Electrochemical approach for the definition of the Pedeferri's diagrams of stainless steels

摘要

Cathodic prevention (CPrev) was proposed by Pietro Pedeferri as an electrochemical method of preventive maintenance of new concrete structures that are expected to become affected by chloride contamination in the future. This brilliant electrochemical technique is based on the principle that the chloride threshold increases as the potential of steel decreases. In other words, the application of low cathodic current density (a few mA/m2) can increase significantly the critical chloride content so that pitting initiation is strongly suppressed, even in high contaminated concrete. The operating conditions of CPrev are represented on the Pedeferri's diagram (Figure) as a function of steel potential and chloride content and are reported as protection criteria on the European standard. These diagrams can also be extended to other materials that operate in passive condition, as carbon steel in uncontaminated concrete. A first effort has been carried out to extend the use of Pedeferri's diagrams to stainless steel in chloride containing environment, i.e. natural waters (fresh or seawater). The Pedeferri's diagram of stainless steels aims to define pitting corrosion, perfect and imperfect passivity conditions as a function of the imposed potential and chloride content and are claimed to be a valid instrument for engineering application of cathodic protection and prevention.