ASTM E2192-13(2018)
(Guide)Standard Guide for Planar Flaw Height Sizing by Ultrasonics
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.
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Designation: E2192 − 13 (Reapproved 2018)
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 service@astm.org. For Annual Book of ASTM
Method. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved July 1, 2018. Published July 2018. Originally approved the ASTM website.
in 2002. Last previous edition approved in 2013 as E2192 - 13. DOI: 10.1520/ AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
E2192-13R18. 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.
*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
E2192 − 13 (2018)
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 (2018)
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
signal
...
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: E2192 − 13 E2192 − 13 (Reapproved 2018)
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*
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.
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 safety, health, and healthenvironmental 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.
2. Referenced Documents
2.1 ASTM Standards:
E1316 Terminology for Nondestructive Examinations
E543 Specification for Agencies Performing Nondestructive Testing
2.2 ASNT Standards
SNT-TC-1A Personnel Qualification and Certification in Nondestructive Testing
ANSI/ASNT-CP-189 Standard for Qualification and Certification of Nondestructive Testing Personnel
2.3 AIA Standards
NAS-410 Nondestructive Testing Personnel Qualification and Certification
3. Terminology
3.1 Definitions—Related terminology is defined in Terminology E1316.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 corner reflection—the reflected ultrasonic energy resulting from the interaction of ultrasound with the intersection of a
flaw and the component surface at essentially 90 degrees.
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 June 1, 2013July 1, 2018. Published June 2013July 2018. Originally approved in 2002. Last previous edition approved in 20082013 as
E2192 - 08.E2192 - 13. DOI: 10.1520/E2192-13.10.1520/E2192-13R18.
This Standard Guide is adapted from material supplied to ASTM Subcommittee E07.06 by the Electric Power Research Institute (EPRI).
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.
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, VA22209-3928, 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
E2192 − 13 (2018)
3.2.2 doublet—two ultrasonic signals that appear on the screen simultaneously and move in unison as search unit is manipulated
toward and away from the flaw. During tip-diffraction flaw sizing, the flaw tip signal and flaw base signal (corner reflector) will
appear as a doublet.
3.2.3 far-surface—the surface of the examination piece opposite the surface on which the search unit is placed. (For example,
when examining pipe from the outside surface the far-surface would be the inside pipe surface).
3.2.4 focus—the term as used in this document applies to dual crossed-beam search units that have been manufactured so that
they have a maximum sensitivity at a predetermined depth or sound path in the component. Focusing effect may be obtained with
the use of dual-element search units having both refracted and roof angles applied to each element.
3.2.5 near-surface—the surface of the examination piece on which the search unit is placed. (For example, when examining pipe
from the outside surface the near-surface would be the outside pipe surface).
3.2.6 sizing—measurement of the through-wall height or depth dimension of a discontinuity or flaw.
3.2.7 30-70-70—term that is applied to the technique (and sometimes the search unit) using an incident angle that produces a
nominal 70° L wave in the examination piece. Provided that a parallel far-surface exists, the 30° shear wave, produced
simultaneously at the near surface, reflects as a 30° shear wave and generates a nominal 70° L wave as a result of mode conversion
off the far-surface. The 70° L wave reflects off a planar flaw and is received by the search unit as a 70° L wave.
4. Summary of Guide
4.1 This guide describes methods for the following flaw sizing techniques.
4.1.1 Far-surface creeping wave or mode conversion method,
4.1.2 Flaw-tip-diffraction method,
4.1.3 Dual element bi-modal method, and
4.1.4 Dual element, (focused) longitudinal wave or dual element, (focused) shear wave methods.
4.2 In this guide, ultrasonic sound paths are generally shown diagrammatically by single lines in one plane that represent the
center of the ultrasonic energy.
4.3 Additional information on flaw sizing techniques may be found in the references listed in the Bibliography section.
5. 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
1 1 1
inner ⁄3, the middle ⁄3 and the near ⁄3. Using the far-surface Creeping Wave Method the user can qualitatively segregate the flaw
into the approximate ⁄3 zone.
1 1
5.5 The sizing methods are used in ⁄3 zones to quantitatively size the crack, that is, Tip-diffraction for the far ⁄3, Bi-Modal
1 1 1
method for the middle ⁄3, and the Focused Longitudinal Wave or Focused Shear Wave Methods for the near ⁄3 . These ⁄3 zones
are generally applicable to most sizing applications, however, the various sizing methods have applications outside these ⁄3 zones
provided a proper reference block and technique is demonstrated.
6. Basis of Application
6.1 The following items are subject to contractual agreement between the parties using or referencing this standard.
6.2 Personnel Qualification
6.2.1 If specified in the contractual agreement, personnel performing examinations to this standard shall be qualified in
accordance with a nationally or internationally recognized NDT personnel qualification practice or standard such as ANSI/ASNT-
CP-189, SNT-TC-1A, NAS-410, or a similar document and certified by the employer or certifying agency, as applicable. The
practice or standard used and its applicable revision shall be identified in the contractual agreement between the using parties.
6.3 Qualification of Nondestructive Agencies—If specified in the contractual agreement, NDT agencies shall be qualified and
evaluated as described in Specification E543. The applicable edition of Specification E543 shall be specified in the contractual
agreement.
E2192 − 13 (2018)
6.4 Procedures and Techniques—The procedures and techniques to be utilized shall be as specified in the contractual agreement.
6.5 Reporting Criteria/Acceptance Criteria—Reporting criteria for the examination results are not specified in this standard,
they shall be specified in the contractual agreement.
6.6 Reexamination of Repaired/Reworked Items—Reexamination of repaired/reworked items is not addressed in this standard
and if required shall be specified in the contractual agreement.
7. Ultrasonic Flaw Sizing Methods
7.1 30-70-70 Mode Conversion or Far-surface Creeping Wave Method—The far-surface Creeping Wave or 30-70-70 Mode
Conversion method (as illustrated in Fig. 1) provides qualitative additional depth sizing information. This method has considerable
potential for use when approximating flaw size, or, determining that the flaw is far-surface connected.
7.1.1 Excitation of Creeping Waves—The excitation of refracted longitudinal waves is always accompanied by refracted shear
waves. In the vicinity of the excitation, the separation between these two wave modes is not significantly distinct. At the surface,
a longitudinal wave cannot exist independently of a shear wave because neither mode can comply with the boundary conditions
for the homogeneous wave equation at the free surface alone; consequently, the so-called headwave is formed. The headwave is
always generated if a wave mode with higher velocity (the longitudinal wave) is coupled to a wave mode with lower velocity (the
direct shear wave) at an interface. The longitudinal wave continuously energizes the shear wave. It can be concluded that the
longitudinal wave, which in fact “creeps” along the surface, is completely attenuated a short distance from the location of the
excitation. (See Fig. 2 for generation of the near-side creeping wave). With the propagation of the near-surface creeping wave and
its continuous conversion process at each point it reaches, the energy converted to shear is directed into the material as shown in
Fig. 3. Thus, the wave front of the headwave includes the head of the creeping wave, direct and indirect shear waves.
7.1.2 Far-Surface Creeping Wave Generation—When the headwave arrives at the far-surface of the component, the same wave
modes will be generated which were responsible for generating the shear wave energy, due to the physical law of reciprocity. Thus,
the indirect shear wave and part of the direct shear wave will convert into a far-surface creeping wave and a 70-degree longitudinal
wave. The far-surface creeping wave will be extremely sensitive to small surface-breaking reflectors and the longitudinal wave will
be engulfed in a bulk longitudinal beam created by beam spread. Additionally, these reflection mechanisms are responsible for a
beam offset so that there is a maximum far-surface creeping wave sensitivity at about 5 to 6 mm (0.20 to 0.24 in.) from the ideal
conversion point on the far surface. The sensitivity range of the far-surface creeping wave extends from approximately 2 to 13 mm
(0.080 to 0.52 in.) in front of the index point. The far-surface creeping wave, as reflected from the base of a far-surface notch or
flaw, will convert its energy into a headwave since the same principles apply as established earlier for the near-surface creeping
wave. The shear wave will continue to convert at multiple V-paths if the material has low attenuation and noise levels.
7.1.3 Typical Echoes of the Far-Surface Creeping Wave/30-70-70 Mode Conversion Technique—When the search unit
approaches a far-surface connected reflector, three different signals will occur in sequence: (1) 70-degree longitudinal wave direct
reflection; (2) 30-70-70 mode-converted signal; and (3) A far-surface creeping wave signal, as a result of mode conversion of the
indirect shear wave.
7.1.3.1 Direct Longitudinal Wave Signal—If the flaw extends to within approximately 10 to 16 mm (0.375 to 0.625 in.) of the
scanning surface (near surface), the direct longitudinal wave will reflect from the upper extremity of the flaw face, which is very
similar to the high-angle longitudinal wave sizing method discussed later.
7.1.3.2 Mode Converted Signal—If the flaw exceeds a height of 10 to 20 % of the wall thickness, an indication from the mode
converted signal will occur at a typical wall thickness-related position. This mode converted signal results from the headwave or
direct shear wave, which mode converts the 70-degree longitudinal wave that impinges on the reflector at its highest part; it is
reflected as a 70-degree longitudinal wave back to the search unit as depicted by position 1 in Fig. 4. The presence of the
mode-converted echo is a strong indication of a flaw with a height greater than 10 to 20 % of the wall thickness. In the case of
smooth or at least open flaws, amplitude versus height function curves can give a coarse estimate of flaw height.
FIG. 1 Wave Generation for the Far-surface Creeping Wave/30-70-70 Mode-Conversion Search Unit
E2192 − 13 (2018)
FIG. 2 Near-Surface Creeping Wave Occurs for a Short Distance in Association with the Inci
...
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