The ball is stainless also. Not sure of seat material. The valve is used to divert between two safetys and each has a .25 purge valve to bleed off pressure for maintenance.
Welcome to the board. For oxygen piping systems I'd recommend using CGA specification G-4.4 "Oxygen Pipeline Systems". Our company uses CGA religiously for stuff like this.
Per G-4.4, para 4.2.5.3, "Materials that are found to be flammable within the very high pressure range [which this falls into] should be subject to oxygen gas velocity limitations as indicated in 4.4. Thickness limitations, where applicable, must be observed." Stainless steel is most definately flammable in this pressure range. In fact, Appendix D of G-4.4 lists austenitic stainless steels as being flammable above 290 psig at any thickness.
Because this is a diverter valve, I'm assuming flow inside the valve is going to turn a corner. That is, I'm assuming the ball has an L shaped internal port where any particles in the flow stream are likely to impinge on the inside of the ball. That leads you to para. 4.4.2, "Impingement velocity curve and metallic material selection for piping and equipment". Figure 1 under this paragraph shows that velocity must be less than roughly 15 ft/second. Flow velocity higher than that can result in impingement incidents igniting the stainless steel.
So to answer your question, stainless steel is not suitable for this type of installation because this is a diverter valve for a relief tree and as such, velocities much higher than 15 ft/s are expected. If you can show velocity won't be higher than 15 ft/s, then per the rules you could use it, but it would be considered very poor practice to do so. As EdStainless has eluded to, plastics in oxygen systems (ie: valve seats) are much more readily ignited and are often found to be ignition points in these systems similar to a blasting cap is the initial ignition point for a large amount of explosive. Once you ignite something like plastic inside a stainless valve or pipe, it's all over - call the fire department! lol
A much better material for the ball and body would be those materials listed in Appendix D which includes exemption pressures for all types of alloys. Those that are exempt up to 3000 psi include:
Brass Alloys (Cast and wrought mill forms)
Copper
Copper-Nickel alloys (Cast and wrought mill forms)
Monel 400
Monel K-500
Nickel 200
Tin Bronzes
That's it. Basically copper and nickel and their alloys are what you need to look for in a valve or pipe material for high pressure oxygen. Red brass pipe for example is very common. Monel is very common for balls in ball valves, and brass alloys for the body. I'd suggest getting a copy of CGA G4.4 here:
Thank you for the answer, that helps me alot.
This system was installed over ten years ago, have the rules changed since then or was it installed incorrectly at that time?
Thanks for all the information. Also there are two straight thru ball valves that are isolation valves for gauges, I assume they would fall into the same catagory as the diverter being that they are stainless and I assume some sort of plastic or tephlon seat.
The isolation valves are .25. Again thanks for the help.
The CGA specification looks at velocity and suggests limits on velocity for any SS system. For a pressure gage isolation valve, the chances of getting high velocity gas through the valve is relatively small. A valve there is much less a risk than on the relief valve system, but it still isn't a good material since it will burn if ignited.
The risk for an isolation valve is primarily high velocity when it's opened (if there is a high pressure difference across it when closed) and rapid downstream pressurization and temperature rise due to adiabatic compression. Also, because of the rapid pressurization issue, quick opening valves on oxygen systems are generally discouraged. Using ball valves on an oxygen system increases the potential for fire due to adiabatic compression.
Note that compliance with the CGA code is voluntary so you aren't doing anything illegal by having stainless valves in an oxygen system. It's really just a matter of how much risk you want to accept. Understanding the problem with using stainless steel when designing the system, you can easily avoid them without much, if any, added cost (ie: use brass and monel, and use globe valves instead of ball valves). If you already have a high pressure oxygen system with stainless ball valves in it, the risk of a fire is greatly increased. I don't think people at our company, if we found these issues, would allow the system to continue in use indefinitely. We would make a concerted effort to remove the offending materials.
Again thanks for the help. I tried finding things online but you have to be a member to get the information I need to look at.
I appreciate your help, thanks.
There are some special hard materials for valve seats also, mostly Co alloys as I recall.
The Ox valves that I have used have no non-metallics in them at all.
Lots of great information here, thanks!
I'm looking around for regulators and shut-off valves for a similar system. Is there a particular brand that you favor for high pressure O2 systems? I was looking in ASTM "Safe Use of Oxygen and Oxygen Systems" and it details the preferred valve style for use in O2 systems - non-rotating stem (to minimize particulate generation during actuation). I'm having difficulty in finding a valve of this type in the 2" size range. I'm also wary of installing a 2" ball valve as the main shut-off, I can imagine that eventually, someone is going to snap it open and potentially cause some damage.
Any suggestions?
Thanks
