This research unveils a case study on the structural integrity management of an ageing Floating Production Storage and Offloading (FPSO) unit and Single-Point Mooring (SPM) calm buoy, with a primary focus on the degradation effects of corrosion. Historically, as FPSO and SPM calm buoys exceed their initial design life, the threat of corrosion wastage poses a significant threat to structural reliability, particularly in critical areas such as the hull and deck plates. This paper presents a comprehensive assessment methodology involving in-service survey data, corrosion wastage computations, and structural reassessment to evaluate the remaining thickness of these components, which is a measure of their remaining strength. In conclusion, for the FPSO hull, since 20.12 mm is greater than 19.75 mm, it will serve for the intended 15 years. Thus, the hull is adequate for an additional 15 years in service. Similarly, for the SPM calm buoy hull, since 11.73 mm is greater than 9.725 mm, it will also serve for the intended 15-year extension. Thus, the hull is adequate for the 15-year life extension. Therefore, in each case, the t-end of design life is greater than the t-minimum for life extension. Hence, no steel plate renewal is required on the hulls for the FPSO and SPM calm buoy. These computations were made possible by a computer program code-named HULL LIFE written in the C++ programming language. On the other hand, the computations carried out on the deck plates allowed the recommendation of various mitigation strategies to remedy the corroded deck plate strakes that had fallen below the limiting values. Other strakes or zones that fell within the regime of substantial corrosion were recommended for close monitoring.