Numerical Simulation Of The Influences Of Deposited Corrosion Products On Localized Corrosion Behavior

Localized corrosion can be commonly found in the construction of various fields of the national economy. It is difficult to detect and prevent because it has the characteristics of rapid development, diversity and concealment. Localized corrosion often gives rise to catastrophic accidents causing enormous damage to economic development and safety in production. In order to better predict and prevent localized corrosion, researchers have done numerous simulations on the mechanism of localized corrosion. However, these reports basically do not consider the influences of deposited corrosion product on localized corrosion behavior.In this work, a special research method including theoretical analysis, simulation and experimental validation was applied to study how the corrosion product deposition influences the galvanic corrosion and crevice corrosion behavior, respectively. The highlights are summarized as follows:(1) An arbitrary Lagrangian-Eulerian model was established to simulate the galvanic corrosion of magnesium alloy (AE44)-mild steel (MS) couple in sodium chloride solution by considering geometric deformation of crevice, which is caused by corrosion damage and corrosion product deposition. A piecewise linear function was applied to fit the experimental results of potentiodynamic polarization data. The fitting results were used for the boundary condition of the ALE model, making the ALE model to be a nonlinear model. The COMSOL Multiphysics (?) finite element software was used to solution the model predicting the galvanic corrosion rate. The numerical results show that applying the piecewise linear fitting results as nonlinear conditions can provide reasonable numerical results. The predicted galvanic corrosion rate measured values match the experiment well and the deposition of corrosion products can inhibit corrosion of magnesium alloy-mild steel couple. Furthermore, the corrosion depth is in an exponential relationship with the porosity of corrosion product deposition.(2) An arbitrary Lagrangian-Eulerian model was presented to describe the chemical reactions within the corroding long and narrow crevice. The model describes the transient potential distribution, dynamic concentration profiles and time-dependent crevice geometry deformation within a corroding crevice, which is made of AISI304stainless steel. The model includes7parallel electrochemical reactions and hydrolysis reactions. The current model predicted the pH profile, as well as the time-dependent pH distribution, inside crevice. The numerical results of the pH distribution inside the crevice are in a good agreement with the experiment. The adaptive automatic remeshing method is able to timely remesh the computational domain during calculation, which assures the accuracy of numerical results. The numerical results show that, during the crevice corrosion process, the deposition of corrosion products at the crevice mouth will promote the formation of occluded cell, thus accelerating the crevice corrosion.