Abstract
Separated decision-making for maintenance and spare ordering is unrealistic in the industry, so this paper aims to optimize them together. A joint policy of inspection-based preventive maintenance (PM) and spare ordering considering two modes of spare ordering, namely, a regular order and an emergency order, is proposed for single-unit systems using a three-stage failure process. If the system is recognized to be in the minor defective stage, the original inspection interval is shortened and a regular order is placed. However, replacement is undertaken preventively or correctively if the severe defective stage is identified or a failure occurs. Depending on the system state and the state of the regular ordered spare when replacement is needed, all possible scenarios are considered to construct optimization model I. The decision variables are the optimal inspection interval and the times of shortening the original inspection interval. Additionally, model II on the basis of an assumption that the spare is always ordered at time 0 is also developed. The results from a numerical example illustrated the applicability and the effectiveness of model I compared to model II, and the irregular inspection policy is validated to be cost-saving compared to the regular inspection policy.
Highlights
Condition-based maintenance (CBM) has been the most common used preventive maintenance policy in the practical industry [1]
It can be explained that more frequent inspection actions with smaller inspection t lead to higher inspection costs, but the inspection scheme with longer interval t may miss the identification of defects, resulting in a system failure and bringing about higher cost loss. It is in line with our previous studies and the practice. k = 1 means that there is an inspection plan with a fixed interval which has been assumed in most studies, and from Figure 14 it can be concluded that when the system has been detected to be in the minor defective stage, shortening the inspection interval is a better option compared with keeping it unchanged
The joint policy of inspection-based preventive maintenance (PM) and spare ordering is proposed for a single-unit system in this study, in which the three-stage deterioration process is introduced to depict the system lifetime
Summary
Condition-based maintenance (CBM) has been the most common used preventive maintenance policy in the practical industry [1] With such a policy, a system can be inspected online or offline to check the deterioration state and, some repair actions can be arranged and performed in advance to reduce the loss caused by a functional failure. Note that an assumption that a spare used for preventive or corrective replacement is always available is shared by most previous works [8,9,10]. This limits the application of these studies, since the delivery time cannot be ignored in real case. An inspection-based PM policy will be combined with spare ordering policy by considering the delivery time in this work, rather than optimizing them separately
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