This publication is set within the context of current trends whereby nuclear power plants (NPPs) are extending their operation beyond their original licence period. Complexities, including the fact that older NPPs may now be in a better technological condition than when they first went into operation, are considered. This publication addresses material degradation, in particular flow accelerated corrosion, with details of past incidents. The main results and lessons learned from incidents or accidents associated with material degradation are identified wherever weaknesses in the associated management processes of NPP operation have been involved. The aim of this publication is to highlight what operators, owners and regulators should do to prevent or decrease the risk of occurrences and to enhance maintenance and inspection activities in the future.