Storing a tank

[Jay82]

I just bought a Faber 12L tank and i dont know whether its best to store them full or with 15-20 bar left in it? I heard a while ago that storing tanks full was a bad idea (cant remember why), however just recently i was told that it was better to store them full so now i am a bit confused. Having never owned a tank before it had never occured to me! whats the general consesus?

 

[knowone]

I was going to say like mine start in a corner follow a wall until you reach another corner and then some in another room but instead I grabbed a mallet and whacked a few and some are full and others are empty and some have no valves and a few are outside and some are in NSW and others in VIC and then I wondered why you want to store it if you just bought it so now I'm back and typing into my computer machine
"storing scuba cylinders"
You have made an excellent choice but I suppose they are the most predominant tank in the country so best wishes.
Very good.

 

[DA Aquamaster]

Storing a steel tank full has no real downside, and the advanatage, at least in the US, is that storing it full will ensure that in a fire the burst disc will rupture and release the gas before the tank fails. For a Eurpoean tank where burst discs might not be used, the safety of a full tank in a fire is highly questionable.

At the other extreme, if stored near empty (a few bar or a couple hundred psi) then it is unlikely the tank will burst in a fire even if a burst disc is not used, so it can be argued that the near empty approach is safer if no burst disc is present.

What you want to avoid in either case, is storing the tank half full and creating a situation where the tank may rupture before the burst disc fails (or fails as no burst disc is present) with enough pressure to do serious damage when the failure occurs.

------

Then there is the practical side. Air is cheap so if I am storing the tank, I either fill it or drain it. Trimix on the other hand is expensive, so I am not likely to dump 1200-2000 psi remaining in a set of doubles or in sidemount tanks if they have trim mix in them, but I also may not want to top it off as it may not be the mix I want on the next dive. So they get stored with what they have in them.

 

[tech3324]

Charlie Royer's book Scuba Equipment Care and Maintenance recommends "Always store the tank with at least 200 to 300 pounds of air pressure in it. Never allow a full tank or an empty tank to sit for extended periods of time. The tank should be stored in an upright position in a cool place."

I think the reasoning behind storing it upright is to allow any interior rust or pitting to occur at the bottom of the tank where the metal is thicker making removal easier.

 

[Doc Harry]

There are already at least 1,000,000 threads on this topic.

Here are but a few threads that I found on a cursory search on "storing a tank":

http://www.scubaboard.com/forums/tanks-valves-bands/260189-scuba-cylinder-long-term-storage-fact-fiction.html

http://www.scubaboard.com/forums/tanks-valves-bands/284901-proper-way-store-tanks.html

http://www.scubaboard.com/forums/basic-scuba-discussions/282858-does-nitrox-tank-rust-more-inside.html

http://www.scubaboard.com/forums/basic-scuba-discussions/254495-scuba-tank-storage.html

http://www.scubaboard.com/forums/new-divers-those-considering-diving/250808-air-time-tanks.html

http://www.scubaboard.com/forums/tanks-valves-bands/321408-understanding-moisture-water-cycle-tank.html

http://www.scubaboard.com/forums/tanks-valves-bands/338895-safe-tank-storage.html

http://www.scubaboard.com/forums/basic-scuba-discussions/348117-new-tank-owners-guide.html

http://www.scubaboard.com/forums/tanks-valves-bands/354174-how-long-air-can-safe-inside-tank.html

http://www.scubaboard.com/forums/tanks-valves-bands/304692-able-stop-rust-inside-tank.html

 

[Troutmaster]

Aluminum tanks should be stored full, because of failure in a fire. When an aluminum tank gets really hot, the metal weakens and if there is not enough pressure in the tank to pop the burst disk before this occures it can be a bad day for the firefighters.

Steel tanks do not weaken as much so it is unlikely they will fail if not full. Best to store them with 2-300 psi in them. Lower pressure also lowers the speed of corrosion in the tank if any water got in. Likewise, if you had a an oxygen rich mix, best to bleed it off and fill it with air.

Having said that, I don't do any of that. I leave my tanks stuffed full of whatever I am likely to use next.

 

[spectrum]

Troutmaster

Aluminum cylinders are best not stored full for long periods especially those 6351 cylinders that are still in service. Unlike steel, aluminum is subject to sustained load cracking. For aluminum the low holding pressure is safest for the cylinder and in the event of high heat exposure there will be a limited energy release.

 

[DA Aquamaster]

Aluminum tanks should be stored full, because of failure in a fire. When an aluminum tank gets really hot, the metal weakens and if there is not enough pressure in the tank to pop the burst disk before this occures it can be a bad day for the firefighters.

Steel tanks do not weaken as much so it is unlikely they will fail if not full. Best to store them with 2-300 psi in them. Lower pressure also lowers the speed of corrosion in the tank if any water got in. Likewise, if you had a an oxygen rich mix, best to bleed it off and fill it with air.

Having said that, I don't do any of that. I leave my tanks stuffed full of whatever I am likely to use next.

I agree with the theory and I also mirror your actual practice, but also note that the practice means more than the theory.

I am really anal about my tanks, do my own VIPs and O2 cleaning. I am also very picky about the gas that goes in my tanks.

In the last 3 years I have kept track of individual tanks and I have noted that my steel deco botles with 80% and 100% are still perfect inside with no flash rust. Obviously, without moisture, high FO2s make no difference.

I have made similar observations with most of my nitrox tanks and in the one case where I noted flash rust and tumbed a tank in addtion to re-cleaning, it was evident from the pattern of water/flash rust streaks in the tank that water had been blown in from the valve - most likely from water hiding in the DIN valve or being introduced from a wet fill whip or getting splashed into the valve when filled in a water bath (common in N FL.)

The population of steel tanks sampled includes 7 sets of doubles and or sidemount bottles and 4 deco bottles, (plus two sets of double steel 72's that see nothing but air). Not a huge sample, but more than the average diver.

So my thoughts are that if you are using good quality gas that is suitably dry and ensure the valve is dried/water blown out prior to the fill, rust is a non issue and moisture is a far greater factor than FO2.