Are you sure the correct kind of paint was available when it was installed? And how long of a lifespan does that paint have? Surely not the life of the hydrant. This isn’t a one and done sort of thing. This is something you have to do every few to several years, depending on the specific coating you use. Every so often, the laws change regarding what can be used where, and advances in coating technology means a specific product might only be available for a few years before it’s replaced with something else, if it’s replaced at all. Working in the paint industry, I can tell you that some products died when COVID hit and the companies that made them went under.