Environmental factors affecting corrosion of galvanized steel wires

It was found from field surveys that suspension bridge cables were under severe corrosion environments due to the water and high temperature inside the cable. Corrosion environments depended on the wire positions inside the cables. Wires were found to be continuously wet at the side, wet at night and dry during the day on the top, highly humid at the center, and soaked in the water at the bottom. Accelerated corrosion tests using galvanized steel wires showed that the side wires were most severely corroded, the bottom wires were also significantly corroded, but the upper and the center wires were rarely corroded. These phenomena agreed with the actual cable corrosion. The tests also showed that galvanized steel wires did not corrode when they were kept with a relative humidity below 60%, but became corrosive with the higher relative humidity. Larger amounts of sodium chloride increased corrosion considerably. The corrosion rate also exponentially increased with temperature. It was predicted that the zinc layer would be consumed within 10 years when wires were kept in the wet or soaked environments, 34 years with a relative humidity of 100%, and 211 years with a relative humidity below 60%.