Top RPN's, do you use Values or Percentages?
April 23, 2014
A discussion of best practices for evaluating and prioritizing RPN values.
FMEA has been established as an invaluable tool to prevent failures from ever reaching the customer and increase the reliability of a product before it is sold.
To improve quality the emphasis is on improving Occurrence, Detection, and RPN rankings.
A company may set a threshold for the RPN, with the intention to address any RPN over this specified value. However, it is often the case that many RPN values that would normally exceed the threshold are manipulated so that the RPN falls below the threshold to avoid having to document an action. Also, even the most accurately calculated RPN values may fall below a specified threshold and so continuous improvements are not made. These examples are where companies frequently run into trouble.
Take for example, where RPN's over a threshold of 100 are considered urgent. The Potential Effect of a Failure Mode for this example is assigned a severity ranking of 7. It is established that the potential cause of this failure mode has a low occurrence with a moderate detection rate and assign an occurrence ranking of 3 and a detection ranking of 5. The RPN calculation is 7 x 3 x 5 = 105. This exceeds our threshold and is flagged as a high risk. However, just by improving the detection ranking to 4, the RPN is now calculated at 7 x 3 x 4 = 84, below the threshold to be considered a high risk.
Instead of attending to RPN over a pre-determined threshold value, concentration could be level at for example the top 20% RPN’s or continuous improving the top 5 RPNs regardless of the RPN value. The continuous improvement plan may be established at a document, group, or company-wide depending on what best suits your team. In this way there is continuous improvement to quality and that remains the primary focus.
We have recently introduced new and improved RPN reporting features. The report now includes the ability to include row numbers, functions, requirements, and Severity x Occurrence values. The algorithm for collecting and ordering information has significantly been improved and this will result in faster reporting.
Under report options, you will find additional selections including a feature for selecting top percentage RPN’s as well as top RPN values. We have also added additional functionality for highlighting these in red, amber and green. You may also select to include all documents or specific documents to be included in the results.
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