Im not 100% certain, but that looks a lot like stainless steel pipe to me....
304 is code for stainless (at least that's what i have welded before, 304 and 308 stainless) which is probably the most common stainless steel used. I would use 308L filler rod when TIG welding to it and back purge so the weld wont "sugar" on the inside.... if that is what you had in mind....
Also, if you are going to do any abrasive cutting on stainless, its a really good idea to wear a decent respirator because it produces hexavalent chromium that is a known/potent lung carcinogen.
Ahh, crap. I don't know why I didn't just Google it to begin with.
You're right, that's stainless. I only have a MIG at home, setup with 75/25 argon/co2. We have a TIG at work, but I'm not really good at it yet... I barely get to use it.
Oh well. I'll find something else to make a tank out of. I have some of this...
....so whatever I end up using will be sealed up nicely.
A buddy of mine said he may have a hunk of 3" or 4" pipe (not stainless). We'll see.
Thanks for the heads up. I would've welded that **** up without even thinking about it. I don't have the means to back purge, I only have one tank... for the shielding gas.