Zinc-coated roofing steel loses its zinc coat after about ten years because of being exposed to elements and it has to be painted. Zinc-coated powerline posts lose zinc too and experience corrosion, however they are built of thick parts which are "eaten up" slowly and once enough cross-section is lost they are replaced.
However I've recently seen a culvert assembled from pieces of corrugated steel with coating looking like zinc. Parts were something like 5 millimeters thick and connected with numerous bolts and the culvert diameter was about 1,5 meters.
The water passing through a culvert bring sand and other particles which surely grind the surface. I assume this should remove the coating from the submerged part of the culvert within several years and then corrosion will start and eat the not so thick steel rather quickly.
How is abrasion by solid particles addressed in culverts made of galvanized steel?