AMMJ - Library

AMMJ
2 Maintenance Approach
Maintenance is traditionally performed in either time based fixed intervals as so-called preventive maintenance,
or by corrective maintenance when a breakdown or fault actually occurs. In the latter, it is often necessary
to perform the maintenance actions immediately, but in some cases this may be deferred depending on the
criticality of the equipment. With predictive maintenance, an advanced warning is given of an impending
problem and repairs are only carried out when necessary and can be planned to avoid major disruption. A
summary of all three approaches is given in Figure 1 and discussed briefly below
Reactive
Maintenance
DISADVANTAGES
High risk of catastrophic failure
or secondary damage. High
repair & replacement costs
Loss of key assets due to high
downtime. Lost production &
missed contract deadlines
Inventory - high cost of spare
parts or replacement equipment
High labour cost – overtime,
subcontracting. High cost due
to hire of equipment
Increased health & safety risks
Environmental concerns
ADVANTAGES
No upfront costs, e.g.
equipment, training. Seen as
an easy option
2.1 Reactive Maintenance
Role of Vibration Monitoring in Predictive Maintenance
Preventive
Maintenance
High replacement costs - parts
replaced too early
Risk of early failure – infant
mortality. Human error during
replacement of repaired or
new parts.
Parts may often have many
years of serviceable life
remaining
Maintenance is planned and
helps to prevent unplanned
breakdowns
Fewer catastrophic failures
resulting in expensive
secondary damage
Figure 1 Comparison of different types of maintenance
Predictive
Maintenance
High upfront costs including
equipment & training
Additional skills or outsourcing
required
Risk of unexpected breakdowns
are reduced
Equipment life is extended
Greater control over inventory Reduced inventory & labour
costs
Maintenance can be planned
and carried out when
convenient
Reduced risk of health & safety
& environmental incidents.
Opportunity to understand why
equipment has failed and
improve efficiency
Reactive maintenance of machinery, often referred to as the “run till failure” approach, involves fixing problems
only after they occur. Of course, this is the simplest and cheapest approach in terms of upfront costs for
maintenance, but often results in costly secondary damage along with high costs as a result of unplanned
downtime and increased labour and parts costs. Since there are no upfront costs, it is often seen as an easy
solution to many maintenance strategies – or there is no strategy at all.
In rotating equipment, rolling element bearings are one of the most critical components both in terms of their
initial selection and, just as importantly, in how they are maintained. Bearing manufacturers give detailed
guidelines as to what maintenance is required and when which is often overlooked. This can have disastrous
consequences in terms of poor quality output, reduced plant efficiency or equipment failure. Monitoring the
condition of rolling bearings is therefore essential and vibration based monitoring is more likely to detect the
early onset of a fault.
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Vol 24 No 1