Importance sampling-based system reliability analysis of corroding pipelines considering multiple failure modes

The importance sampling (IS) technique is employed to evaluate the time-dependent system reliability of corroding pipeline segments containing multiple active corrosion defects by considering two competing failure modes, small leak and burst. The IS density functions in the standard normal space for incremental probabilities of small leak and burst of the pipe segment over a short time period are established as the weighted averages of the IS density functions for small leak and burst, respectively, at individual corrosion defects. The IS density functions for incremental probabilities of small leak and burst of individual defects are centred at the design points in the corresponding failure domains. Four numerical examples that are representative of the onshore gas transmission pipelines in the US are used to illustrate the application of the proposed methodology. The results demonstrate the excellent accuracy and efficiency of the methodology.