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[TxAggie]

I have a process where I have cooling water circulating in a loop to maintain temperature on a process gas (via HX). The process gas is at 300 psi, where the cooling water pressure is 110 psi. The loop has been protected against tube rupture by rupture discs, but the discs (150 psig, 5% MDR) have been failing fairly regularly (with no HX leaks). I calculate that the pump deadhead should only be something like 145 psig (including supply pressure, head). The downstream CWR should be 25 psig, but 9 psig minimum (head back up into the cooling water tower)

Upon investigating the issue, I found that the system is seeing pressure surges up to 162+ psi (local PI with stop needle). I suspect, but am not sure if this is due to control valve action or something else. I have been exploring the option of a rupture pin, which for a while made a great sell, especially on the concept that they can essentially replace any RD. However, when we got into the details, it appears that I need to change my inlet/outlet piping (size), requiring hottaps. If I am going to do this, I might as well install a relief valve, so pretty much all my options are back on the table (cost would be the same).

The lack of sizing details from the RP vendor upfront has been very frustrating as I was already moving forward on this project going on their word that they had something that I could basically drop in place with minimal piping mods (cutting pipe length and welding new flanges only)

The lowest MAWP in the system is 196 psig. Early on I made an assumption that RDs would not work due to the problems with surge and concerns about weakening the disc. Most everyone involved has a great deal of trepidation about going forward with RDs as a solution, due to the fact that if the disk bursts it upsets the process.

Still, because I am back at square one, I am evaluating all options again. I believe that I could put in a RD designed for 171 psig (196-25 psig CWR). However, given the process data above, I still would not feel 100% certain that the disk would not fatigue and burst prematurely.

Any suggestions?


Thanks

[pleckner]

Consider an expansion tank off the main line. The air in the tank acts as a cushion against just this type of problem. Chilled water systems use them all the time.