Modelling quality in replacement and inspection maintenance

Heterogeneity in component and maintenance quality is considered in the context of age-based inspection and replacement for a single component system. A three-state component failure model is assumed, with a defective state preceding the failed state. Heterogeneity in maintenance intervention is modelled by supposing that inspections may induce the defective state. Component heterogeneity is modelled by supposing that the population of components comprises a mixture of the weak and strong, and that the mixing proportion and cost of components vary between suppliers. Within this framework, the impact, on system reliability and cost, of switching component or maintenance supplier is determined. Broadly, our finding is that one is much more inclined to switch supplier in order to obtain higher quality maintenance than to obtain higher quality components. A gas pressure control valve is used to illustrate our ideas.