Fragility of open-topped oil storage tanks under wind in Patagonia

Abstract

Oil storage tank farms are complex systems and the eventual failure of one of their components could affect the whole system. A risk assessment requires identifying the magnitude of the damage that can occur under certain load levels. Fragility curves for oil storage tanks with a floating roof are obtained in this work, to estimate the probability of exceeding a given damage state under wind loads. Steel tanks with height-diameter ratio between 0.20 and 0.60 designed with American Petroleum Institute standard 650 are analyzed. The loads are represented by wind-speed and the structural response of the tank is evaluated through computational simulations using finite element analyses. Damage is characterized by deformations in the geometry of the cylinder and wind girder. Damage levels are obtained using linear bifurcation analysis and geometric nonlinear analysis with imperfections, and loads are related to wind speed based on wind data of Patagonia in Argentina. The fragility curves are constructed by means of a log-normal distribution. The results allow establishing ranges of wind speeds for which the damage can affect the integrity of the tank. It is expected that the present results serve as the basis for the development of simplified models, so that a much larger tank database may be considered.