Why is X-ray or ultrasonic testing still required after γ-ray testing for large pressure vessels?
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The \"Regulations on Safety Technical Inspection of Fixed Pressure Vessels\" require that when gamma-ray panoramic radiographic inspection is used for the butt joints of large pressure vessels, X-ray inspection or ultrasonic inspection using the diffraction time difference method shall also be employed as an additional 50% inspection. If any defects exceeding the specified limits are detected, 100% X-ray inspection or ultrasonic inspection using the diffraction time difference method must be carried out for re-inspection. This is why; could the teacher please explain it? Thank you.
Different testing methods target different types of defects; additional testing methods are introduced to better ensure quality and reduce the likelihood of defects existing.
The γ source is mainly used to reduce costs and simplify things; however, the actual imaging quality is not as accurate as that of an X-ray machine.
In terms of imaging quality, X-rays are more precise, while gamma rays are relatively easier to use since they don’t require a power source. For accurately quantifying requirements, X-rays are the reliable choice!