An analysis method for reliability assessment of repairable mechanical systems is presented in the context of the hot strip mill section of large steelworks. The reliability analysis process is defined and operated using a three-level modelling procedure, each of which functions within a different time base, thus enabling the timely identification of potential deviations in reliability performance. The main modelling approach deployed is based upon the Power Law Process, which is embedded within an automated analysis tool. The efficacy of each of the deployed modelling process is determined by the application of appropriate statistical tests. The results from this process are used to enable an in-depth analysis of why the reliability performance of the system under review has changed. A practical application is presented with reference to two strip coilers that operate within the hot strip mill. The approach is, however, generic and would be applicable to any large-scale mechanical repairable system. Copyright © 2013 John Wiley & Sons, Ltd.