PSV on Steam side of Heat Exchanger

[silvz71]

Hello,

I nned to size a relief valve on the steam side (inlet, tubes) of a heat exchanger. The shell side material is like that of "mineral oil." The steam is at 125 psig and is in a 1/2" line. Where do I begin with this one? Do I just determine the relieving rate by using the flowrate of the steam (~5 lbs/hr....pilot plant operation)? I would guess I need to start by looking at the fire case. If anyone has any suggestions about where to start, please let me know. I've taken the API pressure relief class, but they didn't really touch on this particular case, at least not for the tube side. Thanks!

David

 

[Latexman]

David,

Yes, looking at the fire case is a good start. Consider the heat from a fire that enters through the heads and the heat that can transfer through the shell. Next, obtain a field verified P&ID and look over the operation. Do a "What If" analysis to ferret out all credible scenarios. Is there a steam supply regulator? What if it fails wide open? Is there a control valve in the steam line? What if it fails wide open? Is the shell side pressure greater than the MAWP of the tube side and piping? If so, tube failure may be a reasonable scenario to consider. Then, if the shell side fluid is not compatible with steam/water, you may have a reactive relief scenario. What if the tubeside fills with condensate, gets blocked in (like in a shutdown), and then thermal expansion (ambient heating or heated by shell side fluid) ruptures a(the) tube(s)? What if the steam trap fails closed or a condensate valve is closed? And on and on until you know all scenarios have been considered.

Good luck,
Latexman