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The solid particle impurities generated by pipe wall corrosion might deposit at the elbow of hilly pipelines during the production shutdown of oil pipelines. These solid particle impurities will seriously affect the safety of the pipeline operation and the quality of the petroleum products. Thus, it is necessary to study the methods of removing these trapped particles from pipelines. At present, the most common way to remove these solid particle impurities is pigging oil pipelines periodically by utilizing the mechanical pigging method, while the frequent pigging operation will increase the cost and risk of pipeline operation. It is very convenient and economical to remove the accumulated particles out from the pipeline by oil stream, which can be named Hydraulic Pigging Method (HPM). However, the behavior mechanism of particle in flowing oil is still unclear. This motivates the present research on the particles flushed out by the flowing oil. A numerical model governing the trapped particles displacement from the elbow of an inclined oil pipeline is established in the Euler-Lagrangian framework. The simulation is achieved via CFD coupling with DEM. The CFD method is employed to solving the continuous phase flow, while the discrete particle phase is tracked by the DEM. The numerical model is first validated by comparison with results taken from the published literature. From the simulation results, it is observed that the oil stream, carrier phase, can only flush out the solid particles in a certain diameter range under the given operation conditions, and the particles whose diameter beyond that diameter range will cannot be removed out from the pipeline. The influence of the pipe inclined angle, the oil bulk velocity and the particle diameter on the particle migration characteristics is examined in detail. Furthermore, in order to enhance the efficiency of HPM, an Enhanced Hydraulic Pigging Method based on Multi-Physical Field Collaboration (EHPM-MPFC) is also proposed in the present work. The EHPM-MPFC is validated for having high pigging efficiency via the comparison of the migration characteristics of particles during the EHPM-MPFC and HPM process. The present results can provide the guidance to the HPM operation of products pipelines.

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