Multistage Replacement Strategies with Finite Duration of Transfer

For failing type of equipment, two-stage and multistage replacement strategies are available in literature. The strategies bring economy by transfering failure rates from groups where the replacement cost is higher to those where it is smaller. Certain important aspects, which prevail in practice, were neglected in those works. The finite time taken for the transfer of units manifests into the down-time loss and, together with the transportation medium, gives possible failures during transfer. In this paper the effects of finite transfer time, as well as the possibilities of failures during insertion and removal of units, are considered, and the condition for multistage strategies to be more economical is derived. The role of transportation medium, the possibility of reducing the down time by inter-stage inventories and the method to arrive at optimum sizes of such inventories are also presented. The impact of these factors on the economy and the optimum number of stages are brought out. The strategies are, thus, more powerful as they cover the realities of actual situation.