Abstract
This paper describes a research program of stress corrosion cracking (SCC) of Inconel Alloys 600 and 690 in all-volatile treated (AVT) water. Specimens of Alloys 600 and 690 were exposed to AVT water at 288°, 332°, 343°, and 360°C. Alloy 600 generally resists SCC in high-purity water under normal service conditions but is susceptible under other specific conditions. In general, mill-annealed Alloy 600 is more susceptible than stress-relieved material. Susceptibility to SCC increases rapidly with increasing exposure temperature. Very high stresses (near or above yield) are required to induce cracking in AVT or other high-purity waters. Most of the data obtained in this research effort were for Alloy 600; Alloy 690 did not fail by SCC. Longitudinally-oriented, shallow (e.g., 0.02 mm) crack-like defects became evident on Alloy 690 split-tube U-bend specimens after autoclave exposures. These defects on the 690 specimens were from three to ten times longer after exposure than similar defects found on unexposed Alloy 690 specimens. However, in cross section, the morphology of these defects was not classic SCC. The observed longitudinal lengthening of these defects on the Alloy 690 split-tube U-bend specimens may have been the consequence of these pre-existing defects opening-up upon exposure to the elevated temperature water.
