API 650 Appendix F - max design pressure

[JES1812]

I am checking the allowable internal pressure for a tank designed to API 650. The plant wants to add a nitrogen blanket and the process engineer wants this information in order to design the pressure-vacuum relief valve. I was using the equation in F.4.1, which includes the tank diameter, but does not give units for this variable. If I use 'feet' I come up with a pressure greater than allowable for API 650 tank construction. If I use 'inches' I get a rather small value (around 1 in-H20) which seems too low. So, what are the units for this calculation?

 

[JStephen]

D is feet, P is in inches of water. Pressure will also be limited by F.4.2 if applicable. For a small tank, you may calculate a pressure higher than the 2.5 psi, but it's limited to the 2.5 psi to use API-650.

 

[IFRs]

Don't forget to check the need for or adequacy of anchors when adding internal pressure, especially if the tank is not small in diameter...

 

[JES1812]

JStephen, IFRs,

Thanks for the responses.

Another question, in F.4.2 when calculating the weight of shell and structural attachments (for evaluating WDL), do you include the floor plate as well? I assume the intent is the total weight of the tank, minus the roof and any roof structure.

 

[JStephen]

Floor plate is not included.