Optimised asset replacement strategy in the presence of lead time uncertainty

This paper develops an optimal replacement strategy for capital intensive equipment with long delivery lead time. The strategy is based on an extended version of the real options approach to repeated replacement decisions, in which the goal is to determine the operating cost and delivery lead-time conditions upon which a replacement should be ordered.The real options approach to capital replacement problems is superior to traditional net present value (NPV) approaches, as it values of the option to adapt decisions based on current (rather than predicted) system conditions. However, previous applications of the real options approach to repeated replacement have not considered the impact of long and uncertain lead times, and have therefore focused on when to replace rather than when to order. Delivery lead times are an important consideration in an expanding mining sector in which demand for heavy mobile equipment (HME) exceeds the capacity of suppliers to provide the equipment in a timely manner.The inclusion of a lead time element results in a decision with an “option” period and an “option-less” period. Simulations are used to demonstrate the improved outcome of real options based replacement strategies compared with those derived using a traditional NPV approach, both with and without lead times. Further the performance of the order placement strategy with different boundary conditions, bounded and reflecting, is explored. No appreciable difference in performance of these strategies was identified. The optimal order placement strategy incorporating delivery lead times is displayed on a simple chart which is accessible to fleet management personnel.