Arrangement of discharge piping from Pressure Relief Valves

[malarfra]

Hi to everybody,

I'm looking for references over arrangement of discharge piping from Pressure Relief Valves, specially when discharge piping has slope toward up. Is allowed to have piping with ascending route? Anyone knows is allowed by any code? Is there any restriction about it? If an arragement with ascending route is allowed, is necessary to have arragements for liquid recovery? All comments are welcome. Thanks in advance.

[d.durante4486]

Hi to everybody,

I'm looking for references over arrangement of discharge piping from Pressure Relief Valves, specially when discharge piping has slope toward up. Is allowed to have piping with ascending route? Anyone knows is allowed by any code? Is there any restriction about it? If an arragement with ascending route is allowed, is necessary to have arragements for liquid recovery? All comments are welcome. Thanks in advance.

Hi Malarfra,
here are some best practices I found and I followed in previous projects:
"The relief valves or depressuring valves will discharge via plant sub-headers with connections into a main header running outside the battery limits. If
this is not possible the flare/vent piping should at least be routed through areas where there is little possibility of a dangerous situation due to local failure of the flare/vent piping."
"The flow area through all pipe and fittings downstream a relief valve, shall be at least the same as that of the valve outlet. "
"If possible, connecting sub-headers shall be connected to the top of the header; in any case, they shall drain into the headers. The sub-headers shall be connected in such a way that there are no welds in the lower one third of the circumference of the header."

This last sentence does not allow to have discharge piping from PRV with ascending route, moreover, considering API RP 520 5th Ed., the inlet piping to a PRV shall be fitted with a flanged spool piece to elevate the PRV respect to the main header, so that the discharge onto it will take place place on the top.

[malarfra]

Dear d.durante4486,

I have seen your advices in order to solve a situation with a flare with ascending route, but is not clear for me that the only solution is to elevate the PRV, because of in API RP 520 5th Ed Section 8 is indicated: "When the discharge piping is not self-draining and the device is located where liquids could accumulate at the outlet, drain piping should be provided. This drain piping could be installed on the discharge piping or installed at the pressure relief valve in the body connection provided for this purpose". For this reason I'd like to believe that considering a pipe arrangement to "catch" liquids immediately at outlet of PRV could be a choice to comply with requirements for this systems. The pipe arrangement could be a "leg" of same diameter of flare piping with level indicator and connection with oily sewer. What is your opinon about it?