Corrosion Behavior of Alloy 22 in Oxalic Acid and Sodium Chloride Solutions Available to Purchase

Nickel-based Alloy 22 (UNS N06022) is used extensively in aggressive industrial applications, especially due to its resistance to localized corrosion and stress corrosion cracking in high-chloride environments. The purpose of this work was to characterize the anodic behavior of Alloy 22 in oxalic acid (COOHCOOH) solution and to compare its behavior to sodium chloride (NaCl) solutions. Standard electrochemical tests such as polarization resistance and cyclic polarization were used. Results show that the corrosion rate of Alloy 22 in oxalic acid solutions increased rapidly as the temperature and the acid concentration increased. Extrapolation studies show that even at a concentration of 10^–4 M oxalic acid, the corrosion rate of Alloy 22 would be higher in oxalic acid than in 1 M NaCl solution. Alloy 22 was not susceptible to localized corrosion in oxalic acid solutions. Cyclic polarization tests of artificially creviced specimens in 1 M NaCl showed that Alloy 22 was susceptible to crevice corrosion at 90°C but was not susceptible at 60°C.