Analysis of locally starting corrosion phenomena using mass change measurements

This paper describes a mathematical approach for the evolution with time of area-specific mass changes when locally starting enhanced corrosion processes occur simultaneously with general corrosion. For the formation of a single corrosion pit in a surface of limited size, the approach yields an analytical expression which qualitatively predicts the characteristic features of mass change versus time curves over the whole time range. Steps towards the mathematical description and numerical simulation of complex pitting situations, including pit coalescence, are outlined. The benefit from a mathematical analysis of mass changes in cases of local corrosion is exemplified using discontinuously measured mass changes of high-alloyed iron- and nickel-base materials after exposure to a simulated waste incineration environment.