ASTM A418-99
(Test Method)Standard Test Method for Ultrasonic Examination of Turbine and Generator Steel Rotor Forgings
Standard Test Method for Ultrasonic Examination of Turbine and Generator Steel Rotor Forgings
SCOPE
1.1 This test method for inspection applies to turbine and generator steel rotor forgings covered by the following specifications of the American Society for Testing and Materials: ASTM Title of Specification Designation A Steel Forgings, Carbon and Alloy, for A 293 Turbine Rotors and Shafts Vacuum-Treated Steel Forgings for Generator A 469 Rotors Vacuum-Treated Carbon and Alloy Steel Forgings A 470 for Turbine Rotors and Shafts A The reference is to the latest issue of these designations which appear in the Annual Book of ASTM Standards, Part 5, or are available as separate reprints. It shall also apply to product specifications which may be issued when specifically referenced therein.
1.2 This test method describes a basic procedure of ultrasonically inspecting turbine and generator rotor forgings. It shall in no way 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. The procedure utilizes different calibration techniques than had been used in previous issues. The frequency or amplitudes of recordable indications should not be interpreted necessarily as a change in quality of the product being examined.
1.3 This test method 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 X 10 in./s (5.85 X 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, etc. tend to reduce the overall inaccuracy which is apt to develop.
1.5 This test method for inspection applies to solid cylindrical forgings having outer diameters of not less than 2.5 in. (63.5 mm) nor greater than 100 in. (2540 mm). It also applies to cylindrical forgings with concentric cylindrical bores having wall thicknesses of 2.5 (63.5 mm) in. or greater, within the same outer diameter limits as for solid cylinders. For solid sections less than 15 in. (381 mm) in diameter and for bored cylinders of less than 7.5 in. (190.5 mm) wall thickness the transducer used for the inspection will be different than the transducer used for larger sections.
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: A 418 – 99
Standard Test Method for
Ultrasonic Examination of Turbine and Generator Steel
Rotor Forgings
This standard is issued under the fixed designation A 418; 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 (e) 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 test method for ultrasonic examination applies to
instruments are used, etc. tend to reduce the overall inaccuracy
turbine and generator steel rotor forgings covered by Specifi-
which is apt to develop.
cations A 293, A 469, and A 470. This standard shall be used for
1.5 This test method for inspection applies to solid cylin-
contact testing only.
drical forgings having outer diameters of not less than 2.5 in.
1.2 This test method describes a basic procedure of ultra-
(63.5 mm) nor greater than 100 in. (2540 mm). It also applies
sonically inspecting turbine and generator rotor forgings. It
to cylindrical forgings with concentric cylindrical bores having
shall in no way restrict the use of other ultrasonic methods such
wall thicknesses of 2.5 (63.5 mm) in. or greater, within the
as reference block calibrations when required by the applicable
same outer diameter limits as for solid cylinders. For solid
procurement documents nor is it intended to restrict the use of
sections less than 15 in. (381 mm) in diameter and for bored
new and improved ultrasonic test equipment and methods as
cylinders of less than 7.5 in. (190.5 mm) wall thickness the
they are developed. The procedure utilizes different calibration
transducer used for the inspection will be different than the
techniques than had been used in previous issues. The fre-
transducer used for larger sections.
quency or amplitudes of recordable indications should not be
1.6 This standard does not purport to address all of the
interpreted necessarily as a change in quality of the product
safety concerns, if any, associated with its use. It is the
being examined.
responsibility of the user of this standard to establish appro-
1.3 This test method is intended to provide a means of
priate safety and health practices and determine the applica-
inspecting cylindrical forgings so that the inspection sensitivity
bility of regulatory limitations prior to use.
at the forging center line or bore surface is constant, indepen-
dent of the forging or bore diameter. To this end, inspection
2. Referenced Documents
sensitivity multiplication factors have been computed from
2.1 The reference is to the latest issue of these designations
theoretical analysis, with experimental verification. These are
that appear in the Annual Book of ASTM Standards or are
plotted in Fig. 1 (bored rotors) and Fig. 2 (solid rotors), for a
available as separate reprints. It shall also apply to product
true inspection frequency of 2.25 MHz, and an acoustic
5 5
specifications, which may be issued when specifically refer-
velocity of 2.30 3 10 in./s (5.85 3 10 cm/s). Means of
enced therein.
converting to other sensitivity levels are provided in Fig. 3.
2.2 ASTM Standards:
(Sensitivity multiplication factors for other frequencies may be
A 293 Specification for Steel Forgings, Carbon and Alloy,
derived in accordance with X1.1 and X1.2 of Appendix X1.)
for Turbine Rotors and Shafts
1.4 Considerable verification data for this method have been
A 469 Specification for Vacuum-Treated Steel Forgings for
generated which indicate that even under controlled conditions
Generator Rotors
very significant uncertainties may exist in estimating natural
A 470 Specification for Vacuum-Treated Carbon and Alloy
discontinuities in terms of minimum equivalent size flat-
Steel Forgings for Turbine Rotors and Shafts
bottom holes. The possibility exists that the estimated mini-
E 317 Practice for Evaluating Performance Characteristics
mum areas of natural discontinuities in terms of minimum
of Ultrasonic Pulse-Echo Testing Systems Without the Use
areas of the comparison flat-bottom holes may differ by 20 dB
of Electronic Measurement Instruments
(factor of 10) in terms of actual areas of natural discontinuities.
E 1065 Guide for Evaluating Characteristics of Ultrasonic
This magnitude of inaccuracy does not apply to all results but
Search Units
This test method is under the jurisdiction of ASTM Committee A-1 on Steel,
Stainless Steel and Related Alloys, and is the direct responsibility of Subcommittee Discontinued; Replaced by A 470, see 1983 Annual Book of ASTM Standards,
A01.06 on Steel Forgings and Billets. Vol 01.05.
Current edition approved Sept. 10, 1999. Published November 1999. Originally Annual Book of ASTM Standards, Vol 01.05.
published as A 418–57T. Last previous edition A 418–96. Annual Book of ASTM Standards, Vol 03.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
A 418–99
NOTE—Sensitivity multiplication factor such that a 10 % indication at the forging bore surface will be equivalent to a ⁄8 in. (3.175 mm) diameter flat
5 5
bottom hole. Inspection frequency: 2.25 MHz. Material velocity: 2.30 3 10 in./s (5.85 3 10 cm/s).
FIG. 1 Bored Forgings
3. Application slots, or similar features are machined into the forging before
heat treatment, the entire forging shall be inspected ultrasoni-
3.1 This test method shall be used when ultrasonic inspec-
cally before such machining, and as completely as practicable
tion is required by the order or specification for inspection
after the final heat treatment.
purposes where the acceptance of the forging is based on
4.3 For overall scanning, the ultrasonic beam shall be
limitations of the number, amplitude or location of disconti-
introduced radially. To conform with this requirement, external
nuities or a combination thereof, which give rise to ultrasonic
conical surfaces of the forging shall be replaced by stepped
indications.
surfaces in order to maintain the ultrasonic beam perpendicular
3.2 The acceptance criteria shall be clearly stated as order
to the longitudinal axis. Such stepped surfaces shall be shown
requirements.
on the forging drawing.
4. General Requirements
4.4 Forgings may be tested either stationary or while rotated
by means of a lathe or rollers. If not specified by the purchaser,
4.1 As far as possible, the entire volume of the forging shall
either method may be used at the manufacturer’s option.
be subjected to ultrasonic inspection. Because of fillets at
Scanning speed shall not exceed 6 in./s (15.24 cm/s).
stepdowns and other local configurations, it may be impossible
to inspect some small portions of a forging. 4.5 To ensure complete coverage of the forging volume, the
4.2 The ultrasonic inspection shall be performed after final search unit shall be indexed approximately 75 % of the
heat treatment of the forging. In those cases in which wheels, transducer width with each pass of the search unit. Mechanized
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
A 418–99
NOTE—Sensitivity multiplication factor such that a 10 % indication at the forging centerline surface will be equivalent to a ⁄8 in. (3.175 mm) diameter
5 5
flat bottom hole. Inspection frequency: 2.25 MHz. Material velocity: 2.30 3 10 in./s (5.85 3 10 cm/s).
FIG. 2 Solid Forgings
inspection of the rotating forging wherein the search unit is 6. Pulsed Ultrasonic Reflection Equipment and
mechanically controlled is an aid in meeting this requirement. Accessories
4.6 Frequencies of 1, 2.25, and 5 MHz may be used for
6.1 Electronic Apparatus—A pulse-echo instrument permit-
accurately locating, determining orientation, and defining spe-
ting inspection frequencies of 1 MHz, 2.25 MHz, and 5 MHz
cific discontinuities detected during overall scanning as de-
is required. The accuracy of discontinuity amplitude analysis
scribed in 4.4.
using this test method involves a knowledge of the true
4.7 Axial scanning, if required, shall be performed at that
operating frequency of the complete inspection system. One of
frequency and transducer diameter which minimizes interfer-
the best ways to obtain the desired accuracy is by use of a tuned
ing ultrasonic reflections due to forging geometry and which
pulser and narrow band amplifier of known frequency re-
gives optimum resolution. (Axial tests are normally used as a
sponse, with either a broad-band transducer, or a narrow-band
supplement to radial tests.)
tuned transducer of known and matching frequency.
5. Personnel Requirements
6.1.1 Apparatus Qualification and Calibration—Basic
qualification of the ultrasonic test instrument shall be per-
5.1 Personnel performing the ultrasonic examinations to this
formed at intervals not to exceed 12 months or whenever
practice shall be qualified and certified in accordance with a
maintenance is performed that affects the equipment function.
written procedure conforming to Recommended Practice No.
SNT-TC-1A or another national standard that is acceptable to The date of the last calibration and the date of the next required
both the purchaser and the supplier. calibration shall be displayed on the test equipment.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
A 418–99
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
6.1.2 The horizontal linearity shall be checked on a distance 6.3 Signal Attenuator—The instrument shall contain a cali-
calibration bar using the multiple order technique. See Practice brated gain control or signal attenuator that meets the require-
E 317. The horizontal linearity shall be 62 % of the metal
ments of Practice E 317 (in each case, accurate within 65%)
path.
that will allow indications beyond the linear range of the
6.1.3 If the rotor has a coupling or similar thin axial section
instrument to be measured. It is recommended that these
with parallel sides, the accuracy of the linearity shall be
controls permit signal adjustments up to 25 to 1 (28 dB). See
checked by ultrasonically verifying the thickness of the cou-
Fig. 1 and Fig. 2.
pling or axial section. If necessary, minor adjustments for
6.4 Search Units—Longitudinal wave search units of
differences in the ultrasonic velocities between the calibration
known effective frequency should be used for radial scanning.
bar and the forging shall then be made.
A ⁄4 by 1 in. (6.35 by 25.4 mm) 2.25 MHz transducer, used
6.2 Amplifier—The amplifier and the cathode ray tube shall
with the 1 in. dimension parallel to the forging axis, will give
provide linear response within 62 %, up to 100% of full screen
a desirable combination of resolution and beam width on large
height.
sections 15 in. (381 mm) in diameter or larger if solid or 7.5 in.
6.2.1 Amplifier Calibration—An amplifier vertical linearity
(190.5 mm) or greater wall thickness if bored. A 1 in. (25.4
check shall be made prior to performing the test by observing
mm) diameter, 2.25 MHz transducer may be used. If a
a multiple order pattern from a calibration block using a 2.25
transducer with dimension circumferentially oriented to the
MHz transducer. See Practice E 317. The first back reflection
forging, larger than ⁄4 in. (6.35 mm) is used, additional
shall be set at 100 % of full screen height. The higher order
inspection at lower frequency is recommended to provide a
back reflections, 10 % and higher in amplitude, shall also be
positioned on the screen and their amplitudes noted. The first wide beam for off-axis inspection. A 0.5 in. (12.7 mm) diam-
back reflection shall be reduced to 50 % and then 25 % of full eter 2.25 MHz transducer is suitable for solid sections under 15
screen height. The amplitudes of the higher order back reflec-
in. (381 mm) in diameter and bored sections under 7.5 in.
tions shall be noted at each step. The vertical linearity will be
(190.5 mm) in wall thickness. The multiplication factors given
considered acceptable if the signal heights of the higher order
are valid for the frequency and material velocity indicated
reflections decrease in proportion to the decrease set for the
provided they are used in the far field. (The near field is a
first back reflection. The maximum acceptable error for the
characteristic that is dependent on the transducer frequency and
decrease of the higher order reflections is the greater of 65%
size.) For other frequencies and material velocities, applicable
of the expected back reflection height or 62 % of full screen
sensitivity multiplication factors shall be computed.
height.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
A 418–99
6.4.1 Search Unit Calibration—The transducers used in unit on the surface of the forging when indications are
performing the tests described in this test method shall be observed so that they may be investigated in accordance with
calibrated in accordance with Guide E 1065. 8.1.7 and 8.2.2.
8.1.6 When the forgings are tested while they are rotated,
7. Preparation of Forging for Ultrasonic Inspection the maximum speed of rotation shall be calculated as follows:
7.1 Machine turn the forging to provide cylindrical surfaces
for the radial test.
360/pd = maximum revolutions per min.
7.2 The end faces of the shaft extensions and of the body of
d = diameter of forging in inches.
the forging shall be sufficiently perpendicular to the axis of the 915/pd = maximum revolutions per min.
d = diameter of forging in centimetres.
forging to permit axial test.
The search unit may be held by a suitable fixture attached to
7.3 The surface roughness of exterior finishes shall not
the tool post of the lathe and traversed mechanically for
exceed 250 μin. (6.35 μm) and the surface waviness shall not
scanning of the rotating forging or may be hand-held. If not
interfere with the ultrasonic test.
specified by the purchaser, either method may be used at the
7.4 At the time of ultrasonic testin
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