Impact of correlated component failure on age replacement maintenance policies

A primary goal of maintenance is to minimize the consequences of component and system failures. Two subcategories of maintenance actions include: Preventive Maintenance (PM) at predetermined time intervals prior to failure and Emergency Repair (ER) upon failure, where the cost and downtime of emergency repair is significantly greater than preventive maintenance. Most maintenance models developed over the past several decades assume component failures are statistically independent. This assumption simplifies calculations, but is dangerous for safety critical systems that must be maintained because correlated failures can lower the mean time to failure, increasing the probability that emergency repair will be required. This paper presents a simple method with an explicit correlation parameter to characterize the impact of correlated component failures on the optimal preventive maintenance interval of a system with arbitrary structure. This method is applied to two maintenance policies, including: age replacement to minimize cost and age replacement to maximize availability. Examples illustrate that our approach identifies optimal maintenance strategies for these policies such as cost per unit time and stationary availability despite correlated failures.