LPG - Vacuum Breaker Requirement for Pressurized Vessel 1

[msavila]

Does an LPG (Butanes) Pressurized Storage Sphere require a vacuum breaker? Our existing tanks were designed with a vacuum pressure (actually a duo-check valve) that is set to open at 1" H2O and has a design pressure of 90 psi (tank design pressure) at ambient conditions. I have been unable to locate a vendor that can provide a vacuum breaker that can meet our specs. Can you help me?

 

[MJCronin]

msavila,

Do you have an ASME vessel with a code dataplate ? If not, do you have a mfr's print with the National Board number on it ? For a few bucks, the people in Columbus OH will send to you the design data submitted to them at the time that the vessel was built...

If you can read the dataplate, you may find the vacuum rating on it....remember "FV" means "full vacuum protection/

What are the dimensions of your vessel ? If the diameter is 6 feet or less and the heads are dished, and the design pressure is 90 psig, the chances are good that you have far more than a 1" H2o vacuum rating.

Just my thoughts....

MJC

 

[Montemayor]

msavila (Chemical):

Mike Cronin is giving you some great, basic and essential advice that should go in your hip pocket for when you're dealing with tanks and pressure vessels.

You ask if a vacuum breaker is required for Butane storage. Again, this is a basic and elementary need that is easily resolved if you revert back to your Thermodynamics and physical properties studies. If the tank is going to be dedicated solely to Butane storage (saturated), then you need to refer to the vapor pressure of Butane:

Temp, oF Press, psia
14.000 10.119
16.000 10.590
18.000 11.078
20.000 11.584
22.000 12.107
24.000 12.649
26.000 13.210
28.000 13.790
30.000 14.390
32.000 15.010

Depending on your tank's location and elevation, the above table should tell you if you're going to generate a vacuum by allowing the tank's contents to cool down with atmospheric winter conditions. If you're located in Kingston, Jamaica, Port of Spain, Trinidad or Pucallpa, Peru I wouldn't worry about needing a vacuum breaker in a butane tank. If you're in the North Slope, you'd better have one.

Normally, I would expect to find the tank has been FV'd and I would not rest until I had the documentation that Mike Cronin lists - especially the fabrication drawings. You need these for inspection and as reference for all tank-related calculations (such as the vacuum breaker).


Art Montemayor
Spring, TX

 

[msavila]

Hello MJCronin & Montemayor,

Thank you both for your replies to my post. I was able to dig up the fabrication drawings in our drawing room. The vessel was built in 1969 by Chicago Bridge & Iron Company (CB&I), and the tank was rated for -12.55 psig vacuum. It is 62 ft in diameter, 90 psi MAWP, 135 psi test pressure, with top thickness of 1.044" and bottom at 1 3/16".

I performed several calculations using the most extreme operating conditions and worst case scenarios under our current operation, and have determined that we cannot exceed the -12.55 psi vacuum rating of the sphere. I have reviewed them with our process engineering group here and submitted an MOC to remove the vacuum breakers (check valves) from the sphere all together.

I appreciate your input and look forward to any other comments or suggestions you may have.

Thanks Again,

Mark Avila
Operations Engineer
Los Angeles Refinery
ConocoPhillips