Molding and Simulation of Pig Speed with Brake Unit in Gas Pipeline

Abstract

To provide efficient pigging operation, a stable and moderate speed of the pig is preferred. This paper describes a brake device for controlling the speed of a pig in a gas pipeline. A pigging model of a pig with a brake unit in gas pipeline is presented. In the model, the relevant pig speed equation is combined with the gas flow equations. It is assumed that the velocity of gas at the tail and nose of the pig is equal to that of the pig. Moreover, the inlet flow rate and the outlet pressure are kept constant during the simulation. The method of characteristics (MOC) is applied to solve the transient equation of gas flow, and the Runge–Kutta method is used to solve the pig speed equation and the steady flow equations to obtain the values of initial flow. Two cases for pigging simulation were carried out to verify the performance of the brake unit. The corresponding results indicate that the brake unit can prevent undesired high speed of the pig when the pig restarts under a stoppage condition in a gas pipe. Additionally, a brake device can ensure a more stable speed of the pig. However, due to the drag force generated by the brake unit, a greater differential pressure between the tail and nose of the pig is required to drive the pig in motion.