ASTM E588-03(2009)
(Practice)Standard Practice for Detection of Large Inclusions in Bearing Quality Steel by the Ultrasonic Method
Standard Practice for Detection of Large Inclusions in Bearing Quality Steel by the Ultrasonic Method
SIGNIFICANCE AND USE
Comparison with Other Inclusion Rating Methods—Because the test is performed on a volumetric rather than a surface-examination basis, the ultrasonic method is inherently better able to detect infrequently occurring large inclusions or clusters of small inclusions than eddy current, magnetic particle, microscopical, or macroscopic examination procedures.
Limitation of Inclusion Size and Type—A limitation of the method is that it will not detect all inclusions. Inclusion chemistry, size, shape, location, and distribution may limit the ability of the method to provide indications distinct from those generated by the surrounding metallurgical structure. The recommended practice is only meaningfully applicable to examination of steel wherein the inclusion size and type are within the detection capabilities of the method. For steel wherein inclusion size, dispersion, and chemistry prevent optimum inclusion detection by ultrasonics, microscopical methods detailed in Test Methods E 45 may be applied.
SCOPE
1.1 This practice covers a procedure for the rating of rectangular steel sections by immersion ultrasonic techniques. Its purpose is to provide information on the content of large inclusions or clusters of small inclusions for determining the suitability of a steel lot for bearing applications. This practice in no manner defines or establishes limits of acceptability.
1.2 For this document, large inclusions are defined in ultrasonic terms as those having a reflecting area equivalent to or larger than a 1/64-in. diameter flat-bottom hole in a steel reference block of similar properties and thickness. In metallographic terms, large inclusions, defined in this way, are of approximately the same size as the smallest detectable sizes revealed by the macroscopic methods of Test Methods E 45. In some cases, inclusions smaller than those described previously can be detected either individually or in clusters, depending on their type, chemical composition, orientation to the ultrasonic beam and distance from the sound entry surface of the specimen.
1.3 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: E588 − 03(Reapproved 2009)
Standard Practice for
Detection of Large Inclusions in Bearing Quality Steel by
the Ultrasonic Method
This standard is issued under the fixed designation E588; 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* E214Practice for Immersed Ultrasonic Testing by the Re-
flection Method Using Pulsed Longitudinal Waves (With-
1.1 This practice covers a procedure for the rating of
drawn 2007)
rectangular steel sections by immersion ultrasonic techniques.
E428Practice for Fabrication and Control of Metal, Other
Its purpose is to provide information on the content of large
than Aluminum, Reference Blocks Used in Ultrasonic
inclusions or clusters of small inclusions for determining the
Testing
suitability of a steel lot for bearing applications. This practice
E543Specification forAgencies Performing Nondestructive
in no manner defines or establishes limits of acceptability.
Testing
1.2 For this document, large inclusions are defined in
E1316Terminology for Nondestructive Examinations
ultrasonic terms as those having a reflecting area equivalent to
2.2 ASNT Documents:
or larger than a ⁄64-in. diameter flat-bottom hole in a steel
SNT-TC-1ARecommended Practicefor Personnel Qualifi-
reference block of similar properties and thickness. In metal-
cation and Certification in Nondestructive Testing
lographic terms, large inclusions, defined in this way, are of
ASNT-CP-189STandard for Qualification and Certification
approximately the same size as the smallest detectable sizes
of Nondestructive Testing Personnel
revealed by the macroscopic methods ofTest Methods E45.In
some cases, inclusions smaller than those described previously
3. Terminology
can bedetectedeither individually or in clusters, dependingon
3.1 Definitions—For definitions of terms used in this
their type, chemical composition, orientation to the ultrasonic
practice, see Terminology E1316.
beam and distance from the sound entry surface of the
specimen.
4. Basis of Application
1.3 This standard does not purport to address all of the
4.1 Agreements Between Using Parties— In order for this
safety concerns, if any, associated with its use. It is the
practice to be effectively used, the following items require
responsibility of the user of this standard to establish appro-
agreement between the using parties.
priate safety and health practices and determine the applica-
4.1.1 Evaluation of Nondestructive Testing Agencies —An
bility of regulatory limitations prior to use.
agreement is required as to whether the nondestructive testing
agency, as defined in Specification E543, must be formally
2. Referenced Documents
evaluated and qualified to perform the examination. If such an
2.1 ASTM Standards:
evaluation is specified, a documented procedure such as
E45Test Methods for Determining the Inclusion Content of
Specification E543 shall be used as the basis for evaluation.
Steel
4.1.2 Personnel Qualification—Nondestructive testing
(NDT) personnel shall be qualified in accordance with a
This practice is under the jurisdiction of ASTM Committee A01 on Steel,
nationally recognized NDT personnel qualification practice or
Stainless Steel and Related Alloysand is the direct responsibility of Subcommittee
standard such as ASNT CP-189, SNT-TC-1A, or a similar
A01.28 on Bearing Steels.
document. The practice or standard used and its applicable
Current edition approved April 1, 2009. Published April 2009. Originally
approved in 1976. Last previous edition approved in 2003 as E588–03. DOI:
10.1520/E0588-03R09.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or The last approved version of this historical standard is referenced on
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM www.astm.org.
Standards volume information, refer to the standard’s Document Summary page on Available from the American Society for Nondestructive Testing, 1711 Arlin-
the ASTM website. gate Plaza, P.O. Box 28518, Columbus, OH 43228-0518.
*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
E588 − 03 (2009)
revision shall be specified in the contractual agreement be- various amplitudes, a system reference block, instrument
tween the using parties. calibration block, and an immersion tank with suitable scan-
ning accessories.
4.1.3 Search Unit Performance Tests—Annex A1 defines
the minimum manufacturer’s specifications for search units to
8.2 Ultrasonic Instrument—The ultrasonic instrument shall
beusedwiththispractice.Theextentoftestingandverification
be capable of generating and receiving electrical pulses of
of these parameters to be performed by the manufacturer shall
10-MHz frequency at levels compatible with the test require-
be specified in the contractual agreement between the using
ments. It shall have both anA-scan presentation and an analog
parties.
or digital output. It shall be the ultrasonic instrument manu-
facturer’s responsibility that instruments supplied for use with
5. Summary of Practice
this test meet the minimum requirements delineated in this
recommended practice.
5.1 The general technique used is immersion ultrasonic
8.2.1 Receiver Characteristics—The center frequency shall
testing by the reflection method using pulsed longitudinal
be10 60.5MHz.Thebandpassofthereceivershallbeatleast
waves such as described in Practice E214. Specific additional
1.3 MHz (3 dB points).
requirements for sample preparation, equipment operating
8.2.2 Dynamic Range—The dynamic range of the instru-
parameters and calibration, and expression of results are
ment shall permit detection of steel balls with a 16-to-1
delineated in this procedure. Special focused search units
diameter ratio at a given sensitivity. Balls shall be placed in
having operating characteristics as defined in Annex A1 are
wateratthefocalpointofthesearchunit.Eachsizeballwithin
required.
this range shall give a significantly different amplitude of
indication.
6. Significance and Use
8.2.3 Stability—The signal amplitude of a usable full-scale
6.1 Comparison with Other Inclusion Rating Methods
indication shall not vary more than 5% after1hof instrument
—Because the test is performed on a volumetric rather than a
warm-up, and preferably by less than 2% (4-h test with air
surface-examination basis, the ultrasonic method is inherently
temperature being held to 61.2°C over a temperature range of
better able to detect infrequently occurring large inclusions or
17.5 to 25.5°C).
clusters of small inclusions than eddy current, magnetic
8.2.4 Sweep Length and Linearity—Sweep length of oscil-
particle, microscopical, or macroscopic examination proce-
loscope presentation shall be capable of being adjusted to
dures.
represent 1 mm=1.27 mm of steel. A minimum of 80 mm of
6.2 Limitation of Inclusion Size and Type—A limitation of the sweep display shall be linear to within 5% of full scale.
the method is that it will not detect all inclusions. Inclusion The signal amplitude of an indication from a target shall not
vary more than 64% over the gated portion of the sweep
chemistry, size, shape, location, and distribution may limit the
ability of the method to provide indications distinct from those employed in calibration and testing.
generated by the surrounding metallurgical structure. The 8.2.5 Repetition Rate—Therepetitionrateofthepulsershall
recommended practice is only meaningfully applicable to not be less than 500 pulses per second.
examination of steel wherein the inclusion size and type are
8.3 Search Units—Ultrasonic search units for this test shall
within the detection capabilities of the method. For steel
be spherically focused immersion-type units. Uniform perfor-
wherein inclusion size, dispersion, and chemistry prevent
mance characteristics of search units are critical for obtaining
optimum inclusion detection by ultrasonics, microscopical
reproducible test measurements. (See AnnexA1, which delin-
methods detailed in Test Methods E45 may be applied.
eates search unit performance characteristics to be met by
search unit manufacturers.) Performance characteristics of
7. Interference
searchunitsrequiringconsiderationare:theuniformityoffocal
distance in water, center frequency, frequency spectrum, lens
7.1 Reflections from Multiple Inclusions—An ultrasonic in-
radius, width of field, and beam symmetry.
dication can represent the reflection from a single inclusion;
8.3.1 Focal Length—Afocused beam of radiated ultrasonic
however, it typically represents the vector summation of
energy is recommended to provide lateral resolution of small
reflections from clusters of small inclusions contained within a
defectsandtoimprovetestingsensitivityintheregionnearthe
volume of a few cubic millimetres.
focal point. The focal length of a search unit is defined in this
7.2 Response as a Function of Inclusion Type—The indi-
discussion as the distance in water, on the search unit axis,
vidual inclusion reflections can have different amplitudes
between the search unit and the surface of a ⁄2-in. or 12-mm
because of different inclusion characteristics. In addition, the
diameter ball target at which the highest reflection amplitude
individual reflections may have different phase characteristics
indication is obtained. Different focal length transducers may
when arriving at the search unit if the travel distances are
beusedtoobtainoptimumresponseatselecteddistancesbelow
different.
the test sample surface. (Variation of search unit-to-specimen
surface water path would also affect the focal point within the
8. Apparatus
test sample.)
8.1 Equipment Required—An equipment system with the 8.3.2 Search Unit Characteristics—Search units generally
followingcomponentsisneededtoconductthistest:ultrasonic employed have the following frequency and focal length as
test instrument, search unit, a means of recording signals of purchased:
E588 − 03 (2009)
adjustments and operational testing of the equipment. This
Frequency Focal Length in Water
10 ± 0.5 MHz 8.2 ± 0.3 in. (208.3 ± 7.6 mm)
sample should be selected to provide reflection signals at all
8.3.3 Beam Symmetry—Each search unit should be rotated countinglevels.Depthdistributionofinclusionsintheselected
on its ultrasonic beam axis (not necessarily geometric axis)
reference block should make its response characteristics rela-
until a particular circumferential orientation is found which tively insensitive to minor focal length variations between
givesamaximumseverity,orcount,fromthesystemreference
different search units. The reference block should give a
block. This search unit orientation shall be identified and minimum change in total counts of 10% for each 10%
employed in subsequent tests. Search units that exhibit varia-
increase or decrease in amplitude setting.Amaximum of 30%
tions in indication amplitude in excess of 15% during rotation change in count for each 10% change in amplitude setting
shallnotbeconsideredsatisfactoryforthetest.Thereareother
should not be exceeded. It should be suitably protected from
methods, such as optimum response over a precision and corrosion to assure its longevity.
uniform taut wire, that have been found to be usable.
9. Test Specimens
8.3.4 Performance—The performance capabilities of all
new search units shall be verified by an actual test on the
9.1 General—Test specimens must be either in the rolled or
systemreferenceblock.Thedataobtainedfornewsearchunits
forged condition. If forged, upset forging is prohibited in order
should be compared with that obtained for other search units
to maintain the rolling direction. Care should be taken not to
having the same specifications and tested under identical
overheat the forging to avoid spurious ultrasonic indications.
conditions.
Specimen location and frequency shall be as agreed upon
between the supplier and the purchaser.
8.4 Immersion Tank and Accessories— An immersion tank
with associated scanning and indexing facilities shall be used.
9.2 Specimen Size and Shape—Specimens shall have a
8.4.1 Search Unit Angulation—The tank shall be provided
minimumcross-sectionaldimensionafterpreparationof3 ⁄2in.
with a manipulator capable of continuously angulating the
(88.9 mm). The area scanned shall be sufficient to permit
3 3
search unit in two vertical mutually perpendicular planes
testing of a minimum of 25 in. (410 cm ) of the specimen.
permitting the required normalization.
The tested volume equals the scanned area multiplied by the
8.4.2 Scanning and Indexing—The tank bridge and carriage
gated depth. If special consideration is given, thinner samples
assemblies shall provide X-Y motion to the search unit. The
may be tested.
scanning shall be parallel or perpendicular (depending on the
9.3 Entry Surface Finish—The test surface through which
procedure) to the test specimen axis and the indexing shall be
the sound enters the specimen shall be machined and ground.
perpendicular to the scanning.
Thisfinishinanydirectionoverthesurfaceshallbepreferably
8.4.3 Test Specimen Mounting—The tank shall be provided
10 to 80 µin. (0.25 to 2.0 µm). Final material removal may
with fixturing permitting the mounting of the entry surface of
require a dressed grinding wheel to avoid spurious, near-
the test specimen parallel to the bridge travel so that the
surface indications. All four sides are to be ground.
distance between search unit and specimen remains constant
within 6 ⁄64 in. (0.4 mm). 9.4 Heat Treatment—Thermal conditioning of the speci-
8.4.4 Couplant: mens is required to minimize acoustic anomalies. Typical heat
8.4.4.1 The inspection solution shall consist of tap or treatment may consist of normalizing or quenching and
distilled water to which a wetting agent has been added to tempering, depending on steel type, to meet the ultrasonic
disperse air bubbles. The pH of the water shall be maintained penetrability requirement of Section 9.5. Certain steels may
1 1
require special thermal treatment such as a double temper to
within 7 ⁄2 to 8 ⁄2 . Rust preventives may also be added. All
chemical additives shall be held within concentrations that do obtain suitable acoustic properties.
not adversely affect test performance. Water temperature must
9.5 Ultrasonic Penetrability—The ultrasonic penetrability
beheldbetween19.5and25.5°C.Itisimportantthatexcessive
shall be determined to be suitable for the inspection. The
thermal gradients do not exist betwe
...
This document is not anASTM standard and is intended only to provide the user of anASTM 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:E588–95 Designation:E588–03 (Reapproved 2009)
Standard Practice for
Detection of Large Inclusions in Bearing Quality Steel by
the Ultrasonic Method
This standard is issued under the fixed designation E588; 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
1.1This practice covers a procedure for the rating of rectangular steel sections by immersion ultrasonic techniques. Its purpose
is to provide information on the content of large inclusions or clusters of small inclusions for determining the suitability of a steel
lot for bearing applications. It should be recognized that this method was developed after several years of close cooperation
between bearing manufacturers and bearing steel producers. References (1-8) provide background information on developmental
work. If its use for specification purposes is contemplated for other steel products, thought should be given to the possibility that
a similar cooperative program between users and steel producers might be necessary. This practice in no manner defines or
establishes limits of acceptability. *
1.1 This practice covers a procedure for the rating of rectangular steel sections by immersion ultrasonic techniques. Its purpose
is to provide information on the content of large inclusions or clusters of small inclusions for determining the suitability of a steel
lot for bearing applications. This practice in no manner defines or establishes limits of acceptability.
1.2 For this document, large inclusions are defined in ultrasonic terms as those having a reflecting area equivalent to or larger
than a 1/64-inch ⁄64-in. diameter flat-bottom hole in a steel reference block of similar properties and thickness. In metallographic
terms, large inclusions, defined in this way, are of approximately the same size as the smallest detectable sizes revealed by the
macroscopic methods of PracticeTest Methods E45. In some cases, inclusions smaller than those described previously can be
detected either individually or in clusters, depending on their type, chemical composition, orientation to the ultrasonic beam and
distance from the sound entry surface of the specimen.
1.3 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.
2. Referenced Documents
2.1 ASTM Standards:
E45 Practice Test Methods for Determining the Inclusion Content of Steel
E214 Practice for Immersed Ultrasonic ExaminationTesting by the Reflection Method Using Pulsed Longitudinal Waves
E428428 Practice for Fabrication and Control of Steel Metal, Other than Aluminum, Reference Blocks Used in Ultrasonic
Inspection Testing
E543 Practice for Evaluating Agencies that Perform Nondestructive Testing Specification for Agencies Performing
Nondestructive Testing
E1316 Terminology for Nondestructive Examinations
2.2 ANSI/ASNT Standards:
Recommended Practice SNT-TC-1APersonnel Qualification and Certification in Nondestructive Testing ASNT Documents:
SNT-TC-1A Recommended Practicefor Personnel Qualification and Certification in Nondestructive Testing
CP-189Qualification and Certification of Nondestructive Testing Personnel
2.3 Military Standard:
MIL-STD-410 NondestructiveTesting Personnel Qualification and CertificationASNT-CP-189 STandard for Qualification and
ThispracticeisunderthejurisdictionofASTMCommitteeA-1A01onSteel,StainlessSteelandRelatedAlloysandisthedirectresponsibilityofSubcommitteeA01.28
on Bearing Steels.
Current edition approved Sept. 10, 1995. Published November 1995. Originally published as E588–76. Last previous edition E588–88.
Current edition approved April 1, 2009. Published April 2009. Originally approved in 1976. Last previous edition approved in 2003 as E588–03.
Boldface numbers in parentheses refer to the list of references at the end of this practice.
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Annual Book of ASTM Standards, Vol 03.01.
Available from the American Society for Nondestructive Testing, 1711 Arlingate Plaza, P.O. Box 28518, Columbus, OH 43228-0518.
*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.
E588–03 (2009)
Certification of Nondestructive Testing Personnel
3. Terminology
3.1 Definitions—For definitions of terms used in this practice, see Terminology E1316.
4. Basis of Application
4.1 Agreements Between Using Parties—Inorderforthispracticetobeeffectivelyused,thefollowingitemsrequireagreement
between the using parties.
4.1.1 Evaluation of Nondestructive Testing Agencies —An agreement is required as to whether the nondestructive testing
agency, as defined in PracticeSpecification E543, must be formally evaluated and qualified to perform the examination. If such
an evaluation is specified, a documented procedure such as PracticeSpecification E543 shall be used as the basis for evaluation.
4.1.2 Personnel Qualification—Nondestructive testing (NDT) personnel shall be qualified in accordance with a nationally
recognized NDT personnel qualification practice or standard such as ANSI/ASNTASNT CP-189, SNT-TC-1A, MIL-STD-
410SNT-TC-1A, or a similar document. The practice or standard used and its applicable revision shall be specified in the
contractual agreement between the using parties.
4.1.3 Search Unit Performance Tests—AnnexA1definestheminimummanufacturer’sspecificationsforsearchunitstobeused
withthispractice.Theextentoftestingandverificationoftheseparameterstobeperformedbythemanufacturershallbespecified
in the contractual agreement between the using parties.
5. Summary of Practice
5.1 The general technique used is immersion ultrasonic testing by the reflection method using pulsed longitudinal waves such
as described in Practice E214. Specific additional requirements for sample preparation, equipment operating parameters and
calibration,andexpressionofresultsaredelineatedinthisprocedure.Specialfocusedsearchunitshavingoperatingcharacteristics
as defined in Annex A1 are required.
6. Significance and Use
6.1 Comparison with Other Inclusion Rating Methods —Because the test is performed on a volumetric rather than a
surface-examination basis, the ultrasonic method is inherently better able to detect infrequently occurring large inclusions or
clusters of small inclusions than eddy current, magnetic particle, microscopical, or macroscopic examination procedures.
6.2 Limitation of Inclusion Size and Type—A limitation of the method is that it will not detect all inclusions. Inclusion
chemistry, size, shape, location, and distribution may limit the ability of the method to provide indications distinct from those
generated by the surrounding metallurgical structure. The recommended practice is only meaningfully applicable to examination
of steel wherein the inclusion size and type are within the detection capabilities of the method. For steel wherein inclusion size,
dispersion, and chemistry prevent optimum inclusion detection by ultrasonics, microscopical methods detailed in PracticeTest
Methods E45 may be applied.
7. Interference
7.1 ReflectionsfromMultipleInclusions—Anultrasonicindicationcanrepresentthereflectionfromasingleinclusion;however,
it typically represents the vector summation of reflections from clusters of small inclusions contained within a volume of a few
cubic millimetres.
7.2 Response as a Function of Inclusion Type—The individual inclusion reflections can have different amplitudes because of
different inclusion characteristics. In addition, the individual reflections may have different phase characteristics when arriving at
the search unit if the travel distances are different.
8. Apparatus
8.1 Equipment Required—An equipment system with the following components is needed to conduct this test: ultrasonic test
instrument,searchunit,ameansofrecordingsignalsofvariousamplitudes,asystemreferenceblock,instrumentcalibrationblock,
and an immersion tank with suitable scanning accessories.
8.2 Ultrasonic Instrument—Theultrasonicinstrumentshallbecapableofgeneratingandreceivingelectricalpulsesof10-MHz
frequencyatlevelscompatiblewiththetestrequirements.ItshallhavebothanA-scanpresentationandananalogordigitaloutput.
Itshallbetheultrasonicinstrumentmanufacturer’sresponsibilitythatinstrumentssuppliedforusewiththistestmeettheminimum
requirements delineated in this recommended practice.
8.2.1 Receiver Characteristics—Thecenterfrequencyshallbe10 60.5MHz.Thebandpassofthereceivershallbeatleast1.3
MHz (3 dB points).
8.2.2 Dynamic Range—The dynamic range of the instrument shall permit detection of steel balls with a 16-to-1 diameter ratio
at a given sensitivity. Balls shall be placed in water at the focal point of the search unit. Each size ball within this range shall give
a significantly different amplitude of indication on both the visual oscilloscope presentation and the analog output. indication.
8.2.3 Stability—The analog output voltagesignal amplitude of a usable full-scale indication shall not vary more than 5% after
1hofinstrumentwarm-up,andpreferablybylessthan2%(4-htestwithairtemperaturebeingheldto 61.2°Coveratemperature
range of 17.5 to 25.5°C).
E588–03 (2009)
8.2.4 Sweep Length and Linearity—Sweep length of oscilloscope presentation shall be capable of being adjusted to represent
1 mm=1.27 mm of steel. A minimum of 80 mm of the sweep display shall be linear to within 5% of full scale. Analog output
voltageThe signal amplitude of an indication from a target shall not vary more than 64% over the gated portion of the sweep
employed in calibration and testing.
8.2.5 Repetition Rate—The repetition rate of the pulser shall not be less than 500 pulses per second.
8.3 Search Units—Ultrasonicsearchunitsforthistestshallbesphericallyfocusedimmersion-typeunits.Uniformperformance
characteristics of search units are critical for obtaining reproducible test measurements. (SeeAnnexA1, which delineates search
unit performance characteristics to be met by search unit manufacturers.) Performance characteristics of search units requiring
consideration are: the uniformity of focal distance in water, center frequency, frequency spectrum, lens radius, width of field, and
beam symmetry.
8.3.1 Focal Length—A focused beam of radiated ultrasonic energy is recommended to provide lateral resolution of small
defects and to improve testing sensitivity in the region near the focal point. The focal length of a search unit is defined in this
discussion as the distance in water, on the search unit axis, between the search unit and the surface of a ⁄2-in. or 12-mm diameter
balltargetatwhichthehighestreflectionamplitudeindicationisobtained.Differentfocallengthtransducersmaybeusedtoobtain
optimum response at selected distances below the test sample surface. (Variation of search unit-to-specimen surface water path
would also affect the focal point within the test sample.)
8.3.2 Search Unit Characteristics—Search units generally employed have the following frequency and focal length as
purchased:
Frequency Focal Length in Water
10 6 0.5 MHz 8.2 6 0.3 in (208.3 6 7.6 mm)
10 6 0.5 MHz 8.2 6 0.3 in. (208.3 6 7.6 mm)
A search unit shall be discarded as no longer fit for use when its focal length has degenerated to 7.5 in. (190.5 mm).
8.3.3 Beam Symmetry—Each search unit should be rotated on its ultrasonic beam axis (not necessarily geometric axis) until a
particular circumferential orientation is found which gives a maximum severity, or count, from the system reference block. This
search unit orientation shall be identified and employed in subsequent tests. Search units that exhibit variations in indication
amplitude in excess of 15% during rotation shall not be considered satisfactory for the test. There are other methods, such as
optimum response over a precision and uniform taut wire, that have been found to be usable.
8.3.4 Performance—The performance capabilities of all new search units shall be verified by an actual test on the system
reference block. The data obtained for new search units should be compared with that obtained for other search units having the
same specifications and tested under identical conditions.
8.4 Immersion Tank and Accessories— An immersion tank with associated scanning and indexing facilities shall be used.
8.4.1 Search Unit Angulation—The tank shall be provided with a manipulator capable of continuously angulating the search
unit in two vertical mutually perpendicular planes permitting the required normalization.
8.4.2 Scanning and Indexing—The tank bridge and carriage assemblies shall provide X-Y motion to the search unit. The
scanning shall be parallel or perpendicular (depending on the procedure) to the test specimen axis and the indexing shall be
perpendicular to the scanning.
8.4.3 Test Specimen Mounting—The tank shall be provided with fixturing permitting the mounting of the entry surface of the
test specimen parallel to the bridge travel so that the distance between search unit and specimen remains constant within 6 ⁄64 in.
(0.4 mm).
8.4.4 Couplant:
8.4.4.1 The inspection solution shall consist of tap or distilled water to which a wetting agent has been added to disperse air
1 1
bubbles. The pH of the water shall be maintained within 7 ⁄2 to 8 ⁄2 . Rust preventives may also be added.All chemical additives
shall be held within concentrations that do not adversely affect test performance. Water temperature must be held between 19.5
and25.5°C.Itisimportantthatexcessivethermalgradientsdonotexistbetweenthesearchunitandthecalibrationstandards.Billet
inspection shall be made within 1.7°C of the temperature at which calibration was accomplished.
8.4.4.2 A means of circulating the immersion inspection solution shall be employed, when necessary, to dissipate thermal
gradients.
8.5 Readout Equipment—Various types of instrumentation have been employed in conjunction with ultrasonic
...
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