Potentiostatic threshold potentials of stainless steels

Abstract

Potentiodynamic measurements are used to determine key potentials to classify certain corrosion properties. The material selection for components (e.g. shafts) in corrosive environments is widely based upon these potentiodynamic measurements. Criticism for using these potentials for component design has been expressed in literature. Potentiostatic measurements are known to represent the long term corrosive impact experienced by components in a more realistic manner but are prone to scatter. Therefore a statistical approach called staircase method was adapted to the given electrochemical problem. With using this staircase method, a reliable value for the median potential (threshold potential) can be determined. This potential defines the threshold between anodic dissolution and cathodic protection. For the first time, this newly defined potentiostatic threshold potential is offering a validated median potential value for corrosion prediction in a given corrosion system based on potentiostatic measurements. Threshold potentials for the stainless steel grades 1.4057 and 1.4542 were investigated in aerated electrolytes at 25°C with different chloride ion concentrations.