Numerical Simulation Study on the Corrosion Behaviour of Q345 Steel in a Simulated Marine Thermocline

Changes in temperature, pH, dissolved oxygen content, and nutrients, which are key factors that cause metal corrosion, are common in marine thermoclines. To study the corrosion behaviours and reveal the corrosion mechanisms of metals in a marine thermocline, COMSOL 6.2 software is used in this paper. With this software, the corrosion behaviour of Q345 steel in a thermocline is numerically simulated, and a simulated marine thermocline is built indoors for experimental research purposes. The corrosion behaviour and mechanism of Q345 steel in a marine thermocline were investigated through numerical simulation, electrochemical testing, and corrosion morphology observation. After 21 days of immersion in the simulated marine thermocline, Q345 steel specimens at different depths are shown to have undergone vertical galvanic corrosion, with two anodes and two cathodes. At depths of 70 m and 150 m, the Q345 steel becomes the anode in the galvanic corrosion reaction, while at depths of 110 m and 190 m, the Q345 steel becomes the cathode in the galvanic corrosion reaction. The cathode is protected by the anode and has a relatively low corrosion rate. The main reason underlying these phenomena is that there are large differences in the dissolved oxygen contents and temperatures at different depths in a thermocline. The different dissolved oxygen contents lead to differences in the oxygen concentrations of Q345 steel specimens at various depths. These variations trigger galvanic coupling corrosion. Moreover, the difference in temperature further aggravates the degree of galvanic corrosion.