Numerical simulation and experimental verification on the kinetics of droplet corrosion of carbon steel

Abstract

In this paper, we investigate the issue of droplet corrosion in carbon steel, employing both numerical simulations and experimental methodologies. We dissect the corrosion mechanism of carbon steel droplets, considering how droplet shape influences oxygen diffusion, movement of the corrosion interface, and the dynamic deposition of corrosion products to elucidate the corrosion dynamics. Both simulation and experiment results establish that at the droplet's edge, the density of corrosion products and the pH value are elevated compared to the central area, which, conversely, features more porous corrosion products and a lower pH value, leading to heightened anodic current density at the center. This disparity in porosity and pH values accentuates the difference in current densities and intensifies localized corrosion within the droplet. Structurally, the droplet's center functions as a local anode, while its edge serves as a cathode. Corrosion products in the central area primarily consist of green rust (Fe₄(OH)₈Cl), which exhibits higher porosity, whereas the edge is characterized by denser γ-FeOOH. Variations in the composition and protective attributes of these corrosion products further magnify the differences in current density. This autocatalytic progression instigates a stable internal anode-cathode reaction within the droplet, ultimately culminating in the development of a deeper corrosion pit at the central zone. Additionally, the numerical model in the paper can provide support for the prediction of atmospheric corrosion of carbon steel.