BX ring gasket seating load

[DowneastTech]

Since API-6A, BX type ring gaskets, first contact the ring groove with a initial standoff of approximately 1/8-inch, how do I determine the bolt load necessary to bring the flange faces into contact, as required for this type connection. We are having trouble accomplishing face to face contact with Inconel 825 gaskets when using API-6A recommended torque values.

DowneastTech
Mechanical Engineer
Magnus R & D, Cypress, TX

 

[grampi1]

1) BX flange are not always face to face contact type, some mfgs leave a gap when propperly tightened.
2) Typical is to torque to 50% bolt SMYS
3) What is the hardness differential between the PEG and the flange groove? BX types deform substantially and can coin the groove after cold work hardening from compression.
4) 6A prohibits reuse of gaskets

 

[DowneastTech]

Thank you for your thoughtful reply.

All of the API-6A 15000 psi flanges were designed per the Eichenberg paper published by ASME in the Journal of Engineering for Industry, circa 1966 and have a mandatory requirement that the flanges meet face to face. You are absolutely correct that the API-6A recommended bolt preload is 50% of yield but this is only a recommendation and not mandatory. I think that 80% is much better. The hardness of the gaskets are about 180 BHN and the flanges about 235 BHN, that is more than 50 BHN points differential so that should be ok. Gaskets, as you correctly instruct are definately not to be reused.

I would still like to find out how to calculate the gasket seating load in advance in order to be able to predict/verify that the bolt preload will seat the gasket.

DowneastTech
Mechanical Engineer
Magnus R & D, Cypress, TX

 

[grampi1]

The specific load analysis is beyond me. However, I know we have a software program from Glen Stevick of

http://www.bearinc.com

that our sr. mechanical engieer uses for quick analysis of BX and other types of connections.

Suspect its not free.