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Abstract
Long term exposure of austenitic nickel based alloys in the primary water of pressurised water reactors leads to the development of an oxide film that is generally considered to influence the stress corrosion cracking behaviour of the alloys. The structure, composition and thickness of the film depend on the chemical composition of the alloy and the exposure conditions. Previous laboratory tests have indicated that zinc can lower the susceptibility to initiation of primary water stress corrosion cracking of Alloy 600. In the present work, oxide films have been grown on polished samples of Alloy 600 (15 × 20 × 1 mm) under simulated beginning of cycle primary water at 303°C for periods between 485 and 725 h and their morphology, chemical composition and corrosion behaviour examined. Layers oxidised under stable chemical conditions were less porous and showed higher corrosion resistance. Samples oxidised for longer times showed higher transpassive potentials. Initial results from electrochemical data showed an influence of zinc on the corrosion susceptibility of Alloy 600 that requires further evaluation.