Black Pipe inside, Galvanized Outside?
I am running natural gas piping (3/4") to a pool heater outside (for a hottub). A plumber told me that I should use Black Iron on the inside and Galvanized on the outside run. But how do I join these two? I am worried that there will be a corrosive effect if the two touch.
Also, at what point do I switch between the two types? The outside wall is a 2 foot masonry wall (old house!). I know I'm supposed to use a plastic sleeve while running thru tha masonry. So should I change from black to galvanized immediately after getting to the outside?
Also, I understand that galvanized corrodes when exposed to natural gas... wouldn't it be better to use black iron outside then? and to just rust-paint it really well? My outside run is all above-ground.
Thanks,
Leo