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.