AC Corrosion of Carbon Steel under Cathodic Protection Condition: Assessment, Criteria and Mechanism. A Review

Abstract

Cathodic protection (CP), in combination with an insulating coating, is a preventative system to control corrosion of buried carbon steel pipes. The corrosion protection of coating defects is achieved by means of a cathodic polarization below the protection potential, namely −0.85 V vs. CSE (CSE, copper-copper sulfate reference electrode) for carbon steel in aerated soil. The presence of alternating current (AC) interference, induced by high-voltage power lines (HVPL) or AC-electrified railways, may represent a corrosion threat for coated carbon steel structures, although the potential protection criterion is matched. Nowadays, the protection criteria in the presence of AC, as well as AC corrosion mechanisms in CP condition, are still controversial and discussed. This paper deals with a narrative literature review, which includes selected journal articles, conference proceedings and grey literature, on the assessment, acceptable criteria and corrosion mechanism of carbon steel structures in CP condition with AC interference. The study shows that the assessment of AC corrosion likelihood should be based on the measurement of AC and DC (direct current) related parameters, namely AC voltage, AC and DC densities and potential measurements. Threshold values of the mentioned parameters are discussed. Overprotection (EIR-free < −1.2 V vs. CSE) is the most dangerous condition in the presence of AC: the combination of strong alkalization close to the coating defect due to the high CP current density and the action of AC interference provokes localized corrosion of carbon steel.

AC corrosion of steel pipeline under cathodic protection: A state‐of‐the‐art review

“…However, AC voltage is rarely used in experiments to model AC interference because it is reported to be a less accurate parameter. [42][43][44] On the other hand, the measurement of AC current density is hard to perform, but it could be calculated using AC voltage together with the equation below [43] :…”

“…[11,13,14,26,45] There is a general agreement that in the absence of cathodic protection, the DC potential of pipeline steel decreases and the corrosion of steel becomes more severe with increasing AC current density. [10,11,13,14,22,43] Usually, the negative change of the potential means that the steel is less corrosive. This conflict demonstrates the complexity of AC corrosion and how much cathodic protection should be applied becomes complicated when AC is involved.…”

“…However, AC voltage is rarely used in experiments to model AC interference because it is reported to be a less accurate parameter. [ 42–44 ]…”

“…On the other hand, the measurement of AC current density is hard to perform, but it could be calculated using AC voltage together with the equation below [ 43 ] : $$${i}_{\text{AC}}=\frac{8\times {V}_{\text{AC}}}{\rho \times \pi \times \phi },$$$where $${i}_{\text{AC}}$$ is AC current density, A/m 2 ; $${V}_{\text{AC}}$$ is the AC voltage, V; $$\rho $$ is the soil resistivity, Ω·m; and $$\phi $$ is the diameter of the circular coating defect, m.…”

Benzoate‐Based Inhibitor Film to Prevent Chloride‐Induced Corrosion: Simulation Study of Efficiency of Dry or Hydrated Film

“…[1][2][3][4] New organic molecules can be used to mitigate corrosion damage of reinforced concrete forming a protective film that acts as barrier on chloride penetration. [5][6][7] DMEA, triethylenetetramine (TETA), and sodium benzoate have been proposed as promising inhibitors for their efficiency in concrete under long-term DOI: 10.1002/masy.202200165 exposure tests, with a reliable increase in the critical chloride content to initiate corrosion. [7] The formation of a passive film formed by different organic inhibitors that expose COOˉgroups or amine groups on carbon steel has been investigated experimentally and theoretically using molecular mechanics (MM) and molecular dynamics (MD) simulations.…”