A novel methodology for reliability assessment of corroded natural gas pipelines considering two-level correlation

Abstract

One of the main causes for the failure of natural gas pipeline is corrosion, which can induce severe consequences due to the inherent combustibility of natural gas. Therefore, it is of great significance to evaluate precisely the reliability of corroded natural gas pipelines. With regard to the confusion and apparent insufficient consideration of correlations surrounding current reliability assessment methods for corroded natural gas pipelines, this paper divides these correlations into two levels: “random variables correlation” (Level 1) and “spatial correlation” (Level 2), and then proposes a novel methodology for pipeline reliability assessment by examining the effects of a separate “two-level” correlation. Depending on the data provide by in-line inspection, the new methodology can calculate the probabilities of small leak and burst failure of a corroded pipeline with multiple interacting defects more accurately and more realistically. This paper uses Gaussian Copula approach to characterize the dependence among the random variables. The spatial correlation among defects is characterized by using an efficient probabilistic method. Finally, the influence of different kinds of correlation on reliability is studied by sensitivity analysis. The calculation results have indicated that the two-level correlation has great impact on the failure probability. The method in consideration of the two-level correlation is more objective and truly reflects the dynamic reliability changes of the corroded nature gas pipeline.