ABSTRACT

Five different parts of Acacia nilotcaplant (leaves,pods,seed,bark and root) were subjected to the following analyses; extraction, phytochemical screening, corrosion inhibition test of low carbon steel in crude oil using gravimetric analyses, mechanical properties and surface morphology evaluation of the samples.The corrosion rate of low carbon steel specimen in the plant extract was found to decrease with immersion time(120hrs-792hrs) and with increase in concentration of the inhibitor(400ppm-1000ppm). The results further showed a decrease in inhibition efficiency (IE) of the inhibitor at elevated temperatures(40°C,50°C,60°C) indicating a physisorption of extracts on the carbon steel surface.The result from the mechanical properties(tensile,hardness and impact) evaluation showed higher values(741MN/m2,98.2HRBand 11.52J)for the inhibited samples than the uninhibited(692MN/m2,92.6HRB,11.11J) The values of activation energy, free energy of adsorption and heat of adsorption of all the inhibitors were calculated in order to investigate the mechanism of corrosion inhibition.Adsorption on low carbon steel was found to obey the langmuir adsorption isotherm.All the parts of the plant showed good inhibition efficiency in the medium ranging from56.64%to 98.78% but the pod was the best with inhibitor efficiency of 98.78%.

 

 

TABLE OF CONTENTS

Cover page……………………………………………………………………………………..i
Title page ii
Declaration iii
Certification iv
Dedication……………………………………………………………………………………..v
Acknowledgments vi
ABSTRACT vii
TABLE OF CONTENTS……………………………………………………………….……viii
LIST OF TABLE xi
LIST OF FIGURES ..xiii
LIST OF PLATES .xvi
CHAPTER ONE………………………………………………………………………………1
1.0 INTRODUCTION .1
1.1 Background of study .1
1.2 Statement of problem .1
1.3 Present Resarch .2
1.4 Aim and objectives .3
1.5 Significance of the Study 3
1.6 Justification of Research 4
1.7 Scope of the study………………………………………………………………..………5
CHAPTER TWO 6
2.0 LITERATURE REVIEW 6
2.1 Corrosion 6
2.2 Classification of Corrosion 8
2.2.1 Dry Corrosion 8
2.2.2 Wet Corrosion 8
2.3 Forms of Corrosion 8
2.3.1 Uniform Corrosion9
2.3.2 Galvanic or Two MetalCorrosion……………………………………………………………………………………….9
2.3.3 CO2 Corrosion 10
2.3.4 Crevice Corrosion 11
2.3.5 Intergranular Corrosion 12
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2.3.6 Selective Leaching 12
2.3.7 Erosion Corrosion 12
2.3.8 Stress Corrosion 13
2.4 The Problem of Corrosion 14
2.5 Corrosion Inhibitors 15
2.5.1 Types of Corrosion Inhibitors 16
2.5.2 Organic Inhibitors 16
2.5.3 Green Corrosion Inhibitor 17
2.6 Acacia nilotica 18
2.6.1. Plant description 18
2.7 Review of Past Works 20
CHAPTER THREE 22
3.0 EQUIPMENT, MATERIALS AND EXPERIMENTAL PROCEDURE 22
3.1 Equipment 22
3.2 Materials 22
3.3Experimental Procedure 23
3.3.1Preparation of Specimen 23
3.3.2Area and density of specimen….…………………..…………………………………..23
3.3.3 Preparation of Acacia plant extracts 24
3.3.4 Phyto-Chemical Analysis 26
3.3.5 Weight Loss Measurements 29
3.3.6 Effect of Temperature 30
3.4Microstructure Examination 34
3.5 Mechanical Properties 35
3.5.1Tensile Strength 35
3.5.2 Impact 35
3.5.3 Hardness 36
CHAPTER FOUR 37
4.0 RESULTS AND DISCUSSION…………………………………………………………………………….……………37
4.1 Results 37
4.1.1 Results obtained from corrosion test …………………………………………………39
4.2 Discussions……………………….………………….…………………………………. 60
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4.2.1 Phytochemical Analysis of the extracts …………………….…………..…………….. 60
4.2.2 Corrosion Rate …………………………………………………………………….…. 60
4.2.3 Inhibition Efficiency ……………………………………………………………….… 61
4.2.4 Effect of Temperature ………………………..………………………..……………… 61
4.2.5 Activation energy …………………….………………………………………………. 61
4.2.6 Enthalpy and entropy of adsorption………………….……………………………….. 62
4.2.7 Adsorption Isotherm…………………………………………………………………… 62
4.2.8 Free energy of adsorption…………….………………………………………………. 634.2.9 Impact Strength, Tensile Strength and Hardness of the Specimens…………………… 63
4.3 Surface Studies by Scanning Electron Microscopy ………..………………………… 64
CHAPTER FIVE 64
5.0 CONCLUSION AND RECOMMENDATIONS 64
5.1 Conclusions 64
5.2 Recommendations 65
REFERENCES 66
APPENDICES……………………………………………………………………………… 72

 

 

CHAPTER ONE

1.0 INTRODUCTION 1.1 Background of study
Pipelines play an extremely important role all over the world as a means of transporting gases and liquidsover long distances from their sources to ultimate consumers. So corrosion problem exist in the oil industry at every stage of production from initial extraction to refining and storage prior to use requiring the application of corrosion inhibitors (Migahed, 2005). One of the serious problems of oil extracting industry is the corrosion process. The successful application of carbon steels in oil and gas pipelines depends mainly on either the formation of protective corrosion product film or the use of corrosion inhibitors (Hany et al., 2012) Corrosion prevention is an important aspect of oil and gas production. The pipelines are protected from internal corrosion by the application of corrosion inhibitors. In recent years the application of „green chemistry‟ principles to the area of corrosion inhibitors has attracted lot of attention which has resulted in the reduction/elimination of toxic inhibitors and the production of „green‟ or low toxic environmentally friendly formulations. A number of corrosion inhibitors have been developed with low environmental impact while preserving the inhibitor efficiency (Shaheen et al., 2006) 1.2 Statement of problem
Corrosion is an increasingly serious and costly problem that can lead to plant and equipment failures, leakages in oil and gas pipelines as well as steel bridges, ship, and buildings. These failures range from being an annoyance to being catastrophic. Failures caused by corrosion could and do lead to a direct failure of a component which could affect the entire system and
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can not only be very expensive in terms of down time to repair or replace plant and equipment, but can also prove to be very costly in loss of productivity both to human life and health as well as to the environment (www.corr-ex.com/library_corrosion _control, 2013). Organic compounds containing nitrogen, sulfur and oxygen have long been used as potential corrosion inhibitors (Mobin et al., 2011). These compounds get adsorbed, form a protective layer or insoluble complex on the metal surface and block the active corrosion sites. However, most of these compounds are synthetic chemicals, expensive and very hazardous to both human beings and the environments and needs to be replaced with nontoxic and eco-friendly compounds. Over the years, numerous classes of organic compounds have been investigated as corrosion inhibitors. However the trend in green chemistry is concentrated towards the replacement of most of these inhibitors with nontoxic, cheap and eco-friendly compounds. In recent years, a number of eco-friendly corrosion inhibitors have been exploited as green alternative to toxic and hazardous compounds (Mobin et al., 2011). Acacia nilotica has been established as a very important plant since early times as source of tannin (Gupta, 1970) but has not been maximally utilized. 1.3 PresentResearch
In this research, extracts from acacia nilotica pod, leaves, bark, seed and, were usedas corrosion inhibitor for low carbon steel in crude oil. The test specimen were brought out of the test media at various intervals and corrosion rate (C.R) was determine through weight loss analysis, the inhibitor efficiency, film attractive power, activation energy and enthalpy of adsorption of the inhibitors were calculated using the require expression and relationship. The surface condition of the samples were examined using scanning electron microscope, the mechanical properties were also evaluated.
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1.4 Aimand Objectives The aim of this research is to carry out a performance evaluation on the extracts of Acacia nilotica plant (pods, bark, roots, leaves and seed) as a corrosion inhibitor for low carbon steel in crude oil. The specific objectives are to: ICarry out Phyto-chemical(tannins,alkaloids and flavours) analyses of the plant extracts. II Carry out corrosion test using weight loss technique by varying concentration of inhibitors and temperature. IIIAnalyze the kinetic and thermodynamic parameters of the inhibitor in the aggressive medium IVEvaluate the mechanical properties (tensile,hardnessand impact) of the sample. VExamination of the metal surface in contact with crude oil with and without the inhibitors using SEM 1.5 Significance of the Study 1. Development of effective and environmentally acceptable corrosion inhibitors as alternatives to toxic and carcinogenic ones are being researched into for present research interest (Loto, 2012). 2. Most of the corrosion inhibitors are synthetic chemicals, expensive and very hazardous to environment. Therefore, it is desirable to source for environmentally friendly inhibitors (Paul, 2012).
3. Owing to the increasing ecological awareness as well as the strict environmental regulations, and consequently the need to develop environmentally friendly processes,
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attention is currently focused on the development of “green” alternatives to mitigating corrosion. (Special Issue on Green approaches to corrosion mitigation, 2011). 4. Carbon steel is widely used as the constructional material in most of the major industries particularly in petroleum, power production, chemical and electrochemical industries, especially due to its excellent mechanical properties and low cost. Corrosion of carbon steel is a significant problem in the oil& gas production and transportation systems, which causes significant economic loss (Song et al., 2004). As a result of corrosion rupture of the pipe wall frequently causes failure of petroleum and gas pipelines. The breakdowns are followed by large losses of the products, environmental pollution and ecological disasters (Mikhailovskii et al., 1997). The majority of oil and gas pipelines failures result from carbon dioxide corrosion of carbon and low alloy steels (Lopez et al., 2003). It occurs at all stages of production from down hole to surface equipment and processing facilities. 1.6 Justification of Research This work is no doubt justifiable owing to the increasing ecological awareness as well as the strict environmental regulations, and consequently the need to develop environmentally friendly processes, attention is currently focused on the development of “green” alternatives to mitigating corrosion in which the leaves,pods,roots, bark and seed of acacia nilotica happen to fall into this category. The leaves, pods, roots,bark and seed of this plant are not edible. Hence, it is most appropriate to utilize this plant in the production of corrosion inhibitors which will compete or totally replaced some organic and inorganic chemical corrosion inhibitors which are hazardous and toxic to human and the environment (Special bulletin on Green approaches to corrosion mitigation, 2011).
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1.7 Scope of the Study This Study was limited toinvestigation of inhibitory effectiveness of Acacia nilotica plant extracts (pods,seed,leaves,bark and roots) on low carbon steel in crude oil usingweight lossmethod in the presences of each inhibitor at various temperatures. The mechanical properties were evaluated and the surface morphology of the sample was examined using scanning electron microscope (SEM).
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