For continuous operating units such as petrochemical plants, the production loss due to downtime is high, and the economic profitability is conditioned by the implementation of suitable maintenance policy that could increase the availability and reduce the operating costs. In this paper, a preventive maintenance plan approach is proposed for a multi-component series system subjected to random failures, where the cost rate is minimized under general lifetime distribution. The expected total cost is given by corrective and preventive costs, which are related to the components, and by the common costs related to the whole system, especially the production loss during system shutdown. When the system is down, either correctively or preventively, the opportunity to replace preventively non-failed components is considered. A solution procedure based on Monte Carlo simulations with informative search method is proposed and applied to the optimisation of the component replacement for the hydrogen compressor in an oil refinery. (C) 2009 Elsevier Ltd. All rights reserved.