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Figure 2.1 Events leading to compressor failure.

      If you study this example, you can discern the following events leading to the costly failure:

      There were several chances to break the chain of events leading to the catastrophic compressor failure. If the project engineer had ordered spare parts through the OEM, this failure probably would have been avoided. If either the maintenance supervisor or the local machine shop had talked to the OEM, or studied the failed rod, they would have been aware of the importance of rolled threads. Lastly, if a vibration shutdown had been in place, the compressor would have shutdown after only minimal damage. We see there were six major events leading to the secondary compressor damage. These events were as follows:

      After examining the vestiges of the failure, the rotating equipment (RE) engineer would discover a fatigue failure in the threaded portion of the rod. From this, he would conclude an improper thread design led to a stress riser and a shortened fatigue life. After talking to the OEM, he writes a report recommending that all compressor rods in the plant have rolled threads.

      This recommendation will surely reduce rod failures, but the investigation did not uncover the latent root of failure. The stress riser, due to the improper thread design, is called the “physical root,” because it did initiate the physical events leading to the secondary damage. However, there were significant events preceding the physical root that are of interest. If the RE engineer had the time and resources, he would have discovered that the absence of a procedure requiring new equipment to be purchased with adequate spares directly initiated the sequence of events. This basic event is called the “latent root.”

      By requiring spare parts be purchased from the OEM for all new equipment, the latent root is eliminated, not only for this scenario but, potentially, for many other similar events. This example demonstrates the importance of finding out the “latent root” of rotating equipment failures. Stopping at the “physical root,” deprives the organization of a valuable opportunity for improvement. So, an RCFA is a detailed analysis of a complex, multi‐event failure, such as the example above, in which the sequence of events is hoped to be found, along with the initiating event. The initiating event is called the root cause, and factors that contributed to the severity of the failure or perpetuated the events leading to the failure are called contributing events.

      Industry personnel generally divides failure analysis into three categories in order of complexity and depth of investigation.

      They are:

Although the cost increases as the analyses become more complex, the benefit is that there is a much more complete recognition of the true origins of the problem. Using a CFA to solve the causes of a component failure answers why that specific part or machine failed and can be used to prevent similar future failures. Progressing to an RCI, we find the cost is 5–10 times that of a CFA but the RCI adds a detailed understanding of the human errors contributing to the breakdown and can be used to eliminate groups of similar problems in the future. However, conducting an RCA may cost well into six figures and require several months. These costs may be intimidating to some, but the benefits obtained from correcting the major roots will eliminate huge classes of problems. The return will be many times the expenditure and will start to be realized within a few months of formal program implementation.

      One thing that has to be recognized is that, because of the time, manpower, and costs involved, it is essentially impossible to conduct an RCA on every failure. The cost and possible benefits have to be recognized and judgments made to decide on the appropriate type of analysis.

      When RCA Is Justified

      Equipment Damage or Failure

      RCFA are normally justified for those events associated with the partial or complete failure of critical production equipment, machinery, or systems. This type of incident can have a severe, negative impact on plant performance. Therefore, it often justifies the effort required to fully evaluate the event and to determine its root cause.

      Operating Performance

      Many a time deviations in operating performance occur without the physical failure of equipment or components. Chronic deviations may justify the use of RCFA as a means of resolving the recurring problem.

      Product Quality

      RCFA can be used to resolve most quality‐related problems. However, the analysis should not be used for all quality problems.

      Capacity Restrictions

      Many of the problems or events that occur affect a plant’s ability to consistently meet expected production or capacity rates. These problems may be suitable for RCFA, but further evaluation is recommended before beginning an analysis. After the initial investigation, if the event can be fully qualified and a cost‐effective solution not found, then a full analysis should be considered. Note that an analysis normally is not performed on random, nonrecumng events or equipment failures.

      Economic Performance

      Deviations in economic performance, such as high production

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