Stress Intensity Factors of External Surface Cracks in a Vertical Cylindrical Steel Tank

Abstract

The present research deals with external surface cracks in vertical steel tanks. Such defects occur very often. The analytical expression of stress intensity factor (SIF) is need, for prediction residual life of tanks with cracks. There are solutions for the SIF of surface cracks in hollow cylinders. However, all of them can not be used for steel tank. The main purpose of this research is to present analytical expression SIF for longitudinal external surface cracks in vertical cylindrical steel tanks. The finite element method is used for the SIF calculation of the crack in the tank. All SIF values are determined based on the submodel technique. Firstly, the whole shell model of tank without defects is generated. Real service load and tank size take into account. After that the solid submodel with crack is generated. A wide range of cracks geometries and filling level of oil are researched. The finite element models have a good agreement with wellknown analytical decisions. All SIF results are expressed with polynomial functions, that the fracture criteria can be used easily in the estimation of the residual life of tanks. SIF polynomial function should used in Paris-Erdogan equation. Results of this work could be useful for engineers in oil storage field.