The corrosion of Alloy 690 in high-temperature aqueous media – thermodynamic considerations

Alloy 690 (N06690) is a technologically important material that contains a minimum of 58 wt% nickel, 27.0–31.0 wt% chromium and 7.0–11.0 wt% iron. A thermodynamic analysis of the expected behaviour of Alloy 690 in high-temperature (573 K) aqueous media has been carried out. The stabilization or destabilization of chromium, iron and nickel in the alloy has been taken into account using a variation of regular solution theory. Formation of polymetallic corrosion products, such as spinels, has also been considered. Reaction path calculations were performed for Alloy 690 at 573 K. The results are similar to those found from comparable calculations for the more widely used Alloy 600. Comparisons are made with available experimental observations.