09425 Mechanistic Studies of the Localized Corrosion of Alloy 22 in Chloride-Nitrate Solutions

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Product Number: 51300-09425-SG

ISBN: 09425 2009 CP

Author: Licai Mao, Jingli Luo, Mick Apted, Andrew Sowder, Fraser King and John H. Kessler

Publication Date: 2009

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Alloy 22 is susceptibility to crevice corrosion in concentrated chloride solutions at elevated temperature. A number of oxyanions, most notably nitrate, sulfate, and carbonate, inhibit the aggressiveness of the chloride ion. The ratio of aggressive to inhibitive anions is a key parameter in predicting the possibility of the crevice corrosion of waste packages in the Yucca Mountain repository. The results of a preliminary experimental program to study the effects of chloride and nitrate ions on the propagation and stifling of the crevice corrosion of Alloy 22 are described. A coupled-electrode technique was used to study the stifling of crevice corrosion in various solutions following artificial initiation achieved through galvanostatic polarization. The environments studied included CaCl2-NaNO3 mixtures with varying [NO3-]:[Cl-] ratio and total salinity and a solution of 5 mol·dm-3 NaCl with and without added NO3-. The test temperature in all cases was 120oC.

Even with electrochemical polarization, it was found difficult to initiate crevice corrosion in CaCl2 solutions containing nitrate. Some superficial damage was observed in concentrated solutions. In contrast, initiation occurred readily in NaCl solutions, although the coupled current decreased quickly in nitrate-containing solutions, indicating stifling of the crevice.

Keywords: Alloy 22, crevice corrosion, stifling, chloride, nitrate, Yucca Mountain