Dear All,

Here is the situation.

(1) 3rd Party Nitrogen line to Site Plant with Max. Operating pressure 18 barg.
(2) At Battery limit, A PCV control the site header pressure @ 9 barg.
(3) Downstream of the PCV, a PSV protected the site nitrogen header with set pressure @ 12 barg. Relief to Atm. Sizing scenario is the PCV fails. Preliminary sizing result in a 4P6 Pilot valve with modulating action. Pop-up open PSV not selected due to concerns of big impact on site downstream plants.
(4) The Site header line size is 4".
(5) PSV inlet line ( consider 5 feet, one ball valve ) preliminary sizing result in 6" line, . Inlet loss 0.3% of the set pressure.

when i put the exlarger 6"x4" (Nitrogen header to PSV inlet line.) and reducer 6"x4" ( PSV inlet line to PSV inlet nozzle) in the final inlet line calculation, found the exlarger/reducer significantly increase the pressure drop and result in inlet loss 4.1% of the set pressure. I use the Crane book A-26 and Page 2-10,11 to calculate the Enlarger and Reducer K value ( based on 6" line).

question is.
a. whether Crane calculated K value can be used for vapor?
b. Any idea how to deal with this situation?

Thanks in advance,

nli2

Could you please recalculate and recalibrate PSV set pressure considering all these pressure losses.

Yes.



4.1% can be easily managed. Get a high blowdown PSV will help you with inlet line lose more than 3% PSV setpressure. Talk to credible vendor. Tell them your problem, i am sure they can help you.