Pressure A and B?

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Hello "Guest",

I'm quite certain that you're not looking for the gasket's "m" and "y" factors as inferred by others.

With all due respect, if you need "A" and "B" pressures, you won't be torquing the flange: You'll be tensioning it using hydraulically operated Bolt Tensioners.

Bolt Tensioning provides immediate bolt load rather than trying to attain it through an intermediate step of turning a nut (as done when torquing). As such, it is a much more accurate method of bolting used on critical joints (or on those where it's been difficult to achieve leak-free integrity) Here's a link for further information : Bolt Tensioning

The requirement for the "A" and "B" pressures suggests that the procedure calls for 50% tensioning.This means that half of the bolts on the flange will be tightened simultaneously. Once the the first set of bolts has been tightened, the bolt tensioners are indexed to the untightened fasteners where the process is repeated. One can see that this method of bolt tightening not only results in rapid flange assembly but, more importantly, it ensures even gasket compression.

The "A" and "B" pressures refer to the hydraulic pump pressures. The "A" pressure is a higher pressure than the "B" pressure. The reason is as follows:

When tensioning the second set of bolts, there will be some load relaxation in the first set. The "A" pressure is calculated to be somewhat higher than the "B" pressure so that once all of the bolts have been tightened, they are all under a consistent load.

The calculation for these pressures depends on

• the desired bolt stress (this is where the "m" and "y" factors become important)
• the hydraulic piston area of the Bolt Tensioner
  
• the diameter of the bolt
• the grip length of the bolt within the joint
• number of bolts within a flange
  

Is this what you're looking for?