Failure of a splined clutch power transmission shaft
Failure Analysis – the Basics
Failures happen, often despite the best efforts of designers, engineers, and fabricators. The first consideration after a component failure should be to check similar in-service components that may exhibit the same type of failure.
There are many potential causes of failure – and where to begin a related investigation can seem like a formidable task. The investigation of failures is often referred to as a root cause analysis or RCA.
Very often a multidisciplinary approach is used to perform a root cause analysis. For a structural failure, an engineer, materials/metallurgy professional and a welding specialist is often necessary. The engagement of an individual knowledgeable with the process/factors important to the design and the performance of the failed component is also helpful.
An additional consideration is the potential for litigation related to the failure. In such cases, legal counsel should be sought early in the process and failed components must be preserved for examination and involvement by all parties with an interest in the matter in testing and assessment activities. This is particularly important if any destructive testing or inspections are intended.
Tools that are often used in a structural RCA include: Finite Element Analysis (FEA), Computational Fluid Dynamics (CFD), Scanning Electron Microscopy (SEM) — potentially with Energy Dispersive Spectroscopy (EDS) for metallurgical assessments, and fundamental engineering principals & concepts.
In performing any type of component assessment, some criteria against which to judge the findings is needed. In the case of an RCA, design and material requirements are found in Codes and Standards, Customer Specifications and other applicable documents such as Purchase Orders and contracts.
Once a failure analysis is completed, the next logical step is determining how to prevent future occurrences. Such actions may include any or all of the following: design modifications, applying alternate materials, changes in fabrication techniques & operating parameters, and more.
The negative aspects of a failure should not overshadow the valuable lessons that can be learned from it. By analyzing, understanding, and addressing the cause(s) the engineer learns how to ensure there are no future failures.
Additionally, RCA findings and the resolution(s) should be documented for use by peers, co-workers and future generations of engineers and designers who will inevitably ask themselves “I wonder why they did that?”
Interdisciplinary teams are essential for performing most failure analyses, since the root cause is rarely the result of a single variable. Understanding not only the metallurgical properties but also the environmental effects and stresses to a system or component is important in determining the cause of a component failure.
Once we identify component failure modes, we assess remaining life, recommend inspection methods/ intervals, and modify equipment designs to reduce the likelihood for future failures.
@ O’Donnell Consulting Engineers
