Earthquake Natech risk: numerical analysis of floating roof and sealing system in cylindrical storage tanks

Earthquake is one of the natural event that are part of NaTech events (Natural Hazard Trig-gering Technological Disasters). Cylindrical liquid storage tanks with floating roof are com-mon equipment in industrial plants, and they are vulnerable to earthquakes. In fact, seismic damage to tanks with floating roof can lead to major accidents involving hazardous substances, mainly due to convective fluid movement and to the interactions between the tank wall, the fluid, the floating roof, the sealing system, and the bumper bars. In rim seal fires, which occur when the sealing system is damaged and an impact occurs between the bumper bars and the tank wall, the horizontal dynamics of the floating roof is involved. The horizontal dynamics depends mainly on the mechanical characteristics of the sealing system and the type of impact. The objective is to predict the horizontal vibration response of the floating roof of a tank sub-jected to seismic excitation, taking into account different boundary conditions. For this pur-pose, a simplified and reduced model is developed assuming a decoupling hypothesis between the horizontal and the vertical motion of the roof. Different types of sealing systems (i.e., dif-ferent mechanical properties) are investigated, considering the possibility of impact between the bumper bars and the tank wall. This impact is usually rigid. Later, as a proposal for the prevention of major accidents, deformable bumpers are introduced to reduce the maximum contact force and avoid the impact between two metallic parts.