View Full Version : welding a gas tank

08-07-2006, 10:42 PM
a budy of mine is instaling a sump in his gas tank. He is converting it to an in-tank pump. He needs this for his fuel injection conversion in his 1966 chev Malibu.

He brought the gas tank to a TIG welder, who later informed him he was unable to weld the tank because it had been galvanised. I have seen the tank and it does not look that way.

So my questions are the following:

Could the tank have been galvanised ( I mean when it was originaly built)

Can you weld through Galvanised steel with a TIG?

Could you do a good enough job using a MIG?

Rob :)

J. Tranter
08-07-2006, 11:00 PM
Galvanized can be TIG welded you just have to be carefull not to inhale the fumes, they are toxic.

Why doesn't you're friend just use a high flow external fuel pump. He doesn't need to have Aan internal one?

08-07-2006, 11:13 PM
TIG welding is unforgiving to 'dirty' materials. I have tried to TIG weld galvanized metal with poor results. Even rusty material will create poor/bad welds when using TIG.

MIG welding would be better, but I don't know if it would be a good enough weld with galvanized to be used on a fuel tank. I have used the MIG process on galvanized for different things, but none of that stuff was used for holding liquids or pressure.

On your particular question though, I'd have your friend look into an external electric fuel pump for the application. A regulator would probably have to be used to obtain the proper fuel pressure. But, it would be a fairly easy install and would be a lot easier to replace than an in-tank pump!

08-07-2006, 11:23 PM
Welding gasoline tanks is very dangerous, even when empty. Gasoline can remain in the seams, even after all the fumes are expelled. I hope your friend is being very cautious!

08-08-2006, 12:56 AM
Throw a pound of dry ice in the tank and wait 20 minutes before welding. Leave the tank open with the opening on the high side.

08-08-2006, 01:37 AM
The tank could have been aluminized too. In either case, welding on them can be messy. Make sure the conversion includes checking the old fuel line and removing/replacing any rubber hose joints with high pressure line. The in-tank pumps run at 40-50psi with a feedback or regulator. A problem in regulation can send the line pressure to well over 100psi. A broken hose can empty a tank in a few minutes.

By the way, doesn't that tank already have a sump? The baffles should provide a sump area.

08-08-2006, 01:57 AM
If your installing a sump on the tank, I persume the sump is allready fabbed up. If so, lay it out on the tank, and mark it with a marker, then just take a body grinder with a 24 grit disc and grind the coating off.

I do these all the time, and have no trouble tig welding them. I would not try to mig weld it though. It will warp badly, and you will have many leaks to go over with the tig.

Welding tanks is not as dangerous as one might think. I allways rinse them out with rubbing alcohol that can be purchased at any drug store. This will remove all traces of fumes frome the tank, then weld away.

If the tank is a unusual shape to it, that a bady grinder is not practical, then I use a die grinder with those totsie roll abrasive rolls availible in many different grits. You only have to be about an inch back from the weld line.

Cheers Paul

08-08-2006, 02:19 AM
I don't think you have seen a galvanized gas tank. We used to have a line where I worked to make "Terne" coated steel for gas tanks, tin lead mix, similar to solder.

Similar, in fact, to a true "tin can", but a tin can did not have much, if any, lead in it.Have fun.



08-08-2006, 08:24 AM
Thanks for all the safety concerns. The tank has been out of the car for 2 years. The holes are already cut and new pieces already fabricated to hold the pump and sump. Installing an external pump is no longer an option as we would still have to weld up the holes that have been cut.

Rob :)

08-08-2006, 08:42 AM
Ya know, one of my friends has a junkyard and he's been welding them for years. Although I've never watched him; he said as long as it's empty, with no cap, it's a piece of cake. Said he couldn't understand why everyone was so scared to weld them. He gets paid well for those dangerous jobs.

08-08-2006, 01:15 PM
To answer your questions from my humble perspective.

Yes, it's possible the tank was galvanized when manufactured, some are, some aren't.

Galvanized metals can be TIG'd, but not without grinding away the galvanized coating. Otherwise you get dangerous fumes, the zinc will contaminate the weld, pinholes from the inclusions may leak.

You can MIG, same rules apply as TIG except MIG deposits a lot more material a lot faster and can "fill in" a poor fit-up or pin holes.

There is no reason why you can't TIG your bungs on most gas tanks; it looks a lot prettier than stick or MIG. With a good fit-up you can braze or solder too, works best if there is a shoulder on the fitting.

It's common in Hot rod and motorcycle custom fabrication to put the holes and bungs where you want 'em. Fuel migration to the seams and pores can be a potential combustion problem on used tanks so prudent precaution should be taken - no fuel for a couple of years in an otherwise open tank should not present a problem; steam it out if there is gunk inside. You can weld it if it half full of water, dry ice provides a CO2 flood, you can flow an inert gas inside while welding - not, not, not oxygen.

Your situation may be different than we imagine here, but I would find another weldor for a second opinion.

Doc Nickel
08-08-2006, 03:45 PM
Even tanks that have been "open" for a couple of years can still produce enough fumes to be dangerous when you start to work on 'em.

When I welded up a hole in a gas tank, I filled it partway with water, then used a spare 20-lb CO2 tank to purge the rest. Used a MIG to stitch the patch into the hole (basically a bunch of hot, overlapping spotwelds.) Had I had a TIG at the time, I'd have definitely used that.

Any galvanized tank I've ever seen was only galv'd on the outside. As the other poster noted, just (carefully, don't go too deep) grind away the coating so you have clean metal to weld to.

And I'd still purge the inside with CO2 while welding.


Frank Downey
08-10-2006, 05:18 PM
I have been a welding engineer for 25 yrs. TIG welding can be done to any type of metal.It is the only way to seal it off for sure,but proper setup is essential to successful welding as with the lathe or milling mach.You can grind
off the galvenized surface coating and clean the tank or you can try to do it with nitrogen.It is far safer to weld a gas tank full rather than empty.the fumes in the tank is what explodes not the liquid.I would tig weld the tank because you will get a better weld and also the metal is about as thick as toilet paper,it will keep down the distortion in the tank.good luck but always take the time to set up correctly and vent the tank .