ANSI B16.5 Bolt Pretension 4

[meca]

Can anyone tell me the recommended bolt prestress for Standard ASME B16.5 flanges? I have found references that recommend a prestress of 40% of Yield Strength, but I can not find any mention in ASME B16.5 on recommended Bolt Prestress.

I understand that there are many factors that must be considered in a bolt pretension. However, I am only talking about standard ASME B16.5 flanges that are not exposed to unusual vibration, external loads, thermal loads, etc...

 

[vonlueke]

If there's a gasket in the joint, gaskets tend to dominant the bolt installation prestress. Not familiar with that code, but with steel flanges, steel nuts, and no gasket, a fairly typical bolt installation prestress is 75% of bolt proof strength. Since bolt proof strength is roughly 0.90 times bolt yield strength, that would be a bolt prestress of about 67% of bolt yield strength.

Nonetheless, if no gapping occurs and it's not a fatigue environment, then a prestress of 40% of yield strength might still be acceptable. Or it could even be too high if it exceeds the gasket allowable compressive strength (if there's a gasket).

 

[butelja]

Contact the gasket manufacturer to find out what the "m" and "y" values of the gasket material. Run the calculations per Appendix 2 of the ASME Sec VIII, Div. 1 code. This will give you the MINIMUM required bolting torque. The gasket manufacturer will probably also have a PREFERRED minimum torque that is somewhat higher. It is likely in the range of 30-40% of yield. If it is a B16.5 flange, it should be using ASME listed fasteners. As such, only yield and ultimate stress are relevant, as there is no proof stress listed.