Joe Shneehagen accident

[cavedweller]

Properly designed steel tanks don't fatigue and can have a infinite lifespan properly cared for. I would trust them more than CF, but they are too heavy. Aluminum almost never has a infinite lifespan and will in enough cycles eventually fail. The key is to design aluminum tanks strong enough that for all practical use, the number of cycles at a given stress level never gets close the the fatigue limit. What does the curves look like for CF? I don't know, but the deep diving sub makers all use steel not CF, except for the one company in the news for a terrible fatal accident. That sub and a number of problems not only with the CF shell but using windows not rated for the pressure they were subject too. What idiot would get into the sub?

Fatigue limit - Wikipedia

en.wikipedia.org

View attachment 462385

I’m reminded that the CF tanks most of us use are aluminum and are wrapped in CF

 

[cavedweller]

EXACTLY!

Any growth in a carbon fiber wrapped bottle IS destructive. There is no level at which detectable growth is acceptable.

Archaic

I’m reminded that the tank failure in question was NOT a CF wrapped tank.
Note:
Poorly maintained moisture condensation filters / vessels, can allow introduction of caustic materials into HP tanks. Brancato guy on YouTube has a great video on this… of course he is selling stuff.

 

[Peashooter]

People ware these tanks on their backs, you dont hear of firefighters getting into trouble with them . Extreme conditions.
I have worn them for 25 yrs .

Indeed.
I am certified smoke diver too, and fire fighting,,,, well as far as you have to be as a sailor in the Danish merchant marine, but it is a skill that need refresher course every 4 years as i recall.
I always liked those days, well aside for rescuing " Sten " ( Sten is a Danish boy name, it also mean stone, and at the Fire school Sten is indeed a dummy filled with stone gravel to give him the weight of a adult )
Carrying his dead ass up and down smoke filled stairs / ladders and what not, + being in a hot place,,,,, lets just say i have seen unfit PPL suck dry a tank in next to no time.

Personally while also not that fit back in those days ( 90ties ) and still a smoker of both this and that, i would usually just need 1 tank change for the whole day.

 

[F6Hawk]

I’m reminded that the tank failure in question was NOT a CF wrapped tank.
Note:
Poorly maintained moisture condensation filters / vessels, can allow introduction of caustic materials into HP tanks. Brancato guy on YouTube has a great video on this… of course he is selling stuff.

That's why, even though it's not required for SCBA, I will perform visuals annually on my SCBA tanks the same as I do on my SCUBA tanks. An ounce of prevention...

 

[piframbo]

des personnes ont de ces nouvelles a Jo ?

 

[WoodWelder]

des personnes ont de ces nouvelles a Jo ?

Oui

 

[JimD]

I am a retired mechanical engineer and many years ago I had classes on materials and creep behavior. I agree that aluminum always creeps, it just creeps more at higher stress. Steel kept below it's yield stress does not creep. But that does not make me want a steel air tank. I would take carbon fiber reinforced tanks any day. Their key benefit is they separate the sealing up of the air from the mechanical containment of the force the pressurized air generates. So if the aluminum liner leaks, it is prevented from gross mechanical failure by the carbon fiber. If the steel ever exceeds it's yield stress (perhaps due to moisture in the air) then it could grossly rupture in a dangerous way. I think steel tanks are mainly used for diving where their weight is an advantage. But I disagree that they are safer than a carbon fiber reinforced tank. Maybe what we need is a thin steel tank reinforced with carbon fiber. But I say this tongue in cheek because the steel liner would be significantly more susceptible to moisture damage.

I think metal tanks of any design are more likely to hurt somebody than carbon fiber reinforced tanks.

 

[AlanMcD]

I am a retired mechanical engineer and many years ago I had classes on materials and creep behavior. I agree that aluminum always creeps, it just creeps more at higher stress. Steel kept below it's yield stress does not creep. But that does not make me want a steel air tank. I would take carbon fiber reinforced tanks any day. Their key benefit is they separate the sealing up of the air from the mechanical containment of the force the pressurized air generates. So if the aluminum liner leaks, it is prevented from gross mechanical failure by the carbon fiber. If the steel ever exceeds it's yield stress (perhaps due to moisture in the air) then it could grossly rupture in a dangerous way. I think steel tanks are mainly used for diving where their weight is an advantage. But I disagree that they are safer than a carbon fiber reinforced tank. Maybe what we need is a thin steel tank reinforced with carbon fiber. But I say this tongue in cheek because the steel liner would be significantly more susceptible to moisture damage.

I think metal tanks of any design are more likely to hurt somebody than carbon fiber reinforced tanks.

I think the real issue you are speaking of with aluminum has to do with the fact that it has no fatigue limit, not the creep. Steel undergoes no structural change whenever it is loaded below the fatigue limit, but not so with aluminum as it has no such limit - every loading cycle impacts its structural properties, making it more susceptible to things like impact failures sooner than steel.

The other thing that people in general seem to forget is that the carbon fiber wrapping is still susceptible to failure caused by structural damage to either of the two components that make it up - the carbon fiber, or the epoxy stabilizing coating. Impacts and excessive chemical or UV exposure can damage them, and then the tank is every bit as likely to have a structural failure as a metal tank. We still need to take care of them, and visually inspect them - especially if something unusual happens to them.

 

[piframbo]

salut soudeur de bois .
après un tel accident, un mois passé.
la guerisson,va prendre des années,juste quelques nouvelles ?
la bouteille n'est pas mon soucis.
facile a achettée.mais une vie humaine ,difficille a reparée .A+,de la France.

 

[JimD]

I doubt fatigue is a cause of failure in high pressure air storage tanks because the number of cycles is so low. I do not expect to fill mine 1,000 times, I will not live long enough. Others may do much more but fatigue is typically at much higher numbers of cycles (often millions of cycles particularly when the stress is well below yield I looked up 6061 and the source said 10 million cycles at 75% of yield for instance). Creep may not be a great way to refer to the weakness of aluminum in structural applications either. Aluminum just does not have a sharp transition from elastic stress levels to plastic stress levels like steel. Because of this I think of it deforming a little at low stress that are probably in the elastic region even for aluminum.

Regardless of the most likely mode of failure I do not think we have anything to worry about until the tank degrades due to physical damage or corrosion. If the material gets thin enough that the stress exceeds the plastic limit it will creep, possibly to the point of failure. If that occurs I feel more comfortable with carbon fiber over the aluminum liner to limit the fragmentation of the aluminum. I agree we need to keep an eye on the carbon fiber, however. It too can be damaged. Perhaps there is a mechanism with fatigue that could lower the yield strength enough to contribute.