Determination of the Crevice Repassivation Potential of Alloy 22 by a Potentiodynamic-Galvanostatic-Potentiostatic Method

Alloy 22 (N06022) is a nickel-based alloy highly resistant to corrosion. In some aggressive conditions of high chloride concentration, temperature and applied potential, Alloy 22 may suffer crevice corrosion, a form of localized corrosion. There are several electrochemical methods that can be used to determine localized corrosion in metallic alloys. One of the most popular for rapid screening is the cyclic potentiodynamic polarization (CPP). This work compares the results obtained by measuring the localized corrosion resistance of Alloy 22 using both the CPP and the more cumbersome Tsujikawa-Hisamatsu Electrochemical (THE) method. The electrolytes used were 1 M NaCl and 5 M CaCl₂, both at 90°C. Results show that similar repassivation potentials were obtained for Alloy 22 using both methods. That is, in cases where localized corrosion is observed using the faster CPP method, there is no need to use the THE method since it takes ten times longer to obtain comparable results in spite of the mode of corrosion attack is sometimes different in the tested specimens.