Use of relief valve discharge covers/caps required?

[BenThayer]

We typically install weathercaps to prevent snow/ice/bird nests, etc. in the discharge of relief devices as well as install the discharge piping with a weep-hole or drain.

I cannot find any reference to caps being required but have seen many on LPG storage tanks etc.

Is this a good design practice or does anyone know of code type requirements?

 

[Guidoo]

In the past I worked for a client that wanted to have the caps on relief valve outlet to see whether the relief valve had blown. This was for a not normally manned facility, so the caps were used just to know which valves needed to be overhauled. I remember that these valves were all provided with weepholes.

For an LPG sphere something similar could be valid. They are usually located remote from the main facility, so that it is possible that a relief valve would blow without anyone noting it.

When following this logic, the relief valve with cap would still require a weep hole, since relief valve could be there for some time before someone noting that the cap has blown off. In that case, weep hole would still prevent accumulation of liquids...

 

[Montemayor]

BenThayer:

I don't know of any API or ASME mention of a restriction on caps (plastic?) being used on the discharge nozzle of a PSV. I've used hinged metal covers on PSVs to resolve what you describe as a deterrent to a clogged discharge nozzle. I would take care to make sure the cover (or cap) cannot bind, stick, or rust itself in the closed position and that has always bothered me.

I also used a weep hole with the hinges; I felt much better with the "belt and suspenders" philosophy in this case.

Art Montemayor
Spring, TX