Dynamic analysis and simulation of long pig in gas pipeline Malihe Mirshamsi * , Mansour Rafeeyan Department of Mechanical Eng., Faculty of Engineering, Yazd University, Islamic Republic of Iran article info Article history: Received 5 January 2015 Received in revised form 3 February 2015 Accepted 5 February 2015 Available online Keywords: Long pig Dynamic simulation Gas pipeline abstract This paper deals with the dynamic analysis and simulation of long pig through the two-dimensional gas pipelines. In the modeling, the pig's length is noticed. The long pig is considered as a chain body not a particle. Pig is divided into a number of elements, Newton's second law is written for all the different elements of pig and then all the equations are added to get the dynamic equation of the pig's motion. An algorithm is used to solve the differential equation of the motion based on RungeeKutta method. Continuity, momentum and the state equations are employed to achieve the gas flow parameters like density, velocity and pressure along the pipeline since the dynamic behavior of the pig depends on the flow field characteristics. It is assumed that pig is long and there is a bypass valve in pig's body. The path of the pig or geometry of the pipeline is considered as 2D curve. Numerical examples are chosen to show the application of the proposed formulation and algorithm. The simulation results illustrate the validity and efficiency of the derived equations for online estimating of the position and velocity of the long pig in gas pipelines at any time of the motion. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The pipeline is considered as the best and safest way to trans- port different kinds of fluids including oil and gas productions. After a period of time, pipelines do not operate effectively because of debris or residual products. In order to remove this debris and inspect the physical condition of the pipelines, pigging operation is commonly used around the world. Pipeline pigs may be broken into two fundamental groups: 1. conventional pigs, which perform a function such as cleaning or dewatering, and 2. smart or intelligent pigs which are utilized for internal inspection of pipelines. Smart pigs are usually long to install different transducers on them for detection of surface defects such as cracks, corrosion, etc. If pigs run at a constant velocity, they can do their job effectively. This velocity is generally in the range of 1e5 m/s in liquid pipelines and 2e7 m/s in gas pipelines (Nguyen et al., 2001a). Good esti- mations of pig velocity and the time need for the pig to reach to the end of pipeline will help engineers design and perform a suitable pigging operation. The dynamic analysis of a pig in a pipeline can estimate these important parameters for the designers. Smart pigs regularly are long so they cannot be reflected as particle and their length should be considered in the modeling and dynamic analysis. A literature survey has revealed few papers dealing with the motion of the pigs in pipelines. Most of the available work is experimental research or have a commercial basis. McDonald and Baker (1964) introduced probably the first investigation on the motion of pigs in pipelines. They used a successive steady-state approach to model the pigging phenomena. Barus (1982) extended this modeling and removed some limitations. The first pigging model on the basis of full two-phase transient flow formulation proposed by Kohda et al. (1988). This model is composed of correlations for pressure drop across the pig, slug holdup, pigging efficiency, pig velocity model and a gas and liquid mass flow boundary condition applied to the slug front. Some other researchers also reported their results of pigging simulation in two- phase flow straight pipelines (Minami and Shoham, 1991; Taitel et al., 1989; Scoggins and M. W. 1977; Xiao-Xuan and Gong, 1999). Nieckele et al. (2001) presented isothermal transient pigging operation through gas and liquid pipelines. Nguyen et al. (2001b) proposed a computational scheme using method of characteris- tics (MOC) and a regular rectangular grid for estimating the pig dynamics when it flows in natural gas pipeline. Nguyen et al. (2001c) studied dynamic model and its analysis for the pig through a 90  curved pipe with compressible and unsteady flow. One type of pig using bypass flow in natural gas pipeline was considered by some investigators such as Nguyen et al. (2001a). In their research, a simple nonlinear controller is designed based on * Corresponding author. E-mail addresses: mirshamsi@stu.yazd.ac.ir (M. Mirshamsi), rafeeyan@yazd.ac.ir (M. Rafeeyan). Contents lists available at ScienceDirect Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse http://dx.doi.org/10.1016/j.jngse.2015.02.004 1875-5100/© 2015 Elsevier B.V. All rights reserved. Journal of Natural Gas Science and Engineering 23 (2015) 294e303