Uncertainties in Assessing the Corrosion Wastage and its Effect on Ship Structure Scantlings

Summary The paper discusses the uncertainty of corrosion wastage and its effect on steel plates’ thickness. The composition of distribution laws of the constituent variables is used for describing time-variant probabilistic distributions of residual plate thickness when the as-built thickness and the corrosion wastage obey any probabilistic distribution. The results compare satisfactorily with the Monte Carlo simulation method. Numerical examples are given for the inner bottom, bottom shell, side shell and deck plating of a 25,000 DWT bulk carrier for a case in which the as-built plate thickness obeys the normal distribution and that the corrosion wastage follows either the Weibull or normal (including truncated normal) distribution. The probability that the residual thickness of a structural member meets given Renewal Criteria requirements is calculated. A conclusion is made that any of these three distribution laws are suitable for calculating the probability that a given plate thickness will meet specified Renewal Criteria requirements.