Abstract: For systems in which symptoms of failure is delayed and the possible failure can only be detected through inspection, replacement probability and expected lifespan are analyzed by considering imperfection of the inspection in normal state, imminent failure state and failed state, respectively. An optimal inspection model is proposed to minimize the total mean maintenance cost. Influence of system failure rate, maintenance cost and imperfect inspection on the optimal inspection interval is illustrated with a practical example, showing effectiveness of the modele.

Key words: delay-time, inspection model, imperfect inspection, maintenance optimization