Fuel Tank Repair

with a diesel tank, if you fill it completely with water and drain it, the residue left on the walls will not likely be sufficient to combust, if done immediately. Leaving the tank for hours or days between isnt advisable.
You could add a little detergent to the water for added cleaning.
While obviously you should use a Detector, I have done my own LR tank recently with no problem.
Also for ships tanks, these are not even washed. They are vented with a fan for a few hours then checked Gas-Free. Flushing with water is more effective though but impractical obviously with a 100 cubic meter fuel tank.
You can also stand the tank up with the crack at the highest point and fill with water to minimise the area that could hold gas.

You could also get some one to check it with a detector, such as any engineering type workshop first (advisable)

Disclaimer
Do this at your own peril.
DO NOT EVER TRY IT WITH ANY TANK THAT HAS HELD PETROL.
Speak to someone knowledgable not on the internet to confirm any information you get here.

I have repaired a couple of diesel tanks, I just filled them with water and soldered them up. Very easy and I can't see that welding them would be any different. Drained the water and dried the tank out after the repair then checked the sediment/water trap several times in the week after.
Good luck. Rob.

Wayne,
The best method to safely weld the diesel tank is to fill it completely with diesel and then weld the split. Have a hose or fire extinguisher handy to put out the flames if it burns (it will only be a small flame if the weeping fuel does burn). However it won't explode and my advice is based on previous experience.

One of my first trucks had a big rectangular diesel tank slung diagonally under the chassis and used to frequently leak along the seams due to torsional stress. My boss would weld up the seams with an electric arc welder without any problems although I was fairly apprehensive when I watched him do it the first time. The only danger is when the tank is partially empty - the air space is far more dangerous than the diesel fuel.

When you're filling the air space with carbon monoxide from your lawn mover, you're essentially doing the same thing . It's easier though to simply eliminate the air space by filling the tank completely with diesel.

The other safe method is to empty the tank and steam it out. Fuel gets into the pores of the metal and is still resident even when the tank is empty. Putting a steam hose into the tank and letting it steam for 20-30 minutes eradicates the fuel residue in the metal itself. We used this method when operating fuel tankers and is also the recommended method from TAFE welding courses. This is the only safe method for welding petrol tanks.

Regards,

Peter

Wayne

I would never tell you or anyone, not to do something safely, so I wont.

But I will say I have welded diesel tanks up with the oxy & arc welders, never had problems full or empty, petrol, no I stay away from, I have made plenty when I was building House Boats at Eldon.

if you are having problems with the weld cracking all the time, reinforce it by drilling a hole top and bottom, siding a what ever size piece of round mild steel bar through them, leaving 1/4" sicking through and run a fillet around it.

Cheers

Richard