Welding fuel tanks

[Berg400]

or you can do it the the simple easy and cheap way.Which happens to be the best(read safest) method yet.

I would tend to disagree with you here. For few reasons,

1. To purge the tank with argon all you have to do is put the hose from the regulator and turn it on.

2. Argon is cheap, and easy to get your hands on.

3. Argon is an inert gas, it will not only remove the oxygen from the tank, it will also protect the weld pool interally, thus making it easier to weld and get good penetration. This is a teqnique that I have used to weld pressure vessels.

4. As you stated dry ice is frozen co2 and therefore cold, this would also make it harder to weld as it is going to draw the heat away from the weld you are trying to do

PACK TO BRIM WITH DRY ICE. Dry ice is frozen CO2 so no flamable gas can find O2 to mix or burn with and keeps tank cool also.

[pancho]

i have welded,and soldered various fuel tanks of petrol trucks and of cars and motor cycles using a method my dad told of for cars and trucks and for m/cycle tanks a method that i learnt over the years from other bike repairers of the "old school". just because i have never blown myself up doesn't mean i will divulge details for risk of causing injury.  however the system my dad showed me for larger petrol tanks involved running an exhaust pipe into the tank untill the tank material was HOT and then "flaring" it and  welding it before it cools down. be very aware that minute amounts of petrol which has seeped into the folded seams will flare.MAYBE TWICE OR MORE. Another tip Do NOT assume that soldering a tank is safe. pops method when soldering a petrol tank was to use a very large soldering iron [which holds temperature longer], and if the soldering iron is hot enough to make a piece of newspaper glow ITS TO HOT. if you haven't done this sort of thing before don't risk it.....When i was in the nasho's we had to oxy cut a heap of 44gal oil drums. trouble was one had had petrol in it .when it exploded the bottom end bulged out like a balloon, the top end blew straight off and the oxy cutter made a permanent groove in his forehead. there was no petrol in the drum just fumes. cheers wally.

[GMC]

Welding alloy fuel tanks is usually fine, it's the steel tanks that seem to hold fuel in the seems.
I usually just leave in the sun to dry them, squirt a bit of argon inside 7 go for it.
Aluminium doesn't usually give off sparks or glow red to create an ignition source.

I have sworn off doing steel tanks, I put this up once before, must have been on the old forum....

I had welded a couple of steel tanks successfully by filling them with water but  this can cause dramas too. You can’t weld when the water backs onto the weld area as you can’t create a decent weld pool, so you need to leave a small air pocket in the weld zone. This worked okay a couple of times but then quite a few years back now I was asked to weld up a small crack in a seem of a stainless steel boat tank. No problem I thought. I filled it full of water, left a small air pocket behind the weld area & proceeded to weld. I was kneeling down at the time, resting my elbow on the tank. I was doing okay and I just had to get the last little bit when wooooooooopppfh.. It seemed like the blast lifted me to my feet and knocked the welding shield off my head. Despite my heartbeat suddenly being elevated to that of a 20-minute moto, although without the burning lungs, I had a very real fear of being electrocuted as the 40 litres of water from the tank gushed over the factory floor and headed for every extension lead. I had to quickly pick up the leads out of the way and then grab a broom to divert the water away from other machinery. Some guys from the factory next door came running in to see what the blast was. It didn’t seem that loud to me, I think I must have been in the epicentre.
And the tank, well it was completely rooted. It used to be rectangular but now all six sides were rounded and every seem had a crack in it. I had to make a new one from scratch.
In hindsight I realise now that what traces of fuel that was in the tank floated on the water, the welding heated it into fumes in the air pocket and then when it thought I wasn’t looking the ignition source of the weld pool did the rest.
I still weld many alloy tanks but refuse to weld steel tanks now. Life’s too short and I don’t need to speed up the aging process any more than what it already is.