Predictive codes facilitate the surveillance of wall thinning effects

The surveillance of wall thinning effects in piping and vessels is one of the key issues for the safe operation of nuclear power plants, as wall thinning may cause spontaneously occurring component failures. Wall tinning is typically caused by the following flow-induced degradation mechanisms: Flow-accelerated corrosion (FAC), liquid droplet impingement erosion (LDI) and cavitation erosion (CE). Areas affected by wall thinning are difficult to locate, as this degradation process occurs only locally for specific conditions of flow, water chemistry and temperatures. For the safe identification of system areas which are sensitive to wall thinning, a comprehensive plant-wide strategy needs to be applied, considering the effects and superposition of different degradation modes. For this purpose AREVA provides the software tool COMSY which features lifetime analysis for various degradation mechanisms which are commonly experienced in mechanical components in the power generation industry. This includes a predictive degradation model for FAC, which has been further developed based on more than 30 years of research activities. Based on these predictive calculations a degradation potential can be pinpointed and quantified, subsequently targeted wall thickness inspections can be carried out. (authors)