Time-Dependent Reliability Method and Its Application in Mild Steel Pipelines

This research investigates the analytical time-dependent reliability methods for nonstationary and non-Gaussian processes. Two new methods are proposed: one based on the transformation method and the other on a two-component parallel model. The efficiency and robustness of these newly developed methods are subsequently validated through analytical derivation, analytical examples and Monte Carlo simulation. Further, the improvements achieved by the proposed methods are demonstrated by performing comparative analyses with existing methods, including the Li–Melchers’ solution, PHI2+ method and MPHI2 method. Additionally, to apply the proposed new methods for analysing the structural reliability of the fracture failure of ductile materials with elastic-plastic properties, a simple and effective test method is developed to determine the critical values of fracture parameters solely relying on uniaxial tensile tests. These critical values serve as critical barrier levels in the analysis of time-dependent structural reliability. Moreover, a comprehensive investigation is conducted to examine the influences of strain hardening on the evaluation of critical fracture parameters. By combining the newly developed analytical time-dependent reliability methods with the determined critical fracture parameter obtained from the developed test method, the probability of the corrosion-induced fracture failure of mild steel pipes is assessed. This research emphasises the significance of incorporating nonstationary and non-Gaussian processes into analytical time-dependent reliability assessments for the accurate prediction of failure probability. It contributes to the existing knowledge of analytical time-dependent reliability methods pertaining to nonstationary and non- Gaussian processes, as well as fracture behaviours exhibited by elastic-plastic materials. Moreover, it enhances the application of time-dependent reliability methods for evaluating the structural integrity of ductile materials containing cracks.