A Methodology to estimate the remaining service life time of grey cast iron water distribution mains by analyzing the corrosion damage

Abstract

The water distribution main in the Colombo south area itself experiences around about 3000 failures per year and these causes emergency situations where in some cases it causes disruptions in water supply and require emergency repairs at very short notice. One of the major causes to this type of failures is the corrosion of the pipes. About 95% of the total length of the installed water main, the pipe material is grey cast iron. Here the corrosion of the external surface is assumed to be negligible as the outer surface is coated. Therefore only the corrosion of the inner surface of the pipes is considered and the readings related to the inner surface was obtained for further analysis purpose. Due to the internal corrosion of the cast iron water distribution main the thickness of the pipe will reduce gradually over time. When the thickness reduced with time, the bearing capacity (Ability to withstand water pressure) of pipes will reduce eventually and as a result of this there is a greater tendency of pipes to burst. The wastage of water is another un-addressable problem to the peoples of country especially as a utility service at the current socio-economic conditions. In this report an equation was developed to calculate the corrosion penetration rate. Several assumptions were made to apply this equation. Therefore to check the reliability of this equation it was analyzed by statistically. To predict the bursting thickness of the pipes use code of practice AWWA C101-77. According to the equation a utility service like the National Water Supply and Drainage Board can take proactive decision that would benefit financially as well as in an environmentally viable way. Another important thing is from these findings, this can be used as a tool to the future development of distribution system.