As a suggestion, I think for pipeline flange checking it is more realistic the approach of B31.8 APPENDIX E Note 14, i.e. the bending moment to produce leakage of a flanged joint with a gasket having no self-sealing characteristics can be estimated by the equation:
ML=(C/4) (Sb Ab − PAp)
You may compare your bending moment in dynamic scenario with this limit.
Under this approach, an axial compression force is not counted as participating to flange leakage.

Best regards.