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RedSea
April 27th, 2007, 05:30 AM
Hi all.
For how long is the air considered usable if stored in steel tranks?
I have old HP steel tanks, I take them for visual inspection anually and for Hydro. test every three years and always think about that question.
thank you.

Brandon
April 27th, 2007, 06:04 AM
Question is somewhat answered in this thread:

http://www.scubaboard.com/showthread.php?t=156233&highlight=air+tank+stale

General consensus seems to be at least a year.

-B

RedSea
April 27th, 2007, 07:25 AM
Thanx a lot Brandon.

String
April 27th, 2007, 10:21 AM
In theory it'll last indefinitely if fill from a reliable source.

khacken
April 27th, 2007, 10:29 AM
In theory it'll last indefinitely if fill from a reliable source.

The problem is that oxidation will comsume the oxygen in the air. The recommendation from NAUI is to store the tank partially filled, and get a fresh fill before the dive.

OH-JJ
April 27th, 2007, 10:35 AM
The problem is that oxidation will comsume the oxygen in the air. The recommendation from NAUI is to store the tank partially filled, and get a fresh fill before the dive.

Read the aforementioned thread, basically if you adhere to annual V.I.P.s then you will have no problem as it takes more than a year for rust to have an real effect on the O2 content.

Rick Murchison
April 27th, 2007, 10:37 AM
Uh, most banks are steel...
Rick

caymaniac
April 27th, 2007, 10:52 AM
I've used a two year old tank of air before and seemed to have no ill effects. Of course maybe it could now be an excuse for braindamage ;>). This was from a steel tank that sat in storage. I have 3 steel tanks and one alum., I was rotating the others but never used that particular tank. One reason was the tee valve on it is very old and cannot be replaced, I think the tank was from the 1960's, I bought it used in 1982. I had all my tanks VIP'd and hydro'd at the same time and then filled all. Of course when I emptied the tank, I can't refill it because there is no replacement for the valve. The tank is currently in the back room at the LDS.

String
April 27th, 2007, 12:30 PM
The problem is that oxidation will comsume the oxygen in the air. The recommendation from NAUI is to store the tank partially filled, and get a fresh fill before the dive.

The actual rate and amount has been worked out before and found to be statistically insignificant over a human lifetime. Ditto the myth about nitrox making it worse.

Testing interval here for tanks is every 2.5 years and its quite common to see air in them used after this time. No idea what the test interval requirement here is for aluminium tanks though as nobody uses them other than for stages.

khacken
April 27th, 2007, 03:35 PM
Read the aforementioned thread, basically if you adhere to annual V.I.P.s then you will have no problem as it takes more than a year for rust to have an real effect on the O2 content.

I was just stating the recommendations from NAUI. Of course, they also want you to wet your tank straps before every dive as well.

Some people have zero tolerance for risk. For those people, store your tanks partially filled and top off before the dive.

EDIT: I personally have a little more tolerance for risk, so I would not a have a problem storing a full tank for a year. Of course that is all theory only since I haven't gone for more than a month without using my tanks.

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