a pleasant day to everyone here on this forum.

right now, im working on a open type PSV. the outlet is going to the atmosphere. i have 2 supports on the outlet, dummy support on the bend and all-around guide on the straight pipe going to the atmosphere. system is 400 deg C. my configuration is like this:

on the guide ( 15 mm gap on z, 3 mm gap on x)
on the dummy ( fixed support x,y,z w/ no gaps)

is this ok? or my 15 mm gap on the guide on the straight pipe will cause too much movement? but i need that gap for thermal expansion. i need your help guys. thanks...

Chris,

You did not mention if you have an expansion chamber between the exit elbow and the straight vertical pipe, and the length of the pipes.

I normally would not use a support under the elbow due to ineffectiveness of it under the upward vertical thermal movement of the safety valve with high temperature. It will try to separate from the source pipe or vessel under thermal movement.

I would keep vertical discharge centreline as close as possible to the safety valve centreline to reduce the bending moment effect on the safety valve connection and on the nozzle connection to the source. You may find the allowables from the safety valve supplier's catalog and/or the eccentricity permissible.

If the vertical discharge line is short, you may add the weight to the valve discharge reaction force ( do not forget DLF ) and check the resultant bending moment against allowables of PSV and the the nozzle ( if you have bolted flange connection in the line you need to check the flange connection as well ). If the discharge pipe long enough, you may need to think about adding an expansion chamber to separate the discharge pipe from the discharge elbow and short straight line attached to the elbow, and support the upper discharge line separately. Size the chamber by considering the thermal movement of the elbow.

There is a guidance for this application in ASME B31.1 Appx II. However, you need to size the discharge pipe in accordance with the requirements in the code to eliminate blowback, and do not forget condendation in the dicharge line and provide drain for it.

I hope this helps.

Ibrahim Demir