Extrapolation of Extreme Pit Depths in Space and Time

A four parameter model is proposed for data collected on maximum pit depths enabling simultaneous extrapolation into the future and over large areas of exposed metal. This model is based on the generalized extreme value distribution whose use in this context is here justified mainly on statistical, rather than metallurgical, reasoning. Those aspects of the model which allow for extrapolation in time rely on reported power law dependencies for mean pit depths. Use of the model for predicting means, standard deviations, percentiles, bounds, order statistics, hole counts, and size of perforated areas, is demonstrated, both in general and for a particular data set. Comparisons are made with other reported techniques.