In ASME VIII, should the welds that connect the equipment flanges to the shell be of Class C or Class B?
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According to UW-3 in ASME VIII-1, circumferential weld joints on the main shell, connected pressure vessels, nozzles, or reducers are classified as Category B； Class C weld joints refer to those that connect flanges, lap joints, tube sheets, diffusion-welded plate assemblies, or flat heads with the main shell, shaped heads, reducers, nozzles, or passages leading to pressurized chambers ； I can understand that the welds between the flange ring and the shell are classified as Class C welds. I would like to ask whether, in the case of flanges with a neck designed for butt welding, the welds used to connect the equipment flange to the shell should also be considered Class C welds. On the other hand, for flanges with a neck used in butt welding, they can also be regarded as connections between sections of different diameters and the shell; in that case, what class of welds should they be classified as?
According to ASME VIII-1, for the welds that connect the equipment flange to the shell, if it is a flange with a neck, such welds can be considered as welds connecting a tapered section to the shell. Therefore, in this case, the weld should be classified as a Class C weld. .
It seems that Americans aren’t perfect in everything; the GB/T150 classification is more scientific. The quality of butt welds and fillet welds differs, and classifying them as B or C based on whether they are butt or fillet welds allows for better control over quality