Effects of temperature and chloride ion on electrochemical behaviours of a duplex stainless steel

Electrochemical behaviour of a duplex stainless steel, which is one of the candidate structural materials in nuclear-desalination plants, was investigated in a simulated sea water condition. To examine the effect of chloride ion (Cl^-) on its electrochemical behaviours, potentiodynamic and potentiostatic polarization tests were performed in 3.5 wt% NaCl and 4.9 wt% CH₃COONa aqueous solutions. Also, temperature dependence of the pitting potential of the steel in the NaCl solution was determined over the temperature range from 25 to 80 C and AC (alternate current) impedance measurements were performed to examine passive behaviours of the steel in Cl- containing environments. In 3.5% NaCl solution the critical pitting temperature (CPT) was determined to be in the range of 45-55°C. Also, it was found that the steel underwent pitting at transpassive potential even at lower temperatures than the CPT. The impedance measurement results showed that there might be a certain potential above which chloride ions can affect the apparent electrochemical properties of the steel at higher temperatures above the CPT.