[Discussion Thread 63] Why do butt welds of <DN250 not require RT or UT?
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bg4.png【Discussion Thread 63】Why are RT or UT not required for the butt welds of DN250 and below? Is it due to operational difficulties, unsatisfactory inspection results, or some other reason? In my opinion, RT or UT yield much better detection results when detection is possible, compared to MT or PT. Delving deeper: Can welds at the joints of pressure vessel fittings smaller than DN250 be exempt from radiographic inspection? https://bbs.hcbbs.com/thread-2700039-1-1.html
RT can’t do it; for two distances that are close to each other, UT doesn’t say it can’t be done
This also applies only to Class B welds; for Class A welds, RT or UT should still be performed. Using DN250 as the threshold is consistent with the provisions in the code for the main pressure-bearing elements.
1. Safety considerations: similar to those of primary pressure-bearing components, with the difference lying in the leakage rate; the risk is high and the potential harm is significant； There might be statistical data indicating that leaks occur less frequently in steel pipes smaller than DN250. 2. From an operational perspective, the smaller the connections, the more difficult it is to carry out radiographic inspection. 3. Economically speaking, the costs associated with radiographic inspection are high—covering equipment, the location required for testing, and the inspection itself. Many small enterprises that work with smaller-scale equipment do not need such inspection equipment, which helps to save a number of small businesses.
Considerability should be given to practicality – it is indeed difficult to perform RT or UT on very small pipe openings. Moreover, although these pipes are small, they present quite a few challenges; 6 images may need to be taken
It’s not that RT and UT are not performed when DN≤250; rather, they can be omitted if it’s not possible to carry them out. Two are not the same concept. If it can be done, it must be done.