Effective corrosion-inhibition solution for prolonging service lives of pipe materials for seawater-for-toilet-flushing (SWTF) systems: Plant-scale and lab-scale studies

SWTF is an effective water-resource solution for coastal mega-cities but the ageing of pipeline materials by long-term seawater corrosion can be a costly problem to resolve. In this study, the corrosion inhibition effects and inhibition mechanism of 25 mg/L Ca(OH)₂ on ferrous materials under seawater environment were examined by weight-loss measurement and various electrochemical methods. The results indicated that addition of 25 mg/L Ca(OH)₂ serves as a mixed-type inhibitor to decrease the corrosion rate of ferrous materials by around 30 % during 14 days of immersion in simulated seawater environment and around 66 % during 180 days of immersion in fresh seawater environment. Microstructural investigation indicated that the addition of 25 mg/L Ca(OH)₂ promotes the amount of aragonite (CaCO₃) precipitates on the sample surface that can inhibit corrosion by decreasing the diffusion of dissolved oxygen and ions to the surface of steel. These results indicate that Ca(OH)₂ is a promising corrosion inhibitor for ferrous pipe materials for carrying seawater in SWTF systems.