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Dealloying was detected in Monel 400 steam generator (SG) tubes in CANDU® reactors. We use Thermo-Kinetic E-pH diagrams (TK diagrams) to find likely conditions for dealloying of Monel 400 and Alloy 800. Subsequently, immersion tests were conducted under these conditions, to validate predictions and investigate the degradation mechanism. Monel 400 showed selective dissolution of nickel at pH = 6 at 85 °C, with the surface covered in redeposited Cu2O oxide. The dissolution of nickel in the form of acetate complexes appeared to initiate dealloying in Monel 400, leading to the formation of intergranular corrosion. On the other hand, no dealloying was observed in the Alloy 800 coupon under these conditions, attributed to the presence of a protective chromium oxide layer on the surface.

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Comparing the Dealloying Behaviour of Monel 400 and Alloy 800 in Acetate Solutions

  • 会议论文

  • 发表日期：

    2025年

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  • Mohammad Amin Razmjoo Khollari,
  • Hamid Zebardast,
  • Edouard Asselin

摘要

Dealloying was detected in Monel 400 steam generator (SG) tubes in CANDU® reactors. We use Thermo-Kinetic E-pH diagrams (TK diagrams) to find likely conditions for dealloying of Monel 400 and Alloy 800. Subsequently, immersion tests were conducted under these conditions, to validate predictions and investigate the degradation mechanism. Monel 400 showed selective dissolution of nickel at pH = 6 at 85 °C, with the surface covered in redeposited Cu2O oxide. The dissolution of nickel in the form of acetate complexes appeared to initiate dealloying in Monel 400, leading to the formation of intergranular corrosion. On the other hand, no dealloying was observed in the Alloy 800 coupon under these conditions, attributed to the presence of a protective chromium oxide layer on the surface.