Sizing Pressure Relief Devices for Vessels Connected by a Vapour Pressure Balancing Line

[Sirius P.Eng.]

What is the best approach for sizing Pressure Safety Valves for 4No. LPG tanks connected to each other by a Pressure-Equalization line. The balancing line from each sphere connects to a common header. Each line from a Sphere has a Fail Close on/off ball valve which is to remain open during normal operations. There's also a tee off upstream of each of these valves that connects to the flare header. This line is equipped with a Fail Open on/off valve that is to remain closed during normal operations.

All 4No.spheres are installed in a dyke or bund with drainage. Fire fighting equipment exists.

Should the total wetted surface area for all 4No tanks be calculated and relief load calculated as such or can each vessel be considered independently?

 

[Latexman]

You can probably access OSHA 29 CFR 1910.110 (Storage and Handling of Liquefied Petroleum Gases). Heat input rates are based on regulations and industry standards. Maybe you already have it. It may not be legally required in your jurisdiction, but it could give you guidance. I recommend considering the tanks independently.





Good Luck,
Latexman

 

[georgeverghese]

Since you have a valve on tank exit for both common balancing line and flare line, it looks like you have no choice but to install a PSV for each tank.

 

[gerhardl]

Agree. Common sense! Increased risk if one PRV only, this will require other mechanical components both to work properly and have sufficient interconnection capacity for all possible cases.

 

[Sirius P.Eng.]

Very well noted then. Thank you.