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When safe to cut a gas tank?

Discussion in 'The Hokey Ass Message Board' started by olskool34, Oct 30, 2012.

  1. Blue One
    Joined: Feb 6, 2010
    Posts: 10,578

    Blue One
    from Alberta

    I can't believe how many of you guys buy into this BS. :eek:
    In no way is that a safe practice and I don't care how many times you or your cousins brother have done it and got away with it.

    It will not render a tank safe for cutting or welding. Consider this as just part of it.
    When a vehicle is idling the efficiency is pretty low. A lot of the fuel being burned goes out the pipe.

    There are safe ways of doing it, the absolutely best way is to steam the tank with low pressure high volume steam for at least 4 hours and then work on it while the tank is warm.
  2. No oxygen = impossible combustion.

    That's just a plain simple fact.
    Displace the oxygen and that is the end of it.
    This is 8th grade science.
    Inert gas heavier than air will do it, exhaust fumes will do that.

    I've personally seen a thoroughly washed and rinsed drum explode from residuals.

    I've also personally seen water explode, took some scientists to figure out why and it was actually a hydrogen-oxygen explosion via water. I don't think those conditions would come into play on this gas tank situation, but I've seen it happen.

    Removing the fuel source is also another way, but that's not always possible, complete, or easy. Displacing the oxygen is always possible, complete and easy.
    Last edited: Oct 31, 2012
  3. slowmotion
    Joined: Nov 21, 2011
    Posts: 3,200


    Purgeing a fuel tank with steam for 24hrs before repair was the manditory procedure in a locomotive shop I used to work out of. FWIW.
    Joined: Jun 3, 2005
    Posts: 8,049


    Hot water and an excess amount of dish detergent. Done. Can't remember how many sumps I welded into race cars doing just this. Does it still stink? Sometimes. Still flammable? Not yet. To purge with an inert gas is probably better than car exhaust, that is unless everyone has the exact hose needed to run exhaust into the filler just layin around. If you do purge, you should be fairly well regulated too. Too much is a waste of gas and $$$.

    Safety 1st, I agree completely. Don't fear the job, use your head, think ahead. Old fuel? Wash it out with a mild solvent 1st like mineral spirits (available cheap at most hardwares called "paint thinner", read the ingredients), then the hot soap n water. Still scared? Let it dry overnight. Still smelly? Wash it again, then go after it while it's still wet. Then again, a simple sawzall shouldn't make sparks with fresh blade unless you insist on going through the old welds at full tilt. Do a pilot hole with a holesaw to get started. Or just buy a repop replacement panel and sell the tank to fund it (I know, already mentioned, but a good idea).
  5. mynode
    Joined: Sep 22, 2012
    Posts: 25


    One note on welding or braising tanks using water:
    I watched a highly experienced welder attempt to braise a motorcycle gas tank filled with water. He consistently wound up with a pinhole leak in the braise. I realized that the problem was that the remaining small air bubble was not vented to the atmosphere and that when he applied heat, the air expanded pushing air through the braise pool and when he removed the heat the air contracted pulling air back through the pool. This would leave a tiny channel in the solidified braise which would leak fuel. We vented the air bubble with a piece of tubing and the problem was solved.
  6. The dry ice deal works really well - most grocery stores sell dry ice and you just break it up and put it in there. let it mostly evaporate and cut away.
  7. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,428

    Von Rigg Fink
    from Garage

    dish detergent , warm water, a few good rinse jobs, and than..this is how I do it..

    I have a hose i stick on the end of my Harley's exhaust pipe..I start her up and let her run til the tank is warm,, 10 min. or so

    I leave it running and start cutting or welding..

    Dont say I cant do this, and dont tell me im going to kill myself..because if that were the case I'd been dead too many times to count

    I aint dead yet

    but than again..some guys could fuck up a free lunch,, aint that right Highlander;)
  8. 302aod
    Joined: Dec 19, 2011
    Posts: 275

    from Pelham,Tn.

    The guy that ran the body shop did this at the dealership I worked at. He got a piece of exhaust hose that we used during cold temps to get exhaust to behind the vehicles. He drained the tank, exhaust ran through the hose from a running vehicle, to the filler connection, let the vehicle run a few minutes, then brazed the hole in the tank. No clean-up or drying. I used this method a few times over the years.
  9. goose-em
    Joined: Aug 23, 2008
    Posts: 349

    from Louisiana

    Inert gas means no oxygen.

    CO2 is not inert, C=carbon dioxide, O = oxygen

    Argon is and so is Helium. Any mix gas with an O in it is not inert.

    I.e. 75/25, not inert, 80/10 not inert.
  10. Carbon dioxide is one carbon atom bonded to two oxygen atoms.
    For you to add oxygen to anything from C02 you first need to split these atoms.
    If you are splitting atoms you have bigger things to worry about than gas tanks.
  11. Blue One
    Joined: Feb 6, 2010
    Posts: 10,578

    Blue One
    from Alberta

    If you paid attention I was referring to the practice of running a vehicles exhaust through the tank to render it safe.

    The steaming method I posted is accepted as the best and safest method.
    We teach it to our Welders in the Industrial safety portion of our Apprenticeship training.
  12. the metalsurgeon
    Joined: Apr 19, 2009
    Posts: 1,239

    the metalsurgeon
    from Denver

    Water and washing up liquid.wash out and refill and leave to sit for a day or 2.empty and weld or cut away.
  13. the metalsurgeon
    Joined: Apr 19, 2009
    Posts: 1,239

    the metalsurgeon
    from Denver

    Forget about the exhaust idea...
  14. Wild Turkey
    Joined: Oct 17, 2005
    Posts: 903

    Wild Turkey

    Sorry, but your chemistry isn't quite accurate.

    "Inert" means it won't react. Carbon dioxide has two oxygens bonded with each carbon. "Bonded" means not free to react so it's an "inert" gas. If the oxygen was avaliable for reaction it wouldn't be good as a welding shield gas.

    Argon and Helium are examples of "Noble" gases that are also inert.

    I've used the dry ice method with no problem. A little water in the bottom, drop in the dry ice, wait until fog is coming out and get 'er done:D

    My dad was blown out of a truck bed when he tried welding on a tank that had been flushed with plain water several times.:eek:
  15. mynode
    Joined: Sep 22, 2012
    Posts: 25


    CO2 is not a gas mix, it's a chemical compound called carbon dioxide.

    carbon-C di-2 oxide-O

    It will not form a combustible mixture with any fuel. It's actually one of the products of combustion of a hydrocarbon.
  16. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,834


    Yes, and let's not forget it's a great ingredient in fire extinguishers.
  17. If that is the case, then why didn't my tank blow up in my face, a few months ago when I welded it using exhaust to purge it? It had gas in it the day before, all I did was empty it out and let it sit overnight. Don't tell me I was lucky. There is no luck. If you have heat and fumes, you will have an explosion providing there is O2. Without exaggeration, I have welded, soldered or brazed on 50 or 60 tanks over the years and have never had one blow on me. My low pressure, high volume steam machine, which of course we all have in our home shops, is broken, so I guess I'll continue to use the BS system that has worked, for me, for a lot of years.
  18. Bingo!

  19. pitman
    Joined: May 14, 2006
    Posts: 4,933


    The old trick of shutting the ignition off, pumping the accelerator to load the muffler w/ fuel the turning the key back on. Ka-boom.
    What I'm curious about is, that as long as the engine supplying the exhaust is in good tune and running lean enough to complete combustion, the fumes may be eliminated.
    Woe would be if the choke was on, or some residual fuel-gunk, running fat, etc.
  20. Blue One
    Joined: Feb 6, 2010
    Posts: 10,578

    Blue One
    from Alberta

    :rolleyes: I already said :
    In no way is that a safe practice and I don't care how many times you or your cousins brother have done it and got away with it.

    There is no debate.
  21. Well there you have it fellas ! No debate !!!

    you need a steam generator suitable for 24 hrs continuous use.

    Dripping with sticky nasty sarcasm, don't get any on you


    No oxygen , no fire remember that ?
    Of that there is no debate.
    I fear for our future if educators fail to grasp the simple stuff.
    Last edited: Oct 31, 2012
  22. Roger53
    Joined: Aug 8, 2010
    Posts: 383


    An inert gas is the best way it replaces the oxygen in the tank.When I was a young un I did the water deal and well it didn't work so well. Roger
  23. Blue One
    Joined: Feb 6, 2010
    Posts: 10,578

    Blue One
    from Alberta

    We teach safety, sometimes it isn't simple or easy. It is not a matter of grasping anything. I didn't once say this entire thread was wrong, just that one part of it.

    There are safe ways to do things and unsafe ways. There are different ways , some are safer than others, using vehicle exhaust is not one of them.

    There have been a number of good suggestions on this thread, filling with water, or using an inert gas. We also teach alternative methods which have been mentioned.

    Steaming is the best, other ways work but again, running exhaust through a tank is neither safe or acceptable.
  24. I think it's safe when you can throw a match in there and it don't go...... POOF!!!

    I know, I know.... You guys are thinking, "now why didn't I think of that"! Well you see not all of the smart brains can go to everyone, only a select few.
  25. Just be sure to register with the Darwin Award committee first. I'd hate to see you miss out on a chance for fame
  26. Well, since you are the world's foremost authority, I should heed your advise and end the debate. It's just not in my nature.
    Besides the old graybeard who told me about the exhaust trick when I was a pup, it was confirmed by my welding instructor 25 years ago when I decided to upgrade my skill set and get certified. If your credentials exceed those of Jack Compton, then I will deign to your superior knowledge. Click below
  27. Blue One
    Joined: Feb 6, 2010
    Posts: 10,578

    Blue One
    from Alberta

  28. I'm not sure why your cousins brother wouldn't be your also be your cousin ? You even said that twice
    See why I'm worried about our future? Maybe you guys figure cousins differently in Canada.
    Dont be offended if nobody takes you seriously, talk a lot of technical stuff- half of its wrong and you can't even figure out cousins.

    grasp the simple things
  29. Fenders
    Joined: Sep 8, 2007
    Posts: 3,922


    Yup, dry ice...
    I wash it out with soapy water, dump in ten pounds of dry ice, wait a bit, then start cutting.....
  30. F&J
    Joined: Apr 5, 2007
    Posts: 13,214


    This went way too long.... the OP already did the tank, finished the car, drove it for 10k miles, and has since sold it..

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