MSc project: Frictional behavior of pig's in motion

MSc student: Arie den Heijer

Project supervisors: Ir. M. Hendrix, Dr. ir. W.-P. Breugem, Prof. dr. ir. R.A.W.M. Henkes

Project start:  March 2015

Project description:

A pipeline inspection gauge (pig) is a plug being used to clean and inspect pipelines. During steady-state motion three forces work on a pig: a driving force caused by a pressure difference over the pig, a gravity force caused by the mass of the pig, and a resistance force caused by the friction of the pig with the pipe wall. To calculate the magnitude of the resistance force currently empirical models are being used. These models have a small amount of degrees of freedom and therefore factors of which is known that they influence the friction between the pipeline wall and pig are currently being neglected. The goal of this project is: to get a better understanding of the physical phenomena that occur on the wall-pig interface, to model these phenomena and finally validate the model with experiments.

A pig has multiple polyurethane rubber rings which form a seal in the pipeline. The oversize of the rubber rings and the differential pressure over the rubber rings create a contact force normal on the pipeline wall surface. When the pig is in motion the normal contact force creates a tangential friction force parallel to the pipeline. This friction force is typically expressed by the normal force on the pipeline wall times a friction coefficient. Pig’s sometimes run through hundreds of kilometers of corroded pipelines covered with wax deposits. Typical phenomena that will occur are: lubrication trough the creation of a liquid film, liquid buildup in front of the pig and wear of the rubber rings. These three phenomena will be important in determining the friction coefficient of a pig.

To model the magnitude of the normal contact force a solid mechanics model of a rubber ring will be made with the help of finite elements. If the pig is moving a fluid film will form between the rubber disk and pipeline wall. With lubrication theory a velocity dependent friction coefficient can be predicted. Finally the wear of the rubber rings and accumulation of wax in front of the pig have to be taken into account for accurate pig motion predictions.

At Shell Technology Center Amsterdam (STCA) experiments will be done to validate the model. Overall these insights should help in the PhD project ‘Modelling and experiments for by-pass pigging with speed control’.