Purpose – The purpose of this paper is to present a multi criterion failure mode effect and criticality analysis for coal-fired thermal power plants using uncertain data as well as substituting the traditional risk priority number estimation method. Design/methodology/approach – Grey-complex proportional assessment (COPRAS-G) method, a multi criteria decision making tool is applied to evaluate the criticalities of the failure modes (alternatives). In this model the criteria (criticality factor) against each alternative are expressed in grey number instead of crisp values. Findings – Rupture failure of the straight tube of economizer (ECO) due to erosion is the highest critical failure mode whereas rupture failure of the stub of ECO due to welding defect is the lowest critical failure mode. Originality/value – This paper incorporates human and environmental factors as additional factors which also influence the failure modes significantly. The COPRAS-G method is modified according this problem. Uncertainty in the scoring of criticality factors against each failure mode by various maintenance personnel is expressed in grey numbers.

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Reliability of a system varies under different operating conditions like temperature, humidity, dust, maintenance facilities, maintenance personnel skill, operator skill, etc., called "covariates." Under poor operating environments the reliability decreases. Therefore, for precise estimation of system reliability, the influence of various covariates is included. This article aims to investigate the effect of five covariates on the reliability characteristics of a coal-fired boiler using the Weibull proportional hazard model, a semiparametric reliability model. The results from the case study indicate that there is a substantial decrease in reliability. A preventive maintenance program based on this calculated reliability will be safer to use.

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