On Probabilistic Fracture Assessment of Defective Pipeline Based on Target Failure Probabilities

Abstract

This paper investigates the priorities as well as the safety factors of each assessment variable for a defective pipeline based on a partial safety factor concept considering the target failure probabilities during operating period of components of interest. For this, firstly wall-thinned pipeline under internal pressure is considered, which is important in fitness-for-service assessment of corroded pipeline. For the analysis, scatters in the applied pressure, mechanical properties and geometries of wall-thinned pipeline are considered using normal and log-normal distributions. In addition, partial safety factors of a circumferential through-wall cracked pipeline subjected to global bending moment are also evaluated based on the elastic-plastic fracture mechanics. In this case, scatters in the applied bending moment, mechanical and fracture properties are considered based on normal and log-normal distributions. More importantly, two different deterministic integrity assessment methods are applied to wall-thinned pipeline and two different estimation methods of elastic-plastic J-integral are applied to circumferential through-wall cracked pipeline to evaluate the partial safety factors. Resulting values of partial safety factors are calculated using both the advanced first-order second moment method (AFOSM) and the second-order reliability method (SORM). Moreover, the effects of statistical distributions and variations of standard deviations of assessment variables on the partial safety factors are also demonstrated.