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Maintenance Mix

The balance (or ratio) of the different forms of maintenance for all the assets within a building during a particular fiscal year or calendar year

The optimal maintenance mix will vary between buildings of different types (commercial, residential, etc) depending on the types of assets and will also change as the building ages over time.


Purpose
The maintenance mix is one of the criteria used to measure the quality of maintenance and the robustness of the overall maintenance program.

The purpose of a maintenance mix is:

A well-orchestrated program will include a prudent and reasonable mix of the different maintenance strategies. Independent maintenance studies have indicated the following average savings can be achieved by carefully leveraging the advantages of each the three maintenance philosophies:
  • Return on investment: up to 3 times
  • Reduction in maintenance costs: up to 30%
  • Elimination of breakdowns: up to 75%
  • Reduction in downtime: up to 45%
  • Increase in production: up to 25%

Measurement
The maintenance mix can be quantified, measured and evaluated in three different ways:

  • 1 - TbM vs. CbM
  • 2 - RTF, PM and PdM
  • 3 - Contracted v autonomous
Included below is a summary outline of the methods of quantifying the mix.


Maintenance Mix Option #1
The first method establishes the maintenance mix based on the relative ratio of the following two classes of maintenance:
The relationship between TbM and CbM at different stages in the lifecycle of a building are reflected on the P-F interval.


Maintenance Mix Option #2

The degree to which a facility has adopted each of the four types of maintenance strategies for the different assets, which is used in the development of a maintenance optimization model

For example:

  • Reactive (Breakdown/Run to Failure)      5%
  • Preventative (Time-Based)                    60%
  • Predictive (Condition-Based)                10%
  • Reliability Centred                               25%
A “Maintenance Mix” is the degree to which the owner has adopted each of the three types of maintenance strategies and distributed these across the many different assets in the building. For example:
  • Corrective Maintenance (CM) 40% of the assets
  • Preventative Maintenance (PM) 50% of the assets
  • Predictive Maintenance (PdM) 10% of the assets
In the preceding scenario, the owners have not yet optimized their maintenance program to take advantage of the benefits of Predictive Maintenance (PdM) and limit the risks of  Corrective Maintenance (CM).


Maintenance Mix Option 3
The third method establishes the maintenance mix on the basis of the different parties that are performing the maintenance tasks.
For example, a building with 114 assets may have 64 of the assets covered under a service agreement and the reaming assets are addressed on an as needed basis by facility staff. In this example, the mix is 56-to-34%.

The appropriate ratio of contracted-to-non-contracted maintenance will depend on several factors, including:
  • The number of bounded assets (ie., statutorily regulated).
  • The sophistication of the owners' asset management team.

Process
The maintenance mix is derived from the alignment of the following risk metrics to each asset based upon the owners risk tolerance:

Listed below are the key steps in determining the appropriate maintenance mix for the assets;

For proper alignment, maintenance strategies for each asset should be selected based on risk analysis (criticality analysis).


Owner Attributes
A maintenance mix is developed based on the following owner attributes:



Maintenance Mix Relative to Each System
Listed below is an outline summary of the ratios of time-based and condition-based maintenance relative to each of the primary physical systems:
While maintenance of the enclosure system provides the greatest return on investment, the enclosure system is deceptively difficult to manage as it does not lend itself to the fixed-interval maintenance strategies effectively employed by the other systems through traditional service agreements. The enclosure system requires owners to find an appropriate Maintenance Mix that balances Time-Based Maintenance (TbM) on fixed intervals and Condition-Based Maintenance (CbM) on floating intervals.

Finding the optimal balance in the triad of Preventative Maintenance (PM), Corrective Maintenance (CM/RTF) and Predictive Maintenance (PdM) requires a tremendous amount of skill and mountains of data.

Many organizations do not have sufficient structured and quantitive data to prepare a compelling business case to support the appropriate Maintenance Mix - that is, the balance of RTF-PM-PdM. In the absence of this data, most of us rely on criticality assessments to ensure that all maintenance-worthy assets are subject to PM-PdM and RTF is reserved for a particular class of assets where the risks (read, consequences of failure) are deemed acceptable.

Reliability-centred Maintenance (RcM) is a fourth class of maintenance that seeks the optimal maintenance mix that is aligned to each asset across the asset register and then periodically revisited and recalibrated as the assets age and approach potential failure (P) and functional failure (F).

Alignment of the four different types of maintenance strategies across the asset portfolio on decisions that are risk-based and consider the whole-life of assets will result in a maintenance mix that is in conformity with ISO 55001 standards
Fig. Alignment of the four different types of maintenance strategies across the asset portfolio on decisions that are risk-based and consider the whole-life of assets will result in a maintenance mix that is in conformity with ISO 55001 standards.


Alignment between Maintenance, Repairs and Renewals will help the organization find the optimal MRR ratio
Fig. Alignment between Maintenance, Repairs and Renewals will help the organization find the optimal MRR ratio.


Comparing the Maintenance-Repair-Renewal (MRR) trade-offs at different organizations.
Fig. Comparing the Maintenance-Repair-Renewal (MRR) trade-offs at different organizations.


he resource mix should reflect the organization's competencies, which will evolve over time with education, training, mentoring and experience of the team
Fig. The resource mix should reflect the organization's competencies, which will evolve over time with education, training, mentoring and experience of the team.



The changing ratio of the maintenance mix over time.
Fig. The changing ratio of the maintenance mix over time.



1 1
Floor polishing                       Powersweeping

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risk spectrum extending along the P-F interval
Fig. The risk spectrum extending along the P-F interval indicating the relationship between time-based maintenance (TbM) and condition-based maintenance (CbM).


Variable interval events mapped onto the P-F curve to illustrate the relationship between time and condition.
Fig. Variable interval events mapped onto the P-F curve to illustrate the relationship between time and condition.


1  1  Landscaping                         HVAC pump service


The maintenance mix for a building based on the ratio of contracted maintenance to non-contracted maintenance.
Fig. The maintenance mix for a building based on the ratio of contracted maintenance to non-contracted maintenance.


Generator service is routine maintenance.
Fig. Generator service is a form of routine maintenance.



"I. Care" takes us through the challenges of finding the right blend for the maintenance mix
Fig. "I. Care" takes us through the challenges of interpreting the maintenance manual find the right blend for the maintenance mix.
 


Different types of maintenance tasks distributed across the four seasons of an annual maintenance program.
Fig. Different types of maintenance tasks distributed across the four seasons of an annual maintenance program.



1 1
Exterior painting                       Sealant review



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Fig. Window washing is an examples of preventive maintenance carried out on fixed time intervals.


I. Care is trying to blend the optimal replacement mix for the assets in his portfolio
Fig. I. Care is trying to blend the optimal maintenance mix for the assets in his portfolio.


Pool tank cleaning is an example of major maintenance
Fig. Pool tank cleaning is an example of major maintenance.



Maintenance Mix Cost Evaluation
Fig.  The correlation between the  maintenance costs and repair costs associated with the three different maintenance strategies.While Predictive Maintenance (PdM) generally has the highest  maintenance cost, it will result in the lowest repair costs. CM, on the other hand, has the lowest maintenance cost but the highest corresponding costs associated with asset repairs.



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Fig. Thermography is an example of level-3 maintenance since it requires specialized skills and equipment.


Major maintenance tasks mapped to the P-F Curve
Fig.  Different types of maintenance activities at various life stages of an asset.


1  1
Roof drain cleaning                 Carpet cleaning


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