Transient pigging dynamics in gas pipelines: Models, experiments, and simulations

The bypass hole lowers the traditional pig velocity and brings significant uneven pig velocity which rises the pigging stuck risks. Aiming to give the quick evaluations of the uneven pig motion, this paper first proposed a transient steady-state analytical model to describe the trend and the fluctuation range of the uneven pig velocity, then developed the stoppage model to estimate the stoppage time as the result of inlet mass flow, friction force, and bypass character. The accuracy of the analytical model was verified by the consistency between the model calculated velocity, experimental data and the simulated velocity trend. And the stoppage model was verified by the simulated velocity trends. On considering the gas compressibility effect and the variation in friction profile, this paper studied the occurrence of pig stoppage and the extent of slippage with the designed abnormal friction section in simulation procedure. The variation in friction aggravates the slippage and stimulates the occurrence of stoppage. The positive friction deviation is largely responsible for the sudden deceleration and then stoppage. While, the gas compressibility is primarily responsible for the occasional stoppage after the pig acceleration-deceleration procedure when the pig travels into the lower friction region.