A general isodegrading model for predicting mechanical equipment reliability and performance degradation

Abstract

This paper develops an efficient reliability degrading model, referred to as a general isodegrading model, for mechanical equipment reliability and performance prediction under the PM (preventive maintenance) policy that the number of failures in each PM cycle should be kept as near as possible the same, the operational time in each PM cycle is maximized availability, and the equipment should be overhauled or scrapped on time when the economical benefit in a PM cycle is less than the demanded level. The core of the model is that there are isodegrading rates between neighbouring PM cycles for the equipment reliability and the performance parameters optimal operational time, MTBF, output and operational cyclic number, and there is an isodegrading speed between the parameters. This model, introducing an integrated measurement–general isodegrading rate γ and an idea of demanded PM, has broken through the restriction that equipment has the same maintenance time intervals and steady-state availability as in traditional models. It combines natural reliability degradation with performance degradation, and provides a scientific basis for the reliability and performance prediction of equipment both in operation and in development. The model is effectively applied in the determination of recommended PM criteria in the first overhaul cycle of the gantry cranes used at railway terminals in China. The field inspection of the recommend criteria has proved that the general isodegrading model is practical and effective.