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Introduction
Cathodic protection is an important approach to corrosion control. By means of an externally applied electric current, corrosion is reduced virtually to zero, and a metal surface can be maintained in a corrosive environment without deterioration for an indefinite time (Uhlig and Revie, 1985; Bayliss and Deacon, 2002). The combination of coatings and cathodic protection provides maximum corrosion protection for immersed steel structures. The method ensures that corrosion does not occur at damaged bare steel areas or at pinholes or pores in the coating, so the costs of operating the system are less than would be the case with uncoated steel (Talbot and Talbot, 1998; Bardal, 2003). It has been shown that the operating parameters and performance of cathodic protection are dependent upon the resistivity of the environment, and that the resistivity changes with change in temperature (DeGiorgi, 1997). Kelaby (2002) studied the effect of cathode length, salt concentration and distance between anode and cathode on the cathodic protection current density. He concluded that the cathode length does not affect the protection current density, whereas increasing the other variables increases it. Jawary (2005) studied the effect of the distance between cathodes and anodes on cathodic protection current density of buried pipes in soil. He concluded that an increase in that distance leads to an increase in the protection current density. Saleh (2005) studied the effect of sodium chloride (NaCl) concentration, temperature and the solution stirring on the cathodic protection current density of a carbon steel tube sample. The results showed that the protection current density increased with an increase in the studied variables.
The present work aimed to study the effect of the resistivity of the environment and distance between the cathode and the anode on the required cathodic protection current density for buried steel pipes. The impressed current that gives full protection to bare and coated pipes (with two different polymer coats and defects) in different...