Calculation of Age-Replacement with Weibull Failure Times

An age-replacement policy with Weibull failure times is considered. It is troublesome to compute an optimum replacement time numerically. Upper and lower bounds of an optimum time are given in simple terms of replacement costs and parameters of a Weibull distribution. A numerical example shows that the approximation can be used when the ratio of the replacement cost for a failed unit to that for a nonfailed unit is large. The approximation is best when the optimum age of replacement is small.