Cathodic Protection Behavior of API X-52 and API X-65 Steels Buried in Natural Soil

The goal of this work is the evaluation of the affectivity of cathodic protection in API X-52 and API X-65 steel specimens buried in natural soil, using two distinct cathodic protection potentials (-850 mV and -1100 mV vs. CSE), the first protection potential is recommended by the NACE RP0169 standard and the second potential was chosen because it is considered that a pipe is overprotected if the protection potential is more negative than -1100 mV vs. CSE. Soil samples of two villages along the pipelines right of way localized in Veracruz, Mexico were used during the experiments in the laboratory to simulate the in-situ corrosion behavior of pipelines buried in soil. The experimental results show that the cathodic protection was less efficient in acidic soils than in neutral soils, at the same time the experimental results show that the least corroded steel specimens were those overprotected. An inverse relationship between corrosion potential and corrosion rate is demonstrated using a linear regression model, a mechanism involving moisture content, soil resistivity and oxygen content is proposed to explain this inverse relationship, at the same time this mechanism is used to explain why the cathodic overprotection can produce more positive corrosion potentials.