Ship hull ultimate strength reliability considering corrosion

The aim of the present paper is to develop and demonstrate a procedure for assessment of ship hull girder ultimate strength reliability taking into account the degradation of primary members due to general corrosion. The probabilistic model for ultimate hull girder strength is established on the basis of an analytical formula that considers corrosion related time dependent strength degradation in the various failure modes. Corrosion rates and their probabilistic characterization are based on available studies using gauging data. Applicable extreme hull girder loads are calculated using a simplified direct method for wave load calculation together with the IACS design guidance formula for stillwater bending moment. The variability in strength, corrosion rates and loads are accounted for in the second order reliability method (SORM) based on calculations of the time dependent reliability index. The procedure developed is illustrated by application to both tankers and bulk carriers. For a given set of renewal criteria. apart from trends of hull girder section modulus, ultimate strength and the reliability index as a function of vessel age, the probability of steel renewal due to corrosion is also predicted.