"Brian Elfert" writes:

For compressed air, is galvanized or black pipe better?

Black.

Any reasons not
to use galvanized pipe?

Yes, under some conditions, it can flake and become a real PITA.

Much better to use black, pitch it 1/4"/foot and install a drain petcock on
the low end, if you are building a distribution system.

Drain it frequently, say weekly.


HTH


Lew