Synergistic effect of sulfur dioxide and chloride on the corrosion of 3.55 wt% Ni weathering steel

Abstract In this paper, we studied the synergistic effect of sulfur dioxide and chloride on the corrosion of weathering steel containing 3.55 wt% Ni. The weight loss and the rusts formed on weathering steel in atmosphere containing chloride, and a mixture of sulfur dioxide and chloride were studied by wet/dry cyclic corrosion tests. The results showed that in a chloride containing atmosphere, the rust presented a bi-layer structure, with a loose outer layer with chloride clustered and a dense inner layer containing goethite. Due to the synergistic effect of sulfur dioxide and chloride, the sample corrosion was accelerated, which changed the rust structure and phase distribution. Goethite formed in the outer rust layer with a shell-like morphology, which limited the volume changes causing crack formation. Chloride passed through the cracks to corrode the substrate and akaganeite formed in the inner rust layer, which eliminated the cation selectivity.