Optimal replacement policy with age-based inspection scheme for condition-based maintenance

In condition-based maintenance, replacement policy is often defined as a rule for replacement or leaving an item (or a system) in operation until next inspection, depending on monitoring information. The criterion for determining the time at which a preventive replacement should be performed is the minimization of average maintenance costs per unit time due to preventive and failure replacements over a long time horizon. On the one hand, higher frequency of inspections provides more information about the condition of the system and, thus, maintenance actions are performed more effectively. On the other hand, in many real cases, inspections require labours, specific test devices, and sometimes suspension of the operations and, thus, as the number of inspection increases, the inspection cost also increases. This paper proposes an approach in which preventive and failure replacement costs as well as inspection cost are taken into account to determine the optimal replacement policy and an age-based inspection scheme such that the total average cost of replacements and inspections is minimized. The proposed approach is illustrated through a numerical example.