Potentiostatic and potentiodynamic polarization tests for the definition of the Pedeferri’s diagrams of stainless steels

Chloride-induced corrosion (pitting and crevice) of stainless steels is considered the main concern in the industrial applications and takes place in the presence of oxygen and chlorides over a critical threshold. In order to predict the corrosion behavior of stainless steels in chloride containing environment, the Pedeferri’s diagram is proposed as it is defined for carbon steel in concrete. The Pedeferri’s diagram of stainless steels aims to define corrosion and passivity (perfect and imperfect conditions) as a function of the potential and chloride content. The conditions can be obtained by determination of pitting and repassivation potentials by means of proper experimental methods. In this work, initiation of localized corrosion was evaluated by pitting potential measurement by means of anodic potentiostatic and potentiodynamic tests which were carried out on austenitic stainless steel AISI 304L in solution with different salinity, moreover, the effect of potential scan rate is discussed. The results showed that, as expected, the localized corrosion potential decrease as the chloride concentration increases. Tests confirm that potential scan rate is a critical parameter because localized corrosion is time-dependent: at high scan rate (such as defined by ASTM standard test method) test time is reduced but localized corrosion potential is overestimated.