Abstract
The pipeline inspection gauge (PIG, lowercase pig is commonly used) with a bypass valve is widely used in pipeline inspection because it operates at a low speed without reducing the flow rate. Understanding the dynamics of a bypass pig in a gas pipeline would contribute to the design of the pig and the control of pig speed. This paper deals with the dynamic model for the process of a bypass pig travelling through a hilly gas pipeline. The method of characteristics (MOC) is used to solve the equations of unsteady gas flow. The backward flow of the gas in the bypass valve and pipe is shown by a simulation of pigging for a hilly gas pipeline. Parametric sensitivity analysis of pigging in the horizontal gas pipe using a bypass pig is then carried out. The results indicate that the speed of a bypass pig is most sensitive to the gas speed in the pipe followed by the bypass area and the friction of the pig. A formula, obtained from the results of the simulations using response surface methodology (RSM), is presented to predict the steady speed of a bypass pig in the horizontal gas pipeline.
Highlights
Regular pigging for the gas pipelines is one standard procedure for the operators
A calculation scheme using method of characteristics (MOC) to solve the equations of gas flow for estimating the dynamics of the bypass pig has been shown
The backward flow of the gas in the bypass valve and pipe was taken into account, which was shown by a simulation of pigging for a hilly gas pipeline
Summary
Regular pigging for the gas pipelines is one standard procedure for the operators. Generally, a pig is a piston that is installed in a pipe to perform certain operations such as liquid removal, inspection of the pipe, and cleaning out debris. E process of a pig restarting from a stoppage in a horizontal gas pipe was simulated by Nguyen et al In this paper, the gas equations were solved by MOC [11]. Mirshamsi and Rafeeyan analyzed the process of a pig through a 3D gas pipeline by assuming the pig as a rigid body with a bypass [21, 22] It seems that few of the studies pay attention to the backward flow of gas in the bypass valve and pipe. E bypass flow through the pig is assumed to be incompressible for calculating the pressure difference between the tail and nose of the pig In this pigging model, the backward flow of gas in the bypass valve and pipe is taken into account, which is shown by a simulation of pigging for a hilly gas pipeline. A formula, obtained from the results of the RSM simulations, is presented to predict the steady speed of a bypass pig in the horizontal gas pipeline
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