Kinematic analysis of the influence of velocity and elbow angle on the bending performance of a flexible pig based on fluid–structure interaction

As global energy demand rises, the safe and efficient operation of oil and gas pipelines becomes a key focus. Pipeline pigs, essential for inspecting and cleaning pipelines, are vital to maintaining their integrity. While rigid pigs are commonly used, they often experience jamming in medium and small diameter pipes. Flexible pigs, which are more adaptable to complex geometries, are underexplored. To study the kinematics of flexible pigs in bending pipelines, a dynamic motion model was developed and validated through tensile experiments. Using the Coupled Eulerian-Lagrangian method, simulations were performed under various elbow angles and fluid velocities. Results show that at a flow velocity of 1 m/s, the flexible pig experiences a surge in velocity when negotiating bends, with the peak surge decreasing as the elbow angle increases. At higher velocities, the surge disappears, and the time to exit the pipeline shortens. Higher flow velocities also reduce frictional resistance. Friction remains stable in straight sections but fluctuates in bends before stabilizing. This study provides guidance for optimizing operational parameters in pigging and informs safety monitoring strategies for pipeline elbows, enhancing the understanding of fluid–structure interaction in pipeline transport systems.