Hello Rajendra
If y and m are set to zero, that means there is no 'squeeze' on the gasket. It is only pressure or squeeze on the gasket that prevents the fluid inside the flange from escaping. I am not familiar with BPV VIII-1-16-85, but it stands to reason that m and y cannot be zero when designing the flange to ASME Section VIII, Division 1, Appendix 2.
Now, UG-23 states that all loadings have to be considered in vessel analysis. So, technically they should be taken into account. However, if standard B16.5 or B16.47 flanges are used, ASME states that no calculation need be performed provided the flanges are within the rated pressures according to B16.5 or B16.47.
It is instructing to read the first couple of paragraph of Appendix S.
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Sincerely,
Ray Delaforce
CADWorx & Analysis Solutions
Hexagon PPM