4 replies to this topic

[Papps]

There is a plan to connect 2 inch pipeline into a 16 inch pipeline. 16 inch pipeline operating pressure is 7.5 bar (Continuos flow) and PSHH is 13.5 bar. 

 

2 inch line operating pressure is 10.0 bar and this line is having a control valve. Upstream pressure is 120 bar and Downstream pressure is 10.0 bar. 

 

Maximum Flow rate through the line  is 6648 Kg/hr. Service is Natural Gas Condensate.

 

In case, if Gas Blow-by occurs through the control valve what will be the increase in downstream pressure. (Approximately).

 

Looking for hand calculation formula to estimate downstream pressure approximately.

 

 

[Bobby Strain]

It is not necessary to calculate. You need to provide some pressure protection device on the large line to limit the pressure. And the device should relieve whatever quantity of gas flows though the wide open valve. Some would include flow through an open control valve bypass. Or you can use an instrumented pressure protection system.

 

Bobby

[Papps]

Thanks for your reply Mr. Bobby,

 

Flow in the mentioned 16 inch line is 50,000 Kg/hr. As flow is continuous to the plant through the 16 inch line, there is a doubt about PSHH activation present in the 16 inch in case if gas blow by occurs through the 2 inch line.

 

If gas blow by occurs in the 2 inch then a flow of maximum 6400 kg/hr will flow into the 16 inch header with a pressure of 120 bar. (16 inch header operating pressure is 7.5 bar and PSHH setting is 13.5 bar).

 

There is a consideration to provide instrumented pressure protection system in the 2 inch line as you mentioned. Am asked to justify the presence of instrumented pressure protection system in the 2 inch line with some sort of calculation that in case of gas blow by occurs through the 2 inch line then 16 inch PSHH will activate.

 

Seeking guidance in this regard.

[Bobby Strain]

We can't help much until we have more information about what is upstream of the 2-inch valve. A sketch with the various line lengths, origin, and destination will probably get others to respond. Make sure you define where gas exists and where liquid exists. It's quite important in this case. And where are relief valves currently installed?

 

Bobby

[Saml]

That the PSHH may activates is not your main problem.

Your problem is: If you have a credible scenario for overpressure you must chek that the relief is adequate and if it's not, provide the same.

 

And then there are a few things that I don't fully understand:

- 50 000 kg/h of (liquid) condensates is a very low flow for a 16 inch line.

- If the 2" line is 10 bar and the 16 inch line operates at 7,5 bar. Where is the 2.5 bar pressure drop? a nozzle?