fuel tank crack

Originally Posted by Dicky Ticker

As a side comment--I have a 4" scar on my chin where a tank blew up after welding
The tank had been drained and left overnight full of water,drained before welding but the tank itself held residual vapours which exploded on contact with the torch. It is very difficult to completely purge the vapours.

Leave the tank almost full of water when you weld it as this reduces any petrol vapour to a minimum and flash it before welding

You could try liquid metal as an alternative to the other stuff suggested.

Just on that about vapours.
What if you got a good seal with a vac and sucked the air for 5/10 mins???
Might that work?

[Sir Trev]

Fuel vapours whizzing round a hot vacuum cleaner's motor... No thanks!!!!!

[dirtydog]

Originally Posted by Stu

Will the real Blue_SV650 please stand up, please stand up

[Stu]

Originally Posted by vardypeeps

Just on that about vapours.
What if you got a good seal with a vac and sucked the air for 5/10 mins???
Might that work?

A vacuum cleaner will not be strong enough to create a perfect vacuum in the tank. You would have more luck blowing air into the tank to allow the fuel/air mixture to blow out

DD unfortunately time was of the essence and I didn't have the luxury of leaving it standing.

The metal itself retains vapours over time i.e becomes porous and absorbs minute amount of fuel,therefore by leaving water in it you eliminate a large percentage of the area likely to get hot and release vapours.

Someone I knew used to fillem wth fire extiguisher foam on the basis that "If it's full of foam there's not going to be any vapour"

No idea whether this is wise or not - or how he went about cleaning up after.

[yorkie_chris]

Originally Posted by Dicky Ticker

The metal itself retains vapours over time i.e becomes porous and absorbs minute amount of fuel,therefore by leaving water in it you eliminate a large percentage of the area likely to get hot and release vapours.

Also remember fuel doesn't burn, it needs air. If it's full of water you minimise the air present to fuel an explosion, even if fuel sat on top of the water burns it isn't going to do any harm compared to 17l of fuel air mix going off at once.

Originally Posted by Sosha

Someone I knew used to fillem wth fire extiguisher foam on the basis that "If it's full of foam there's not going to be any vapour"

No idea whether this is wise or not - or how he went about cleaning up after.

That would work. Again, displace the air.

I've used water and blown them full of CO2 or argon. No air, no bang.