In a rainy climate, the average lifespan of a powder-coated metal outdoor bench is roughly 5 to 10 years. For a decent-quality bench built on a galvanized steel frame, I would plan on 8 to 12 years, and premium versions can reach 10 to 15 years with basic care.
The real deciding factor is what sits underneath the powder coating. A cheap mild steel frame with a thin finish may start rusting at joints, screw holes, and scratches within 3 to 5 years. A galvanized steel frame with a thick, UV-stable polyester powder coat resists moisture much better because the zinc layer acts as a second line of defense.
Rain is most damaging when water gets trapped under the coating. Scratches, chips, unsealed tube ends, and hardware holes let moisture reach bare metal, and once rust starts beneath the powder coat, it spreads as bubbling or flaking. That is why sealed end caps, stainless steel hardware, and good drainage matter in wet weather.
To extend the life of a powder-coated metal bench in a rainy climate, rinse off dirt and standing water, touch up scratches quickly, keep the feet slightly elevated, and avoid letting wet leaves sit on the seat for long periods. With those habits, a good galvanized powder-coated bench can realistically last 10 to 15 years before the finish needs major attention.