For a rough approximation multiply the pressure by wetted the surface area Of the blank flange and then divide the answer you get by the twenty bolts to get the individual bolt load.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
"You will also need to add to that the bolt preload - which will depend on the gasket."
Really? The bolt stress should be the bolt preload. Added pressure will reduce the clamping force but will not add to the bolt stress until the pressure force exceeds the clamping force, at which point the flange will leak.
If you had a situation where there was no gasket being compressed (and having an axial stiffness) you would be correct. However, when you have a gasket in the mix, the situation is much more complicated. And the gasket will leak well before the clamping load being exceeded by the hydrostatic force, because the gasket compressive contact pressure needs to be a multiple of the internal pressure.
But, yes, in general, the load to be resisted by the bolts is generally going to be equal to the bolt preload. Generally this will be much larger than the hydrostatic pressure load.
I think TGS4 is specifically talking about the bolt preload required for the minimum operating gasket stress, i.e. you will have minimum operating plus hydrostatic when selecting your required assembly bolt stress (plus any additional requirements for thermal loss and relaxation, with a suitable margin).
Excluding any thermal increase or decrease, with the application of pressure only, the actual bolt stress (after assembly preload) may go up, down or stay about the same, and depends on mechanical interaction of the joint components. It is similar for a structural joint without a gasket, except gasket flexibility doesn't factor in to the interaction and you cannot get a decrease in bolt stress with the application of load. This change will be relatively small compared to the preload, but considering your gasket stress is still decreasing with pressure, it could contribute to leakage from the joint.
I am not sure if that paper is meant to be of interest for historical purposes or whether it is intended to be useful for design. Even the conclusion doesn't clearly identify the point of the article. However, the MRBL as they have coined it is related to flange sizing, and doesn't have any relevance to the actual MRBL required to prevent leakage of bolted joints. ASME VIII Div.1 only briefly discusses it under Appendix S.
It’s more historical looking at it, however it talks about a gasket bolted joint, at the end of the day we have no idea what code the OP is working too it was just a link to show he needs to be working to some code or other, mentioned in my previous post.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
