Operations Management

(Shashank Tilak)

Session no: 19

Objectives and Types of Maintenance,

Breakdown & Preventive Maintenance

Fault Tree Analysis

Estimation of Systems Reliability

Notes prepared by: Notes critiqued by:

Name: Vijay Singh Thakur

Roll No 105 Roll No

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Maintenance –
Process of Bringing a Plant / Equipment Back to Desired Status of Performance

Types of maintenances:
Break Down Maintenance: - Breakdown maintenance is basically the ‘run it till it breaks’
maintenance mode. No actions or efforts are taken to maintain the equipment as the designer
originally intended to ensure design life is reached. Studies as recent indicate that, this is still
the predominant mode of maintenance.

Advantages

1. Involves low cost investment for maintenance.

2. Less staff is required.

Disadvantages

1. Increased cost due to unplanned downtime of equipment.

2. Increased labor cost, especially if overtime is needed.

3. Cost involved with repair or replacement of equipment.

4. Possible secondary equipment or process damage from equipment failure.

5. Inefficient use of staff resources.

Preventive Maintenance: - Preventive maintenance can be defined as, “Actions performed on a

time or machine-run-based schedule that detect, preclude, or mitigate degradation of a
component or system with the aim of sustaining or extending its useful life through controlling
degradation to an acceptable level.” Preventive maintenance is a means to increase the
reliability of their equipment. By simply expending the necessary resources to conduct
maintenance activities intended by the equipment designer, equipment life is extended and its
reliability is increased. In addition to an increase in reliability, lot of amount will be saved over
that of a program just using reactive maintenance. Studies indicate that this savings can
amount to as much as 12% to 18% on the average.

Advantages

1. Cost effective in many capital intensive processes.

2. Flexibility allows for the adjustment of maintenance periodicity.

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 3. Increased component life cycle.

4. Energy savings.

5. Reduced equipment or process failure.

6. Estimated 12% to 18% cost savings over reactive maintenance program.

Disadvantages

1. Catastrophic failures still likely to occur.

2. Labor intensive.

3. Includes performance of unneeded maintenance.

4. Potential for incidental damage to components in conducting unneeded maintenance.

Predictive Maintenance: - Predictive maintenance can be defined as “Measurements that

detect the onset of a degradation mechanism, thereby allowing causal stressors to be
eliminated or controlled prior to any significant deterioration in the component physical state.
Results indicate current and future functional capability”.

Basically, predictive maintenance differs from preventive maintenance by basing maintenance

need on the actual condition of the machine rather than on some preset schedule. Preventive
maintenance is time-based. Activities such as changing lubricant are based on time, like
calendar time or equipment run time. For example, most people change the oil in their vehicles
every 3,000 to 5,000 miles travelled. This is effectively basing the oil change needs on
equipment run time. No concern is given to the actual condition and performance capability of
the oil. It is changed because it is time. This methodology would be analogous to a preventive
maintenance task. If, on the other hand, the operator of the car discounted the vehicle run time
and had the oil analyzed at some periodicity to determine its actual condition and lubrication
properties, he may be able to extend the oil change until the vehicle had travelled 10,000 miles.
This is the fundamental difference between predictive maintenance and preventive
maintenance, whereby predictive maintenance is used to define needed maintenance task
based on quantified material/equipment condition.

There are many advantages of predictive maintenance. A well-orchestrated predictive

maintenance program will eliminate catastrophic equipment failures. Schedule of maintenance
activities can be made to minimize or delete overtime cost. It is possible to minimize inventory
and order parts, as required, well ahead of time to support the downstream maintenance
needs and optimize the operation of the equipment, saving energy cost and increasing plant
reliability. Past studies have estimated that a properly functioning predictive maintenance

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program can provide a savings of 8% to 12% over a program utilizing preventive maintenance
alone. Depending on a facility’s reliance on reactive maintenance and material condition, it
could easily recognize savings opportunities exceeding 30% to 40%. Independent surveys
indicate the following industrial average savings resultant from initiation of a functional
predictive maintenance program:

1. Return on investment—10 times

2. Reduction in maintenance costs—25% to 30%

3. Elimination of breakdowns—70% to 75%

4. Reduction in downtime—35% to 45%

5. Increase in production—20% to 25%.

Advantages

1. Increased component operational life/ availability.

2. Allows for pre-emptive corrective actions.

3. Decrease in equipment or process downtime.

4. Decrease in costs for parts and labor.

5. Better product quality.

6. Improved worker and environmental safety.

7. Improved worker moral.

8. Energy savings.

9. Estimated 8% to 12% cost savings over preventive maintenance program.

Disadvantages

1. Increased investment in diagnostic equipment.

2. Increased investment in staff training.

3. Savings potential not readily seen by management.

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Necessity of Maintenance Management:

Maintenance activities are related with repair, replacement and service of components or some
identifiable group of components in a manufacturing plant so that it may continue to operate at
a specified ‘availability’ for a specified period.

Thus maintenance management is associated with the direction and organisation of various
resources so as to control the availability and performance of the industrial unit to some
specified level.

Thus maintenance management may be treated as a restorative function of production

management which is entrusted with the task of keeping equipment/machines and plant
services ever available in proper operating condition.

The minimization of machine breakdowns and down time has been the main objective of
maintenance but the strategies adopted by maintenance management to achieve this aim have
undergone great changes in the past.

Maintenance has been considered just to repair the faulty equipment and put them back in
order in minimum possible time.

Importance of Maintenance Management:

Maintenance management is responsible for the smooth and efficient working of the industrial
plant and helps in improving the productivity.

It also helps to keep the machines/equipment in their optimum operating conditions. Thus
plant maintenance is an important and inevitable service function of an efficient production
system.

It also helps in maintaining and improving the operational efficiency of the plant facilities and
hence contributes towards revenue by decreasing the operating cost and improving the quality
and quantity of the product being manufactured.

As a service function it is related with the incurrence of certain costs. The important component
of such costs are — employment of maintenance staff, other minor administrative expenses,
investment in maintenance equipment and inventory of repair components/ parts and
maintenance materials.

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Objectives of Maintenance Management:

The purpose of maintenance management is to optimize the performance of productive

facilities of an organization by ensuring that these facilities function regularly and efficiently.
This can be achieved by preventing the failures or breakdowns if any, as far as possible and by
minimizing the production loss due to failures.

The main objectives of maintenance management are as follows:

(1) Minimizing the loss of productive time because of equipment failure to maximize the
availability of plant, equipment and machinery for productive utilization through planned
maintenance.

(2) To extend the useful life of the plant, machinery and other facilities by minimizing their wear
and tear.

(3) Minimizing the loss due to production stoppages.

(4) To ensure operational readiness of all equipment’s needed for emergency purposes at all
times such as fire-fighting equipment.

(5) Efficient use of maintenance equipment’s and personnel.

(6) To ensure safety of personnel through regular inspection and maintenance of facilities such
as boilers, compressors and material handling equipment etc.

(7) To maximize efficiency and economy in production through optimum utilization of available
facilities.

(8) To improve the quality of products and to improve the productivity of the plant.

(9) To minimize the total maintenance cost which may consist of cost of repairs, cost of
preventive maintenance and inventory costs associated with spare parts/materials required for
maintenance.

(10) To improve reliability, availability and maintainability.

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 Methodical Approach – Equipment Maintenance
• Identify Weak Links and Susceptible Areas

• Related to Load / Usage / Relative Position

• Design / Physical Limits & Conditions

• Disaster Value Of Any Breakdown

• History of Breakdown & Wear & Tear

• Allied Study of Equipment & System –

• Major Equipment Set, Assemblies, Parts

• Function & Criticality of Task Carried

• Fitment, Tolerances, Reliability,

• Work through Reliability of Entire System

Fault Tree Analysis – II

Method & Tools

• Basically Work Through Probability of Failure

• Identify How Sub Systems May Fail

• Start with an Undesirable Effect (Failure)

• Treat This as Top of the Tree

• Add Individual Contributor Events

• Connect With Logic Gate Symbols

• Add Probability of Failure for Each

• End Up With Undesirable Initiator / Cause

• Each Path is Called Cut Set

• Help to Build Total Probability for Failure.