MAINTENANCE MANAGEMENT

IM – 503

Lecture – 3: Maintenance Strategies

Dr Muhammad Fahad
Associate Professor/Director Product Development Centre
Dept of Industrial & Manufacturing
NED University of Engineering & Technology
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Failure
 Failure:
 An incident or occurrence where a component or equipment
fails to perform satisfactorily its intended function.
 Seizure of a bearing, burning of insulation, fracture of a
shaft/axle.
 Defect:
 Any condition in the equipment which is neither intended nor
desirable.
 A condition that can cause a failure of the component.
 Lack of lubrication, high voltage, crack in a stressed component

Defect is a cause Failure is its effect

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Failure
 Failure Mode:
 Visible, Tangible, or measureable changes in the appearance or
properties of a component.
 Mechanical Failure Modes: Excessive Wear, Cracking, Melting, bending.
 Electrical Failure Modes: Short Circuit, Softening, carbonization.
 Failure Mechanism:
 Physical or chemical process through which the failure mode is
reached.
 Excessive alternating tensile and compressive stresses resulting in fatigue
cracks and subsequent fracture.
 Inadequate contact force between two conductors causing excessive
contact resistance and subsequently resulting in melting/fire.
 Different failure mechanisms can lead to same failure mode.
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Failure
 Why do:
 Some components/equipment fail quite some time after
commissioning while some others fail very soon?
 Some components fail while identical components in identical
equipment working under identical conditions continue to work
satisfactorily?
 Some components continue to work satisfactorily for
months/years and then fail suddenly for no apparent reason?
 Some components fail even though adequate factors of safety
are allowed in the design of the component?
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Failure
 Main reasons for this apparently erratic behavior are
 Variance in the
 Properties of material due to variations in composition and in process
parameters.
 Environmental and operating conditions.
 Rates of degradation in the properties of materials and the quality of
maintenance.
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Failure
 Basic Functions
One must take into account four basic functions related to
the failures of the equipment

 Failure probability density function f(t)

 Failure probability distribution function F(t)

 The reliability function R(t)

 Failure rate
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Maintenance Management
 Maintenance
 All actions appropriate for retaining an item/part/equipment in, or
restoring it to, a given condition.

 Management
 Comprises planning, organizing, staffing, directing (leading),
and controlling a group of people (or an organization).

 Maintenance Management
 Process of managing the maintenance activities within an agreed
policy.
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Maintenance Management
 Important Questions
 Do you have a comprehensive listing of your assets?
 Is it accurate?
 When was it last updated?
 Are the plant diagrams up to date (P&IDs), are they included in
the change process?
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Maintenance Management
 Maintenance Strategies
 Maintenance strategies are different types of tasks including
actions, procedures, resources, and time.
 These activities have to be carried out in accordance with
established time schedules to guarantee maintenance targets.

Probably the most critical aspect of any maintenance

management system
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Maintenance Management
 A plant has a number of pump/motor assemblies
 A number of them serve the final phase of production where the impact
of loss would be loss of finished products.
 Other similar units have recently been installed to deal with waste water,
there are a number of holding tanks that can hold all waste water
produced over 7 days, there is no impact on production should these
units fail.
 If you have a contractor providing vibration analysis on the
production line assemblies, do you automatically extend that to the
new units?
 If you maintain purely on what the asset is the answer is yes
 If you have an overall maintenance strategy the answer is not so
straightforward.
 Cost benefit analysis on the risk associated with failure versus the
cost of the vibration analysis services. If the risk does not justify that
cost then a different maintenance regime would be appropriate.
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Maintenance Management
 Maintenance Strategies
Maintenance

Breakdown/Corrective Preventive
Maintenance Maintenance

Deferred Immediate Condition Based Predetermined

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Corrective Maintenance
Definition
 Maintenance carried out after fault recognition and intended
to put an item into a state in which it can perform a required
function. (BS EN 13306:2010)

 Corrective maintenance is an unscheduled maintenance

action, basically composed of unpredictable maintenance
needs that cannot be preplanned or programmed on the
basis of occurrence at a particular time.
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Corrective Maintenance
 It is performed when the production system stops functioning
correctly, i.e., in accordance with a set of known operating
conditions.
 There are no planning activities to optimize equipment
maintenance and support management decisions.
 Influenced by the spare parts fulfillment and management
system adopted
 Cost of a breakdown maintenance action obviously depends
on the availability (unavailability) of spare parts necessary to
perform the repair action.
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Corrective Maintenance
 Deferred Corrective Maintenance
 Corrective maintenance which is not immediately carried
out after a fault detection but is delayed in accordance with
given maintenance rules.

 Immediate Corrective Maintenance

 Corrective maintenance that is carried out without delay
after a fault has been detected to avoid unacceptable
consequences.
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Preventive Maintenance
Definition
 Maintenance carried out at predetermined intervals or
according to prescribed criteria and intended to reduce the
probability of failure or the degradation of the functioning of
an item (BS EN 13306:2010)

 PM is the care and servicing by individuals involved with

maintenance to keep equipment/facilities in satisfactory
operational state via systematic inspection, detection, and
correction of incipient failures either prior to their occurrence
or prior to their development into major failure.
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Preventive Maintenance
 It deals with planned actions performed to face and counteract
potential failures on a component/system.
 Timing (i.e., frequency) and outcome of a preventive
maintenance action have to be properly planned and
optimized, maximizing the throughput of the production
system and minimizing costs.
 It is supposed that a preventive maintenance strategy can be
performed only with the continuous knowledge of system
operating conditions.
 From time to time PM programs in maintenance organizations
end up in failure (i.e., they lose upper management support)
because their cost is either unjustifiable or they take a
significant time to show results.
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Preventive Maintenance
 Condition Based Maintenance
 Preventive maintenance based on performance and/or
parameter monitoring and the subsequent actions. ...
Monitoring may be scheduled, on request or continuous.

 Predictive Maintenance
 Preventive maintenance carried out in accordance with
established intervals of time or number of units of use but
without previous condition investigation.
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Maintenance
 Improvement Maintenance
 It aims at reducing or eliminating entirely the need for
maintenance.
 Mainly involves activities that are used to
 eliminate the cause of maintenance
 simplify maintenance tasks
 raise machine performance from the maintenance point of view
by redesigning those machines and facilities which are
vulnerable to frequent occurrence of failure and their long
term repair or replacement cost is very expensive.
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Maintenance
 Opportunity Maintenance
 Opportunity maintenance involves set of maintenance activities
that are performed on a machine or a facility when an unplanned
opportunity exists during the period of performing planned
maintenance activities to other machines or facilities.
 There are a multitude of reasons that opportunity periods are often
created in various processes.
 E.g. Unavailability of the primary materials to continue with the
manufacturing process, or reduction in demand for the product.
 Opportunity maintenance can even be caused by the breakdown of
one piece of equipment, leaving associated equipment available for
maintenance.