Need tips for welding a gas tank

[muddstopper]

I have a fuel tank off a piece of equipment I want to modify for another piece of equipment. The filler neck is thick wall steel, maybe 3/16, and has no provisions for a cap. Tank is welded steel, not stamped sheet metal. The original design used a rubber hose to connect of the cap. I am wanting to weld a nipple to accept a standard 2inch vented fueltank cap. The tank was just emptied of gas and I am trying to figure out a way to clean it so it doesnt blowup when I stick a welding rod to it. Since the filler neck sticks up above the rest of the tank by several inches, I am thinking about just filling the tank with water to just below where I will be welding, but want to make sure that is sufficient precaution before I proceed. Any advise will be appreciated.

 

[Tractor Seabee]

I have a fuel tank off a piece of equipment I want to modify for another piece of equipment. The filler neck is thick wall steel, maybe 3/16, and has no provisions for a cap. Tank is welded steel, not stamped sheet metal. The original design used a rubber hose to connect of the cap. I am wanting to weld a nipple to accept a standard 2inch vented fueltank cap. The tank was just emptied of gas and I am trying to figure out a way to clean it so it doesnt blowup when I stick a welding rod to it. Since the filler neck sticks up above the rest of the tank by several inches, I am thinking about just filling the tank with water to just below where I will be welding, but want to make sure that is sufficient precaution before I proceed. Any advise will be appreciated.

Dump out the water you have in it, and that will carry away and residual fuel; then fill it up to running out the filler neck, that will drive out all the fumes, drain it down to 1" or so below the weld spot and then you should be ok. Worked for me one time to gas weld on one with a split in the side. That was a thin sheet metal one. Be sure and dry it out good before you fill it with fuel again.

Ron

 

[muddstopper]

That is more or less what I had planned on doing, I cant see how it could blowup if its full of water. I have heard of a hundred ways weld a gas tank, dryice for a CO2 purge, argon or helium purge, engine exhaust gas purge, ect. To me, all these purges could leave some room for error and a possible oxygen pocket. If i was welding a hole in the bottom of the tank where it would be hard to fill all the way up with water, I probably wouldnt even try it, but the filler neck sticks 4 or 5 inched above the tank body and the only place that wouldnt contain water would be about an inch of a 2inch dia tube.

 

[monckywrench]

Some radiator shops still boil out fuel tanks too, worth it if you have any corrosion or crud you want gone.

 

[Egon]

Boil it out.:thumbsup:

engine exhaust gas purge, /QUOTE]

Exhaust gases may be explosive.

There are purge methods that take into account elimination of dead spots in the vessel.

 

[Sasquatch4100]

I've welded on bike tanks before. I use some strong degreaser like Simple green Industrial and let is sit a while and maybe do that once or twice. I'll then let the tank air out in the sun. That usually makes the tank fresh and removes the majority of crud and residue. After I do my welding or repair I'll coat the inside with a nice tank sealer (not tank Kreem!) I use this and after using other products this stuff is the Bees knees I'm tellin ya Auto Gas Tank Sealer Kit - Gas Tank Sealer - KBS Coatings.

 

[rhett]

... I cant see how it could blowup if its full of water...

When water boils it releases Hydrogen Gas which is highly explosive.
If it collects in a pocket and a spark reaches it, well you get the idea.
That is how lead acid batteries can explode.
Purge with compressed air while welding after a good clean out.
Be careful and good luck

 

[jake98]

When water boils it releases Hydrogen Gas which is highly explosive.

Pretty sure that doesn't happen..

 

[muddstopper]

When water boils it releases Hydrogen Gas which is highly explosive.
If it collects in a pocket and a spark reaches it, well you get the idea.
That is how lead acid batteries can explode.
Purge with compressed air while welding after a good clean out.
Be careful and good luck

I am going to disagree with that statement, unless you can document some evidence to back that claim up. If you could boil water and get hydrogen gas we would be driving hydrogen powered cars by now.

I remember my first, and last attempt to weld a gas tank.(early 1970's) The tank came off of a 59chevy truck and had a pin hole in it. I washed and soaped that tank over and over again and there was no smell of gas. I was still afraid of it. I set the tank out in the driveway away from the house. I think I was more afraid I would burn the house down than I was of getting blowed up. Anyways, I took a long stick and tied a rag to the end. I set the rag on fire and stuck it to the filler neck on the tank. The tank shot flames out the filler neck like a jet engine and the tank slid several feet across the driveway. The tank also sort of rounded out like a balloon from the pressure. I stuck the burning rag down the filler neck and left it burning inside the tank and then brazed up the pinhole.

I am a little older now, not so sure about any smarter. This is one of those things I know I can do, just aint sure i want to do it. The tank is square, wider than it is tall. The filler neck, fuel outlet and vent come out of the top of the tank. There is a pitcock drain in the bottom. If I fill the tank with water, the entire tank should be full except for keeping the water level just below my point of weld on the filler neck. Any vapors, hydrogen or other wise should be neglible and easily atmosphere vented since the filler neck and nipple I want to attach are only 2inch in dia and wont be more than a couple of inches long. Maybe I am just being paranoid, but I keep seeing that first gas tank scooting across the driveway shooting out flames like a jet engine. All my buddies got a big kick out the show, but time and age makes you wonder how we survived.

 

[deereman75]

Ya boiling water lets off steam, not hydrogen. You get hydrogen when you pass electricity though water. So if you stuck the ground clamp and stinger in a bucket of water, then you could get some hydrogen, but welding on it might just make a bit of steam at most.