Because proactive maintenance is a combination of different maintenance strategies, it is crucial that you are using the right ones to inspect, test and determine the condition of a machine and then act to prevent the failure.
Here we outline the various strategies used in proactive maintenance and their advantages and disadvantages.
Reactive Maintenance: This is where a piece of equipment is just let run until it fails with little or no maintenance on it. This would suit units of low value and have minimal impact on failure.
Advantages: Low cost
Disadvantages: It can be difficult to plan maintenance until the failure happens. The number of pieces of equipment this can be used on should be limited.
Preventative Maintenance: This is when the execution of a maintenance plan on equipment and systems is periodically based on time or run time. An example of this would be changing bearings every two years.
Advantages: It is easy to plan and the majority of failures are eliminated before they can happen.
Disadvantages: It can be costly and wasteful and you could end up throwing out good parts. There is also the possibility of introducing faults due to incorrect re-installation.
Predictive Maintenance: This is also known as condition monitoring. It involves monitoring the condition of equipment and detecting defects as they develop. There are a number of technologies that can be used such as: vibration analysis, thermal imaging, ultrasound, lubrication analysis, motion amplification and motor testing.
Advantages: Most techniques are non-intrusive and you only replace faulty parts. It is also good for root cause analysis and is very cost effective.
Disadvantages: Specialist training is needed for diagnosis.
Precision Engineering: Doing it right the first time. Such techniques are laser alignment, fan balancing and torque setting (electrical connections). This is a hands-on maintenance where equipment is installed to high tolerances. Because the machine is installed or fixed to such a high quality the maximum life span will be achieved.
Advantages: Great for high-spec machine, FAT (factory acceptance testing) and commission.
Disadvantages: Intrusive maintenance.
While it is great finding the problem, it still has to be fixed. Taking the appropriate action to fix or amend an issue is the strategy that stops the fail.
Once you’ve decided what maintenance to do on each piece of equipment it is then important to decide the method of how to do it.
This is where training and knowledge sharing is so valuable. Having all personnel carrying out the task in the same way is so important because it leads to consistency in the results. If this wasn’t done the results would deviate and give misleading information and probably bad diagnosis of faults.
An example of this would be in vibration analysis or mechanical ultrasound where the test points are marked so are always taken from exactly the same point. Also, the naming method of equipment and their parts are consistent. The master list created during the initial equipment audit can be used for this.
The P-F interval is the length of time between a defect forming on a piece of equipment and it failing. Obviously this varies from machine to machine and each unit will be different. However, after a number of years of history on each piece of equipment, it would be possible to roughly estimate the P-F Interval.
This is key for deciding the testing frequency. If the testing frequency is too long you may not have time to diagnose the fault, on the other hand if the frequency was too short it would be a very costly and not efficient.
And don’t forget that once the program is up and running, regular reviewing should take place to ensure optimal performance.