Hydrogen embrittlement and corrosion fatigue of corroded bridge wires

Abstract

Cables of old suspension bridges and stays of cable-stayed bridges often suffer from steel corrosion. Corroded galvanized steel wires on different corrosion levels were produced at laboratories, and their mechanical properties and remaining strength were investigated. Actual tensile strength of corroded wires did not decrease with corrosion levels, whereas elongation decreased sharply after the zinc layer was partly depleted and the steel started to corrode. As the accumulated amounts of diffusive hydrogen of corrosion level-2 wires–with and without added tension–were almost the same and less than 0.2 ppm, the applied tension of steel wires did not affect the amount of diffusive hydrogen which was well below the critical concentration of 0.7 ppm to cause brittleness. This indicates that hydrogen embrittlement is unlikely to occur. Fatigue tests showed that fatigue strength did not change when only the galvanized layer was corroded, but it significantly decreased after corrosion of the steel below the galvanized layer progressed. Fatigue strength further lowered when the steel wire was cyclically stressed under wet environments when compared with the fatigue strength under dry environments. The broken wires of an old suspension bridge were also investigated. The fracture surface was similar to that caused by corrosion fatigue rather than hydrogen embrittlement. It was estimated that the wires were fractured by the mixed effects of corrosion, cyclic stresses and hydrogen.