How to prove relieving capacity of a PSV Discharge Line

[adf]

Dear Sir / Madam,

I have been tasked with sizing the relief discharge pipework on an offshore oil and gas High Pressure Mud Pump Outlet. The line in question is a relief line for overpressure protection of the HP Mud Pump system on a drilling rig.

There are three, high pressure mud pumps and each pump has a relief discharge line, routed via a Pressure safety valve on each line to a common atmospheirc sump tank.

Each PSV discharge line shall be sized for 'worst case conditions'. ie. Operation of all three HP Mud Pumps through a common header at maximum flow rates + 20% Surge Flow factor, giving a total output from the three pumps of 675.4m^3/hr @ 7500psi.

I am required to size the relief line and prove th relieving capcity of the pipework is sufficient to accodate worst case relief flow rates.

As per API 14E I shall calculate the flow velocities and pressure drops from the pump outlet, 3" inlet pipework, PSV and 4" discharge pipework to the atmospheric sump tank.

I also need to prove that the discharge pipework size / diameter / configuration has enough capacity to cope with the 'worst case' relief flow rate condition - How can I do this?

ie.
How can I determine the total relieveing capacity of the relief line is greater than the worst case relief flow rate condition of 675.4m^3/hr? ie. That the line will adequately clear to the atmospheric sump and back pressure shall not be generated due to insufficient relief capacity?

Thanks & Regards,

u04ajf3

ps. Very good website & resources.

[admin]

Discharge questions are so frequent that I can promise to finish discharge calculator as soon as possible.

In mean time I can suggest you to calculate manually - using discharge formula.

[adf]

Yes thanks - but how can i use that formula to prove the pipe system can cope with the theoretical maximum relief flow rate?

Does that formula calculate the maximum flow capacity of a pipeline?

[PipeFlowCalcs]

q - is maximum flow capacity for known head loss (pressure drop), internal pipe diameter and resistance coefficient of pipe line system.

So, enter head loss in - m, internal pipe diameter in mm and resistance coefficient K, and calculate maximum flow. If it is more than you have to check than relief flow is possible in required amount.

Head loss is pressure difference between head on the begging and on the end of pipe.

Resistance coefficient can be obtained flow known friction factor - f, pipe length and diameter, as:
K=f (L/D)

Friction factor is function of Re number and relative pipe roughness. For full turbulent flow Re is not important.

Pipe exit resistance K=1 should be added also, as well as resistances due to elbows, tees, reducers, or other valves.