Experimental research on the contact force of the bi-directional pig in oil and gas pipeline

The migration process of the pig in oil and gas pipeline is a complex dynamic problem. During the pigging operation, the variation of friction force caused by the nonlinear contact between the sealing disc and the pipe wall is the key factor affecting the dynamic characteristics of the pig motion. At present, the existed pigging models for predicting pigging behavior regard friction as an invariant constant. Experimental research indicates that the friction force of the pig varies with the contact force and the lubrication conditions. Therefore, the assumption that the friction force is constant cannot reflect the friction dynamic characteristics of the pig during pigging, and will also affect the accuracy of the pigging model. Exploring the variation of friction force of pig under different conditions is the basis of establishing the transient dynamic model of a pig. As a result, in this paper, a method of direct measurement of contact force between the pig and the pipeline is presented, the contact force, the friction force, as well as the friction coefficient of the pig are obtained from the experiment. Research results in this paper can help to establish a more accurate dynamic model of pig.