Numerical simulation of the effects of vaporization on the motion of PIG during pigging process

Abstract

ABSTRACTDuring the course of pigging after water pressure test, when pressure drops to vapor pressure, localized vaporization always occurs at pipeline terminations or at physical high points in the pipeline. PIG is most effective when it runs at a near constant speed. The appearance of a vapor region may dramatically affect the PIG motion and ultimately contribute to impulse pressures at the end of pigging process. Large pressures may cause the PIG to run at extremely high speed, which is a highly dangerous situation. Further, the pigging efficiency can be compromised. The proposed model for estimating the pig dynamics takes into account vaporization. The basic equations governing the conservation of mass and momentum for the gas and liquid fluids were solved together with the momentum equations for the pig by applying the method of characteristics. Moreover, the new pigging model takes advantage of discrete‐vapor‐cavity model to predict the vaporization and location of vapor region. Numerical simulation results for gas–liquid pipeline pigging process are in good agreement with field data to validate the model developed. The model also contains the capability of PIG tracking and the prediction of impulse pressures, which can help the operator to control the PIG speed before it reaches the end of the pipeline. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.