Maintenance Engineering

1. UNIT - I
PRINCIPLES &
PRACTICES OF MAINTENANCE
PLANNING
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2. MAINTENANCE
Maintenance is the routine and recurring process
of keeping a particular machine or asset in its normal
operating condition so that it can deliver the expected
performance or service without any loss or damage.
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The responsibility of the maintenance function should
be to ensure that production equipment/facilities are
available for use for maximum time at minimum cost
within stipulated time period.

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CONCEPT OF PLANNING
Planning ensures the smooth operation of the system. For effective
working of any system, it is necessary to plan and schedule its activities.
The basic objectives of any planning task are to convert the concepts
into workable actions.
There are several approaches in planning which are necessary to fulfill the objectives of
organization. The planning in engineering system is classified into three major approaches:
• Long range Planning
• Short range Planning and
• Planning for immediate activity
Long Range Planning
Long range planning refers to the planning spread over span of five to ten years. In this type
of planning the goals are set, strategies are developed and operational programmed are
devised for the period of planning.
Short Range Planning
Short range planning is prepared by the concerned departments for a relatively shorter period
of time say one to two years.
Immediate Activity Planning
Immediate activity planning is a routine and is done at the working level as and when
required.

4. MAINTENANCE PLANNING
Maintenance planning is the task of organizing
resources to carry out a job satisfactorily at
reasonable cost within a specified period of time.
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Objectives of Maintenance Planning
The most important objective of the maintenance system is the maximization of availability
of equipments and facilities so as to help in achieving the ultimate goals of the
organization. The following are the objectives of planned maintenance activity:
(i) To achieve minimum breakdown and to keep the plant in good working condition at the
lowest possible cost
(ii) To ensure the availability of the machines and services in an optimum working condition
(iii) To keep the Machines and other facilities in a condition to be used to achieve the
maximum profit without any interruption or hindrance
(iv) To keep the time schedule of delivery to the customers or to the sections for further
processing
(v) To meet the availability requirements for critical equipments
(vi) To keep the maintenance costs as low as possible for non critical equipments
(vii) To control the cost of maintenance related activities
(viii) To provide effective and trained supervision
(ix) To meet the quality requirements of the product.
(x) To increase the profits of production systems.

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PRINCIPLES OF MAINTENANCE
The main areas of work governed by these principles are:
(i) Plant Management in Maintenance work
The main role of the maintenance function is to provide safe and effective
operation of the equipment to achieve the desired targets on time with economic usage of
resources.
(ii) Production and Maintenance objectives
The plant operation is driven by the production targets. The objective of
maintenance function is to support these targets. The achievement of desired goals of the
production system is to be supported by both the production and maintenance department to
ensure smooth and successful operation of the industry.
(iii) Establishment of Work order and Recording system
The maintenance system should have proper work order and recording
system. The work order for the maintenance function indicates the nature of work to be
performed and the series of operations to be followed to execute a particular job
(iv) Information Based Decision Making
The maintenance objectives are successfully achieved by the use of reliable
information system. This information is used to meet the manpower and spare parts
requirements of the industry.
(v) Adherence to Planned Maintenance Strategy
A sound maintenance management should adhere to the planned maintenance strategy. This also
includes the use of manufacturer's information on the life and maintenance schedules of the equipment and other
material resources available.

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(vi) Planning of Maintenance Functions
All the maintenance functions are to be carefully executed by a way of proper planning
to ensure the effective utilization of manpower and materials.
(vii) Manpower for Maintenance
The manpower requirements of the maintenance system must be carefully evaluated
based on the time and motion study. The requirements should also satisfies the need arising in
cases of overhauls, component replacement, emergency and unscheduled repairs.
(viii) Workforce Control
Determination of exact workforce required to meet the maintenance objectives of the
system is difficult task due to the element of uncertainty. Hence the proper control and
monitoring of workforce are needs to be ensured.
(ix) Role of Spare Parts
A good maintenance management system requires appropriate tools. So the system
should have good quality tools and that too available in required quantities to ensure the proper
function of the maintenance works.
(x) Training of the Maintenance Workforce
Training of the workforce must be integral part of any good maintenance management
system. Training helps the workforce to learn about the modem techniques, recent trends in
maintenance, knowledge of sophisticated instruments and to chalk out a strategy to meet the
growing demands of the industry.

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SOUND MAINTENANCE MANAGEMENT SYSTEM
The profit of any industry depends solely on the return on the investment. The capital cost
and operating costs are the major factors involved in any industrial investment. The life of
the equipment and maintenance schedule information provided by manufacturer may not
realized in practice to make the need for having a sound management system.
The following are the benefits of sound maintenance management system:
(i) Minimization of down time
(ii) Improvement in availability of system
(iii) Extended life of equipment
(iv) Safety and smooth operation of the process
(v) Provide adequate back up supply
(vi) Minimization of normal expected wear and tear of equipment
(vii) Safety of the personal involved in the organization
(viii) Increased reliability of the system
(ix) Provide proper working environment
(x) Cost effective maintenance boost the profit of the production system

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RELIABILITY
The concept of reliability has found increased use in industrial engineering maintenance
and management. The reliability of any engineering system is based on the reliability of product,
equipment and various components of the system. The application of reliability techniques to
any equipment helps to identify the flaws in system design, compare several possible
configurations, minimize downtime, maximize operational readiness, reduce operating costs and
develop maintenance policies.
NEED FOR RELIABILITY IN MAINTENANCE
The reliability of a system, equipment, and product is very important aspect of quality for its
consistent performance over its expected life span. In case of sudden failure in anyone
component, the entire assembly or system results in loss of production, may cause potential
health hazard, accident and interruption in continuity of service
Examples include electric power generation and distribution system, process plants, aero plane.
automobile vehicles, etc.
Reliability is defined as the probability that a component/system. when operating under given
condition, will perform its intended functions adequately for a specified period of time. It refers
to the like hood that equipment will not fail during its operation. The four important factors
required in the determination of reliability are:
(i) Reliability expressed as probability (ii) Adequate performance requirements
(iii) Duration of adequate perfomance (iv) Environmental or operating conditions

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(i) Reliability Expressed as Probability
Probability is the ratio of the number of times we can expect an event to occur to the
total number of trials undertaken. A reliability factor can be expressed as probability. A
reliability factor equal to one means that device performs satisfactorily for the prescribed
duration under the given environmental condition. A reliability factor of zero means that all
cases the equipment would fail to meet the required performance level.
(ii) Adequate Performance Requirements
This defines the role expected of a device or system. A system may perform
satisfactorily even though one or more components may not be functioning. In reliability analysis
there is a need to define the magnitude of satisfactory or adequate performance of the system.
(iii) Duration of Adequate Performance
The duration of adequate performance is used to state the time up to which the desired
performance of the system is achieved under the given operating conditions.
(iv) Environmental or Operating Conditions
Environmental conditions indicate the prevailing.' conditions at which the system is
under operation.

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FAILURE PATTERN OF EQUIPMENT
The failure pattern of equipment over its whole life cycle can be
represented as shown in Figure
In Phase 1
The failure pattern inherent in a new product because of manufacturing or design defects.
This is refereed to as infant mortality period of equipment.
Phase II
shows the useful life period of an equipment where the failures rates are normally moderate as
the equipment gets set to the working environment.
In Phase III,
the failures are occurring due to wear out failures that are caused due to aging of the equipment.
The equipment life cycle is the essential requirement for the prediction of system reliability. The
other important parameters such as repair time distribution can be used to estimate availability,
maintainability and level of corrective and preventive maintenance.

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Failure Density
Failure density is the ratio of the number of failures during a given unit interval of time to the
total number of items at the very beginning of the test. Let n1 be the number of components that
fail during the first unit interval, n2 be the number that fail during the second unit interval and so
on. Let there are N population.

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Failure Rate (Z)
Failure rate is the ratio of the number of failures during particular unit interval to the average
population during that interval. This failure rate is also known as hazard rate and instantaneous
failure rate.
Reliability (R)
Reliability is the probability of a device performing its purpose adequately for the period in
tenaed under the given operating conditions .Reliability is the ratio of the survivors at any given
time to the total initial population.
Reliability Model
A basic measurement of the reliability of the product i.e., its probability of survival is that of
mean time between failures. Suppose that n products are taken at random from a large group and
let nt of them fail during the time period t. Then the probability of failure during the period t is
given by P =nt /n
It is necessary to evaluate the performance of the product over the intended length of time T for
the determination of reliability. Then
Reliability = 1- Probability of Failure

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PROBABILITY OF FAILURE
The probability of failure is the ratio of the number of units that failed at specified period of time
to the total population.
Mean Failure Rate (h)
The mean failure rate h is obtained by finding the mean of the failures rates for specified period
of time.
Where Z7 represents failure rates over the specified period of time
Mean Time to Failure (MTTF)
Let t1is the time to failure for the first specimen, t2 is the time to failure for the second specimen
and t n is the time to failure for the Nth
specimen. Hence the mean time to failure for N specimens
are
It is difficult to record the failure for each component when the numbers of specimens tested are
large. Instead. we can record the number which fails during the specific intervals of time.
If n1 is the number of specimens that failed during the first hour, n2 is the number that failed
during the second hour and nk is the number that failed during the kill hour. Then the mean time
to failure for N 'specimens is MTTF = (n l + 2n2 + 3n3 + + k nk ) / N
It is better to represent the time as interval instead of the time as such as. Hence the time interval
is ∆ t instead of one hour.

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Mean Time Between Failures (MTBF)
Mean Time Between Failures (MTBF) is the mean or average time between successive failures
of a product. Mean time between failures refers to the average time of breakdown until the device
is beyond repair.
Mean Time to Repair (MTTR)
Mean Time to repair (MTTR) is the arithmetic mean of the time required to perform maintenance
action. MTTR is defined as the ratio of total maintenance time and number of
maintenance action.
Maintenance Action Rate
Maintenance action rate is the number of maintenance action that can be carried out on
equipment per hour.

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1.2.5. TYPES OF RELIABILITY
Reliability can be generally of two types
1. Inherent Reliability
It is associated with the quality of the. material and design of
machine parts.
2. Achievable Reliability
It depends upon other factors such as maintenance and operation of
the equipment.
1.2.6. SERIES RELIABILITY MODEL
In this model, the components are arranged in series and the success of the system depends on
the success of all of its components. Consider the reliability model as shown in Figure 1.6 in
which n
components having reliabilities as R1, R2, •••.• Rn are connected in series .In this system, the
failure of any component puts the complete system in down position. The reliability of the
complete system would be Rs = R1 X R2 X R3 X ••.•.• X R n
.

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PARALLEL RELIABILITY MODEL
In this model, the system can be partially operative even if some of its components are in the
state of failure. Consider the reliability model as shown in Figure. in which n components
having reliabilities as R1 R2 •.•... Rn are connected in parallel. The total system reliability can
be
calculated by the product law of unreliability of the system.
The overall system is given by
PARALLEL RELIABILITY MODEL

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SERIES-PARALLEL RELIABILITY MODEL
In practice, more complex configurations exist where components are arranged in series and
parallel. The reliability structure of such complex system is decomposed into simpler structures
through successive application of the conditional probability theorem. The reliability of the
system can be determined from the failure probability of the arrangement as a consequence of
Let us consider the arrangement as shown in Figure If R1, R2, R3 and R4 be the reliabilities of
units 1,2,3 and 4 respectively. Failure of R, R2 is expressed a s ( l-probability of reliability).
Thus
The increasing complexity of present day equipment maintenance management has brought into
focus two other aspects known as maintainability and availability, both of them are closely
related to reliability.

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Maintenance and Reliability
The total reliability of any equipment is a function of design, maintenance and
field operational reliability. RF = f( D, M, FO)
MAINTAINABILITY
Maintainability is defined as the probability that a unit or system will be restored to
specified working conditions within a given period when maintenance action is taken in
accordance with the prescribed procedures and resources. Maintainability is also expressed in
terms of the minimum cost of maintenance as well as the accuracy of the maintenance functions.
The numerical value of maintainability lies between zero and one.
AVAILABILITY
Availability is the-ratio of the time at which equipment is available for the designated
operation/service to the total time of operation and maintenance of the equipment.
It is also defined as the ratio of equipments uptime to the equipment uptime and
downtime over a specified period of time. The uptime of a machine/equipment is the time for
which it is in actually available to complete the desired function.
The downtime or outage of a machine is the period of time during which it is not in an
acceptable working condition.
There are three types of availability are defined based on the time element. They are
(i) Inherent Availability
(ii) Achieved Availability
(iii) Operational Availability

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Inherent Availability
Inherent availability is the probability that a system or equipment shall operate
satisfactorily when used under prescribed conditions in an ideal support environment without any
scheduled or preventive maintenance at any given time,
Inherent Availability = MTBM / MTBM+MTTR
Ideal support environment means the ready availability of tools, spare pats, manpower,
manual, etc,
Achieved Availability
Achieved availability is the probability that a system or equipment shall operate satisfactorily
when used under prescribed conditions in an ideal support environment with periodic preventive
and corrective maintenance at any given time.
Achieved Availability = MTBM / MTBM+M
where M' is the mean active maintenance downtime resulting from preventive and corrective
maintenance

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Operational Availability
In Industrial system, a certain amount of delay will always caused by time element
such as supply downtime and administrative dowl1time.
Operational Availability is the probability that a system or equipment shall operate
satisfactorily when used under prescribed conditions in an actual supply environment without
any scheduled or preventive maintenance at any given time,
Operational Availability = ------MTBM / MTBM + MDT
where MDT is the mean down time is the statistical mean of the downtimes including
the supply downtime and administrative downtime.
In general availability of a system is a complex function of reliability, maintainability
and supply effectiveness
Maintenance of modern equipment and industry requires a healthy, balanced and rationalized
organization devoted to achieve the goals of the maintenance task. The organization required for
any system can be formed after careful study of the existing conditions and also the future
demands of the industry.

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MAINTENANCE ORGANIZATION
The tasks of the maintenance organization are as follows:
(i) Identification of organization roles pertaining to maintenance function
(ii) Determination of maintenance workload
(iii) Uniform distribution of total maintenance work to all the personal in the department
(iv) Identification and assignment of essential works to the various sections of the maintenance
department
(v) Proper knowledge about the technical expertise/experience of the workers deputed for the
particular job
(vi) Proper training of the staff of maintenance to meet the growing demands of the industry
and to catch up with the modern trends in maintenance
(vii) Designing the policies and procedures at an early stage to help the maintenance
department to achieve the goals of the industry.

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MAINTENANCE FUNCTIONS AND ACTIVITIES
The functions and activities of the maintenance organization are as follows:
(i) Identifying areas for implementation of preventive maintenance program
(ii) Making suitable arrangements for maintenance facilities for carrying out the
maintenance work properly
(iii) Planning and scheduling the total maintenance work
(iv) Ensuring proper and timely supply of spare parts
(v) Managing proper inventory control of materials spares and tools required for the
maintenance
(vi) Standardization of maintenance work
(vii) Implementing modifications to the existing equipment wherever possible
(viii) Assisting the purchase department in procuring materials Disbursement of
services such as water, electricity, steam, compressed air and other amenities required
to carryout the maintenance
(ix) Identification of obsolete and surplus equipment for replacement and disposal
(x) Designing the systematic way for disposal of equipment and for maintaining floor
space
(xi) Training of maintenance personnel
(xii) Analysis of future demands and forecast the role of maintenance activities
(xiii) Implementation safety norms and procedures
(xiv) Ensuring safety of personnel and equipment

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TYPES OF MAINTENANCE ORGANIZATION
The selection of a type of maintenance system will largely depends on the structure of an
industry. Maintenance organization can be broadly classified into three types as follows:
(i) Decentralized
This is suitable for large sized plants where inter unit communication is difficult to get.
In this type of organization, the maintenance is under the control of chief engineer of production
to ensure better understanding between the production and maintenance department.
(ii) Centralized
This is suitable for small units where unit communication is feasible. In this type of
organization, the maintenance is under the control of chief maintenance engineer. The
responsibilities and accountability is with the concerned department heads.
(iii) Partially Centralized
This is the modified version of centralized maintenance organization and suitable for
the industry where units are located at far away locations. In this type of organization, the
maintenance personal attached with production unit will carryout the routine maintenance
works. Scheduled maintenance works such as overhauls, planned maintenance work,
procurement of spare parts are under the control of chief maintenance engineer at the central
office. There are basically two at least two types of organization are followed in most of the
industries. They are Line Organization and Line staff Organization

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Line Organization
Line organization consists of a general foreman and a number of specialist foremen with their
team under them as shown in Figure. The specialist foremen execute maintenance work in their
respective areas while the general foreman supervises the total work under his control and
coordinates the various maintenance tasks carried out in the industry. This kind of structure is an
old type maintenance organization.

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Line Staff Organization
A few more staff members such as storekeeper and clerk are added to the line
organization to form the line staff organization structure as shown in Figure The advantage
lies in separating the maintenance work from the storekeeping and the role of clerk is to record
the maintenance activities. The recording of maintenance related activities helps the organization
to restructure the strategies adopted to achieve the objectives of maintenance.

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Maintenance functional organization
Maintenance functional organization is the structure based on craft concept. In this
Organization structure persons joined the organization as apprentices and elevated to higher
positions such as foreman after sufficient experience in their respective jobs. This
organization structure is based on the craft skills acquired through experience. There is no
formal training mechanism available at each stage of the organization. The recent trends in
maintenance management also favors this kind of functional based organization based on craft
skills. Fig. shows the maintenance functional organization in which few workers are placed
under each functional foreman.

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GENERAL ORGANIZATION OF MAINTENANCE DEPARTMENT
The general Organization structure of a maintenance department is shown in Figure

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MAINTENANCE ECONOMICS
LIFE CYCLE COST ANALYSIS
The factors to be considered in the purchase of equipment for industries include the cost, quality,
performance and maintenance requirements. Some balance is to be made between the capital cost
and operating cost of the equipment in finding the suitability of the equipment. The evaluation of
any equipment for purchase should be made by keeping into considerations that total cost incurred
by the equipment over a span of time say ten years.
Life cycle costing is the cost analysis for the equipment in an industry
that accounts the total cost of the equipment over a span of time
which includes the capital cost, operating cost and maintenance
costs.
This analysis is the integration of engineering, economic and financial strategies in relation to the
equipment to be purchased. The aim of life cycle costing is to ascertain the total cost of equipment
over the span of its entire life period.
Advantages of Life Cycle Costing
(i) Integration of engineering, economics and financial aspects lead to the way of robust metric for
the selection and purchase equipment required for the industry.
(ii) Reduced operating and maintenance cost of equipments due to cost analysis over span of time.
(iii) It leads to the selection of proper and economically viable equipment

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ESTIMATION OF ECONOMIC LIFE OF EQUIPMENT
The economic life of equipment depends on the maintenance and repair costs,
availability and operational efficiency. A plot of cumulative efficiency and
maintenance and repair cost per cumulative hours Vs operating hours of the equipment
to find the economic life of the equipment is shown in Figure

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MAINTENANCE COST
Budgets are allocated for all the activities in planning stage itself which
includes the maintenance cost. The cost of maintenance is difficult to measure due to
random nature of failures. The records on maintenance history may be useful in
determining the cost. The analysis of maintenance cost is helpful in taking a decision
regarding replacement of a machine or any of its components.
Component of Maintenance Cost
The maintenance cost is comprised of two factors:
(i) Fixed cost and (ii) Variable cost
(i). Fixed Cost
This includes the cost of support facilities including the maintenance staff.
(ii). Variable Cost
This includes the consumption of spare parts, replacement of components and
cost other facilities required to meet the requirements of maintenance.

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Factors Considered For Evaluation of Maintenance Cost
The evaluation of maintenance cost should consider the following factors:
(i) Cost of maintenance from the recorded data (past experience)
(ii) Level and requirements of maintenance
(iii) Cost of spare parts and materials
(iv) Cost of replacement of components and assemblies subjected wear and tear
(v) Accounting the number of breakdowns with their levels
(vi) Downtimes of the equipment for want of maintenance and repair
(vii) Penalty cost due to the loss of production
(viii) Cost of manpower involved
(ix) Cost of additional manpower requirements for emergency breakdown and
maintenance.

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MAINTENANCE BUDGET
The maintenance budget is used to set aside certain amount of money to meet the
expenditures incurred in achieving the objectives of maintenance.
The following are the types of maintenance budget
(i) Appropriation Budget
Budget used to allocate money for each activity independently.
(ii) Fixed Budget
Fixed used to allocate money for a specified period of time.
(iii) Variable Budget
Dynamic allocation of expenditure based on maintenance requirements
and activities.

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Factors to be considered in Preparation of Maintenance Budget
The factors to be considered in preparing the maintenance budget
(i) Data on failure, downtime cost due to equipment breakdown, cost of
damage, loss of production, penalty cost due to loss of production and replacement cost
(ii) Proper judgment of repair or replacement:
If the cost involved in operation of a machine is in increasing trend, a proper
judgment can be made for replacing the machine instead of frequent repairs
(iii) Comparison between in-house maintenance and hired maintenance :
The cost involved in hiring the maintenance personal outside the
organization to carry out the specific tasks of maintenance needs to be compared with
the cost
involved in using the available resources
(iv) Equipment overhaul periods - Overhaul schedule is to be carried out in
time that will improve the performance of equipment and may enhance its service life
(v) Cost of obsolescence - Expenses associated with fuel, oil,
wages and maintenance of older machines