I have been checking the results of a flange calculation done in the Caesar module and have a question regarding the gasket seating bolt stress calculated. It appears that the safety factor calculated is based on the stress due to the minimum initial bolt load for gasket seating Wm2 as per equation 2 ASME VIII Div 1 app2 rather than the flange design bolt load 'W' as per equation 4.

Is this correct? If so why is the design bolt load not used in calculating the bolt stress and safety factor?

The safety factor should be the calculated Code Stress divided by the corresponding allowable.

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The safety factor calculated is the code stress divided by the allowable however Caesar seems to base the code stress on the bolt load value 'Wm2'. Can you confirm this?

My interpretation of the code is that the code stress should be based on the design bolt load 'W' (equation 4) not Wm2. Is this how others interpret this?

To check the bolts the maximum of the load required for the operating case (WM1) or the seating case (WM2) is used.

Now, to check the flange the code adds abuse factor to account for the fact that "bubba" in the field could over tighten the bolts and cause overstress in the flange. Moreover, if the flange has leakage it is common to re-tighten the bolts.

This is how it’s done,

Am - required bolt area

= Max( WM1 / Sb, WM2 / Sba )

Ab – available bolt area

W – flange design bolt load in gasket seating condition
= Sba * ( Am + Ab ) / 2

Hence, the flange is designed for average of the Minimum required bolt load and total bolt load (before the bolt fails).

This what the program does.