Reliability estimation and risk-cost optimisation of underground pipelines

The safety of infrastructure facilities is the primary objective of any civil engineering design. A large section of underground pipelines in the UK are classified as structurally deficient and functionally obsolete. Due to low visibility, condition assessment and rehabilitation of underground pipelines are frequently neglected until a catastrophic failure occurs. Providing an acceptable level of service and overcoming the practical difficulties, the concerned industry has to plan how to operate, maintain and renew (repair or replace) the pipeline systems under the budget constraints. This research is focused on estimating pipe reliability and deciding when and how interventions are needed to prevent unexpected failures of flexible underground metal pipelines subject to externally applied loadings and pipe material corrosion during the whole service life at the optimal cost. The time-dependent reliability due to corrosion induced excessive deflection, buckling, wall thrust and bending has been estimated. First, Hassofer-Lind and Rackwitz-Fiessler (HL-RF) algorithm and Monte Carlo Simulation (MCS) have been used to estimate the reliability. Then Subset Simulation (SS) method is developed to enhance the applicability, especially for small failure probability prediction. Accuracy prediction method, Receiver Operating Characteristic (ROC) curve has been introduced in this research to assess the accuracy of pipeline reliability analysis. Then the study has been extended to determine the intervention year for maintenance and identify the most appropriate renewal solution by optimising the risk of failure and life cycle cost, including carbon dioxide emissions mitigation cost, using Genetic Algorithm (GA). Optimisation technique, SS has also been developed for risk-cost optimisation of underground pipelines. Examples are presented to validate the proposed methods with a view to prevent unexpected failure of pipes by prioritising maintenance based on failure severity and system reliability. The proposed reliability estimation and risk-cost optimisation approach can be utilised to form a maintenance strategy and to avoid unexpected failure of pipeline networks during service life