ASTM E1814-96
(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: E 1814 – 96
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 2.2 ASNT Standards:
SNT-TC-1A Recommended Practice for Personnel Qualifi-
1.1 This practice covers a uniform procedure for the exami-
cation and Certification in Nondestructive Testing
nation of castings by the computed tomography (CT) tech-
ANSI/ASNT CP-189 Personnel Qualification and Certifica-
nique. The requirements expressed in this practice are intended
tion of Nondestructive Testing Personnel
to control the quality of the nondestructive examination by CT
2.3 Military Standard:
and are not intended for controlling the acceptability or quality
MIL-STD-410 Nondestructive Testing Personnel Qualifica-
of the castings. This practice implicitly suggests the use of
tion and Certification
penetrating radiation, specifically X rays and gamma rays.
2.4 Code of Federal Regulations:
1.2 This practice provides a uniform procedure for a CT
21 CFR 1020.40 Safety Requirements of Cabinet X Ray
examination of castings for one or more of the following
Systems
purposes:
29 CFR 1910.96 Ionizing Radiation
1.2.1 Inspecting for discontinuities, such as porosity, inclu-
sions, cracks, and shrink;
3. Terminology
1.2.2 Performing metrological measurements and determin-
3.1 Definitions—Definitions of terms applicable to this
ing dimensional conformance; and
practice may be found in Terminology E 1316 and Guide
1.2.3 Determining reverse engineering data, that is, creating
E 1441.
computer-aided design (CAD) data files.
3.2 Definitions of Terms Specific to This Standard:
1.3 This standard does not purport to address all of the
3.2.1 fixturing—the mounting hardware used to place the
safety concerns, if any, associated with its use. It is the
test object in the CT system.
responsibility of the user of this standard to establish appro-
3.2.2 representative quality indicator (RQI)—a real part, or
priate safety and health practices and determine the applica-
a fabrication of similar geometry in radiologically similar
bility of regulatory limitations prior to use. For specific safety
2 material to a real part, that has features of known characteris-
statements, see Section 7, NBS Handbook 114, and 21 CFR
tics that represent all of the features for which the test parts are
1020.40 and 29 CFR 1910.96.
being examined.
2. Referenced Documents 3.2.3 scan plan—scan locations and the system configura-
tion parameters for a specific part examination.
2.1 ASTM Standards:
3.2.4 test object—a part or specimen being subjected to CT
E 543 Practice for Evaluating Agencies that Perform Non-
examination.
destructive Testing
E 1316 Terminology for Nondestructive Examinations
4. Significance and Use
E 1441 Guide for Computed Tomography (CT) Imaging
4.1 The CT may be performed on a test object when it is in
E 1570 Practice for Computed Tomographic (CT) Exami-
3 the as-cast, intermediate, or final machined condition. A CT
nation
examination can be used as a design tool to improve wax forms
E 1672 Guide to Computed Tomography (CT) System Se-
3 and moldings, establish process parameters, randomly check
lection
process control, perform final quality control (QC) examina-
E 1695 Test Method for Measurement of Computed Tomog-
3 tion for the acceptance or rejection of parts, and analyze
raphy (CT) System Performance
failures and extend component lifetimes.
4.2 The most common applications of CT for castings are
for the following: locating and characterizing discontinuities,
This practice is under the jurisdiction of ASTM Committee E-7 on Nonde-
such as porosity, inclusions, cracks, and shrink; measuring
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 Standardization Documents Order Desk, Bldg. 4 Section D, 700
Annual Book of ASTM Standards, Vol 03.03. Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1814
as-cast part dimensions for comparison with design dimen- system components and the overall system configuration is
sions; and extracting dimensional measurements for reverse provided in Guide E 1672. Guidance on the initial qualification
engineering. and periodic requalification of the CT system is provided in
4.3 The extent to which a CT image reproduces an object or Test Method E 1695. The suitability of the CT system shall be
a feature within an object is dictated largely by the competing demonstrated by attainment of the required image quality and
influences of spatial resolution, contrast discrimination, and compliance with all other requirements stipulated herein.
artifacts of the imaging system. Operating parameters strike an 6.2 Computer/Image Processing System—Image processing
overall balance between image quality, inspection time, and systems may be used for image enhancement operations that
cost. will facilitate dimensional measurements and discontinuity
4.4 Artifacts are often the limiting factor in CT image detection or characterization.
quality. (See Practice E 1570 for an in-depth discussion of 6.2.1 Dimensional measurements, with tolerance, can be
artifacts.) Artifacts are reproducible features in an image that obtained from the CT image. There is a degree of blurring in
are not related to actual features in the test object. Artifacts can the CT image that makes sharp boundaries indistinct. A
be considered correlated noise because they form repeatable common approach for on-screen dimensional measurements is
fixed patterns under given conditions yet carry no test object to generate a density profile along a straight line between the
information. For castings, it is imperative to recognize what is points in the image representing the distance to be measured.
and is not an artifact since an artifact can obscure or masquer- The end points of the measurement are generally taken to be
ade as a discontinuity. Artifacts are most prevalent in castings the density profile values located at the half maximum value
with long straight edges or complex geometries, or both. point on each slope. This is called the full-width-at-half-
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, or a similar document. The written
E 1441 and Sections 5, 8, and 9 for further discussion.
procedure shall include training that addresses CT issues
6.2.3 Some tools require the availability of a test object that
specifically.
can be scanned and then dissected (destructive evaluation) for
5.1.3 General Requirements—General requirements shall
comparison with actual dimensional measurements. The CT
be specified in accordance
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