Relief Valve-Orifice size

[jeanfrancois3869]

Hi,

I search a formula to determine the orifice sizes of my relief valves. The operating pressure is 70 bars (Class 600). I know the flow (Oil and Gas) which circulate in my pipes (2300m3/h at 70bars).

How do I fix opening pressure? What are the flow to evacuate?

Thanks you to help me.

 

[MortenA]

I think that you should look for someone in your company with the relevant experience. This is a subject with many pitfalls even though it may sound simple engineers spend quite a lot of time on this subject.

However, API 520 and 521 will tell you a lot.

Best regards

Morten

 

[dcasto]

the question is to broad. Morten's reference is a good start, but it will take some guidance from others that have hit problems.

You'll need to know so of the gases properties like Cp and mole weight. You need the operating condtions of temperature. You need to know the process and where the gas comes from or how it is generated. You'll need to know about the pipe and vessels. Where the gas will be evacuated too.

 

[jeanfrancois3869]

I found a solution thanks to calculations which are given by ASME Section VIII, Division 1.

Meanwhile, for Crude oil I find a orifice size too large and it doesn't exist in industry. I conform to formula for liquid, but here, with the oil (for thermal expansion and for the fire), the fluid to evacuate it's vapor or mixing gas/liquid.Is it correct?
Does someone know how I must proceed?

Futher more, I search a breather valve to limit the expansion phenomenon (with simultaneous opening and closing). Does it exist for a class 600.

Thanks you for your help.

 

[MortenA]

Its very uncommon that a PSV sized for fire is larger than a size T (the vessel have to be very big and the set-point low) - and i would say impossible for thermal expansion.

If you find this i would double check the calculations.

If the calculations are correct then you can use more than one valve in parallel.

A breather valve for a class 600 systems seems contradictionary? But stranger things are seen i guess.

Check with the vendors e.g. Tyco (Anderson Greenwood, Crosby etc).

Best regards

Morten

 

[dcasto]

I agree with Morten with multiple valves. However, something is not correct with your calculations unless you have a huge (at least 10,000 bbl) tank that you are sizing for a pooling fire.