Preventive Maintenance Approach
of 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 the
number and variety of assets that need to be maintained, complexity in their
designs & 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 evolution
of maintenance strategies.
the past decades, preventive maintenance was the most widely used maintenance
technique. It was considered the most advanced and effective maintenance
technique 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 and
operating reliability. In turn, this assumption was based on the hypothesis that
since mechanical parts are subjected to wear and tear, the reliability of any
equipment is directly associated to its operating lifetime. Hence, it was
conjectured that, the more routinely an equipment was overhauled, the more secure
it was against the possibility of failure.
this strategy of preventive maintenance comes with a lot of limitations :
of system downtime:
Shutting down of a system, results in loss of productive time and therefore
loss of revenue.
of system maintenance:
Utilization of resources to routinely perform inessential scheduled maintenance
of grave safety or environmental ramifications: Shutting down and starting-up a
facility is one of the high-risk operations, thus intrusive preventive
maintenance practice tends to increase the risk of environmental damage.
of systems: The
more complex the systems are, the more strenuous it is to perform planned/
Reliability Centered Maintenance
intent of an efficient maintenance strategy is to avert or assuage the
consequences of failure, not to avert the failure itself. In other words: if
the ramifications of a failure do not have a deleterious effect on safety, operations,
environment or cost, then there is no exigency to carry out scheduled
centered maintenance (RCM) is the maintenance strategy implemented when
following a procedure that evaluates equipment condition and formulates the
maintenance specifications of a physical asset in its operating context. RCM accentuates the practice of
Predictive maintenance, in addition to conventional preventive methods.
“A reliability-centered maintenance program includes only those tasks
which satisfy the criteria for both applicability and effectiveness. The
applicability of a task is determined by the characteristics of the item, and
its effectiveness is defined in terms of the consequences the task is designed
to prevent.” (Source: Nowlan and Heap,
strategy provides an organized framework for exploring the functions and likely
failures for a physical asset, with an emphasis on safeguarding the system
functions, rather than preserving equipment.
practice implements techniques such as Planned Preventive Maintenance, Predictive
Testing and Inspection, Reactive Maintenance and Proactive Maintenance in a
manner so as to augment the possibility that a component/equipment will operate
in the requisite fashion over its intended life-cycle. The motive of this
practice is to provide the requisite reliability and availability at reasonable
cost. RCM entails that the maintenance decisions be founded on maintenance
requirements validated by sound scientific and financial rationale.
critical functions of any equipment or component to be safeguarded, with
routine maintenance are ascertained, and their chief failure modes and causes
are recognized. Consequences of these failures are also ascertained. The degree
of criticality are ascribed to the outcomes of failure. Certain functions are
not paramount, thus are allowed to “run to failure” while other
crucial functions must be protected at all cost. Maintenance tasks which
address the primary failure causes are adopted. It is to be noted that this
process can only address the failures that can be prevented, it cannot guard against
unforeseen circumstances, arbitrary events, etc.
Principles of Reliability Centered
chief principles upon which Reliability Centered Maintenance is based are as
RCM is function oriented: This primary aim of reliability
based maintenance is to protect the system and its function.
RCM is device group focused: RCM is predominantly concerned
with sustaining the overall functionality of a group of devices rather than an
practice of RCM gauges the relationship between the operating age and the
failures. RCM is not totally concerned with basic failure rate; it seeks to realize
the possibility of failure at specific ages.
Recognizes design limitations: One of the objectives of RCM is
to sustain the innate reliability of the component design, recognizing that
changes in reliability are subject to design rather than maintenance.
Maintenance can only accomplish and maintain the level provided for by design
of the component/equipment.
RCM is steered by safety and
of 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 undesirable
Therefore, failure may either be defined as a loss of function or a loss of adequate
RCM uses a logic tree method to assess
This provides a harmonious approach to the maintenance of all sorts of components
Maintenance tasks must be suitable: The various tasks must tackle
the different failure modes .
Maintenance Tasks must be effectual: The various tasks must minimize
the prospect of failure and be cost effective simultaneously.
RCM recognizes two types of maintenance
tasks 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 data
from the results accomplished and inputs this information back in order to enhance
future maintenance. This feedback is an essential part of the Proactive
Maintenance constituent of the RCM technique.
RCM determines the
maintenance requirements by considering the following questions:
Function – What is the component required to
do? What are the corresponding operation
Modes of Failure – In what ways can the system fail
to fulfill the requisite functions ?
Causes of Failure – What are the circumstances that
cause such failure of systems/components ?
Failure Ramifications – What transpires when each failure
Significance of failure – In what way is each failure important
Preventative Measures – What systematic tasks need to be
performed 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 appropriate
preventive task cannot be established ?
Essentially, RCM methodology addresses critical issues that are not dealt with,
by other maintenance strategies. This approach acknowledges that all components
of an infrastructure asset are not of identical importance. Focusing on the reliability
of components means accepting that their design and functions differ, and that
each component will have a different possibility of encountering failure from wear
and tear than the others. A reliability based approach will mean organizing a
maintenance program established on the understanding of equipment requirements and
preference, as well as constrained economic and human resources. The tasks have
to be planned in a manner, such that maintenance of the equipment is given priority
while operations are optimized.
To summarize, RCM is a systematic technique of assessing an asset’s components
and equipments. This leads to a higher degree of functional reliability and
cost-efficiency. This approach is highly dependent on predictive maintenance
practices. However, it also acknowledges that maintenance tasks on components that are inexpensive and less essential to the
overall reliability of the asset may be best left to a reactive maintenance
approach, focusing both labor and financial resources on critical and more
Advantages & Disadvantages of
RCM is so reliant on the application of
predictive maintenance strategies, its advantages and disadvantages reflect
those of predictive maintenance.
be the most efficient maintenance strategy.
costs by avoiding needless equipment or system maintenance.
the frequency of such system overhauls.
the possibility of sudden component/system failure.
the maintenance activities on essential components of the system.
the reliability of component.
root cause analysis.
have exceptionally high startup costs pertaining to personnel training and
potential is not readily seen by the management.