Repassivation and Crack Propagation of Alloy 600 in 288°C Water

Abstract Polarization and repassivation behaviors of alloy 600 (UNS N06600) were evaluated at 288°C in 0.1 M boric acid (H3BO3) titrated with sodium hydroxide (NaOH, pH25°C = 7.9) as a function of dissolved hydrogen (0 cm3/kg to 48 cm3/kg [0 ppm to 2.7 ppm] H2) and Zn (0 wppb and 60 wppb). 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 −800 mVSHE to −550 mVSHE, with addition of H2. At 0 cm3/kg H2, dissolved Zn at 60 wppb reduced the current density at ∼ −650 mVSHE. However, 60 wppb Zn did not affect repassivation kinetics at 0 cm3/kg and 48 cm3/kg H2. Repassivation kinetics experiments conducted slightly above the open-circuit potential (EOC) revealed a monotonic decrease in the oxidation current transient with increasing H2 at short times. Reduced current transients at higher levels of...