Corrosion behavior and mechanism of ductile iron with different degrees of deterioration of cement mortar lining in reclaimed water pipelines

Abstract

The deterioration of cement mortar lining (CML) has a significant impact on the corrosion of ductile iron pipes, and further affects the water quality of transported reclaimed water. In this study, the different coverage levels of CML (such as lined (100%), 90% and 50% lining coverage and unlined) were used for simulating different degrees of deterioration of CML. Electrochemical measurements, water quality testing and corrosion product microanalysis were carried out to monitor the corrosion process and investigate the corrosion mechanism. The results showed that the order of maximum corrosion rate under different conditions was: 50% lining coverage (0.159 mm a⁻¹) > unlined (0.110 mm a⁻¹) > 90% lining coverage (0.042 mm a⁻¹) > 100% lining coverage (0.007 mm a⁻¹). The complete lining can provide a higher pH to passivate the ductile iron to achieve perfect protection. When the damage of CML was very small, the self-healing of the lining can restore the protection ability to a great extent. The corrosion of the ductile iron with 50% lining was even more serious than the unlined ductile iron. The negative effect of the silicate dissolved from the lining on the crystal structure, growth and stabilization process of the corrosion products was considered to be the reason for the more acute corrosion of the pipeline with a large area lining spalling.