Modeling and vibration analysis of pipeline in the course of pigging operation, using FEM and experimental modal analysis

In this paper, a linear dynamic model of simply supported Above-Ground pipeline during pigging process has been developed and verified by experimental tests. The PIG (Pipeline Inspection Gadget), is an internal moving sprung mass pushed by the fluid pressure, which itself act as a flowing varying mass. The governing equations of motion for the system including the pipeline, moving PIG as a moving vibrational sub-system, and flowing fluid with varying mass were obtained using Hamilton’s principle. Then, the extracted equations were discretized and solved via finite element method. Modal parameters of the pipeline system were calculated during intermittent passage of PIG through the pipe under different fluid flow rates, and their variations were extracted. Validation of the model was carried out using an experimental setup, including a 2.5 meter length Carbon Steel pipe, a simple bi-directional PIG with rubber discs and a centrifugal pump, connected to a control valve, providing required fluid pressure to push the PIG through the pipe. Using data acquisition system to acquire the vibration signals, and employing experimental modal analysis, frequency responses of the system at different points were obtained and the modal parameters were extracted and compared to that of the simulated model. A comparable results have been achieved between theoretical and experimental methods. Also variation of the system natural frequency versus speed and position of PIG in the pipe, were investigated. Moreover, the displacement of the mid-span of considered pipe during pigging process has been obtained using suggested theoretical model.