Can the butt welds of nozzles on pressure vessels smaller than DN250 be exempt from radiographic inspection?
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I heard someone say today that there’s such a requirement in GB150 – is that true? I didn’t see it anywhere
In the minor provisions of GB150, it states that those with DN≥250 are the same as those of Class AB, but it does not mention what to do in the case of values <250. GB150 specifies explicitly that the butt welds of nozzles smaller than 250 shall be carried out in accordance with the provisions of the design documents. In other words, follow the specifications outlined in the drawings.
@kareale88, come and take a look at this problem.
There is no contradiction; it is not necessary to conduct 100% RT or UT, but 100% surface inspection using MT or PT is required. Generally, if the manufacturer does not have certification for MT or PT inspections (i.e., does not meet the requirements for two or more of these methods), it is possible to specify that for butt welds with DN < DN250, 100% RT or UT can be used as a substitute for surface inspection.
This question would be more meaningful if it were rephrased as: Why can the butt welds of those with a diameter less than DN250 omit RT or UT?