Speed Simulation of Pig Restarting from Stoppage in Gas Pipeline

Abstract

Pigging is a common operation in the oil and gas industry. Because of the compressibility of the gas, starting up a pipeline inspection gauge (pig) from a stoppage can generate a very high speed of the pig, which is dangerous to the pipe and the pig itself. Understanding the maximum speed a pig achieves in the restarting process would contribute to pig design and safe pigging. This paper presents the modeling of a pig restarting from a stoppage in gas pipeline. In the model, the transient equations of gas flow are solved by method of characteristics (MOC). Runge-Kutta method is used for solving the pig speed equation. The process of a pig restarting from a stoppage in a horizontal gas pipe is simulated. The results indicate that the maximum speed a pig achieves from a stoppage is primarily determined by the pressure of the pipe and the pressure change caused by the obstructions. Furthermore, response surface methodology (RSM) is used to study the maximum speed of pig. An empirical formula is present to predict the maximum speed of a pig restarting from a stoppage in gas pipeline.

Modeling and Simulation of Pigging for a Gas Pipeline Using a Bypass Pig

“…(1) e gas is an ideal gas (2) e gas flow is quasi-steady heat flow (3) e fluid in the pipeline is a single-phase gas (4) e diameter of the pipeline is unchanged during pigging e unsteady flow dynamics can be modeled based on the fundamental fluid dynamic equations [11,17,18,23]: continuity equation, momentum equation, and energy equation, respectively, as follows:…”

“…To understand the dynamic behavior of the pig, the pig dynamic equation must be coupled with the governing equations of flows [14][15][16]. e method of characteristics (MOC) was employed to transform the partial differential equations of flows to ordinary differential equations [17][18][19]. is method is quite efficient to solve the governing equations of transient gas flows.…”

Inlet pressure simulation of pigging in uphill gas pipeline

“…Figure 1 shows the forces acting on a pig in a twodimensional pipe. The dynamic equation of the pig can be written as follows [15]:…”

“…The unsteady flow dynamics can be modeled based on the fundamental fluid dynamic equations as below [13][14][15]20,21]:…”

“…The maximum speed a pig achieves from a stoppage in gas pipeline is studied by Honggang and Zheng [15]. In this paper, the gas equations are solved by the MOC.…”