Do my U-stamped Coils require a PSV?

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?

Might be repeating what you already know, but in my experience UG-125 (g) is describing a steam reducing station (or similar) installation. If you have a 150 psig to 50 psig steam letdown station with PSVs sized to handle the full flow of 150 psig steam (limiting the low pressure side to ~50 psig), those PSVs can be taken credit for on any equipment downstream with an MAWP of 50 psig or higher and no additional device is required.

Can’t exactly tell from your post if this is your situation or not. Strictly per ASME VIII and NBIC you need a device on every U-stamped vessel. A call to your local jurisdiction may reveal that they don’t require a device to be installed if there is no overpressure scenario (similar to invoking UG-140).

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Thanks! No, my situation is not a steam letdown station. Multiple coils (2-5 depending on RX size) inside our RXs have CW in them. After the CW from all the coils from 1 RX collect into one pipe, we have a TCV before the CW goes into the CWR header.

I think I can CSO the manual valves in the CWR header all the way to the cooling towers and then invoke UG-140. They are only closed for maintenance anyway.

Sounds reasonable, but strictly per UG-140 it has to be on the U-1 (aka invoked before construction of the pressure vessels). In the real world… completing the engineering study to show that there are no scenarios and documenting may be enough for your AHJ.


What got me on this was the PSV on the coils is a non-Code PSV. The plant had replaced Code PSVs with non-Code PSVs on the CW side of the coils, half-pipe jacket, and S&T heat exchanger. I don’t know why they did this, but that’s what happened. I was going through the exercise of seeing what needed replacing with Code PSVs, what could be left non-Code, and what could just be removed.

Some of the plants don’t have a PSV on their coils. The only credible scenario I come up with is thermal expansion after isolation valves are closed for maintenance, but I don’t think a relief has ever been reported. We’ve got over 500 RX-years experience with no problem.

Authority Having Jurisdiction… aka your local government (or could even be your plant’s insurance policy holder). In my state there is legislation that says following ASME VIII and NBIC is law (not just guidance). Could be different for you or you could have a reasonable inspector.

And I agree - I’ve seen this before where there is no credible scenario, but per the code you gotta have a valve. The thing to do (upfront if you can) is just not stamp the coil. Then you can do what makes sense.

A cheap way out is to just slap on the smallest, cheapest stamped PSV you can find, but that comes with the overhead of inspection, testing, etc.

Good advice! I’m stuck though, because these coils were U-stamped in 1992 and Code Case 2211 (pre-cursor to UG-140) was not invoked in the documentation.

Yeah that’s what usually trips people up when analyzing existing installations (vs specifying new equipment).

Might be worth a call to your Authorized Inspector or insurance and see if they even enforce it. If they do, then put on the cheapest code-stamped valve you can find. If they don’t, document well and move on.