Elucidating the Electrochemical Corrosion of a Water Pump Impeller in an Industrial Cooling System with Zero Liquid Discharge

The electrochemical corrosion of a single-suction centrifugal water pump impeller made of gray cast iron operating at 85 °C was investigated in two industrial water media, i.e., groundwater extracted from a borehole and treated wastewater. Open circuit potential (OCP) measurement plus potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques elucidated the electrochemical corrosion performance and inductively coupled plasma-optical emission spectroscopy (ICP-OES) characterized the water samples. The retired and brand-new impellers were studied using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and visual and metallographic examinations. Impeller trailing edges were vulnerable to corrosion damage due to increased total fluid pressure, velocity, and temperature. The groundwater was more contaminated with Ca, Mg, Na, Si, and S elements and possessed higher conductivity, pH, and suspended solids than the treated wastewater. The impeller was more susceptible to graphitic corrosion in the groundwater due to emerging microgalvanic cells. A kinetic control electrochemical mechanism was elucidated as the corrosion rate-controlling step in the wastewater. A mixed kinetic and diffusion control mechanism was predominant in the groundwater because a short Warburg impedance element emerged. This study showcased the significance of integrated industrial water management and treatment strategies to protect pumps’ integrity and uptime in critical industrial units implementing a zero-liquid discharge program.