As allowed for in Appendix 4 of ASME Section VIII, Division 2 - which you can get to from Division 1 through article U-2(g). Note, however, that any mandatory requirements in either of the Divisions may not be over-ridden by analysis (be it elastic or elastic-plastic).
I have come across this issue before with heat exchanger design. This one instance involves an ASME tubeshhet which is integral with the channel. TS material is SA336 F11 Cl.2, mating flange is SA266-2, Tubes are SA268 410. Existing tubesheet is 11 1/8" thk x 62-3/8" od. Existing flange is 9-11/16" thk. Design conditions are shell side 1260 psig 650°F tube side 875 psig at 780°F. Time dependent properties are in the 900°F range for the SA336 F11 and 750°F for the SA266.
