Determination of Optimal Rehabilitation Time for Types of Cast Iron Pipes of Small Pipe Diameter on Water Distribution System in Metropolitan

The drinking water network serving are up to 100 years old in Korea. Therefore, pipelines suffer various degrees of deterioration due to aggressive environments. Water supply system is one of the major urban infrastructures based on activities of mankind. Its most expensive facility is the water distribution network which is an important component in both quantitative and qualitative sides. Therefore, its effective maintenance and operation (M&O) has essential effect on sustaining human life. Moreover, factors of pipe deterioration and models to predict failure and optimal rehabilitation time are needed to support network management strategies. This study has performed to set up the determination of optimal rehabilitation time for Cast Iron Pipes (CIP) with diameter less than 300 mm. And the determination model for optimal rehabilitation time was developed by using cost analysis and deterioration evaluation on rehabilitation alternatives. In the result from the application of the field, the renovation time was faster about 10 years than the replacement time. Especially, as the difference between rehabilitation and replacement time on E-CIP was about from 3 to 5 years, and it was thought that the replacement was effective on E-CIP. To model sensitivity analysis, the discount rate of coefficient was fixed at 0.08, and the values of initial year break rate(N(t₀)) and growth rate coefficient(A) were adjusted in values of 0.0009, 0.0018, 0.0027, and 0.05, 0.10, 0.15 respectively. When the values of N(t₀) and A was increased, the results from the time of rehabilitation and replacement was faster. It was thought that N(t₀), 0.018 was reliable values on the applied pipeline through the result of the study. In case of A, the values of A above 0.1 was thought to be proper.