Effect of Alloying on Maximum Depth of Pits in Mild Steel in Marine Immersion Environments

Laboratory studies have shown the influence of alloying on the pitting potential of modern mild- and low-alloy structural steels in a marine immersion environment. A similar effect would be expected infield studies, although these have not been able to isolate the effect of alloying on maximum pit depth as afunction of time, and correlation studies have been inconclusive. It is argued here that the reasons for this are twofold. One is that the nature of the pitting mechanics changes with time, from micropitting as typically observed in laboratory studies, to macropitting as seen in field studies. The second reason is that, so far, efforts at correlating field data have attempted to use a simplistic model for the growth of maximum pit depth as a function of time. A more realistic model that distinguishes between the corrosion mechanics in different phases has been introduced recently. This is applied to the literature data. It has been discovered that the effects of alloying depend on the corrosio...