Corrosion characteristics of unlined cast iron pipe used in water supply system and impact of corrosion on water quality

A three-electrode cell has been developed to investigate corrosion characteristics of cast iron pipe and impact of the corrosion on water quality. The cast iron pipe corrosion parameters were measured by electrochemical workstation with microbe as controlled variable. The water quality was analysed in the corrosion system meanwhile. The results indicated that the average free-corrosion potential of the cast iron pipe was -0.515 V in non-sterile group during 66 days and the free-corrosion current was 7.61×10^-4 mA/cm², while the parameters for the reference group were -0.471 V and 5.26×10^-4 mA/cm², respectively. The water in non-sterile group deteriorated quickly with total iron exceeding 0.3 mg/L 3 days later. And chroma and turbidity of the water were 70 and 115 NTU. Corrosion rate of reference group was lower compared to non-sterile group, while the water became "red water" finally. Cast iron pipelines are prone to comprehensive corrosion characterized by electrochemical corrosion when there is little anti-corrosive coating on internal wall, leading to water quality deterioration.