How long a tank can remain fully filled?
- Thread starter stargost
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
A tank can remain filled pretty much indefinitely. Obviously thats assuming normal storage conditions. A tank remaining pressurized does not degrade the tank; rather it is the constant pressurizing and emptying of a tank that stresses, loads and stretches on the steel until it becomes weak beyond a point that is safe.
As far as breathing on it- with the cheap cost of air fills, I probably would refill a tank that was more than a year old, although I honezstly think it would be fine for many years. Again assuming normal storage conditions, and no funny odors or tastes were noted when you breathed on it.
Leadking
Contributor
No moisture=no problems
aku321
Contributor
I had a tank that sat about 5 years. Air tasted kind of funny so I had it refilled, no problem.
As long as there is no moisture and no corrosion, a HP steel tank can stay full indefinitely. However, you cannot determine whether or not there was mositure in the cylinder without removing the valve and inspecting the cylinder. 
Therefore, before you can safely use a steel cylinder after prolonged storage (> 3 months) you'll need to test the gas to verify the oxygen content, and to test for the presence of elevated carbon monoxide levels.
In the presence of moisture and oxygen, steel corrodes. Oxygen is consumed in the corrosion process. In one instance, someone died because his steel cylinder contained only 3% oxygen. The cylinder sat in a hot shed for 3 months and became severely corroded, unbeknownst to the owner. Almost all of the oxygen was consumed in the corrosion process. He jumped into 10 feet of water with the cylinder to look for an outboard motor and immediately lost conciousness due to hypoxemia and drowned.
In another study conducted in the 1970s by the University of Rhode Island on steel 3AA cylinders, researchers found elevated levels of carbon monoxide in corroded steel cylinders but not in uncorroded control cylinders. The CO was a product of corrosion.
So... the recommendation is that if you are going to store a steel cylinder more more than 3 months, either (1) drain it to 300 psi so that you have to fill it with fresh gas before you use it, or (2) test the gas in the cylinder for O2 and CO before you use it.
Therefore, before you can safely use a steel cylinder after prolonged storage (> 3 months) you'll need to test the gas to verify the oxygen content, and to test for the presence of elevated carbon monoxide levels.
In the presence of moisture and oxygen, steel corrodes. Oxygen is consumed in the corrosion process. In one instance, someone died because his steel cylinder contained only 3% oxygen. The cylinder sat in a hot shed for 3 months and became severely corroded, unbeknownst to the owner. Almost all of the oxygen was consumed in the corrosion process. He jumped into 10 feet of water with the cylinder to look for an outboard motor and immediately lost conciousness due to hypoxemia and drowned.
In another study conducted in the 1970s by the University of Rhode Island on steel 3AA cylinders, researchers found elevated levels of carbon monoxide in corroded steel cylinders but not in uncorroded control cylinders. The CO was a product of corrosion.
So... the recommendation is that if you are going to store a steel cylinder more more than 3 months, either (1) drain it to 300 psi so that you have to fill it with fresh gas before you use it, or (2) test the gas in the cylinder for O2 and CO before you use it.
Last edited:
LeadTurn_SD
Contributor
Sounds like good advice, Doc Harry.
An air fill is cheap insurance.... plus, unless you are filling your own, you'll need a visual to get the fill... and eventually a hydro inspection.... so hopefully "bad air" would never be a safety issue.
I have a steel 72 that sat for well over a decade stored with about 500psi. When I put it back into service, I had it hydro'ed and inspected... very light internal corrosion that tumbling took care of.
An air fill is cheap insurance.... plus, unless you are filling your own, you'll need a visual to get the fill... and eventually a hydro inspection.... so hopefully "bad air" would never be a safety issue.
I have a steel 72 that sat for well over a decade stored with about 500psi. When I put it back into service, I had it hydro'ed and inspected... very light internal corrosion that tumbling took care of.
If it's been sitting for an extended period of time and you have doubts about it, have it VIP'd and if it passes fill it up and dive!
DeepSeaExplorer
Contributor
I also say indefinitely. I use tanks that are stored for for months at at time, both steel and AL. In one case, over two years because the VIP expired. I wouldn't bat an eye at using a tank that had set for only 3 months. I routinely leave full (steel) tanks in cave country and I only make it up there about every 6 or 8 weeks. I currenlty have 14 tanks, so some of them sit for a while between use. Sometimes you get a custom fill for a dive that gets canceled and they sit even longer. (That's part of the reason I don't use 30/30 anymore.)
In one of the studies by the University of Rhode Island, a steel cylinder contaminated with salt water became so badly corroded in just 3 months of storage that the cylinder wall was less than 1/2 of its original thickness (wall thickness before: 0.151 inches after: 0.070 inches. The oxygen content was significantly reduced (15.0%) and carbon monoxide was elevated (10 ppm). Carbon dioxide was normal (0.01%).
In contrast, the steel cylinders in the study that had been contaminated with fresh water demonstrated fairly insigificant corrosion over the 3 month study period.
I dive predominantly in fresh water with steel cylinders, but still recheck my gas if the tanks have been sitting over the winter. Who is right, me or DeepSeaExplorer? It all depends on the degree of risk that you perceive. I dive solo 90% of the time, so I need to have 500% confidence in my gas. DeepSeaExplorer is clearly less concerned and there is factual evidence to support his practice, too. Whatever floats your boat!
Just float your boat with informed decisions based on real data.
Gilldiver
Contributor
The test that Doc references did show very substantial corrosion within 3 months. But when you look at the test, they:
"used 6 new DOT-3AA uncoated 4130 high-pressure steel cylinders for the test. They put 500 milliliters of either fresh or salt water in the cylinders."
Now, 500 ml is a 16 oz beer or a bit more then a pint, if you are going to get a pint of water into your tank, well there is a very long discussion we need to have. Let's just say that this study is way out at the end of the bell curve of abuse and is into the BS test category.
If you keep your tanks in vis, don't drain them below say 300 PSI in the water (if you do, just take the valve off and check for water intrusion) and use a compressor that in at least fair maintenance, you can keep a tank filled forever.
"used 6 new DOT-3AA uncoated 4130 high-pressure steel cylinders for the test. They put 500 milliliters of either fresh or salt water in the cylinders."
Now, 500 ml is a 16 oz beer or a bit more then a pint, if you are going to get a pint of water into your tank, well there is a very long discussion we need to have. Let's just say that this study is way out at the end of the bell curve of abuse and is into the BS test category.
If you keep your tanks in vis, don't drain them below say 300 PSI in the water (if you do, just take the valve off and check for water intrusion) and use a compressor that in at least fair maintenance, you can keep a tank filled forever.
Similar threads
