Reliability based integrity assessment of steel pipelines under corrosion

Currently, the assessment of mechanical integrity of pipelines damaged by corrosion is performed through deterministic procedures and, in special cases, by using random variables. Rigorously, the calculations require the use of probabilistic methods because they provide the proper framework to include explicitly the uncertainties involved. Some recent treatments consider the corrosion events to be independent, which may lead to errors in estimating the failure probability of the pipeline. In this paper, pipeline integrity is assessed in terms of failure probability and recent models are utilised that estimate the resistance to failure using improved representations of the corrosion defect. Also, a simplified way to consider the space correlation between different segments of a corroding steel pipeline is introduced and the procedure is applied to the specific case where the defect geometry is modelled to be of parabolic shape. The geometrical and mechanical pipeline properties are considered to be random variables; their mean values are taken from experimental results and the interdependence between them is characterised using the model's correlation matrix.