4 replies to this topic

[SAprocessGD]

Hello,

My query involves vacuum set/design pressures on tanks and PVRV's.

I am looking to set the vacuum design pressure of a PVRV on a few of our atmospheric storage tanks. All of our tanks (designed to a modified API 650 design) currently has a vacuum design pressure of 0.4oz.

With a tank vacuum design pressure of 0.4oz, the PVRV set pressure MUST be below 0.4oz as to prevent collapsing the tanks.

I have a few questions regarding the above pressures:

1. Is it common to set PVRV vacuum design pressures below 0.4oz? If so, what is the lowest set pressure anyone has seen? I hear this can be done, but the cost of the valve (for say a 4" or 6" PVRV) will be expensive.
2. What is the minimum vacuum design pressure for atmospheric storage tanks (API 650)?

[simadri]

SAprocess GD

Sorry for the doubt, but I cant understand how oz can be unit of vacuum/pressure ?

[fallah]

SAprocessGD,

As per API 650 the design vacuum of the atmospheric storage tanks shall not be less than 0.25 kPa (equal to 1" WC or 0.577 OZ/in2). Then, set vacuum of the PVRV's should be less than this value.

Fallah

[SAprocessGD]

Simadri - I am so used to just writing oz, I forgot others may not see it expressed that way. Should be oz/in2.

fallah - I have seen designs where P&IDs state vacuum pressure as 0.4oz/in2 for API 650 and API 12F tanks along with the thief hatches. Is it possible that P&IDs state the vacuum to 0.4 oz/in2 but the maximum vacuum design rating is 0.577 oz/in2 for API 650 and 0.5 oz/in2 for API 12F (small tanks)?

In your experience, have you ever seen API 650 tanks vacuum pressures set at 0.4 oz/in2? I'm just trying to good understanding of the situation.

I appreciate your help,

Cheers!

[fallah]

SAprocessGD,

P&ID might not reflet the right value. At first, you should refer to the tank data sheet. Design code of the tank is also reflected there.

Fallah