Whether you
own a car,house ,building or
professionally involved in operation and maintenance of machines ,you need to know some basics about maintenance.
Some form of
maintenance you are practicing already but you always need to re-look at
maintenance program so that you keep your asset(s) in correct form with minimal
cost.
Maintenance is not only “the restoration of any asset to function after it
has failed “instead spectrum of maintenance is broadened now .
This post
covers the basic maintenance types with special focus on following topics related
to maintenance Programs.
- Maintenance
definition
- Objectives
of maintenance
- Nature of
maintenance
- Types of maintenance
programs
- Comparison of maintenance programs
Maintenance
definition
British Standard Glossary of terms
(3811:1993) defined maintenance as:
"The
combination of all technical and administrative actions, including supervision
actions, intended to retain an item in, or restore it to, a state in which it
can perform a required function"
"Maintenance
is a set of organized activities that are carried out in order to keep an item
in its best operational condition with minimum cost acquired."
In general,
Maintenance means to hold, keep, sustain or preserve the building ,machine or structure
to an acceptable standard.
Objectives of Maintenance Program
- Maximising
production or increasing facilities availability at the lowest cost and at the
highest quality and safety standards.
- Reducing
breakdowns and emergency shutdowns.
- Optimizing resources utilization.
- Reducing
downtime.
- Improving
spares stock control.
- Improving equipment efficiency and reducing scrap rate.
- Minimizing energy usage.
- Optimizing the useful life of equipment.
- Providing reliable cost and budgetary control.
- Identifying and implementing cost reductions.
Types of Maintenance Programs
Different types of maintenance are being practiced in various parts of world.Adoption of particular Maintenance type greatly depends upon the resources of organization or company.One maintenance approach may cost less than other so each professional has to see the resources and then decide for "which maintenance type is best for his plant".
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| types of maintenance programs |
1. Reactive or Corrective Maintenance
Reactive 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.
Advantages to reactive maintenance can be viewed as a
double-edged sword. If we are dealing with new equipment,we can expect minimal incidents of failure. If our
maintenance program is purely reactive, we will not expend manpower dollars or
incur capitol cost until something breaks.
Advantages of reactive maintenance
Disadvantages of reactive maintenance
- Increased cost due to unplanned downtime of
equipment.
- Increased labor cost, especially if overtime is needed.
- Cost involved with repair or replacement of equipment.
- Possible secondary equipment or process damage from
equipment failure.
- Inefficient use of staff resources
2. Preventive Maintenance
Preventive maintenance can be defined as follows:
"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 frequency may be machine operating hours based or after fixed time interval as decided by maintenance engineer or recommended by vendor of machine.
Advantages of Preventive maintenance
- Cost effective in many capital intensive processes.
-
Flexibility allows for the adjustment of
maintenance periodicity.
-
Increased component life cycle.
-
Energy savings.
-
Reduced equipment or process failure.
-
Estimated 12% to 18% cost savings over
reactive maintenance program.
Disadvantages of Preventive maintenance
- Catastrophic failures still likely to occur.
- Labor intensive.
- Includes performance of unneeded maintenance.
- Potential for incidental damage to components in conducting unneeded
maintenance.
3. Predictive Maintenance
Predictive maintenance can be defined as follows:
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. You will recall that
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 traveled.
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/she may be able to extend the oil change until the vehicle had traveled
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.The
advantages of predictive maintenance are many.
A well-orchestrated predictive
maintenance program will all but eliminate catastrophic equipment failures. We
will be able to schedule maintenance activities to minimize or delete overtime
cost. We will be able to minimize inventory and order parts, as required, well
ahead of time to support the downstream maintenance needs. We can optimize the
operation of the equipment, saving energy cost and increasing plant
reliability.
Advantages of predictive
maintenance
- Increased component operational life/availability.
- Allows for preemptive corrective actions.
- Decrease in equipment or process downtime.
- Decrease in costs for parts and labor.
- Better product quality.
- Improved worker and environmental safety.
- Improved worker moral.
- Energy savings.
- Estimated 8% to 12% cost savings over preventive maintenance
program.
Disadvantages of predictive
maintenance
- Increased investment in diagnostic equipment.
- Increased investment in staff training.
-
Savings
potential not readily seen by management.
4. Proactive Maintenance
The latest innovation in the field of predictive maintenance
is so-called pro-active maintenance, which uses a variety of technologies to
extend the operating lives of machines and to virtually eliminate reactive
maintenance.
The major part of a pro-active program is root cause failure
analysis, which is the determination of the mechanisms and causes of machine
faults. The fundamental causes of machine failures can thus be corrected, and
the failure mechanisms can be gradually engineered out of each machinery
installation. It includes routine preventive and predictive maintenance
activities and work tasks identified from them.
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| typical maintenance practices |
It has been known for a long time that imbalance and
misalignment are the root causes of the majority of machine faults. Both of
these conditions place undue forces on bearings, shortening their service life.Rather than continually replacing worn bearings in an
offending machine, a far better policy is to perform precision balance and
alignment on the machine, and then to verify the results by careful vibration
signature analysis.
Among above maintenance types ,Proactive maintenance programs has privilege of having advantages which are sum of advantages of each of reactive maintenance ,preventive maintenance & predictive maintenance program.While it shares its disadvantages mostly with predictive maintenance program.
Predictive maintenance vs proactive maintenance
- Predictive maintenance is the technique to determine the
condition of machine by sensing, measuring tools etc.
- Example- Suppose one fan having abnormal
vibration that find out by sensing tools (vibrometer etc. ) and we attend the
job and rectified the current problem in fan. but in proactive maintenance , we
search-out the main cause of the problem, which may, design problem, weather
problem, operation problem etc, that to solve the actual problem .
