Modeling of Pig Operations in Natural Gas and Liquid Pipeline

Abstract The use of pigs has become a standard industry procedure. This expanding demand has driven manufactures to produce a great variety of pig models. Most of the available knowledge is based on field experience. Hence, selecting the best pig, estimating its speed and required driving pressure, often involves some guesswork and consequently, a high degree of uncertainty. The pig is most effective when it runs at a near constant speed but will not be effective when it runs at too high speed. The typical speeds for pigging are about 1-5 m/s for on stream liquids and 2-7 m/s for on-stream gas (Cordell and Vanzout 1999). In this work, the pig motion is modeled using Continuity, Momentum, Energy and State equations. These equations simultaneously are solved under unsteady state condition to obtain the pressure; pig velocity profile and the time that pig reaches at the end of the pipeline. This information can help the operator to control speed of pig before the pig reaches the end of pipelines. The change area and elevation profile has been investigated. The results are obtained for gas and liquid pipelines. The programs have been run for various values of time step and distance increment. The results are more accurate when time step and distance increment are getting smaller according to CFL (Courant-Friedrich-Lewy) condition