Originally Posted by rdupree
If you are going to use iron pipe, be sure to use galvanized pipe. At a former employer, they installed a new air system, all of it in black iron pipe. Inside of about 6 months, the inside of the pipe was already rusting and generating lots of rust that clogged the insides of air tools, etc.
Galvanized pipe has issues also. The galvanize will start to flake off, check out this article by Exair, very informative: Compressed Air Piping