25.4 Factors which Influence Maintenance Strategy

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While there are some general guidelines for choosing the most appropriate maintenance strategy, each

case must be evaluated individually. Principal considerations will always be defined in economic terms.

Sometimes, a specific company policy (such as safety) will outweigh all other considerations. Below is a

list of factors (in no particular order) that should be taken into account when deciding which

maintenance strategy is most appropriate for a given situation or machine:

* Classification (size, type) of the machine

* Critical nature of the machine relative to production

* Cost of replacement of the entire machine

* Lead-time for replacement of the entire machine

* Manufacturers’ recommendations

* Failure data (history), MTTF, MTBF, failure modes

* Redundancy

* Safety (plant personnel, community, environment)

Machine Duty (Load)

Estimated

Capacity

and

Load

Time In Service

Machine Capacity (Est.)

Maintenance

Activity

Minimum Margin

FIGURE 25.4 Time versus estimated capacity and actual load (condition-based maintenance).

* Maintenance strategies can be divided into three main types: (1) run-to-failure, (2)

scheduled, and (3) condition-based maintenance.

* No one strategy should be considered as always superior or inferior to another.

* Run-to-failure, or breakdown maintenance, is a strategy where maintenance, in the form of

repair work or replacement, is only performed when machinery has failed.

* When specific maintenance tasks are performed at set time intervals (or duty cycles) in

order to maintain a significant margin between machine capacity and actual duty, the type

of maintenance is called scheduled or preventative maintenance.

* Condition-based maintenance requires that some means of assessing the actual condition of

the machinery is used in order to optimally schedule maintenance, in order to achieve

maximum production and still avoid unexpected catastrophic failures.

Machine Condition Monitoring and Fault Diagnostics 25-7

© 2005 by Taylor & Francis Group, LLC

* Cost and availability of spare parts

* Personnel costs, administrative costs, monitoring equipment costs

* Running costs for a monitoring program (if used)

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