Welding a fuel tank

[QSIMDO]

Based on the results of juvenile experiments with gasoline, 55 gal. drums and the resulting carnage, I have a deep seated policy (based on deep seated fear) of never welding/grinding any vessel that ever held combustible fluids.

Yeah, I'm weird like that.

However, a friend has a motorcycle gas tank which needs repair and hasn't held any gasoline in maybe 5-6 years.
This I know because it's been in my shop for that long.
The cap was on the empty tank but no petcock.

When I opened the cap the inside smelled like the Pharaoh's out house but that dissipated quickly.

I'm thinking I'll sacrifice a length of cannon fuse in the filler neck to prove it weld-worthy.

TOO cautious?
What cleaning methods are reliable?

[Willy]

Fuel tankers I drove that needed to be welded would have a steam wand inserted into the compartment that needed welding for six to eight hours prior to welding. In addition the double walled bulkheads either side of said compartment were given the same treatment and all three were then checked with a flammable gas sniffer to verify that all was well prior to welding. If It did not pass the sniffer test the boys would leave the steam wands in there for another 4-6 hours.
Mind you these were huge compartments with a lot of volume and the potential for violent consequences if accepted guidelines were not followed.

The MC tanks that I have personally welded were not steamed and given the sniffer test, however I did minimize the threat of a mishap by eliminating as much potential flammable vapor as possible by first using a boiling water/detergent mix to clean as much fuel residue out of the tank. When satisfied that it was clean, I cleaned it again.

Prior to welding if possible purge the tank with an inert gas, this always eliminates the potential for an explosive mixture to form inside the tank.
When this is not possible fill as much of the tank with water as possible in order to diminish the volume of where an explosive gas can form. For instance if doing a repair at the neck, fill the tank almost to the neck leaving only enough metal exposed so that the repair can take place.
I've done mounting tabs and fittings all over the tank following these guidelines and have not had any issues, nor have I had to change my shorts half way through a repair.

I'm sure others will have different techniques but I believe it boils down to threat assessment and threat management.
Better to ask first like you're doing rather than flying (literally) by the seat of your pants.

[QSIMDO]

Interesting you should mention steam.
I just read a review of the McCulloch steam generator. Not too pricey, I may grab one.

Problem with filling the tank with water is the tank is aluminum and I gas weld these tanks.
Water will suck the heat right out.
I could just set up a Argon purge but this is a freebie fix

[Willy]

The water is only used to decrease the air space to a comfortable/safe level rather than having the tank completely empty.
Use a bit less water, you'll have slightly more air in the tank but you'll still end up with a significantly reduced air space.

Being aluminum I realize the requirement for retaining heat, bad enough with steel when brazing and the water level is too high. You don't need the water to be within a 1/4", allow yourself some working room, you should still end up with a very small air space relative to the tanks total volume.

Not sure what the exact situation you have there but if the repair area cannot be directly vented thru a fitting or opening, I sometimes use a piece of bent copper tubing to vent the underside of the area being welded or brazed just to relive any pressure buildup due to heat or possible minor explosion in the limited air space. I just place this bent tube into the air bubble on the backside of the weld. It has never been an issue.

[George Seal]

check out 65 ford on utube

his latest on is on welding a truck tank

[randyjaco]

Way back when I was 17, I had a motorcycle with a leaking fuel tank. I stopped by a local welding shop to see about getting it fixed. The old guy there said that he could fix it on the spot for 5 bucks. Now this is the motorcycle I just rode up on. The old guy emptied the tank into a milk bottle, went and got a Shop rag and wet it down good with water. He took the cap off the tank and wrapped the rag around the opening. He then grabbed a soldering rod and his torch and struck it. I took off like a scalded dog expecting to hear a big explosion. About 5 minutes later the guy yelled at me to come back. The torch was off and there was a nice blob of solder covering the hole. I told him I thought it would blow up. He laughed and said "It won't blow up if you put a cool rag over the filling hole." I paid him his 5 bucks filled the tank from the milk bottle and rode off. I have never tried that trick myself but it sure worked for him.

Randy

[Willy]

check out 65 ford on utube

his latest on is on welding a truck tank

Took me a while to find it because I was looking for 65 ford.
After looking at more 65 Fords than I though were ever built it dawned on me to try sixtyfiveford. Duh!

Anyhoo, here's the link.

https://www.youtube.com/watch?v=G3qToCjW-hc

[CalM]

Just purge the tank with a constant flow of compressed air while you do the hot work.

Ultra Lean mixes won't ignite. I've done it dozens of times.

[Carm]

Gas tank empty 5 years, childhood fears, mmm.
Brief review of fire triangle:
Fuel
Oxygen (remember, breathable air has ~around 21%)
Ignition source (flame, spark, heat)

Remove one leg, ya got nada. IMO, your tank at this time has less fuel than a beer fart.
Nothing wrong with safety. Mix up some vinegar and baking soda either in the tank or tube the gas into it.
Weld away.

[Magicniner]

Part fill a petrol tank with an incompressible liquid to weld it, in the event of a flammable gas explosion that's a smart move how?

- Nick

[GNM109]

All of the above methods for stopping explosions might work and they might not. When welding a fuel tank, you never know.

[Carm]

All of the above methods for stopping explosions might work and they might not. When welding a fuel tank, you never know.

Respectfully disagree.
There are times in life when "you never know".
Welding, or any hot work in a potentially flammable situation, requires knowing.
Nothing to do with the vagaries of fate.

[GNM109]

Respectfully disagree.
There are times in life when "you never know".
Welding, or any hot work in a potentially flammable situation, requires knowing.
Nothing to do with the vagaries of fate.

Your answer is rather mystical but I get the idea that you are believe that you are capable of welding a fuel tank, any fuel tank, with no fear of there being an explosion.

God speed.

[Carm]

Mysticism sounds intriguing, but that wasn't my intent.
"Believing" implies, at least to me, an act of faith.
No, I specifically meant fact based knowledge.

[jdunmyer]

Most of the mentioned methods of "safeing" the tank are well-tested and accepted for preventing explosions, it's not "this might work". My personal favorite is using the mig welding gas, either argon or argon/CO2. It doesn't have to be blasting away, especially in a M/C tank, just put the hose in there and let it bleed in for a few minutes, then go to work.