Sep 24, 2018

Unplanned Maintenance



Unplanned maintenance is also known as: reactive maintenance, corrective maintenance, breakdown maintenance, or run-to-failure maintenance.


Unplanned maintenance occurs in any asset maintenance plan and unfortunately is unavoidable.  A common example of this type of maintenance (and the inconvenience that it can cause) is having your car break down on the side of the road, and having to wait for a mechanic to come to repair it.

The trigger for this type of maintenance is a breakdown trigger.

Problems associated with unplanned maintenance

Because this maintenance type is both unplanned and unscheduled this method of performing maintenance activities is highly inefficient. Time needs to be spent investigating and determining the problem as well as determining a maintenance plan to get the equipment fixed quickly. Time is also likely to be spent waiting for parts, supplies or other personnel to complete the maintenance task.

This type of maintenance can also be very expensive. Additional costs include time spent waiting, the premium costs that may be spent on fast part orders and shipping, and the possible overtime payments that may be required for additional, or specialised personnel needed to complete the task. In addition, because it is likely that the operation of other parts of the facility will be negatively impacted by the breakdown of the machine in need of repair, the costs of lost production need to be also factored into the cost of this type of maintenance.

If no maintenance planning is undertaken then this style of maintenance becomes the default maintenance style. This is because the planned and predictive maintenance styles described later need an investment in planning before they can be successfully utilised.

While it is intended that this type of maintenance should be avoided in the planned maintenance strategies such as predictive and preventative maintenance , it is inevitable that, at some stage, a machine will break down and unplanned maintenance of this type will be required. This incurs all of the additional costs associated with this type of maintenance.

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  • What is planned maintenance? Planned maintenance is planned, documented and scheduled to be completed before a breakdown occurs. This is unlike unplanned maintenance. The process of planning the maintenance makes the tasks more efficient and eliminates the effect of maintenance on the operations of the facility. Planned maintenance can be one of two types: Maintenance can be planned and scheduled (like getting your car services every six months), or planned and unscheduled (like planning to replace a lightbulb whenever it stops working). Scheduled maintenance Also known as  preventative maintenance ,  planned maintenance . Planned maintenance activities are planned with regard to the maintenance tasks and their timing. All of the triggers for scheduled maintenance are used as triggers for this type of maintenance. These include time, usage, event and condition based triggers. Being planned, the resource requirements are known and can be made available in advance. Being scheduled, a time for the maintenance is also known. When this is combined with the resource planning, the resources can be pre-arranged so that they are ready to go as soon as the job can begin. The maintenance may be scheduled with both short and long lead times. Some scheduled maintenance may be planned years in advance, as would be the case for a yearly maintenance schedule, such as one to replace air-conditioner filters every year before summer. Other scheduled maintenances may have shorter lead times. These may be as a result of usage based schedules. For a maintenance technician, this style of maintenance is more efficient than unplanned maintenance because the task is known in advance. As a result, the parts and supplies can be ready to go and other equipment that might make the job site unsafe can be safely shut-down. Consequently, a planned maintenance task can get done faster with the equipment returning to production faster, too. Unscheduled maintenance Also known as run-to-failure maintenance. Planned but unscheduled maintenance occurs in situations where the maintenance plan for an asset is to wait for breakdown before performing maintenance. A common example is waiting for a lightbulb to blow before replacing it. With this style of maintenance the process for performing the maintenance is planned without knowing when it will occur. This means that the resources such as parts, supplies and personnel are ready and available to use so that the repair can be made within a reasonable time. The trigger used for this maintenance type is a breakdown trigger. This type of maintenance can be efficient for a technician when the maintenance has a low impact on production. It means that no extra maintenance resources are wasted on a part that can be replaced on an as-needs basis. For more information see the run-to-failure maintenance information page.
  • What is Run To Failure Maintenance (RTF)? Definition The simplest maintenance strategy is to execute run to failure maintenance (also known as “run to fail”). In this strategy, assets are deliberately allowed to operate until they break down, at which point reactive maintenance is performed. No maintenance, including preventative maintenance, is performed on the asset up until the failure event. However, a plan is in place for ahead of the failure, so that the asset can be fixed without causing any production issues. Under the run to fail method, it is important to have spare parts and staff on hand to replace the failed part and to maintain equipment availability. This strategy should not be confused with reactive maintenance, because of the active plan to allow the asset to run to failure. This strategy is useful for assets that, on breakdown, pose no safety risks and have minimal effect on production. A common example of run to failure maintenance is the maintenance plan for a general-purpose light bulb. The bulb is allowed to run until it fails. At this time, the plan to fix the asset is carried out. A new light bulb is obtained from stocks and replaced at a convenient time. Advantages Minimal planning – Since maintenance does not need to be scheduled in advance, the planning requirements are very low. Maintenance only needs to happen  after  breakdown has occurred. Easy to understand – Because of the plan’s simplicity, this system is easy to understand and implement. Disadvantages Unpredictable – Because most asset failures are unpredictable, it is difficult to anticipate when manpower and parts will be needed for repairs. Inconsistent – The intermittent nature of failures means efficient planning of staff and resources can be difficult. Costly – All costs associated with this strategy need to be considered when it is implemented. These costs include production costs and breakdown costs, in addition to direct parts and labour costs associated with performing the maintenance. Inventory costs – The maintenance team needs to hold spare parts in inventory, to accommodate for intermittent failures. Types of Maintenance Plans Unplanned, reactive maintenance is the only type of maintenance task used for the run to failure maintenance strategy. Run-to-failure Maintenance Triggers Asset breakdown is the only trigger used in the run to failure maintenance strategy. If the asset is not working, then maintenance is required. Appropriate Applications for Run-to-failure Maintenance Run to failure maintenance makes sense when the total cost of repairing equipment after breakdown is less than the cost of performing other types of maintenance on the equipment beforehand. For example, let’s say that you have a machine that’s involved in a continuous, 24/7 production process. Shutting it down for monthly maintenance would stop production and create the same disruption as if you had just let it break down (which might happen 1 time a year). In this case, it makes sense to simply repair it when it breaks. Run to fail maintenance requires an understanding of how a machine might break and what the consequences of breakdown are. Run to failure would also be more appropriate for redundant, or non-critical assets (i.e. when you have 40 trucks and 1 rock crusher in a mine, run to failure maintenance might make sense for the trucks but not for the crusher). Inappropriate Applications for Run-to-failure Maintenance Run to failure maintenance is unsuitable for applications where equipment failure creates a safety risk (oil pipes bursting) or where equipment availability is necessary (a bakery where each hour of downtime costs many thousands of dollars). It is also undesirable for assets where total maintenance costs would be reduced with a more proactive approach to maintenance such as preventative or predictive maintenance strategies. How to Impliment Run-to-failure Maintenance Run to failure maintenance may be implemented using many maintenance methods. This strategy can be adequately managed from memory. Other tools can also be used, including paper-based systems, spreadsheets, CMMS and EAM systems. If an entire facility is working on a run to failure strategy (such as a small home office), then CMMS and EAM systems will provide much more functionality than required. For facilities where run to failure is used for some assets and more complex strategies are used for other assets, the CMMS and EAM will allow these different types of maintenance strategies to happen simultaneously. A CMMS can also be useful to track the number of times the asset has been repaired or replaced and associated costs. A good run to failure maintenance strategy will likely require an inventory management tool because of the large number of spares that may be needed for breakdowns.
  • Traditional models of asset management Reliability-centered maintenance: An extensive system that lacks real world applicability. Manufacturer-suggested schedule: Ignores the benefits of experience within the actual operating context. Purely estimated PM schedule: Enacting in response to breakdown/incentive, based on OEM schedule or approximations. 3 Elements of Preventative Maintenance What tasks are necessary for PM? Scheduling PMs to fit in with parts/tools availability and a production schedule How frequently should you perform these tasks to optimize maintenance of that asset? The necessary tasks can be determined by experienced maintenance personnel, or from following OEM guidelines.  Likewise, collaborating with production schedules and parts/tools availability is simply a matter of good planning. The only thing left is to determine the frequency of these actions. Asset Healthcare Model vs. RCM Less cumbersome than RCM – designed to be used without detailed equipment knowledge Covers entire equipment spectrum Minimizes data re-entry Can be implemented by hourly workforce with minimal guidance beyond initial training RCM, in it’s many forms, is generally too unwieldy for real world application.  Its use should be reserved for complex pieces of machinery with very involved maintenance requirements. Stages to Implementing a PM Program Develop your asset hierarchy Creating asset hierarchies has a twofold effect. It allows for easy reference to and builds relationships between all maintainable assets The process of going through assets and categorising them down to each maintainable component gives the operators a more thorough understanding of the individual machinery, right down to the component level.  You might hear comments like, “I didn’t even know this thing HAD a washer – we never change it!” Determine Criticality The importance of the component itself is ranked separately in the next  phase.  A rudimentary ranking system is shown below. An alternative scale can be used, provided it ranks along similar lines. Then rank the individual component as how it supports the process it is tied to. The next step is to combine the two rankings for a table that looks like this: Now that we have discussed the pros and cons of the various popular maintenance strategies and have started to define what is essentially a quickly deployed hybrid between complex strategies like RCM and simple PM schedules, we rank the assets on criticality of failure and the importance of the process they support. These tables can be combined into a quick reference for overall asset importance. Determine Current Operating Condition of Equipment This goes hand-in-hand with the relative importance ranking principle established in Step 2.  Old machinery that also has high criticality will need much more attention or possible replacement.  Newer, less critical machinery can be given little attention. Develop a Maintenance Strategy for each Equipment There are a wide variety of available maintenance strategies.  A few are listed below.  Assets with low criticality (eg. C5) can be maintained with a run-to-failure strategy.  High criticality assets however, (eg. A2) should have either intensive PM schedules and inspections, or an investment into some kind of condition monitoring technology.  Available strategies include: Run to failure Preventive (PMs) Predictive/condition based RCM Continuous monitoring Finalize Specific Maintenance Activities After all the groundwork has been laid, the specific activities need to be decided on.  What needs to be done for each weekly PM?  For each monthly PM?  Each strategy implies a different level of asset care, and its corresponding activities.  PM’s will include largely inspections and possible repair.  RCM and continuous monitoring involve a much more intensive set of activities like different tests and calibrations.  Build out a plan for every asset including as many details as possible for each maintenance activity.  This plan should be re-examined and changed at different intervals.

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