The Role of Sulfur Oxidizing Bacteria on Corrosion of X65 Low Carbon Steels and its Mitigation Using Sodium Tungstate and Nickel Biocides
– The Role of Sulfur Oxidizing Bacteria on Corrosion of X65 Low Carbon Steels and its Mitigation Using Sodium Tungstate and Nickel Biocides –
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ABSTRACT
Metals in service often give a superficial impression of permanence, but all except gold are chemically unstable in air and air-saturated water at ambient temperatures and most are also unstable in air-free water.Corrosion can be defined in general terms as the degradation of a material, usually a metal, or its properties because of a reaction with its environment. It results to damage cost between 1 – 5 % GNP as reported from different countries.
Corrosion can be initiated by differences in chemical potential, stress or chemical reactivity between two points. It can also be influenced or initiated by microorganisms, a form of corrosion that is often ignored by many people.
The latter is a form of corrosion called Microbial Induced Corrosion (MIC) or Biocorrosion and it accounts for 50% of the total corrosion damage cost.
The focus of this work is to understand the role played by Sulphur Oxidizing Bacteria (SOB) on corrosion of X65 low carbon steels, its kinetics and the possible ways to mitigate this form of corrosion.
The experiment for the isolation of SOB showed a maximum pH drop of 3 in the Thiosulphate broth, followed by 2.3 in the Starkey broth and 1.5 in the NCL broth.
The results from the corrosion experiment show a higher weight loss for samples 3 and 4, which were exposed in the culture media with SOB, compared to samples 1 and 2 in the same media but without SOB.
Corrosion by SOB was reduced by 96.73% using 80 mg/L of Sodium Tungstate and 100 mg/L of Nickel.
TABLE OF CONTENTS
ABSTRACT …. iii
LIST OF FIGURES …………. vii
LIST OF TABLES ……… xi
1.0 INTRODUCTION …………… 1
1.1. Background …….1
1.2. Corrosion Basics ……………… 2
1.3. Microbial Influenced Corrosion (MIC) or Biocorrosion …..……… 2
1.3.1. The Role of Biofilms ………. 3
1.4. Biocides …………..…… 4
1.4.1. What is a Biocide? ……… 4
1.4.2. Mechanism of Oligodynamic Effect ……….. 4
1.4.3. Applications of Biocides ………. 4
1.5. PROBLEM STATEMENT ……..……….… 5
1.6. RESEARCH OBJECTIVES AND HYPOTHESES ………. 5
1.6.1. Objectives ……..… 5
1.6.2. Hypotheses ……..…….. 6
1.7. REFERENCES ………. 6
- OVERVIEW OF THE LITERATURE ……… 8
2.1. Economic Significance and Principle Reactions during Corrosion … 8
2.2. Electrochemical corrosion …… 11
2.2.1. Anodic Processes …… 11
2.2.1.1. Faraday‗s law …… 12
2.2.2. Cathodic Processes ………… 13
2.3. CORROSION OF BURIED SYSTEMS ………. 15
2.3.1. Pipelines ………… 15
2.3.2. Underground Tanks … 16
2.4. Biocorrosion or Microbial Influenced Corrosion (MIC) ….. 16
2.4.1. Microbes Classification ………. 20
2.4.1.1. Bacteria ….. 20
2.4.1.2. Sulphate Reducing Bacteria ……………. 21
2.4.1.3. Sulphur/Sulphide Oxidizing Bacteria ………. 22
2.4.1.4. Planktonic or sessile ……. 24
2.4.2. Enzymes and biocorrosion …….. 25
2.4.3. Metal binding by extracellular polymeric substances … 27
2.5. Corrosion in Soils …….. 28
2.5.1. Soil Parameters Affecting Corrosivity … 29
2.5.1.1. Water ……….. 30
2.5.1.2. Degree of Aeration ……… 30
2.5.1.3. pH of the soil ………… 30
2.5.1.4. Soil resistivity …………… 31
2.5.1.5. Redox potential ……..… 32
2.5.1.6. Chlorides ……. 32
2.5.1.7. Sulphates ………. 32
2.5.1.8. Oxidation of Sulphide … 33
2.5.1.9. Oxidation of Elemental Sulphur ……….. 33
2.6. REFERENCES ……….… 35
- MATERIALS AND METHODS … 41
3.1. Sample Collection …………. 41
3.2. Preparation of Culture Media … 41
3.3. Screening of Isolates by pH reduction test ……..… 42
3.4. Materials 44
3.5. Thiobacillus media preparation 45
3.6. Bio-corrosion Experiment ……. 45
3.6.1. The Control Experiment ……… 46
3.6.2. The Test Experiment ………….. 46
3.6.3. The Bio-corrosion Mitigation Experiment ………… 47
3.7. REFERENCES …….. 48
- RESULTS AND DISCUSSIONS ……….. 49
4.1. pH Reduction by SOB … 49
4.2. Weight change measurement ……… 51
4.2.1. Sample 1(Control Experiment) at original pH 5.0 ……. 51
4.2.2. Sample 2 (Control Experiment) at original pH 8.0 …. 54
4.2.3. Sample 3 (with local SOB) at original pH 5.0 ………56
4.2.4. Sample 4 (with local microbes) at original pH 8.0 58
4.2.5. Sample 5 (MIC mitigation) at original pH 5.0 … 60
4.2.6. Sample 6 (MIC mitigation) at original pH 8.062
4.2.7. Comparison of weight changes between Control and Test Experiments 64
4.2.7.1. Samples 1 & 3 …… 64
4.2.7.2. Samples 2 & 4 … 64
4.2.8. Comparison of weight changes between MIC Mitigation and Test Experiments … 68
4.2.9. GENERAL DISCUSSION ….. 69
4.2.10. REFERENCES .. 71
- CONCLUSIONS AND RECOMMENDATIONS ……….. 73
5.1. CONCLUSIONS ………… 73
5.1.1. Isolation of Sulphur Oxidizing Bacteria …….. 73
5.1.2. Corrosion Experiment ………….. 73
5.2. Recommendations …. 74
5.3. References ……… 74
INTRODUCTION
1.1 Background
Metals in service often give a superficial impression of permanence, but all except gold are chemically unstable in air and air-saturated water at ambient temperatures and most are also unstable in air-free water.
Hence almost all of the environments in which metals serve are potentially hostile and their successful use in engineering and commercial applications depends on protective mechanisms.
In some metal/environment systems, the metal is protected by passivity, a naturally formed surface condition inhibiting reaction.
In other systems the metal surface remains active and some form of protection must be provided by design; this applies particularly to plain carbon and low-alloy irons and steels, which are the most prolific, least expensive, and most versatile metallic materials.
Corrosion occurs when protective mechanisms have been overlooked, break down, or have been exhausted, leaving the metal vulnerable to attack.
Corrosion can be defined in general terms as the degradation of a material, usually a metal, or its properties because of a reaction with its environment.This definition indicates that properties, as well as the materials themselves, may and do deteriorate.
In some forms of corrosion, there is almost no visible weight change or degradation, yet properties change and the material may fail unexpectedly because of certain changes within the material [Pierre, 2008]. Such changes may defy ordinary visual examination or weight change determinations.
REFERENCES
Starkey, R. L., V. G. Collins, 1923. Autotrophs. In: Methods in Microbiology, J. R. Norris, D. W. Ribbons (Eds), New York: Academic Press, 38, 55-73.
Waksman, S. A, 1922. J. Bacteriol., 7, 605-608.
Beijerinck, M. W., 1904. Arch. Sci. Exactes Nat. Haarlem., Ser. 2, 9131-9157.
Rajagopal Vidyalakshmi and R. Sridar: Isolation and characterization of sulphur oxidizing bacteria; Journal of Culture Collections, Volume 5, 2006-2007, pp. 73-77.
Pierre R. Roberge; Corrosion Engineering Principles and Practice, 2008
