My choices hearken back to my plumbing days.
Galvanized Pipe is for water.
Black Pipe is for air/gas/oil/steam.
Plastic, copper (several different types), brass, stainless steel, cast iron and.......darn I've forgotten the other one(s)
all had their specific uses and were at times interchangeable.
Let's see if I can remember why on the galvanized........
They didn't use galvanized on much other than water because of reactions it might have with acids that formed in some the other substances (i.e. engine oil) and costs, as it is more expensive. Also poorly applied galvanizing could break free and cause problems too.
Galvanized will be ok in that application though, as oil is not "flowing" through it.