Effect of Sodium Hypochlorite Concentration and Medium Temperature on Corrosion of 45# Steel in Artificial Seawater and Simulated Concrete Pore Solution

• • In artificial seawater at 25 °C, 100 mg/L NaClO drives a 87% increase in weight-loss corrosion rate (0.202 mm/a vs. 0.108 mm/a baseline), while 10 mg/L causes only a 13% rise (0.123 mm/a). This non-linear threshold effect dictates that chlorination system upsets above 10 mg/L demand immediate corrosion inhibitor injection or material upgrade to avoid accelerated structural degradation. • • The alkaline SCPS environment (pH≈10) reduces NaClO-induced corrosion acceleration: at 100 mg/L NaClO, weight-loss rate reaches only 0.108 mm/a (+25% over 0.0865 mm/a control), compared to +87% in AS. This buffering capacity of concrete pore solution provides a critical safety margin for reinforced concrete structures exposed to chlorinated seawater, but does not eliminate pitting risk. • • Localized corrosion depth in SCPS increases significantly with 100 mg/L NaClO, despite lower overall mass loss. This inversion—uniform corrosion in AS versus deep pitting in SCPS—means that non-destructive thickness measurements alone are insufficient for concrete-embedded steel; pitting factor must be monitored via electrochemical noise or localized corrosion sensors. • • Lowering temperature from 25 °C to 10 °C consistently reduces corrosion current density, product layer thickness, and pit depth in both AS and SCPS. This validates the operational practice of discharging cold LNG regasification water as a corrosion-mitigation measure, provided residual chlorine remains ≤0.2 mg/L, which is 5-fold below the 1 mg/L threshold where no corrosion rate change was observed.