welding holes in fuel tank

[OneWithWood]

Welding on fuel tanks has been covered previously on the forum and I have learned that the best approach is to fill the tank with and inert gas such as argon.

Just exactly how is this done?

I have acquired a 300 gal tank with two 1/4 inch holes drilled into it by the previous owner.  I would like to fill the holes and use the tank to store biodiesel.  The tank held either diesel fuel or gasoline.  The PO could not remember which (he is over 90 and is losing some of those memories).  I intend to flush the tank with water and air before I do anything.

I have a small bottle of argon I use with my wire feed welder.

Can I just use part of this to fill the tank?

Do I plug all openings exept the holes I intend to fill?

How do I know I have suffficient argon in the tank to displace any fumes?

[zopi]

You can do that, but I wouldn't trust it too far....My grandfather was an old pipeline welder in the 30's and he taught me to put the patch you are welding on top of the tank and fill it with water just below the weld site...pain in the butt but it is safer...

I'm sure there are others with more experience, but that is how i've always done it...sucks for a 1000 galln tank though..

[Gary_C]

How about an alternative? Use JB Weld or any other two part epoxy and just repair the holes. Or get two pop rivets that size and use a sealer like JB Weld on them to make sure they do not leak.

If you are set on welding, the cheapest method is to fill the tanks with water to just under the holes and weld away. Or probably the next cheapest would be to rent a bottle of nitrogen and just stick a hose in the tank and turn it on for a short time. I suppose if you knew the rate the nitrogen was entering the tank you could calculate the time it would take to get the oxygen and flammable vapor content below the LEL but if the tank is relatively clean it will not take much.

But by far, the water method is the best if you are set on welding. Don't leave much air space and don't try to weld with water behind the holes unless you are a expert steam fitter/welder.

[DR_Buck]

I had a real bad experience with that about 30 years ago.   I filled the dry, empty tank with water.  It didn't help.   
 
If they're  drilled holes, why not just put in a couple of bolts with gasket washers on them?   If  it's a matter of reaching to the inside where the holes are, you could try to tape the bolt to the end of a long pole or stiff wire to feed it through from the inside and put the nut on the outside..

I'll NEVER take a torch or welder to a fuel tank again.

[Gary_C]

So I am curious Dr. Buck. What happened and what went wrong?

The key to the water method is to eliminate as much air as you can from the tank. Depending on where the holes are, that may not be possible.

If the water method will not work, you can use compressed air and continously purge the tank even while welding. That will keep the concentration of flammable vapors below the flammable limits. Kind of like running an engine so lean that it quits running.

[bandmiller2]

Tank welding is a tricky deal,I would avoid it if possible.I would take a 5/16 tap to the holes install a bolt with gasket,clean and epoxy over them.Frank C.

[SPIKER]

im with frank, tap the holes, insert bolt with good sealer on the bolt/threads and some around too...   much safer than welding...

mark

[PineNut]

Had a diesel tank that needed welding on it a couple of years ago. I took the safest approach for me. Took it to a pro and let him do it. Came back later, paid him and took it home in good condition.

[shinnlinger]

water is what I have done, but I hear that running diesel exhaust in the tank for a while can do it too.  THe problem is you don't know if the exhaust or argon has completely filled the tank and the cost of a welder with the correct detection equipment is alot less than any kind of explosion.

[Ironwood]

I am with PineNut and I am a welder! Pay someone w/ the experience to do it right (or wrong, hell who cares you wont be there)


 Ironwood

[scsmith42]

Robert, I've had both good and bad experiences welding fuel tanks.  Welding gasoline tanks is much more dangerous than diesel tanks, so that is one plus.

If you go the Argon Route, simply calculate the volume of your fuel tank (in cubic feet), and then run your argon line into the tank via a gas regulator (such as what you use with your MIG or TIG).  If your tank is 50 cubic feet, set your regulator on 10 CFM and in 5 minutes the tank will be full of argon.

I like to run the hose down to the bottom of the tank, and keep the regulator on a fairly slow setting (such as 10 cfm) so that the gas slowly displaces the air in the tank.  I leave the regulator on while welding too.

[TimRB]

I also agree that just putting a bolt with washer/sealer in the holes would be safest and most expedient.  That said, another method I know of to purge the tank is to put a few good-sized chunks of dry ice in there and let the CO2 fill the tank as it sublimes. 

Tim 

[sawdust]

It was suggested to me once that you put a gallon of water in the bottom of the tank and put a torch under it. Steam displaces the air and gasoline vapour, apparently gasoline vapour will continue to migrate out of the metal. The steam also prevents the interior from reaching ignition point of gasses.

Never had occasion to try it.

I cut up propane bottles quite often and just take the valves out for a month before hand.

Sawdust.

[DR_Buck]

It was suggested to me once that you put a gallon of water in the bottom of the tank and put a torch under it. Steam displaces the air and gasoline vapour, apparently gasoline vapour will continue to migrate out of the metal. The steam also prevents the interior from reaching ignition point of gasses.

Never had occasion to try it.

I cut up propane bottles quite often and just take the valves out for a month before hand.

Sawdust.

Yea,  and that gasoline vapor migrating out of the metal EXPLODES!   

[Toolman]

OWW, I plugged a couple of small holes in a used 275 gal tank about 5 yrs ago with a self tapping screw and JB weld. My tank holds B50 fuel. I painted the tank and the plugs are holding up well. The tank is outside and exposed to all the elements. I'd say save your eye lashes and eyebrows!!

[sawdust]

I think the idea was that the heat is left going and the steam continues to displace any air. There is never a chance for the off-gassing vapour to reach a combustible mix. Though how you are supposed to weld shut a hole with steam rushing through it is beyond me. You would want to leave the cap off as well of you would suddenly have a boiler explosion!

sawdust

[Randy88]

I'm curious how did the tank welding go?   I read over the repies here and I have a different idea, how about a new tank, 300 gallon tanks are quite cheap and for the dolllars they hold maybe a new one is a better all around deal, nothing lasts forever and when mine leak its time to replace them because they usually leak somewhere else in a few months or a year anyhow.   We've welded fuel tanks on tractors and equipment and most times we end up replacing them later on due to another leak if it rusted out and thats what caused the leak, a puncture is different theres still enough good metal left to hold and those are worth fixing.   Price a new tank and ditch the old one if your needing a long term storge solution, it'll pay in the end.  Just my two cents.

[OneWithWood]

Great suggestion, Randy.  I did junk the tank and repladed it with another, though not new.