A Comprehensive Model for Cup Pig Incorporating Deposits Rheology and Pig Deformation

Abstract

Over the past two decades, mechanical pipeline pigging has been the most common remediation technique to reduce the hazards of wax deposition, but describing pressure changes during the pigging process remains a challenge. In this work, a mathematical model was developed to predict the wax breaking force and the wax removal efficiency of the cup pigs at different pigging velocities. Based on the rheological properties of the wax deposits, static yield stress and dynamic yield stress were used to characterize the strength of the wax layer in different zones. The model prediction results are in good agreement with the results of indoor pigging experiments. In addition, the effect of pigging velocity on the wax breaking force and wax removal efficiency was experimentally investigated. It was shown that the wax breaking force at high velocities was 3–4 times higher than that at low velocities, while the wax removal efficiency decreases as the pigging velocity increases. This experimental phenomenon can be well interpreted by the model prediction results.