a study on failure of mechanical pump

A Study on Failure of Mechanical Pump and

other Equipments

This report was submitted to AstralPool India Pvt Ltd, Chennai, Tamil Nadu as a part of Internship offered by Fluidra.

Submitted by

Azif Ali S

MM08B027

Department of Metallurgy and Materials Engineering

Indian Institute of Technology

2 A Study on Failure of Mechanical Pump and other Equipments

Preface

This report titled “A Study on Failure of Mechanical Pump and other Equipments” was submitted to

AstralPool India Pvt. Ltd., Chennai, Tamil Nadu a division of Fluidra group. For this venture, I associated

myself with AstralPool India Factory and Warehouse at Coimbatore. It is a compilation of information

collected from the technicians and other people there and Product Data base available on the AstralPool

website. Credits have been given to all other information sources.


Acknowledgement


Contents

Introduction

Failure in Mechanical Pumps

Parts and Materials Used

Pump failure Identification Methodology

Visual Inspection

Preliminary Tests and Checks

Inspection of Sounds

Universal Pump Testing Machine

Different types of stresses acting on motor parts

Cases of Failure in Mechanical Pump – A Part by

Part Analysis

Motor Shaft

Corrosion

Reasons for Corrosion of shaft

Measures for combating Corrosion

Shaft bend

Bearing

Stator

Rotor

Fan and Fan cover


Terminal Box

Pump body

Pump foot

Pre-filter Assembly

Front and rear Motor Covers

Motor Bridle and Mechanical Closure bridle

Impeller – Mechanical Seal - Diffuser Assembly

Metallurgical failure Analysis

Methodology

Analysis of Service Data from 2008-2011*

Year by Year

Appendices

Suggested Methodology for Motor Failure Analysis


Introduction

AstralPool Pvt. Ltd, one of the world’s largest suppliers of equipment for private and public

swimming pools and spas produces wide range of equipments including Mechanical Pumps,

Filters, Heaters etc. The theme for this report is to understand the reasons of failure of different

Mechanical pump parts and other associated equipments. Root cause failure analysis (RCFA)

scheme is used to identify the causes of the failure.

Services data for the past 3

years have been compiled and failures are categorized based on

different parts. A basic data analysis also has been done at various parts of the report and

conclusions have been reported.


Failures in Mechanical Pumps

Astral-Pool produces three types of pumps for swimming pools:-

I. Plastic Self priming Pumps

II. Cast Iron Self priming Pumps

III. Bronze Self priming Pumps

Astral Splash Pump

Astral Splash Pumps are built using state of the art thermoplastics.

The pumps are of self-priming type from ½ Hp to 3 Hp and are

provided with single phase and three phase motors. All Pump

metal parts that come in contact with water are made of stainless

steel (AISI 316). A pre-filter has been incorporated into the pump

body to prevent the foreign bodies to enter the pump hydraulic

parts.

The motors are supplied with the motors pump unit which has

been protected by Thermal Overload Protector (TOP).

The present study does a study on the reasons of failure of different pump parts of both cast Iron and

Plastic Self Priming Pumps. It does a part to part analysis of different suppliers, different materials used

and the design of the materials.

Parts and Materials Used (Plastic Self Priming Pump)

Part Material Used Shaft Stainless Steel (AISI 316)

Rotor Silicon based alloy

Impeller Noraiy with FRP

Diffuser Luranye

Other Plastic Pump body parts Engineering Plastic

Fig 1: Astral Splash Pump (1 Hp)


Pump failure Identification Methodology (Currently in use)

Visual Inspection

Visual Inspection is done to know whether there is any external body damage on the pump. Issues like

fan not running bending of the fan cover, motor not priming due to clogging of pre-filter basket,

breakage of pump body or foot can be found out by visual inspection.

Preliminary Tests and Checks

Preliminary tests/Checks include

1. Checking the terminal box:- Checking whether the connections are intact or whether there is

any capacitor damage

2. Checking the shaft rotation:- Improper shaft rotation might be due to any of the following

reasons:-

Fig 2: Process tree for Pump Failure Identification

(Currently in Practice)

Visual Inspection

Preliminary Tests

Checking for Sounds

Using the Pump Testing

Machine


a. Shaft getting bend

b. High bearing friction

c. Motor Coil getting short

d. Contact between the impeller and the diffuser.

3. Checking the continuity of the circuit:- This is done using the digital multimeter. This passes

very high voltage current through the circuit. This can also identify presence any short in the

motor.

4. Check the pre-filter basket for clogging of any impurities which prevent water flowing in.

Inspection of Sounds

Any abnormal sound coming from the motor is due to malfunctioning of it. Different types of sound

produced by the motor include:-

1. Bearing Sound: This is due to high bearing friction or failure. Bearing friction increase in the

course of time due to vaporization of the grease in the bearing. This can be also due running the

rotor in unbalanced condition in which the load on the motor shaft is not evenly distributed.

This can lead to war of the bearing and in long run can cause bearing failure.

2. Touching sound: This due to the touching of the rotor with stampings in the motor hindering

the smooth rotation of the motor. This will damage the rotor and the stampings.

3. Fan Cutting Sound: Fan cutting sound is due to the unbalanced rotation of the cooling fan. This

doesn’t have much consequence but can affect the cooling of the motor.

4. Vibration Sound: This is again due to unbalancing. This happen in equal frequency during testing

of new pumps. This is basically a design problem. It is due to the play of the rotor bearing

assemble in the motor casing. This can also happen due to over-tightening front and back

covers.

5. Air Sound: This happen due to air choking

6. Over-tight Sound: This happens due to over-tightening front and back covers which restrict the

rotation of the motor shaft. This can be costly as it leads to high motor current which in-turn can

result in motor coil burning and rotor damage.

Checking using Universal Pump Testing Machine

Universal Pump testing machine is an instrument used for Pump testing. Every pump supplied by

AstralPool India is Tested for verification of the performance. This is machine is also used for finding the

reasons of failure of Pumps coming there for service. The machine basically consists of different meters

which can measure and set the following operating conditions:-


1. Current in Amperes

2. Pressure in bars

3. Flow rate m3/h

4. Voltage

5. Vacuum

6. Motor rpm

Each pump will be having a specification which describes different operating conditions and different

min and max values. Example of a specification of a 1 Hp motor (Supplier: Sabari) is given below:-

Specification Value Power(KW/Hp) 1/0.75

Input Voltage (MAX) 230 V

Input Frequency 50 Hz

Rotation Speed(MAX) 2800 rpm

Input Current (MAX) 4.9 A

Capacitor 25 pF

Pressure Head (H) 10 m.c.a

Flow Rate (Q) 16 m3/h

Fig: Universal Testing Machine for testing motor


Different types of stresses acting on motor parts1

1 A.H. Bonnett, Root Cause AC Motor Failure Analysis with a Focus on Shaft Failures, IEEE Trans. Industry Application, 36(5), 11971209, 2000

Type of stress Stator winding

Rotor assembly Bearings Shaft

Thermal • • • •

Electrical /dielectric • •

Mechanical • • • •

Dynamic • • •

Shear •

Vibration/shock • • • •

Residual • •

Electro-magnetic • • • •

Environmental • • • •

Table 1: Types of Stresses on Motor


Cases of Failure in Mechanical Pump – A Part by Part Analysis

Motor Shaft

Motor shaft failure happen due to several reasons. Table 1 summarizes the different types of stresses

acting on the motor shaft. The following table2 shows the general frequency of shaft failure due to

different reasons:-

2 Root cause AC motor failure analysis with focus on shaft failures, Intelligent Mechanics Lab, Department of Mechanical Design, Pukyong National University, South Korea

0 0

8

1

0

2

4

6

8

10

2008 2009 2010 2011*

Year

No. of Failures associated with Motor Shafts

Cause of shaft failure Percent

Corrosion 29%

Fatigue 25%

Brittle fracture 16%

Overload 11%

High-temperature corrosion 7%

Stress corrosion fatigue/hydrogen embitterment

6%

Creep 3%

Wear, abrasion and erosion 3%

Table 2: General Frequency of different causes of shaft failure

Graph: Year by year rate of Shaft failures during 2008-11


Out of these the major shaft failure modes are:-

a. Corrosion

b. Fatigue

c. Overload

Corrosion

The above table says that corrosion is the most critical reason of shaft failure which accounts for 29% of

all Shaft failure cases. Wear pitting, fretting and cavitations are the corrosion most common corrosion

modes found in shaft. This increases the chances of fatigue and brittle failure of the shaft.

Reasons for Corrosion of shaft

a. Absence of Rust-off Coating

Rust-off coating is a layer of plastic like coating which cuts the atmospheric contact of

rotor-shaft assembly. In course of time the coating gets removed due to the variation in

the temperature.


b. Damage of the mechanical sealing

Mechanical sealing is a very integral part of the Motor which lies in between Motor

Bridle and the Impeller. Its damage gives opportunity for water to leak into the shaft

area and can cause corrosion.

c. Environmental Conditions

The service conditions also play an important role in corrosion. Eg: Installation at Coastal

Regions, Flooding of Pump room etc. aid the corrosion damage tendency

Measures for combating Corrosion

1. Using AISI 416 or other 400 series of stainless steel for shafts in corrosive environment.

2. Use of Rust-off coatings.

Shaft bend

Shaft bend mainly occurs due to uneven distribution of load along the axis. A uniform distribution of

load around the axis is necessary for the free rotation of the motor. This can be result due to several

reasons:-

1. Due to Off-centered hole in impeller:-

To counter this weight imbalance

material is usually removed from the

heavier sides by punching. But this is

not very efficient in restoring the

balance.

2. Lack of intimate contact of bearing with

the shaft or due to defect in bearing.

3. Due to play in the bearing and bearing

seating in the motor flanges.

Fig: Off-Centered hole in the impeller


Bearing

Bearing used in the Astral Motors are ball bearings. It provides constrained motion of the rotor along the shaft axis without touching the stator or the motor chase. The bearing is seated on the space provided in the front and rear motor cover. Intimate contact is necessary to prevent the bearing from rotating itself.

Failures in Motor Bearings

Smear Marks due to presence of impurities on bearing

Metallic Contamination in the Raceaway

Damage caused by water Intrusion Fretting Corrosion due to vibration and loss of fit

Failure Mode Failure Pattern

Fatigue spalling Thermal

Fretting Vibration & noise

Smearing Lubricant quality

Skidding, wear Mounting/fits

Lubrication failure Contamination

Electric pitting Mechanical damage

Fluting Electrical damage

Crack and Seizures Load pattern

Table 4: Failure Modes and Failure Pattern in Bearings

Fig: A Typical motor bearing


Pitting caused by electrical currents Fluting caused by internally generated current

Advanced stages of spalling False brinelling and fretting caused by vibration in a non-operating condition

Causes of Failure (Focus on Astral Pumps)

1. Over-tight front and rear cover:- Over tightening can increase the friction between the bearing the

shaft core hindering the free rotation of shaft.

2. Due to dry up of grease:- Similar to over tightening it leads to increase in friction between the shaft

and bearing.

3. Thermal expansion of front and rear cover:- Earlier the front and rear cover of the motors where

made of Cast Iron. Subsequently it was changed to Aluminum to make it cost lower and lighter. As

the thermal expansion of Al is more than that of the Cast-Fe, at higher temperature during

functioning of the motor, the front and rear cover expands and the intimate contact of bearing and

the covers are lost which reduces the relative motion of bearing and the shaft.

4. Astral pump uses wave washers between the bearings and the bearing seating. This gives better

friction between the bearing and motor cover gives tolerance for slight differences in the depth of

the bearing seating. In long run due to fatigue, these wave washers lose their elastic property and

the tolerance is lost and the seating wouldn’t be as effective as before. Using better quality of wave

washer can help us in this account.

Table: Conventional failures in a typical Electric motor bearing


Stator

0

1

2

3

4

5

6

7

8

9

2008 2009 2010 2011*

No

. of

Be

arin

g Fa

ilure

s

Year

Fig: Stator of 1 Hp astral pump

Graph: Year by Year analysis of bearing failures during 2000-2011


The stator is the stationary part of a rotor system. It consists of:-

a. Stampings: - A premium steel frame encloses a hollow cylindrical core. It is made of laminations of

silicon steel. Silicon laminations reduce hysteresis and eddy currents. Astral Motors uses

electromagnetic stators.

b. Stator windings: - A stator winding is simply the stationary winding over the stampings framework.

Stator Stamping

Motor Burn

Short

0

2

4

6

8

10

12

2008 2009 2010 2011*

3

1

7

310

11

2

Cases of failure due to stator

Motor Burn

Short

Fig: Stator and Stampings

Graph: Failures due to Stator during 2008-2011


Stator failure

The first source of startup failure is the stampings touching the rotor. This causes a touching

sound and also leads to damaging of the rotor.

Second source is the stator winding. If there is any shorting in the stator copper winding due to

a cut or loss of insulation coating, this leads to shorting of the motor. The motor in this case

would draw high current and can get burned. This can be diagnosed by checking the continuity

between the motor body and one of the terminals. If positive there is motor short.

If the pump shows some humming sound and rotates with jerks, it is expected to have problems

associated with the coil. Coil might be burned or one of the coils might not be working. Also if

the input current is too high, then there is a short inside the pump.

Stampings in the motor need to be cold rolled. Only then it can sustain large number of heat and

reheat cycles.

Rotor

The rotor is the non-stationary part of a rotary electric motor which rotates because the wires and

magnetic field of the motor are arranged so that a torque is developed about the rotor's axis. It is the

most crucial part of the motor. The rotors in Astral Pumps are made of Cu-Si-Fe alloy which are joined

together by induction brazing. The rotor end rings are made of pure aluminum to give electrical

connection.

Fig 13: Damaged motor Rotor (1Hp)

http://en.wikipedia.org/wiki/Torque


Causes of Failure

1. End-Rings: - The end rings in motors delivered to Astral India are made of Aluminum. The

international norm for end-rings to use Cu instead of Al so as to give better conductivity. Also as

Cu is stronger than Al, the chances of breaks in the end-rings are also less.

2. The rotor central part in motors delivered to Astral India is made of Cu-Si-Fe alloy. From the

preliminary observation the percentage of Fe in the rotor is more in case of motor supplied to

Astral India than the international norms. This leads to failure of motors due to rust formation

on the surface if serviced under Corrosion prone condition. Additional Rust off coating is

recommended for such rotors.

To improve motor energy efficiency, the following strategies may be adopted:

1. Using of improved magnetic materials (e.g. Premium steel) 2. Replacement of Aluminum cage with Copper end-rings. 3. Using high Cu and Si alloy in rotor. 4. Silicon steel to prevent eddy current loss.

Fan and Fan cover

A fan is provided at the rear end of the motor with the sole purpose of cooling the motor. Fan is made of

engineering plastic and the fan cover is made of mild steel. The two major issues associated with these

parts are:-

Bend in the fan cover

Breakage of fan

0

5

10

15

20

25

2008 2009 20102011*

0

610

50 3

2219

Defected part: Fan

Defected part: Fan Cover

Note: 2011 data value is estimated

Graph: No. of defected fans and

fan covers during 2008-2011


Breakage of fan Bend in the fan cover

Using sheet metal of greater thickness than the present for making fan cover can go a long way in

reducing the number of cases of fan cover bend.

Terminal Box Terminal box contains a condenser (capacitor), which controls spike or surges in input AC. Cases

associated with the terminal box are bulging of capacitor and missing of terminal box cover. Astral uses

Siemens capacitor.

1

6

13

7*

0

2

4

6

8

10

12

14

2008 2009 2010 2011*

No

. of

case

s as

soca

ite

d w

ith

Te

rmin

al B

Bo

x

Year

Fig: Defective fans and fan

covers

Fig: Failure cases associated with Terminal Box during 2008-11


Pump body

The pump body of Astral Splash pumps is made of engineering plastic. The most

prominent Engineering plastic used is called ABS(Acrylonitrile butadiene

styrene) which is a thermoplastic material. It can be used between -25 and 105 0C. These are made by high pressure injection moulding process. The major

types of failure in Pump body are :-

As it is made of a hard plastic material, there are chances of pump

getting cracked/ broken during transit or improper usage.

Loss of threading in the drainage plug. This leads to leakage.

Over-tightening of the screws can also result in the cracking of the pump body. Similarly under-

tightening result in leakage.

Failure of the bottom of pump body Loss of threading in the drainage plug

Breakage of pump body foot Chipping off the side edges

Table: Different types of damages of Astral Splash Pump body

Fig: Pump Body


Pump foot It is the part on which the pump body rests. Pump body is attached to pump foot with good care. It is

done so using pairs of distancing washer, nuts, silent blocks, foot screw and anti shake washer. The lack

of any of the above components causes vibration and unusual sound from the motor. The main type of

failure found in pump foot is breakage which mainly happens during transit. This has decreased in the

recent years with better packing methods using thermocole cushioning.

0

2

4

6

8

10

12

14

20082009

20102011*

Pu

mp

Fo

ot/

Bo

dy

Failu

re

Year

Pump Body Failure

Pump Foot Failure

Estimated foot failure by EOY

Fig: Damage of Astral Splash Pump foot

Fig (b): Pump foot-Pump body assembly

Fig (a): Pump foot

Graph: Service summary of Astral Splash Pump body and foot during 2008-11


Pre-filter Assembly

Pre-filter as the name suggests removes the initial debris from the input water supply. Sizes of the debris

depend on the grit size of the pre-filter basket.

Pre-filter consists three parts

Pre-filter basket

Pre-filter cover

Pre-filter cover joint

Failures in Pre-filter basket

More than 3/4th of cases noted till date associated with the pre-filter baskets are due to breakage of pre-

filter basket handle. Other problems found at the project sites are due to clogging of it with debris. This

result in the closing of the grits in the pre-filter basket which in-turn lead to reduced inflow of water into

the pump. Motor dry run has several bad effects on the motor like motor burning caused by drawing

large currents from the supply line. So it is really important to clean the pre-filter basket at regular

intervals.

Fig: Failed of Astral Splash Pre-Filter Baskets


Front and rear Motor Covers

Front Cover (Cast Iron Made) Front Cover (Cast Iron Made)

It is usually made of Cast Iron. But recently, to reduce the weight of the motor Aluminum and steel have

also found place. The front and rear covers seats the entire motor between them. It has a slot for

seating the bearing. The intimate contact between the bearing and the cover help in the relative motion

of the rotor and the motor body.

The major types of defects found in motor covers are: -

Corrosion of front and rear cover.

Specification: - If the dimension of the slot for the bearing does not exactly match the size of the

bearing, the relative motion is not possible.

Cast Iron when compared to Aluminum has an advantage as motor cover. As the coefficient of

thermal expansion of the Al is more than Cast-Fe, there would be more variation in the slot size

for the bearing from the specification in case of Al – motor covers than Cast-Fe based motor

covers.

Fig: Front and Rear motor covers


Motor Bridle and Mechanical Closure bridle

Marks on the mechanical closure bridle due to

diffuser touching it Motor Bridle attached to front motor cover

Other bridle defects are non-matching of the holes bridle with the motor cover. This can lead to crack in

the bridle and also unbalanced running conditions.

0

1

2

3

4

5

6

7

8

2008 20092010

2011*

0

4

6

21

5

8

4

Mechanical Closure Bridle

Motor Bridle

Note: 2011* is estimated

Graph: No. of cases of failure of Mechanical closure bridle and Motor bridle during 2008-11

Fig: Mechanical closure bridle and Motor bridle


Fig: Pre-Filter Baskets clogged with

debris

Fig: Defects in Astral motor Shafts

Impeller – Mechanical Seal - Diffuser Assembly

An impeller is a rotating component of a centrifugal pump,

usually made of iron, steel, bronze, brass, aluminum or plastic,

which transfers energy from the motor that drives the pump to

the fluid being pumped by accelerating the fluid outwards from

the center of rotation. Impeller is the part attached to the shaft

which is threaded in.

Diffuser consists of a stationary vane that surrounds the

impeller. The purpose of the diffuser is to increase the

efficiency centrifugal pump by allowing a more gradual

expansion and less turbulent area for the liquid to reduce in

velocity. It also prevents debris going into the impeller. In

Astral splash pumps, impeller is made of Noraiy with FRP and

diffuser is made of Luranye.

Mechanical shaft seal forms a barrier between what is inside

the pump and the atmosphere Mechanical seal consists of a

carbon ring, spring and a ceramic. The ceramic is made of

extremely hard materials which are highly wear resistant

material is of very high finish.

Failures associated with Impeller – Mechanical Seal - Diffuser Assembly

Shaft hole off-centered Weight balancing by removal of material


Fig: Marks in Astral motor

mechanical closure bridle made by

diffuser

Fig: Mechanical seal: Rubber ring

(bottom) and Ceramic

Fig: Mechanical seal: Spring

Fig: Mechanical seal: Spring

1. Off-centered hole in impeller for shaft

causes unbalanced distribution of mass

around the shaft axis and lead to bend in

the shaft. This in long run can cause wear

of the bearing. This also can lead to the

detachment of the impeller from the shaft

2. Defects as shown in the above figure happen due to either

over-tightening of the diffuser or defect of non-returnable

valve.

3. If the non-returnable valve doesn’t function as expected

there is a chance for the impeller to detach itself from

shaft and get attached to the diffuser. The figure shows

scratch marks on the diffuser due to this.


Graph: Failures due to Impeller-Mechanical seal-Diffuser Assembly

4. Mechanical Seal failures can be caused due to:-

Lubrication failures.

Contamination failures: - If sand/debris which is filtered gets into the mechanical seal it can

damage the mechanical seal which can result in the entry of water into the motor core.

Chemical and physical degrading and wear.

Systems failure: -If the motor is run without water, mechanical seal heats up and gets damaged.

From the above chart we can easily make it out that Impeller-Diffuser-Mechanical Seal is the most fault

prone part of the entire pump. All the three are very much interconnected that, failure of any of them

can lead to failure of others. Hence they were analyzed together. For Ex: - The presence of sand or any

other particle in the region between the impeller and the diffuser can damage the entire assembly.

0

2

4

6

8

10

12

14

20082009

20102011*

2008 2009 2010 2011*

Failure due to Impeller 2 4 14 7

Failure due to Diffuser 0 4 7 11

Failure due to Mechanical seal 0 5 12 11

Failure due to Impeller

Failure due to Diffuser

Failure due to Mechanical seal

*Failures in 2011 EOY is estimated


Fig: Scratch marks on the Impeller due to diffuser

Note: All the plastic parts are associated with plastic self priming pumps are replaced by Cast-

Iron in Cast Iron self priming pumps.


Metallurgical failure Analysis

Methodology

Fig: Methodology of Metallurgical failure analysis3

The Metallurgical failure analysis can be applied to all cases of failure due to metal material. It uses

different techniques like Chemical Analysis, Mechanical Testing, Metallographic Examination, Non-

Destructive Testing etc. This technique is versatile in identifying the root cause of failure and finding the

failure mechanism. It guides you to find whether the failure has occurred due to metallurgical

deficiencies or mechanical overload or service environment etc. The methodology of metallurgical

failure analysis has been given in the Diagram above.

Metallurgical failure analysis has been implemented in understanding failure of different parts like shaft,

bearings, rotor etc. In this report a complete metallurgical analysis couldn’t be undertaken due to the

lack of necessary testing facilities. But however metallurgical analysis has been made in some parts of

the report based on the physical observation.

3 Derrick Sarafinchan, M.Eng., P.Engg., Ludwig & Associates Engineering Ltd.


Analysis of Service Data from 2008-2011*

A total of 98 pumps had been serviced in Astral India Pvt. Ltd., Coimbatore warehouse during 2008-

2011*. The pump had been received here from different project sites all over India. Each of these pumps

undergoes a thorough checking procedure (Checking/testing methodology already described) and

possible corrections are made. If any issue related to the motor is pertaining in the pump it is send to

the supplier. The pumps during the period have been supplied by majorly by either Sabari Motors or

Sharp Motors.

A detailed data has been compiled in pump service has been categorized based different pump parts.

Failure of the pump has been associated with 23 different pump parts. Following analysis give some

insights and patterns pump failure based on the data taken during the period.

Year by Year

From the above graph it can be seen that the number of pump failures is remarkably high during 2010.

The increase in the number of failures during this period can be attributed to the______. There has

been a decreasing trend in the number of failures in 2011 during which 8 pumps have been serviced till

date and no. of service pumps is expected to be 19* by the end of the year.

Graph 1: A year by year analysis of pump failure during 2008-11

19*

Note: 19* is estimated no. of

cases in 2011


Appendices

1. Suggested Methodology for Motor Failure Analysis

1. Checklist for evaluating assembly conditions

i. Is there any sign of moisture present on the stator, rotating assembly, bearing system or any other parts?

ii. Are there any signs of movement between rotor and shaft or bar and lamination? iii. Is the lubrication system as intended or has there been lubricant leakage or

deterioration? iv. Are there any signs of stalled or locked rotor? v. Was the rotor turning during the failure?

vi. What was the direction of rotation and does it agree with the fan arrangement? vii. Are any mechanical parts missing? such as balance weights, bolts, rotor teeth, fan

blades, etc., viii. Has any contact occurred between rotating parts that should maintain a clearance?

ix. What is the condition of the coupling device, driven equipment, mounting base, and other related equipment?

x. What is the condition of the bearing bore, shaft journal, seals, shaft extension, keyways, and bearing caps.

xi. Is the motor mounted, aligned, and coupled correctly? xii. Is the ambient usual or unusual?

xiii. Do the stress risers show signs of weakness or cracking?

2. Checklist : Appearance of motor and system

i. Does the motor exhibit any foreign material? ii. Are there any signs of blocked ventilation passages?

iii. Are there signs of overheating exhibited by insulation, lamination, bars, bearings, lubricant, painted surfaces, etc.?

iv. Has the rotor lamination or shaft rubbed? Record all locations of rotor and stator contact.

v. Are the top-sticks, coils, or coil bracing loose? vi. Are the rotor cooling passages free and clear of clogging debris?

vii. What is the physical location of the winding failure? viii. Is it on the connection end or opposite connection end?

ix. If the motor is mounted horizontally, where is the failure with respect to the clock? x. Which phase or phases failed?

xi. Which group of coils failed? Was the failure in the first turn or first coil? xii. Are the bearings free to rotate and operate as intended?

3. Checklist : Application considerations


i. What are the load characteristics of the driven equipment and the loading at time of failure?

ii. What is the operating sequence during starting? iii. Does the load cycle or pulsate? iv. What is the voltage during starting and operation? v. Is there a potential for transients?

vi. Was the voltage balanced between phases? vii. How long does it take for the unit to accelerate to speed?

viii. Have any other motors or equipment failed on this application? ix. How many other units are successfully running? x. How long has the unit been in service?

xi. Did the unit fail on starting or while operating?

xii. How often is the unit starting, and is this a manual or automatic operation?

xiii. Is it part winding, wye-delta, or variable-frequency drive (VFD), or across the line? xiv. What type of protection is provided? xv. What removed or tripped the unit from the line?

xvi. Where is the unit located and what are the normal environmental conditions? xvii. What was the environment at time of failure?

xviii. What was the ambient temperature, at time of failure, around the motor? xix. Is there any recalculation of air? xx. Is the exchange of cooling air adequate?

xxi. Was power supplied by a VFD? xxii. What is the distance between the VFD and the motor?

xxiii. How would you describe the driven load method of coupling and mounting?

4. Checklist : Maintenance history

i. How long has the motor been in service? ii. Have any other motor failures been recorded and what was the nature of the failures?

iii. What failures of the driven equipment have occurred? iv. Was any welding done? v. When was the last time any service or maintenance was performed?

vi. What operating levels (temperature, vibration, noise, insulation, etc.) were observed prior to the failure?

vii. What comments were received from the equipment operator regarding the failure or past failures?

viii. How long was the unit in storage or sitting idle prior to starting? ix. What were the storage conditions? x. How often is the unit started?

xi. Were there shutdowns? xii. Was correct lubrication procedures utilized?

xiii. Have there been any changes made to surrounding equipment? xiv. What procedures were used in adjusting belt tensions? xv. Are the pulleys positioned on the shaft correctly and as close to the motor bearing as

possible?

a study on failure of mechanical pump

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