API 650 Tank Design and Operation Pressure

[JoseAcevedo]

I have to design a tank and the customer specify an internal design pressure of 0.2 psi. The custumer also specify that the tank must have an open vent with flame arrestor and in case of flame arrestor obstruction the customer require additionally a Pressure & vaccumm relief valve with flame arrestor too. The tank diameter is lesser than 40 feet thus an emergency vent it is required too.

In our case we have the following:
1.- The operation pressure of the open vent with flame arrestor (almost atmospheric).
2.- The Operation pressure of Pressure & vaccumm relief valve with flame arrestor setting at aproximatetelly 2" w.c.
3.- the operation pressure of the emergency vent setting at aproximatelly 4" w.c.

My question is: What is the notmal operation that we have consider for the tank, the number 1 or 2?

 

[JoeTank]

Jose,
That is really a question to ask the client. Operating and Design pressures are to be specified by the client. I don't think they have given you enough info yet.

For example, the 2" WC for the pressure/vaccuum relief vent is the setting at which the pallets START TO OPEN. Normally a 100% over-pressure is required to fully open the vent. So in this case, I would expect that the design pressure would be 4" WC (2" + 1005 over-pressure = 4"WC).

API-650, Appendix R (Load Combinations)now assumes that the OPERATING pressure is 40% of DESIGN presuure. But, that may not always be the case.

Joe Tank

 

[MJCronin]

Jose....

Many large engineering & design firms establish a minimum design pressure for API-650 tanks regardless of the service or the wishes of the client. I believe that API-650 also sets a minimum design pressure (!!???)

The corporate minimum design pressures vary with the particular project and with the diameter of the tank.

For a tank of about 40 ft diameter, I suggest that you consider a minimum design pressure of 8-10 IWC and a minimum design vacuum of about -2 IWC.

I have no hard-and-fast reference for you on this issue....just recollections of previous tank projects

Anyone else have suggestions..???

My opinion only

-MJC

 

[IFRs]

Per API, the minimum design external pressure is 1 inch of water. There is no minimum design internal pressure. The maximum design internal pressure is 2.5 pounds per square inch.