You got allot of anwers here. Most of em won't kill you, but some won't get
yery good results. Oxygen in water will combine with iron to make iron oxide
(rust/slag) and you won't get a very good weld

Gas can't combust if there's no free oxygen present, so flooding with inert
gas is the safest. Argon will work, but you have to make sure you have a
good flow (positive pressure) of argon in the tank all the while you are
welding. Even so, Argon (atomic weight 18) is heavier than air, mostly
nitrogen (A.W. 7), and oxygen (A.W. 8). If you're working on an area at the
highest point of the tank, there may be a bubble of trapped air behind it.
If the welding is to be done on a boss or fitting, you can open (or remove
what ever is in it) and let the gas flow out.

Probably the safest would be helium. It's definitly light enough to
accumulate at the high spot, and displace the air. And this is usually the
position you want to weld in.

Be careful


Mark


"Modat22" wrote in message
...
I need to make sure it won't explode and was thinking about letting it
sit in the sun open for a few days then fill it completely with water.

Any other ideas?