Corrosion Control of a Steel Pipeline in Aqueous Chloride Solutions by Using CP Technique
|Engineering and Technology Journal
|Volume 24, Issue 8, August 2005, Pages 1076-1096 PDF (1.78 M)
|Wathik Issa Mahdi; Fahim F. Al-Himdani; Abdul-Wahab Hassan Khuder
|The aim of this work is to improve the corrosion resistance of the steel pipeline structures utilizing concrete coating by using the cathodic protection technique. It deals with the matter of steel structures upon the survey periods, electrochemical dormant period because of the continuous cathodic preventation and the activation corrosion upon interruption period of this cathodic preventation and treatment this case of corrosion by using the cathodic protection technique. The initial free corrosion potential (Ecorr) upon intermittently intervals and corrosion rate measurement of the specimens by using full polarization curve (Tafel method) has been observed. The required level of protection potential is achieved by using potentiostatic controlled potential.
The results indicate that the moisture progressive within each specimen has produced different potentials along the steelpipe. Greater polarization has been associated with the submerged part of the specimen where the concrete coating resistance is at minimum. Whereas the degree of polarization is directly proportional with the level of external voltage. The results clearly indicated that to achieve efficient design of a cathodic protection, the protected area should be divided into discrete electrochemical areas, these areas are depending on the electrical resistance and steel potential which prevent the over-protection in the low electrical resistance areas when applying the designing criteria on the high electrical resistance areas. Furthermore, the results indicate that the absolute value of protection potential does not adequately to describe the electrochemical changes undergone by the polarized coated steelpipe. The instant off potential value (Ear) does not provide quantitative informations about the state of corrosion. The mechanism of the polarization behavior of steelpipe structure in aqueous solution is a fundamental different because of the high resistance of concrete coating and the alkali environment in which becomes the dominance factor on the polarization trends. Also, the results indicated that the relationship between the steelpipe potential and flowing current in calculated the electrical
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