This publication addresses trends and patterns in material degradation as a function of nuclear power plant ageing, which is a key topic in the regulation of ageing management programmes, codes and standards, reliability and integrity management, and the many supporting research programmes. It documents insights reached from operating experience involving passive metallic components in commercial nuclear power plants during periods of extended operation and long-term operation. These evaluations are enabled by an NEA joint project entitled the Component Operational Experience, Degradation and Ageing Programme (CODAP). Established in 2002, the project has developed a comprehensive database on the operating experience with material degradation mechanisms that have produced failures of piping and selected non-piping passive components. Examinations of graphical plots were performed to reach insights about the different material degradation mechanisms as a function of plant age. The report also includes recommendations for future work.