Question about a scuba tank

[syntaxerrorsix]

It should say the brand on the top of it. Some older aluminum tanks...well we would need to know the brand before condemning them.

If you can, steel tanks are better for backmount diving. Aluminum singles work great as stage bottles. A steel tank is negative at the end of the dive vs an aluminum tank that you now have to carry more weight to offset it's buoyancy. You are probably going to want two tanks too.

If it was born in '93 it isn't 6351 alloy and it wouldn't matter who made it. A visual and an eddy test could still determine if sustained load cracking was an issue in an older bottle and if it wasn't it would still be fine to use. It's important to avoid cryptic statements in the Basic Forum especially if you aren't willing to expound on all of the information.

Steel bottles may be fine for some types of diving but claiming that steel is better for everyone is simply not true, besides as a diver with 0-24 dives I'm pretty sure they won't be staging anytime soon.

To the OP, the bottle appears to be a standard AL80 likely Luxfer or Catalina. Unless there is known abuse there is no reason to suspect a problem. It will require a hydro and VIP and will serve you for years

 

[muddiver]

Aluminum cylinders are good for about 15 years, so this one is pushing the end of its life as a compressed gas cylinder.

Steel cylinders have different buoyancy carateristics that a lot of use like. They also will last for ever because the stress of being pressurized and drained, over and over does not affect them like aluminum. The down side is they will rust, and if moisture gets inside they can pit which will end their useful life.

Aluminum does not rust, it gets a neutral coating of oxidation on its surface that protects it. regardless of the composition (6351 or not) aluminum will eventually fail due to the stress of the cylinder being streached when filled and not returning to its original size when discharged.

Otherwise its probably a fine deal for a cylinder.

 

[syntaxerrorsix]

Aluminum cylinders are good for about 15 years, so this one is pushing the end of its life as a compressed gas cylinder.

This is simply not true.

"Luxfer scuba cylinders are cycle-tested in excess of 100,000 cycles at service pressure."


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You would have to fill the bottle ~18 times a day for 15 years to approach that.


ETA - Perhaps you are thinking of composite wrapped SCBA bottles?​

 

[Recneps]

Aluminum cylinders are good for about 15 years

Not true!!!!

Where do you guys get this from....you kids crack me up .

Just got a 1988 AL80 hydro and VIP done. Filled and ready to get wet.

 

[beanojones]

This is simply not true.

"Luxfer scuba cylinders are cycle-tested in excess of 100,000 cycles at service pressure."


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You would have to fill the bottle ~18 times a day for 15 years to approach that.
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And then hydrotested at 5/3 working pressure. It's not the fills that get most aluminums. It's corrosion (especially internal or on the neck O-Ring) or the Hydros. In the tropics, we figure on 15 years being the max, if the tank is actually being used.

Fresh water is a different animal. Salt water eats aluminum quickly. Now that tank manufacturers have stopped painting AL tanks external corrosion has gotten better but that tank has a stainless band on it.

 

[syntaxerrorsix]

Damage from corrosion is a fault of the operator not the bottle. Hydros don't hurt the tanks either.

The misinformation in this thread is amazing.

 

[Culcuhain]

I guess I need to put my AL80 from 1983 out of service... as well as the one from 1989....
I guess that leaves me with only my steels from 1959, 1968, 1972, 1974.....

 

[beanojones]

Damage from corrosion is a fault of the operator not the bottle. Hydros don't hurt the tanks either.

The misinformation in this thread is amazing.

Corrosion on the neck O-ring seal is not the fault of anyone but nature as it is completely inaccessible to the end user at surface pressures. Eventually the seating surface just won't seal the O-ring. The tropics work different than other places with regard to corrosion. Other people think reg last forever. We are lucky to get ten years out of them, except for the titanium parts in them.

Go ahead and walk me through the hydro testing steps again to make sure that permanent shape change does not occur from hydros. Especially concentrate on what the permanent displacement test at the end is measuring. If hydros did not 'hurt' tanks, then tanks would never fail them either. That's what a hydro test is, is a measure of the ratio of permanent deformation. Steel is relatively elastic, and aluminum is not, which is why I own tanks from steel tanks 1960 which have had all the hydros, and aluminums fail over time, even ignoring corrosion. Because aluminum is not as elastic, and it permanently deforms past it structural soundness point faster than steel.

http://www.sounddive.com/hydro test illustration.htm

Your scuba cylinder is condemned when the Percent Expansion exceeds the predetermined limits set for your particular cylinder

That's a good overview of how a hydro works.

The lack of knowledge in the quoted post is amazing.

(See, wouldn't it be nicer if there were no insults at the end of posts? I know I feel a little nasty just for copying that form.)

 

[syntaxerrorsix]

Corrosion on the neck O-ring seal is not the fault of anyone but nature as it is completely inaccessible to the end user at surface pressures. Eventually the seating surface just won't seal the O-ring. The tropics work different than other places with regard to corrosion. Other people think reg last forever. We are lucky to get ten years out of them, except for the titanium parts in them.

Go ahead and walk me through the hydro testing steps again to make sure that permanent shape change does not occur from hydros. Especially concentrate on what the permanent displacement test at the end is measuring. If hydros did not 'hurt' tanks, then tanks would never fail them either. That's what a hydro test is, is a measure of the ratio of permanent deformation. Steel is relatively elastic, and aluminum is not, which is why I own tanks from steel tanks 1960 which have had all the hydros, and aluminums fail over time, even ignoring corrosion. Because aluminum is not as elastic, and it permanently deforms past it structural soundness point faster than steel.

how a hydro test is completed


That's a good overview of how a hydro works.

The lack of knowledge in the quoted post is amazing.

(See, wouldn't it be nicer if there were no insults at the end of posts? I know I feel a little nasty just for copying that form.)

I worked as a hydro test facility operator for over 5 years. I'll tell you what, we can exchange RIN numbers and then we can talk.

Your experience in the "tropics" is no different than my experience in Florida save for the fact that here we understand that proper maintenance and servicing can most certainly extend an AL tanks life WELL past 15 years as some have alluded to. As someone who has had thousands of tanks pass through my inspections and a dive shop FULL of of AL80's older than 15 years I'll ask that you excuse my jaded eye towards some of the absolute fiction posted here. I'm sure your mileage may vary..

 

[windapp]

Steel is relatively elastic, and aluminum is not

Where did you get this information? This is simply not true. Here are some actual facts.

Metals (including alluminum) deform elastically within their elastic range. The spring constant (known as Young's modulus) describes the linear relationship between the elastic deformation and the applied stress. Within this range, there is no permanent deformation. Once this range is exceeded, the metal will continue to deform elastically, but will also deform plastically (permanent deformation).

Steel has a much higher modulus of elasticity than aluminum, and requires a higher force to move into the plastic range. Aluminum will start deforming plastically with a lower force, and will deform substantially more before failing. However, both types of tanks will be designed with adequate wall thickness so that neither will be permanently deformed during the hydro test if they are undamaged.

The other issue which differentiates steel from aluminum is fatigue. Fatigue is the formation of cracks due to cyclic loading. Steel has a limit where more loading cycles will not decrease its strength any further. Aluminum does not. However, the number of cycles we are talking about are in the millions, so fatigue is really irrelevant to a scuba cylinder that will see no more than a few thousand load cycles in its lifetime as compared to say, an airplane wing, that will see thousands of cycles each flight.

Of course, their are issues with corosion, with aluminum tending to come out on top when moisture enters the tank.

The reason why aluminum tanks fail hydro more often than steel tanks is that steel tanks are more resistant to damage when they get dropped and banged around.