We have a pressure vessel (reactor) with half-pipe jacket on the bottom head and straight sides and internal coils in our Illinois factory. There are three, separate U-stamp nameplates. One each for the reactor, jacket and “INTERNAL COIL ASSEMBLYS”. The single U-1 lists all three as well. The coils are fabricated from 1.5", schedule 10S, 304/304L piping.
The reactor is in a fire zone, but not much heat will get to the internal coils from the fire. The only credible case for the coils, in my opinion, is thermal expansion.
Downsteam of the coils is a 2", metal-to-metal seat, fail-open control valve. It’ll leak through enough to relieve the thermal expansion.
If the coils did not have the U-stamp, I wouldn’t hesitate to NOT have a PSV on the B31 piping, but it does have a U-stamp. We have many set-ups exactly like this that are not U-stamped and have no PSV and they have had no issues. Some have been in service 50 years. Do I still require a PSV for the coils? Or, does UG-125 (g) (2) apply here?