Abstract:

Dry/wet cyclic corrosion tests, combined with electrochemical measurements, cross-sectional morphology observation of rust layer and X-ray diffraction (XRD) analysis of corrosion products, are conducted to investigate the effect of SO₂ content on corrosion behaviors of E690 steel in simulated polluted marine atmosphere. The results show that SO₂ can change the electrochemical corrosion mechanism of E690 steel in marine atmosphere. The anodic branch is transformed from weak passivation to active dissolution feature while the cathodic branch is transformed from oxygen diffusion process to mixed-control of oxygen reduction reaction and hydrogen evolution reaction, leading to great acceleration of anodic and cathodic reaction process. Meanwhile, SO₂ can significantly promote the formation of α-FeOOH and enrichment of Nickel and Chromium in the inner rust layer, resulting in the decrease of uniform corrosion rate and growth of corrosion pits under the rust layer. With the increase of NaHSO₃ concentration, the average corrosion rate of E690 steel within 60 days in simulated marine atmosphere is increased accordingly, and then appears a certain degree of decline when the concentration of NaHSO₃ obtained 0.03 mol/L. Meanwhile, the corrosion pits under the rust layer grew up significantly with the increase of NaHSO₃ concentration.

Key words: dry/ wet cyclic corrosion, polluted marine atmosphere, rust layer, sulfur dioxide, E690 steel