Abstract Pit depth distribution curves were constructed for 2S aluminum immersed in tap water for time period of two weeks, one, two, four and six months, and one year, respectively. The distribution curves were found to consist of two superimposed curves. A “J” shaped curve resulted from pits which initiated and stifled within two weeks of immersion, whereas the other, a “bell” shaped curve, resulted from pits that initiated and continued to propagate. The “bell” shaped curve retained its shape and moved in the direction of increasing pit depth. After about two months the majority of these latter pits ceased propagating, the mode of the bell shaped curve became stationary, and only a small number of the deeper pits continued to propagate, the tail of the distribution curve lengthening with time. The maximum pit depths obtained on each of replicate samples were analyzed by the statistical theory of extreme values using the appropriate probability paper and were found to fit the extreme value distribution:...