)
Vertical limit, in. (mm) or percent
Vertical limit, percent of full screen height
of full screen height
Upper vertical linearity limit in. (mm)
or percent of full screen height
Upper vertical linearity limit, percent of full screen height
Lower vertical linearity limit in. (mm)
or percent of full screen height
Lower vertical linearity limit, percent of full screen height
Ultrasonic sensitivity, hole size,
Ultrasonic sensitivity, Reflector size, in. (mm)
64 ths, distance, in (mm)
Entry surface resolution, in. (mm)
Back surface resolution in. (mm)
Horizontal limit, in. (mm) or
percent of full screen width
Horizontal limit, percent of full screen width
Horizontal linearity range, in. (mm) or percent of full screen width
or percent of full screen width
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.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), 1, ch. de la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org.
E1901 − 23
4.1.7 Type of reference block standards including surface curvature,curvature.
4.1.8 Standardization details, including attenuation compensation and DAC techniques,techniques.
4.1.9 The surfaces to be examined and the scanning path, path.
4.1.10 Acceptance standards,standards.
4.1.11 Personnel certification level, andlevel.
4.1.12 Instrument characteristics.
4.2 Written Procedure—Ultrasonic examinations performed in accordance with this guide should be detailed in a written
procedure. Documentation of procedure qualification should be maintained by the preparer. Procedures should be sufficiently
detailed so that other qualified personnel may duplicate the examination and obtain equivalent results.
4.3 Personnel Qualifications—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, should be identified in the contractual agreement
between the using parties.
4.4 If specified in the contractual agreement, NDT agencies should be qualified and evaluated as described in Practice E543.
5. Summary of Guide
5.1 This guide describes a means for obtaining an evaluation of discontinuities in materials by contact examination using
longitudinal waves. Equipment, reference standards, examination and evaluation procedures, and documentation of results are
described in detail.
6. Significance and Use
6.1 This guide provides procedures for the application of contact straight-beam examination for the detection and quantitative
evaluation of discontinuities in materials.
6.2 Although not all requirements of this guide can be applied universally to all examinations, situations, and materials, it does
provide basis for establishing contractual criteria between the users, and may be used as a general guide for preparing detailed
specifications for a particular application.
6.3 This guide is directed towards the evaluation of discontinuities detectable with the beam normal to the entry surface. If
discontinuities or other orientations are of concern, alternate scanning techniques are required.
7. Apparatus
7.1 Apparatus should include the following:
7.1.1 Electronic Equipment—The electronic equipment should be capable of producing and processing electronic signals at
frequencies in the range of the search unit frequencies being used. The equipment and its display should provide characteristics
as listed in Table 1, that are suitable for the specific application at the specified frequency, as determined in accordance with the
procedures and tolerances described in Practice E317. The equipment, including the search unit, should be capable of producing
echo amplitudes of at least 60 % of full screen height from the reference reflector required for the examination, with the material
noise level, from front to back surface not exceeding 20 % of full screen height. Alternatively, if these conditions can be met at
one half the part thickness, the part may be inspected from both sides.
NOTE 1—The using parties should agree on the minimum instrument characteristics prior to conducting an examination.
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7.1.2 Voltage Regulator—If fluctuations in line voltage cause indication amplitude variations exceeding 6 ⁄2 dB, a voltage
regulator should be required on the power source. This requirement is not applicable to battery-operated units.
7.1.3 Search Units—The contact search unit selected should be capable of transmitting and receiving ultrasound at the required
frequencies and energy levels necessary for discontinuity detection in the material being examined. Only longitudinal wave,
straight beam, non-focused search units should be used. Dual element search units may provide better near-surface resolution and
detection of small discontinuities. Generally, round or rectangular search units are used for examination whereas round search units
with symmetrical sound beam patterns are used for evaluation. Typical search unit sizes range from ⁄8 in. (3.2 mm) in diameter
to 1-1 ⁄8 in. (28.6 mm) in diameter with other sizes and shapes available for special applications. Search units may be fitted with
contoured shoes to enhance coupling with curved surfaces.
7.1.4 Alarm(s)—For the examination of parts with regular shape and parallel surfaces such as machined cylinders, rounds, bars,
forgings, etc. an audible/visual alarm may be used in conjunction with visual monitoring of the display for the detection of
discontinuities or for the monitoring and detection of loss of back surface reflection, or both. The alarm should be adjustable to
allow triggering at commonly required indication amplitudes, back-echo heights, and depths. During examination the audible
visual alarm should be easily detectable by the operator.
7.1.4.1 When reduction in the amplitude of back-surface reflection is monitored simultaneously with the detection of lower
amplitude signals from small, discrete discontinuities, two separate gate/alarm systems are required. The negative slaved alarm
system may also provide for a significantly lower receiver gain at the gated depth to avoid back-echo saturation. See 10.1 and 10.4.
7.1.4.2 For some applications it may be advantageous to utilize a flaw gate system in which the echo-amplitude alarm level can
be varied as a function of target depth. Refer to distance/amplitude gate (DAG) in 9.3.2.1.
7.2 Couplant—A couplant, usually a liquid or semi-liquid, is required between the face of the search unit and the examination
surface to permit transmittance of ultrasound from the search unit into the material under examination unless the transducer is
specially designed for “dry” coupling by the manufacturer. Typical couplants include water, cellulose gel, oil, and grease.
Corrosion inhibitors or wetting agents or both may be used. Couplants selected must not be detrimental to the product or the
process. The same couplant used for 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 that will reduce the effective contact area,
or excess couplant, will reduce the amount of energy transferred between the search unit and the examination surface. These
couplant variations, in turn, result in examination sensitivity variations.
7.2.1 The couplant should be selected such 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 and will result in some deterioration of near-surface
discontinuity detection. The temperature of the material surface can change the couplant’s viscosity as in the case of oil and grease.
See Table 2 for the suggested viscosity of oil couplants for given surface roughnesses.
7.2.2 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 part surface or auxiliary cooling of the search unit may be
necessary to avoid temperature changes that affect the ultrasonic characteristics of the search unit. At higher temperatures, certain
couplants based on inorganic salts or thermoplastic organic materials, high-temperature delay materials (shoes) and search units
that are not affected by high temperatures may be required.
7.2.3 Where constant coupling over large areas is required, as in automated examination, or where severe changes in surface
TABLE 2 Suggested Viscosities-Oil Couplants
NOTE 1—This table is a guide and is not meant to exclude the use of a
particular couplant that is found to work satisfactorily on a surface.
Approximate Surface Roughness Average Equivalent Couplant Viscosity
(Ra) μin. (μm) Weight Motor Oil
5-100 (0.1 to 2.5) SAE 10
50-200 (1.3 to 5.1) SAE 20
100-400 (2.5 to 10.2) SAE 30
250-700 (6.4 to 17.8) SAE 40
Over 700 (18+) Cup Grease
E1901 − 23
roughness are found, other methods of coupling 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 0.02 in. (0.5 mm) (0.5 mm) filled
with couplant. Liquid flowing through the search unit mechanism 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 warm.
7.2.4 Another means of direct contact coupling is provided by the wheel search unit. The search unit is mounted at the correct
angle to a stationary axle about which rotates a liquid-filled flexible tire. A minimum amount of couplant provides for ultrasonic
transmission into the examination surface since the elastic tire material is in rolling contact and conforms closely to the surface.
7.3 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, charts such as Distance Gain Size (DGS, also known as AVG in German translation),
representing distance-amplitude relationships of known reflector sizes for a particular search unit, frequency and material may be
used for standardization and evaluation of discontinuities.
7.3.1 Reference Blocks—Ultrasonic reference blocks, often called test blocks, are used to standardize the ultrasonic equipment and
to evaluate the indications received from discontinuities within the part. The ultrasonic characteristics of the reference blocks such
as attenuation, noise level, surface condition, and sound velocity, should be similar to the material to be examined. Standardization
verifies that the instrument search unit is performing as required and establishes a detection level for discontinuities.
7.3.2 Flat Blocks—The three most commonly used sets of reference block are area-amplitude set, containing blocks with the same
material path and various sizes of reference reflectors; distance-amplitude set, containing blocks with one size reference reflector
at various material distances; and a combination including both area-amplitude and distance-amplitude blocks in one set. These
sets are described in PracticesPractice E127 and E428.
7.3.3 Curved Surfaces—Reference blocks with flat surfaces may be used for establishing gain settings for examinations on
concave surfaces and convex surfaces with radii of curvature 4 in. 4 in. (101.6 mm) or greater. For convex surfaces with radii of
curvature less than 4 in. 4 in. (101.6 mm) it is recommended that reference blocks with approximately the same nominal radius
of curvature should be used. Guide E1158 illustrates typical curved entry surface blocks.
7.4 Reference Reflectors—Flat-bottomed holes, (FBH), or other artificial discontinuities, located directly in the material, in a
representative sample of the part or material, or in reference blocks, should be used to reference echo amplitude or to perform
distance-amplitude correction (DAC), or both. For most examinations, the bottom surface of a suitable flat-bottom hole is the
common reference reflector. However, other types of artificial discontinuities (notches, side-drilled holes, areas of unbond or lack
of fusion, etc.) may be used.
8. General Examination Requirements
8.1 Material Condition—Unless otherwise agreed upon, the surface finish of the article under examination should not exceed 250
μin. (6.4 μm) rms and should be free from waviness that may affect the examination. Ultrasonic examination should be performed
in the simplest configuration possible and after all operations that may cause a discontinuity. Examinations of parts or material prior
to machining is acceptable provided surface roughness and part geometry are within the tolerance specified in the written
procedure. When it is determined that surface roughness or waviness, or both, precludes adequate detection and evaluation of
subsurface discontinuities, smooth the areas in question by machining, grinding, or other means prior to the examination. During
examination and evaluation ensure that entry surface free from loose scale, grinding particles, or other loose matter.
8.2 Coverage—In all examinations, perform scanning to locate discontinuities that are oriented parallel with the entry surface, or
plane, or both, approximately normal to the major propagation direction that is parallel to the grain flow of the part.
8.3 Resolution and Penetration—When the complete standardization cannot be accomplished due to excessive noise levels (based
on 3:1 signal-to-noise ratio) or material thicknesses, the examinations should be performed from opposite sides. Examinations
conducted from opposite sides should provide for examination of a minimum of one-half material thickness and should provide
for the resolution and penetration necessary to detect the minimum size reflector at the minimum and maximum metal path
distance.
8.4 Ultra
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