A theoretical model for predicting the wax breaking force during pipeline pigging

Pipeline pigging is a major conventional wax remediation technique for waxy crude oil transportation. Predicting the wax breaking force, a decisive parameter for pigging arrangements, however still remains an open question, primarily due to the ambiguities in wax removal physics as well as a lack of methods. To address this issue, here we propose a new theoretical wax breaking model to explain the wax removal mechanism and predict the wax breaking force, allowing the no empirical parameters or correction factors. It is met by introducing orthogonal cutting in wax removal explanation and employing slip-line field theory in wax breaking force calculation. Scraping disk deformation is incorporated in this model. An indirect trial method is adopted for the wax-disk frictional angle determination. To check its correctness, we conducted verification experiments with 29-mm-ID and 50-mm-ID pipes. Good agreement between the predicted and measured wax breaking forces has been observed with the maximum and average relative deviations being 21.98% and 8.85% respectively. Moreover, case study suggests this model can potentially enable applications in pig design. Recommendations on pig geometry are accordingly given in detail. On the whole, calculating the wax breaking force, this presented model benefits in optimizing the pig design. In a broader perspective, it further helps to avoid pig stall.