For decades, we used Appendix M-5 in Section VIII as our design basis for having intervening/stop valves before and/or after a Pressure Relief Device (PRD). But in 2021 (amid the global pandemic), ASME published its new Section XIII, Rules for Overpressure Protection. We now use Appendix B of this new ASME section when we have a design basis using “stop valves” (or sometimes called “intervening valves”) either before or after the PRD.
This article is a breakdown of the new Appendix and any new requirements from the old Appendix M-5.