Dear Friend,

Whether your vessel is Code stamped or non code stamped, if your design Code is ASME Section VIII, Div-1, then said paragraph of Appd-2 is mandatory to follow except for following.

Flange rigidity calculations can be disregarded per followings for specific cases:

As per Appendix 2-14 of Addenda-2008, “Successful service experience may be used as an alternative to the flange rigidity rules for fluid services that are non lethal and non flammable and designed within the temperature range of -20 ˚F (-29 ˚C) to 366 ˚F (186 ˚C) without exceeding design pressures of 150 psi (1035 KPa)"

Also note that "It is the opinion of the Committee that alternatives may be used for design of flange rigidity in lieu
of the rules in Appendix 2-14. Acceptable alternatives
include successful service experience with a specific
design, or any method that satisfies the requirements of
U-2(g). This Case number (~2547) shall be recorded on the Manufacturer’s
Data Report."

Regards,

Mukesh