Imaging Autoclave Development for In-Situ Optical Measurement of High Temperature Aqueous Corrosion Processes P. M. Wood, J. A. Duff , T. J. Marrow Materials Performance Centre, School of Materials, The University of Manchester, Manchester, UK Abstract Stress corrosion cracking, oxidation and high temperature aqueous corrosion are life limiting factors in many nuclear process plant components. An Imaging Autoclave has been developed to study these processes, in-situ. The system combines refreshed-loop high temperature and pressure aqueous testing facilities under dynamic loading, with the optical techniques of Digital Image Correlation and Raman Spectroscopy. This paper reports an in-situ study of stress corrosion crack nucleation and growth in Stainless Steel under simulated BWR environments, using digital image correlation. This allows crack opening displacements to be measured that are below normal optical resolution. The aim is to measure crack propagation rates and determine nucleation sites. 1 INTRODUCTION Stress Corrosion Cracking (SCC) and high temperature aqueous corrosion are significant degradation processes in many components in the nuclear power industry and in process plant. In these environments failure of structural mechanisms presents a substantial hazard to both safety and economic performance. Uncertainties in the kinetics of these damage mechanisms and their sensitivity to microstructure have a strong influence on lifetime prediction and arise due to both the complexity of the oxidation mechanisms and the difficulties of making in-situ experimental observations [1]-[4]. Some materials (e.g. stainless steels) used in these systems are generally resistant to corrosion by virtue of a thin self-healing film of oxide, but may be prone to cracking and localised corrosion under certain conditions [5], [6]. Other materials (e.g. zirconium alloys) undergo quite complex general corrosion mechanisms, with the development of thick oxide layers [7]. Our ability to study both the protective films and the development of thick oxide layers in conventional studies is limited by the need to remove the sample from the high-pressure, high- temperature aqueous environment in order to perform the examination under ambient conditions [5], [8], [9]. For environmentally assisted cracking, it can be very important for the sample to remain in the active environment throughout the observation of the cracking process, as the kinetics of crack development are sensitive to the development of the crack tip chemistry, which may differ from the bulk environment [10]. Interruption of testing for examination may interfere with this, and provide inaccurate measurements of crack development rates. It is highly desirable to be able to “see” into the sealed chamber, which is usually used for high temperature and pressure autoclave testing.