Characterization of the pressure loss coefficient using a building block approach with application to by-pass pigs

A building block strategy for modelling the pressure loss coefficient of flow through a complex geometry is presented. The approach relies on decomposing a complex flow geometry into geometrical building blocks of which the pressure loss coefficients are characterized individually. The different contributions are subsequently combined to describe the pressure loss of the geometry as a whole. This approach is applied and tested to an industrially relevant application: a by-pass pig (Pipeline Inspection Gauge). This is a cylindrical device that travels inside a pipeline and is commonly used in the oil and gas industry for pipeline maintenance. An important factor in determining the ultimate velocity of the device is the pressure drop over the by-pass pig, which is characterized by a pressure loss coefficient due to the by-passing fluids. In this study the pressure loss coefficient of three frequently used by-pass pig geometries in a single phase pipeline is investigated with Computational Fluid Dynamics (CFD). The CFD results are used to validate the simple 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. It is shown that the pressure loss models can capture the CFD results for each of the three pig geometries. The pressure loss models can be combined with pig/pipe-wall friction models to predict the velocity of a by-pass pig in a single phase pipeline, which is important for a safe and effective pigging operation. The applied building block approach may also be suitable to characterize pressure loss coefficients of complex geometries in general.