FMEA (Failure Mode Effect Analysis) is one of the most popular methodologies for the analysis of failure risks of systems. It is a qualitative, quantitative and corrective method.
The forefather of analysis methodologies, FMEA, originated in the United States in the late 1940s, with the introduction of the MIL-P-1629 military procedure (Procedures for Performing a Failure Mode, Effects and Criticality Analysis), with the aim of classifying failures according to their impact on mission success and on the safety of personnel and equipment. In the 1960s it was applied by NASA to the Apollo space missions. In the 1980s and 1990s it was used by Chrysler, Ford, and General Motors, sponsored by USCAR (United States Council for Automotive Research), who came to formalize a common procedure for implementing FMEA. Currently, the use of FMEA is required by several quality management systems. It is one of the main components of the PPAP (Production Part Approval Process) and it is also applied as part of the Six Sigma methodology.
FMEA is a tool for risk analysis and management in both project and process phases. The risk management strategy of FMEA is based on checking the reliability characteristics of a system from a qualitative point of view, also allowing the evaluation of other aspects such as maintainability and safety. FMEA is a failure prevention tool, a project development methodology, and is used in a variety of areas related to management quality assessment and analysis of production and administrative processes. Very often it is applied to small parts of systems for the analysis of behavior in the presence of single faults. Typical is the use in plant engineering to verify the behavior of pumping systems with several pumps in parallel.
FMEA techniques aim to search for potential defects, the effects that these defects may cause, the causes and the related corrective actions, both in the study of a new product and in an innovation and improvement plan for the maintenance of existing plants. In general terms, the product or system is broken down into different units or functional areas and studied by different experts who contribute to its creation or maintenance. This phase of teamwork is one of the most important for the dissemination of knowledge within the group. Each function involved in the project must produce clear documentation of the requirements that the product or system must meet. The set of these contributions represent a real dossier that includes the requirements and characteristics of the product or plant system. The benefits of FMEA include savings on development costs, test scheduling, developing a preventive maintenance strategy, reducing unnecessary controls in production, and availability of testing and validation requirements.
FMECA evolution
A well-known evolution of FMEA is the FMECA (Failure Mode Effect Critical Analysis) technique. This involves the search for potential defects of each basic function among those highlighted (e. g. absence, stoppage, degradation, untimely intervention of a given function). It also includes the determination of the effects and causes of defects, with indications of their criticality and the development of a ranking of critical defects. The FMECA analysis can examine similar products or plants, detecting the degree of defect on the basis of three parameters: P (Probability of occurrence), G (Severity of defect), R (Detectability, i.e. the probability that the defect can be detected). A criticality index is then calculated equal to P x G x R. Numerical limits are then set, beyond which the defect must be corrected or repaired.
We are therefore talking about a methodology which involves drawing a general framework of operation of the plant, defining its most frequent failure modes and which allows to proceed either from a detailed information to arrive at a synthesis (bottom-up), or to do the opposite (top-down).
FMECA, in other words, makes it possible to identify the parts of the system that are weaker from the point of view of reliability and to understand the nature and extent of the effects associated with the malfunctioning of those parts. As a result, a priority and hierarchy are established in the maintenance work aimed at increasing the availability of the machine or plant. The FMECA methodology achieves the expected results of improving the reliability, safety and availability of plants at controlled cost only if the described implementation procedure is strictly followed.
