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GB/T 41123.3-2021 PDF in English


GB/T 41123.3-2021 (GB/T41123.3-2021, GBT 41123.3-2021, GBT41123.3-2021)
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GB/T 41123.3-2021: PDF in English (GBT 41123.3-2021)

GB/T 41123.3-2021
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 19.100
CCS J 04
GB/T 41123.3-2021 / ISO 15708-4:2017
Non-Destructive Testing – Radiation Methods for
Industrial Computed Tomography – Part 3: Qualification
(ISO 15708-4:2017, Non-Destructive Testing – Radiation
Methods for Computed Tomography – Part 4: Qualification, IDT)
ISSUED ON: DECEMBER 31, 2021
IMPLEMENTED ON: JULY 01, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
Introduction ... 5
1 Scope ... 6
2 Normative References ... 6
3 Terms and Definitions ... 6
4 Detection and Verification ... 7
5 Verification of CT System ... 12
6 Examples of Evaluation Methods for CT System Resolution ... 14
Non-Destructive Testing – Radiation Methods for
Industrial Computed Tomography – Part 3: Qualification
1 Scope
This Document specifies the basic requirements for performance verification of radiation
methods for industrial computed tomography (CT) system when performing different testing
tasks.
This Document is applicable to radiation methods for industrial computed tomography (non-
medical applications); and gives a unified set of CT performance parameter definitions, and the
relationship between these performance parameters and CT system technical specifications.
This Document is applicable to computed axial tomography and inapplicable to other types of
tomography such as translational scan tomography and tomosynthesis, etc.
2 Normative References
The provisions in following documents become the essential provisions of this Document
through reference in this Document. For the dated documents, only the versions with the dates
indicated are applicable to this Document; for the undated documents, only the latest version
(including all the amendments) is applicable to this Document.
GB/T 41123.2-2021 Non-Destructive Testing - Radiation Methods for Industrial
Computed Tomography - Part 2: Operation and Interpretation (ISO 15708-3:2017, IDT)
ISO 15708-1 Non-Destructive Testing – Radiation Methods for Computed Tomography –
Part 1: Terminology
NOTE: GB/T 12604.12-2021 Non-Destructive Testing – Terminology - Part 12: Radiation Methods
for Industrial Computed Tomography (ISO 15708-1:2017, MOD)
3 Terms and Definitions
For the purposes of this Document, the terms and definitions given in ISO 15708-1 apply.
The terminology databases maintained by ISO and IEC for standardization are located at the
following addresses:
--- IEC Electronic Encyclopedia: http://www.electropedia.org/;
--- ISO online browsing platform: https://www.iso.org/obp.
4 Detection and Verification
4.1 Overview
Industrial CT is used for defect detection and size measurement. The size measurement value
(such as aperture or wall thickness) cannot be directly given by CT scanning, which shall be
calculated according to the X-ray attenuation data characterized by CT gray value. Feature
detectability and detection accuracy depend on the detection task, detection equipment, and the
employed analysis and evaluation methods. When the detection task, detection equipment and
the employed analysis and evaluation methods are determined, the CT system shall be verified
accordingly. See 4.2 and 4.3 for the verification methods. Validation should be performed by
trained personnel. Trainees shall demonstrate that they are trained and qualified in digital
radiography or computed radiography.
4.2 Verification of defect detection
4.2.1 Overview
In the detection verification, it should confirm whether the CT detection technology meets the
detection accuracy requirements. The following verification is a typical process for determining
applicability for industrial CT.
4.2.2 Quality characteristics
Typical detected features include the sizes of pores, holes, cracks, inclusions, contamination, as
well as material distribution and assembly and mounting locations of components. Since the
detection performance of a CT system depends on the type, location, and size of the test sample
and features to be detected, the following information should be known.
a) Detected object:
1) Size;
2) Weight;
3) Material;
4) The thickness of X-ray transillumination in the material.
b) Detected characteristics:
1) Type;
2) Location;
Determine the CT system settings and image quality parameters as described in 4.2 and 5.1 of
GB/T 41123.2-2021.
4.2.4 Verification of applicability
4.2.4.1 Overview
A reasonable description of the defect detection sensitivity and defect detectability of the CT
system shall be reflected in the detection accuracy (tolerance, fluctuation degree) required by
the test. Below are a few options.
4.2.4.2 Reference samples for natural defects
If there are reference samples with known defects, verify the defect detectability by testing the
samples.
If the reference sample has unquantified defects, test the sample first, and then re-verify the
defect detectability, for instance, using a destructive test for verification.
4.2.4.3 Reference samples for artificial defects
If the detected feature can be simulated by artificial defects (such as holes), the defect
detectability shall be verified by the method of 4.2.4.2.
4.2.4.4 Reference samples with unknown parameters
If the reference sample status is unknown and revalidation is impossible, use the system
sensitivity for detection. Defect detectability can be estimated by sample structure (e.g., wall
thickness, external dimensions, etc.). Other wire and spherical reference samples of known size
can also be used.
4.2.5 Consistency checking
CT scanning steps are complex, so it cannot be guaranteed that errors shall be completely
eliminated during the scanning process. After the CT scan is complete, possible sources of error
can be traced through the following points:
--- Reconstruction: size, CT slice position, possible artifacts;
--- CT image scale;
--- Sinogram (CT gray value and curve changes) or CT projection sequence (comparison
between projections, such as projected image quality, intensity changes);
--- System status (error message).
If there is an error, the error shall be corrected or the source of the error shall be eliminated,
then re-tested.
4.2.6 Documentation
All parameter settings and verification results in the verification steps are described and
presented in the verification report. The CT image archive period is determined according to
the end user requirements. Save test parameters for repeated testing of parts and features using
the same test flow.
4.3 Verification of dimensional measurement
4.3.1 Overview
CT detection provides the three-dimensional structural information of the sample; and the
external contour and geometric structure data of the sample can be obtained through the three-
dimensional structural information. Since these data are based on differences in the physical
absorption of X-rays at contour transitions, small differences in measured values can occur
compared to conventional contact methods or optical measurement processes. The following
Clauses describe CT scan parameters that affect the results and process steps that affect the
accuracy of the results.
4.3.2 Detection and measurement tasks
Dimensional measurement tasks include single dimension measurement, wall thickness
measurement, surface extraction, volume extraction or nominal-actual comparison. The
measurement accuracy is specified for each task and, if necessary, separately specified for
different parts of the sample.
4.3.3 Dimensional measurement/detection system/system parameter setting
The achievable measurement accuracy depends on the object to be measured, the limitations of
the physical principle of X-ray measurement, and the data processing method. The following
parameters are used to preliminarily estimate the CT dimensional measurement accuracy.
a) Spatial resolution of the measured object:
1) Image size;
2) Geometric magnification, voxel size;
3) detector resolution;
4) Focus size.
b) X-ray transmission characteristics of the measured object:
1) Materials;
2) Maximum penetration thickness of X-ray;
accuracy. Using spherical and dumbbell-shaped reference test pieces is also a method of
estimating measurement accuracy.
Typical parameters include the following:
a) Reference dimensions;
b) Compare the measurement procedure information with the information on the different
test areas within the sample;
c) Record the standard deviation of the measurement error as the reference data.
4.3.5 Consistency Checking
See 4.2.5.
4.3.6 Documentation
See 4.2.6.
5 Verification of CT System
5.1 Overview
The ability of a CT system to guarantee high quality, stable, and reproducible result depends on
the consistency of all system components and how they work together. To ensure this in daily
operations, periodic system verification should be carried out in accordance with the relevant
requirements.
A distinction should be made BETWEEN short-period (e.g., weekly) verification based on
"overall performance" testing, AND long-term (e.g., annual) verification based on quality level
descriptions and testing of possible changes to individual system components.
5.2 Verification of overall system
For routine system monitoring, the reference sample should be similar to a typical sample used
by CT systems. During the overall validation process, system parameters similar to those used
for testing typical samples should be used.
To evaluate system quality, the current test results are compared with reference measurement
results. The measurement results of different object structures, such as material defects (pores,
cracks), the thinnest and thickest parts of the reference test block, and wall thickness should be
used as the quality evaluation criteria.
If combined systems (two ray tubes and/or detectors) are used, separate reference blocks shall
be used for each system combination (e.g., application of microfocus and small focus).
Test results and system status shall be recorded and archived.
If discrepancies are found, further examination shall be performed to determine the cause (see
5.3). After system maintenance or major adjustment, system performance verification should
be carried out before using the system.
5.3 System component checking
5.3.1 Overview
Periodically and when changes to the system are suspected (after maintenance or in the event
of a crash), the following system components that may be affected shall be checked.
5.3.2 Mechanical system
The positioning accuracy of trajectories and axes shall be checked, and the measuring
equipment can use coordinate measuring machines (CMMs).
5.3.3 Image magnification
According to Figure 1 in GB/T 41123.2-2021, it should use a high-accuracy sphere group (such
as a club, dumbbell) with a known spatial structure to check the CT image magnification.
Differences in the CT grayscale thresholds used by these samples did not affect the obtained
size results.
5.3.4 Perpendicularity of beam
Use a suitable test sample (e.g., tungsten wire or tip, sphere, etc.) to check the perpendicularity
of the beam axis to the detector.
5.3.5 Focus position
The focal position of the radiation source shall be checked using a suitable method, for example,
by checking the consistency of the dimensions (within a specified error range) obtained from
CT scans at different magnifications to ensure the focal position.
5.3.6 Dose stability
Measuring the dose rate can check the stability of the X-ray tube output.
5.3.7 Detectors
The dynamic behavior of the detector can be checked by comparison with delivery conditions,
e.g., by imaging a stepped reference block. Detectors should be regularly checked for pixel
failures.
The stability of the detector can be checked using time-varying intensity measurements.
Reference test piece shall be suitable for specific equipment, such as microfocus systems and
high-energy systems. In general, the reference test piece should be as close as possible to the
measured object in attenuation and size. If necessary, customize more reference test pieces to
meet the requirements.
The following Clauses describe the method of partial implementation of the comparative
system on the reference test piece and several devices with different designs, fabrication
methods, and ages.
The recommended method should be selected according to the detection situation. Guidelines
for making reference test pieces are given in 6.3.
Theoretically, the measurement values given by the following methods are suitable for all cases.
6.2 Acquisition parameters
Since each CT system has its own method of image acquisition and reconstruction, it is
important for each system to establish resolution standard measurement method based on
optimal voltage, voxel size, and division increment (where possible).
6.3 Recommendations for making reference test pieces
The recommended method uses two types of reference test pieces, including the following types:
--- It is consisted by the components containing a row of calibrated holes for measuring
spatial resolution described in Figure A.1 of GB/T 41123.2-2021;
--- It is consisted by the components containing additives for measuring density resolution,
see Figure 1.
Since all measurements are related to the properties of the reference test piece, great care should
be taken when defining and creating them.
In order to ensure optimal measurement conditions, the reference test piece should meet specific
requirements. To avoid edge artifacts due to angular effects as described in GB/T 41123.2-2021,
a cylindrical geometry is chosen.
In order to measure the density resolution, the linear attenuation coefficient of the additive shall
be close to that of the base material to avoid the "edge effect" artifacts described in GB/T
41123.2-2021. Differences in attenuation coefficients between additives shall be kept low to
ensure higher detection sensitivity. Appropriate beam hardening correction should be
performed during CT image reconstruction. In addition, to ensure applicability, the material of
the reference test piece shall be chemically and densely similar to the object to be tested. This
is due to the fact that CT images measure X-ray attenuation coefficients that are related
(indirectly proportional) to material density.
The materials that make up the matrix and additives should be uniform; density variations shall
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Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.