Thesis Abstract

Abstract
Cathodic protection is a crucial technique used to prevent corrosion of metal structures by making them the cathode of an electrochemical cell. In this project, a cathodic protection system using zinc anodes was designed and installed to protect a metal structure from corrosion. The project involved detailed design calculations, material selection, and installation procedures. The design phase began with an assessment of the structure to determine the extent of corrosion and the required level of protection. Design calculations were carried out to determine the number and placement of zinc anodes needed to provide adequate protection. Factors such as structure size, current demand, and soil resistivity were taken into account to ensure the system's effectiveness. Material selection was a critical aspect of the project, with a focus on choosing high-quality zinc anodes that would provide long-term protection. The anodes were carefully inspected for defects before installation to ensure their integrity. Installation procedures were meticulously followed to ensure proper bonding between the anodes and the structure, as well as the effective connection of the system to a power source. The effectiveness of the cathodic protection system was evaluated through regular monitoring of the structure's corrosion rate. Periodic inspections were conducted to assess the condition of the zinc anodes and ensure that they were providing adequate protection. Any signs of corrosion or degradation were addressed promptly to maintain the system's efficiency. Overall, the design and installation of the cathodic protection system using zinc anodes proved to be successful in preventing corrosion of the metal structure. The project demonstrated the importance of proper design, material selection, and installation procedures in ensuring the effectiveness of cathodic protection systems. By implementing these strategies, metal structures can be safeguarded against corrosion, extending their service life and reducing maintenance costs.

Thesis Overview

INTRODUCTION

1.1 Background of study

Cathodic protection (CP) is a method of controlling corrosion or a means of preventing corrosion of metal and can be applied to any buried and/or submerged metallic structures. It is normally used in conjunction with coatings and can be considered as a secondary corrosion control technique.

Cathodic protection can, in principle, be applied to any metallic structure in contact salty media (electrolyte). In practice its main use is to protect steel structures buried in soil or immersed in water. Structures commonly protected, includes:

    Cross country pipelines

    Exterior surfaces of pipelines immersed in water

    In plant piping

    Above ground storage tank bases

    Buried tanks and vessels

    Internal surfaces of tanks, vessels, condensers and pipes

    Well casings

    Foundation piling, steel sheet-piling

    Piling – tubular, sheet steel and foundation

    Marine structures including jetties, wharfs, harbours, piers

    Ships, hulls

    offshore platforms

    Reinforcing steel in concrete

Corrosion is a very serious problem. Three areas in which corrosion are important are in economic, improved safety and conservation of resources. The leakage of hazardous materials from a transport pipeline represents not only the loss of natural resources but also the potential for serious and dangerous environmental impact, and human fatalities. While pipelines are designed and constructed to maintain their integrity, diverse factors (e.g., corrosion) make it difficult to avoid the occurrence of leakage in a pipeline system during its lifetime.

All metals needs energy to be transformed from their oxide (natural) state to a refined state. The process of taking this energy away from the metal is called corrosion. Metals tend to revert back to their natural state when reacting with the environment. This corrosion reaction that occurs is an oxidation-reduction reaction. The purpose of cathodic protection is to stop this corrosive process.

Cathodic protection is the most important of all approaches to corrosion control techniques. One of the types of cathodic protection is sacrificial anode or galvanic cathodic protection. Corrosion occurs through the loss of the metal ions at anodic area to the electrolyte. Cathodic areas are protected from corrosion because of the deposition of hydrogen or other ions that carry current (Sandoval, A., et.al 2001). By using the sacrificial anode technique, the steel pipe will be protected from corrosion but the other metal which is the anode will corrode. In designing this method we must analyze parameters such as factor affecting corrosion, the amount of anode and rate of corrosion, the current densities and the total resistance.

Corrosion is an electrochemical process in which a current leaves a structure at the anode site, passes through an electrolyte, and reenters the structure at the cathode site. Differences in potential at different points along the pipe begin to develop. For example, because it is in a soil with low resistivity compared to the rest of the line, current would leave the pipeline at that anode site, pass through the soil, and reenter the pipeline at a cathode site. These potentials generate corrosion currents which leave the pipe to enter the soil at certain selective locations.