A corrective maintenance strategy, also known as a reactive or ‘run to failure’ strategy, works on the premise that an item is allowed to fail and is only then repaired or replaced. In order for this to work, the consequence of failure needs to be acceptable and have no significant impact on the environment or safety. The failure should also have no detrimental economic impact for the asset owner. Corrective maintenance is also necessary when failure occurs.
This type of maintenance needs to be performed once a malfunction occurs in order to restore an asset to the correct operating conditions so it can perform its intended action. For example, leaving a lightbulb to operate until it fails before replacing it constitutes corrective maintenance.
Advantages
Given the right circumstances, corrective maintenance can offer a number of advantages:
1. Reduced Short-Term Costs
As a reactive maintenance procedure, there is little cost associated with monitoring and assessment either before or after failure.
2. Minimal Planning Required
This type of maintenance requires minimal planning, short of possibly ensuring a replacement part is available at the time of failure.
3. Simple Process
This is a simple and easy to understand process, since action is only required once a problem occurs.
Limitations
While corrective maintenance offers some advantages, there are also a number of potential drawbacks to this technique:
1. Unpredictable
Since equipment is not monitored during use, flaws can be highly unpredictable.
2. Unscheduled Downtime
Because you may not know when a problem will occur, you can be faced with delays or even unexpected outages while you source replacement materials or parts. This downtime is increased further by the time taken to repair.
3. Shorter Equipment Lifecycles
Running an item to failure provides no opportunity to protect or care for the equipment by assessing wear. This reduces the lifecycle of your assets.
4. Potential for Higher Long-Term Costs
A corrective maintenance plan is best followed where shutdown and repair costs are outweighed by the cost of planned maintenance. In the case of a lightbulb, for example, this makes sense as the cost and time taken for replacement are minimal. However, this is not always the case and a catastrophic failure can lead to additional unforeseen expenses as well as being detrimental to customer satisfaction, security, safety and reputation.
Preventive maintenance (also known as preventative maintenance) is maintenance conducted regularly on an asset to reduce the likelihood of failure. This is undertaken while an asset or item of equipment is working so that it doesn’t break down unexpectedly.
This maintenance style falls between the reactionary corrective maintenance and a predictive maintenance strategy. Preventive maintenance is performed to minimise cost and increase an asset’s lifecycle, while avoiding unscheduled outages or breakdowns.
This strategy can be divided into two types:
- Time-Based Preventive Maintenance
This type of preventive maintenance is triggered periodically to deliver a regular inspection of a piece of equipment. This could, for example, be a weekly, six-monthly or annual inspection.
- Usage-Based Preventive Maintenance
Usage-based maintenance procedures are triggered after a set amount of production cycles, hours in use, or even distance travelled. For example, a vehicle could be due an inspection for every 10,000 miles that are travelled.
There are a number of advantages but also some disadvantages with both types of preventive maintenance:
Advantages
1. Improved Safety
By undertaking regular checks on your equipment, you reduce the chance of it breaking down unexpectedly. Depending on the equipment in question, this can create a safer working environment for your staff.
2. Improved Budgeting
By monitoring the condition of your equipment, you can maintain your budget for replacements or necessary servicing.
3. Longer Lifecycles for Assets
Well-maintained equipment will perform better and for longer. Routine check-ups can improve the lifecycle of your assets, cutting down the requirement for costly (and unexpected) replacements.
4. Save Money
Because the lifecycles of your equipment are extended, you will not have to replace items as frequently. Money is also saved on unplanned maintenance, which may not only be more expensive than a scheduled repair, but can also have other consequences in relation to meeting client orders on time.
5. Save Energy
Well-maintained equipment tends to use less energy than poorly maintained items. Not only is this better for the environment, but it also saves you money on utilities.
6. Less Disruption or Unscheduled Downtime
If you maintain a procedure of regular checks, you are less likely to be surprised by something going wrong. Unplanned outages can cause disruption to your workforce, your output and your deadlines for work. This can all cost reputation and money, especially if a large problem occurs. Regular monitoring can even mitigate against unforeseen breakdowns, as your maintenance may provide information on where a breakdown was most likely to have occurred.
Limitations
1. Increased Upfront Costs
A preventive maintenance plan will cost you more upfront than allowing something to run to failure. Regular servicing comes at a cost in time, salaries, and parts. However, you need to decide whether this is more than the potential cost of simply letting something run to failure.
2. Over Maintenance
A badly prepared plan can lead to over-maintenance. Sometimes an asset may not need to be checked as often as your plan sets out, meaning you are wasting time and money on unnecessary maintenance. By following advice related to your assets and changing your plan accordingly, this can be avoided.
3. More Employee Costs
You may entail more employee costs with preventive maintenance rather than relying on a corrective maintenance approach. Regular checks may require more on-site staff or specialists being called in when compared to simply calling for an occasional one-off fix. However, as shown above, these costs also need to set against the multiple potential costs of unexpected failure.
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Predictive maintenance differs slightly from preventive maintenance as it takes an even more robust approach to determining when maintenance is necessary. Rather than using a set time-scale or usage frequency to determine when maintenance is required, predictive maintenance uses analytics and continual monitoring of data to detect if equipment failure is likely to occur.
This type of monitoring allows for maintenance to be performed when required to address a specific problem and prevent an asset from breaking down. Because maintenance is only flagged up as required when failure is imminent, predictive maintenance is often more cost-effective than preventive maintenance.
Advantages
1. Reduced Spending
Because maintenance is only performed when required, this approach removes the unnecessary maintenance costs associated with preventative maintenance. Maintenance tasks are often less expensive than with reactive maintenance too, since problems are addressed before complete equipment failure is reached. Not only does this reduce the cost of time spent performing maintenance, but can also reduce other costs, such as overtime, by being able to schedule repairs and equipment downtime.
2. Improved Asset Reliability
Your equipment will be more reliable and perform better if it is properly maintained. A predictive maintenance system can ensure your equipment is running correctly, increasing the lifespan of your machinery. This improved reliability includes many of the other advantages of preventive maintenance as mentioned above, including improved safety, budget control, energy saving, and less disruption to work schedules.
3. Less Downtime
This maintenance technique can greatly reduce downtime or outages resulting from equipment failure. Small repairs and tune-ups can prevent larger-scale problems from occurring, maintaining productivity and customer satisfaction.
4. Scheduled Maintenance
Understanding the condition of your equipment means that you are in control of scheduling your maintenance. You can ensure the required experts and parts are on-site when you have time to make repairs rather than having to take a costly reactive approach, while also minimising disruptions to workflow to boost productivity and profits.
5. Improved Product Quality
Badly maintained machines can lead to them not working properly and creating defective products. By monitoring your equipment, you ensure all parts are running smoothly to produce consistently high-quality products.
Limitations
1. Requires Condition Monitoring Equipment
Predictive maintenance requires the use of condition monitoring equipment to collect data to be reviewed by technicians. This incurs additional upfront costs for asset owners, although these costs are frequently offset against the potential cost of unnecessary maintenance or unexpected failure.
Advances in technology mean that condition monitoring equipment is becoming both more effective and affordable. This includes more cost-effective data collection and storage technologies.
2. Requires Data Interpretation Expertise
Your predictive maintenance equipment will need skilled staff to be able to interpret the data. It is important that your critical data analysis is done correctly in order to effectively determine when failure is imminent or maintenance is required. Your technicians will need to understand both the asset and the monitoring system. This may require staff training or new employees being hired, however these costs may be worthwhile in the long run.
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Corrective
Despite the inherent advantages of preventive and predictive techniques, corrective maintenance can be the best solution in some cases. Where the cost of part failure and repair is less than the preventive or predictive maintenance costs, corrective maintenance is often the best solution.
So, for example, in the case of our light bulb, corrective is certainly the best option as the cost and time taken to replace the bulb is unlikely to dramatically impact budgets or work schedules. However, this changes as the part becomes more imperative to operations such as with, for example, a wind turbine blade or ship’s engine.
Corrective maintenance can be particularly damaging when it has not actually been decided upon as a plan of action, letting something unwittingly run to failure can be costly in time, money and safety.
Preventive
Preventive monitoring is used where the cost of letting something keep running until it breaks is too high, the part is too critical, is difficult to replace or repair, or could have serious implications for employee safety or work schedules.
This approach is not necessary for all items, but allows for those that are more important to be maintained. This will reduce the likelihood of unplanned outages, extend the lifecycle and performance of your asset, and also help to better determine any unexpected cause of failure.
Predictive
Asset owners are increasingly using predictive maintenance as their preferred option. Not only does it offer many of the benefits of preventive maintenance, but it does so in a more efficient and cost-effective manner. While there are costs associated with set-up, once these are budgeted for, a condition-based monitoring system can be used to alert you only when action is required, thereby reducing unnecessary maintenance costs while keeping your equipment in good condition. Sensors can be used to remotely monitor a range of operational aspects, from vibration and cracking to oil quality.
This type of maintenance is becoming more accessible as improvements in technology deliver advances in monitoring and data collection performance alongside reduced costs.
The decision as to which monitoring approach to take will vary between organisations and applications. While it is perfectly acceptable and even preferable to take a corrective, reactionary approach with some items, many will require some form of regular maintenance or monitoring. This applies for everything from a machine component to whole structures or buildings.
Preventive maintenance can be based upon past inspection knowledge, which will help determine the frequency of inspection required. Equipment manufacturers and even codes and standards may also set out maintenance requirements for particular items or assets. These maintenance schedules may need to be adjusted over time to make them more effective, both in terms of maintenance and cost.
Predictive maintenance is using new technologies (such as with the artificial intelligence mentioned in the DiMOS Project case study above) to deliver an even more effective approach. Although of course, this all still depends on the exact nature of your asset or equipment - we don’t think you need to set up sensors for your desk lamp’s lightbulb!