How to use MSG-32 July 2010
The engineer starts with the (draft) list of systems and their functions provided by the design and their suppliers. Reliability engineers can then query the suppliers (both of the overall plant and its constituent subcomponents) for the ways in which equipment fails–its failure modes.
With failure modes they can perform failure modes and effects analysis (FMEA). Once they have produced a list of calculated effects, they can rank the failure consequences on four levels: safety, operational, cost or none (no direct consequence). With the failure modes information, they can identify likely causes of failures. In many instances, no direct consequences result from a failure, due to backup or redundant equipment. In such a case, identifying component failures as they occur is acceptable and effective. In every other case, failure experts must identify the cause and find an effective task to control failure. Where no countermeasure can be found, the component must be redesigned to eliminate the risk.
The only special case is dealing with hidden failures. Because hidden failures occur so often in modern complex designs, methods must be developed to control them. Often that includes a failure-finding task loosely translating into what the US nuclear programme calls a surveillance test. Under such a test, standby equipment is operated to verify the performance of the real equipment at risk from hidden failures. Most other tasks are found from querying the equipment’s suppliers and understanding their maintenance regimes. Very often, simple operator checks can use instrumentation to reveal failures. Other times, such as with filters or lubricants, it is simpler to just replace the component. On other occasions, a performance test is an effective condition monitoring task to monitor degradation.
Once engineers have identified tasks for every component in the plant based on risk, an engineer groups together tasks to perform on one piece of equipment at one time as ‘work scopes.’ Task blocking puts all equipment work elements together on a common schedule to perform at the same times and intervals, when the equipment is available. Task blocking greatly simplifies maintenance execution around an operating schedule.
The end result of the exercise is a list of each piece of equipment in the plant that has a ranked, scheduled task. When provided to a nuclear plant starting up, such a list can be implemented as a complete, effective scheduled maintenance reliability assurance plan. Every task in the plan is objective, actionable and has specific acceptance criteria, so the plan is performance-based. The final plan can be loaded into commercial software as a computerized maintenance management system (CMMS) and implemented as a scheduled maintenance plan, loaded on personal digital assistant (PDA) tablet PCs, and carried out on operations staff rounds.
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