Who is using what for air in their shop

I'm sure that copper would work fine, but look at the price.

You could easily do it in either galvanized iron or regular black iron. You'd probably get more rust in the black iron, so galvanized would be better.

Iron comes in 21' lengths, and most places carry shorter, pre-threaded pieces also. I'm sure that you could rent a hand-threader somewhere locally. I have my own, so it's not an issue.

To help eliminate water, install every take-off vertically up from the main line. The installation of a water separator is an added bonus, but a drip leg at the end of the line is a cheap alternative.

Whatever you choose to install, make sure that it isn't plastic. Safety first:cheers:.

Mark. (20 yrs as a plumber/pipefitter)