Re-rounding analysis of API X60 pipelines containing an unconstrained dent subjected to internal pressure using finite element method

As a common defect on pipelines, a dent normally re-rounds under internal pressure, which impacts the integrity of a dented pipeline. In this study, a 3D finite element (FE) model of an X60 dented pipeline under internal pressure was established. The stress/strain distributions and displacement variation of the indentation region due to re-rounding were examined. Moreover, the effects of dent depth, diameter-to-thickness ratio, and internal pressure on the dent re-rounding performance were analyzed. The prediction equation of dent geometry parameters due to re-rounding was proposed. The results reveal that the stress/strain distribution in the dented area is strongly impacted by the re-rounding behavior. In addition, re-rounding on the deformed region to decrease the diameter-to-thickness ratio becomes increasingly difficult. The internal pressure may cause a significant change in the dent length during the re-rounding process. The prediction equation can provide a reference for computing the dent geometric dimension after re-rounding.