PSV in series

[wpm1]

Is there a code specifically preventing two pressure relief devices in series?

Hypothetically could you send the psv of say a vessel to a tank which has a pvrv venting to atm?
Assume inlet and outlet losses meet code for both the psv and the pvrv, for all design cases.

Thanks to all.

 

[e43u8]

wpm1,

As far as i know there is no direct prohibition in relevant codes having PSVs in series; but there are many strong preventing notes having no excessive back pressure than limited in PSV relieving conditions. Then, in my opinion, at first it's recommended having no PSVs in series at all but if one has to have such configuration it should be studied by a reputable risk assessment/analysis to make a safe and proper decision...

 

[MortenA]

If you are looking for flare gas recovery resent verswions of API 521 will give you examples.

 

[LittleInch]

I think you could, but can't see the point if you're just venting to atmosphere. It would make the second vent bigger as it has to cope with its own venting requirement plus that of the second unit coming into it. I doubt you could make the case that only one flow rate should be considered.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[don1980]

There's no problem with the type installation described by the OP. For example, it's advantageous in hazardous liquid services to route the PSV to another vessel in order to avoid releasing that liuid to the atm. If it's an all-vapor application which is discharged to the atm, then (as Littleinch says) it generally doesn't make much sense. However, there are other cases in which it does make sense. For example, one may do this to avoid having to make a separate connection to the flare header, or to avoid the need for a lengthy new line to the flare header.

The bottom line is that this is a perfectly allowable practice. The important point is that the relief devices have to meet all the relevent design criteria (sufficient capacity, piping pressure loss, proper valve selection for the resulting superimposed backpressure).

Codes leave broad discretion to the user to do what makes sense for specific applications. Codes purposely don't say what you can and can't do in terms of application design.

 

[nasim123]

Dears
I need your advice for below query.
We have one Lube oil PSV(Conventional design), which is located in one compressor. PSV set pressure is 11Kg/cm2g and there is 1 atm(stad)g Constant back pressure. While calculating CDTP, is it required to deduct the constant back pressure?

Or CDTP is same as Set pressure?

If the constant back pressure is atmospheric, is it required to consider while calculating the CDTP?

PZV data sheet is attached for your reference.

Pls advice us as soon as possible.