On Mon, 15 Aug 2005 23:15:10 GMT, "MM" wrote:

,;
,;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.

Argon is a heavier molecule but your data is wrong. You have given the
atomic numbers for those gases not the molecular weights. The
approximate molecular weights are Ar=40, O2=32, and N2= 28. Note that
both oxygen and nitrogen are diatomic gasses. (Two atoms per
molecule.)

I would fill the tank completely with water and then dry with a argon
purge and weld while the argon is flowing.

You also can buy a plastic which will form a polymer coating inside
the tank. If you have a rust hole this would be a better choice as it
will seal the holes which will show up next week after you finish
welding and put the tank back.
,;
,;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?
,;