welding gas tank.

[2fpower]

Here is the situation. I am working on our 80 UTE project. For those not reading that thread, the basics are that we are making a 80 into a pickup truck. As part of this, we added 9" to the frame to make it longer. This additional 9" is the same place the gas tank is, so my thought was to cut and weld two tanks together, to make it 9" longer with only one welded seam. This should add maybe 5 gallons of capacity, as it is at the tall part of the tank, which is very needed on an 80. Also the input and output to the tank would not be effected then by the added frame dimension.

This all sounds great until you hear about gas tanks exploding while trying to weld them together. Even sitting out empty and airing out for years.

After reading on the internet, my plan was to cut them both down to diminsions, pressure wash them, maybe take them to a machine shop and have hot cleaned, then prep for welding.

Get a car exhaust pipe routed to the tank and have it pump in C0 the entire time we are welding the tank together.

So, the question is: Should I do this, or is this crazy? And any other recommendations?

paging @SuperBuickGuy

 

[aae42]

most folks say to fill it up with water to weld, if you're cutting it in half, that... might be tough...

 

[mct75]

If you fill it up with water, it can't be filled with gas, so if you pour out all the water it will have no water and no gas in it.

 

[Hornd]

Purge with Inert Gas like Nitrogen (Tire Gas), Carbon Dioxide (beer gas) or Argon.
If you try Acetylene take pics or whoever finds the wreckage can.

 

[2fpower]

purging that large of a vessel seems to be the issue. CO should also be inert - carbon monoxide from tailpipe.

 

[2fpower]

If you fill it up with water, it can't be filled with gas, so if you pour out all the water it will have no water and no gas in it.

I am lost, is the gas tank half full or half empty?

 

[BlueCruiser84]

Throw the two halves in a campfire.

 

[LandCruisinMy93]

My tank sat outside completetly open for a year and I welded it without issue. Maybe if the damn thing were sealed off for the time it was outside it may have been an issue, but it wasn't. So you want to weld a fuel tank because you're a glutton for punishment? If you go to do it, take both tanks to a metal cleaners and have them clean your tanks and then cut them and weld them. Be warned, fuel is slippery stuff (molecularly) so you can't have half @$$ welds or it will leak like a collandar.

 

[Mandrake]

This is one of the few thing's I'd rather pay someone to take the risk then do it myself. Sure, everyone online says just do this or do that and you'll be fine, but my life and my property are more valuable than free Internet advice.

Also, I think it will be a pain in the dings to get the halves lined up right and to get a gasproof weld. Or maybe I'm just a s***ty welder.

 

[bahamasair]

I've welded quite a few gas tanks and a couple propane tanks and always just fill with water first then dump it out and throw in a match or road flare. If it doesn't explode I start welding.

 

[Pascoscout]

Careful on the CO idea. If the cars emission system isn't working perfectly there could be unburt fuel vapor in the exhaust. Straight carbon dioxide isn't all that expensive and probably worth the money if you feel the extra step is needed.

have you considered just making a custom tank from some sheet metal?

 

[BILT4ME]

First, use a match to give enough light to look into the filler neck.........









The tank is not half full or half empty. It's twice as big as it needs to be.

 

[SUMMIT CRUISERS]

Spray tank with mean green degreaser, slosh around, then rinse with water (power wash or take to a carwash would be great). To be extra safe pour a pound of dry ice into the tank to remove the oxygen while welding.

 

[bigshrek]

Dry Ice in the tank. It'll displace the oxygen and makes it so the vapors are not ignitable. Make sure there's a vent on the tank when you get ready to weld, the off gas of the dry ice which is CO2, will pressurize the tank and could make another possible bomb...
Dry ice is what they (whoever they are), put into fuel tanks when they pull them from the ground and transport them for disposal.

 

[LINUS]

I just did a extra port onto my tank for a fuel return going LS3 from a Vortec 350 & TIG'ed a threaded collar (AL tank)

I filled the tank with water to flood out the high point, then drained.
Used the output of the shop vac to blow air in, then put a argon purge on while striking arc.

It took ~15 mins to purge fumes from wet tank with vaccum (used that since I didn't want to make a 'tank balloon' - 3-4psi max)

I used to work in a Shell refinery in the alky/poly/SRU - so super light hc's like propane, butane, isobutane were our process liquids & I permitted for maint guys (I was a operator).

It's not bad at all as long as a tank doesn't have alot of laydown scale like refinery vessels get. If you can water purge & air dry to a level you nod at (so less than standing at the gas pumps on a warm day) - and the tank is scale-free/minimal -you'll be fine.

If you're cutting these open with a sawzall & water, you'll have plenty of time to clean pre-weld. I'd just at least wash them both if using a grinder & disc to open them.

 

[2KCruiser]

x2 on filling with water and flushing out a couple times. I have welded 3 tanks and I still have all 10 fingers and 2 brows.

 

[lastresort576]

Back purge with Argon..Thats how most do motorcycle tanks at least. You also could back purge with exhaust fumes from an engine of sorts.

 

[Hornd]

I am lost, is the gas tank half full or half empty?

To the Engineer: Why is the container 2X as large as it needs to be?

 

[reconranger]

Shoot it with a .50cal tracer. Good to go if it doesn't explode.

 

[cjmoon]

Back filling with a welding gas will keep the inside from oxidizing and will make a better weld. Thin material like that needs back fill for better welds. Helps prevent blow through and what not. I would take a torch or rosebud to the tanks first and give them a quick once over on the inside and call it a day, but still use back flow. Shops do that on innercooler tubes and sst headers and items like that.