FACTORS INFLUENCING ACCELERATED CORROSION OF CARGO OIL TANKS
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ABSTRACT
This study was carried out to critically examine the factors influencing accelerated corrosion of cargo oil tanks using Cheron Oil and Gas Company as a case study. To achieve this objective, three research questions and one research hypothesis were formulated to guide this study. The data collected were analyzed using simple percentages and tables to analyze research questions and Chi-square statistical technique was used for testing the research hypothesis using Statistical Package for Social Sciences (SPSS) software. A structured questionnaire was used as the major instrument for data collection from the respondents in Cheron Oil and Gas Company. After careful analysis of the data, the following findings were revealed that; there are factors influencing accelerated corrosion of cargo oil tanks in Nigeria. The study was concluded with some recommendations that; the effectiveness of coal tar and pure epoxy coatings should be evaluated in an environment that includes microbial influenced corrosion; the composition and moisture content of inert gas should be examined to determine its influence on the corrosion rate as well as methods for decreasing the corrosive constituents of the gas and an effort should be made to determine if some crudes are more susceptible to creating accelerated corrosion than others.
TABLE OF CONTENTS
Cover page
Title page
Certification
Dedication
Acknowledgments
Abstract
Table of contents
Chapter One: Introduction
1.1 Background of the Study
1.2 Statement of the Problem
1.3 Objectives of the Study
1.4 Research Questions
1.5 Research Hypothesis
1.6 Significance of the Study
1.7 Scope of the Study
1.8 Limitation of the Study
Chapter Two: Review of Related Literature
2.1 Introduction
2.2 Single Hull Tankers
2.3 Shore Tanks
2.4 Types of Corrosion
2.5 Potential Causes of Accelerated Corrosion
2.6 Associated Risk
Chapter Three: Research Methodology
3.1 Introduction
3.2 Research Design
3.3 Area of the Study
3.4 Population of the Study
3.5 Sample Size and Sampling Techniques
3.6 Sources of Data
3.7 Method of Data Collection
3.8 Method of Data Analysis
Chapter Four: Presentation, Analysis and Interpretation of Data
4.1 Introduction
4.2 Presentation and Analysis of Data
4.3 Testing of Hypotheses
4.4 Discussion of Findings
Chapter Five: Summary, Conclusion and Recommendations
5.1 Introduction
5.2 Summary
5.3 Conclusion
5.4 Recommendations
References
Appendices
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Corrosion of cargo tank structure is a fact of life when operating oil tankers in the harsh environment encountered at sea. The internal structure of the cargo tanks, often un-coated, is exposed to potentially corrosive gases, sea water, crude oil and oil products (Towers, 2010). The effect of this corrosion over a period of years is to reduce the material thickness and hence the strength of the structure. Classification Society design rules typically incorporate an allowance for corrosion that is based on a certain amount or degree of corrosion. Should corrosion proceed at an accelerated rate greater than that allowed for in the design of the cargo tank structures and be allowed to continue unchecked, then a structural failure with consequent oil spillage, explosion or loss of the ship could be the result (OCIMF, 1997).
Individual tankers usually exhibit a unique, but controllable corrosion pattern. However, recent experiences of OCIMF members have indicated problems in new single and double hull tonnage from excessive pitting corrosion of up to 2.0 mm per year in the un-coated bottom plating in cargo tanks due, inter alia, to microbial induced corrosion processes. In addition accelerated general corrosion up to
0.24mm per year has been found in vapour spaces. This type of wastage and the increased rate of corrosion, which is much greater than that which would be normally expected, gives cause for serious concern.
Recognizing the potentially serious impact of marine incidents, the Oil Companies International Marine Forum (OCIMF), has carried out an investigation into the factors which may be influencing accelerated cargo tank corrosion (Prince, 2010). The results of this investigation and areas for further study are presented in this paper. Also included are practicable long and short term mitigating and remedial actions which may be considered as appropriate to reduce the rate of corrosion in the cargo tanks of oil tankers (OCIMF, 1997).
1.2 Statement of the Problem
The normal corrosion rate of uncoated cargo tank deck plating is 0.10 mm or less per year. However, annual wastage rates as high as 0.16mm to 0.24mm have been reported on ships less than 3 years old. This accelerated corrosion rate, which is approximately 2 to 3 times that which would normally be anticipated, is sometimes accompanied by accelerated general corrosion of the vapour space steelwork. In addition to accelerated general corrosion, there has also been an increase in the incidence and severity of pitting corrosion in cargo tank bottom plating. In one specific instance a 150,000dwt tanker is reported as having an average pit depth of between 2.0mm & 3.0mm with a maximum pit depth of 4.0mm. This after only 2 years in service (DeCola and Fletcher, 2006).
In addition to the more conventional corrosion mechanisms, a possible contributory cause of accelerated corrosion has been microbial attack from bacteria in the cargo oil. It would appear that, as crude oil is often loaded at temperatures higher than ambient air and sea temperatures, during the loaded passage the temperature of the cargo tank structure is being maintained at higher levels than normal due to the insulating effect of the double hull spaces.
Higher tank temperatures, coupled with residual water in the cargo tank can:
i) offer favourable conditions for SRB anaerobic bacteria to proliferate, and;
ii) activate the formation of corrosive cells on the surface of the inner bottom.
1.3 Objectives of the Study
1. To determine the factors influencing accelerated corrosion of cargo oil tanks in Nigeria.
2. To examine the various types of corrosion of oil tanks in Nigeria.
3. To determine the potential causes of accelerated corrosion of oil tanks in Nigeria.
4. To make useful recommendations based on the research findings.
1.4 Research Questions
The following research questions were stated to guide this study:
1. Are there any factors influencing accelerated corrosion of cargo oil tanks in Nigeria?
2. What are the various types of corrosion of oil tanks in Nigeria?
3. Are there any potential causes of accelerated corrosion of oil tanks in Nigeria?
1.5 Research Hypothesis
In order to achieve the above stated objectives, the following research hypothesis were formulated to guide this study:
H0: There are no factors influencing accelerated corrosion of cargo oil tanks in Nigeria.
H1: There are factors influencing accelerated corrosion of cargo oil tanks in Nigeria.
1.6 Significance of the Study
This study will be significance to the following:
1 Management Experts and Policy Makers: It would enable management experts and policy makers in the formulation and implementation of policies internally; it will benefit the management and staff as well as the shareholders of the offshore operations. Through this study, managers will be informed of various motivational factors that are helpful in obtaining improved work performance by the employees.
2 The Staff: The staff of Cheron Oil and Gas Company will stand to benefit by availing them the opportunity for training on offshore cargo lifting operations.
3. The Government: The findings of this study will be beneficial to government in its policy formulation and review of existing laws, regulations and bye laws for achieving maximum efficiency in maritime sector in Nigeria. The staff of Cheron Oil and Gas Company is interested to improved work performance of her employees as a way of enhancing productivity. Thus it would attain growth through improving the workers motivational factors of efficiency.
4. Future Researchers: It will help the future researchers and students of higher learning who may wish to carry out research on the similar topic.
1.7 Scope of the Study
The study concerns about the factors influencing accelerated corrosion of cargo oil cargo tanks in Nigeria.
1.8 Limitation of the Study
a) Financial constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).
b) Time constraint: The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.
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