Development of pitting corrosion of stainless steel 403 in sodium chloride solutions

Pitting corrosion of stainless steel 403 in the NaCl solutions is studied. It is shown that the experimental results obtained under the potentiostatic conditions do not provide sufficient information on the behavior of steel under the conditions of free corrosion. The corrosion experiments take long time, their results exhibit poor reproducibility; however, they are necessary for obtaining reliable data on the corrosion behavior of steel. The development of corrosion process is reflected in the variation of corrosion potential with time. The effect of concentration and temperature of NaCl solutions on the development of pitting corrosion is studied. The peculiarities of the distribution of pits over the test specimen surface are revealed. In 1 M NaCl solution at 20°C, few pits arise. Some of them repassivate; some pits grow, initially, in diameter and depth and, then, almost only in depth. The examples of through pit formation on the specimens 4 mm thick are presented.