Reliability of corrosion protected and maintained ship hulls subjected to corrosion and fatigue

A formulation is presented for the assessment of the reliability of a ship hull with respect to failure of the longitudinal members as a result of fat igue and corrosion. The model allows for the existence of multiple cracks a nd it accounts for the crack growth process. The midship section modulus is described by a stochastic process. A new model is presented for the effect of corrosion, which is a time-dependent process with two stages. In the fi rst one, there is no corrosion due to the existence of coating protection. Upon failure of the protection system, general corrosion decreases plate th ickness and affects the midship section modulus. The inspection is modeled as a random process. One repair policy is considered in the example, which consists of plate replacement when its thickness reaches 75% of the origina l thickness. The time-dependent degrading effect of corrosion and crack gro wth are modeled as a random process also. The reliability is predicted by a time variant formulation and the effects of maintenance actions in increas ing the reliability are shown. The sensitivity of the reliability estimates with respect to several parameters is also studied. The formulation has be en applied to a tanker.