Crevice Corrosion of Nickel Alloys for Steam Generator Tubing of Pressurized Water Reactors

摘要

Ni-Fe-Cr alloys, such as alloys N06600, N06690 and N08800, are used in steam generator tubing of nuclear power reactors due to their high mechanical strength and corrosion resistance at high temperature. Failure of those alloys is associated with crevices formed between tubing and tube sheet or tube support plates, or fouling formed during operation. In this work, the crevice corrosion susceptibility of these alloys was analyzed. Crevice corrosion was studied at atmospheric pressure in 5 M, 1 M, 0.1 M and 0.01 M NaCI solutions at 30 °C, 60 °C and 90 °C using artificially creviced specimens. Alloy specimens were polarized potentiodynamically up to 300 μA (`25 μA/cm~2) and held at that current for 2 hours; then the potential scan was reversed until reaching alloy repassivation. All the alloys suffered from crevice corrosion. Test reproducibility was higher under more aggressive conditions (i.e., higher temperature and chloride concentration). The repassivation potential decreased with increasing temperature and chloride concentration indicating higher crevice corrosion susceptibility. Crevice corrosion resistance increased in the order alloy N06690 ＜ alloy N06600 ＜ alloy N08800. Corrosion potential measurements and potentiodynamic polarization experiments were performed in simulated crevice-like solutions to understand these results.