Predictive maintenance study

Finally, the third limitation of predictive maintenance in process machinery is that downtime must be scheduled to allow for inspection of the equipment, which in itself poses risk. It is not an exaggeration to say that the source of the majority of equipment failures, which were studied, began shortly after predictive maintenance inspections made disassembly of equipment necessary. Figure 62.2 shows how trouble incident frequencies can increase contrary to expectations after inspection and overhaul. 

Studies in the early 1980s reported predictive maintenance programs were more cost effective than the preventive maintenance programs. These studies showed that PM programs cost about 11— 13 per horsepower of a machine, while a predictive maintenance program cost 7— 8 per horsepower. [11]... 

In the FEED stage, conduct process hazard analysis, RAM, predictive maintenance, value engineering and constructability studies for accurate scoping of the most profitable revamp option... 

Other study (Bertolini Bevilacqua 2006) deals with efficiency and risk, using inspection, repairs and the manpower involved. Here the tool is also the Analytic Hierarchy Process, where the purpose was to select the optimal maintenance policy, the criteria used were the occurrence, severity and detectability (as a traditional FMEA) and the alternatives to choose were corrective, preventive or predictive maintenance. 

The predictive maintenance component involves the use of a variety of modern diagnostic systems and is viewed as a natural outcome of RCM studies. Such smart systems diagnose equipment condition (often in real time) and provide warning of imminent problems. Hence, timely maintenance can be performed, while avoiding unnecessary maintenance and overhauls. 

Small details can impact how successfully an installation is viewed. The unforeseen window coatings and associated maintenance were not sufficient for the plant to stop using the analyzer, but they probably reduced the personnel s satisfaction with the technology. Since it is simply not possible to predict and investigate every possible issue during feasibility studies, owners of any kind of on-line analyzer must be prepared to consider the need to make changes to the system over time. 

While correlation may not be the optimal measure of the usefulness of the Epworth scale for discrimination or prediction (32), there also appears to be no categorical association between ESS score and sleep latency (30,33,34). Thus, although the ESS may be predictive of other variables such as general health status (16) or respiratory disturbance index (12), most of the evidence suggests that its association with sleep latency is tenuous. Similar results emerge from studies comparing ESS with the other (newer) objective measure of EDS, the maintenance of wakefulness test (MWT). In a large narcolepsy sample, the correlation between ESS and MWT was weak (r = -0.29, p <. 001) (35). 

In summary, studies of the basic components of respiration associated with growth, ion uptake, and maintenance suggest that total plant respiration should be a relatively constant fraction of GPP. These predictions are consistent with the results of model simulations of plant carbon balance. These modeling studies indicate that total plant respiration is about half (48-60%) of GPP, when a wide range of ecosystems is compared... 

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