Butterfly Valves and Natural Gas

A pipe pig will pass readily through the open port of a ball valve without significant damage to either, whereas any attempt to do this with a butterfly valve will result in anything from the thing jamming, to the thing being sliced in half to the thing carrying off the butterfly vane ahead of it in fragments.

The differential pressure across the valve when closed also needs to be considered. In principle, ball valves are more resilient in this regard. It is a greater challenge to get a butterfly valve to seat against a high differential pressure than it is a ball valve, which is inherently better able to seal in high differential pressure situations.

Butterfly valves have ready application in the industrial and municipal water sectors, particularly in applications where low differential pressure when closed and large line sizes would preclude the selection of a ball valve, simply on the basis of economics.

thank you Slack

But the lines I am talking about are not require any Pigging , so that ascept is no more important.

regarding sustaining differential pressure across the valve, there are triple eccentric buttefly valve design which can sustain high differenctial pressure apx. 200 bar in any direction. So I thik application of butterfly valves is no more limited to water service only.

Thank you again for your view

Personally I prefer ball valves in smaller line sizes with Low(ish) pressures.

What are your line sizes? pressures? Flowrate?

If the pressure ratings of the valves are suitable I don't see a problem. I've used butterfly valves 100 - 300mm dia. on biogas (those sizes aren't limits, just my experience) but pressure was more like 200 mbar than 200 bar!

Need to watch elastomer selection. If you don't specify, good chance seals and seats will be EPDM, and according to the published data, EPDM is not suitable for methane. I think nitrile or Viton are OK, but I haven't got data to hand, you need to check.

Cheers.........Codey

I would bet you'd have trouble during high pressure differentials of the elastomer coming loose at almost closing position. Also, you may not achieve bubble-tight shutoff, which usually is required for natural gas applications.

A ball valve does not have these concerns.

Although i have only had experience with butterfly valves in marine applications, that experience has not been good. They have a particularly bad habit of not sealing effectively, even after a short period of service.

Personally I would not use a butterfly valve in any application............even if you gave me the valve, because I certainly wouldn't pay for one.

Today one of my students informed me that when his vessel was surveyed a few weeks ago, the engineering surveyor made him remove four sea cocks that were butterfly valves and replace them with gate valves, because of sealing problems and fire risk (the rubber parts) that are present in machinery spaces.

When selecting a valve for any application, the selection criteria is more important than the type of valve - if you identify your needs, the valve type will become intuitively obvious.

In gas applications, I would include two imperitives - leakage and reliability. I would want a valve that has class VI shut off, which does not eliminate leakage but minimizes it. For reliability, I look for valves with a SIL (Safety Integrity Level) of 3 or 4. SIL is awarded to valves that have been cycle tested and is the closest thing to verifying MTBF (Mean Time Between Failure) that I have found.

To eliminate leakage, a double block and bleed configuration is a way to completely stop gas from progressing through a pipe or system.

Of course, there are many other parameters to consider depending on your application. I'll leave the rest to you.