Spatio-Temporal Assessment of the Reliability of Corroded Pipeline Considering Time-Dependent Failure Modes

Assessing the reliability of corroded onshore pipelines represents a spatial and temporal challenge. Pipe operators seek to estimate segment degradation and design an effective maintenance plan with imperfect information, where multiple failure modes can occur. This paper proposes a probabilistic framework for assessing segment reliability, incorporating the spatio-temporal variability of corrosion defects. Based on In-Line Inspection (ILI) measurements, critical segments are identified along the pipeline using a preliminary condition-based segmentation with a changepoint algorithm and two simultaneous failure modes, i.e., small leaks and bursts, with an inverse Gaussian process for the temporal degradation. Reliability is assessed by considering dependent failure limit states using a copula approach with Monte Carlo simulations. The proposed methodology is evaluated on a 60 km pipeline section to characterize spatial variability. The robustness and effectiveness of the changepoint approach in characterizing the spatial variability of corrosion defects as well as in identifying and locating critical segments along the pipeline is well demonstrated. The findings show that evaluating the dependence of pipeline failure events using the copula approach yields to a more realistic estimate of pipeline reliability. In addition, it was found that ignoring spatial variability and failure mode interdependence leads to overly pessimistic estimates, consequently leading to premature maintenance.