Steven,

The incompatability I mentioned is not to do with the 'equivalent pressure method' which is used to include external loads into a flange analysis otherwise based on pressure alone.

My reference was to many ASME B16.5 flanges in the lower pressure catagories, when analysed using either ASME VIII Div 1 App. 2 or ASME VIII div 2 section 4.16 (2007), and incorporating a hard, wide gasket such as a spiral wound type, then apllying the ASME B16.5 allowable pressure.

These flanges will often fail the seating stress limit but be acceptable in the operating case. This makes no sense. In addition, countless such units have been in use worldwide for decades.