Reliability with respect to ultimate strength of a corroding ship hull

A reliability assessment relative to the ultimate strength failure of a ship hull experiencing structural degradation due to corrosion is presented. The midship section modulus is considered a random process with a monotonically decreasing mean value. ‘Failure’ occurs when the maximum wave-induced bending moment associated with the extreme loading condition plus the stillwater bending moment exceeds the ultimate strength of the hull. Effects of uncertainties in the design variables (including wave and stillwater bending moments, yield strength, and section modulus) on structural performance can be quantified using statistical methods. A reliability analysis method for ultimate strength is developed and, as an example, the reliability assessment of a corroding tanker is illustrated. Reliability as a function of time (as predicted prior to service) is estimated. Also, conditional reliability, given that the ship has survived up to time τ s , is computed as a function of t. The purpose of these reliability analyses is to provide information to ship designers and/or owners to be used for general risk assessment relative to decisions on corrosion margins and corrosion protection during construction, as well as decisions on steel replacement during the ship's life.