Probably Stupid Welding Question

Safe to weld on an underseat gas tank that has been sitting on the shelf for years, empty with no cap on it ???? Wanting to switch filler neck around or use another filler neck in order to make a passenger side underseat tank.

Beeg Dummy

 

Technically, by the book, not recommended in general. Heated residues could create fumes?

In real life.... just because I would do it, doesn't mean anyone else should. Maybe I've just been lucky. But I usually flush with water and detergent.

 

X2 on what Pete says.
You could also fill the tank with an inert gas such as argon /CO2 from a mig welder before you strike an arc.

 

I have seen where people have filled with water just shy of where they plan on welding to keep the water from leaching the heat from the welding. Had an electrical shop instructor tell a story where he welded on his model A fuel tank and it exploded and scared the poo out f him. The plus was he was able to get another gal of gas in the tank lol

 

Should be ok. My local car wash has hot, soapy, high pressure, H2O.

On mine it was only for one trip so I just cut two inches out of the neck to keep the body unharmed. You can see the passenger filler in this picture I always post. The tank is now long gone.

 

When it comes to safety the only "stupid" questions are the ones you don't ask.

Probably a tank that has sat for years without a cap would not have much risk, but were it me I would do as suggested and rinse the tank thoroughly with hot soapy water as JW suggests.

 

I often have that kind of thought. Along with 'hold my beer.' But then I try to ask myself, 'what if it's not okay?'

Probabilities need to be weighed versus consequences.

Or as I tried to teach my daughter, it's okay to make mistakes - but try to avoid the ones that kill you.

 

Even if it had gas sitting in it that long, it’s barely flammable at this point, no-less explosive. It might burn and smell nasty, but the chances of it doing more than that are extremely slim. I’d probably go as far as to squirt some MIG gas in there and go for it.

 

My uncle had a welding shop on his farm. He would wash out old tanks and then test them with a long pole and some kind of flame to make sure it was OK. He said one that had been sitting for years took off burning, but he only saw that once. I had old GI gas cans that the bottom had rotted out. Sat for years all dried out and I cleaned them out, dried them, and TIG welded a new bottom in them. Worked fine, they were just for display anyway. They will probably never hold fuel again. I did it outside where I could get away if they caught fire.

Dave

 

I was a welder by trade. I taught myself to and have successfully welded many Jeep gas tanks.

First off they don’t catch fire. They explode !

One of the very first tanks I welded on blew up so I know what not to do.
As a teenager I tried to weld my motorcycle tank.
I filled it with water just shy of the area to be welded.
It exploded anyway right there in front of me.
The minute tiny area that was not full of water blew up and caused the whole tank to swell way out big time.
I would absolutely never use any water method again.

It is stricktly the fumes that are a problem.
For that reason I suspect purging will do little good because you still are not eliminating the gasoline fumes. The sure way to do it is to DRY the TANK OUT.
Run your hot idling Willy Jeep exhaust pipe direct into the tank for one full hour.
Next the tank must be tested. Place tank out of site around the corner of a solid structure. Reach around that corner with along acetylene flame directed into the fuel neck. I have never had another explosion so long as the tank was dried with hot exhaust gas.
One explosion learned early on was enough.
If your tank has sat for years with the cap off you might consider going direct to the long flame test procedure. Your call on that. Just don’t skip the flame test.

 

Well Lamont, I can't say it will or will not be safe but at least we will know what to tell them happened if it don't work out as you planned.. Seriously though, I like your new avatar.

I know a guy who ran a long wire down the filler neck and out thru the sending unit hole, tied a wad of rags to the wire and lit them, got behind the barn and pulled the burning rags into the tank. there was a little puff of smoke and some fire but no explosion. while the rags were still burning inside he brazed in a fitting. He is still alive. But don't try this at home.

 

This. This is how I've "prepped" every tank I've ever needed to weld on. And I've never had one pop on me. Caught the paint/coating on fire, yes, because I was lazy and didn't strip enough of it from the area I was welding/brazing, but exploding? No.

 

Hydrocarbons (and its vapors) are not flammable until oxygen is introduced. If the fuel tank is purged with an inert gas, no combustion is possible.

Ever wonder how the flame on a propane torch doesn’t burn back into the bottle and explode? There’s no oxygen in there. It’s being mixed with atmospheric o2 at the tip.

Oxy/acet outfits need burnback valves in the event that one tank pressure becomes less than the other’s regulated pressure, and the fuel and oxidizer can back feed and blend inside a tank or hose.

 

Does that mean that when I'm burning yellow jackets with a cigarette lighter and a can of carb cleaner there's no risk of the can blowing up?

 

As long as you trust the manufacturer didn’t introduce an oxidizer into the mix.

 

Blow it up blow it up!

 

Hydrocarbons (and its vapors) are not flammable until oxygen is introduced. If the fuel tank is purged with an inert gas, no combustion is possible.

Absolutely true. But there is no practical way unless you have a purge chamber to be certain that ALL oxygen has been purged.
And it’s also relative to the weld technique being used. Oxyacetylene is perhaps the most common method used to weld a tank. If the flame is anything beyond neutral (aka an oxidizing flame) then one can easily introduce the required agent. Besides the hole itself can let air right back into the tank unless the tank is “pressurized” with inert gas. (Overflowing with inert gas)

 

Thanks folks. I'm a bit concerned about cutting the old filler neck out as well. I'll likely use a grinder with a cut off wheel. I guess that could potentially spark an explosion. Then I was planning to weld that area shut, cut a hole for the new filler ( sourced from a second tank perhaps) and Mig that in to place.

I dunno. Maybe I'll see if the old guy in town who repairs tanks is busy or not. Let him play with it. I was thinking that after so many years the risk would be non existent. Glad I asked.

I decided that, to go along with my signature, I needed the matching avatar.

 

If you can get a flame into the tank and she does not blow then your 100% safe to grind and or weld as you see fit.