On the mechanics of thermal buckling of oil storage tanks

Abstract

This paper addresses the thermal buckling behavior of tanks having a fixed roof, as employed to store fuel in the oil industry. The study is performed based on finite element analyses of the shell, including linear analysis, linear bifurcation analysis, and geometrically and constitutive nonlinear analysis, in order to elucidate the mechanics of stress redistribution at pre-buckling and buckling states. Based on previous works, the roof is modeled as a conical shell with an equivalent uniform thickness. The results show that the stress field due to a uniform temperature around the circumference is considerably different from that obtained for a non-uniform field as modeled in cases of temperatures due to an adjacent fire: Under uniform temperatures around the circumference the shell does not provide vertical restrain and buckling is dominated by hoop action; whereas displacement constraints are present under a non-uniform temperature, leading to buckling dominated by meridional stresses. Contrary to what has been suggested, the tank under uniform temperature cannot be taken as an upper bound to the buckling of a tank under an adjacent fire. In the evaluation of critical temperatures, the influence of geometric relations H/D (height to diameter) and R/t (radius to thickness) are independent of each other. It is shown that the problem is not imperfection-sensitive. Finally, thermal buckling mode and critical temperatures are strongly dependent on the H/D ratio of the cylindrical shell.