Reliability analysis of corroded pipelines: Novel adaptive conjugate first order reliability method

The burst pressure of oil and gas pipelines with corrosion defects is the major failure mode of these structures. Structural reliability analysis is normally conducted to evaluate the robust design-based safe levels of corroded pipelines using the probabilistic failure model. In the current work, the abilities for robustness and efficiency of first order reliability method (FORM) formulas are investigated for corroded mid-strength grade steel pipes. These methods are mainly enhance FORM algorithms-based steepest descent search direction as directional stability transformation method (DSTM), finite-step length (FSL), finite-step adaptive length (FAL) and conjugate steepest descent search direction as conjugate HL-RF (CHL-RF), conjugate finite-step length (CFSL) and a proposed adaptive conjugate finite step length (ACFSL). In proposed ACFSL algorithm, the FORM formula is adaptively enhanced using the dynamical conjugate search direction to adapt the new iterations for the burst pressure failure mode which is computed using a probabilistic combined by plastic flow theory-based average shear stress yield criterion and remaining stress factor-based semi-elliptical defects. Comparative results indicate that three algorithms e.g. FAL, CFSL and ACFSL are the perfect convergence performances for reliability analysis of corroded pipeline compared to other formulas, while ACFSL provides the superior performances in term of efficiency and robustness. The safety level of these structures is highly sensitive to the corrosion defect depths and operating pressure.