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cutting with poor oxygen purity

Discussion in 'Commercial Divers' started by Papyone, Jun 10, 2018.

  1. Papyone

    Papyone Angel Fish

    # of Dives:
    Location: Belgium
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    Cutting with ultra-thermic electrodes is a technique frequently used for cutting under water. Its principle is to create an electric arc and simultaneously send a jet of oxygen through the electrode which then allows the cutting of the piece. In order to achieve maximum efficiency, manufacturers of all kinds advocate the use of oxygen with a purity of at least 99.5% and specify that otherwise the user can expect a loss of performance equal to 25% per less percent of oxygen. Clearly this would mean that it would no longer be possible to cut with oxygen whose purity would be equal to or less than 95%.
    But is this really true, because some claim to dilute oxygen with air and thus cut with a much lower percentage that can even reach 60% purity.
    This seems very little, but maybe after all that remains possible.
    So I realized a small cutting test whose results can be seen here on this video :

    https://www.youtube.com/watch?v=zz5i_O4b73I
     
  2. glennster

    glennster Angel Fish

    # of Dives: 2,500 - 4,999
    Location: illinois
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    i have an arcair sea torch and use the sea jet rods for cutting underwater. i use industrial oxygen from my welding supplier that is about 99.5 percent pure. the nice thing with this system is you can use a 12v truck battery to start the rod, then it will continue to burn as long as you supply oxygen to it. i watched the video and see he is cutting on land. as the sea jet rods run about 325 dollars U.S. for a box of 50, i dont see why he would do that. oxy-propane would be a far cheaper process, the oxy acetylene the next for on land cutting.
     
  3. Akimbo

    Akimbo Lift to Freedom Volunteer Staff Member ScubaBoard Supporter

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    Industrial Oxygen is usually closer to 99.997% pure, just like medical grade. That level of purity is a byproduct of the cryogenic production process. We usually got our O2 in 6 to 12-packs.

    full.jpg
     
    rjack321 likes this.
  4. Papyone

    Papyone Angel Fish

    # of Dives:
    Location: Belgium
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    Glennster, you're partly right, for surface cuts in most cases the oxy / propane torch or oxy / acetylene is much better.

    However, there are other situations where the gas torch is unsuitable and can then be advantageously replaced by exothermic cutting.

    If you have read the generic of the video, you will have seen that the purpose of this video was simply to check if contrary to what is said in most of the cutting manuals it was still possible to cut with less 95% purity.

    Well yes it still works, and I must say that when I did this test, I was the first surprised because I was convinced that it would not do.

    Obviously, as you can see, the performance of a 70% is far from that obtained with pure oxygen and is therefore not interesting in using anything other than pure oxygen.
     
    Last edited: Jun 15, 2018
  5. Jean M Luchard

    Jean M Luchard Banned

    # of Dives: 1,000 - 2,499
    Location: Les Baux-de-Provence France
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    I watch your video with interest it is of great importance in work related principle. While I agree pure oxyen is 99.5% or better from liquification into pressure ballon it is heavy expensive and add additional risk and space. A alternative use is oxygen generator from compressed air and PSA generator producing 98% oxygen would this be a suitable alternative solution to having heavy ballon d'oxygène

    Although reducing cutting length for each rod with 98% I would be interested in what the loss is also used for thin sheet pile the standard 18 inch by 9mm rod is maybe too thick and 6mm may be quicker but with more possibility of metal adheasion back again after the first cutting run.

    If 98% and direct manufacture of the gas on vessel or dock were found to be usable then long pile runs and cheaper production of oxygen would make the costing of work much easier and safer.
     
  6. Papyone

    Papyone Angel Fish

    # of Dives:
    Location: Belgium
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    Akimbo likes this.
  7. michael-fisch

    michael-fisch Manta Ray

    # of Dives: 2,500 - 4,999
    Location: Germany
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    In europe, industrial O2 is speced to be 99.5%, since the tanks are not vaccumed before refilling and analysing each and every O2 would not be cost effective.
    IOW guaranteed to .995 and if analized probably at least .9995 percent pure.
    The gasses I use are at least an order of magnitude or 2 better than necessary. No one needs .99999 pure helium for diving when the only possible contaminant can be less than 10 ppm hydrogen.

    Michael
     
  8. Papyone

    Papyone Angel Fish

    # of Dives:
    Location: Belgium
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    Michael, you are perfectly right. I can’t imagine that when you buy oxygen for cutting purpose they would deliver bottles with an O2 purity of less than 99 or 98 % even if you’re working in third World countries.
    The purpose of these tests is just to demonstrate that contrary to what some divers and others sometimes claim, the loss of 1 or 2 percent purity in the O2 will have very little influence on the cutting performances.
     
  9. michael-fisch

    michael-fisch Manta Ray

    # of Dives: 2,500 - 4,999
    Location: Germany
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    If you're really far away from civilization on a 3rd world island the only source of O2 could be off a membrane seperator, and they traditionally don't go much beyond 80% O2.
    Some hospitals far away from access to normal medicine are forced to use membrane seperators to create O2 for their patients (actually they are creating denitrogenated air through a membrane with around 4% Argon left in the O2 mix and a healthy dose of nitrogen that didn't come out through the membrane.)

    Michael
     
  10. Akimbo

    Akimbo Lift to Freedom Volunteer Staff Member ScubaBoard Supporter

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    True, but I can't imagine a commercial diving or salvage operation where shipping HP Oxygen supplies would be significant compared to all the rest of the mobilization and supply requirements. The problem with salvage or object recovery work in remote locations is the cost of mobilization and demobilization often dwarfs the value of the recovery. I have found that the objective can often be met with explosives in these cases -- which is often a clearance rather than recovery job.
     
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