Abstract:
A pig is a maintenance tool used in the Oil and Gas Industry, chiefly to remove solids or liquids from pipelines. It is in essence a sliding seal, which moves due to the action of the fluid pushing it. The aim of this work is to describe the steady state motion of the pipeline pig in terms of several key characteristics.
An analytical model of the pig motion has bey prepared to calculate these parameters. The model also shows how these characteristics vary with velocity and distance due to wear. All assumptions and limitations are listed. The model has been verified by tests performed on a 10" carbon steel pipeline.
The model works by f rstly calculating the force exerted by the pig seal on the pipe wall. A generalisation of the seal shape allows calculation of the contact parameters. A simplified lubrication analysis ensues, enabling calculation of the seal film profile. Knowledge of film thickness allows estimation of friction, differential pressure and leakage rates. Varying pig velocity affects the film shape and thickness, which in turn affects seal friction and therefore alters the program output. Changes in pig characteristics due to abrasive wear are accounted for using a wear coefficient and estimating the volume of material removed over successive distance increments.
The model compares well with the experimental remits for characteristics such as differential pressure and friction For this reason the wall force, contact and surface roughness models (i.e. the mechanical We of the problem) are considered to be accurate. However, agreement between leakage test results and the model was less well defined and it is apparent that the hydrodynamic analysis requires further study.
