ASTM E2192-13(2022)

Standard Guide for Planar Flaw Height Sizing by Ultrasonics

SIGNIFICANCE AND USE
5.1 The practices referenced in this document are applicable to measuring the height of planar flaws open to the surface that originate on the far-surface or near-surface of the component. These practices are applicable to through-wall sizing of mechanical or thermal fatigue flaws, stress corrosion flaws, or any other surface-connected planar flaws.  
5.2 The techniques outlined describe proven ultrasonic flaw sizing practices and their associated limitations, using refracted longitudinal wave and shear wave techniques as applied to ferritic or austenitic components. Other materials may be examined using this guide with appropriate standardization reference blocks. The practices described are applicable to both manual and automated examinations.  
5.3 The techniques recommended in this standard guide use Time of Flight (TOF) or Delta Time of Flight (ΔTOF) methods to accurately measure the flaw size. This guide does not include the use of signal amplitude methods to determine flaw size.  
5.4 Generally, with these sizing methods the volume of material (or component thickness) to be sized is divided into thirds; the inner 1/3 , the middle 1/3 and the near 1/3. Using the far-surface Creeping Wave Method the user can qualitatively segregate the flaw into the approximate 1/3 zone.  
5.5 The sizing methods are used in 1/3 zones to quantitatively size the crack, that is, Tip-diffraction for the far 1/3 , Bi-Modal method for the middle 1/3 , and the Focused Longitudinal Wave or Focused Shear Wave Methods for the near 1/3 . These 1/3 zones are generally applicable to most sizing applications, however, the various sizing methods have applications outside these 1/3 zones provided a proper reference block and technique is demonstrated.
SCOPE
1.1 This guide provides tutorial information and a description of the principles and ultrasonic examination techniques for measuring the height of planar flaws which are open to the surface. The practices and technology described in this standard guide are intended as a reference to be used when selecting a specific ultrasonic flaw sizing technique as well as establishing a means for instrument standardization.2  
1.2 This standard guide does not provide or suggest accuracy or tolerances of the techniques described. Parameters such as search units, examination surface conditions, material composition, etc. can all have a bearing on the accuracy of results. It is recommended that users assess accuracy and tolerances applicable for each application.  
1.3 This guide does not purport to provide instruction to measure flaw length.  
1.4 This standard guide does not provide, suggest, or specify acceptance standards. After flaw-sizing evaluation has been made, the results should be applied to an appropriate code or standard that specifies acceptance criteria.  
1.5 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
1.6 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 requirements prior to use.  
1.7 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-2022
• 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 E1316-14e1 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jun-2014
• Refers: ASTM E1316-14 - 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 E2192-13(2022), Standard Guide for Planar Flaw Height Sizing by Ultrasonics, is an international standard issued by ASTM that details guidelines for measuring the through-wall height of planar flaws open to the surface using ultrasonic examination. This standard provides essential tutorial information, technical definitions, and best practices for flaw height sizing, focusing specifically on ultrasonic techniques applied to flaws originating from the far or near-surface of a component. ASTM E2192 is applicable for both manual and automated nondestructive testing (NDT), emphasizing methods suitable for examining ferritic and austenitic materials, but it can also be adapted for other materials with appropriate reference blocks.

Key Topics

• Principles of Ultrasonic Flaw Height Sizing: Describes the fundamentals and sound path modeling for measuring the height of surface-connected planar flaws using ultrasonic testing.
• Applicable Flaw Types: Covers flaw sizing for mechanical or thermal fatigue cracks, stress corrosion cracks, and any surface-connected planar flaws.
• Techniques Covered: Focuses on proven ultrasonic sizing methods such as:
  • Refracted longitudinal and shear wave techniques
  • Time of Flight (TOF) and Delta Time of Flight (ΔTOF) methods
  • Far-surface Creeping Wave and Tip-Diffraction techniques
  • Dual-element Bi-Modal and Focused Wave methods
• Limitations Noted: Specifically excludes the use of signal amplitude methods for flaw sizing and provides no explicit tolerances or measurement accuracy, as sizing may vary based on material properties, equipment, and operator procedure.
• Standardization and Calibration: Stresses the importance of instrument standardization using suitable reference blocks and emphasizes practitioner familiarization with the equipment.

Applications

The ASTM E2192-13(2022) guide has broad practical applications across industries where nondestructive ultrasonic examination is utilized:

• Power Generation: Inspection of pressure vessels, piping, and structural components for fatigue or stress-corrosion flaws.
• Petrochemical and Refining: Assessment of weld integrity and crack height in pipelines and vessels.
• Aerospace: Detection and evaluation of planar flaws in critical aerospace structures and components.
• Manufacturing and Heavy Industry: Quality control and maintenance to ensure component reliability and safety.
• Field and Laboratory Settings: Procedures are applicable for both manual and automated ultrasonic testing, making them useful for field inspections and controlled laboratory analyses.

The guide recommends dividing the material thickness into thirds (near, middle, far) when applying specific sizing methods and selecting the most appropriate technique based on flaw location and material characteristics. Practitioners must select relevant tip-diffraction, bi-modal, or focused wave techniques to match the inspection objective, and standardize instruments with blocks that match component materials.

Related Standards

To ensure complete compliance and effective implementation, users should refer to related standards and documents:

• ASTM E1316 – Terminology for Nondestructive Examinations
• ASTM E543 – Specification for Agencies Performing Nondestructive Testing
• ASNT SNT-TC-1A – Personnel Qualification and Certification in Nondestructive Testing
• ANSI/ASNT CP-189 – Qualification and Certification of Nondestructive Testing Personnel
• AIA NAS-410 – Nondestructive Testing Personnel Qualification and Certification

Users should ensure that personnel are qualified according to recognized certification standards and that agency qualifications and examination procedures are specified in project agreements.

Practical Value

Using ASTM E2192-13(2022) ensures:

• Consistent and reliable flaw height measurements in surface-connected cracks.
• Applicability across multiple industries and materials, promoting safety and code compliance.
• Up-to-date ultrasonic testing practices that meet internationally recognized NDT and trade requirements.
• Clear basis for instrument calibration and standardization, enabling accurate, reproducible sizing results.

Adopting this standard enhances the effectiveness of ultrasonic nondestructive testing and supports the integrity and longevity of critical infrastructure.

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: E2192 − 13 (Reapproved 2022)
Standard Guide for
Planar Flaw Height Sizing by Ultrasonics
This standard is issued under the fixed designation E2192; 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 2. Referenced Documents
1.1 This guide provides tutorial information and a descrip- 2.1 ASTM Standards:
tionoftheprinciplesandultrasonicexaminationtechniquesfor E1316 Terminology for Nondestructive Examinations
measuring the height of planar flaws which are open to the E543 Specification forAgencies Performing Nondestructive
surface. The practices and technology described in this stan- Testing
dard guide are intended as a reference to be used when
2.2 ASNT Standards
selecting a specific ultrasonic flaw sizing technique as well as
SNT-TC-1A Personnel Qualification and Certification in
establishing a means for instrument standardization.
Nondestructive Testing
ANSI/ASNT-CP-189 Standard for Qualification and Certifi-
1.2 This standard guide does not provide or suggest accu-
cation of Nondestructive Testing Personnel
racyortolerancesofthetechniquesdescribed.Parameterssuch
2.3 AIA Standards
as search units, examination surface conditions, material
composition, etc. can all have a bearing on the accuracy of NAS-410 Nondestructive Testing Personnel Qualification
and Certification
results. It is recommended that users assess accuracy and
tolerances applicable for each application.
3. Terminology
1.3 This guide does not purport to provide instruction to
3.1 Definitions—Related terminology is defined in Termi-
measure flaw length.
nology E1316.
1.4 This standard guide does not provide, suggest, or
3.2 Definitions of Terms Specific to This Standard:
specify acceptance standards. After flaw-sizing evaluation has
3.2.1 corner reflection—the reflected ultrasonic energy re-
beenmade,theresultsshouldbeappliedtoanappropriatecode
sulting from the interaction of ultrasound with the intersection
or standard that specifies acceptance criteria.
of a flaw and the component surface at essentially 90 degrees.
1.5 The values stated in SI units are to be regarded as the
3.2.2 doublet—two ultrasonic signals that appear on the
standard. The values given in parentheses are for information
screen simultaneously and move in unison as search unit is
only.
manipulated toward and away from the flaw. During tip-
1.6 This standard does not purport to address all of the
diffraction flaw sizing, the flaw tip signal and flaw base signal
safety concerns, if any, associated with its use. It is the
(corner reflector) will appear as a doublet.
responsibility of the user of this standard to establish appro-
3.2.3 far-surface—the surface of the examination piece
priate safety, health, and environmental practices and deter-
opposite the surface on which the search unit is placed. (For
mine the applicability of regulatory requirements prior to use.
example, when examining pipe from the outside surface the
1.7 This international standard was developed in accor-
far-surface would be the inside pipe surface).
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the 3.2.4 focus—the term as used in this document applies to
Development of International Standards, Guides and Recom- dualcrossed-beamsearchunitsthathavebeenmanufacturedso
mendations issued by the World Trade Organization Technical that they have a maximum sensitivity at a predetermined depth
Barriers to Trade (TBT) Committee. or sound path in the component. Focusing effect may be
1 3
This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc- For referenced ASTM standards, visit the ASTM website, www.astm.org, or
tive Testing and is the direct responsibility of Subcommittee E07.06 on Ultrasonic contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Method. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Dec. 1, 2022. Published December 2022. Originally the ASTM website.
approved in 2002. Last previous edition approved in 2018 as E2192 – 13(2018). AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
DOI: 10.1520/E2192-13R22. 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org
2 5
ThisStandardGuideisadaptedfrommaterialsuppliedtoASTMSubcommittee Available fromAerospace IndustriesAssociation ofAmerica, Inc. (AIA), 1000
E07.06 by the Electric Power Research Institute (EPRI). Wilson Blvd., Suite 1700,Arlington,VA22209-3928, http://www.aia-aerospace.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2192 − 13 (2022)
obtained with the use of dual-element search units having both 5.5 The sizing methods are used in ⁄3 zones to quantita-
refracted and roof angles applied to each element. tively size the crack, that is, Tip-diffraction for the far ⁄3,
Bi-Modal method for the middle ⁄3, and the Focused Longi-
3.2.5 near-surface—the surface of the examination piece on
tudinal Wave or Focused Shear Wave Methods for the near ⁄3
whichthesearchunitisplaced.(Forexample,whenexamining
. These ⁄3 zones are generally applicable to most sizing
pipe from the outside surface the near-surface would be the
applications, however, the various sizing methods have appli-
outside pipe surface).
cations outside these ⁄3 zones provided a proper reference
3.2.6 sizing—measurement of the through-wall height or
block and technique is demonstrated.
depth dimension of a discontinuity or flaw.
6. Basis of Application
3.2.7 30-70-70—term that is applied to the technique (and
sometimes the search unit) using an incident angle that
6.1 The following items are subject to contractual agree-
produces a nominal 70° L wave in the examination piece.
ment between the parties using or referencing this standard.
Provided that a parallel far-surface exists, the 30° shear wave,
6.2 Personnel Qualification
produced simultaneously at the near surface, reflects as a 30°
6.2.1 If specified in the contractual agreement, personnel
shear wave and generates a nominal 70° L wave as a result of
performing examinations to this standard shall be qualified in
mode conversion off the far-surface. The 70° L wave reflects
accordance with a nationally or internationally recognized
off a planar flaw and is received by the search unit as a 70° L
NDT personnel qualification practice or standard such as
wave.
ANSI/ASNT-CP-189, SNT-TC-1A, NAS-410, or a similar
document and certified by the employer or certifying agency,
4. Summary of Guide
as applicable. The practice or standard used and its applicable
4.1 This guide describes methods for the following flaw
revision shall be identified in the contractual agreement be-
sizing techniques.
tween the using parties.
4.1.1 Far-surface creeping wave or mode conversion
6.3 Qualification of Nondestructive Agencies—If specified
method,
in the contractual agreement, NDT agencies shall be qualified
4.1.2 Flaw-tip-diffraction method,
and evaluated as described in Specification E543. The appli-
4.1.3 Dual element bi-modal method, and
cable edition of Specification E543 shall be specified in the
4.1.4 Dual element, (focused) longitudinal wave or dual
contractual agreement.
element, (focused) shear wave methods.
6.4 Procedures and Techniques—The procedures and tech-
4.2 In this guide, ultrasonic sound paths are generally
niques to be utilized shall be as specified in the contractual
shown diagrammatically by single lines in one plane that
agreement.
represent the center of the ultrasonic energy.
6.5 Reporting Criteria/Acceptance Criteria—Reporting cri-
4.3 Additional information on flaw sizing techniques may
teria for the examination results are not specified in this
be found in the references listed in the Bibliography section.
standard, they shall be specified in the contractual agreement.
5. Significance and Use
6.6 Reexamination of Repaired/Reworked Items—
5.1 Thepracticesreferencedinthisdocumentareapplicable Reexamination of repaired/reworked items is not addressed in
to measuring the height of planar flaws open to the surface that this standard and if required shall be specified in the contrac-
originate on the far-surface or near-surface of the component. tual agreement.
These practices are applicable to through-wall sizing of me-
7. Ultrasonic Flaw Sizing Methods
chanical or thermal fatigue flaws, stress corrosion flaws, or any
other surface-connected planar flaws.
7.1 30-70-70 Mode Conversion or Far-surface Creeping
Wave Method—The far-surface Creeping Wave or 30-70-70
5.2 The techniques outlined describe proven ultrasonic flaw
Mode Conversion method (as illustrated in Fig. 1) provides
sizingpracticesandtheirassociatedlimitations,usingrefracted
qualitative additional depth sizing information. This method
longitudinal wave and shear wave techniques as applied to
has considerable potential for use when approximating flaw
ferritic or austenitic components. Other materials may be
size, or, determining that the flaw is far-surface connected.
examined using this guide with appropriate standardization
7.1.1 Excitation of Creeping Waves—The excitation of re-
referenceblocks.Thepracticesdescribedareapplicabletoboth
fracted longitudinal waves is always accompanied by refracted
manual and automated examinations.
shear waves. In the vicinity of the excitation, the separation
5.3 The techniques recommended in this standard guide use
between these two wave modes is not significantly distinct.At
Time of Flight (TOF) or DeltaTime of Flight (∆TOF) methods
the surface, a longitudinal wave cannot exist independently of
toaccuratelymeasuretheflawsize.Thisguidedoesnotinclude
a shear wave because neither mode can comply with the
the use of signal amplitude methods to determine flaw size.
boundaryconditionsforthehomogeneouswaveequationatthe
5.4 Generally, with these sizing methods the volume of free surface alone; consequently, the so-called headwave is
material (or component thickness) to be sized is divided into formed. The headwave is always generated if a wave mode
1 1 1
thirds; the inner ⁄3, the middle ⁄3 and the near ⁄3. Using the with higher velocity (the longitudinal wave) is coupled to a
far-surface Creeping Wave Method the user can qualitatively wave mode with lower velocity (the direct shear wave) at an
segregate the flaw into the approximate ⁄3 zone. interface. The longitudinal wave continuously energizes the
E2192 − 13 (2022)
FIG. 1 Wave Generation for the Far-surface Creeping Wave/30-70-70 Mode-Conversion Search Unit
shear wave. It can be concluded that the longitudinal wave, A far-surface creeping wave signal, as a result of mode
which in fact “creeps” along the surface, is completely attenu- conversion of the indirect shear wave.
ated a short distance from the location of the excitation. (See 7.1.3.1 Direct Longitudinal Wave Signal—If the flaw ex-
Fig. 2 for generation of the near-side creeping wave). With the tends to within approximately 10 to 16 mm (0.375 to 0.625 in.)
propagation of the near-surface creeping wave and its continu- of the scanning surface (near surface), the direct longitudinal
ous conversion process at each point it reaches, the energy wave will reflect from the upper extremity of the flaw face,
convertedtoshearisdirectedintothematerialasshowninFig. which is very similar to the high-angle longitudinal wave
3. Thus, the wave front of the headwave includes the head of sizing method discussed later.
the creeping wave, direct and indirect shear waves. 7.1.3.2 Mode Converted Signal—If the flaw exceeds a
7.1.2 Far-Surface Creeping Wave Generation—When the height of 10 to 20 % of the wall thickness, an indication from
headwave arrives at the far-surface of the component, the same the mode converted signal will occur at a typical wall
wave modes will be generated which were responsible for thickness-related position. This mode converted signal results
generating the shear wave energy, due to the physical law of from the headwave or direct shear wave, which mode converts
reciprocity. Thus, the indirect shear wave and part of the direct the 70-degree longitudinal wave that impinges on the reflector
shear wave will convert into a far-surface creeping wave and a at its highest part; it is reflected as a 70-degree longitudinal
70-degree longitudinal wave. The far-surface creeping wave wave back to the search unit as depicted by position 1 in Fig.
will be extremely sensitive to small surface-breaking reflectors 4. The presence of the mode-converted echo is a strong
and the longitudinal wave will be engulfed in a bulk longitu- indicationofaflawwithaheightgreaterthan10to20 %ofthe
dinal beam created by beam spread.Additionally, these reflec- wall thickness. In the case of smooth or at least open flaws,
tion mechanisms are responsible for a beam offset so that there amplitude versus height function curves can give a coarse
is a maximum far-surface creeping wave sensitivity at about 5 estimate of flaw height.
to 6 mm (0.20 to 0.24 in.) from the ideal conversion point on 7.1.3.3 Far-Surface Creeping Wave Signal—If a far-surface
thefarsurface.Thesensitivityrangeofthefar-surfacecreeping connected reflector is within the range of sensitivity (as
wave extends from approximately 2 to 13 mm (0.080 to 0.52 described above), the far-surface creeping wave will be re-
in.) in front of the index point. The far-surface creeping wave, flected and mode converted into the headwave or shear wave
as reflected from the base of a far-surface notch or flaw, will directed to the search unit (Fig. 5). Since the far-surface
convert its energy into a headwave since the same principles creeping wave is not a surface wave, it will not interact with
apply as established earlier for the near-surface creeping wave. weld root convexity and will not produce an indication from
The shear wave will continue to convert at multiple V-paths if the root as shown by position 1 in Fig. 6. However, if the
the material has low attenuation and noise levels. search unit is moved too far toward the weld centerline, the
7.1.3 Typical Echoes of the Far-Surface Creeping Wave/30- direct shear wave beam could result in a root signal, but there
70-70 Mode Conversion Technique—When the search unit is at least 5 mm (0.2 in.) difference in positioning as shown in
approaches a far-surface connected reflector, three different Fig. 6. The far-surface creeping wave signal is a clear, sharp
signalswilloccurinsequence:(1)70-degreelongitudinalwave signal with a larger amplitude than the mode converted signal.
direct reflection; (2) 30-70-70 mode-converted signal; and (3) It does not have as smooth an echo-dynamic behavior as does
FIG. 2 Near-Surface Creeping Wave Occurs for a Short Distance in Association with the Incident Longitudinal Wave
E2192 − 13 (2022)
FIG. 3 Generation of S-Waves (Headwaves) by an L-Wave with Grazing Incidence
1—Mode-Converted Signal
2—Far-Surface Creeping-Wave Signal
FIG. 4 Search Unit Index Point Position
FIG. 5 Generation of Far-Surface Creeping Wave Signal
the mode converted signal, and it cannot be observed over as 7.2 Tip-Diffraction Method—Ultrasonic diffraction is a phe-
long a distance as shown in Fig. 7. nomenon where ultrasound tends to bend around sharp corners
E2192 − 13 (2022)
1—Flaw indication maximized for mode-converted wave signal
2—Flaw indication maximized for creeping-wave signal
FIG. 6 Far-Surface Creeping Wave Search Unit Position Related to Index Point
or ends of an object placed in its path, as illustrated in Fig. 8. 7.2.1 Time of Flight (TOF) Sizing Technique—The TOF
While the flaw tends to cast a shadow, diffraction occurs at the sizing technique is a tip-diffraction technique that takes advan-
flaw tips and ultrasonic energy is bent to fill part of the shadow tage of uniquely locating the flaw tip. The signal from the flaw
region. Sharp edges are diffraction centers tending to radiate tip is peaked (maximized), and its arrival time or sound path is
spherical or cylindrical wave fronts as though they were measured without regard to the arrival time of other signals.
actually ultrasonic point or line sources. If the screen signals This time of flight or sound path is then a direct measurement
correlating to these diffraction centers are identified, it is of the remaining ligament (material) above the flaw, or the
possibletodeterminetheirpositionsrelativetothethicknessof distance from the flaw tip to the examination surface. This
the component. The tip-diffraction method relies on this technique is illustrated in Fig. 9. Note that here the second
principle. Although the tip-diffraction concept sounds simple, half-V path is possible also. When the search unit is moved
there are many other signals that may complicate screen away from the flaw, the tip echo may again be obtained after
interpretation. This is due to the fact that the ultrasound/planar the tip-diffracted signal reflects off the opposite surface of the
flaw interaction is very complex. When ultrasound strikes a component. With the second half-V path technique, the tip
flaw, specular reflection from the main plane of the flaw and signal will occur later in time than the signal from the flaw
texture reflections from flaw surface facets occur in addition to corner reflector.
diffraction and mode conversions. There are two standardiza-
NOTE1—Itisveryimportantthattheuserbeextremelyconsciousofthe
tion and measuring techniques for tip-diffraction sizing: (1 )
weld geometry when using the second half-V path since, for example, the
The Time of Flight (TOF) technique that measures the arrival
counterbore can exaggerate flaw height.
time of the tip-diffracted signal from the top of the flaw and
NOTE2—Longitudinalwavesshouldnotbeappliedwhenpracticingthe
secondhalf-Vpathtechniqueasthiscancausemodeconversionsthatmay
locates the top of the flaw with respect to the near surface; and
interfere with the ability to interpret the instrument display.
(2) The Delta Time of Flight (∆TOF) technique that measures
the difference in arrival time of the tip-diffracted signal and the 7.2.2 Delta Time of Flight (∆TOF) Technique—The ∆TOF
corner reflector signal at the far surface. Technique is applied by observing the arrival time difference
E2192 − 13 (2022)
FIG. 7 Echo-Dynamic Behavior of Mode-Converted Echo Signal and Far-Surface Creeping-Wave Signal
FIG. 8 Corners or Ends of Reflectors are Diffraction Centers and Tend to Radiate Spherical or Cylindrical Waves
between the flaw corner reflector signal and the diffracted to its shorter sound path.The tip signal amplitude is very small
signal from the flaw tip while both are simultaneously present in comparison to the flaw corner reflector signal; and the flaw
on the ultrasonic instrument display. While using this
tip and corner signals are out of phase due to one signal being
technique, the ultrasonic beam diameter must be greater than
diffracted and the other reflected twice. To measure flaw
the projected height of the flaw (actual height multiplied by the
height, it is necessary to note the difference in the time of
sine of the refracted beam angle) and the flaw must be
arrival between the two signals, then apply the following
essentially perpendicular to the examination surface. In this
formula:
situation, the tip-diffracted signal will occur earlier in time due
E2192 − 13 (2022)
FIG. 9 Various Metal Paths (MP) from Different Search Unit Positions Used in the TOF Technique
v~δt! readily confused with the true tip signal. Some flaws produce
h 5
2cosθ
multiple tip signals that must be resolved. The ability of the
operator to distinguish between tip and corner signals can be
where:
compromised if several cracks are clustered in the same area.
h = flaw height,
In areas of clustered cracks, corner reflections will dominate
v = ultrasonic velocity in the material,
and mask tip signals. In cases of clustered cracks, the depth of
δt = difference in arrival time, and
thepeakedsignalmaybetheonlyreliablemeanstodistinguish
θ = refracted beam angle.
the tip signals from the corner signals. The tip-diffraction
Alternately,theultrasonicinstrumentmaybestandardizedto
methods can be valid for a wide range of flaw heights. The
read directly in flaw height. This standardization method will
prerequisites are that the tip of the flaw and the tip signal be
be addressed in the standardization section. Separation be-
distinguishable from other signals. For very shallow flaws, the
tween the doublets should remain constant as the signals move
tip signal may be masked by the flaw corner-reflector signal
across the screen. The echo dynamic of the doublet is asyn-
due to poor resolution. A search unit with a shorter pulse
chronous; however, since it is the fixed interval between the
duration will improve this limitation. Broadband search units
doublet arrival times that is measured, it is not necessary to
havebeennotedfortheirshortpulsedurations;however,dueto
maximize the response from either signal. This technique
dispersion in austenitic stainless steel weld metal, it may be
allows measurement when the weld crown is wide, preventing
beneficial to select a narrow-band search unit with greater
maximization of the tip signal. It may also be possible to note
a tip signal after reflection from the back surface (second penetrating characteristics. This argument holds true for very
half-V path). The principles are the same as for the first half-V deep flaws also. When the flaw is located in the weld region or
path except that the tip signal will appear later in time than the
very near the weld region, longitudinal waves may be consid-
cornerreflectorsignal.Whetherusingthefirstorsecondhalf-V
ered for the tip-diffraction method. Longitudinal waves may
path, accuracy of the height measurement depends on the flaw
help locate weak tip-diffracted signals in highly attenuative
orientation. If the flaw is vertical, then the measurement is
stainless steel but reflection from the component far surface
accurate. If the flaw is oriented toward the search unit, the first
should be avoided due to mode conversion. A very important
half-V path measurement will overestimate the height and the
factor in the sizing of planar flaws using the tip-diffraction
secondhalf-Vpathmeasurementwillunderestimatetheheight.
method is signal pattern recognition. To size with this method,
The opposite occurs for flaws oriented away from the search
the user must be able to identify two signals: (1) a signal that
unit.
is diffracted from the flaw tip and (2) a second signal that is
7.2.3 Application Considerations—For all of the physics
reflected from the base of the flaw. The task of identifying the
involved in tip diffraction, the method relies on the user’s
two signals is complicated by the high-amplitude noise signals
ability to uniquely identify the location of the flaw tip. The
and geometric signals from the component surface. Some
signal need not originate singly from diffraction, since reflec-
ultrasonic instruments allow the user the option of using the
tion can also occur very near the flaw tip. In fact, reflection is
un-rectified or rectified display (RF display) signals. In many
the mechanism that will primarily be observed when using
cases, an RF display facilitates in distinguishing the tip signal
notched reference blocks. It is reasonable to expect some
from noise signals by identifying the phase of the signals. The
reflection to occur at an actual flaw tip. The associated rough
signal from the tip of the flaw must always peak when the
texture will often act as a good scattering center. It should be
search unit is moved forward from the point where the corner
noted, however, that this may not be true in every case and the
signal is maximized (for first half-V path) or backed up from
amplitudes of the signals received may be 20-30 dB below the
the point where the corner signal is maximized (for second
flaw corner-reflector signal amplitude. Each component and
half-V path). This distance traveled is directly related to flaw
material type examined should be considered as a separate
height. The examiner must become accustomed to the search
examination problem. The flawed area should be adequately
unitmovementasitrelatestoflawheightbybecomingfamiliar
scanned so that all signals, which occur in the region, can be
with the characteristics observed when sizing notches of
identified. Care should be taken to define the tip signal since
some geometries or weld flaws produce signals that can be known heights.
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7.3 Dual-Element Bi-Modal Method—The Bi-Modal Sizing examination, however, this is also applicable to carbon steel
Method is based on the use of a dual-element search unit. This materials. As shown in Fig. 10, the Bi-Modal search unit
dual-element search unit is designed to insonify the entire wall transmits one longitudinal wave, and two shear waves and
thickness by transmitting and receiving high-angle refracted receives two longitudinal waves (one from the tip of the flaw
longitudinal waves as well as low-angle shear waves. For this and one from the base of the flaw), one mode-converted signal
reason, the Bi-Modal sizing methods that feature the dual- from the flaw face, and one far-surface Creeping wave signal
element search unit are applicable to far-surface connected from the base of the flaw when the search unit is operated in its
planarflawsfrom10to90 %through-wall.TheTOFtechnique normal dual element mode. Depending upon search unit
requires that the first signal, the longitudinal wave, be maxi- design, either element can be used as the transmitter or the
mized or peaked and the peaked first signal is measured along receiver. The directivity patterns of the Bi-Modal search units
the instrument time base which is standardized in through-wall are quite broad due to the relatively small active element size
depth. The ∆TOF technique is particularly useful because the and low operating frequency in the region of 3 MHz.
flaw height-related separation between the direct longitudinal Therefore, the high-angle longitudinal waves and the low-
wave and mode-converted signal can be measured before the angle shear waves insonify the entire component wall thick-
search unit is restricted by the weld crown. For the ∆TOF ness. Four associated signals that move together on the
technique, both measurements are independent of signal am- instrument screen can be expected when the search unit is
plitudes. A20 % far-surface notch and an 80 % far-surface scanned over a far-surface connected flaw with broad back-
notcharesufficienttostandardizethetimebaseforcomponents and-forth movements, (Fig. 11).This follows from the premise
in the thickness range of 10 to 40 mm (0.4 to 1.6 in.). Flaw that while the longitudinal waves interact effectively with both
height may then be read directly on the screen in percent of extremities of the flaw (the tip and the base), the shear waves
wallthickness.Theextentoftheflawisindicatedbythesignals interactonlywiththeflawbase.Thefirstsignaloriginatesfrom
that are observed in the left half of the instrument screen. The theuppertipoftheflaw.Ifeachelementwereatransmitter,the
furtherthedirectlongitudinalwaveispeaked,orthegreaterthe longitudinal wave energy from the two elements would con-
separation of the signals from the mode-converted signal, or verge to this area. The usually weak tip-diffracted signal is
peaks from mid-screen, the deeper the flaw. Signals originating enhanced while the background of irrelevant indications is
from the interaction of shear waves with the base of the flaw, suppressed by restricting the longitudinal wave beams to the
with or without mode conversion, are confined to the right half upperflawtiparea.Thenextsignalcansometimesbeobserved
of the instrument screen and merely indicate that the flaw is from a flaw and is usually observed from a far-surface notch as
far-surface connected. a result of the longitudinal wave from the transmitter reflecting
7.3.1 Wave Propagation Through the Material—It is ac- at the flaw base and being received as a longitudinal wave by
knowledged that shear waves cannot interact effectively with the receiver. The third signal is usually the strongest because it
the upper extremities of tight and branched, medium to large results from the mode-converted shear wave from the face of
flaws that are located near the sound-scattering fusion lines of the flaw. The reflection of the incident shear wave at the flaw
austenitic welds. These may not produce readily recognizable opening results in the fourth signal which is analogous to the
tip-diffracted signals for flaw sizing purposes. The Bi-Modal far-surface creeping wave signal. The echo-dynamic curve is
search unit is designed specifically for austenitic weld broadest for the longitudinal wave signal and narrowest for the
Subscript ’a’ denotes travel to the receiver and subscript ’b’ denotes travel from the transmitter. Enlarged detail note refers to Fig. 11.
FIG. 10 Bi-Modal Search Unit Longitudinal Wave and Shear Wave Signals
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Subscripts as in Fig. 10.
FIG. 11 Interaction of the Incident L-Wave and S-Wave from a Bi-Modal Search Unit with a far-surface Connected Flaw Resulting in Four
Associated Signals
creepingwavesignalasshowninFig.12.Themode-converted divisions and the flaw height in percent of wall thickness is
signal peaks shortly after the flaw is insonified. It follows from very nearly linear and independent of wall thickness.
geometrical considerations that the echo-dynamic curves for 7.3.3 Principles of the ∆TOF Technique—The longitudinal
the longitudinal wave signal and the far-surface creeping wave wave signal may be considered as a satellite of the mode-
signal are nearly synchronous for a large flaw (that is, the rise converted signal since their separation, measured in screen
in the amplitude of one signal is in unison with the amplitude divisions, is practically independent of the axial coordinate of
rise of the other). When the center of the incident longitudinal the search unit relative to that of the flaw. Figs. 14 and 15
wave beam is directed toward the flaw tip, the center of the illustrate the nearly linear relationship between normalized
incident shear wave beam is directed toward the flaw base, and flaw height and this signal separation. The most useful feature
theamplitudeofthelongitudinalwavesignal,aswellasthatof of the Bi-Modal sizing method is that the flaw height can be
the far-surface creeping wave signal, is maximized. Upon measuredanywherealongthelengthoftheflawaslongasboth
movingthesearchunitclosertotheflaw,thelongitudinalwave the longitudinal wave and the mode-converted signals are seen
signal will again recede into the background of irrelevant moving in unison on the screen, allowing height measurements
indications. To determine the arrival time of this signal, the to be made even when a wide weld crown is present.Asecond
user typically moves the search unit toward the flaw until the ∆TOF measurement may sometimes be used to confirm the
amplitude drops. flaw height. This second measurement is obtained by noting
7.3.2 Principles of Bi-Modal TOF Technique—Weld crown the difference in arrival time of the longitudinal wave signal
permitting, the search unit may be moved toward the weld far and the longitudinal wave signal reflected from the flaw base.
enoughtopeakthelongitudinalwavesignal.Fig.13showsthat These two signals also move in unison and form a linear
the relationship between the signal arrival time in screen relationship when the flaw is oriented vertically.
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FIG. 12 Asynchronous Echo-Dynamic Curves for a 50 % Deep far-surface Notch
FIG. 13 Correlation of Normalized Flaw Height With Time Delay, τ, Obtained by the Bi-Modal Time of Flight Technique
7.4 Focused Longitudinal Wave or Dual-Elements Focused which are mid-wall to very deep. The use of high beam angles
Shear Wave Methods—The dual-element focused longitudinal results in this technique being the most accurate for very deep
or dual-element focused shear wave flaw sizing techniques are flaws. As with the tip-diffraction method, the signal from the
essentially the TOF or sound-path measurement techniques flaw tip is maximized or peaked and its time of flight or sound
withtheuseoffocusedlongitudinalorshearwavesearchunits, path is recorded without regard to the arrival time of other
generally greater than 50 % from the far surface in depth. signals.Thefocusedlongitudinalwaveandfocusedshearwave
These techniques are particularly suitable for sizing flaws sizing techniques are used to measure the remaining ligament
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FIG. 14 Relationships Among Normalized Flaw Height, h/t, Doublet Separation, σ and Time Delay, τ
FIG. 15 Correlation of Normalized Flaw Height With Doublet Separation, σ, Obtained by the Bi-Modal ∆TOF Technique
of good material between the flaw and the scanning surface. ligamentfromthelocalwallthickness.Occasionally,thesignal
Actual flaw height is obtained by subtracting the remaining associated with the upper extreme of a flaw is due to beam
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reflection rather than diffraction.This is most prevalent when a beams at the far surface and utilize the responses from these
flaw follows the weld fusion line toward the outside surface of beams to categorize flaw height. This goal is met by using
theweldandisorientedawayfromtheweldandthesearchunit 70-degree longitudinal waves or refracted longitudinal waves
is placed on the weld reinforcement and directed at the flaw. In at 55 degrees and higher.
this case instead of a diffracted wave returning to the search
8.1.1.2 Frequency—To limit beam spread and its degrada-
unit, the upper extreme of the flaw face reflects ultrasonic
tion of sizing accuracy, higher frequencies than those com-
energy back to the search unit. The result is a high-amplitude
monly used during examination are suggested. Narrow-band
signal with a long or broad echo-dynamic pattern. Due to an
search units will avoid the beam spread caused by the
obliquely oriented flaw, a flaw height measurement obtained in
low-frequency components of the spectrum. A frequency of 2
thismannertendstoundersizetheflawwhenthelocationofthe
MHz seems ideal for austenitic material, while 4 MHz seems
peak reflection is used as the tip location. The user must
more effective for carbon steel materials.
compensatebymovingthesearchunittowardtheflawuntilthe
8.1.1.3 Elements—Specially designed search units with
signal drops by about 3 dB or by finding the slight rise in
single- or dual-element search units may be used. It is very
amplitude along the leading edge of the echo-dynamic pattern,
difficult to eliminate internal wedge reflections and entry
which is due to the diffracted wave from the flaw tip.
surface noise with a 70-degree, single-element search unit.
These single-element problems can only be avoided with long
NOTE 3—Alimitation of this method with a focused longitudinal wave
search unit is that associated shear waves (if not properly identified) may
wedge paths. This can lead to increased beam size and make
cause confusion and could result in mode-converted signals that may
search unit movement difficult. Element size is significant.
produce erroneous measurements.
Very small elements will have excessive angular beam spread,
Search unit frequency, refracted angle, element size, and
and very large elements may produce beams with too much
focal depth are factors for determining the effective range of
penetration. The optimal size will probably be a function of
the technique. Common search unit frequencies are 2 MHz and
wall thickness, with larger elements being acceptable for
4 MHz, with the lower frequency preferred for coarse grain
greater thickness. Generally, a 10 mm or a 0.375 in. diameter
materials, for example, austenitic. The effectiveness of sizing
or square search unit will work for most applications.
with high-angle longitudinal waves is strongly dependent on
8.1.1.4 ContactArea—Thesearchunitcontactareaor“foot-
the selection of a search unit that produces a beam shape
print” should be as small as practical. With dual search units,
appropriate to the application. When sizing a flaw in thin-wall
smallsearchunitwidthisnecessaryforpropercouplingofboth
material, select a beam angle that does not penetrate very
elements to the scanning surface. Short length is desirable for
deeply into the component. For thicker-wall material, increase
adequate coupling in pipe weld conditions of diametrical weld
the penetration depth by reducing the frequency to increase
shrinkage, especially if the shrinkage is made more severe by
beam spread or by reducing the incident angle for a lower
grinding of the weld crown. If the search unit is too long, there
central refracted angle, that is, a 60-degree or a 45-degree
may be entry angle variations with strong effects on the
longitudinal wave or shear wave search unit. It is essential to
refracted angle.
measure the focal depth of the search unit using a reference
8.1.2 Instrument—A pulse-echo ultrasonic instrument ca-
block that contains a series of known reflectors at different
pable of generating and receiving frequencies in the range of at
depths.
least 1 to 5 MHz should be suitable for sizing with the
8. Ultrasonic Flaw Sizing Standardization Requirements far-surface Creeping Wave or 30-70-70 mode conversion
method.The instrument should exhibit adequate resolution and
8.1 Far-Surface Creeping Wave Method—The far-surface
high filtering capabilities.
Creeping Wave Sizing Method depends upon pattern recogni-
8.1.3 Reference Block—Standardization for the far-surface
tion of the three potential signals that may be observed, for
Creeping Wave technique requires special far-surface notch
example, 70-degree L wave, the mode converted signal or the
reference blocks. The block must have a set of notches located
far-surface creeping wave signal. By observing the absence or
at various depths from the far surface. The simplest design is a
presence of these three signals, the echo dynamics of the
flat plate or pipe section with far-surface notches located at
signal, and the time of flight of the 70-degree L wave signal, a
increments of 10 % or 20 % depths, for example, 10 %, 20 %,
user can classify a far-surface connected crack into the far ⁄3,
1 1
40 %, 60 %, 80 %. The user should become familiar with the
middle ⁄3, or the near ⁄3 zone of the material thickness to be
absenceorpresenceofthe70-degreeLwavesignal,thetimeof
inspected.
flight of the 70-degree L wave signal, the amplitudes and
8.1.1 Search Unit—The pattern of the three signals strongly
echo-dynamic patterns of the mode-converted signal and the
depends on several search unit parameters. Before attempting
far-surface creeping wave signal as different depth notches are
to apply this method with a new search unit, the sound wave
encountered. If these notches are used to familiarize the user
patterns should be evaluated using known notch reflectors at
with various signals that may be encountered, the block should
various depths, 20 %, 40 %, 60 %, and 80 %. There may be
equal the thickness of the component to be examined.
significant variations between search units with identical face-
plate parameter values, even if they are from the same 8.1.4 System Standardization—The far-surface Creeping
manufacturer. Generally, a single-element search unit is suit- Wave or 30-70-70 mode conversion technique does not depend
able for most applications. onthearrivaltimeoftheflawtipsignal,sothesystemdoesnot
8.1.1.1 Beam Angle—The primary intent when sizing with have to be standardized accurately for distance. The same
the far-surface Creeping Wave method is to produce different search unit used for the refracted longitudinal wave sizing
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method may be used for the far-surface Creeping Wave standardize the screen to read directly in depth as a function of
technique. Use a notched block for standardization following a percent of component thickness. This approach is generally
these steps:
more convenient.
8.1.4.1 Adjustthedelaytodisplaytheinitialpulseattheleft
8.2.1 Search Units—When selecting a search unit for sizing
side of the screen.
planar flaws using the tip-diffraction method, the following
8.1.4.2 Place the search unit near the end of the reference
guidelines should be considered: (1) A very high signal-to-
block. Observe the 70-degree mode converted L wave signal
noise ratio is desired. This characteristic is governed by the
and creeping wave signals.
frequency, diameter, and wave mode; (2) High-resolution
8.1.4.3 Peak the creeping wave signal, and adjust delay and
search units (higher frequency, shorter pulse length) will aid in
range controls to position the 70-degree mode converted L
sizing very shallow flaws because the tip and base signals are
wave and creeping wave signals at 4 and 5 screen divisions
close together and nearly coincident in time; (3) High-
respectively.
resolution search units work well with the time of flight (TOF)
8.1.4.4 Adjust the creeping wave signal amplitude to 80 to
technique; (4) Large beam spread may be beneficial when
100 % full screen height. Then increase the instrument ampli-
sizing suspected midrange flaws with the delta time of flight
tude by 8 dB.This reference level is now the primary scanning
technique because this technique requires viewing of the tip
and evaluation level.
and base signals simultaneously; (5) The characteristics of the
8.1.4.5 Place the search unit to peak the creeping wave
search unit selected should be thoroughly investigated with
signal from the 20 % notch. Record echo dynamic movement
reference blocks before attempting any sizing techniques; (6)
of the 70-degree mode converted L wave signal as the search
Longitudinalwavescanenhancethetipsignalbutmayproduce
unit is scanned toward and away from the far-surface con-
spurious mode-converted indications; (7) The distance from
nected notch.
the front of the search unit to the beam index point should be
8.1.4.6 Place the search unit to peak the creeping wave
minimal in order to maximize the diffracted signal from the
signal from the 40 % notch. Record the echo dynamic move-
flaw tip when a wide weld crown is present; and (8) Beware of
ment of the 70-degree mode converted L wave signal as the
reflections that may occur from within the search unit wedge.
search unit is scanned toward and away from the far-surface
These can occur in the area of interest on the display and can
connected notch. If present, record the amplitude of the
increase the difficulty of identifying the tip signal. Various
70-degree L wave signal.
search unit designs with different element sizes and arrange-
8.1.4.7 Place the search unit to peak the creeping wave
ments can be used. It must be pointed out that the individual
signal from the 60 % notch. Then record echo dynamic
search unit design parameters greatly influence their effective-
movement of the 70-degree mode converted L wave signal as
ness. For the Tip-diffraction method using delta time of flight
the search unit is scanned toward and away from the far-
technique, a search unit that is highly damped to a maximum
surfaceconnectednotch.Ifpresent,recordtheamplitudeofthe
pulse length of one and one half to two cycles at the -6 dB
70-degree L wave signal. Increase the gain to bring the
points is desirable.This will improve resolution for sizing very
70-degree L wave signal up to at least 40 % full screen height
shallow flaws, that is, less than 10 % wall thickness. Search
(FSH). Peak the longitudinal wave signal and record the
unitcharacteristicsmustbedocumentedadequatelypriortouse
horizontal screen division position, for example, 2.5 divisions.
if examination repeatability is necessary.
8.1.4.8 Place the search unit to peak the creeping wave
signal from the 80 % notch. Then record echo dynamic
8.2.1.1 Beam Angle—Re
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