Using the Limit Analysis Theory to Estimate the Static Strength of the Vertical Cylindrical Oil Tank Shell

Vertical cylindrical tanks for oil and petroleum products are high-level structures and are classified as hazardous production facilities in accordance with Federal Law No.116-FZ "About industrial safety of hazardous production facilities." The safety and performance of oil production, processing, transportation and processing facilities depends on the operational reliability of such facilities. The technical condition of the tanks is closely monitored. Technical diagnostics of tanks shall be carried out within the framework of industrial safety expert review under the supervision of Rostekhnadzor territorial specifications. During the technical diagnostics, mandatory control measurements of the geometry of the bottom plate, shell, tank coating with measurement of wall thicknesses and examination of the metal condition are provided. Taking into account the measurement results, strength and buckling analyzes are performed. The methods for calculating the strength of the tank shell used in the current regulatory and technical documents consider the membrane stress state of the wall, which does not fully assess the limit state of the tank shell. In this regard, the author of the article proposes to apply the theory of limit analysis to the analysis of the strength of the tank shell. The theory of limit analysis makes it possible to estimate the limit total load of an oil tank by solving the system equilibrium equations in the state of reaching the limit at the expected limit values of internal forces under the condition of static equilibrium - static calculation method. Or the total limit load is determined by considering the operation of external loads on a possible kinematic mechanism of structure destruction based on the condition of equality of external work and internal energy of structure deformation at the beginning of destruction - kinematic method. The paper presents expressions obtained by static and kinematic methods. The numerical finite element method is additionally used to derive and justify the design formulas.