The present work investigates the ultimate capacity of inelastic tubes under combined external pressure, bending and axial force. A geometrically and materially nonlinear finite element technique is adopted. Some special features of tube response such as the effects of initial imperfections, residual stresses and localized deformation, are taken into account. Particular emphasis is placed on the analysis of ring-stiffened tubes under combined loading. The numerical results are compared with the available experimental data, as well as with design formulas, and are of immediate significance in the design of tubular numbers of deep-water structures.