The hub-flange interaction moment ( Ms) is included explicitely in Appendix Y analysis.

This term is not used in the Appendix 2 analysis.

What is the reason behind this?

Hello Aninda

Firstly, sorry about the delay in responding to your question.

There is a fundamental difference between Appendix Y, and Appendix 2 flanges. In the case of Appendix 2 flanges, the mechanical joint is maintained by the ability of the flange to resist rotation about the bolt. This rotation is prevented by the stiffness of the flange. Appendix 2 flanges do not make contact at the outside diameters. Should this be the case, then the rotation would be so gross, that leakage would result. Now, in the case of Appendix Y flanges, the outside diameters of the flanges do touch. This causes a moment to be exerted on the flange from the outside the gasket effective diameter. An Appendix Y flange is treated (in simplified terms) as a cantilever that is 'built-iin' ad the location of the bolts. The moments acting on the hub of an Appendix Y flange are different from those acting on an Appendix 2 flange because the forces acting on the flange are quite different.

I do not confess to know the theory behind the formulae in the code, but the sealing mechanism is quite understandable.

Thank you for your question.