[oldred]

I hope I am not out of line by bringing up a subject that was being discussed in general rodding tech about welding on gas tanks but this one hits a nerve with me because I had a friend die a terrible death and every time someone mentions welding on a gas tank those visions of that terrible day come back. Seems this fellow was using the common and VERY misguided trick of purging a tank with exhaust gas from a gasoline engine to make it "safe" to weld on! This was a diesel fuel tank that in all probability would not have exploded if he had not purged it at all but he did and the exhaust fumes exploded and killed him, he lived for several hours but eventually died from the burns. Being in the welding and mine machinery repair business for many years I personally know of three accidents that have occurred from doing this including the one that killed my friend, the other two guys were luckier and only received injuries although one of these was quite serious. The IMSHA investigator that investigated the fatal accident I mentioned at the mine said that he had seen several accidents caused by purging with exhaust gas including another fatality and that it happens more often than you might think, more so in the auto repair business than at a mine. This all too common myth still persists because some people think that exhaust gas is "dead air" (whatever that means ) and is an inert gas but nothing could be farther from the truth and exhaust gas is quite explosive when mixed with the right amount of Oxygen from the air. I have attempted to argue this point with several welders, one of which was later injured doing it, but usually with little success and it simply amazes me how common this dangerous and just plain stupid myth is. DON'T DO THIS! It can and does kill people!

[Irelands child]

There is, IMO, no safe way to weld on a gas tank, though I have heard that steam cleaning for hours will work. Most replacement tanks are too cheap(from China??) to consider risking your health or even your life.

Diesel exhaust purging - probably the worst kind of purge as there are significant unburned lower end hydrocarbon strings in the exhaust gases - especially on older trucks or non-EPA regulated off road equipment.

Dave

[oldred]

In the case I mentioned the tank was a diesel fuel tank however the exhaust was from a gasoline engine. I would not do it myself but I have seen several diesel tanks welded with no purging at all and I am convinced, as was the IMSHA investigator, that the tank that exploded would not have done so if it had not been purged with exhaust gas. There is heck of a lot of unburned fuel in engine exhaust and all it takes is the right mix of air in that exhaust to create an explosion even if the tank was otherwise free of fumes.

[Irelands child]

Originally Posted by oldred

In the case I mentioned the tank was a diesel fuel tank however the exhaust was from a gasoline engine. I would not do it myself but I have seen several diesel tanks welded with no purging at all and I am convinced, as was the IMSHA investigator, that the tank that exploded would not have done so if it had not been purged with exhaust gas. There is heck of a lot of unburned fuel in engine exhaust and all it takes is the right mix of air in that exhaust to create an explosion even if the tank was otherwise free of fumes.

Diesel fuel is relatively inert until it is atomizied then high heat (compression ratio) is used ignite it. Gasoline has a very low flash point, like -40 F while Diesel is +150 more or less, depending on the time of the year and the type. The introduction of volitile gasoline fumes did it. Frightening what people will try!!

Dave

[CDJr]

As always, good info oldred I always thought ya were supposed to fill any tank with water and drain it before applying any type of heat to it, whether its welding it, cutting it open with a torch, etc. I damn sure wouldnt trust anything less myself.

[trees]

I have one rule when it comes to welding on gasoline (or other fuel) tanks: DON'T!!!!

The track record for this activity is very poor, both on the professional side and the amateur side.

Trees

[oldred]

When I still ran my shop we did fuel tank repair but before we did ANYTHING to a tank we dipped it in the radiator cleaning tank for 24 hrs, rinsed it well and then purged it with CO2 or Argon leaving the CO2/Argon source in a "trickle" state while welding to maintain a slight positive pressure assuring 100% purging at all times. While it may have been unnecessary to leave the gas on it darn sure did'nt hurt anything and sure was reassuring to the man using welder!

[toddshotrods]

Just stating for the record here as well, because I think my post in the other thread was not clear...

I DO NOT condone welding on a tank with exhaust gas fumes running in it. My point in the other thread was that I went the other way when I saw someone doing that.

Personally, I would just buy or build a new tank.

[LUCKYRUNSMOLLY]

Hello all i am new to this site and hope to bring some usefull knowledge here, and can allways use something new. I have been turning wrenches for 21years now and building racecars and streetrods and sport trucks. and have cut gas tanks and welded sumps for carb cars . all i have done is drain the gas then wash it with the hose for a few minutes then grab the air gun. I have never had a problem with fire or explosion ever. as long as u smell inside the dry tank and dont smell a strong odor of gas your good. The great thing about gas is that it drys out very fast, faster than water.

[lakeroadster]

I work for a shop that builds and repairs pressure vessels for the oil and gas industries. Everything from small tanks to 60,000 gallon propane tanks. We routinely repair vessels that contained hydrocarbons (Oil, Gas, etc.) The vessels are steamed out and a "sniffer" is used (electronic device) to ensure that there are no remaining fumes.

http://www.isre.com/specs-euro7890-gas_sniffer.htm

[deadbodyman]

Originally Posted by trees

I have one rule when it comes to welding on gasoline (or other fuel) tanks: DON'T!!!!

The track record for this activity is very poor, both on the professional side and the amateur side.

Trees

Thats what I say too. DONT DO IT........... But if there was no alternitive and it had too be done...mabee you are in the alaskan tundra working your gold mine and you have to weld your generator tank or freeze to death...wouldnt filling it with common carbon dixide be the thing to use ? its heavier than air and if theres no oxygen there cant be an explosion....right ?????
I'm no scientist but water does contain oxygen and can actually make a fire burn hotter once it reashes a certain temp....
And everybody knows that internal combestion engines have unburnt gasses in the exhaust dont they thats the reason for a catylitic converters but even they dont get it 100%

[willowbilly3]

I think the practice goes back to a time before emissions systems. Even then it probably wasn't safe but the engines were putting out more inert gas with lass oxygen.
I have repaired dozens of gas tanks over the years but never use any open flame near the tank. I use a big soldering copper that you heat with a torch away from the tank. For holes or tears I use pennys for patches.

[timothale]

I have welded a lot of gas tanks, out of vehicle I have always drained them and them steam cleaned or pressure washed with soap and hot water. Then filled with water and positioned them to make sure there is ABSLOUTELY NO AIR POCKETS. I usually rigged up a way to keep water flowing in then I used the torch and brazed them. sometimes open up the hole to let water run out and heat the area around the hole to burn off the residue inside then stop the water flow but keep maximum water and brazed it shut.

[belchfire]

OK I'll admit that I welded on a tank using the exhaust trick. It was an old motorcycle tank and it didn't blow. I was young & dumb and this was just one of many things that over the years should have gotten me killed, but didn't.
The problem with tanks that "seem" to be high & dry is that there can still be oils in the pores of the metal and these will come out and vaporize with heat.
I welded an aluminum oil pan once and it wicked forever. There is the old fill it with water trick and that works (as well as creating a heat sink to control distortion) but then you have to get all of it out and good luck with that. I was told by an ex GI that they put dry ice in the tank and purged it that way. The last job of that sort was welding on a motorcycle engine case in the bike. I stuck the end of the hose from my MIG CO2 tank in the oil filler hole and let it run for a few minutes. While continuing to let it run, I welded away. Argon or C25 will work also but are more expensive. We routinely purge pipe when welding to prevent contamination and there is no sign of burning.

[nine4gmc]

i have mig welded one like timothale described. i got a 87 blazer fuel tank with float and pump from the upullit for $5 because it fit behind my axle and between my frame rails and the sending unit was compatible with my yukon fuel gauge. it had a stab hole in it from the salvage yard draining it to protect the environment. anyway, i made sure it was empty then poured a few ounces of dawn dish washing detergent in and ran water through it till it came out clean. next i positioned the stab hole to the highest point and filled it with clean water again. i made sure i wasn't standing in a mud hole then started mig welding it. it took longer to dry out then it did to fix, literally like a week to dry inside and minutes to repair.

its not smart, but it can be done somewhat safely if you pay attention.