NB/T 47013.14-2023Nondestructive testing of pressure equipments - Part 14: X-ray computed radiographic testing (English PDF)

3.1 Imaging plate (IP)

A flexible board coated with a compound of the rare earth elements europium, barium, and fluorine that can store information in the form of a latent image after exposure.

3.6 Structure noise of IP

The inherent noise in digital images that is caused by the uneven structure of the photosensitive layer and surface of the imaging plate.

3.7 Pixel

The basic unit of a radiographic digital image. A radiographic digital image is composed of points, and the points that make up the image are called pixels.

3.8 Grey value

A numerical value that represents the brightness or darkness of a pixel in a digital image.

3.9 Linearized grey value

Grey value that is proportional to the exposure of the imaging plate.

3.10 Image sensitivity

The ability of an inspection system to detect the smallest details in the image of the inspected workpiece.

4.1 Testing personnel

4.1.1 The general requirements for personnel engaged in computed radiographic testing (hereinafter referred to as "testing personnel") shall comply with the relevant provisions of NB/T 47013.1.

4.2 Testing system and equipment

4.2.1 X-ray machine

4.2.1.1 The energy range of the X-ray machine shall be selected according to the thickness, material and focal length of the object to be tested.

4.2.2 gamma-ray machine

4.2.2.1 The type and activity of the gamma-ray source shall be selected according to the thickness, material and focal length of the object to be tested.

4.2.2.2 The performance indicators of the used gamma-ray machine shall comply with the provisions of GB/T 14058.

4.2.3 CR system

The applicable CR system shall be selected according to the testing object and technical requirements. The system performance testing conditions and testing methods shall be implemented in accordance with the provisions of GB/T 21356. The system shall at least meet the following performance indicators.

4.2.4 Computer system

The basic configuration of the computer system is determined according to the performance and scanning speed requirements of the adopted CR system. It should be equipped with a memory of no less than 512MB, a hard disk of no less than 40GB, a high-brightness and high-resolution ratio display, a CD writer, a network card, etc. The display shall meet the following minimum requirements.

4.2.5 System-specific software

4.2.6 Image quality indictor

4.2.6.1 The image quality indicators used in this Document include wire type image quality indictors and duplex wire type image quality indicators. The supplier of the image quality indicator shall provide corresponding quality certification documents.

4.3 Testing technology level

4.3.1 The computed radiographic testing technology level specified in this Document is divided into three levels from low to high. A, AB and B.

4.4 Testing process documents

4.4.1 Testing process documents include process procedures and operating instructions.

4.4.2 In addition to meeting the requirements of NB/T 47013.1, the process procedures shall also specify the specific scope or requirements of the following related factors. If the changes in related factors exceed the provisions, the process procedures shall be re-compiled or revised.

4.5 Safety requirements

4.5.1 The testing environment shall meet the requirements of the system operation on environment (temperature, humidity, grounding, electromagnetic radiation, vibration, etc.).

4.5.2 Radiation protection shall comply with the relevant provisions of GB 18871 and GBZ 117.

4.5.3 When conducting CR testing on site, the control area and supervision area shall be divided according to the provisions of GBZ 117; and warning signs shall be set up; during the inspection operation, the radiation level shall be measured around the boundary of the control area. The inspector shall wear a personal dosimeter and carry a dose alarm.

5.1 Testing timing

5.1.1 The testing timing shall meet the requirements of relevant laws, regulations, standards and design technical documents; and shall also meet other technical requirements agreed upon by both parties to the contract.

5.1.2 Unless otherwise specified, the testing shall be carried out after welding is completed. For materials with delayed cracking tendency, the testing shall be carried out at least 24 hours after welding is completed.

5.2 Testing area

5.3 Surface requirements

Before testing, the surface of the welded joint shall be visually inspected and qualified. The image of the irregular state of the surface on the digital image shall not cover or interfere with the defect image, otherwise the surface shall be properly trimmed.

5.4 Imaging plate and metal screen

5.5 Transillumination arrangement

5.5.1 Transillumination method

The appropriate transillumination method shall be selected according to the characteristics of the object to be tested and the requirements of the technical conditions. For typical transillumination methods, please refer to NB/T 47013.2. Except for the special case where double-wall transillumination is allowed for small-diameter tubes or the contracting parties agree to select double-wall transillumination; when single-wall transillumination conditions are available, single-wall transillumination should be selected.

5.5.3 Effective length of a single exposure

5.5.4 Overlap of effective evaluation area

5.5.4.1 The effective evaluation area refers to the imaging area that meets the requirements of this Document FOR the ratio between max. and min. penetrated thicknesses AND image quality.

5.5.4.2 When 100% testing is performed on butt welds, the number of exposures and the overlap of the effective evaluation area shall ensure that the entire volume range of the detected area is detected.

5.15 Selection of scanner parameter

5.15.1 The selection of the scanner photomultiplier tube voltage or gain shall match the exposure so that the grey value of the digital image is in an appropriate range (5%~90%).

5.15.2 The selection of the scanning resolution ratio shall ensure that the image resolution ratio meets the requirements specified in the standard and shall match the characteristics of the imaging plate.

5.16 Image evaluation environment requirements

Image evaluation shall be carried out in a dedicated evaluation room, which shall be clean and tidy, with appropriate temperature and humidity.

6.1 General requirements

6.1.1 The marked image on the diagram shall be displayed complete and correctly positioned.

There shall be no pseudo-defect images caused by scratches, indentations, folds, delamination, foreign matter adhesion, and metal screen defects that interfere with defect identification in the effective image evaluation area.

6.2 Image sensitivity requirements

6.2.1 When a single-wall transillumination wire type image quality indicator is placed on the radioactive source side, it shall comply with the provisions of Table 6; when a double-wall double-shadow transillumination wire type image quality indicator is placed on the radioactive source side, it shall comply with the provisions of Table 7;

6.2.2 For welded joints with pads, the penetrated thickness may include the pad thickness.

6.3 Requirements for resolution ratio

6.4 Normalized signal-to-noise ratio

6.4.1 The normalized signal-to-noise ratio of the image shall meet the requirements of Tables 12 and 13.The measurement and calculation of the normalized signal-to-noise ratio (SNRn) are shown in Appendix C.

7.1 Defect identification

7.1.1 Defect identification can be done by manual identification or computer-assisted identification.

7.2 Defect measurement

7.2.1 Before defect measurement, the testing image containing the standard sample shall be collected according to the actual testing process; and the geometric size shall be calibrated.

7.2.3 When the system and transillumination parameters change, recalibration shall be performed.

8.1 Image storage

8.1.1 The image storage format shall be implemented in DICONDE format.

8.1.3 When image processing technology is used, the processed image shall be labeled and saved together with the raw digital image.

8.1.4 The image number shall correspond to the weld number.

8.2 Image preservation

8.2.1 Images shall be stored in digital storage media and archived.