how long air can be safe inside the tank

[telitalabella]

hi, i live in New York City and i spend 3 months diving in Honduras in the summer, i have most of my gear there, but when i have to como to the states i have to leave my tanks there, i would like to know what is the best way to leave my tank, rigth now i left the tanks with about 500 psi, can i live it full? the air is still good for breathe after 9 months in the tank? . thank you in advance.

 

[GrumpyOldGuy]

One year is a typical value bantered about because it syncs with the 1 year VIP cycle. but some people think more or less.

It really depends on how confident you are of ALWAYS getting a clean, dry fill. If yes, then no worries, 9 months is not an issue.

If there is any possibility you had a wet fill, then I would suggest you have the tanks emptied, inspected and refilled before you depart from a shop with known good clean dry air. This will prevent oxidation while you are away and everything will be ready when you return.

 

[Scared Silly]

If it is clean dry air then it is good for a long time, years. For storage, it best to leave them either full or near empty. I prefer to leave them empty. But have no problems leaving them full so I can dive when I want.

 

[DevonDiver]

I'd warrant that, after a year, the air in your tank will still be fresher and more delightful than any lungful you'd care to take in NYC.

It's a misconception that air goes stale. The only concern is the tank condition. Providing the tank was filled properly in the first case...and has been serviced according to the recommended schedule (annual visual inspection/5 year hydro test) it will be fine.

 

[bleeb]

I'd warrant that, after a year, the air in your tank will still be fresher and more delightful than any lungful you'd care to take in NYC.

It's a misconception that air goes stale. The only concern is the tank condition. Providing the tank was filled properly in the first case...and has been serviced according to the recommended schedule (annual visual inspection/5 year hydro test) it will be fine.

Ditto.

To elaborate, the concern about the tank is also more for steel tanks than aluminum, although it's possible to corrode aluminum tanks too if the handling was bad enough. As previous posters have alluded to, a wet fill or having completely drained the tank underwater since its last inspection can leave water inside. In a worst case scenario, this can dangerously weaken the tank as well as use up most of the oxygen inside within a few months.

For long term storage, it's also a common recommendation to not empty a tank completely, but leave a few hundred psi inside to make sure nothing seeps in over time and have enough air so that you can crack a valve to check whether the thing is pressurized without completely emptying it in the process. Not everyone considers this necessary.

 

[Superlyte27]

A steel tank I feel pretty safe around a year. With aluminum tanks... a few years no problem.

 

[telitalabella]

Thank you very much, very helpful tips.

 

[FritzCat66]

I highly advise reading through this post for more information on storage of gas cylinders than you can imagine.

While the perspective in that post and in the referenced tests are more about the condition of the cylinder rather than the condition of the gas being stored, nevertheless after reading that I would be leery of gas in any cylinder stored more than three months. The tests were 100 days and depending upon the kind and amount of water in the tanks, how much O2 was stored in them, and what pressure, some of them were severely corroded, the O2 level in one had dropped to 15%, and in any case I would not want to breathe that gas.

 

[Superlyte27]

that was salt water in a steel tank. How are you going to get salt water in tank except by bleeding the tank to 0 underwater in the ocean during the dive. If you do that, and don't do a VIP, you are dumb, and deserve what you get. That is all. Goodbye

 

[FritzCat66]

Yes, we were all exposed to your opinions on the matter on the Bleed old air from tank? thread.

From one of the studies: "The fresh-water aluminum cylinder that was stored vertically but inverted showed substantial internal corrosion despite having fresh water, not salt water. Wall thickness was preserved but pits were as deep as 0.047 inches. Residual oxygen was measured at 20.9 percent."

So, even with the best case - freshwater and an aluminum cylinder - the risk might be small, but it's there, and it's measurable. With my own steel tanks these days, based on that information, if I were not planning to dive them in more than three months, I would put a low-oxygen mix in there, keep them at a minimal pressure only (like 200psi), and store them vertically. I might not have a viz done before I used them next, but of course I would get a fresh fill.

The OP should have the facts on hand, as well as the bluster, and consider both. It all comes down to our personal decisions.