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Safety/Relief Valve Discharge Piping

Safety/Relief Valve Discharge Piping

(OP)
Other than structural, what criteria should be used in designing Safety/Relief Valve Discharge piping? For example:
Flow velocity, pressure drop, quality (if two phase),etc.
Thanks

RE: Safety/Relief Valve Discharge Piping

A good start to understand SRV outlet piping is API 521.

Per ISO, only the term Safety Valve is used regardless of application or design.

RE: Safety/Relief Valve Discharge Piping

No pockets.
Weep holes to drain accumulated liquids.
I'm sure API 521 lists these.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Safety/Relief Valve Discharge Piping

Excluding structural mechanical strength considerations, the determining variable is backpressure on the PSV. If the resulting backpressure is within the allowable limit for the particular PSV type, then the tailpipe size is OK. This minimizes the costs, and for vapor streams released to the atm, this maximizes the dispersion rate. Some engineers also consider other factors such as Mach No.,RhoV2, noise, etc. Most PSVs will never lift, so I don't often get concerned about the long term wear on the pipe. If there's a choke in the tailpipe, that's OK too as long as the PSV can tolerate the resulting backpressure.

From a structural perspective, don't overlook acoustic induced vibration (AIV) risks which are associated with tailpipes connected to a collection header. Use the simple equation in API 521 to calc the sound power level. This sound power level is a screening criterion for assessing whether there's a risk of AIV failure at the point where the tailpipe connects to the header. Tailpipes < 10" diameter are potentially exposed to this failure mechanism.

RE: Safety/Relief Valve Discharge Piping

PSV exit piping must also always slope DOWN into the plant main flare / relief stream gathering header through a top entry connection.

RE: Safety/Relief Valve Discharge Piping

You should look to API 520 Part 2.

API 520 Part 2 breaks down the guidelines for the design of proper discharge line design.

There is far too much information there for me to adequately break it down in a forum post. However, after you review the document you can feel free to come back and ask clarifying questions.

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