welding 300 gal fuel tank

fill it with a constant purge of argon or carbon dioxide. they will swell large with just water . Be carefull.

If you have a pinhole in it now you will have more shortly.  It is rusting out from the inside.  I don't think it's worth taking the chance of blowing yourself up over it.  Only way I would try to fix it is with JB Weld....  I have seen what happens when one explodes.  It's not pretty...........

There's enough of them out there for sale, I wouldn't mess with trying to fix one. J.B.Weld isn't a permanent repair. I've repaired gas tanks with it and it lasts about 1 1/2 years. 

If it's 'just a pinhole', I'd drill it out a bit,clean the area REAL good, mix up some JB Weld,spread it over the area, then screw in a bigheaded selftapping screw into the hole,and laying some more JB Weld over it. Wait couple of days for it to get good and hard.

We used to fill many of them with water and cut them in half with a cutting torch to make burn barrels.  Never had a problem with the water doing that, thats why I asked.

pankey has it right, the only way to do it is with an inert gas purge.  My father and I used to repair gasoline tankers quite often, buy a tank of liquid nitrogen and start pumping it in to purge the oxygen out.  The nitrogen was cheaper but argon or co2 will work as well, just make sure you purge it well and keep it purged as you weld. 

I would take a chipping hammer and pick the area that you intend to weld with the sharp end.  This will tell you where the extent of the rust damage is.  You may need to cut a large section out and weld a new one in. 

I would have thought a former buisness agent of the pipefitters would have known how to weld up a fuel tank without the kaboom. . We welded a six inch diesel line up this summer . we drained it purged it with argon and welded it . after welding it we blew our purged down .the volume found about ten gallons of fuel that we didnt have drained due to a low spot.

yes the promblem with water is fuel and vapors is lighter goes to the top and finds air. the promblem with automobile exhaust is it can have unburned fuel in it that when combined with air oxygen can relite.  A continuos flow of inert gas at 2 psi with a oxygen monitor alarming no oxygen at purge tape is the only way to weld a fuel tank safely.

My grandpa and his neighbor bought an old gas truck one time to use for hauling water. After hauling water in it for 2 years, they decided one day that they needed to do some modifications to it (i.e., weld on it). They backed it into my grandpa's garage to do the work. His neighbor crawled up on top of it to do the welding, and grandpa walked out of the garage and around the corner (Thank God he went around the corner). The neighbor barely struck an arc, and the whole end of the tank blew out. Fortunately no one was hurt, but I know it'll be a cold day in he!! when I strike an arc of any kind on a tank that has ever had gas in it.  Darrel

I am speaking for myself but i dont think firebrick or dmiller along with me would post a method on enternet that would cost someone their life. ever weld up a live natural gas line?

Believe it or not, we have peened them shut. Propane tanks, Just start working the metal slowly.

There is a way to weld anything in any condition or with any content, it just comes down to cost or preperation to value of finished work.

300 gallon fuel tanks sell for next to nothing on farm sales.  Get another and scrap this one.  As someone above posted, if you have one leak now, you'll keep getting more...

A good article on Nitrogen, and I learned something also ..LOL .. it is lighter than air (as it is 78% of air already)  yet it is used as a purge gas as it will absorb any other fumes into itself and dispell them into surroundings in less than explosive amounts. 

Edited by Coke-in-MN - 07 Nov 2010 at 10:32am

I would opt for buying a new tank. While purging with CO2 or Argon is best, O2 monitoring would be an absolute must. Both for you as well as the inside of the vessel. N2 will rise. Argon and CO2 are indeed heavier and will pool. One thing to be aware of is it pooling in your shop as well. You need to be well ventillated. The CO2 and Argon will slowly fill you shop area like a bath tub. You kneel down into that invisible volume of gas to work. One breath and you are out like a light, done, end of story. Keep in mind that the environment we breath is only about 20 percent O2. Deviate either way and it can be your end. All of these gases are inert, do not smell, and are invisible. I work in the compressed gas business, 15 years now. Usually deaths from asphyxiation happen in 2s or 3s. Rescuers get to the victim down not knowing the environment, they to become overcome and die. Would need about 5-6 peoples figera to count the times I have heard about McDonalds or other fast food chains having O2 displacement deaths due to mis handling of the CO2 for the beverage carbonation. Same in the refining industry, huge pipelines are inerted with N2 and Ar. Someone avoids a confined space entry or even somthing as simple as looking in a man way is their end. Cant see the gas or smell it. They stick their head in to see whats inside or going on, breath normally and are gone.