A cured powder coat film is a single cross-linked layer locked onto the metal, which is why it resists nicking, scratching and impact so much better than an air-dried paint film.
Indoor parts — furniture frames, machine housings, interior metalwork — routinely stay sound for decades, since they're under neither UV nor moisture pressure.
Outdoors, a standard polyester system typically holds its colour and integrity for 10–15 years; a super-durable architectural system goes noticeably longer.
Three things shorten this lifespan the most: insufficient cleaning before coating, too thin a film, and incomplete curing in the oven. All three are process errors, not material limits.
Maintenance is simple but matters. Washing the surface with warm water and neutral soap once or twice a year removes salt and industrial deposits that quietly accelerate degradation.