Pipelines used for product transportation require regular cleaning. A new method has emerged using slurry for the cleaning process, during which the flow pattern and pressure drop in the slurry are essential. The flow of slurry containing polypropylene particles was investigated using a laboratory-scale, closed-circuit pipeline facility. While the slurry was pumped, the pressure drop was measured, and the flow pattern was observed regarding particle type, slurry particle concentration, and slurry flow velocity. The results showed that after the critical flow velocity, the particles mixed uniformly with the water in the pipe, increasing the pressure drop in conjunction with the flow velocity. Although a higher particle mass fraction and small particle size reduced the critical flow velocity, the mass fraction and particle size had no significant influence on the pressure drop. This research establishes a solid foundation for the practical application of this cleaning method.