On determining optimal inspection interval for minimizing maintenance cost

The majority of system failures do not occur without any warning signs. This is especially true for failures caused by degradation. By examining the failure-critical indexes during scheduled inspections, actions can be taken to address degraded components and prevent big losses due to failures. In this paper, we assume that an imminent failure can be noticed when an inspection is conducted during a short time period right before the failure. Clearly, by conducting frequent inspections, failures can always be detected and prevented. However, the total inspection cost will be very high if the inspection interval is too short. On the other hand, if the inspection interval is too long, a coming failure may not be effectively detected and the total cost due to failures will be high. Therefore, an optimal inspection interval balancing these two costs needs to be identified. A model for determining the optimal inspection interval to minimize the maintenance cost is proposed in this paper. The analytical solution of the model is provided and compared with simulation results. The proposed method is especially useful for process industries such as oil and gas refineries, food processing and pharmaceutical manufacturing. By conducting optimal inspections for components with degradation characteristics, failures will be prevented, maintenance cost will be reduced and the process throughput can be improved.