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.
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机译：基础设施的安全是任何土木工程设计的主要目标。在英国，大部分地下管线被归类为结构缺陷和功能已过时。由于能见度低，经常会忽略地下管线的状况评估和修复，直到发生灾难性故障为止。提供可接受的服务水平并克服实际困难，相关行业必须计划在预算限制下如何操作，维护和更新（维修或更换）管道系统。这项研究的重点是估计管道的可靠性，并确定何时以及如何需要采取干预措施，以最佳的成本在整个使用寿命期间防止柔性地下金属管道在外部使用载荷和管道材料腐蚀下遭受意外损坏。由于腐蚀引起的过度挠曲，屈曲，壁推力和弯曲，随时间变化的可靠性得到了评估。首先，已经使用Hassofer-Lind和Rackwitz-Fiessler（HL-RF）算法以及Monte Carlo Simulation（MCS）来评估可靠性。然后，开发了子集仿真（SS）方法，以增强其适用性，特别是对于小故障概率预测。为了评估管道可靠性分析的准确性，本文引入了精度预测方法，接收器工作特性曲线。然后，研究已扩展到确定维护的干预年，并通过使用遗传算法（GA）优化故障风险和生命周期成本（包括减少二氧化碳排放的成本）来确定最合适的更新解决方案。优化技术SS也已开发用于地下管线的风险成本优化。给出了一些示例，以验证所提出的方法，以通过基于故障严重性和系统可靠性确定维护优先级来防止管道意外故障。所提出的可靠性估计和风险成本优化方法可用于形成维护策略，并避免在使用寿命期间发生管网意外故障。
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