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| Proforma Safety, LLC Proforma PSI…when performance counts. Metal Fatigue Causes Beam Failure What's your process for checking for metal fatigue? An incident occurred recently in which the walking beam on a pump jack failed, landing on the wellhead, releasing sour oil and gas. The cause: metal fatigue near the tail assembly of the walking beam, resulting in the beam breaking off at the saddle bearing. Investigation showed that the damage had occurred over a long period of time, but inspection failed to detect cracks at the early stages. Experts believe failure occurs in three stages: (1) the structure begins to experience micro-cracks as early as one-percent into its life span. Small surface defects - some introduced at or after manufacturing -- contribute to creating these micro-cracks. (2) The cracks grow at an increasing rate due to continued external forces. (3) The structure suddenly ruptures as the remaining portion is too small to resist the external forces. Metals are not the only substances subject to fatigue; ceramics, composites, aggregates, and other engineering materials are also vulnerable. A thorough process in checking for metal fatigue may include the following: 1) Identifying each area of the structure and components to be checked; accountabilities and frequency 2) Listing specific actions to be performed, such as opening all inspection plates, access doors, etc. 3) Listing specific tasks to be performed when analyzing each area; for example:
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