What is a Work Order Priority?
The Maintenance Planner faces a daily process of balancing out the resources available based on the demand from Operations and Maintenance on how to achieve the best outcomes in terms of risk to productive output, quality, safety and waste in the daily management of the plant or manufacturing, process facility. The initial action in determining how to establish the priority for each Maintenance Work Order is to establish what is a Work Order Priority? Almost every Computerised Maintenance Management System (CMMS) contains a field where you can set the work order priority, but few define exactly how it is to be used (which in turn determines what it should be).
While there are a number of different interpretations of Work Order Priority that are possible, our view is that the Work Order Priority should represent an indication of the level of business risk that relates to the condition, fault or failure that has been raised by a Work order. The higher the overall risk associated with the fault or failure, then the higher the priority.
Risk is generally represented as the combination of Consequences and Likelihood, so when assessing the priority of a work order, the following questions should be asked:
If we do not perform this work:
what is the impact on quality, safety, environmental conditions, energy and waste?
what happens if the equipment suffers a functional failure, in what way would this impact on the ability to meet the output or production planned, and how large would that impact be?
how likely would the equipment be to suffer that functional failure within the next (predetermined) time period?
The first and second of these questions assesses the potential consequences of the likelihood of not performing the work; with absolute consideration of safety, quality, etc. and then the impact on the equipment, and the third question assesses the likelihood of those consequences occurring.
While absolute priority must be given to the safety, quality, etc. needs the other conditions can then be evaluated using a risk matrix similar to the one shown in Figure 1.
Applying Work Order Priorities in Practice
Now we have looked at the principals how do we do this in practice?
The phrase “functional failure” in the context used above comes from the methods defined in Reliability Centred Maintenance. What this means is that we first need to understand which function(s) are likely to be impacted by the fault or defect. RCM tells us that equipment can have many functions in addition to its primary function. For example, a pump, in addition to its primary function of being able to pump fluid from one location to another at a specified minimum rate, may have secondary functions that relate to Safety, Protection, Control, Containment etc. Further, RCM tells us that equipment can suffer a functional failure, in some cases, not just by failing to operate at all, but by failing in such a way that, although still operating, it fails to meet one or more specified minimum performance standards. So instead of operating at 20 m3/hr it has dropped to 15 m3/h. So careful thought is required when assessing each Work Order to understand which functions and associated functional failures may be impacted by the fault.
Second, in order to ensure consistency in prioritisation among different equipment items, we need to understand the impact of the possible functional failure on overall business objectives. Bear in mind here that by “objective” we are using the (ISO 9001:2015) definition of an objective as being a “result to be achieved”. Those objectives could relate to the achievement of target performance levels in the areas of production throughput (failure to meet production targets), costs (failure to meet cost targets), or risk (failure to meet safety, environmental or social responsibility targets).
So, when assessing consequences, it is important to be thorough, and it is also important to take a “big picture” view of the nature of these consequences on the overall business.
Assessing the likelihood of failure requires you to determine, in advance and in a consistent manner, the time period over which the likelihood of failure is to be assessed. For example, are we assessing the likelihood that the equipment will fail within the next week, within the next month, the next year, or some other time period? The correct answer will depend on your situation, but we would suggest that the time period should be consistent with your work order scheduling horizon. If, for example, you issue a work schedule for the maintenance execution team to complete once per week, then the timeframe for assessment of likelihood should also be weekly. Bear in mind that if the nature of the fault is such that the equipment will continue to degrade, then the likelihood of failure will increase as time passes, and so the work order priority should be reassessed periodically to take account of this. Too many organisations, in our experience, determine the work order priority when the work order is first raised, and then never reassess that priority (at least until, unfortunately, the equipment fails “unexpectedly”).
Who Should Set Work Order Priorities?
As you can see from the discussion so far, setting the priority for a work order requires knowledge of:
The likelihood of impact on the safety, quality, environment, energy usage, etc.
The current condition of the asset for which the work order has been raised
The likelihood speed of progression from current condition to a functionally failed state
The potential impact of this failed state on operational and organisational objectives, given the current situation regarding overall plant status, production plans, stockpile levels, potential workarounds etc.
It is unlikely that any one person will have sufficient knowledge of all of these items to make a fully informed decision regarding work order priority. For this reason, we highly recommend that work order priorities be established jointly by maintenance and production/operations personnel, each of whom will bring different knowledge and skills to the decision-making process. Most likely, the production and maintenance representatives will be front-line supervisors, as they have the most intimate knowledge of the plant, but higher-level management supervision and/or involvement is likely also to be of value, in order to ensure that decisions align with overall management priorities.
Work Order Priorities and Scheduling Work Orders
The next question to ask is how Work Order priorities are applied?. Can we, or should we, always schedule the highest priority work orders for completion first? Regrettably, the answer is “no”.
We should, however, as a general rule, start work on the highest priority work orders first, but when the work is actually completed will depend on a number of other factors. For example, if the work order requires spare parts that are not in stock, then there is little point in scheduling the work for completion until such time as the parts are actually available. For long lead-time items, this may be several weeks in the future. High work order priority may, however, indicate that acquisition of these spare parts is expedited with some urgency, which also raises a cost consideration. Similarly, if, to perform the work, the equipment needs shutting down, then the work will need to be scheduled for a time that has minimum overall impact on plant objectives, and performance of this work may be completed at the same time as a number of other work orders that require equipment to be shut down. This then also raises the question of contracting-out some of the work due to insufficient internal resources.
Sometimes we may also schedule work for completion that is assessed as “lower” priority using the risk matrix approach. For example, from time to time Work Orders can be raised for Maintenance personnel to execute those that are not directly related to impending equipment failures. These are often proactive tasks that relate either to equipment service or improvement activities which are intended to improve overall equipment reliability. But note, for example, that while fixing machine guards is generally not done to prevent impending failure, however, if assessed using a risk matrix would definitely be rated always as high priority as it impacts on safety which overrides other lower priority tasks.
We hope you’ll find the points we’ve raised helpful in your planning and scheduling of Work Orders.