An inspection policy for deteriorating processes using delay-time concept

A method for determining the discrete time points of inspection for a deteriorating single-unit system under condition-based maintenance is developed. The system is in a normal state, a symptom state or a failed state. A delay-time model is utilized to describe the transition of the states. The transition time from a normal state to a symptom state and that from a symptom state to a failed state are derived assuming continuous deteriorating processes based on a reaction rate model which is categorized as a failure physics model. Failed-dangerous and failed-safe probabilities of an imperfect inspection are considered. A method for minimizing the long-run average cost per unit time is formulated. The characteristics and sensitivity of the proposed method are investigated.