Technical Any body know best way to make gas tank safe to cut and weld on.

If you decide to go with engine exhausts for purging, do NOT use a diesel engine. They always draw in as much air as they can, but they only add as much fuel as needed to produce the desired power = they Always work with excess air, meaning there is plenty of pure oxygen in the exhausts, especially at idle.

 

You might pay attention to where the hole is that is being welded. If the hole is at the bottom you should probably invert to keep the hole at the top so the CO 2 does not run out.

I, also, wear ear plugs just in case.

 

Another easier way for me was to purchase some dry ice , cut it into pieces drop into the filler neck it will boil off and fill the tank with CO2 displacing flammable fumes . I was taught this method from my experience working on Liquid Propane Pipelines . They must be welded 100% and pass X-ray tests . We would pack the line full with dry ice butt the pipe together and weld it up no issues . Checking the vent with a small propane torch is a great idea . Have some one continue to hold the torch at the vent while you weld . We did this many times pipeline welding when there was always a small amount of gas present , burning at the vent means it will not burn in the tank or pipe in my case . Safer to say if it burns at your vent it’s not time to weld , keep purging until it will not support a flame . Believe me a flash in the tank will make the devil proud of the ball of fire that will happen . Welding full of water is almost impossible to do , the water will cool the area to be welded and you will never get a good weld . It will be full of porosity and contaminates and never last if you do get it to weld . Always wear your PPE. Gloves , FR jacket , etc . God only gave us one pair of eyes and a certain number of digits , once gone super hard to find them in the swap meet . If you are the lease bit uncomfortable and don’t understand the purging procedure , please don’t attempt the repair send it out to a pro or buy a new one , the effects of the unknown could be beyond your greatest experience.

 

I welded mounting brackets and a fitting for a dip-tube on the stainless tank in my roadster after filling it with water, but it was fabricated from material think enough that I could use a stick welder with 3/32 " rod. Worked well...

 

stop posting --->yer avatar<--- is giving this old man a heart attack j/k ...lol

 

I never have any luck getting them soldered or welded ,I use a sealer from Speedway.

 

Filling with water works. Remove all bungs and fittings, then submerge your tank in a suitably large water container where you can immerse almost all of it. Use rocks or whatever is handy to put the bit you wish to weld just above the water level. Full of water is much safer than full of gas / air / CO2 mix. Have done tanks this way with no problems.
Garpo

 

If you don't have access to a CO2 tank, a couple of pounds of dry ice pellets will do the trick nicely. I use the pellets for explosion proofing large service station tanks before removal.
Exhaust fumes : being an old timer at this game I can state without hesitation that engine exhaust gas CAN explode. I've witnessed it. More than once.
Be safe - take it to the radiator shop and have the boil it out and solder the leaks. Money well spent.

 

I will add . If you have a buddy who works for the Fire Dept. They use a product to seal gas tanks that have a rupture. Many years ago I saw them seal a quarter inch wide gap about 1 inch long in a tank at a wreck site. I do not know what it is but it works.

 

Had a bunch of pin holes in an old car used for auto crossing. Cleaned the area around the hole, put a nylon washer on a self taping screw, screw into the hole,top the repair with epoxy. Then spray the area with under coating. Stopped the leaks till I located a better tank.