Overfilling LP Steel Tanks -- How bad is it?

[rjack321]

After all, if regular overfilling takes 30 years off the life of the tanks, they'll probably still outlast me.

Exactly.
They are not bursting.
They do have a shortened life but its measured in a decade or so - not months or years.

I have 3AA tanks in my garage from before WW2. While they probably have never been overfilled beyond 10%, if they had and it wacked their life in half that ~35yrs would still be quite reasonable.

 

[WD8CDH]

I think you misundertood me. I did not ay the HP and LP are the same, but it may have sounded like that. Years ago, I was reading an article (if I still had it I would post the link) that stated the "same" tanks that the US rates at 2400 are rated at over 4000 in Europe. This was when Genesis had the only hp bottles that were widely used. The newer HP bottles are a whole other animal.

Hi Spd,

That article was not true. I have read the DOT 3AA specs and many of the Euro specs. The allowed stress/yield strength ratio is surprisingly close. The biggest difference that I ever saw was about 15%.

Having owned many Faber 300 bar cylinders, I can tell you they are heavy, much heavier than their LP equivalents.

Faber makes several versions of each size tank. In most cases, if you look at the specs, you will see at least 3 different weights for each tank size. They basically change the wall thickness and/or material for different service pressures.

When you include the 10% "standard overfill" of a DOT 3AA tank, Euro tanks don't have significantly less safety factor.

 

[ianr33]

Incorrect. The shop where I worked, prior to when I started, had an AL40 Deco tank explode while it was hooked up to the O2 whip but not yet being filled. Sadly, the fill station attendant was killed. It was dropped from waist level and landed on the valve. The explosion, in addition to killing the attendant, completely destroyed the front of the shop. The valve was found about a year later out in the woods about 1000 feet from the shop. The pictures I've seen indicate the tank fragmented. There was a hole in it with missing material.

This is somewhat misleading. Seems the initiating event was an O2/fuel fire that led to the failure of the tank. http://www.scubaboard.com/forums/741028-post107.html

While obviously a horrible tragedy if the tank had contained air this would not have happened. It was an O2 problem,not an alloy problem.

 

[Cave Bum]

This is somewhat misleading. Seems the initiating event was an O2/fuel fire that led to the failure of the tank. http://www.scubaboard.com/forums/741028-post107.html

While obviously a horrible tragedy if the tank had contained air this would not have happened. It was an O2 problem,not an alloy problem.

True, not an alloy problem. The statement was made that aluminum tanks never fracture creating sharp pieces. I was trying to show that they do.

Also, the Luxfer analysis doesn't jive with what people who were actually there have told me. I was told when the valve was finally found a couple of years ago, the dip tube was completely melted away up to the valve base. The best guess at this point is that the force of the impact split the valve, allowing a rapid flow of gas through the dip tube, which caused friction heating on the thin lower edge. This, they think, was the ignition source.

For this reason, now when we set up deco bottles we usually remove the dip tube and give it to the customer.

 

[PhilEllis]

Also, the Luxfer analysis doesn't jive with what people who were actually there have told me. I was told when the valve was finally found a couple of years ago, the dip tube was completely melted away up to the valve base. The best guess at this point is that the force of the impact split the valve, allowing a rapid flow of gas through the dip tube, which caused friction heating on the thin lower edge. This, they think, was the ignition source.

In almost every instance of a scuba cylinder failure, the events as presented by first-hand and close witnesses seldom EVER match the analysis of the organizations with a vested financial interest in the problem. While I can't search for them now, there are several reported instances of aluminum cylinders failing in ways that Luxfer, the DOT, and other organizations say they CAN'T fail! If I remember correctly, there are at least two instances widely reported on the internet that involve failures simply from HANDLING the cylinders. Oh well.

Note: Oxygen involvement is a completely different matter. Oxygen in scuba presents a unique set of dangers, and the reports of accidents and near-misses involving scuba oxygen are pretty easy to find. Scuba equipment (valves, cylinders, and regulators) is simply not purpose-designed for oxygen, so challenges abound.

Phil Ellis
www.divesports.com

 

[Cave Bum]

So I live in Florida & I've noticed my LDS routinely overfills tanks...I wanna buy something like an LP80/85 to be overfilled. My question is..how bad/dangerous is it really to do this?

To AceszHigh,

Sorry, I didn't mean to highjack your post. Just wanted to state that we were talking about the newer LP80 through LP121 series of tanks and it got dragged off on this side street of if aluminum tanks fracture or not.

If the moderators want to split off that other part, that might be a good idea.

Again, sorry to OP, it wasn't my intent to divert it from the original question.

 

[Mark Michaud SELAUSAR]

Hi Spd,

That article was not true. I have read the DOT 3AA specs and many of the Euro specs. The allowed stress/yield strength ratio is surprisingly close. The biggest difference that I ever saw was about 15%.

Having owned many Faber 300 bar cylinders, I can tell you they are heavy, much heavier than their LP equivalents.

Faber makes several versions of each size tank. In most cases, if you look at the specs, you will see at least 3 different weights for each tank size. They basically change the wall thickness and/or material for different service pressures.

When you include the 10% "standard overfill" of a DOT 3AA tank, Euro tanks don't have significantly less safety factor.

If you say so. Not really a big deal for me to bat back and forth. I have watched the last ten years of cave fills by teams and individuals without hearing of a single failure due to fill pressure. That is enough for me. As far as being heavy...pst, heiser, and even worthington's are much heavier than the fabers. Faber's have been the lightest tanks out there for sometime. Again, not worth arguing about to me.

 

[DeepSeaExplorer]

I think one reason to get a LP tank would be because the boats can't fill your HP tank ... but, my HP 100 is the same size as that LP80 and holds about the same amount of air at 3000psi, and 100cf at 3442psi ... sorta like a legal overfill isn't it

Yes, but I can overfill my LP 104s and get 300 cubes of gas. You can't do that with HP tanks with a regular compressor.

 

[SharkDiver36]

Any answer that isn't a NO is a wrong answer.

I'm disappointed to see Dive Masters, Asstinant Instructors and Instructors advising someone that's ok to over pressurize a tank.

DOT Regs are very specific and can only be filled to the operating pressure stamped on the tank - period - no exceptions.

Giving advice to the contrary exposes one's self to liability, not to mention most likely a violation of your own certifying agency standards.

Any question can be answered based on "experience" or the "Right Answer"....sometimes these answers differ.

The "right" answer is: You should never overfill your tank.

 

[H2Andy]

The "right" answer is: You should never overfill your tank.

why is that the right answer?