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Welding a fuel tank

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  • Juiceclone
    replied
    The water system works well in sits where it seems applicable. Object being to reduce the available volume of any flammable mixture to a point where it's not damaging. I have used the exhaust from a shop vac blasting in a tank prior to and during welding/brazing and that has been ok also ..prevents any buildup of fumes. All methods should include a thorough clean out first. When u heat the tank surface to repair, the heat will drive additional flammable vapors out of the pores in the metal and rust? and must be taken into consideration. Also when using oxy/acet torch it's possible to unintentionally introduce oxy thru the flaw you're repairing which ain't good!!

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  • Mike279
    replied
    I welded my Motorcycle tank in July and have ridden it thru the Summer. I have been looking at the weld to see if there is any issues and so far everything is good. I found out the area I welded was prone to failure from another forum. The replacement cost of my tank would have been close to 1000 dollars and used tanks were not looking as good as what I have. Welding with the Dry Ice in the tank was very easy and I would say very safe. Dry ice was cheaper than trying to use inert welding gases and easily bought. Ventilation was as easy as an open door. I consider it a very good option for a hard to replace tank. Mike

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  • GNM109
    replied
    There are some excellent methods mentioned above but even though I'm a pretty fair welder, I'm going to let others do all the welding on fuel tanks. Whatever method you use, I'm of the opinion that you never really know what's going to happen when you weld a fuel tank.

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  • flylo
    replied
    Originally posted by Magicniner View Post
    The tank should either be steamed clean or have an inert gas piped in whilst working to maintain a non flammable mixture, a very easy way to achieve the second is to pipe the exhaust from an internal combustion engine into the tank, clean breathing air for the welder should be a consideration ;-)
    Filling with water and just leaving the area to be welded unfilled doesn't make a tank safe, it confines the potential explosion with an incompressible liquid - very un-smart and well documented bad practice for tank welding!

    - Nick
    This is how I've seen done & done some myself & it works fine, not a lot of extra work or cost.

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  • 914Wilhelm
    replied
    A pound of dry ice will produce 62 gallons of CO2 and is 1 2/3 denser than atmospheric air. I've use dry ice and let it sublimate with the exit of the tank at the highest point.
    Last edited by 914Wilhelm; 11-03-2016, 06:12 PM.

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  • Mike279
    replied
    I enjoyed reading this thread and as it happens I had to weld one of my motorcycle tanks. Having soldered a few way back and not really pleased with how they came out I opted for using the mig. The tank in question had a crack in an area midway up the tunnel next to a strengthening rib. A rust free, near perfect tank that would cost way too much to replace. Pulled all the fittings and washed it out with a degreaser. Then a bit of the sunshine treatment for a couple of days. Being able to get the faintest of gas odors I ran some compressed air thru a couple of different times. Then to the store to get some dry ice which I found is sold in handy pellets about 2 inches long and about an inch in diameter. I bought five lbs for just over six dollars. So my five gallon tank is suppose to need about a pound of dry ice to displace the air. I throw in a couple of pounds and get the welder ready. The dry ice goes from solid to gas and will build pressure while settling at the bottom. A shop towel in the filler hole oriented up to vent air first and then keep out regular air, all other openings plugged. After awhile the tank is getting cold. I try to position it for welding and move the dry ice away from the weld area. I use a heat gun to dry the condensation that is formed near the area I want to weld. With a steady amount of CO2 exiting the tank I fire up the welder. The CO2 is building a little too much pressure so I adjust the shop towel to let more gas out. First weld ground down and redone. Realizing that installing the gas cap will pressurize the tank I pop off a cap on one of the fittings and just hold finger over it and get out the bubble solution. Find a second crack and install the shop towel again. Weld crack number two. Decide to strengthen the area a bit and retest. All good and the tank is perfectly clean inside after the the CO2 is gone. Leftover dry ice for drinks, break into smallish bits to get that Halloween mist. Two weeks and a few heat and cool cycles and the tank weld is holding great. Mike

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  • vpt
    replied
    Originally posted by Don Young View Post
    In the 40's and 50's, Harley and Indian tanks were small and strong enough to contain any fire/explosion. It was common practice to empty the tank, blow it out a bit with air, and stick a lit torch in the filler opening. The result was a pretty good boom but I never saw any evidence of tank deformation. When the torch was applied a second time there was often a second smaller reaction. I have no idea how close the tanks were to rupturing and certainly do not claim this procedure to be safe.
    .
    That was "paintless dent removal" before there was paintless dent removal.

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  • Don Young
    replied
    In the 40's and 50's, Harley and Indian tanks were small and strong enough to contain any fire/explosion. It was common practice to empty the tank, blow it out a bit with air, and stick a lit torch in the filler opening. The result was a pretty good boom but I never saw any evidence of tank deformation. When the torch was applied a second time there was often a second smaller reaction. I have no idea how close the tanks were to rupturing and certainly do not claim this procedure to be safe.

    I have a 300W American Beauty electric soldering iron which I have used to solder automobile gas tanks. I won't get a torch close to one.

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  • flylo
    replied
    No gas for 5 years I'll weld it. I've welded many by dumping out the gas & running a hose from an exhaust pipe purging all the air out of the tank. In the rental business the insurance company insisted when a machine came back to fill the tank before putting them back on the showroom floor. They were smart enough to know that a full tank is safe & a almost empty is not.

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  • GNM109
    replied
    Originally posted by J Tiers View Post
    I suppose the point is that there cannot be any explosion unless there is air, fuel, and an ignition source. If full of water, there can be fuel and ignition, but no air. Water is not air, so there could be no burning.

    Presumably everyone thought it was full of water. Myself, I suspect there was an air pocket at the weld location, that supplied the oxygen for the explosion. And there could not have been much else between the pocket and the filler neck, because otherwise there would have likely been a seam split, or at least some distortion of the tank from internal pressure.

    Welding otherwise than backed by air would have developed a bubble of steam there. You can weld underwater, even stick weld, I am told. I know cutting torches can work underwater. But you can't get things to explode in a steam atmosphere, the oxygen is already bound to hydrogen, forming its oxide (water).


    It's possible that there was an air pocket. We will never know. I can only tell what happened.

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  • J Tiers
    replied
    I suppose the point is that there cannot be any explosion unless there is air, fuel, and an ignition source. If full of water, there can be fuel and ignition, but no air. Water is not air, so there could be no burning.

    Presumably everyone thought it was full of water. Myself, I suspect there was an air pocket at the weld location, that supplied the oxygen for the explosion. And there could not have been much else between the pocket and the filler neck, because otherwise there would have likely been a seam split, or at least some distortion of the tank from internal pressure.

    Welding otherwise than backed by air would have developed a bubble of steam there. You can weld underwater, even stick weld, I am told. I know cutting torches can work underwater. But you can't get things to explode in a steam atmosphere, the oxygen is already bound to hydrogen, forming its oxide (water).

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  • GNM109
    replied
    Originally posted by J Tiers View Post
    If it was "full of water", then where was the air and fuel to MAKE the explosion?

    OK, you were there.... So what?

    Obviously some part of the story is not true. That does not make you a liar, it makes you a person who didn't have all the information.

    The tank obviously was not "full of water" as you thought it was. There had to be some air and fuel mix in it, or no explosion was possible. It did explode, so it WAS there, and the tank was NOT "full" of water. Done.

    ************************************************** *************

    Just for the sake of curiosity..... I did a little figuring

    Assume a gas tank in the form of a 1 foot cube.... with residual gasoline a thou thick over the surface. That's not a lot, but it should still be visible.

    Gasoline has a stoichiometric ratio of 14.7 to 1 in mass. Limits are about 1.5% to 7.5% for explosive mixes, by volume of gas (harder to figure than masses/weights) The tank holds air of about 0.08 lb weight. A uniform coating of gasoline all over the inside of the tank of thickness 0.001 inch would have a volume of 0.001 x 144 x 6, or about 0.86 cubic inch. The fuel weighs .026 lb per cubic inch, so there is about .022 lb of fuel involved.

    Ratio of air to fuel is .08/.022 or about 3.5 to 1. Way richer than stoichiometric if it all evaporated into the volume of the tank. Obviously, depending on how much of the film of fuel evaporates, you can get a variety of ratios that will span the flammability range up to what is likely to be too rich. So it does not take much fuel in the tank to set up an explosion.

    Even in the case of insufficient fuel to mix with the air and be in limits, the fuel may not necessarily mix evenly, so a portion of the volume may be explosive, and the rest too lean. Still may be enough to pop the tank.
    There was obviously some petrochemical residue that the torch ignited, possibly in the crack at the lower right hand corner of the tank. The tank was indeed full of water and had been exposed to a car exhaust for a few minutes before the welder filled it with water and got started. There was an explosion, actually two, although there was no damage and they exited through the gas tank filler hole. Obviously I was there and you were not but thank you for not calling me a liar. Your post would have been more complete had you done that, however since others on this site don't often hold back as I've seen in many other threads here having nothing to do with myself.
    .
    The remainder of your post addressing issues of fuel to air mixtures, although interesting is irrelevant in this context.

    Done.

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  • Willy
    replied
    He told me the guy swore it only ever had diesel in it but doubted that was true
    It probably was true and only did ever have diesel in it.
    Anybody that thinks they are safe welding a tank because it has "only" had diesel in it probably should not be welding tanks. It's a motor fuel, why would he not think that it couldn't form a combustible mixture?
    There are literally hundreds of compounds, liquid and solid that given the right conditions are capable of producing a lethal explosion.

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  • Iceman Motorsports
    replied
    Guy with a machine & fab shop in the area was welding on a diesel tank, as he said he has done hundreds. In the end he got a short hospital stay and he had great insurance, got a new shop and all new equipment, much better than he had before. He told me the guy swore it only ever had diesel in it but doubted that was true.

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  • Dieseldoctor
    replied
    If you talk to the family and friends of anyone killed or hurt by a fuel tank being welded on you will always hear, "he has done that for years" or "he has welded hundreds of those with no problem". Very few people get hurt at their first rodeo or first car race etc. Just saying.

    Now I had a friend years ago whose job was to keep chain saws, axes, etc. in operating shape for a crew of about 20 woodcutters. When his metal gas cans would get all dented and even crushed from throwing around he would line them up, take all the caps off, and then take a torch and go around sticking it in the neck of the can. Can would jump and a flame about a foot long would fire out both openings but the dents etc. were usually pretty well ironed out. Never saw a can fire off but one time which evidently took care of all the fumes.

    I have only worked on lawnmower gas tanks and very few of those. I either hook a hose to the outlet (with cap off of course) and let approximately 5 PSI of air circulate through the tank as I solder (with a big electric soldering iron) or if I can get my hands on some dry ice I put several chunks of it in the tank and just a little water to help it melt. When the "fog" starts boiling out I know it is safe to have flame around the tank. But I also do like the man I mentioned above. I stick a flame from a torch into the filler to see if anything with light off whether I am using air or dry ice. Never even had even a little pop but that's not saying the next one won't take my head off. But I still only use the soldering iron to actually do the work with.

    Now the last one I did was my own tank off a Cub Cadet and I used JB Weld and it has not given me any problem after about two years. Sanded around the hole real good. Used thin layers with drying time between layers. Your outcome could vary.

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