PSV in Tube side of Shell & Tube Heat exchanger

[kashasa]

Hello all,
I have a question regarding the necessity of PSV on tube side of Shell & Tube Heat exchanger.

1. The HEX (heat exchanger) is design by ASME BPVC Section IIIV Division 1.
2. Fluids in HEX:
Shell side - Hydrocarbon fluid (Liquid/Gas phase).
Tube side (the heat source) - case 1: Brine (Liquid), Case 2: Steam (Gas). Cases refer to different HEXs.
3. By UG-125, any Pressure vessel shall be provided with over-pressure protection, if by mechanical device (e.g. PSV) or by system design (UG-140).
I could not find any reference for HEXs on the UHX part.
4. On Shell side - PSV is installed anyway.
5. In case of any failure (e.g. external fire), the Tube side is in Blocked flow (meaning, no regular heat source).
6. By API 521(5.1 Table 2), the only credible scenario of over-pressure for my application, which the Tube side is not protected, is external fire.

My question:
Do I need PSV on Tube side, if I already have on Shell side?
Thanks

 

[met11]

Yes, you also need one on the tube side.

If fire is a credible scenario (or blocked-in thermal expansion), you'll need the PSV on both the shell and tube side.

The alternative is overpressure protection by system design, as outlined in ASME VIII Div 1, UG-140. However based on your description, I don't think that's really an option here.