Preventive Maintenance ApproachMaintenanceof Infrastructure assets has evolved remarkably over the past couple of decades.This evolution is due to a variety of factors, such as, a huge rise in thenumber and variety of assets that need to be maintained, complexity in theirdesigns & structure, new and upcoming maintenance tools & methods,safety standards and the ever changing views on maintenance organization.Reliability-Centered Maintenance (RCM) has played a pivotal role in this evolutionof maintenance strategies.
Inthe past decades, preventive maintenance was the most widely used maintenancetechnique. It was considered the most advanced and effective maintenancetechnique available to the infrastructure industry. A Preventive Maintenance(PM) strategy was established on the assumption of a cause-and-effect co-relation between scheduled maintenance andoperating reliability.
In turn, this assumption was based on the hypothesis thatsince mechanical parts are subjected to wear and tear, the reliability of anyequipment is directly associated to its operating lifetime. Hence, it wasconjectured that, the more routinely an equipment was overhauled, the more secureit was against the possibility of failure.However,this strategy of preventive maintenance comes with a lot of limitations :· Costof system downtime:Shutting down of a system, results in loss of productive time and thereforeloss of revenue.· Costof system maintenance:Utilization of resources to routinely perform inessential scheduled maintenanceis exorbitant.· Probabilityof grave safety or environmental ramifications: Shutting down and starting-up afacility is one of the high-risk operations, thus intrusive preventivemaintenance practice tends to increase the risk of environmental damage.· Complexityof systems: Themore complex the systems are, the more strenuous it is to perform planned/Preventive Maintenance Reliability Centered Maintenance(RCM)IntroductionTheintent of an efficient maintenance strategy is to avert or assuage theconsequences of failure, not to avert the failure itself. In other words: ifthe ramifications of a failure do not have a deleterious effect on safety, operations,environment or cost, then there is no exigency to carry out scheduledmaintenance.
Reliabilitycentered maintenance (RCM) is the maintenance strategy implemented whenfollowing a procedure that evaluates equipment condition and formulates themaintenance specifications of a physical asset in its operating context. RCM accentuates the practice ofPredictive maintenance, in addition to conventional preventive methods. “A reliability-centered maintenance program includes only those taskswhich satisfy the criteria for both applicability and effectiveness. Theapplicability of a task is determined by the characteristics of the item, andits effectiveness is defined in terms of the consequences the task is designedto prevent.” (Source: Nowlan and Heap,1978)Thisstrategy provides an organized framework for exploring the functions and likelyfailures for a physical asset, with an emphasis on safeguarding the systemfunctions, rather than preserving equipment. RCM MethodologyRCMpractice implements techniques such as Planned Preventive Maintenance, PredictiveTesting and Inspection, Reactive Maintenance and Proactive Maintenance in amanner so as to augment the possibility that a component/equipment will operatein the requisite fashion over its intended life-cycle. The motive of thispractice is to provide the requisite reliability and availability at reasonablecost.
RCM entails that the maintenance decisions be founded on maintenancerequirements validated by sound scientific and financial rationale. Thecritical functions of any equipment or component to be safeguarded, withroutine maintenance are ascertained, and their chief failure modes and causesare recognized. Consequences of these failures are also ascertained. The degreeof criticality are ascribed to the outcomes of failure. Certain functions arenot paramount, thus are allowed to “run to failure” while othercrucial functions must be protected at all cost. Maintenance tasks whichaddress the primary failure causes are adopted.
It is to be noted that thisprocess can only address the failures that can be prevented, it cannot guard againstunforeseen circumstances, arbitrary events, etc. Principles of Reliability CenteredMaintenance Thechief principles upon which Reliability Centered Maintenance is based are asfollows:· RCM is function oriented: This primary aim of reliabilitybased maintenance is to protect the system and its function. · RCM is device group focused: RCM is predominantly concernedwith sustaining the overall functionality of a group of devices rather than anindividual component · Fundamentally Reliabilitycentered: Thepractice of RCM gauges the relationship between the operating age and thefailures.
RCM is not totally concerned with basic failure rate; it seeks to realizethe possibility of failure at specific ages. · Recognizes design limitations: One of the objectives of RCM isto sustain the innate reliability of the component design, recognizing thatchanges in reliability are subject to design rather than maintenance.Maintenance can only accomplish and maintain the level provided for by designof the component/equipment. · RCM is steered by safety andeconomics: Oneof the key yardstick of RCM is that safety must be ensured at all cost;thereafter cost-efficiency becomes the benchmark. · RCM elucidates failure as any undesirablecondition:Therefore, failure may either be defined as a loss of function or a loss of adequatequality. · RCM uses a logic tree method to assessmaintenance tasks:This provides a harmonious approach to the maintenance of all sorts of componentsand equipment. · Maintenance tasks must be suitable: The various tasks must tacklethe different failure modes .
· Maintenance Tasks must be effectual: The various tasks must minimizethe prospect of failure and be cost effective simultaneously. · RCM recognizes two types of maintenancetasks and run-to- failure:The different maintenance tasks are Interval Based or Condition-Based. In RCM,Run-to-Failure is a purposive decision and is justifiable for certain equipments. · Continuous Feedback: RCM process accumulates datafrom the results accomplished and inputs this information back in order to enhancefuture maintenance.
This feedback is an essential part of the ProactiveMaintenance constituent of the RCM technique. RCM determines themaintenance requirements by considering the following questions:· Function – What is the component required todo? What are the corresponding operationstandards ?· Modes of Failure – In what ways can the system failto fulfill the requisite functions ?· Causes of Failure – What are the circumstances thatcause such failure of systems/components ?· Failure Ramifications – What transpires when each failureoccurs ?· Significance of failure – In what way is each failure important?· Preventative Measures – What systematic tasks need to beperformed proactively to avert, or to reduce the consequences of the failure,to a reasonable or an acceptable degree ?· Alternative Measures – What must be done if an appropriatepreventive task cannot be established ?Essentially, RCM methodology addresses critical issues that are not dealt with,by other maintenance strategies. This approach acknowledges that all componentsof an infrastructure asset are not of identical importance.
Focusing on the reliabilityof components means accepting that their design and functions differ, and thateach component will have a different possibility of encountering failure from wearand tear than the others. A reliability based approach will mean organizing amaintenance program established on the understanding of equipment requirements andpreference, as well as constrained economic and human resources. The tasks haveto be planned in a manner, such that maintenance of the equipment is given prioritywhile operations are optimized.To summarize, RCM is a systematic technique of assessing an asset’s componentsand equipments.
This leads to a higher degree of functional reliability andcost-efficiency. This approach is highly dependent on predictive maintenancepractices. However, it also acknowledges that maintenance tasks on components that are inexpensive and less essential to theoverall reliability of the asset may be best left to a reactive maintenanceapproach, focusing both labor and financial resources on critical and moreexpensive equipment. Advantages & Disadvantages ofRCMSinceRCM is so reliant on the application ofpredictive maintenance strategies, its advantages and disadvantages reflectthose of predictive maintenance. Ø Advantages · Canbe the most efficient maintenance strategy.· Reducescosts by avoiding needless equipment or system maintenance.· Minimizesthe frequency of such system overhauls.· Reducesthe possibility of sudden component/system failure.
· Focusesthe maintenance activities on essential components of the system.· Improvesthe reliability of component.· Integratesroot cause analysis. Ø Disadvantages · Canhave exceptionally high startup costs pertaining to personnel training andequipment requirements· Savingspotential is not readily seen by the management.