Butane Storage Bullet PSV or RD

[duncan8943]

I have an existing PSV on a butane bullet which is set at 250 PSIG. The PSV is too small for fire sizing. I have two choices: (1) Replace the PSV with a larger one or (2) Add an additional rupture disk to give the required relief rate. The vessel MAWP is 300 PSIG. I am thinking about installing a 300 PSIG rupture disk on the vessel. With fire sizing, I have thought about incidents where the metal weakens and the vessel explodes. A rupture disk would prevent this. How many of you do the above or protect your bullets with rupture disks? Any other ideas or comments are greatly appreciated. Thanks.

 

[CMA010]

Instead of adding a RD you could also install an additional PSV. Why is the existing PSV set at 250 psig and not at 300?

What are the incidents you are referring to?

 

[duncan8943]

When I was doing consulting, 99% of the time we set the relief valve setting to the MAWP of the vessel. The only time that we wouldn't would be for a case where the material would get too hot at the higher pressure. I would say that for this refinery, the previous mentality was that lower relief valve setting meant that we were safer. I've seen it on other vessels in the plant that were rated for 400 PSIG--that had a relief at 250 PSIG.

 

[Chance17]

A rupture disk on tanks with liquified gases such as Butane is a bad idea (in my opinion).
1) There are few convenient methods to stop a release if the disk happens to activate.
2) Would you really send an operator out (in a fire) to block an activated disk?
2) An open disk is path for possible flame flash back into the tank.
3) The fluid will auto-refrigerates but hopefully not below the minimum metal temperature.

This sounds like an application for dual safety valves.

 

[JoeWong88]

duncan8943,

No doubt you can install a small PRV for small relieving scenario and a large relief device for large relieving load. This is pretty common in many installation.

Neither PRV nor RD will definitely protect a vessel from fire. Vessel will eventually collapse due to fire. Nevertheless, PRV (RD even better) may minimize catastrophe failure of vessel and buy time for passive protection.

One of the problem of installing RD is premature opening due to fatigue failure and lead to unnecessary release of inventory. Another issue is premature opening due to RD manufacturer tolerance.

Still think that a PRV is a better consideration...



JoeWong
Chemical & Process Technology

 

[dcasto]

since butanes will reach 300 psig at under 250 F, there will not be a significant reduction in the vessels yield strenght. If you had a lquid that didn't vapourize at 600F and 300 psig, you would need to re-evaluate the situation.

 

[MortenA]

If you are working on a Shell project then you should consult the DEP - i think it covers this subject.

Best regards

Morten