A dent is a common type of pipeline defect that causes a local stress and strain concentrations, which can threaten the safety and integrity of the pipeline. In actual engineering, unconstrained dents tend to re-round as the internal pressure of the pipeline increases. In this paper, the process of re-rounding of a dented pipeline was investigated by numerical study. A 3D numerical model was established. The strain variation of the re-rounding process was analyzed in detail. The effect of various factors (loading depth, indenter diameter, pipe diameter-thickness ratio, initial internal pressure and material) on the re-rounding coefficient were analyzed. The results show that the elastic recovery occurs in the re-rounding process. And no secondary plastic damage occurred in the dented pipeline. The coefficient of re-rounding increases with the increase of the dent depth and initial internal pressure; while the diameter-thickness ratio and indenter diameter display a negative effect. Based on the finite element results, an engineering calculation equation of the re-rounding coefficient was fitted by the nonlinear regression method.

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