Introduction to maintenance methods

When it comes to determining the maintenance policy to be implemented on a piece of equipment or a plant, the maintenance man is faced with a classic alternative: should he wait for the equipment to fail, and therefore be led to intervene on this equipment which no longer performs all or part of its required function, or should he do everything possible to prevent this failure from developing and leading to the "breakdown" of the equipment? In the first case, a corrective maintenance strategy as defined in standard NF EN 13306 will be implemented, while in the second, a preventive maintenance strategy will be adopted. Answering this question may seem straightforward, and an initial cursory analysis would lead us to favour preventive maintenance, in the mistaken belief that it will totally eliminate the risk of breakdown. In fact, this is not the case, as preventive maintenance merely "reduces the probability of a failure occurring" (NF EN 13306). A more detailed analysis shows that the choice between corrective and preventive maintenance requires knowledge and examination of a number of criteria which, depending on the context, will be of greater or lesser importance. These criteria relate to :

• technical: reliability, maintainability, etc. ;

• economic: maintenance costs, downtime, etc. ;

• safety: of goods and people ;

• environmental ;

• quality.

Together, these criteria form the basis of the more global concept of criticality of the asset in the process.

The topics covered are designed to examine the two maintenance strategies mentioned above, the methodologies used, and the technical methods and tools available today for the practical implementation of preventive maintenance and the control of corrective maintenance.