Numerical simulation of contact force on bi-directional pig in gas pipeline: At the early stage of pigging

Periodic pigging of oil and gas pipelines for dewatering, cleaning and inspecting is a standard industry procedure. Predicting the motion of a pig to estimate its velocity, position and required driving pressure is essential before pigging. To enhance these predictions, the frictional force between pig and pipeline is a key determinant and insufficient understanding of the frictional force characteristics leads to significant inaccuracies. As the frictional force acting parallel to the pipeline wall plane is a function of contact force in the radial direction, a 2D axisymmetric nonlinear finite element model was proposed to predict the contact force experienced by bi-directional pig by using ANSYS. The impacts of four parameters (including interference, thickness, chamfer dimension and clamping rate of the sealing discs) on the contact force and the deflection angle of the sealing disc are studied at different differential pressures over the pig. Results obtained in this study shows that the thickness of the sealing disc has the greatest impact on contact force of the bi-directional pig, followed by the chamfer dimension, then the clamping rate and finally the interference. A linear relationship between the contact force and the differential pressure can also be observed from the results. Research findings on the characteristic of contact force and deflection angle of sealing disc may provide useful information for the formulation of theoretical or mathematical models to predict the frictional force on the pig, and pigging risks may be efficiently reduced by establish mitigating strategies on the basis of prediction.