Composition of rust layer and fatigue strength of weathering steel welded joints weathered for 41 years

Many weathering steel bridges have been in service for more than 40 years, and therefore, it is necessary to clarify the fatigue strength of the weathering steel welding joints that have the protective rust layer. This study included corrosion property measurements, rust composition analyses, and fatigue tests of weathering steel welded joints that have been exposed to the atmosphere environment for 41 years. The rust layer thickness, corrosion pit depth, and weld toe radius tended to be similar to or relatively increase from those in the results of a study conducted after 25 years of exposure. Based on the rust composition, the presence of the protective rust layer in which the α-FeOOH layer was distributed near the interface with the steel surface was confirmed. The fatigue strength tended to be about the same as or larger than that after 25 years of exposure. Thus, the fatigue strength has been kept due to the corrosion reduction of corrosion progress by the protective rust that has been maintained after 25 years. In addition, a visual inspection and magnetic particle testing were conducted from the surface over the rust layer. Detecting the early stage of crack initiation was difficult due to the rust over the crack, but the crack became detectable after it had propagated up to certain lengths.