So, trying to get
this straight... I think what I'm taking from all this is if I use a high
pressure air system for my ballast and high pressure O2 and on my vents and my
depth gauges, use SS on everything. The wall thickness needs to be .035 and as
far as how I connect the tubing, I'm still confused. Also any recommendations
where to order from?
Thanks,
Scott Waters
Sent from my U.S.
Cellular BlackBerry® smartphone
Date:
Sun, 6 May 2012
18:14:43 -0400 (EDT)
Subject:
[PSUBS-MAILIST]
Fittings for O2
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.