Joint Optimization of Preventive Replacement and Spare Part Ordering for Single-Unit Systems With Mixed Inspections

This paper introduces a unified policy for preventive replacement and spare parts ordering for systems whose degradation follows a gamma process. It considers N$N$ types of orders, each with variable lead times, and employs a combined inspection approach that integrates sequential and opportunistic inspections to monitor the system condition. The proposed policy coordinates the scheduling of spare parts orders, preventive replacements, and inspections based on the current state of the system. To assess its performance, the renewal reward theorem is used to calculate the average cost rate, the average availability, and the mean time to the first failure. The objective is to minimize the average cost rate, achieved through a grid search algorithm that identifies the optimal inspection and ordering policy. The effectiveness of the proposed policy is further validated by comparing its performance with three other policies in existing research works.