Welding petrol tanks

[1340banditpaul]

How safe Is it to weld a petrol tank? I've had a tank sitting empty for a few months and noticed a couple of pin prick holes that need welding.

I don't mind welding it but I've heard a few horror stories of tanks going bang even when cleaned, filled with water or exhaust fumes ran through them.

This tank has been empty and no cap for a few months, so how long can petrol fumes hide in the metal pores/tank joins?

Tia

Paul

[dupersunc]

Far, far, longer than you would think.

Flush  it out thoroughly with a hose and some detergent. 

Do it a few times to be sure.

Welded lots of tanks, had a few go up because I couldn't be arsed/ didn't have time to flush them out. 

Make sure the filler neck is open and pointing away from you or anything flammable. 

Dont try the second method.

 

[Joseph]

Exhaust connected to tank for 10 minutes trick is how they did it on the old school Paris Dakar for years apparenlty

Edited May 1, 2022 by Joseph

[clivegto]

I have brazed tanks before and I put the tank over the car exhaust beforehand. 

[Devilman]

Could possibly incorporate a CO2 backpurge setup so you're flooding the tank with CO2, which is both heavier than air and more importantly, petrol fumes 

[Kamikaze]

what they said. Used to repair tanks alot. Flush out with detergent a few times. I used to drill a small pin hole in the corner of the tank to drain all water and chemicals out, then just spot weld it up after i was done.

Abit like ur clothes dryer water condensation catchbottle. they all have a big and small hole to drain the water completely out. thats where i got the idea from.

I stick a hair dryer in the filler cap to dry it out afterways. Job done.

[Dezza]

2 hours ago, Devilman said:

Could possibly incorporate a CO2 backpurge setup so you're flooding the tank with CO2, which is both heavier than air and more importantly, petrol fumes 

That sounds like a great idea. After doing all the usual flushing, use one of those small CO2 cylinders for emergency tyre repair to fill the tank with CO2. It would then be impossible for any remaining fuel to ignite (unless any oxidising agent was present too).

[1340banditpaul]

Thanks for the replies, I'm gonna rinse it out with detergent then run my van exhaust through it for abit just to make sure before I weld it.

It's got me thinking though how long does petrol stay flammable even if its sealed in a container? I always though once it gets that sweet smell of off fuel it was no longer flammable.

[dupersunc]

4 hours ago, 1340banditpaul said:

Thanks for the replies, I'm gonna rinse it out with detergent then run my van exhaust through it for abit just to make sure before I weld it.

It's got me thinking though how long does petrol stay flammable even if its sealed in a container? I always though once it gets that sweet smell of off fuel it was no longer flammable.

I bought a ducati monster tank a few years back, they have a big removable access plate on top that filler neck screws into. That plate had been removed and it had been sat for months like this, barely trace of fuel smell.

Gave it to friend to pull the dentis out of the side and paint. He used one of those slide hammers that spot weld pins to the metal to pull on.

He was welding a third pin on when it went woof. Took his fringe and put a groove up the middle of his curly locks. Only other injuries were a few chuckle muscle were pulled by his colleagues.

Edited May 2, 2022 by dupersunc

[TLRS]

Stick a vacuum cleaner on it, maybe it'll make a small fire tornado

[slayer61]

On 5/2/2022 at 10:16 AM, TLRS said:

Stick a vacuum cleaner on it, maybe it'll make a small fire tornado

Did that job recently. Put the shop vac on backwards to make a "blower" out of it. Let it run for several hours.

[TLRS]

3 hours ago, slayer61 said:

Did that job recently. Put the shop vac on backwards to make a "blower" out of it. Let it run for several hours.

If that heats the blowing air with the electromotor, that's even much more betterer for clearing the vapours

[Upshotknothole]

In the past when I've had it done, they did the car exhaust for a bit and then hooked up a second tank of argon to keep the tank purged while tig welding it.

[Dezza]

Yesterday I took a leaky aluminium alloy tank to Rory at Spondongia for welding. I drained the tank last week and flushed it with water a couple of times.  He was completely unfussed about the prospect of vapour and checked by holding a lit lighter inside the tank. Nothing happened