Dynamic modeling and its analysis for the PIG (pipeline inspection gauge) flow through a 90/spl deg/ curved pipe with compressible and unsteady flow are studied. The PIG dynamics model is derived by using a Lagrange equation under the assumption that it passes through 3 different sections in the curved pipeline such that it moves into, inside and out of the curved section. The downstream and up stream flow dynamics including the curved sections are solved using the method of characteristic. The effectiveness of the derived mathematical models is estimated by simulation results for a low pressure natural gas pipeline including downward and upward curved sections. The simulation results show that the proposed model and solution can be used for estimating the PIG dynamics when we pig the pipeline including curved sections.