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  1. 1. CECOS University Of IT and Emerging Sciences Peshawar Mechanical Department TOPIC:RELIABILITY,CENTRED MAINTENANCE RELIABILITY By:kifayat ullah
  2. 2. Reliability Reliability is a measure of the probability that an item will perform its intended function for a specified interval under stated conditions. There are two commonly used measures of reliability: * Mean Time Between Failure (MTBF), which is defined as: total time in service / number of failures * Failure Rate (λ), which is defined as: number of failures / total time in service. Reliability centeredmaintenance: Definition: Reliability centered maintenance (RCM) is a corporate-level maintenance strategy that is implemented to optimize the maintenance program of a company or facility. The final result of an RCMprogram is the implementation of a specific maintenance strategy on each of the assets of the facility. The maintenance strategies are optimized so that the productivity of the plant is maintained using cost-effective maintenance techniques. There are four principles that are critical for an reliability centered maintenance program. 1. The primary objective is to preserve system function. 2. Identify failure modes that can affect the systemfunction. 3. Prioritize the failure modes. 4. Select applicable and effective tasks to control the failure modes. RCM History: 1965: Studies show scheduled overhaul of complex equipment has little or no effect on in- service reliability 1970: RCM had its beginning in the commercial airline sector in 1970's. At that time, the commercial airline industry was experiencing high number of crashes in the take-offs which majority of them was related to equipment failures After applying the RCM method, it proved to be highly successful; in commercial airlines it reduced crashes from 60 per million take-offs to only 2 per million and more important than that reduced the equipment related crashes from 40 per million to only 0.3 per million take- offs.
  3. 3. Types of RCM: There are different ways to conduct and implement an RCMprogram;  Classical/Rigorous Classical or rigorous RCM provides the most knowledge and data concerning system functions, failure modes, and maintenance actions addressing functional failures of any of the RCM approaches.  Intuitive/Streamlined/Abbreviated The intuitive approach identifies and implements the obvious, usually condition-based, tasks with minimal analysis. In addition, it culls or eliminates low value maintenance tasks based on historical data and Maintenance and Operations (M&O) personnel input. The Principles of RCM: • RCM is Function Oriented. • RCM is System Focused • RCM is Reliability-Centered • RCM Acknowledges Design Limitations • RCM is Driven by Safety, Security, and Economics • RCM Defines Failure as "Any Unsatisfactory Condition • RCM Uses a Logic Tree to Screen Maintenance Tasks. • RCM Tasks Must Be Applicable • RCM Tasks Must Be Effective • RCM Acknowledges Three Types of Maintenance Tasks : o Time directed (PM) o Condition directed (CM) o Failure finding (Proactive Maintenance) • RCM is a Living System The RCM Process –Basic Steps: RCMis nota stand-alone process,itmustbe an integral partof the Operationsand Maintenance program.the followingstepcanbe define asfollows. 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. The stages can be summarised as follows:
  4. 4.  System Selection.  Definition of the system boundaries.  Acquisition of Documentation and Materials.  Interviews with Plant Personnel. 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 analysis involves the following stages.  Identificationof SystemFunctions  SystemFunctional failure analysis  Equipmentidentification  ReliabilityandPerformance Datacollection  Identificationof failure modes  Identificationof failure effects  Determinationof ComponentCriticality Task Selection 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 Failure 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.
  5. 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. 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. ADVANTAGES  Can be the most efficient maintenance program.  Lowers costs by eliminating unnecessary equipment maintenance or system overhauls.  Minimizes the frequency of overhauls.  Reduces probability of sudden equipment failures.  Focuses maintenance activities on critical system components.  Increases component reliability.  Incorporates root cause analysis. DISADVANTAGES  Can have significant startup costs associated with staff training and equipment needs  Savings potential is not readily seen by management.  RCM is not cheap; it imposes many accomplishing costs to system, for example training costs and costs of employing some new experts for replacement with those who entered in the program and have not enough time to fulfill their responsibilities as before.  Dealing with hidden failures causes challenges for many analysts (and then others) not familiar with the concept
  6. 6. Reliability-CenteredMaintenanceMethodology Reliability-centered maintenance (RCM) is the optimum mix of reactive, time or interval-based, condition-based,andproactive maintenance practices. These principal maintenance strategies, rather than being applied independently, are integrated to take advantage of their respective strengths in order to maximize facility and equipment reliability while minimizing life-cycle costs. Total productive maintenance (TPM), total maintenance assurance, preventive maintenance, relia- bilitycenteredmaintenance (RCM),andmanyotherinnovative approachestomaintenance problems all aim at enhancing the effectiveness of machines to ultimately improve productivity Reliability-CenteredMaintenanceComponents The components of RCM program are shown in Figure 1. This figure showing that RCM program consists of (reactive maintenance, preventive maintenance, condition based maintenance, and proactive maintenance) and its patterns.