I want to build a custom lumber rack for my pick-up truck, and the most easily available material for the job that I can think of is the so-called "black iron" pipe used for plumbing natural gas lines, etc. (I'd be using ~2" diameter pipe). I don't know what "black iron" is, but I suspect that it is not iron at all. Probably some sort steel. Is this stuff weldable (I'll be using MIG with C-25 gas)?