Optimal Age-based Inspection Scheme for Condition-based Maintenance using A* search algorithm

Abstract

In condition-based maintenance (CBM) with periodic inspection, the system is preventively replaced if failure risk, which is calculated based on the information obtained from inspection, exceeds a pre-determined threshold. The determination of optimal replacement threshold is often based on minimization of average maintenance costs per unit time due to preventive and failure replacements over a long time horizon. It is often assumed that inspections are performed at equal time intervals with no cost. However, in practice, inspections require labours, specific test devices, and sometimes suspension of operations and, thus, it is reasonable to inspect less frequently during the time the system is in its early age and/or it is in healthier state, and, perform inspections more frequently as time passes and/or the system degrades, namely, an age-based inspection scheme.

This paper proposes a novel two-phase approach for determination of optimal replacement threshold and optimal age-based inspection scheme for CBM such that total long-run average cost of replacements and inspections is minimized. First, it takes into account failure and preventive replacement costs to determine the optimal replacement threshold assuming that inspections are performed at equal time intervals with no cost. This assumption is, subsequently, relaxed and its consequences on total average cost are evaluated using a proposed iterative procedure based on A* search algorithm to obtain the optimal age-based inspection scheme. The proposed approach is illustrated through a numerical example.