Subset simulation based approach for space-time-dependent system reliability analysis of corroding pipelines

This paper proposes a subset simulation (SS) based approach for space and time-dependent reliability analysis of corroding pipelines. It is assumed that the pipeline can fail either due to leakage and/or burst. We propose two distinct approaches for tackling the problem. In the first approach, we treat the problem as a time-variant system reliability problem. The problem is formulated as a series system where failure at one of the defect locations will result in failure of the pipeline. This approach is particularly suitable when there are only a limited number of corrosion defects. In the second approach, the reliability analysis problem is treated as a 'space-time variant' reliability analysis problem. This approach is particularly suitable when exact knowledge about the number of defects is not available. In both the approaches, the time-dependent probability of failure is represented in an auto-regressive form such that the probability of failure at a given time can be computed based on the probability of failure at the previous time and an incremental failure probability. A simple composite limit-state function is proposed for computing the incremental failure probability. SS is used for computing the initial and incremental failure probabilities. To illustrate performance of the proposed approach, four pipeline problems representing different scenarios are considered. For all cases, the proposed approach is found to yield highly accurate results.