Alloy X-750 condition HTH stress corrosion crack growth rate (SCCGR) tests have been conducted at 360°C (680°F) with 50 cc/kg hydrogen as a function of coolant pH. Results indicate no appreciable influence of pH on crack growth in the pH (@ 360°C) range of ~6.2 to 8.7, consistent with previous alloy 600 findings.1 These intermediate pH results suggest that pH is not a key variable which must be accounted for when modeling pressurized water reactor (PWR) primary water SCC. In this study, however, a nearly three fold reduction in X-750 crack growth rate was observed in reduced pH environments (pH 3.8 through HCl addition and pH 4-5.3 through H2804 addition). Crack growth rates did not directly correlate with corrosion film thickness. In fact, 10x thicker corrosion films were observed in the reduced pH environments.

Subject
Acids, Crack growth, Water, Corrosion rate, Nickel based alloys, Autoclaves, Oxide films, Coolants, Acidity, Purification, Stress corrosion cracking, Conductivity, Hydrogen
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2003
Association for Materials Protection and Performance (AMPP)
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