Reproducibility of Critical Crevice Temperature (CCT) Measurements for two Duplex Stainless Steels

The critical crevice temperature (CCT) is widely used as a measure of stainless steel resistance to crevice corrosion, yet its reproducibility and statistical distribution remain underexplored, despite its importance for reliable materials selection. Potentiostatic CCT tests were conducted on SAF 2205 and Zeron® 100 duplex stainless steels (DSS) under varying conditions, such as chloride levels, with and without corrosion inhibitors, applied potential, crevice geometry, surface finish, and passivation. Each test condition was repeated eight times to assess variability. Although the average CCT depends on environment and surface condition, the statistical scatter under each condition was limited, with CCT values typically contained within a range of 3−9.5 °C (standard deviations ≤2.8 °C). Inhibitors, including sulfate and nitrate, increased both the median CCT and distribution upper bounds, while surface passivation and fine polishing also enhanced resistance to crevice corrosion. Zeron® 100 had higher CCT values than SAF 2205, within a statistical distribution of about ±4 °C. Moreover, combining surface passivation, fine polishing, and an applied potential of 550 mV (Ag/AgCl) in 0.01 M NaCl did not increase the statistical scatter and the CCT distribution remained confined within ±3.7 °C. These results confirm that CCT is a consistent threshold parameter and indicate that it can be reliably used for selecting materials for chloride service.