STRESS CONCENTRATION IN CYLINDRICAL CARGO TANKS OF LIQUEFIED GAS CARRIERS

摘要

A short introduction to liquefied gases and types of cargo tanks is given. Attention is paid to the independent tanks, especially those of C type operating under pressure up to 20 bar, for which pressure vessel criteria are relevant. Strength analysis for such a cylindrical tank with dished heads, design in accordance with the Classification Rules, is performed. The analytical and numerical approach, based on the theory of shells of revolution and the finite element method respectively, are employed. The stress concentration in the cylindrical shell at the stiffening ring and in the sphere edge at its connection with the toroidal shell is analysed. In the former case the strength criteria are satisfied but in the latter they are not. The AD Merkblatt B3 tolerates such situation assuming that the FEM results are not realistic enough. Since the analytical solution indicates that the numerically determined stress level is overestimated only by 5%, the reinforcement of the tank head by a thicker spherical segment is recommended. The maximum stress is reduced to the allowable level.