Optimization of joint maintenance strategy for safety-critical systems with different reliability degrees

In safety-critical systems, components with high reliability are required. Once a component's reliability fails to meet the minimum safety requirements, either the component should be replaced or, transferred to another system which is allowed to operate on a lower reliability level. Safety standards are not only related to the cost of maintenance, but also to the system's (wear-and-tear) and repair degrees. In this paper, two different repair degrees are discussed, and the best safety virtual age criterion is studied in order to minimize financial cost. These results are supported by numerical examples.