EPRV for API 650 Tank

[Encho]

Hi,

I am sizing the Emergency Pressure Relieve Valve for an API 650 Tank. It does not have internal pressure so the MAWP is limited to the basic calc of roof weight/cross sectional area of the tank which results in MAWP=1.96 inWC.

I have already sized the set for the PVRV in 1 inWC. When I try to size the EPRV. And look for the EPRV´s available on the market, I find that the lowest set for this valves is 2 inWC.

Am I setting properly the MAWP for this kind of tank?
Any information you can give me for the EPRV´s?


Thanks in advance.

 

[JStephen]

Can you use a free vent rather than a p/V valve?
You might also contact some of the suppliers for input.

 

[IFRs]

Emergency vents are typically designed to relieve their full flow at a pressure not exceeding the weight of the roof plates. See API 2000 for more info. If the tank qualifies, a frangible shell-to-roof joint is all you need. 1.96 inches of water column is about equal to 0.250 inch thick roof plate. There are several emergency roof vents that activate at much less than 2 inches of water column. See Protectoseal or Shand and Jurs. A free vent can be used as an emergency vent if it flows the required rate at the required pressure. If you are using conservation vents then a free vent is a poor choice for an emergency vent. I would stay away from defining MAWP as it relates to emergency vents.

 

[Encho]

Thanks for the answers. By the design of the tank it isn´t possible to have frangible joint, either cann´t use free vent. Yes it is a 1/4" thick roof plate. I have just check and the lowest roof vent activation is 1.73 inWC.

 

[fegenbush]

I checked the data sheets from a major vent suppliers website, and their product can be set to 1 in WC minimum. Perhaps your chosen vendor does not have a product which can be set to your needs. It may be necessary to source an alternate vendor.