PORV during and after steaming operation 1

[hageye]

Good morning,

When steaming is performed on a vessel protected by pilot-operated relief valve, steam will enter the sensing line and the dome. Most likely steam will condense and accumulate on top of the dome and probably remain there even after the plant start-up. This is not a problem in itself for the operation of the PORV... until winter arrives. There is a possibility that the water freezes and prevents the PORV from opening.

Advice from the vendor has been to trace/insulate the valve or isolate the valve during steaming or cycle the pilot control. I believe none of them are ideal.

I am looking for your experience with this situation. Thank you.

 

[CJKruger]

Relief valves are dead ends and should always be traced if traces of water can be present and winterizing temperature is less than or equal to zero degrees C.

Cilliers

 

[hageye]

I see two potential issues with tracing:
1- the PORV soft goods might not sustain high temperatures (AGC recommends pressures not higher than 30 psig for steam tracing).
2- the high temperatures might favor fouling of the sensing line.

If you have PORV in your plant, have you ever had issues after a plant or unit shutdown?

THank you for your help,

 

[greenche]

We have had the scenario hageye describes actually happen. We considered this a very serious near-miss. As a result, in pilot operated RVs that could encounter water (from the process or steaming) we have changed the soft goods to withstand higher temperatures and have added steam tracing and insulation. The integrity of the insulation and steam trace gets put on a PM schedule so it is checked every year before winter arrives.

Regarding fouling, if it is possible, a pilot operated RV is not usually recommended for the service.