Seismic fragility in life cycle cost analysis for gas pipelines: design and cost optimization framework

This study proposes an innovative approach to optimizing the seismic design of pipeline network by incorporating life-cycle cost analysis (LCCA). The research integrates seismic design, which includes evaluating wave propagation, with a comprehensive LCCA. The LCCA includes the calculation of both initial and secondary costs. Initial costs cover pipeline construction costs, such as materials and installation. Secondary costs include expected seismic loss and maintenance. The research involves modeling the pipeline using FEM, conducting incremental dynamic analyses, extracting seismic fragility curves, calculating expected seismic annual losses, and using a Markov corrosion model to simulate corrosion growth rates and calculate expected maintenance costs. The developed method is applied to a gas pipeline network, which includes varying diameters and thicknesses. Results indicate that among different scenarios, a slight increase in pipe wall thickness leads to a noticeable reduction in the secondary costs, achieving the minimum LCC value. Among secondary costs, expected seismic loss are significantly higher than maintenance costs. However, increasing wall thickness has a greater impact on reducing maintenance costs. Among the various scenarios, those with the greatest wall thickness exhibit the lowest expected seismic loss, with the expected maintenance costs effectively reaching zero. As the diameter-to-wall-thickness ratio decreases, secondary costs decrease, while initial costs and LCC increase. For scenarios with diameter-to-wall-thickness ratios of 95 and 119, the optimum LCC is achieved. Also, the results show that with an increase in diameter of up to 50% and the same thickness, the LCC increases up to 60.63%.