Introduction

In previous RCM articles, I have discussed Failure Mode and Effect Analysis (FMEA), Failure cause determination and task selection. These articles covered the foundations of RCM and provider the reader with a simple and structured methodology for identifying those critical maintenance tasks that must necessarily be performed in order to achieve the designed reliability of the system being analyzed. Before integrating these tasks into the existing enterprise maintenance program, three important activities must take place:

ú Deletion of duplicate tasks

ú Coordination of tasks

ú Reconciliation with existing maintenance programs

Duplicate Tasks

While the structured process of an RCM analysis starts at the function level and ultimately ends up with a single maintenance task for each cause of failure, maintenance programs generally start at the task level and build up to a comprehensive and coordinated PM and CM program. No matter how simple the system being analyzed with an RCM process, there is a great probability that a maintenance tasks may be employed numerous times to prevent various failure causes. Significant labor and cost savings may be realized if these duplicate tasks are combined or eliminated.

Consider a transmission line protection scheme. It is recognized that a key function of the scheme is for the proper breaker(s) to trip in the event of a line fault, isolating the electric system from the fault. There are several key pieces of equipment that support the tripping function including the protective relays and circuit breakers. From the protective relay point of view, an open trip circuit represents a possible hidden failure. From a breaker mechanism point of view, periodic exercising of the breaker between lubrication intervals may be deemed prudent. Both of these two failure causes suggest the implementation of a periodic functional trip test. If planned correctly, only one of these trip tests is required and the second is redundant.

The key to eliminating duplicate maintenance tasks is understanding the goal or expected outcome of each task. Many times the results of one task are just a subset of another. If such task redundancy exists, elimination of the subordinate task is justified.

Coordination of Tasks

A goal of RCM is to keep equipment and system availability high. To meet this availability goal, RCM suggests the implementation of on-line monitoring or continuous in-service diagnostic tasks wherever possible. By definition, these tasks warn of the onset of a failure without requiring diagnostic outages. Unfortunately, not all maintenance tasks can be performed with the equipment in-service. For those maintenance tasks requiring the equipment removed from service, efficient use of the outage period is desirable.

In order to achieve optimal maintenance, no maintenance task can be viewed in isolation. All maintenance tasks requiring an outage must be reviewed together and determined:

ú What are the age drivers for the most frequent tasks

ú What are the most time consuming tasks

ú Do certain tasks facilitate the performance of other tasks?

ú Are there regulatory requirements that drive any of the task intervals?

ú Are there opportunities to perform the maintenance tasks during shutdowns scheduled for other reasons?

Once the above questions are fully answered, maintenance task can be logically grouped. Tasks requiring the equipment to be out-of-service should be segregated from in-service tasks. Periodic tasks taking place at the same frequency should also be grouped together.

Task Reconciliation

Most utility RCM work is focused on improving existing maintenance programs rather than developing a new maintenance program from scratch. RCM will suggest areas for improving one’s maintenance program but one should not be to over zealous on implementing the RCM findings without some formal review. We must recognize the fact that:

ú The current maintenance program may have completely eliminated certain failure causes that were not considered by the analyst.

ú The RCM analysis may have been incomplete.

ú Utility Regulatory Commissions may require notification when maintenance programs change.

ú Utility maintenance culture may view the RCM based maintenance program with suspicion.

For all the above reasons, it is necessary to compare and reconcile the proposed RCM based maintenance program with the traditional maintenance program. All differences must be identified, justified and documented. If the new RCM task can not be supported, continuation of the historical maintenance task is justified. If historical maintenance tasks have no equivalent RCM replacement, it must be determined if the failure cause and resulting failure effect have no consequence or was an error in the RCM analysis.

Comparing RCM recommended maintenance tasks to the current PM program tasks should be a documented process. All the current and proposed tasks should be included in the documentation as well as the final reconciliation. A simple four column list containing a column each for:

ú RCM Recommended TASK

ú Present PM Task

ú Resultant PM Program

ú Reconciliation Note

The reconciliation column should indicate:

ú Traditional PM Task deleted

ú New Tasks added

ú Traditional PM Tasks retained

ú New Tasks modified

ú Traditional PM Tasks modified

Resolving Conflicts

Maintenance is not an exact science and neither is RCM. From time to time, it may appear that the RCM recommendations are in conflict with other findings or traditional approaches to maintenance. While these types of conflicts are rare, they do occur. In resolving the conflicts one must make sure that the RCM findings are:

ú Technically accurate and based on solid data.

ú Supported by all on-site technical resources

ú Not in conflict with contractual or legal commitments and obligations

If the RCM findings do comply with the above, it must be determined the conflicting maintenance recommendations also comply with the above. In most cases, a technical flaw will be identified and the conflict resolved. If no flaws can be found and conflicts still exists, the more conservative maintenance approach is chosen until future events unmistakably reveal one maintenance approach to be better than the other.

In the Next Doble Exchange:

Task Interval Determination.

Editors Note: John Skog is a Doble Consultant in the area of Maintenance Management. He introduced the Client Group to RCM in 1993. John performs RCM training and consulting services through Doble and is available to assist clients in the refinement of their current maintenance programs.