In this study the frictional force between a pig and the pipe wall is studied by investigating the properties of the sealing disk of the pig. This is done by subjecting the sealing disk to a wall normal force and a frictional force in a lab facility. The experimental results are compared with values obtained by Finite Element Analysis and by a simplified mechanistic model. The obtained results are important for estimating the steady state pig velocity in a pipeline, and thus for the arrival time of the pig. In addition, the results can be used to improve 1D transient pig modelling in a pipeline, where the frictional force is an input parameter.
The use of a pig (Pipeline Inspection Gauge) is often part of the operation or maintenance of pipelines in the oil and gas industry: a cylindrical or sometimes spherical object is launched into the pipeline and runs through the pipeline while being propelled by the production fluids [6]. Such pipelines can transport oil/water, dry gas, or multiphases (such as gas/condensate/water). While a conventional pig seals the pipeline completely and will travel with the mixture velocity, a by-pass pig allows part of the production fluids to by-pass the pig, resulting in a lower pig velocity [1]. Figure 1a shows an example of a by-pass pig. The reduction in pig velocity has proven to be beneficial for both inspection and cleaning purposes [3,8,9,10,13]. As the velocity of the by-pass pig is not dictated by the mixture velocity anymore, detailed understanding of the force balance on the pig is needed in order to predict its velocity. In steady state this implies that the driving pressure force of the production fluids balances with the frictional force of the pig with the pipe wall, see Figure 1b.
