ABSTRACT

Cathodic protection is used for stabilizing buried metal pipeline. In this study, photovoltaic current was used for the cathodic protection of metallic pipes at Nsukka. This was achieved by identifying the effective depths at which anodes could be placed in order to achieve corrosion control of buried pipes. This improved on the monitoring of cathodic protection systems. Two steel pipes, each measuring 300cm in length, 2.54cm diameter, and 0.01cm thickness were prepared by attaching lengths of wires at known positions. The steel pipes were labeled A and B and buried in a soil at Nsukka. Pipe A was protected while pipe B was not protected and thus served as the control. Pipe A was connected to photovoltaic cell while B was not and used as the control. The electrical connection was accomplished by connecting the negative terminal of the photovoltaic cell to the buried pipe while the positive terminal is the anode. The anodes were buried at nine different depths of 20, 30, 40, 50, 60, 70, 80, 90, 100cm. The sites were monitored for one month at the different depths by measuring the current and pipe-to-soil potentials.

The averaged data obtained were statistically analyzed. The results of the analysis showed that three depth positions met the protection criteria of the pipe-to-soil potential along the entire length of the pipe surface being below -850mV. The depths that met the protection criteria were at 20, 30, and 60cm with cathodic protection efficiencies of 23.6%, 71.5%, and 95.6% respectively. The results show an efficiency of 33.3%. Also, the best depth for cathodic protection was at 60cm manifesting a cathodic protection efficiency of 65%.
CHAPTER ONE

INTRODUCTION

1.0 Cathodic protection

Cathodic protection (CP) is one of the electrical methods of controlling corrosion of metals in any environment. Generally, cathodic protection is the corrosion control leading technique of a metallic structure by making the metal the cathode (i.e. electron sink) in an environment by means of an impressed voltage. Cathodic protection is also a method of preventing oxidation (rusting) of exposed metal structures by imposing between the structure and the ground a small electrical voltage that opposes the flow of electrons, and is greater than the voltage that is present during oxidation [1]. It is one of the most effective anticorrosion methods. CP is used to protect various types of steel structures in contact with different environments [2]. It is therefore relevant in the protection of the outer metal surfaces, for example, underground-buried pipelines, and ship hulls, as well as interior surfaces of heat exchangers, and chemical reactors [3].

1.1 General Corrosion Principles

Corrosion is the gradual degradation of a metal by the environment. The degradation can either be biochemical, chemical or electrochemical as shown below. Also, corrosion is the destruction of metals by means other than straight mechanical process [4]. Corrosion is a natural process that cannot be prevented, but may be controlled through correct intervention [5]. The corrosion process involves the removal of electrons (oxidation) from the metal [Equation (1.1)…