Offshore renewable energy systems, including wind, wave, and tidal devices, are exposed to highly aggressive marine environments where corrosion is a primary factor limiting service life. Stainless steels are widely employed in these structures, yet their long-term performance is challenged by localized corrosion phenomena such as pitting and crevice attack, exacerbated by fluctuating oxygen levels, chloride concentration, and mechanical stresses. This study presents a simulation- and literature-based assessment of corrosion resistance in stainless steel components designed for offshore renewable energy applications. Electrochemical models were implemented in MATLAB and Python to reconstruct polarization curves for commonly used alloys, including 316L, duplex, and super-duplex stainless steels, under seawater conditions. Corrosion rates were estimated using current density data, while sensitivity analyses examined the influence of chloride concentration, temperature, and passive film stability on corrosion susceptibility. A simple diffusion model was also applied to capture oxygen depletion within crevices, highlighting geometry-driven risks in bolted or welded joints. To extend the analysis beyond baseline alloy behavior, the effect of surface engineering strategies, such as laser polishing and surface texturing, was incorporated by parameterizing improvements in passive film resistance and pitting potential based on reported experimental data. The results demonstrate how alloy selection, component geometry, and surface state collectively influence the durability of offshore energy structures. By integrating electrochemical modelling with a materials perspective, this study outlines design guidelines for selecting and engineering stainless steels in marine renewable energy systems. The findings emphasize the importance of combining material choice with preventive surface engineering to extend service lifetimes and reduce maintenance in harsh ocean environments.