Duration of Charged Cylinder Storage

[MusicManBlue]

I always like to be ready to dive -

I have two steel 100 HPs, and various other bailout bottles to tote about with me.

Recently, due to the closure of my local quarry, I ended up with all my tanks gussied up and no dance to go to!

What are the considerations for how long you should/can leave a tank charged in storage? I have HP and LP tanks, which may be one variable.

Thanks for any experience out there!

 

[tbone1004]

Not great to leave them full to working pressure for extended periods of time, but isn't really going to kill them. Before you dive, make sure to put an O2 analyzer on them to make sure nothing oxidized in there which would be bad.

How long are you planning on having to store them? If it's going to be beyond when their next VIP is due, then I would say try to find somewhere to burnt he gas down to around a grand or so and then leave them until your next vip.

 

[halocline]

I don't think there's any evidence that storing tanks full causes any problem at all, so don't worry about it. There's an old-school idea about storing tanks either completely full or close to empty in case of a fire. The thought is that if they're full, the burst disc will blow as the tank heats up before the metal fails due to heat, and close to empty they're not a hazard even if they fail.

I would be a bit concerned about a wet fill, though, with steel tanks, as tbone mentioned. If there's any moisture inside, it will oxidize, maybe damaging the tank and lowering the O2 content of the air.

 

[akdeepdiver]

If your a public safety diver, or use them for lifesaving purposes then 29 CFR and OSHA says they need to be drained and refilled annually. If they are for personal use, there is no regulatory limit. Like a previous poster said, hook them up to a analyzer just in case before you dive, and then hit the water.

 

[spectrum]

I was diving 2 year old air this summer with to ill effects, that's a few data points. They were mostly HP steel.

Sustained Load Cracking is a phenomenon usually associated with aluminum cylinders, 6351 alloy in particular. Unless you are nursing some of those along there's no need to fret.

In terms of fire, a full cylinder is expected to activate the burst disc before failure. A low fill, like 500 PSI or less has limited energy and is usually considered low risk. Thoughts are that there is a middle range where there is enough pressure, especially when the gas is heated to cylinder failure temperatures that there is an energy release risk.

There have been calculations posted that a cylinder would be a pile of dust before corrosion could meaningfully deplete the oxygen content. I read it, I didn't validate it so take it as such.

If we're talking about storing over the off season i would leave the fulls alone and bleed the partials down low.

 

[Doc Harry]

Not a lot of hard data to answer your questions. There are a few small studies from 40 years ago - too small for any statistical power - so expert opinion is all you got. Many non-experts will ridicule the expert advice. You need to make an informed decision about what you will do.

Long-term storage is no big deal, unless you have water in your cylinder. Water causes corrosion, which can be especially problematic for thin-walled steel cylinders. The ONLY way to tell if your cylinder contains water, and is at risk for developing a problem, is to drain that tank and inspect the interior.

Alternately, analyze the gas of your cylinder before use. If there is any drop in O2 or rise in CO, then you have a serious corrosion problem inside. If your O2 is fine, then your tank was probably put away dry. There is one recorded death from low pO2 caused by corrosion - but the tank was so poorly maintained, and was way overdue for a visual inspection, that a similar scenario is unlikely to happen again.

After one year of storage, drain the tank and get a visual inspection.

Higher pressure = higher pO2 = accelerated corrosion, so if you have a choice store the tank with only a few hundred PSI. As far as the tank itself is concerned, if the cylinder is still within hydro then storing at full pressure is not a problem as long as there is no moisture in the tank.

The bottom of the cylinder is thicker, so store the tank upright - if there is any water then the corrosion will be focused on the thick base.

Aluminum cylinder storage is much less complicated.

Again, much of this expert advice is based on old, small studies from 40 years ago. The studies were too small to have any statistical power, but a "common sense" review of the studies leads to some logical conclusions that form the basis of expert opinion.

Bottom line is that the current recommendations for cylinder inspection and maintenance schedules are based on decades of problems, explosions and deaths. If you take care of your tanks, then many of the problems that have occurred in the past will be very unlikely to happen today.

http://www.scubaboard.com/community...er-long-term-storage-fact-and-fiction.260189/

 

[beester]

The air you fill your tanks with is millions of years old in any case ;-) So at least from that point of view there is no expiration date on it .