The manufacturing systems must be maintained well to keep them working with full efficiency achieving maximum yield. In addition, the regular as well as preventive maintenance is necessary in order to minimize the downtime and eventually the cost of the finished product. The review of several contributions underscores that the optimal maintenance policy plays a vital role. There are several sectors serving the manufacturing industry such as energy sector, which also need to have optimal maintenance schedule. Efficient power generation of steam and electricity will be a key part of reliable systems usually used in industrial assets, including thermal power plants. The chapter reviews an optimal preventive maintenance strategy for a steam turbine in a thermal power plant with reliability cantered maintenance -oriented cost minimization. In addition, the work associated with ageing of the equipment, possible failures, and importantly the optimal schedule of equipment replacement is also discussed. The multi-objective optimization solution approach for the best sequence of jobs, optimal production rate and optimum preventive maintenance time is also discussed in very details. A Bayesian approach analysing data for probabilistic prediction of structure failures is also quite important application. Its applications are discussed with real world case studies.