Evaluating Corrosion Wastage and Structural Safety of Aging Ships

Probabilistic approach has long been recognized as a preferred tool for the handling of the uncertainty of ship's strength calculations. By factoring in corrosion wastage over time, such an approach can be expanded to account for time-dependency of structural strength. In ABS, analytical techniques had been developed to express the geometric properties of the hull girder and its components in the form of time-dependent distribution laws. Other analytical techniques were also developed to express the design wave-induced bending moment in probabilistic terms for any given life span. This paper shows, using examples, how these loads and geometric properties, all represented in the form of time-dependent distribution laws, could now be utilized to express hull girder bending stresses in the form of time-dependent distribution laws as well. Then, the probability of exceeding given permissible total stresses was calculated and suggestions for a reliability measure based on this probability of exceedence were made. They can be used as a quantitative decision-making assistance at time of initial design or steel renewal.

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