Reliability Analysis of Pipelines With Local Corrosion Defects Under External Pressure

Abstract

This paper aims at assessing the reliability of pipelines with local corrosion defects subjected to external pressure. Several collapse strength models are calibrated and then used to formulate the reliability problem of corroded pipelines. Model uncertainty factors are derived for the various collapse strength models based on available experimental results to better predict the effect of local corrosion defects on the reduction of the collapse strength of pipelines. The model uncertainty factor is defined as function of the depth of the local corrosion defect and calibrates the overconservative predictions of collapse strength models that deal with the effect of corrosion defects by considering a uniform reduction of the pipe thickness. The collapse strength models together with the corresponding model uncertainty factors are then used to formulate the reliability problem of pipelines with local corrosion defects subjected to external pressure. Parametric and sensitivity analyses are performed for different levels of corrosion damages to identify the influence of the various parameters on the collapse probability of corroded pipelines under external pressure. Finally, an approach is suggested to calibrate a design code formulation that is conservative when the minimum pipe thickness is used to represent a local corrosion defect. The approach consists of identifying an equivalent depth of the corrosion defect, corresponding to an intermediate thickness of the corroded pipeline larger than the minimum thickness, that adjusts the design code to match the safety levels of the collapse strength model calibrated to the experimental results.