|
Excerpt from UPDATE TO THE OXYGEN HACKER'S COMPANION. This
appears to be a good, concise discussion of the different materials to be used
with O2. Note the last sentence of the second paragraph.
For metal parts, brass in
definitely the metal of choice when it comes to HP O2. It doesn't spark and
doesn't (for all practical purposes) burn.
Aluminum and titanium are definitely out - they ignite easily and burn violently in the presence of HP O2. Steel is not a good choice either - it burns, as anyone who has ever used a cutting torch knows. But the big problem with steel is that it sparks so readily, making it a prime potential source of ignition. SS falls somewhere in between. While it doesn't spark or burn nearly as easily as steel, it is not completely immune. The catch is, even good brass fittings are often rated only for only 1500-2000 psi, (100-133 bar), and rarely for more than 3000 psi or so (200 bar). For higher pressure systems, then, there really isn't any affordable choice but stainless steel, and just about everyone uses it. It's hard to get a definitive answer on how suitable SS really is for HP O2. The first editions of this book cautioned against it, based on recommendations in several NASA publications, but dig a little deeper and you find that for every one that says not to use it there seems to be another that says it's OK. While the NASA Glenn Safety Manual says that only iconel or monel are suitable for high pressure O2, the NASA Safety Standard For Oxygen Systems NSS 1740-15 says that "Stainless steels are used extensively in HP O2 systems" and that "few problems are experienced with the use of SS storage tanks and lines" but that "ignitions have occurred in SS components such as valves at high pressures and high flow rates", though they are probably talking about pressures much greater than the average nitrox whip sees (both documents are available on the web). And the CGA specifies that valves for O2 tanks should be made of either brass or SS. |