Work Classification and Prioritization Maintenance Work Task Classifications

Maintenance work tasks can be classified in two major categories:

Preventive and Corrective.

Figure 4.5 Work Type Category Codes

Chapter4

Figure 4.6 Work Flow Process.

Preventive Maintenance (PM)

• Time (Calendar)-based maintenance (TBM) (age related)

• Run-based maintenance (RBM) (usage related)

• Condition-based maintenance (CBM aka Predictive) (health related)

• Operator-based maintenance (OBM aka Autonomous Maintenance, a pillar of TPM) (operations related) Corrective Maintenance (CM)

• CM Routine work resulted from PMs: Planned and Scheduled

• CM Major Repairs/Projects: Planned and Scheduled

• CM Reactive:Unplanned/Unscheduled (aka Breakdown/

Emergency)

Preventive Maintenance (PM)

Preventive maintenance refers to a series of actions that are performed on an asset on schedule. That schedule may be either calendar time-based or machine operations dependent (i.e., runtime or the number of machine cycles). These actions are designed to detect, preclude, or mitigate degra-dation of a system and its components. PM includes cleaning, adjusting, and lubricating, as well as minor component replacement, to extend the life of assets and facilities. The goal of a preventive maintenance approach is to minimize system and component degradation and thus sustain or extend the useful life of the asset. Assets within your facilities should not be allowed to run to the breaking point unless a run-to-failure strategy has been selected for that specific asset. The PM work can be further classi-fied into four categories:

PM—Calendar-Based

PM—Calendar-Based Maintenance (Time-Based Maintenance or TBM) is typically performed based on the calendar time. Maintenance personnel schedule periodical visits to an asset based on fixed time inter-vals, for example, every three or six months. Although better than no PM at all, calendar-based PMs are not the optimal way to run PM programs.

They may result in too much time being spent on an asset. Numerous vis-its to assets with “no data – abnormalities found” can be regarded as wast-ed maintenance dollars. If this happens, the PM periodicity should be reevaluated and adjusted. Nevertheless, time-based PMs are a good approach for assets having fixed operating schedule such as 24/7 or 80 hours/week operation.

PM—Run-Based

PM—Run-Based Maintenance (RBM) is typically the next step up from calendar-based maintenance. It involves performing PMs based on asset cycles or runtime. Intuitively, this approach makes sense. An asset does not have to be checked repeatedly if it has not been used. Generally speaking for some failure modes, it is the actual operation of the asset that wears it down, so it makes sense to check the asset after it has been work-ing for a specified amount of time to cause some wear. It may be neces-sary either to adjust or replace the component.

PM—Condition-Based

PM—Condition-Based Maintenance (CBM), also known as Predictive Maintenance (PdM), attempts to evaluate the condition of an asset by performing periodic or continuous asset monitoring. This approach is the next level up from runtime-based maintenance. The ulti-mate goal of CBM is to perform maintenance at a scheduled point in time when the maintenance activity is most cost effective yet before the asset fails in-service. The “predictive” component stems from the goal of pre-dicting the future trend of the asset’s condition. This approach uses prin-ciples of statistical process control and trend analysis to determine at what point in the future maintenance activities will be appropriate and cost effective.

PM—Operator-Based

PM—Operator-Based Maintenance (OBM) uses the fact that opera-tors are often the first line of defense against unplanned asset downtime.

OBM assumes that the operators who are in daily contact with the assets can use their knowledge and skills to predict and prevent breakdowns and other losses. OBM is synonymous with autonomous maintenance, one of the basic pillars of Total Productive Maintenance (TPM). TPM is a Japanese maintenance philosophy that involves operators performing some basic maintenance activities. The operators learn the maintenance skills they need through the training program and use those skills on a daily basis during operations.

Corrective Maintenance (CM)

CM, sometimes called repair, is performed to correct the deficiencies found during PM and CBM assessment; it restores the asset in good work-ing condition after it has failed or stopped workwork-ing. CM is also an action

initiated as a result of an asset’s observed or measured condition before or after the functional failure. The CM work can be further classified into three categories:

CM—Scheduled

CM—Scheduled is a repair activity performed to mitigate potential asset failure or correct deficiencies found during PM and CBM tasks. It brings an asset to its designed capacity or to an acceptable level in a planned way. This work should be planned and scheduled.

CM—Major Repairs / Projects (Planned and Scheduled)

In many organizations, all major repairs or improvement work valued over a certain threshold—e.g., overhauls and turnaround projects—are treated as capital projects for tax purposes. If these projects are to bring the asset back to the designed capacity, not to add additional capabilities, they should be treated as corrective maintenance. In that case, they should always be planned and scheduled.

CM—Reactive (Unscheduled) aka Breakdowns / Emergency

Corrective Maintenance—Reactive (Unscheduled) is basically repair-ing of the assets after they fail. This work is also known as breakdown or failure repair work. Most of the time, completing this work interferes with the regular weekly schedule. Unscheduled work costs much more than planned and scheduled work.

Some maintenance professionals classify maintenance in the follow-ing categories: PM, CBM/PdM, Proactive Work resultfollow-ing from PM and CBM/PdM, and CM—Reactive (Breakdowns / Emergency). It really does not matter how we classify them as long as maintenance management sys-tems can provide us data in the format to help us to make the right deci-sions. Our objective is to reduce reactive breakdowns and then adjust or increase PM and CBM work accordingly.

Sometimes we try to mix maintenance work types with how we respond to get the work done. For example, is emergency work really CM—Unplanned/Unscheduled or is it reactive work that needs to be done now? In some organizations, the breakdown work is called urgent main-tenance, but could be done within 48 hours. Some regular work, also sometimes called routine work, may need to be completed in 5 or 7 days.

These examples are not the work type, but just how we respond to get it done.

Sometime a decision is made to take no actions or make no efforts to maintain the asset as the original equipment manufacturer (OEM) origi-nally intended. Therefore, no PM program is established for that particu-lar asset. This maintenance strategy, called Run-to-Failure (RTF), should be applied only after a risk to the business has been analyzed and its cost effectiveness determined. In reality, this work should not be considered failure or reactive work because we made the decision in advance not to perform any PM or CBM based on economic justification.

All maintenance work-tasks are needed to be documented and clas-sified in CMMS/EAM system as described earlier and then, to optimize resources, all work-tasks are prioritized per the organization’s priority system for execution. Every organization should, if don’t have one;

establish a work-tasks order priority system.

Job Priority

Priority codes allow ranking of work orders to get work accom-plished in order of importance. Too many organizations neglect the ben-efits of a clearly-defined prioritization system. Organizational discipline that comes through communication, education, and management support is key to the correct usage of priority codes.

Many organizations have more than one prioritization systems; how-ever, most of them have been found to be ineffective. The drawbacks of not clearly defining the priorities include:

• Wasted maintenance man-hours on tasks of low relative importance

• Critical tasks being lost in the maintenance backlog

• Dissatisfied operations customers

• Lack of faith in the effectiveness of the maintenance delivery functions

A disciplined method of prioritization will eliminate tasks being done on a whim and instead allow work to proceed according to its true impact on the overall operations of the plant. It will also allow the maintenance delivery function to be executed in a far more effective manner.

Priority System Guidelines

The system needs to cater to the following requirements equally and provide a universal method of coding all works orders.

• Plant-wide asset priorities, allowing for better plant-wide utilization of resources

• Operations requirements

• Improvement projects

Accurate prioritization covers two distinct decision-making process-es. These are:

• Asset criticality

• Impact of task or work to be done on overall operations

The original priority of the work orders needs to be set by the origi-nator of the work order and should be validated by the coordiorigi-nator. The work originator is the most qualified to make an initial assessment of asset criticality and impact of the work. Listings of major assets and their icality will help in decision-making for final priority ranking. Lower crit-icality items or areas will then be easier to recognize. The following cri-teria can be used to assign asset criticality and work impact (if not correct-ed), which can then be used to make an objective assessment of overall job priority.

Asset Criticality Criticality # Description

5 Critical safety-related items and protective devices 4 Critical to continued production of primary product 3 Ancillary (support) system to main production process 2 Stand-by unit in a critical system

1 Other ancillary assets

Work Impact, If Not Corrected Work Impact # Description

5 Immediate threat to safety of people and/or plant 4 Limiting operations ability to meet its primary goals 3 Creating hazardous situations for people or machinery,

although not an immediate threat

2 Will affect operations after some time, not immediately 1 Improve the efficiency of the operation process

Work Priority = Asset Criticality X Work Impact WO #1:

Asset Criticality of 5 and Work Impact of 4 gives an over all job priority of 20.

WO #2:

Asset Criticality of 4 and Work Impact of 4 gives an over all job priority of 16.

In this case, WO #1 will have the higher priority when compared to WO #2. The combination of the criticality and impact of the work can be cross-referenced to give a relative weight to each task when compared to all other work.

Backlog Management

The combination of work classification and job priority allow an organization to make sense out of their maintenance backlog. A mainte-nance backlog is very simply the essential maintemainte-nance tasks to repair or prevent equipment failures that have not been completed yet. By classify-ing these maintenance tasks into different categories and then prioritizclassify-ing within those categories, maintenance backlogs can be developed from an overall organizational perspective or within smaller organizational groups or categories (e.g., PM, CM).

Why manage your backlog at all? Why not just work whatever main-tenance tasks come due? The more toward proactive mainmain-tenance that an organization moves, the more likely it is, at least in the beginning, that the organization will identify more maintenance tasks than can possibly be addressed within that immediate time period (typically that week).

Therefore, to keep from addressing the low priority tasks or the categories of work that will not have the largest impact to the overall reliability of the organization, a backlog management system must be developed. Then the most effective approach to the backlog management system requires appropriate work classification and priority.