3 replies to this topic

[chris]

We have two, 3x4 full port PSVs on a pressure vessel and the combined capacity seems to be more than adequate.  However our contracting engineering firm is trying to get each PSV to be capable of relieving the worst case blow by.  Has anyone run into this before?  My understanding is that unless there is some way to isolate each section from the other, you can take credit for both PSVs (and stagger the PSV set points).

 

Any guidance would be greatly appreciated.

[Bobby Strain]

I don't have a copy of 14c, but ASME and API RP allow 2 safety valves with staggered set to achieve the required capacity. If they are equipped with isolation valves, they should be carsealed open and safeguard maintained to assure that they are always open. Your contractor may hire anyone who walks in off the street. So watch out!

 

Bobby

[fallah]

chris,

 

If each PSV is capable of relieving the worst case scenario, you can lock close upstream isolation valve of one PSV and leave it as stand by...

[Zauberberg]

It is not clear from the original post if the PSV's are designed as 2x50% or 2x100% configuration (1 spare).

 

For 2x100%, Fallah is correct. You need only one PSV lined up.

For 2x50% configuration, you need to keep both PSV's lined up and stagger the set points (e.g. 100% and 105% of MAWP).

 

In order to resolve the query we need to know the maximum relief rate (governing case for PSV sizing), and type/size of PSV's used.

 

Regards