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Time-Based Maintenance (TbM)

Also called "clock-based" maintenance, or "condition- independent" maintenance or "calendar-based" maintenance.

A form of maintenance of an asset according to a strict timetable, with the following general attributes:

Example Tasks
Listed below are some examples of time-based maintenance tasks: 

  • “Inspect exterior sealant every 3 years”. 
  • "Clean gutters every six months"
  • 'Lubricate pumps every 6,000 run hours"

Time-based maintenance is best suited and appropriate for the following assets and circumstances:

Listed below are some of the merits and limitations of this form of maintenance.

  • It provides for consistency and predictability in the administration of the maintenance program.
  • TbM may be quantitative but not necessarily qualitative in so far as it does not seek to find an optimal interval for tasks.
  • TbM may result in over-maintenance of some assets.
  • It does not recognize the changing condition of assets over time and may not be the optima risk management strategy.

Management Principles
Listed below are some of the asset management principles that can be applied to this form of maintenance in pursuit of a maintenance optimization model.
  • Usually best suited during the Pre-P period on some assets.
  • TbM is often applied to short-life assets, such as pumps, overhead gate motors, fire extinguishers, etc.
  • The maintenance mix will include an appropriate balance of assets on a time-based maintenance.
  • The replacement policy and replacement mix will include a time-based replacement policy for appropriate assets.
  • Time-based maintenance lends itself perfectly to service agreements as the scope of the tasks and their intervals are clearly defined and can be appended to the agreement or referenced to applicable standards.
Run to Failure (RTF) is one of the four principal maintenance philosophies
Fig. Time-based maintenance (TbM) forms an underlying principle that applies to all four maintenance strategies.

risk spectrum extending along the P-F interval
Fig. The risk spectrum extending along the P-F interval with Time-Based Maintenance (TbM) shown in the green zone.

fire extinguisher
Fig. Fire alarm equipment is usually maintained on fixed intervals of time according to local regulations.

Fig. Maintenance performed according to a hard time schedule.

See also:
Compare with:

From a maintenance perspective, the interruption is largely independent of the condition of the asset and, hence, largely independent of the maintenance of the asset. 

For example, trees, birds and lightning generally do not discriminate among new, old and deteriorated facilities when causing interruptions and these causes are classified as independent of the condition of asset. 

Tree trimming and vegetation management programs can, therefore, be administered without factoring in the condition of the asset.    

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