How long can an AL80 sit full?

[TeddyDiver]

There was a thread concerning this issue in some board a while ago. There was stated that there have been two different al alloys used to scuba tanks. The other, used today, is safe stored full. The other have had some tank explosions cause of the stress of the pressure. Anyway this alloy haven't been used after '78 (if I remember correctly)...

 

[hardhat]

When I took my PSI course a few years back I was tought that an aluminum cylinder stored at full preasure long term (around a year) can bulge and the neck threads can also crack. In the shop I work in I have seen cylinders come back from hydro and fail it's visual inspection when the visual plus part of the VIP is done. Now we done a VIP on every cylinder going out to hydro before it goes out. Visual plus is an Eddy Current (similar to sonar) inspection of the threads of the cylinder that is preformed on aluminum cylinders each year when the VIP is done. We have found cracks in the threads that you can not see, but are very dangerous none the less. If you are interested in finding out more about the Visual Plus System take a look here http://www.visualplus.net/. Air as a general rule of thumb, we say after six months in a cylinder don't bother breathing it, get it replaced.

 

[redacted]

When I took my PSI course a few years back I was tought that an aluminum cylinder stored at full preasure long term (around a year) can bulge and the neck threads can also crack. In the shop I work in I have seen cylinders come back from hydro and fail it's visual inspection when the visual plus part of the VIP is done. Now we done a VIP on every cylinder going out to hydro before it goes out. Visual plus is an Eddy Current (similar to sonar) inspection of the threads of the cylinder that is preformed on aluminum cylinders each year when the VIP is done. We have found cracks in the threads that you can not see, but are very dangerous none the less. If you are interested in finding out more about the Visual Plus System take a look here http://www.visualplus.net/. Air as a general rule of thumb, we say after six months in a cylinder don't bother breathing it, get it replaced.

Are you failing Al cylinders based on the eddy test result even when no crack can be discerned by eye? If so, what types of cylinders are you applying this criterion to?

 

[Charlie99]

Now we done a VIP on every cylinder going out to hydro before it goes out. Visual plus is an Eddy Current (similar to sonar) inspection of the threads of the cylinder that is preformed on aluminum cylinders each year when the VIP is done. We have found cracks in the threads that you can not see, but are very dangerous none the less. If you are interested in finding out more about the Visual Plus System take a look here http://www.visualplus.net/. Air as a general rule of thumb, we say after six months in a cylinder don't bother breathing it, get it replaced.

Are you using Visual Plus III for the 6061 tanks, or the older Visual Plus eddy current testing systems?

Luxfer only approves the new III system for inspecting today's 6061 tanks. There were way too many false rejects of good tanks.

http://www.luxfercylinders.com/support/faq/sustainedloadcracking-australia.shtml#q9

When I took my PSI course a few years back I was tought that an aluminum cylinder stored at full preasure long term (around a year) can bulge and the neck threads can also crack.

And what type of cylinders were your instructors referring to when warning of this sustained load cracking? If you look into it a bit, you will find the SLC is a problem only with the older 6351 alloy.

 

[Trisha]

This is not a newbie question -- it's a great question!
Thanks, and I'm bookmarking it for future reference.

 

[ChrisA]

How long can you leave an AL80 filled? I don't think there is a limit. You may
want to get a tank inspected once a year and they have to empty the tank
to do the inspection.

I only fill my tanks every few weeks. I dive two or three days a week but I
own five tanks

I think most shops keep thier rental tanks full so they can just hand them out
they likey set around for months, some of them.

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

 

[SDAnderson]

Full or nearly full won't realistically impact the lifespan of the tank. Empty is bad since it can result in contamination, especially by humidity, and damage or destroy the tank. As a general rule, if you're planning on storing your tanks for more than a few months, the recommendation is to drain the tanks until there is only a couple of hundred pounds remaining in them and then to stand them in a cool dry place with the valves covered. I drain mine down to about 200 psi and then crack the valve once a month or so to make sure I haven't lost positive pressure.

Aluminum tanks can be stored full for a long time without major issues. I wouldn't breathe them after a year, but I don't have any science to back that up with, just cooties.

Steel tanks may rust enough on the inside to reduce the oxygen levels in the gas. Leave them alone for more than a month or two and you should analyze the gas before you use it or just replace it.

Remember, it's just a fill. When in doubt, dump the gas and start over. Always smell and taste any gas before you breathe off the tank and if it seems funky, dump the gas and have the tank inspected. And if you have a tank full of gas for more than a couple of months, you aren't diving as much as you should.

PSI Visual Cylinder Inspector #13092
TDI Advanced Gas Blender #117127
Reformed Dive Shop Monkey

 

[StSomewhere]

Steel tanks may rust enough on the inside to reduce the oxygen levels in the gas. Leave them alone for more than a month or two and you should analyze the gas before you use it or just replace it.

This is why IMO you should always analzye the contents of any cylinder that has been sitting around a while. Regardless of what you think was in it (even air), check it to be sure.