A question regarding non-destructive testing in the major standards
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Paragraph 3.2.10.2.4 (1) on page P25 of the comprehensive regulation TSG 21-2016 states that \"the non-destructive testing methods, testing ratios, and acceptance criteria for the welded joints of pressure vessel nozzles with a nominal diameter greater than 250 are the same as those required for the welded joints of the pressure vessel shell.\" However, this statement is rather general; welded joints of pressure vessel nozzles can be of butt type, fillet type, or plate fillet type. 1) If it is a butt joint, it generally falls under Category B seams; according to the requirements specified in the drawings for Category A and B seams, there are no issues with conducting non-destructive testing on such joints. 2) However, if it is a corner joint or a joint at the tube sheet, it usually belongs to Category C or D seams. But since the drawings do not specify requirements for Category C and D seams, how should non-destructive testing be carried out on the Category C seams between the tubes and the flanges, and on the Category D seams between the tubes and the cylinder? They all refer to fittings with a size greater than 250. I hope everyone can offer some guidance; I’m extremely grateful and look forward to learning and improving together with all of you
The weld joints between the nozzles of pressure vessels should generally be butt joints, with no fillet joints...
But this sentence is referring to the weld joints at the connections, not the weld joints between the pipes themselves. What I meant by corner joints might not be covered by the specifications; I was referring to corner welds like those between flanges and pipes
How can the welding joint of a pressure vessel nozzle be related to a flange? In that case, the housing or other things can also be involved...
Regarding this issue, GB/T150.4 explains it more clearly:
Okay, our understanding so far has not been accurate. Let me ask another question: for the main weld of the cylinder, where 20% RT inspection is required, how should non-destructive testing be carried out on the joints between the nozzles with a diameter greater than 250 mm and the butt-welded flanges? How is non-destructive testing carried out on the joints between the shells?
Please read Section 10.4 of GB/T150.4 in detail. Page 336.
Fillet welds cannot be inspected by radiography or ultrasonic testing; surface inspection is used for non-destructive testing, with the same acceptance criteria and grade as those for the main welds
It’s actually quite clear: for connections larger than DN250, they are treated as part of the cylinder body. All joints on such connections are to be inspected in accordance with the standards applicable to joints on the shell. For example, the fillet welds formed where the connection meets flanges or globe valves are considered to be of type C or D welds. The takeover joint is treated as a cylinder joint weld. ,
This post was last edited by taozb on 2017-10-13 08:45. For the non-destructive testing of butt weld joints, GB150 provides clearer guidelines; one should not be too literal in interpreting the ‘Code for Large-Diameter Vessels’, as the quality of the editorial board members varies. If precision is important, look to ASME.