Balve valve throttling characteristics

[geoffreydavies]

We have a 24-inch full bore pipeline ball valve in shut-off service in an isolated desert oilfield location.
Normal duty is valve closed with 60 bar on one side and 15 bar on the downstream side. Questions / problems:
1. What are our chances of using this valve for a short time to flow into the low pressure side. Downstream line rating is OK for the 60 bar, it is potential damage to the ball valve that concerns us.
2. We have concerns that we might not be able to open the valve against the dp anyway.
3. We want to flow 75,000 barrels of oil a day into the downstream side - is there anywhere we can find valve characteristics of large diameter ball valves in throttling service?

Any help appreciated. We know we probably should not be trying to do this but finding definitive guidance is proving difficult

Geoff

 

[Cirrus9]

Cv of a 24" Grove B ball valve:
310 at 15 deg. open;
560 at 20 deg open;
1390 at 30 deg open;
2600 at 40 deg open
4500 at 50 deg open
7800 at 60 deg open
13150 at 70 deg open
27000 at 800 deg open
98600 fully open.
You need to calculate the Cv for your conditions and determine at what percentage open your valve will be.
Your flow rate is very low for a 24" line. The Cv for your conditions (assuming crude oil with 870 kg/m3 density) is 25, that means the valve should be almost closed. You will not be able to control the flow rate with this valve.
I would install a real control valve downstream of the 24" valve. The size might be 6" ANSI 600.

In regard to damage to the 24" valve, you can ask the valve manufacturer, but I do not believe it will be a problem if you will operate for a few hours.
If the valve is manual operated with a gear operator you will be able to open it. You need to turn the ball only a few degrees.

Let me know if my answer helped.

 

[bh1999]

Does the valve have steam purge ports? The manufacturer may need to know this because there may be things you can do with steam pressure to prevent build up in the valve body. Depending on the design of the valve throttling may not be possible if there are contaminates in the fluid. Closing the valve again is the concern.