4 replies to this topic

[processengineer1998]

Dear All;
I want to know the requirement for installation of bypass line for Blow down valve.
Blowdown valve to be installed in multiphase gas stream for fire and gas situation.
Is there any requirement for bypass line installation regarding elevation.should the bypass line to be installed in same elevation of blowdown valve line or by pass line can be in lower or upper elevation?
thanks in advance

[fallah]

Dear All;
I want to know the requirement for installation of bypass line for Blow down valve.
Blowdown valve to be installed in multiphase gas stream for fire and gas situation.
Is there any requirement for bypass line installation regarding elevation.should the bypass line to be installed in same elevation of blowdown valve line or by pass line can be in lower or upper elevation?
thanks in advance

processengineer1998,

Considering bypass line for BDVs is not usually authorized due to safety issues.On the other hand, they are TSO,FO,and NC valves make them needless to have bypass line.

Fallah

[paulhorth]

Processengineer,

It is not clear what kind of bypass you are asking about, or what its intended function is. It is common practice to provide a small line from a vessel to the flare header which is intended for manual purging only. On the PID this line has the appearance of a bypass around the BDV, but the line is not intended to allow manual blowdown from full pressure. Typically the line will have a manual globe valve and an isolation valve. Its function is to allow manual purging with nitrogen to about 5 barg when the vessel is out of service. The vessel is filled with N2 and then depressured to flare using this manually operated valve, while the main BDV remains closed.
In this service I do not think there is any specific requirement for elevation of this manual purge connection, except that it should enter the flare header from above, to avoid forming a pocket for liquid draining back from the header.

Paul

[processengineer1998]

Dear Fallah
Thanks for your response
But in our project it is going to be installed.
My question is about the elevation of bypass line(same as blowdown valve line elevation or lower or upper of blowdown valve line elevation)

Edited by processengineer1998, 31 August 2011 - 05:40 AM.

[fallah]

Dear Fallah
Thanks for your response
But in our project it is going to be installed.
My question is about the elevation of bypass line(same as blowdown valve line elevation or lower or upper of blowdown valve line elevation)

Dear processengineer,

The BDV itself, because of the requirement to be free drain toward upstream vessel/column/...should be almost at same (or at higher) elevation which valve's upstream line connects to that vessel/column/....

Obviously, the bypass line could be installed in any situation with respect to relevant BDV provided that the needed drain/access/maintenance facilities would be predicted.But, if liquid formation around bypass valve (supposed to be normally closed) is to be a concern, it is better the elevation of the bypass line to be more than the BDV itself with considering adequate slope in upstream/downstream lines of bypass valve toward the main line.

Fallah

Edited by fallah, 31 August 2011 - 06:58 AM.