CHAPTER ONE:
INTRODUCTION
1.1 Background of study
Cathodic protection (CP) is a method of controlling corrosion or a means of preventing corrosion of metaland 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.
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