Sensitivity analysis of the stress state in shell courses of welded tanks for oil storage

Abstract

The paper deals with the analysis of reliability and safety of a welded tank for the storage of oil, which is located in the Czech Republic. The oil tank has a capacity of 125 thousand cubic meters. It is one of the largest tanks of its kind in the world. Safety is ensured by a steel outer intercepting shell and a double bottom. The tank was modelled in the programme ANSYS. The computational model was developed using the finite element method – elements SHELL181. A nonlinear contact problem was analysed for the simulation of the interaction between the bottom plate and foundation. The normative approach in design and check of tanks according to standards API 650, ČSN EN 14015, EEMUA 159 and API 653 is mentioned. The dominant loading of the filled tank is from oil. The normative solution is based on the shell theory, which considers constant wall thickness. For real tanks sheet thicknesses of individual courses increase with increasing depth. Stochastic sensitivity analysis was used to study the effect of the variability of the thickness of the ith course on the stress of adjacent courses. The Latin Hypercube Sampling method was implemented during analysis.

Keyword : reliability, safety, crude oil, steel, plate, tank, course, shell, ANSYS, stress, thickness, stiffness