Effect of the Concentration of a Nitrite-Based Inhibitor and Chloride Ions on the Corrosion Behavior of FCD-500 in a Simulated Marine Engine Cooling Water System

This study aims to evaluate the corrosion behavior of ductile cast iron (FCD-500) under simulated marine engine operating conditions and to determine the optimal corrosion inhibitor conditions under chloride contamination. Experiments were conducted at 50 °C and 80 °C, with different Cl− concentrations (0–500 ppm) and sodium nitrite (NaNO2)-based inhibitor concentrations (0; 9000; 15,000; 17,000 ppm). Immersion and electrochemical tests were performed to analyze the microstructural corrosion characteristics and inhibitor efficiency. The results indicated that as the Cl− concentration increased, proportionally higher levels of inhibitor were required to maintain surface stability. The maximum inhibition efficiency, approximately 97.3%, was achieved with an inhibitor concentration of 17,000 ppm, at a Cl− concentration of 100 ppm.