Fuzzy FMECA (failure mode effect and criticality analysis) of LNG storage facility

Abstract In high hazard industries like nuclear and chemical, a failure could lead to catastrophic events resulting in multiple fatalities, significant economic loss and reputation damage. Failure Mode and Effects Analysis (FMEA) is a safety and reliability analysis tool that systematically identifies the consequences of component failure on systems and determines the significance of each failure mode with regard to the system performance. FMEA uses a Risk Priority Number (RPN) for ranking the failure modes. RPN is commonly calculated as the product of the risk factors occurrence (O), severity (S) and non-detection (D) of the failure modes. When FMEA is used in criticality analysis of failure modes of components, it is also referred to as failure mode effect and criticality analysis (FMECA). Many researchers have pointed out the deficiencies of conventional risk priority number (RPN) used in FMEA. This paper describes a method for developing a fuzzy RPN (FRPN) that may rectify the limitations cited in the literature such as questionable nature of the mathematical formula for calculating RPN and the difficulties in prioritizing the RPN in the case of complex systems due to identical RPN values for different failure modes.The analysis was carried out by using fuzzy linguistic variables for occurrence, severity and non-detection and then using an if-then rule base to interconnect these variables to reach FRPN. The results obtained by using traditional FMECA and the fuzzy FMECA methods are compared. The difficulty in prioritizing the RPN in the case of complex systems such as LNG storage has been addressed in fuzzy FMECA.