Criticality evaluation for spare parts initial provisioning

Abstract

Based on the experience of operations and support, the demands for spare parts are usually uncertain and excess stocking is expensive. The provisioning of spare parts frequently experiences variations over a system's life cycle. The provision of insufficient critical items results in costly system downtime. However, the excess of stock can also be costly. The purpose of this paper is to develop an efficient and effective evaluation method to facilitate the initial provisioning of the critical spare parts that have significant impacts on the operational availability and total life-cycle cost as well. The criticality of spare parts is utilized to estimate an appropriate amount of items for the initial provisioning so that the optimal maintenance plan can be achieved. The repair rates of critical items are analyzed and applied to calculate the turn-around-time of repair items. Criticality is used to determine the importance of each end-item in order to accurately derive the initial spare parts lists. The effects of turn-around-time on spares are discussed and applied to evaluate the spare parts criticality. The failure mode, effects and criticality analysis (FMECA) is modified to incorporate both grey relation number (GRN) and turn-around-time (TAT) with the calculation of risk priority number (RPN) of the spares. A system under development is selected to demonstrate the applicability of the evaluation method. The results indicate that both the criticality of spares and the turn-around-time of repairable items have significant influence on the cost-effectiveness curves of the system. Finally, an efficient procedure for the spare parts initial provisioning is suggested to reduce the total life-cycle cost and improve the effects of maintenance planning.