THE USE OF VERY WEAK GALVANOSTATIC POLARIZATION TO STUDY LOCALIZED CORROSION STABILITY IN STAINLESS-STEEL

Galvanostatic anodic polarization is sometimes used to study pitting of stainless steel, but has never been very popular despite the clear and interpretable results that can be obtained. In this paper it is shown that the galvanostatic technique provides a rapid way of assessing the relative performance of different heats of a particular stainless steel, or the stabilizing effects of inclusions and sulphur anions on pit growth. It is suggested that the importance of slow scan rate in potentiodynamic tests has been exaggerated, and that the most appropriate combination of test methods is a relatively rapid potentiodynamic scan and a galvanostatic test (or series of tests) at very low anodic current, to test the stability of localized corrosion over a relevant time scale. Remarkable evolutionary phenomena occur when a population of active pits is grown by a low applied current, and these dynamics must be relevant to the long-term performance of passive alloys in practice.