4 replies to this topic

[Nasiruddin]

I am working on a Pipeline replacement project, brief description is following:

 

From an on-shore oil and gas separation facility, unstabilized condensate is transported through 18” diameter 103 km long pipeline to another facility for further treatment.

 

During initial years of operation of the facility the first stage separator operating at 85 bar-g. Condensate taken directly from the separator and transport through the above mentioned pipeline. Separator and pipeline both have Design pressures of 112 bar-g.

 

During later years after declining of wells separator pressure reduced to 70 bar-g, and a surge drum and export pump is installed between 1^st stage separator and export pipeline to transport the unstabilized condensate. Normal operating pressure at pump discharge is 90 bar-g. Shut-off head of the selected pump is 140 bar-g. To protect the pipeline a SIL-2 rated Instrumented Protected Function (IPF) has been installed at pump discharge that will trip the pump at 112 bar-g.

 

After seven (07) years of operation pipeline has leaked because of poor maintenance and low fluid velocities and it is decided that existing 18" pipeline should be replaced with two (02) new pipelines each having diameter of 10”. Design pressure for new pipelines will be same as the original one i.e. 112 bar-g. Surge analysis of new condensate pipeline indicates that surge pressure in one of the scenario (ESD Valve closure at pipeline outlet) is 130 bar-g. Please note that client do not want to increase the design pressure of the pipline as the pipeline material is already ordered, so this is a constraint in desgin.

 

Now question is

 

1. Credit can be taken for same SIL-2 rated function or not to avoid surge relief valve on pipeline.
2. Whether any code allowed using IPF function as ultimate protection instead of surge relief valve?

Appreciate quick feedback.

 

Regards,

Nasiruddin

 

 

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[Bobby Strain]

Seems like you have not included all the information for proper comments.

 

Bobby

[Nasiruddin]

Bobby,

 

Kindly let mw know what additional information required for better understanding.

 

Naisruddin

[AlertO]

Hi Nasiruddin

 

From my opinion, PSHH is quite not a proper protection device for surge pressure because when the ESD valve is shut, the surge pressure is already in your system. Although your PSHH is very very fast to trip the pump, the surge pressure is higher than your design pressure already (The peak pressure may be below 130 barg, need to check in dynamic mode). The surge pressure devices e.g. Surge PSV, Surge accumulator are reccomended.

 

Note: I have never used PSHH as surge protection. If others have this experience, please share.

[fallah]

Nasiruddin,

 

Tripping the pump by PSHH while the downstream ESD valve are closing, can protect the pump against dead head conditions but even might amplify the surge pressure due to ESD valve closure. Then, as Alerto mentioned, using a PSV or surge accumulator is better chose to protect the downstream piping against surge pressure higher than relevant design pressure...