Cylinder storage

[Shipwreckscanada]

When storing my steel cylinders, what is the lowest psi needed to avoid rust?

Also, how long in advance before a dive can I have my cylinders filled. Does the air slowly leak out after a number of months?

 

[Kunundrum]

when storing a cylinder you want 100-200PSI or a Complete fill. this is for safety in case the cylinder is exposed to fire.

If the Cylinder never got water in it, and the fills were with good dry air it will be ok.

 

[Scared Silly]

Any pressure above ambient is fine. As said above either 100-200 above or full. If gas is leaking out there is a problem.

 

[GrumpyOldGuy]

I am being picky, you don't need any pressure to prevent rust. If the gas in the cylinder is dry, it wont rust. If the gas has moisture present, it will rust at any pressure.

You need a little pressure to A) keep water from entering through the valve should it get soaked and B) to prevent the fill station from demanding a VIP.

I store mine full so I can use them whenever possible on short notice. Some of mine go up to 6 months between use and are still full (no detectable leaks).

 

[Shipwreckscanada]

Am I to understand that I must have between 100 and 200 psi or a full cylinder? Does this indicate that I need to remove air if I have 1000 psi for example, or fill it up?

 

[supergaijin]

Anywhere from 2psi to 3400psi is fine.

Full is better IMO.

 

[chrpai]

How long are you storing them for? It might make sense to just sell them and buy back used ones again down the road.

 

[Rich Keller]

As long as the tank is pressurized you will keep out any moisture. The only other thing you should do is store it upright. If there is moisture in the tank when you store it you want the rust to form on the thicker bottom part of the tank rather then on the thinner sides.

 

[GrumpyOldGuy]

There is a theory that if the tank is in a fire, a full tank will empty itself via burst disk rupture before the metal softens from heat and "explodes". If the cylinder has 100-200psi, it will not rupture the bust disk but the pressure is not enough to not bee a big concern. Someplace in the middle, the pressure build up from heat combined with the soft metal (from the heat) will cause a bigger problem and injure fire fighters.

I am not sure if this has been proven to be a problem, but that is one reason why many people recommend either 100-200 or full tank. Its a long shot. The only time I lower the pressure for long term storage is with the old AL tanks (20yrs+) with bad alloy that are suspect to SLC (Sustained Load Cracking). I find storing tanks full ensures I make the most out of every dive oppertunity.

 

[halocline]

As long as the tank is pressurized you will keep out any moisture. The only other thing you should do is store it upright. If there is moisture in the tank when you store it you want the rust to form on the thicker bottom part of the tank rather then on the thinner sides.

This is a bit of an old school truism but PSI (and the DOT, presumably) makes no distinction between pit depth/size on the bottom of the tank and on the sides. Just make sure your air is dry (how exactly to do that is a little trickier!) and store them in whatever position you want.