GB/T 17925-2024Practice for X-ray digital radioscopic examination of cylinder weld (English PDF)

1 Scope

GB/T 17925-2024 governs the X-ray digital radiographic examination of the butt welds of gas cylinders. A cylinder is a pressure vessel that will be filled and emptied thousands of times and carried around by people, so its longitudinal and circumferential welds are examined on every unit rather than by sampling, and the examination has moved from film to flat panel detectors. Digital radiography is faster and leaves an image that can be stored and re-examined, but it introduces its own variables - detector pixel pitch, magnification, grey level and image processing - which have to be controlled or the sensitivity claimed for the technique is not achieved. The standard sets the technique, the equipment, the process and the image quality requirements: the general requirements, the testing environment and working conditions, the timing of the examination and the surface preparation, the examination technique and process, the marking of image information, the measurement of the image quality indicator and the limits on it, the observation, processing and dimensional measurement of the image, the quality classification of the cylinder butt weld, and the storage of the images. It replaces the 2011 edition and takes effect on 1 July 2025.

This document specifies the flat panel detector X-ray digital radioscopic (DR) examination technology, equipment, process and image quality requirements for fusion welded butt joints of gas cylinders during manufacturing. This document is applicable to DR examination of cylinder weld made of steel and nonferrous metal materials with a nominal thickness of

16.0 mm and a nominal diameter of 100 mm ~ 1 200 mm. This document can be used as a reference for DR examination of other gas cylinders of similar specifications, sizes, and materials, as well as fusion-welded butt joints of in- use gas cylinders.

2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

GB/T 12604.11, Non-destructive testing - Terminology - Terms used in X-ray digital radioscopic testing

GB/T 23901.1, Non-destructive testing - Image quality of radiographs - Part 1. Determination of the image quality value using wire-type image quality indicators

GB/T 23901.5, Non-destructive testing - Image quality of radiographs - Part 5. Determination of the image unsharpness and basic spatial resolution value using duplex wire-type image quality indicators NB/T 47013.1, Nondestructive testing of pressure equipments - Part

1.General requirements NB/T 47013.2, Nondestructive testing of pressure equipments - Part 2. Radiographic testing

JB/T 7902, Non-destructive testing - Specification for wire-type image quality indicators

3 Terms and definitions

For the purpose of this document, terms and definitions given in GB/T 12604.11, NB/T 47013.1 and NB/T 47013.2, as well as the following apply.

3.1 system resolution ratio The measured value of a duplex wire image quality indicator placed directly on the detector surface.

3.2 image resolution ratio The measured value of a duplex wire image quality indicator placed on the base material on the source side of the weld being inspected.

3.3 total unsharpness The image unsharpness composed of the inherent unsharpness of the detector and the geometric unsharpness.

3.4 normalized signal-to-noise ratio Normalized signal-to-noise ratio based on resolution ratio.

3.5 amount of exposure during single frame The product of tube current and the time of exposure during single frame.

3.6 multiframe superposition The signal processing process of superimposing and averaging the gray-scale values of multiple images collected while keeping the relative positions of the radiation source, workpiece and imaging plate unchanged.

3.7 accumulated exposure

6 Testing environment and working conditions

6.1 The indoor temperature of the operating room and the assessment room shall be 15 °C ~ 25 °C; the relative humidity shall be less than or equal to 80%.

6.2 The temperature of the X-ray exposure room shall be 5 °C ~ 30 °C; the relative humidity shall be less than or equal to 80%; there shall be an exhaust device in the room.

6.3 The power supply voltage fluctuation range shall not exceed ±5%.

6.4 The detection equipment housing and the high-voltage generator of the radiation source shall be effectively grounded, and the grounding resistance shall be less than or equal to 4 Omega; the high-voltage generator of the radiation source shall have an independent grounding wire.

7 Testing timing and workpiece surface preparation

7.1 Testing timing Cylinder weld DR testing shall generally be carried out after welding and before heat treatment. For products made of materials that are prone to delayed cracking after welding, testing shall be carried out 24 hours after welding is completed. For products made of materials prone to reheat cracking, another test shall be carried out after heat treatment.

7.2 Surface preparation The weld surface of the gas cylinder under inspection shall not have grease, rust, oxide scale or other factors that affect the inspection (such as rough welding waves, surface grooves between multi-layer welding beads, and surface pits, gouges, spatter, weld scars, welding slag, etc. of the weld). The irregular state of the surface shall not affect the correctness and completeness of the inspection results. The weld bead height shall not be greater than 2 mm, otherwise it shall be ground.

8 Testing technology and process

8.1 Testing technology level The X-ray testing technology level specified in this document shall meet the AB level specified in NB/T 47013.2 - medium sensitivity technology.

8.2 Imaging method Imaging shall be performed using a motionless detection method.

8.3 X-ray energy selection The tube voltage selected for cylinder weld DR examination should be higher than that selected for film photography.