ASTM E1814-96(2002)
(Practice)Standard Practice for Computed Tomographic (CT) Examination of Castings
Standard Practice for Computed Tomographic (CT) Examination of Castings
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.
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. For specific safety statements, see Section 7,NBS Handbook 114, and 21 CFR 1020.40 and 29 CFR 1910.96.
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Designation:E1814–96 (Reapproved 2002)
Standard Practice for
Computed Tomographic (CT) Examination of Castings
This standard is issued under the fixed designation E 1814; 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 E 1695 TestMethodforMeasurementofComputedTomog-
raphy (CT) System Performance
1.1 This practice covers a uniform procedure for the exami-
2.2 ASNT Documents:
nation of castings by the computed tomography (CT) tech-
Recommended Practice SNT-TC-1A Personnel Qualifica-
nique.The requirements expressed in this practice are intended
tion and Certification in Nondestructive Testing
to control the quality of the nondestructive examination by CT
ANSI/ASNT CP-189 Standard for Personnel Qualification
and are not intended for controlling the acceptability or quality
and Certification of Nondestructive Testing Personnel
of the castings. This practice implicitly suggests the use of
2.3 Military Standards:
penetrating radiation, specifically X rays and gamma rays.
MIL-STD-410 Nondestructive Testing Personnel Qualifica-
1.2 This practice provides a uniform procedure for a CT
tion and Certification
examination of castings for one or more of the following
NAS-410 Certification and Qualification of Nondestructive
purposes:
Test Personnel
1.2.1 Examining for discontinuities, such as porosity, inclu-
2.4 Code of Federal Regulations:
sions, cracks, and shrink;
21 CFR 1020.40 Safety Requirements of Cabinet X Ray
1.2.2 Performing metrological measurements and determin-
Systems
ing dimensional conformance; and
29 CFR 1910.96 Ionizing Radiation
1.2.3 Determining reverse engineering data, that is, creating
computer-aided design (CAD) data files.
3. Terminology
1.3 This standard does not purport to address all of the
3.1 Definitions—Definitions of terms applicable to this
safety concerns, if any, associated with its use. It is the
practice may be found in Terminology E 1316 and Guide
responsibility of the user of this standard to establish appro-
E 1441.
priate safety and health practices and determine the applica-
3.2 Definitions of Terms Specific to This Standard:
bility of regulatory limitations prior to use. For specific safety
2 3.2.1 fixturing—the mounting hardware used to place the
statements, see Section 7, NBS Handbook 114, and 21 CFR
object in the CT system.
1020.40 and 29 CFR 1910.96.
3.2.2 representative quality indicator (RQI)—a real part, or
2. Referenced Documents a fabrication of similar geometry in radiologically similar
material to a real part, that has features of known characteris-
2.1 ASTM Standards:
tics that represent all of the features for which the parts are
E 543 Practice for Agencies Performing Nondestructive
being examined.
Testing
3 3.2.3 scan plan—scan locations and the system configura-
E 1316 Terminology for Nondestructive Examinations
tion parameters for a specific part examination.
E 1441 Guide for Computed Tomography (CT) Imaging
3.2.4 object—a part or specimen being subjected to CT
E 1570 Practice for Computed Tomographic (CT) Exami-
examination.
nation
E 1672 Guide to Computed Tomography (CT) System Se-
4. Significance and Use
lection
4.1 CT may be performed on an object when it is in the
as-cast, intermediate, or final machined condition. A CT
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
examinationcanbeusedasadesigntooltoimprovewaxforms
structive Testing and is the direct responsibility of Subcommittee E07.01 on
Radiology (X and Gamma) Method.
Current edition approved May 10, 1996. Published July 1996.
2 4
NBS Handbook 114, General Safety Standard for Installations, Using Non- Available from American Society for Nondestructive Testing, 1711 Arlingate
Medical X-Ray and Sealed Gamma-Ray Sources, Energies Up to 10 MeV, National Plaza, P.O. Box 28518, Columbus, OH 43228-0518.
Institute of Standards and Technology (NIST), Gaithersburg, MD. Available from DODSSP, Bldg. 4, Section D, 700 Robbins Ave., Philadelphia,
Annual Book of ASTM Standards, Vol 03.03. PA 19111-5098.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1814–96 (2002)
and moldings, establish process parameters, randomly check 5.1.7 Records—Records requirements shall be specified in
process control, perform final quality control (QC) examina- accordance with Section 10.
tion for the acceptance or rejection of parts, and analyze
6. Apparatus
failures and extend component lifetimes.
6.1 The success of the CT application depends on the
4.2 The most common applications of CT for castings are
overall system configuration and the selection of appropriate
for the following: locating and characterizing discontinuities,
subsystem components. Guidance on the selection of sub-
such as porosity, inclusions, cracks, and shrink; measuring
system components and the overall system configuration is
as-cast part dimensions for comparison with design dimen-
provided in Guide E 1672. Guidance on the initial qualification
sions; and extracting dimensional measurements for reverse
and periodic requalification of the CT system is provided in
engineering.
Test Method E 1695. The suitability of the CT system shall be
4.3 The extent to which a CTimage reproduces an object or
demonstrated by attainment of the required image quality and
a feature within an object is dictated largely by the competing
compliance with all other requirements stipulated herein.
influences of spatial resolution, contrast discrimination, and
6.2 Computer/Image Processing System—Image processing
artifacts of the imaging system. Operating parameters strike an
systems may be used for image enhancement operations that
overall balance between image quality, examination time, and
cost. will facilitate dimensional measurements and discontinuity
detection or characterization.
4.4 Artifacts are often the limiting factor in CT image
quality. (See Practice E 1570 for an in-depth discussion of 6.2.1 Dimensional measurements, with tolerance, can be
obtained from the CT image. There is a degree of blurring in
artifacts.) Artifacts are reproducible features in an image that
are not related to actual features in the object.Artifacts can be the CT image that makes sharp boundaries indistinct. A
common approach for on-screen dimensional measurements is
considered correlated noise because they form repeatable fixed
patterns under given conditions yet carry no object informa- to generate a density profile along a straight line between the
points in the image representing the distance to be measured.
tion. For castings, it is imperative to recognize what is and is
The end points of the measurement are generally taken to be
not an artifact since an artifact can obscure or masquerade as a
the density profile values located at the half maximum value
discontinuity.Artifacts are most prevalent in castings with long
point on each slope. This is called the full-width-at-half-
straight edges or complex geometries, or both.
maximum (FWHM) method. This method or various other
5. Basis of Application
techniques, that is, the area under the curve or determining
5.1 The following items shall be agreed upon between the
contours for CAD output, can be generalized for wall thick-
purchaser and the supplier and specified in the contract or job
ness, hole diameter, and crack width measurements.
order:
6.2.2 Each dimensional measurement technique has its own
5.1.1 Nondestructive Testing Agency Evaluation—The use
precision, and for its determination, the creation of the CT
of a nondestructive testing (NDT) agency, as defined in
image must be understood thoroughly. Due to the finite spot
Practice E 543. If a systematic assessment of the capability of
size of the source, and the finite aperture size of the detector, a
the agency is specified, a documented procedure, such as that
point-like object will not appear in an image as a sharp point.
described in Practice E 543, should be used as the basis for
Instead, the “true” image will be convolved with a Gaussian
evaluation.
distribution-like function called the point spread function
5.1.2 Personnel Qualifications—All CT examination per-
(PSF).Therefore, when looking at a density profile along a line
sonnel shall be qualified and certified in accordance with a
in a CT image, an abrupt density change (that is, from material
written procedure conforming to ANSI/ASNT CP-189, SNT-
to air) will not appear as a step but as a curve. See Guide
TC-1A, MIL-STD-410, NAS-410, or a similar document. The
E 1441 and Sections 5
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