Up Time Magazine - February/March 2009 - (Page 34) maintenance mgmt upload Going Rogue Rogue Components – Their Effect and Control by Thomas Carroll I f an asset management program includes repaired, reconditioned or overhauled parts, there is an everpresent risk of “rogue” components developing in the population. The compounding negative effect of these aberrant individuals is felt across these facets of the organization: • • • • • Operational Reliability Asset Management Programs Maintenance Effectiveness Preventive Maintenance Programs Maintenance Support • • • • • Maintenance Training Programs Component Repair Facility Components Themselves Mechanical System Hardware Operator / OEM Engineering Rogue Component Definition A rogue component is defined as an individual repairable component, which repeatedly experiences short in-service periods, manifesting the same mechanical system fault each time it is installed, and when it is removed from the mechanical system, the fault is corrected. The primary reason a component becomes rogue is because shop repair bench tests do not address 100% of the component’s operating functions, characteristics or environment. Interviews with various component Original Equipment Manufacturers (OEM) revealed the bench test coverage is typically about 85% of the component’s complete functionality. Even if all the functions were covered, the operating environment of the component when it is installed in the mechanical system is usually quite different than the repair shop, so if a failure is dependent upon a particular in-service environmental condition, it is unlikely that it will be duplicated during testing. Additionally, the bench test is crafted to identify anticipated failures – focused on things that are expected to fail. For instance, it would not make sense to check all the screws or electrical ground straps each time the component comes into the shop, since the chance of failure for those pieces is practically zero and the cost of performing such extensive testing during each shop visit would be exorbitant. When a component experiences a failure that was unaddressed or unanticipated by the shop testing procedures, a rogue is born. Since every test that is performed misses that specific aspect of the component’s functionality, the fault will never be identified and resolved. “Natural Selection” Phenomenon There is a Darwinian-like “natural selection” process that ensures the rogue components are placed in the most disadvantageous position in the asset management program. The following depictions demonstrate the mechanics of this phenomenon. Figure 1 shows a pristine condition where the component spare inventory and the in-service population are comprised of serviceable (Good) components that function as designed and expected (the In-Service Population shown in the diagram is a small representation of the general population). There are no rogue components yet. Spares Inventory Good Good Good Good In-Service Population Good Good Good Figure 1 In this situation, the asset management process will follow all the applied models. As a part fails in service, it is removed and replaced with a good part from the spare inventory. The component repair facility duplicates the problem with the failed unit, repairs it and returns it to the spare inventory. The “natural selection” phenomenon begins when a rogue component develops as shown in Figure 2. 34 february/march 2009
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