ASTM A418/A418M-15(2020)
(Practice)Standard Practice for Ultrasonic Examination of Turbine and Generator Steel Rotor Forgings
Standard Practice for Ultrasonic Examination of Turbine and Generator Steel Rotor Forgings
SIGNIFICANCE AND USE
3.1 This practice shall be used when ultrasonic inspection is required by the order or specification for inspection purposes where the acceptance of the forging is based on limitations of the number, amplitude, or location of discontinuities, or a combination thereof, which give rise to ultrasonic indications.
3.2 The acceptance criteria shall be clearly stated as order requirements.
SCOPE
1.1 This practice for ultrasonic examination covers turbine and generator steel rotor forgings covered by Specifications A469/A469M, A470/A470M, A768/A768M, and A940/A940M. This practice shall be used for contact testing only.
1.2 This practice describes a basic procedure of ultrasonically inspecting turbine and generator rotor forgings. It does not restrict the use of other ultrasonic methods such as reference block calibrations when required by the applicable procurement documents nor is it intended to restrict the use of new and improved ultrasonic test equipment and methods as they are developed.
1.3 This practice is intended to provide a means of inspecting cylindrical forgings so that the inspection sensitivity at the forging center line or bore surface is constant, independent of the forging or bore diameter. To this end, inspection sensitivity multiplication factors have been computed from theoretical analysis, with experimental verification. These are plotted in Fig. 1 (bored rotors) and Fig. 2 (solid rotors), for a true inspection frequency of 2.25 MHz, and an acoustic velocity of 2.30 in./s × 105 in./s [5.85 cm/s × 105 cm/s]. Means of converting to other sensitivity levels are provided in Fig. 3. (Sensitivity multiplication factors for other frequencies may be derived in accordance with X1.1 and X1.2 of Appendix X1.)
FIG. 1 Bored Forgings
Note 1: Sensitivity multiplication factor such that a 10 % indication at the forging bore surface will be equivalent to a 1/8 in. [3 mm] diameter flat bottom hole. Inspection frequency: 2.0 MHz or 2.25 MHz. Material velocity: 2.30 in./s × 105 in./s [5.85 cm/s × 105 cm/s].
FIG. 2 Solid Forgings
Note 1: Sensitivity multiplication factor such that a 10 % indication at the forging centerline surface will be equivalent to a 1/8 in. [3 mm] diameter flat bottom hole. Inspection frequency: 2.0 MHz or 2.25 MHz. Material velocity: 2.30 in./s × 105 in./s [5.85 cm/s × 105 cm/s].
FIG. 3 Conversion Factors to Be Used in Conjunction with Fig. 1 and Fig. 2 if a Change in the Reference Reflector Diameter is Required
1.4 Considerable verification data for this method have been generated which indicate that even under controlled conditions very significant uncertainties may exist in estimating natural discontinuities in terms of minimum equivalent size flat-bottom holes. The possibility exists that the estimated minimum areas of natural discontinuities in terms of minimum areas of the comparison flat-bottom holes may differ by 20 dB (factor of 10) in terms of actual areas of natural discontinuities. This magnitude of inaccuracy does not apply to all results but should be recognized as a possibility. Rigid control of the actual frequency used, the coil bandpass width if tuned instruments are used, and so forth, tend to reduce the overall inaccuracy which is apt to develop.
1.5 This practice for inspection applies to solid cylindrical forgings having outer diameters of not less than 2.5 in. [64 mm] nor greater than 100 in. [2540 mm]. It also applies to cylindrical forgings with concentric cylindrical bores having wall thicknesses of 2.5 [64 mm] in. or greater, within the same outer diameter limits as for solid cylinders. For solid sections less than 15 in. [380 mm] in diameter and for bored cylinders of less than 7.5 in. [190 mm] wall thickness the transducer used for the inspection will be different than the transducer used for larger sections.
1.6 Supplementary requirements of an optional nature are provided for use at the option of the...
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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: A418/A418M − 15 (Reapproved 2020)
Standard Practice for
Ultrasonic Examination of Turbine and Generator Steel
Rotor Forgings
This standard is issued under the fixed designationA418/A418M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* should be recognized as a possibility. Rigid control of the
actual frequency used, the coil bandpass width if tuned
1.1 This practice for ultrasonic examination covers turbine
instruments are used, and so forth, tend to reduce the overall
and generator steel rotor forgings covered by Specifications
inaccuracy which is apt to develop.
A469/A469M, A470/A470M, A768/A768M, and A940/
A940M. This practice shall be used for contact testing only.
1.5 This practice for inspection applies to solid cylindrical
forgings having outer diameters of not less than 2.5 in. [64
1.2 This practice describes a basic procedure of ultrasoni-
mm] nor greater than 100 in. [2540 mm]. It also applies to
cally inspecting turbine and generator rotor forgings. It does
cylindrical forgings with concentric cylindrical bores having
not restrict the use of other ultrasonic methods such as
wall thicknesses of 2.5 [64 mm] in. or greater, within the same
reference block calibrations when required by the applicable
outer diameter limits as for solid cylinders. For solid sections
procurement documents nor is it intended to restrict the use of
less than 15 in. [380 mm] in diameter and for bored cylinders
new and improved ultrasonic test equipment and methods as
oflessthan7.5in.[190mm]wallthicknessthetransducerused
they are developed.
for the inspection will be different than the transducer used for
1.3 This practice is intended to provide a means of inspect-
larger sections.
ing cylindrical forgings so that the inspection sensitivity at the
1.6 Supplementary requirements of an optional nature are
forging center line or bore surface is constant, independent of
provided for use at the option of the purchaser. The supple-
the forging or bore diameter.To this end, inspection sensitivity
mentary requirements shall apply only when specified indi-
multiplication factors have been computed from theoretical
vidually by the purchaser in the purchase order or contract.
analysis, with experimental verification. These are plotted in
Fig. 1 (bored rotors) and Fig. 2 (solid rotors), for a true
1.7 This practice is expressed in both inch-pound units and
inspection frequency of 2.25 MHz, and an acoustic velocity of
in SI units; however, unless the purchase order or contract
5 5
2.30 in./s × 10 in./s [5.85 cm/s × 10 cm/s]. Means of
specifies the applicable M specification designation (SI units),
converting to other sensitivity levels are provided in Fig. 3.
the inch-pound units shall apply. The values stated in either
(Sensitivitymultiplicationfactorsforotherfrequenciesmaybe
inch-pound units or SI units are to be regarded separately as
derived in accordance with X1.1 and X1.2 of Appendix X1.)
standard. Within the practice, the SI units are shown in
brackets. The values stated in each system are not necessarily
1.4 Considerableverificationdataforthismethodhavebeen
exact equivalents; therefore, to ensure conformance with the
generated which indicate that even under controlled conditions
standard,eachsystemshallbeusedindependentlyoftheother,
very significant uncertainties may exist in estimating natural
and values from the two systems shall not be combined.
discontinuities in terms of minimum equivalent size flat-
bottom holes. The possibility exists that the estimated mini-
1.8 This standard does not purport to address all of the
mum areas of natural discontinuities in terms of minimum
safety concerns, if any, associated with its use. It is the
areas of the comparison flat-bottom holes may differ by 20 dB
responsibility of the user of this standard to establish appro-
(factorof10)intermsofactualareasofnaturaldiscontinuities.
priate safety, health, and environmental practices and deter-
This magnitude of inaccuracy does not apply to all results but
mine the applicability of regulatory limitations prior to use.
1.9 This international standard was developed in accor-
dance with internationally recognized principles on standard-
This practice is under the jurisdiction of ASTM Committee A01 on Steel,
Stainless Steel and RelatedAlloys and is the direct responsibility of Subcommittee
ization established in the Decision on Principles for the
A01.06 on Steel Forgings and Billets.
Development of International Standards, Guides and Recom-
Current edition approved March 1, 2020. Published March 2020. Originally
mendations issued by the World Trade Organization Technical
approved in 1957. Last previous edition approved in 2015 as A418/A418M–15.
DOI: 10.1520/A0418_A0418M–15R20. Barriers to Trade (TBT) Committee.
*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
A418/A418M − 15 (2020)
NOTE 1—Sensitivity multiplication factor such that a 10% indication at the forging bore surface will be equivalent to a ⁄8 in. [3 mm] diameter flat
5 5
bottom hole. Inspection frequency: 2.0 MHz or 2.25 MHz. Material velocity: 2.30 in./s × 10 in./s [5.85 cm/s × 10 cm/s].
FIG. 1 Bored Forgings
2. Referenced Documents A768/A768MSpecificationforVacuum-Treated12%Chro-
mium Alloy Forgings for Turbine Rotors and Shafts
2.1 The reference is to the latest issue of these designations
(Withdrawn 2018)
that appear in the Annual Book of ASTM Standards or are
A788/A788MSpecification for Steel Forgings, General Re-
available as separate reprints. It shall also apply to product
quirements
specifications, which may be issued when specifically refer-
A940/A940M Specification for Vacuum Treated Steel
enced therein.
Forgings, Alloy, Differentially Heat Treated, for Turbine
2.2 ASTM Standards: 3
Rotors (Withdrawn 2017)
A469/A469MSpecification for Vacuum-Treated Steel Forg-
E317PracticeforEvaluatingPerformanceCharacteristicsof
ings for Generator Rotors
Ultrasonic Pulse-Echo Testing Instruments and Systems
A470/A470MSpecificationforVacuum-TreatedCarbonand
without the Use of Electronic Measurement Instruments
Alloy Steel Forgings for Turbine Rotors and Shafts
E1065/E1065MPractice for Evaluating Characteristics of
Ultrasonic Search Units
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 last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
A418/A418M − 15 (2020)
NOTE 1—Sensitivity multiplication factor such that a 10 % indication at the forging centerline surface will be equivalent to a ⁄8 in. [3 mm] diameter
5 5
flat bottom hole. Inspection frequency: 2.0 MHz or 2.25 MHz. Material velocity: 2.30 in./s × 10 in./s [5.85 cm/s × 10 cm/s].
FIG. 2 Solid Forgings
2.3 Other Standard: and other local configurations, access to inspect some portions
Recommended Practice No. SNT-TC-1APersonnel Qualifi- of a forging may be limited.
cation and Certification in Nondestructive Testing
4.2 The ultrasonic inspection shall be performed after final
heat treatment of the forging. In those cases in which wheels,
3. Significance and Use
slots, or similar features are machined into the forging before
3.1 Thispracticeshallbeusedwhenultrasonicinspectionis
heat treatment, the entire forging shall be inspected ultrasoni-
required by the order or specification for inspection purposes
cally before such machining, and as completely as practicable
where the acceptance of the forging is based on limitations of
after the final heat treatment.
the number, amplitude, or location of discontinuities, or a
4.3 For overall scanning, the ultrasonic beam shall be
combination thereof, which give rise to ultrasonic indications.
introducedradially.Toconformwiththisrequirement,external
3.2 The acceptance criteria shall be clearly stated as order
conical surfaces of the forging shall be replaced by stepped
requirements.
surfacesinordertomaintaintheultrasonicbeamperpendicular
to the longitudinal axis. Such stepped surfaces shall be shown
4. General Requirements
on the forging drawing.
4.1 Asfaraspossible,theentirevolumeoftheforgingshall
besubjectedtoultrasonicinspection.Becauseoffilletsatsteps
4.4 Forgingsmaybetestedeitherstationaryorwhilerotated
bymeansofalatheorrollers.Ifnotspecifiedbythepurchaser,
either method may be used at the manufacturer’s option.
AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org. Scanning speed shall not exceed 6 in./s [15 cm/s].
A418/A418M − 15 (2020)
FIG. 3 Conversion Factors to Be Used in Conjunction with Fig. 1 and Fig. 2 if a Change in the Reference Reflector Diameter is Required
4.5 To ensure complete coverage of the forging volume, the either a broadband transducer, or a narrow-band tuned trans-
search unit shall be indexed no more than 75% of the ducer of known and matching frequency.
transducerwidthwitheachpassofthesearchunit.Mechanized
6.1.1 Apparatus Qualification and Calibration—Basic
inspection of the rotating forging wherein the search unit is
qualification of the ultrasonic test instrument shall be per-
mechanically controlled is an aid in meeting this requirement.
formed at intervals not to exceed 12 months or whenever
maintenance is performed that affects the equipment function.
4.6 Frequencies of 1, 2.25, and 5 MHz may be used for
Thedateofthelastcalibrationandthedateofthenextrequired
accurately locating, determining orientation, and defining spe-
calibration shall be displayed on the test equipment.
cific discontinuities detected during overall scanning as de-
6.1.2 Thehorizontallinearityshallbecheckedonadistance
scribed in 4.4.
calibration bar using the multiple order technique (see Practice
4.7 Axial scanning, if required, shall be performed at that
E317). The horizontal linearity shall be 62% of the metal
frequency and transducer diameter which minimizes interfer-
path.
ing ultrasonic reflections due to forging geometry and which
6.1.3 If the rotor has a coupling or similar thin axial section
gives optimum resolution. (Axial tests are normally used as a
with parallel sides, the accuracy of the linearity shall be
supplement to radial tests.)
checked by ultrasonically verifying the thickness of the cou-
pling or axial section. If necessary, minor adjustments for
5. Personnel Requirements
differences in the ultrasonic velocities between the calibration
5.1 Personnelperformingtheultrasonicexaminationstothis
bar and the forging shall then be made.
practice shall be qualified and certified in accordance with a
written procedure conforming to Recommended Practice No. 6.2 Amplifier—The amplifier and display shall provide lin-
SNT-TC-1A or another national standard that is acceptable to ear response within 62%, up to 100% of full screen height.
both the purchaser and the supplier.
6.2.1 Amplifier Calibration—An amplifier vertical linearity
check shall be made prior to performing the test by observing
6. Pulsed Ultrasonic Reflection Equipment and
a multiple order pattern from a calibration block using a 2.25
Accessories
MHz transducer (see Practice E317). The first back reflection
6.1 Electronic Apparatus—Apulse-echo instrument permit- shall be set at 100% of full screen height. The higher order
ting inspection frequencies of 1, 2.25, and 5 MHz is required. back reflections, 10% and higher in amplitude, shall also be
The accuracy of discontinuity amplitude analysis using this positioned on the screen and their amplitudes noted. The first
practice involves a knowledge of the true operating frequency back reflection shall be reduced to 50% and then 25% of full
of the complete inspection system. One of the best ways to screen height. The amplitudes of the higher order back reflec-
obtain the desired accuracy is by use of a tuned pulser and tions shall be noted at each step. The vertical linearity will be
narrow band amplifier of known frequency response, with considered acceptable if the signal heights of the higher order
A418/A418M − 15 (2020)
reflections decrease in proportion to the decrease set for the in. [380 mm] in diameter and bored sections having wall
first back reflection. The maximum acceptable error for the thicknesses of less than 7.5 in. [190 mm].
decrease of the higher order reflections is the greater of 65%
8.1.1.2 Use a ⁄4 in. by 1 in. [6 mm by 24 mm] (or 1 in. [24
of the expected back reflection height or 62% of full screen
mm] diameter), 2.0 MHz or 2.25 MHz transducer to inspect
height.
solidsections15in.[380mm]orgreaterindiameterandbored
sectionshavingwallthicknessesof7.5in.[190mm]orgreater.
6.3 Signal Attenuator—The instrument shall contain a cali-
8.1.2 The reference signal shall be the signal reflected from
brated gain control or signal attenuator that meets the require-
the diametrically opposed surface for solid (unbored) forgings
ments of Practice E317 (in each case, accurate within 65%)
and from the bore surface of bored forgings. The signal
that will allow indications beyond the linear range of the
amplitude shall be set to 100% full screen height while
instrument to be measured. It is recommended that these
scanning in an indication-free area.
controls permit signal adjustments up to 25 to 1 (28 dB) (see
Fig. 1 and Fig. 2). 8.1.3 The required evaluation sensitivity shall be obtained
by increasing the 100% full screen height reference signal by
6.4 Search Units—Longitudinalwavesearchunitsofknown
the appropriate multiplication factor calculated as follows.
effectivefrequencyshouldbeusedforradialscanning.A ⁄4in.
Establish the inspection sensitivity in accordance with the
by 1 in. [6 mm by 24 mm], 2.0 MHz or 2.25 MHz transducer,
curves in Fig. 1 (bored rotors) and Fig. 2 (solid rotors), which
used with the 1 in. [24 mm] dimension parallel to the forging
show the multiplication factors that shall be used to adjust a
axis, will give a desirable combination of resolution and beam
100% full screen height, bore, or back reflection to the
width on large sections
...
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: A418/A418M − 15 (Reapproved 2020)
Standard Practice for
Ultrasonic Examination of Turbine and Generator Steel
Rotor Forgings
This standard is issued under the fixed designation A418/A418M; 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* should be recognized as a possibility. Rigid control of the
actual frequency used, the coil bandpass width if tuned
1.1 This practice for ultrasonic examination covers turbine
instruments are used, and so forth, tend to reduce the overall
and generator steel rotor forgings covered by Specifications
inaccuracy which is apt to develop.
A469/A469M, A470/A470M, A768/A768M, and A940/
A940M. This practice shall be used for contact testing only.
1.5 This practice for inspection applies to solid cylindrical
forgings having outer diameters of not less than 2.5 in. [64
1.2 This practice describes a basic procedure of ultrasoni-
mm] nor greater than 100 in. [2540 mm]. It also applies to
cally inspecting turbine and generator rotor forgings. It does
cylindrical forgings with concentric cylindrical bores having
not restrict the use of other ultrasonic methods such as
wall thicknesses of 2.5 [64 mm] in. or greater, within the same
reference block calibrations when required by the applicable
outer diameter limits as for solid cylinders. For solid sections
procurement documents nor is it intended to restrict the use of
less than 15 in. [380 mm] in diameter and for bored cylinders
new and improved ultrasonic test equipment and methods as
of less than 7.5 in. [190 mm] wall thickness the transducer used
they are developed.
for the inspection will be different than the transducer used for
1.3 This practice is intended to provide a means of inspect-
larger sections.
ing cylindrical forgings so that the inspection sensitivity at the
1.6 Supplementary requirements of an optional nature are
forging center line or bore surface is constant, independent of
provided for use at the option of the purchaser. The supple-
the forging or bore diameter. To this end, inspection sensitivity
mentary requirements shall apply only when specified indi-
multiplication factors have been computed from theoretical
vidually by the purchaser in the purchase order or contract.
analysis, with experimental verification. These are plotted in
Fig. 1 (bored rotors) and Fig. 2 (solid rotors), for a true
1.7 This practice is expressed in both inch-pound units and
inspection frequency of 2.25 MHz, and an acoustic velocity of
in SI units; however, unless the purchase order or contract
5 5
2.30 in./s × 10 in./s [5.85 cm/s × 10 cm/s]. Means of
specifies the applicable M specification designation (SI units),
converting to other sensitivity levels are provided in Fig. 3.
the inch-pound units shall apply. The values stated in either
(Sensitivity multiplication factors for other frequencies may be
inch-pound units or SI units are to be regarded separately as
derived in accordance with X1.1 and X1.2 of Appendix X1.)
standard. Within the practice, the SI units are shown in
brackets. The values stated in each system are not necessarily
1.4 Considerable verification data for this method have been
exact equivalents; therefore, to ensure conformance with the
generated which indicate that even under controlled conditions
standard, each system shall be used independently of the other,
very significant uncertainties may exist in estimating natural
and values from the two systems shall not be combined.
discontinuities in terms of minimum equivalent size flat-
bottom holes. The possibility exists that the estimated mini-
1.8 This standard does not purport to address all of the
mum areas of natural discontinuities in terms of minimum
safety concerns, if any, associated with its use. It is the
areas of the comparison flat-bottom holes may differ by 20 dB
responsibility of the user of this standard to establish appro-
(factor of 10) in terms of actual areas of natural discontinuities.
priate safety, health, and environmental practices and deter-
This magnitude of inaccuracy does not apply to all results but
mine the applicability of regulatory limitations prior to use.
1.9 This international standard was developed in accor-
dance with internationally recognized principles on standard-
This practice is under the jurisdiction of ASTM Committee A01 on Steel,
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
ization established in the Decision on Principles for the
A01.06 on Steel Forgings and Billets.
Development of International Standards, Guides and Recom-
Current edition approved March 1, 2020. Published March 2020. Originally
mendations issued by the World Trade Organization Technical
approved in 1957. Last previous edition approved in 2015 as A418/A418M–15.
Barriers to Trade (TBT) Committee.
DOI: 10.1520/A0418_A0418M–15R20.
*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
A418/A418M − 15 (2020)
NOTE 1—Sensitivity multiplication factor such that a 10 % indication at the forging bore surface will be equivalent to a ⁄8 in. [3 mm] diameter flat
5 5
bottom hole. Inspection frequency: 2.0 MHz or 2.25 MHz. Material velocity: 2.30 in./s × 10 in./s [5.85 cm/s × 10 cm/s].
FIG. 1 Bored Forgings
2. Referenced Documents A768/A768M Specification for Vacuum-Treated 12 % Chro-
mium Alloy Forgings for Turbine Rotors and Shafts
2.1 The reference is to the latest issue of these designations
(Withdrawn 2018)
that appear in the Annual Book of ASTM Standards or are
A788/A788M Specification for Steel Forgings, General Re-
available as separate reprints. It shall also apply to product
quirements
specifications, which may be issued when specifically refer-
A940/A940M Specification for Vacuum Treated Steel
enced therein.
Forgings, Alloy, Differentially Heat Treated, for Turbine
2.2 ASTM Standards:
Rotors (Withdrawn 2017)
A469/A469M Specification for Vacuum-Treated Steel Forg-
E317 Practice for Evaluating Performance Characteristics of
ings for Generator Rotors
Ultrasonic Pulse-Echo Testing Instruments and Systems
A470/A470M Specification for Vacuum-Treated Carbon and
without the Use of Electronic Measurement Instruments
Alloy Steel Forgings for Turbine Rotors and Shafts
E1065/E1065M Practice for Evaluating Characteristics of
Ultrasonic Search Units
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 last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
A418/A418M − 15 (2020)
NOTE 1—Sensitivity multiplication factor such that a 10 % indication at the forging centerline surface will be equivalent to a ⁄8 in. [3 mm] diameter
5 5
flat bottom hole. Inspection frequency: 2.0 MHz or 2.25 MHz. Material velocity: 2.30 in./s × 10 in./s [5.85 cm/s × 10 cm/s].
FIG. 2 Solid Forgings
2.3 Other Standard: and other local configurations, access to inspect some portions
Recommended Practice No. SNT-TC-1A Personnel Qualifi- of a forging may be limited.
cation and Certification in Nondestructive Testing
4.2 The ultrasonic inspection shall be performed after final
heat treatment of the forging. In those cases in which wheels,
3. Significance and Use
slots, or similar features are machined into the forging before
3.1 This practice shall be used when ultrasonic inspection is
heat treatment, the entire forging shall be inspected ultrasoni-
required by the order or specification for inspection purposes
cally before such machining, and as completely as practicable
where the acceptance of the forging is based on limitations of
after the final heat treatment.
the number, amplitude, or location of discontinuities, or a
4.3 For overall scanning, the ultrasonic beam shall be
combination thereof, which give rise to ultrasonic indications.
introduced radially. To conform with this requirement, external
3.2 The acceptance criteria shall be clearly stated as order
conical surfaces of the forging shall be replaced by stepped
requirements.
surfaces in order to maintain the ultrasonic beam perpendicular
to the longitudinal axis. Such stepped surfaces shall be shown
4. General Requirements
on the forging drawing.
4.1 As far as possible, the entire volume of the forging shall
be subjected to ultrasonic inspection. Because of fillets at steps 4.4 Forgings may be tested either stationary or while rotated
by means of a lathe or rollers. If not specified by the purchaser,
4 either method may be used at the manufacturer’s option.
Available from American Society for Nondestructive Testing (ASNT), P.O. Box
28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org. Scanning speed shall not exceed 6 in./s [15 cm/s].
A418/A418M − 15 (2020)
FIG. 3 Conversion Factors to Be Used in Conjunction with Fig. 1 and Fig. 2 if a Change in the Reference Reflector Diameter is Required
4.5 To ensure complete coverage of the forging volume, the either a broadband transducer, or a narrow-band tuned trans-
search unit shall be indexed no more than 75 % of the ducer of known and matching frequency.
transducer width with each pass of the search unit. Mechanized
6.1.1 Apparatus Qualification and Calibration—Basic
inspection of the rotating forging wherein the search unit is
qualification of the ultrasonic test instrument shall be per-
mechanically controlled is an aid in meeting this requirement.
formed at intervals not to exceed 12 months or whenever
maintenance is performed that affects the equipment function.
4.6 Frequencies of 1, 2.25, and 5 MHz may be used for
The date of the last calibration and the date of the next required
accurately locating, determining orientation, and defining spe-
calibration shall be displayed on the test equipment.
cific discontinuities detected during overall scanning as de-
6.1.2 The horizontal linearity shall be checked on a distance
scribed in 4.4.
calibration bar using the multiple order technique (see Practice
4.7 Axial scanning, if required, shall be performed at that
E317). The horizontal linearity shall be 62 % of the metal
frequency and transducer diameter which minimizes interfer-
path.
ing ultrasonic reflections due to forging geometry and which
6.1.3 If the rotor has a coupling or similar thin axial section
gives optimum resolution. (Axial tests are normally used as a
with parallel sides, the accuracy of the linearity shall be
supplement to radial tests.)
checked by ultrasonically verifying the thickness of the cou-
pling or axial section. If necessary, minor adjustments for
5. Personnel Requirements
differences in the ultrasonic velocities between the calibration
5.1 Personnel performing the ultrasonic examinations to this
bar and the forging shall then be made.
practice shall be qualified and certified in accordance with a
written procedure conforming to Recommended Practice No. 6.2 Amplifier—The amplifier and display shall provide lin-
SNT-TC-1A or another national standard that is acceptable to ear response within 62 %, up to 100% of full screen height.
both the purchaser and the supplier.
6.2.1 Amplifier Calibration—An amplifier vertical linearity
check shall be made prior to performing the test by observing
6. Pulsed Ultrasonic Reflection Equipment and
a multiple order pattern from a calibration block using a 2.25
Accessories
MHz transducer (see Practice E317). The first back reflection
6.1 Electronic Apparatus—A pulse-echo instrument permit- shall be set at 100 % of full screen height. The higher order
ting inspection frequencies of 1, 2.25, and 5 MHz is required. back reflections, 10 % and higher in amplitude, shall also be
The accuracy of discontinuity amplitude analysis using this positioned on the screen and their amplitudes noted. The first
practice involves a knowledge of the true operating frequency back reflection shall be reduced to 50 % and then 25 % of full
of the complete inspection system. One of the best ways to screen height. The amplitudes of the higher order back reflec-
obtain the desired accuracy is by use of a tuned pulser and tions shall be noted at each step. The vertical linearity will be
narrow band amplifier of known frequency response, with considered acceptable if the signal heights of the higher order
A418/A418M − 15 (2020)
reflections decrease in proportion to the decrease set for the in. [380 mm] in diameter and bored sections having wall
first back reflection. The maximum acceptable error for the thicknesses of less than 7.5 in. [190 mm].
decrease of the higher order reflections is the greater of 65 %
8.1.1.2 Use a ⁄4 in. by 1 in. [6 mm by 24 mm] (or 1 in. [24
of the expected back reflection height or 62 % of full screen
mm] diameter), 2.0 MHz or 2.25 MHz transducer to inspect
height.
solid sections 15 in. [380 mm] or greater in diameter and bored
sections having wall thicknesses of 7.5 in. [190 mm] or greater.
6.3 Signal Attenuator—The instrument shall contain a cali-
8.1.2 The reference signal shall be the signal reflected from
brated gain control or signal attenuator that meets the require-
the diametrically opposed surface for solid (unbored) forgings
ments of Practice E317 (in each case, accurate within 65 %)
and from the bore surface of bored forgings. The signal
that will allow indications beyond the linear range of the
amplitude shall be set to 100 % full screen height while
instrument to be measured. It is recommended that these
scanning in an indication-free area.
controls permit signal adjustments up to 25 to 1 (28 dB) (see
Fig. 1 and Fig. 2). 8.1.3 The required evaluation sensitivity shall be obtained
by increasing the 100 % full screen height reference signal by
6.4 Search Units—Longitudinal wave search units of known
the appropriate multiplication factor calculated as follows.
effective frequency should be used for radial scanning. A ⁄4 in.
Establish the inspection sensitivity in accordance with the
by 1 in. [6 mm by 24 mm], 2.0 MHz or 2.25 MHz transducer,
curves in Fig. 1 (bored rotors) and Fig. 2 (solid rotors), which
used with the 1 in. [24 mm] dimension parallel to the forging
show the multiplication factors that shall be used to adjust a
axis, will give a des
...
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: A418/A418M − 15 A418/A418M − 15 (Reapproved 2020)
Standard Practice for
Ultrasonic Examination of Turbine and Generator Steel
Rotor Forgings
This standard is issued under the fixed designation A418/A418M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This practice for ultrasonic examination covers turbine and generator steel rotor forgings covered by Specifications
A469/A469M, A470/A470M, A768/A768M, and A940/A940M. This standardpractice shall be used for contact testing only.
1.2 This practice describes a basic procedure of ultrasonically inspecting turbine and generator rotor forgings. It does not restrict
the use of other ultrasonic methods such as reference block calibrations when required by the applicable procurement documents
nor is it intended to restrict the use of new and improved ultrasonic test equipment and methods as they are developed.
1.3 This practice is intended to provide a means of inspecting cylindrical forgings so that the inspection sensitivity at the forging
center line or bore surface is constant, independent of the forging or bore diameter. To this end, inspection sensitivity multiplication
factors have been computed from theoretical analysis, with experimental verification. These are plotted in Fig. 1 (bored rotors) and
Fig. 2 (solid rotors), for a true inspection frequency of 2.25 MHz, and an acoustic velocity of 2.30 in./s × 10 in./s [5.85 cm/s ×
10 cm/s]. Means of converting to other sensitivity levels are provided in Fig. 3. (Sensitivity multiplication factors for other
frequencies may be derived in accordance with X1.1 and X1.2 of Appendix X1.)
1.4 Considerable verification data for this method have been generated which indicate that even under controlled conditions
very significant uncertainties may exist in estimating natural discontinuities in terms of minimum equivalent size flat-bottom holes.
The possibility exists that the estimated minimum areas of natural discontinuities in terms of minimum areas of the comparison
flat-bottom holes may differ by 20 dB (factor of 10) in terms of actual areas of natural discontinuities. This magnitude of inaccuracy
does not apply to all results but should be recognized as a possibility. Rigid control of the actual frequency used, the coil bandpass
width if tuned instruments are used, and so forth, tend to reduce the overall inaccuracy which is apt to develop.
1.5 This practice for inspection applies to solid cylindrical forgings having outer diameters of not less than 2.5 in. [64 mm] nor
greater than 100 in. [2540 mm]. It also applies to cylindrical forgings with concentric cylindrical bores having wall thicknesses
of 2.5 [64 mm] in. or greater, within the same outer diameter limits as for solid cylinders. For solid sections less than 15 in. [380
mm] in diameter and for bored cylinders of less than 7.5 in. [190 mm] wall thickness the transducer used for the inspection will
be different than the transducer used for larger sections.
1.6 Supplementary requirements of an optional nature are provided for use at the option of the purchaser. The supplementary
requirements shall apply only when specified individually by the purchaser in the purchase order or contract.
1.7 This practice is expressed in both inch-pound units and in SI units; however, unless the purchase order or contract specifies
the applicable M specification designation (SI units), the inch-pound units shall apply. The values stated in either inch-pound units
or SI units are to be regarded separately as standard. Within the practice, the SI units are shown in brackets. The values stated in
each system mayare not benecessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be
used independently of the other. Combiningother, and values from the two systems may result in nonconformance with the
standard.shall not be combined.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.9 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
This practice is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.06
on Steel Forgings and Billets.
Current edition approved May 1, 2015March 1, 2020. Published May 2015March 2020. Originally approved in 1957. Last previous edition approved in 20102015 as
A418/A418M – 10.A418/A418M–15. DOI: 10.1520/A0418_A0418M-15.10.1520/A0418_A0418M–15R20.
*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
A418/A418M − 15 (2020)
NOTE 1—Sensitivity multiplication factor such that a 10 % indication at the forging bore surface will be equivalent to a ⁄8 in. [3 mm] diameter flat
5 5
bottom hole. Inspection frequency: 2.0 MHz or 2.25 MHz. Material velocity: 2.30 in./s × 10 in./s [5.85 cm/s × 10 cm/s].
FIG. 1 Bored Forgings
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
A418/A418M − 15 (2020)
NOTE 1—Sensitivity multiplication factor such that a 10 % indication at the forging centerline surface will be equivalent to a ⁄8 in. [3 mm] diameter
5 5
flat bottom hole. Inspection frequency: 2.0 MHz or 2.25 MHz. Material velocity: 2.30 in./s × 10 in./s [5.85 cm/s × 10 cm/s].
FIG. 2 Solid Forgings
2. Referenced Documents
2.1 The reference is to the latest issue of these designations that appear in the Annual Book of ASTM Standards or are available
as separate reprints. It shall also apply to product specifications, which may be issued when specifically referenced therein.
2.2 ASTM Standards:
A469/A469M Specification for Vacuum-Treated Steel Forgings for Generator Rotors
A470/A470M Specification for Vacuum-Treated Carbon and Alloy Steel Forgings for Turbine Rotors and Shafts
A768/A768M Specification for Vacuum-Treated 12 % Chromium Alloy Forgings for Turbine Rotors and Shafts (Withdrawn
2018)
A788/A788M Specification for Steel Forgings, General Requirements
A940/A940M Specification for Vacuum Treated Steel Forgings, Alloy, Differentially Heat Treated, for Turbine Rotors
(Withdrawn 2017)
E317 Practice for Evaluating Performance Characteristics of Ultrasonic Pulse-Echo Testing Instruments and Systems without the
Use of Electronic Measurement Instruments
E1065/E1065M Practice for Evaluating Characteristics of Ultrasonic Search Units
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.
The last approved version of this historical standard is referenced on www.astm.org.
A418/A418M − 15 (2020)
FIG. 3 Conversion Factors to Be Used in Conjunction with Fig. 1 and Fig. 2 if a Change in the Reference Reflector Diameter is Required
2.3 Other Standards:Standard:
Recommended Practice No. SNT-TC-1A Personnel Qualification and Certification in Nondestructive Testing
3. Significance and Use
3.1 This practice shall be used when ultrasonic inspection is required by the order or specification for inspection purposes where
the acceptance of the forging is based on limitations of the number, amplitude, or location of discontinuities, or a combination
thereof, which give rise to ultrasonic indications.
3.2 The acceptance criteria shall be clearly stated as order requirements.
4. General Requirements
4.1 As far as possible, the entire volume of the forging shall be subjected to ultrasonic inspection. Because of fillets at steps
and other local configurations, access to inspect some portions of a forging may be limited.
4.2 The ultrasonic inspection shall be performed after final heat treatment of the forging. In those cases in which wheels, slots,
or similar features are machined into the forging before heat treatment, the entire forging shall be inspected ultrasonically before
such machining, and as completely as practicable after the final heat treatment.
4.3 For overall scanning, the ultrasonic beam shall be introduced radially. To conform with this requirement, external conical
surfaces of the forging shall be replaced by stepped surfaces in order to maintain the ultrasonic beam perpendicular to the
longitudinal axis. Such stepped surfaces shall be shown on the forging drawing.
4.4 Forgings may be tested either stationary or while rotated by means of a lathe or rollers. If not specified by the purchaser,
either method may be used at the manufacturer’smanufacturer’s option. Scanning speed shall not exceed 6 in./s [15 cm/s].
4.5 To ensure complete coverage of the forging volume, the search unit shall be indexed no more than 75 % of the transducer
width with each pass of the search unit. Mechanized inspection of the rotating forging wherein the search unit is mechanically
controlled is an aid in meeting this requirement.
4.6 Frequencies of 1, 2.25, and 5 MHz may be used for accurately locating, determining orientation, and defining specific
discontinuities detected during overall scanning as described in 4.4.
Available from American Society for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
A418/A418M − 15 (2020)
4.7 Axial scanning, if required, shall be performed at that frequency and transducer diameter which minimizes interfering
ultrasonic reflections due to forging geometry and which gives optimum resolution. (Axial tests are normally used as a supplement
to radial tests.)
5. Personnel Requirements
5.1 Personnel performing the ultrasonic examinations to this practice shall be qualified and certified in accordance with a written
procedure conforming to Recommended Practice No. SNT-TC-1A or another national standard that is acceptable to both the
purchaser and the supplier.
6. Pulsed Ultrasonic Reflection Equipment and Accessories
6.1 Electronic Apparatus—A pulse-echo instrument permitting inspection frequencies of 1, 2.25, and 5 MHz is required. The
accuracy of discontinuity amplitude analysis using this practice involves a knowledge of the true operating frequency of the
complete inspection system. One of the best ways to obtain the desired accuracy is by use of a tuned pulser and narrow band
amplifier of known frequency response, with either a broadband transducer, or a narrow-band tuned transducer of known and
matching frequency.
6.1.1 Apparatus Qualification and Calibration—Basic qualification of the ultrasonic test instrument shall be performed at
intervals not to exceed 12 months or whenever maintenance is performed that affects the equipment function. The date of the last
calibration and the date of the next required calibration shall be displayed on the test equipment.
6.1.2 The horizontal linearity shall be checked on a distance calibration bar using the multiple order technique (see Practice
E317). The horizontal linearity shall be 62 % of the metal path.
6.1.3 If the rotor has a coupling or similar thin axial section with parallel sides, the accuracy of the linearity shall be checked
by ultrasonically verifying the thickness of the coupling or axial section. If necessary, minor adjustments for differences in the
ultrasonic velocities between the calibration bar and the forging shall then be made.
6.2 Amplifier—The amplifier and display shall provide linear response within 62 %, up to 100% of full screen height.
6.2.1 Amplifier Calibration—An amplifier vertical linearity check shall be made prior to performing the test by observing a
multiple order pattern from a calibration block using a 2.25 MHz transducer (see Practice E317). The first back reflection shall be
set at 100 % of full screen height. The higher order back reflections, 10 % and higher in amplitude, shall also be positioned on the
screen and their amplitudes noted. The first back reflection shall be reduced to 50 % and then 25 % of full screen height. The
amplitudes of the higher order back reflections shall be noted at each step. The vertical linearity will be considered acceptable if
the signal heights of the higher order reflections decrease in proportion to the decrease set for the first back reflection. The
maximum acceptable error for the decrease of the higher order reflections is the greater of 65 % of the expected back reflection
height or 62 % of full screen height.
6.3 Signal Attenuator—The instrument shall contain a calibrated gain control or signal attenuator that meets the requirements
of Practice E317 (in each case, accurate within 65 %) that will allow indications beyond the linear range of the instrument to be
measured. It is recommended that these controls permit signal adjustments up to 25 to 1 (28 dB) (see Fig. 1 and Fig. 2).
6.4 Search Units—Longitudinal wave search units of known effective frequency should be used for radial scanning. A ⁄4 in. by
1 in. [6 mm by 24 mm], 2.0 MHz or 2.25 MHz transducer, used with the 1-in. [24-mm] 1 in. [24 mm] dimension parallel to the
forging axis, will give a desirable combination of resolution and beam width on large sections 15 in. [380 mm] in diameter or larger
if solid or 7.5 in. [190 mm] or greater wall thickness if bored. A 1-in. [24-mm] 1 in. [24 mm] diameter, 2.0 MHz or 2.25 MHz
transducer may be used. If a transducer with dimension circumferentially oriented to the forging, larger than ⁄4 in. [6 mm] is used,
additional inspection at lower frequency is recommended to provide a wide beam for off-axis inspection. A 0.5-in. [10-mm] 0.5
in. [10 mm] diameter 2.0 MHz or 2.25 MHz transducer is suitable for solid sections under 15 in. [380 mm] in diameter and bored
s
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