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GB/T 35839-2018

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GB/T 35839-2018English259 Add to Cart Days<=3 Non-destructive testing—Test method for measuring industrial computed tomography(CT) density Valid GB/T 35839-2018
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Detail Information of GB/T 35839-2018; GB/T35839-2018; GBT 35839-2018; GBT35839-2018
Description (Translated English): Non-destructive testing--Test method for measuring industrial computed tomography(CT) density
Sector / Industry: National Standard (Recommended)
Classification of Chinese Standard: J04
Classification of International Standard: 19.100
Word Count Estimation: 14,181
Date of Issue: 2018-02-06
Date of Implementation: 2018-09-01
Drafting Organization: Chongqing University, Chongqing True Measurement Technology Co., Ltd., China Ordnance Science Research Institute Ningbo Branch, China Aerospace Science and Technology Group Chuannan Machinery Factory, Chinese People's Liberation Army 96630, Chongqing Hongyu Precision Industry Co., Ltd., Hubei Sanjiang Aerospace Jiangbei Machinery Engineering Co., Ltd.
Administrative Organization: National Nondestructive Testing Standardization Technical Committee (SAC/TC 56)
Proposing organization: National Nondestructive Testing Standardization Technical Committee (SAC/TC 56)
Issuing agency(ies): General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China, China National Standardization Administration

GB/T 35839-2018
Non-destructive testing-Test method for measuring industrial computed tomography(CT) density
ICS 19.100
J04
National Standards of People's Republic of China
Nondestructive testing
Industrial Computer Tomography (CT) Density Measurement Method
Non-destructivetesting-
Testmethodformeasuringindustrialcomputedtomography(CT)density
Published on.2018-02-06
2018-09-01 implementation
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
China National Standardization Administration issued
Content
Foreword III
1 range 1
2 Normative references 1
3 Terms and Definitions 1
4 Basic requirements 1
5 Detection method 2
6 Detection Process 3
7 Measurement process 4
8 Test records and reports 5
Appendix A (informative) Density comparison test piece production specification 6
Appendix B (informative) The mass attenuation coefficient of typical materials at different energies 7
Appendix C (informative appendix) Equivalent energy calculation method 8
Foreword
This standard was drafted in accordance with the rules given in GB/T 1.1-2009.
This standard is proposed and managed by the National Non-Destructive Testing Standardization Technical Committee (SAC/TC56).
This standard was drafted. Chongqing University, Chongqing Zhen Test Technology Co., Ltd., China Academy of Ordnance Science Ningbo Branch, China Aerospace
Technology Group Chuannan Machinery Factory, People's Liberation Army 96630 Unit, Chongqing Hongyu Precision Industry Co., Ltd., Hubei Sanjiang Space River
North Mechanical Engineering Co., Ltd.
The main drafters of this standard. Shen Kuan, Wang Wei, Cai Yufang, Liu Fenglin, Duan Xiaojiao, Lu Yanping, Ni Peijun, Zhang Zheng, Su Zhijun, Yang Dahong,
Wang Xiaoyong, Gao Rui, Guo Zhimin, Zhang Weiguo.
Nondestructive testing
Industrial Computer Tomography (CT) Density Measurement Method
1 Scope
This standard specifies methods for measuring the density of objects using industrial computer tomography (CT) equipment.
This standard is applicable to common metal and non-metal materials using industrial CT systems with energy ranges from.200 keV to 10 MeV.
Density measurement.
2 Normative references
The following documents are indispensable for the application of this document. For dated references, only dated versions apply to this article.
Pieces. For undated references, the latest edition (including all amendments) applies to this document.
GB/T 9445 Non-destructive testing personnel qualification and certification (GB/T 9445-2015, ISO 9712.2012, IDT)
GB/T 29069 Non-destructive testing industrial computer tomography (CT) system performance test method
General requirements for industrial computer tomography (CT) testing of non-destructive testing GB/T 29070
GB/T 34365 Non-destructive testing terminology industrial computer tomography (CT) detection
3 Terms and definitions
The following terms and definitions as defined in GB/T 34365 apply to this document.
4 basic requirements
4.1 Testing personnel
4.1.1 Personnel engaged in industrial CT density measurement shall meet the requirements of relevant inspection personnel in GB/T 9445 and GB/T 29070.
4.1.2 Personnel engaged in industrial CT density measurement shall have knowledge of materials, structures, processes, etc., and undergo industrial CT density measurement.
Technical training.
4.2 Environmental conditions
4.2.1 Meet the requirements of GB/T 29070 on environmental conditions.
4.2.2 The radiation protection conditions of the test room and control room shall meet the requirements of the user.
4.3 Testing equipment
4.3.1 Equipment composition
Industrial CT systems generally consist of a ray source system, a detection system, a data acquisition and transmission system, a mechanical system, a control system, and an image processing system.
It consists of a system of radiation protection systems.
4.3.2 Equipment Performance
The energy of the source of industrial CT equipment should meet the penetrating requirements of the workpiece being tested. Density resolution performance indicators should meet the actual
For the detection of workpiece density, the density resolution index should be better than 0.5%. Other indicators such as spatial resolution, scan time, etc.
The actual product inspection requirements should be met.
4.3.3 Equipment performance check
The main performance indicators such as spatial resolution and density resolution of the CT system are regularly tested in accordance with GB/T 29069. in
After the equipment is installed, commissioned, repaired, or replaced, the main performance indicators should be tested and the test results recorded.
4.4 Density comparison test piece
4.4.1 Overview
The density comparison test piece is a standard sample set for density comparison with the workpiece to be tested when using industrial CT for density measurement.
Each of the density standard samples consists of a homogeneous material whose density values are calibrated and the ray attenuation characteristics are the same or similar to the sample being measured. dense
The comparative test piece contains a plurality of density standard samples, and the density range covers the density range of the object to be tested.
4.4.2 Production requirements
The density comparison test pieces should be individually designed and manufactured for different materials, different density ranges, and different parts. Density comparison test
See Appendix A for the design and fabrication requirements of the parts.
4.4.3 Calibration and verification of density values
The density value of the density comparison test piece should be calibrated when first used. In the course of use, drainage or other means should be used every six months.
Proper methods for verification. If it is found that the density value varies by more than 0.5%, it should be recalibrated.
5 Detection methods
5.1 Method 1
The basic principle is to establish the CT scan of the density comparison test piece under the current scanning conditions by industrial CT scanning of the density comparison test piece.
See the equation (1) for the relationship with the linear attenuation coefficient. Using the relationship to calculate the linear attenuation coefficient of the material to be tested, and then divide by the material
The mass attenuation coefficient gives the corresponding mass density, see equation (2). See Appendix B for the mass attenuation coefficient of common substances.
NCT=kμ c (1)
In the formula.
NCT---the average number of CTs of the sample to be tested;
μ --- linear attenuation coefficient;
k, c---constant.
ρ=μμm
(2)
In the formula.
ρ --- the density value of the sample to be tested, in grams per cubic centimeter (g/cm3);
μ --- linear attenuation coefficient;
Mm --- mass attenuation coefficient.
This method cannot measure the substance of unknown components or it is difficult to measure the quality because it requires the mass attenuation coefficient of the known substance to be tested.
Attenuating coefficient of polymer species. Since the mass attenuation coefficient is different at different energies, it is first necessary to determine when using this method.
See Appendix C for the equivalent energy of the CT system and the equivalent energy calculation method. When the equivalent energy is between.200keV and 2MeV, the mass attenuation system
The number hardly changes with the change of energy, so if the mass attenuation coefficient of the substance to be tested is unknown, you can try the known substances with similar density.
Replace the mass attenuation factor.
5.2 Method 2
A density standard sample in the density comparison test set is selected as the density reference sample for density measurement. Specify according to the density reference sample
The average CT density f0 of the region and the scaling factor K set by the CT system (determined according to the overall parameters of the CT system, generally 1000~)
5000), normalizing the average CT density f of the designated area of each density comparison test piece according to formula (3) to obtain the flatness in the area
CT number μ.
μ=
F-f0
F0
×K (3)
In the formula.
μ --- density comparison of the average CT number of the designated area of the test piece;
f --- density comparison of the average CT density of the designated area of the test piece;
F0---the average CT density of the designated area of the density standard sample;
K --- CT system set the scale factor.
Using the average CT number μ of the specified area of each density contrast test piece and the known density ρ of the standard sample, a polynomial fit measurement is used.
The relationship between the average CT number μ and the material density ρ is ρ = f (μ), and a cubic polynomial fit is recommended.
The method has a wide range of applications for measuring material density directly from CT numbers, but has the same linear attenuation coefficient and has no
The same mass attenuation coefficient of material density measurement has a large measurement error.
6 Testing process
6.1 Analysis of material characteristics
6.1.1 Before the test, the shape, structure, material, quality, density distribution range, detection accuracy and other requirements of the workpiece to be inspected should be known in detail to ensure CT.
The equipment meets the density detection requirements of the material being inspected.
6.1.2 Before the test, the maximum equivalent steel penetration thickness of the ray of the workpiece to be tested should be considered to ensure that the ray can completely penetrate the workpiece to be inspected.
6.2 Scan parameter determination
6.2.1 The ray attenuation conditions and scanning parameters of the density calibration and density measurement process should be consistent. Ray energy is guaranteed to pass through
Under the premise of the test piece, the system should also meet the signal-to-noise ratio requirement. The lower energy should be selected to improve the contrast of the system and select a larger current.
To improve the signal to noise ratio.
6.2.2 Use front and rear collimators to control the width and shape of the rays to reduce scattered rays.
6.2.3 Pre-filtering with filters to remove unwanted soft rays and reduce the effects of scattered rays.
6.2.4 The workpiece to be tested is placed as shown in Figure 1. The magnification M is defined by equation (4).
M =
SDD
SOD
(4)
In the formula.
SDD—the distance from the focus of the ray source to the center detector, in millimeters (mm);
SOD—The distance from the focus of the ray source to the center of rotation, in millimeters (mm).
Figure 1 CT scan geometry
The optimal magnification Mopt detected is determined by equation (5).
Mopt=1
(5)
In the formula.
d---the effective width of the detector, in millimeters (mm);
a --- ray source focus size in millimeters (mm).
For some types of industrial CT equipment, since the magnification cannot be adjusted, the scanning field should be set to rotate the workpiece under test.
1.5 times the diameter.
6.2.5 If the detection time allows, the number of sampling points selected should be sufficient, generally not less than 512 × 512. In specific applications, sampling
The size of the points should be optimized according to the actual conditions of the workpiece and the detector.
6.2.6 In the case where the detection time is allowed and the output of the integrator is not saturated, the selected integration time should be long enough to make the material uniform.
CT images have a small CT standard deviation. In specific applications, the integration time should be based on the actual condition of the workpiece and detector being inspected.
It is preferred by the test method.
6.3 Image reconstruction, display and processing
6.3.1 Select the appropriate data filtering and image reconstruction method, and adjust the reconstruction parameters to the parameter setting with the optimal system density resolution. weight
The construction scope should be larger than the measured workpiece section, and a larger reconstruction matrix should be selected to improve the spatial resolution, and the reconstruction matrix should be no less than 512×512.
6.3.2 Select the image display mode such as black and white, color, 2D or 3D as needed. Make images by window width/window level adjustment
Easy to observe.
6.3.3 If necessary, use appropriate image processing methods for image processing to improve contrast and sharpness.
7 Measurement process
7.1 Overview
If method 1 is used for density measurement, it is first necessary to determine the equivalent energy under the current scan parameters (see Appendix C for the calculation method).
With Method 2, there is no need to calculate the equivalent energy.
7.2 Density calibration
7.2.1 Density calibration of industrial CT equipment using density comparison specimens. The density comparison test piece group should be placed as far as possible in the center of the system turntable
It is distributed on the circumference of the center of the circle and at equal intervals. The density standard sample rotation axis should be perpendicular to the scanning slice plane, and the slice position should be at the density standard.
1/2 of the height of the sample. The CT scan process parameters for density calibration should be the same as the actual product test parameters.
7.2.2 Determination of density A certain range of density standard specimens in the test piece (the measurement range should be a circular area, each circular area image
The average number of primes should be no less than 100, but not more than 2/3 of the entire standard sample image area, and the number of measurements is not less than 5 times.
Number, if using Method 1 for density measurement, it is recommended to use the least squares method to establish the function between the average CT number and the linear attenuation coefficient.
If method 2 is used for density measurement, it is recommended to use a polynomial fitting method to establish a function between the average CT number and the standard density.
relationship.
7.2.3 The change in gray level in the CT image reflects the true change in the density of the object being measured rather than an artifact. Due to inconsistent detector response, shot
For line scattering, ray hardening, etc., CT images may exhibit a certain degree of artifacts, and artifacts are often mistaken for density changes. for
To ensure the effectiveness of the density measurement method, errors in CT artifacts and ray hardening should be minimized in the detection, and the measurement range is selected.
Should try to avoid the area affected by the artifacts, the selected pixels should be guaranteed to be valid pixels, if necessary, the filtering method can be used to remove invalid
Pixel.
7.3 Density measurement
7.3.1 Select the same density reference sample (the density comparison test piece closest to the density of the substance to be tested) used in the density calibration.
The reference sample is placed in the vicinity of the area to be tested of the object to be tested and CT scan is performed simultaneously with the object to be measured; or the density reference sample is placed separately
(The same scanning position as the area to be tested of the object to be measured), using the same process parameters as when the object to be measured is scanned, for the density comparison test piece alone
Scan.
7.3.2 CT scanning process conditions for density measurement such as specimen placement, scanning mode, scanning parameters (tube voltage, tube current, focus size, filtering)
Method, slice thickness, field of view diameter, scan matrix, sampling time, etc.), reconstruction parameters, etc. should be compared with the density test specimens.
All consistent.
7.3.3 Taking into account the stability of the equipment itself, during the actual inspection process, the density comparison test specimens are periodically re-scanned according to the situation.
Determine the change in the CT value of the density comparison test piece, and if necessary, correct the function relationship between the CT number and the density to improve the detection accuracy.
Authenticity.
7.3.4 Obtain the specified area from the CT image of the density reference sample (the number of pixels in the specified area should be no less than 100 and not more than the whole
The average CT density f of 2/3 of the standard sample image area.
7.3.5 Obtain the average CT density f of the area to be tested (the number of pixels in the area should be no less than 100) from the CT image of the measured object.
If the density measurement is performed using the second method, normalization is performed according to the equation (3) to obtain an average CT number μ of the region to be tested.
7.3.6 According to the average CT number of the area to be tested of the measured object and the calibrated functional relationship, the average material density of the area is obtained.
7.3.7 Repeat the measurement of different areas of the same uniform material at least 5 times, and use the average value of the density measured 5 times as the density value of the material.
Calculate the standard deviation of the density measurement.
7.3.8 If the composition and mass attenuation coefficient of the substance to be tested are known, it is recommended to use method 1 for density measurement.
8 Test records and reports
8.1 Test record
8.1.1 The test record shall include the workpiece name, number, the detected part, the density comparison test piece, the device model, the scanning method, and the measuring side.
Method, scanning process, reconstruction parameters, image description, data recording, curve drawing, test results, and testers, reviewers, test dates, etc.
8.1.2 The image data file shall contain the CT equipment model, source, detector, scanning method, test piece number, image number, and test piece position.
Set, scan parameters, rebuild parameters, and more. Image data should be kept on a disc, tape or hard disk for at least five years.
8.2 Test report
The contents of the test report should generally include. the name of the workpiece, the number, the location of the test, the condition of the density test piece, the model of the device, and the tester.
Method, slice position, slice thickness, reconstruction matrix, test results, tester, reviewer, approver, test date, report date, etc.
Appendix A
(informative appendix)
Density comparison test piece production specification
A.1 Basic structure
The density comparison test piece is made of a homogeneous material (the attenuation characteristic is the same as or similar to the material surrounding the density detection area of the workpiece to be tested).
A series of workpiece samples of known density are inserted into a specific part and uniformly distributed along the circumference on the substrate. The basic structure is as shown in A1, which is straight.
The diameter is preferably 2/3 of the maximum imaging diameter of the CT system.
Figure A.1 Density comparison test piece
A.2 Design requirements
A.2.1 Density comparison test piece is a series of standard samples made of materials with uniform composition, stable density and easy processing. The density range should be included.
Contains the material to be tested, and the density of each standard sample is known.
A.2.2 Each standard sample shall be of uniform material, and the size specifications of each standard sample shall be the same. The density comparison test piece height shall be CT slice.
More than 3 times the thickness.
A.2.3 The density block of each standard sample shall be strictly calibrated, the density calibration accuracy shall be higher than the measurement requirement accuracy by an order of magnitude, and the density block
The diameter is not more than 1/7 of the diameter of the base. It is best to ensure that the density block is installed stably during CT scanning, and the cross section is flat with the CT system.
The faces are parallel.
A.2.4 The density test specimens of powder and liquid materials shall be sealed and stored.
A.3 Requirements for use
In the density test, the detection conditions of the density comparison test piece should be the same as the conditions of the actual workpiece to be tested, for example, the density comparison test piece is placed.
In the same housing as the actual workpiece, the ray attenuation conditions are consistent.
Appendix B
(informative appendix)
Mass attenuation coefficient of typical materials at different energies
The mass attenuation coefficient μm of typical materials at different energies is shown in Table B.1.
Table B.1 Typical material mass attenuation coefficient μm in different energies in grams per cubic centimeter
Photon Energy /
Mev
Magnesium aluminum silicon ferrotitanium nickel copper lead air water
Polyphenylene
Ethylene
High borosilicate
glass
0.01 20.8 26.2 34.1 113 172.0 213.8 224.2 136.6 5.04 5.21 2.17 17.1
0.02 2.7 3.39 4.36 15.8 25.5 31.7 33.7 85.5 0.758 0.778 0.429 2.24
0.03 0.914 1.12 1.41 4.88 8.11 10.3 10.9 29.1 0.35 0.371 0.261 0.785
0.04 0.481 0.565 0.693 2.18 3.61 4.62 4.88 13.8 0.248 0.267 0.216 0.43
0.05 0.327 0.367 0.435 1.19 1.94 2.52 2.61 7.71 0.206 0.0225 0.197 0.299
0.06 0.257 0.277 0.319 0.752 1.2 1.52 1.6 4.87 0.187 0.0205 0.186 0.241
0.08 0.195 0.201 0.223 0.4 0.59 0.723 0.768 2.37 0.167 0.0185 0.173 0.19
0.1 0.169 0.17 0.184 0.271 0.37 0.446 0.462 5.78 0.155 0.171 0.164 0.166
0.2 0.125 0.122 0.128 0.132 0.147 0.159 0.157 1.104 0.124 0.137 0.132 0.125
0.3 0.107 0.104 0.108 0.104 0.11 0.116 0.112 0.406 0.107 0.119 0.115 0.107
0.4 0.09480.09260.09610.09080.09410.09780.0942 0.233 0.0954 0.106 0.103 0.0953
0.5 0.08630.08440.08750.08180.0841 0.087 0.08350.16140.08680.0966 0.0937 0.0868
0.6 0.07960.07790.0806 0.075 0.07680.07930.07620.12490.08040.0894 0.0867 0.0801
0.8 0.06990.06820.07080.06570.06690.06880.06590.08860.07060.0785 0.0761 0.0704
1.0 0.06280.06130.06340.0589 0.06 0.0615 0.059 0.07080.06350.0706 0.0683 0.0633
1.5 0.05120.05000.05170.04780.0487 0.05 0.04790.05180.05170.0575 0.0567 0.0515
2 0.04410.04310.04470.04170.04250.04370.04190.04550.04440.0493 0.0476 0.0444
3 0.036 0.03530.03670.03500.03610.03730.03590.04170.03580.0396 0.0381 0.036
4 0.03160.03110.03240.03180.03310.03440.03320.04150.0308 0.034 0.0326 0.0314
5 0.02880.02840.02970.02980.03150.03290.03180.04240.02760.0303 0.0289 0.0284
6 0.02680.02660.02790.02860.03060.0321 0.031 0.04360.02520.0277 0.0263 0.0263
8 0.02440.02440.02570.02750.02990.03160.03070.04670.02230.0243 0.0227 0.0237
10 0.02310.02320.02460.02730.02990.0319 0.031 0.04960.02050.0222 0.0206 0.0221
Appendix C
(informative appendix)
Equivalent energy calculation method
C.1 Calculation process
C.1.1 Set the test parameters to the highest density resolution and use industrial CT to test the density comparison test pieces.
C.1.2 Determination of density A certain range of density standard specimens in the test piece (the measurement range should be a circular area, each circular area image
The average number of primes should be no less than 100, but not more than 2/3 of the entire standard sample image area, and the number of measurements is not less than 5 times.
The number is used to establish a functional relationship between the average CT number and the linear attenuation coefficient using the least squares method [Eq. (1)].
C.1.3 Multiply the density of each sample by the mass attenuation coefficient to obtain the linear attenuation coefficient μ1 of the sample, and select a set of energy ranges respectively.
(The range should include the equivalent energy of the system) The mass attenuation coefficient is used to calculate the linear attenuation coefficient of each sample, which can be obtained under different energies.
The linear attenuation factor for each sample.
C.1.4 Calculate the linear attenuation coefficient μ2 of each sample using the function relation [Equation (1)], and calculate the linear attenuation coefficient at different energies respectively.
Correlation coefficient between μ1 and the linear attenuation coefficient μ2.
C.1.5 Select the energy corresponding to the maximum value of the correlation coefficient as the equivalent energy of the CT system.
C.2 Calculation example
Using 9MeV industrial CT system for three substances methylmethacrylate (H8C5O2), tetrafluoroethylene
Density detection of tetrafluoroethylene (C2F4) and aluminum (aluminum, Al), respectively measuring the average CT number of the three substances, so that
The coefficients k and c of equation (1) are calculated by the least squares method, and the linear attenuation coefficient μ1 of each substance is calculated using equation (1); the table is obtained to obtain 3700 keV~
The mass attenuation coefficient of each substance at 4000 keV is multiplied by the corresponding density to obtain the linear attenuation coefficient μ2 of each substance, which is calculated separately.
Correlation coefficient between the linear attenuation coefficient μ1 and the linear attenuation coefficient μ2 at different energies. The results are shown in Table C.1.
Table C.1 CT system equivalent energy calculation table
Substance name
Empirical linear attenuation coefficient μ
CT number 3700keV 3800keV 3900keV 4000keV
Methyl methacrylate 1286 0.0404 0.0399 0.0393 0.0388
Tetrafluoroethylene 2119 0.0670 0.0661 0.0652 0.0644
Aluminum 2756 0.0870 0.0862 0.0851 0.0843
Correlation coefficient - 0.9999887 0.9999996 0.9999991 0.9999893
The energy value corresponding to the maximum correlation coefficient is selected as 3800 keV as the equivalent energy of the system.
Related standard:   GB/T 35977-2018
   
 
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