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  • GARAGEGADGETS
    replied
    Originally posted by jolane
    Garagegadgets,
    Do you really leak test with pressureized air first? It seems to me that if a crack was to form, or worse yet a weld failed, you would end up with a bomb. I would think that is why they Hydro test tanks, probably because the potiental energy of uncompressible liquid is low relative to that of a compressible gas. Just a thought. Maybe you want to use water instead (although cleanup could be a bigger problem, and the pressure won't be as high as with air).
    Joshua

    Joshua, when I pressurize a tank I use between 1 and 3 psi of air depending on the size of the tank. There are some tanks that are not removable and some are to large to be moved. Try filling a thousand gallon fuel tank with water only to have to drain it because you have a pin hole in your weld from a piece of contamination. You have to use common sense when your working with this kind of stuff or you will not be around long to talk about it.

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  • jolane
    replied
    Garagegadgets,
    Do you really leak test with pressureized air first? It seems to me that if a crack was to form, or worse yet a weld failed, you would end up with a bomb. I would think that is why they Hydro test tanks, probably because the potiental energy of uncompressible liquid is low relative to that of a compressible gas. Just a thought. Maybe you want to use water instead (although cleanup could be a bigger problem, and the pressure won't be as high as with air).
    Joshua

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  • GARAGEGADGETS
    replied
    From my experience welding fuel and hydraulic tanks - I always leak check by pressurizing the tank with compressed air before refilling the tank with fuel or oil.

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  • burninbriar
    replied
    I went back to the manual and found that I forgot a step.After purging 30 minutes with exhaust they say to then blow out the exhaust gas with compressed air.Then seal it up for 15 minutes and then check with explosion meter.
    Since the exhaust is followed by compressed air it seems to rule out simply displaceing the oxygen and leads me to believe that the exhaust gas has some other efect.

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  • burninbriar
    replied
    Originally posted by fun4now
    some manuals are to be used in combat emergencys only. this may be what you have.there are lots of manuals put out to only be used in a quick fix to get out of a bad area, it dose not mean the army recomends doing it on a dayly baisis just that it is reasnably safe as a last resort to alow you to remobilize.
    I thought about that,but the explosion meter doesn't seem in place on a combat feild?

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  • fun4now
    replied
    combat only

    some manuals are to be used in combat emergencys only. this may be what you have.there are lots of manuals put out to only be used in a quick fix to get out of a bad area, it dose not mean the army recomends doing it on a dayly baisis just that it is reasnably safe as a last resort to alow you to remobilize.

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  • aametalmaster
    replied
    I work in a refinery we do this daily. Purge with NITROGEN period. We also use steam but it is not at every house in America. So use N2. Get a small tank its cheaper then blowing yourself up...Bob

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  • burninbriar
    replied
    I was a heavy equipment mechanic with the 429th combat engineers for 6 years and never heard of this exhaust practice untill recently.Maybe becouse I was an army reservist and we were known as heavy drinkers at that time.I don't think they trusted us with matches let alone fuel tanks and welders.

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  • jolane
    replied
    Having used the 'fill with water' method before, once the weld is complete, what next? The problem we had was rust formation inside the tank. We did the best we could with WD-40, but the tank still rusted a lot. Should the tank then be filled with gasoline right after welding (after it cools)?
    Welding on or near gas tanks is VERY nerve racking.
    Joshua

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  • brainfarth
    replied
    Just yesterday, I welded an aluminum toolbox to an aluminum fueltank that was 1/2 full of 100+ gallons of deisel. All I did was purge it with argon @ 50 psi for about 5 minutes and kept the purge going while I welded. But I did allow the gas to funnel out another plug on the otherside of the tank. No boom.

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  • burninbriar
    replied
    Originally posted by tooldude56
    Hello;
    I live on the coast of lake Michigan ,reffered to as the gold coast,where salmon fishing is huge.I had a part time job with a local marine repair facility for approx. 15 years.I did all of the outboard repairs and all of the aluminum welding for this company.It ranged from lower unit repairs and scag replacements to boat bottoms,pontoons and fuel tank repairs on the large boats.I have tig welded literaly dozens of aluminum fuel tanks by circulating exhaust from an old ford tractor through the tank while welding.Some of these tanks were as large as 200 gallons.The proccess went like this: I would remove the tank from the boat and drain all of the fuel from it,next I would position the tank on a bench so that the inlets and outlets were accessable,then I would fill the tank with as much water as possible with out having it run out of the inlet or outlet or get too near the weld area.I was as nervous as a dog crapping razor blades on the first try,it's hard to tig weld when you are shaking,but it went extremely well,the tank welded like butter, and I have never had a problem with welding fuel tanks since.I do remember thinking on the first couple of tanks,at least with this big tank,if it blows,I wont feel anything or have to worry about limping away...............he he

    tooldude56

    I can certainly apreciate the nervousness.The manual does not say to keep the exhaust flowing but it makes sense.There procedure is flush with detergent and water,flush 20-30 minutes with exhaust,check with meter,fill with water and begin work.The reason I was thinking the exhaust gas did something other than displace O2 is you would think the military would use an inert gas instead of exhaust fumes that could contain unburned fuel to displace oxygen.

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  • GARAGEGADGETS
    replied
    I have seen this done before, it does work.The theory behind it is that carbon monoxide is a nonflammable gas as long as the vehicle is not running rich. It is use to purge the flammable gases out of the tank. Most people who weld on them use nitrogen or CO2 instead of exhaust for purging. That is a backyard method when nothing esle is available.

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  • tooldude56
    replied
    Hello;
    I live on the coast of lake Michigan ,reffered to as the gold coast,where salmon fishing is huge.I had a part time job with a local marine repair facility for approx. 15 years.I did all of the outboard repairs and all of the aluminum welding for this company.It ranged from lower unit repairs and scag replacements to boat bottoms,pontoons and fuel tank repairs on the large boats.I have tig welded literaly dozens of aluminum fuel tanks by circulating exhaust from an old ford tractor through the tank while welding.Some of these tanks were as large as 200 gallons.The proccess went like this: I would remove the tank from the boat and drain all of the fuel from it,next I would position the tank on a bench so that the inlets and outlets were accessable,then I would fill the tank with as much water as possible with out having it run out of the inlet or outlet or get too near the weld area.I was as nervous as a dog crapping razor blades on the first try,it's hard to tig weld when you are shaking,but it went extremely well,the tank welded like butter, and I have never had a problem with welding fuel tanks since.I do remember thinking on the first couple of tanks,at least with this big tank,if it blows,I wont feel anything or have to worry about limping away...............he he

    tooldude56

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  • hankj
    replied
    The intent is that the CO in the exhaust gas will render the atmosphere in the tank non-combutible by reducing the O2 content below the flash point of the flamable liquid. Compressed air is oxygen-rich. Not a "purging gas", such as CO2 or Argon. The idea is no oxygen, no BOOM!

    If you have an exposimeter, that's cool, but most of us can't afford one, and the annual cost of calibration is not cheap, either. You know for sure that if the tank is full of water, no BOOM!

    Hank

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  • burninbriar
    replied
    I think what bothers me the most is what the exhaust gas does.If it just flushes the container,compressed air would seem easyer and safer.

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