Influence of residual stress due to the equatorial weld on the ultimate strength of a Ti80 spherical pressure shell

Titanium alloys are widely used for pressure hulls in deep manned/unmanned submersibles. A manned pressure hull is generally manufactured by joining two hemispheres with an equatorial weld that inevitably contains residual stress. In this study, the residual stress in a butt-welded Ti80 plate was first measured and used to confirm a nonlinear finite element simulation. The distribution of the residual stress due to the equatorial weld and its influence on the ultimate strength of the Ti80 spherical pressure shell were then studied. The application of different pressures to the outside of the shell was found to have a minor influence on the residual stress in the shell, and the ultimate strength of the shell showed an insignificant decrease when considering the influence of the residual stress. Thus, a relatively reliable method for determining residual stress due to the equatorial weld and its influence on the ultimate strength of a large-scale spherical pressure shell was obtained.