metuge okane e. end of course dissertation final revision 2015

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UNIVERSITE DE YAOUNDE I

ECOLE NATIONALE SUPERIEURE

POLYTECHNIQUE

DEPARTEMENT DES GENIES INDUSTRIEL

ET MECANIQUE

UNIVERSITY OF YAOUNDE I

NATIONAL ADVANCED SCHOOL OF

ENGINEERING

DEPARTEMENT OF INDUSTRIAL AND

MECHANICAL ENGINEERING

End of course dissertation

Prepared and presented by

METUGE OKANE ENONGENE

In partial fulfillment for the award of a Masters of Engineering in Industrial

Engineering

Under the supervision of

Dr. Gerald MBOBDA

Eng. FOKO Thierry

Before the jury composed of

President: Pr. OUMAROU Hamandjoda, Associate Professor

Supervisor: Dr. Gerald MBOBDA, Lecturer

Examiner: Dr. ELIME Aimé, Lecturer

Invitee: Eng. FOKO Thierry, Engineer at SONARA

Presented on the…..of July 2015

To my entire family.

Especially my parents;

Mr. and Mrs. OKANE, Mr. and Mrs. NGOME, and Mr. and Mrs.

ORLOH ENONGENE

And my brothers and sisters;

ENONGENE, MUNGE, NGOME, EWANE AND LOMBE

OKANE; LISA TARH, LOMBE, NGOME, EBANGHA AND

ARREY NGOME; DIONE, ADU, LONGE AND ENONGENE-

ETTA ORLOH ENONGENE AND OJONG-OBI

Who have always been there for me .

ANALYSES AND OPTIMISATION OF THE INSTALLATION AND MAINTENANCE OF THE DRUM LIQUID LEVEL MEASUREMENT SYSTEM AT THE SONARA REFINERY

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OBTAINING A MASTERS OF ENGINEERING IN INDUSTRIAL ENGINEERING

I wish to extend my sincere gratitude to the following for their unwavering support during my engineering

training and for the realization and presentation of this thesis:

Pr. OUMAROU Hamandjoda, professor of universities for accepting to preside over this jury;

Dr. MBOBDA Gerald for his academic support and supervision;

Dr. ELIME Aimé for accepting to examine this work;

Eng. FOKO Thierry for his professional support and supervision during this study;

Eng. MBANTAPAH Pascal, Eng. KONGSO Derick, Eng. EKOE BEA Rodrigue, Eng. NANA Arthur,

Eng. METUTU Wilson, Eng. MOUDELSOU Joel, M. AKOU Cyprian, M. TALLA, M. ESSISSING, Pa.

MOKI and all the personnel of the Instrumentation Service and the Maintenance Department as a whole for

their advice and field training;

All the teachers and staff of ENSP Yaoundé, especially those of the Industrial and Mechanical Engineering

department whose support and advice during my Engineering training was invaluable;

My friends and class mates of the Industrial Engineering department whose assistance was and remains

priceless;

The members of the Lectors group at St. Francis Xavier Parish who assisted in my spiritual and moral

upbringing;

My friends ACHE Amstrong, Claude DAIGA, CHOPGWE Leonard, Delma SINGMIA, Rita ESUKA

and everyone who in one way or another contributed to my training as an engineer and to the completion of

this thesis;

And above all to the LORD Almighty.


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Abbreviation Definition

BAD CTL Bad Control

BAD PV Bad Process Value

DAG Direction des Affaires Générales

DARH Direction d’Administration et Ressources Humaines

DCT Direction de Controle Technique

DEX Direction d’Exploitation

DFC Direction Financier Et Comptable

DM Direction de Maintenance

DQHSEI Direction de Qualité Hygiène Sécurité Environnement et Inspection

DRPCT Direction des Relations Publiques Communication et Traduction

ISO International Organisation for Standardisation

KPI Key performance indicator

LG Level Glass

LNG Liquified Natural Gas

LPG Liquified Petroleum Gas

LT Level Transmitter

MDT Mean Down Time

MTBF Mean Time To Failure

MTTF Mean Time To (First) Failure

MTTR Mean Time To Repair

MUT Mean Up Time

PID Piping and Instrumentation Diagram

SONARA Societe Nationale de Rafinnage

TP Tapping points

TPM Total Productive Maintenance


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The instrumentation and systems services at the National refining Company (SONARA) are in charge of

monitoring the systems that measure and control process functional parameters such as temperature, pressure,

flow and liquid level. The objective for this is the maintenance and optimization of the functioning of these

systems, to make sure they are online and transmitting information in real time every hour and day of the week,

with zero failure or unplanned shutdown.

This brings us to the topic of this dissertation which is the “ANALYSES AND OPTIMISATION OF THE

INSTALLATION AND MAINTENANCE OF THE DRUM LIQUID LEVEL MEASUREMENT SYSTEM

IN THE SONARA REFINERY“

The requirement therefore is to analyze the liquid level measurement system put in place, to identify the

problems and propose corrective actions so as to tend towards zero failure and unplanned shutdowns.

The most common problem noticed with the level measurement system is the discrepancy issue between the

readings of level transmitters that are supposed to be showing the same values, it accounts for 74.07% of the

work permits emitted to the service, this is followed by BAD PV, BAD CTL and frozen transmitter, which

accounts for 9.25% of the work permits, the remaining 16.67% of these permits were distributed among 9

different problems. These problems are characteristic of the functional failures of the level measurement

system.

For the analyses and resolution of the problems mentioned above and others, we used a tool called PM-

analyses. This tool is a system analysis tool that has as objective to tend towards ZERO FAILURE of a system.

With the use of this tool we better understood the problems that cause the operational failure of the system.

Finally technical and strategic1 solutions were proposed, some of which are:

T-junction to install the level transmitters at the same height thus reduce discrepancy problems

Distribution tube to bring the tapping points to de same

Graduated scale plates for the level glass gauges

A radar level transmitter for the under-ground drum 70B3

1 Strategic solutions are solutions that will help in decision making for the follow up and continuous amelioration of the

maintenance policy.


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A maintenance intervention report

KPI’s and a web database application to help follow them up

The institution of Autonomous maintenance to help in the man-power problem as well as

decrease possible equipment down time

An archiving policy to ease the storing and use of maintenance Logs

A preventive maintenance plan for the level measurement instruments.

The cost of implementing some of the solutions was evaluated at 6,488,500 FCFA

Key words: Level measurement, PM-analysis, zero failure, Maintenance, KPI


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Les services Instrumentation et Systèmes de SONARA, sont chargés d’assurer la surveillance des équipements

mis en place pour la mesures et le contrôle des paramètres fonctionnels du procédé de raffinage qui sont la

température, la pression, le débit et le niveau liquide dans les ballons et les équipements statiques mis à leur

disposition. L’objectif est de garantir le bon fonctionnement en temps réel et 24 heures sur 24 avec zéro

défaillance et zéro arrêt non programmé.

Dans le cadre des activités associées, on présente une étude qui s’étend sur « L’ANALYSE ET

OPTIMISATION DE L’INSTALLATION ET DE LA MAINTENANCE DU SYSTEME DE MESURE

DU NIVEAU DE LIQUIDE D’UN BALLON DANS UNE RAFFINERIE: CAS DE LA SONARA »

Nous avons analysé le système mis en place pour la mesure du niveau de liquide dans les ballons et identifié

un ensemble de problèmes. Ceci nous a permis de proposer des actions correctives nécessaires pour faire tendre

baisser considérablement le nombre de défaillances et d’arrêts non-programmés.

Le problème le plus récurrent qu’on a constaté (74.07%) suite à l’analyse de l’historique des pannes de mesure

est le décalage entre les lectures opérées sur les transmetteurs qui sont censés donner les mêmes valeurs. Ce

problème étais suivi par les défaillances locales des transmetteurs (9.25%). Les défaillances restant

correspondent à 16.67% .

L’outil d’analyse choisi est Analyse PM, qui a pour objectif la résolution des problèmes d’un système pour

tendre vers zéro défaillance fonctionnelle. Les actions correctives qui en découlent sont les suivantes :

Ajout de « jonction de tuyauterie » de forme T pour la connexion des transmetteurs, ceci pour

la résolution des problèmes de décalage des mesures

Ajout de « tube de distribution » pour ramener les points de piquage au même niveau, ceci

résout également le problème de décalage de mesure.

Ajout des « plaques graduées » aux niveaux à glasses

Un transmetteur de niveau de type radar pour le ballon enterré 70B3

Une fiche d’intervention à remplir pour le suivi de la maintenance

Les indicateurs de performances et une base de données SQL ayant une interface web

programmé en java pour le suivi de ces indicateurs.

Une nouvelle politique d’archivage pour l’historique d’interventions de maintenance


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Un plan de maintenance préventive pour les instruments de mesure de niveau du liquide.

Le cout d’implémentation des certaines actions correctives proposés est 6 488 500 FCFA

Mots clefs : Mesure de niveau, analyse PM, Zéro défaillance, Maintenance, KPI


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Table 1: Number of work permits per year [2] ................................................................................................ 10

Table 2: Level measurement problems gotten from the analysis of work orders ............................................ 11

Table 3: Percentage importance of level measurement techniques used in SONARA [3] .............................. 12

Table 4 : Summary of steps 1 to 4 [5] .............................................................................................................. 33

Table 5: Problems due to the discrepancies between readings of level transmitters supposed to be taking the

same value ........................................................................................................................................................ 37

Table 6: Example of discrepancy between the level transmitters found at the units and the control room. .... 38

Table 7: Example of discrepancy between the process and security transmitters ............................................ 38

Table 8: Example of discrepancies between the process and security level transmitters and the level glass

gauge. ............................................................................................................................................................... 39

Table 9: WWWWH analysis of the discrepancy problems .............................................................................. 40

Table 10: WWWWH analysis of BAD PV and BAD CTL problem ............................................................... 42

Table 11: WWWWH analysis of the unclassified problems ............................................................................ 43

Table 12: Steps 2 and 3 of the PM-analysis of the system ............................................................................... 46

Table 13: 4P table for the identification of root causes(step 4 of PM analysis) ............................................... 49

Table 14: PM-analyses steps 5-7 ...................................................................................................................... 54

Table 15: Recapitulation of the engraved scale plates to be made with respect to their unit scales ................ 62

Table 16: Specifications of the T-junction [10] ............................................................................................... 63

Table 17: Properties of the 70B3 drum [7] ...................................................................................................... 66

Table 18: Rosemount 5402 antenna selection guide, Maximum Recommended Measuring Range, ft (m) [9]

.......................................................................................................................................................................... 68

Table 19: Other properties of the chosen transmitter ....................................................................................... 70

Table 20: Engraved scale plates costing .......................................................................................................... 83

Table 21: Cost of radar level transmitter [11] .................................................................................................. 84

Table 22: Recapitulation of the proposed solutions ......................................................................................... 84


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Figure 1: Percentage share distribution of SONARA ........................................................................................ 4

Figure 2: Example of typical installation of liquid level monitoring system in SONARA ............................... 8

Figure 3: An example of an armored sight glass, a sight glass used for high pressure applications [16] ........ 17

Figure 4: measuring Level using the Bubbler method ..................................................................................... 18

Figure 5: Depiction of differential pressure level transmitter [13] .................................................................. 18

Figure 6: Capacitance level transmitter installed on a tank [12] ...................................................................... 20

Figure 7: Depiction of a cylindrical capacitor .................................................................................................. 20

Figure 8: Ultrasonic level transmitter [12] ....................................................................................................... 22

Figure 9: Magnetic level gauge equipped with a float system [2] ................................................................... 24

Figure 10: Depiction of a magnetostrictive level transmitter [1] ..................................................................... 25

Figure 11: Radar transmitter installed on a tank [12] ....................................................................................... 26

Figure 12: Guided wave radar installed on a tank [12] .................................................................................... 27

Figure 13: Example nuclear level measurement [2] ......................................................................................... 27

Figure 14: Principle of step 2 [5] ..................................................................................................................... 30

Figure 15: Principle of step 3 [5] ..................................................................................................................... 31

Figure 16: Summary of PM analysis ................................................................................................................ 35

Figure 17: Functional tree diagram of a differential pressure level transmitter ............................................... 45

Figure 18: Disposition of tapping points on a drum ......................................................................................... 53

Figure 19: Armored level glass equipped with an engraved scale plate [6] ..................................................... 61

Figure 20: T-junction pipe to equate the level of tapping points ..................................................................... 63

Figure 21: TP1.1 and TP2.1 as well as TP1.2 and 2.2 brought together by T-junction pipe ........................... 64

Figure 22: Distribution tube ............................................................................................................................. 64

Figure 23: Use of a distribution tube to bring tapping points together ............................................................ 65

Figure 24: Section view of drum-tube mount to show the principle of communicating vessels ..................... 65

Figure 25: Radar level transmitter mounted with still pipe [1] ........................................................................ 69

Figure 26: Radar process seal level transmitter [15] ........................................................................................ 70

Figure 27: Schematic representation of some of the KPI's defined ................................................................. 73

Figure 28: Relationship Diagram showing the structure of the Database ........................................................ 75

Figure 29: Logical model of the instrumentation management database ......................................................... 76


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Figure 30: Application home page ................................................................................................................... 77

Figure 31: Populating the Instruments table of the database............................................................................ 78

Figure 32: Confirmation dialogue box ............................................................................................................. 79

Figure 33: Showing the success of the entry .................................................................................................... 79

Figure 34: Instrument information ................................................................................................................... 80

Figure 35: Create-View-Delete-Edit drop down menu .................................................................................... 80

Figure 36: Confirm Delete ............................................................................................................................... 81

Figure 37: Flow chart showing the steps for archiving work permits .............................................................. 82

Figure 38: Example of archiving flow chart for the Instrumentation service .................................................. 82


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DEDICATION .................................................................................................................................................... i

ACKNOWLEGEMENTS .................................................................................................................................. ii

GLOSSARY ...................................................................................................................................................... iii

ABSTRACT ...................................................................................................................................................... iv

RESUME ........................................................................................................................................................... vi

LIST OF TABLES .......................................................................................................................................... viii

LIST OF FIGURES ........................................................................................................................................... ix

TABLE OF CONTENTS .................................................................................................................................. xi

GENERAL INTRODUCTION .......................................................................................................................... 1

CHAPTER 1: CONTEXT AND PROBLEM STATEMENT ............................................................................ 3

1.1 CONTEXT OF STUDY ..................................................................................................................... 3

1.1.1 PRESENTATION OF SONARA ................................................................................................ 3

1.1.2 PRESENTATION OF THE REFINING PROCESS .................................................................. 5

1.1.3 PRESENTATION OF THE LEVEL MEASUREMENT SYSTEM .......................................... 7

1.1.4 MAINTENANCE MANAGEMENT .......................................................................................... 9

1.2 PROBLEM STATEMENT ................................................................................................................. 9

1.2.1 ANALYSIS OF WORK PERMITS AND PIPING PID’S ....................................................... 10

1.2.2 DEFINITION OF THE PROBLEM.......................................................................................... 12

1.2.3 OBJECTIVES OF THE STUDY .............................................................................................. 13

1.3 PARTIAL CONCLUSION ............................................................................................................... 13

CHAPTER 2: LITERATURE REVIEW ......................................................................................................... 14

2.1 BASICS OF LEVEL MEASUREMENT [4] [5] [6] [7] [8] ............................................................. 14

2.1.1 IMPORTANCES OF LEVEL MEASUREMENT.................................................................... 14


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2.1.2 TYPES OF LEVEL MEASUREMENT ................................................................................... 15

2.1.3 SOME LEVEL MEASUREMENT METHODS IN THE PETROLEUM INDUSTRY .......... 16

2.2 BASICS OF PM (2P 4M) ANALYSES METHODOLOGY [9] [10] .............................................. 28

2.2.1 STEP 1: CLARIFY THE PROBLEM WITHOUT ANY PRECONCIEVED IDEAS ............. 29

2.2.2 STEP 2: CONDUCT A PHYSICAL ANALYSIS OF THE SYSTEM .................................... 29

2.2.3 STEP 3: IDENTIFY THE POTENTIAL FACTORS FOR CHANGE ..................................... 31

2.2.4 STEP 4: IDENTIFY ALL THE POSSIBLE CAUSES OF THE PROBLEM .......................... 32

2.2.5 STEP 5: DEFINE THE OPTIMAL CONDITIONS ................................................................. 33

2.2.6 STEP 6: MEASURE THE GAP BETWEEN THE EXISTING AND OPTIMAL STATES ... 34

2.2.7 STEP 7: DEFINE THE ANOMALIES TO BE TREATED ..................................................... 34

2.2.8 STEP 8: CORRECT, AMELIORATE AND STANDARDISE ................................................ 34


CHAPTER 3: APPLICATION OF PM (2P-4M) ANALYSIS ON THE LEVEL MEASUREMENT SYSTEM

.......................................................................................................................................................................... 36

3.1 INTRODUCTION ............................................................................................................................ 36

3.2 PM (2P 5M) ANALYSIS OF THE LEVEL MEASUREMENT SYSTEM. .................................... 36

3.2.1 STEP 1: CLARIFICATION OF THE PROBLEM WITHOUT ANY PRECONCIEVED IDEAS

36

3.2.2 STEP 2: PHYSICAL ANALYSES OF THE LEVEL MEASUREMENT SYSTEM .............. 44

3.2.3 STEP 4: IDENTIFICATION OF CAUSES .............................................................................. 49

3.2.4 STEPS 5, 6 AND 7: OPTIMAL CONDITION, GAP ANALYSES AND DEFINITION OF

ANOMALIES .......................................................................................................................................... 54


CHAPTER 4: PRESENTATION OF RESULTS AND CORRECTIVE ACTIONS ...................................... 61

4.1 INTRODUCTION ............................................................................................................................ 61

4.2 TECHNICAL SOLUTIONS ............................................................................................................. 61

4.2.1 UNGRADUATED LEVEL GLASS GAUGES ........................................................................ 61


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4.2.2 DIFFERENCE IN THE LEVEL OF TAPPING POINTS ........................................................ 62

4.2.3 OBSOLETE LEVEL TRANSMITTER FOR THE DRUM 70B3 ............................................ 66

4.3 STRATEGIC SOLUTIONS ............................................................................................................. 70

4.3.1 INSUFFICIENT MANPOWER ................................................................................................ 70

4.3.2 LACK OF MAINTENANCE INTERVENTION REPORT ..................................................... 72

4.3.3 LACK OF MAINTENANCE METRICS AND KPI’S ............................................................. 72

4.3.4 INSUFFICIENT WORK PERMIT ARCHIVING POLICY .................................................... 81

4.3.5 PREVENTIVE MAINTENANCE AND FOLLOW-UP RELATED PROBLEMS ................. 83

4.4 PROJECT COSTING ....................................................................................................................... 83

4.4.1 COST OF ENGRAVED SCALE PLATES .............................................................................. 83

4.4.2 COST OF PROPOSED LEVEL TRANSMITTER................................................................... 83

4.5 PARTIAL CONCLUSION: RECAPITULATION OF THE CORRECTIVE ACTIONS ............... 84

GENERAL CONCLUSION AND PERSPECTIVES ...................................................................................... 86

BIBLIOGRAPHY ............................................................................................................................................ 87

APPENDICES .................................................................................................................................................. 89


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Energy is an undisputable necessity for the development of a nation, this energy being used mainly to generate

electricity for diverse uses. These uses range from the driving of heavy machinery for mega scale production

of goods and services to domestic consumption like driving cars and cooking.

The primary sources of energy in the world nowadays are solar power, fossil fuels (petroleum products),

nuclear power, wind, and hydro-power. In the Cameroon context hydropower and fossil fuels are our main

energy sources, and Liquefied Natural Gas (LNG) will soon be added to the list.

In the context of The National Refining Company (SONARA), the refining of petroleum to meet the nation’s

energy demand and for export is the order of the day. SONARA being the only local producer of petroleum

products, it has great challenges to overcome so that from the high scale demand in fuel for the production of

electrical energy by the thermal power plants and the running of transport vehicles, to the lowest scale demand

by the citizen who buys a bottle of cooking gas to sustain his family is met.

In order for SONARA to meet her objectives, many factors come into play. These factors range from the

availability of crude oil that is beyond her control to factors like the control of process parameters to provide

good quality products and a safe working environment, which she puts all the necessary resources to master.

Some of the process parameters that she controls are temperature, pressure, flow and liquid level. The

instruments that are used to control these parameters need to be maintained so that they are always available

to perform their functions, this brings us to instrumentation service of the maintenance department, the service

in charge of maintaining these equipment.

For this dissertation, I worked with the instrumentation service to study the liquid level measurement system

put in place, identify the problems that are most common and the potential problems that could be faced and

propose corrective actions to these problems. The objective of this being to increasing the reliability of their

level measurement system and to tend towards zero failure and zero unplanned shutdown of this system,

bringing us to the topic of the dissertation which is “ANALYSES AND OPTIMISATION OF THE

INSTALLATION AND MAINTENANCE OF THE DRUM LIQUID LEVEL MEASUREMENT SYSTEM IN AN

OIL REFINERY: CASE OF SONARA”

For the study therefore, we will:




Start with a context within which we will present SONARA, explain the process of refining crude oil,

then present the level measurement system and finally the way maintenance is managed. We will then

proceed to introduce the problematic of the study. All this will be done in chapter 1.

In chapter 2, we will explain the basics of level measurement and the basics of PM-analysis, which is

the methodology we will use to carry out our project.

Chapter 3 will follow with the use of the afore mentioned methodology to analyze the system;

And finally we will present and discuss the corrective actions proposed and the cost of some of these

corrective actions in chapter 4.




In this chapter, we will do a general presentation of the company where the internship was carried out, present

the company’s main activity then go further into presenting the problem that was posed, then conclude with

the expected results.

1.1 CONTEXT OF STUDY

1.1.1 PRESENTATION OF SONARA

1.1.1.1 History of the National Refining Company [1]

The National refining company Ltd (SONARA) was created by presidential decree No. 73/135 of 24 March

1973, inaugurated on the 07th of December 1976, and an establishment convention was signed between the

Government of Cameroon and SONARA on the 11th of January 1978. The initial capital of 400,000,000 CFA

Francs was increased to 4 billion CFA Francs in November 1977, then to 14 billion CFA Francs in January

1990, and then to 17.8 billion CFA Francs in January 1992. It now stands at 23 billion CFA Francs.

SONARA is a parastatal company. Its shares are owned both by the Cameroon government and private oil

companies. The government’s ownership distribution is as follows:

National Hydrocarbon Corporation : 20%

National Investment Company: 17%

Ministry of Economy and Finance: 10%

Office for Stabilization of Hydrocarbon Prices: 19%

The share capital distribution for the private companies is as follows:

Total: 18%

Mobil OIL Petroleum company: 8%

Pecten Victoria Company: 8%

This share distribution is depicted by the pie chart below (figure 1)




Figure 1: Percentage share distribution of SONARA

1.1.1.2 Administrative structure of SONARA

SONARA is managed by a board of directors composed of 15 members and headed by a chairman. Directly

under the chairman is the General Manager who is appointed by the president of the republic.

Under the General Manager, there are eight directions each headed by a Director. The directions are further

divided into departments managed by Department Heads, and finally the departments are divided into services

managed by service heads. The hierarchical chart of SONARA showing the directions with emphasis on the

maintenance direction is depicted in APPENDIX 1

1.1.1.3 Organization of the maintenance department in SONARA

The role of the maintenance department is to ensure that the installations of the SONARA refinery, both in the

refining units and at the administrative block are functioning properly. As depicted on the flow chart

(APPENDIX 1), the maintenance direction is divided into three departments which are:

Short term maintenance department: which is in charge of preventive and curative maintenance

interventions of the equipment in the refinery. It is made up of three services which are:

o The mechanics service: in charge of the maintenance of all rotating machinery like motors,

pumps and generator sets.

o The systems service: in charge of the maintenance and follow up of the digital control system.

This system ensures the real-time follow-up of refining process conditions and some of the

instruments found in the refining units.

o The instrumentation service: in charge of preventive and curative maintenance of all the

measuring instruments in the refinery, including valves, and other actuators.

20%

17%

10%18%

8%

8%

19%

Shareholders National HydrocarbonCorporation

National InvestmentCompany

Ministry of Economy andfinance

Total

Mobil Oil PetroleumCorporation

Pecten Victoria Company

Office for Stabilization ofHydrocarbon Prices




Mid and long term maintenance department: this department is made up of two services,

o The heat works and storage service which is in charge of all the mechanical construction tasks

involving heat. They do mostly welding, metal fabrication and maintenance of the storage

tanks.

o Studies and work in progress: this service is in charge of the studies related to amelioration of

the technologies used, drawing and documenting changes in the units and follow up of the

changes in progress, which may be civil engineering construction, changes on a pipeline, etc.

Procurement department: this department is in charge of all the procurement services needed by the

exploitation and maintenance departments.

Following the description of the administrative structure of SONARA, we will proceed by describing the

refining process.

1.1.2 PRESENTATION OF THE REFINING PROCESS

The National Refining Company Ltd is a topping reforming refinery which produces bupro, gasoline, kerosene,

jet fuel, gas oil and fuel oil. The refinery is designed to treat crudes of varying properties and different origins,

and this flexibility makes room for various sources of supply.

The refining capacity of SONARA was increased from 1.600.00 to 2.100.000 tons of crude oil per year. With

the extension and modernization project, this capacity will increase to more than 3.500.000 tons. Excess

products are meant for export. The refinery is spread over a total surface area of 54 hectares.

The refining schema in SONARA is divided into unit, each unit representing a step of the refining process.

The end product of some units are the inputs of others. The refining schema as depicted by APPENDIX 2 is

explained as follows:

1.1.2.1 Unit 10: Atmospheric distillation

Atmospheric distillation is the fractional distillation of crude oil in the presence of normal atmospheric air, as

opposed to vacuum distillation which is done in a vacuum. Fractional distillation of crude oil is the process

where crude oil is heated to very high temperatures to separate it into its different components. This is done in

a fractionating column, which in the case of SONARA is referenced 10C1.

The different components of the crude oil are separated based on their different boiling points and collected at

varying heights on the fractionating tower. The lightest products are generally those with the lowest boiling

points and are collected at the top of the column and the heaviest at the bottom, thus the temperature decreases

as you go up the tower.




The different products and by-products of the fractional distillation of crude oil are:

Gaseous mixtures composed of butane, propane, hydrogen sulfide and other gases as well as unstable

full range naphtha (gasoline).

Kerosene which is extracted and sent for desulfurization

Light and heavy gasoil

Distillate which is directly sent to the storage reservoirs

Residue composed mostly of heavy fuel oil which is also directly sent to storage tanks

1.1.2.2 Unit 20: Hydro-treatment of gasoline

The gasoline is sent to this unit for desulfurization and extraction of impurities that may have a negative effect

on the catalyzers during the catalytic reforming phase (unit 50). This unit has a reactor 20R1 which takes

hydrogen as input and uses it to remove the Sulphur present in the form of hydrogen sulfide gas. From this

unit the mixture of gasoline and other lighter gases go to the next phase which takes place at unit 30.

1.1.2.3 Unit 30: Stabilization and fractioning of gasoline

After the gasoline has been hydro treated at unit 20, it is sent to unit 30 for stabilization and fractioning. This

unit has two columns, 30C1 and 30C2.

30C1 is a debutanizer, it’s role is to separate the gas from the mixture. The gas removed here will be sent to

unit 40 for treatment. The gaseous end product of unit 30 is impure LPG.

The column 30C2 has as role to fractionate the liquid components of the gasoline to give light and heavy

gasoline (naphtha), this process is called splitting. The light gasoline is cleaned and sent to the storage tanks.

The naphtha on the other hand is sent to unit 50, which is the catalytic reforming unit.

1.1.2.4 Unit 40: Treatment of liquefied petroleum gas (LPG)

This unit serves in the production of Bupro, which is the commercialized cooking gas and has about 80%

butane and 20% propane. Unit 40 is equipped with the column 40C1 which is a depropanizer. This column

eliminates part of the propane found in the LPG and sends to the torch for burning.

1.1.2.5 Unit 50: Catalytic reforming

The naphtha or heavy gasoline originating from unit 30 has octane numbers between 62 and 64. This unit has

as objective to convert this low octane gasoline to a product with a higher octane number called reformate, the

fuel known in the market as super is derived from this reformate. The furnace in unit 50 where the reforming

takes place is 50F1, from where the product is sent to 50C1 for further stripping. The products of unit 50 are

LPG which is sent for treatment at unit 40 and super which is stored ready for distribution.




1.1.2.6 Unit 60: Hydro-desulfurization of Gasoil and kerosene

The kerosene that originates from the fractionating column 10C1 is sent to this unit for the removal of sulfur

in the form of hydrogen sulfide gas. The end product is then stripped at 60C1 to produce Jet A1 which is used

in planes and petrol.

The gasoil that originates 10C1 meets specifications for distribution, but still contains some kerosene which

can has to be desulfurized in the presence of hydrogen. After desulfurization, the gasoil is sent to a column

where it’s acidity is reduced, before being sent to the storage tanks.

In order to make refining possible, there are other units that act as accessories, these are:

Unit 70 where process water is treated,

Pumping stations 1, 2 and 3 where products are mixed and transferred to tanks for storage and

distribution.

Unit 200 where the vapor needed in the refining process is being produced,

Unit 210 where electricity is produced and

Unit 221 where water is demineralized, i.e. all the salts are removed before being used in the different

equipment. This is important because deposition of salts in the equipment will reduce their lifespan.

The refined products are distributed either by land with the used of tankers or by sea with the use of ships.

1.1.3 PRESENTATION OF THE LEVEL MEASUREMENT SYSTEM

The typical level measurement system in the SONARA refinery is designed such that certain tasks can be

automatically controlled, these tasks are mostly drum or silo process level regulation and security assurance.

Each drum whose level is supposed to be monitored has three level measuring instruments connected to it,

these are:

A digital electronic level indicator for process control and level regulation in the drum (LT1)

A digital electronic level indicator for security assurance (LT2)

A visual level indicator (mostly mechanic) for onsite appreciation of the level by an operator. These

are mostly level glass gauges or magneto-restrictive level gauges (LG).

The process control level transmitter LT1 is connected to a level control loop which is composed of actuators

and controllers, for the purpose of level regulation. The signal is also sent to the control room for real time

monitoring of the level in the drum.




The security level transmitter LT2 is connected to a programmable logic controller whose main function is

security based.

The unit of level measurement in the SONARA refinery is the percentage (%), the value computed is a

percentage of the total hydrostatic head pressure in the drum. For the control room reading, the hydrostatic

head pressure signal is converted to an electric signal which is scaled from 4-20mA, where:

4mA2: lower value on the level scale (the 0% level). Here the 0mA value could not be chosen because

a zero reading may also denote an interruption on the cable line (like a cut cable), making it difficult

to differentiate between a transmission break and an actual minimum drum level.

20mA: this is the maximum level reading (or the 100%), and corresponds to the maximum calibrated

hydrostatic head.

In the ideal case, all the tapping points for these level transmitters are supposed to be at the same level, but as

depicted on figure 2, that is not the case with all the installations at the SONARA refinery.

Figure 2: Example of typical installation of liquid level monitoring system in SONARA

2 It is worth noting that 0% may not necessarily mean that the hydrostatic head in the drum is zero, it just means that the level

corresponds to the minimum calibrated hydrostatic head pressure.




1.1.4 MAINTENANCE MANAGEMENT

1.1.4.1 Work permits

In the SONARA refinery, the main maintenance management tool is called a work permit. This is a document

without which a task cannot be performed. The reasons for this vary from the security of the personnel to the

security of the installations being maintained. Any technician can emit a work permit to another service if the

task is not in his domain of expertise, or get one written for himself in the case where the task to be performed

is in his domain.

Most of the work permits that concern instrumentation are issued by the exploitation department, this being

because the operators of the exploitation department do a round the clock follow-up of all the installations and

their functioning, as well as a real time follow-up of process conditions in the control room, so they are always

the first to identify problems.

Upon discovery, the problem is reported and then a work permit is issued to the department concerned, which

in our case is the instrumentation department. The task is then planned according to the criticality of the work

permit and then executed. After successful execution, the permit is then closed by the chief operator on call at

the time, then archived for two years in the department in question before being discarded.

The criticality of the task to be performed varies from 1 to 3, with the most pressing tasks having a criticality

of 1 and the relatively least pressing a criticality of 3. The criticality of the operations is determined by the

person emitting the work permit following a grill determined by company procedures.

1.1.4.2 Logistics

In terms of maintenance management, the main logistics concern is that of spare parts management. The

database application used for logistics management in SONARA is called Maximo.

If equipment or spare parts are needed by a technician, he first consults the database to check if the part is

available in storage. If it is available, an order is placed and signed by hierarchy before the part is collected

from the storeroom. In case the part is unavailable a purchase request is emitted to the procurement department

so that the part can be bought.

1.2 PROBLEM STATEMENT

In order to identify the problems plaguing level measurement at the SONARA refinery, the following tasks

were realized:

Analysis of work permits

Analysis of PID’s




Interviews with operators, engineers and technicians

General observation on how maintenance is carried out in the instrumentation department, both in

the workshop and in the production units.

Onsite observation of how level transmitters were installed.

1.2.1 ANALYSIS OF WORK PERMITS AND PIPING PID’S

The analysis of work orders permitted us to identify the problems that are prevalent during the measurement

of liquid level in the drums. The problems identified using this method are mostly technical problems, i.e.

problems concerning the installation of the level monitoring and regulation system and the problems that are

directly related to the level measurement equipment that are installed onsite. In total 54 work permits were

found and analyzed, these work permits concern the years 2012 (the year that the new level measurement

system went operational), 2013 and 2014. Table 1 below shows the yearly distribution of work permits.

Table 1: Number of work permits per year [2]

Year Number of work permits Percentage occurrence of faults

(%)

2012 15 27.78

2013 15 27.78

2014 24 44.44

TOTAL 54 100

Table 1 above shows a constancy in the number of faults between 2012 and 2013 but a 16.66% increase in the

year 2014 which is not negligible.

The problem with this data however is that it is incomplete due to the archiving system of work permits.

The fact that only the permits of successful interventions are archived means that there may have been

more problems than those identified here,

During the analysis it was noticed that some work permits had not been placed in the folders that were

allocated for them,

The way some of the work permits were carelessly placed on the tables is an indication that before

archiving some of them might have been lost.

The problems identified using the analyses of the available work permits are enumerated and described in

detail on table 2 overleaf




Table 2: Level measurement problems gotten from the analysis of work orders

PROBLEM DETAILED DESCRIPTION

1. Discrepancy between the

readings of the process

regulation and security level

transmitters

The readings of both the level transmitters LT1 and LT2 are

supposed to have the same readings given that they are measuring

the same level, so this discrepancy is registered when the values

shown by these level transmitters are different.

2. Discrepancies between the

readings of the process

regulation and security level

transmitters and the level gauge

This discrepancy describes the situation where the level transmitters

LT1, LT2 and LG don’t show the same reading.

3. Discrepancies between the onsite

level indicators and transmitter

readings and the reading

received in the control room

This discrepancy is registered when the readings between the onsite

level transmitters (level transmitters found in the production units)

and the control room monitoring interface show different values.

4. BAD PV This is the message that the level transmitters shows when the

hydrostatic head pressure goes above or below that defined during

the calibration of the level transmitter.

5. BAD CTL This problem is local to the transmitter

6. Fixed reading This problem describes a situation where the reading shown by a

level transmitter does not vary, even when the level changes.

7. Maximum level indication

despite the drum’s emptiness

This problem describes the situation where the reading on the level

transmitter shows that the drum is full, even when it is actually

empty.

8. No reading at the level of the

control room

This has to do with the lack of a reading transmitted to the control

room.

9. No level visibility This depicts a situation where none of the level transmitters shows

the level in the drum.

10. Malfunctioning of the level

transmitter

This is a situation where the problem encountered is undoubtedly

related to the level transmitter itself.

Before posing the problem however, it is important to know the different level transmitters that are installed

in the production units, this will help us to better understand the reasons why some problems are faced. Table




3 below is a statistical analyses of the PIDs to bring out the different level measurement technologies used in

SONARA and their percentage importance.

Table 3: Percentage importance of level measurement techniques used in SONARA [3]

TECHNOLOGY NUMBER OF

INSTRUMENTS

PERCENTAGE

Differential pressure level transmitter 112 95.73

Capacitive level gauge 1 0.85

Torque tube level gauge 1 0.85

Tuning fork level gauge 1 0.85

Radar level gauge 1 0.85

Ultrasound level gauge 1 0.85

TOTAL 117 100.00

From table 3 we notice that 95.73% of the level measurement instruments are differential pressure level

transmitters, this shows that in order to get to the root cause of the level measurement problems faced in the

SONARA refinery it will be important to focus more of our attention on these level transmitters, while not

neglecting the others of course.

1.2.2 DEFINITION OF THE PROBLEM

Following the presentation of how the level measurement system works, we proceeded with the statistical

analyses of work orders and PIDs. We then had interviews with instrumentation technicians, operators and

engineers, all this in order to better understand the level measurement system put in place.

The results of the statistical analyses showed that:

Between 2013 and 2014, the faults in the level measurement system increased by 16.6%, thereby sparking

our curiosity and pushing us to ask “why?”.

74.07% of the problems faced by the level measurement system are discrepancy issues between readings

on transmitters that are supposed to be giving the same values when subjected to the same process

conditions. This also compels us to look for the reasons why, so that we can get the causes and address

them to get our system running.

95.73% of the level measurement instruments installed in the refining units are based on the hydrostatic

pressure principle, differential pressure to be specific.




From these analyses and the primal objectives of most process companies, which are zero defects, zero faults,

zero accidents, zero unplanned shutdowns as well as continuous amelioration, we were asked to work on

ameliorating the level measurement system put in place for the drums at the SONARA refinery. This thus

gives reason for the theme, “ANALYSES AND OPTIMISATION OF THE INSTALLATION AND

MAINTENANCE OF THE DRUM LIQUID LEVEL MEASUREMENT SYSTEM AT THE SONARA

REFINERY”

1.2.3 OBJECTIVES OF THE STUDY

The objective of this study as defined above is the optimization of level measurement in the drums of the

SONARA refinery, this study has as aim to increase the reliability of the level measurement results, and the

performance of the level measurement system as well as move towards zero failure of this system.

In order to meet these objectives, the expected results from this study are:

The proposal of solutions to resolve the problems brought about by the faults found on the level

measurement system.

The other possible problems that can be faced and how to control them;

Indicators to follow-up the maintenance policy( metrics and KPI’s)

To better understand the problems plaguing the level measurement system, so as to meet the objectives of the

study, we will use a methodology called P-M analysis or 2P-5M analysis. This method will permit us to

analyses the system in detail so that we can get the root causes of the problems faced, as well as other possible

problems not yet faced, and then propose corrective actions for these problems.

1.3 PARTIAL CONCLUSION

In this chapter, we situated the context of our study, shed some light on the level measurement system, carried

out statistical analyses to determine the problems with the level measurement system and classified the

problems. This permitted us to expose the problematic and the method we will use to solve the problems.

In the next chapter we will do a literature review which will give basic knowledge on level measurement

technologies and a detailed explanation of how the 2P 5M methodology works.




In order to better understand this study, it is important that the concepts, methods and technologies used are

explained. At the end of this chapter therefore, the reader should be familiar with:

The basics of level measurement, which constitutes:

o The importance of measuring and controlling the level in drums

o The different types of level measurement;

o The different techniques of measuring level in drums;

The basics of PM-analysis (the 2P 4M analysis)

2.1 BASICS OF LEVEL MEASUREMENT [4] [5] [6] [7] [8]

Process companies in general and SONARA in particular have certain physical conditions or process

parameters that are monitored to ensure good product quality, security of personnel, good performance of

equipment, etc. These physical conditions are:

Pressure

Temperature

Flow and

Liquid level measurement.

Given that our study is based on the liquid level measurement system, we will then proceed by giving the

general objectives of liquid level measurement, then the types of liquid level measurement and finally the

techniques used for measuring the level of liquids in drums.

2.1.1 IMPORTANCES OF LEVEL MEASUREMENT

Liquid level measurement is very important in a process company, especially an oil refinery where all the

products and processes have a negative impact on the environment if not properly controlled.

The importance of level measurement may be environmental and safety related, product quality, inventory

control or process control related.

From the environmental and safety point of view, liquid level measurement is imperative because the chemical

composition of SONARA’s products and byproducts are all dangerous to the environment. These products




range from the known liquid hydrocarbons marketed by the company such as petrol and kerosene whose

spillage may:

Condemn all fauna growing around the area;

Infiltrate into the soil and whose contact with the water bed pollutes the sources of drinking water

found around the refinery,

Flow into the Atlantic Ocean, which shears a boundary with the refinery thus posing problems to

marine life, etc.

And the known gaseous utility products like hydrogen and byproducts like hydrogen sulfite and carbon dioxide

whose escape into the atmosphere have effects such as:

Poisoning of both human and animal life present around, especially the personnel who are always

present at the production sites,

Speed up global warming, etc.

From the product quality and inventory point of view, it is important to know that some of the products are

mixtures of other products, to get the compositions right therefore, it is important to know the quantities of

each product entering the production process. This is best done by monitoring the level of the products in the

drums and the optimal compositions of these products. Control of these processes by the level measurement

system therefore increases the potential for high quality end products.

Level measurement for process regulation is also a safety requirement, the level in the drums are not supposed

to go higher than a given threshold which is defined by the company, depending on the process conditions. If

this happens, the dangers vary from product spillage to even explosion of the tank or drum.

Some concrete examples of the cases where level measurement is imperative are:

The water level in a boiler tank in unit 200 must never be too low, otherwise there is a risk of

overheating the steam produced and thus the tank may explode. Nor must the level be too high;

otherwise the liquid water may enter the steam system

To automate tank filling or emptying. This is very important because most of the drums in the refinery

are closed and pressurized, the liquid cannot be evacuated via an overflow thus the efficient filling or

emptying of the tank will have to be carried out.

2.1.2 TYPES OF LEVEL MEASUREMENT

There are two types of level measurement, these are point and continuous level measurement.




2.1.2.1 Point level measurement [4]

This is a type of level measurement where a specific point or level is defined and an indication on the level is

perceived only when this point or level is attained. This type of level measurement is very popular in alarm

systems.

Point level measurement is accomplished by placing a level sensing element at the selected level position. If

high and low level operations are required, one sensor is required at each location. Examples of point level

measurement could include the prevention of a tank or silo from overfilling, avoidance of pump cavitation

when emptying a tank, or to sound an alarm when a tank’s liquid level is above or below the normal level.

2.1.2.2 Continuous level measurement [4]

Continuous level measurement is a method used to track the changes of liquid level over a range of values to

monitor inventory or for determining when to add or remove material from containers.

This method of level measurement is obtained by placing a sensor or sensors throughout the range defined for

measurement and a scale defined for interpretation purposes.

2.1.3 SOME LEVEL MEASUREMENT METHODS IN THE PETROLEUM INDUSTRY

There are many methods used for the measurement of liquid level both generally and in the petroleum industry.

We will start by explaining those used at the SONARA refinery before proceeding to explain some of the other

existing methods. It is important to note that the main objective of level measurement in the SONARA refinery

and in the petroleum industry in general is “process regulation” and security assurance, therefore the type of

level measurement which is predominant is the continuous level measurement.

The use of each technology depends on its aptitude to be translated into a linear scale that can be used as the

4mA and 20mA set points for digital signal transmission to the control room. Some are however used only for

onsite visual appreciation of the level in the drums.




2.1.3.1 Level gauge glass or sight glass [4]

These are liquid level indicators that give a visual indication of the

liquid level in the tank, silo or reservoir of interest. A level glass

gauge consists of a glass tube which is connected to tapping points

which are made at the required maximum level indication point and

at the minimum point.

The principle supporting the use of level glasses is “The principle of

communicating vessels”, it holds that if a set of vessels connected to

each other are filled with a homogeneous fluid, it will balance out

to the same level irrespective of the shape or volume of the

containers. This is because hydrostatic pressure depends only on

depth, not on the shape or volume of the container. The sight glasses

used in the petroleum industry are usually armored, i.e. assembled

using a thick flat gauge glass inside an armored enclosure to provide high pressure protection and safety

protection against breakage in high pressure vessels or boilers.

In addition to the conventional sight glass, we also have the reflex gauge glass. Reflex gauge glasses are

similar to an Armored Gauge Glass in construction using the thick flat glass. These devices are used for

applications where the liquid is hard to see in a standard gauge class and uses light refraction to show level

[1].

The reflex gauge is a flat gauge with a special vertical saw-tooth surface that acts as a prism to improve

readability. The light entering the portion of the prism in contact with the liquid is refracted into the tank and

the glass appears dark. The light entering the portion of the prism above the liquid is refracted back out of the

gauge and the glass appears silvery white. This feature is useful with clear or translucent liquids that are hard

to see in a conventional gauge glass.

2.1.3.2 Static Pressure methods [5] [4]

Hydrostatic pressure techniques of level measurement are the most widely used, among these are some that

can be automated for real-time level monitoring and others that cannot. The most common static pressure

methods are:

Figure 3: An example of an armored sight

glass, a sight glass used for high pressure

applications [16]




2.1.3.2.1 THE BUBBLER METHOD:

This method consists of blowing compressed air

or an inert gas at a constant flow rate into a liquid

whose level is to be determined, while monitoring

the pressure. The moment when the first bubbles

are observed, the pressure is recorded and the level

of the liquid calculated with the static pressure

formula:

𝑃 = 𝜌𝑔ℎ [5]… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … 𝐸𝑞. 1

Where:

o ρ: density of the liquid, in kg/m3

o g: the acceleration due to gravity( 9.81N/Kg)

o h: the liquid level, in metres

From Eq.1 above, it follows that:

ℎ =𝑃

𝜌𝑔… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … 𝐸𝑞. 2

2.1.3.2.2 DIFFERENTIAL PRESSURE METHOD

This is the most widely used method of level

measurement in the SONARA refinery, it

accounts for more than 95% of the level

transmitters used.

This method of level measurement is based on

the principle that “the pressure at a point in a

liquid depends solely on the height of the

liquid above the point and on the physical

properties of the liquid (density)”. For the

Figure 5: Depiction of differential pressure level transmitter [13]

Figure 4: measuring Level using the Bubbler method




determination of the level of the liquid thus, the hydrostatic pressure in the liquid is determined and the height

derived using Eq.2.

To determine this pressure, two tapping points are made on the drum to cover the required maximum level of

interest. These are

A high pressure (HP)tapping point at the minimum point of the drum defined for level measurement

and

A low pressure (LP) tapping point at the maximum level.

These points are connected together with a level transmitter which uses either piping connections or capillary

connections depending on the standard’s requirements. To determine the height thus we proceed as follows:

Get the high pressure point in the liquid

𝐻𝑃 = 𝑃0 + 𝜌𝑔𝐻ℎ

Get the low pressure point

𝐿𝑃 = 𝑃0 + 𝜌𝑔𝐻𝑙

The pressure difference ∆𝑃 is then calculated

∆𝑃 = 𝐻𝑃 − 𝐿𝑃 = 𝜌𝑔(𝐻ℎ − 𝐻𝑙)

Finally, the level is determined

𝐻 = 𝐻ℎ − 𝐻𝑙 =∆𝑃

𝜌𝑔… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … . 𝐸𝑞. 3

Where

o 3P0= pressure of the gas in the tank in the case of a closed tank or the atmospheric pressure in the case

of an open tank, in Bars

o HP= high pressure, in bars

o LP=low pressure, in bars

o Hh= height at high pressure, in metres

o Hl= height at low pressure point, in metres

o 𝜌= density of the liquid, in kg/m3

o 𝑔= acceleration due to gravity(9.81N/m2)

3 It is worth noting that all pressures are in bars and distances in metres except if stated otherwise




o 𝐻= the liquid level in the tank, in metres

2.1.3.3 Capacitance method [7] [8]

The principle of capacitive level measurement is based on the change in

capacitance of the capacitor due to the change in the level detected by the

capacitance probe in the tank. A capacitance probe may be compared to a

cylindrical electric capacitor. As the tank is filled, the probe capacitance

increases, this change is electrically analyzed and the level of the liquid

determined.

In SONARA and the petroleum industry in general, this method is used to

measure the level in drums that contain more than one fluid, usually water and

a hydrocarbon. The dielectric constants of water and the hydrocarbons being

stored in the tanks are usually known and this is the basis under which the

levels of each of the fluids in the tank is known. The formula that characterizes

the capacitance between two plates separated by a dielectric material is as follows:

𝐶 =2𝜋𝜀𝐿

ln𝑏𝑎⁄

[6]… … … … … … … … … … … … … … … … … … … … … … … … … . . … … … … … … … … … … … … . 𝐸𝑞. 4

𝐶: The capacitance between the plates

o 𝜀: the dielectric constant of the material between the

plates

o L: the length of the capacitance level probe

o a : the internal diameter of the probe

o b: the external diameter of the probe

When the capacitance probe is inserted into the tank, it acts as

2 capacitors in series when in contact with both liquids. The

height of the interface can be determined thus:

𝐶 = 𝐶1 + 𝐶2 =2𝜋(𝜀1𝑙1 + 𝜀2𝑙2)

ln 𝑏𝑎⁄

… … … … … … … … … … … … … … … … … … … … … … … … … … . 𝐸𝑞. 5

Where l1 and l2 are the lengths of the liquid column occupied by each of the corresponding liquids in the tank,

and 𝑙1 + 𝑙2 = 𝐿. Similarly 𝜀1, 𝜀2 𝑎𝑛𝑑 𝐶1, 𝐶2 are the corresponding dielectric constants and capacitances

respectively.

Figure 6: Capacitance level

transmitter installed on a tank [12]

Figure 7: Depiction of a cylindrical capacitor




It follows from Eq.5 that the level of the interface h is given by:

ℎ = 𝑙1 =ln( 𝑏 𝑎⁄ )

2𝜋(𝜀1 − 𝜀2)𝐶 −

𝜀2𝐿

𝜀1−𝜀2

… … … … … … … … … … … … … … … … … … … … … … … … … … . 𝐸𝑞. 6

Which shows that the function ℎ = 𝑓(𝐶) is linear. Thus it suffices to calibrate the minimum and maximum

points to determine the level at any point in the drum.

The determination of the level parameters is as follows:

Minimum level reading (0%)

For the minimum level the tank is considered to contain only the hydrocarbon and the capacitance is

calculated using the formula:

𝑐(0%) =2𝜋𝜀𝐻𝐶𝐿

ln(𝑏 𝑎⁄ )… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … . . 𝐸𝑞. 7

o C(0%): the capacitance measurement when there is no water in the tank.

o 𝜀𝐻𝐶 : Dielectric constant of the hydrocarbon Maximum level reading (100%)

In this case the calculations are done with the consideration that the tanks contains only water, the

capacitance is therefore determined thus:

𝐶(100%) =2𝜋𝜀𝐻2𝑂𝐿

ln(𝑏 𝑎⁄ )… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … 𝐸𝑞. 8

o C(100%): the capacitance measurement when the tank is filled with water

o 𝜀𝐻2𝑂 : Dielectric constant water

The minimum and maximum points are then used to calibrate the 4mA and 20mA points of the transmitter

respectively. For more accuracy, the midpoint (12mA point) can also be determined.

The Advantages of capacitance level transmitters are:

They are very cost effective

Fast response speed thus real-time level monitoring is made easy

Interface measurement possible

Effective for high temperatures and pressures applications

They have certain disadvantages too, which are:

Not suitable for liquids with high viscosity as clogging or coating of the probes may lead to faulty

readings




It’s functioning depends on the homogeneity of the process fluid since calibration depends on the

dielectric constant of the fluid whose level is to be determined

Presence of foam in the medium can give faulty readings

Chemical compatibility between the probe material and the liquid to be measured is imperative

2.1.3.4 Ultrasonic level transmitter [7]

Ultrasonic measurement is based on the time-of-flight principle of sound waves.

A sensor emits ultrasonic pulses (of frequency greater than 20MHz) which the

surface of the medium reflects and the sensor detects again. The required time of

flight is a measure of the distance travelled in the empty part of the tank. This

value is deducted from the overall height of the tank to yield the level.

The speed of sound in different media depends on the physical properties of the

media, in gases the speed of sound is characterized by the equation:

𝑣 = √𝛾𝑅𝑇0

𝑀 [2] … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … . 𝐸𝑞. 9

o v: speed of sound

o R: molar gas constant (approximately 8.3145 J·mol-1·K-1)

o M: the molar mass of the gas

o γ: adiabatic index(sometimes assumed 7/5 = 1.400 for diatomic molecules and 5/3 =

1.6667 for monatomic molecules)

o T0: the absolute temperature of the gaseous medium

𝑣 = 𝑑𝑥𝑑𝑡⁄ → 𝑣 = √

𝛾𝑅𝑇0

𝑀=

𝑑𝑥

𝑑𝑡

→ 𝑡 = ∫𝑑𝑥

√𝛾𝑅𝑇0

𝑀

𝑥

0

Figure 8: Ultrasonic level

transmitter [12]




𝑡ℎ𝑢𝑠 𝑡 =𝑥

√𝛾𝑅𝑇0

𝑀

… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … . 𝐸𝑞. 10

But on emission, the ultrasound wave travels twice the distance between the emitter and the surface of the

liquid. Thus the time of flight

𝑡𝑓 =2𝑑

√𝛾𝑅𝑇0

𝑀

… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … . 𝐸𝑞. 11

From Eq.11 above, we see that the time of flight is directly proportional to the distance between the liquid and

the transmitter.

Minimum level determination:

To determine the minimum level (0%), the minimum distance d0 is fixed and the time of flight

calculated or measured practically and it’s value associated to the 4mA end of the scale. i.e.

𝑡𝑓0 =2𝑑0

√𝛾𝑅𝑇0

𝑀

… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … 𝐸𝑞. 12

Maximum level determination:

For the maximum level (100%) the maximum distance d100 is fixed and it’s corresponding time of

flight calculated or measured and the value attributed to the 20mA end of the scale.

𝑡𝑓100 =2𝑑100

√𝛾𝑅𝑇0

𝑀

… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … . . 𝐸𝑞. 13

With these two points determined and positioned and due to the linear relationship between the time

of flight and the distance covered, the level can be determined at any position between these points (tf0

and tf100 ).

This method of level measurement also has its advantages and disadvantages, some of the advantages are:

The sensors do not come in contact with the process fluid

They have no moving parts thus highly maintainable.

They are very accurate since measurement does not depend on process parameters

Some disadvantages are:




The time of flight of a sound wave depends on the temperature and pressure of the medium so changes

in temperature and pressure may falsify readings.

Turbulence in the liquid may falsify level measurement due to inconsistency in the reflecting surface.

Not suitable for high pressure applications

Not suitable for liquids that foam

2.1.3.5 Float level transmitter

Floats work on the simple principle of placing a buoyant object with a specific gravity intermediate between

those of the process fluid and the headspace vapor into the tank, then attaching a mechanical device to read

out its position. The float sinks to the bottom of the headspace vapor and floats on top of the process liquid.

The float is a basic solution to the problem of locating a liquid's surface, the main problem is locating the

position of the float. Different methods are used to locate this position. Early float systems used mechanical

components such as cables, tapes, pulleys, and gears to communicate level. Magnet-equipped floats are popular

today.

2.1.3.6 Magnetic and magneto-restrictive level gauges

2.1.3.6.1 Magnetic level gauges

These gauges are similar to float devices, but they communicate the

liquid surface location magnetically. The float, carrying a set of strong

permanent magnets, rides in an auxiliary column (float chamber)

attached to the vessel by means of two process connections. This

column confines the float laterally so that it is always close to the

chamber's side wall. As the float rides up and down with the fluid level,

a magnetized shuttle or bar graph indication moves with it, showing

the position of the float and thereby providing the level indication. The

system can work only if the auxiliary column and chamber walls are

made of nonmagnetic material. They are good substitutes for the level

glass gauge.

2.1.3.6.2 Magnetostrictive level gauge

Instead of mechanical links, magnetostrictive transmitters use the speed of a torsional wave along a wire to

find the float and report its position.

Figure 9: Magnetic level gauge equipped

with a float system [2]




A sensor wire is connected to a piezo-ceramic sensor at the transmitter and a tension fixture is attached to the

opposite end of the sensor tube. The tube either runs through a hole in the center of the float or is adjacent to

the float outside of a nonmagnetic float chamber.

To locate the float, the transmitter sends a

short current pulse down the sensor wire,

setting up a magnetic field along its entire

length. Simultaneously, a timing circuit is

triggered ON. The field interacts immediately

with the field generated by the magnets in the

float. The overall effect is that during the brief

time the current flows, a torsional force is

produced in the wire, much like an ultrasonic

vibration or wave. This force travels back to

the piezo-ceramic sensor at a characteristic

speed. When the sensor detects the torsional

wave, it produces an electrical signal that notifies the timing circuit that the wave has arrived and stops the

timing circuit. The timing circuit measures the time interval (TOF) between the start of the current pulse and

the wave's arrival. From this information, the float's location is very precisely determined and presented as a

level signal by the transmitter.

Key advantages of this technology are that the signal speed is known and constant with process variables such

as temperature and pressure, and the signal is not affected by foam, beam divergence, or false echoes. Another

benefit is that the only moving part is the float that rides up and down with the fluid's surface.

Figure 10: Depiction of a magnetostrictive level transmitter [1]




2.1.3.7 Radar (microwave) and guided wave radar

2.1.3.7.1 Radar level transmitters

Radar level transmitters work with high-frequency radar pulses which are emitted

by an antenna and reflected from the product surface. The time of flight of the

reflected radar pulse is directly proportional to the distance traveled. If the tank

geometry is known, the level can be calculated from this variable.

Radar is an electromagnetic wave, thus travels at the speed of light in a vacuum.

In different media however, the time of flight of a Radar pulse depends on the

permeability (𝜇 ) and permittivity (𝜖)of the medium. The speed of an

electromagnetic wave (𝜐) is characterized by the equation:

𝑣 =1

√𝜇𝜖 [3]… … … … … … … … … … … … … … … … … . . 𝐸𝑞. 14

Following Eq.14 above, the time of flight can therefore be characterized by the

equation:

𝑡𝑓 =2𝑑

√𝜇𝜖… … … … … … … … … … … … … … … … … … … … … . … … … … … … … … … … … … … … … … … … . . 𝐸𝑞. 15

The calculation of the calibration parameters is similar to the procedure used above in the calculation of the

calibration parameters of ultrasonic level transmitters. The formulae used are derived from Eq.15 above and

are presented as follows:

Minimum level indication:

𝑡𝑓0 =2𝑑0

√𝜇𝜖… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … 𝐸𝑞. 16

Maximum level indication:

𝑡𝑓100 =2𝑑100

√𝜇𝜖… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … 𝐸𝑞. 17

The advantages of radar level transmitters are:

They are very accurate ±0.5 mm (0.02 inches)

Installation is done at the top of the tank, making it relatively easier to install

Non-contact thus the physical properties of the liquid like temperature and density don’t influence its

accuracy.

Figure 11: Radar transmitter

installed on a tank [12]




No re-setup required when changing liquids

The disadvantages associated with using these are:

Efficiency of transmitter is affected by the shape of the tank

Foaming may cause faulty readings

Turbulent surfaces may affect the readings

Radar transmitters cannot measure interfaces

Not suitable for use in small tanks and for dangerous products because the difference between the

transmitted and received signal may be difficult to measure due to the high speed of the waves

2.1.3.7.2 Guided Radar level transmitters

Guided Radar level transmitters work with high-frequency radar pulses which

are guided along a probe which extends to the bottom of the tank. As the pluses

impact the medium surface, the characteristic impedance changes and part of the

emitted pulse is reflected. The time between pulse launching and receiving is

measured and analyzed by the instrument and constitutes a direct measure for the

distance between the process connection and the product surface. Calibration

calculations are similar to those for radar level transmitters. The main advantage

of the guided wave radar over the radar level transmitters is their ability to

measure interfaces. They are more accurate than the radar transmitters, can read

levels in the presence of foam and are not disturbed by turbulent interfaces

2.1.3.8 Nuclear level transmitter

A nuclear level transmitter is a level measuring system consisting of a

radioactive source that directs radiation through a vessel to a detector,

such as a Geiger counter on the other side of a vessel. Nuclear level

sensors are used for process materials that are extremely hot, corrosive,

toxic, or under very high pressure and so are not suitable for intrusive

level detectors. Radioactive elements such as cesium 137 or cobalt 60

provide the radioactive source in the form of gamma rays. The

absorption of gamma rays vary with the amount of liquid between the

source and detector, and hence is a function of liquid level. The

radiation level measured by the detector is related to the length of

liquid in the path x according to:

Figure 12: Guided wave radar

installed on a tank [12]

Figure 13: Example nuclear level

measurement [2]




𝐼 = 𝐼0 exp(−𝜇𝜌𝑥) [3]… … … … … … … … … … … … … … … … … … … … … … … … … … 𝐸𝑞. 18

Where

o I= the radiation level received by the detector in the presence of a liquid in the drum

o I0= the radiation level received by the detector in the absence of a liquid in the drum

o ρ= the density if the liquid

o 𝜇 = The mass absorption coefficient of the liquid.

Nuclear level sensors are relatively expensive to purchase, install, and operate. However, they are sometimes

the only way to measure level under extreme conditions.

We have described the principles used by some level sensors, it is worth noting that this is far from being an

exhaustive list of technologies. Other technologies are:

The vibrating or tuning fork used for point level measurement. The fork vibrates at a particular

frequency as soon as it comes in contact with the liquid.

The optical or laser level sensors which function with the same principle as radar transmitters but for

the fact that light is used instead of radio or microwaves;

The displacer liquid level sensor which function by the Archimedes principle. This liquid level

measuring system consisting of a buoyant cylindrical object, heavier than the liquid, immersed in the

liquid and connected to a spring or torsion device that measures the buoyancy of the cylinder as level

increases or decreases.

2.2 BASICS OF PM (2P 4M) ANALYSES METHODOLOGY [9] [10]

This tool was created by the Japanese Institute of Plant Maintenance (JIPM) to aid in the diagnostics of system

failures, It may be defined as:

P-M analysis is a problem-solving approach to improving equipment effectiveness which states: There are

phenomena that are physical, that cause problems which can be prevented (the 2Ps) because they are to do

with materials, machines, mechanisms and manpower (the 4Ms). [4]

Or

2P-4M analysis is a systemic method for the analysis of a problem which examines all the causal factors and

identifies all the abnormalities with the aim of reducing them to ZERO [5]

The 2Ps in this methodology stand for:




2P= problem: chronic loss (in quality, reliability, performance) + physical: principle or physical law

that governs the system or is at the origin of the problem.

4M= the problem generation mechanism

+ 4Ms (manpower, machine, method, materials)

The 2P-4M methodology is composed of 8 steps which are supposed to be applied meticulously in order to be

sure you are geared toward ZERO defects. These steps are:

2.2.1 STEP 1: CLARIFY THE PROBLEM WITHOUT ANY PRECONCIEVED IDEAS

This step has as primal objective the clear definition of the problem as it is observed through its external

manifestations.

To succeed in this step it is imperative to do away with all preconceived ideas and assumptions. In order to do

this,

Describe the problem as it is observed onsite. It is important to precisely express these observations by

decomposing them as much as possible to small verifiable elements. If we do general observations, an

exhaustive analysis may not be possible and the causal factor may not be found.

Following the onsite observations, classify the problems following the what, when, who, where, how

problem solving tool.

And finally do an inventory on the system of what is good and what is not.

2.2.2 STEP 2: CONDUCT A PHYSICAL ANALYSIS OF THE SYSTEM

This step has as objective to decompose the problem from a physical pint of view, this will permit you to see

above experience, impressions or intuitions. To do this it is important to divide the step into phases as presented

on figure 14 below




PHASE 1:Define the functioning principle

PHASE 2Identify the required functioning standards and conditions of the

functional elements and structures to obtain ZERO defects

PHASE 3Bring out the interactions between the functional elements and the structures

PHASE 4Bring out the possible variations

between the elements

Units of measurement

Figure 14: Principle of step 2 [5]

PHASE 1: Understand the functioning principle of the process or system

For this phase, it is important to:

Determine the principle or physical laws that govern the process or the system being analyzed

Draw the diagram or process schema of the system in question

Identify the functional modules and the structures that are directly related to the problem.

Drawing the process schema permits us to ask questions that are directly related to the process, how it functions

and the position of the elements with respect to each other. This permits the analysts to build a mental image

and thus bring to light certain ideas which could have been out of reach.

PHASE 2: Describe the required standard conditions relating to the functional elements as well as the

structure of the system to obtain ZERO failure.

Before we describe this stage, it is important for us to define some terms.

Functional element: this is a group of subsets or components that have just one function in the system

or process.

Structure: this denotes the links between the different functional elements as well as their modes.

In this phase, all the functional elements and structures which are related with the functioning principle that

was explained in phase 1 are supposed to be identified. Following their identification, their characteristics and

standard conditions that ensure ZERO failure are defined.




PHASE 3: The different interactions between the elements of the process or system

In this phase we look for all the possible interactions between the functional elements of the system

PHASE 4: Possible changes in interactions

This is the final phase of step2, in this phase we look for all the possible changes in the system and quantify

their variations.

2.2.3 STEP 3: IDENTIFY THE POTENTIAL FACTORS FOR CHANGE

This step has as objective the exhaustive identification of the potential factors that are liable to have caused

the changes in the interactions between the elements of the system. It is imperative to enlist all the causal

factors, whether they contributed directly or not to the problem.

PHASE 1:

Define the functioning principle

PHASE 2

Identify the required functioning

standards and conditions of the

functional elements and structures to

obtain ZERO defects

PHASE 3

Bring out the interactions between the

functional elements and the structures

PHASE 4

Bring out the possible

variations between the

elements

Units of

measurement

STEP3

Identify potential factors that can be changed

Figure 15: Principle of step 3 [5]

Step 2 permitted us to bring out the interactions between the elements in the system and the different variations

that could be observed.

In this step thus we look for the impact of each of the M’s on these interactions (cause-effect) by basing

ourselves on the 4M principle, while limiting ourselves to the functional elements.

The 4Ms taken into consideration are the following:

Machine: considering the normal functioning of each of the functional elements or components of the system,

what is the impact of the degradation of a system component on the variations of the interactions?




Methods: what are the links between these variations on the exploitation parameters of the components?

Man power: if the previous 2Ms are correct, we verify if the variations are due to the precision of the standards

or the non-respect of these standards by operators.

Materials: in case the previous Ms are correct we verify of the quality of the materials are not the cause of the

problem. In our case this will take into consideration the environmental conditions.

When attempting to exhaustively identify the potential factors that need to be changed, it is very important to

understand that these factors can only be identified using the correlations between the 4Ms and the system.

2.2.4 STEP 4: IDENTIFY ALL THE POSSIBLE CAUSES OF THE PROBLEM

Step 4 of the PM analyses has as primal objective the identification of all the possible causes of the anomalies

that can plague the components of the system using the 4Ms. For that the 4M analysis is cascaded from the

primary causes to the most basic. In basic terms what we do is create a cascade of cause/effect, where each

potential cause becomes an effect.

It is important to shed light on some concepts before we continue explaining this step. We call:

Primary 4Ms: all the causes from which the changes of the interactions between the equipment can originate.

Secondary 4M: all the causes originating from the primary 4Ms. The number of levels of 4M depends on the

problem being solved.

Properties of the primary 4Ms:

Don’t take into consideration the degree of criticality of the causes, prioritization is of no object here.

List all the possible logical causes relative to:

o Materials: precision that originates from the process

o Methods: functioning, startup, modus operandi, measurements

o Man power: expertise, respect of the rules.

o Machine, environment and accessories should also be analyzed in this light.

Properties of the secondary 4Ms:

List all the factors without considering their impact or degree of criticality

Take each primary 4M as an independent component and find all it’s causal factors.

Apply the same methods used in the determination of the primary 4Ms

The steps 1 to 4 can be summarized by table 4 below:




Table 4 : Summary of steps 1 to 4 [5]

Step 1 Step 2 Step 3 Step 4

problem Physical

analysis Possible factors

Possible deviation of factors

Observed

phenomena

What is the

physical

principle by

which the

system

functions?

What are the factors that

could possibly have

changed in the system or

that can possible be

changed?

Analyzing the mechanism Analyzing each of the

components

Verification of

anomalies onsite

Effect Cause Effect cause

Control chart

Management

conditions for zero

failure.

2.2.5 STEP 5: DEFINE THE OPTIMAL CONDITIONS

The objective here is to look for all the quantifiable anomalies of the components and subsystems, even the

ones that seem insignificant. It is worth noting that an anomaly here is gap that may exist between the existing

conditions and the reference state. This is the optimal state.

𝑜𝑝𝑡𝑖𝑚𝑎𝑙 = 𝑛𝑒𝑐𝑒𝑠𝑠𝑎𝑟𝑦 + 𝑛𝑜 𝑟𝑖𝑠𝑘 [5]

Where:

Necessary: the state that permits the system to function as required in terms of reliability, quality and

productivity.

No risk: this is the supplementary condition that is necessary and sufficient so that no chronic failure

risk occurs.

anomalies possibles

secondary 4M

primary 4M

factor 1

factor 2




The optimal state is therefore a high reliability state which is associated with productivity and reliability that

conforms to specifications

2.2.6 STEP 6: MEASURE THE GAP BETWEEN THE EXISTING AND OPTIMAL

STATES

To measure the gap between these states:

For each possible causal factor of change of state that was identified during steps 3 and 4, determine

the most precise and reliable way to measure the gap

Define the modus operandi for each measurement.

Take the required measurements, compare with the optimal values and then with the gap determine the

anomalies; these are the causes of the problem.

2.2.7 STEP 7: DEFINE THE ANOMALIES TO BE TREATED

The objective of this step is to choose the deviations from the standard conditions which are supposed to be

treated as anomalies.

It is therefore important to;

Reexamine all the potential factors

Compare all the abnormal conditions to the standard

Consider as abnormal all the conditions that are at the border between the normal and abnormal

conditions.

It is important to think in terms of optimal conditions and not in terms of conditions that are “just necessary”

2.2.8 STEP 8: CORRECT, AMELIORATE AND STANDARDISE

In this step, the objective is the definition of the corrective end ameliorative actions for each anomaly

identified. The different actions carried out are:

Group as many factors as possible for simultaneous repairs and amelioration.

After the repairs, replace obsolete technologies and then draw a continuous amelioration plan.

Draw up a preventive actions plan and set standards for the measurements and routine.

Confirm the efficiency of your actions by checking:

o If some factors have not been forgotten

o If the standards created are correct




Define the problem.

How does it manifest itself?

What are your observations?1.CLARIFY THE PROBLEM

What, who, where, when, why

Inventory of problems

Determine the interactions between

the components on a physical level

Diagram showing functioning

principle, standard operating

conditions, interaction diagrams,

quantify the changes

2.REALISE THE PHYSICAL

ANALYSES OF THE PROBLEM

3.IDENTIFY ALL THE

POTENTIAL FACTORS FOR

CHANGE

4.IDENTIFY ALLA THE

POSSIBLE LOGICAL CAUSES

5.DEFINE THE OPTIMAL

CONDITIONS

7.FIX THE ANORMALIES

6.DETECT THE GAPS WITH

RESPECT TO THE OPTIMAL

CONDITIONS

Define the best method for analyses,

start by analysing the potential

cause factors

Optimal condition= necessary + no

risk

Identify the mechanisms, understand

how they function, use 4M to

determine the possible cause factors

Primary 4M, secondary 4M, anomalies

Do an exhaustive determination of

the potential factors that can be at

the origin of the problems and

changes in the interactions

Using the 4Ms identify all the logical

causes that can be at the origin of

the previous potential factors

For each logical cause define the

expected optimal characteristics

For each logical cause, detect the

gap between the existing and

optimal conditions

Decide which of these deviations are

anomalies and are to be treated

8.CORRECT/AMELIORATE/

STANDARDISE

Figure 16: Summary of PM analysis


In this chapter, we defined level measurement and then proceeded to underline it’s importance in a petroleum

company such as SONARA, taking the control of water level in the boilers and the automation of the level

regulation system as concrete examples. The types of level measurement which are Point and continuous level

measurement were later defined and explained. The level measurement basics were then concluded with a

detailed explanation of the technologies and mathematical proof that gave basis to some of the level

measurement techniques, with emphases put on the techniques commonly used in the petroleum industry.

Following the basics of level measurement, a detailed explanation of PM analysis, a TPM tool which has as

primary objective the analysis and troubleshooting of a system with the aim of tending towards zero failure

was given. This is the methodology that we used to diagnose the problems at the instrumentation service of

the maintenance department in SONARA so that this thesis could be written.




3.1 INTRODUCTION

In this chapter we delved into the analyses of the system using PM-analysis. The results of this chapter are the

following:

Analysis of the components of the level measurement system;

The technical and strategic problems plaguing the system;

Justification of the above mentioned problems with statistically analyzed data.

The causes of these problems

3.2 PM (2P 5M) ANALYSIS OF THE LEVEL MEASUREMENT SYSTEM.

This analysis has as objective the reduction of the faults in a system to zero. Given that the level measurement

system is supposed to monitor process, and is not supposed to malfunction for any reason when the installations

are running, it is therefore important to try as much as possible to reduce the faults to zero.

3.2.1 STEP 1: CLARIFICATION OF THE PROBLEM WITHOUT ANY PRECONCIEVED

IDEAS

PROBLEM OBSERVED: Lack of reliability and low performance of the level measurement system.

3.2.1.1 OBSERVATIONS FROM ANALYSES:

OBSERVATION 1: Discrepancies between the readings of the level transmitters that manage the same

process.

Statistics supporting observation 1:

To realize this quantification, the data was collected from work permits that were archived since the year 2012.

To be precise, the work permits that were analyzed were those of the 2012, 2013 and 2014. In total, 54 work

permits were identified and analyzed in order to quantify the inconsistencies that plague the system most.

The problem that resulted due to discrepancies between the readings of level transmitters are summarized in

table 5 below.




Table 5: Problems due to the discrepancies between readings of level transmitters supposed to be taking the same value

Problem Number of

work permits

Percentage

Discrepancy between the process regulation level transmitters and the

security level transmitters

14 25.92%

Discrepancies between the process regulation, security and level glass

gauges

18 33.33%

Discrepancies between the level transmitters found at the production units

and the values received at the level of the control room

8 14.81%

Out of the 54 work permits, we noticed that 40 of them were emitted as a result of discrepancies, giving a

percentage of 74.07% of the total work permits that were analyzed.

DECOMPOSITION OF OBSERVATION 1 TO VERIFIABLE ELEMENTS:

The verification of these discrepancies was done with the values that were taken down by the operators when

reporting the problem. The various verifiable elements of this problem are listed as follows:

Take the readings on the level transmitters that are found in the units

o Process regulation transmitter reading:

o Security transmitter reading:

o Level glass gauge reading:

Take the reading from the control room:

Quantify the difference between the readings taken

Compare with the defined tolerance.

The following are examples of cases from the analyzed work permits. Each quantification is chosen from a

specific problem that was reported.

It is to be noted that a tolerance of 5% was defined to ensure proper functioning of the system.




Table 6: Example of discrepancy between the level transmitters found at the units and the control room.

Work permit No: 78241

Drum concerned 50TKV1

Process level transmitter (PLT)% 28.7

Security level transmitter(APS)% 26.3

Level glass gauge (LG)% 27

Control room (CR)% 35.5

Discrepancy parameter PLT-

APS(%)

PLT-LG

(%)

PLT-

CR(%)

APS-

LG(%)

APS-

CR(%)

LG-

CR(%)

difference 2.4 0.7 6.8 1.3 9.2 8.5

Respect of tolerance (5%) YES YES NO YES NO NO

Table 7: Example of discrepancy between the process and security transmitters


Drum concerned 10B1

Process level transmitter (PLT) 52

Security level transmitter(APS) 61

Level glass gauge (LG) 50

Control room (CR) 53.5

Discrepancy

parameter

PLT-APS

%

PLT-LG

%

PLT-CR

%

APS-LG

%

APS-CR

%

LG-CR

%

difference 9 2 1.5 11 8.5 3.5

Respect of

tolerance (5%)

NO YES YES NO NO YES




Table 8: Example of discrepancies between the process and security level transmitters and the level glass gauge.


Drum concerned 60B3

Process level transmitter (PLT) % 50

Security level transmitter(APS) % 51

Level glass gauge (LG) % 66

Control room (CR) % 50

Discrepancy parameter PLT-APS

%

PLT-LG % PLT-CR % APS-LG % APS-CR % LG-CR %

difference 1 16 0 15 1 16

Respect of tolerance

(5%)

YES NO YES NO YES NO

In order to better understand the discrepancy problem, we will proceed by doing a what, when, who, where,

how analyses.

This analysis consists of answering the following questions:

What problem was observed?

When was this problem observed?

Who observed the problem or who was affected by the problem?

Where was the problem observed?

How was the problem observed?

This analyses will however not be done for all the previously analyzed work orders to avoid too much

repetition. We will therefore do analyses for problems in groups. The table below gives the results of the

analyses




Table 9: WWWWH analysis of the discrepancy problems

WHAT WHEN WHO WHERE HOW

Discrepancy

between the

measurements of

the onsite level

transmitters and

the control room

2012 Control room operators

and onsite operator

posted at unit 10

Unit 10

Drum: 10B2

Alarm at the level of the

interface in the control room

and visual inspection


and the onsite operators

in charge of the unit in

question.

Unit 30

Equipment:30LDT305

Unit 20

Equipment:20LDI310

Unit 60

Equipment:60LI038

Alarm at the control room

and visual confirmation by

the operator onsite.


and the onsite operators

in charge of the unit in

question.

Unit 50

Equipment:50LI0055

Unit 50

Equipment:50LDC0054

Alarm at the control room

and visual confirmation by

the operator onsite.

Discrepancy

between the

process control

level transmitter

and the security

level transmitter

2012 onsite operators during

routine checks

Unit 60

Equipment:60LI0009

Visual inspection by

operator onsite and alarm in

the control room

2013 Onsite operators during

routine checks and the

control room operators

in case of alarm

Unit 10

Equipment involved:

10LT0014 and 10LT0010

Unit 40

Equipment involved:

40LC003 AND 40LC0010

Unit 50

Equipment involved:

50LT0001 and 50LT0003

Unit 50

Visual inspection by onsite

operators

And alarm in the control

room





Equipment:

50LI0013 and 50LI0022

Unit 60

Equipment involved:

60LT0027 AND

60LT0327

Unit 251

Equipment involved:

251LI0003 and

251LI0001

2014 Onsite operators during

routine checks, control

room operators in case

of alarm

Unit 40

Equipment involved:

40LC0010 and 40LC0003

Unit 50

Equipment involved:

50LI0013 and

50LI0022

Unit 60

equipment involved:

60LT0027 and 60LT0327

60LDT025 and

60LDT0325

Unit 251

Equipment involved:

251LI0001 and

251LI0003

Visual inspection by onsite

operators

And alarm in the control

room

As evident from the table above, there is a lot of repetition as concerns the who’s and the how’s, this is as a

result of the routine involved in the performance of certain tasks. For the third discrepancy problem

(discrepancy between the readings of the process and security transmitters and that of the level gauge),

the results of the analysis are similar to the ones on table….above, showing that it is sufficient for us to continue

our 2P 5M method.




OBSERVATION 2: level transmitter shows BAD CTL or BAD PV or frozen at a fixed value

The BAD PV and BAD CTL problems accounted for 3 work permits, thus 5.56% of the total number

of work permits that were analyzed.

The frozen or fixed value problem accounted for 3 permits, thus giving a percentage of 3.7%

These problems cannot be disintegrated into small verifiable elements because they are present at their most

basic states and can directly be verified. We will therefore proceed to the analysis of these problems.

Table 10: WWWWH analysis of BAD PV and BAD CTL problem

WHAT WHEN WHO WHERE HOW comments

Transmitter

shows BAD

CTL

2012 Control room

operators and

onsite operator

posted at unit 50

Unit 50

Equipment:

50LC0009


interface in the control

room during visual

inspection

This error

occurred twice

during this

year

BAD PV 2012

Unit 50

Equipment:

50LC0009



room during visual

inspection

Frozen

transmitter

(transmitter

showing fixed

value)

2012 Control room

operators and

onsite operator

posted at units 60

and 10

Unit 60

Equipment:

60LDC029



room during visual

inspection

2014

Unit 10

Equipment:

10LDT024

OBSERVATION 3: Other problems

These are problems that did not fall in any of the categories above, and appeared just once each. They account

for the remaining 16.6% of the analyzed work orders. Their analyses is presented on table 11 below.




Table 11: WWWWH analysis of the unclassified problems


The level transmitter

gives no reading

despite the level

present

2012 Operator on site Unit 60

Drum: appendix of 60B6

Equipment: 60LDC0025

Visual inspection during

routine check

Malfunctioning of the

level transmitter

2012 Operator onsite Unit 50

Equipment: 50LC0031

Alarm at control room

and onsite verification

Indication of maximum

value even though the

column is empty

2013 Operator in the

control room and

the operator

onsite

Unit 10

Equipment: 10LI00308

Visual inspection after

emptying the column

No reading at the level

of the control room


control room

Control room

Equipment: 50LC0001

Noticed visually on the

screen at the control

room during real time

process monitoring

Level transmitter

shows rising level

when the drum is being

emptied and despite the

fall of the values of the

other indicators

connected to the same

drum


control room

Unit 50

Equipment: 50LC0001

Noticed visually on the

interface at the level of

the control room

No level visibility 2014 Operator at the

level of the

control room

Control room

Drum: 50B9

Noticed at the level of

the control room

Synchronization of the

transmitters with the

control loop

2014 Instrumentation

technicians

Unit 30

Equipment: 30LT0018




The next phase after describing and analyzing the problems is the establishment of an inventory of processes

and classification as good or bad. This can’t be done at this level due to a lack of information.

Conclusion of step 1

In this step,

we identified the problems plaguing level measurement,

did a quantitative analysis of each of the problem with respect to their occurrences in the work permits,

disintegrated the problems into small verifiable elements

And finally did a what, when, who, where, how analysis to better understand the problem.

From this step, we go to Step 2 which will consist of doing a physical analysis of the system in order to identify

all the possible problems that the system can have.

3.2.2 STEP 2: PHYSICAL ANALYSES OF THE LEVEL MEASUREMENT SYSTEM

PHASE 1: Better understanding of the functioning principle of the level measurement system

Physical principle that the system resides on:

Hydrostatic pressure:

This is the principle that the differential pressure level transmitters work with. Amongst all the level

transmitters present at the SONARA refinery, 95% of them are differential pressure level transmitters, making

the Hydrostatic pressure principle the most used and thus the principle requiring the most attention.

The principle of communicating vessels:

All the drums in the refinery except those that are buried (like the 70B3 drum that collects all the

purges) have level glass gauges. This principle is that that governs the functioning of level glass gauges.

Following the identification of the main principles that govern level measurement, it is necessary to draw the

diagram that brings to light these principles. This diagram will help us to identify the different functional

modules that are directly related with the problem at hand.

The following (figure 17) is a functional decomposition of the level measurement system in the form of a tree

diagram to better understand the system, as well as bring out the functional elements.




Figure 17: Functional tree diagram of a differential pressure level transmitter

APPENDIX 3 shows the picture of a Rosemount differential level transmitter, it will give a more vivid view

of some of the components of the system. The continuation of step 2 and the step 3 analysis is done on table

12 below.

level measurement system

level measurement equipment

level glass gaugeelectronic level

transmitters

mechanical components

pipes or capillaries diaphragm

electrical components

electrical cables

energy cablesdigital cables for

transmission of 4-20mA signal to the control room

electronic module

tapping points on the drum

connection components

pipes valves


46 END OF COURSE DISSERTATION WRITTEN AND DEFENDED BY METUGE OKANE ENONGENE IN VIEW OF OBTAINING A MASTERS OF

ENGINEERING IN INDUSTRIAL ENGINEERING

Table 12: Steps 2 and 3 of the PM-analysis of the system

PM analyses step 2 and 3

What is the problem? What functions have been affected? What has changed?

Discrepancy between the values

read on the level transmitters as

well as the control room

The level readings in the control room are not reliable

The level readings on the electronic modules in the refining units are not

reliable

Uncertainty in the process regulation parameters

Opening of release valves at high levels

Closing of valves at low levels

Functioning of security alarms, both high and low level alarms

Calibration parameters

System passed from

pneumatic to digital between

2011 and 2012

Diagram showing operating principle under normal conditions(see figure 2 for more

visibility)

Physical principles of the system

Hydrostatic pressure:

This is the principle that the differential pressure

level transmitters work with. Amongst all the level

transmitters present at the SONARA refinery, 95%

of them are differential pressure level transmitters,

making the Hydrostatic pressure principle the

most used and thus the principle requiring the most

attention.




LT1LT2 LG

DRUM

TO CONTROL AND REGULATION ACTUATORS

(VALVES)

TO CONTROL

ROOM

KEY

LT

LG

VALVE

DIGITAL SIGNAL

ELECTRIC SIGNAL

CAPILLARY TUBE

DRUM

LEVEL TRANSMITTER

LEVEL GLASS

PIPING

The principle of communicating vessels:

All the drums in the refinery except those that are

buried (like the 70B3 drum that collects all the

purges) have level glass gauges. This principle is

governs the functioning of level glass gauges.

Known standard conditions of the system

The total volume of the drum

The positions of the various tapping points on the

drums are supposed to be at the same level

The

A 4-20mA digital signal conveys the level

readings to the control room

The calibration parameters of the level

transmitters




Interaction diagrams Elements interacting with each other Possible variations between

interactions Interacting elements Link method

drum/tapping points

welding

tapping point/valve

Bolts for connection and gasket against

leaking

valve/diaphragm Bolts for connection and gasket against

leaking

valve/level glass Screw pipe

diaphragm/sensor module

Capillary with silicon fluid for pressure

transmission or inox pipes for direct contact

with process liquid

sensor module/electronic

module

Screws

sensor module/control room

Digital cable conveying a 4-20mA signal

Electronic module/regulation

valves

Pneumatic links or digital links depending

on the valve being controlled

Control room/regulation

valves

Digital links

Physical analysis:




The transmitters that are supposed to be taking the same measurement don’t have their tapping points the same level

most of the level glass gauges are blackened rendering the liquid in the tubes invisible

the graduations on the level glass gauges only permit approximation of readings

3.2.3 STEP 4: IDENTIFICATION OF CAUSES

Table 13 below is the detailed analysis of the problems noticed to get to the root causes, it is a cause effect table spanning from the primary

causes of the problem to the tertiary level which in our case is the root cause of each problem. The problems are classified according to the

4M’s which are man, machine, method and material or environment.

Table 13: 4P table for the identification of root causes(step 4 of PM analysis)

problem 4M class Primary 4M Secondary 4M Tertiary 4M

Discrepancies

between the

readings of the

process and

security level

transmitters as

well as level glass

and control room

Man power

Misinterpretation of the level

reading

1.1 blackened reading interface of

level glass

1.2 graduations on the level glass

not labelled

1.3 some of the level transmitter pairs

have different scales

1.3.1 difference in position of

tapping points

Incompetence of some

personnel 2.1 Training technique of technician

Insufficient manpower 3.1 many technicians have gone on

retirement but no replacement done

machine 4.1.1 bad contact at junction box





Level transmitter electronic

module failure

4.1 insufficient power reaching

transmitter 4.1.2 signal clipping failure

4.2 short circuits in junction box 4.2.1 condensed water present on

junction box

4.3 static electricity interfering 4.3.1 problem with transmitter

grounding

4.4 internal electronic component

failure

4.4.1 power surges

4.4.2 short circuit

4.4.3 Ageing of transmitter

4.4 Temperature fluctuations in the

units

5. Drift of transmitter

calibration parameters

5.1 error during the calculation of

parameters before calibration

5.2 pressure surges or electrical

surges

6. Erroneous or no level

visibility at the level of the

control room

6.1 Cable cut

6.1.1 Careless working conditions

around cables

6.1.2 cables loose from supports

6.2 External electrical interference

6.3 Bad contact at the level of the

junction box





Material and

environment

7. Insufficient spare parts 7.1 poor logistics policy

Method

8. No preventive maintenance

of instruments

8.1 Lack of preventive maintenance

plan

8.2 insufficient manpower

9. Insufficient corrective

maintenance 9.1 Insufficient manpower

10. No follow up of

maintenance key performance

indicators and metrics

10.1 No maintenance KPIs defined 10.1.1 No long term maintenance

amelioration plan 10.2 No end of maintenance

intervention report

10.3 No archiving of permits for

failed maintenance interventions

10.3.1 Poor policy for the archiving

of work permits

BAD PV and

BAD CTL

Machine

Transmitter off 11.1 Sensor not powered

Transmitter scale undersized or

oversized

12.1 Faulty calculations during the

definition of the scale

Material and

Environment

13. Process value under zero(

an example is when the drum is

empty)

Machine 14. Malfunction of transmitter

electronic components





Fixed reading or

freezing of

transmitter

15. Oversized scale defined

16. Malfunction of transmitter

probes(diaphragm)

Material and

environment

Trapped fluid in the transmitter

tapping or pipes

17.1 Transmitter tapping or pipes

blocked

17.1.1 Solidification of high

viscosity process fluid

17.2 entry of process fluid at the

low pressure tapping of the

transmitter in the case of piping

connection

17.2.1 failed regulation

The causes of the other problems not mentioned on this table have already been raised above, so including the problems on this analysis table will

only bring about unnecessary repetition.

3.2.3.1 Special case for the discrepancy between level readings

The discrepancy of level readings is the most common problem faced by the Instrumentation service, it accounts for 74.07% of the level

measurement problems. This raises particular interest to study it more closely from the technical point of view. From the STEP 4 analysis,

and onsite visits, we were able to identify the main cause of this problem as the difference in the level of tapping points (item 1.3.1, table 13)

Since pressure depends on height in a fluid, and the level measurement depends on pressure, it is clear that such a difference in height will

generate faulty level readings.

The disposition of the tapping points on drums is as shown on figure 18.




Figure 18: Disposition of tapping points on a drum

As depicted on the PID (figure 2);

TP1.1 and TP1.2 are connected to the level glass gauge

TP2.1 and TP2.2 are connected to the security level transmitter

TP3.1 and TP3.2 are connected to the process regulation level transmitter.

These is how the tapping points were disposed when the drums were produced, and that can’t be changed. As a result, these discrepancies are

inevitable because the scales are not even the same. Under normal conditions, the height difference TP1.1- TP1.2 and TP2.1-TP2.2 as

depicted on figure 18 is supposed to be zero (i.e. d=0) but as we can see, that is not the case.




This difference in the level of the tapping points is the main cause of the discrepancy in the readings of the level transmitters, so correcting

this anomaly, will solve the discrepancy problem by more than 90%

The remaining 10% is due to the other causes like

Blockage of tapping points by solidified viscous liquids

Failed regulation and

Electronic failure of the transmitters.

3.2.4 STEPS 5, 6 AND 7: OPTIMAL CONDITION, GAP ANALYSES AND DEFINITION OF ANOMALIES

The root causes identified in table 13 above are being further analyzed on table 14 below, this with the aim of identifying the optimal condition

of the system to prevent or reduce the probability of failure. The causes were each referenced on table 13 and the references act as the items

for analyses on table 14. This is a combination of steps 5, 6 and 7 of the PM-analyses of the system.

Table 14: PM-analyses steps 5-7

ITEM POTENTIAL CAUSE

STEP 5: OPTIMAL CONDITION STEP 6: GAP

DETECTION

STEP 7: ANOMALIES TO BE

TREATED

Necessary condition No risk Method of

measurement Corrective actions comments

1.1 Blackened reading interface

of level glass gauge

Clean level glass

interphase Colored fluid visual

Replace level glasses with

reflex or magnetostrictive glass

gauges and plan cleaning






DETECTION


TREATED



1.2

Graduations on the level

glass not labelled, thus

imposing approximations

Uniform divisions on

level glass

Visible

graduations

from 0-100%

visual

Add engraved scale plates to

the existing reflex level glass

gauges

1.3.1 Difference in the level of

the tapping points

Tapping points

should cover the

measuring range

Tapping points

should have the

same level

Observation

Devise a method to connect all

sensors at the same level or

change method of measurement

3.1

Insufficient manpower due

to retirement of many

technicians

observation Do recruitment or Institute

autonomous maintenance

4.1.1 Bad contact of cables in the

junction box

Check cable contacts

regularly visual Check contacts twice a year

4.2.1 Condensation of water in

junction box

Interior of junction

box should be

completely dry

Ensure water

tightness of the

junction box

visual

Use gasket to make box water

tight

Place silica gel in the boxes to

absorb water

4.3.1 Transmitter grounding

problem

All equipment should

be properly grounded

Check

grounding

regularly

Visual Check grounding annually






DETECTION


TREATED



4.4.1 Electrical power surges

Make sure supply is

between 10.5 and

42.4Vdc for

Rosemount and

Endress Hauser

_

HART field

communicator or

digital

multimeter

Check power twice a year

10.5 and 32Vdc for

Yokogawa

4.4.2 Short circuits Well insulated

connections _

HART field

communicator or

digital

multimeter

Check all electrical connections

after every 3 months

4.4.3 Ageing of transmitter

Use of transmitter

which has not

attained life cycle

_ Audit Replace after life cycle is

reached

4.4 Temperature fluctuations in

units

Ensure temperatures

between -50oC and

80oC

Ambient

temperature

Ta=25oC

Thermometer

Use equipment with

temperatures within process

range






DETECTION


TREATED



Or thermally insulate the

equipment

5.1 Calibration parameters

calculation errors

Use The HART field

communicator for

calibration

_ Observation

5.2 Pressure surges Stable pressure _ Control room

observation

6.1.1 Careless working conditions

around cables

Organization of the

cables on supports _ Observation

Recycling of workers training

on security at work

Institute 5S at workplace

6.1.2 Cables get loose from their

supports Cable supports - visual Check cable supports annually

7.1 Poor logistics policy observation Review logistics and spare

parts procurement policy

8.1 Lack of preventive

maintenance plan

Maintenance

planning - Observation Define maintenance plan






DETECTION


TREATED



10.1 No maintenance KPIs

defined

Minimum KPI’s

should be defined for

maintenance folowup

_ observation Define and follow-up KPI’s

10.2 No end of maintenance

intervention report

Institute maintenance

intervention reporting _ Observation

Design a maintenance

intervention report

10.3.1 Poor work permit archiving

policy

Archive all work

permits, both failed

and successful

_ observation

Make provisions for archiving

all permits including failed

permits

11.1 Transmitter sensor not

powered

Check power of

transmitters egularly visual

Check cable connections twice

a year

12.1 Faulty calculations for the

definition of the scale

Correctly defined

scale _

Check scale after every

recalibration intervention

13 Process value under zero

due to empty drum - - visual

Recalibrate transmitter when

drum is filled

14 Malfunction of electronic

components of transmitter

Good functioning of

electronic cards _

Digital

multimeter

Change circuit boards at the

end of their lifecycle

15 Malfunction of transmitter

diaphragm - - Test

Check diaphragm seals every 3

months






DETECTION


TREATED



16

Solidification of high

viscosity process fluid in

the pipes

Maintain temperature

at the required to

keep fluids from

solidifying

- observation Purge pipes monthly

17.1.1 Failed regulation or

asynchronous loop

Synchronous control

loop

Check and

Rectify

parameters

quarterly

Visually on

Process control

interface at

control room

Check loop parameters

quarterly

18 Obsolete level sensors Propose new sensors





This chapter was dedicated to the analysis of the level measurement system using the PM-analysis

methodology. The goal here was to identify all the possible problems that can plague the system, understand

these problems, propose corrective actions for the problems already existing and put in place a strategy to

prevent the problems that have not yet been encountered, as well as a corrective strategy if they are ever

encountered. The objective of this analysis as underlined above is to tend towards zero failure and for the

prevention of unplanned shutdown of the level measurement system. In this chapter, just 7 steps of this

methodology were applied, step 8 being the object of chapter 4.

At the end of this chapter the root causes of the problems identified for resolution are:

Difference in the level of measurement tapping points on the drums

Graduation of level glass gauges

Insufficient manpower

Lack of maintenance metrics and KPI’s

Maintenance intervention reporting

Obsolete level sensor for the drum 70B3

Bad archiving policy for the work permits

Insufficient logistics policy

Preventive maintenance and follow-up related problems




4.1 INTRODUCTION

Following the identification of problems and their root causes using the PM-analysis method in chapter 3

above, this chapter will be dedicated to STEP 8 of the PM-analyses methodology, which is the presentation of

results and corrective actions to be taken. These corrective actions will be divided into two categories which

are technical and strategic solutions depending on the nature of their causes.

4.2 TECHNICAL SOLUTIONS

These are the corrective actions proposed for the problems which are directly related to the technical aspects

of level measurement and maintenance.

4.2.1 UNGRADUATED LEVEL GLASS GAUGES

For this problem there are two possible solutions,

Graduate the present level glass gauges or

Change them with graduated magnetic level glass gauges.

Among these two solutions, the best in terms of feasibility and cost is the first, which is the graduation of the

level gauge glasses present at the refining units.

This can be achieved by either commanding engraved scale plates or having them produced at the workshop.

Figure 18 below is a level glass equipped with an engraved scale plate.

Figure 19: Armored level glass equipped with an engraved scale plate [6]




The following table gives a recapitulation of the level glass gauges found on the re-instrumentation plans, their

total height for measurement and the unit divisions of the appropriate scale plates that should be attached to

them.( for detailed table see APPENDIX 5)

Table 15: Recapitulation of the engraved scale plates to be made with respect to their unit scales

Scale plate measurement

height(mm)

Width

(mm)

Thickness(mm) Number of

scale plates

Unit division

(1%=__mm)

525 30 2.5 2 5.25

584 30 2.5 2 5.84

604 30 2.5 1 6.04

750 30 2.5 1 7.5

907 30 2.5 9 9.07

1266 30 2.5 2 12.66

1270 30 2.5 1 12.7

1375 30 2.5 2 13.75

1485 30 2.5 1 14.85

1626 30 2.5 1 16.26

1786 30 2.5 2 17.86

1986 30 2.5 1 19.86

TOTAL 26 scale plates

This is just the number of level glasses accounted for on the re-instrumentation plans, there are far more level

glass gauges found in the unit than those presented on this table, but they could not be used in the calculations

because the PID’s that show them do not have the required measurement dimensions.

4.2.2 DIFFERENCE IN THE LEVEL OF TAPPING POINTS

The difference in the level of the tapping points for the process and security level transmitters cannot be solved

completely because the tapping points are welded to the drums, this means they cannot be changed without

very long production stops and exorbitant costs. Rather than proceeding to change the tapping points, it is

better to leave them the way they are due to:

The cost of such a project;

The time it will take to realize such a project;

The loss in production that will be incurred by SONARA, Etc.




However the impact of the problem can be reduced by 2 simple solutions, depending on the positioning of the

tapping points on the drums and the size of the drums.

4.2.2.1 Use of T-junction pipe

A T-junction (APPENDIX 6 is a PID showing the correction of this problem using a T-junction) can be

used to connect some of the equipment, thereby eliminating the level difference and by extension the difference

in the scales of the transmitters. Figure 20 is an example of the T-junction to be used.

Figure 20: T-junction pipe to equate the level of tapping points

The references of the T-junction and it’s specifications are given on table 16 below.

Table 16: Specifications of the T-junction [10]

Designation Diameter Material Standard Series

TE EGAL SW 1”1/2(38.1mm) A105N ASTM 3000#

Figure 21 is a depiction of the tapping points brought to the same height so that all the level instruments can

be calibrated with the same scale and hence solve the level measurement problem.




Figure 21: TP1.1 and TP2.1 as well as TP1.2 and 2.2 brought together by T-junction pipe

4.2.2.2 Distribution tube

The second solution that can bring the tapping tubes to the same level is a distribution tube. The use of this

tube relies on the principle of communicating vessels. Figure 22 shows a connection tube.

Figure 22: Distribution tube




This tube can be mounted on a set of tapping points on the drum and it’s and the transmitters connected to it’s

own set of tapping points. Since it’s mounting will respect the principle of communicating vessels, all the

process parameters that determine the level of the liquid in the drum will be the same. Figure 23 is a visual

depiction of the use of a distribution tube.

Figure 23: Use of a distribution tube to bring tapping points together

Figure 24 Shows the drum assembly filled with water to depict the principle of communicating vessels.

Figure 24: Section view of drum-tube mount to show the principle of communicating vessels




The advantage of this method over the T-connection is that the tube can be designed to consider new level

requirements, but the disadvantages are:

The cost

The tube is to be designed for each drum separately since their operating conditions and positioning of

tapping points vary.

The tube is more adequate for use on small drums.

The T-junction and the distribution tube will bring the tapping points to the same level, thereby correcting the

discrepancy problem by about 90%.

The remaining causes of discrepancy problems can be resolved by preventive maintenance (cf. APPENDIX 8

for the preventive maintenance plan)

4.2.3 OBSOLETE LEVEL TRANSMITTER FOR THE DRUM 70B3

The drum with code 70B3 is used to collect the purged water and hydrocarbons in the refining units, it is a

buried drum with the properties presented on table 17

Table 17: Properties of the 70B3 drum [7]

Code 70B3

Designation Vidange des hydrocarbures

Design pressure 3.5 bars eff

Design temperature 180oC

Internal diameter 1721.44 m

Height 5 m

Liquid present Mixture of hydrocarbon and water

4.2.3.1 Criteria of choice for level measurement instruments [8]

In order to adequately choose level measurement equipment, the following are the properties that TOTAL

specifications advises us to consider:

The use of the equipment- process and/or security control

Physical and chemical characteristics of the product whose level is being monitored

The range of measurement

The precision




Operational minimum and maximum values

Study conditions ( temperature and pressure)

Quantity of instruments required for the function

Environment and installation conditions

4.2.3.2 Choice proper of level instrument for 70B3

The level measurement instrument currently installed here is a Masoneilan 12400 series torque tube displacer

digital level transmitter/controller which needs to be replaced.

Due to the dependence of contact level measurement technologies like the differential pressure

transmitters on process parameters, they were not considered as an alternative. In addition to that the

buried nature of the drum makes their installation impossible.

The position also makes it impossible to install any transmitter that works on the principle of

communicating vessels.

The best level measurement technologies to use here are non-contact technologies like radar and

ultrasonic technologies because:

o They are very accurate,

o Their dependence on process parameters for level measurement is limited

o They require very little or close to no maintenance

o Installation and commissioning is relatively easy and takes very little time.

Due to the Limitation of the ultrasonic level sensors however to pressure applications below 3 bars, the Radar

level transmitter is the best option. The following is the selection procedure of the different components of the

instrument.

1. Selection of the antenna specifications:

The selection of the antenna depends on:

The drum geometry

The measuring range required (which is 5m for 70B3)

The dielectric constant of the process liquid ( which is between 4.0 and 10.0 for a mixture of

oil and water)




Table 18: Rosemount 5402 antenna selection guide, Maximum Recommended Measuring Range, ft (m) [9]

The selected antenna is therefore the 5402 2-in. Cone/process seal with:

Maximum recommended distance= 15m

Transition zone4 limitation = 200 mm

Near zone5 limitation = 450mm

Near zone accuracy= ±15 𝑚𝑚

2. Selection of antenna model

For the Rosemount 5402 Radar level transmitter, there are two models of antennas, on the bases of their shape

and performance, these are the cone and process seal. For our case, the process seal is the most appropriate

because:

It is more suitable for condensation build-up than the cone, and the 70B3 tank was designed to

work at 180oC thus condensation buildup is inevitable;

4 Transition zones are areas where measurements are not recommended(transition zone=antenna length+150mm) [9] 5 Near zones are areas where the measurement accuracy is reduced(near zone = transition zone +250mm) [9]




The antenna is also cleanable but the cone is not cleanable for some applications.

For the model selection chart, confer APPENDIX 9

3. Accessories

An internal torque tube guide was built into the 70B3 drum, this will obstruct the radar waves if not

taken care of, for this reason a still pipe will be needed for the installation of the level transmitter. The

installation of the radar level transmitter with a still pipe is depicted on figure 25 below.

Figure 25: Radar level transmitter mounted with still pipe [1]




Table 19: Other properties of the chosen transmitter

Transmitter

Figure 26: Radar process seal level transmitter [15]

properties

Model: 5402 high frequency process seal

Housing material: Polyurethane covered

aluminum

Signal output: 4-20mA with HART

communication

Conduit/Cable threads: 1/2” 14NPT

Ingress protection: IP67

ATEX certified

Microwave output power < 1mW

Internal power consumption < 50mW in

normal operation

Supply Voltage Ui : 30 Vdc

Supply Current Ii: 130mA

Power Pi : 1W

Capacitance Ci : 7.2 nF

4.3 STRATEGIC SOLUTIONS

These are the corrective actions proposed for problems whose causes are human and maintenance management

based.

4.3.1 INSUFFICIENT MANPOWER

For the problem regarding man power, there are two possible solutions which can both be applied, both of

them being a long term solution to the problem of manpower shortage. These are:

4.3.1.1 Recruitment more workers or subcontracting certain tasks

These are the most obvious solutions to the problem of worker shortages. The subcontracting of some tasks is

already being done, an example is the follow-up and maintenance of the filling arms at the seaport by SACIM

AUTOMATIONS. But some tasks are not worth being given out to sub-contractors, these should be done by




the SONARA workers themselves for strategic reasons. This thus imposes internal or external recruitment to

supplement the already existing labor force.

4.3.1.2 Instituting autonomous maintenance

Autonomous maintenance is the implication of the production operators in certain maintenance tasks. It is a

long term solution to this problem. Some of these tasks are already being done by the operators. The tasks the

operators are charged with performing now are:

Operate some machines;

Startup machines

Shutdown machines

Report machine malfunctions

Maintain a safe environment at the production units

Collect product samples for quality testing.

In addition to these tasks, the operators can be trained to carry out certain predictive and preventive

maintenance tasks as well as some less complicated corrective maintenance tasks. In the case of

instrumentation, some of these tasks are:

Check instrument grounding;

Clean the sight glasses regularly;

Check the junction boxes for condensation, short-circuits and entry of oil;

Purge the pipes to prevent blockages.

Most preventive and predictive maintenance tasks have level 3 priority on the work permits while corrective

maintenance is level 1 which is very normal. As a result, even if present, a preventive and predictive

maintenance plan’s success is at the mercy of the corrective maintenance tasks. So implicating the operators

in some first and second level maintenance tasks will go a long way to reduce the workload of the maintenance

technicians.

In addition to solving the manpower problem to a certain degree, it will also:

Decrease equipment downtime: this will be achieved because the time taken for the maintenance

technicians to react to the permit emitted for the maintenance tasks will be eliminated, the downtime




will only depend on the time taken to sign the permit by the chief operator and the time taken to

complete the task.

Decrease unplanned shutdowns

Increase the reliability of the instruments and machines.

Etc.

From my observations at the instrumentation department, even if an autonomous maintenance program is to

be adopted, some workers still need to be hired to complement the present shortage since an autonomous

maintenance program takes a lot of time and resources to put in place.

4.3.2 LACK OF MAINTENANCE INTERVENTION REPORT

After preventive or corrective maintenance interventions, it is very important to make reports. A non-

exhaustive list of reasons why this report is very important is as follows:

The follow-up of maintenance KPI’s

Follow-up and continuous amelioration of the maintenance policy in place.

The report serve as archives for real explanations of the problems encountered and how they can be

solved,

Update of solution manuals for some problems whose solutions are not found or are not well explained

in the user manual of the instrument.

Etc.

The lack of this report therefore creates an insufficiency in the maintenance policy which may have very bad

effects.

For the end of intervention report designed, consult APPENDIX…..

4.3.3 LACK OF MAINTENANCE METRICS AND KPI’S

I noticed a lack in maintenance KPI’s, given that SONARA is certified ISO 9001:2000, it is possible that these

indicators have been defined but are just not being followed up. In principle the work permit is supposed to

integrate the follow up of these indicators, if not a maintenance intervention report should do. The work permit

has certain fields that can help but are not sufficient and there is no maintenance intervention reporting done

at the instrumentation department. A maintenance intervention report (APPENDIXE 4) has been designed

which can assist in the follow-up of these indicators if it is accepted. The following is a schematic

representation of the KPI’s to be followed up




TTF TTRUT

DT

TBF

STARTUP OF

EQUIPMENT FIRST FAILURE

INTERVENTION START

TIME

EQUIPMENT RESTART

TIME

SECOND FAILURE

LIFE CYCLE TIME

Good functioning Delay Repairs Good functioning

Figure 27: Schematic representation of some of the KPI's defined

These indicators are defined as:

1. MUT (mean up time): this is the average time between each equipment startup time and the next

failure time. It can be calculated by:

𝑀𝑈𝑇 =∑ 𝑈𝑇𝑁

1

𝑁 [15]… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … . 𝐸𝑞.19

UT = date_time of reception of next permit - last restart date_time

2. MDT (mean down time): this is the average time between two successive failures of an equipment.

𝑀𝐷𝑇 =∑ 𝐷𝑇𝑁

1

𝑁 [15]… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … . . 𝐸𝑞. .20

DT = restart date_time – previous failure date_time = TTR + Delay time

3. MTTR (mean time to repair): this is the difference between the time a maintenance intervention is

started and the next.

𝑀𝑇𝑇𝑅 =∑ 𝑇𝑇𝑅𝑁

1

𝑁 [15]… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … 𝐸𝑞. 21

TTR= Equipment restart date_time – repair start date_time – delays between maintenance

4. MTBF (mean time between failures): this is the average time between two successive failures

𝑀𝑇𝐵𝐹 =∑ 𝑇𝐵𝐹𝑁

1

𝑁 [15]… … … … … … … … … … … … … … … … … … … … … … … … … … … … . . … … … … … 𝐸𝑞. 22




TBF = current permit reception date_time – previous permit reception date_time

Or

TBF = successive (DT + UT)

5. EQUIPMENT FAILURE RATE: this is the number of times an equipment has failed during a defined

duration.

𝐹𝑎𝑖𝑙𝑢𝑟𝑒 𝑟𝑎𝑡𝑒 = 𝜆 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑒𝑟𝑚𝑖𝑡𝑠 𝑟𝑒𝑐𝑖𝑒𝑣𝑒𝑑 𝑓𝑜𝑟 𝑎𝑛 𝑖𝑛𝑠𝑡𝑟𝑢𝑚𝑒𝑛𝑡 𝑖𝑛 𝑎 𝑓𝑖𝑥𝑒𝑑 𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛

𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑚𝑒𝑎𝑠𝑢𝑟𝑒… . 𝐸𝑞. 23

6. OPERATIONAL AVAILABILITY OF THE EQUIPMENT:

𝐴𝑣𝑎𝑖𝑙𝑎𝑏𝑖𝑙𝑖𝑡𝑦 = 𝐴𝑜𝑝 = 𝑀𝑇𝐵𝐹

𝑀𝑇𝐵𝐹+𝑀𝑇𝑇𝑅 [15]… … … … … … … … … … … … … . … … … … … … … … … 𝐸𝑞. 24

7. MAINTENABIITY: this is the aptitude of an equipment to be brought back to a state at which it can

accomplish it’s required functions under certain conditions and using the prescribed procedures and

means [10].

𝑚𝑎𝑖𝑛𝑡𝑒𝑛𝑎𝑏𝑖𝑙𝑖𝑡𝑦(𝜇) = 1

𝑀𝑇𝑇𝑅 [15]… … … … … … … … … … … … … … … … … … … … … … … … … … … … 𝐸𝑞. 25

8. RELIABILITY: the aptitude of an equipment to perform it’s functions under certain conditions and

at required time interval [10]. For reliability studies, statistical models are used. The indicators

required are:

N the number of failures

The failure rate λ

The TBF of the equipment

Following the collection of this data, statistic models are used, some of these are:

The exponential distribution [10] in the case of a constant and known failure rate

The Weibull distribution [10], when the failure rates calculated using the empirical methods follows

no noticeable trend.

9. RATE OF USE OF SPAREPARTS: This is the number of a particular spare-part used during the

repairs of an equipment divided by the number of time the equipment has been repaired. This helps

decide on the security stock for spare parts and can even help in the choice of manufacturers.




Technological solution for KPI follow-up

Given that we are in the technology age, it is imperative to adapt to the computer tools placed at our disposal,

in addition to that, hard copy archives are becoming obsolete. For this reason a database application which has

as objective the follow-up of these KPI’s was written.

The application is made up of an SQL database for data handling and a JAVA WEB interface. To this

application was added a level calculator based on the differential pressure measuring principle.

The database is made up of four tables, following the relationship schema below:

Figure 28: Relationship Diagram showing the structure of the Database

Refining units

ex. U10

Drums

10B1

10B2

Measuring instruments

10LT25

10LT325

maintenance interventions

DO1

DO2

DO3

DO4




PRESENTATION OF THE APPLICATION

Database logical model

Figure 29: Logical model of the instrumentation management database

Requirements for the use of the application

To use this application, the following are required;

A database server(a dedicated computer can play this role)

SQL server

Glassfish server 3.1.1 or higher

Java runtime environment 8 or higher

Java development kit 1.7 or higher

A Local area network connection




An internet browser( internet explorer, Mozilla Firefox of google chrome)

NetBeans 8 or higher

Description and use of the application

This application is a web based computer maintenance management tool, written with the java programming

language. It can be used to manage the maintenance logs of all the measuring instruments that are used to

measure process parameters on drums (level, temperature and pressure transmitters), and with a little

customization be extended to flow transmitters, valves and other instruments maintained by the

instrumentation department.

It is composed:

A homepage that can be used to calculate calibration parameters for the differential pressure

transmitters,

Figure 30: Application home page

The four tables that are represented by the red circled links on figure 24 are

o Unit

o Drum

o Instrument




o Maintenance operation

These tables are supposed to be filled in the order mentioned above, that is because

o The refinery is divided into units;

o The units have drums (a drum cannot exist without a unit)

o The drums have measuring equipment installed on them( no drum implies no instrument)

o Each instrument has a maintenance operations done on it ( no instrument implies no operation)

The application has been written to allow creating, deleting, editing and viewing the records in the database.

A. Populating the database

The following procedure shows how to add an instrument into the database. For all the other tables, the

procedure is the same. We will add an instrument called “ TEST INST”

1. Click on instrument on the task bar to open it’s table

2. Click on the create button under the instrument table( big blue circle on figure below)

3. Fill in the details on the window that appears(figure 31)

Figure 31: Populating the Instruments table of the database

4. Click save( small blue circle on figure 31)

5. Click yes on the dialogue box(figure32)




Figure 32: Confirmation dialogue box

6. The instrument has been successfully added(figure 33)

Figure 33: Showing the success of the entry

7. Double click on the instrument to display it’s properties(figure 34)




Figure 34: Instrument information

As underlined above, the procedure to add units, drums and maintenance operations to the database is the same.

B. Deleting and editing records

We will simulate the delete operation with an entry we created in the units table called “DELETION TEST

UNIT”. The procedure for deletion is as follows;

1. Right click on the entry you want to delete, a dropdown menu will appear(figure 35)

Figure 35: Create-View-Delete-Edit drop down menu

2. Click delete on the menu, you’ll get a confirmation dialogue box




Figure 36: Confirm Delete

3. Click yes and your item will be deleted.(figure 36)

The procedure is the same for editing entries.

The completion of this application is at 95%, what remains is the debugging of the KPI-table.

4.3.4 INSUFFICIENT WORK PERMIT ARCHIVING POLICY

To ameliorate the archiving policy of work permits, so that it can meet its basic objectives, the following

archiving policy has been defined.

PROPOSED ARCHIVING POLICY FOR WORK PERMITS

The following steps should be taken during the archiving of permits.

STEP 1: For each year assign cupboard space and label it

STEP 2: Open a folder for the different instruments and divide it into sections, each section denoted by a color

code which overlaps enough to be visible. A folder can be opened for instruments characterized by too many

problems. The first page of the folder should be reserved for the color-code key.

STEP 3: Divide each folder section into sub-sections for the successful and unsuccessful permits

Below is a depiction of the procedure




Figure 37: Flow chart showing the steps for archiving work permits

Figure 38 gives a concrete example of this policy

Figure 38: Example of archiving flow chart for the Instrumentation service

FOLDER SUBSECTIONS

FOLDER SECTIONS

CUPBOARD

YEAR

INSTRUMENT 1

SUCCESSFUL INTERVENTIONS

UNSUCCESSFUL INTERVENTIONS

INSTRUMENT 2


UNSUCCESSFUL INTERVENTIONS

FOLDER SUB-SECTIONSFOLDER SECTIONCUPBOARD

2015

FLOW MEASUREMENT


FAILED INTERVENTIONS

LEVEL MEASUREMENT


FAILED INTERVENTIONS

TEMPERATURE MEASUREMENT .........

PRESSURE MEASUREMENT

VALVES

OTHERS




4.3.5 PREVENTIVE MAINTENANCE AND FOLLOW-UP RELATED PROBLEMS

To ensure that we tend towards zero equipment failure, it is imperative to favor preventive and predictive

maintenance over corrective maintenance. For this reason a good preventive maintenance plan is supposed to

be drawn up and followed rigorously.

A good preventive maintenance plan is drawn using both the MTBF of the equipment and the intervention

history, but since this information was not reliable, we used the empirical knowledge gotten from the

technicians to draw the provisional preventive maintenance plan shown on APPENDIX 8. Using the defined

KPI’s however, continuous improvement of this plan can be done.

4.4 PROJECT COSTING

To show the feasibility if the proposed solutions, it is important to approximate the costs of these solutions.

4.4.1 COST OF ENGRAVED SCALE PLATES

The cost of making 26 engraved scale plate assemblies is presented on table 20 below

Table 20: Engraved scale plates costing

Item Quantity Unit price(CFA) Total (CFA)

Aluminum plate (length=2.5m, width=1.25m

thickness=2.5mm)

1 129000 129000

Machining of scale plate supports ( stainless steel

brackets)

52 1000 52000

Cutting and finishing of scale plates 26 1000 26000

Engraving the scales 26 4000 104000

Hexagonal M5-L22-G8.86 completely threaded

bolt-washer-nut assembly

120 100 12000

TOTAL 323 000

4.4.2 COST OF PROPOSED LEVEL TRANSMITTER

The cost of the level transmitter proposed in section 4.2.3 above is presented on table 21 below. The costing

will be done for 2 transmitters, one for installation and one for security storage.

6 M=metric diameter, L=metric length and G=grade under ISO 4017-1979 standard




Table 21: Cost of radar level transmitter [11]

Item Quantity Unit price($) Total price ($)

Rosemount 5402 process seal high frequency Radar

level transmitter

2 5098 10196

Still pipe(accessory) 1 254 254

TOTAL WITH OUT TAX 10450

TAX(VAT) 1881

GRAND TOTAL($) 12331

GRAND TOTAL(FCFA) 6,165,500

From tables 20 and 21, the total cost of the ameliorations without the T-junction is

Total cost = 6,488,500 FCFA

4.5 PARTIAL CONCLUSION: RECAPITULATION OF THE CORRECTIVE

ACTIONS

Below is a recapitulation of the different problems and the possible corrective actions to be taken following

the presentation and justification of the solutions done in the previous sections of this chapter and in chapter

3.

Table 22: Recapitulation of the proposed solutions

Problems Corrective actions

Graduation of level glass gauges Make engraved scale plates for each level glass (section

4.2.1)

Difference in the level of measurement tapping

points on the drums.

Proposed a T-junction for the connection of instruments for

some drums (table 16) (APPENDIX 6)

Proposed distribution tube for bringing tapping points to the

same level (figures 22 and 23) APPENDIX 7

Insufficient manpower Hire more workers

Institute autonomous maintenance

Lack of KPI’s Define KPI’s and a method for their follow-up

(section4.3.3)

Maintenance intervention reporting Design maintenance intervention report (APPENDIX 4)




Problems Corrective actions

Obsolete level sensor for the drum 70B3 Proposed Rosemount 5041 high frequency radar level

transmitter with process seal antenna.(table 19)

Bad archiving policy for the work permits Proposed new archiving policy (section 4.3.4)

Logistics policy Propose the study and institution of an adequate logistics

and spare parts acquisition policy

Preventive maintenance and follow-up related

problems

Proposed a preventive maintenance plan (APPENDIX 8)




In any process environment where parameters are to be monitored and real time information analyzed, system

failure is too much to bear, for this reason, the engineers in charge put in all the necessary resources to prevent

the systems from failing and/or shutting down. However zero system failure being impossible, engineers prefer

to have planned system shutdowns for maintenance purposes. This permits a better mastery of the process

parameters and production as a whole.

Zero system failure may be impossible, reducing the failures to a minimum is not, so continuous amelioration

of the system and the maintenance plan to progressively reduce the probability of the system failing is what

we refer to as tending towards zero system failure.

The task that we were given was to study the system and the maintenance policy applied so that the level

measurement system of the SONARA refinery can function optimally, thereby tending towards zero failure

and unplanned shutdown.

In the course of the project therefore, we used the PM-analysis methodology to identify the potential problems

of the liquid level measurement system and propose solutions to these problems.

Some of the proposed solutions were costed and the investment required to apply them was evaluated at Total

cost = 6,488,500 FCFA

We were however unable to estimate the cost of some of the solutions due to the unavailability of data.

As perspectives, we will recommend that:

A similar study be carried out for the pressure, temperature and flow measurement systems.

The maintenance management application written for the follow-up of maintenance metrics and KPI’s

be implemented and it’s use imposed on the technicians.

The database written for the KPI monitoring was designed to consider other instruments used to

monitor process parameters on a drum, these are temperature and pressure and could even be extended

to monitor the maintenance of flowmeters and valves installed on pipes.

The logistics policy needs to be reviewed, so I propose that a study be made on the logistics policy, its

effect on maintenance be evaluated and revisions be proposed. This will go a long way to increase the

availability of spare parts.




[1] SONARA, presentation of SONARA, Limbe, 2014.

[2] SONARA, Instrumentation Maintenace Logs.

[3] Cegelec, Etudes de niveau, Limbe, 2011.

[4] Idaho State University's College of technology, Instrumentation and control, module 9: Level

Measurement, Idaho.

[5] IRA, Les mesures de niveaux, Pole IRA, 2004.

[6] A. S. Morris, Measurement and instrumentation principles, third edition, Oxford: Butterworth-

Heinmann, 2001.

[7] Process Industry Forum, "How do different types of level measurement devices work?," 29 April 2015.

[Online]. Available: How do different types of level measurement

devichttp://www.processindustryforum.com/article/different-types-level-measurement-devices-work.

[8] wikipedia, "differential pressure level measurement," wikipedia, [Online]. Available:

http://automationwiki.com/index.php?title=Differential_Pressure_Level_Measurement. [Accessed may

2015].

[9] J. Bufferne, Le guide de la TPM-Total Productive Maintenance, Paris: Eyrolles, 2006.

[10] D. M. Peter Wilmoth, TPM-A route to world class performance, Oxford: BUTTERWORTH-

HEINMANN, 2001.

[11] ARCHON, Liquid Level Gauges, New York: Archon Industries Inc.

[12] TOTAL RAFFINAGE DISTRIBUTION, SPECIFICATIONS POUR LE MONTAGE ET LA

PROTECTION DES EQUIPEMENTS DE MESURE DE NIVEAU, Paris La defense.




[13] SONARA, PCF UNITE 70, TRAITEMENT DES EAUX DE PROCEDES-RESEAU FERME DE PURGE

ET DE VIDANGE DES HYDROCARBURES, LIMBE.

[14] Emerson Process Management, Rosemount 5400 Series - Superior Performance Two-Wire Non-

Contacting(user manual), New York, 2014.

[15] J.-P. V. Francois Monchy, MAINTENANCE- Methodes et Organisations, 3rd edition, Paris: Dunod,

2010.

[16] Emerson Process Management, 19 June 2015. [Online]. Available: store.rosemount.com.

[17] B. S. Dillon, ENGINEERING MAINTENANCE- A modern approach, CRC press, 2002.

[18] A. Y. J. AGBOR, FAULTS ANALYSIS OF LEVEL TRANSMITTER IN DRUMS IN THE PRODUCTION

UNITS FROM 2012 TO 2014 AND A MAINTENANCE PLAN FOR THE LEVEL TRANSMITTERS,

Limbe, 2015.

[19] Emerson Process Management, Rosemount 5400 Series(Product data sheet)-Superior Performance Two-

Wire Non-Contacting Radar Level, Shakopee, 2015.

[20] Pr. Lucien Meva'a, Industrial Maintenance Lecture, Yaounde: National Advanced School of

Engineering, 2014.




APPENDIX 1: Administrative chart of SONARA with emphasis on the maintenance direction

CHAIRMAN OF THE BOARD OF

DIRECTORS

GENERAL MANAGER

DEX DCT DAG DQHSEI DM

MCT

MECHANICS

METHODE

MECHANICAL WORKS

INSTRUMENTATION

SYSTEMS

MMLT

CHAUDRONERIE AND ARRET STOCKAGE

HEAT WORKS

STORAGE

ETUDES ET TRAVAUX NEUF

APPRO

ACHAT

ACHAT

MARCHE

MAGASIN

SECRETARIAT

SECRETARIAT

DFC DARH DRPCT




APPENDIX 2: The SONARA refining schema




APPENDIX 3: Exploded view of level measurement system




APPENDIX 4: Proposed maintenance intervention report




APPENDIX 5: Level glasses found on the instrumentation plans and their measurement heights

Drum Height defined(mm) Unit division( 1%=__mm)

10B2 APPENDICE 907 9.07

10B3 APPENDICE 907 9.07

10B4A APPENDICE 907 9.07

10B4B APPENDICE 907 9.07

10C3 LG009.1 1626 16.26

10C4 LG006.1 1266 12.66

20B1 APP 907 9.07

20B1 APP 907 9.07

30B1 APP 907 9.07

30C1 LG2A 907 9.07

30C1 LG2B 1626 16.26

30C1 LG2C 1375 13.75

30C1 LG2D 1375 13.75

40C1 LG2A 1485 14.85

40C1 LG2B 1986 19.86

50B6 LG0025 907 9.07

60B1 LG4 584 5.84

60B3 LG8 1786 17.86

60B5 LG28 604 6.04

60B4 LG11 1786 17.86

120B1 LG1 584 5.84

200H1A LG006 525 5.25

200H1B LG56 525 5.25

251B1 LG02 1266 12.66

251E1 LG005 750 7.5

310T1 LG5 1270 12.7




APPENDIX 6: Tapping points brought to the same level using a T-junction




APPENDIX 7: Correction of the level of tapping points with a distribution tube




APPENDIX 8: Provisional preventive maintenance plan

National Refining Company Ltd

PROVISIONAL PREVENTIVE MAINTENANCE PLAN FOR THE LIQUID

LEVEL MEASUREMENT SYSTEMS

SCOPE OF PLAN

THIS PLAN CONCERNS ALL THE DRUMS,

TANKS AND COLUMNS ON WHICH LIQUID

LEVEL MEASUREMENT AND CONTROL

INSTRUMENTS ARE INSTALLED

MAINTENANCE DIRECTION

SHORT TERM MAINTENANCE

DEPARTMENT

INSTRUMENTATION SERVICE

Maintenance task Jan Feb Mar April May June July Aug Sep Oct Nov Dec

PROCESS RELATED TASKS

Check for leakages on the lines( valves, junctions

and tapping points)

ZONE

1 ZONE 2 ZONE 3 ZONE 1 ZONE 2 ZONE 3

Purge the transmitter pipes and recalibrate the

transmitters

ZONE

1 ZONE 2 ZONE 3 ZONE 1 ZONE 2 ZONE 3 ZONE 1 ZONE 2 ZONE 3 ZONE 1 ZONE 2 ZONE 3

Check and clean impulse pipes ZONE


ELECTRICAL AND POWER RELATED TASKS

Check the junction boxes for condensates, oil and

short circuits and place/replace silica gel pellets

ZONE


check the electrical connections and grounding of

the transmitters

ZONE


Check input voltages and currents and ensure they

are within the range

ZONE


Verify if the readings at the control room and

onsite coincide Do weekly for all zones

KEY

ZONE COLOUR CODE UNITS CONCERNED

1 GREEN U10, U50, U200

2 RED U20, U30, U40, U60

3 BLUE U120, U202, U223, U230, U240, U251, U260, U310,




APPENDIX 9: Rosemount Radar level transmitter model selection chart [9]

metuge okane e. end of course dissertation final revision 2015

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