Failure modeling and maintenance optimization for a railway line

This paper presents a model for deterioration and repair of a railway line. The critical failure is “broken line”. Two main failure mechanisms are considered: either shock failure, i.e. an immediate critical failure (without “warning”), or the critical failure occurs as the result of a degradation process, i.e. a degraded failure (crack) occurs first. Various types of inspection and maintenance are performed on the line. Inspection by Ultrasonic Inspection Cars (UIC) is carried out at regular intervals, and there is a probability q that the inspection shall detect a degraded failure. Additional inspection will be initiated on a segment of the line if degradation above a certain level is observed. A piece of rail which is degraded is more prone to suffer a critical failure (broken line), and when the degradation has reached a certain level, this will require immediate repair. The degradation/repair process within the fixed inspection interval is modeled as a time continuous Markov chain. Also the change of state implemented at the end of an inspection interval is modeled as a (time discrete) Markov chain. The model is based on actual inspection and failure data for a specific railway line in Norway. These data are used to estimate the parameters of the model. The given failure/maintenance model and estimation technique should generally be useful for systems that experience deterioration and are subject to imperfect inspection.