29. While designing a AutoPIPE Vessel heat exchanger tubesheet flange, the "Use EN 13445 Annex G/EN 1591" option is greyed out, why?

Answer:

This is because there is nothing (no method) in Annex G about how to design the extended part of the tubesheet (as a flange).

Consequently when a flange is associated to a tubesheet this option is disabled in AutoPIPE Vessel.