Quote Originally Posted by dom14 View Post
That means the tank has to be air tight while welding, otherwise oxygen would squeeze in, regardless of the purge.
Why wouldn't oxygen get into the tank from the very crack you're trying to weld??!!
No, just purge it or wash out all the fuel or take it to a professional.
The crack has nothing to do with the oxygen, you are removing the inner space oxygen with the purge.