Maintenance strategies

Early failures may occur almost immediately, and the failure rate is determined by manufacturing faults or poor repairs. Random failures are due to mechanical or human failure, while wear failure occurs mainly due to mechanical faults as the equipment becomes old. One of the techniques used by maintenance engineers is to record the mean time to failure (MTF) of equipment items to find out in which period a piece of equipment is likely to fail. This provides some of the information required to determine an appropriate maintenance strategy tor each equipment item. 

The failure mode of an equipment item describes the reason for the failure, and is often determined by analysing what causes historic failures in the particular item. This is another good reason for keeping records of the performance of equipment. For example, if it is recognised that a pump typically fails due to worn bearings after 8,000 hours in operation, a maintenance strategy may be adopted which replaces the bearings after 7,000 hours if that pump is a critical item. If a spare pump is available as a back-up, then the policy may be to allow the pump to run to failure, but keep a stock of spare parts to allow a quick repair. 

If maintenance is performed, there are two principal maintenance strategies preventive and breakdown maintenance. These are not mutually exclusive, and may be combined even in the same piece of equipment. Take for example a private motor car. The owner performs a mixture of preventive maintenance (by adding lubricating oil, topping up the battery fluid, hydraulic fluid and coolant) with breakdown maintenance (e.g. only replacing the starter motor when it fails, rather than at regular intervals). 

A suitable maintenance strategy should be developed for equipment by considering the criticality and failure mode, and then applying a mixture of the forms of maintenance described above. In particular, the long-term cost of maintenance of an item of equipment should be estimated over the whole life of the project and combined with its capital cost to select both the type of equipment and form of maintenance which gives the best full lifecycle cost on a discounted basis), while of course meeting the technical, safety and environmental specifications. 

Too little maintenance results in unexpected failures and consequential major losses of production and/or customers (Figure 7-1). This impractical approach is termed reactive strategy and should be avoided on all important machinery. Optimum maintenance strategy balances reasonable costs with maximum possible availability and reliability. The two main maintenance strategies employed by companies today are labelled predictive strategy and preventive strategy. These are part of a balanced approach as shown in Figure 7-2. 

With a predictive maintenance strategy, long-term plans typically involve as few as only two regular procedures ... 

The maintenance strategy for a system will significantly affect both the number and severity of failures ... 

The third step is to proceed to the component level because more than likely, the cause will be uncovered here. Table 62.2 shows machinery component failure modes commonly encountered in machinery failure analysis together with suggested standard life values, Weibull indices (/J), and responsiveness to preventable or predictable maintenance strategies. Referring to this table will help decision-making. To assist the analyst in documenting bad actor failure modes on the component level. 

Failure Mode Weibull Standard Maintenance Strategy... 

Marlatt, G. A. (1985). Relapse prevention Theoretical rationale and overview of the model. In G. A. Marlatt J. R. Gordon (Eds.), Relapse prevention Maintenance strategies in the treatment of addictive behaviors (pp. 3-70). New York Guilford Press. 

For most children and adolescents, multimodal therapies are recommended. However, if antidepressant medications are used alone, psychosocial maintenance strategies should be implemented to help the patient manage inner and interpersonal conflicts, improve coping and social skills, deal with the psychosocial and personal scars left by the depression, and improve academic and social functioning. The reduction of family stress, promotion of a supportive environment, and the effective treatment of parents and siblings with psychiatric disorders may also help diminish the risk for... 

Marlatt GA Gordon JR (eds.) (1985). Relapse Prevention Maintenance Strategies in the Treatment of Addictive Behaviours. New York Guilford Press... 

FIG. 5-10. Maintenance strategy for the treatment of chronic psychotic disorders. (Adapted from Davis JM, Janicak PG, Preskorn S, Ayd FJ Jr. Advances in the pharmacotherapy of psychotic disorders. In Janicak PG, ed. Principles and practice of psychopharmacotherapy update. Vol 1. Baltimore, Williams Wilkins, 1994 1.)... 

ECT is the most effective treatment for more severe depressive disorders, often characterized by melancholic and/or psychotic features. Although primarily used for an acute episode, ECT may also be a useful maintenance strategy for patients with frequent relapses despite adequate pharmacotherapy. 

However, site services and infrastructure are not only a major driver of cost competitiveness. Some of the services are also crucial for improving plant effectiveness. Maintenance performance, for instance, can have a huge impact on plant output. Unplanned breakdowns, often caused by failure to implement the most effective maintenance strategy or by poor execution, can lead to as much as a 20 percent loss in overall equipment effectiveness (OEE see also Chapter 18). On the utilities side, significant cost advantages can be captured, e.g., by providing... 

Several studies have been conducted, including some small randomised studies, to assess the use of ciclosporin in Crohn s disease. The evidence suggests that intravenous ciclosporin can induce disease remission in severe flares of ulcerative colitis that are unresponsive to corticosteroids. Oral ciclosporin has only been shown to be useful as a bridging treatment between intravenous ciclosporin and more long-term maintenance strategies. 

Some firms use Reliability Centered Maintenance (RCM) as part of their preventative maintenance strategy. 

Operation and maintenance strategies, plans, SOPs, and SLAs have been developed and issued. 

Maintenance strategy records (e.g., reliability centered maintenance records)... 

Maintenance tasks are either implemented proactively in order to prevent or minimize the chance of failure or reactively to correct a situation following failure. Preventive maintenance plans are derived from the EMEA process that will define the tasks and task frequencies required in order to maintain system reliability, consistency, and capability. Flaving applied the FMEA process in order to determine the maintenance strategy, it is essential that the system... 

Maintenance strategy development (FMEA, performance monitoring, etc.)... 

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