Using a Ball Valve to reduce pressure

[giralhu]

Hi everyone,

I'm an Instrument & Control engineer, I'm currently selecting 2 Control Valves that will be installed upstream two SKIM Tanks (two separate lines), hence we will control the amount of water (with 450 PPM of heavy crude API 12 oil) entering the tank.

The control valve will be a 20" Ball Valve (Fisher V150)

Due to hydraulic restrictions inside the tank when it's clean, pressure drop in the control valve would be too big for a regular control valve to work without risk of cavitation, we have some alternatives such as installing restriction orifices but that's not an option here due to the distance to the tank. Downstream the control valve we have a 24" ball valve, we're evaluating using this valve as a restriction so the control valve wouldn't have to provide the required pressure drop by itself.

This ball valve would be adjusted to a 40-50 %open position and would work like this for about 1 year until the tank starts to get clogged again (this is expected)and the operator would adjust the valve position depending on the desired pressure drop in the control valve, until it's fully open. After 5 years the tank will be cleaned again and this process repeats.

I would like to know how much this service could affect the valve materials (ball specially)? do you have experience in a similar application?

Expected Process conditions:
Flow rate min: 357840 barrels per day
Flow rate normal: 511200
Flow rate max: 630000
Temperature: 145ºF
Specific Gravity: 0.982
Dynamic viscosity: 0.45

Thank you in advance and sorry for my rusty english.

 

[mk3223]

Suggest to have different vendors to propose proper valves for the operation conditions as stated, such as Fisher, Flowserve, etc. Also, ask them to provide the application references in the past.

 

[georgeverghese]

Ask for anti cavitation trim on the control valve. Dont know if anti cavitation trim is available for ball type control valves.

 

[1503-44]

You did not mention the most important aspect of control valve selection. Pressures! What is your expected range of both inlet and outlet pressures?

Ball valves do not perform well as control valves. Ball valves should really only be used for ON/OFF services. They will certainly not perform in a satisfactory manner at your intended position setting of 40-50% open. Movement of 0-90% full open is reached within the first 10-20% of travel from closed, so you will get 40% open at around as low as 5% of full travel from the full closed position.

Ball valves are also the most unsuitable type of valve to use for pressure control, for the same reason. If you use a ball valve for pressure control, pressure will pretty much be full pressure or no pressure, so you can forget about controlling it with any degree of precision. With the high density, dirty tank service you propose, gum, seal damage and erosion of ball opening edges could be a problem, if they are left partially open. Remember, ball valves = ON/OFF only.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[LittleInch]

Sounds to me like you've got the wrong size/trim of your control valve.

If you're doing 600000 bpd that's over 4000m3/hr or in a 20" pipe over 5.5 m/sec.

Too much.

Resize your valve.

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