Implementation
This topic covers:
The FMECA process is carried out to:
- Provide a means of systematically and logically evaluating the maintenance requirements based on a number of criteria
- Provide a means of documenting the process for subsequent reviews
- Provide the source for compiling the Technical Maintenance Plan for the plant.
The task of defining the initial maintenance requirements is one of the most significant activities associated with the introduction of the maintenance philosophy. Initial maintenance policy decisions form the basis for a wide range of “follow-up” decisions that will ultimately consume a large proportion of resources and that have a significant bearing on both the plant performance and long term costs. For example:
- Maintenance requirements form the basis of the spare parts inventory, and thus influence the range and quantity of spares, which will be required
- Maintenance requirements are an important factor in determining the range of equipment and facilities necessary to support the workforce
- Maintenance requirements have a bearing on the range of technical data required, the level of training necessary, and the number of personnel required to support the total maintenance effort.
The direct relationship between maintenance requirements, resource costs and work capability makes it essential that maintenance policies are determined as accurately as possible. Subsequent decisions can then be developed from a sound basis, which should ensure that the required levels of support are provided as economically as possible. This leads to the consideration of a maintenance concept. The following graph indicates the likely effect on a large plant, which has been operating without a RCM philosophy.
The following considerations are addressed when considering a maintenance concept:
- The plant operational requirement and availability of the workforce
- The design and maintenance philosophies of the manufacturer, where these have a bearing on the forms of maintenance which may be adopted e.g. modular electronic equipment.
There are three concepts and any one or a combination may be considered suitable for a particular situation:
This process involves grouping together all of the tasks identified as having the same or similar frequency and performing them at that interval. For example, all one-month tasks carried out at the same time and the same for three month etc. Obviously this places an extreme demand on resources but it minimizes operation interference.
This concept is similar to Periodic Maintenance in that it groups like intervals but it spreads them over a period, say 1 year. For example if there are 24 tasks with 6 monthly intervals they could be programmed at two a month for 12 months.
The phased maintenance concept does not alter in any way the total maintenance work that will be performed. The same tasks are performed at the same basic frequency as under a periodic maintenance concept. However, it spreads the workload and makes the maintenance more manageable.
Under a flexible maintenance concept, routine servicing requirements are not grouped into “packages”. Instead, maintenance tasks required on each item, or small groups of related tasks, are individually programmed and controlled such that the complete maintenance requirement for the plant is performed progressively.
Although the same maintenance tasks are required at the same frequency as under a periodic or phased concept, flexible servicing is inherently the most efficient form of servicing. Because tasks on each item are individually controlled, they can be programmed to coincide with unscheduled work on the item, or to take advantage of short periods of downtime. In addition, unscheduled replacement of an item “resets” the interval at which a scheduled routine maintenance tasks must be performed, thus overcoming the situation of over- maintenance. Flexible maintenance is obviously inappropriate for activities that require a large effort in preparation or access.
A computerized maintenance management system should be adopted as the management program to plan, direct, and control the maintenance that is performed. The results of the maintenance analysis are input to the system and become the Maintenance Plan.
In addition to scheduling preventive maintenance, a WIMS should have a number of other capabilities to ensure the future effectiveness of the RCM strategy. In particular, the recording of relevant history against a scheduled task or a defect is significant when reviewing the plant performance. Future rationalization of the maintenance plan will be based on history, which must be captured as the RCM strategy matures.
The output from a WIMS will also be used to assist in determining the effectiveness of the RCM strategy.
Adequate information is essential for effective execution and review of maintenance requirements. Information must be RELEVANT, ACCURATE and RETRIEVABLE and is necessary to:
- Plan the maintenance work
- Execute the task by describing what is to be done
- Record the action taken.
History recording is used to provide a record of performance of an item and may incorporate some or all of the following:
- The type of failure
- The number of failures
- The circumstances when the failure was discovered
- The method that detected the failure
- The failure effect
- The condition of the item when the failure occurred.
Information can be used to:
- Control the cost of maintenance
- Identify the need for modification or redesign
- Ensure desired level of plant availability
- Evaluate the resource support
- Assist in replacement decisions
- Interface with the plant inventory requirements.
The purpose of obtaining information is to develop a sound basis for maintenance policy decisions.
The information available covers a sample of the events that have already taken place, and can be used to predict the behavior of items in the future. For this reason, it does not need to be comprehensive, i.e. knowledge of all failures of a certain type is unnecessary, but does need to be sufficiently detailed to ensure that it is indicative of a trend.
The information used for analysis purposes should normally cover a substantial period of operation i.e. two to three years. Information covering a lesser period may not provide an accurate indication of a trend, while information covering a longer period may not reflect current conditions.
Decisions based on a single incident, particularly one occurring early in the life of an item, will rarely be effective and should be avoided.
The Reliability Centered Maintenance philosophy and procedures detailed in the previous Sections form the basis for determining maintenance requirements that are effective and efficient. However, the situation with any plant is dynamic and the maintenance requirements may not remain valid for an extended period of time. For instance, modifications, new equipment or changed operations will impact on the maintenance requirements and lead to variations in the parameters on which the requirements were established.
The initial maintenance requirements should be reviewed after one year to:
- Determine whether the maintenance requirements specified are serving their intended purpose, and as a result, eliminate those which are either ineffective or inefficient
- Identify those items not included in an existing program for which some scheduled task is justified, and to introduce the necessary tasks into the program.
Performance of a full review is particularly time consuming and the cost-effectiveness of performing these at regular intervals must be assessed. While a full review is appropriate for the initial review, subsequent reviews may not warrant the detailed examination of a full review. Some considerations when determining a review are:
- Introduction of new/replacement systems as modifications or more reliable equipment should be accompanied by review of maintenance requirements to identify associated changes to maintenance tasks in all cases
- Information accumulated during operation regarding failures may generate the need for review of the complete maintenance program covering just those tasks pertaining to a particular system or item
- Change in the conditions under which the plant is operated may generate a need for review.
The review process should follow the same process used for establishing the initial maintenance requirements.