There are two distinct areas of maintenance strategy; an overall approach to how a plant or site will be maintained and individual asset maintenance strategy.

Overall maintenance strategy

An overall maintenance strategy is the approach used to maintain all assets constituting a plant or site.  Such a maintenance strategy is commonly risk based where…

Risk = Impact x likelihood

Impact being the consequence of the loss of an asset or the function/service it provides or contribute to.  Likelihood being the probability of failure based on experience or industry data on past performance (e.g. OREDA in the oil and gas sector). Such a maintenance strategy can be very economic in that the maintenance regime adopted for an asset is based on the consequences of failure not just on what kind of equipment it is.


A plant has a number of 30kW pump/motor assemblies serving different functions within the site.  A number of them serve the final phase of production where the impact of loss would be a total loss of finished product.  However, other similar units have recently been installed to deal with waste water, there are a number of holding tanks that can hold all waste water produced over 7 days, there is no impact on production should these units fail. 

Do you maintain all units the same?  What if you have a contractor providing vibration analysis on the production line assemblies, do you automatically extend that to the new units?  If you maintain purely on what the asset is the answer is yes, if you have an overall maintenance strategy the answer is not so straightforward.  The truth is you would carry out a cost benefit analysis on the risk associated with failure versus the cost of the vibration analysis services.  If the risk does not justify that cost then a different maintenance regime would be appropriate.

When such a risk based maintenance strategy is adopted a criticality analysis (assessing the risk associated with the failure across all site functions) will produce the following type graph…

maintenance strategy

Reproduction courtesy of Functional Criticality Analysis software (a CSA/VV Ltd maintenance strategy tool)

The graph demonstrates the functions of a site that have been scored against the risk equation.  This allows the assets that support the functions to be maintained economically and appropriately based on the impact of their loss.

Overall to individual maintenance strategy

The graph allows us to set a generic approach to individual asset maintenance strategy (or regimes). 

These are
•    Condition based maintenance (CBM)
•    Planned preventive maintenance (PPM)
•    Nil maintenance (run to failure) (RTF)

Whereby…assets serving the higher scoring functions could justify higher technology (and therefore more expensive) CBM techniques such as vibration analysis.  As we move down the graph lesser CBM techniques might be justifiable (oil analysis etc) and PPM techniques will come to the fore.  On the lowest scoring functions the risk associated with failure is minimal and RTF may be justified.    

Individual asset maintenance strategy

The aim of individual asset maintenance strategy is to stop breakdowns.  The higher the risk associated with loss of function the more the application of advanced analysis techniques such as Failure Modes and Effects Analysis (FMEA) or Reliability Centred Maintenance (RCM) might be justified.  These techniques examine how an asset might fail and any early indicators of deterioration and generate individual maintenance strategy to the extent of what should be done, how often and at what level of expertise.

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