Non-periodic preventive maintenance with reliability thresholds for complex repairable systems

• The PM problems for repairable deteriorating systems are formulated.
• The structural properties of the proposed PM models are investigated.
• The corresponding algorithms to find the optimal PM strategies are provided.
• Imperfect PM activities are allowed to reduce the occurences of breakdowns.
• Provide managers with insights about the critical factors in the planning stage.

In general, a non-periodic condition-based PM policy with different condition variables is often more effective than a periodic age-based policy for deteriorating complex repairable systems. In this study, system reliability is estimated and used as the condition variable, and three reliability-based PM models are then developed with consideration of different scenarios which can assist in evaluating the maintenance cost for each scenario. The proposed approach provides the optimal reliability thresholds and PM schedules in advance by which the system availability and quality can be ensured and the organizational resources can be well prepared and managed. The results of the sensitivity anlysis indicate that PM activities performed at a high reliability threshold can not only significantly improve the system availability but also efficiently extend the system lifetime, although such a PM strategy is more costly than that for a low reliabiltiy threshold. The optimal reliability threshold increases along with the number of PM activities to prevent future breakdowns caused by severe deterioration, and thus substantially reduces repair costs.