Corrosion Behavior of E690 Low Alloy Steel in SO2 Polluted Marine Splash Zone

摘要

Effect factors in marine splash zone are complex, which lead to the marine splash zone be the most severe environment where marine structure steel is operating. Marine structure steel usually suffers from industrial pollutions, such as SO_2. This work is based on the marine field exposure tests, combining morphology observation, electrochemical potentiodynamic polarization and electrochemical impedance spectroscopy, scanning Kelvin probe microscopy and rust layer statistical analysis, to inspect the corrosion behavior of an E690 marine structure steel in a real sea splash environment with industrial pollutant SO_2. Results show that the rust layer of E690 has diffusion channels in the vertical direction and cracks in the parallel direction. Thin liquid infiltrates the rust/substrate interface, forming part of the local corrosion under the rust layer. Anions concentration in the oxide/metal interface has a more negative potential. The rust layer with anionic charge exhibits stable cation-selective permeability which lead to sulfide and chloride in the rust layer has a gradient distribution in the vertical direction of the rust layer. Dry/wet alternate process of splash zone makes ions into the rust layer, but only cations are easy to come out, leading to the rust layer acidification and anionic. SO_2 promote the formation of α-FeOOH and lead to the broad pitting isolated. Broad pitting with SO_2 acidification is prone to deeper development in the vertical direction of the rust layer.