Influence of Instantaneously Noble Potential on Corrosion Protection of Buried Steel Pipes under Cathodic Protection in Some Kinds of Soil

Abstract

Instantaneously noble potential caused by DC stray current has been observed in rare cases under cathodic protection of pipelines in service. Moreover, anodic current was simultaneously observed. In this study, the influence of instantaneously noble potential on corrosion protection of buried steel pipes under cathodic protection was studied in three kinds of soil by using IR-free probe. Furthermore, the relationship between corrosion weight loss of the steel and total electric quantity of anodic current caused by the noble potential was investigated. Results of this study indicate that the corrosion caused by noble potential below -0.75 V (vs. Cu/CuSO₄ (sat.)) is negligibly small. Moreover, the results also indicate that the percentage of corrosion current to the anodic current is no more than 1%; most of the anodic current is estimated to be contributed by repeated oxidation reaction of iron rust on the steel surface.