Optimization and Stress Analysis of Welded Joints in Deep-Sea Titanium Alloy Spherical-Cylindrical Pressure Hull

A spherical-cylindrical pressure hull is a new form of pressure-resistant structure that is distinguished from traditional large deep-sea equipment. The residual stresses and deformations introduced by out-of-tolerance welded joints pose a great threat to structural safety under deep-sea service conditions. In this paper, the angular joint of the spherical-cylindrical structure is optimized as a skirted butt joint, and the simulation method is employed to focus on the changes in stress and deformation in the two structural models before and after applying 20 MPa external pressure. The results identify that under hydrostatic pressure, the stress level in the skirt model decreases significantly compared to the residual stress of welding, while the stress in the fillet model increases slightly at the local location. After unloading, the structural stress and deformation return to the post-weld state. The effect of heat treatment on stress relief is very significant and can improve the bearing capacity of the structure.