Corrosion tests of metal pipes in drinking water systems using electrochemical methods

Metals constitute some of the major materials for making water delivery pipelines. However, the service life of metallic pipelines is affected by corrosion. Mild Steel (MS), Galvanized Steel (GS) and Copper were selected based on their strength and corrosion resistance. They were subjected to Potentiodynamic Polarization (PP) and Electrochemical Impedance Spectroscopy (EIS) investigations using water as the electrolyte from selected sampling points (A, B, C, D and E) on the University of Lagos, Akoka water distribution network. Corrosion current density (I-corr) and Impedance (Z) were measured in A/mm(2) and ohms respectively. The morphology of the corroded samples was examined using Scanning Electron Microscope (SEM). The result obtained from PP investigation showed I-corr in the low range for the three metals considered. Similarly, for EIS, Z values measured were high for MS, GS and Cu. Both methods indicated that Cu was the most corrosion resistant material, closely followed by GS and lastly MS. The SEM images clearly showed that among the three specimens, the morphology of Cu remained unaffected by the environment. On the other hand, MS and GS showed evidences of corrosion with pits. The large amounts of iron established in the studied water distribution system, confirmed corrosion of water pipes.