Repassivation and crack propagation of alloy 600 in 288 C water
- General Electric Corporate Research and Development Center, Schenectady, NY (United States)
Polarization and repassivation behaviors of alloy 600 were evaluated at 288 C in 0.1 M boric acid titrated with sodium hydroxide as a function of dissolved hydrogen and Zn. Potentiodynamic scans measured polarization behavior, while a combination of drop-weight straining and cathodic reduction/potential pulse techniques measured repassivation behavior. Potentiodynamic scans revealed larger current densities, especially over the range from {minus}800 mV{sub SHE} to {minus}550 mV{sub SHE}, with addition of H{sub 2}. At 0 cm{sup 3}/kg H{sub 2}, dissolved Zn at 60 wppb reduced the current density at {approximately}{minus}650 mV{sub SHE}. However, 60 wppb Zn did not affect repassivation kinetics at 0 cm{sup 3}/kg and 48 cm{sup 3}/kg H{sub 2}. Repassivation kinetics experiments conducted slightly above the open-circuit potential (E{sub oc}) revealed a monotonic decrease in the oxidation current transient with increasing H{sub 2} at short times. Reduced current transients at higher levels of H{sub 2} agreed with the Pourbaix diagram showing Ni metal becoming more stable at potentials associated with H{sub 2} addition. Residual oxidation transients exhibited with 18 cm{sup 3}/kg (1 ppm) and 48 cm{sup 3}/kg H{sub 2} likely were associated with H{sub 2} oxidation on the oxide surface, which was unaffected by time. Repassivation results were consistent with recent observations of a decrease in the crack growth rate of alloy 600 in water at 288 C as H{sub 2} content increased from 0 cm{sup 3}/kg to 18 cm{sup 3}/kg, indicating slip oxidation was the mechanism for crack advance.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 449636
- Journal Information:
- Corrosion, Journal Name: Corrosion Journal Issue: 2 Vol. 53; ISSN 0010-9312; ISSN CORRAK
- Country of Publication:
- United States
- Language:
- English
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