Liquid PSV Inlet/Outlet Pipe Sizing
Liquid PSV Inlet/Outlet Pipe Sizing
(OP)
I have a PSV that needs to be upsized from an E to an F orifice as the capacity needs to increase. The body is changing from a 1x1 to a 1.5x2. The orifice area is going from 0.212 in2 to 0.337 in2 as a result.
I'm hoping to avoid having to re-weld the inlet and outlet TOL's for the new PSVs and keep most of the existing piping.
The PSVs are located fairly close to the piping and I'll confirm we don't exceed dP limits on the inlet and outlet.
(sch 80)
1" pipe has an inside area of 0.7190 in2
1.5" pipe has an inside area of 1.767 in2
2" pipe has an inside area of 2.952 in2
Given that inside area of the 1" pipe is larger than the orifice size of the PSV, why can't I reduce down on the outlet of the PSV from a 2" outlet to the existing 1" pipe? This is brine water service so I'm not concerned with vaporization.
Thank you for your help!
-M
I'm hoping to avoid having to re-weld the inlet and outlet TOL's for the new PSVs and keep most of the existing piping.
The PSVs are located fairly close to the piping and I'll confirm we don't exceed dP limits on the inlet and outlet.
(sch 80)
1" pipe has an inside area of 0.7190 in2
1.5" pipe has an inside area of 1.767 in2
2" pipe has an inside area of 2.952 in2
Given that inside area of the 1" pipe is larger than the orifice size of the PSV, why can't I reduce down on the outlet of the PSV from a 2" outlet to the existing 1" pipe? This is brine water service so I'm not concerned with vaporization.
Thank you for your help!
-M





RE: Liquid PSV Inlet/Outlet Pipe Sizing
Is this a pop or modulating PSV?
Why did you mention vaporization? Is this cold brine or hot brine?
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: Liquid PSV Inlet/Outlet Pipe Sizing
It's a pop PSV.
It's produced water, so, probably kind of warm, maybe 80F, 100F worst case. I will, of course, double check. But it was at atmospheric pressure before entering the pump. Sounds weird to say that about water...
Thank you for your reply!
-M
RE: Liquid PSV Inlet/Outlet Pipe Sizing
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: Liquid PSV Inlet/Outlet Pipe Sizing
-M
PS Seems like, looking at an H orifice at 0.865 in2, if the dP in the piping downstream doesn't create significant backpressure, you could get away with using smaller piping than the orifice. That can't be right tho, no?
RE: Liquid PSV Inlet/Outlet Pipe Sizing
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: Liquid PSV Inlet/Outlet Pipe Sizing
RE: Liquid PSV Inlet/Outlet Pipe Sizing
See the table that I've attached. Specifically look at the ratios for inlet-area/orifice-area and outlet-area/orifice-area. This explains why you almost never have pressure drop problems with 1D2 PSVs, and why you almost always have pressure drop problems with larger PSVs like 4P6 and 8T10. When up-sizing the inlet and/or outlet piping isn't enough to solve a pressure drop problem, the most cost-effective solution is to restrict the lift of the PSV. Effectively, this allows you to reduce the rated capacity (the flowrate used to calculated the pressure losses) for the PSV. Since pressure drop increases proportionately to the square of the flowrate, it doesn't take much of a flow reduction to make a big impact on the pressure drop. Obviously, the reduced flowrate must be high enough to satisfy the required flow. Contact you PSV supplier when implementing this option. Based on your required flowrate, they will determine the necessary lift reduction, and they will supply the necessary part which is installed by a professional valve shop. The vendor will also provide the new rated capacity for this restricted-lift PSV.