75% of Yield Bolt Pretension for ASME Pressure Bound Joint

[beh188]

If I design a pressure bound bolted joint with metal to metal contact and an o-ring sealing method, what bolt preload can be used per ASME B31.3 / VIII Div. 1 Code?

This joint would fall outside the configuration types of Appendix Y (Flanges with metal to metal contact). Appendix Y tells you to compare the calculated bolt stress to the allowable bolt stress. Appendix S seems to say that you can expect to exceed the allowable bolt stress during actual tightening.

I want to design this joint in a simplified way, and compare hydrostatic forces to bolt preload, and neglect contact forces calculated in Appendix Y. I want to utilize as much bolting strength as possible. The allowable bolting stresses are very conservative, and given what is stated in Appendix S, don't seem to be hard rules. Can you base a bolt preload on 75% yield and be OK with regards to ASME code?

 

[TGS4]

You must design the bolted flange joint based on the allowable bolt stresses.

In actual operation, there is no limit on the stress in the bolt, other than actual yielding of the bolt. You choose what margin against yield you like - just make sure to take all factors into account, particularly external bending moments.