Evaluations of maintenance effectiveness on unavailability and risk

A methodology is presented for quantifying the effectiveness of maintenance on unavailability and on risk. The methodology is based on standard Markov modeling principles. What is new is the application to quantify maintenance effectiveness by explicitly quantifying maintenance benefits as well as maintenance's negative contributions. Maintenance effects are quantified by defining a degraded state for the component in addition to an operational state and a failed state which are usually defined. The maintenance model which is developed is a natural extension of the standard models used in reliability analysis and in Probabilistic Risk Assessments (PRAs). The results which are obtained can be directly used in PRAs. Applications of the methodology are presented by quantifying maintenance effectiveness on component performance and component unavailability for specific maintenance schedules