Bypass Pigging of Subsea Pipelines Suffering Wax Deposition

Abstract

Which criteria to pay attention to is important when finding the optimal pigging frequency. This thesis illustrates the forces acting on a bypass pig in operation. Expressions for both the frictional force and wax removal force have been presented. Results presented in this thesis show that the frictional forces are much higher than the forces for wax removal. The most important factor for the contact forces for a cleaning pig seems to be due to the oversize of the discs. However, it is difficult to obtain accurate values for the friction force without experimental data. The insulating effect of wax deposition on the overall heat transfer has been confirmed by analytical calculation. Results do also show that the simulation software Hysys do not account for wax deposition when estimation the U-value. Pressure drop calculations for a pipe with wax deposition have been done. Results show that the roughness of wax has a large influence on the pressure drop in a pipeline. Ageing of wax leads to higher wax removal forces and may decrease the removal efficiency for a cleaning pig. Pigging operations should happen at a given frequency to prevent wax from hardening. It would be beneficial to have more knowledge about wall adhesion and ageing for the given composition when estimation the wax removal forces