Choice of Valves: Gate vs. Ball

[TJAvery]

I'm doing some research into the choice of valves for subsea service. What are the advantages and disadvantages of using ball valves instead of gate valves?

Some details of the intended service:
• high design pressure: >70 MPa (>10.2 ksi)
• bore sizes: 13 to 18cm (5" to 7&quot
• valves will have a geared operator, and be operated by ROV
• water depth is >1000m (>3,281 feet)
• the frequency of operation will be only a few times during the design life (~25 years).
• valve should be open for all of life, but could be closed at some point
• operational fluids will be raw, directly from a subsea well

many thanks,
TJAvery

 

[11echo]

I have to admit I don't have a lot of sub sea experience, BUT I see one advantage/disadvantage ...ball valves are a 1/4 turn operation, so it would be a minimumal operation to open and close ...even with an ROV. Gate valves would require more of an effort to do the same operation. Cost would be more of a draw at those sizes I suspect. My 2 cents anyway, GOOD LUCK! ...Mark

 

[pennpoint]

TJAvery
I will echo, 11echo's post, but add that operating one, two or "a few" times in twentyfive years warrants some consideraton to crustation growth and corrosion. This has been done before, the requirements are not new! Search subsea valve sites, etc. Call and discuss your needs with various manufactures. Check with experienced fellow engineers within your company.
The last thing you want to have happen in a really critical situation is THAT valve's failure to close when you really need it to.

Good Luck
pennpoint

 

[abcmex]

I agree that you need the comment frome someone that has done this before (not me!) but I will comment:
a) even with a 1/4 turn valve I would be very careful when closing a long piping system, if you do this too fast with flow you could have transient pressure peaks (geared actuator is a good thing).
b) I suppose the fluid may have solids and this could prevent a good closing of a Gate valve and with long periods between action I would feel better with a ball valve. Still, I would follow the advice of pennpoint.
RGS

 

[4carats]

I do not have experience with subsea control valve applications.

Please check with The Valve Doctors, CCI. (Tel:1-949-858-1877)

 

[abeltio]

talking only from the reliability point of view... a question you have to ask yourself is...
is it critical that the valve closes when it should close?
and:
would a valve test (close and reopen) disrupt the service?
if the answer to any of the two questions is YES... then i would consider having two valves in parallel so you can test them periodically and make sure they will operate when required.
By all means the ball valves will have better tightness than the gate valves and will not be subject to the same wear and tear because the erosion will not affect as badly the sealing surfaces.
HTH

saludos.
a.

 

[davefitz]

corrosion and encrustation are big issues- it is a good idea to stroke the valve every few months to be assured it will close when required.

The ball valve can be re-opened if there exists a large pressure drop across across the valve , but a closed gate valve cannot be easily opened if a large DP exists.

 

[Scipio]

I've never worked subsea before, so the general construction of the valves might be a lot different than I'm used to seeing on surface pipelines, however a couple things jump out at me here;

1. 5" to 7" bore pipe? Aren't those rather obscure line sizes?
2. Even if you went with a ball valve, you're correct you'd still need a geared operator with a 10.2 ksi design. Torque on a lever-operated ball valve would probably be in excess of 40,000 in-lbs at full differential, and I doubt an ROV could manage that without the mechanical advantage of a geared operator.
3. I would expect you'd have fewer problems with the ball valve stem leaking over the long run than you will with the gate valve - that 1/4 turn operation does have the advantage of minimal impact on packing. In order to close the gate valve I'd think you would have to hope material (either corrosion or plants/crustaceans) hasn't built up on the exposed stem of the open gate valve, unless it's been sealed with some sort of bellows.

 

[MikeONeill]

If particulate is an issue, and you decide to use a ball valve, a metal-seated ball valve would be in order. Just a precaution with ball valves, if you were to close the valve and bring it to the surface at some point, the ball would trap the pressurized media. You may wish to consider a vented ball.

 

[within]

Try going to a company that makes both types of valve. Weir Valves and Controls manufacture both gate and globe valves. The web site is:

http://www.weirvalve.com/

 

[MikeONeill]

http://www.velan.com/

Velan manufactures ball and gate valves and has an awesome engineering group.