On the Use of Replacements to Extend System Life

We consider an extreme version of the replacement problem. A vital component of a system must be replaced before it fails, otherwise the system fails with no possibility of repairing the system. We assume that n spares are available and that the distribution of a component life is known; the objective is to schedule the replacements so that the expected life of the system is maximized. Our results range from an iterative formula for constructing the optimal schedule to more general mathematical properties of optimal schedules and expected times.