Appendix 2 contains equations that attempt to determine whether or not a given flange geometry will leak. If the computed rigidity factor is > 1.0, then leakage is predicted.

Appendix 2 calculations are mandatory as of Addenda2005 and flange designs must satisfy these calculations. These rigidity factor calculations are not mandatory for Pre1999 Addenda users

Appendix S is nonmandatory appendix and that these calculations are also nonmandatory.