Alloy 22, a nickel based alloy rich in chromium and molybdenum, shows an outstanding corrosion resistance in most environments. Studies carried out in chloride solutions under aggressive environmental conditions, reported crevice corrosion behavior of this alloy and also inhibition effect of several oxyanions, such as nitrate, sulfate, carbonate and bicarbonate. Since there is little information regarding phosphate effect, the objective of this work is to study its effect on the corrosion behavior of Alloy 22.

Electrochemical tests were performed to study uniform and localized corrosion of Alloy 22 in deaerated aqueous solution of 1M NaCl and 1M NaCl with different phosphate additions at 90°C and pH near neutral. The anodic films obtained were studied by SEM/EDS. Comparison of the results indicates that the passivity potential range depend on phosphate presence and might be related with the incorporation of the anion in the passive film. Results of the tests performed with PCA specimens showed a strong inhibitory effect of phosphate ions on chloride induced crevice corrosion of Alloy 22.

Subject
Corrosion rate, Nickel based alloys, Repassivation potentials, Sodium chloride, Corrosion products, Crevices, Phosphates, Film formation, Crevice corrosion, Salt concentration, Localized corrosion, Alloys, Corrosion potential
Keywords:
Localized corrosion, N06022, repassivation potential, inhibition, phosphates
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2010
Association for Materials Protection and Performance (AMPP)
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