The prime objective of a maintenance management strategy is to achieve the optimum balance between equipment performance, availability and the cost of maintenance. Reducing the spend on maintenance can have serious consequences to production.
In one pottery company, in an attempt to reduce costs following reduced profits, the maintenance staff was halved. As a direct result, a machine failed causing £90,000 of damage and lost production. Later, with outside help and improved maintenance procedures, they were able to save 15% of their total production costs.
A Ministry of Technology Working Party report in 1971 estimated that maintenance was costing the United Kingdom around £3 billion per year. They considered that by improving maintenance management and paying greater attention to other factors in the equipment life cycle, substantial savings could be made. The life cycle approach to maintenance cost reduction has since been defined as terotechnology.
The British Standards Institution defines terotechnology as:
“A combination of management, financial, engineering, building and other practices applied to physical assets in pursuit of economic life cycle costs. … Its practice is concerned with the specification and design for reliability and maintainability of plant, machinery, equipment, buildings and structures, with their installation, commissioning, operation, maintenance, modification and replacement, and with feedback of information on design, performance and costs.”
During its life cycle, equipment passes through a number of stages, from specification to replacement. The figure above shows these stages and the inter-relation between them. It can be seen that the successful operation of the equipment is dependent on all the stages in the life cycle.
The maintenance function has traditionally only had an influence on the latter stages of the life cycle, from commissioning through to replacement. However, the earlier stages in the life cycle are where the maintainability of the equipment is set and, without major redesign, maintenance can only really be considered as a “fire-fighting” function, responding to unexpected events with no ability to plan accurately in advance. Ideally, the maintenance function should contribute at all stages of the life cycle, allowing for equipment to be specified, designed and manufactured with the future maintenance implications in mind.
Reactive And Preventative Maintenance
Maintenance activities can be split into two broad areas, reactive and preventative. Reactive maintenance, often known as unplanned or corrective maintenance, occurs where the plant is allowed to run until something fails; after which it is repaired. Preventative maintenance, also known as planned maintenance, aims to forecast when failures are likely to occur, and to fix the problem before it occurs, at a time that is convenient to both production and maintenance.
Traditionally, maintenance was mainly reactive in nature; as machines broke down they were fixed. It is only since the 1970′s that preventative maintenance has become more common within UK industry. The Central Policy Review Staff report in 1975 identified poor plant maintenance as a significant cause of low productivity in the British motor industry. The report stated;
“Effective preventative maintenance programmes are essential to maintaining consistent levels of output in car assembly plants. Despite the fact that British manufacturers employ 50 to 70% more plant maintenance personnel than continental competitors, on identical equipment, mechanical breakdowns result in the loss of about twice as many production hours in the UK as on the continent.”
This situation occurred as a result of the UK plants employing an almost exclusive reactive maintenance strategy and dealing with breakdowns as and when they occurred. On the continent, the use of preventative maintenance was commonplace, resulting in more effective maintenance being obtained for lower cost. Also as preventative maintenance actions are by definition deterministic they can be scheduled in advance, usually according to a planned preventive maintenance programme. This allows maintenance resources to be utilised more effectively as resource usage can be levelled by reducing the peaks and troughs commonly caused by a reactive maintenance policy.
In addition to the two broad categories of predictive and reactive maintenance, maintenance can be further sub-divided into four major strategies. These strategies may be employed, individually or in any combination, to maintain any individual asset throughout its lifetime.
The four strategies are as follows:
- Design Out Maintenance (DOM)
- Fixed Time Maintenance (FTM)
- Condition Based Maintenance (CBM)
- On Failure Maintenance (OFM)
It is highly improbable that equipment failure can be eliminated completely through the adoption of other maintenance strategies; there is always the possibility that equipment will fail in an unexpected manner. As a result, a combination of strategies tend to be used by maintenance departments in order to cover all eventualities.
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