A Critical Comparison of Alternative Risk Priority Numbers in Failure Modes, Effects, and Criticality Analysis

Abstract

Risk priority number (RPN) is a widely used approach, and it is a powerful means to assess the criticality of modes in a failure modes, effects, and criticality analysis (FMECA) worksheet. In the application of the traditional FMECA, the RPN is determined to rank the failure modes; however, the method has been criticized several times for having many drawbacks and weaknesses, such as the presence of gaps in the range of admissible values, the duplicates value provided by different combinations of the base factors, and the high sensitivity to small changes. This paper analyses and compares some alternative RPN formulation proposed in the literature to overcome these limits. This paper takes into account only the alternative RPN, which proposes a powerful solution without increasing the computational complexity and remaining coherent to the classical idea included in the international standard IEC 60812. In order to compare the advantages and disadvantages of these alternative RPNs, an FMECA was developed for a heating, ventilation, and air condition (HVAC) system in railway application. The critical analysis of the comparison can provide recommendations and suggestions regarding the choice of the alternative RPN based on the type of application. Finally, this paper takes into account the scales reduction of possible values related to the parameters (i.e., occurrence, severity, and detection), which influence the assessment of the RPN. This approach allows the designers to mitigate the drawbacks related to the full scale and provide an easier and faster assessment of the scores to evaluate the criticality analysis and prioritization. INDEX TERMS FMECA, railway engineering, reliability theory, risk priority number.

Comparison and Verification of Reliability Assessment Techniques for Fuel Cell-Based Hybrid Power System for Ships

“…Afterwards, the QS-9000 standard was established by the United States automobile industry, and FMEA was introduced in all industries, including shipbuilding [4]. The FMEA method prioritizes resources, ranks risks, and creates an activity and control plan to analyze the target system [5,6], thereby analyzing failure types and their influence and examining improvement measures with consideration of criticality [17].…”

“…To assess safety in the ship construction stage, a hazard identification and risk analysis (HIRA) is conducted to identify and evaluate the risk of the system installed in a ship. Specific evaluation ranks risks, and creates an activity and control plan to analyze the target system [5,6], thereby analyzing failure types and their influence and examining improvement measures with consideration of criticality [17].…”

“…(5) Provide a basis for establishing sector-specific measures to eliminate or reduce defects. (6) Enhance efficiency by verifying design and production problems. Figure 1 illustrates the typical FMEA process.…”

“…It is extensively used to assess the design, process, and system risks across all industries including the shipbuilding and marine sectors.FMEA is advantageous in that it enables systematic analysis using simple methods. The evaluation criteria for the expected severity, occurrence, and detection are established using the risk priority number (RPN) technique, and the failures for individual components are assessed [5,6]. These results are combined to obtain the criticality.…”

A Novel Approach to Support Failure Mode, Effects, and Criticality Analysis Based on Complex Networks

“…On the basis of the CEI EN 60812 standard [ 6 ], FMEA is a systematic procedure for the analysis of a system to identify potential failure modes, and their causes and effects on system performance. On the other hand, Criticality Analysis plans and focuses the maintenance activities according to a set of priorities by giving failures with the highest risk the highest priority [ 7 ]. Carrying out a typical FMECA, a complex product can be considered as a system, and the system is divided into several subsystems based on the fundamental principle of functional independence.…”