According to standard NBR-5462, Preventive Maintenance is maintenance performed at predetermined intervals, or according to prescribed criteria, designed to reduce the likelihood of failure or degradation of an item’s operation. The NBR-5462 lists three types of maintenance: Corrective Maintenance, Preventive Maintenance and Predictive Maintenance. What will define which type to use and when to use is the maintenance strategy adopted to maintain availability and reliability of the equipment.
Contrary to what many practitioners imagine, preventive maintenance is still not the most cost-effective maintenance of the three. Preventive maintenance strategy costs, on average, 3 times more than predictive maintenance strategy and is applicable in only 11% of equipment.
Only 11%?
That’s it. Preventive maintenance results only in equipment where failures that are directly related to the age of the equipment. That is, it is inefficient in 89% of the equipment, where failure rates are not related to the age of the equipment, but to the operating conditions.
Definition of Preventive Maintenance
To be clear, one must analyze the definition of Preventive Maintenance according to NBR-5462 and highlight three points: predetermined intervals, specific criteria and reduction of probability of failure. These points are known as “triggers”, that is, once a predetermined trigger event occurs, a maintenance action is performed. Triggers are specific criteria or conditions that will determine when an equipment must undergo maintenance.
There are basically four types of triggers:
– Time
– Hours of Operation
– Productivity
– Mixed Trigger
The purpose of preventive maintenance is to re-establish the original conditions of the equipment in order to reduce the probability of failure. However, it is important to clarify some fundamental concepts for a complete understanding of the possibilities of preventive maintenance applications.
There are two main types of failures: Potential Failure and Functional Failure
Potential Failure:
What is preventative maintenance? The potential failure is an early-stage failure, which denounces that there is something wrong, but the equipment is still performing its function in the production process.
Example: Imagine that in a certain hydraulic system, there is a leak in one of the hoses. Despite the leakage, the hydraulic system is still performing its function within the production process (triggering with the parameters of pressure, speed and force required).
We can say that there is a potential failure (leakage). That is, if it is not treated, it will take the equipment to functional failure. The potential failure often happens when a maintenance process doesn’t apply a clear work order. Therefore, the use of a CMMS system in this context is highly recommended.
Functional Failure:
Functional failure is when the equipment is no longer able to perform its function in the production process.
Example: Assuming that the leak mentioned above evolves and the oil level of the hydraulic system falls severely, making it impossible to operate. At this point we have a functional fault, the hydraulic system is no longer able to perform its function due to leakage in the hydraulic hose. If the leak were repaired when it was still in the initial stage and was only a potential failure, the functional failure would not have occurred. Therefore, Corrective Maintenance will always be linked to potential failure or functional failure.
It can be said that preventive maintenance brings solid results in only 11% of the equipment. In 89% of the equipment it is not feasible to apply preventive maintenance.
