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Scuba Cylinder Long-Term Storage: Fact and Fiction

Discussion in 'Tanks, Valves and Bands' started by Doc Harry, Nov 10, 2008.

  1. Leadking

    Leadking Dive Shop

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    Looks like the word "proprietary" is key here. I would think that any conditioning of the metal would be negated by the work-hardening, annealing, and tempering processes.
     
  2. Doc Harry

    Doc Harry Solo Diver

    # of Dives: 500 - 999
    Location: Appalachia
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  3. cawzt3

    cawzt3 Angel Fish

    # of Dives: I'm a Fish!
    Location: Ft. Lauderdale
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    both were out of hydro by 1 year, stored with 3200 psi 35% ean.

    1'st tank had was perfect, just re 02 cleaned valve.
    2'nd tank had about a quarter size spot on the very bottom where it was rusted.
    looks from what i can see, maybe the fill whip had a few drops of water in it, and the tank had 3 little lines of flash rust where i assume the water came across it.
    tanks where store vertically, only minor pitting on bottom of tank, im going to have it tumbled. and hydro'd.
     
  4. Luis H

    Luis H Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Maine
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  5. Texfrazer

    Texfrazer Barracuda

    # of Dives: 500 - 999
    Location: Knoxville, TN
    349
    13
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    Any specific reason why Luis? Thanks in advance!
     
  6. Luis H

    Luis H Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Maine
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    When I worked at a dive shop in the 70’s I did a lot of tank tumbling. I haven’t done it since, but I still think of it as hard work… and I was a lot younger then.

    The only advantage that I can think about tumbling is that it can probably handle heavy rust better.

    Tumbling:
    • Requires the investment of an expensive tumblers (or some home made device).
    • Requires the tumbling media that has to be clean and some can eventually loose its cutting edge
    • It involves a lot man handling of tank full of gravel
    • It is in general a mess
    • Although it can be done dry, it is often recommended to be done wet or at least the tank should be rinsed.
    • It is very slow
    • The tank has to be cleaned just to inspect the results
    • It doesn’t do a good job of cleaning the very bottom of the tank (which can be the most rusted section).


    Wire brushing:
    • The brushes are relatively inexpensive.
    • There are wire brushes that do a great job on the bottom and other brushes for the sides.
    • It is very quick to take care of most light to medium surface rust.
    • It requires very little lifting of the tank and it is never full of gravel.
    • The rust dust can be easily blown out with the inverted tank and HP from another tank (no real need for water rinse).


    The only time that my tanks might have had anything more than very light rust is when I bought them used. Even with medium rust the wire brushes polished the inside into a clean nice finish. With the brushes it is very easy for me to keep the inside very clean when I am doing a VIP.


    Note:
    Some brusher will not work with narrow neck tanks (like 1/2 in tapered threads, I don’t know about the 7/8 inch treaded tanks). Tumbling can be used with narrow neck tanks, but it is a royal pain filling and empting the gravel with the narrow neck. My personal solution was to get rid of any steel 72 with 1/2 inch neck.

    Except for my European vintage (1957) tanks they all have the standard 3/4" NPS threaded opening.
     
  7. Texfrazer

    Texfrazer Barracuda

    # of Dives: 500 - 999
    Location: Knoxville, TN
    349
    13
    18
    Thanks for the info!

    My only potential issue (and this is coming from someone who has never used a tank brush, only a tumbler) is with the rust dust, but you indicate that this isn't an issue if you blow it out while inverted.

    I may have to consider this.

    What are your brushes made of (stainless, brass, weedeater string)?

    Thanks again for your expertise!

    Tex
     
  8. Luis H

    Luis H Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Maine
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    I use stainless steel wire brushes like the ones shown in the link above.

    The heavy duty bottom brush does a great job. You do have to move it around to get the whole bottom. I use a plastic tank plug with a hole to protect the tank threads.

    The whip also does a good job, but I also have a different wire brush that I like better. It was made from a rod with holes. The stainless steel wires where threaded through the holes and small set screws hold them in place. I think someone in Mass was making this wire brushes.



    Blowing the dust from inside the tank is easy or you can rinse it and then blow it dry. I use a copper tube attached to a cut off HP hose. I use HP air from another tank to blast the dust of. I just control the flow of air with the valve.

    Blasting HP air will also dry the inside of a wet tank in seconds. Blasting with air the inside of a wet tank will dry it quickly enough that there is no time to form any flash rust.

    Note: the HP hose I use has no added restriction, it doesn't have a small orifice.


    Pictures of brush
    [​IMG]


    Picture of whip
    [​IMG]
     
    Last edited: May 29, 2010
  9. Texfrazer

    Texfrazer Barracuda

    # of Dives: 500 - 999
    Location: Knoxville, TN
    349
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    Thanks for the awesome description!
     
  10. Hashime

    Hashime Manta Ray

    # of Dives: 100 - 199
    Location: Southern Ontario
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    The mechanism that causes tanks to deform over a long period of static fill time is called "creep".
    E=ce^(-Q/Rt) where E is the creep rate, c is a constant, Q is the activation energy, R is the ideal constant, and t is the temperature.

    For metals like steel this rate (dependent on metal strain, force/ area) ) is very very small unless under high temperatures. It is however a factor. Creep occurs in three stages, the last of which is catastrophic failure however in a metal like steel this requires several hundred years at least.
    Steel SCUBA tanks as far as my research shows use ANSI 41xx alloys. Which according to the database I have access to (used 4135)have a max elastic strength of 1210 MPa and a max elongation of 6-12% which are quite high.
    An aluminum tank made from a 5xxx alloy (this case 5456) has a max elastic strength of 103-131 MPa and elongate 12-16%.
    What the means? Well scuba cylinders are very strong and do not deform permanently easily.
    Just a note, 5456 costs $2.00 a Kg compared to $0.85 for the steel however steel is harder to work and corrodes easily.
     
    Last edited: Apr 3, 2011

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