Experiments and modelling for by-pass pigging of pipelines

(Pipeline Inspection Gauge), which is a cylindrical device that just fits the pipe and propagates through the pipe along with the transport of fluids. While a conventional pig completely seals the pipeline and travels with the same velocity as the production fluids, a by-pass pig has an opening which allows the fluids to partially by-pass the pig. The purpose of the present study is to get a better understanding of the physics of the pigging of a pipeline with multiphase flow transport. The focus is on pigs with by-pass. An important factor in determining the ultimate travel velocity of a by-pass pig is the pressure drop over the by-pass pig, which is characterized by a pressure loss coefficient. We investigate the pressure loss coefficient of three frequently used by-pass pig geometries in a single phase pipeline with Computational Fluid Dynamics (CFD). We present a building block approach for systematic modelling of the pressure loss through the by-pass pigs, which takes the geometry and size of the by-pass opening into account. The CFD results are used to validate the simple building block approach for systematic modelling of the pressure loss through a by-pass pig. It is shown that the models for the pressure loss closely resemble the CFD results for each of the three pig geometries.