Fatigue Life Reduction Due to Weld Defects in Submarine Pressure Hull Materials: A Review

Weld defects represent a critical challenge in the structural reliability of submarine pressure hulls, where components operate under severe cyclic hydrostatic loading and corrosive deep sea environments. In high strength steels and titanium alloys commonly used for submarine fabrication, welding introduces microstructural heterogeneity, residual tensile stresses, and geometric discontinuities that significantly reduce fatigue life. Even small imperfections such as porosity, inclusions, lack of fusion, and weld toe cracks act as potent stress concentrators, accelerating crack initiation and early propagation. These effects are intensified in spherical and cylindrical pressure hulls, where complex three dimensional stress fields and nonstandard crack shapes limit the applicability of conventional fatigue models. Hydrostatic compression, combined with residual stress redistribution, further promotes unexpected crack growth behavior, reducing fatigue thresholds and shortening service life. Evidence from experimental studies and numerical simulations consistently reveals that defect morphology, HAZ softening, local stiffness reduction, and environmental factors jointly govern fatigue degradation in submarine welds. Moreover, early short crack growth contributes disproportionately to total fatigue damage, emphasizing the need for defect sensitive assessment methods. Furthermore, localized plastic deformation at defect tips under extreme hydrostatic pressure necessitates fracture mechanics models explicitly accounting for non idealized crack geometries. This review synthesizes current understanding of how welding induced imperfections influence submarine pressure hull fatigue performance and highlights major research gaps related to multi axial loading, crack shape evolution, and deep sea failure mechanisms. The findings support the development of improved welding practices, advanced inspection techniques, and refined fatigue life prediction frameworks tailored for submarine structural safety.