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[Dressing]

Hi,

I am working in a company operating FPSOs. I would kindly like to ask for some advice regarding water hammering effect on our water injection line.

I have attached a figure to better explain the situation.

We have a huge deaerator coloumn (approximately 20 m height, 3 m OD) supplying seawater to a water injection pump (E-2). When the water injection pump trips the pumps' rpm slowly drops. When the RPM has reach about 2/3 of full rpm the non-return valve V-1 closes due to low DP/low flow over the valve (the NRV is very stiff), and isolate the pipe segment. Since V-1 closes very fast, oscillating pressure peaks are observed and pressure rises inside the isolated pipe segment. The pressure in the segment will continue to rise until it reaches about 40 barg. At 40 barg the V-5 actuated valve will open to depressurize the system. The opening of this valve is slow and therefore unable to kill the water hammering effect.

It is therefore suggested to install a 4"x6" PSV on the pipe segment to immediately open on set pressure (8.0 barg) to kill the effect of water hammer by routing a portion of the produced water to different location.

Please find the following data:

Downstream water injection pump:

F = 1100 m3/h
P = 175 bar
T = 40 degC

Upstream water injection pump:

P = 3.5 barg

Calculated flow through PSV:

F = 400 m3/h

Will the installation of this PSV be a good solution to the issue? Sizing of the PSV is a challenge. It is difficult to calculate the required capacity (flow) of the valve. Could anybody give some advice regarding sizing of a PSV for this service?

I may have provided insufficient data for a proper evaluation of the system. Please let me know if so is the case and I will provide the required info.

Comments and advises are highly appreciated!

Best regards,
Robert

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