Corrosion behavior of carbon steels in nuclear second loop under simulated marine and nitrogen protection atmospheres

The corrosion behavior of nuclear-grade carbon steels (Q235A, 20#, and Q245) was systematically investigated under simulated marine atmospheric conditions and nitrogenprotected environments.Corrosion weight loss tests, scanning electron microscopy (SEM), Xray diffraction (XRD), and potentiodynamic polarization techniques were employed to evaluate the effect of nitrogen protection, while a corrosion simulation model was established to study the dissolution behavior of oxygen in the electrolyte solution.The weight loss measurements demonstrated that nitrogen protection significantly decreased the corrosion rate of carbon steels, reducing it to nearly 1/100 of that observed under marine atmospheric exposure.Polarization curves further revealed that nitrogen effectively suppressed corrosion, as evidenced by a corrosion potential shift of -0.239 V. SEM observations and XRD analyses confirmed the protective role of nitrogen, showing delayed penetration of chloride ions and verifying the prolongation of the corrosion cycle in carbon steels.These findings were consistent with the simulation results, which indicated that a low-oxygen environment effectively inhibits the initiation and progression of corrosion.Overall, the study provides both experimental and theoretical evidence that nitrogen protection can serve as an efficient approach to mitigating corrosion of carbon steels in harsh atmospheric conditions, with important implications for the durability and safety of nuclear power applications.