Automated Monitoring of Metal Corrosion for Water Delivery Infrastructure

Abstract

The real-time corrosion rate of mild steel in drinking water and the properties of that water are measured and recorded in time using a newly build computed automated system. A non-destructive electrochemical method is used to find the corrosion rate (CR) of mild steel coupons in time and these are compared to the average corrosion rate of a coupon determined by weight change. In the lab, at room temperature, when the pH is 7, typical corrosion rates of mild steel in synthetic drinking water (1000-2000 ppm Na2SO4 aqueous solution) in aerobic still water and aerobic water with bubbling air (100 sccm) are 64.8 µm yr-1 and 241.5 µm yr-1 determined electrochemically, and 27.9 microns per year and 81.5 microns per year determined gravimetrically. In comparison, the corrosion rates of mild steel in still anaerobic water with bubbling inert gas (100 sccm) are 18.9 µm yr-1 and 29.8 µm yr-1 determined electrochemically, and 27.9 µm yr-1 determined gravimetrically anaerobic water with bubbling inert gas (100 sccm).The computer automates and data logs two properties: 1) the corrosion rate of pipe metal in drinking water and 2) the water quality by using 6 in-line water sensors for flow, pressure, conductivity, temperature, dissolved oxygen, and pH. The corrosion rate of the metal in water is done by using a LabView program to control a power source to find the corrosion current which is converted to a corrosion rate of the metal. These measurements are repeated several times a day over several months. Using the automated system, the corrosion rate of mild steel in real water is typically 57.7 µm yr-1 after 11 days of immersed in drinking water and when the water properties are 200 ccm flow, 640 to 670 µS cm-1 conductivity, 26 to 27°C temperature, 10 ppm dissolved oxygen, and 7.5 to 7.7 pH. Knowing the rate of pipe corrosion as a function of water quality in time gives a rational guide for predicting pipe failure. The sponsor of this work, Tucson Water, plans to install corrosion and water monitoring stations at 10 nodes in Tucson’s water grid to guide the scheduled maintenance of water delivery pipes to minimize the interruption of water service and the loss of drinking water