While predictive and preventive maintenance activities are useful in preventing failures, they do not permanently eliminate the defects inherent in an asset that allow the deterioration leading to the failure. On the other hand, it is possible to modify the asset in a manner that eliminates the defects.
Frequently, defects are embedded in an asset after the initial design as a result of oversight or lack of understanding. On other occasions, the presence of defects is the result of economics. In these cases, the designer knows of the defect, but is unable to take steps needed to eliminate the defects while still maintaining the final cost or profitability of the asset at an acceptable level.
In the second situation, it should be hoped and expected that the OEM has shared the knowledge of the defect with the future owners. With that knowledge, the owner could make one of two choices:
- Pay a little more for the asset and eliminate the defect.
- Perform the appropriate predictive and preventive maintenance while living with the defect, yet still avoiding failures.
In the frequent situations where either designers did not know about inherent defects or knew of their existence and failed to report them to the future owner, the task of finding and eliminating the defect is up to the owner.
In the case where the owner must deal with an inherent defect, the owner has the same choices to make as did the OEM. The owner can either spend the money to make the asset more robust and permanently eliminate the asset’s susceptibility to a specific failure mechanism or, if that is not an economic choice, deal with the ongoing deterioration.
Some defects are relatively simple and straightforward, like the use of an alloy that will withstand various forms of corrosion as a replacement for carbon steel. Other forms of defect elimination are not so simple. An example is a defect in software that allows specific forms of malfunction in certain infrequent circumstances. In either case, it is important to be certain that the changes made to eliminate the defects do not do more harm than good.
About this title
As the title of this book implies, the objective is to describe the links between failure modes, failure mechanisms, predictive maintenance and preventive maintenance. As you might expect, a clear understanding of the links between those elements is based on a clear understanding of the definitions for those elements. It is possible, and even likely, that you will find other sources that apply somewhat different definitions to these terms.
It is my experience that despite the source of the operative definitions, the mental images being used by participants tend to vary and are, therefore, inadequately defined. It is not so much what is written on paper as what is inside your head that counts. Much of the effort of this book is to place an operative definition in the minds of readers that is clear, understandable and easily shared with others.