hi just wondering what is the best method of welding a fuel tank???

there is on feul in the tabk it has now been drained of a day but still smells of petrol.

ideas please.


cheeers steve

I'd be sticking a hose in it and running it through with water for a good bit before I went anywhere near it with a welding torch!

I really would be VERY careful with a tank, the pro's steam clean them for a fair while. I heard that sticking a car exhaust into the tank for a bit can do the trick, I guess that is just steaming it though.

Tanks that have been emptied and left are explosive for some time. Measured in at least weeks.

I've heard of people sticking the filler over the exhaust pipe and running the engine for a while, to clear them out.
Then filling with water before welding.

No personal experience of it though..

After washing it needs to be steamed out for at lest a couple of hours ----- a steam wallpaper stripper should provide enough steam.

i have one to weld as well
mines been sitting next to the wood burning stove in the workshop for the last 6 weeks.... hasnt blown up yet, so i guess it should be ok

Hi done this many time's all I've done is run a hose pipe through it for 1/2 hr or so with some washing up liquid and the dried it out.........and no problems.........Gordon

I would washitoutwithsoapy water and fill up to overflowing. This removes any vapour. Which iswhatwill cause any explosion. Then, once flushed it should be safe to weld.

Washing out alone is not enough, petrol has the habit of lingering in seams and reapears when heated this can enough to give rise a mixture within the explosive range, the lower explosive limit of typical pump petrol is is just over 1% by volume (ie. 1 part petrol vapour to 99 parts air). Also The auto ignition temperature of petrol can be as low as 250c. Because there is not enough fuel present ignition at levels close to the explosive limit usually result in a flash fire rather than a fully explosion --- remember the school chemistry demonstration of hydrogen burning.


The hot work rule is Empty, then Wash, then Steam, then Ventilate.

Put a pipe from your exhaust in to the tank and fill it full of fumes. Sounds daft but works !!

washing out with soapy water (washing machine soap) worked for me with calor gas cylinders before i cut it open with a grinder. poured some soap in, filled with water, left a few days, emptied, and dropped a match in to make sure it was ok
no explosions... ok, its not petrol, so petrol might behave different, but what i'd do, fill with water, leaving a tiny air space, and position the tank so that the air is under the bit you're welding, so there's no water pressure on the molten metal.
should be ok

quote:

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Originally posted by britishtrident
Washing out alone is not enough, petrol has the habit of lingering in seams and reapears when heated this can enough to give rise a mixture within the explosive range, the lower explosive limit of typical pump petrol is is just over 1% by volume (ie. 1 part petrol vapour to 99 parts air). Also The auto ignition temperature of petrol can be as low as 250c. Because there is not enough fuel present ignition at levels close to the explosive limit usually result in a flash fire rather than a fully explosion --- remember the school chemistry demonstration of hydrogen burning.


The hot work rule is Empty, then Wash, then Steam, then Ventilate.

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^ agree, and soap essentially being a de-greasser, should help either remove the petrols oily film residue, and coat whatever is left behind.

The exhaust pipe method does work, but, be sure the car's exhaust is up to temperature and the tailpipe is hot, run it into the tank, when the tank is hot, leave it another 15 - 30 minutes.

A couple of months ago I did braze up some un needed holes in my tank using this method.

I guess having the tank hot teazes out the fuel which has capailaried into the seams.

last time i welded a tank i washed it out with a high pressure steam cleaner with dilute traffic film remover soap, then washed with soap free cold water then blew it out with an air line.

I left the air line in the tank still blowing whilst welding with the filler pointing down and away from me with all of the other holes pluged so that there would only be one exit blow point ( i may well have been wrong with that assumption ) anyway it worked and held fine until well after i sold the car

regards

Ewan

well thanks for all the replies and all very helpful.

i will tell you how i get on, if you hear in the news a bloke made a bomb and killed himself in the high peak its only me (lol).
thanks again for the info.

cheers steve

When i had to repair my tank, i pressure washed it out first .Then filled it with argon shield gas off the mig welder,kept it running at a low pessure then welded the tank.

As above, my local ally welder steams then fills with inert welding gas argon on steady feed.

Car exhaust can be combustible, depending on mixture.