The worldwide fleet of ships is ageing, with many vessels being over 15 years old. For such vessels, corrosion is an on-going concern. Thus, to guarantee structural integrity, facilitate maintenance decisions economically, and even extend the structural life, it is essential to investigate the ultimate strength of such aged and corroded ship structures based on a comprehensive understanding of the corrosion mechanisms. This work has developed numerical models simulating steel plate corrosion degradation and presents a series of novel finite element (FE) modelling to assess the influence of localised pit distribution and bench-shape pits, which are often observed in long-term exposures. Four location patterns of one-side corroded shipping steel plates have been considered which include both geometric and material non-linearities. Validation of the FE method is achieved by a thermoelastic stress analysis (TSA), which provides the principal stress distribution over the plate surface. The modelling results demonstrate that localised pit distribution can be more detrimental than randomly distributed pits (up to 10.3%). In addition, the bench-shape pits may further decrease the ultimate strength by up to 14% compared to the unbenched condition with the same degree of pitting (DOP).