How long can an AL80 sit full?

[Sasquatch]

I've looked around and can't find an answer to this one. Here's my deal: I filled it then the dive was postponed a week. Now I know that the book says if you're storing your tank store it with 200-300 psi, but what about a full tank?

Is this a newbie question or what? LOL!

Thanks in advance!

Dave

 

[Diver0001]

I've looked around and can't find an answer to this one. Here's my deal: I filled it then the dive was postponed a week. Now I know that the book says if you're storing your tank store it with 200-300 psi, but what about a full tank?

Is this a newbie question or what? LOL!

Thanks in advance!

Dave

I don't think there are any real written-in-stone rules about this. I very much doubt that a week will make any difference to the lifespan of the tank. 6 months might.

R..

 

[spectrum]

I've looked around and can't find an answer to this one. Here's my deal: I filled it then the dive was postponed a week. Now I know that the book says if you're storing your tank store it with 200-300 psi, but what about a full tank?

Is this a newbie question or what? LOL!

Thanks in advance!

Dave

Storing it full long term puts a prolonged stress on the tank and should be avoided. You may not realize it yet but the tank actually stretches measurably when pressurized! As for the air it should be good for along time however there are some marginal tyings that may happen. I think in a recent thread refilling after 6-12 months was a common practice. After 12 months the valve needs to come off anyway for the annual visual inspection.

The 200-300 PSI is a holding pressure to make certain that moist or contaminated open air dosen't get in the cylinder.

Pete

 

[Charlie99]

I don't think there are any real written-in-stone rules about this. I very much doubt that a week will make any difference to the lifespan of the tank. 6 months might.

As far as tank lifespan, it might not matter at all if the real problem is work hardening or fatigue caused by cycling the pressure up and down, much like how airframe lifespan is strongly affected by the number of takeoff/landing i.e., expansion/contraction cycles the fuselage has been through.

 

[Diversion]

Just to add a bit to Spectrum's comments....

The 200-300 PSI is a norm for storing 'empty' tanks...

 

[Finnatic]

I'm glad you asked this question as we've just bought our first tanks. They were filled six weeks ago and we have not had an opportunity to dive with them yet. I would not have thought we couldn't store them full for an extended period. We also have a pony sitting full since last year.

 

[Gary D.]

We have something over 50 tanks in the locker. All are kept full except between operations where they might be a few days before they get refilled.

In the past 30+ years we have not had a tank fail a hydro. About 3 years ago we started replacing some or our oldest tanks just because of age as a few date back to the late 60’s.

Gary D.

 

[airsix]

Talk to a metalurgist or a mechanical engineer and they'll tell you that like Charlie99 said - its the number of cycles that cause the fatigue, not the length of time between cycles. Same goes for springs, bolts, beams, etc.

-Ben

 

[Sasquatch]

Thanks for all the great feedback everyone!

Dave

 

[Rick Murchison]

You can certainly store 'em full... I've often had a tank go months between fill and use just because I didn't need that tank for a dive.
However, tanks, especially aluminum, should be stored either full or nearly empty (200-300 psi) as a fire safety precaution. Here's why... if exposed to fire, a full tank will blow the burst disk before the tank heats up to the point that the aluminum is dangerously weakened by the heat, while even a tank weakened by the heat can take the pressure likely to be reached in a tank that starts out with only 200-300 psi in it.
A tank with some intermediate pressure in it, however, may not blow the burst disk, but may have enough pressure in it to cause a catastrophic failure of the tank should the tank temperature get high enough to weaken the aluminum. The guys trying to put out the fire would not be amused.
Rick