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Scuba Forum / General / February 20056160 Aluminum tank question
A freind of mine from my workplace was into diving years ago. He had two aluminum 80's filled, and then never used them. For 10 years now they have been in a storage closet. He is now wanting to sell his gear. Would storage for that long at full pressure cause the aluminum molecules to start to crystallise? Do you think that in a short time, like one or two seasons, these tanks will fail? I am guessing some of you have run across tanks in a similar condition, and could share your experience. Thanks, Gummi > A freind of mine from my workplace was into diving years ago. He > had two aluminum 80's filled, and then never used them. For 10 years > now they have been in a storage closet. He is now wanting to sell > his gear. Would storage for that long at full pressure cause the > aluminum molecules to start to crystallise? No. The aluminum alloy may work harden or develop sustained load cracking, but the "aluminum molecules" won't "crystallize." Do you think that in a > short time, like one or two seasons, these tanks will fail? Probably not, but it's not a good idea to store Al cylinders full. Are you sure of the alloy? Al cylinders used for scuba are usually either 6061-T6 or 6351-T6. If they're 6351, run away. If they're 6061 they're probably OK, but at minimum they'll need a new hydro (assuming they've really been sitting unused for 10 years) and a VIP+ (the "plus" is an eddy current test that is generally unnecessary for 6061 tanks, but in this case it's worth doing) > I am guessing some of you have run across tanks in a similar > condition, and could share your experience. > > Thanks, Gummi > Al cylinders used for scuba are usually either 6061-T6 or 6351-T6. If > they're 6351, run away. If they're 6061 they're probably OK, but at > minimum they'll need a new hydro (assuming they've really been sitting > unused for 10 years) Yes sure > and a VIP+ (the "plus" is an eddy current test that is generally > unnecessary for 6061 tanks, but in this case it's worth doing) ON It is NOT worth doing. It has been fairly conclusivly proved that an eddy current test is ONLY of value with 6351, It often generates false positives with 6061 and has never been proved to show evidence of SLC in 6061 Which itself has no record of SLC See Luxfer and Fill express under >> After the introduction of eddy-current technology, Luxfer received >>reports of cracking in 6061-alloy cylinders. We accepted returns on >>about 1,200 of these cylinders to conduct extensive tests. Not a >>single cylinder was found to be cracked. http://www.fillexpress.com/library/fillfaq.shtml > >>> Will you fill an SCUBA cylinder over 15 years old? Yes. If it meets > >>>all our other cylinder qualification requirements, we will fill any [quoted text clipped - 4 lines] > >>>manufactured by Luxfer prior to July 1988 as well as all cylinders > >>>manufactured by Walter Kidde. >replace spamblock with my family name to e-mail me > > Al cylinders used for scuba are usually either 6061-T6 or 6351-T6. If > > they're 6351, run away. If they're 6061 they're probably OK, but at [quoted text clipped - 10 lines] > positives with 6061 and has never been proved to show evidence of SLC in > 6061 Which itself has no record of SLC I see your point, and normally I would agree that eddy current testing is unnecessary and even potentialy harmful (because a false positive could condem an otherwise good tank) with 6061 Al tanks. But while there is no record of SLC in 6061 Al tanks, that doesn't mean the alloy is absolutely impervious to the failure mode, and I don't know of any studies that have involved having tanks stored full for ten or more years. Under these circumstances, I think the additional peace of mind afforded by doing an eddy current test outweighs the very slight downside. > See Luxfer and Fill express under Neither of these statements addresses the situation of a 6061 Al tank being stored at full pressure for 10+ years. > >> After the introduction of eddy-current technology, Luxfer received > >>reports of cracking in 6061-alloy cylinders. We accepted returns on [quoted text clipped - 10 lines] > > >>>manufactured by Luxfer prior to July 1988 as well as all cylinders > > >>>manufactured by Walter Kidde. > • ON It is NOT worth doing. It has been fairly conclusivly proved that an > • eddy current test is ONLY of value with 6351, It often generates false [quoted text clipped - 7 lines] > there is no record of SLC in 6061 Al tanks, that doesn't mean the alloy > is absolutely impervious to the failure mode, That is the point. There is no known case of SLC in 6061 Al tanks. > and I don't know of any > studies that have involved having tanks stored full for ten or more > years. While there may have been no studies (I don't know) I'm sure there have been lots of tanks used in exactly that way, many will be O2 that may be checked for pressure but are never used. Should they be hydroed? Yes Are they? Often, no I think. Would I hydro a full O2 tank never used at full pressure and for private use only? Probably not. > Under these circumstances, I think the additional peace of mind > afforded by doing an eddy current test outweighs the very slight > downside. The slight downside :-( is that there have been 100s may be 1000s of 6061 Al tanks condemned for SLC and not one of them had that problem. So I fail to see how or why getting a test done that has proved to have had manny false results and no true ones should give peace of mind. Further if you look at the data it is the hydrostatic tests that drastically accelerate crack growth. These tanks have not had that extra stress. Ther haven't even had the stress of usual filling. Also a good visual inspection will pick up the crack. They are all visible. The eddy test should never be the only reason to condem a tank. It is a reason to spend more time and check really closely. If you look at the usage of eddy testing in other fields you will see that it is used to check groups of items and will only disqualify when one of a group gives different readings. The usage in Scuba tanks is drastically different and needs highly trained operators combined with good visual examination. I would get a hydro which includes a visual of course and if you are concerned ask that they do a really carefully neck area exam before and after and that it is the same tech who does both. >replace spamblock with my family name to e-mail me > http://www.fillexpress.com/library/fillfaq.shtml >> >>> Will you fill an SCUBA cylinder over 15 years old? Yes. If it [quoted text clipped - 6 lines] >> >>>manufactured by Luxfer prior to July 1988 as well as all cylinders >> >>>manufactured by Walter Kidde. They don't mean it. Fill Express routinely turns away pre 1988 Luxfers. I agree with them. Lee |
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