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life span of aluminum tanks

Discussion in 'Tanks, Valves and Bands' started by granthammer, Feb 5, 2004.

  1. granthammer

    granthammer Angel Fish

    What is the average life span of aluminum tanks? Yes of coarse they were stored properly with air in them...I found a set in the local paper, but they havn't been used in 10 years! Should It be a problem?
  2. SDAnderson

    SDAnderson Dive Charter

    # of Dives:
    Location: On a good day, Lake Michigan
    Have them visually inspected and hydrostatically tested before you buy. Treated right, an aluminum tank will last indefinitely.

  3. Big-t-2538

    Big-t-2538 Divemaster

    # of Dives: 100 - 199
    Location: Dayton, OH
    Yeah...Viz and Hydro are a small price to pay to verify they're a good set.
  4. pasley

    pasley Instructor, Scuba

    # of Dives: I just don't log dives
    Location: Lakewood, CA
    Check the MFG and date of MFG before you buy. There are a lot of AL tanks out there made of an alloy 6351-T6 that DOT has issued a safety notice on. Small problem with them exploding. http://www.connected.bc.ca/~baquatics/explode.html

    Before you buy have them HYDRO tested and an EDDY CURRENT (VIS PLUS) Test on the neck. Personally, if they are of the suspect AL alloy, I would pass on them.

    Check these DOT websites
    I have quoted the DOT informtion on the alloys to avoid below:

    LUXFER, who mfg a lot of these tanks did NOT issue a recall, but did offer a $50.00 rebate to anyone who turned in an AL 6351-T tank made by them (essentially ther pre Jul 1990 AL tanks). That rebate offer ended Dec 31, 2003.

    From DOT http://hazmat.dot.gov/rules/68fr-53314.htm
    Cylinders manufactured of aluminum alloy 6351-T6 prior to July 1990
    include seamless aluminum cylinders marked ``DOT 3AL'', including those
    marked with ``DOT 3AL'' above or near one of the following exemption or
    special permit numbers: 6498, 7042, 8107, 8364, and 8422. In addition,
    unless determined otherwise, affected individuals should assume that a
    DOT 3AL or DOT-E 7235 cylinder manufactured outside the United States
    is constructed of aluminum alloy 6351-T6.
    On August 8, 2002, we published a final rule (Docket HM-220D, 67 FR
    51626) that amended the requirements of the HMR applicable to the
    maintenance, requalification, repair, and use of DOT specification
    cylinders. In that final rule, we added the following amendments
    pertaining to DOT specification cylinders made with aluminum alloy
    [sbull] We removed the authorization for the manufacture of DOT
    specification cylinders from aluminum alloy 6351-T6 because cylinders
    manufactured with this aluminum alloy have a greater risk of failure
    than other aluminum cylinders.
    [sbull] We prohibited these cylinders for Hazard Zone A materials
    effective on October 1, 2002. After that date, cylinders made of
    aluminum alloy 6351-T6 may not be filled and offered for transportation
    in toxic inhalation hazard service.
    [sbull] We prohibited the use of cylinders manufactured of aluminum
    alloy 6351-T6 for gases having pyrophoric properties.
    [sbull] We required a DOT specification or exemption cylinder made
    of aluminum allow 6351-T6 to be inspected for evidence of sustained
    load cracking in the neck and shoulder area.
    As stated earlier, the majority of the SLC-related ruptures
    occurred in SCUBA, SCBA and oxygen services. Additionally, for these
    services, the probability of cracking increases due to the increased
    frequency with which cylinders in these services are filled. We
    recognize that cylinders used in beverage service are also filled on a
    frequent basis. However, beverage service cylinders typically are
    filled to lower pressures than cylinders used in SCUBA, SCBA, and
    oxygen services, thereby reducing the stress levels to which beverage
    service cylinders are subjected. Moreover, in SCUBA and SCBA services,
    the cylinder is attached to the back of a diver or firefighter, which
    substantially increases the risk of injury or fatality in the event of
    a rupture. Similarly, an oxygen cylinder may be placed close to a
    patient in the hospital or home. SLC could also result in an oxygen
    leak that may cause an explosion. Therefore, because of the higher risk
    in SCUBA, SCBA and oxygen services, this rulemaking (HM-220F) proposes
    to adopt a standard for early detection of SLC to reduce the risk of a
    cylinder rupture.​
  5. SDAnderson

    SDAnderson Dive Charter

    # of Dives:
    Location: On a good day, Lake Michigan
    Good point on passing on the 6351 alloy tanks no matter what condition they are in. I wouldn't buy them either, even though the kaboom problem does seem to have been the subject of some hysteria - it's not like they're popping off all over the place.

    The two principal eddy current tests for scuba and scba cylinders should be taken with a grain of salt - although they are very accurate they are also very finicky to perform. Further examination has shown that as many as 50% of the positives they give for 6351 are false, the ratio climbs even higher for other alloys and some of the manufacturers and inspection training agencies are recommending against their use for any but 6351 tanks.

    More information about the 6351 issue is available on the Professional Cylinder Inspectors website.

  6. granthammer

    granthammer Angel Fish

    All this information is great, thanks alot, but at the same time, it a bit confusing and unclear. Is there a web site or some where I can punch in the "dot" and find out for sure if the tank is safe or not?
  7. Big-t-2538

    Big-t-2538 Divemaster

    # of Dives: 100 - 199
    Location: Dayton, OH
    I don't think the alloy is all that big of a deal if you get the tanks eddy current tested every year with the viz. But I'm not a tank geek.
  8. Bob3

    Bob3 Dive Shop

    Actually, ALL aluminum tanks will eventually fail because of sustained load cracking if filled enough times.
    Happily the minimum number of fill cycles designed into the tanks is a minimum of 10,000, a number that's probably going to take a heck of a long time to rack up.
    You're looking at almost 100 years if used on average of twice a week.

    See pasley's & reefraff's posts & follow the links.

    Pass on the tanks if they're 6351-T6, more & more outfits will be refusing to fill them.
    I hear Canada is clamping down on them more & more, as are some places in FL.
  9. reubencahn

    reubencahn SoCal DIR

    There are a number of shops here in Southeast Florida that won't fill any aluminum tank older than 15 years.
  10. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: NC
    I agree a lot of the hype on exploding 6351 alloy tanks is hysteria as with proper inspection they are not unsafe to fill and use.

    But the reality is that many shops are refusing to fill them, and whether this is out of ignorance, an unfounded fear of an explosion, or a desire to sell you a new tank, the end result is the same - they might not fill your 6351 tank.

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