2 replies to this topic

[SR22]

Hello,

I am looking for information on minimum distance requirement requirements between a blowdown or start-up (pressurisation) orifice and the upstream blowdown / start-up valve.

I am involved in the design of a gas import system (gas enters topsides at 134-147 barg and 5deg C) which will experience significant JT cooling on blowdown or start-up. These cold temperatures could pose problems with ice formation if allowed to creep back to the upstream valve and I have found some information suggesting that it is good practice to have at least 600mm between the orifice and the valve but do not have anything from an official standard - API, NORSOK, etc.

Can anyone offer any advice if this 600mm is acceptable or point me to any other relevant info?

Thanks.

[fallah]

I have found some information suggesting that it is good practice to have at least 600mm between the orifice and the valve but do not have anything from an official standard - API, NORSOK, etc.

Can anyone offer any advice if this 600mm is acceptable or point me to any other relevant info?

Thanks.

I think such above mentioned distance just included in "Engineering Practices" and not in official standards.

Anyway,the mentioned distance depends on the coldness intensity,duration,material,...and could be evaluated in each case.

[Zauberberg]

The only place where ice formation can take place is downstream of the orifice, due to large pressure drop and the J-T cooling effect. Pressure drop across the valve is usually quite small when compared to that across the orifice, and I doubt it can lead to ice formation unless the feed gas is already quite cold and contains water.

"Creeping back" of ice doesn't sound as a very much likely scenario to me.