How long do steel tanks last?
- Thread starter DiverDMD
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steel tanks can last forever or they can last 1 hydro.
It has little or nothing to do with surface rust, although that is not good either. the key to making a cylinder last for a long time is to fill it properly. The problem is that many dive shops don't have a clue. the simple fact is that filling a tank from 500psi to 3000psi should take 25 minutes, filling at a whole 100psi per minute. If you submerge the entire tank you can bump that up to about 300psi/min. If you tanks are filled faster than that you will be getting significant heating of the inside of the tank and the heat tends to concentrate at the neck of the tank (weakest part) and the heat stress will eventually cause the tank to fail hydro. This is one reason why we see storage cylinders that are 100 years old, because only true professionals fill these tanks (not your average $10/hr dive shop monkey) and they know how to fill tanks properly. If a dive shop fills your tanks on the spot for you and they take less than 20 minutes your should be seriously pissed off, not because of the hot fill, but because that fill will kill your tank.
It has little or nothing to do with surface rust, although that is not good either. the key to making a cylinder last for a long time is to fill it properly. The problem is that many dive shops don't have a clue. the simple fact is that filling a tank from 500psi to 3000psi should take 25 minutes, filling at a whole 100psi per minute. If you submerge the entire tank you can bump that up to about 300psi/min. If you tanks are filled faster than that you will be getting significant heating of the inside of the tank and the heat tends to concentrate at the neck of the tank (weakest part) and the heat stress will eventually cause the tank to fail hydro. This is one reason why we see storage cylinders that are 100 years old, because only true professionals fill these tanks (not your average $10/hr dive shop monkey) and they know how to fill tanks properly. If a dive shop fills your tanks on the spot for you and they take less than 20 minutes your should be seriously pissed off, not because of the hot fill, but because that fill will kill your tank.
Have you ever seen them fill industrial cylinders? They slam the tanks and fill them in less than a couple of minutes, and these are 280-336 cu ft bottles. They overfill them and let them cool down to the correct pressure.
captain
Contributor
No way a tank can get hot enough to weaken it by fast fills. Just another urban diving legend.
Gilldiver
Contributor
Just about what the last 2 posts say, a large gas fill house can fill up to 1,000+ tanks a day in batches of 6. How much time do you think they can spend on each tank?
For steel, you need to get up above 600F before you are anywhere close to temper temps, for aluminum its age temp you have to watch out for which can start as low as 250 for some alloys.
For steel, you need to get up above 600F before you are anywhere close to temper temps, for aluminum its age temp you have to watch out for which can start as low as 250 for some alloys.
I have been at commercial (Praxair) sites that fill tanks, last time I was there they were filling about 50 tanks at a time.
after sending a pair of Fabers back that failed after their first hydro, I was explained in great detail by the factory rep with a metalurgy degree that infact reaching tempering temperatures is actually very easy, didn't take as much as you might think. By their paperwork, they actually certify their tanks to a ton of cycles, but they also expect that filling rates never exceed 300psi/min and they recommend much less.
after sending a pair of Fabers back that failed after their first hydro, I was explained in great detail by the factory rep with a metalurgy degree that infact reaching tempering temperatures is actually very easy, didn't take as much as you might think. By their paperwork, they actually certify their tanks to a ton of cycles, but they also expect that filling rates never exceed 300psi/min and they recommend much less.
Gilldiver
Contributor
If I were to bake a tank to 200F, which is well below temper, and you moved it bare handed, you would then be on your way to the hospital burn ward to have 3rd degree burns worked on. Any metal items with a temp above 100-120 are very uncomfortable and will start to cause blisters at the high end.
Have you ever moved a tank that has sat on the back of a boat in direct sun all day on a day in the high 90's? The actual tank temp will be as much, if not more then, what you will have from a fast fill.
Have you ever moved a tank that has sat on the back of a boat in direct sun all day on a day in the high 90's? The actual tank temp will be as much, if not more then, what you will have from a fast fill.
captain
Contributor
Back when I first started diving in 1957 there was a store, can't say dive shop as it sold diving gear, hunting sand fishing equipment and military surplus, that had a fill whip right next to the front door and they would fill your tank in about a minute or less. As Gilldiver said it got hot enough to be uncomfortable to touch. I still have that tank that got all those hot fills and it passes hydro everytime.
any one else smell a cover-up?? perhaps the degree holding metallurgist might have been (t/s)elling you the company line ??
IIRC the recommended (CGA) fill rate is 600 psi/min...
since no-one fills that slowly unless they are filling in their own garage or boat off a baby Coltri 3.5 or similar compressor, I think it would be a great line for a tank mfr to try and use to weasel out of standing behind their defective merchandise
my 2psi
The more likely failure issue would be from someone not doing the testing correctly. These tanks have a very different test protocol that, depending on the testing location, is not always followed.
Talking with different shops, some places get testing done with almost zero failures, others get really high numbers. Seems to depend of if the test place sees lots of HP tanks or not.
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