An Accessible Way to Establish Reliability and Expected Time-to-Failure for Cold Standby Redundant Systems Subject to Periodic Inspections

Cold standby systems subject to periodic inspections are widely applied in industry. However, the establishment of system reliability, expected time to failure, and appropriate time interval between inspections in a form accessible to industrial and maintenance engineers are still challenging issues. This paper aims to develop equations that solve this problem based on an analysis of expected exposure time for active and redundant components. A table and a general analytic expression along with graphs were elaborated to allow for the establishment of the appropriate time interval between inspections, given the level of reliability required and the number of standbys available. The main advantage of the results presented in this paper is the ability to conduct the reliability evaluation without the use of complex formulations such as Markov process or Laplace transforms that are usually beyond the skills of the industrial and maintenance staff. Also, a comparison with the exact solution using probability theory is presented, and it is proved that the method developed in this study provides a good approximation for practical applications.