Influence of chloride deposition rate on rust layer protectiveness and corrosion severity of mild steel in tropical coastal atmosphere

Abstract

A field exposure test of mild steel was conducted in a real tropical coastal atmosphere with the range of chloride deposition rate between 100–600 mg Cl−/m2 day. The effect of the chloride deposition rate on the atmospheric corrosion behavior of mild steel was investigated by weight loss measurement, confocal laser scanning microscope (CLSM), scanning electron microscope (SEM), X-ray diffraction (XRD) technique and Pearson correlation coefficient method. Results indicated that a high chloride deposition rate would reduce the protective ability of rust layer due to the increasing of detrimental akaganeite (β-FeOOH) and maghemite (γ-Fe2O3) in the corrosion products. Also, the existences of β-FeOOH and γ-Fe2O3 induced severe corrosion pits on the underlying mild steel surface. Quantitatively, strong positive correlations were obtained among the chloride deposition rate, the corrosion rate and the protective ability index (PAI) of rust layer by means of Pearson correlation coefficient. Thus chloride deposition rate could be directly related to the protectiveness of rust layer as well as corrosion severity of mild steel in the tropical coastal atmosphere.