ABSTRACT

Galvanic cathodic protection involves protecting a metal surface of a piece of equipment using another metal that is more reactive. The latter metal, usually called the galvanic or sacrificial anode, has a less negative electrochemical potential compared to the metal component being protected. Therefore, the sacrificial anode undergoes oxidation rather than the operating equipment. This technique is illustrated in Figure 1 below for an offshore platform with a steel pipe submerged into seawater. The sacrificial anode is an aluminum anode in this example. Sometimes, steels are galvanized rather than connected to galvanic anodes. Galvanized steels are steels that are coated with a protective zinc layer. The zinc layer acts to cathodically protect steel against corrosion in most underground and marine environments. Corrosion of metals has been known to be disastrous in industrial setup and even more so in the petroleum industry. Transportation of crude oil, gas and processed petroleum products takes place in pipes, most often steel pipes. Several methods have been used to combat the problem of buried pipeline corrosion among which is cathodic protection. Cathodic protection of a buried steel pipe using zinc anode and a 12 volt DC power source has been studied. The experiment was set up in the laboratory for 35days using moist soil sample of Nigeria and weight loss recorded every seven days. Results show that after twenty one days, the protected steel began to lose a very small amount of weight, compared to weight losses for unprotected steel and the anode. A total of 0.04g of the cathodically protected steel was lost after 35days compared to a loss of 0.43g for the unprotected steel. The experiment shows that 90.69% protection was achieved with cathodic protection method of corrosion control. The work demonstrates that buried steel pipes in Nigeria can be cathodically protected against failure with very small quantity of electricity. It is recommended that this study be carried out in a soil with high salinity, typical of the Atlantic Ocean shore where several oil pipelines are laid.