Do I need a shell-side safety relief on my steam-to-water HX?

[MinnesotaSlinger]

I'm confused as to how to interpret the BPVC Section VIII for my heat exchanger. UG-140 of the code, about overpressure protection by system design, would seem to apply, given that pressure reliefs in the steam distribution system serving my HX are set to relieve at a lower pressure than my HX's design pressure of 150 psig. The tube side of my HX is cooling water from the river (which is being heated by the steam). Therefore, there would seem to be no good reason to need a safety relief on the shell side for overpressure protection based on, say, control valve failure, blocking condensate flow out, or anything else related to failure of a mechanical or control component; the system is just not capable of exceeding the shell design pressure of my HX.

However, there's the issue of a plant fire. That, it would seem, would be the only way the vessel could exceed its design pressure up to the point of rupture or explosion. But this too is far fetched. The unit is surrounded by steel and concrete, isn't around anything particularly flammable, and is going to be heavily insulated. For there to be a fire of sufficient magnitude to heat up steam or air within the unit to the point of castostrophic failure, I would think the whole area of the plant would become so uninhabitable that no amount of fire fighting PPE would allow a fire fighter, much less an unprotected person, to survive anywhere near the HX.

So, I am wondering if I need a steam-side safety relief on the shell of the HX. It just doesn't seem that one should be required by common sense, and routing a safety relief to a safe place would be quite expensive, much more expensive than the valve itself. It would seem to me there would be more danger in an inadvertent safety valve discharge than there would be in not having a safety valve at all.

Anyway, do I need a shell-side safety valve?

As for the tube-side (i.e., the water side), I am planning on installing a safety valve given that closure of valves combined with application of steam to the HX could cause overpressure on the tube-side.

Thanks.

 

[racookpe1978]

Is there ANY possible way to isolate the river water flowing through the dhell side?

For example: Inlet valve and outlet valve are shut. The trapped river water heats up (due to ambient, trapped steam, hotter air, sunshine on pipes, whatever.) If isolated it cannot escape and threatens, not the HX itself, but the pipes and seals and pumps and valves in the river water system.

 

[novakoni]

If you already have safety valves at steam distribution system which are set to open at lower pressure then design pressure of your HX - than there is no need for safety valve at shell side.

The reason for placing valve at shell side could be if your cooling water system is at higher pressure. In case of tube crack and leak to shell side from tube side.

So if tube side is at higher pressure than shell side design pressure - than you would need safety valve on shell side.