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Steel Tank Condemned: Cracks in Threads?

Discussion in 'Tanks, Valves and Bands' started by Barnaby'sDad, Oct 19, 2020.

  1. abnfrog

    abnfrog Tech Instructor

    # of Dives: 2,500 - 4,999
    Location: great white north
    i would love to get it .....i might even trade for a new tank ? pm me
    StefinSB, rjack321, couv and 3 others like this.
  2. Cio

    Cio Angel Fish

    # of Dives: 100 - 199
    Location: NJ
    I can see you want to err on the side of caution and that's commendable BUT, I wouldn't call that a crack so quick. The base of The threads isn't affected, this leads me to believe it is not a neck crack but marks left over from something. Many refer to the tap leaving the marks but those threads look like rolled threads which could answer why the marks look like they do, rolled threads are formed not cut and don't leave a straight line like a tap would. Also, I have seen cracked tanks and a crack that big (you took a phot of it) would be visible from the outside. Most small cracks are found due to leakage after a hydro.
    If it were my tank, I would do the following, bring it to a firehouse, put it in their containment fill and put 500 Psi in it, look for pressure loss, increase pressure up to service pressure and look for leakage.(while in the containment)
    Still not convinced, do as other suggested an magnaflux it, local machine shops should be able to do this for you if they weld castings regularly.
    Still not convinced, have it hydroed, direct at the local place should be super cheap, I get them done for $5
    Sonic would be the best but I'm guessing that wont be cost effective for you. (you can ring it like a bell, if it sounds bad to you, it is a serious crack)

    Now, you are probably saying, why should I listen to another Internet expert, well in real life I am what would be called a professional, I design, build and maintain HP gas systems, I actually do have real (paid) experience with this stuff.

    What is it the pics is worthy of an investigation and I'm not arguing its good to go from a photo, it could be a legit crack in the grain that's not noticeable with the human eye, but it can also a non issue.

    Good thing with a hydro is it will open that up, it may even pass hydro but the test will open it up and make it leak, don't consider it good just because it passes hydro. ( your hydro guy can hydro it, fill it and put it in his bath to look for bubbles if you ask nicely.)

    Good luck and remember that blowing yourself up is highly unlikely, these things are engineered against the generally stupidity of people, look at how successful cave filling is. Most people get it from fittings or tube not the tanks.
    Johnoly and uncfnp like this.
  3. lexvil

    lexvil ScubaBoard Sponsor ScubaBoard Sponsor

    # of Dives: 1,000 - 2,499
    Location: jamestown, ca.
    While I’m not convinced that it is definitely a crack, I would do what was mentioned above what I did with an 80 with the bad alloy, mine too passed all testing but the thought of a 3000 psi bomb on my back on a hot day led me to self condemn the tank which now serves as a tank strap adjustment and backplate web adjuster model. No tank is worth the risk even if it’s just perceived risk.
    Johnoly and rjack321 like this.
  4. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    I'd be doing this.
    Barnaby'sDad likes this.
  5. Barnaby'sDad

    Barnaby'sDad ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 50 - 99
    Location: Virginia
    PM sent.

    I lack the time necessary to do what you suggest. I did another search...there are no local hydro facilities. I’d have to leave the area to do this and like I said...literally not worth my time. I’d rather break out my angle grinder and cut it open for the LOL’s.
  6. Ghost95

    Ghost95 Barracuda

    # of Dives: 1,000 - 2,499
    Location: Florida
    Whatever happens or whoever gets this cylinder, please keep us updated. I'd love to find out what the mark really turns out to be.

    To me, it looks like a crack but it is really strange that it is interrupted by the threads. You'd think a crack would continue through the threads at both the peaks and valleys.

    Johnoly, couv, grf88 and 2 others like this.
  7. shurite7

    shurite7 Dive Shop

    # of Dives: 1,000 - 2,499
    Location: In transit
    There is a tiny bit of doubt. However, I agree with the decision not to approve the VIP. If at all possible, it would be interesting to see the results from further investigation.
    BurhanMuntasser likes this.
  8. wnissen

    wnissen ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 50 - 99
    Location: Livermore, Calif.
    If money (or safety) were no object, that is what I would love to see. Presumably if you took it to twice service pressure, it would go boom, so let's get the Mythbusters in here and see if the apparent crack in the threads is the weak spot or not. You'd presumably be able to differentiate the threads and the neck from the main body of the cylinder, without doing extensive fragment capture (through surrounding it with newspaper or some other packing material probably wouldn't hurt).
  9. GJC

    GJC Solo Diver

    # of Dives: 200 - 499
    Location: Southern California, USA

    Above are from the SDI/TDI VIP Inspector online training course. I am far from being an expert on thread evaluation, but looking at the posted pic of the cylinder in question, I am leaning toward it being a machine mark. Additional views may be helpful.
    rsingler, Bob DBF, BRT and 5 others like this.
  10. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, WA
    These are tool marks

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