Electrochemical polarisation measurements on a 12Cr martensitic stainless steel in dilute NaCl.

Electrochemical polarisation tests were carried out to provide input data to the model of crack chemistry being developed for a 12Cr martensitic stainless steel (FV566) in simulated steam turbine solutions. Potentiodynamic tests with two sweep rates and potentiostatic tests were used to characterise the passive current density of FV566 in neutral NaCl solution at 90 oC with chloride ion concentration of 1000 ppm. The method chosen affected the passive current density obtained. Expressions were obtained for the water reduction kinetics in deaerated neutral solutions and for hydrogen ion reduction kinetics in deaerated acidic solutions of varying pH. The depassivation pH of FV566, measured in deaerated solutions with ~2000 ppm Cl-, was found to be between 1.7 and 1.9.