Mechanical Failure-Rate Data for Low-Demand Applications
Failure-rate determination for mechanical components of an SIS is not straightforward. Several methods and recommendations are presented
Chris O'Brien, Exida Consulting
The use of safety standards, particularly IEC 61508  and IEC 61511 , has increased rapidly in the past several years. Along with the adoption of these standards has come an increase in the need for accurate reliability data for devices used in safety instrumented systems (SIS), both electronic and mechanical. While the methodology of determining failure rates for electronic equipment is fairly well accepted and applied, the same cannot be said for mechanical equipment. Several methods are currently used for generating failure rates for mechanical components. These methods vary in their approach and often lead to dramatically different failure rates, which can lead to significant differences when calculating the reliability of a safety instrumented function (SIF).
This article reviews the methods utilized to determine mechanical reliability for components of safety systems and provides a recommendation for the most appropriate methodology....
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