3 replies to this topic

[asade abiodun]

Hi

Please, I need to design a PRESSURE VACUUM SAFETY VALVE (PVSV). I am confuse if need to use API 520/ 521. Also, i would appreciate information on how to differentiate it from normal PSV.

I would appreciate information on how to size the valve.

Thanks.

[ankur2061]

Asade,

I think the issue is straight forward. You determine the maximum of the inbreathing and out breathing rates for normal venting (I am assuming it is normal venting case & not external fire case). Your venting rate through the proposed PVSV or PVRV is the maximum of the inbreathing or outbreathing. The pressure setpoint for the PVSV will be your design pressure of the tank and the vacuum setpoint for the PVSV will be the design vacuum of the tank.

This data i.e. the venting rate and pressure/vacuum setpoints have to be given to the PVSV vendor, for him to advise you the size of the PVSV. "Protectoseal" and "Protego" are some of the more recognized vendors.

Alternatively, Protectoseal provides a free download for its software called 'Pro-Flow II' which you can download by registering and use it to determine the size of your PVSV with the actual Protectoseal PVSV model provided as part of the sizing calculation.

Goodluck in your PVSV selection and sizing.

Regards,
Ankur.

[Art Montemayor]

Asade:

Just to add to Ankur's positive response, I would say that what you should refer to is API 2000 - and not API 520 or 521 - when dealing with atmospheric storage tanks and PVSVs.

Also, I have prepared a lot of material on pressure relief for storage tanks which I have posted in our Forums. Use the SEARCH feature with key words and you will find the material posted and be able to download it for your use.

[JoeWong]

Asade:

Just to add to Mr. Montemayor's response...

Extract from API STD 2000 scope section
"This standard covers normal and emergency vapor venting requirements for

• aboveground liquid petroleum or petroleum products storage tanks and;
• aboveground and underground refrigerated storage tanks

designed for operation at pressures from vacuum through 15 pounds per square inch gauge (1.034 bar gauge)...".
API STD 2000 is specific for tank.

API STD 520 is more in providing information / guidelines to assist engineer in selection of the system that is most appropriate for the risks and circumstances involved in various installations. It should be compliment to API STD 2000, but not exclusive.