Statistical study of the critical pitting temperature of 22-05 duplex stainless steel

Using a multichannel electrochemical cell, critical potentials for passive film breakdown of a duplex stainless steel were measured at different temperatures in a 0.5 M NaCl aqueous solution. Statistical analysis shows that the transition between pitting and transpassivity does not occur at a well-defined “critical pitting temperature” (CPT) but takes place within a transition temperature interval (TTI), the width of which (∼10 to 1 °C) decreases as the size of the specimen increases. For practical purposes, the lower TTI bound appears to be the most reliable indicator of the CPT. Potentiostatic techniques were found to overestimate the CPT value compared to potentiodynamic estimations.

► Statistical analysis is applied to measurements of duplex stainless steel pitting temperature.
► Transition between pitting and transpassivity occurs within a transition temperature interval.
► TTI width decreases from 10 to 1 °C as the size of the specimen increases.
► The lower TTI bound appears to be the most reliable critical pitting temperature.
► Potentiostatic technique overestimates the CPT value compared to potentiodynamic estimation.