CHANGE OF STEEL’S YIELD STRESS OVER SHIP’S SERVICE LIFE AND ITS EFFECT ON THE FIRST YIELD HULL GIRDER BENDING MOMENT

Abstract

The publication deals with the decrease of the yield and tensile stress of high tensile shipbuilding steel AH-32 over ship’s service life and its effect on the first yield bending moment as a representative of the hull girder capacity. An example is given for a sample 25K DWT (25 thousand tons deadweight) bulk carrier. The probability of failure is calculated as the probability of the total hull girder bending moment exceeding the first yield bending moment. The probabilistic distributions of yield and tensile stress are obtained from laboratory test of the specimen of AH-32 steel (corroded plates of a 20 year old ship). It is found that although the decrease of yield stress may not be great, the increase of the probability of failure (i.e., the probability yield bending moment) could be substantial.