Optimizing maintenance through reliability (OMF)

All equipment in an industrial plant is subject to degradation mechanisms due to operating and/or environmental conditions: wear and tear, fatigue, ageing, various physico-chemical alterations. When faced with the resulting failures, we can simply carry out corrective maintenance, but this does not avoid the consequences of the breakdowns we suffer. A more defensive attitude is to implement preventive maintenance designed to limit, or even prevent, these failures, but this runs the risk of excessive expenditure and unnecessary downtime.

Faced with such a situation, the maintenance manager must do more than simply monitor and repair: he or she must consider strategies. Part of his job is to anticipate events and evaluate the various alternatives open to him, in order to find the optimum solution, or at least come close to it. The forces at his disposal, limited by his technical and financial resources, must be placed in the right places.

It is against this backdrop that maintenance has developed methods that consider both, and to a greater or lesser extent, technique and organization. Process industries have generally applied approaches combining risk assessment, feedback analysis and maintenance task selection. Optimization of Maintenance through Reliability (OMF) is the name given to the method implemented by EDF, and now used by other industrial sectors, and which this article aims to describe.

We'll start by outlining the main principles of this method and presenting a general description. Then, after giving a few pointers on how to manage a study, we'll look at each of its stages:

• functional analysis, which provides representations of how the systems under study operate;

• systems failure analysis, which identifies the failure modes of equipment, or groups of equipment, which have an important functional role and whose failures are considered serious;

• analysis of feedback, which provides essential data for making maintenance choices;

• analysis of equipment malfunctions, which gathers the information needed to assess the criticality of failure modes;

• the selection of maintenance tasks, which involves proposing justified elementary tasks to cover significant failure modes and, after grouping them together, writing the preventive maintenance program.

If this method owes a lot to common sense, it can be said that it brings it in return:

• a structured set of simple analysis techniques;...