Condition Monitoring of Rotary Machines by swenthomasovelil

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									AJCE                                                 Condition Monitoring of Rotary Machines


                                    CHAPTER 1

                     ABOUT THE ORGANIZATION
       The Fertilizers and Chemicals Travancore Ltd. (FACT), is a pioneer in the
manufacture of the chemical fertilizers in India. It started with the aim in promoting the
use of fertilizers in agriculture to meet the growing need of food grains in the country.

       FACT being the first large-scale fertilizer unit was set up in 1943. The company
started its operation in 1947 with wood gasification plant at the Eloor Island, near
Cochin. Ammonium Sulphate was their first product to enter the market, followed by
super phosphate and ammonium chloride. FACT became a Kerala State Public Sector
Enterprise in 1960 with the Government of India as a major share holder by 1962.

       FACT having undergone several stages of expansion and modernization with
processes ranging from electrolysis to steam reforming expanded its horizon with a
second production unit at Ambalamedu in 1971, of large capacity and latest technology
of the time. It entered in to the field of petrochemicals with the commissioning of
50,000 tons per annum Caprolactum plant at Udyogmandal.              FACT today has an
engineering consultancy division, FACT Engineering and Design Organization (FEDO),
FACT Engineering Works (FEW) and a Research and Development division, besides
the three production divisions. FACT has 900 tons per day Ammonia plant with over
5500 employees in its rolls.



1.1 The Petrochemical Division (PD)

       Petrochemical Division of FACT produces about 50,000 tons per annum of
Caprolactum as its major product. Caprolactum is the principle raw material in the
manufacture of Nylon. Ammonium Sulphate, Soda ash and Nitric Acid are the major
by products. The plant employee‟s latest state of the art distributed digital control
system and is one of the most modern plants in the country.




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                                  CHAPTER 2

                    OBJECTIVE OF THE PROJECT
       Basically condition monitoring is the process of monitoring some parameters
from the machinery, such that a significant change in the parameter can give
information about the health of the machinery. It involves the continuous or periodic
assessment of the condition of a plant or a machinery component while it is running. A
machine running in a good condition has stable vibration parameters. The vibration
parameters change when the condition changes. Identification of noise sources and
comparing their vibration parameters with that of stable vibration parameters of a
machine or plant in good condition can prove to be an important tool for condition
monitoring. The main objectives for the condition monitoring can be listed as,


       1. Prediction of faults
       2. Diagnosis of faults
       3. More safety at work place
       4.   Less down time leading to more production and
       5.   Better inventory management for the spare parts




       Although the main use for condition monitoring is to predict and hence assist in
avoiding the unplanned equipment failures. However, there are other means in which
condition monitoring can assist in improving maintenance during the Planned
Maintenance phase. It helps in minimizing total equipment downtime by taking an
overall view of plant condition, and combining planned maintenance tasks. It makes
workplace safer by reducing the equipment failure. Information obtained during the
condition monitoring also helps in optimizing the equipment performance.




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                                    CHAPTER 3

                                  INTRODUCTION
       Machinery distress very often manifests itself in vibration or a change in
vibration pattern. Vibration analysis is therefore, a powerful diagnosis tool, and trouble
shooting of major process machinery would be unthinkable without modern vibration
analysis.

       It is natural for machines to vibrate. Even machines in the best of operation
condition will have some vibration because of minor defects as a result of
manufacturing tolerances. Therefore each machine will have a level of vibration which
may be regarded as normal or inherent.

       When machinery vibration increases or becomes excessive, some mechanical
trouble is usually the reason. Machinery vibration levels just do not increases or
become excessive for no reason at all. Something causes it unbalance, looseness etc.

       Each mechanical defect generates vibration in its own unique way. This makes
it possible to positively identify a mechanical problem by simply measuring and
studying its vibration characteristics.

            The success of a process industry often depends on the continued, safe and
productive operation of rotating machinery. An effective maintenance program is vital
to this kind of success. The quality of the company‟s maintenance program determines
how long the machines will run, how safe they are for the people working around them.
The benefits of a good maintenance program are:

       1.        Prolonged machinery life.

       2.        Minimizes unscheduled down time.

       3.        Eliminates unnecessary overhaul.

       4.        Eliminates standby equipment.

       5.        Provides more efficient operations.

       6.        Increases machinery safety.

       7.        Improves quality performance




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                                   CHAPTER 4

                           LITERATURE SURVEY
       Condition monitoring is one of the maintenance methods which are used to
access the health and condition of equipments, machines system or process by
absorbing, checking, measuring and several parameters. This technique is also called
Equipment Health Monitoring (EHM). The concept of condition monitoring is to
monitor the several performance parameters such as vibration, temperature, noise etc
and to study their characteristics. Once an abnormality I encountered, the system is then
investigated and problems are rectified. His type of monitoring is applied especially on
the continuous running machines such as compressors, pumps, turbines, power
generators, generator sets etc.


4.1 HISTORY OF CONDITION MONITORING
       Condition monitoring has been developed extensively over a period of
approximately 35 years. From 1960 to the mid of 1970s, simple practical methods were
used, along with a careful watch on the machines behavior, often reinforced by frequent
maintenance. Elementary instruments were sometimes used to measure and record the
variables on which maintenance decisions were based. This required highly skilled and
experienced personals to ensure efficient operation and to avoid failures. During 1970s
there were developments in analogue instrumentations and mainframe computer.
Analogue instrumentation became popular in the form of portable vibration measuring
and recording instruments and frequency analysis. Although some instruments were
available during the early 1970s, significant developments took place during the late
1970s and 1980s due to the availability of the microprocessor. On board
microprocessors gave instruments the ability to capture the data, analyze it via a suitable
algorithm, then store and display the information. From the mid 1980s onwards, the
development shave been associated with the desktop computer, its interfaced equipment
and the software. Many manufacturers have produced hand held instruments for the
instant measurements, recording and analyzing of the variables, information often
available from the instrument on a component or a machine condition. The use of digital
computers and advanced instruments has played a key role in condition monitoring.
Condition monitoring is considered as the most reliable, cost effective and efficient
technique for maintaining the majority of the critical equipments such as engines,

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turbines , compressors etc,       used in most of the industries today. An effective
maintenance can serve approximately 20 to 30% of the possible production time.


4.2 DEMAND FOR CONDITION MONITORING
       The demand for condition monitoring system has increased as the companies
have tried to minimize the consequences of the machine failures, and to utilize existing
maintenance resources more effectively. The following factors are contributed in
increasing the demand of condition monitoring.
      Increased quality expectations reflected in produces liability legislation
      Increased automation to improve profitability and main competitiveness
      Increased safety and reliability
      Increased cost of maintenance due to labor and material cost

4.3 FUNDAMENTAL STEPS IN CONDITION MONITORING.
   An effective condition monitoring system follows the following steps:
      Identifying the critical systems.
      Selecting the suitable techniques for the condition monitoring
      Selecting base lines
      Data assessments
      Fault diagnosis
      System review

4.4 PROCESSES INVOLVED IN CONDITION MONITORING
   The various processes involved are:
      Identifying the critical systems:
       The first step in condition monitoring is to identify equipment which would be
       benefit from the application of condition monitoring. This is achieved by
       examining all the equipments in the industry or by looking only at the problem
       causing equipment. The selected equipments will probably have a poor record of
       efficiency availability, reliability and safety, repair and maintainability; this is
       likely to increase the cost.
      Selecting the suitable technique:
       The next step is to understand equipment deterioration, its causes, warning
       effects and criticality of failure. After completing the failure analysis, it is then



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       necessary to select the most effective monitoring technique in terms of cost and
       results.
      Setting the threshold values:
       This stage involves identifying where and how often to take the measurements,
       collecting the base line readings and settings the threshold value for alarm or
       warning. The alarm levels would be referred to a known standard and the
       warning levels set near to the system normal reading.
      Data collection for equipment:
       The heart of condition monitoring lies in the collection storage and interpretation
       of data. Processing of large amount of data consumes time. It is important to
       make the collection and assessment as efficient as possible, using the few staff
       and incurring the lowest running cost. The method of data collection may be a
       manual system, computerized automated system or hybrid system. The choice of
       method will depend on the level of protection that the equipment warrants, and
       the cost of the method itself.
      Condition assessment:
       Data assessment aims to detect the deterioration in the equipment condition. It
       needs to be performed each time a new set of measurements are taken. The new
       readings may be checked against absolute threshold levels, compared with the
       past readings to detect any variations, or compared with the past readings of the
       other similar equipment being run under similar conditions. In addition, readings
       should be checked for validity to ensure that a false alert has not been generated.
      Fault diagnosis :
       After identifying the problem, it is necessary to find the cause and ensure that
       correct maintenance action is taken. This may involve specialist knowledge to
       analyze the existing data or to carry out more detailed checks.
      Equipment repairs:
       Based on the fault diagnosis report, the workman can repair the equipment. The
       supervision can be done by the maintenance engineer.
      System review:
       Once the repair of the equipment is done, then the equipment has o undergo the
       steps 2 to 7 for the system review.




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                                    CHAPTER 5
                   MAINTENANCE STRATERGIES

       The respective function and operation in modern production system are so
interrelated that is to consider each as a separate isolated element. Efforts to reduce the
cost of either one of these functions may easily result in increased cost in the order, up
to extent where all the savings are eventually lost. It is therefore important that both the
maintenance and operation of the plant are considered and planned on a unified basis
with the objective of achieving the minimum overall production cost. To carry out
these functions and to obtain the required objectives there are four alternatives,

   1. Operate the equipment until it breaks down, then scrap it and buy a new one.

   2. Operate the equipment and then sell it before it either breaks down or requires
       extensive overhaul

   3. Operate the equipment until it breaks down, then repair it

   4. Carryout regular maintenance, planned carefully in conjunction with production
       requirement to prevent failure of the equipment during production runs.

These four alternatives are leading to different forms of maintenance.

5.1 TYPES OF MAINTENANCE SYSTEM

       Once we have decided to introduce a maintenance system, the problem arises
that which type of maintenance program to implement or introduce. To give the proper
answer to this question we should consider the following factor.

   1. Type of industry

   2. Critically of process

   3. Critically of machine

   4. Quality of the product

   5. Requirement of stand by equipment

   6. Cost of machine and equipment

   7. Load condition of the machines


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       Based upon the above factors we can classify the various maintenance systems as



      Breakdown maintenance or repair maintenance

      Preventive maintenance or scheduled maintenance.

      Predictive or Condition based maintenance (E.g.: chemical fertilizer and
            petroleum refining industries)

      Planned maintenance

      Productive maintenance

      Pro-active maintenance.




       5.2 BREAKDOWN MAINTANENCE

                  With this, a machine is allowed to run until complete failure,
        inefficiently or product spoilage forces a shut down. The number of breakdown
        actually shows the efficiency of the maintenance action.

       It has a lot of disadvantages

             It occurs most untimely

             Machine requires extensive repairs

             Some failure can be catastrophic, requiring total replacement of the machine

   5.3 PREVENTIVE MAINTENANCE

        Preventive maintenance is sometimes called “historical maintenance”. This is
where the histories of each machine type are analyzed and periodic overhauls are
scheduled to acquire before the statically expected problems occur. Compared to
previous case, a program of periodic disassembly and inspection has the distinct
advantage of lessening the frequency of breakdown repairs and permitting schedule
shutdown. Under this program each critical machine is shutdown after a specified
period of operation and partially or completely dismantled off with thorough
inspection and replacement of worn parts, if an. It has been long known that most



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groups of similar machines will exhibit failure rates that are somewhat predictable if
averaged over a long time.

   Preventive maintenance also includes such activities as changing tube, oil and
   filters, periodic cleaning and inspection, etc. Maintenance activity can be scheduled
   on the basis of calendar time, machine operating hours, number of pars produced
   and so on.

   Disadvantage include

          Periodically dismantling every critical piece of the equipment in plant is
           expensive and time consuming.

          Interval between periodic inspection is difficult of predict.

          If the program is so successful that no machinery failures occur, it may be
           that the intervals are too short and money is being lost.

   5.4 PREDICTIVE MAINTENANCE

       This is also called condition based maintenance, which is based on the
   determination of machines‟ condition while in operation.                The technique is
   dependent on the fact that most machine component will give some type of warning
   before they fail. To sense the symptoms by which the machine is warning as
   requires several type of non-destructive testing; such as oil analysis, wear particle
   analysis, vibration analysis and temperature measurement. Use of these techniques
   to determine the machines condition result in a much more efficient use of
   maintenance effort compared to any earlier type of maintenance.

   Its advantages include,

          Shut down for repairs can be scheduled for a convenient time

          A work scheduled together with the requirement of man power, tool and
           replacement part can be prepared before the scheduled breakdown

          Extensive damage to the machine resulting from forced failure can be
           minimized

          Repair time can be kept to a minimum resulting in less machinery down
           time

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          Time and money is not wasted dismantling machines which are already
           operating smoothly

   The disadvantage is that,

          It requires skilled personal and costly equipment for monitoring the faults of
           the equipment/ plant

   5.5 PLANNED MAINTENANCE

       By using different network analysis technique like PERT, CPM, etc the
   downtime can be reduced. The time and labor can be effectively utilized. In
   planned maintenance modern techniques plans the action.

   5.6 PRODUCTIVE MAINTENANCE

       By frequent inspection are necessary for the preventive maintenance, the cost
   involved is more.     More labor and money have to be utilized for preventive
   maintenance to reduce the cost involved. The machine, which is vital for the
   production or components of machineries which are more critical, are only
   subjected to preventive maintenance, such a maintenance scheme is called
   productive maintenance.

   5.7 PRO-ACTIVE MAINTENANCE

       The latest innovation in the field of predictive maintenance is so called
   proactive 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 proactive program is to find root cause of failure, which is the determination of
   machines and causes of machine fault. The fundamental cause of machine failure
   can thus be corrected, and the failure mechanism can be gradually engineered out of
   each machinery installation.




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                             BREAKDOWN          PREVENTIVE            PREDICTIVE
                            MAINTENANCE        MAINTENANCE          MAINTENANCE


    BREAKDOWN                     Highest           Small           Almost negligible


       DOWNTIME                    High             Low                    Low


  PRODUCT OUTPUT                   Low              High                   High


    WASTE INDEX                                     High                   Low


MAINTENANCE LEVEL                                   High                   Low


                                                                           Low
 MAINTENANCE COST                  High             Low



   RELIABLITIY OF
                                   Low              High                Very High
 EQUIPMENT/PLANT



   AVAILABLITY OF
                                   Low              High                Very High
        PLANT




       PERCETAGE
   UITILIZATION OF                 Low              High                   High
 EQUIPMENT/PLANT




 CONTROL OF SPARE
                                    No               Yes                   Yes
   AND INVENTORY




   PRIOR WARNING
  OBTAINED BEFORE                   No               Yes                   Yes
    BREAKDOWN



                 Table 5.1: Comparison of different types of maintenance



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                                  CHAPTER 6

                       CONDITION MONITORING
       The main function of condition monitoring is to provide the knowledge of
machine condition and of its rate of change which is essential to the operation of this
method. The knowledge may be obtained by selecting suitable parameters such as
vibration for measuring and reading its value at intervals. With condition monitoring,
repairs are carried out only when the condition of machine has deteriorated to a
predetermined level. Thus repairs or replacement of parts take place only when it has
definitely been proved that a fault exists and if it left unrepaired would result in
unsatisfactory operation or breakdown with possible damage to other machine parts and
disruption of production.



6.1 CONDITION MONITORING OF ROTARY EQUIPMENTS:

       1. Continuous monitoring of vibration and bearing temperature of critical
           machines.

       2. Vibration and noise measurement and analysis on all rotary equipments.

       3. Bearing temperature monitoring by surface thermometers.

       4. Condition monitoring of anti-friction bearings using shock pulse meters.

       5. Measurement of RPM by stroboscope/tachometer.

       6. Measurement of shaft residual magnetism.

       7. Detection of cavitations in pumps by SPM.




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6.2 DEVELOPING A MONITORING PROGRAM

Condition monitoring is being considered as a basis for maintenance, a series of step
need to be followed to develop a satisfactory monitoring program.

1. Select the plant and the component that justify condition monitoring

       Plants and components for which condition monitoring is appropriate are those
       ,which on breakdown give rise to high cost ,seriously destruct the normal
       function of a building or that represents a particular safety hazards . This
       improves plant that

              Is expensive to maintain

              Is expensive to replace if run to failure (e.g.: where spare parts are not
               readily available)

              Leads to high subsequent cost should failure occur

              Causes an unacceptable situation to arise ,should failure occur

              It critical to the overall operations of the building

              Examples of plants are those which

              Operate at a high pressure, temperature or voltage

              Operate continuously

              Having minimum or no stand by capacity

              Handling dangerous materials

              May create a health or safety hazards while manufacturing




   2. Identify the parameters that need to be monitored

       Identify where experience of failure modes does not exit all components that are
       monitored initially to identify that are crucial.     This however is likely to the
       impractical, so selection of component to monitor should be based on:

              Those most critical in terms of plant reliability
              Those with a performance duty


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              Those with long delivery time for replacement expectancy
              Those anticipated has having a low life expectancy the other items
              Those recommended by manufactures

   3. Select appropriate monitoring techniques

               Determining failing system at component level will provide the most
        sensitive measure of plant condition give the longest lead time before failure,
        and reduce the effect of external factors which might interface with interface
        with the results.     The monitoring techniques need to be selected after
        considerations of the components mostly likely to fail and failure mode.
        Technique for monitoring complete plant may determine that problems exist
        but provide little lead time before failure and imprecise about the mode of
        failure.

               Ideally the simplest possible monitoring method should be chosen. The
        time to interpret measured data should be minimised to enable none specialist
        to be used. The measurement interpretation time must be less than the time for
        failure propagation. If this time is not known, frequent or even continuous
        trend monitoring may be required at least initially.

               Experience of operating particular plant may allow failure to be detected
        by secondary symptoms, however recommend as an initial procedure when
        condition monitoring.

   4. Select and obtain necessary instrumentation

               The selection of instrumentation will depend on the type plant and
       component to be monitored.        The parameters selected to be measured and
       whether continuous or periodic monitoring is required. If a facility exists for
       linking permanent sensors to continue monitoring equipments, this should be
       compared with other options.

   5. Equipment selection should also consider

           Any need for calibration, this should be carried out regularly put for
       permanent sensors and before each test or at regular intervals for portable
       equipment




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           a) Robustness f instruments :portable instruments must be able to with
               stand frequent handling and travelling permanent sensors need to be
               compatible with working environment

           b) Reliability: Equipments need to give reliable results over a reasonable
               period of time

           c) Interception and analysis of results: For most benefits this should be
               under taken in the house but certain equipment may require specialised
               assistance.

           d) Ease of use: this include both versatility of instruments and any training
               to obtain the necessary skill or experience.

           e) Weight: portable instruments carried from place to place need to be
               reasonably light particularly, if several are taken at once.

           f) Method of recording result :This should be simple and should be easily
               interpreted

           g) Price: These needs to be compared with potential benefit




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                                    CHAPTER 7

       CLASSIFICATIONS OF ROTARY EQUIPMENTS
       Rotary equipment will be classified into three categories depending upon
critically for on-stream condition monitoring as described below.



7.1 Category-I (Critical Machines)

       These are vital machines which will be generally of high cost, high speed, too
large and complex in their design and duties and does not justify the economics of
having another spare set and breakdown of which result in immediate and serious
interruption in production.

       These equipments will have continuous on-line vibration and bearing
temperature monitoring systems.      These machines will be monitored for vibration on
bearing housings once a week using portable monitoring instruments.

7.2 Category-II (Semi-critical Machines)

       These are essential machines which will be needed for normal operation of the
plant, but having stand by set, and also the running speed of which will not be very
high. Failure of such equipments will not cause immediate production loss as the stand
by set will come in line in case of failure.    These machines will be monitored for
vibration on bearing housing once in two weeks.       However, some of the important
machines may be monitored once in a week depending upon the requirement and
equipment behavior.

7.3 Category-III (Non-critical Machines)

       These are desirable auxiliary and general purpose machines which, owing to its
function, can be allowed to remain temporarily out of operation without having a
serious effect on operations.     These equipments will be normally having spare sets.
These machines will be monitored for vibration housings once in a month.




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                                      CHAPTER 8

                                      VIBRATION
           Vibration is simply the back and forth movement of an object from its position
of rest.     It is like an oscillatory motion. Vibrations in machines above certain limits
are harmful to their functioning.

                 The most common causes of vibration are:
                 Unbalance of motor.
                 Looseness
                 Misalignment
                 Bend shaft
                 Eccentrically
                 Bad belt drive and drive chains
                 Electromagnetic forces
                 Hydraulic forces



8.1 VIBRATION CHARACTERISTICS

           Machines condition and mechanical problems are identified by simply noting its
vibration characteristics are:

           1) Amplitude (Displacement, Velocity, Acceleration)

           2) Frequency

           3) Phase



8.1.1 Vibration Displacement (peak to peak)

           The total distance traveled by the vibrating part from one extreme limit of travel
to the other extreme limit of travel is referred to peak to peak displacement.           The
vibration displacement is usually expressed in micrometer where one micrometer
equals one thousandth of a millimeter (0.001mm).




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8.1.2 Vibration Velocity

       The velocity of the motion is definitely a characteristic of the vibration but since
it is constantly changing throughout the cycle, the highest peak velocity is selected for
measurement. Vibration velocity is expressed in millimeter per second peak.




                              Graph 8.1: Vibration Velocity

8.1.3 Vibration Acceleration

       Vibration acceleration is another important characteristic of vibration.
Technically acceleration is the rate of change of velocity. It is normally expressed in
“g” “s” peak, where one “g” is the acceleration produced by the force of gravity at the
surface of the earth.




                                  Graph 8.2: Vibration Acceleration

8.1.4 Vibration Frequency

       The amount of time required to complete one cycle of a vibration pattern is
called the period of vibration. Vibration frequency is the measure of complete cycles
that occur in a specified period of time.

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                                     Frequency =     1/period

        The frequency of vibration is usually expressed as the number of cycles that
occur in each minute or CPM (cycles per minute) or number of cycles per second or
Hertz (Hz).

8.1.5 Vibration Phase

        Phase is defined as the position of a vibrating part at a given instance with
reference to a fixed point or another vibrating part.      Phase measurements offer a
convenient way to compare one vibration motion with another or to determine how one
part is vibrating relative to another part.



8.2 VIBRATION SEVERITY

        There are no realistic figures for selecting a vibration limit which, if exceeded
will result in immediate machinery failure. The events surrounding the development of
a mechanical failure are too complex to set any reliable limits. On the other hand we
must have some general indications of machinery condition that can be evaluated on the
basis of vibration amplitude.




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             Fig.8.3: General machinery vibration severity chart (Velocity)


       On the fig 8.3 the horizontal axis is scaled in terms of vibration frequency and
the vertical axis in terms of displacement.      The area between the diagonal lines
represents levels of vibration severity from extremely smooth to very rough.




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       The fig 8.4 is a severity chart which works much the same way but uses velocity
and acceleration parameters and covers a higher CPM range




                 Fig. 8.2: General Vibration acceleration severity chart




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                                   CHAPTER 9

                                  TRANSDUCERS
   Transducer is a sending device which converts one form of energy into another.
The Vibration Transducer (Pick-Up) converts mechanical vibration into an electrical
signal. There are mainly three types of Vibration Transducers,

   1) Velocity Transducers.

   2) Accelerometer Transducers.

   3) Proximity Transducers.

   Velocity Transducer and Accelerometer Transducer are called Seismic Transducers.
Proximity Transducer is called Non-contact Transducer.



9.1 VELOCITY TRANSDUCERS

       Velocity transducers respond directly to vibration velocity.       Most vibration
measurement instruments have provision for processing the electrical signal from a
velocity pick up to show vibration displacement as well. In theory it is also possible to
convert signals from velocity pickups to units of acceleration, however, this is not done
in practice, because the results have been found to be unreliable.

9.1.1 Moving coil type




                                  Figure 9.1 Moving coil type




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        Fig 9.1 is a simplified diagram of a seismic velocity vibration transducer. The
system consists of a coil of fine wire supported by soft spring. A permanent magnet,
firmly attached to the case of the transducer, provides a strong magnetic field around
the coil.   Whenever this transducer is fixed or held tightly against a vibrating object,
this permanent magnet vibrates while the spring suspended coil of wire remains
stationary in space.    When the coil of wire cuts magnet lines of force, a voltage is
generated in that wire.     The voltage is proportional to the velocity of motion, the
strength of the magnetic field, and number of turns of wire in the coil.       The voltage
generated is transmitted by cable to a vibration meter, monitor or analyzer.



9.1.2 Direct Prod Transducer

        Many times it is necessary to measure the vibration of a small light weight part
or structure.   However, holding or attaching the standard velocity pickup to a small
part can actually reduce the vibration.      We can solve this problem by using a direct
prod pickup such as the one shown in figure.




                                  Figure 9.2: Direct prod transducer

        The principle of operation of a direct prod pickup is identical to that of a seismic
velocity pickup. With the direct prod pickup, a thin prod extends through the end cap
of the pickup and is attached directly to the movable coil inside. To measure vibration
with a direct prod pickup, we should fasten the main body of the unit to a rigid structure
to serve as a point of reference.     The tip of the prod is then attached to the vibrating
part, using a threaded tip or a special magnetic tip. We should hold the direct prod unit
by hand movements that naturally result; we should use an analyzer whose filter is
tuned to the vibration frequency of interest.     The low frequency vibration dye to the
hand movements are thus eliminated from the measurements.

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AJCE                                                Condition Monitoring of Rotary Machines

        One of the advantages of the advantages of this type pickup is that it adds only
the weight of the weight of the prod and moving coil to the vibrating part. This makes
the pickup especially useful on small, light weight objects where the mass of a standard
seismic velocity pickup can affect the actual vibration. It is often selected for use on
balancing machines where parts may be balanced at speeds as low as 50 RPM with
excellent results.



9.1.3 Piezoelectric velocity transducer

         These transducers have an output that is proportional to velocity, but have no
internal moving parts.    Stresses due to vibration forces applied to the pickup cause a
crystal or special ceramic material to produce an electric charge. These are designed
specifically for low frequency applications. It can measure down to 60 CPM.



9.2 ACCELEROMETER TRANSDUCER

        An accelerometer is a self generating devise with a voltage charge output
proportional to vibration acceleration. Vibration acceleration is the measure of the rate
of change of velocity and is normally expressed in terms of “g‟s”.      Acceleration is a
function displacement and frequency. As a result Accelerometer is extremely sensitive
to vibration occurring at high frequencies.

9.2.1 Piezo-electric with built in amplifier

        The figure shows a simplified diagram of piezoelectric with built in amplifier.
When this pickup is fixed or held against a piece of vibrating machinery, the
mechanical vibrations are passed through the frame to a piezoelectric material.      This
material has the ability to generate an electrical charge in response to a mechanical
force applied to it.   In this instance mechanical vibration producers the force and the
piezoelectric material responds by generating an electrical charge that is proportional to
the amount of vibration acceleration.




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AJCE                                                 Condition Monitoring of Rotary Machines




                         Figure 9.3: Accelerometer Transducer

9.3 Non-contact (Proximity) Transducers

       Many high speed machines consist of relatively light weight motors mounted in
massive cases and rigid bearings.      Because of weight and stiffness of the massive
machine case and bearings, externally mounted vibration and acceleration pickups often
show little outward evidence of motor or shaft vibration. It is necessary to measure the
actual shaft vibration in order to know when bearing clearances are in danger.        It is
displacement transducer measuring the shaft displacement relative to it fixing object.

9.4 Shaft Rider Accessory

       A shaft stick is usable for periodic vibration checks and some analysis and in-
place balancing operations.       When it is necessary to monitor shaft vibration for
extended periods of time, it is recommended that we use a shaft rider.

       The figure shows that a shaft rider is permanently installed in the bearing
housing.   It consists of a spring loaded probe that is held firmly against the rotating
shaft so that is held firmly against the rotating shaft so that it accurately follows shaft
motion.




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AJCE                                               Condition Monitoring of Rotary Machines




                            Figure 9.4: Shaft rider accessory




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AJCE                                                 Condition Monitoring of Rotary Machines


                                   CHAPTER 10
                VIBROMETER 810 (IRD Mechanalysis)
       This is a compact, portable instrument used to measure vibration amplitude. It
consists of a control and indicator input unit signal cable, accelerometer and a straight
extension probe for accelerometer.

10.1 CONTROL AND FUNCTIONS

       1. Amplitude Selector

           Amplitude selector is used select of range of amplitude for indication in
           amplitude meter.       It can measure velocity from 0-300 pk mm/sec and
           acceleration/spike energy from 0 to 100 g peak in metric units.

       2. Mode Selector

           To select desired measurement unit, a mode selector in provided in the
           instrument.    There are five modes provided in this instrument, which
           facilitates reading different vibration levels

                   i. Velocity Mode: This mode facility measuring vibration levels in
                       mm/sec.

                   ii. Acceleration Mode: This mode facilities measuring vibration
                       level in g‟s peak

                  iii. SE mode:      This modes provide measurement in g‟s SE of
                       bearing. SE stands for spike energy, which is a trademark of
                       IRD Mechanlysis Ltd. Spike energy measurements include very
                       short duration, high frequency spike like pulses that occur in
                       machinery as a result of

                              Surface flaws in rolling elements of bearing or gears

                              Rubs, impacts and metal to metal contact in rotating
                               machines

                              High-pressure steam or air leaks.

                              Cavitations of flow turbulence in fluids.




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AJCE                                                    Condition Monitoring of Rotary Machines




       3. Amplitude Meter

           Amplitude meter indicate the vibration amplitude and the condition of the
           internal batteries. It has got two scales:

              i.   Top scale which reads from (0-10)

             ii.   Bottom scale which reads from (0-3)

          The two scales are in designed in such a way that as upscale reading of at
          least one-third full scale is possible for all vibration measurement. These
          minimize the inherent motor errors. The range can be adjusted by using a
          range selector. Top scale reading being with one such as 10,000 etc., bottom
          scale can be used take measurement if the range begins which 3 such as 0.3,
          3, 30, etc.

       1) Range Selectors

           Range selector helps to select the range so that the pointer moves well inside
           the scale.

       2) Power Switch

           This is used to switch on the instrument i.e., to connect instrument circuits to
           the battery provision is provided in the instrument to check battery
           condition.

       3) Pickup Signal Input

           This is twist pieces lock type connector to connect input cable from the
           accelerometer.




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AJCE                                            Condition Monitoring of Rotary Machines




           Figure.10. 1: Accelerometer Transducer 810 (IRD Mechanalysis)




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AJCE                                                Condition Monitoring of Rotary Machines


                                  CHAPTER 11

                          VIBRATION ANALYSIS
       Vibration Analysis is a two step process involving the ACQUISITION and
INTERPRETATION of machinery vibration data.             Its purpose is to determine the
mechanical condition of a machine and specific mechanical or operational defects.

       The Data Acquisition procedure is a means of systematic measuring and
recording of the vibration characteristics needed to analyze a problem.

       The Data Interpretation involves comparing the recorded data with the details of
the machine, like its speed or speeds, its foundations, the construction details etc. Then
the characteristic of vibration typical of various defects are compared with the
characteristics that have been measured. By this, one can pinpoint the trouble and take
corrective measures.




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AJCE                                                Condition Monitoring of Rotary Machines


                                  CHAPTER 12

                             DATA ACQUISITION


       Data acquisition is the essential first step in vibration analysis, since the right
data must be acquired under the right conditions to completely interpret a machine‟s
condition.

       Data acquisition can be done in several ways depending on the available
instruments. Apart from data acquisition, additional data acquisition procedure such as
semi-automatic, automatic and real time analysis are employed where the job can be
quicker and more accurate.

       In the semi-automatic method, the operator manually adjusts the filter through
the frequency ranges, while the data is automatically recorded in a recorder.      These
types of plots are records of vibration amplitudes in the „Y‟ axis and the frequencies in
the „X‟ axis.   Such a plot is called Machinery Vibration Profile (Signature) and the
analysis of the same is called as Signature Analysis.

       Automatic data acquisition is the term used to describe the procedure of
obtaining the data, where the instrument automatically plots the vibration profiles.
This type of instrument incorporates and electronically swept filter as well as provisions
for simultaneous plotting of data with the recorders.



12.1 SELECTION OF MEASUREMENT PARAMETERS

       The various measurement parameters are displacement, velocity, acceleration:

12.1.1 Displacement

       Displacement can be measured with both velocity and acceleration pickups.
This is accomplished by means of integrator circuits that are normally included in the
circuit of vibration meters and analyzers.    Pickups that respond directly to vibration
displacement are readily available, but are usually used in the non-contact pickups.




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AJCE                                                Condition Monitoring of Rotary Machines

12.1.2 Velocity

       Velocity can also be measured with both velocity and acceleration pickups.
Seismic and piezoelectric velocity pickups obtain vibration directly. The output from
an accelerometer can be integrated to produce the equivalent of a velocity
measurement, down to about 3Hz, or 180 CPM.

12.1.3 Acceleration

       Acceleration should be measured only with an accelerometer. It is theoretically
possible to differentiate signals from a velocity transducer to produce acceleration
readings, but this would be needlessly complicated and expensive.

12.2 COMMON TYPES OF MEASUREMENTS

       The common types of measurements are:-

       1) Overall vibration amplitude measurements.

       2) Amplitude Vs Frequency measurements.

       3) Amplitude Vs Time measurements.

       4) Phase measurements.

They are described below:-

12.2.1 Overall vibration amplitude measurements

       Overall vibration amplitude measurements provide a quick check of general
machinery condition.         A vibration meter or analyzer can be used for these
measurements.     This measurement is generally manually recorded in tabular form, or
the data automatically stored in memory for computer based automated instruments.

12.2.2 Amplitude Vs Frequency measurements

       Amplitude Vs Frequency measurements provide frequency spectrum which is
used to pinpoint the problem to a specific frequency or range of frequencies.        Full
capacity or advanced check analyzers are required to take these measurements. Data
can be recorded manually in tabular form, or by semi automatic or automatic swept
filter analysis with tabular or graphic hard copy recording of the data.        FFT type
analyzer can also provide tabular/graphic hard copy of visual display of the data.

       It is estimated that over 85% of the mechanical problems occurring on rotating
machinery can be identified by displaying the vibration Amplitude Vs Frequency data.

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12.2.3 Importance of tri-axial readings

         It is common practice to record the Amplitude Vs Frequency data measured in
the horizontal, vertical and axial pickup directions at each bearing of the machines
being analyzed.      Obtaining measurements in all the three directions is extremely
important for distinguishing between various mechanical problems.             E.g. Unbalance,
Misalignment, bend shaft structural weakness (loose parts) will generally cause
vibration at a frequency 1X RPM.            Unbalance will almost always produce high
amplitudes in the horizontal direction while lower amplitudes in the axial direction.
Misalignment of couplings and bearings or a bend shaft will generally show relatively
high amplitude of vibration in the axial direction.           Amplitudes due to structural
weakness, loose parts are shown in Vertical direction.




     Figure 12.1: Vibration are normally taken in horizontal, vertical and axial directions



12.2.4 Amplitude Vs Time measurements

       Time measurements can be made during machine operation to detect vibrations
that would not be apparent from Amplitude Vs Frequency analysis.                Amplitude Vs
Time measurements can be made for very fast transient vibrations or for slowly
occurring vibrations.      For fast transient vibrations use an oscilloscope with the
horizontal axis scaled in milliseconds.      For slowly varying vibrations use a recorder
with the horizontal axis scaled in seconds.          It can be taken with a DC recorder
connected to an analyzer with that built-in-capability.




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12.2.5 Phase measurements

       Phase measurements are important when analyzing mechanical problems in
machinery. Phase is defined as the position of a vibrating part at a given instance with
reference to a fixed point or another vibrating part.        Phase measurements offer a
convenient way to determine how one part is vibrating relative to another part.

       To obtain phase measurements, an analyzer with a strobe light or remote
reference pickup is required. The use of strobe light necessities visual observation of
the rotating shaft and the capability to fire the strobe light with vibration signal in order
to obtain phase. The remote phase pickup, which is usually an electromagnetic pickup,
non-contact transducer or photocell must be installed so that to observe mechanical
protrusion (depression) or a reflective mark on the shaft.

       The strobe light measurement involves observing the angular position of the
reference mark that appears under the strobe light, while the remote reference pickup
provides phase readout (digital or analog) using a meter on the analyzer.




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                                     CHAPTER 13

                         DATA INTERPRETATION


        Once the necessary information have been collected by manual, or semi-
automatic or automatic, the next step is to review and compare the reading with the
characteristics of vibration typical of various types of troubles.         A key to this
comparison is the frequency.         If a machine part has some defect, the frequency of
vibration resulting from this defect will some multiple of the RPM.       The multiple is
different for different defects.       Also there are some defects which will produce
vibration frequencies that are not related with the RPM.

13.1 CAUSES OF VIBRATION

The major causes of vibration on Rotary machines are:-

13.1.1 Unbalance

       The horizontal, vertical and axial vibration signatures presented in the figure
given below illustrate typical Amplitude Vs Frequency analysis data resulting from an
unbalance condition.     It can be noted that, the predominant vibration occurs at 2200
CPM corresponding to the 2200 RPM fan speed. Since the amplitude of vibration in
the axial direction is relatively low compared to the radial amplitudes, a bent shaft or
misalignment is not indicated.       The appearance of small amplitudes at the harmonic
frequencies is common and does not necessarily indicate any unusual problems such as
mechanical looseness.

13.1.2 Mechanical looseness

       The vibration may be the result of loose mounting bolts, excessive bearing
clearance, a crack or break in the structure or bearing pedestal, a rotor which is loose on
the shaft, or some other loose machine component.          The vibration characteristic of
mechanical looseness will not occur unless there is some other exciting force such as
unbalance or misalignment can result in large amplitudes of looseness vibration. The
vibration due to looseness can be detected from Amplitude Vs Frequency when taking
the reading in vertical direction.




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AJCE                                                Condition Monitoring of Rotary Machines

13.1.3 Misalignment

       Misalignment is an extremely common problem.            Misalignment, even with
flexible couplings, results in two forces, axial and radial vibration.    The significant
characteristic of misalignment and bent shafts is that vibration will be noted in both the
radial and axial directions.      As a result, a comparative axial vibration is the best
indication of misalignment or a bent shaft.

13.1.4 Defective antifriction bearing

       Flaws on the raceways, balls or rollers of rolling element bearings cause high-
frequency vibrations and the frequency is not the multiple of the shaft RPM.          The
amplitude of vibration depends on the extent of the bearing fault.           The natural
frequency vibrations typically occur as vibration peaks in the 10,000 to 100,000CPM.
Defects in the bearing components can generate vibration peaks at frequencies related
to the bearing geometry.        The vibration generated by the bearing is not normally
transmitted to other points of the machine.

The other reasons for the vibration are:-

       1) Defective sleeve bearing.

       2) Defective gears.

       3) Eccentricity.

       4) Oil whirl.

       5) Bad drive belts or chain.

       6) Electrical defects.

       7) Rubbing.

       8) Bend shaft.

       9) Cavitation




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13.2 RECOMMENDED METHOD OF VIBRATION CLASSIFICATION

       The machines are classified into five groups as per ISO 2372.

They are:

13.2.1 Class I

       Individual parts of engines and machines integrally connected with the complete
machine in its normal operating condition (Production electrical motors of up to 15KW
are typical examples of machines in this category).



13.2.2 Class II

       Medium sized machines (typically electrical motors of 15-75KW output)
without special foundations rigidly mounted engines or machines (up to 300KW) on
special foundations.

13.2.3 Class III

       Large prime movers and other large machines with rotating mass mounted on
rigid and heavy foundations which are relatively stiff in the direction of vibration
measurement.

13.2.4 Class IV

       Large prime movers and other large machines with rotating masses mounted on
foundations which are relatively soft in the direction of vibration measurement (e.g.
Diesel-generator sets, especially those with light weight substructures).

13.2.5 Class V

       Machines and mechanical drive systems with un-balanceable inertia effects (due
to reciprocating parts) mounted on foundations which are relatively stiff in the direction
of vibration measurement.

13.2.6 Class VI

       Machines and mechanical drive systems with un-balanceable inertia effects (due
to reciprocating parts) mounted on foundations which are relatively stiff in the direction
of vibration measurement.         Machines with rotating slack-coupled masses such as
beater shafts in grinding mills, machines like centrifugal machines with varying
unbalances capable of operating as self contained units without connecting components,

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AJCE                                                Condition Monitoring of Rotary Machines

vibrating screens, dynamic fatigue-testing machines and vibration exciters used in
process plants.

       In practice, instead of good/Allowable/Just permissible, the following colloquial
is used to stipulate the health condition of machines.

                 Good
                 Satisfactory
                 Just satisfactory
                 Unsatisfactory
                 Dangerous




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AJCE                                                Condition Monitoring of Rotary Machines


                                        CHAPTER 14

                     PROCEDURE FOR THE PROJECT


       The various processes involved in project are:

       a) Identifying critical system

           The first step in condition monitoring is to identify equipment which would
           be benefit from the application of condition monitoring. This is achieved by
           examining all equipments in the industry or by looking only at problem
           causing equipment.       The selected equipment will probably have a poor
           record of efficiency, availability and safety or repair and maintainability this
           is likely to show up increased costs.

       b) Selecting suitable technique

           The next step is to understand how the equipment deteriorates.

       c) Set threshold value/baseline

           This stage involves identifying where and how often to take the
           measurements, Collecting the baseline readings and settings the threshold
           value for alarm or warning. Here we are taking vibration severity chart as
           the reference.

       d) Data collection for equipment

           The heart of condition monitoring lies in the collection storage and
           interpolation of data.     Processing of large amount of data may be time
           consuming it is therefore important to make Collections and assessment as
           possible ,using the few staff and incurring the lowest running cost The
           method of data collection may be a manual system, computerised automated
           system or a Hybrid system. The choice of method will depend on the level
           of protection that the equipment warrants and the cost of the method itself.
           Here the vibration analysis using IRD Mechanalysis 810.

       e) Condition assessment

           Data assessment aims to detect the deterioration in the equipment condition.
           It needs to be performed each time, a new set of measurements are taken.

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AJCE                                                Condition Monitoring of Rotary Machines

           The new readings may be checked against absolute threshold levels,
           compared with the past readings to detect any variation, or compared with
           past reading of other similar equipment being run under similar operating
           conditions.   In addition, the readings should be checked under validity to
           ensure that a false alert has not been generated

       f) Fault diagnosis

           After identifying a problem, it is necessary to find the cause and to ensure
           that correct maintenances action is taken. After the fault has been diagnosed
           (using the severity chart) suitable recommendation is been given to the
           company.




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AJCE                                               Condition Monitoring of Rotary Machines




                             Figure 14.1: Vibration Severity Chart




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AJCE                                              Condition Monitoring of Rotary Machines


                        Frequency of
 Nature of fault      domain vibration       Direction              Remarks
                            (RPM)

Rotating members                                           A common cause of excess
                           1X RPM             Radial
 out of balance                                              vibration in machinery

Misalignment &        Usually 1X RPM.        Radial &
                                                                A common fault
   Bent shaft          Often 2X RPM.           Axial

Damaged Rolling       Impact rates for the
                                             Radial &     Uneven vibration level, often
Element Bearings      individual bearing
                                               Axial        with shocks, impact rates
(Ball, Roller etc)       components.

                                                          Looseness may only develop
                      Sub harmonics of
 Journal bearing                                           at operating speed and high
                      shaft rpm, exactly      Radial
loose in housing                                             temperature (e.g. turbo-
                         ½ or 1/3 rpm
                                                                    machines)

Oil film whirl or
                       Slightly less than                   Applicable to high speed
 whip in journal                              Radial
                          half speed                                machines.
     bearing

                                                             Vibrations exited when
                                                             passing through critical
Hysteresis whirl      Shaft critical speed    Radial
                                                             speed are maintained at
                                                               higher shaft speeds.




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   Mechanical                                Radial &     Also sub harmonics for loose
                           2X RPM
    looseness                                 Axial             journal bearings.

                                                            The precise problem can
Faulty belt drive       1,2,3,4 X RPM         Radial      usually be identified with the
                                                              help of a strobe light.

   Unbalanced                                Radial &
                           1X RPM                           Easily felt by hand touch
  reciprocating                               Axial

    Increased           Blade passing
                                             Radial &        Increased level indicate
  turbulence or        frequencies and
                                              Axial          increasing turbulences
  recirculation           harmonics

                                                            No phase difference with
   Cavitations             1X RPM             Radial
                                                                    strobe light

                      1X RPM or 1 or 2
Electrical induced                           Radial &     Disappear immediately when
                      times synchronous
    vibrations                                Axial            turn-off the power
                          frequency



                      Table 14.1: Vibration Troubleshooting chart




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                                      CHAPTER 15

                                  CASE STUDIES
15.1 CASE STUDY 1: OXIDATION PUMP

Phase                                        :      3Φ

Frequency                                    :      50 Hz

Casing mount/Split/Type                      :      Centerline/Radial/Single, Volute

        1) Machine Analyzing

            The first step involves analyzing the machine thoroughly.        It involves
            analyzing the machine design and operating characteristic such as RPM,
            bearing type, gears etc

        2) Purpose of analysis

            Excess vibrations are found in the machine .So a machine troubleshooting
            is required.

        3) Selection of measuring parameter

            The frequency of machine is found to be nearly 50hz.usually for the
            frequency range of 1-50 Hz displacement is selected as the measurement
            parameter .But the frequency range of machine never falls below 50 Hz .But
            there are some occasions when it increases beyond 50hz.For the frequency
            range of 50-100 Hz velocity is taken as the measuring parameter for
            vibration analysis.

        4) Transducer position and direction

            Usually the readings are taken near the bearing surface .The systematic
            diagram for pump & motor combination is given below. For the pump
            reading are taken at appoint A and B at three mutually perpendicular
            directions i.e. horizontal, vertical and axial. These points are located
            between the coupling and the pump .For the motor the readings are taken
            from C and D which are located at front and rear of the motor.




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AJCE                                               Condition Monitoring of Rotary Machines

       5) Measuring instrument

               IRD 810

       6) Measuring procedure

                  Attach the accessories of the IRD 810 instrument.

                  Select the appropriate amplitude range using the range selector.

                  Set the measuring parameter as velocity.

                  Take the reading at the appropriate points

       The obtained result is shown in the data sheet.




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AJCE                                                Condition Monitoring of Rotary Machines

15.1.1 CAUSES

   It was found that the overall vibrations in vertical directions are high, so the bearing
conditions are monitored using spike reading. This indicates the deterioration of motor
bearing. The possible causes are found out and they are



          Dirt: particles entrained in the lubrication system are one of the most
           frequent causes of bearing damage.
          Insufficient lubrication: A total absence of lubrication of the ball-bearing
           system.
          Blockage of oil holes
          Out of shape shaft
          Overloading
          Corrosion
          Cavitation
          Oil seal failure

15.1.2 RECOMMENDATIONS

          Pump and motor bearing should be checked for deterioration.
          Dirt: Ensure that the entire lubrication system is carefully cleaned.
          Oil seal failure: check for possible loss of oil at the seals and replace these
           wherever necessary.
          Bearing reversal: during the installation of new bearings, the correct
           positioning of each is checked.
          Use a grindstone in perfect condition to achieve correct shaft geometry.
          Check that the assembly clearances and bearing material areas specified for
           the application.




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AJCE                                                Condition Monitoring of Rotary Machines


15.2 CASE STUDY 2: CIRCULATION PUMP

Phase                                        :       3Φ

Frequency                                    :       50 Hz

Casing mount/Split/Type                      :       Centerline/Radial/Single, Volute

   1. Machine Analyzing

        The first step involves analyzing the machine thoroughly. It involves analyzing
        the machine design and operating characteristic such as RPM, bearing type
        gears etc.

   2. Purpose of analysis

        It is that excess vibrations are found in the machine .So a machine
        troubleshooting is required.

   3. Selection of measuring parameter

               The frequency of machine is found to be nearly 50hz.usually for the
        frequency range of 1-50 Hz displacement is selected as the measurement
        parameter .But the frequency range of machine never falls below 50 Hz .But
        there are some occasions when it increases beyond 50hz.For the frequency range
        of 50-100 Hz velocity is taken as the measuring parameter for vibration analysis.

   4. Transducer position and direction

        Usually the readings are taken near the bearing surface .The systematic diagram
        for pump & motor combination is given below. For the pump reading are taken
        at appoint A and B at three mutually perpendicular directions i.e. horizontal,
        vertical and axial. These points are located between the coupling and the pump
        .For the motor the readings are taken from C and D which are located at front
        and rear of the motor.

   5. Measuring instrument

        IRD 810




Dept. of Mechanical Engineering                                                         47
AJCE                                                Condition Monitoring of Rotary Machines

15.2.2 CAUSES

   It was found that the overall vibrations in horizontal directions are high, so the shaft
conditions are monitored; this indicates the unbalance of shaft. The possible causes are
found out and they are



          Assembly Errors
          Couple unbalance
          Over hung rotor unbalance
          Cocked Rotor



15.2.3 RECOMMENDATIONS

          Proper Assembling
          Placements of balance weights in at least two planes
          Static & dynamic balancing
          Proper Alignment




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15.3 CASE STUDY 3: COOLING WATER PUMP

Phase                                        :       3Φ

Frequency                                    :       50 Hz

Casing mount/Split/Type                      :       Centerline/Radial/Single, Volute

   1. Machine Analyzing

        The first step involves analyzing the machine thoroughly. It involves analyzing
        the machine design and operating characteristic such as RPM, bearing type
        gears etc.

   2. Purpose of analysis

        It is that excess vibrations are found in the machine .So a machine
        troubleshooting is required.

   3. Selection of measuring parameter

               The frequency of machine is found to be nearly 50hz.usually for the
        frequency range of 1-50 Hz displacement is selected as the measurement
        parameter .But the frequency range of machine never falls below 50 Hz .But
        there are some occasions when it increases beyond 50hz.For the frequency range
        of 50-100 Hz velocity is taken as the measuring parameter for vibration analysis.

   4. Transducer position and direction

        Usually the readings are taken near the bearing surface .The systematic diagram
        for pump & motor combination is given below. For the pump reading are taken
        at appoint A and B at three mutually perpendicular directions i.e. horizontal,
        vertical and axial. These points are located between the coupling and the pump
        .For the motor the readings are taken from C and D which are located at front
        and rear of the motor.

   5. Measuring instrument

        IRD 810




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15.3.1 CAUSES

   It was found that the overall vibrations in axial directions are high; this indicates a
case of misalignment. The possible causes are found out and they are:



      Increased friction
      Premature bearing and seal failure
      Bent shaft
      Failure of coupling and foundation bolts



15.3.2 RECOMMENDATIONS

      Ensure Proper lubrication
      Proper lubricant should be selected
      Provide proper machining of shaft
      Ensure the foundation bolts are tight




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                                   CHAPTER 16

                                  CONCLUSIONS

        Predictive maintenance yields great benefits over other types of maintenance
practices. A maintenance philosophy that incorporates predictive maintenance with
preventive maintenance greatly improves equipment reliability.

       The many benefits of predictive maintenance are highlighted below

       Increased safety

Predictive maintenance provides the reassurance of safe, continued plant operation. By
reducing the likelihood of unexpected equipment breakdown, the safety of employees is
improved.

       Improved operating efficiency:

There are many areas in which a predictive maintenance program can increases the
efficiency of process.

       Reduction in Lost Production

Predictive maintenance aims to identify problems in equipment so that the necessary
downtime can be scheduled. By identifying problems in the initial stages, the predictive
maintenance system gives notice of impending failure, so downtime can be scheduled
for the most convenient and inexpensive time.

       Reduced Cost of Maintenance

As equipment is only repaired when needed ( as opposed to routine disassembly ),
maintenance staff have more satisfying and worthwhile work and the cost of
maintaining the machinery are reduced as resources ( labour, equipment and parts) are
only used when needed.

       Less Likelihood of Secondary Damage

By identifying potential failures in advance, the severity of these failures can be
substantially diminished by reducing or preventing secondary damage.




Dept. of Mechanical Engineering                                                        51
AJCE                                                Condition Monitoring of Rotary Machines


      Reduced Inventory

Predictive maintenance reduces inventory costs because, as substantial warning of
impending failures is provided, parts can be ordered as required, rather than keeping a
large backup inventory.

      Extending the Life of Plant Items

Using a predictive maintenance program, machines are only dismantled when
necessary, so the frequency of equipment disassembly is minimized, and thus the
probability of „infant mortality‟ is reduced.

Predictive maintenance programs such as vibration analysis can only accentuate lean
production practices in an ever – competitive global market place.

Vibration analysis is the main part of the predictive maintenance program. Using this
technique we can predictive maintenance program. Using this technique we can predict
exact problem for failure of the equipment. So the severe damage to the equipment is
avoided by taking actions based on the vibration analysis technique.

  Vibration detection and analysis play important roles in development and testing of
new and prototype machines. Vibration measurements provide overall performance
data. Analysis techniques reveal troubles that might be the result of improper
installation and adjustment as well as improper design.




Dept. of Mechanical Engineering                                                           52
AJCE                                              Condition Monitoring of Rotary Machines


                                  CHAPTER 17

                                  REFERENCES
   [1]. S. S. Rattan, Theory of Machines, Tata McGraw-Hill, New Delhi, 2004.
   [2]. Vibrotech, Training Manual, Chennai.
   [3]. IRD Mechanalysis, Instruction Manual.
   [4]. A.Tsang, "Condition-based maintenance: tools and decision making", Journal
       of Quality in Maintenance Engineering, Vol. 1, No. 3, 1995, pp. 3-17.
   [5]. M. Bengtsson, "Condition Based Maintenance System Technology – Where is
       Development Heading?", Proc.17th European Maintenance Congress, 2004
   [6]. Handbook of condition Monitoring, A. Davies, and London: Chapman & Hall
       1998, ISBN 0-412-61320-4
   [7]. Vibration Severity charts and Vibration Standards from, Available from:
       www.relaibilityweb.com,




Dept. of Mechanical Engineering                                                       53

								
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