ABSTRACT
The corrosion behavior of uncoated and cut-back bitumen coated X65 Steel samples are being investigated in environments of different pH (2, 3, 4 and 7). Immersion tests were carried out on the samples at 25ºC. The comparison of the corrosion behavior of uncoated, spray-coated and brush-coated X65 steel samples in the different pH media and temperature were observed using the weight measurements approach and visual examination. With 72 hours intervals in the weight measurement of the samples, the weight loss of the uncoatedX65 samples in the pH 2 was more than the pH (3, 4, and 7). This is mostly due to the attack of chloride ions on the surface of the steel. It was also observed that there was different weight gained measurements for both spray-coated and brush-coated samples which is expected to be due to water absorption. The visual examination and weight changes showed that spray-coated samples are more likely to corrode less than brush-coated samples.
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
Corrosion is the greatest source of deterioration and the degradation of materials that are used in engineering structures and components. It accounts for few hundred billion dollars in losses to the global economy [1,2]. There is therefore a need to explore different approaches to the reduction of the economic losses due to corrosion. Although several definitions of corrosion have been proposed [3], corrosion has been defined by Fontana [4] to be the deterioration of materials as a result of reactions with the environment. It is nature’s way of reducing metals to its original states (Andrew et al., 2007)
[5]. Despite different definitions, it can be observed that corrosion is the interaction of materials and their environment. It is a natural and costly process of destruction. However, corrosion can be prevented or at least controlled by the use of protective coatings [6] and cathodic protection [7].
In the case of the oil and gas industry where pipelines, refineries and offshore structures are used to transport liquid and gaseous fuels, the reactions between these fuels and the carbon steels result in corrosion [8]. Similarly, the environments that surround pipelines (soil, oceans and humid environments) can react with the carbon steels that are often used to fabricate pipelines, offshore structures and refineries. There is therefore a need to develop improved methods for the environmental protection of structures that are used in the oil and gas industry.
In the case of pipelines, corrosion can be reduced by the use of corrosion resistant materials, chemical treatment, electrochemical protection and protective coatings. The coatings may also be organic, inorganic and metallic coatings. However, the large surface areas that have to be coated have limited the practical application of several lab-scale coatings in the industrial environment. This is due largely to the cost and availability of the coating materials for use in extensive networks of oil and gas pipelines across the world.
1.2 PROBLEM STATEMENT:
Due to the availability and relatively low cost of bitumen, recent efforts have been made to explore the use of bitumen as a coating material for pipelines in the oil and gas industry. However, although some studies of corrosion have been performed on bitumen-coated steels, our fundamental understanding of the swelling and stress induced deformation and interfacial cracking of bitumen-coated steels have not been performed with the required combination of micromechanics and materials characterization. There is also a need to develop a fundamental understanding of substrate corrosion mechanisms in bitumen-coated steels.
1.3 AIMS AND OBJECTIVES OF THE THESIS:
The objective of this thesis is to study the mechanism of corrosion in a bitumen-coated pipeline steel (X65 steel) that is used in the fabrication of steel pipes. The mechanisms of swelling, stress-induced deformation, cracking and corrosion are studied in coated structures exposed to different environments.
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