Hydrostatic Relief Valves with Anhydrous Ammonia
Hydrostatic Relief Valves with Anhydrous Ammonia
(OP)
My question pertains to the placement of HRVs on extremely short sections of pipe between a manual shut off valve and a blind flange. The fluid being used is anhydrous ammonia and we have the ability to lock the manual valves open if necessary. All of the resources I have found require an HRV on a section of pipe between 2 or more shut off valves, but none of them make mention of the situation between 1 valve and a blind flange. Any help would be greatly appreciated.





RE: Hydrostatic Relief Valves with Anhydrous Ammonia
Another option may be an expansion chamber with a rupture disc isolating the chamber from the blocked in section. The disk is normally instrumented to alarm when blown. This system ensures total containment. These are used in liquid chlorine systems, but I'm not sure about ammonia.
RE: Hydrostatic Relief Valves with Anhydrous Ammonia
If one of the valves is a blind flange, it's fair to say that leakage is going to be zip from that direction so overpressure becomes even potentially more of an issue.
RE: Hydrostatic Relief Valves with Anhydrous Ammonia
RE: Hydrostatic Relief Valves with Anhydrous Ammonia
Best Regards
Morten
RE: Hydrostatic Relief Valves with Anhydrous Ammonia
RE: Hydrostatic Relief Valves with Anhydrous Ammonia
I also previously worked in an ethylene plant years ago which has low temperature liquids. We did not provide relief valves on piping that 'could' be blocked in just because there were block valves. On the other hand, you don't have the cross connection issue to the same degree as in a refinery.
On another job I did on the North Slope for an NGL injection skid, the client did want relief valves on all sections of piping that could be blocked in.
I think at the end of the day you'll need to look at when these valves are going to be used. If they are routinely used as part of normal operations, it would be much easier in a Hazop to say that misoperation is likely. If they are only used during specific times, you might be willing to rely on operating procedure depending what the plant philosophy and history is (if you routinely blow out flanges, that's a sign procedures likely aren't enough <g>).
The type of valves is another issue. On my previous post, I should have added that on some of the specs where relief valves are discussed for blocked in piping, they do state if the valves are truly bubbletight, then relief valves may be necessary even on short runs.