FMEA (Failure Mode and Effect Analysis )

FMEA
Failure Mode and Effect Analysis

The Failure Mode and Effect Analysis (FMEA) is an Engineering Technique used to define, identify and eliminate known and/or potential problems from a system. The FMEA is an ongoing process that should start as a part of the first Design Review and continue throughout the life of the product.

The failure mode is a function of the part number. In general, each component part number in a system is analyzed to determine its possible failure modes (open, short, mechanical failure etc.). Every part has numerous potential failure modes and theoretically, there is no limit as to the depth one could go. Practically, there is a point of diminishing returns where the added cost exceeds the benefits derived. It is OK to combine similar failure modes if they have the same effect, they can always be separated for finer resolution if necessary in the future. The initial FMEA should include all of the system components that would be repaired or replaced during a maintenance action. Additional components and failure modes should be added as failures occur.

The effect of a part failure depends upon the function of the part in the system. Two valves may have the same part number but the effect of a failure will depend upon what the valve is controlling. Therefore, it is very important that each system component be assigned a unique symbol or designator that is completely independent from the part number. The system schematic is the key document used to determine the effect of a failure of a specific part, in a specific failure mode. The FMEA considers each part and determines the effect that each failure mode will have on the overall system.

The severity of a potential failure is represented by the variable S and is assigned a value between 1 & 10, where 10 is the most severe. The occurrence of the failure (Relative Failure Rate) is represented by the variable O and is assigned a value between 1 & 10, where 10 is the highest failure rate. The ability to detect a failure is represented by the variable D which is assigned a value between 1 & 10 with 10 being the most difficult to detect. The relative importance of a failure modes represented by its RPN number is calculates as RPN = S*O*D.

The FMEA process develops several very useful databases that provides manufacturers with the basic tools necessary to control the quality of their product.

RPN Report
Failure modes are sorted by RPN number to identify and prioritize the issues that should be addressed as potential product improvements.
FMEA Report
Provides a record of the various kinds of failures that the system is subject to. The FMEA database can be queried to generate special reports concerning system performance.
Parts List Summary
Provides an easy to use Part Symbol vs. Part Number Cross Reference.
Part Number Summary
Inventory and count Part Numbers used in the system.

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