A CBM policy for systems subject to finite maintenance times

This paper proposes a condition-based maintenance (CBM) policy for a gradually deteriorating system that could only be repaired for finite times. Periodical inspections are performed to measure the degradation level, and the system is preventively or correctively repaired when the level reaches the preventive and failure threshold, respectively. Both preventive and corrective maintenance actions in this paper are considered imperfect. After each maintenance action, the system is restored to a 'better than old' state but the effectiveness of maintenance is stochastically reduced as its number increases. In this way, the system can only keep its desired function for a very small period after sufficient number of maintenances. Therefore, the system cannot be in service for infinite duration and its usage life which is defined as number of maintenance actions needs to be determined systematically. In this respect, system service life is jointly optimized with periodical inspection interval and preventive threshold by minimizing life-cycle cost rate. A nonhomogeneous Markov model is developed to describe the evolution of maintained system and corresponding cost function. Numerical examples are presented to illustrate the application of this maintenance policy.