[14p-317-1~10] 1.3 Novel technologies and interdisciplinary engineering

[14p-317-2] Simulated corrosion diagrams based on kinetics: current density contour mapping

〇Yasushi Ogimoto¹ (1.Fuji Electric)

Keywords:corrosion, steel, simulation

Recently, much attention has been focused on corrosion problems especially for steels not only as a material of geothermal turbines or oil pipelines but also as infrastructure materials, because severe accidents of buildings, bridges, and tunnels, are arising from an unexpected failure due to corrosion damages. To overcome such emerging problems, a model to predict a corrosion-rate is crucially important, enabling us to assess the degree of damages and also to implement a timely maintenance based on real-time monitoring the amount of specific ion species in an environment. One can understand a boundary between corrosion and passive states together with a possible reaction product of materials plotted on Pourbaix-diagram, which, however, is a thermal equilibrium diagram and cannot provide any information of time evolution of corrosion. Thus a kinetics-based corrosion diagram is necessary to evaluate the rate of general corrosion that depends on pH and potential values in an environment. Here we demonstrate a simulation-derived corrosion diagram based on kinetics, namely, current density contour mapping by using a simulation software (OLI Analyzer) for pure Fe, 13Cr-steel, and sus304 in a mixture solution of H₂S, Na₂SO₄, and NaCl as a major corrosion constituent. A current density (i) contour map has a horizontal axis of pH and a vertical axis of potential (V), respectively, which is constructed by calculating polarization (i-V) curves at varying pH values in the range of 0 to 14. Tracing the time evolution of pH and potential values in an operating environment on the current density contour map provides us with a corrosion speed (proportional to current density) and a cumulative amount of dissolution of steels, therefore allowing us to predict the remaining time to prepare for an upcoming maintenance. Indeed, a simulation approach is a powerful handle to create a current density contour map for various combinations of steels and corrosion environments, compared to the experimental approach that needs a lot of measurements under widely-changed conditions. We believe this simulation technology is practically useful to predict the corrosion, even to design a corrosion-resistant steel in the near future.