Maintenance and Quality

Management (PGS-MQM-611)
MSc. Sustainable Energy
Reliability Centred
Maintenance
 Background
The power industry worldwide has been the subject of
major reviews and reforms in recent years, which have
resulted in changing demands in respect of enhanced
safety, reliability, environmental safeguards and
commercial competition. In such an environment it is
essential that the personnel and the plant and equipment
involved, perform to their optimum levels of capability.
Reliability Centred Maintenance is a maintenance
Optimization tool which has a role in providing an
effective response to such demands on the industry, by
enhancing the effectiveness of operations and
maintenance programmes.
 Background
Previously, preventive maintenance was primarily
time-based (e.g., overhauling equipment after a certain
number of hours of flying time). In contrast RCM is
condition-based, with maintenance intervals based on
actual equipment criticality and performance data.
After adopting this approach, airlines found that
maintenance costs remained about constant, but that
the availability and reliability of their aircraft improved
because effort was spent on maintenance of
equipment most likely to cause serious problems. As a
result, RCM is now used by most of the world's
airlines.
Maintenance and Reliability Centred Maintenance
(RCM)
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”.
Reliability-centred maintenance

Reliability-centred maintenance (RCM): A

systematic consideration of system
functions, the way functions can fail, and a
priority-based consideration of safety and
economics that identifies applicable and
effective PM tasks.
Reliability Centred Maintenance (RCM)

Reliability Centred Maintenance (RCM) is a

proven methodology for developing
effective maintenance strategies. It is a
reliability optimization tool that captures
daily decisions on repair procedures, their
impact on planned execution and analyze the
information for understanding future
reliability, resulting in:
Reliability Centred Maintenance
(RCM)
Reliability Centred Maintenance (RCM)
• Doing the right things at the right time
• Applications of appropriate strategies for
each type of cost equipment
• Minimizing
• Employing the right tool
• Identifying and correcting the faults quickly
• Taking appropriate actions with required
information being captured
 RCM basic questions
1. What are the functions and associated desired standards of
performance of the asset in its present operating context
(functions)?
2. In what ways can it fail to fulfill its functions (functional
failures)?
3. What causes each functional failure (failure modes)?
4. What happens when each failure occurs (failure effects)?
5. In what way does each failure matter (failure
consequences)?
6. What should be done to predict or prevent each failure
(proactive tasks and task intervals)?
7. What should be done if a suitable proactive task cannot be
found (default actions)?
 RCM main steps of analysis
1. Study preparation
2. System selection and definition
3. Functional failure analysis (FFA)
4. Critical item selection
5. FMECA
6. Selection of maintenance actions
7. Determination of maintenance intervals
8. Preventive maintenance comparison analysis
9. Treatment of noncritical items
10. Implementation
11. In-service data collection and updating
 System selection
Should consider:
 To which systems are an RCM analysis beneficial
compared with more traditional maintenance planning?
 At what level of assembly (plant, system, subsystem)
should the analysis be conducted?
The following system hierarchy levels are used:
1. Plant (e.g., process plant)
2. System (e.g., gas compression system)
3. Subsystem (e.g., one gas compressor)
4. Maintainable item (is an item that is able to perform at
least one significant function as a stand alone item (e.g.,
pumps, valves, electric motors)
Functional failure analysis
The criticality of functional failures must be judged
on plant level and should be ranked in the fours
consequence classes:
S: Safety of personnel
E: Environmental impact
A: Production availability
M: Material loss
The consequence may be ranked as high (H),
medium (M), low (L), or negligible (N). If at least
one of the four entries are medium (M) or high (H),
the functional failure should be subject to further
analysis.
 Critical item selection
 Functional significant items (FSI) FSIs are items
for which a functional failure has consequences
that are either medium (M) or high (H) for at
least one of the four consequence classes (S, E,
A, and M)
 Maintenance cost significant items (MCSI) MCSIs
are items with high failure rate, high repair cost,
low maintainability, long lead time for spare parts,
or that require external maintenance personnel
 Maintenance significant items (MSI) MSIs are
items that are either FSIs or MCSIs, or both
Functional Failure Modes Effects and
Criticality Analysis (FMECA)
Classical RCM focuses on the functional failures of systems and
components. A systematic process is employed to determine the
functions of physical assets, failure modes, consequences of
failure, their significance and hence their criticality.
In its most comprehensive form this process is described as a
failure modes effects and criticality analysis or FMECA. The
electricity, gas and the automotive industry have typically used a
simplified form of the process which is FMEA.
Some utilities have developed checklists that are designed to follow
the logical steps of the process without explicitly defining each of
the steps. Checklists are used to assist the assessment of the
consequences of equipment failure. The checklists implicitly
assume that the failure modes of the equipment and the impact of
systems functions are understood.
 Functional Failure Modes Effects and
Criticality Analysis (FMECA)

For example an auxiliary boiler might supply

steam to a key production process as its
primary function and provide factory heating as
its secondary function.
 System Functions
Every physical asset has one or more functions to
perform. The objective of maintenance is to ensure that
those assets continue to perform their functions. In the
RCM process the first step of the analysis requires that
the functions of the selected system be defined. Simple
schematic diagrams illustrating the system components,
flow paths and interactions are useful.
Physical assets usually have a primary function which is
often defined by the name of the asset, e.g. condensate
extraction pump. Secondary functions are not so easy to
identify but are critical to the successful outcome of the
RCM process.
 General Benefits
•ƒ
People understand why each task is being done ƒ
• All Tasks now getting included on the work order;
• F
ƒailures that would have occurred because no PM
existed are being captured; ƒ
• The whole inspection program is becoming more
precise ƒ
• The risks (Effects) being managed by each task is
documented ƒ
• Work history is being used;
• P
ƒarts are being put in the right location. ƒ
• For safety critical plant every possible function and
mode of failure is being examined to leave no doubt;
Primary Goals of RCM - Reliability
The overall aim of the RCM process is not
necessarily to reduce the cost of the maintenance
programmes but to improve the functional
performance of the plant equipment. Enhanced
reliability and efficiency will in turn contribute to
improved economic and safety performance of
the plant equipment.
 Key RCM questions
 What are this component‟s failure modes?
 For each failure mode:
 How likely is this failure to occur?
 Is the probability of this failure:
•Higher when component is old? (“age-related”)
•Higher when component is young? (“infant mortality”)
•Unrelated to component age? (“random”)
 How serious are the consequences of this failure?
 Can we detect an incipient failure before it occurs?
Total productive maintenance (TPM)
Total productive maintenance (TPM) was developed
in Japan (Nakajima, 1988) to support the
implementation of just-in-time manufacturing and to
improve product and process quality.

TPM comprises
 A philosophy to permeate throughout an
operating company touching people on all levels.
 A collection of techniques and practices aimed at
maximizing the effectiveness (best possible
return) of business facilities and processes.
 TPM
TPM is a Japanese approach aimed to:
 Create a company culture that will give maximum
efficiency
 Prevent losses with minimum efforts and cost
• i.e., zero breakdowns and failures, zero
accidents, and zero defects
 Create team work (small group activity) focused
on condition and performance to achieve zero
loss
 Involve all employees from top management to
operators
 TPM
Six major losses
 Availability losses
 Equipment failure (breakdown) losses
 Setup and adjustment losses
 Performance (speed) losses
 Idling and minor stoppages
(≤10minutes)
 Reduced speed losses
 Quality losses
 Defects is process and reworking losses
 Yield losses
 Overall equipment effectiveness
The overall equipment effectiveness (OEE) is determined
by the six major losses. The time concepts used are
illustrated in the table below.
Gross available time: t
Available time: tO
Net available time: tR
Operating time: tF Planned
downtime
Net operating time: tN Setup, (vacation,
Valuable Rejects, Breakdowns, adjustments, holidays,
operating nonquality and machine lubrication, changeover
time: tU Speed losses failures and testing time)
Overall equipment effectiveness
The factors used to determine the OEE are
 Operational availability AO = tF/tR
 Performance rate RP = tN/tF
 Quality rate RQ = tU/tF
The quality rate RQ may alternatively be measured as

RQ = No. of processed products−No. of rejected products

No. of processed products

The OEE is defined as

OEE = AO  RP  RQ
Reliability and Availability
• Reliability:
The ability of an item to operate under designated operating
conditions for a designated period of time or number of
cycles.
Remark: The ability of an item can be designated through a
probability, or can be designated deterministic

• Availability:
The probability that an item will be operational at a given time
Remark: Mathematically the Availability of an item is a
measure of the fraction of time that the item is in operating
conditions in relation to total or calendar time
Maintainability
• Maintainability:
The probability that a given active maintenance action, for an item
under given conditions of use can be carried out within a stated
time interval when the maintenance is performed under stated
conditions and using stated procedures and resources (IEC
60050)1)
Remark: probabilistic definition
• Safety:
Freedom from unacceptable risk of harm
Remark: very vague definition
• RAMS: An acronym meaning a combination of Reliability,
Availability, Maintainability and Safety
Dependability

Reliability Availability

Dependability

Maintainability Safety
Terms
• Hazard: A physical situation with a potential for
human injury, damage to property, damage to the
environment or some combination of these
• Individual Risk: The frequency at which an individual
may be expected to sustain a given level of harm from
the realisation of specified hazards
• Social Risk: The frequency with which a specified
number of people in a given population, or population
as a whole, sustain a specified level of harm from the
realisation of specified hazards
Calculations
MTBF = 80 MTBF = 80
RS = Ri n
 = 1/80 = 0,0125 = 1/80 = 0,0125 Serial System
R = 0,9 R = 0,9

We know
R(t) = e –  . t =  – Q(t)
Q(t) = 1 – R(t) Qav ~  . t / 2
 = 1 / MTBF [h-1]
MTBF = Operational Time / Number of Stops
MTTR = Sum of Repair Time / Number of Repairs
For the System we yield:
S =  = 0.0125 + 0.0125 = 0.025 1/h
MTBFS = 1/(1/MTBF + 1/MTBF) =1/(1/80 + 1/80) = 40 h
RS = R x R = 0,9 x 0,9 = 0,81
QS = Q + Q – (Q x Q) = 0.1 + 0,. – 0.01 = 0.19 = 1 - 0,81
 System Reliability
• Most products are made up of a number of components
• The reliability of each component and the configuration of the
system consisting of these components determines the system
reliability (i.e., the reliability of the product).
• The components may be in
– series: system operates if all components operate
– parallel: system operates is any component operates
– combination of series and parallel

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 Components in Series
• If the components are in series, the system operates
if all the components operate
• If there are n components in series, where the
reliability if the i-th component is denoted by ri , the
system reliability is
Rs  ( r1 )(r2 )( rn )

A B C

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 Components in Series
Example 6 A module of a satellite monitoring system
has 500 components in series. The reliability of each
component is 0.999. Find the reliability of the
module. If the number of components is reduced
to 200, what is the reliability?

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 Components in Parallel
• If the components are in
parallel, the system A
operates if any
component operates
• If there are n
components in parallel, B
where the reliability of
the i-th component is
denoted by ri , the system
reliability is C
Rp  1  (1  r1 )(1  r2 )(1  rn )
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 Components in Parallel
Example 7 Find the reliability of a system with three
components, A, B, and C in parallel. The reliabilities
of A, B, and C are 0.95, 0.92, and 0.90, respectively.

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 Redundant Systems and
Backup Components
• If a system contains a
backup or spare components, Power
Source
it can be treated as the one
with components in parallel.
The following formula
is equivalent to
Battery
Rb  r1  rb (1  r1 )

R p  1  (1  r1 )(1  rb )

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 Combination System
Example 8 Find the reliability of the following system

0.89

0.99 0.98 0.95

0.89 0.95

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 FMEA, FMECA, and CBM
It is often wrongly believed that Reliability Centred
Maintenance (RCM), Failure Modes and Effects
Analysis, (FMEA), Failure Modes, Effects, and Criticality
Analysis (FMECA) and Condition Based Maintenance
(CBM) are independent processes.
They‟re not.
 RCM Process
As shown below, the four steps of the RCM process
produce a FMEA.
 Generation of FMECA
So, when you do RCM, the requirement for a FMEA
and a FMECA is largely satisfied.
 RCM Process
FMEA, FMECA, and CBM…when you do RCM, you
do „them all. And don‟t let anyone else tell you
differently
Reliability Centred Maintenance

Reliability Centred Maintenance, abbreviated as RCM,

and Failure Mode and Effects Analysis, also known as
FMEA, are both practical tools that work towards
enhancing the dependability and maintenance
procedures of systems or equipment. Although they
have different approaches to the issue, each tool
provides unique benefits and faces its own set of
challenges.
 RCM
7 questions to ask when starting an RCM program

1. What is the item‟s purpose?

2. What are ways it can fail to perform main action?
3. What events are the causes of each failure?
4. What happens when each failure occurs?
5. How does each failure impact the system?
6. What task can be performed proactively to
prevent, or lessen the impact of, failure?
7. What actions must be taken if preventive task
can‟t be found?
Thank You