analysis and application of maintenance strategies …574931/fulltext01.pdfanalysis and application...

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Analysis and application of maintenance strategies for

Omnicane Thermal Energy Operations

(St Aubin) Ltd

Jasbeersingh BUNDHOO

Student ID: 800630A751

DSEE

Mauritius

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Master of Science Thesis EGI 2012 – 102

MSC EKV920

Analysis and application of maintenance

strategies for Omnicane Thermal Energy

Operations

(St Aubin) Ltd

Jasbeersingh

BUNDHOO

Approved

Date

Examiner

Name

Supervisor

Name

Commissioner

Contact person

Abstract Maintenance costs at Omnicane Thermal Energy Operations (St Aubin) Ltd contribute a significant part of

the unit cost of electrical energy produced and affect the profitability of the power plant. Hence it is necessary

and crucial to minimize maintenance costs by optimizing maintenance processes to make the plant more

reliable and to run economically.

The total maintenance cost for OTEOSAL from year 2008 to 2011 is seen to be increasing and has even

double from 2008 to 2011. The cost of external labor during operation has increased by nearly four times due

to a lot of breakdown on different equipments and also the value of the spare parts store is seen to rise

because many spare parts are bought at random in fear of having a shut down due to unavailability of spare

parts. These excess expenses contribute to a loss in profitability. With a good maintenance strategy, the total

maintenance cost can be reduced by about 30%.

Fault Tree Analysis (FTA) and Failure Mode Effect Analysis (FMEA) were done and allowed identifying

critical equipments at the power plant and the Grate Stocker, one of the most important and critical

equipment for the plant was selected to perform a Quantitative Analysis of the FTAs. The probability of

failure for the Grate Stocker is seen to be 0.98 and has reliability as low as 0.02. Quantitative Analysis of FTA

and Pareto Analysis will allow having the right quantity of spare parts at the right time without overstocking.

From this thesis, it can be said that combining different maintenance and management methods and

strategies based on FTA, FMEA and Pareto Analysis and all these well formalized and documented according

to ISO 9001 will certainly allow the power plant to gain a lot like availability, reliability and even financially

from maintenance and also will make OTEOSAL ready for new challenges appearing in the energy sector in

Mauritius.

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Table of Contents

Introduction ............................................................................................................................................ 1

1.1 OTEOSAL .................................................................................................................................. 1

1.2 Aim of Thesis ............................................................................................................................ 1

1.3 Objectives of Thesis ................................................................................................................. 2

1.4 Maintenance data for OTEOSAL ............................................................................................... 2

2 Background and Literature Review .................................................................................................. 3

2.1 Process Description .................................................................................................................. 3

2.1.1 Coal Handling Plant .......................................................................................................... 3

2.1.2 Feeders and Spreaders ..................................................................................................... 5

2.1.3 Traveling Chain Grate ....................................................................................................... 5

2.1.4 Bottom Ash ...................................................................................................................... 5

2.1.5 Air preheater .................................................................................................................... 7

2.1.6 Primary and Secondary Air ............................................................................................... 7

2.1.7 Induced Draught Fan ........................................................................................................ 7

2.1.8 Re-injection of Fly Ash ...................................................................................................... 7

2.1.9 Economizers ..................................................................................................................... 8

2.1.10 Electrostatic Precipitator and Fly Ash ................................................................................ 8

2.1.11 Boiler Water ................................................................................................................... 10

2.1.12 Steam Turbine and Electric Generator ............................................................................ 10

2.1.13 Condenser and Cooling Tower ........................................................................................ 12

2.2 Maintenance at OTEOSA ........................................................................................................ 14

2.3 Maintenance Management Strategies and Methods .............................................................. 14

2.3.1 Preventive Maintenance ................................................................................................. 14

2.3.2 Condition based maintenance ........................................................................................ 16

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2.3.3 Corrective Maintenance ................................................................................................. 18

2.3.4 Reliability-centered maintenance (RCM) ......................................................................... 18

2.3.5 Lean Maintenance .......................................................................................................... 23

2.3.6 Six Sigma ........................................................................................................................ 24

3 Analysis of main equipments and evaluating maintenance needs .................................................. 28

3.1 Main equipments at OTEOSAL ................................................................................................ 28

3.2 Evaluating maintenance needs at OTEOSAL ............................................................................ 28

4 Analysis of FTA ............................................................................................................................... 31

4.1 Introduction ........................................................................................................................... 31

4.2 Objectives .............................................................................................................................. 31

4.3 Commonly used symbols ........................................................................................................ 31

4.3.1 Fault Tree “Gates” and “Event” Symbols. ........................................................................ 32

4.4 Benefits of Fault Tree Analysis ................................................................................................ 32

4.5 Drawbacks of Fault Tree Analysis ........................................................................................... 33

4.6 Fault Tree Analysis on OTEOSAL Main Systems ....................................................................... 33

4.7 Observations made on FTA performed at OTEOSA ................................................................. 46

5 Failure Mode and Effects Analysis (FMEA) ...................................................................................... 47

5.1 Introduction ........................................................................................................................... 47

5.2 FMECA Benefits...................................................................................................................... 48

5.3 Applying FMECA at OTEOSAL.................................................................................................. 48

5.4 Risk Priority Number Method ................................................................................................. 48

5.5 Severity(S) .............................................................................................................................. 49

5.6 Occurrence (O) ....................................................................................................................... 50

5.7 Detection (D) ......................................................................................................................... 50

5.8 FMECA Table .......................................................................................................................... 51

5.9 Maintenance Strategy determination ..................................................................................... 51

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5.10 FMECA Tables for OTEOSAL .................................................................................................... 53

5.11 Analysis of FMECA .................................................................................................................. 55

5.12 Maintenance Tasks Comparisons. .......................................................................................... 55

6 Applying FTA to a specific equipment at the OTEOSAL power plant ................................................ 57

6.1 Grate Stocker ......................................................................................................................... 57

6.2 FTAs for the grate stocker ...................................................................................................... 57

6.3 The quantitative analysis of the FTA ....................................................................................... 61

6.3.1 6.3.1 Equations for quantitative analysis ........................................................................ 61

6.3.2 Reliability of k-out-of-n for the coal spreader and feeder ................................................ 63

6.4 Analysis of results .................................................................................................................. 67

6.5 Pareto Analysis....................................................................................................................... 67

6.5.1 Definition of Pareto Analysis ........................................................................................... 67

6.5.2 Steps to identify the important causes using Pareto analysis ................................................. 68

6.5.2 Pareto Analysis for Grate Stocker ................................................................................... 69

6.5.3.1 Pareto Analysis for driving part of Travelling Grate ................................................................. 69

6.5.3.2 Pareto Analysis for Rear Driving part of Travelling Grate ........................................................ 72

6.5.3.3 Pareto Analysis for Chain Assembly parts of Travelling Grate ................................................. 75

6.5.3.4 Pareto Analysis for Fixed Parts of Travelling Grate .................................................................. 78

6.5.3.5 Pareto Analysis for whole Travelling Grate ............................................................................. 81

6.5.3.6 Pareto Analysis for Coal Feeder .............................................................................................. 83

6.5.3.7 Pareto Analysis for Coal Spreader ........................................................................................... 86

7 Setting Up of Maintenance Strategy and Guidelines for OTEOSAL .................................................. 89

7.1 Company’s expectations from the Maintenance Department ................................................. 89

7.2 Documents for maintenance strategy guidelines and maintenance quality system ............... 100

8 Discussion and Conclusion ........................................................................................................... 104

8.1 Overview.............................................................................................................................. 104

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8.2 Maintenance and management methods ............................................................................. 104

8.3 Maintenance Strategy based on FTA and FMEA .................................................................... 104

8.4 Quantitative Analysis of FTA and Pareto Analysis ................................................................. 105

8.5 Quality Management System ............................................................................................... 106

8.6 Conclusion ........................................................................................................................... 106

9 REFERENCES ................................................................................................................................ 107

APPENDIX 1 – FTA Diagrams ........................................................................................................... 109

APPENDIX 2 – FMECA Table ............................................................................................................ 136

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Table of Figures and Tables

FIGURE 1.4-1 [A] BAR CHART REPRESENTING EVOLUTION OF TOTAL MAINTENANCE COST AND [B] CHART REPRESENTING EVOLUTION OF

THE VALUE OF THE SPARE PART STORE ............................................................................................................................ 2

FIGURE 2.1-1 CONVEYOR IN THE COAL HANDLING PLANT .......................................................................................................... 4

FIGURE 2.1-2 COAL HANDLING PLANT .................................................................................................................................. 4

FIGURE 2.1-3 COAL SPREADER AND FEEDER ........................................................................................................................... 5

FIGURE 2.1-4 TRAVELLING GRATE STOKER AND BOTTOM ASH CONVEYOR ..................................................................................... 6

FIGURE 2.1-6 COAL SPREADER AND FEEDER ........................................................................................................................... 9

FIGURE 2.1-7 DEMINERALISED WATER TREATMENT PLANT ..................................................................................................... 10

FIGURE 2.1-8 TURBINE OPERATION DIAGRAM ...................................................................................................................... 11

FIGURE 2.1-9 CONDENSER ................................................................................................................................................ 12

FIGURE 2.1-10 COOLING TOWER ........................................................................................................................................ 12

FIGURE 2.1-11 PROCESS DIAGRAM .................................................................................................................................... 13

FIGURE 2.3-1 THE BATHTUB CURVE FOR PREVENTIVE MAINTENANCE (MOBLEY, R.K., 2002) .......................................................... 15

FIGURE 3.2-1 PROCESS SCHEMATIC OF MAIN EQUIPMENTS AT OTEOSAL ................................................................................... 29

FIGURE 4.3-1 TWO REGULARLY USED FAULT TREE GATE SYMBOLS : (1) OR GATE; (2) AND GATE. ................................................... 32

FIGURE 4.3-2 TWO FREQUENTLY USED FAULT EVENT SYMBOLS: (1) CIRCLE; (2) RECTANGLE. ........................................................... 32

FIGURE 4.6-1 FTA FOR WHOLE POWER PLANT ...................................................................................................................... 35

FIGURE 4.6-2 FTA FOR COAL HANDLING PLANT .................................................................................................................... 36

FIGURE 4.6-3 FTA FOR WATER TREATMENT PLANT ............................................................................................................... 37

FIGURE 4.6-4 FTA FOR COMBUSTION AIR ............................................................................................................................ 38

FIGURE 4.6-5 FTA FOR FEED WATER .................................................................................................................................. 39

FIGURE 4.6-6 FTA FOR BOILER .......................................................................................................................................... 40

FIGURE 4.6-7 FTA FOR STEAM DISTRIBUTION ....................................................................................................................... 41

FIGURE 4.6-8 FTA FOR WASTE DISPOSAL SYSTEM ................................................................................................................. 42

FIGURE 4.6-9 FTA FOR TURBO-ALTERNATOR AND AUXILIARY EQUIPMENTS ............................................................................... 43

FIGURE 4.6-10 FTA FOR INSTRUMENTATION AND CONTROL .................................................................................................... 44

FIGURE 4.6-11 FTA FOR COMPRESSED AIR .......................................................................................................................... 45

FIGURE 6.2-1 FTA FOR COAL SPREADER .............................................................................................................................. 57

FIGURE 6.2-2 FTA FOR COAL FEEDER .................................................................................................................................. 58

FIGURE 6.2-3 FTA FOR GEARBOX ....................................................................................................................................... 58

FIGURE 6.2-4 FTA FOR DRIVE MOTOR ................................................................................................................................ 59

FIGURE 6.2-5 FTA FOR TRAVELLING GRATE .......................................................................................................................... 60

FIGURE 6.2-6 FTA FOR GRATE STOCKER ............................................................................................................................... 61

FIGURE 6.5-1 EXAMPLE OF PARETO CHART ........................................................................................................................... 68

FIGURE 6.5-2 PARETO FOR DRIVING PART OF TRAVELLING GRATE FOR THE YEAR 2008 .................................................................. 69



FIGURE 6.5-5 PARETO FOR MEAN FREQUENCY OF BREAKDOWN ............................................................................................... 70

FIGURE 6.5-6 PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR DRIVING PARTS IN TRAVELLING GRATE ................... 71

FIGURE 6.5-7 PARETO FOR REAR DRIVING PART OF TRAVELLING GRATE FOR THE YEAR 2008.......................................................... 72



FIGURE 6.5-10 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR REAR DRIVING PART OF TRAVELLING GRATE .............................. 73

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FIGURE 6.5-11 PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR REAR DRIVING PARTS IN TRAVELLING GRATE ......... 74

FIGURE 6.5-12 PARETO FOR CHAIN ASSEMBLY PARTS OF TRAVELLING GRATE FOR THE YEAR 2008 .................................................. 75



FIGURE 6.5-15 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR CHAIN ASSEMBLY PARTS OF TRAVELLING GRATE ........................ 76

FIGURE 6.5-16 PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR CHAIN ASSEMBLY PARTS IN TRAVELLING GRATE ..... 77

FIGURE 6.5-17 PARETO FOR FIXED PARTS OF TRAVELLING GRATE FOR THE YEAR 2008 ................................................................. 78

FIGURE 6.5-18 PARETO FOR FIXED PARTS OF TRAVELLING GRATE FOR THE YEAR 2009 ................................................................. 78

FIGURE 6.5-19 PARETO FOR FIXED PARTS OF TRAVELLING GRATE FOR THE YEAR.......................................................................... 79

FIGURE 6.5-20 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR FIXED PARTS OF TRAVELLING GRATE ....................................... 79

FIGURE 6.5-21 PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR FIXED PARTS IN TRAVELLING GRATE .................... 80

FIGURE 6.5-22 PARETO FOR WHOLE TRAVELLING GRATE FOR THE YEAR 2008 ............................................................................ 81



FIGURE 6.5-25 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR WHOLE OF TRAVELLING GRATE ............................................... 82

FIGURE 6.5-26 PARETO FOR COAL FEEDER FOR THE YEAR 2008 ............................................................................................... 83



FIGURE 6.5-29 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR COAL FEEDER ..................................................................... 85

FIGURE 6.5-30 PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR COAL FEEDER .................................................. 85

FIGURE 6.5-31 PARETO FOR COAL SPREADER FOR THE YEAR 2008 ........................................................................................... 86



FIGURE 6.5-34 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR COAL SPREADER .................................................................. 87

FIGURE 6.5-35 PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR COAL SPREADER .............................................. 88

FIGURE 7.2-1 THE MAINTENANCE WORKFLOW (BS EN13460:2002, 2002) ......................................................................... 101

FIGURE 7.2-2 INPUT/OUTPUT DOCUMENTS (BS EN13460:2002, 2002)............................................................................... 102

Tables

TABLE 1.4—1 EVOLUTION OF TOTAL MAINTENANCE COST ........................................................................................................ 2

TABLE 3.2—1 SUMMARY OF THE MAIN EQUIPMENTS WITH THEIR CONSTITUENT PARTS.................................................................. 30

TABLE 5.5—1 RANKING FOR SEVERITY ................................................................................................................................. 49

TABLE 5.6—1 RANKING FOR OCCURRENCE OF FAILURES .......................................................................................................... 50

TABLE 5.7—1 RANKING FOR DETECTION OF FAILURES ............................................................................................................ 51

TABLE 5.9—1 MAINTENANCE TASK ..................................................................................................................................... 52

TABLE 5.10—1 FMECA TABLE FOR COAL HANDLING PLANT – TIPPER ...................................................................................... 53

TABLE 5.10—2 SUGGESTED MAINTENANCE STRATEGY AND RPN FOR COAL HANDLING PLANT – TIPPER ......................................... 54

TABLE 5.11—1 RPN RANGE .............................................................................................................................................. 55

TABLE 5.12—1 MAINTENANCE TASKS ................................................................................................................................. 55

TABLE 5.12—2 PERCENTAGE CONTRIBUTION OF RESPECTIVE MAINTENANCE TASK FOR BOTH ACTUAL & RCM STRATEGY. ................... 56

TABLE 6.3—1 QUANTITATIVE ANALYSIS FOR THE FTA OF THE COAL SPREADER ........................................................................... 64

TABLE 6.3—2 QUANTITATIVE ANALYSIS FOR THE FTA OF THE COAL FEEDER ............................................................................... 65

TABLE 6.3—3 QUANTITATIVE ANALYSIS FOR THE FTA OF THE TRAVELLING GRATE ........................................................................ 66

TABLE 7.1—1 SHOWS GUIDELINES IN THE NORMATIVE PART FOR THE PREPARATORY PHASE. (BS EN13460:2002, 2002) ................. 90

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TABLE 7.1—2 SHOWS GUIDELINES / DOCUMENTS NEEDED WITHIN THE OPERATIONAL PHASE OF EQUIPMENT. (BS EN13460:2002,

2002) ................................................................................................................................................................... 94

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Nomenclature

CEB Central Electricity Board

CBM Condition based maintenance

CM Corrective maintenance

CMMS Computer maintenance management system

DMAIC Define, Measure, Analyze, Improve, Control

DFSS Design for Six Sigma

ESP Electrostatic precipitator

FMEA Failure Mode Effect Analysis

FF Fault-finding

FTA Fault Tree Analysis

ID Fan Induced Draught Fan

ISO International Standard Organization

IPP Independent power producers

LCE Life Cycle Engineering

LP Heater Low Pressure Heater

MDC Mechanical dust collector

MTTF Mean Time to Failure

OTEOSAL Omnicane Thermal Energy Operations (St Aubin) Ltd

OEE Overall equipment effectiveness

PPA Power purchase agreement

PM Preventive maintenance

RCM Reliability Centered Maintenance

RPN Risk priority number

SCADA Supervisory Control and Data Acquisition

TD Time-directed

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Introduction

1.1 OTEOSAL Omnicane Thermal Energy Operations Limited (OTEOSAL) is an 82 bar coal power plant of capacity 34.5

MW with a Condensing Extraction Steam Turbine system (CEST). Since the price of coal is very volatile on

the international market, it is primordial that the optimum potential of electricity generation from coal is

tapped and used sustainably. Also, as a result of the tougher competition brought on by future and new

entrants into the power market in Mauritius, OTEOSAL must meet strong demands to reduce maintenance

and repair costs if they are to gain the upper hand over the competition. Along with that, it is becoming

increasingly necessary to guarantee plant reliability and economic efficiency.

Being used as a base load power plant, the reliability of OTEOSAL is crucial and this put a lot of stress on

maintenance departments. Hence it is important to view maintenance as a positive activity and see it as a

profit center instead of a cost center. A cost-center approach for maintenance is strictly concerned with

adhering to the budget and decreasing expenses as much as possible whereas moving rapidly away from the

conventional way and with the appropriate management method to optimize maintenance, the power plant

can gain a lot like availability, reliability and even financially from maintenance.

1.2 Aim of Thesis The aim of this thesis is to select and plan the maintenance strategies that will address the maintenance needs

of the power plant at the least cost and also to determine the most critical components of the station based

on Failure Mode Effect Analysis (FMEA). Also a critical equipment will be taken for a more in depth

investigation using FTA (Fault Tree Analysis) and Pareto Analysis to see the potential failures of different

constituent parts of the equipment. This will allow seeing the evolution of failures over the past years and will

help to identify the recurrent failures on particular parts and will help to have the right and optimum spare

parts without spending too much for unnecessary spare parts or putting into danger the power plant for not

having the critical spare parts. Since the management of OTEOSAL wants the power plant to be an ISO9001

certified company in 2012 so as to be able to implement Quality Management Systems, maintenance

strategies and guidelines will be proposed for OTEOSAL. The British Standard, BS EN13460:2002, 2002

“Maintenance – Documents for Maintenance” will be analyzed and adapted for OTEOSAL power plant.

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1.3 Objectives of Thesis The outcomes expected from this thesis are to reduce maintenance cost and downtime losses of the steam

power plant and increase profitability by adopting the proper maintenance strategies that ensure its reliable

availability and thus, satisfy the maturing and growing electricity demand of the Mauritian economy.

1.4 Maintenance data for OTEOSAL The total maintenance cost (in Mauritian Rupees) as in Table 1.1 for OTEOSAL from year 2008 to 2011 is

seen to be increasing and has even double from 2008 to 2011. According to the people from the maintenance

department, the cost of external labor during operation has increased by nearly four times due to a lot of

breakdown on different equipments and has needed urgent intervention of external labor to prevent the

power plant from shutting down. Also the value of the spare parts store is seen to rise (Figure 1.4-1 [B])

because many spare parts are bought at random in fear of having a shut down due to unavailability of spare

parts. But these excess expenses on unnecessary spare parts prevent the power plant from using wisely its

finance and also contribute to a loss in profitability. All this is due to a lack of a good maintenance strategy

and knowledge of the criticalities and failure rates of particular equipments.

Table 1.4—1 Evolution of Total Maintenance Cost

2008 2009 2010 2011

Cost of Spare Parts used (Rs) 14,680,737.78 23,303,201.60 12,508,640.50 26,751,309.20

Cost of External Labour during operation (Rs) 2,985,074.87 4,543,213.92 7,195,333.01 12,818,026.67

Cost of External Labour during shut down (Rs) 4,028,727.77 4,609,677.35 8,674,446.14 5,034,165.81

Total Maintenance Cost (Rs) 21,694,540.42 32,456,092.87 28,378,419.65 44,603,501.68

Figure 1.4-1 [A] Bar Chart representing Evolution of total Maintenance Cost and [B] Chart representing

Evolution of the value of the spare part store

[A] [B]

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2 Background and Literature Review

Omnicane Thermal Energy Operations St Aubin Limited

The power plant OTEOSAL (Omnicane Thermal Energy Operations (St Aubin) Limited) is found in Union

Ducray, Rivière des Anguilles in the southern part of Mauritius and forms part of the independent power

producers (IPP) in the island. Under a power purchase agreement (PPA), OTEOSAL sells the electricity

generated to the CEB (Central Electricity Board) which is the governing body for power distribution in

Mauritius. OTEOSAL is a consortium of Omnicane (65%), Séchilienne-SIDEC (25%), and the Sugar

Investment Trust (15%). The PPA was signed in October 2005 and is guaranteed by the government. The

boiler was supplier by Stein Industrie (now Alstom). The Turbine/Generator was supplied by Thermodyn

and Jeumont. Water treatment system was from VWS Envig.

The company is under operation since November 2005 and almost 6 years later it continues to be a base load

power plant.

2.1 Process Description

2.1.1 Coal Handling Plant Bituminous coal is imported from South Africa and Mozambique and is stored at the port here in Mauritius.

Then trucks transport the coal (approximately 30 tons per truck) to the power plant. The coal is unloaded in a

hydraulic auto-tipper where it is then sent on a vibrating table to be discharged on a conveyor. This first

conveyor direct the coal through a vibrating screener where coal smaller than 25mm is allowed to proceed to

the next conveyor. Coal bigger than 25mm is directed towards a crusher where the bigger coal is reduced to

about 25mm and then allowed to proceed.

Under the screening and crushing plant, there are two conveyors, one conveyor can bring coal directly to the

daily hopper to be then sent to the boiler or one conveyor can direct coal to a silo with storage capacity of

800 tons. Coal from the silo can be extracted with the aid of an extraction screw at night or during the week

end and then be sent to the daily hopper. The daily hopper has a capacity of 200 tons and it supplies the coal

feeders and spreaders which in turn supply the furnace in the boiler with coal.

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Figure 2.1-1 Conveyor in the Coal Handling

Plant

Figure 2.1-2 Coal Handling Plant

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2.1.2 Feeders and Spreaders After the coal handling plant, the next step for coal is to pass through the coal feeders and spreaders. The

boiler is equipped with four feeders and spreaders. The feeders are conveyors of about 1.5m long made of

metal plates which push coal towards the spreaders. The feeders are powered by variable speed motors so as

to be able to control the amount of coal to the boiler depending on the load.

The spreaders are metal elements rotating on a metal shaft where the speed can be controlled for an optimum

projection. The spreaders project coal in the furnace of the boiler at a certain angle. The angle of projection is

very important because the coal should be well spread on the travelling grate so as to be able to burn

completely and prevent wastage of coal.

Figure 2.1-3 Coal Spreader and Feeder

2.1.3 Traveling Chain Grate The furnace is equipped with a traveling chain grate stoker powered by a variable speed motor. The speed of

the grate is around 7 m/hr so as to give coal enough time to burn completely. Also another function of the

traveling grate is that combustion air enters the furnace form under the grate.

2.1.4 Bottom Ash The traveling grate also help to unload the remaining bottom ash or slag on a conveyor immersed in water so

as to cool down the hot bottom ash. Then the bottom ash is carried outside of the boiler to be loaded on

trucks.

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Figure 2.1-4 Travelling Grate Stoker and Bottom ash conveyor

Travelling Grate

Botton Ash Conveyor

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2.1.5 Air preheater Combustion air from the primary and part of the secondary air is channeled through an air preheater. This air

preheater uses hot boiler water which comes from the economizers to preheat combustion air. The air

temperature then varies from 80 °C to 120 °C

2.1.6 Primary and Secondary Air The combustion of coal in the furnace is done by primary and secondary air. Primary air is obtained from a

fan equipped with dampers so as to be able to control the amount of air entering the furnace. The primary air

enters the furnace from under the traveling grate. Before entering the furnace, the primary air passes through

an air pre-heater to be heated up to around 110 °C. The secondary air is also obtained from a fan equipped

with dampers. For the secondary air, part of it is heated and part of the air is left at room temperature. Part of

the heated air is injected in the boiler from under the spreaders in order to burn small particles of coal

projected and the other part enters the furnace at the back of the boiler where this air is injected about 3

meters high in the furnace so as to complete combustion at this height. On the other hand, the unheated air is

injected in front of the furnace just above the traveling grate.

2.1.7 Induced Draught Fan The combustion of coal produces flue gas and this flue gas must be evacuated from the furnace. This is done

by the induced draught fan which is driven by a variable speed motor and equipped with dampers. The ID

Fan also keeps a slight depression in the furnace chamber to prevent flue gas from getting out of the furnace.

2.1.8 Re-injection of Fly Ash As a result of coal combustion, there is a lot of fly ash produced and this fly ash is rich in unburned carbon.

The fly ash is taken away from the furnace by the action of the induced draught fan (ID Fan). Since fly ash is

rich in unburned carbon and represents a useful source of energy, it is collected via a mechanical dust

collector (MDC), channeled through pipes and rotating valves and then re-injected in the furnace with the aid

of a blowing fan.

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Figure 2.1-5 Mechanical dust collector

2.1.9 Economizers The flue gas duct is fitted with two finned tubes economizers and since after the mechanical dust collector

(MDC) the temperature of the flue gas is around 450 °C, this source of heat is used to pre-heat boiler water.

The boiler water before the first economizer which is second in the flow of flue gas is about 110 °C and after

the economizer it is around 170 °C. Then after the second economizer, the boiler water reaches around 230

°C. This heated water then passes through the air preheater as described before.

2.1.10 Electrostatic Precipitator and Fly Ash The next step is to pass the flue gas through an electrostatic precipitator (ESP) in order to gather and convey

all the fly ash into a silo. The fly ash is then channeled to trucks and transported away.

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Figure 2.1-5 Coal Spreader and Feeder

Mechanical

Dust Collector

Economizer

Electrostatic

Precipitator Boiler

Chimney

Secondary Air

Fan

Primary Air Fan

Air Heater

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2.1.11 Boiler Water The demineralised water plant generates the boiler water which is directed to the feed water tank. The

demineralised water is then heated from the extracted steam at 3 bars from the turbine. The feed water tank

provides the feed water pumps which propels water at 115 bars and this water passes via the economizers and

finally to the boiler. Added to that, the flowrate of feed water to the boiler is about 128 m3/hr. The boiler is

of water tube type. This type of boiler is used for the production of high pressure and superheated steam up

to 160 bars and 500 ˚C. Water tube boilers consist of a series of the water tubes arranged inside a furnace in a

number of possible configurations. These tubes receive water from the feed water tank and connect the lower

drum to the upper drum. In the furnace where combustion takes place the heat is transferred mainly by

radiation to tubes. Saturated steam is generated in the boiler and then goes through superheaters to come at

82 bars and 525 ˚C superheated. The superheated steam then passes into the turbine for expansion.

Figure 2.1-6 Demineralised Water Treatment Plant

2.1.12 Steam Turbine and Electric Generator Superheated steam enters the turbine at 82 bars and is expanded to about 100 mbars. The amount of

superheated steam at the inlet of the turbine is controlled by inlet valves which allow the optimum flow of

steam in the turbine. The energy produced turns the turbine at 5000 rpm. Steam is extracted from the turbine

at 2 stages. The first extracted steam is used to heat feedwater in the feedwater tank. The second extraction is

to heat return condensate in a LP (Low Pressure) Heater (close feedwater heater). The steam turbine is

coupled to a reduction gear where the speed of the turbine is reduced to 1500 rpm and the reduction gear is

coupled to an electric generator to produce 34.5 MW net. The electric generator produces voltage at 11 KV

and then is stepped up in transformers to 66KV to then be sent to the national grid.

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Figure 2.1-7 Turbine Operation Diagram

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2.1.13 Condenser and Cooling Tower After expansion in the turbine, the saturated steam is cooled down in the condenser to around 80 ˚ C. The

condenser is basically a shell and tube heat exchanger. The return condensate is then pumped back to the

feedwater tank with the help of a centrifugal pump. The cooling of the saturated steam is done with the help

of recirculating water at about 35 ˚ C in the condenser and this recirculated water is cooled down in the

cooling tower. The cooling tower is an induced draught type making the use of fans to create the draught.

Figure 2.1-8 Condenser

Figure 2.1-9 Cooling Tower

13

OTEOSAL – Process Diagram

Figure 2.1-10 Process Diagram

Ash Storage

Ash Handling Plant

Boiler

Coal Handling Plant

Economiser

Superheater

Air Preheater

Main Valve Generator

National Grid

Aux. Power Plant

Equipments

Condenser

Condensate extraction pump LP Heater

Feed Water Tank

& Dearator

Boiler Feed

Water Pump

Cooling

Tower

Sand Filters

Circulating Water

Pump

Water Treatment Plant

Make up water

Flue gases Flue gases Turbine

14

2.2 Maintenance at OTEOSAL

Since OTEOSAL is operated as a base load power station, this put greater challenges to the maintenance

teams so as to ensure high availabilities and reliabilities of the power plant. Also since Mauritius is an island

deprived of natural resources like coal, a good maintenance management is important to ensure sustainability

of the resources and meet the growing expectations from its sole client the CEB.

OTEOSAL and like many other coal power plants in Mauritius build their own maintenance management

systems depending on their maintenance needs, their intuitive judgment and experiences and supported by

recommendations of the manuals of the different equipments composing the power stations.

Most manufacturers of equipment recommend maintenance practices accompanying their equipment in the

maintenance manuals. Their recommendations assume application and operation of equipment according to

design conditions. In practice, equipment are rarely operated according to design. Overloading or

underutilizing equipment and operating them in environmental conditions not always according to design

conditions result in maintenance recommendations in the maintenance manual ineffective.

2.3 Maintenance Management Strategies and Methods

The maintenance cost in probably most industries is quite significant and therefore, an evolution in

maintenance management has certainly been the driving force to reduce maintenance costs, improve

productivity, the quality of work and ensure human, equipments and environmental safety.

The literature about the different maintenance methods is quite numerous. For this thesis, maintenance

management methods like preventive maintenance (PM), condition based maintenance (CBM), corrective

maintenance (CM) along with six sigma, lean maintenance and reliability centered maintenance (RCM) will be

reviewed.

2.3.1 Preventive Maintenance

Preventive maintenance (PM) is a time based maintenance method in which the maintenance activities are

planned and scheduled based on predetermined counter intervals in order to prevent breakdowns and failures

from occurring (Clety, 2008). The book ‘applied reliability centered maintenance’ (Jim August, 1999) defines

PM as any scheduled preventive tasks intended to reduce the probability of failure of equipment. Also a

15

preventive maintenance (PM) approach is to prevent the problems associated with CM so as to get rid of the

waste and decrease asset life cycle costs.

PM tasks are carried out to avoid failure, to detect initial failure, or to determine hidden failure (Smith, 1993).

This results in three types of PM task:

(1) time-directed (TD);

(2) CBM; and

(3) fault-finding (FF).

A TD task may refer to the replacement of a component, in which case it is an suitable choice only when the

hazard rate is an increasing function of age (i.e. new items are better than old ones in terms of probability of

imminent failure or other measures of usefulness), and the cost of a preventive replacement is considerably

less than the cost of a failure and its associated repair (Mann et al., 1995).

A CBM task is carried out to notice early failures long before their occurrence. CBM uses condition

monitoring techniques to find out whether a problem exists in equipment, how severe the problem is, and

how long the equipment can run before failure; or to detect and identify specific components (e.g. gear sets,

bearings) in the equipment that are deteriorating (i.e. the failure mode) .

An FF task is carried out at a fixed plan decided in advance to verify the health conditions of rarely used

items such as protective devices and standby units.

The aim of PM is to enhance equipment performance and reliability by preventing failure of equipment. PM

is commonly used where equipment failure is age related or where the equipment failure rates follow what is

called bath-tub curve. (Figure 2.3-1)

Figure 2.3-1 The bathtub curve for preventive maintenance (Mobley, R.K., 2002)

16

The different tasks that are performed in a PM include inspections, adjustments, tests, calibrations, rebuilding

and replacements of parts.

By adopting PM, the objectives and benefits are (Clety, 2008):

• Improved system reliability.

• Decreased cost of replacement.

• Decreased system downtime.

• Better spares inventory management.

However, for the good running of a PM system, a list of tools, spare parts and instruments required should

be available. A procedure to record the measurements to be made should also be present. Emphasis should

also be made on the limits or ranges for the parameters to be measured.

Required safety procedures such as isolation and locking out must also be available.

In order to be able to organize a PM strategy, recommendations in maintenance manuals from equipment

suppliers should be available along with the knowledge of the different persons working in the maintenance

teams.

As all maintenance systems, advantages and disadvantages do exist as are discussed below. The performance

of PM has many advantages including increase in equipment availability, performed as convenient, balanced

workload, increase in production revenue, consistency in quality, reduction in need for standby equipment,

stimulation in preaction instead of reaction, reduction in parts inventory, improved safety and easy availability

of scheduled resources. Whereas, some disadvantages of PM are: exposing equipment to possible damage,

using a greater number of parts, increases in initial costs, failures in new parts/components, and demands

more frequent access to equipments. (B.S Dhillon, 2002)

2.3.2 Condition based maintenance

CBM Systems or Predictive Maintenance (PdM) methods are an extension of preventive maintenance and

have been proved to minimize the cost of maintenance, improve operational safety and reduce the frequency

and severity of in-service machine failures. The basic theory of condition monitoring is to know the

deteriorating condition of a machine component, well in advance of a breakdown.

Condition based maintenance is a set of maintenance actions based on the evidence of need for maintenance

obtained from real time assessment of equipment condition obtained from embedded sensors and external

17

tests and measurement taken by portable equipment. (Michael V Brown, 2003). Also, Predictive maintenance

(PdM) involves comparing the trends of measured physical parameters against known engineering limits for

the purpose of detecting, analyzing and correcting problems before failure occurs

There are varieties of critical equipments in power plants. These components require routine inspection to

ensure their integrity. The purpose of the inspection is to identify any degradation in the integrity of the

systems during their service life and to provide an early warning in order that remedial action can be taken

before failure occurs. Assessing the condition is necessary to optimize inspection and maintenance schedules,

so as to be able to make decisions and to avoid unplanned outages.

To maintain an efficiently power plant and avoid failure of critical equipments, it is necessary to maintain the

critical parts of these equipments. The effect of planned maintenance is depending upon the methods used

for maintenance. The combination of corrective, preventative and condition based maintenance is primordial

for critical equipments. This type of maintenance policy and strategy will improve performance of power

plants through the availability of critical equipments.

CBM is system that strives to identify faults before they become critical which enables accurate planning of

PMs. With CBM, the different critical equipments are assessed while in operation and a decision is made as to

whether they need maintenance or not and if so, when it should be done to prevent failures. Assessments can

be of all kind ranging from like simple visual inspection or fully automated system to sense, receive and

process performance data, monitor, diagnose and predict failure.

Condition monitoring techniques and their applications to a power plant

Vibration monitoring measures the frequency and amplitude of vibrations which are mainly caused by

misalignment, rotational imbalance, wear and improper installation of equipment, and looseness of assembled

parts. Vibrations are undesirable because they lead to damage and the eventual failure of the equipments.

Vibration monitoring and analysis are important means to detect future failures in rotation machines and can

be used to prevent costly failures.

In oil analysis, samples of lubricating, hydraulic, or dielectric oil are examined at frequent periods to

determine the quality and metal contents of the oil. If these measurements show that the oil quality has

deteriorated to an intolerable level, it will be substituted to guarantee adequate operation of the equipments.

The analysis comprises of spectrographic techniques and diagnostic procedures to examine the elements

contained in the oil sample. The state of health of the machine can also be revealed by scrutinizing the size,

shape, quantity and composition of wear particles in the oil samples.

18

Ultrasonic technology is also used in CBM because ultrasonic apparatus are sensitive to high-frequency

sounds. These high-frequency sounds are inaudible to the human ear and therefore ultrasonic apparatus

distinguishes them from lower-frequency sounds and mechanical vibration. Machine friction and stress

produce distinctive sounds in the upper ultrasonic range and changes in these friction and stress waves can

indicate deteriorating conditions for a particular equipment. An ultrasonic apparatus can differentiate normal

wear from abnormal wear, physical damage, imbalance conditions and lubrication problems. Therefore this

give sufficient time to prepare for maintenance and helps in spare part management.

Infrared Thermography is also widely used in power plants to detect heat signature created by faulty

mechanical equipment, high electrical resistance or high current flow in electrical systems.

2.3.3 Corrective Maintenance

Corrective maintenance (CM), also known as breakdown maintenance, is done to bring back an equipment in

a state of working condition after a failure has occurred. The logic of run-to-failure management is easy and

direct.

A plant using run-to-failure management does not spend any money on maintenance until a machine or

system break down. However, few plants use a true run-to-failure management philosophy. In almost all

instances, plants carry out basic preventive tasks (i.e., lubrication and machine adjustments) even in a run-to-

failure environment. The major expenses linked with this type of maintenance management are:

• High spare parts inventory costs.

• High overtime labor costs.

• High machine downtime.

• Low production availability.

2.3.4 Reliability-centered maintenance (RCM)

In a reliability-centered maintenance (RCM) process, systematically all of the functions and functional failures

of assets should be identified. This process also identifies all likely causes for these failures. Then RCM

proceeds to identify the effects of these likely failure modes and to identify in what way those effects matter.

Once it has gathered this information, the RCM process then selects the most appropriate asset management

policy. (L.R. Higgins, 2008)

19

On the other hand, Reliability centered maintenance (RCM) magazine provides the following definition of

RCM: “a process used to determine the maintenance requirements of any physical asset in its operating

context.”

Basically, RCM methodology deals with some key issues not dealt with by other maintenance programs and it

is aware that all equipment in a facility is not of equal importance to either the process or facility safety. Also

it recognizes that equipment design and operation differs and that different equipment will have a higher

probability to undergo failures from different degradation mechanisms than others.

RCM also approaches the structuring of a maintenance program recognizing that a facility does not have

unlimited financial and personnel resources and that the use of both need to be prioritized and optimized.

Hence, RCM is a systematic approach to evaluate a facility’s equipment and resources to best combine the

two and result in a high degree of facility reliability and cost-effectiveness.

Some advantages and disadvantages of RCM are:

Advantages

• Can be the most efficient maintenance program.

• Lower costs by eliminating unnecessary maintenance or overhauls.

• Minimize frequency of overhauls.

• Reduced probability of sudden equipment failures.

• Able to focus maintenance activities on critical components.

• Increased component reliability.

• Incorporates root cause analysis.

Disadvantages

• Can have significant startup cost, training, equipment, etc.

• Savings potential not readily seen by management

The procedure involves asking questions on the following subjects in a RCM:

• The functions and related performance standards of an item in its present working condition.

• Possible ways in which the item may fail to carry out its required tasks.

• Causes of each functional failure.

• Events that follow each failure.

• Significance of each failure.

• Measures to prevent failure.

• Corrective measures that may be taken if there is no appropriate preventive step.

20

RCM Process

The RCM process takes place first during the equipment design and development stage, when it is used to

develop maintenance plans. During product process and use, these plans are then revised based on field

experience. The following two criteria are keys to the maintenance plans:

• Parts that are not critical to safety. In this case, preventive maintenance tasks should be chosen

that will decrease the ownership life cycle cost.

• Parts that are critical to safety. In this case, preventive maintenance actions should be chosen

that will help to prevent reliability or safety from reducing to an undesirable stage, or will help to

decrease the ownership life cycle cost. It is through the preventive maintenance program that initial

failures are identified and corrected, the probability of failure is decreased, hidden failures are

detected, and the cost-effectiveness of the maintenance program is improved.

RCM methodology

The RCM methodology is completely described in four unique features:

• Safeguard functions.

• Detect failure modes that can make the functions fail.

• Prioritize function need (via failure modes).

• Select applicable and effective PM tasks for the high priority failure modes.

21

RCM Procedure (Kelly, 1997)

Figure 9: RCM Procedure

1. SYSTEM DEFINITION System partitioning Functional/ Reliability Block Diagram Analysis Data Acquisition

2. IDENTIFICATION OF MSI’s Fault Tree Analysis Maintenance Cost Pareto Analysis

3. IDENTIFICATION OF SIGNIFICANT FAILURE MODES

Failure Modes, Effect and Criticality Analysis

6. IMPLEMENTATION, COLLECTION AND ANALYSIS OF IN-SERVICE DATA

5. SCHEDULING

4. SELECTION OF MAINTENANCE TASKS

Decision Tree Analysis

22

The basic RCM process is composed of the following steps:

1. Identify important items with respect to maintenance.

Usually, maintenance important items are identified using techniques such as failure, mode, effects, and

criticality analysis (FMECA) and fault tree analysis (FTA).

2. Obtain appropriate failure data.

In determining occurrence probabilities and assessing criticality, the availability of data on part failure rate,

operator error probability, and inspection efficiency is essential. These types of data come from field

experience, generic failure databanks, etc.

3. Develop fault tree analysis data.

Probabilities of occurrence of fault events— basic, intermediate, and top events are calculated as per

combinatorial properties of the logic elements in the fault tree analysis.

4. Apply decision logic to critical failure modes.

The decision logic is designed to lead, by asking standard assessment questions, to the most desirable

preventive maintenance task combinations. The same logic is applied to each crucial mode of failure of each

maintenance-important item.

5. Classify maintenance requirements.

Maintenance requirements are categorized into three classifications: on-condition maintenance requirements,

condition-monitoring maintenance requirements, and hard-time maintenance requirements.

6. Implement RCM decisions.

Task frequencies and intervals are set as part of the overall maintenance strategy or plan.

7. Apply sustaining-engineering on the basis of field experience.

Once the system/equipment start operating, the real-life data begin to accumulate. At that time, one of the

most urgent steps is to re-evaluate all RCM-associated default decisions.

RCM Components

The four major components of RCM are: corrective maintenance, preventive maintenance, predictive testing

and inspection, and proactive maintenance.

23

Industries can benefit a lot from RCM in various ways as enumerated below:

• Traceability. The information, assumptions and reasoning that led to all maintenance policy

decisions are fully documented. Hence, subsequent plant reliability can be periodically audited

maintenance experience reviewed and strategy updated (where necessary) on a rational basis.

• Rationalism. By identifying unnecessary preventive work unachievable maintenance workload is

eliminated.

• Cost saving. Overall workload is reduced due to a general shift from away from time-based

preventive works towards condition-based work. Hence, a reduction in spares holding.

• Plant improvement. Re-design eliminates recurrent failures or poor maintainability‘s.

• Education. The whole exercise raises the workforce‘s overall level of skill and technical

knowledge. Moreover, the actual existence of a RCM regime will itself tend to attract better-skilled

personnel in maintenance.

2.3.5 Lean Maintenance Lean Maintenance means reliability and reduced need for maintenance troubleshooting and repairs. Also Lean

Maintenance comes from protecting against the real causes of equipment downtime and not just their

symptoms. (Howard C. Cooper, 2002)

On his part, Ricky Smith of Life Cycle Engineering (LCE) defines lean maintenance as ‘a proactive

maintenance operation employing planned and scheduled maintenance activities through total productive

maintenance practices using maintenance strategies developed through application of reliability centered maintenance

(RCM) decision logic and practiced by empowered (self-directed) action teams using the 5S process, weekly Kaizen

improvement events, and autonomous maintenance together with multi-skilled, maintenance technician-performed

maintenance through the committed use of their work order system and their computer managed maintenance

system (CMMS) or enterprise asset management system’ (Ricky Smith, 2004).

The key elements of a lean maintenance method can be summarized as described below (Clety, 2008 and

Ricky Smith, 2004):

• Proactive maintenance means that lean maintenance uses PM and CBM strategies to prevent

and predict failure instead of reacting to it.

24

• Planned and scheduled means that the maintenance activities are documented in such a way

that the required activities, labour needs, spare parts and time needed to complete the tasks are

known in advance. By being scheduled, the maintenance activities are prioritized and assigned a

designated action time.

• Application of RCM decision logic means lean maintenance tasks are optimized.

• Self empowered teams’ means lean teams are designed so that a maintenance team has all the

skills required to execute all the tasks within the team.

• Application of 5S: sort (remove unwanted items), straighten (organize), scrub (clean),

standardize (make routine), spread (expand to other areas).

• Kaizen means that lean focuses on continuous evaluation and improvement of the

maintenance processes in terms of time, resources use and quality of work.

In his article ‘lean principles’ Jerry Kilpatrick classifies the benefits of lean maintenance into three types (Jerry

Kilpatrick, 2003):

1. Operational gains– reduced lead time, increase productivity, reduced inventory and improved quality.

2. Administrative improvements – reduced paperwork, reduced staffing, reduced process errors, streamlined

customer care, cost reduction, job standardization.

3. Strategic gains in achieving overall company goals.

Kishan Bagadia in the white paper from Infor global solutions identifies four areas that can benefit from lean

maintenance as optimization of spare parts inventory management, achieving quality preventive maintenance

through better management, cross training of staff for multi-skilled task force and a continuous improvement

drive in the maintenance spectrum.

2.3.6 Six Sigma According to Stan Grabill, a certified Six Sigma expert (Black Belt) writing for Maintenance Technology’s

Viewpoint column, Six Sigma focuses on reducing variation in a business’ internal processes using a

rigorously structured, statistical approach that is tied to business results.

25

He also states that Six Sigma for asset dependability reduces the variation in design, procurement, installation,

operation, reliability, and maintainability of equipment assets in order to provide predictable performance at

optimal cost of ownership.

Stan Grabill thinks of Six Sigma as root cause variation analysis, where a different set of tools is used to

identify sources of variation and determine a means to mitigate “bad” variation and control “good” variation

to enhance output productivity. The reason to do this highly structured methodology is to reap the business

benefits of reducing variation, which results in break-through productivity improvements. (Stan Grabill, 2001)

Originated by Motorola, Six Sigma took hold in a big way in the early 1990s. The focus was reducing variation

in manufacturing processes.

Six Sigma does not create new tools but uses existing ones. The main methodologies of Six Sigma are Define,

Measure, Analyze, Improve, Control (DMAIC) and Design for Six Sigma (DFSS).

DMAIC (Robson Quinello, 2003)

Robson Quinello explains that to apply Six Sigma in maintenance, work groups that have a good

understanding of preventive maintenance techniques in addition to a strong leadership commitment should

be first found.

The methodology is divided into five distinct phases:

• Phase D (Define). Establish the objectives of the department and identify the critical-for-quality

processes. In this phase, leaders, planners, maintenance staff, need to work together to set

departments goals.

• Phase M (Measure). After teams have made their choices, the indexes, data collection plan, and

analysis method can be chosen. Some common indexes include frequency of preventive

maintenance, frequency of predictive maintenance, productivity, number of corrective occurrences,

maintenance costs, downtime, pulse survey, overall equipment effectiveness (OEE), etc.

• Phase A (Analyze). Teams will use analysis graphs (Pareto, scatter, run chart, box plots, etc.) to

visualize trends and to search for root causes.

• Phase I (Improve). An action plan and failure mode and effects analysis (FMEA) can help in the

action definition to improve the performance of the chosen indexes.

• Phase C (Control). Teams will outline a plan to retain the gains after the conclusion of the project.

The finance department can assist in investment calculations, profits, ROI, etc.

26

Some points are important for a healthy maintenance program:

• Everyone in the organization must be informed and involved. If only top management participate

and managers or supervisors are not involved completely, the program may fail.

• Roles and responsibilities should be clearly defined.

• Compensation, career plans, and retention plans of those involved in the program must be defined.

• It is essential to find the commonalities among distinct groups (quality control people, managers,

supervisors, controllers, etc.).

• Targets need to be established and coherent goals set.

• A selection process should be set up to search for the best talent in the company. A strong

commitment from top leaders is essential.

• Extra programs should be developed.

• Future activities should be defined for the best talent after the learning phase as they will be in a

special position to influence the department structure.

• Support should be available for the jobs and projects.

• If the maintenance department is already involved in techniques of maintenance like TPM, predictive

maintenance or CMMS, it will be easier to apply Six Sigma as there is a good base from which to

work.

• Departments that are led by managers or supervisors with no vision or goals are not environments

that will stimulate the growth of the program. Mentality and culture change may be necessary.

• The maintenance department must be strategically located within the organization because it will be

in the spotlight.

• Work groups need to be able to function independently and be results driven.

• Projects, activities, methods or programs of quality, in maintenance areas may not be well

understood. Adaptation is the key for success.

27

These results can be expected from Six Sigma:

• Sustainable results in short and medium timeframes.

• Disciplined work groups.

• Autonomy of the maintenance professionals.

• Data driven maintenance.

• Optimized resources.

• Improved relationship between finance and operations.

• Increased financial return.

• High performance environment.

• Creativity support.

• World class maintenance.

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3 Analysis of main equipments and evaluating maintenance

needs

3.1 Main equipments at OTEOSAL OTEOSAL is composed of many types of equipment that all combined allow the good functioning of the

power plant. For the sake of this thesis, the power plant will be divided into 10 parts composing of the main

equipments.

The different parts are:

1. Coal Handling Plant

2. Water Treatment Plant

3. Combustion Air

4. Feed water Pump

5. Boiler

6. Steam Distribution Systems

7. Waste Disposal (Flue Gas, Fly Ash and Bottom Ash)

8. Turbo-Alternator (including auxiliary equipments, cooling tower and condenser)

9. Instrumentation, Power Control and SCADA

10. Compressed Air

An overview of the power plant can be observed in Figure 3.2-1and a summary of the main equipments with

their constituent parts can be seen in Table 3.2-1

3.2 Evaluating maintenance needs at OTEOSAL In order to understand and evaluate the maintenance needs at OTEOSAL, Failure Mode Analysis (FTA) and

Failure mode, effects, and criticality analysis (FMECA) were conducted.

In chapter 4, a Failure Mode Analysis (FTA) is done for all the equipments and they are categorized in

diagrams so that a clear idea is obtained of how failure in different systems can bring about failure in main

equipments and consequent failure for the whole power plant.

A Failure mode, effects, and criticality analysis (FMECA) was conducted in Chapter 5 so as to evaluate the

criticalities of the failures, the severities of the effects of the failures and the probabilities of their occurrences.

29

Figure 3.2-1 Process Schematic of main equipments at OTEOSAL

30

Table 3.2—1 Summary of the main equipments with their constituent parts

System/process Main Equipment Main Components

Coal Handling Plant

Coal Receiver

Coal Separation and Crushing

Coal Conveying

Silo

Tipper, Vibrating Table, Hydraulic Circuits, Hydraulic

Pump, Motor

Vibrating Screener and Crusher

Conveyor Belt, Gearbox, Motor

Extracting Screw, Gearbox, Motor

Water Treatment Plant

Pumping Station

Clarifier

Demineralised Water Plant

Pumps and Piping

Structure of Clarifier

Pumps, Filters, Pneumatic Valves, Ion Beds

Combustion Air

Primary/Secondary Fan

Air Heater

Fan, Motor, Bearings, Dampers

Air Heater Tubes, Control Valves

Feed water Pump

Pumps

Feed Water Tank

Impellers, Bearings, Seals, Non Return Valves, Motor

Piping and Valves, Deaerator, Safety Valves, Sensors

Boiler

Traveling Grate

Boiler Tubes

Steam Drums

Grate Chain constituent parts, Gearbox, Motor

Superheater Tubes, Furnace Tubes, Economizers

Upper/Lower Drums, Safety Valves, Main Bank Tubes

Steam Distribution

Systems

Piping and Valves

Sensors

High Temp./Press. Pipes, Actuators, Seals, Discs

Instrumentation and Control Equipments, SCADA

Waste Disposal (Flue

Gas, Fly Ash and Bottom

Ash)

I.D Fan

Electrostatic Precipitator

Ash Silo

Conveyor

Fan, Motor, Bearings, Dampers

Positive/Negative Plates, Gearbox, Motor,

Transformer

Boosters, Pipings, Evacuation Valves

Conveyor Belt, Gearbox, Motor

Turbo-Alternator

(including auxiliary

equipments, cooling

tower and condenser)

Steam Turbine

Oil/Lubrification System

Gas Extraction System

Cooling Tower

Condenser

Generator

Transformers

Protection

Main Valves, Governor Valves, Rotor, Nozzles,

Diaphragms, Bearings, Casing, Gland Seals, Control

Oil, Pumps, servomotors, oil tanks, oil pipes, Filters,

Coolers

Steam Jet Ejector, Valves, Intercoolers, Nozzles

Fans, Gearbox, Motor, Splash Pack Fill, Cold Water

Pond, Recirculation Pumps

Condenser Heat Exchangers

Rotor, Stator, Exciter, Bearings, Coolers

Step up transformers, High Voltage Equipments

Relays, switchgears

31

Instrumentation, Power

Control and SCADA

Instrumentation

SCADA

Sensors, Data Transmission Lines, PLC, Relays

Servers, Relays, PLC

Compressed Air

Compressor

Piping

Rotary Screw, Solenoid Valves, Motor, Sensors

Pipes and Valves

4 Analysis of FTA

4.1 Introduction This effective reliability analysis tool can be used for different troubles associated with maintainability. Fault

tree analysis (FTA) examines the system or product, in terms of its operation and environment, to determine

all possible ways in which the undesirable event can occur. Furthermore, FTA is a useful tool to analyze the

system and to identify all possible failure causes at all possible levels associated with a system.

4.2 Objectives Fault tree analysis of a system can be used to identify critical components. In doing so, it can help for cost-

effective improvements. It also provides input to testing, maintenance, and operational procedures and

policies, that is, it confirms the ability of the system to fulfill its imposed safety requirements.

4.3 Commonly used symbols Commonly used symbols to construct a fault tree: (a) an OR gate, (b) an AND gate, (c) a resultant event, (d) a

basic event, (e) an incomplete event. Two commonly used fault event symbols: (a) circle; (b) rectangle.

• Or gate. This represents a condition in which an output event occurs if any one or more of the n

input events occur.

• And gate. This represents a condition in which an output event occurs only if all of the n input

events occur.

• Resultant event. This represents a condition in which an event is a result of the combination of

fault events that precede it.

• Basic event. This represents the failure of an elementary component or a basic fault event.

• Incomplete event. This represents a fault event whose cause has not been fully determined either

due to lack of interest or due to lack of data.

32

4.3.1 Fault Tree “Gates” and “Event” Symbols. A fault tree diagram contains two basic elements, “gates” and “events”. “Gates” allow or prevent the passage

of fault logic up the tree and show the relationships between the “events” needed for the occurrence of a

higher event. But the two most commonly used logic symbols are the OR gate and the AND gate:

Input Events

Output Events

Output Events

Input Events

(1) (2)

Figure 4.3-1 Two regularly used fault tree gate symbols : (1) OR gate; (2) AND gate.

The OR gate symbol implies that an output fault event takes place if one or more of the input fault events

occur. The AND gate symbol implies that the output fault event only takes place if all of the input fault

events occur.

The figure below illustrates the two frequently used fault event symbols, the circle and the rectangle. The

circle denotes the failure of an elementary component or a basic fault event that need not any further. The

rectangle denotes fault event that results from a combination of preceding fault events.

(1) (2)

Figure 4.3-2 Two frequently used fault event symbols: (1) circle; (2) rectangle.

4.4 Benefits of Fault Tree Analysis

• It is a tool that designers, management, and users can use to analyze failures and potential failures in

visual terms.

• It reveals failures based on reasoning.

• It provides insight into the behavior of the system or equipment.

• It provides options for conducting qualitative and quantitative analysis.

33

• It makes reliability, maintainability, and safety analysts to know the system or equipment under

consideration completely.

4.5 Drawbacks of Fault Tree Analysis

• The end result is difficult to verify.

• It can be a costly and time-consuming.

• It has difficulty handling states of partial failure.

4.6 Fault Tree Analysis on OTEOSAL Main Systems The Fault tree analysis of the different systems that have been performed at OTEOSA is shown from Figure

4.6.1 to Figure 4.6.11

It should be noted that only the FTA of the main equipments are shown here and the FTA of subsystems can

be seen in Appendix 1.

Figure 4.6.1 shows the whole power plant with its main systems and a failure in any one of the systems will

cause break down of the power plant.

Figure 4.6.2 describes the Coal Handling Plant. It is composed of a Tipper to transfer coal from lorries to the

plant, followed by a vibrating table, conveyors, vibrating screener, coal crusher, silo for coal storage and a

travelling shuttle for coal distribution in the boiler.

Figure 4.6.3 represents the Water Treatment Plant which is composed of the Raw Water Plant and the

Demineralised Water Plant. Subsystems for these two plants can be seen in Appendix 1.

Figure 4.6.4 is about Combustion Air and is mainly composed of the Primary Air and Secondary Air Fans.

Failure in any one fan brings along break down for the power plant.

Figure 4.6.5 describes the Feed Water Pumps and the system is made up of high pressure feed pumps and is

fed by a Feed Water Tank.

Figure 4.6.6 illustrates the main constituent equipments of the Boiler. It is composed of the travelling grate,

coal feeders and spreaders and the furnace and superheaters tubes.

34

Figure 4.6.7 represents the Steam Distribution System and is made up of pipings, manual and automatic

valves and instrumentation sensors.

Figure 4.6.8 is the Waste Disposal System and is composed of the I.D Fan, Ash Handling Plant, Ash Silo for

ash storage, Electrostatic Precipitator and conveyor belt for bottom ash carriage.

Figure 4.6.9 describes failures in the Turbo-Alternator system. This important system is made up of the Steam

Turbine, Turbo-Alternator Gear, Alternator, Transformers, Protection, Cooling Tower and Condenser.

Figure 4.6.10 analyses the Instrumentation, Power Control and SCADA.

Figure 4.6.11 shows the main failures that can occur in the Compressed Air System.

35

Figure 4.6-1 FTA for whole Power Plant

8 9 15 4

2

3 6 7 10

Failure of Power

Plant

Failure in Coal

Handling Plant

Failure in

Water

Treatment

Failure in

Combustion Air

Failure in Feed

Water Pump

Failure in

Boiler

Failure in

Compressed

Air

Failure in

Instrumentation

& Control

Failure in Waste

Disposal

Failure in Steam

Distribution

System

1

Failure in

Turbo-

Alternator

36

Figure 4.6-2 FTA for Coal Handling Plant

2

12 13 14 15 16 17 18

37

Figure 4.6-3 FTA for Water Treatment Plant

2

Failure in Water Treatment

Plant

Failure of Raw

Water Plant

Failure of

Demineralised

Water Plant

19 20

38

Figure 4.6-4 FTA for Combustion Air

4

Failure in Combustion Air

Failure in

Primary Air

Failure in

Secondary Air

21 22

39

Figure 4.6-5 FTA for Feed Water

14

40 38 41

40

Figure 4.6-6 FTA for Boiler

6

21

22

41 38 39

23 27

5

24

25

25 25

41

Figure 4.6-7 FTA for Steam Distribution

7

Failure in Steam Distribution

System

Failure in Pipings

and Valves

26

Failure in

Compressed

Air

11

Failure in

Instrumentation

& Control

Failure in

SCADA

10 48

42

Figure 4.6-8 FTA for Waste Disposal System

8

Failure in Waste Disposal System

Failure in Ash

Handling Plant

28

Failure in

Conveyor for

Bottom Ash

15

Failure in Ash

Silo

Failure in

Electrostatic

Precipitator

29 30

Failure in

Compressed

Air

11

Failure in I.D

Fan

27

43

Figure 4.6-9 FTA for Turbo-Alternator and Auxiliary Equipments

9

Failure in Turbo-Alternator and

Auxiliary Equipments

Failure in

Turbine Gear

32

Failure in

Cooling Tower

36

Failure in

Condenser

37

Failure in

Steam Turbine

31

Failure in

Turbine

Protection

Failure in

Alternator

33

Failure in

Transformer

Failure in

Instrumentatio

n & Control

34 10

44

Figure 4.6-10 FTA for Instrumentation and Control

10

45

Figure 4.6-11 FTA for Compressed Air

40 38 46

11

46

4.7 Observations made on FTA performed at OTEOSA The FTAs that have been worked out in Chapter 4 can be utilized as a primary step when first

identifying a failure, since they show in the diagrams all the potential failures of the systems

examined. From these FTAs, it will be simple and straight forward to rapidly establish what the

possible causes of a problem are in a particular system and therefore, optimize time and focus more

on one particular part instead of analyzing the whole system.

Once these analyses have been made, a failure mode, effects, and criticality analysis (FMECA) are

being conducted to establish the maintenance strategies that must be used for the various systems

(see Chapter 5).

47

5 Failure Mode and Effects Analysis (FMEA)

5.1 Introduction Failure mode and effects analysis (FMEA) is a structured qualitative analysis of a system,

subsystem, component, or function that underlines possible failure modes, their causes, and the

effects of a failure on system operation. FMEA also evaluates the criticality of the failure, that is,

the severity of the effect of the failure and the probability of its occurrence. This type of analysis is

referred to as failure mode, effects, and criticality analysis (FMECA) and the failure modes are

assigned priorities.

For the case of a power plant, at design level, FMECA helps to identify and prevent failures right

from the system design. It analyzes the design that has been developed and examines how failures

of individual equipments would affect the system operation. The purpose of doing FMECA is to

analyze the process by which the system is to be run and assess how potential failures in the

process would affect the system operation.

Information related to an FMECA and sources for obtaining it are:

• Item identification numbers, available from the parts list for the system.

• Item functional specifications, available from the engineer or from the parts list.

• System function, available in the customer requirements or from the engineer.

• Provisions or design changes to prevent or compensate for failures, available from

the engineer.

• Mission phase/operational mode, available from the engineer

• Failure effects, available from the engineer.

• Failure modes, causes, and rates, available from the factory database and the field

experience database.

• Failure probability/severity classification, available from the engineer.

• Failure detection method(s) available from the engineer.

48

5.2 FMECA Benefits Some of the advantages of performing an FMECA are that it:

• Proves useful for making design comparisons.

• Serves as a visibility tool for managers.

• Provides a systematic approach to classifying hardware failures.

• Identifies all possible failure modes and their effects on mission, personnel and

system.

• Generates useful data for use in system safety and maintainability analyses.

• Helps improve communication among design interface personnel.

• Effectively analyzes small, large, and complex systems.

• Is easy to understand.

• Starts from the level of greatest detail and works upward.

• Detect risks to system performance and safety.

5.3 Applying FMECA at OTEOSAL From the FTA performed, the critical components have already been identified. Then, before

performing the FMECA, respective table of detection, severity and occurrence have been worked

out based on the function of the plant. Added to that, the help of the employees from the

maintenance department was taken to build up properly these tables in accordance with the

functioning of the power plant.

5.4 Risk Priority Number Method This technique bases the risk priority number for an item failure mode on three factors: probability

of occurrence, the severity of the failure's effects, and probability of failure detection. RPN

evaluates the risks related with possible failures that have been found.RPN is calculated as the

product of a ranking from 1-10 allocated to each factor:

RPN= Severity(S) * Occurrence (O) * Detection (D)

49

Failure modes with a high RPN are more critical and given a higher priority than ones with a lower

RPN. When the scales used range from 1 to 10, the value of an RPN will be between 1 and 1,000.

However, the scales and categories used can vary from one organization to another.

5.5 Severity(S) The severity of a failure can be described as the degree to which a failure of a component will affect

the proper running of the machines or systems.

Table 5.5—1 Ranking for Severity

Description of Ranking Level of

Severity, S

Rank

No effect on any system.

Have bypass route.

Remote 1

Repair is simple. No stoppage of plant or machine is required. Minor 2

Repair may take between 30 minutes and 1 hour. Easy replacement of

spare parts required. No stoppage of plant required.

Low 3

Repair may take between 2 and 5 hours and important spare parts

required. No stoppage of plant required.

Moderate 4

Repair may take between 5 to 24 hours and costly spare parts required.

No stoppage of plant required.

High 5

Repair may take more than 1 day and can cause machine failure. Very High 6

Repair may take more than 1 day and can cause total plant failure Extremely

High

7

50

5.6 Occurrence (O) The occurrence of a failure is defined as the probability that a failure of a part occurs or the relative number

of failures expected during the item’s useful life. With the help of the employees from the maintenance

department, it was decided to take a lifetime of 3 years.

Table 5.6—1 Ranking for Occurrence of failures

Definition Rank

Remote Frequency of failure of part is btw 0-2 1

Extremely Low Frequency of failure of part is btw 2-4 2

Very Low Frequency of failure of part is btw 4-6 3

Low Frequency of failure of part is btw 6-8 4

Reasonably Low Frequency of failure of part is btw 8-10 5

Moderate Frequency of failure of part is btw 10-12 6

Reasonably High Frequency of failure of part is btw 12-14 7

High Frequency of failure of part is btw 14-16 8

Very High Frequency of failure of part is btw 16-18 9

Extremely High Frequency of failure of part is greater than 18 10

5.7 Detection (D) Detection can be defined as the capacity to identify problems or potential source for faults. The earlier a fault

is detected, the better it is. If a failure is not detected in time, the resulting outcomes may prove fatal for the

plant in terms of maintenance cost of repair and cost of production loss.

51

Table 5.7—1 Ranking for Detection of failures

Detection is certain. 1

Can still be detected by human senses but machines have to be stopped. 2

Detection is moderate and requires certain amount of time and experience. 3

Detection is difficult and external devices must be used. 4

No sensors available and highly sophisticated testing devices must be used to detect

failure

5

5.8 FMECA Table After describing and locating the indices for the three parts that make up the Risk Priority Number, the

criticality assessment was then carried out. The outcomes are obtainable in Appendix 2 (Appendix 2 shows all

the data used to assign values to the three Critical factors (S, O and D).

5.9 Maintenance Strategy determination After the criticality index has been performed, the most appropriate maintenance strategy must be suggested.

In line with this, manufacturer’s manuals were consulted and interviews were done with employees at

OTEOSAL in order to have an idea of what strategy might be suitable for each and every component. The

appropriate maintenance strategies were therefore determined. Respective RPN values have also been added.

The maintenance strategy suggested will aid the company to forecast upcoming failures and consequently the

company will be able to take corrective measures to eradicate them totally and hence reducing downtime cost.

Thus, there will be better monitoring of the system.

52

Table 5.9—1 Maintenance task

Maintenance

Strategy

Remarks

Breakdown • Routine Inspection must be done.

• Low occurrence.

• Must ensured availability of spare parts.

Preventive • Check alignment.

• Greasing.

• Daily or periodic checking.

• Daily or periodic cleaning.

• Visually inspect for wear, corrosion, cracking, or leakage of

lubricant.

Predictive • Periodic inspection.

• Periodic analysis of data and sample obtained.

53

5.10 FMECA Tables for OTEOSAL Below, only one FMECA table for a system is shown and the rest can be viewed in Appendix 2.

Also only one table of maintenance strategy is presented here and the whole can be seen in Appendix 3.

Table 5.10—1 FMECA Table for Coal Handling Plant – Tipper

System Sub-system &

Function

Failure Mode Effect of Failure Cause of Failure Criticality Analysis

S O D RPN

CO

AL

HA

ND

LIN

G P

LA

NT

Tipper

[Lifting of coal]

Lubrification failure Degraded

performance

Oil seal failure 3 1 1 3

Contamination of

oil

5 2 5 50

Valve failure 3 1 2 6

Oil filter failure 3 1 2 6

Oil tank failure 3 1 1 3

Hydraulic cylinder

failure

Shutdown Cylinder fails 6 1 3 18

Failure due to

misalignment

5 1 3 15

Hydraulic pump

failure

Shutdown Valve failure 3 1 2 6

Bearing failure 4 1 1 4

Pipe failure 3 1 1 3


Mechanical seal

failure

3 1 1 3

54

Table 5.10—2 Suggested Maintenance Strategy and RPN for Coal Handling Plant – Tipper

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Tipper

Lubrification

failure

Oil seal failure Breakdown Breakdown 3

Contamination

of oil

Predictive Predictive 50

Valve failure Breakdown Breakdown 6

Oil filter

failure

Breakdown Breakdown 6

Oil tank failure Breakdown Breakdown 3

Hydraulic

cylinder

failure

Cylinder fails Preventive Preventive 18

Failure due to

misalignment

Preventive Preventive

15

Hydraulic

pump failure


Bearing failure Preventive Breakdown 4

Pipe failure Breakdown Breakdown 3

Oil seal failure Preventive Breakdown 3

Mechanical

seal failure

Preventive Breakdown 3

55

5.11 Analysis of FMECA From Tables 5.6 and A.3, it can be noted that the required maintenance strategies are between a range of

RPN values.

Table 5.11—1 RPN range

Maintenance Strategy RPN range

Breakdown 1 ≤ RPN < 10

Preventive or Predictive RPN ≥ 10

Added to that, the selection of these strategies was not based only on these RPN values. As a matter of fact,

the RPN value can be lower for certain component but their importance to the proper operation of the plant

and also due to their high detection factor. Therefore, greater significance was given to detection and severity

indices as these components are very critical for the plant. Subsequently, appropriate maintenance strategies

were suggested as listed in Tables 5.10-2 and A.3.

5.12 Maintenance Tasks Comparisons. A maintenance task comparison was carried out between the suggested maintenance based on RCM and the

actual maintenance carried out. From these tables, the number of maintenance tasks carried out is listed in

Table 5.12-1. Added to that, a percentage of the different maintenance strategies performed over the overall

maintenance tasks were carried out so as to give a clear indication of the contribution of each maintenance

task. This is shown in Table 5.12-2.

Table 5.12—1 Maintenance Tasks

Type of Maintenance Actual Maintenance RCM

(Proposed maintenance)

Breakdown Maintenance 156 87

Preventive Maintenance 142 211

CBM 102 102

56

Table 5.12—2 Percentage contribution of respective maintenance task for both Actual & RCM strategy.

Type of Maintenance % of respective

maintenance task

compares to the total

actual maintenance task

% of respective

maintenance task

compares to the total

proposed maintenance task

Breakdown Maintenance 39.00 21.75

Preventive Maintenance 35.50 52.75

CBM 25.50 25.50

In the existing maintenance tasks, there are 156 breakdown maintenance tasks, which represent around 39%

of the total maintenance tasks. This clearly shows that breakdown maintenance is currently being used greatly.

So, in a power plant which runs for 24 hours continuously and is a base load station, some measures must be

taken so as to prevent some failures to occur. Therefore, preventive maintenance is adopted and from Table

5.12-2 and A.3, it is evident that from the proposed RCM tasks, preventive maintenance is greatly used and

has a major part in the overall maintenance task. This is to ensure a smooth running of the power plant.

Furthermore, it can be deduced from Table 5.10-2 and A.3 that the company have been using CBM

techniques for many machines. From the proposed maintenance tasks, it can be observed that this is the

required technique that must be used as these machines are certainly critical for the plant.

Furthermore, from the FMECA that has been carried out, it can be deduced that many machines are critical

and can cause plant failure. So, it is unwise to practise one maintenance strategy on the machine. It is

preferable to perform a combination of the maintenance task because a machine can have many types of

causes related to its failure.

57

6 Applying FTA to a specific equipment at the OTEOSAL power

plant

6.1 Grate Stocker At the power plant, after data collection and interview with the people from the maintenance department, it

has been observed that the equipment that needed more attention is the grate stocker.

The grate stocker is composed of the travelling grate, the coal feeders and coal spreaders. Many resources are

allocated for the good functioning of the grate stocker and hence it has been decided to carry a more in depth

investigation so as to be able to make the equipment more reliable and be able to prevent unnecessary

failures.

First FTA diagrams will be done for the different equipment composing the grate stocker followed by

quantitative analysis of the FTAs presented on excel sheets and then Pareto Analysis will be presented to

show the proportion of different failures.

6.2 FTAs for the grate stocker

Figure 6.2-1 FTA for Coal Spreader

58

Figure 6.2-2 FTA for Coal Feeder

Figure 6.2-3 FTA for Gearbox

59

Figure 6.2-4 FTA for Drive Motor

60

Figure 6.2-5 FTA for Travelling Grate

61

Figure 6.2-6 FTA for Grate Stocker

6.3 The quantitative analysis of the FTA

6.3.1 6.3.1 Equations for quantitative analysis From the data collected, the mean frequency of breakdown for the year 2008, 2009 and 2010 was calculated

for all the different parts of the stoker. The mean probability of failure (F (t)) was then obtained by dividing

the mean frequency of breakdown to the number of parts initially on the grate stoker.

F (t) =

Also, R (t) is the probability that the component is in the functioning state is given by:

R (t) = 1- F (t)........................................................................................................................... (1)

The reliability of each component is hence calculated.

62

The following calculations were based on the assumption of a constant hazard rate, as this pattern accounts

for 89% of all failures. The exponential distribution is hence considered relevant.

From f (t) = ...................................................................................................................... (2)

Replacing equation (1) in (2),

f (t) = ....................................................................................................... (3)

The constant hazard rate is denoted as l, where l= ...................................................... (4)

Combining equations (3) and (4)

l x R (t) =

-l=

Integrating both sides,

dt =

lt = - ln R (t)............................................................................................................................ (5)

Multiplying both sides by exponential, e:

R (t)

The failure rate can be calculated from the equation number (5) as follows;

From the equation (5), the failure rate, l =

Where, t is taken as one year.

The mean time to failure, MTTF is given as the reciprocal of the failure rate.

Hence MTTF = (Narayan, 2004)

63

6.3.2 Reliability of k-out-of-n for the coal spreader and feeder There are four coal spreader and feeder arranged in parallel to each other and for the system to work at least

2 out of the 4 spreader must be working similarly 2 out of the feeder must be working.

For the calculation of the reliability of the coal spreader and that of the feeder the following formula is used:

(Marvin Rausand and Arnljot Heyland, 2004)

For the current system of the coal feeder:

As indicated before 2 out of 4 coal feeder must be in the up state for the system to work. Hence, k =2 and n

=4, the reliability (R(t) ) was found from the analysis of the failure and from the data collected (refer to

equation 1 ), R(t) = 0.29833 also F(t) = 1- R(t) which is equal to F(t) =0.70167.

Therefore, Rs

Rs =0.2705

Hence the reliability of the coal feeder is 27.05%

Similarly for the calculation of the coal spreader:

As indicated before 2 out of 4 coal spreader must be in the up state for the system to work. Hence, k =2 and

n =4, the reliability (R(t) ) was found from the analysis of the failure and from the data collected (refer to

equation 1 ), R(t) = 0.29833 also F(t) = 1- R(t) which is equal to F(t) =0.70167.

Therefore, Rs

Rs = 0.2557

Hence the reliability of the coal spreader is 25.57%

64

Table 6.3—1 Quantitative analysis for the FTA of the Coal Spreader

Spreader parts Quantity

Frequency of breakdown in 2010



Mean frequnecy of breakdown

Mean % freq of

breakdownF(t) R(t) Failure rate/ ƛ MTTF Reliablilty

FTA top event calculation

Probability of spreader fail

Reliability of Spreader

Bearings 8 2 3 2 2.3333 29.1667 0.2917 0.7083 0.3448 2.899891514Transmission belt 8 2 4 0 2.0000 25.0000 0.2500 0.7500 0.2877 3.476059497Blade cylinder 4 1 2 1 1.3333 33.3333 0.3333 0.6667 0.4055 2.466303462

MotorMotor Bearing 8 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0Motor shaft 4 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0Motor fuse 4 1 1 1 1.0000 25.0000 0.2500 0.7500 0.2877 3.476059497Motor relay 4 0 1 0.3333 8.3333 0.0833 0.9167 0.0870 11.49274997Motor windings 4 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0Motor contactor 4 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0

0.3125

0.243489580.7565104171 0.0000

0.31250.6875

65

Table 6.3—2 Quantitative analysis for the FTA of the Coal Feeder

Feeder parts Quantity

Frequency of

breakdown in 2010

Frequency of breakdown in

2009


2008

Mean frequnecy of breakdown

Mean % freq of



Probability of feeder fail

Reliability of

Feeder

Bearings 16 1 3 2 2.0000 12.5000 0.1250 0.8750 0.1335 7.488875689Metal bars of belt 100 25 36 18 26.3333 26.3333 0.2633 0.7367 0.3056 3.272039599Transmission chain 4 1 0 1 0.6667 16.6667 0.1667 0.8333 0.1823 5.484814948Metal chains 8 1 3 1 1.6667 20.8333 0.2083 0.7917 0.2336 4.280549781Projection plate 24 3 0 0 1.0000 4.1667 0.0417 0.9583 0.0426 23.49645347

motorBearing 8 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0Shaft 4 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0Fuse 4 1 0 1 0.6667 16.6667 0.1667 0.8333 0.1823 5.484814948Relay 4 0 0 1 0.3333 8.3333 0.0833 0.9167 0.0870 11.49274997Windings 4 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0Contactor 4 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0

GearboxBearing 8 0 1 0 0.3333 4.1667 0.0417 0.9583 0.0426 23.49645347Gear 8 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0Shaft 4 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0

0.7016758161 0.0000

0.236110.763888889 0.2361

0.958333333 0.0417 0.0417

0.29833456

66

Table 6.3—3 Quantitative analysis for the FTA of the Travelling Grate

Grate partsQuantity on

grate

Frequency of

breakdown in 2010

frequency of breakdown in

2009


2008

Mean frequency of breakdown

Mean % freq of


Probability of failure of the

grate

Reliability of Grate

Probability of failure of the

travelling grate stoker

Reliability of the travelling grate stoker

Grate chain 40 1 2 1 1.3333 3.3333 0.0333 0.9667 0.0339016 29.49717492Grate bars support 2000 14 18 36 22.6667 1.1333 0.0113 0.9887 0.0114 87.73434428Link rods 2000 8 6 12 8.6667 0.4333 0.0043 0.9957 0.0043 230.2688689Link rod spacer 2000 1 2 3 2.0000 0.1000 0.0010 0.9990 0.0010 999.4999166Grate bars 12600 350 180 124 218.0000 1.7302 0.0173 0.9827 0.0175 57.29671073Connecting rod 2000 1 3 3 2.3333 0.1167 0.0012 0.9988 0.0012 856.6427599Side rails 100 2 1 1 1.3333 1.3333 0.0133 0.9867 0.0134 74.49888142Deslagger 18 1 3 2 2.0000 11.1111 0.1111 0.8889 0.1178 8.490187016End foot block 72 1 2 3 2.0000 2.7778 0.0278 0.9722 0.0282 35.49765246Hanging metal plate 17 3 1 1 1.6667 9.8039 0.0980 0.9020 0.1032 9.691402839Sliding plates 142 1 3 2 2.0000 1.4085 0.0141 0.9859 0.0142 70.49881795Sprocket 40 1 2 1 1.3333 3.3333 0.0333 0.9667 0.0339 29.49717492Bearing housing 16 1 0 1 0.6667 4.1667 0.0417 0.9583 0.0426 23.49645347Grate shaft 4 1 0 0 0.3333 8.3333 0.0833 0.9167 0.0870 11.49274997Sprocket 40 2 1 1 1.3333 3.3333 0.0333 0.9667 0.0339 29.49717492Bearing housing 16 0 1 2 1.0000 6.2500 0.0625 0.9375 0.0645 15.49462216Grate shaft 4 1 0 0 0.3333 8.3333 0.0833 0.9167 0.0870 11.49274997

GearboxGearbox bearing 4 1 0 0 0.3333 8.3333 0.0833 0.9167 0.0870 11.49274997

Gearbox gear 10 0 0 1 0.3333 3.3333 0.0333 0.9667 0.0339 29.49717492

Gearbox shaft 2 0 1 0 0.3333 16.6667 0.1667 0.8333 0.1823 5.484814948Motor

Motor Bearing 4 0 0 1 0.3333 8.3333 0.0833 0.9167 0.0870 11.49274997Motor shaft 2 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0Motor fuse 2 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0Motor relay 2 0 0 1 0.3333 16.6667 0.1667 0.8333 0.1823 5.484814948Motor windings 2 1 0 0 0.3333 16.6667 0.1667 0.8333 0.1823 5.484814948Motor contactor 2 0 0 0 0.0000 0.0000 0.0000 1.0000 0.0000 0

0.933081058 0.0669

0.765387949

0.758247216 0.2418

0.849189815 0.1508

0.1693

0.60951

0.390494878 0.2616

0.916666667 0.0833

0.363430.694444444 0.3056

0.982958055 0.017041945


0.234612051

67

6.4 Analysis of results From Table 6.3.1 for Coal Spreader, it can be seen that the table has been categorized into mechanical and

electrical parts. The MTTF (Mean Time to Failure) and Failure Rate for different constituent parts can be

observed and the probability of failure for the Spreader is seen to be 0.76 whereas the reliability for the

Spreader is 0.24. These results are from the year 2008 to 2010.

Results for Coal Feeder can be observed in Table 6.3.2. Here again, the MTTF and Failure Rate can be seen

for different constituent parts of the Coal Feeder. The probability of failure for the Feeder is seen to be 0.70

whereas the reliability for the Feeder is 0.30.

Table 6.3.3 shows the results for the Travelling Grate. Here the constituent parts have been categorized in

fixed, moving and bearings for the grate and analysis for the gearbox and motor for the drive system can also

be seen. The MTTF and Failure Rates for each part can be observed and the probability of failure for the

Travelling Grate can be seen to be 0.77 and having reliability of 0.23. Also from Table 6.3.3, the probability of

failure of the Grate Stocker, that is, combining Coal Feeders, Coal Spreaders and Travelling Grate is seen to

be 0.98 and the reliability as low as 0.02.

These results reflect the reality as the people in the maintenance department all agree that the Grate Stocker

causes a lot of problem and need great attention.

6.5 Pareto Analysis A Pareto Analysis will be done for the Grate Stocker. It will start with the different parts of the Travelling

Grate and will include Coal Feeder and Coal Spreader. The Travelling Grate has been divided into Fixed

Parts, Front and Rear Driving Part, Chain Assembly and Grate Chain.

6.5.1 Definition of Pareto Analysis Pareto analysis is a statistical technique in decision making that is used for selection of a limited number of

tasks that produce significant overall effect. Pareto implies that the idea that by doing 20% of work, 80% of

the advantage of doing the entire job can be generated. Pareto analysis is a formal technique useful where

many possible courses of action are competing for attention. In essence, the problem-solver estimates the

benefit delivered by each action, then selects a number of the most effective actions that deliver a total

benefit reasonably close to the maximal possible one. This technique helps to identify the top 20% of causes

that need to be addressed to resolve the 80% of the problems.

An example is where the Pareto analysis in risk management allows management to focus on the 20% of the

risks that have the most impact on the project. (Wikipedia, accessed December 2011)

68

6.5.2 Steps to identify the important causes using Pareto analysis

(Wikipedia, accessed December 2011)

• Step 1: Form an explicit table listing the causes and their frequency as a percentage.

• Step 2: Arrange the rows in the decreasing order of importance of the causes (i.e., the most

important cause first)

• Step 3: Add a cumulative percentage column to the table

• Step 4: Plot with causes on x- and cumulative percentage on y-axis

• Step 5: Join the above points to form a curve

• Step 6: Plot (on the same graph) a bar graph with causes on x- and percent frequency on y-axis

• Step 7: Draw line at 80% on y-axis parallel to x-axis. Then drop the line at the point of intersection

with the curve on x-axis. This point on the x-axis separates the important causes (on the left) and

trivial causes (on the right)

• Step 8: Explicitly Review the chart to ensure that at least 80% of the causes are captured

Failures in 2008 3 2 2 1 1

Percent 33.3 22.2 22.2 11.1 11.1

Cum % 33.3 55.6 77.8 88.9 100.0

Fixed parts

side rai ls

hang

ing metal p

late

sliding

plates

des lag

ger

end foot b

lock

9

8

7

6

5

4

3

2

1

0

100

80

60

40

20

0

Failu

res in

20

08

Pe

rce

nt

Pareto Chart of Fixed parts

Figure 6.5-1 Example of Pareto Chart

69

6.5.2 Pareto Analysis for Grate Stocker 6.5.3.1 Pareto Analysis for driving part of Travelling Grate

Failures in 2008 0 0 0 02 1 1 1 1 0 0 0

Percent 0.0 0.0 0.0 0.033.3 16.7 16.7 16.7 16.7 0.0 0.0 0.0

Cum % 100.0100.0100.0100.033.3 50.0 66.7 83.3100.0100.0100.0100.0

Driving parts

mot

or w

inding

s

mot

or sha

ft

mot

or fus

e

mot

or con

tact

or

grat

e sha

ft

gearbo

x sh

aft

gearbo

x be

aring

sprock

et

mot

or relay

mot

or B

earin

g

gear

box ge

ar

Bearing

hous

ing

6

5

4

3

2

1

0

100

80

60

40

20

0

Failu

res i

n 2

00

8

Pe

rce

nt

Pareto Chart of Driving parts

Figure 6.5-2 Pareto for driving part of Travelling Grate for the year 2008

Failures in 2009 0 0 0 01 1 1 0 0 0 0 0

Percent 0.0 0.0 0.0 0.033.3 33.3 33.3 0.0 0.0 0.0 0.0 0.0

Cum % 100.0100.0100.0100.033.3 66.7 100.0100.0100.0100.0100.0100.0

Driving parts

mot

or w

inding

s

mot

or sha

ft

mot

or re

lay

mot

or fu

se

mot

or con

tact

or

mot

or Bea

ring

grat

e sha

ft

gear

box

gear

gear

box be

aring

spro

cket

gear

box sh

aft

Bear

ing h

ousin

g

3.0

2.5

2.0

1.5

1.0

0.5

0.0

100

80

60

40

20

0

Fa

ilu

res in

20

09

Pe

rce

nt



70

Failures in 2010 0 0 0 02 1 1 1 0 0 0 0

Percent 0.0 0.0 0.0 0.040.0 20.0 20.0 20.0 0.0 0.0 0.0 0.0

Cum % 100.0100.0100.0100.040.0 60.0 80.0100.0100.0100.0100.0100.0

Driving parts

mot

or sha

ft

mot

or re

lay

mot

or fus

e

mot

or con

tact

or

mot

or B

earin

g

gearbo

x sh

aft

gearbo

x ge

ar

Bearing

hous

ing

mot

or w

inding

s

grate

sha

ft

gearbo

x be

aring

spro

cket

5

4

3

2

1

0

100

80

60

40

20

0

Failu

res in

20

10

Perc

en

t



mean frequnecy of breakdown 0.3330.0000.0000.0001.3331.0000.3330.3330.3330.3330.3330.333

Percent 7.1 0.0 0.0 0.028.6 21.4 7.1 7.1 7.1 7.1 7.1 7.1

Cum % 100.0100.0100.0100.028.6 50.0 57.1 64.3 71.4 78.6 85.7 92.9

Driving parts

motor sha

ft

motor

fuse

motor

con

tactor

motor w

inding

s

motor

relay

motor

Bea

ring

grate sha

ft

gearbo

x sh

aft

gearbo

x ge

ar

gear

box be

aring

Bear

ing ho

using

sprock

et

5

4

3

2

1

0

100

80

60

40

20

0

me

an

fre

qu

ne

cy

of

bre

akd

ow

n

Pe

rce

nt


Figure 6.5-5 Pareto for Mean Frequency of Breakdown

71

Figure 6.5-6 Pie Chart representing Mean Frequency of Breakdown for Driving Parts in Travelling Grate

The Pareto chart for the driving parts of the travelling grate for the year 2008 indicates that 80% of the

failures are due to the failure of the bearing housing, the gearbox gear and motor relay. While that of 2009

clearly points out that 80% of failures are due to failures of the bearing housing and the gearbox shaft. The

Pareto analysis of the year 2010 also shows that the sprocket, gearbox bearing and the grate shaft accounts

for 80% of the failure of the driving parts of the travelling grate.

The Pareto analysis of the mean frequency of breakdown for these three years allow a more global analysis of

which parts of the driving parts of the travelling rate accounts for the 80% of failures. From this it can be

deduced that the sprocket and bearing housing are the most important failed parts in this system as the two

of them make up to 51% failures for the driven parts of the travelling grate.

72

6.5.3.2 Pareto Analysis for Rear Driving part of Travelling Grate

Failures in 2008 1 1 0

Percent 50.0 50.0 0.0

Cum % 50.0 100.0 100.0

Rear driven parts grate shaftsprocketBearing housing

2.0

1.5

1.0

0.5

0.0

100

80

60

40

20

0

Failu

res in

20

08

Pe

rce

nt

Pareto Chart of Rear driven parts

Figure 6.5-7 Pareto for Rear Driving part of Travelling Grate for the year 2008


Percent 66.7 33.3 0.0

Cum % 66.7 100.0 100.0

Rear driven parts Bearing housinggrate shaftsprocket

3.0

2.5

2.0

1.5

1.0

0.5

0.0

100

80

60

40

20

0

Failu

res in 2

009

Perc

ent



73


Percent 33.3 33.3 33.3

Cum % 33.3 66.7 100.0

Rear driven parts sprocketgrate shaftBearing housing

3.0

2.5

2.0

1.5

1.0

0.5

0.0

100

80

60

40

20

0

Failu

res in

20

10

Pe

rce

nt



mean frequnecy of breakdown 1.333 0.667 0.333

Percent 57.1 28.6 14.3

Cum % 57.1 85.7 100.0

Rear driven parts grate shaftBearing housingsprocket

2.5

2.0

1.5

1.0

0.5

0.0

100

80

60

40

20

0

me

an

fre

qu

ne

cy

of

bre

akd

ow

n

Pe

rce

nt


Figure 6.5-10 Pareto of Mean Frequency of Breakdown for Rear Driving part of Travelling Grate

74

Figure 6.5-11 Pie Chart representing Mean Frequency of Breakdown for Rear Driving Parts in Travelling Grate

The Pareto chart for the rear driving parts of the travelling grate for the year 2008 indicates that 80% of the

failures are due to the failure of the bearing housing. While that of 2009 clearly points out that 80% of failures

are due to failures of the sprocket. The Pareto analysis of the year 2010 also shows that bearing housing and

the grate shaft accounts for 80% of the failure of the rear driving parts of the travelling grate.

The Pareto analysis of the mean frequency of breakdown for these three years indicates that, the sprocket is

the most important failed parts in this system as it makes up to 57% failures for the rear driven parts of the

travelling grate

75

6.5.3.3 Pareto Analysis for Chain Assembly parts of Travelling Grate

Failures in 2008 124 36 12 3 3 1

Percent 69.3 20.1 6.7 1.7 1.7 0.6

Cum % 69.3 89.4 96.1 97.8 99.4 100.0

Chain assenbly parts

Grate ch

ain

link ro

d sp

acer

conn

ectin

g rod

link rods

grate ba

rs sup

port

Grate ba

rs

200

150

100

50

0

100

80

60

40

20

0

Failu

res in

20

08

Pe

rce

nt

Pareto Chart of Chain assembly parts

Figure 6.5-12 Pareto for Chain Assembly parts of Travelling Grate for the year 2008

Failures in 2009 180 18 6 3 2 2

Percent 85.3 8.5 2.8 1.4 0.9 0.9

Cum % 85.3 93.8 96.7 98.1 99.1 100.0


link ro

d sp

acer

Grate ch

ain

conn

ectin

g rod

link rods

grate ba

rs sup

port

Grate ba

rs

200

150

100

50

0

100

80

60

40

20

0

Failu

res in

20

09

Pe

rce

nt



76

Failures in 2010 350 14 8 1 1 1

Percent 93.3 3.7 2.1 0.3 0.3 0.3

Cum % 93.3 97.1 99.2 99.5 99.7 100.0


link ro

d sp

acer

Grate ch

ain

conn

ectin

g rod

l ink rods

grate ba

rs sup

port

Grate ba

rs

400

300

200

100

0

100

80

60

40

20

0

Failu

res in

20

10

Pe

rce

nt



mean frequnecy of breakdown 218.0 22.7 8.7 2.3 2.0 1.3

Percent 85.5 8.9 3.4 0.9 0.8 0.5

Cum % 85.5 94.4 97.8 98.7 99.5 100.0


Grate ch

ain

link rod sp

acer

conn

ectin

g ro

d

l ink rods

grate

bars sup

port

Grate ba

rs

250

200

150

100

50

0

100

80

60

40

20

0me

an

fre

qu

ne

cy

of

bre

akd

ow

n

Pe

rce

nt

Pareto Chart of Chain assenbly parts

Figure 6.5-15 Pareto of Mean Frequency of Breakdown for Chain Assembly parts of Travelling Grate

77

Figure 6.5-16 Pie Chart representing Mean Frequency of Breakdown for Chain Assembly Parts in Travelling

Grate

The Pareto analysis for Mean Frequency of Breakdown for the Chain Assembly parts for the years 2008 to

2010 indicates that the grate bars are responsible for more than 80% of the failures of the chain assembly

parts.

This value of 80 % shows that a lot of man hours and spare grate bars are needed.

78

6.5.3.4 Pareto Analysis for Fixed Parts of Travelling Grate

Failures in 2008 3 2 2 1 1

Percent 33.3 22.2 22.2 11.1 11.1

Cum % 33.3 55.6 77.8 88.9 100.0

Fixed parts

side rai ls

hang

ing metal plate

sliding

plates

deslag

ger

end foot block

9

8

7

6

5

4

3

2

1

0

100

80

60

40

20

0

Failu

res in

20

08

Perc

en

t


Figure 6.5-17 Pareto for Fixed Parts of Travelling Grate for the year 2008

The Pareto analysis for the year 2008 indicates that 80% of failures occurred due to the failure of the end foot

block, deslagger and the sliding plates.

Failures in 2009 3 3 2 1 1

Percent 30.0 30.0 20.0 10.0 10.0

Cum % 30.0 60.0 80.0 90.0 100.0

Fixed parts

side ra

ils

hang

ing metal plate

end foot block

sl iding

plates

deslag

ger

10

8

6

4

2

0

100

80

60

40

20

0

Failu

res in 2

009

Perc

ent


Figure 6.5-18 Pareto for Fixed Parts of Travelling Grate for the year 2009

79

While for the year 2009 the Pareto analysis showed that the end foot block, deslagger and the sliding plates

are once again the major influence for the 80% of breakdown of the fixed parts failure.

Failures in 2010 3 2 1 1 1

Percent 37.5 25.0 12.5 12.5 12.5

Cum % 37.5 62.5 75.0 87.5 100.0

Fixed parts

sl iding

plates

end foot block

deslag

ger

side rai ls

hang

ing metal plate

9

8

7

6

5

4

3

2

1

0

100

80

60

40

20

0

Failu

res in 2

010

Perc

ent


Figure 6.5-19 Pareto for Fixed Parts of Travelling Grate for the year

For the year 2009, Pareto analysis showed that hanging metal plates and the side rails and the deslagger

account for 80% of breakdown of the fixed parts failure.

mean frequnecy of breakdown 2.000 2.000 2.000 1.667 1.333

Percent 22.2 22.2 22.2 18.5 14.8

Cum % 22.2 44.4 66.7 85.2 100.0

Fixed parts

side rails

hang

ing metal plate

sliding

plates

end foot block

deslag

ger

9

8

7

6

5

4

3

2

1

0

100

80

60

40

20

0

mean f

requnecy o

f bre

akdow

n

Perc

ent


Figure 6.5-20 Pareto of Mean Frequency of Breakdown for Fixed Parts of Travelling Grate

80

The Pareto of the mean frequency of breakdown indicates that 80% of failures are due to the failure of the

deslagger, end foot block, the sliding plates and the hanging metal plates. These parts are thus the most

critical parts among the fixed parts of the grate.

Figure 6.5-21 Pie Chart representing Mean Frequency of Breakdown for Fixed Parts in Travelling Grate

For years 2008 to 2010, it can be observed that the Mean Frequency of Breakdown of different constituent

parts for the fixed parts of the travelling grate is almost the same. This implies that spare parts for these

constituent parts should be available each year.

81

6.5.3.5 Pareto Analysis for whole Travelling Grate

Failures in 2008 2 2 1 1 1 1 1 1 0 0124 0 0 0 0 0 036 12 3 3 3 3 2

Percent 1 1 1 1 1 1 1 1 0 063 0 0 0 0 0 018 6 2 2 2 2 1

Cum % 96 97 97 98 98 99 9910010010063 10010010010010010082 88 89 91 92 94 95

Travelling grate chain parts

moto

r windings

mo to

r sh

aft

mot

or fus

e

mo to

r co

ntac

tor

grate sh

aft

grate sha

ft

gearbo

x sh

aft

gear

box be

aring

side rails

mo to

r relay

motor

Bea

ring

hanging metal p

late

Grate cha

in

gear

box ge

ar

spro

cket

sliding

plates

desla

gge

r

link

rod sp

acer

end fo

ot block

conn

ectin

g rod

Bearin

g h

ousing

link r

ods

gra

te b

ars su

ppor

t

Grate bar

s

200

150

100

50

0

100

80

60

40

20

0

Failu

res in

20

08

Pe

rce

nt

Pareto Chart of Travelling grate chain parts

Figure 6.5-22 Pareto for whole Travelling Grate for the year 2008

Failures in 2009 2 2 1 1 1 1 1 1 0 0180 0 0 0 0 0 018 6 3 3 3 3 2

Percent 1 1 0 0 0 0 0 0 0 079 0 0 0 0 0 08 3 1 1 1 1 1

Cum % 96 97 98 98 99 9910010010010079 10010010010010010087 89 91 92 93 95 96


moto

r winding

s

mo to

r sh

aft

motor re

lay

mo to

r fuse

motor

contac

tor

moto r

Bear

ing

gearbo

x g ea

r

gearbox

bea

ring

side ra

ils

hanging metal p

late

grate sh

aft

grate sha

ft

gearbo

x sh

aft

Bear

ing hou

sing

link ro

d sp

acer

Grate cha

in

end fo

ot b

lock

spro

cket

sliding

plates

d eslagge

r

conn

ectin

g ro d

link

rods

gra

te b

ars su

ppo

rt

Grate bar

s

250

200

150

100

50

0

100

80

60

40

20

0

Failu

res in

20

09

Pe

rce

nt



82

Failures in 2010 1 1 1 1 1 1 1 1 1 0350 0 0 0 0 0 014 8 3 3 2 1 1

Percent 0 0 0 0 0 0 0 0 0 090 0 0 0 0 0 04 2 1 1 1 0 0

Cum % 98 98 98 99 99 99 9910010010090 10010010010010010093 95 96 97 97 97 98


mo to

r sh

aft

motor relay

mot

or fus

e

mo to

r co

ntac

tor

motor

Bea

ring

gearbo

x sh

aft

gear

box ge

ar

sliding

plates

motor windin gs

link

rod sp

acer

grate sh

aft

Gra

te cha

in

grate sha

ft

gear

box be

aring

end fo

ot block

d eslagge

r

conn

ectin

g rod

Bearing hou

sing

side ra

ils

spro

cket

hanging m

etal plate

link r

ods

gra

te b

ars su

ppor

t

Grate bar

s

400

300

200

100

0

100

80

60

40

20

0

Failu

res in

20

10

Pe

rce

nt



mean frequnecy of breakdown 2.0 1.71.7 1.3 1.30.3 0.3 0.3 0.30.3218.0 0.3 0.30.3 0.0 0.00.022.78.7 2.72.3 2.02.02.0

Percent 1 1 1 0 0 0 0 0 0 080 0 0 0 0 0 08 3 1 1 1 1 1

Cum % 97 97 98 99 99 99 99 9910010080 10010010010010010089 92 93 94 95 95 96


moto r

shaft

mo to

r fuse

moto r

con ta

ctor

motor wind in

gs

motor re

lay

mo to

r Be

aring

grate sh

aft

g rate s

haft

gearbo

x sh

aft

gearbo

x ge

ar

gearb

ox bea

ring

side rails

Gra

te cha

in

Bearing hous

ing

hanging m

etal plate

slid in

g plates

link r

od sp

acer

end fo

ot b

lock

desla

gge

r

conn

ectin

g rod

spro

cket

link ro

d s

gra

te b

ars su

ppor

t

Gra

te b

ars

300

250

200

150

100

50

0

100

80

60

40

20

0

me

an

fre

qu

ne

cy

of

bre

ak

do

wn

Pe

rce

nt


Figure 6.5-25 Pareto of Mean Frequency of Breakdown for whole of Travelling Grate

83

The Pareto analysis for the years 2008 to 2010 for the whole Travelling Grate indicates that the failures of the

grate bars account for 80% of the failures.

However, with the help of the second level Pareto performed on the sub parts of the travelling grate, it has

been clearly demonstrated that there are other critical parts that must also be taken into considerations when

analysing the travelling grate breakdown.

6.5.3.6 Pareto Analysis for Coal Feeder

Failures in 2008 0 0 0 0 0 018 2 1 1 1 1 0 0

Percent 0 0 0 0 0 075 8 4 4 4 4 0 0

Cum % 100 100 100 100 100 10075 83 88 92 96 100 100 100

Feeder parts

projec

tion plate

Motor w

inding

s

Motor sha

ft

Motor con

tactor

Motor Bea

ring

Gear

box sh

aft

Gearbo

x ge

ar

Gearbo

x be

aring

trans

miss

ion ch

ain

Motor re

lay

Motor

fuse

metal cha

ins

bearings

metal bars of belt

25

20

15

10

5

0

100

80

60

40

20

0

Failu

res in

20

08

Pe

rce

nt

Pareto Chart of Feeder parts

Figure 6.5-26 Pareto for Coal Feeder for the year 2008

84

Failures in 2009 0 0 0 0 0 036 3 3 1 0 0 0 0

Percent 0 0 0 0 0 084 7 7 2 0 0 0 0

Cum % 100 100 100 100 100 10084 91 98 100 100 100 100 100

Feeder parts

trans

miss

ion ch

ain

projec

tion plate

Motor w

inding

s

Motor sha

ft

Motor

relay

Motor fu

se

Motor

con

tactor

Motor Bea

ring

Gearbo

x sh

aft

Gearbo

x ge

ar

Gearb

ox bea

ring

metal cha

ins

bearings

metal bar

s of belt

40

30

20

10

0

100

80

60

40

20

0

Failu

res in

20

09

Pe

rce

nt



Failures in 2010 0 0 0 0 0 025 3 1 1 1 1 0 0

Percent 0 0 0 0 0 078 9 3 3 3 3 0 0

Cum % 100 100 100 100 100 10078 88 91 94 97 100 100 100

Feeder parts

Motor

winding

s

Motor sha

ft

Motor re

lay

Motor

con

tactor

Motor Bea

ring

Gear

box sh

aft

Gearbo

x ge

ar

Gearbo

x be

aring

trans

miss

ion ch

ain

Motor fu

se

metal cha

ins

bearings

projec

tion plate

metal bars of belt

35

30

25

20

15

10

5

0

100

80

60

40

20

0

Failu

res in

20

10

Pe

rce

nt



85

mean frequnecy of breakdown 0.000.000.000.000.000.0026.332.001.671.000.670.670.330.33

Percent 0 0 0 0 0 080 6 5 3 2 2 1 1

Cum % 10010010010010010080 86 91 94 96 98 99100

Feeder parts

Motor w

inding

s

Motor sha

ft

Motor

con

tactor

Motor

Bea

ring

Gear

box sh

aft

Gearbo

x ge

ar

Motor

relay

Gearbox

bea

ring

trans

miss

ion ch

ain

Motor fu

se

projec

tion plate

metal cha

ins

bearings

metal bars of belt

35

30

25

20

15

10

5

0

100

80

60

40

20

0

me

an

fre

qu

ne

cy

of

bre

akd

ow

n

Pe

rce

nt


Figure 6.5-29 Pareto of Mean Frequency of Breakdown for Coal Feeder

From the Pareto analysis and from Figure 6.5-30 it can be seen that the metal bars of the belts accounts for

80% of failures of the feeder for the year 2008 to 2010.

Figure 6.5-30 Pie Chart representing Mean Frequency of Breakdown for Coal Feeder

86

6.5.3.7 Pareto Analysis for Coal Spreader

Failures in 2008 02 1 1 1 0 0 0 0

Percent 0.040.0 20.0 20.0 20.0 0.0 0.0 0.0 0.0

Cum % 100.040.0 60.0 80.0 100.0 100.0 100.0 100.0 100.0

Spreader parts

tran

smiss

ion be

lt

Motor

winding

s

Motor

sha

ft

Motor con

tactor

Motor

Bea

ring

Motor relay

Motor fu

se

blad

e cy

linde

r

bearings

5

4

3

2

1

0

100

80

60

40

20

0

Failu

res in

20

08

Pe

rce

nt

Pareto Chart of Spreader parts

Figure 6.5-31 Pareto for Coal Spreader for the year 2008

The Pareto analysis for the year 2008 shows that 80% of the failures of the spreader are due to the failure of

the bearings, blade cylinders and the motor fuse.

Failures in 2009 04 3 2 1 1 0 0 0

Percent 0.036.4 27.3 18.2 9.1 9.1 0.0 0.0 0.0

Cum % 100.036.4 63.6 81.8 90.9 100.0100.0 100.0100.0

Spreader parts

Motor w

inding

s

Motor sha

ft

Motor

con

tactor

Motor

Bea

ring

Motor relay

Motor

fuse

blad

e cy

linde

r

bear

ings

tran

smiss

ion be

lt

12

10

8

6

4

2

0

100

80

60

40

20

0

Failu

res in 2

009

Perc

ent



87

For the year 2009 the Pareto indicates that the transmission belt, bearings and the blade cylinder account for

more than 80% of the failure of the spreader.

Failures in 2010 02 2 1 1 0 0 0 0

Percent 0.033.3 33.3 16.7 16.7 0.0 0.0 0.0 0.0

Cum % 100.033.3 66.7 83.3 100.0 100.0 100.0 100.0 100.0

Spreader parts

Motor

winding

s

Motor sha

ft

Motor

relay

Motor con

tactor

Motor

Bea

ring

Motofus

e

blad

e cy

linde

r

tran

smiss

ion be

lt

bearings

6

5

4

3

2

1

0

100

80

60

40

20

0

Failu

res in 2

010

Perc

ent



The Pareto for the year 2010 is similar to that of 2008, that is, the bearings, transmission belt and the blade

cylinder are identified as the parts that failed the most on the spreader.

mean frequnecy of breakdown 0.0002.3332.0001.3331.0000.6670.0000.0000.000

Percent 0.031.8 27.3 18.2 13.6 9.1 0.0 0.0 0.0

Cum % 100.031.8 59.1 77.3 90.9100.0100.0100.0100.0

Spreader parts

Motor w

inding

s

Motor

sha

ft

Motor con

tactor

Motor Bea

ring

Motor relay

Motofus

e

blad

e cyl in

der

tran

smiss

ion be

lt

bearings

8

7

6

5

4

3

2

1

0

100

80

60

40

20

0mean fre

qunecy o

f bre

akdow

n

Perc

ent


Figure 6.5-34 Pareto of Mean Frequency of Breakdown for Coal Spreader

88

Figure 6.5-35 Pie Chart representing Mean Frequency of Breakdown for Coal Spreader

Therefore, the Pareto analysis of the mean breakdown frequency for 2008 to 2010 also points out that the

bearings, the transmission belt and the blade cylinders are accountable to 80% of the failure of the spreaders.

89

7 Setting Up of Maintenance Strategy and Guidelines for OTEOSAL

7.1 Company’s expectations from the Maintenance Department OTEOSAL is projecting to be an ISO9001 certified company in 2012 so as to be able to implement Quality

Management Systems at the power plant. Therefore it is of upmost importance to set up a maintenance

strategy to be in line with the quality policy the company wants to put forward.

After interviewing the maintenance staff and going through the maintenance procedures that are already in

place, it has been observed that overall the power plant has a software for maintenance management

including work order generation, data recording of incidents and other useful functions that maintenance

software offers. But till now, maintenance procedures were not carried out to standard maintenance

management.

As it is well known, maintenance, as any other function in a power plant, requires a suitable information flow

between the different points of the internal organization and with the rest of the functional and

organizational units of the plant, in order to fulfill its objectives of reaching an acceptable performance.

The maintenance strategy and guidelines that will be proposed for OTEOSAL will be divided into normative

and informative parts. The British Standard, BS EN13460:2002, 2002 “Maintenance – Documents for

Maintenance” has been analyzed and adapted for OTEOSAL power plant.

The normative part concerns the first part of the life cycle of the equipment to be maintained, namely the

preparatory phase. When an equipment is acquired, the maintenance department requires certain

documentation to maintain and operate the equipment properly. The appropriate documentation has to be

provided by the supplier of this equipment.

The informative part concerns the operational phase of the life cycle of the equipment to be maintained. The

informative part, in addition to the normative part, develops the documentation for maintenance having

regard to the maintenance function as a part of the quality system of the company. (BS EN13460:2002, 2002)

The strategy adopted for OTEOSAL specifies general guidelines for:

• The technical documentation to be supplied with an equipment, at the latest before it is ready

to be put into service, in order to support its maintenance; see Table 7.1-1;

• The documentation of information to be established within the operational phase of an

equipment, in order to support the maintenance requirements; see Table 7.2-1, Figure 7.1-1 and Figure

7.2-2.

90

Table 7.1—1 Shows guidelines in the normative part for the preparatory phase. (BS EN13460:2002, 2002)

Guideline Name Guideline Description Information Items

Technical data

Manufacturer’s specification of the item.

Manufacturer

Date of manufacture

Model/type/serial number

Size, Weight, & Capacity

Power and service requirements

Operation

manual

Technical instructions to reach proper

equipment function and performance

according to its technical specifications and

safety conditions.

Model/type

Manual date (edition)

Technical details of the equipment

Functional description of the equipment

Procedures for:

-commissioning / starting-

-warming-up;

-steady operation;

-controlled shutdown

Operation limitations/Precautions

Laws and regulations to be abided to.

Maintenance

manual

Technical instructions intended to preserve

equipment in, or restore it to, a state in which

it can perform a required function.

Model/type

Manual date (edition)

Technical details of the equipment

Preventive maintenance operations/actions:

— inspections; calibration/adjustment; parts replacements; lubrication

Procedures for:

— troubleshooting; dismantling/assembly; repair;

& adjustment

Cause and effect diagrams

Special tools required

Spare parts recommendations

Safety requirements

91


Components list

Comprehensive list of equipments which

constitute part of another one.

Model/type/serial number

Part number

Part description

Part quantity.

Arrangements

Drawing showing replacement components

layout for an equipment.

Drawing code and identification

Date (issue/revision)

Dimensions

Equipment components location and

identification

Necessary space for disassembly and

maintenance

Relevant information about connection details

When necessary: lifting lugs, inspection hatches, ladders, etc.

Detail

Drawing with part list to ensure dismantling,

repair and assembly of items.

Code identifying the equipment which is detailed

Assembly drawing showing parts positions

Identification of each part of the drawing:

— part number;

— description;

— number of units.

Any other relevant information for assembly and disassembly operations.

Lubrication map

Drawing showing position of each equipment

lubrication point, with lubrication data and

specifications.

Map code and identification


Item identification (code and name)

Lubrication point position (drawing)

Lubrication point identification

Lubrication point description

Lubricant specifications

Routing, when necessary.

92


Single line

diagram

Overall power distribution diagram:

— electrical;

— pneumatic;

— hydraulic.

This kind of diagram includes switchboard circuits.

Diagram code and identification


Power distribution units (generators, transformers, switch gears, rectifiers, etc)

End consumers (for high voltage switchgears only)

Earthing lines for systems, equipment and cables (general earthing principles will be included).

Logic diagram

System control diagram to clarify the overall

system logic.



Logic functions (symbols, internetworking and control flow)

Modes of operation (e.g. starting, shutdown, alarm, trip functions).

Circuit diagram

Overall feeder and control circuits diagram.



All internal connections for control, alarms,

protection, interlocks, trip functions, monitoring, etc

Settings of timers, thermal overload and protection relays

Wire and cable numbers

Terminal numbers

Component list for in line, control and protection systems

Switch gear/board location code

Consumer/supplier location code

Termination details and type of external signal (fire and gas trip signal, etc.)

Power and current rating

Reference drawings.

Location

Drawing showing the position of all field

equipments within the considered area



Area identification (code and name)

Equipment identification and location code

Equipment drawings or symbols, without dimensional details.

93


Pipe and

instrument

diagram

Overall fluid conduction (air, steam, oil, fuel)

and control diagram.



All internal connections for control, alarms,

protection, interlocks, trip functions, monitoring

Pipe numbers

Valves location code

Terminal numbers

Component list for in line control and protection

systems

Consumer/supplier location code

Termination details and type of external signal

(Color, fire and gas trip signal)

Pressure, flow and temperature rating

Reference drawings.

Layout

Drawing showing all areas of the power plant.



Plant name (and code, when necessary)

Areas: relative position, dimensions, names and codes.

Test program

report

Commissioning report which demonstrates

that an item is in compliance with

specifications.

Manufacturer with Model / type / serial number

Date of commissioning

Warranty period and conditions

Fulfillment of the technical details:

— size (when required);

— weight(when required);

— power and Service Requirements

— capacity/performance (output);

Assembly details and operation data.

Certificates

Specific safety and statutory regulations

certificates for items (lifting equipment, steam

boilers, pressure vessels, etc).

Manufacturer with Model/type/serial number

Date of manufacture

Subject to be certified

Date of certificate

Certification body/office and signature/stamp.

94

Table 7.1—2 Shows guidelines / documents needed within the operational phase of equipment. (BS

EN13460:2002, 2002)

Guideline/Document Name Document Description Information Items

D1

Document index

Relevant aspects concerning the

issue of each maintenance

document.

Document number

Document title

Document originator (design, manufacturer, operation, maintenance, etc.)

D2

Equipment basic data

Equipment basic information

coming from either the

preparatory or the operational

phase. This information is related

to technical, contractual,

administrative, locational and

operational aspects of an

equipment, in order to define it

within the company.

Location code

Equipment name

Acquisition price of the equipment

Manufacturer/Model/type/serial number

Date of manufacture/Date of installation

Warranty period

Responsible maintenance department

Standard estimated maintenance time

(preventive and corrective)

D3

Equipment history record of

maintenance operations

List of work orders of a

particular equipment.

Equipment code and name

Date (issue)

List of work orders chronologically ordered

including:

— number

— date

— complaint/cause

— failing part

— running hours of the item

— registration/open/closure dates

— cost of job covered by the work order

D4 Work order Main document to release, to

follow and to manage each

maintenance operation.

The format will be based on the software that the power plant already possesses.

95


D5

Spare parts cross reference list

Catalogue of spare parts and

articles stored

Article code, Name & Description

Stock location

Main supplier, Lead time & Price

Unit of measure & Unit of purchase

Minimum level & Order quantity

Supplier article code

D6

Cause and effect diagram

Diagram showing, by order of

importance, the different causes

which produce a given failure for

a particular equipment.

Effect description and code

Serial number/location codes

Diagram date (issue date)

Period of time analyzed

List of causes in descendent order, including

for each cause:

— cause description

— relative cause importance % (in cost, downtime, number of failures, etc.)

— total importance (cost or downtime or number of failures produced, etc.)

D7

Parameter history record

Set of values given by any

equipment inspected/ monitored

parameter during a certain period

of time.

Item code and name

Parameter description and measure units

Measurement point identification

Date (issue)

Period of time analyzed (since/to)

For each record:

— time

— parameter value

— measurement point identification

Cross-reference to technical procedure

D8 MTBF-MTTR control chart Statistical information document.

Contains the referred values for

equipment considered of major

interest

Item code and Identification

Date(issue)

Cause of failure analyzed and code

MTTR — MTBF

96


D9

Planning sheet

List of work orders according to

a given priority

Date (issue)

Item code and identification

Planning period (from/to)

List of work orders sorted including:

— number

— expected date

— complaint

— item (lower level)

D10 Scheduling sheet Work orders planning and time

schedule assignment for a given

period. It is obtained by

assigning the available resources

to the work orders backlog.

Date (issue)

Equipment code and identification

Planning period (since/to)

List of work orders sorted including:

— number

— start date

— due time –complaint

— resources required by the work order

D11 Production planning Planning of the use of

production resources

(installations, personnel),

defining availability window for

maintenance operations implying

complete or partial shutdown.

Annual production program

Monthly production program

Weekly/daily production program

D12

Maintenance cost history record

Maintenance expenses classified

according to the maintenance for

a given period of time.

Date issued

Period of time analyzed (since/to)

97


D13

Management reviews of

maintenance quality goals and

policies

Manual of the company's

maintenance quality policy and

system

General policy

Governing principles

Organization and responsibility

Elements of the maintenance quality system

List of quality-relevant documents

D14 Procedure for maintenance

contract

Check list of points to be verified

when reviewing a contract.

Company's contracting policy.

D15

Procedure to review causes of

critical failures

Instructions regarding the

periodic review of causes for

critical failures.

History recording of critical failures per machine/element.

Failure cost.

Causes of failure.

Work carried out.

D16 Procedures to evaluate

maintenance operations time for

critical failures (MTTR, MTTM)

Description of work

measurement techniques to be

used.

History recording of critical failures per machine/element.

Time between failures

Time to repair each failure.

D17 Acceptable maintenance

suppliers

List of qualified maintenance

suppliers.

Address, Ownership, Size, Occupancy

Financial Situation

References & Expertise

Proximity

D18

Procedure to issue maintenance

items purchase orders

Instructions for technical

purchasing.

Definitions

Purchase requisitions

Offer requests

Offer selection

Purchase orders

Technical and general specifications

Commercial and legal terms

Payment conditions

98


D19

Maintenance equipments

purchase orders

Written request to make or

supply maintenance items.

Order number & Date

For each maintenance item:

— equipment code

— equipment description/specifications

— quantity

— price

Destination (store or direct use)

Lead time & Commercial terms.

D20

Procedure to verify purchased

items

List of criteria to be checked and

specification of the verification

procedure.

Purchase orders

Supplier’s catalogue

Machine card

Maintenance instructions

Catalogue of articles stored.

D21

Procedure to control

maintenance activities

List and form of maintenance

reports

Elements for planning maintenance activities, among others:

Priority assessment backlog

Schedule compliance

Labour efficiency & Material cost

Percent downtime maintenance cost

Recommendations and action plan

D22 Procedures for carrying out the

critical maintenance activities

Guidelines for carrying out

specific maintenance activities

with direct impact on the

production means.

Nature and sequence of sub activities

Precautions to be taken

Means

Tools and resources required

Objective to be met.

D23 Procedure for equipments

monitoring (during downtime

and operation)

Guidelines for carrying out

monitoring



Means



99


D24 Procedure to calibrate critical

equipment/apparatus

Guidelines for instruments

calibration.



Means



D25 Procedures to identify

equipment affecting production

mean effectiveness.

Guidelines for analyzing root

causes of effectiveness

abatement in critical equipment.



Means



D26 Critical equipment calibration

records

Register of calibration of

instruments that shows the status

of a production mean, especially

the critical ones.

Test equipment code number

Date and time

Calibration data

Calibration record number

D27 Procedure for preventive and

corrective actions

Maintenance instructions

describing preventive and

corrective actions to be

undertaken.

Asset number and name

Location

Maintenance work description

Standard man-hours required.

D28 Maintenance records control. Logbook of all records. Record maintained

History (date of event and description) of important observations and maintenance job performed.

D29 Internal maintenance audits List of criteria to be checked

indicating the minimum

performance required and results

obtained.

Schedule compliance

Labor efficiency & Material cost

Percent downtime maintenance cost

Recommendations and action plan

D30 Procedure to identify training

requirements.

Action plan with periodic

progress review.

Actions to be taken on the basis of observations and/or audits in the field of personnel training.

100

7.2 Documents for maintenance strategy guidelines and maintenance quality

system In order to fulfill the quality policy which OTEOSAL wants to put forward as specified in ISO 9001, this

thesis, based on the British Standard, BS EN13460:2002, 2002 “Maintenance – Documents for

Maintenance”, provides a list that defines the adequate set of documents that support the information needed

to perform the different tasks involved in the maintenance function of the power plant.

From the document BS EN13460:2002, 30 documents including records and procedures (see Table 7.1-2) has

been identified and selected to cover the requirements for the maintenance quality system that best suite

OTEOSAL.

To find out the kind of information necessary to perform the maintenance activities, first of all, all the tasks

have to be studied in detail. The starting point of the analysis to be carried out to obtain the required

documentation of information for maintenance is the “Maintenance workflow” (see Figure 7.2-1). At the

power plant, the management of the maintenance department can make use of the “Maintenance workflow”

in order to realize the documents of information that they will need for setting up a standard maintenance

strategy.

A combination of the 30 documents (from Table 7.1-2 – D1 to D30) and the use of the chart found in figure

7.2 will bring as end product a standard maintenance policy as part of ISO 9001.

The correct fulfillment of each one of the maintenance workflow steps requires the supply of certain

information, contained in the INPUT DOCUMENTS (see Figure 7.2-2). Each step of the maintenance

workflow generates information, contained in the OUTPUT DOCUMENTS (see Figure 7.2-2), which will be

necessary to carry out other steps.

Each step is detailed for easy comprehension of the information which is required and generated as seen in

figure 7.2-2 (BS EN13460:2002, 2002)

101

Figure 7.2-1 The Maintenance Workflow (BS EN13460:2002, 2002)

STUDY DEFINE

PREVENTIVE CORRECTIVE

MAINTENANCE OPERATIONS

WORK PLANNING

RELEASE – ASSIGNMENT OF THE WORK ORDER

CARRY OUT THE WORK

CLOSURE OF THE WORK ORDER

PRODUCTION OF REPORTS

REPORTS ANALYSIS

WORK SCHEDULING

102

Continued

Figure 7.2-2 Input/Output Documents (BS EN13460:2002, 2002)

Study – Define

Maintenance Activities

• Preventive

o Spare Parts

o Estimated Resources

• Corrective

Work Planning

Ordered list of works according to a

priority and for a given period

Work Schedule

Date to start and finish each

maintenance work.

Resources assignation

Work Order Release and Assignment

Input Documents Maintenance Activities Output Documents

-Documents required from

the preparatory phase

-Feedback Documents

-Procedures

-Other Plant Specific

Documentation; E.g: D13 &

D29 (see Table 7.2)

-Preventive Plan (See Table 7.2: D27)

-Procedures

-Spare Part List (D5)

-Required Resources

-W.O Request (D4)

-Production Planning (D11)

-Procedures

-Feedback Documents

Planning Sheet (D9)

-Planning Sheet (D9)

-Spare Parts in Stock

-Tools

-Resources

-Man Power Resources (D30)

Scheduling Sheet (D10)

-Scheduling Sheet (D10)

-Spare Parts in Stock

-Tools

-Resources

-Man Power Resources (D30)

Work Order (D4)

103

Figure 7.2-2 Input/Output Documents (BS EN13460:2002, 2002) Continued

Carry Out the Work

Closure of the Work Order

Production of Reports

Reports Analysis

Input Documents Maintenance Activities Output Documents -Documents required from

the preparatory phase

-Procedures

-Work Order (D4)

-Spare Part List (D5)

-Tools

-Feedback Documents

-Work Order (D4)

-Procedures

History Records (D3 & D7)

-History Records

-Procedures

Records (Reports) E.g: D12

Records (Reports)

Feedback Documents

Improvement Proposal

104

8 Discussion and Conclusion

8.1 Overview From the data in Table 1.1, it can be seen that the total maintenance cost for the power plant is increasing

each year and therefore this tends to make the management of OTEOSAL to view maintenance as a cost

center when it is actually an important economic activity to the organization. This view can change if

maintenance activities are optimized so that only the right activities are done by the right personnel at the

right time using the right tools, resources and procedures. The management strategies and methods are useful

in optimizing maintenance through proper planning and execution of maintenance tasks. The fact that

OTEOSAL is operated as a baseload power plant puts high demand on plant maintenance teams to ensure

high availability, reliability and safety of the plant.

8.2 Maintenance and management methods The literature review part has showed that the RCM method is suitable for determining and optimizing

maintenance strategies for newly installed equipment, determining PM procedures for complex systems and

for analyzing and cutting down excessive maintenance costs. Also when new design or equipment different

from the existing ones are brought forward, new maintenance procedures must be developed for the new

equipment or design. Another case where RCM is useful is when the plant has high down time. An RCM

method can be used to analyze the maintenance needs for the new plant by doing FMEA analysis and

develop maintenance procedures that will meet the requirements at the same time fitting into the existing

maintenance programs.

From the chapter Literature Review, it can be observed that there are many maintenance problems in the

power plant that can be addressed by lean method. They include waste of manpower when maintenance staff

are used to do non-maintenance tasks, long delays of work due to lack of spare parts or waiting for people,

maintenance tasks taking long because of delays of transport, spare parts, waiting for the equipment to be

stopped and isolated or waiting for the people. Lean can be used to identify man hours wasted because of

unnecessary human movements for example to pick tools or to go to the stores and return back. When these

wasted man-hours are eliminated, manpower costs can be reduced significantly and these resources can be

used for other more important works.

8.3 Maintenance Strategy based on FTA and FMEA It has been seen in the introductory chapter that the cost of maintenance for the company is weighing a lot

on the budget and this is mainly due to a lack of knowledge of the different failures that can occur on

particular equipments and their effect and criticality on the different systems.

105

The power plant has been divided into 10 major parts composing of the main equipments and Fault Tree

Analysis has been performed for these equipments where the people of the maintenance department can have

an overview of the different failures that can occur. The analysis was followed by a FMEA and has showed

that many machines are critical and can cause plant failure. So, it is unwise to practice one maintenance

strategy on the machine. It is preferable to perform a combination of the maintenance task because a machine

can have many types of causes related to its failure. Also greater significance was given to detection and

severity indices as these components are very critical for the plant. Subsequently, appropriate maintenance

strategies were suggested as listed in Tables 5.6 and A.3.

The maintenance methods of PM, CBM and CM have their strengths and weaknesses and suitability. CBM is

presented in many literatures as the most optimum maintenance method because the maintenance tasks are

based on the measured need of the equipment. The cost of CBM tools is high. PM is the most widely used

method but is only suitable where failure is age related. Most failures are not age related. CM is most

appropriate where failure has little consequences.

It can be said that to address the high downtime, RCM method will employ the root cause analysis, Fault Tree

Analysis and FMEA to identify the causes of the down time. Hence, by identifying and solving the root

causes of downtime, down time costs will be greatly reduced.

8.4 Quantitative Analysis of FTA and Pareto Analysis FTA and FMEA allow identifying critical equipments at the power plant and the Grate Stocker, one of the

most important and critical equipment for the plant was selected to perform a Quantitative Analysis of the

FTAs. The MTTF (Mean Time to Failure) and Failure Rates as well as the probability of failure and reliability

of the Grate Stocker have been calculated from the Quantitative Analysis. The probability of failure for the

Grate Stocker is seen to be 0.98 and has reliability as low as 0.02.

The Grate Stocker is composed of the Travelling Grate, the Coal Feeders and Coal Spreaders and Pareto

Analysis has revealed for the last 3 years the parts of the different equipments that are more susceptible to

failure. Also the Mean Frequency of Breakdown for the different parts was presented.

With Quantitative Analysis of FTA and Pareto Analysis, equipments needing more attention are identified

and particular parts of equipment that are prone to breakdown are also identified. As can be seen in Figure

1.2, the value of the spare parts store is seen to rise because many spare parts are bought at random in fear of

having a shut down due to unavailability of spare parts. But these excess expenses on unnecessary spare parts

prevent the power plant from using wisely its finance and also contribute to a loss in profitability. All this is

due to a lack of a good maintenance strategy and knowledge of the criticalities and failure rates of particular

106

equipments. Quantitative Analysis of FTA and Pareto Analysis will allow having the right quantity of spare

parts at the right time without overstocking.

8.5 Quality Management System Interviews and observations at OTEOSAL have revealed that a number of concepts in the conventional

management are already being practiced under the classical concepts. All that is lacking is formalizing and

documenting the processes as required in the conventional methods. Selective application of the formal

methods would be very cost effective and beneficial for the company.

Fortunately OTEOSAL is projecting to be an ISO9001 certified company in 2012 so as to be able to

implement Quality Management Systems at the power plant. Therefore it was of upmost importance to set up

a maintenance strategy to be in line with the quality policy the company wants to put forward.

The British Standard, BS EN13460:2002, 2002 “Maintenance – Documents for Maintenance” has been

analyzed and adapted for OTEOSAL power plant.

8.6 Conclusion Maintenance costs at OTEOSAL contribute a significant part of the unit cost of electrical energy produced

and affect the profitability of the power plant. Hence it is necessary and crucial to minimize maintenance

costs by optimizing maintenance processes to make the plant run economically. This is achieved by

optimizing maintenance methods. Combining different maintenance and management methods and strategies

based on FTA, FMEA and Pareto Analysis and all these well formalized and documented according to

International Standard will certainly allow the power plant to gain a lot like availability, reliability and even

financially from maintenance and also will make OTEOSAL ready for new challenges appearing in the energy

sector in Mauritius.

107

9 REFERENCES

British Standard, BS EN 13460:2002, Maintenance —Documents for maintenance, BSI, London.

Balbir S. Dhillon - 1999 - Business & Economics [Online], Available at:

books.google.com/booksisbn=088415257X... (Accessed August 2011)

Clety Kwambai Bore, 2008: Analysis of Management Methods and Application to Maintenance of Geothermal Power

Plants. MSc Thesis. University of Iceland. 2008.

Howard C. Cooper, 2002: Lean maintenance for lean manufacturing; A white paper by Amemco company Infor

Global Solutions GmbH, 2007: Lean maintenance best practices to turn asset management into a profit-

centre.

Jerry Kilpatrick, 2003: Lean Principles. Utah manufacturing extension partnership.

Jim August, 1999: Applied Reliability Centered Maintenance. Pennwell publishers, 500pp.

Kelly, A. 1997, Maintenance Strategy: Business Centred Maintenance, Oxford Butterworth Heinemann

Marvin Rausand and Arnljot Heyland, 2004. In SYSTEM RELIABILITY THEORY. 2nd ed. John Wiley

& Sons, Inc., Hoboken, New Jersey. p.160.

Michael V Brown, 2003: Building a PM program brick by brick, new standard institute Inc publications.

http://www.newstandardinstitute.com

Mobley, R.K., 2002, Introduction to Preventive Maintenance, 2nd ed, Butterworth Heinemann, Elsevier, 2002.

Pp4.

Mobley, R.K, Higgins, R.L., Darrin, J., Wikoff, D.J., 2008, Maintenance Engineering Handbook, 7th ed,

McGraw-Hill

Narayan, V., 2004. In Effective maintenance management. New York: Industrial Press Inc. p.33.

Ricky Smith, 2004: What is lean maintenance? Maintenance Technology October 2004, Life Cycle Engineering

Robson Quinello, 2003: Ford Motor Co. Brasil, Maintenance and Six Sigma. Web based article.

Stanley (Stan) T. Grabill, 2001: Sigma Breakthrough Technologies, Inc. Web based article.

http://en.wikipedia.org/wiki/Pareto_analysis (Accessed December 2011)

108

http://www.mt-online.com/component/content/article/187-may2001/643-process-mapping-in-six-

sigma.html and http://www.mt-online.com/component/content/article/188-september2001/655-the-new-

world-of-six-sigma-dont-get-left-behind.html?Itemid=90 (Accessed August 2011)

http://www.mt-online.com/component/content/article/208-november2003/1104-maintenance-and-six-

sigma.html?Itemid=90 (Accessed August 2011)

109

APPENDIX 1 – FTA Diagrams

135

Pump failure

Failure of

non-return

valve at

delivery

Mechanical

seals worn

out

Coupling

problemDrive motor

failure

Bearing

failureOil problem

Due to

misalignment

Filters

blocked due

to debris

Failure of

regulating

valve

Excessive

piping stress

44

136

APPENDIX 2 – FMECA Table

Table A.2: FMECA Table

System Sub-system &

Function


S O D RPN

COAL H

ANDLIN

G P

LAN

T

Vibrating table

[Drive out coal to a conveyor]

Drive motor failure Shutdown Bearing failure 6 1 2 12

Fuse fails 6 1 2 12

Contactor fails 6 1 2 12

Relay fails 6 1 2 12

Winding fails 6 1 2 12

Misalignment due

to coupling

6 1 3 18

Limit switch failure

Low operation Sensor actuation

fails

3 1 1 3

Spring failure Low operation Failure of spring

due to excessive

stress

3 1 1 3

Screener

[separate the coal depend on their sizes]


Fuse fails 6 1 2 12




137

System Sub-system &

Function


S O D RPN

COAL H

ANDLIN

G P

LAN

T

Vibrating table

[Drive out coal to a conveyor]


Fuse fails 6 1 2 12




Misalignment due

to coupling

6 1 3 18


Low operation Sensor actuation

fails

3 1 1 3

Spring failure Low operation Failure of spring

due to excessive

stress

3 1 1 3

Screener

[separate the coal depend on their sizes]


Fuse fails 6 1 2 12




138

System Sub-system &

Function


S O D RPN

COAL H

ANDLIN

G P

LAN

T

Screener

[separate the coal depending on their sizes]

Drive motor failure Shutdown Misalignment due

to coupling

6 1 3 18

Bearing failure Shutdown Overloading 6 1 3 18

Lubrification failure 6 1 3 18

Shock absorber

fails

Low operation Component fails

due to excessive

stress

5 1 2 10

Bolt failure Low operation Bolts broken 3 10 1 30

Loosening of bolts

due to excessive

vibration

3 10 1 30

Screen failure Shutdown Misalignment 5 1 3 15

Conveyor

[Transportation of

coal]

Sensor failure Low operation Jam sensor fails 3 5 2 30

Rotational sensor 3 1 1 3

Bearing failure

Shutdown Overloading 6 1 3 18


139

System Sub-system &

Function


S O D RPN

COA

L H

AN

DLIN

G P

LA

NT

Conveyor

[Transportation of

coal]


Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18

Roller failure Low operation Component fails

due to friction and

wearing

3 2 1 6

Conveyor belt

failure

Shutdown Misalignment of

belt

5 1 3 15

Tearing 6 1 1 6

Failure of joints 3 2 1 6

Gear box failure Shutdown Seals fail 5 1 2 10

Wearing of gear 5 1 2 10

Gear clogged 5 1 2 10

140

System Sub-system &

Function


S O D RPN

CO

AL H

AN

DLIN

G P

LA

NT

Conveyor

[Transportation of

coal]

Gear box failure Shutdown Lubrification failure 5 1 4 20




Crusher

[Reduce the coal in

size between 0-50

mm]

Belt drive failure Low operation Fatigue failure 3 1 1 3

Cracking 3 1 1 3






Crusher teeth

failure

Shutdown Component fails

due to wearing

5 1 1 5

Coupling problem 5 1 3 15

141

System Sub-system &

Function


S O D RPN

CO

AL H

AN

DLIN

G P

LA

NT

Crusher

[Reduce the coal in

size between 0-50

mm]



Sensor failure Low operation Component

defective

3 5 1 15

Crusher clogged Low operation Component fails

due to big

unwanted particles

3 3 2 18

Silo

[Storage of coal]









Fuse fails 6 1 2 12

142

System Sub-system &

Function


S O D RPN

CO

AL H

AN

DLIN

G P

LA

NT

Silo

[Storage of coal]

Drive motor failure Shutdown Contactor fails 6 1 2 12



Misalignment due

to coupling

6 1 3 18

Extracting screw

failure

Shutdown Wearing problem 6 1 1 6

Coupling problem

due to

misalignment

6 1 2 12

Fatigue 6 1 1 6


Sensor failure Low operation Component

defective

3 5 1 15

Shuttle

[Transportation of

coal to the boiler]

Conveyor failure Shutdown Sensor failure 3 5 2 30

Belt failure 6 1 1 6


143

System Sub-system &

Function


S O D RPN

CO

AL H

AN

DLIN

G P

LA

NT

Shuttle

[Transportation of

coal to the boiler]

Conveyor failure Shutdown Roller failure 2 2 1 4

Gear box failure 4 1 4 16

Drive motor failure 4 1 2 8






Roller failure Low operation Wearing of

component

3 2 1 6

Sensor failure Low operation Defective

component

3 5 2 30


Fuse fails 6 1 2 12


144

System Sub-system &

Function


S O D RPN

CO

AL H

AN

DLIN

G P

LA

NT

Shuttle

[Transportation of

coal to the boiler]

Drive motor failure Shutdown Relay fails 6 1 2 12


Misalignment due

to coupling

6 1 3 18

Belt failure Low operation Fatigue 3 6 1 18

Misalignment 3 6 1 18

145

System Sub-system &

Function


S O D RPN

BO

ILER W

ATER A

ND

STEA

M

Primary air

[Regulates the

quantity of air

moving into the

furnace]

Belt failure Low operation Cracking due to

fatigue

3 1 1 3



Damper failure Shutdown Compressed air

failure

7 1 2 14


Pulley failure Low operation Wearing 4 1 2 8

Fatigue 4 1 2 8


Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18

146

System Sub-system &

Function


S O D RPN

BO

ILER W

ATER A

ND

STEA

M

Primary Air

[Regulates the

quantity of air

moving into the

furnace]

Fan failure Shutdown Bearing failure 6 1 4 16

Blade failure 6 1 2 12


Shaft failure 6 1 3 18

Electrical circuit

failure

6 1 4 24

Secondary Air

[Air is injected into

the exhaust gases

to allow for a full

combustion ]




Fatigue 4 1 2 8


failure

7 1 2 14



Fuse fails 6 1 2 12


147

System Sub-system &

Function


S O D RPN

BO

ILER W

ATER A

ND

STEA

M

Secondary Air

[Air is injected into

the exhaust gases

to allow for a full

combustion ]

Drive motor failure Shutdown Relay fails 6 1 2 12


Misalignment due

to coupling failure

6 1 3 18





Electrical circuit

failure

6 1 4 24

Induced Draught

(ID) fan

[Removes flue

gases from the

furnace and forces

the exhaust gas up

the chimney]




failure

7 1 2 14



148

System Sub-system &

Function


S O D RPN

BO

ILER W

ATER A

ND

STEA

M

&

BO

ILER C

OA

L

Induced Draught

(ID) fan

[Removes flue

gases from the

furnace and forces

the exhaust gas up

the chimney]

Drive motor failure Shutdown Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18





Electrical circuit

failure

6 1 4 24

Coal feeder

[Direct coal to the

spreader]




Fuse fails 6 1 2 12

149

System Sub-system &

Function


S O D RPN

BO

ILER W

ATER A

ND

STEA

M

&

BO

ILER C

OA

L

Coal feeder

[Direct coal to the

spreader]

Drive motor failure Shutdown Contactor fails 6 1 2 12



Misalignment due

to coupling failure

6 1 3 18

Transmission chain

failure

Low operation Fatigue failure 3 1 1 3

Metal bar failure Low operation Cracking due to

fatigue

3 10 1 30

Projection plate Low operation Wearing and

cracking

5 1 1 5






Metal chain failure Low operation Fatigue failure 3 3 2 18

150

System Sub-system &

Function


S O D RPN

BO

ILER W

ATER A

ND

STEA

M

&

BO

ILER C

OA

L

Coal spreader

[project coal in the

furnace of the

boiler at an angle]

Blade cylinder

failure

Shutdown Fatigue 6 1 1 6

Rotational

controller failure

Shutdown Component

defective

6 3 1 18



Transmission belt

failure

Low operation Fatigue and

wearing

3 1 1 3


Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18

Reinjection of ash Belt failure

Low operation Cracking due to

fatigue

3 1 1 3

151

System Sub-system &

Function


S O D RPN

BO

ILER W

ATER A

ND

STEAM

&

BO

ILER C

OAL

Reinjection of ash

[Reinsert ash and

unburned coal to

the boiler]




Fatigue 4 1 2 8


Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18





152

System Sub-system &

Function


S O D RPN

BO

ILER W

ATER AN

D S

TEAM

&

BO

ILER C

OAL

Reinjection of ash Fan failure Shutdown Electrical circuit

failure

6 1 4 24

Boiler

[water is

superheated to

produce

superheated

steam]

Regulating valve

failure

Shutdown Component

defective

7 2 1 14

Travelling grate Shutdown Wearing 7 2 1 14

Safety valve failure Shutdown Component broken 7 1 1 7

Furnace tube

failure

Shutdown Fatigue and excess

temperature

7 5 1 35

Economizer failure Shutdown Fatigue and excess

temperature

7 2 1 14

Superheater tube

failure

Shutdown Fatigue and excess

temperature

7 2 1 14

Feedwater pump


performance



Contamination of

oil

5 2 5 50



153

System Sub-system &

Function


S O D RPN

BO

ILER

WA

TER

AN

D S

TEA

M

Feedwater pump

[Pump feedwater

into a steam boiler]

Regulating valve

failure

Shutdown Component

defective

6 1 1 6

Non-return valve

failure

Shutdown Valve defective 6 1 1 6


Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18



Pipe failure Shutdown Excessive stress 6 1 1 6

Filter clogged Low operation Filter blocked due

to debris

5 1 1 5

Mechanical seal Shutdown Wearing 6 1 1 6

154

System Sub-system &

Function


S O D RPN

CO

MPR

ESSE

D A

IR

Compressor

[a mechanical

device that

compresses a gas]


performance



Contamination 5 2 5 50




Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18

Drain failure Low operation Presence of dirt

and algae

3 1 1 3

Air filter clogged Low operation Presence of debris 3 1 1 3

Failure to

discharge air

Low operation Solenoid valve fails 5 1 1 5

155

System Sub-system &

Function


S O D RPN

CO

MPR

ESSED

AIR

Compressor

[a mechanical

device that

compresses a gas]





Electrical circuit

failure

6 1 4 24

Radiator failure Low operation Excessive

temperature

5 1 1 5

156

System Sub-system &

Function


S O D RPN

RA

W W

ATER P

LA

NT

Clarifier

[Proper filtering of

water]

Rotating scraper

failure

Shutdown Fatigue 6 1 1 6


Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18






Tank failure Shutdown Tank clogged due

to debris

6 1` 1 6

Pump Valve failure Low operation Component fails 4 1 1 4

157

System Sub-system &

Function


S O D RPN

RA

W W

ATER P

LA

NT

Pump

[used to move

water through a

piping system]


performance


Contamination of

oil

5 2 5 50





Fuse fails 6 1 2 12







Pipe failure

Shutdown Excessive stress 6 1 1 6

158

System Sub-system &

Function


S O D RPN

CO

OLIN

G T

OW

ER

Pump Impeller Shutdown Fatigue 5 2 1 10

Cooling tower

[A heat rejection

device, which

extracts waste

heat to the

atmosphere

though the cooling

of a water stream

to a lower

temperature]

Pump failure Shutdown Lubrification failure 5 1 4 20



Pipe failure 6 1 1 6

Filter clogged 5 1 1 5

Wearing of

mechanical seal

5 1 1 5

Pipe failure Shutdown Leakage 6 1 1 6

Fatigue 6 1 1 6

Gear box failure

Shutdown Seals fail 5 1 2 10





159

System Sub-system &

Function


S O D RPN

CO

OLIN

G T

OW

ER

Cooling tower

[A heat rejection

device, which

extracts waste

heat to the

atmosphere

though the cooling

of a water stream

to a lower

temperature]


Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18




Electrical circuit 6 1 3 18

Gear Box 6 1 4 24

Sand filter

[For water

purification]

Pressure vessel

failure

Shutdown Corrosion 6 3 1 18

Valve failure Low operation Component

defective

4 3 1 12

160

System Sub-system &

Function


S O D RPN

DEM

INERA

LIS

ED

WA

TER P

LA

NT

Pneumatic valve

[converting air

pressure into linear

or rotary motion]

Compressed air

failure

Shutdown Lubrification failure 6 1 2 12

Drain failure 3 1 1 3

Air filter clogged 3 1 1 3

Radiator failure 5 1 1 5


Actuator Low operation Component

defective

4 2 1 8

Sand filter

[For water

purification]

Pressure vessel

failure


Valve failure Component

defective

4 3 1 12

Spray nozzle failure Shutdown Low pressure 6 1 1 6

Carbon filter

[Remove

impurities and

contaminants ]

Pressure vessel

failure



defective

4 3 1 12

Pump

Valve failure Low operation Component fails 4 1 1 4

Impeller Shutdown Fatigue 5 2 1 10

161

System Sub-system &

Function


S O D RPN

DEM

INERA

LIS

ED

WA

TER P

LA

NT

Pump

[used to move

water through a

piping system]


performance



Contamination 5 2 5 50




Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18




Filter clogged Low operation Due to debris 4 1 1 4

162

System Sub-system &

Function


S O D RPN

STEA

M

Turbine

[rotary engine that

extracts energy

from steam flow

and converts it into

useful work]

Very low lube oil

header pressure

Shutdown Leakage 7 1 4 28


Pump failure 7 1 4 28

Filter clogged 7 1 4 28


Very low

temperature steam

inlet

Shutdown Boiler failure 7 1 4 28

Very high steam

exhaust pressure

Shutdown Ejector system

failure

7 1 4 28

Air ingression 7 1 4 28

Condensing system

failure

7 1 4 28

Rotor axial

displacement

Shutdown Excessive load 7 1 4 28

Radial bearing

failure

Shutdown Excessive

temperature

7 1 4 28


163

System Sub-system &

Function


S O D RPN

STEA

M

Turbine

[rotary engine that

extracts energy

from steam flow

and converts it into

useful work]

Journal bearing

failure

Shutdown High pressure 7 1 4 28

Fault with gland

condenser

7 1 4 28

Vacuum failure 7 1 4 28

Excessive

temperature

7 1 4 28

Thrust bearing

failure

Shutdown Overloading 7 1 4 28

Excessive

temperature

7 1 4 28

Coupling defect 7 1 4 28

Reducer

[ Decrease the rpm

of the rotor to

1500]

Gear bearing Shutdown Teeth failure 7 1 4 28


Excessive vibration 7 1 4 28


Radial bearing


164

System Sub-system &

Function


S O D RPN

STEA

M

Reducer

[ Decrease the rpm

of the rotor to

1500]

Radial bearing

Shutdown Excessive

temperature

7 1 4 28

Trust bearing Shutdown Coupling defect 7 1 4 28

Overloading 7 1 4 28

Excessive

temperature

7 1 4 28

Alternator

[converts

mechanical energy

to electrical energy

in the form of

alternating

current]

Cooling air

outlet(cold)

Shutdown Air inlet too cold 7 1 4 28

Cooler clogged 7 1 4 28

Fan failure 7 1 4 28

Generator bearing Shutdown Excessive

temperature

7 1 4 28


Bearing damaged 7 1 4 28

Overloading 7 1 4 28

Excessive vibration 7 1 4 28

Rotor damaged 7 1 4 28

165

System Sub-system &

Function


S O D RPN

STEA

M

Alternator

[[converts

mechanical energy

to electrical energy

in the form of

alternating

current]

Generator winding Shutdown Excessive electric

load

7 1 4 28

Air cooler fault 7 1 4 28

Excessive

temperature

7 1 4 28

Cooling air

outlet(hot)

Shutdown Air inlet too hot 7 1 4 28

Cooler clogged 7 1 4 28

Fan failure 7 1 4 28

166

System Sub-system &

Function


S O D RPN

ASH

HA

ND

LIN

G P

LA

NT

Mechanical dust

collector

[Assemble fly ash

together]

Blade failure Low operation Fatigue 4 4 2 32

Excessive impact of

ash

4 4 2 32

Injection air fan

{Reinsert the fly

ash by a force

driven air]

Blade failure Low operation Fatigue 4 1 3 12


Fuse fails 6 1 2 12




Misalignment due

to coupling failure

6 1 3 18

Booster Screw failure Low operation Wearing 5 1 1 5




167

System Sub-system &

Function


S O D RPN

ASH

HA

ND

LIN

G P

LA

NT

Booster

[Used where high

pressure is

required to force

air so as to allow a

smooth passage of

the ash ]

Belt failure Low operation Fatigue 3 1 1 3





defective

3 1 1 3


performance


Contamination of

oil

5 2 5 50




Silo

[Storage of ash]

Pressure vessel Shutdown

Corrosion

6

1

1

6

Cracking

6

1

1

6

168

System Sub-system &

Function


S O D RPN

ASH

HA

ND

LIN

G P

LA

NT

Silo

[Storage of ash]



Compressed air

failure



Drain failure 5 1 1 5

Air filter clogged 5 1 1 5

Failure to

discharge air

5 1 1 5





Electrical circuit

failure

6 1 4 24

169

System Sub-system &

Function


S O D RPN

ASH

HA

ND

LIN

G P

LA

NT

Electrostatic

precipitator

[uses electrical

force to remove

dirt from flue

gases]

Transformer failure Shutdown Dielectric oil failure 6 1 5 30

Loose connection 5 1 2 10

Electrical

components fail

6 1 4 24


Plate failure Shutdown Misalignment 6 1 1 6

Hammer failure Shutdown Breaking 6 1 2 12

Bolt failure Shutdown Excessive vibration 6 2 3 36

Isolator failure Shutdown Cracking 6 2 1 12

Clogging failure Shutdown Due to dirt 6 2 1 12

Gear box failure Shutdown Bearing failure 5 1 4 20



Seals fail 5 1 2 10


170

APPENDIX 3 – Suggested Maintenance Strategies

Table A.3: Suggested Maintenance Strategies

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Vibrating

table

Drive motor

failure

Relay fails Breakdown Preventive 12

Winding fails Breakdown Preventive 12

Misalignment

due to

coupling

Preventive Preventive 18


Sensor

actuation fails


Spring failure Failure of

spring due to

excessive

stress


Screener

Drive motor

failure

Bearing failure Preventive Preventive 12

Fuse fails Breakdown Preventive 12

Contactor fails Breakdown Preventive 12



Misalignment

due to

coupling


Bearing

failure

Overloading Predictive Predictive 18

Lubrification

failure

Predictive Predictive

18

171

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Screener

Shock

absorber fails

Component

fails due to

excessive

stress


Bolt failure Bolts broken Preventive Preventive 30

Loosening of

bolts due to

excessive

vibration


Screen failure Misalignment Preventive Preventive 15

Conveyor

Sensor failure Jam sensor

fails

Breakdown Preventive 30

Rotational

sensor

Breakdown Breakdown

3

Bearing

failure


Lubrification

failure


Drive motor

failure






Misalignment Preventive Preventive 18

172

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Conveyor

Roller failure Component

fails due to

friction and

wearing

Breakdown

Breakdown

6

Conveyor belt

failure

Misalignment

of belt

Breakdown Preventive

15

Tearing Breakdown Breakdown 6

Failure of

joints


Gear box

failure

Seals fail Preventive Preventive 10

Wearing of

gear


Gear clogged Preventive Preventive 10

Lubrification

failure


Bearing failure Predictive Predictive 20

Bearing

failure


Lubrification

failure


Crusher

Belt drive

failure

Fatigue failure Breakdown Breakdown 3

Cracking Breakdown Breakdown 3

Gear box

failure

Seals fail Preventive Preventive

10

173

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Crusher

Gear box

failure

Wearing of

gear



Lubrification

failure



Crusher teeth

failure

Component

fails due to

wearing

Preventive

Breakdown

5

Coupling

problem


15

Bearing

failure


Lubrification

failure


Sensor failure Component

defective


Crusher

clogged

Component

fails due to

big unwanted

particles


Silo

Bearing

failure


Lubrification

failure


Gear box

failure

Seals fail

Preventive

Preventive

10

174

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Silo

Gear box

failure

Wearing of

gear



Lubrification

failure



Drive motor

failure






Misalignment

due to

coupling


Extracting

screw failure

Wearing

problem

Preventive Breakdown

6

Coupling

problem due

to

misalignment

Preventive

Preventive

12

Fatigue Preventive Breakdown 6


Sensor failure Defective Breakdown Preventive 15

175

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Shuttle

Conveyor

failure

Sensor failure Breakdown Preventive 30

Belt failure Breakdown Breakdown 6


Roller failure Breakdown Breakdown 8

Gear box

failure

Predictive Predictive

16

Drive motor

failure


Gear box

failure


Wearing of

gear



Lubrification

failure



Roller failure Wearing of

component


Sensor failure Defective

component


Drive motor

failure



176

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Shuttle

Drive motor

failure




Misalignment

due to

coupling


Belt failure Fatigue Breakdown Preventive 12

Cracking Breakdown Preventive 12

Primary air

Belt failure Cracking due

to fatigue

Breakdown Breakdown

3

Bearing

failure


Lubrification

failure


Damper

failure

Compressed

air failure



Pulley failure Wearing Breakdown Breakdown 8

Fatigue Breakdown Breakdown 8

Drive motor

failure


Fuse fails


177

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Primary air

Drive motor

failure




Misalignment

due to

coupling

failure


Fan failure Bearing failure Predictive Predictive 16

Blade failure Preventive Preventive 12


Shaft failure Preventive Preventive 18

Electrical

component


Secondary

Air

Bearing

failure


Lubrification

failure




Damper

failure

Compressed

air failure


Bearing failure


178

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Secondary

Air

Drive motor

failure






Misalignment

due to

coupling

failure






Electrical

component


Induced

Draught (ID)

fan

Bearing

failure


Lubrification

failure


Damper

failure

Compressed

air failure


14

Bearing failure

Predictive

Predictive

14

179

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Induced

Draught (ID)

fan

Drive motor

failure






Misalignment

due to

coupling

failure






Electrical

component

failure


Coal feeder

Bearing

failure

Overloading Preventive Preventive 18

Lubrification

failure


Transmission

chain failure

Fatigue failure Breakdown Breakdown 3

Metal bar

failure

Cracking due

to fatigue


180

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Coal feeder

Drive motor

failure






Misalignment

due to

coupling

failure


Projection

plate

Wearing and

cracking


Gear box

failure


Wearing of

gear



Lubrification

failure



Metal chain

failure

Fatigue failure Breakdown Preventive 18

Coal

spreader

Blade cylinder

failure


Transmission

belt failure

Fatigue and

wearing


181

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Coal

spreader

Drive motor

failure






Misalignment

due to

coupling

failure


Bearing

failure

Overloading Preventive Preventive 18

Lubrification

failure


Rotational

controller

failure

Component

defective

Breakdown Preventive

18

Reinjection

of ash

Belt failure

Cracking due

to fatigue

Breakdown

Breakdown 3

Bearing

failure


Lubrification

failure



Fatigue

Breakdown Breakdown

8

182

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Reinjection

of ash

Drive motor

failure






Misalignment

due to

coupling

failure






Electrical

component


Boiler

Regulating

valve failure

Component

defective


Travelling

grate

Wearing Breakdown Preventive 14

Safety valve

failure

Component

broken

Breakdown Breakdown

7

Furnace tube

failure

Fatigue and

temperature


35

183

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Boiler

Economizer

failure

Fatigue and

excess

temperature


Superheated

tube failure

Fatigue and

excess

temperature


Feed water

pump

Lubrification

failure

Oil seal failure Breakdown Preventive 24

Oil tank fails Breakdown Preventive 24

Contamination Predictive Predictive 50

Valve failure Breakdown Preventive 10

Oil filter

failure


Regulating

valve failure

Component

defective


Non-return

valve failure

Valve

defective


Drive motor

failure






Misalignment

due to

coupling


184

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Feed water

pump

Bearing

failure


Lubrification

failure


Fan failure Bearing failure Preventive Preventive 16




Electrical

component


Pipe failure Excessive

stress


Filter clogged Filter blocked

due to debris


Mechanical

seal

Wearing Breakdown Breakdown 6

Compressor

Drive motor

failure






Misalignment

due to

coupling


185

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Compressor

Lubrification

failure



Contamination

of oil



Oil filter

failure


Drain failure Presence of

dirt and algae


Air filter

clogged

Presence of

debris


Failure to

discharge air

Solenoid valve

fails






Electrical

component

failure


Radiator

failure

Excessive

temperature


186

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Clarifier

Rotating

scraper

failure

Fatigue Breakdown

Breakdown

6

Drive motor

failure






Misalignment

due to

coupling


Gear box

failure


Wearing of

gear



Lubrification

failure



Tank failure Tank clogged

due to debris


Pump


fails


Impeller Fatigue Breakdown Preventive 10

187

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Pump

Lubrification

failure


Contamination

of oil



Oil filter

failure



Drive motor

failure






Misalignment

due to

coupling


Bearing

failure


Lubrification

failure


Filter clogged Due to debris Breakdown Breakdown 2


stress


188

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Cooling

tower

Pump failure Lubrification

failure


Drive motor

failure



Pipe failure Breakdown Breakdown 6

Filter clogged Breakdown Breakdown 5

Wearing of

mechanical

seal


Pipe failure Leakage Breakdown Breakdown 6


Gear box

failure


Wearing of

gear



Lubrification

failure






189

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Cooling

tower

Fan failure Electrical

component


18

Gear Box Predictive Predictive 24

Sand filter

Pressure

vessel failure

Corrosion Preventive Preventive 18


defective


Spray nozzle

failure

Low pressure Preventive Breakdown

6

Carbon

filter

Pressure

vessel failure

Corrosion Preventive Preventive 18


defective


Pneumatic

valve

Compressed

air failure

Lubrification

failure


Drain failure Preventive Breakdown 3

Air filter

clogged


Radiator

failure


Drive motor

failure


Actuator

Component

defective

Breakdown

Breakdown

8

190

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Turbine

Very low lube

oil header

pressure

Leakage Predictive Predictive 28


Pump failure Predictive Predictive 28

Filter clogged Predictive Predictive 28

Valve failure Predictive Predictive 28

Very low

temperature

steam inlet

Boiler failure Predictive Predictive 28

Very high

steam

exhaust

pressure

Ejector

system failure


Air ingression Predictive Predictive 28

Condensing

system failure


Rotor axial

displacement

Excessive load Predictive Predictive 28

Radial

bearing

failure

Excessive

temperature


Lubrification

failure


Journal

bearing

failure

High pressure Predictive Predictive 28

Fault with

gland

condenser


191

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Turbine

Journal

bearing

failure

Vacuum

failure


Excessive

temperature


Thrust

bearing

failure


Excessive

temperature


Coupling

defect


Reducer

Gear bearing Teeth failure Predictive Predictive 28


Excessive

vibration


Shaft failure Predictive Predictive 28

Radial

bearing

Lubrification

failure


Excessive

temperature


Trust bearing Coupling

defect



Excessive

temperature


192

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Alternator

Cooling air

outlet(cold)

Air inlet too

cold


Cooler clogged Predictive Predictive 28

Fan failure Predictive Predictive 28

Generator

bearing

Excessive

temperature


Misalignment Predictive Predictive 28

Bearing

damaged



Excessive

vibration


Rotor

damaged


Generator

winding

Excessive

electric load


Air cooler fault Predictive Predictive 28

Excessive

temperature


Cooling air

outlet(hot)

Air inlet too

hot


Cooler clogged Predictive Predictive 28

Fan failure Predictive Predictive 28

193

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Mechanical

dust

collector

Blade failure Fatigue Preventive Preventive 32

Excessive

impact of ash


Injection air

fan

Blade failure Fatigue Preventive Preventive 12

Drive motor

failure






Misalignment

due to

coupling

failure


Booster Screw failure Wearing Preventive Breakdown 5

Lubrification

failure




Belt failure

Fatigue Preventive Breakdown 3

Misalignment Preventive Breakdown

2

194

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Booster

Bearing

failure


Lubrification

failure


Lubrification

failure


Contamination

of oil



Oil filter

failure




defective


Silo(Storage

of ash)

Pressure

vessel

Corrosion


6

Cracking


6



stress


Compressed

air failure

Lubrification

failure


Drive motor

failure

Preventive

Preventive 12

195

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Silo(Storage

of ash)

Compressed

air failure

Air filter

clogged


Failure to

discharge air


Drain failure Preventive Breakdown 5





Electrical

component

failure


Electrostatic

precipitator


stress


Plate failure Misalignment Breakdown Breakdown 6

Hammer

failure

Breaking Breakdown Preventive 12

Bolt failure Excessive

vibration


Isolator

failure

Cracking Preventive Preventive

12

Clogging

failure

Due to dirt Preventive Preventive

12

196

Sub-system

Failure mode

Cause of

failure

Actual

Maintenance

Strategies

Suggested

Maintenance

Strategies

RPN

Electrostatic

precipitator

Gear box

failure


Wearing of

gear


Gear clogged Breakdown Preventive 10

Lubrification

failure


Bearing

failure


Transformer

failure

Dielectric oil

failure


Loose

connection


Electrical

components

fail
