design pressure of above ground steel tank 1

[onshore]

What should be the basis for design pressure for a Atm crude oil tank 30 m dia which is having breather valves? should the pressure at whihc the breather valve operates be considered?

 

[SeanB]

I have normally seen storage tanks designed for 2.5 in. H20 Pressure and 1.5 in. H2O vacuum.

 

[StoneCold]

While I don't know any design numbers off the top of my head. Remember that the design numbers are for the top of the tank. You have to take in to account the hydaulic head of the liquid at the bottom of the tank as well.

Regards
StoneCold

 

[IFRs]

Depends on the code it was designed and built to.
For regular unahchored API tanks it is 2 1/2 psi gauge.
Another guideline might be the weight of the roof plates.

 

[JoeTank]

The settings of the tank breather valve are only the points at which the valves START to open. Most of the low pressure valves (that use weighted pallets) often have to achieve 50 to 100% overpressure before they are fully open and flowing at their rated capacities. You should consider the overpressure values when establishing the design pressures and vacuums for a storage tank.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[JStephen]

The basis for design pressure should be keeping the pressure as low as possible.

Can you use free vents, no pallets? That's ideal choice from a structural standpoint.

If emissions or blanketing or other considerations don't allow this, then check into the breather valves you're going to use, and what the minimum reliable pressures are. Perhaps someone here or at your plant can offer some guidance as well- I suppose if you try to hold it too low, wind will be flapping the pallets open and closed, or they won't seal well, etc.

The 2.5 PSI gauge above is not the normal pressure for tanks, that is the maximum that you can build it to, under API-650. Even at that pressure, you may be incurring major extra expenses in the tank and foundation design, though.

Normally, pressure on a tank doesn't make too much difference until it is close to the weight of the roof plate. Typical roof plate is 3/16", or 7.66 PSF, or 0.05 PSI or 0.85 oz/in2. So you can go up to 1/2 oz and not make much difference. Over that, you may or may not be adding cost to the tank to contain the pressure. Even the 1/2 oz could affect the tank if the tank was otherwise close to borderline stability in wind conditions.