What pressure would you fill a pair of AL80s to?

In the interest of generating discussion, let's see what people would be comfortable filling their aluminum tanks to. Assume the following:

1. You want the most gas you can get without endangering the longevity of the tank from stress/fatigue
2. AL40, AL80 or similar common aluminum tank rated to 3000psi.
3. You're filling for a dive and will use it within a week or will bleed it.
4. Tank is in viz (which means it has good hydro) and is "good" aluminum (not older crack-prone models)
5. Choose the pressure you're aiming to get after the tanks cools

3600

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Originally Posted by Superlyte27

3600

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haha I just noticed the poll.

hmmm, having inspected thousands of tanks in the day and taken a few courses on them alum gets no more than a 10% overfill from me, expecting a cool to ~rated pressure. They scare the #### out me to overfill them. They just aren't that forgiving to repeated overfilling, the alum stretches, does not contract and gets lots of little cracks in the alum, that is why the visual eddy process is now used. newer alloy alum tanks still have the same tendencies, just not as bad by far but they still get respect.

Steel tanks that aren't exemption cylinders...what will the compressor do?

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Originally Posted by Superlyte27

haha I just noticed the poll.

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Yeah, I was a bit slow in getting the poll up. Apparently you have to create a thread first and then complete the poll as a second step.

3300 hot, 3000 cool.

Interesting. Some people fill to 3300 to cool to 3000, and others fill to 3200 to cool to 3000.

Is it a function of the compressor? Faster-filling = more heat = higher fill level to cool to 3000?

3000, because of the elasticity of steel I'm ok with pumping steel tanks to 3600, Aluminium tanks I do not like to over fill because they fatigue faster than steels. An over pumped aluminium tank scares me.

I would guess that the folks that fill to 3200 to cool to 3000 have more patience than those of us that fill to 3300...the 3300 crowd fills faster. The 3200 crowd is more cautious.

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Originally Posted by Jax

Interesting. Some people fill to 3300 to cool to 3000, and others fill to 3200 to cool to 3000.

Is it a function of the compressor? Faster-filling = more heat = higher fill level to cool to 3000?

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I don't think Jon is looking for how high do you fill so that it cools to 3000... I think he's looking for more of a how high would you fill it to go on a dive, particularly an exploration type dive. It might be hard to get an honest answer on an open forum but "rumor has it" that in the circumstances described, 3900 shouldn't be a problem.

on a exploration type dive if I must die I would prefer it happen on the dive, not while filling a stupid scuba tank where I could possibly kill and injure others.... Filling a alm 80 to 3900 psi is bone dead stupid

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Originally Posted by firemedic1015

I don't think Jon is looking for how high do you fill so that it cools to 3000... I think he's looking for more of a how high would you fill it to go on a dive, particularly an exploration type dive. It might be hard to get an honest answer on an open forum but "rumor has it" that in the circumstances described, 3900 shouldn't be a problem.

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I'm going to go out on a limb and guess that the overwhelming majority of responders advocate keeping AL 80 tanks close to their rated pressures while feeling fine with overfilling LP steel tanks. I'm in that camp myself. I therefore found the approach of a shop I used this winter in south Florida interesting.

The shop was near where I was staying for more than a month, so I happily purchased a fill card, using it for both my LP 108 doubles and my LP 85 singles. It took a while first for me to convince them that it was OK to fill them the 10% beyond the 2400 PSI allowed by the + rating. I did eventually get them to risk going all the way to 3,000 PSI. Then I had friends join me there so I could certify them for AOW. We used the same shop, and they rented AL 80s for the dive. They were all filled routinely to between 3,400-3,500 PSI. I asked them why their policies were the opposite of most thinking, and the people doing the fills really didn't know.

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Originally Posted by JohnAd

They were all filled routinely to between 3,400-3,500 PSI. I asked them why their policies were the opposite of most thinking, and the people doing the fills really didn't know.

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:-) and that is why buying used AL tanks is mostly a crapshoot unless you really know the person who owned and took care of them...just my 2 psi.

Dive safe,

Celia

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Originally Posted by JohnAd

the overwhelming majority of responders advocate keeping AL 80 tanks close to their rated pressures while feeling fine with overfilling LP steel tanks...
... AL 80s for the dive. They were all filled routinely to between 3,400-3,500 PSI. I asked them why their policies were the opposite of most thinking, and the people doing the fills really didn't know.

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I'm 200 miles away from the two compressors I have used for almost twenty years, so I decided to scope out the shops in PCB to see if anybody would do cave fills (for my open water LP-95s). One shop will take them "all the way to 2600," while they take AL-80s to 3500 without batting an eye.

Depends on the dive. If they are going to be stored in the garage, then 3000 cool, if we are jumping in the water that day, 3500, warm.

OK, how much do you guys fill your steel 72's ?

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Originally Posted by OFG-1

...OK, how much do you guys fill your steel 72's ?

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Today, or 40 years ago? :-D

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Originally Posted by cerich

Filling a alm 80 to 3900 psi is bone dead stupid

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And why would it be bone dead stupid ?


They have a 3000 PSI Rating..
Filling to 3900 therefore equals filling to 130% of the reated pressure.


At DOT hydro procedures (not sure which applies for Alis) they are at least tested to 143%, 150% or even 166%..
Either one giving still additional margin towards the maximum test pressure being applied to the tank regularily during hydro testing at least..


In Germany it is generally 150% and all Ali tanks are US manufactured.. so there should not be a difference also..


So as long as one does not make this to a ususal Habit but does this for infrequent occasional purpose based use (as it is indicated by the Poll description as well) I completely can not follow whay this should be "bone dead stupid" !


Due to the fatigue issues described in the thread I personally do not like overfilling my Ali tanks, so I just overfill about 10% in order to get to rated pressure once the tank has cooled down and I oftenly overfill almost all steel tanks (other than those with a conic valve) at around 20-30%..
But stupid ????

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Originally Posted by Nitrogenius

At DOT hydro procedures (not sure which applies for Alis) they are at least tested to 143%, 150% or even 166%..
Either one giving still additional margin towards the maximum test pressure being applied to the tank regularily during hydro testing at least..

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Hydrotesting, by definition, is a DESTRUCTIVE testing procedure. The act of Hydrotesting causes damage to the Al tank. The tank IS designed to tolerate a LIMITED amount of hydrotesting during it's lifespan. Not every day!

In the fire service we are allowed to hydrotest Al based tanks NO MORE than five times (hydro at 3 yr intervals). At age 15 years, the tanks is retired and destroyed no matter how good shape it's in. If a tank requires extra hydrotests (service damage/repairs) during it's life span, it is retired before the 6th hydrotest is required.

Can someone explain this to me? It was my understanding that most (if not all) firefighter's gas/air tanks were made out of some material OTHER THAN aluminun. Fiberglass, maybe? Anyway, something with a limited cycle life. So I am not clear what they have to do with the question at hand.... Neither steel nor aluminum tanks "expire" after 15 years, I understood that the fiberglass (?) tanks do... These are fundamentally different types of tanks, no?

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Originally Posted by gschaut

Hydrotesting, by definition, is a DESTRUCTIVE testing procedure. The act of Hydrotesting causes damage to the Al tank. The tank IS designed to tolerate a LIMITED amount of hydrotesting during it's lifespan. Not every day!

In the fire service we are allowed to hydrotest Al based tanks NO MORE than five times (hydro at 3 yr intervals). At age 15 years, the tanks is retired and destroyed no matter how good shape it's in. If a tank requires extra hydrotests (service damage/repairs) during it's life span, it is retired before the 6th hydrotest is required.

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For clarification... I generally aim for my aluminum tanks to be at 3000 when cool... 😊... I just wasn't sure what a different type of tank had to do with it?

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Originally Posted by lv2dive

Can someone explain this to me? It was my understanding that most (if not all) firefighter's gas/air tanks were made out of some material OTHER THAN aluminun. Fiberglass, maybe? Anyway, something with a limited cycle life. So I am not clear what they have to do with the question at hand.... Neither steel nor aluminum tanks "expire" after 15 years, I understood that the fiberglass (?) tanks do... These are fundamentally different types of tanks, no?

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They weren't always composite tanks. Some rural fire departments can't afford composite tanks and still use alum tanks.

The solid AL tanks don't have a limited service life. It's the fiberglass or carbon hoop wrapped aluminum composites (three year retest interval) and the modern carbon fiber cylinders (five year retest interval) that have a 15 year service life.

So do the aluminum ones still have to be discarded after 15 years?

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Originally Posted by firemedic1015

The solid AL tanks don't have a limited service life. It's the fiberglass or carbon hoop wrapped aluminum composites (three year retest interval) and the modern carbon fiber cylinders (five year retest interval) that have a 15 year service life.

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Not the solid aluminum ones.

I'm conservative with aluminum cylinders, I'll go a hundred or two over 3000 while filling but not much more than that. Steel on the other hand, "what do you want?", is met with my reply "as high as your banks & compressor can do".

I like to fill AL 80's to 3000 psi let them cool overnight then top them to 3000.
In a perfect world you always have the option.
I do not push AL cylinders it just is not worth the stress on the tank.
STEEL? Well depends on the diving.
In Cave Country 3600+
Deco dives 3600+
Quarry dives 3200-3400 routinely

+translates rarely beyond 3800.
I do not like hot fills always like to take time to keep the heat down.

JCG

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Originally Posted by gschaut

Hydrotesting, by definition, is a DESTRUCTIVE testing procedure.

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Yes. It is a destructive testing procedure by defintion, because if it Fails the test it is destroyed, thus the test is done in a confied compartment..

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Originally Posted by gschaut

The act of Hydrotesting causes damage to the Al tank.

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No, sir, I disagree. It causes extra and exceptional high stress on the tanks. All materials have a limited stress-release-hysterisis lifespans and thus such test (and a fill Close to test pressure) does have an Impact on the lifespan.. But it is not damage as such..

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Originally Posted by gschaut

The tank IS designed to tolerate a LIMITED amount of hydrotesting during it's lifespan. Not every day!

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All tank materials tolerate a limited amount of stress-release cycles.. so does Aluminium.. Stell just tolerates a bit more cycles.. the mechnic as such though does not Change and higher stress always Impacts the possible cycle numbers..


Nobody had been saying anything about everyday.. I just oposed the Statement that overfilling to a range of 3900 PSI is stupid!
It certaintly isn't without danger and should, if at all only be done by someone knowing their stuff..
But it is not Stupid per se!

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Originally Posted by Nitrogenius

...Nobody had been saying anything about everyday.. I just oposed the Statement that overfilling to a range of 3900 PSI is stupid!
It certaintly isn't without danger and should, if at all only be done by someone knowing their stuff..
But it is not Stupid per se!

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Regardless of semantics or however you wanna try and spin it, I think most people would agree filling aluminum tanks to 3900psi isn't wise.

Sent via flying butt monkie using Tapatalk 2

if a tank fails during hydro, nobody dies. If during filling, maiming and death almost always.

I respect the people filling my tanks too much to hand them alum tanks to fill that I know have been potentially compromised by repeated filling beyond the rated pressure. I have failed too many tanks, seen to many that have failed during filling and know personally two people that died when filling them. The process of filling the tank is much more cumulative damage with aluminum than with steel. That's science, not speculation. So I am very conservative.

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Originally Posted by cerich

So I am very conservative.

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And that is ok to be.. So am I.. Nevertheless someone not being as conservative filling up to 3900 once for a Special purpose is not necesarily stupid..
I would just get the right tank for the Job instead, but that is another Story..

The poll is talking about not severely limiting the life of an AL tank.
There are folks who would fill lot's of al 80's to 3900 on a regular basis. How many hydro cycles did they get out of them?

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Originally Posted by Jay

The poll is talking about not severely limiting the life of an AL tank.

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Good Point! Every single Fill to 3900 would definately Limit the lifespan of such tank..

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Originally Posted by Nitrogenius

Good Point! Every single Fill to 3900 would definately Limit the lifespan of such tank..

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... and maybe the filler!

Aluminum fatigues with every fill. Period. It has a finite fatigue life. Steel does not. It requires a certain amount of stress before it fatigues. It has an infinite fatigue life below a certain threshold. I'd be surprised if anyone here know what those figures are for the tanks they dive. Even if they did, it would be for tanks in good condition, without accounted for stress raisers. Pitting and cracking will concentrate the stress. Filling a good AL80 to 3900 once is almost certainly never going to be a problem... but asking someone else to do it repeatedly on tanks they know little or nothing about is stupid.

I believe Faber once stated their tanks were designed to withstand 10,000 hydros. That tells me that cave filling steel tanks is fatiguing the tank, but within a considerable safety margin.

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Originally Posted by Greenwood_60

Steel does not. It requires a certain amount of stress before it fatigues. It has an infinite fatigue life below a certain threshold.

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Well If I haven't been sleeping in my Steel Structure class back in 96-97 during my masters in Civil Engineering and my memory does not Play tricks on me, then there is no such thing like an infinite fatigue life for any material, also not for steel.
Repeated stress-no stress cycles are the most fatiguing element in structural Engineering. Steel can cope quite well with it in comparison to ther materials, but it fatigues with every cycle and eventually fails no matter the treshhold..

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Originally Posted by Greenwood_60

Filling a good AL80 to 3900 once is almost certainly never going to be a problem... but asking someone else to do it repeatedly on tanks they know little or nothing about is stupid..

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This I concur with 100% !!

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Originally Posted by Greenwood_60

I believe Faber once stated their tanks were designed to withstand 10,000 hydros. That tells me that cave filling steel tanks is fatiguing the tank, but within a considerable safety margin.

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Sounds plausible.. ;)

My understanding is a bit simplistic. From wikipedia: "Ferrous alloys and titanium alloys have a distinct limit, an amplitude below which there appears to be no number of cycles that will cause failure. Other structural metals such as aluminium and copper, do not have a distinct limit and will eventually fail even from small stress amplitudes."

http://en.wikipedia.org/wiki/Fatigue_limit

Ok.. Looking to small scale stress as it seems to be indicated in the Wikipedia source (which by the way as everyone should know always maybe flawed since there is only proofreading by other users) there might be such "distinct Limit" which is so low, that it results in a Close to unmeasureable cycles until it would fail..
I still do not believe there is a complete "no failure" treshhold..
I also very much doubt that the stress Levels applied to a steel tank would fall under such threshhold that would seem an ineffective use of the material and cause unreasonable thinkness of walls and thus also unreasonable weight and cost..
However without looking deeper into the steel formulas I would am sure that even the test pressure during hydro would fall into a load Scenario being far away from the with steel critical elastic Limit and the reasonable cycles of a steel tank which certaintly would fall into a 4 Digit number over a reasonable lifetime with corrosion and potential outside damages affecting hull thinkness etc. would be far away from any cycle number getting critical below such elastic Limit. If memory serves well getting closer to such elastic Limit the cycles to failure a definately 5-7 Digits..
So conceptually one could say that load cycle fatigue for steel tanks should not Play a role in a steel dive tanks lifetime..

For years Faber had on thier site "....10,000 cycles to 4000 psi...."

3000 Cold

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Originally Posted by Nitrogenius

Ok.. Looking to small scale stress as it seems to be indicated in the Wikipedia source (which by the way as everyone should know always maybe flawed since there is only proofreading by other users) there might be such "distinct Limit" which is so low, that it results in a Close to unmeasureable cycles until it would fail..
I still do not believe there is a complete "no failure" treshhold..
I also very much doubt that the stress Levels applied to a steel tank would fall under such threshhold that would seem an ineffective use of the material and cause unreasonable thinkness of walls and thus also unreasonable weight and cost..
However without looking deeper into the steel formulas I would am sure that even the test pressure during hydro would fall into a load Scenario being far away from the with steel critical elastic Limit and the reasonable cycles of a steel tank which certaintly would fall into a 4 Digit number over a reasonable lifetime with corrosion and potential outside damages affecting hull thinkness etc. would be far away from any cycle number getting critical below such elastic Limit. If memory serves well getting closer to such elastic Limit the cycles to failure a definately 5-7 Digits..
So conceptually one could say that load cycle fatigue for steel tanks should not Play a role in a steel dive tanks lifetime..

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So, you're right....there IS no "no failure" threshold. The phenomenon by which this occurs is plastic deformation. Under a certain strain threshold, the deformation is "purely" elastic and therefore has no permanent crystalline structure changes. By "purely" elastic, I mean 99.999%+ elastic. Plastic deformation is a permanent crystalline structure shift. This is what "hardens" the tank. I'm not sure what the pressure is (tank mfgs won't release sufficient specs for my math, and I'm NOT cutting a tank apart for this forum :D )......but there's a point where plastic deformation actually becomes "relevant." The higher the pressure, the more lifespan reduction. From what I understand (and based off of math based off of a bunch of guesses).....our "normal" fill pressures will give our steel tanks long enough lifespans that rust and physical damage will take the tanks LONG before elastic deformation causes an issue. This is all under the assumption that we fill our tanks to "normal" pressures at "normal" speeds and treat them like "normal" people.

What Jay said is right. Faber stated that 10,000 fill cycles to 4000psi was their guarantee. However 3900psi fills in an Al 80, if not stupid, is at least not too bright, plus the extra amount of gas is negligible compared to doing this with a low pressure steel cylinder.

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Originally Posted by victorzamora

So, you're right....there IS no "no failure" threshold. The phenomenon by which this occurs is plastic deformation. Under a certain strain threshold, the deformation is "purely" elastic and therefore has no permanent crystalline structure changes. By "purely" elastic, I mean 99.999%+ elastic. Plastic deformation is a permanent crystalline structure shift. This is what "hardens" the tank. I'm not sure what the pressure is (tank mfgs won't release sufficient specs for my math, and I'm NOT cutting a tank apart for this forum :D )......but there's a point where plastic deformation actually becomes "relevant." The higher the pressure, the more lifespan reduction. From what I understand (and based off of math based off of a bunch of guesses).....our "normal" fill pressures will give our steel tanks long enough lifespans that rust and physical damage will take the tanks LONG before elastic deformation causes an issue. This is all under the assumption that we fill our tanks to "normal" pressures at "normal" speeds and treat them like "normal" people.

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Thanks Victor. That's what I figured and was trying to say.. It has been a while since that class but that's what I took away from it.. ;)

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Originally Posted by diverdarren

What Jay said is right. Faber stated that 10,000 fill cycles to 4000psi was their guarantee. However 3900psi fills in an Al 80, if not stupid, is at least not too bright, plus the extra amount of gas is negligible compared to doing this with a low pressure steel cylinder.

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I absolutely agree about not over filling an al80. The deformation of aluminum is such that the plastic threshold is MUCH lower and much less forgiving than most steels. Super high carbon steels are the exception, but they'd have terrible performance as a dive cylinder.

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Originally Posted by lv2dive

Can someone explain this to me? It was my understanding that most (if not all) firefighter's gas/air tanks were made out of some material OTHER THAN aluminun. Fiberglass, maybe? Anyway, something with a limited cycle life. So I am not clear what they have to do with the question at hand.... Neither steel nor aluminum tanks "expire" after 15 years, I understood that the fiberglass (?) tanks do... These are fundamentally different types of tanks, no?

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While I wouldn't say SCBA cylinders are fundamentally different, the lack of the U in SCBA drives a different set of materials to reduce the weight while handling the higher pressure. In other words, we don't have buoyancy in water to help the weight issue!

Current SCBA cylinders are mostly 4500 PSI though there are now 5500 PSI available. The construction is based on a thinner wall of aluminum then in SCUBA and these cylinders are then wrapped in aerospace carbon fiber and then coated with a glass and epoxy sacrificial layer. Current carbon fibers have a 5 year hydro and I am not aware of a maximum number of hydro's for these. There life is 15 years.

Keep in mind, due to the nature of their use, there are design, cost and lifecycle policies that are in place to protect the safety of FF's and wells as manage the liability of manufacturers.

Every dive in Mexico (cca 3480 psi)

http://img.tapatalk.com/d/14/07/09/y6aqe3u6.jpg

I suppose they fill it daily to that pressure

John

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Originally Posted by victorzamora

Super high carbon steels are the exception, but they'd have terrible performance as a dive cylinder.

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Can you elaborate? This would be great for the sake of discussion.

I've done a lot of really cool dives in carbon cylinders. We used these cylinders because they made more sense for the mission (and the guy buying them had deep pockets). Of course they require *a lot* of lead, but most of the lead makes a one-way trip to the dive site. Carbon tanks are way better for carrying above ground than any other cylinder out there.

-Jon

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Originally Posted by jlillest

Can you elaborate? This would be great for the sake of discussion.

I've done a lot of really cool dives in carbon cylinders. We used these cylinders because they made more sense for the mission (and the guy buying them had deep pockets). Of course they require *a lot* of lead, but most of the lead makes a one-way trip to the dive site. Carbon tanks are way better for carrying above ground than any other cylinder out there.

-Jon

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I think he is talking about high carbon steel alloy, not carbon fiber wrapped.

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Originally Posted by FW

I think he is talking about high carbon steel alloy, not carbon fiber wrapped.

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That's exactly what I meant.

Jon: I'm sure you know that steel comes in a bunch of different alloys with a wide array of properties. Steels can be very soft and malleable, other MUCH stronger but brittle. One method of making steel stronger is by introducing Carbon into the alloy. High carbon steel is used a lot in tools, especially in things like endmills. The issue with high carbon steel alloys is actually their strength. Alloys that are that strong are very brittle. A high-carbon steel tank would fail all at once, with no warning, after very few cycles, and they would actually do so VERY inconsistently due to differing fill rates and treatment methods. I mean, if we treated a full high-carbon steel alloy tank like we do our current tanks.....we'd have a bomb in our hands.

This conversation is way over my head, lol! Sounds absolutely Greek to me. Never took a physics class in high school or college. :-) Go engineers, lol!

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Originally Posted by TracyN

This conversation is way over my head, lol! Sounds absolutely Greek to me. Never took a physics class in high school or college. :-) Go engineers, lol!

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Great observation - engineers rock :)

To give some perspective imagine a scuba tank made out of the type of steel a [bendy] nail is made from or the type of steel a manhole cover [not bendy] is made of.........

3200 hot, let sit, top to 3200 max in a cool fashion.
They scare me too, even though I've had a local shop give them to me at 3600ish looking crusty. Didn't know until someone commented after a predive check and went wow! That just is not cool.
Eddy is ALs best friend.

3300

If we are talking about stages there is no tactical reason to over pressure AL tanks - they will be hard to work with multiple stages (too negative). In fact when multi-staging I under-pump my stages and/or add helium. So what you can gain in a gas volume of over-pressurized tank has not much value for dive planning because when you have multi-hop route 2-5 min extra on tank doesn't mean much. If we are talking about main gas (back gas) the story can be different but unless you are in situation when ALs are only available rentals I would prefer more compact over-pressurized steels. For recon diving day on a river I would rather also have a compact steel 46 or 50 as it sinks better w/wetsuit and no weights needed.