Cumulative steel replacement prediction in severely corrosion - affected bulk carriers

Systematic studies on long-term cumulative steel replacement in ships are virtually absent, despite their importance for ship design, maintenance of ageing vessels, and sustainable shipping. Extensive ultrasonic thickness measurement reports and steel renewal records collected throughout the operational lives of 12 bulk carriers were presented and analysed to quantify cumulative steel replacement at both the ship and their lightweight groups. By combining these data with benchmark shipyard information, the total lightweight mass of the ships is estimated. The findings indicate that cumulative steel replacement may exceed 1000 t over a typical 25-year service life in severely corrosion-affected Handymax bulk carriers. Steel renewal was dominated by the inner bottom and hopper plating, while ships carrying iron, ore and coal generally required substantially greater steel replacement than grain carriers. The main contribution of this work is a complementary predictive framework that combines cell-level machine-learning point estimation with stochastic renewal-based modelling. It provides ship-level and structural-area forecasts, time-dependent replacement schedules, and predictive intervals, and can be applied prospectively to technically specified ships not included in the historical dataset. The proposed methodology provides a practical framework for maintenance planning, structural assessment, ship design, and life-cycle management of ageing vessels.