OP
SparticleBrane
Contributor
Thanks for adding some more info to the thread, SS. 
Life of aluminum -- age or # of cycles based?
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I've done quite a few VIP inspections, and have found quite a few AL80s that had severe oxidation. Especially with tanks that had been Nitrox tanks but then sat empty for awhile.
The outside of the tank looked perfectly clean but the inside..not so good.
In order to O2 clean a tank like that, the inside walls had to be scoured with an abrasive whip, sometimes tumbled with abrasive ceramic beads, cleaned with a solution, and dried. Its a few hours labor, unless you have the means to do it yourself.
The outside of the tank looked perfectly clean but the inside..not so good.
In order to O2 clean a tank like that, the inside walls had to be scoured with an abrasive whip, sometimes tumbled with abrasive ceramic beads, cleaned with a solution, and dried. Its a few hours labor, unless you have the means to do it yourself.
Sparticle.......in theory, wrought aluminum does undergo property changes with age. This is the concept of age hardening or age treatment in aluminum manufacturing. However, since most of the age hardening of wrought aluminum occurs in the first 2 to 20 days, there is not much material change left for the remaining years.
With an aluminum cylinder, which is manufactured with a draw and iron process, there is solution treatment of the cylinder as a post-processing step. This "eliminates" much of the potential for "age" hardening, but does not completely remove it. It is important to point out that any change, due to age hardening, sufficient to alter the use of an aluminum cylinder for its intended purpose, is so small and the length of time is so long that it is likely insignificant.
Repeated "cycling" or "working" of an aluminum part has an impact, even if that work is well below the stress (there are a variety of them) points of the alloy. For an aluminum cylinder, the number of "cycles" (fill and empty cycle) would take so many years that it is probably not an issue. However, a more realistic example would be airplane wings on a large Boeing aircraft. These parts are "cycled" thousands of times in a typical 2 hour flight. The aluminum parts in that wing structure, including the aluminum wing skin, are subjected to amazing amounts of "work" as the wings flex and bend during flight operations. The FAA and the airplane manufacturers propose a "lifespan" for some of these parts. Most airplanes become obsolete due to economy issues before most of these parts reach their "lifespan" limit. However, replacement of aluminum parts in airplane wings does occur due to "lifespan" issues.
In my previous life, we tested "out cycled" used aircraft wing skins when they were removed from service and found some pretty interesting property changes. Airplane wing skins are a cool example of life and death property testing, because when the skin is returned, we have access to the EXACT testing of that particular skin when it was put in service. This can then be compared to the properties of the same part when it is removed from service years later. We also have access to exact "in service" hours, and can therefore make some rough statistical estimates of the number of work cycles to which they have been exposed. In addition, information about any "unusual" service stresses would also be available. Some of the changes are both amazing and a little frightening if you are a frequent "passenger" of older commercial aircraft.
All that I have written is for reading for the bored, but doesn't say much about scuba cylinders. In short, neither age or reasonable cycling would matter much to an aluminum cylinder. Us divers can't dive one enough for cycle to matter and we can't live long enough for age to matter. Sorry for the hijack, but I was bored this morning.
Phil Ellis
www.divesports.com
With an aluminum cylinder, which is manufactured with a draw and iron process, there is solution treatment of the cylinder as a post-processing step. This "eliminates" much of the potential for "age" hardening, but does not completely remove it. It is important to point out that any change, due to age hardening, sufficient to alter the use of an aluminum cylinder for its intended purpose, is so small and the length of time is so long that it is likely insignificant.
Repeated "cycling" or "working" of an aluminum part has an impact, even if that work is well below the stress (there are a variety of them) points of the alloy. For an aluminum cylinder, the number of "cycles" (fill and empty cycle) would take so many years that it is probably not an issue. However, a more realistic example would be airplane wings on a large Boeing aircraft. These parts are "cycled" thousands of times in a typical 2 hour flight. The aluminum parts in that wing structure, including the aluminum wing skin, are subjected to amazing amounts of "work" as the wings flex and bend during flight operations. The FAA and the airplane manufacturers propose a "lifespan" for some of these parts. Most airplanes become obsolete due to economy issues before most of these parts reach their "lifespan" limit. However, replacement of aluminum parts in airplane wings does occur due to "lifespan" issues.
In my previous life, we tested "out cycled" used aircraft wing skins when they were removed from service and found some pretty interesting property changes. Airplane wing skins are a cool example of life and death property testing, because when the skin is returned, we have access to the EXACT testing of that particular skin when it was put in service. This can then be compared to the properties of the same part when it is removed from service years later. We also have access to exact "in service" hours, and can therefore make some rough statistical estimates of the number of work cycles to which they have been exposed. In addition, information about any "unusual" service stresses would also be available. Some of the changes are both amazing and a little frightening if you are a frequent "passenger" of older commercial aircraft.
All that I have written is for reading for the bored, but doesn't say much about scuba cylinders. In short, neither age or reasonable cycling would matter much to an aluminum cylinder. Us divers can't dive one enough for cycle to matter and we can't live long enough for age to matter. Sorry for the hijack, but I was bored this morning.
Phil Ellis
www.divesports.com
Gilldiver
Contributor
I am an ME with Sikorsky aircraft specialized in aluminum processing and coating. Just a few points:
What Boeing considers High cycle fatigue, I call a 20 minute ground run. Take the CH-53E, it has 7 main rotor blades and each time a blade passes over the tail structure a vibration cycle is imparted into the airframe.
Now lets see 7 blades x 200 RPM = 1400 cycles per minute
1400 x 60 minutes = 84,000 cycles per hour
84,000 x 20,000 hour life span of the airframe = 1,680,000 cycles
But then we rebuild and run them another 10,000 hours.
we use a lot of 6061, 7075, and 2024 and it all has to last for the above. An avg SCUBA tank will be lucky to 100 cycles per year.
Also, never, ever say how aluminum will corrode in any general way. It has many differing ways and the coatings, be they anodize Type I, IB, IC, II, or type III, primer and type of primer, and finally the topcoat paint will all effect the corrosion process to surprising degrees. If we fully understood the corrosion process involved with aluminum, the US Navy would not be spending over 2.5 billion dollars per year fixing corrosion on its aircraft.
For any SCUBA tank, keep the insides dry, if you took the pressure real low in the water, take the valve off and have a look, only get fills at compressors that are maintained correctly, make sure that the valve connection is dry when you hook up to the compressor, and always rinse any tank to get the salts off when you get home.
What Boeing considers High cycle fatigue, I call a 20 minute ground run. Take the CH-53E, it has 7 main rotor blades and each time a blade passes over the tail structure a vibration cycle is imparted into the airframe.
Now lets see 7 blades x 200 RPM = 1400 cycles per minute
1400 x 60 minutes = 84,000 cycles per hour
84,000 x 20,000 hour life span of the airframe = 1,680,000 cycles
But then we rebuild and run them another 10,000 hours.
we use a lot of 6061, 7075, and 2024 and it all has to last for the above. An avg SCUBA tank will be lucky to 100 cycles per year.
Also, never, ever say how aluminum will corrode in any general way. It has many differing ways and the coatings, be they anodize Type I, IB, IC, II, or type III, primer and type of primer, and finally the topcoat paint will all effect the corrosion process to surprising degrees. If we fully understood the corrosion process involved with aluminum, the US Navy would not be spending over 2.5 billion dollars per year fixing corrosion on its aircraft.
For any SCUBA tank, keep the insides dry, if you took the pressure real low in the water, take the valve off and have a look, only get fills at compressors that are maintained correctly, make sure that the valve connection is dry when you hook up to the compressor, and always rinse any tank to get the salts off when you get home.
OP
SparticleBrane
Contributor
Pete, thanks for posting this information. I am always thankful when people who are much more knowledgeable than I can come in and contribute to the discussion.
Rudebob
Contributor
I believe the Catalina was manufactured using 6061 in the T-6 condition which means the material has been artificially aged. As mentioned, while many aluminum alloys will naturally age harden over time after solution anneal (Type 'O' condition), they cannot fully hardened to the same limits obtained from artificial precipitation hardening. In other words, a 6061 T-6 tank sitting for several years cannot naturally age more beyond what what was artificially done at the time of manufacture.
Obviously, other factors such as corrosion attack and possible crack progression (fatigue) can alter the life of an aluminum tank. You could likely rule out the possiblity of these mechanisms being present by visual inspection for corrosion and know service life for fatigue. Fortunately, stress corrision cracking is not much of a consideration for 6000 series materials like 2000 or 7000 series materials are susceptible to.
While the working pressures of these tanks are well within the elastic limit of the material that does not automatically eliminate the potential for fatigue failures. However, these type of failures (low stress, high cycle) usually require an initiation site such as a gouge, scratch, pit, etc. for crack advancement and a very high rate of cyclic exposure. I don't believe most aluminum tanks will ever experience these levels of loading/unloading mechanisims if was used mulitple times everyday for the rest of your life. The only way this would likely occur if the wall thickness were compromised due to corrosion or severe wear.
On the other, exceeding the elastic limit (yield strength) can result in high stress, low cycle fatigue failures which require no initiation sites. Hopefully, reduant safety measures, including burst disks, popoff valves, hydrostatic testing, etc. can prevent and/or identify this condition.
'bob
Obviously, other factors such as corrosion attack and possible crack progression (fatigue) can alter the life of an aluminum tank. You could likely rule out the possiblity of these mechanisms being present by visual inspection for corrosion and know service life for fatigue. Fortunately, stress corrision cracking is not much of a consideration for 6000 series materials like 2000 or 7000 series materials are susceptible to.
While the working pressures of these tanks are well within the elastic limit of the material that does not automatically eliminate the potential for fatigue failures. However, these type of failures (low stress, high cycle) usually require an initiation site such as a gouge, scratch, pit, etc. for crack advancement and a very high rate of cyclic exposure. I don't believe most aluminum tanks will ever experience these levels of loading/unloading mechanisims if was used mulitple times everyday for the rest of your life. The only way this would likely occur if the wall thickness were compromised due to corrosion or severe wear.
On the other, exceeding the elastic limit (yield strength) can result in high stress, low cycle fatigue failures which require no initiation sites. Hopefully, reduant safety measures, including burst disks, popoff valves, hydrostatic testing, etc. can prevent and/or identify this condition.
'bob
Gilldiver
Contributor
What you list is what is looked for on a normal inspection. As I said above, all tanks are done "On Condition."
Get your head out of SCUBA and look at what other things Aluminum tanks are use for such as medical O2, soda and beer CO2, and thousands of industrial uses. These tanks may be stored is unheated/un-cooled sheds for tens of years without testing as they will only get inspected when they go back to the gas fill company. If they are in permanent banks, they may never get re-inspected and they may be upright or horizontal.
All of these other uses, which far out number SCUBA, only do a visual inspection of the outer surfaces at time of fill and a 5 year Hydro.
The one thing SCUBA does is subject the same bottles to an abusive and highly corrosive environment and relatively uncontrolled filling practice - compressors which may or may not be properly maintained and immersion and/or storage near salt water. It is the SCUBA industry that came up with the yearly visual requirement to address these special/abusive practices.
Finally, at least for the US, there are no DOT required inspections/recalls that are particular to SCUBA and there are no lawyers and class action suits in the land where the lawyers are always looking for a meal ticket. That should tell you something.
Get your head out of SCUBA and look at what other things Aluminum tanks are use for such as medical O2, soda and beer CO2, and thousands of industrial uses. These tanks may be stored is unheated/un-cooled sheds for tens of years without testing as they will only get inspected when they go back to the gas fill company. If they are in permanent banks, they may never get re-inspected and they may be upright or horizontal.
All of these other uses, which far out number SCUBA, only do a visual inspection of the outer surfaces at time of fill and a 5 year Hydro.
The one thing SCUBA does is subject the same bottles to an abusive and highly corrosive environment and relatively uncontrolled filling practice - compressors which may or may not be properly maintained and immersion and/or storage near salt water. It is the SCUBA industry that came up with the yearly visual requirement to address these special/abusive practices.
Finally, at least for the US, there are no DOT required inspections/recalls that are particular to SCUBA and there are no lawyers and class action suits in the land where the lawyers are always looking for a meal ticket. That should tell you something.
DaleC
Contributor
Not wanting to hijack here but you guys sound smart so I'll ask a Q.
I have 3 Al 80's and want to see what alloy they are made of but I'm not sure which numbers I should use for ref. Here is what is written on the shoulders:
Tank 1:
(a Catalina) CTC DOT-3Al 3000 S80 M4002
A44991 12 IA/11 87
Tank 2:
CTC SP922 - 3000 3 B 82 (The B is inside a circle.. Hydro mark?)
P3352 USD 11 A 76 (the "A" has a vertical line decending from the cross brace)
Tank 3: Same as tank 2 but with a different P # (P2809)
Which is the date and which is the serial #?
I have 3 Al 80's and want to see what alloy they are made of but I'm not sure which numbers I should use for ref. Here is what is written on the shoulders:
Tank 1:
(a Catalina) CTC DOT-3Al 3000 S80 M4002
A44991 12 IA/11 87
Tank 2:
CTC SP922 - 3000 3 B 82 (The B is inside a circle.. Hydro mark?)
P3352 USD 11 A 76 (the "A" has a vertical line decending from the cross brace)
Tank 3: Same as tank 2 but with a different P # (P2809)
Which is the date and which is the serial #?
Scared Silly
Contributor
Cylinder 1 - AL 6061. Why Catalina never used any alloy but AL 6061
Cylinder 2&3 - AL 6351. Why made by Luxfer in 1976 ( 11 "A" 76 hydro mark is Luxfer's). Luxfer used Al 6351 up until 1988 or so.
Source:
http://phmsa.dot.gov/staticfiles/PHMSA/DownloadableFiles/Files/3al_advisory.pdf
Some light reading:
http://www.epa.gov/EPA-IMPACT/2006/August/Day-29/i14255.htm
Cylinder 2&3 - AL 6351. Why made by Luxfer in 1976 ( 11 "A" 76 hydro mark is Luxfer's). Luxfer used Al 6351 up until 1988 or so.
Source:
http://phmsa.dot.gov/staticfiles/PHMSA/DownloadableFiles/Files/3al_advisory.pdf
Some light reading:
http://www.epa.gov/EPA-IMPACT/2006/August/Day-29/i14255.htm
Right -- in this particular instance I was planning on using it for a stage bottle and Catalina 80s aren't known to 'ride'very well, hence why I passed on the deal.
I stumbled onto this forum while researching three Catalina tanks that I recently inherited. I see that this is a rather old thread but had a question after reading through it.
I am planning to use these strictly as paintball fill tank stations. They will be transported in the trunk strapped side-by-side while lying on their sides. At home, they are stored upright in the garage. The last visual inspection certificates were back in '94 shortly after the manufacture date (02A94). I don't see any other visual inspection certificates affixed. They have been stored topped-off in a cool basement for a very long time (exact duration unknown, but I am guessing for about 10 years). The tanks look to be in very good condition from the exterior (e.g. no corrosion, nicks or dents). All three are painted with a semi-black paint. I have no idea how many times these were filled.
I would like to ask if you (or anyone) could expand on the comment around why Catalina's are not known to 'ride' well? Reason being, I plan to bring these with me to the fields and don't want to be ignorant to a potential hazard. I am carefully handling the tanks (don't lift by the regulator or allow to roll around in the trunk) but they are subjected to quite a bit of road vibrations and the occassional bumps on the road.
Is this something that I should be concerned about?
I know this isn't a SCUBA question, so many thanks in advance.
Jack
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