The relationship between RCM and traditional maintenance practices can best be summarised as follows:
“Plant and equipment are installed and employed to do what the users want them to do.
Maintenance is undertaken in a variety of forms, to ensure that the plant and equipment continues to do what the users want it to do. Reliability Centred Maintenance determines what maintenance needs to be performed and what testing and inspection needs to be performed to support the maintenance strategy”.
The outcomes of an RCM analysis can result in changes to existing preventive maintenance tasks, the use of condition monitoring, inspections and functional testing, or the addition or elimination of such tasks. Figure 1 shows the structure of maintenance.
Fig.1. Maintenance Structure.
When used effectively it can result in the enhancement of safety and reliability of plant and equipment and the optimization of operations and maintenance activities.
RCM is not a process, which will result in short term benefits, so those adopting it should be prepared for a 5 to 10 year payback term.
2.2. RCM as a tool for Optimization of Operations and Maintenance activities
RCM is a decision making tool. Operations and maintenance programmes can benefit both the processes involved in the decision-making, “soft“ benefits and the outcomes, that result in the changes to maintenance and operations programmes. The following are some examples:
⎯
The act of performing the RCM decision-making process provides a benefit in promoting better co-operation among all of those involved in the process.⎯
The process demands that all established tasks are challenged with the objective of justifying continued use or removing/replacing them with other tasks, in doing so it promotes a healthy questioning attitude.⎯
The process raises awareness of the functions of the systems involved, the consequences of failure of those functions and the economics of operating and maintaining them.The clear aims of RCM are to improve reliability and optimise the cost effectiveness of maintenance activities. When performed effectively it will result in the elimination of unnecessary maintenance tasks and the introduction of measures to address omissions and deficiencies in maintenance programmes.
2.3. The Principles of RCM
The RCM analysis process centres on the functions of plant and equipment, the consequences of failure and measures to prevent or cope with functional failure. The process must establish answers to the following questions and an effective response to them:-
⎯
What are the functions and performance standards of the plant?⎯
In what ways does it fail to fulfil its functions?⎯
What causes each functional failure?⎯
What happens when each failure occurs?⎯
In what way does each failure matter?⎯
What can be done to predict or prevent each failure?⎯
What should be done if a suitable proactive task cannot be found?2.4. The RCM Process – Basic Steps
RCM is not a stand-alone process, it must be an integral part of the Operations and Maintenance programmes. The introduction of the RCM process will involve changes to established working processes. For the successful introduction of such changes it will be important that management demonstrate their commitment to the changes, possibly in the form of a policy statement and personal involvement and that measures are taken to establish the engagement of those who will be involved or affected by the changes. RCM works best when employed as a bottom up process, involving those working directly in the operation and maintenance of the plant and equipment.
2.4.1. Preparation
The preparatory phase has a number of steps which basically involve the selection of the systems to be analysed, gathering the necessary data for the analysis. In addition the ground rules or criteria to be used in the selection and analysis process must be established. For
example; Key Assumptions, Critical Evaluation Criteria, Non Critical Evaluation Criteria and Establishment of a review process. The stages can be summarised as follows:
⎯
System Selection⎯
Definition of the system boundaries⎯
Acquisition of Documentation and Materials⎯
Interviews with Plant PersonnelThese stages will be discussed in more detail later in the document 2.4.2. Analysis
Once the systems have been selected for analysis and the preparations have been completed the analysis can commence. Experience in the analysis process is important for effective decision-making. Such experience may exist in the utility or it may be bought in from specialist service providers in this area.
The data contained in formal systems is usually very comprehensive but knowledge management is not so well developed in NPPs that all experience is captured in data basis.
For this reason it is important that personnel with local experience in the operation and maintenance of the plant are involved in the analysis process.
The first stage of the analysis process therefore is the assembly of a team with a suitable range of qualifications and experience for the task. The analysis involves the following stages.
⎯
Identification of System Functions⎯
System Functional failure analysis⎯
Equipment identification⎯
Reliability and Performance Data collection⎯
Identification of failure modes⎯
Identification of failure effects⎯
Determination of Component Criticality 2.4.3. Task SelectionWhen the analysis has been completed the next part of the process is to allocate suitable maintenance tasks to the systems and equipment identified in the analysis process, in accordance with the significance ascribed to them, be they critical or non-critical. This part of the process will seek to establish the most cost effective means of delivering the maintenance strategy in respect of achieving safety, reliability, environmental and economic goals.
The task selection process uses various forms of logical decision making to arrive at conclusions in a systematic manner. The outcomes can include:
⎯
Preventive maintenance⎯
Condition monitoring⎯
Inspection and functional testing⎯
Run to Failure2.4.4. Task Comparison
When the task selection has been completed and reviewed, the recommendations arising from the task selection process will be compared against the current maintenance practices. The purpose of this comparison is to identify the changes needed to the maintenance programme and the impact on resources and other commitments.
2.4.5. Task Comparison Review
The outputs of the analysis will result in a change to the maintenance programme. It is important that such changes are consistent with the maintenance philosophy of the plant and with regulatory and social obligations. For this reason it is important that the process and its outcomes be subjected to a final review.
2.4.6. Records
RCM should form part of a living programme. The outcomes of the analysis process and the implementation of the recommendations will have an impact on the effectiveness of the operations and maintenance programmes. It is important therefore, that all decisions, the basis for them and those involved in making them are effectively recorded, so that the information is available to those carrying out subsequent reviews of the maintenance strategy.
3. PRACTICAL APPLICATIONS