Galvanized EMT conduit will rust, especially if you let water get inside and it does not drain. I use silver spray paint on all cut or drilled spots, and drill tiny holes on the underside of any horizontal runs that descend from verticals. (E.g. I've bent EMT into four-sided frames for doors, etc). I have outdoor EMT structures (trellises, garden gates, chicken run frames, geodesic domes) that are 25 years old and going strong. :)
Agreed though -- PVC pipe (the white stuff) does very poorly with exposure to UV light. The beige CPVC stuff is worse. The black PVC (ABS?) is supposed to be better, but less available in small gauges. And the grey plastic stuff used for electrical conduit is also supposedly UV-safe, but is far less structurally rigid than any of the others, or of course galvanized EMT. Sometimes that flexibility is a virtue, but usually not.
> PVC pipe (the white stuff) does very poorly with exposure to UV light
To my understanding, this is primarily an aesthetic issue. PVC pipes have been tested over years of UV exposure and remain structurally sound. This is a topic that comes up periodically on the pool forums since it is pretty common to have some amount of exposed PVC pipes above ground.
Agreed though -- PVC pipe (the white stuff) does very poorly with exposure to UV light. The beige CPVC stuff is worse. The black PVC (ABS?) is supposed to be better, but less available in small gauges. And the grey plastic stuff used for electrical conduit is also supposedly UV-safe, but is far less structurally rigid than any of the others, or of course galvanized EMT. Sometimes that flexibility is a virtue, but usually not.