The Influence of the Environment on the Atmospheric Corrosion of Weathering Steel: Field and Laboratory Studies

Weathering steel (WS) describes a class of material, presenting higher corrosion resistance and enhanced mechanical properties than carbon steel when exposed to medium-aggressive environments (rural, urban and light-industrial). The chemical composition of WS, including elements such as Cu, Cr, Ni, Mn, promotes the creation of an adherent passivation layer, which opposes the entry of corrosive species and protects material from further corrosion. However, depending on the exposure environment, the evolution and the composition of patinas can strongly change; the exposure to corrosive atmospheres (i.e., marine sites and industrial/urban areas) destabilizes the patina and reduces corrosion resistance, leading WS to be more susceptible to corrosion and wash-out processes. Consequently, WS releases a certain quantity of alloying metals that could disperse in surrounding areas (soil or water); depending on their chemical form, mobility and bioavailability, some of these elements could represent an hazard to the environment and to living organisms, because of their persistence and potential chronic toxicity. In this work, the issue of atmospheric corrosion of WS was extensively investigated through field and laboratory tests, to evaluate and quantify the effects that surface treatments, exposure geometry, environmental factors and main atmospheric contaminants may have on WS corrosion. Specifically, the characterization of the composition and morphology of corrosion products formed on WS was combined with an innovative approach, that is the quantification of metal dissolution during the early years of exposure, when environmental impact could be greater, and the application of multivariate data analysis. A specific focus was made on the interaction of material with the main aggressive saline ions contained in particulate matter. This work allowed to give a more complete and comprehensive characterization of the environmental behavior of weathering steel and to point out interesting conclusion on the main environmental aspects affecting outdoor corrosion of this material.