A competing risk model for the reliability of cylinder liners in ship Diesel engines

Ship Diesel engines are requested to have high reliability and availability levels in order to satisfy strong in service requirements. A critical component of heavy-duty Diesel engines is the cylinder liner whose failure can occur mainly due to wear or thermal crack. In this paper a competing risk model is proposed to describe the failure process of a cylinder liner under the realistic hypotheses that a) the liner fails when the first of the competing failure mechanisms reaches a failure state, and b) the failure mechanisms proceed independently of each other. The wear process is described through a stochastic process, whereas the failure time due to the thermal crack is described by the Weibull distribution. The proposed model enables the analyst to determine the hierarchy of the failure mechanisms for every given age and wear level of the liner. It has been applied to a real data set relative to 30 cylinder liners of Sulzer RTA 58 engines equipping twin ships of the Grimaldi Group. Estimate of the liner reliability and of other quantities of interest under the competing risk model is obtained. Again, we obtained the probability that the liner fails due to one of the failure modes when both of these modes act, as well as the conditional failure probability and mean residual lifetime, given the survival age and the accumulated wear.