Reliability Centered Maintenance (RCM) measures all recognised maintenance parameters and ensures repair before failure to maximise equipment availability at minimum cost, writes Dr. Ahamed Mohideen.
Plant and machinery dependency rate has become very high due to requirement of fast track projects in construction sector, which is the necessity in the present times. This has resulted in a consistent growth in demand of about 700 per cent during the period from FY98 to FY15.
Consider this: The demand for hydraulic excavators, in the construction sector, has grown from 2,000 units in FY1998 to 14,000 units in FY2016. The same scenario prevails for other construction machinery.
Maximum availability for effective utilisation of plant and machinery is one of the critical success factors in construction. Nowadays the construction contractors even monitor equipment asset versus revenue ratio to rationalise their fleet size.
Evidently, equipment performance will deteriorate with usage resulting in unplanned failures causing surprise losses to the contractor. Highest quality maintenance is the answer to such situations.
Gone are the days of breakdown and routine maintenance, and preventive maintenance became the norm. The latest concept is Reliability Centered Maintenance (RCM) which measures all recognised maintenance parameters and ensures repair before failure to maximise equipment availability at minimum cost.
RCM in construction industry
Over a hundred different categories of equipment are deployed in modern construction. They range from simple hand tools to most heavy, complex and application specific equipment comprising of state of the art prime movers, mechanicals, electrical, electronics and software controlled technologies. These various types of technology/category mix on the construction machinery demand a robust maintenance system of proper planning of maintenance strategies. Some of the systems require simple preventive maintenance techniques, while the others may require a scheduled or condition-based maintenance technique.
Although construction equipment operate in highly dusty or wet or other very challenging working environment, total Productive Maintenance and RCM needs to be analysed to arrive at the best-fit of maintenance practice, depending on the type of machinery.
Objectives of world class RCM
As RCM is part of the world class maintenance, and WMS (World Class Maintenance Systems) play a key role in reducing cost, minimising machinery downtime, improving quality, increasing productivity, providing reliability and as a result achieving the organisational goals and objectives, it is better to know the objectives of world-class maintenance systems (WMS) which are listed in the table below. The result of RCM analysis is the maintenance management strategy to ensure that asset performs reliably through specific, properly-timed inspections, analysis and preventive maintenance. Critical functions will receive extensive attention. Low priority functions may have a ôrun to failureö strategy.
RCM, one of the World Class Maintenance (WCM) strategies when implemented in letter and spirit, delivers rich dividends to equipment owners in terms of timely execution of projects through equipment availability in excess of 90 per cent, 30 to 40 per cent reduced maintenance costs and long term preservation of equipment at rated performance parameters. As a result, the traditional term ´maintenance is a necessary evil´ becomes obsolete.
4 Critical principles of RCM
Preserve the system function
Identify the failure modes affecting system function
Prioritise the failure modes
Select the applicable tasks to control the failure modes
7 Questions for RCM
What are the functions and desired performance standards of each asset?
How can each asset fail to fulfil its functions?
What are the failure modes for each functional failure?
What causes each of the failure modes?
What are the consequences of each failure?
What can and/or should be done to predict or prevent each failure?
What should be done if a suitable proactive task cannot be determined?
Analysis tools in RCM
Decision support tools including hazard studies
Root Cause Analysis (RCA)
Root Cause Failure Analysis (RCFA)
Failure Mode Effects and Analysis (FMEA)
Failure Mode Effects and Criticality Analysis (FMECA)
Total Failure Mode Effects and Analysis (TFMEA) etc.
Seven steps to implement RCM
Step 1: Selection of equipment for RCM analysis
The first step is to select equipment for RCM analysis. The equipment selected for RCM should be critical, in terms of its effect on operations, its previous costs of repair and previous costs of preventative maintenance.
Step 2: Differentiate the systems
The equipment belongs in a system that performs a function that is important to the process. The system can be as large or small as necessary, but the function of the system should be known as should its inputs and outputs. For example, the function of a conveyor belt system is to transport goods. Its inputs are the goods and mechanical energy powering the belt, while its outputs are the goods at the other end. In this case, the electric motor supplying the mechanical energy would be considered as part of a different system.
Step 3: Define the ways that the system can fail - the failure modes
In step 3 the object is to list all of the ways that the function of the system can fail. In the case of the conveyor belt it can fail by being unable to transport the goods from one end to the other, or it can fail if it does not transport the goods sufficiently quickly.
Step 4: Define the boundaries and function of the systems that contain the selected equipment
With the help of operators, experienced technicians, RCM experts and equipment experts, the root causes of each of the failure modes can be identified. Root causes for failure of the conveyor could include a lack of lubrication on the rollers, a failure of a bearing, or an insufficiently tight belt.
Step 5: Identify the root causes of the failure modes
In this step the effects of each failure mode are considered. The effects include the effects on safety, operations and other equipment. Criticality of each of these failure modes can also be considered. There are various recommended techniques that are used to give this step a systematic approach.
Failure Mode and Effects Analysis (FMEA)
Failure Mode Effect and Criticality Analysis (FMECA)
Hazard and operability Studies
Fault Tree Analysis (FTA)
Risk Based Inspection (RBI)
The most important failure modes will be determined at the conclusion of the systematic analysis of each failure mode. This will be determined by asking questions such as ´Does this failure mode have safety implications´, and ´Does this failure mode result in a full or partial outage of operations?´. It is these important failure modes that are then prioritized for further analysis. Importantly, the failure modes that are retained include only those that have a real probability of occurring under realistic operating conditions.
Step 6: Assess the effects of failure
At this step, the most appropriate maintenance tactic for each failure mode is determined. Importantly, the maintenance tactic that is selected has to technically and economically feasible.
Condition Based Maintenance is selected when it is technically and economically feasible to detect the onset of the failure mode.
Time or Usage Based Preventative Maintenance is selected when it is technically and economically feasible to reduce the risk of failure using this method.
For failure modes that do not have satisfactory condition based maintenance or preventative maintenance options, then a redesign of the system to eliminate or modify the failure mode should be considered.
Failure modes that were not identified as being critical in Step 6 may, at this stage, be identified as good candidates for a run-to-failure maintenance schedule.
Step 7: Select a maintenance tactic for each failure mode
Importantly, the RCM methodology will only be useful if its maintenance recommendations are put into practice. When that has been done, it is important that the recommendations are constantly reviewed and renewed as additional information is found.