AC-Induced Corrosion of Underground Steel Pipelines. Faradaic
               Rectification under Cathodic Protection: I. Theoretical Approach with Negligible
               Electrolyte Resistance

Underground pipelines protected with a thick coating and by cathodic polarisation may suffer a serious external corrosion damage in the presence of stray alternating current (AC) voltage induced by high voltage industrial electric transport system, such as power lines or electrified railroads. The origin of the corrosion enhancement comes from the nonlinearity of the currentpotential characteristics of the metal-soil interface. In this paper, we will theoretically evaluate the increase of the corrosion current density and the potential shift induced by a high amplitude AC signal to models of corroding systems: anodic polarisation curves obeying an exponential law with respect to the potential, and cathodic process under the mixed activation-diffusion kinetics. The originality of the present work lies in the use of a relatively small number of dimensionless variables to describe the faradaic rectification for the corrosion potential shift and the corrosion current enhancement. In this article, the effect of the electrolyte resistance was neglected.

Tafel law; dissolved oxygen reduction; partially diffusion limited kinetics; corrosion potential shift; corrosion current enhancement

Authorship

Ibrahim Ibrahim

Al-Andalus University, Tartus, Al Qadmus, SyriaAl-Andalus UniversitySyriaTartus, Al Qadmus, SyriaAl-Andalus University, Tartus, Al Qadmus, Syria

CNRS, UMR 8235, LISE, Case 133, 4 place Jussieu, 75005 Paris, FranceLISEFranceParis, FranceCNRS, UMR 8235, LISE, Case 133, 4 place Jussieu, 75005 Paris, France

Bernard Tribollet

Laboratoire Interfaces et Systèmes Electrochimique (LISE), Sorbonne Universités, UPMC Univ. Paris 06, UMR 8235, 75005 Paris, FranceUPMC Univ.FranceParis, FranceLaboratoire Interfaces et Systèmes Electrochimique (LISE), Sorbonne Universités, UPMC Univ. Paris 06, UMR 8235, 75005 Paris, France

CNRS, UMR 8235, LISE, Case 133, 4 place Jussieu, 75005 Paris, FranceLISEFranceParis, FranceCNRS, UMR 8235, LISE, Case 133, 4 place Jussieu, 75005 Paris, France

Hisasi Takenouti ^**e-mail: hisasi.takenouti@upmc.fr

CNRS, UMR 8235, LISE, Case 133, 4 place Jussieu, 75005 Paris, FranceLISEFranceParis, FranceCNRS, UMR 8235, LISE, Case 133, 4 place Jussieu, 75005 Paris, France

Michel Meyer

GDF SUEZ, 361 avenue du Président Wilson, 93211 Saint Denis La Plaine, FranceGDF SUEZFranceSaint Denis La Plaine, FranceGDF SUEZ, 361 avenue du Président Wilson, 93211 Saint Denis La Plaine, France

*e-mail: hisasi.takenouti@upmc.fr

SCIMAGO INSTITUTIONS RANKINGS

Al-Andalus University, Tartus, Al Qadmus, SyriaAl-Andalus UniversitySyriaTartus, Al Qadmus, SyriaAl-Andalus University, Tartus, Al Qadmus, Syria

CNRS, UMR 8235, LISE, Case 133, 4 place Jussieu, 75005 Paris, FranceLISEFranceParis, FranceCNRS, UMR 8235, LISE, Case 133, 4 place Jussieu, 75005 Paris, France

GDF SUEZ, 361 avenue du Président Wilson, 93211 Saint Denis La Plaine, FranceGDF SUEZFranceSaint Denis La Plaine, FranceGDF SUEZ, 361 avenue du Président Wilson, 93211 Saint Denis La Plaine, France

Figures | Tables | Formulas

Figures (9)
Tables (1)
Formulas (45)

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Figure 1
(a) Schematic representation of the potential-pH diagram with potential excursions for a steel electrode under cathodic protection (CP) at E_CP, in the presence of AC perturbation E(t); (b) its equivalent electrical circuit with anodic and cathodic contributions by two parallel circuits; anodic reaction with a diode, and cathodic reaction with a diode and a direct current limiter.

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Figure 2
Mean DC current density – I_F-E curves under AC perturbation for the three reaction mechanism, and with negligible solution resistance. Kinetic constants displayed in Table 1.

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Figure 3
Effect of r_O₂/a and <ΔE> on the reduced shift of corrosion potential <E_corr,AV> for the mixed corrosion mechanism. A small diffusion component at E_corr,0 (r_diff,O₂ = 0.1), with negligible electrolyte resistance. r_O₂/a values from top to bottom: blue = 10, green = 5, brown = 3, pink = 2, black = 1, yellow = 0.5, purple = 1/3, red = 0.2, and orange = 0.1.

Thumbnail

Figure 4
Similar curves to Figure 3, but r_diff,O₂ = 0.01. The curves for various r_O₂/a are represented as Figure 3. The dot-dashed curve at the most bottom position represents r_diff,O₂ = 1 (cathodic kinetics entirely controlled by the diffusion).

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Figure 5
Relative enhancement of the corrosion current (solid lines), for the same system as Figure 3, r_diff,O₂ = 0.1 with negligible electrolyte resistance. Comparison with a bi-Tafelian corrosion mechanism shown as dashed curves. For r_diff,O₂ = 1 (cathodic kinetics entirely controlled by the diffusion), shown as a dot-dashed curve, no effect of <ΔE> is observed.

Thumbnail

Figure 6
Effect of r_O₂/a (or r_H₂O/a), and <E_corr,AV> with respect to <ΔE>, for a three reaction corrosion mechanism. The water reduction contribution to the total cathodic faradaic current is minor (λ_H₂O = 0.05), and the oxygen reduction reaction is characterised by a small diffusion contribution (r_diff,O₂ = 0.1) at E_corr,0. Electrolyte resistance R_E is neglected. Comparison with a bi-Tafelian corrosion mechanism is shown as dashed lines. The Tafel constant ratio r supplies different curves, which are distinguished as indicated in Figure 3.

Thumbnail

Figure 7
Variation of <ΔE_corr,AV> with respect to <ΔE>. The conditions are the same as those presented in Figure 6. Comparison with a bi-tafelian corrosion mechanism is shown as dashed lines.

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Figure 8
Same as in Figure 6 but with λ_H₂O = 0.001.

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Figure 9
Enhancement of the corrosion current density; the same simulation conditions as in Figure 7, but with λ_H₂O = 0.001.

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Table 1
Corrosion kinetic parameters used for the simulation calculations

Thumbnail

Figure 1 (a) Schematic representation of the potential-pH diagram with potential excursions for a steel electrode under cathodic protection (CP) at E_CP, in the presence of AC perturbation E(t); (b) its equivalent electrical circuit with anodic and cathodic contributions by two parallel circuits; anodic reaction with a diode, and cathodic reaction with a diode and a direct current limiter.

Figure 2 Mean DC current density – I_F-E curves under AC perturbation for the three reaction mechanism, and with negligible solution resistance. Kinetic constants displayed in Table 1.

Figure 3 Effect of r_O₂/a and <ΔE> on the reduced shift of corrosion potential <E_corr,AV> for the mixed corrosion mechanism. A small diffusion component at E_corr,0 (r_diff,O₂ = 0.1), with negligible electrolyte resistance. r_O₂/a values from top to bottom: blue = 10, green = 5, brown = 3, pink = 2, black = 1, yellow = 0.5, purple = 1/3, red = 0.2, and orange = 0.1.

Figure 4 Similar curves to Figure 3, but r_diff,O₂ = 0.01. The curves for various r_O₂/a are represented as Figure 3. The dot-dashed curve at the most bottom position represents r_diff,O₂ = 1 (cathodic kinetics entirely controlled by the diffusion).

Figure 5 Relative enhancement of the corrosion current (solid lines), for the same system as Figure 3, r_diff,O₂ = 0.1 with negligible electrolyte resistance. Comparison with a bi-Tafelian corrosion mechanism shown as dashed curves. For r_diff,O₂ = 1 (cathodic kinetics entirely controlled by the diffusion), shown as a dot-dashed curve, no effect of <ΔE> is observed.

Figure 6 Effect of r_O₂/a (or r_H₂O/a), and <E_corr,AV> with respect to <ΔE>, for a three reaction corrosion mechanism. The water reduction contribution to the total cathodic faradaic current is minor (λ_H₂O = 0.05), and the oxygen reduction reaction is characterised by a small diffusion contribution (r_diff,O₂ = 0.1) at E_corr,0. Electrolyte resistance R_E is neglected. Comparison with a bi-Tafelian corrosion mechanism is shown as dashed lines. The Tafel constant ratio r supplies different curves, which are distinguished as indicated in Figure 3.

Figure 7 Variation of <ΔE_corr,AV> with respect to <ΔE>. The conditions are the same as those presented in Figure 6. Comparison with a bi-tafelian corrosion mechanism is shown as dashed lines.

Figure 8 Same as in Figure 6 but with λ_H₂O = 0.001.

Figure 9 Enhancement of the corrosion current density; the same simulation conditions as in Figure 7, but with λ_H₂O = 0.001.

Table 1 Corrosion kinetic parameters used for the simulation calculations

Items	E_corr,0/V	I_corr,0/(μA cm^-2)	b_a/V^-1	b_c,O₂/V^-1	b_c,H₂O/V^-1	λ_H₂O	r _diff,O₂
	–0.7	20	38.4	–12.8	–12.8	0.1	0.3

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AC-Induced Corrosion of Underground Steel Pipelines. Faradaic Rectification under Cathodic Protection: I. Theoretical Approach with Negligible Electrolyte Resistance

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[1] *e-mail: hisasi.takenouti@upmc.fr