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Thread: Would you buy these tanks?

  1. #21
    A good book to read on this subject and it has some useful information for owning a scuba tank: A Guide for Visual Inspection of Scuba and Scba Cylinders by William L. High.

    Or pop over to PSI-PCI - Home and read the articles in the Library section.
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  2. #22
    Grouper
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    Thanks for the links.
    Say When....

  3. #23
    Grouper
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    Just be pleased you don't have the same hydro rules as we do... in Oz, it's annual
    Cheers, TD.

  4. #24
    Quote Originally Posted by Tassie Diver View Post
    Just be pleased you don't have the same hydro rules as we do... in Oz, it's annual
    Doh. That would totally suck. I wonder if that shortens the life of the cylinder. I've been told a cylinder can be filled to 5/3 working pressure 10,000 times and still not fail. However that was by a guy trying to justify doing cave fills. He had no hard evidence to support this belief.

    If the percentage of cylinders failing in Oz is higher than in say Canada, it could be evidence overfilling is bad for a cylinder.
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  5. #25
    Grouper
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    Quote Originally Posted by scubadiver888 View Post
    Doh. That would totally suck. I wonder if that shortens the life of the cylinder. I've been told a cylinder can be filled to 5/3 working pressure 10,000 times and still not fail. However that was by a guy trying to justify doing cave fills. He had no hard evidence to support this belief.

    If the percentage of cylinders failing in Oz is higher than in say Canada, it could be evidence overfilling is bad for a cylinder.
    It's been a while since I studied properties of materials, so forgive me if I go astray...

    Relevant to tanks, there are two kinds of 'stretching' - elastic and plastic. Elastic deformation returns to its original state when a force is removed, plastic deformation is permanent. Think of a small spring - gentle stretching will return to original, basically forever, but over-stretching will result in permanent deformation.

    Also think of a piece of wire worked backwards and forwards, eventually the resistance to deformation reduces and the wire breaks. One name for this is cold-working. It's also known as cyclical fatigue. One of the characteristics of cyclical fatigue is a reduction in 'resistance' force, prior to fracture.

    With tanks, the engineering is supposed to ensure that the plastic deformation point is never reached - even when hydrotesting. This is why the test pressure is embossed on the tank. If it's never exceeded, there's never permanent deformation.

    The testing process measures the contraction of the tank after testing. This is the elastic stretch returning to original. If a tank is cyclically fatigued, it will stretch too far. This is detected in the testing and the tank fails the test. Fortunately the same thing occurs after plastic deformation, so the test will fail a tank that has been plastically deformed.

    Anyway, I seem to recall (could be wrong) the 10,000 tests thing comes from the standard that the tanks are manufactured too. The tank must be able to reach test pressure (not fill pressure) 10,000 times, before failing the test. This has nothing to do with catastrophic failure (explosion).

    So, excess annual testing should never damage a tank, only the wallet of the owner.
    Cheers, TD.

  6. #26
    Shark snagel's Avatar
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    Did I just listen to an episode of the Big Bang Theory?

  7. #27
    Guppy
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    Nope, just the facts on the topic without the seemingly obligatory "dumbing down" that, sadly, a lot of folks expect these days . . . .

    - Tim

  8. #28
    Grouper
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    Oops, I guess I shoulda added an O/T warning...

    ... or maybe OTT
    Cheers, TD.

  9. #29
    I liked it but then my wife says I'm Sheldon.
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  10. #30
    If the Aluminum tanks are in good shape on the outsie and they have air,even if they havent been hydro,they may still be in good shape to pass Hydro,make sure they dont hace any cracks on the neck and no XXXXXXXX mark on the neck

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