There are a number of reliability engineering tools & methodologies that are routinely used by reliability engineering professionals. In this post we will give a brief overview of the most heavily used reliability tools.
System Reliability Modeling & Reliability Block Diagrams
System reliability modeling can help systematically predict the overall reliability of a complex system, or system of systems. The Reliability Block Diagram (RBD) defines the system components and how they are dependent on each other for the overall system function and reliability. Each component is represented by a block on the diagram and is assigned a failure rate. The blocks are arranged in parallel or in series according to the design of the system or product. The RBD creates an outline of each sub system linked to functional and operational equipment and parts. Implementation of failure analysis may be predicated upon the RBD outline that highlights potential for failure.
The reliability block diagram can be rolled up from the lowest level of component to the entire end product, such as an aircraft. Using this tool allows reliability professionals to predict the reliability of an aircraft based on the reliability of the components that make up that aircraft.
Failure Mode, Effects and Criticality Analysis
Failure Mode Effects Analyses (FMEA) is a useful tool to systematically, from the bottom up, identify the potential failure modes of a product or system, identify the effects and causes of those failures and evaluate the risk associated with those failure modes.
Failure mode, effects and criticality analysis (FMECA) is used as an extension of FMEA with the addition of criticality analysis. Criticality analysis analyzes the probability of failure modes and their potential impact or severity. The result of this analysis highlights the relative highest risk and highest impact failure modes and systems so that remedial action can be taken to improve the product and lessen their chance of occurrence or their impact. FMEA and FMECA can be performed on a part-by-part basis, or on systems, or systems of systems (i.e. end products).
The benefits of FMEA and FMECA include improved designs for products and processes, resulting in:
- higher reliability
- better quality
- increased safety
- enhanced customer satisfaction
- reduced costs
- reduced warranty costs
- identification of corrective and preventative maintenance actions
Once a system or asset is in an operational environment, the FMECA analysis can be integrated into the Failure Reporting and Corrective Action System (FRACAS) in order to classify each reported failure with corresponding failure mode identified in the FMECA. This level of integration also helps discover perviously unknown failure modes, which would then drive an update to the FMECA.
Failure Reporting and Corrective Action System (FRACAS)
During the operational life of a system or asset it is essential to report and track failures over time in order to calculate the actual reliability of systems and sub-systems. This is the purpose of the FRACAS, which is usually a computerized data system where operational or flight time is documented along with any failures occurrences, analysis, and corrective actions taken. Periodically a Failure Reporting and Corrective Action Report (FRACAR) would be generated from the FRACAS to summarize the mean time between failure of various systems or subsystems, the failures that occurred and the corrective actions taken.
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