Flanged Joint detailed stress analysis is performed by Caesar II Flange Module in accordance with ASME BPVC VIII-1 App. 2 & S, completed with additional leakage assessments based upon COADE methodology (this latest issue is described by an older COADE Engineering News bulletin, and is not relevant for this discussion).

The original flange stress analysis as documented by ASME BPVC VIII-1 App. 2 & S (POST-2007 editions!) does not make any discrimination between Operating/Design and Occasional loading conditions. The allowable limit of the Maximum Averaged Stress is 1.50 times Basic Allowable Stress, which is supposed not to exceed the Yield Strength.

Now, when ASME B31.3 refers to bolted flanged joints' design, it recommends (e.g. "...MAY be performed...") ASME BPVC VIII-1 App. 2 & S method, with the requirement to replace ASME BPVC VIII-1 allowable stresses with corresponding (homologous) ASME B31.3 allowable stresses.
In my opinion, this requirement regards the BASIC ALLOWABLE STRESS value only, meaning the safety factors employed with respect to Tensile Strength and Yield Limit only, and NOT the loading cases and corresponding allowable stress adjustments assumed by B31.3 Code.

Therefore, for Maximum Averaged Stress check, if Basic Allowable Stress would be increased by 1.33 times, the corresponding allowable limit of the effective Maximum Averaged Stress would be 1.33 x 1.50 x (Basic Allowable Tensile Stress), which might exceed material Yield Strength. This is against ASME VIII-1 philosophy and would mean un-safe elastic stress levels.
For all the other flange stress types, as long as the allowable limit, although increased by 1.33 times, still remains below material yield strength (e.g. 1.33 x S-allowable < 1.50 x S-allowable <= Yield-Strength), it may be accepted that stress states are satisfactorily limited below material yield-limit.

To conclude, in my opinion, it is fair Caesar II Flange Module to ignore Maximum Averaged Stress allowable limit increase even if flange allowable stress increase has been required by the user.

Regards,