PVRV Set Pressure 1

[oil198]

Hi all,

We have an atmospheric storage tank containing chemical. I believe it is an API 620 storage tank, as the MAWP is 14.5 psig.

We need to install a PVRV (breather) on this tank. I am confused as to what the set pressure should be. I know an API 650 tank is not allowed any accumulation, I believe that an API 620 tank is allowed 10% accumulation. But for arguments sake, I will go with 0 accumulation.

Most of the valves I have seen from different manufacturers have a maximum set pressure of around 26 oz/in^2. Wouldn't a setting this low on a tank that has a MAWP of about 15 psig be too low? Since weight loaded devices require 50-100% overpressure to fully relieve at their rated capacity, I would have thought to set for pressure at around 7 psig, at 100% overpressure the valve is fully open, and pressure in the vessel is at or slightly below MAWP (0% accumulation). Can anyone advise? Am I missing something?

 

[Chance17]

Be advised that at least one major vendor (first letter "G")has a new product line being fully open at 10% overpressure.
This may fit your needs.

The API-620 tank does have 10% allowable accumulation.
At 14.5-psig, the conventional hardware would be a pallet plus spring.
You would have to work with a vendor for correct sizing.
If the vendor has certified curves, you don't need 100% overpressure.
Simply use the curve data. Be sure you are in a predictable part of the curve (above simmer).