Evaluating different Maintenance Strategies

Common maintenance strategies

Outlined below are the more widely used maintenance strategies, as well as their pros and cons and situations when they are best applied.  Typically we see plants employing either run-to-failure (only fix after a breakdown) or preventive maintenance (on a predetermined schedule).  However, depending on the value of the asset or its criticality in the plant’s operations, we may see this strategy escalated to predictive or even RCM-based maintenance.

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Run to failure (breakdown maintenance)

An acceptable strategy for equipment that is of minimal importance to operations (rarely used or duplicates the function of some other equipment) or has low cost.   Take, for example, a $1000 belt feeder, whose lifetime value can be extended by 10% by servicing it every 3 months.  How hard are you willing to work to save $100?  For a non-critical piece of machinery, the answer should be “not hard.”

Equipment designated as run-to-failure are fixed in the event of a breakdown (by repair, restoration or parts replacement) until it is more feasible to simply order a replacement equipment.

Preventative (scheduled) maintenance (PM)

This strategy is employed by most companies and almost all small to mid sized companies make exclusive use of it.  It consists of assets being taken offline, inspected at periodic, predetermined intervals and repaired if necessary.  Although it’s a relatively easy strategy to set up and execute, it can prove quite costly in the long run as a majority of the time these inspections are a straightforward pass.

It’s recommended that serious attention be given to the efficiency of these schedules.  Annual review of a schedule’s effectiveness in raising overall equipment effectiveness by preventing breakdowns and see if the schedule can be lengthened or swapped out for predictive maintenance is ideal.

Predictive maintenance (PdM)

PdM is a condition-based approach to asset management.  Typically, monitoring equipment is linked to a CMMS, and generates work orders based on some meter reading (PSI, vibration analysis, widgets/hour) gathered by the monitoring device.  It may also be simpler than this, such as visual inspection by operators on the quality or speed at which the equipment is performing.  Eg. A conveyor drops below 1000 widgets per hour, trigger an inspection work order.

The advantage of PdM (over PM) is the potential for cost savings from reduced man-hours spent on maintenance, and more insight as to the performance and potential issues arising with the machine.  ie: Vibration analysis + visual inspection gives more insight than visual inspection alone.

Reliability-centered maintenance (RCM)

Emerging from the realization that equipment failure probability is not linear, RCM is an in-depth, highly involved process that seeks to analyze all the possible failure modes for each piece of equipment, and customize a maintenance strategy for each individual machine.

The general consensus is that RCM is too sophisticated a technique to be of much practical use.  RCM is therefore reserved for an elite class of organizations that have already mastered the basics – maintenance prevention, basic inspections and predictive maintenance.

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