ANSI 900 ball valves

[CRG]

I am reviewing several ANSI 900 # pipe specs that are used for the oil & gas industry in this area. Several of the pipe specs, call for gate valves instead of ball valves for sizes ½” to 1 ½”. Ball valves are allowed for larger dia. (ANSI 900 RTJ flanged 2” to 24 “) and smaller dia.(threaded instrumentation valves ¼” to 3/8”). In several of the valve specs from (different oil companies & large engineering firms) it states for ½” to 1 ½” to use gate valves. The gate valve specs call for SW ends. Can anyone tell me why socket weld or flanged ball valves are typically not used for sizes ½” to 1 ½” in this pressure class? Or is this just because it is a local custom that has unknown roots? Is this concern for seal damage from welding a 900 # pressure class SW ball valve? The same companies allow 800 API SW ball valve for 600 # spec. Service is B31.3 hydrocarbon gas, oil, or condensate.

 

[Scipio]

Not entirely sure where 'this area' is, however my company does something similar, requiring gate valves instead of ball valves smaller than 2". On our specs, however, this applies across all pressure classes, but only in sour service, which is something fairly common in specs I've seen in my area, which is the Alberta oilpatch.

Our reasoning, based on experience, is smallbore ball valves are simply less reliable off-the-shelf than smallbore gate valves in terms of positive isolation. A lot of time they're just a simple three piece body screwed or through-bolted together, with seals not much more complicated than simple o-rings. After a year or two in service, it's about 50/50 whether or not they'll actually hold, with chances of holding obviously falling off with rising pressure. This is regardless of NPT or socket-weld ends.

That said, it is possible to buy ball valves that are more reliable, however at this size it's easier to just go with more reliable gate valves.

 

[TD2K]

I am not used to seeing many ball valves used in oil and gas installations (upstream and downstream) I've been in. However, on one facility in the North Slope, they used ball valves pretty much exclusively for everything including the smaller 3/4" and 1" sizes as well as larger for oil and gas up to class 600. They also used class 2500 for their gas reinjection but off the top of my head, I'm not sure what the types of valves they commonly used in this service.

When I asked operations how they liked the ball valves, they said they worked well, they had few problems and were quite happy with them. The ball valves in the smaller services were used for throttling in lots of cases and again, Operations said they worked well and did not have problems later providing a good shutoff. If you are interested, I can likely dig out the specs and see if they were flanged, SW or threaded ends. I suspect they were SW but I'm not positive.

 

[CRG]

Hello TD2K,

Odd you should mention the North Slope. One of the pipe specs I referenced above is ARCO’s 900 # spec for hydrocarbon service. The spec came from a North Slope project.

CRG

 

[TD2K]

It wasn't Arco so that should narrow it down a bit for you