External design pressure on a tank

[SrChemE]

Hello,
There is some discrepancy between our tank UBRS and the Tank Data sheet, (both call out no external pressure) but the engineering drawing states -.22 psig.
I was wondering when I would need a tank to be built for the external design pressure of -0.22 psig?
This will most likely rise the construction price, but is it necessary?
Many thanks in advance,

 

[LittleInch]

when you're pumping out liquid or when your vapour space cools down and your vent system can't cope with it.

Or you have some sort of standing water on the outside.

I don't know where 0.22 psi comes from. API 650 allows only 1 inch of water ( 0.25 kPa) before you need to stiffen up the tank. 0.22 is ~1.5 kPa.

Thin shell tanks really really don't like external pressure.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

You need to provide some details on the application, for example, what type and size of tank.