relief flow for vessel with a jacket

[cheme89]

I have to size a relief valve for a vessel with a jacket (the relief valve protects the shell). The jacket is not used and is empty and open to atmosphere. For the external fire case, I can't find any guidance on whether or not it is appropriate to take some sort of insulation credit for the jacket. Ideally I could exclude the jacket surface area from the vessel area and calculate heat input based on that. But I've never seen it done. Any thoughts or suggestions would be appreciated.

 

[Chance17]

I am not aware of any Industry Standard that addresses this design.
But I have done almost exactly as you described.
It passed pier review based on the jacket not being in direct heat transfer contact with the inner shell.
The design also models a heat exchanger shell protecting the internal tubes from Fire exposure.

There are exposed inner shell portions on bottom and top end. There are also exposed shell at the end heads.
All exposed end wetted areas should be the basis for Fire overpressure of the inner shell.

 

[Latexman]

What kind of jacket?

Good luck,
Latexman

 

[cheme89]

Chance, good point about the comparison to S&T exchangers. Should have thought of that.

Latex, it's a conventional, annular space type jacket.

 

[Latexman]

Good. I think your logic is sound then.

Had you said half-pipe jacket, it may not have passed review. The many half-pipes can act like fins, aiding heat transfer from the fire to the shell.

Good luck,
Latexman

 

[cheme89]

Latex, also good point. Thanks for the help.

 

[moltenmetal]

As long as nobody fills the jacket, you're fine!

Empty, your jacket is no different than taking credit for SS-clad mineral insulation. It won't come off in a fire nor in subsequent firefighting activity.

 

[knapee]

Dear Sir

Insulation materials, for fire resistant insulation, typically include calcium silicate with stainless steel jacketing (at least to the vertical fire zone limit).

By the way, Credit for use of water sprays to reduce relief loads is generally not permitted.

Hope this is help

 

[moltenmetal]

Thanks for clarifying my remark- "mineral" insulation isn't clear enough, as calcium silicate is a lot more mechanically durable than mineral fibre etc. It stands to reason that you can't count on fire water to reduce relieving rate, as it may not be available when needed. Just look at that refinery on fire in Japan right now...