Time-dependent reliability analysis of buried water distribution network: Combined finite-element and probabilistic approach

Corrosion deterioration is the predominant factor for a large number of cast iron (CI) water main breaks. The reliability of CI pipelines decreases overtime as corrosion growth on pipe walls significantly reduces the strength of pipeline materials. To predict the reliability of water pipelines accurately, this study used a finite-element analysis (FEA) approach to determine the maximum pipeline stress at various stages of the pipeline's life. A series of FEAs was performed to consider uncertainties in parameters associated with stress analysis. The circumferential stress was found to be the most critical stress for pipelines. Time-variant circumferential stress was obtained by accounting for the time-dependent corrosion pit growth on the pipeline wall. The time-variant failure probability of pipelines was determined by comparing the circumferential stress and the tensile failure strength of the pipeline at the burst limit state. The FEA model developed in this study was validated with the results obtained from previous studies. Monte Carlo simulation was performed to generate the fragility curves in a probabilistic manner. This study also compared the fragility curves obtained utilizing FEA and conventional equations (elastic ring theory and the Spangler formula). The results showed that analytical equations are too conservative and provide a higher failure probability of pipeline. A sensitivity analysis was performed to identify the relative importance of parameters contributing to the pipeline's performance. Additionally, the reliability of the water distribution network (WDN) was calculated based on the minimum cut set (MCS) and graph decomposition methods. The results showed that the two methods provide similar outcomes, however, MCS provides a greater safety margin. The proposed approach was illustrated for an example WDN.