Free vibration of large-diameter, thin-walled oil pipelines considering the influence of longitudinal force and mass of flowing liquid

This study examines the free vibrations of thin-walled, large-diameter oil pipelines, considering the influence of longitudinal force and the mass of flowing liquid. It confirms that these factors critically affect the structural reliability of the pipelines and therefore must be included in calculations. The numerical analysis was based on the semi-instantaneous shell theory, accounting for internal pressure, the thickness of the protective reinforced concrete layer, the soil’s spring constant, and the applied longitudinal force. The results showed that, during oil transport, the natural vibration frequencies of the pipeline decrease more rapidly than during gas transport. Increasing the thickness of the reinforced concrete shell and the internal operating pressure increases the frequencies and the overall stiffness of the system. The soil’s spring constant also place a significant role by offsetting some of the loads and increasing the vibration frequencies. The study confirmed that the longitudinal force has the greatest influence on the dynamic characteristics of the pipeline, leading to a significant decrease in the free vibration frequencies. The findings and established relationships should be used in the design and operation of large oil pipelines in heterogeneous soils to ensure the required stability and minimize the risk of resonance.