GB 17925-1999 X-ray real-time imaging inspection of butt welds of gas cylinders
Some standard content:
GB17925-1999
This standard is formulated on the basis of summarizing the research and application results of X-ray real-time imaging detection in my country's gas cylinder industry, and referring to the relevant contents of foreign advanced standards.
Appendix A, Appendix B and Appendix C of this standard are all appendices of the standard. This standard is proposed and managed by the National Technical Committee for Gas Cylinder Standardization. The drafting units of this standard are: Boiler and Pressure Vessel Testing Research Center of the State Administration of Quality and Technical Supervision, Guangdong Yuehai Cylinder Factory, Lanzhou Sanlei Electronics Company, Beijing Freda Electronic Technology Engineering Company of Aerospace Industry Corporation and Jiangsu Minsheng Group Company. The main drafters of this standard are Kang Jiqian, Zeng Xiangzhao, Sun Zhongcheng, Liu Jianchun and Tang Penglin. 467
GB179251999
Due to the development of computer digital imaging technology, X-ray real-time imaging technology can be applied to non-destructive testing of gas cylinder butt welds. After X-rays pass through metal materials, the image multiplier converts the implicit X-ray signals into visible images. After being captured by a camera, the image is input into a computer for analog/digital conversion to form a digital image, which is stored in the computer hard disk in a certain format and displayed on the screen. There will be a short delay in the generation of digital images, which depends on the computing speed of the computer. Digital images can provide information about the nature, size, location and other information of surface and internal defects of metal materials. Computer programs are used to assist in evaluation according to relevant standards, so as to achieve the purpose of non-destructive testing. The test images can be saved on computers and CDs or digital tapes. In terms of test results, the X-ray real-time imaging test method has the same effect as the X-ray film photography method. 468
1 Scope
National Standard of the People's Republic of China
X-ray real-time imaging test of cylinders weld
Standard practice for X-ray real-time examination of cylinders weld1.1 This standard is the standard for X-ray real-time imaging non-destructive testing of cylinders weld. GB 17925—1999
1.2 This standard applies to nondestructive testing of butt welds of gas cylinders made of steel and nonferrous metal materials with a base material thickness of 2.0 to 20.0 mm. 2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and the parties using this standard should explore the possibility of using the latest versions of the following standards. GB4792—1984 Basic Standard for Radiation Health Protection JB.4730—1994 Nondestructive Testing of Pressure Vessels 3 Definitions
This standard adopts the following definitions.
3.1 Real-time imaging
The image acquisition speed reaches 25 frames/second (PAL format) or 30 tons/second (NTSC format), which is regarded as real-time imaging. 3.2 Image Processing
After the detection signal is digitized by the computer, it is stored in a certain format in the computer. The digital image processing technology is used to enhance the image contrast and clarity to obtain better image quality. 3.3 Gray Scale
The degree of black and white in the image is expressed in gray. This standard defines the range of black and white changes in the image as 8bit, i.e. 256 gray levels. 3.4 Image Resolution
The minimum spacing of the line separation that can be identified on the display screen image, in units of line pairs per millimeter (LP/mm). 3.5 Image Unsharpness
A physical quantity corresponding to the clarity of the image. After a device with a clear and sharp boundary is imaged, the image of its boundary will become blurred. The width of the blurred area is the image unsharpness, in units of millimeters (mm). 4 Personnel Requirements
4.1 Personnel engaged in X-ray real-time imaging detection should receive technical training on this detection method, and be assessed in accordance with the "Qualification Assessment Rules for Boiler Pressure Vessel Nondestructive Testing Personnel" and relevant regulations. Only after obtaining the corresponding level of qualifications can they perform the corresponding work. 4.2 The inspectors shall understand the basic computer knowledge related to this inspection technology and master the basic computer operation methods. 4.3 The image assessors shall be able to distinguish a group of printed letters with a height of 0.5mm and a spacing of 0.5mm at a distance of 400mm. Approved by the State Administration of Quality and Technical Supervision on December 17, 1999 and implemented on October 1, 2000
GB 17925 -- 1999
4.4 The image assessors shall be trained in the visual adaptation ability of the display screen before the assessment. 5X-ray real-time imaging system
5.1 Composition of X-ray real-time imaging system
The X-ray real-time imaging system mainly consists of X-ray machine, X-ray image intensifier, optical lens, TV camera, computer system, image acquisition unit, image display and image storage unit and inspection tooling and other equipment. 5.2 X-ray machine
It is advisable to use a constant pressure small focus continuous detection X-ray machine. When the rated voltage is less than or equal to 320kV, the focal spot size should be less than or equal to 0.6mm×0.6mm; when the rated voltage is less than or equal to 160kV, the focal spot size should be less than or equal to 0.4mm×0.4mm. The energy of the X-ray should be able to meet the requirements of the thickness of the weld to be inspected and have a certain reserve of penetration ability. 5.3 Image intensifier
The diameter of the image intensifier input screen shall not be less than 150mm, and the resolution shall not be less than 3.6LP/mm. 5.4 Television camera
Optically coupled device (CCD) or electron tube line camera can be selected, and the acquisition resolution shall not be less than 800×600 pixels. 5.5 Computer system
5.5.1 Basic configuration of computer
Mainboard: with PCI bus, and a certain number of slots should be provided to facilitate the installation of display card, graphics accelerator card, image acquisition card, and network card. Central processing unit (CPU): Pentium 166MMX. Memory: 32MB.
Display card: flat graphics accelerator card.
Image acquisition card: acquisition resolution 768×576 pixels. Hard disk: 2.0GB.
Display: Display screen size 380mm, dot pitch 0.25mm, progressive scan, display resolution 1024×768 pixels. Also equipped: CD drive, 1.44MB floppy disk drive and mouse. Image storage media: CD or digital tape. Image transcription device: CD recorder or digital tape recorder. 5.5.-2 Basic software configuration
Under DOS or Windows Chinese operating system, support image processing and image-assisted assessment program operation; image storage file format should use universal and standard format as much as possible. 5.6 System resolution
The resolution of X-ray real-time imaging system should be greater than or equal to 1.4LP/mm. The system resolution detection method is shown in Appendix A (Standard Appendix). The system resolution should be tested regularly. 5.7 Inspection tooling
The inspection tooling should have at least degrees of freedom and should have high operating accuracy. 6 Detection environment
Room temperature of the operating room: 10~28℃; relative humidity: ≤80%; radiation health protection conditions shall comply with the requirements of GB4792. Room temperature of the X-ray detection room: 5～35℃; relative humidity: ≤85%. The indoor power supply shall have a dedicated ground wire, and the ground wire resistance shall be less than or equal to 0.32.7 Image processing
The following methods can be used to process the collected image data to optimize the image quality: a) continuous frame superposition;
b) grayscale enhancement;
c) edge sharpening;
d) smoothing intensity;
e) others.
GB 17925—1999
Any processing method shall not change the original data collected. 8 Image quality
8.1 Image quality index The image quality index shall meet the requirements of AB level in Table 5-3 of JB47301994. 8.1.1 Selection of image quality meter
The material of the metal wire of the linear image quality meter should be consistent with the material of the gas cylinder to be tested. The image quality meter should be selected according to the provisions of Table 5-2 in JB4730-1994.
8.1.2 Placement of image quality meter
The linear image quality meter should be placed on the surface of the gas cylinder weld near the side of the radiation source. The metal wire should cross the weld and be perpendicular to the weld direction. When the image quality meter cannot be placed on the side of the radiation source, it can also be placed on the surface of the weld near the image intensifier, but the image quality meter index should be increased by one level; or through comparative tests, the actual image quality index should meet the specified requirements. When the image quality meter is placed on the surface of the weld near the image intensifier, an "F" mark should be added to distinguish it.
8.1.3 Placement of image quality meter during continuous testing
During continuous testing, at least one image quality meter should be placed on each weld under the condition that the imaging process conditions remain unchanged. If one of the images has a complete image quality meter image, the image quality index of this image can represent the image quality index of other images of the same weld. 8.1.4 Identification of the Image Quality Indicator
Directly observe the image of the image quality indicator at the weld position of the image. If the image of the metal wire of the image quality indicator can be clearly seen at the weld position, the image quality indicator is considered to be identifiable.
8.2 Image resolution
8.2.1 Resolution in the effective assessment area of the image The resolution in the effective assessment area of the image shall meet the requirements of Table 1. The resolution required to be achieved in the effective assessment area of the image is shown in Table 1 [
Thickness of penetration, mm
8.2.2 Verification of image resolution
The image resolution shall be verified at least once for every 10 cylinders of the same model tested continuously. 8.3 Image grayscale
The grayscale range in the effective assessment area of the image shall be controlled within the range of 80 to 230. 8.3.1 Verification of image grayscale
The image grayscale shall be verified at least once for every 10 cylinders of the same model tested continuously. 8.4 Timing of image assessment
Weld defect level assessment can only be carried out after the image quality meets the specified requirements. 9 Imaging technology
Image resolution, LP/mm
9.1 Selection of X-ray energy
9.1.1 The maximum X-ray tube voltage allowed for penetrating materials of different thicknesses shall be selected according to the provisions of Figure 5-6 in JB4730-1994. 471
GB17925--1999
9.1.2 X-ray penetrating equivalent coefficient of non-ferrous metal materials The X-ray penetrating equivalent coefficient of non-ferrous metal materials is shown in Table 5-1 in JB4730-1994. 9.2 Image magnification
Since the test gas cylinder cannot be closely attached to the surface of the image intensifier input screen, the test image is magnified according to the relative positions of the X-ray machine, gas cylinder and image intensifier, as shown in Figure 1. The magnification M is: M-
Wu Zhong: L
Distance from the focus of the X-ray tube to the surface of the image intensifier input screen, mm; distance from the focus of the X-ray tube to the surface of the weld to be inspected, mm; distance from the surface of the weld to the surface of the image intensifier input screen, mm. L2
1—Focus of the X-ray tube; 2--gas cylinder, 3-inspected weld: 4-image intensifier; 5 optical lens; 6-camera Figure 1 Relative positions of X-ray source, gas cylinder, and image intensifier Figure 9.3 Image unsharpness
The unsharpness U after image magnification is:
Wu Zhong: U.
Unsharpness before image magnification.
The test method for unsharpness after image magnification is shown in Appendix A. 9.4 Unsharpness before image magnification
(1)
Under certain testing conditions, the unsharpness before image magnification is determined by the inherent unsharpness U of the X-ray real-time imaging system and the geometric unsharpness U according to formula (3):
U3 = (U3+U3)
The test method for the inherent unsharpness of the X-ray real-time imaging system is shown in Appendix A. 9.5 Geometric unsharpness
The relationship between the geometric unsharpness U3 and the magnification M is: d×L?
= d(M- 1)
Where: d—the focal spot size of the X-ray tube, mm. 472
（3）
·（4）
9.6 Optimal magnification of image detection
GB17925—1999
As the magnification increases, the geometric unsharpness also increases. According to the relationship between the inherent unsharpness U of the X-ray real-time imaging system and the focal size d of the X-ray machine, the optimal magnification Mopr of image detection is determined: Mop = 1 →
9.7 Minimum detectable defect size
Under certain conditions, the minimum detectable defect size dmin of the image is: U
9.8 Image storage
The detected image is stored in the computer and can be transferred to a storage medium such as a CD. 9.9 Image display mode
The image can be displayed on the display screen in positive or negative image mode; it can also be displayed in black and white or in color. 10 Process evaluation
10.1 Through process tests and evaluations, determine the process parameters that can meet the image quality requirements, see Appendix C (Appendix to the standard) for details. 10.2. After the process conditions are changed, the process evaluation should be repeated. 11 Detection method
(5)
11.1 Transillumination method
The transillumination method of the gas cylinder weld can be longitudinal seam transillumination, annular seam external illumination, annular seam internal illumination, and double-wall single-image transillumination. When the double-wall single transillumination method is used, when the image magnification M≤2, the weld close to the image intensifier side should be used as the test weld; when the image magnification is M2, the weld close to the radiation source side should be used as the test weld. However, regardless of the transillumination method, a certain distance is maintained between the surface of the gas cylinder and the surface of the image intensifier input screen to protect the image intensifier from damage. 11.2 Weld transillumination thickness ratio
The weld transillumination thickness ratio K is determined according to formula (7). The K value of the circumferential seam is not greater than 1.1, and the K value of the longitudinal seam is not greater than 1.03. The weld penetration thickness ratio is:
parent material thickness, mm.
Where: T—-
maximum oblique penetration thickness of the ray beam, mm. T
11.3 Penetration thickness
K= T\/T
The penetration thickness is determined according to Appendix C "Butt Weld Penetration Thickness" in JB4730-1994. 11.4 Measurement of detection length
11.4.1 Actual detection length
The actual detection length of the image can be measured by a computer program. The calibration of the image detection length is based on the lead ruler that is imaged at the same time as the weld to be inspected. The structure of the ruler is shown in Appendix B (Standard Appendix). 11.4.2 Effective detection length
The effective detection length should be less than the actual detection length, and the difference should be greater than or equal to 5mm. 11.5 Number of images
11.5.1 During continuous inspection of welds, the number of images N to be inspected in one weld is: length of weld
N=effective inspection length of two images
The number of images N should be an integer greater than or equal to the value calculated by the above formula. The numbering of multiple inspection images in one weld should be continuous and can be automatically numbered by a computer program. 11.5.2
GB 17925—1999
11.5.3 During continuous inspection, if the first image in a weld has a complete lead type number image, the lead type images of other images can be omitted.
11.6 Shielding of useless rays and scattered rays
Useless rays and scattered rays should be shielded:
a) Use lead windows to limit the area of the main beam; b) Use high-density materials as filter plates to reduce low-energy scattered rays12 Image observation
Observe the test image in a soft light environment. The image display screen should be clean and without obvious light reflection. The observation distance is 300~500 mm.
13 Image evaluation
13.1 Computer-assisted evaluation
Computer programs can be used to evaluate image quality and weld defects. The determination of the nature of weld defects should be based on non-destructive testing personnel with corresponding qualifications. The length measurement and rating of weld defects can be computer-assisted. 13.2 Measurement of image grayscale
Use a computer program to measure the image grayscale level. 13.3 Measurement of weld defect size
Use a computer program to measure the weld defect size. 13.3.1 Calibration of image assessment scale
Place the lead scale (see Appendix B) close to one side of the weld to be inspected and image the weld simultaneously. Use a computer program to measure the size of the lead scale on the image multiple times. When the measurement result approaches a certain value, it means that the calibration result has been confirmed. After the cylinder model and inspection process are changed, the calibration should be re-performed.
13.3.2 Measurement error
The measurement error of the image size should be less than or equal to 0.5mm. 14 Weld defect grade assessment
Weld defect grade assessment is carried out in accordance with the contents of "weld defect grade assessment" in Chapter 6 of Part II of JB4730-1994. 15 Test report and image preservation
15.1 Test report
The main contents of the test report should include: product name, model, number, material, parent material thickness, test device model, test location, transillumination method, process parameters, image quality, defect name, assessment grade, repair situation and test date, etc. The test report must be signed by the operator and assessor and indicate their qualification level. 15.2 Image backup and preservation
The test image should be backed up in two copies and kept for more than 7 years. The corresponding original records and test reports should also be kept for the same period. During the effective preservation period, the image data shall not be lost.
15.2.1 Storage environment
The optical disk or digital tape used to store the test images should be anti-magnetic, moisture-proof, dust-proof, anti-extrusion and anti-scratch. 16 Radiation protection
Radiation protection should comply with the relevant provisions of GB4792. 474
Process documents
GB17925-1999
In order to facilitate the correct interpretation of the results of X-ray real-time imaging detection, detailed information on the technology used should be provided along with the test results. These information should include the following: a) Scope of application;
b) Test basis;
c) Personnel requirements;
d) Equipment conditions;
e) Workpiece requirements;
f) Technical requirements;
g) Illumination method;
h) Test parameters;
i) Image evaluation;
j) Record report;
k) Safety management;
1) Other necessary contents.
A1 Overview
GB 17925—1999
Appendix A
(Appendix to the standard)
Test method for image resolution and image blur Use the image test card to test the X-ray real-time imaging system and detect the resolution and blur of the image. A2 Structure of the image test card
A2.1 Lead bars and line pairs
Within a certain width, a number of lead bars with equal width and thickness of 0.1 to 0.2 mm are evenly arranged, and the spacing between the bars is equal to the width of the bars. --A bar and a spacing adjacent to it constitute a line pair, and the line pair is represented by LP. A2.2 Millimeter line pairs
The number of line pairs arranged within a width of 1 mm is called a millimeter line pair, and is represented by LP/mm. A2.3 Line pair group
A number of identical line pairs are evenly arranged within a width of 5 mm to form a group of line pairs. A2.4 Composition of the test card
Within a certain width, 7 groups of line pairs are evenly arranged, and the distance between two adjacent groups is 3mm; the order of the number of line pairs of the 7 groups is 1.2 LP/mm, 1. 4 LP/mm, 1. 6 LP/mm, 1.8 LP/mm, 2. 0 LP/mm. 2.2 LP/mm, 2. 4 LP/mm. A2.5 Composition of the grid
A2.5.1 The length of the grid l=20mm.
A2.5.2 The width a of the grid is calculated as follows: a
Where: α
grid width, mm;
number of pairs, IP/mm.
grid width deviation is ±5%.
A2.5.3 The number of bars n is calculated as follows:
n = 5p＋ 1
A2.5.4 The spacing b between bars is equal to the width α of the bars. A2.6 The structure and corresponding relationship of the image test card The structure and corresponding relationship of the image test card are shown in Table A1 Table Al [
The structure and corresponding relationship of the image test card
Number of line pairs No. 1
Bar width
Bar spacing b
Number of bars
（A1）
（A2)
Resolution
GB17925—1999
A2.7 The number of line pairs is marked in lead type above each group of line pairs of bars, and the standard code and line pair unit are marked in lead type below the bars.
A2.8 The bars of each line pair are tightly clamped between two 1mm thick organic glass plates. A3 Test method for resolution and inherent unsharpness of X-ray real-time imaging system A3.1 Test method
Place the image test card tightly against the center area of the image intensifier input screen surface, with the line pair bars perpendicular to the horizontal position, and perform transillumination according to the following process conditions, and image on the display screen: a) The distance from the focus of the X-ray tube to the surface of the image intensifier input screen is not less than 700mm; b) The tube voltage is not greater than 40kV;
c) The tube current is not greater than 2.0mA;
d) The image contrast is moderate.
A3.2 Determination of the resolution of the X-ray real-time imaging system Observe the image of the test card on the display screen, and observe a group of line pairs that are just separated by the bars. The resolution corresponding to this group of line pairs is the system resolution.
A3.3 Determination of the inherent unsharpness of the system
Observe the image of the test card on the display screen, and observe a group of line pairs whose bars just overlap. The bar spacing corresponding to this group of line pairs is the inherent unsharpness of the system.
A4 Test method for image resolution and unsharpness A4.1 Test method
Place the image test card tightly on the surface of the weld to be tested, with the line pair bars perpendicular to the weld and imaged simultaneously with the weld. A4.2 Determination of image resolution
Observe the image of the test card on the display screen, and observe a group of line pairs whose bars just separate. The resolution corresponding to this group of line pairs is the image resolution.
A4.3 Determination of image unsharpness
Observe the image of the test card on the display screen, and observe a group of line pairs whose bars just overlap. The bar spacing corresponding to this group of line pairs is the image unsharpness.
Appendix B
(Standard Appendix)
Lead Ruler
B1 Structure
Use a lead strip with a thickness of 0.1~0.2mm to make a lead ruler with a length of 170mm and a width of 25mm. The scale range of the ruler is 0~150mm, the minimum scale within the range of 50mm at both ends is 1mm, and the minimum scale within the range of 50mm in the middle is 0.5mm; mark the number of centimeters above the scale of the ruler, and mark the unit of measurement below the ruler. The lead ruler is tightly clamped between two layers of soft packaging strips. B2 Usage
Place the lead ruler tightly on the weld to be inspected, and image it simultaneously with the weld to be inspected. 477
C1 Process assessment
GB17925—1999
Appendix C
(Appendix to the standard)
Process assessment
Before using X-ray real-time imaging detection technology, or after the type of detection gas cylinder, process factors, and detection equipment are changed, a process assessment should be carried out.
Process factors
The main process factors of X-ray real-time imaging detection are: X-ray tube voltage, X-ray tube current, imaging distance, magnification, scattered ray shielding, absorption of low-energy rays, and image frame superposition frequency. C3 Result of process assessment
C3.1 The result of process assessment should be able to meet the requirements of image quality. The process assessment document should be approved by the technical person in charge of the unit and stored in the technical file. C3.2IP/mm.
The deviation of the width of the grid is ±5%.
A2.5.3 The number of grid bars n is calculated as follows:
n = 5p＋ 1
A2.5.4 The spacing b of the grid bars is equal to the width α of the grid bars. A2.6 The structure and corresponding relationship of the image test card The structure and corresponding relationship of the image test card are shown in Table A1 Table Al [
The structure and corresponding relationship of the image test card
Number of line pairs No. 1
Grid width
Grid spacing b
Number of grid barswww.bzxz.net
（A1）
（A2)
Resolution
GB17925—1999
A2.7 The number of line pairs is marked in lead type above each group of line pairs of grid bars, and the standard code and line pair unit are marked in lead type below the grid bars.
A2.8 The bars of each line pair are tightly clamped between two 1mm thick organic glass plates. A3 Test method for resolution and inherent unsharpness of X-ray real-time imaging system A3.1 Test method
Place the image test card tightly against the center area of the image intensifier input screen surface, with the line pair bars perpendicular to the horizontal position, and perform transillumination according to the following process conditions, and image on the display screen: a) The distance from the focus of the X-ray tube to the surface of the image intensifier input screen is not less than 700mm; b) The tube voltage is not greater than 40kV;
c) The tube current is not greater than 2.0mA;
d) The image contrast is moderate.
A3.2 Determination of the resolution of the X-ray real-time imaging system Observe the image of the test card on the display screen, and observe a group of line pairs that are just separated by the bars. The resolution corresponding to this group of line pairs is the system resolution.
A3.3 Determination of the inherent unsharpness of the system
Observe the image of the test card on the display screen, and observe a group of line pairs whose bars just overlap. The bar spacing corresponding to this group of line pairs is the inherent unsharpness of the system.
A4 Test method for image resolution and unsharpness A4.1 Test method
Place the image test card tightly on the surface of the weld to be tested, with the line pair bars perpendicular to the weld and imaged simultaneously with the weld. A4.2 Determination of image resolution
Observe the image of the test card on the display screen, and observe a group of line pairs whose bars just separate. The resolution corresponding to this group of line pairs is the image resolution.
A4.3 Determination of image unsharpness
Observe the image of the test card on the display screen, and observe a group of line pairs whose bars just overlap. The bar spacing corresponding to this group of line pairs is the image unsharpness.
Appendix B
(Standard Appendix)
Lead Ruler
B1 Structure
Use a lead strip with a thickness of 0.1~0.2mm to make a lead ruler with a length of 170mm and a width of 25mm. The scale range of the ruler is 0~150mm, the minimum scale within the range of 50mm at both ends is 1mm, and the minimum scale within the range of 50mm in the middle is 0.5mm; mark the number of centimeters above the scale of the ruler, and mark the unit of measurement below the ruler. The lead ruler is tightly clamped between two layers of soft packaging strips. B2 Usage
Place the lead ruler tightly on the weld to be inspected, and image it simultaneously with the weld to be inspected. 477
C1 Process assessment
GB17925—1999
Appendix C
(Appendix to the standard)
Process assessment
Before using X-ray real-time imaging detection technology, or after the type of detection gas cylinder, process factors, and detection equipment are changed, a process assessment should be carried out.
Process factors
The main process factors of X-ray real-time imaging detection are: X-ray tube voltage, X-ray tube current, imaging distance, magnification, scattered ray shielding, absorption of low-energy rays, and image frame superposition frequency. C3 Result of process assessment
C3.1 The result of process assessment should be able to meet the requirements of image quality. The process assessment document should be approved by the technical person in charge of the unit and stored in the technical file. C3.2IP/mm.
The deviation of the width of the grid is ±5%.
A2.5.3 The number of grid bars n is calculated as follows:
n = 5p＋ 1
A2.5.4 The spacing b of the grid bars is equal to the width α of the grid bars. A2.6 The structure and corresponding relationship of the image test card The structure and corresponding relationship of the image test card are shown in Table A1 Table Al [
The structure and corresponding relationship of the image test card
Number of line pairs No. 1
Grid width
Grid spacing b
Number of grid bars
（A1）
（A2)
Resolution
GB17925—1999
A2.7 The number of line pairs is marked in lead type above each group of line pairs of grid bars, and the standard code and line pair unit are marked in lead type below the grid bars.
A2.8 The bars of each line pair are tightly clamped between two 1mm thick organic glass plates. A3 Test method for resolution and inherent unsharpness of X-ray real-time imaging system A3.1 Test method
Place the image test card tightly against the center area of the image intensifier input screen surface, with the line pair bars perpendicular to the horizontal position, and perform transillumination according to the following process conditions, and image on the display screen: a) The distance from the focus of the X-ray tube to the surface of the image intensifier input screen is not less than 700mm; b) The tube voltage is not greater than 40kV;
c) The tube current is not greater than 2.0mA;
d) The image contrast is moderate.
A3.2 Determination of the resolution of the X-ray real-time imaging system Observe the image of the test card on the display screen, and observe a group of line pairs that are just separated by the bars. The resolution corresponding to this group of line pairs is the system resolution.
A3.3 Determination of the inherent unsharpness of the system
Observe the image of the test card on the display screen, and observe a group of line pairs whose bars just overlap. The bar spacing corresponding to this group of line pairs is the inherent unsharpness of the system.
A4 Test method for image resolution and unsharpness A4.1 Test method
Place the image test card tightly on the surface of the weld to be tested, with the line pair bars perpendicular to the weld and imaged simultaneously with the weld. A4.2 Determination of image resolution
Observe the image of the test card on the display screen, and observe a group of line pairs whose bars just separate. The resolution corresponding to this group of line pairs is the image resolution.
A4.3 Determination of image unsharpness
Observe the image of the test card on the display screen, and observe a group of line pairs whose bars just overlap. The bar spacing corresponding to this group of line pairs is the image unsharpness.
Appendix B
(Standard Appendix)
Lead Ruler
B1 Structure
Use a lead strip with a thickness of 0.1~0.2mm to make a lead ruler with a length of 170mm and a width of 25mm. The scale range of the ruler is 0~150mm, the minimum scale within the range of 50mm at both ends is 1mm, and the minimum scale within the range of 50mm in the middle is 0.5mm; mark the number of centimeters above the scale of the ruler, and mark the unit of measurement below the ruler. The lead ruler is tightly clamped between two layers of soft packaging strips. B2 Usage
Place the lead ruler tightly on the weld to be inspected, and image it simultaneously with the weld to be inspected. 477
C1 Process assessment
GB17925—1999
Appendix C
(Appendix to the standard)
Process assessment
Before using X-ray real-time imaging detection technology, or after the type of detection gas cylinder, process factors, and detection equipment are changed, a process assessment should be carried out.
Process factors
The main process factors of X-ray real-time imaging detection are: X-ray tube voltage, X-ray tube current, imaging distance, magnification, scattered ray shielding, absorption of low-energy rays, and image frame superposition frequency. C3 Result of process assessment
C3.1 The result of process assessment should be able to meet the requirements of image quality. The process assessment document should be approved by the technical person in charge of the unit and stored in the technical file. C3.2
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