Seating stress failure for spiral wound gasket

Hi everyone,

I have saw many posts for my confusion "seating stress failure of 150# flanges using the spiral wound gasket", but I didn't find the suitable conclusion.
In my analysis results, 150# flanges using the spiral wound gasket of several size shown failure on seating stress of ASME BPVC VIII Div.1 appendix 2 method even without pressure, temperature and external force & moment. It seems to be due to seating stress 'y' specified in ASME code.
I am very surprised and I could not believe this result because many 150# flanges using the spiral wound gasket is normally operating in the numerous sites.

Shall we increase the flange rating to 300# or higher due to seating stress result?
or
Can we remain the 150# flange rating?

I attached the output for 8" and 16" flange leakage check.
Please review and help me anyone.

Flange calculations of all types have been subject to contention for a decades.

I believe the general consensus is that (excepting perhaps API 6A charts) they're all fairly to extremely conservative most of the time, and while I haven't seen it personally, occasional leaks do come up despite the calculations.

To answer your question, I haven't delved into this calculation method, but if you're obligated to both perform flange calculations and use this calculation method, you can bring it to the attention of the obligator and work out alternative methods for this case (or all other cases).

If you're obligated to perform flange leak calculations, but not any particular method, you might consider another method.

If you're not specifically obligated to perform flange leak calculations, it's common practice in some industries to not perform them for ASME flanges unless specifically requested.

Finally, you might look into using different flanges or removing flanges. But it would be suspicious to say you can't use 8" or 16" 150# flanges at all in B31.3 piping because an annex in ASME BPVC states they all leak, regardless of lack of load applied to them.