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Welding on OBA tanks?

Discussion in 'The Garage' started by dremu, Feb 11, 2005.

  1. dremu

    dremu Officious Thread Derailer Premium Member

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    Saw in one of the OBA threads about how one shouldn't weld on air tanks ... whyzzat? Stress on the metal, it's likely to explode under pressure, or ... ?

    I have a nice ex-air compressor just waiting to go into the truck, but the bracketry on it is all wrong...

    -- A
     
  2. 84gmcjimmy

    84gmcjimmy 1 ton status

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    Your not supposed to weld on closed containers, no matter was is in them, gas or just air. The heat will likely make the tank explode from the pressure.
     
  3. divorced

    divorced 3/4 ton status

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    But what if there is no pressure in them, like if they have an open port?
     
  4. 84gmcjimmy

    84gmcjimmy 1 ton status

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    if there is an opening it's okay. There just has to be someway for the pressure to escape to prevent explosion.
     
  5. K5Chris

    K5Chris 1/2 ton status

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    i remember hearing about a guy who either died or was seriously injured here in houston that decided to weld on a steel wheel........... with a tire on it...... with air pressure still in the tire. i'm sure you can piece together what happened.
     
  6. TrcksR4ME

    TrcksR4ME 1/2 ton status

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  7. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Weld it up. Just make sure it's not sealed and has some kind of vent.
     
  8. fatbob

    fatbob 1/2 ton status

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    Think of it this way. The tank has a nice wall that is the same thickness all the way around it. When you weld two pieces of it tends to pull material away from piece even though you are adding metal. Look closely at some welds and you will see recess where the weld meets the material*. That will make the wall of your tank thinner/weaker in that area. And then there is the brittleness factor. All that heat will change the temper:mad: of the metal, and I think make it more brittle. The tank will tend to expand under pressure but it cant where you welded it, and over time it will tend to crack there. This is why a band or strap would be better to hold the tank.
    *Disclaimer. this has been my experience with a stick welder:grin:
    Now I have seen those propane tanks at the gas stations with things welded on them, but I'm guessing the walls are a lot thicker:dunno: .
    Maybe one of our metalurgy gurus will chime in.
    Bob
     
  9. darkshadow

    darkshadow 1 ton status

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    no air compressor anyone will have on there truck will exploade a tank because of the welds weaking the metel (unless you make a hole because you cant weld)

    you want to change the brackits go for it, if it was a small tank and it had no holes i would be worryed if you were doing a lot of welding, but you just doing small brackits right so go for it crack the valve and weld it.
     
  10. dremu

    dremu Officious Thread Derailer Premium Member

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    It's got three or four bungs, including a great big 1/2" or somesuch NPT, so I'll pull all the plumbing off and give it a roll.
    Thanks all!

    -- A
     
  11. jarheadk5

    jarheadk5 1/2 ton status

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    As long as the tank's open to the atmosphere somehow (open port, open valve, etc.) you'll be fine while welding.
    And as long as you're reasonably skilled at welding, you shouldn't cause any damage to the tank itself.
     
  12. velocitiii

    velocitiii Registered Member

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    The reason that it's standard practice to strap tanks in place is that vibration and time will attempt to crack the tank around the welds. Then you'll have a leaky tank. Nobody will die from a welded tank, it's just less reliable than straps. Look at how factories mount tanks of all types fuel, oil, a/c, catch can... Unless you use large tabs welded to a large portion of the tank, time and vibration will take its tole. I wouldn't be worried about it exploding though.


    One note on the bs about someone being harmed by welding on a closed tank is most likely just that, bs. I have welded a LOT of tube frame type stuff and the only thing that happens if there is no hole for the heating air to escape from is that the weld pool blows a hole out at you while welding.
     
  13. dremu

    dremu Officious Thread Derailer Premium Member

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    Hmm. That is something I had not taken into consideration ... and given where I wanna put the tank (more or less where the tailgate was), there's gonna be shakin' goin' on.

    I will stink about strapping it, like the gas tank ... rubber between the strap and the tank. Question is how to mount the straps so as to be structurally sound ... hmm. :thinking:

    Thanks all!

    -- A
     
  14. ntsqd

    ntsqd 1/2 ton status

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    Strapping it is easy. Make your mounts to have a curved feature that cradles the side of the tank. Allow room for a large hose clamp to wrap around both the tank and the curved feature. I would use one of the T-bolt type clamps rather than a std hoser clamp, but that's mostly for looks. The std type hose clamp will work fine. No need for rubber either. Fuel tanks need it b/c they're so big and the frame will move a lot over their length. Don't have that issue with any air tank you're likely to put on a truck.
     
  15. Jonny-K5

    Jonny-K5 1/2 ton status

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    definatly NOT BS! if you weld enough to build the pressure high enough on a sealed tank it will explode. im enrolled in a welding class and thats one of the first things they teach you. welding on a tube frame isnt the same as welding on a pressure tank.
     
  16. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Most stuff we build at work goes for stress relief after welding. They'll stick it in a big oven at 500 F or more for 'X' number of hours. Anywhere there is an enclosed space we have to drill a vent hole, then circle it with a paint pen. The guys at the stress relief shop get really nervous when they don't see vent holes. Stuff does blow up...

    rene
     
  17. RustBuket

    RustBuket 1/2 ton status

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    One port should do fine. Its not like there will be a massive rush of air. The gas will just slowly be expanding.
     
  18. velocitiii

    velocitiii Registered Member

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    I can see an explosion on a thick walled tank with lots of welding being done on it, but an air compressor tank where the weld penitration is close to 100 percent is just going to blow out through the weld puddle.

    It's not hard for a tube frame to get up to 5 or 10 gallons of air inside when all the cores are tied together, which is very similar to welding on an air compressor tank.

    No it doesn't take much of a hole. I usually just use a 1/8th or 1/16th bit.

    I'm not saying you shouldn't have an open port when welding on a tank, but a thin walled tank I don't see killing anyone.
     

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