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IB Slingin
09-18-2007, 08:29
I filled my tanks a couple of months ago and recently hurt my knee. I dont believe I'll be going diving soon:smiley19:. Is there a shelf-life on fills? Thanks.........

WV Diver
09-18-2007, 08:38
Not really, as long as the tanks are not contaminated and they should not be, an air fill should last from one annual visual inspection to the next.

ScubaToys Larry
09-18-2007, 08:39
On aluminum tanks, there really is no problem. Nothing happens to the air in there. With steel tanks, people would worry for long storage times as if there was any moisture in the tank, the rusting process (oxidation) might affect O2 levels in the tank. Now that's what they said... but I doubt there would be much O2 reduction - maybe someone who knows something about that can chime in... but for an aluminum tank, I've used some that I had filled 8 months earlier and left in my Garage. (But maybe that explains this weird tic I have? :smiley2:)

willardj
09-18-2007, 08:47
I filled my tanks a couple of months ago and recently hurt my knee. I dont believe I'll be going diving soon:smiley19:. Is there a shelf-life on fills? Thanks.........

It's not the shelf life on the gas. It's the prolong stress on the tank that a person should worry about. The prolong stress on a tank is what can be a problem when hydro comes around.

IB Slingin
09-18-2007, 09:37
Thanks guys! Actually Larry, I got the tanks from you. They are steel 100's filled to about 3400-3500 psi. Do you guys think I should bleed them out or leave them alone? I hope to get wet in a couple of months. Im in Miami, so water temps. aren't really an issue.

skdvr
09-18-2007, 09:57
On aluminum tanks, there really is no problem. Nothing happens to the air in there. With steel tanks, people would worry for long storage times as if there was any moisture in the tank, the rusting process (oxidation) might affect O2 levels in the tank. Now that's what they said... but I doubt there would be much O2 reduction - maybe someone who knows something about that can chime in... but for an aluminum tank, I've used some that I had filled 8 months earlier and left in my Garage. (But maybe that explains this weird tic I have? :smiley2:)

I read on scubaboard one time about this subject and someone replied that seemed to be ALOT more educated in this area than I am and they said that the entire inside of the tank could be completely filled with rust and the O2 levels in the tank would still be fine. Obviously that is not their exact wording but that was my take on it.

I will see if I can find it and post a link...

Phil

ScubaToys Larry
09-18-2007, 10:00
Thanks guys! Actually Larry, I got the tanks from you. They are steel 100's filled to about 3400-3500 psi. Do you guys think I should bleed them out or leave them alone? I hope to get wet in a couple of months. Im in Miami, so water temps. aren't really an issue.

As long as you are pretty sure the place you filled them has good filters and hasn't filled them with moisture - you should be fine. Let us know after the dives how it turned out... and if we never hear from you, we'll know I was wrong. :smiley2:

jo8243
09-18-2007, 10:45
IF you're worried about reduced O2 levels in a steel tank there is a simple and conclusive test... use a nitrox O2 analyzer and see if it is still 21%. I doubt there will be any problem.

skdvr
09-18-2007, 11:17
OK, well I could not find it at scubaboard so I posted a new one and someone said that the University of Rhode Island did a study on it and after 3 months the cylinder only contained 15% O2. Now I do not know how much rust was in there but 15% would not be healthy to breathe. Here is a link (http://www.scubaboard.com/forums/showthread.php?p=3105853&posted=1#post3105853) to the post at scubaboard. I am sure that there will be a few more responses...

Phil

quasimoto
09-18-2007, 12:10
There are several sites that I have seen the rusty steel tank issue. Also it takes a good deal of time for a tank to rust a lot. Of course conditions change and could cause the tank to rust faster. Right now I have a set of LP77's that I haven't dove in 5 months..I'm not worried about the air even if there is water in the tank.

willardj
09-18-2007, 12:12
Thanks guys! Actually Larry, I got the tanks from you. They are steel 100's filled to about 3400-3500 psi. Do you guys think I should bleed them out or leave them alone? I hope to get wet in a couple of months. Im in Miami, so water temps. aren't really an issue.

I would bleed them down to at least 1500 or less just to be safe.. If it's only air you want be losing much. Air is cheap.

jo8243
09-18-2007, 13:40
OK, well I could not find it at scubaboard so I posted a new one and someone said that the University of Rhode Island did a study on it and after 3 months the cylinder only contained 15% O2. Now I do not know how much rust was in there but 15% would not be healthy to breathe. Here is a link (http://www.scubaboard.com/forums/showthread.php?p=3105853&posted=1#post3105853) to the post at scubaboard. I am sure that there will be a few more responses...

Phil

I wouldn't recommend using a tank of 15% but for arguments sake it will still sustain life at the sea level. And at depth it will for sure because every 33 feet the partial pressure will go up.....

Of course if there is that much rust in there the air would have to "taste"/smell funny and probably have particles in it you wouldn't want to breathe anyway.

CompuDude
09-18-2007, 14:26
If you are storing the gas for under 6 months, don't give it a second thought. Seriously. People keep tanks full over the winter all the time, in those areas where winter is a legitimate concern (unlike SoCal).

Between 6 months and a year, I would consider bleeding them down to 500 psi (for storage), and getting a new fill before diving.

Over a year, definitely bleed it down lower and get a new fill before diving.

If you have reason to suspect moisture has gotten into your tank, I wouldn't wait one week, let alone several months to drain the tank and have it inspected.