Like preventive maintenance, predictive maintenance has many definitions. To some workers, predictive maintenance is monitoring the vibration of rotating machinery in an attempt to detect incipient problems and to prevent catastrophic failure. To others, it is monitoring the infrared image of electrical switchgear, motors, and other electri- cal equipment to detect developing problems. The common premise of predictive maintenance is that regular monitoring of the actual mechanical condition, operating efficiency, and other indicators of the operating condition of machine-trains and process systems will provide the data required to ensure the maximum interval between repairs and minimize the number and cost of unscheduled outages created by machine-train failures. Predictive maintenance is much more, however. It is the means of improving pro- ductivity, product quality, and overall effectiveness of manufacturing and production plants. Predictive maintenance is not vibration monitoring or thermal imaging or lubri- cating oil analysis or any of the other nondestructive testing techniques that are being marketed as predictive maintenance tools.Predictive maintenance is a philosophy or attitude that, simply stated, uses the actual operating condition of plant equipment and systems to optimize total plant operation. A comprehensive predictive maintenance management program uses the most cost- effective tools (e.g., vibration monitoring, thermography, tribology) to obtain the actual operating condition of critical plant systems and based on this actual data schedules all maintenance activities on an as-needed basis. Including predictive main- tenance in a comprehensive maintenance management program optimizes the avail- ability of process machinery and greatly reduces the cost of maintenance. It also improves the product quality, productivity, and profitability of manufacturing and production plants.Predictive maintenance is a condition-driven preventive maintenance program. Instead of relying on industrial or in-plant average-life statistics (i.e., mean-time-to-failure) to schedule maintenance activities, predictive maintenance uses direct monitoring of the mechanical condition, system efficiency, and other indicators to determine the actual mean-time-to-failure or loss of efficiency for each machine-train and system in the plant. At best, traditional time-driven methods provide a guideline to “normal” machine-train life spans. The final decision in preventive or run-to-failure programs on repair or rebuild schedules must be made on the basis of intuition and the personal experience of the maintenance manager.
The addition of a comprehensive predictive maintenance program can and will provide factual data on the actual mechanical condition of each machine-train and the oper- ating efficiency of each process system. This data provides the maintenance manager with actual data for scheduling maintenance activities. A predictive maintenance program can minimize unscheduled breakdowns of all mechanical equipment in the plant and ensure that repaired equipment is in acceptable mechanical condition. The program can also identify machine-train problems before they become serious. Most mechanical problems can be minimized if they are detected and repaired early. Normal mechanical failure modes degrade at a speed directly proportional to their severity. If the problem is detected early, major repairs can usually be prevented.
Predictive maintenance using vibration signature analysis is predicated on two basic facts: (1) all common failure modes have distinct vibration frequency components that can be isolated and identified, and (2) the amplitude of each distinct vibration component will remain constant unless the operating dynamics of the machine- train change. These facts, their impact on machinery, and methods that will identify and quantify the root cause of failure modes are developed in more detail in later chapters.
Predictive maintenance using process efficiency, heat loss, or other nondestructive techniques can quantify the operating efficiency of nonmechanical plant equipment or systems. These techniques used in conjunction with vibration analysis can provide maintenance managers and plant engineers with information that will enable them to achieve optimum reliability and availability from their plants.
Five nondestructive techniques are normally used for predictive maintenance management: vibration monitoring, process parameter monitoring, thermography, tribology, and visual inspection. Each technique has a unique data set that assists the maintenance manager in determining the actual need for maintenance.
How do you determine which technique or techniques are required in your plant? How do you determine the best method to implement each of the technologies? How do you separate the good from the bad? Most comprehensive predictive maintenance pro- grams use vibration analysis as the primary to
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