What is it about?

The reliability analysis of an API 5L X60 steel-made Algerian natural gas pipeline, in service for thirty years, and exposed to active corrosion attack, is presented. The sensitivity analysis of the basic random variables within the nonlinear limit state function was carried out to bring out the relative contribution of each variable affecting the remaining life of corroded pipelines. The reliability analysis is carried out by using Breitung's formula, based on the second-order reliability method (SORM). The reliability assessment of the corroded pipeline is based on the usage of the notched failure assessment diagram (NFAD), different codes for the calculation of the failure pressure, and the numerical results using the finite element analyses (FEA) software ANSYS.

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Why is it important?

The proposed probabilistic methodology for the prediction of the reliability degradation of a pipeline brings out the level of conservatism of each assessment technique and applied engineering mechanical codes. It further identifies the impact of the corrosion defect on the remaining strength and the probability of failure of the corroded steel pipeline. Therefore, the presented comprehensive probabilistic approach for estimation of the remaining life and reliability assessment of corroded pipelines provides enhanced integrity management of gas and oil pipelines exposed to severe corrosion during exploitation.

Perspectives

The enhanced corrosion management, according to the comprehensive probabilistic approach presented in this paper, is mainly provided by the proposed calculation of the predicted reliability index decrease for the particular pipeline sections with different corrosion attack rates rather than for the pipeline as an integral structure. Furthermore, the applied sensitivity analysis provides the tool for the detection of potentially most influential random variables on the reliability of a corroded pipeline. Therefore, corrosion asset managers and oil and gas pipeline operators are enabled to predict and prevent the catastrophic failures of oil and gas pipelines due to corrosion.

Professor Milos B. Djukic
University of Belgrade, Faculty of Mechanical Engineering

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This page is a summary of: A probabilistic approach to estimate the remaining life and reliability of corroded pipelines, Journal of Natural Gas Science and Engineering, December 2021, Elsevier, DOI: 10.1016/j.jngse.2021.104387.
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