ASTM E1814-96(2007)
(Practice)Standard Practice for Computed Tomographic (CT) Examination of Castings
Standard Practice for Computed Tomographic (CT) Examination of Castings
SIGNIFICANCE AND USE
CT may be performed on an object when it is in the as-cast, intermediate, or final machined condition. A CT examination can be used as a design tool to improve wax forms and moldings, establish process parameters, randomly check process control, perform final quality control (QC) examination for the acceptance or rejection of parts, and analyze failures and extend component lifetimes.
The most common applications of CT for castings are for the following: locating and characterizing discontinuities, such as porosity, inclusions, cracks, and shrink; measuring as-cast part dimensions for comparison with design dimensions; and extracting dimensional measurements for reverse engineering.
The extent to which a CT image reproduces an object or a feature within an object is dictated largely by the competing influences of spatial resolution, contrast discrimination, and artifacts of the imaging system. Operating parameters strike an overall balance between image quality, examination time, and cost.
Artifacts are often the limiting factor in CT image quality. (See Practice E 1570 for an in-depth discussion of artifacts.) Artifacts are reproducible features in an image that are not related to actual features in the object. Artifacts can be considered correlated noise because they form repeatable fixed patterns under given conditions yet carry no object information. For castings, it is imperative to recognize what is and is not an artifact since an artifact can obscure or masquerade as a discontinuity. Artifacts are most prevalent in castings with long straight edges or complex geometries, or both.
SCOPE
1.1 This practice covers a uniform procedure for the examination of castings by the computed tomography (CT) technique. The requirements expressed in this practice are intended to control the quality of the nondestructive examination by CT and are not intended for controlling the acceptability or quality of the castings. This practice implicitly suggests the use of penetrating radiation, specifically X rays and gamma rays.
1.2 This practice provides a uniform procedure for a CT examination of castings for one or more of the following purposes:
1.2.1 Examining for discontinuities, such as porosity, inclusions, cracks, and shrink;
1.2.2 Performing metrological measurements and determining dimensional conformance; and
1.2.3 Determining reverse engineering data, that is, creating computer-aided design (CAD) data files.
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. For specific safety statements, see Section 7,NBS Handbook 114, and 21 CFR 1020.40 and 29 CFR 1910.96.
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Standards Content (Sample)
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Designation: E1814 − 96(Reapproved 2007)
Standard Practice for
Computed Tomographic (CT) Examination of Castings
This standard is issued under the fixed designation E1814; 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 E1570 Practice for Computed Tomographic (CT) Examina-
tion
1.1 This practice covers a uniform procedure for the exami-
E1672 Guide for Computed Tomography (CT) System Se-
nation of castings by the computed tomography (CT) tech-
lection
nique.The requirements expressed in this practice are intended
E1695 Test Method for Measurement of Computed Tomog-
to control the quality of the nondestructive examination by CT
raphy (CT) System Performance
and are not intended for controlling the acceptability or quality
2.2 ASNT Documents:
of the castings. This practice implicitly suggests the use of
SNT-TC-1A Recommended Practice for Personnel Qualifi-
penetrating radiation, specifically X rays and gamma rays.
cation and Certification in Nondestructive Testing
1.2 This practice provides a uniform procedure for a CT
ANSI/ASNT CP-189 Standard for Personnel Qualification
examination of castings for one or more of the following
and Certification of Nondestructive Testing Personnel
purposes:
2.3 Military Standards:
1.2.1 Examining for discontinuities, such as porosity,
MIL-STD-410 Nondestructive Testing Personnel Qualifica-
inclusions, cracks, and shrink;
tion and Certification
1.2.2 Performing metrological measurements and determin-
NAS 410 Certification and Qualification of Nondestructive
ing dimensional conformance; and
Test Personnel
1.2.3 Determining reverse engineering data, that is, creating
2.4 Code of Federal Regulations:
computer-aided design (CAD) data files.
21 CFR 1020.40 Safety Requirements of Cabinet X Ray
1.3 This standard does not purport to address all of the
Systems
safety concerns, if any, associated with its use. It is the
29 CFR 1910.96 Ionizing Radiation
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3. Terminology
bility of regulatory limitations prior to use. For specific safety
3.1 Definitions—Definitions of terms applicable to this
statements, see Section 7, NBS Handbook 114, and
practice may be found in Terminology E1316 and Guide
21 CFR 1020.40 and 29 CFR 1910.96.
E1441.
3.2 Definitions of Terms Specific to This Standard:
2. Referenced Documents
3.2.1 fixturing—the mounting hardware used to place the
2.1 ASTM Standards:
object in the CT system.
E543 Specification for Agencies Performing Nondestructive
3.2.2 representative quality indicator (RQI)—a real part, or
Testing
a fabrication of similar geometry in radiologically similar
E1316 Terminology for Nondestructive Examinations
material to a real part, that has features of known characteris-
E1441 Guide for Computed Tomography (CT) Imaging
tics that represent all of the features for which the parts are
being examined.
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
3.2.3 scan plan—scan locations and the system configura-
structive Testing and is the direct responsibility of Subcommittee E07.01 on
tion parameters for a specific part examination.
Radiology (X and Gamma) Method.
Current edition approved July 1, 2007. Published July 2007. Originally approved
3.2.4 object—a part or specimen being subjected to CT
in 1996. Last previous edition approved in 2002 as E1814 - 96(2002). DOI:
examination.
10.1520/E1814-96R07.
NBS Handbook 114, General Safety Standard for Installations, Using Non-
Medical X-Ray and Sealed Gamma-Ray Sources, Energies Up to 10 MeV, National
Institute of Standards and Technology (NIST), Gaithersburg, MD. AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
Standards volume information, refer to the standard’s Document Summary page on Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://
the ASTM website. www.dodssp.daps.mil.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1814 − 96 (2007)
4. Significance and Use 5.1.5 Image Processing—Image processing routines used in
analysis of the CT data shall be specified in accordance with
4.1 CT may be performed on an object when it is in the
6.2:(1)dimensionalmeasurements,6.2.1;and(2)discontinuity
as-cast, intermediate, or final machined condition. A CT
characterization, 6.2.2.
examinationcanbeusedasadesigntooltoimprovewaxforms
5.1.6 Discontinuity Types—A listing of the expected kinds
and moldings, establish process parameters, randomly check
of discontinuities shall be provided or referenced, and the
process control, perform final quality control (QC) examina-
acceptance and rejection criteria shall be stipulated.
tion for the acceptance or rejection of parts, and analyze
failures and extend component lifetimes. 5.1.7 Records—Records requirements shall be specified in
accordance with Section 10.
4.2 The most common applications of CT for castings are
for the following: locating and characterizing discontinuities,
6. Apparatus
such as porosity, inclusions, cracks, and shrink; measuring
as-cast part dimensions for comparison with design dimen-
6.1 The success of the CT application depends on the
sions; and extracting dimensional measurements for reverse
overall system configuration and the selection of appropriate
engineering.
subsystem components. Guidance on the selection of sub-
system components and the overall system configuration is
4.3 The extent to which a CTimage reproduces an object or
provided in Guide E1672. Guidance on the initial qualification
a feature within an object is dictated largely by the competing
and periodic requalification of the CT system is provided in
influences of spatial resolution, contrast discrimination, and
Test Method E1695. The suitability of the CT system shall be
artifacts of the imaging system. Operating parameters strike an
demonstrated by attainment of the required image quality and
overall balance between image quality, examination time, and
compliance with all other requirements stipulated herein.
cost.
6.2 Computer/Image Processing System—Image processing
4.4 Artifacts are often the limiting factor in CT image
quality. (See Practice E1570 for an in-depth discussion of systems may be used for image enhancement operations that
will facilitate dimensional measurements and discontinuity
artifacts.) Artifacts are reproducible features in an image that
are not related to actual features in the object.Artifacts can be detection or characterization.
considered correlated noise because they form repeatable fixed
6.2.1 Dimensional measurements, with tolerance, can be
patterns under given conditions yet carry no object informa-
obtained from the CT image. There is a degree of blurring in
tion. For castings, it is imperative to recognize what is and is
the CT image that makes sharp boundaries indistinct. A
not an artifact since an artifact can obscure or masquerade as a
common approach for on-screen dimensional measurements is
discontinuity.Artifacts are most prevalent in castings with long
to generate a density profile along a straight line between the
straight edges or complex geometries, or both.
points in the image representing the distance to be measured.
The end points of the measurement are generally taken to be
5. Basis of Application
the density profile values located at the half maximum value
point on each slope. This is called the full-width-at-half-
5.1 The following items shall be agreed upon between the
maximum (FWHM) method. This method or various other
purchaser and the supplier and specified in the contract or job
techniques, that is, the area under the curve or determining
order:
contours for CAD output, can be generalized for wall
5.1.1 Nondestructive Testing Agency Evaluation—The use
thickness, hole diameter, and crack width measurements.
of a nondestructive testing (NDT) agency, as defined in
Practice E543. If a systematic assessment of the capability of 6.2.2 Each dimensional measurement technique has its own
precision, and for its determination, the creation of the CT
the agency is specified, a documented procedure, such as that
described in Practice E543, should be used as the basis for image must be understood thoroughly. Due to the finite spot
evaluation. size of the source, and the finite aperture size of the detector, a
point-like object will not appear in an image as a sharp point.
5.1.2 Personnel Qualifica
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