Influence of Anodic Current on Corrosion Protection of Buried Steel Pipeline under Cathodic Protection

Abstract

Cathodic protection is being applied to buried steel pipelines and polarized potential of pipelines is kept less noble than the protection potential criterion,-0.85 V vs. Cu/CuSO 4. However, instantaneous anodic current has been infrequently observed in some fields even though polarized potential of pipelines is kept less noble than the protection potential criterion. In this study, the influence of instantaneous anodic current on corrosion protection of buried steel pipelines under cathodic protection was evaluated and the oxidation reaction causing anodic current was investigated to some extent. As a result, it was found that most of the anodic current was not attributed to corrosion reaction and the maximum value of corrosion rate of steel was as little as 1.8 m/year. Therefore, it was considered that there was no matter on buried steel pipelines even though the instantaneous anodic current occurred under the protection potential criterion. It was estimated that some part of the anodic current was attributed to the oxidation reactions of components in soil and of rust on the steel surface.

On the Mechanism of Cathodic Protection and Its Implications on Criteria Including AC and DC Interference Conditions

“…There is wide agreement in literature that temporary anodic current discharge results in limited corrosion. 5,[23][24][25][26][27][28] The efficiency of the anodic current with respect to anodic metal dissolution is typically very limited. These observations are difficult to explain with a concept of CP that is based on activation polarization.…”

“…All of the more recent investigations of stray current induced corrosion on cathodically protected pipelines confirm that the electric charge will not be consumed for the corrosion reaction as long as the steel surface is passive. 5,[23][24][25][26][27][28] Hence, anodic current discharge is not inevitably related to a corrosive dissolution of the metal following Faraday's law, i.e., an anodic current does not always result in corrosion. This is due to the fact that the anodic charge is consumed for the reaction Fe(II)/ Fe(III) on the passive surface, rather than the reaction Fe(0)/ Fe(II) in the case of time-variant stray current interference.…”

Research on Corrosion Resistance of Steel Pipes in Water of Oilfield

“…Therefore, adopting effective and economic anti-corrosion measures is an urgent need for relevant enterprises [1]. The main anticorrosive technologies are the use of corrosion resistant alloy steel, cathodic protection [2,3], adding inhibitor [4,5] pipeline coating [6], etc. The selection of corrosion resistant pipes is the most reliable anti-corrosion means at present.…”