Alternative scales in reliability models for a repairable system

In an industry, the lifetime of a technical system is often assessed according to its accumulated throughput/usage e.g., the performance of a Blast Furnace in terms of accumulated quantity of its product, the lifetime of a vehicle in terms of accumulated number of miles it has travelled. Most of these systems are repairable systems. The failure process of a repairable system is conventionally measured in the time domain also termed as a time scale in the literature. Nevertheless, the lifetime of some repairable systems and their failures may be measured in terms of their throughput/usage. Therefore, it makes sense to quantify their failure processes in terms of throughput/ usage which may be better indicators than time, of system failure and reliability. Time, usage or a combination of both time and usage may be used as alternative domains/scales of measurement for modelling the failure process of a repairable system. This paper proposes such alternative scales in reliability models for a repairable system. A method is devised in the paper to identify the better alternative scale to model the failure process and thus identify the appropriate scale to assess the system reliability. Industrial failure data are used to illustrate the proposed method.