Risk-based decision-making on corrosion delay for ship hull tankers

Corrosion addition, as defined by the International Association of Classification Societies (IACS), is a proactive design measure against corrosion-induced structural deterioration. In conjunction with regular dry-docking maintenance (e.g., coating and steel renewal), corrosion addition is aimed to sustain the intended functionality of a corroding ship toward the end of its service life. It is expected that corrosion addition can improve hull strength and save the lifetime maintenance cost. However, the benefit of upfront steel investment in corrosion addition on the ship's life-cycle cost, including construction, dry-docking maintenance, and failure consequence, remains unclear. Obtaining such knowledge is very helpful in ship design and lifetime dry-docking planning. This paper presents a risk-based approach to study the most economically optimal corrosion addition. The method is illustrated on a very large crude carrier (VLCC) and the benefit analysis takes into account different magnitudes of the construction, dry-docking, steel renewal, and failure costs. The results show that corrosion addition by IACS may not be economically optimal; the reduction in the life-cycle cost through corrosion addition and the optimal corrosion addition achieving the maximum benefit varies with the item costs specified.