Improving the availability and lengthening the life of power unit elements through the use of risk-based maintenance planning

The reliability of power systems, in terms of uninterrupted electricity supplies, is dependent on the reliability of the system's elements, especially the generation sources and transmission lines. The reliability of a coal-fired power unit's operation is essentially affected by the unit's main components, i.e. the turbine, the boiler and the generator. According to the statistics, the boiler is the most failure-prone element of the power unit. Therefore, efforts aimed at improving the reliability must include actions that enable early diagnostics of the state of the individual devices. In this paper it has been proposed that the optimal time to perform diagnostic testing of boiler tubes should be determined using risk analysis. Using the net present value (NPV) discounted cash flow index and the avoided risk criterion, a procedure has been put forward that optimizes the time when diagnostic tests should be carried out. The method has been applied to optimize diagnostic testing of boiler tubes, where corrosion is the principal cause of damage. Methods have also been given to determine the probability of the failure of such elements.