Age-dependent models for evaluating risks and costs of surveillance and maintenance of components

To determine in a quantitative way how surveillance and maintenance activities are reflected in component reliability, some age-dependent models to determine risks and associated economic costs are presented which explicitly consider how activities affect the component age as a function of the maintenance effectiveness. The models are based on reliability parameters such as demand-failure probability, standby failure rate, aging rate, and degradation rate. Also introduced are the concept of `characteristic function of maintenance´ that states the relationship between maintenance effectiveness, its period, and the age setback. Several sensitivity analyses are performed on the reliability parameters and the maintenance effectiveness that allow establishment of important differences among activities with regard to their risks and costs. These models are: (1) important in maintenance improvement, particularly within the reliability centered maintenance (RCM) methodology; (2) useful in finding a degradation vs maintenance effectiveness relationship. They are used in assessing maintenance effectiveness within a program based on RCM at Cofrentes Nuclear Power Plant (Spain), where several policies of integrating surveillance and maintenance activities are analyzed