Investigations on the re-rounding performance of dented-pipelines at the service and shutdown stages

Dental defect is one of the most typical mechanical damage to pipelines. Consequently, the investigation of dented-pipeline performance at the service and shut-down phases is therefore critical to the integrity of the pipelines. In practice, dent defects tend to re-round due to the influence of internal pressure. Therefore, in this paper, the influence of the internal pressure on the dent re-rounding is investigated. Three-dimensional finite element (FE) model is established to simulate the indentation and re-rounding process of the dented pipeline. The numerical model was firstly validated against the experimental test data founded in the literature. Thereafter, a comprehensive parametric study on the key geometrical and operational parameters was investigated. The effects of pipe wall thickness, indenter geometry, internal pressure and dent depth on the re-rounding behavior of the dented pipelines in the service and shutdown stages were studied. The FE results demonstrated that a thicker wall thickness of the pipeline or a larger indenter tends to cause less re-rounding of the dented pipeline. Besides, the re-rounding behavior of the dented pipeline is strongly affected by the amplitude of the internal pressure. The parametric study on the magnitude of the re-rounding coefficients of the running dented pipeline (at service stage) and during the maintenance period (at shutdown stage) was in the range of 1.0-1.9 and 1.0-1.4, respectively. Thereafter, a nonlinear regression analysis was carried out to establish a new parametric equation of the dent re-rounding coefficients.