Yes, if you live in a coastal area, urban benches can rust from salt air, but whether yours will depends on the material, finish, and upkeep. Salt spray, humidity, and onshore wind carry tiny salt particles onto metal surfaces. This accelerates oxidation, especially on untreated steel, cast iron, and cheap fasteners. You will usually see rust first at welds, bolt holes, scratches, and joints.
If you are choosing benches for a seaside location, look for marine-grade materials. 316 stainless steel is the best common metal for coastal furniture because it contains molybdenum and resists salt corrosion well. 304 stainless is more affordable but can still develop light tea staining with heavy salt exposure. Hot-dip galvanized steel with a quality powder-coated finish also performs well, as long as the coating is not scratched through to bare metal. Powder-coated aluminum does not rust like steel, though it can form white oxide spots if the finish breaks. Hardwoods such as teak or ipe and high-density plastic lumber are also good low-maintenance options.
To keep coastal benches looking good, rinse them with fresh water every few weeks during dry, salty periods. Check welds, joints, and footplates for early rust, and treat small spots quickly with a rust converter or touch-up paint. Avoid harsh chemical cleaners, and make sure drainage holes stay clear so water does not pool inside the frame. With the right materials and a simple cleaning routine, urban benches can handle coastal salt air for many years without serious rust.