Maintenance Management Legends (part 7)

part 1, part 2, part 3, part 4, part 5, part 6, part 7

Torbjorn Idhammar IDCON - Maintenance consultants
Posted 4

There are many paradigms and legends surrounding maintenance management in plants. Often, the legends are known to be untrue, but people live with them because it is politically correct, or simply convenient. To be successful in improving equipment reliability and maintenance management, plants must break the legends that exist in their organizations. Some of the legends will be addressed in this article. You may find that these legends are uncomfortably close to describing how your plant operates.

Legend 7: Equipment criticality decides inspection frequency

It is common to see plants base component inspection frequency on a criticality analysis study. At first, it may seem sensible to base inspection frequency on criticality of equipment, but let's illustrate the misconception with an example.

Let's assume we are setting the inspection frequency for a very simple component such as a bolt. Let's assume the bolts in question are holding a mechanical seal on a pump. The pump and seal are very critical according to the criticality study. The inspection frequency for the highest criticality score is often recommended to one inspection every shift.

Intuitively, you notice that it doesn't make any sense to inspect a bolt every shift. Why? Because the inspection frequency must be based on how long, on average, it takes to develop a failure in a component. The bolt in our example will not fail from one shift to another unless there is a completely random event. The most likely failure is that the bolt comes loose over a 2-6 month period. We should therefore set the inspection frequency according to the Failure Developing Period (FDP), by estimating the FDP, and set the inspection frequency to FDP over two. In our example, we estimate an FDP of 4 months and set the inspection frequency to 2 months.

to be continued....