During the fabrication of pressure hulls, plastic processing is indispensable, which is an environmental, highly effective, and economical processing method. However dimensional error is also induced during plastic processing. This kind of error is one type of defection, which makes the hulls in danger, especially when the hulls suffer eternal pressure. Von Mises theory is an effective approach to study failure of pressure hulls. In this paper, numerical simulations are performed to investigate influence of distribution of defections along the axial direction on the ultimate strengths of titanium alloy pressure hulls of long barrel shape with two vessel heads using ABAQUS. The results of numerical simulations show that the ultimate strengths of pressure hulls with defections are relative to the location and distribution of defections, and they are decreasing with reduction of the average ratio and standard deviation when the hull suffers eternal pressure. The method of evaluating degradation of ultimate strength based on simulations can be employed to check the safety of pressure hulls.

TC4 ELI alloy is widely used in the marine, medicine, and aviation fields. The failure performance of TC4 ELI alloy is significantly different from that of other metal materials, such as steels. In this paper, a modified Mohr–Coulomb criterion is calibrated based on several kinds of specimens under different stress states and a 3D geometric representation of a modified Mohr–Coulomb fracture locus for TC4 ELI is obtained based on these parameters. The effectiveness of the modified M-C criterion is studied by a ring-stiffened cylinder made of TC4 ELI. The ultimate strength of the cylinder obtained in the simulation with the modified M-C criterion is close to that obtained in an external pressure experiment, which shows that the modified M-C criterion is suitable for predicting failure in pressure hulls made of titanium alloy used in the deep-sea field.