Ball Valve Sizing matters? 1

[oredigger]

Just got brought into a project team for topside facilities upgrade for subsea well. Been doing drilling engineering for last 10 yrs and am quite rusty on facilities.

I was looking over some drawings of the flowline boarding the platform (5" w/ 3.5" ID.)and noticed that the 4" boarding valve that is being installed had an ID of 2.60". Piping on each side has 3.5" ID. We essentially have a positive choke in the line. We plan on producing ~ +40 mmscfd of dry gas @ ~9K-10K flowline pressure.

I asked the young engineer who specified the valve as to whether the high rates across the valve may cut it out. He said at such high pressure we should be able to easily push the volume through the valve w/o problems. i agree with that, but how much damage will the valve be subjected to at those rates?

Are there manufactured recommended max flow rates through ball valves?

Any help would be appreciated.

 

[BigInch]

Pipeline seems to be small diameter for 40 MMSCFD, but you have very high pressure, and a rather high velocity if I'm not wrong.

For production, you'll probably get a lot of sand, right, in which case, cutting out the valve is probably going to happen eventually.

What's wrong with a full port ball, too expensive?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[oredigger]

We have sand control in place, so hopefully sand will not be an issue. Getting a full port 4-1/16" 15K ball valve may be a problem given they want to bring the well online in 4 weeks. The high velocity will probably cut the ball, but will it also cut out the body?

i agree with you that the flowline (3.5" at 22 miles long) may be a bit under sized. Down sizing everything was the only way to make the project economical. Of course now they want to produce it at rates in which it should have been designed for.

 

[MikeHalloran]

I really hate hearing the word 'hopefully' in an engineering discussion. It bodes ill.





Mike Halloran
Pembroke Pines, FL, USA

 

[zdas04]

The velocity in the valve will be around 20 ft/s, the pipe on either side of it is around 11 ft/s. Neither number is very high for normal gas density of around 0.2 lbm/ft^3, but your density at that pressure is nearly 32 lbm/ft^3. This causes you to need to look at allowable liquid velocites. At that density, most companies would limit the flow to 18 ft/sec.

It looks like a reasonable application for the heavy-wall 4-inch but the reduced port valve is too small and could very well have major erosion issues in a short period of time even if your sand-control is perfect (it never is).

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[oredigger]

David,

thank you for your help. I plan on getting in touch with the valve manufacturer to make sure they are comfortable having their valve in this type of service.

again, thank you for your help.

John

 

[zdas04]

John,
The problem with going over the "critical velocity" (I hate that ambigious term, but I don't have a better term for the onset of errosion) is that it will scrub the passivation layer on the mild-steel parts of the valve (the ball will be stainless, but the body won't) and leave it open to several kinds of attack. This is often called erosion-corrosion and can be very agressive. The valve manufacturer my be fine with the velocity (he probably will be) from a pure velocity and noise perspective, but I still wouldn't do it from a long-term performance standpoint.

I just get chicken when dealing with 9,000+ psi and 40 MMCF/d since a failed component can have such huge health, safety, and economic impacts.

David

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem