Forecasting the residual life of pipelines taking into account the analysis of its defective area segments

Abstract

This article focuses on the development of a comprehensive method for assessing the residual life of a corroded pipeline, based on the analysis of its segments in the defective section. Approaches defined by the international standards ASME B31G and API 570, as well as the probabilistic-physical failure model — the diffusion-monotonic DM-distribution — have been used as components of the method to analyze the pipeline’s suitability for continued operation. The parameters of this failure model include the coefficient of variation of the degradation process, which reflects the dispersion of random variable values, and the mathematical expectation of the operating time to the limiting state. The key parameter of this model is the residual thickness of the defective pipe wall, particularly its threshold value. The initial parameters for the residual life estimation method are derived from measured corrosion depths in defective pipeline segments, to which classical statistical methods are subsequently applied. Two methods have been applied to predict the residual life of the defective pipeline, both based on a probabilistic-physical failure model in accordance with the DSTU 8646 standard: the cumulative DM-distribution function for operating time to the limiting state and the gamma-percentile method for residual life estimation. In order to ensure a more optimal and accurate comparison of these methods, an additional formula has been derived, since the applied approaches utilize different forms of probabilistic representation of results, which requires consistent interpretation. The developed comprehensive approach enables prediction of the residual life of the defective pipeline for specified probabilities of failure-free operation or failure, as well as for any values of operating time until the limit state is reached.