GB/T 37930-2019Non-destructive testing instruments—Technical specifications of X-ray real-time imaging system for automobile wheel (English PDF)

3.1 X-ray Digital Radioscopy

X-ray digital radioscopy refers to an imaging method, which adopts photoelectric

3.8 Linear Diode Array; LDA

Linear diode array refers to an X-ray detector which receives and converts into digital signals through linear array image sensor after X-ray is converted into optical (electric) signal through a conversion screen.

NOTE: linear diode array needs to utilize the relative motion with objects to form a digital image of the testing zone.

3.9 Image Intensifier Tube; IIT

Image intensifier tube refers to a device which utilizes the method of photoelectric multiple to obtain high-brightness visible light image on the output screen after X-ray is converted into visible light through a scintillator.

NOTE: generally speaking, it couples with CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor), then, outputs video electrical signals or direct digital signals.

3.10 Sensitivity

Sensitivity refers to the minimum diameter of image quality indicator that is visible to the naked eyes in the displayed perspective image.

NOTE: it shall be expressed in image quality indicators.

3.11 Dynamic Range

Dynamic range refers to the ratio of the maximum value that a detector can output to the dark field signal standard deviation under the condition of conducting no calibration.

3.12 Pixel

Pixel refers to the minimum constitutional unit of digital image and the minimum geometric dimension that can be identified in display image.

NOTE: different grayscale values of various pixels constitute different brightness of digital image.

3.13 Line Pair

Line pair is constituted of a line and a spacing, and the width of the spacing equals to the width of the line.

NOTE: the number of identifiable line pairs within the range of each millimeter of width is

5.1 System Composition

X-ray real-time imaging system is mainly constituted of X-ray machine, X-ray detector, computer image processing system, mechanical transmission system and testing equipment and tooling, etc.

5.2 X-ray Machine

In accordance with the thickness and texture of the tested part of automobile wheel, and the focal length, select X-ray machine's energy range. The dimension of X-ray tube focus shall be not more than 3.0 mm.

5.3 X-ray Detector

In accordance with different testing requirements and testing conditions, the following X-ray detectors may be selected:

---Flat panel detector;

---Linear diode array detector;

---Image intensifier tube;

---Other detectors that have similar functions as mentioned above.

5.4 X-ray Air Kerma Rate

Under the rated working conditions, the leaking ray air Kerma rate of X-ray device at a distance of 1 m from X-ray tube focus shall comply with the requirements in Table 1.

5.6.2 Testing of system resolution

After a system is determined or altered, its resolution shall be tested.

Adopt the radiographic testing system resolution indicator described in GB/T 23903 to test system resolution. Please refer to Appendix B for system resolution testing method.

5.6.3 Validation of system resolution

Under the condition of unchanged system, in every 30 d, system resolution shall be validated at least once; validation record shall also be kept. When abnormal image quality is found, system resolution shall be validated at any time.

6.1 X-ray Tube Voltage

X-ray energy shall select relatively low tube voltage. Figure 1 stipulates the maximum X-ray tube voltage that is allowed to be adopted under different materials and different transillumination thicknesses.

6.5.3 Imaging mode

6.5.3.1 Static imaging

Under the static state of automobile wheel, the detector absorbs a larger radiation dose, then, generates image data, which obtains testing images through multi-frame overlaying (or uniform) processing. The testing images shall be considered as a basis for original image data storage and quality evaluation.

6.5.3.2 Dynamic imaging

When automobile wheel is in uniform motion, dynamically observe the testing images.

This method may be applied to general quality inspection beyond the testing range.

Due to the relatively small absorbed dose, large noise and low sharpness of the detector, dynamic real-time image cannot be considered as a basis for the grading of welding quality.

6.5.4 Image marking

6.5.4.1 On the testing images, information that is advantageous to image evaluation and validation, such as workpiece No., base metal thickness, external diameter, testing personnel and testing date, shall at least be marked. When the same welding seam is saved as multiple testing image files, each image shall contain the above-mentioned information. In image storage, marking information shall be directly written into image files by software and shall be irreversible; there is no need to use typeface images here.

6.5.4.2 When the same test part is under continuous testing, the serial No. of multiple testing images shall be continuous and automatically set up by system software.

6.5.4.3 Through system software, provide positioning indication of the central position of testing images and the range of one-time transillumination length. In the images, center marking, and typeface image, which overlaps and connects the marking are unnecessary.

6.5.5 Shielding of unwanted rays and scattered rays

Unwanted rays and scattered rays shall be shielded as much as possible. Proper measures, such as lead plate, copper filter plate and collimator (grating) may be adopted to shield unwanted rays and scattered rays; restrict the range of the irradiation field.

7.1 Sensitivity of Image Quality Indicator

7.1.1 Requirements of image quality indicator

7.3 Image Grayscale Distribution Range

Grayscale range of testing images within the valid evaluation zone should be controlled between 40% ~ 90% of the system's maximum grayscale range. Through image grayscale histogram, directly measure image grayscale distribution range.

7.4 Timing of Image Evaluation

After the quality of testing images satisfies the stipulated requirements, defect grading evaluation of the test parts may be conducted.

7.5 Testing Environment

Protection against ionizing radiation shall comply with the stipulations in GB 18871.

Temperature in operating chamber: 15 °C ~ 25 °C; relative humidity <= 80%.

Temperature in X-ray exposure chamber: 5 °C ~ 30 °C; relative humidity <= 80%; there shall be air ventilation device inside the exposure chamber.

The fluctuation of power source and voltage shall be not more than ± 10%.

The outer shell of the testing equipment shall have favorable ground connection.

X-ray source high-voltage generator shall have independent ground electrode; resistance <= 4 ohm.

8.1 Image Display

Testing images may be displayed on black-and-white display or color display through the mode of positive image or negative image. Through the adjustment of the brightness and contrast ratio of display, it shall guarantee that all data in the image in Appendix A can be identified.

8.2 Image Observation

Under the environment of soft light, observe testing images. Image display screen shall be clean; there shall be no obvious light reflection.

8.3 Paper Print Output of Images

Use high-definition printer to output paper testing images. The size of the printed images shall be identical to the full size of the test part, so as to make it convenient for on-site validation of defect locations and on-site quality analysis.

B.3 Testing Methods for Image Resolution and Unsharpness

B.3.1 Testing methods

Place the resolution indicator for X-ray testing images in the position of the test part.

B.3.2 Determination of image resolution

On the display screen, observe images of the resolution indicator for X-ray testing images. When a line pair with separated grid is observed, then, the corresponding value of this line pair shall be image resolution.

B.3.3 Determination of image unsharpness

On the display screen, observe images of the resolution indicator for X-ray testing images. When a line pair with superposed grid is observed, then, the corresponding grid width of this line pair shall be image unsharpness.

B.4 Relations between System Resolution and Image Resolution

System resolution is image resolution when magnification equals to or approaches 1.

It eliminates the influence of process factors on image quality and purely reflects the resolution of X-ray digital imaging equipment itself. When magnification is larger than 1, if the X-ray source adopts small focus, then, image resolution is generally higher than system resolution; if focus dimension is relatively large, image resolution might be lower than system resolution due to the influence of geometric unsharpness.

B.5 Conversion Relations between Image Resolution and Image Unsharpness

The conversion relations of image resolution and image unsharpness in magnitude is "one-half of the reciprocal". […]