Seismic risk assessment of an existing oil refinery subjected to earthquake swarms

Steel oil refineries are subject to ageing due to corrosive chemicals and harsh atmospheric conditions, leading to the degradation of their structural integrity. This deterioration affects the resilience of process units against seismic events, particularly during strong aftershocks. Leaks in pipelines or damage to tanks containing hazardous materials pose health risks and can necessitate shutdowns for essential repairs. Hence, maintaining the integrity and safety of both structural and non-structural components and adopting a proper maintenance plan is essential. This paper investigates the performance of a petrochemical unit in a seismic area, estimating damage risks from earthquake swarms considering soil-structure interactions and damage accumulation. Fragility curves, based on defined damage states, were developed to create a customized risk assessment model for oil refineries. A life cycle cost analysis was also conducted, considering an effective corrosion maintenance plan over the lifetime of the structure. The results showed that inadequate maintenance and aftershocks, increase life cycle costs by 2% for uncorroded structures and 4% for corroded structures due to aftershocks. The combined effects of aging and aftershocks significantly increase annual failure rate and reduce structural resilience. Corroded structures under sequence motions face the highest failure risk, with a 1,000-year return period at low damage level. Aftershocks further decrease resilience by 2% and double the annual slight damage rate under sequence motions. The results also reveal that structural components are more prone to damage than non-structural ones. The proposed framework systematically evaluates seismic risk and resilience in refinery units under harsh atmospheric conditions.