Effect and Mechanism of Cathodic Protection Conditions on the Corrosion Behavior of X80 Steel Under HVDC Interference
GU Shaojie1, LIU Yang1, LI Caixia1, HU Shangmao2, DU Yanxia1()
1 Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China 2 CSG Electric Power Research Institute, China Southern Power Grid, Guangzhou 510663, China
Cite this article:
GU Shaojie, LIU Yang, LI Caixia, HU Shangmao, DU Yanxia. Effect and Mechanism of Cathodic Protection Conditions on the Corrosion Behavior of X80 Steel Under HVDC Interference. Acta Metall Sin, 2025, 61(6): 917-928.
Recently, the problem of high-voltage direct current (HVDC) interference suffered by buried oil and gas pipelines has attracted widespread attention among research communities. Hence, accurately assessing the corrosive impact of HVDC interference on buried metal pipelines and performing effective protection procedures for the prevention of such corrosion have become priority issues that need to be resolved for producing reinforced pipelines. To date, the effect of the cathodic protection of the pipeline on the corrosion behavior of X80 steel under HVDC interference has rarely been reported. Hence, in this study, the corrosion behavior of X80 steel without cathodic protection conditions before HVDC interference and the effect of these protection conditions on the corrosion behavior of X80 steel under HVDC interference were studied through laboratory simulation experiments. Results showed that the corrosion rate of X80 steel was 170.81 μm/h without cathodic protection under 20 V DC interference for 1 h. When the cathodic protection pretreatment potentials were -0.85, -0.95, -1.05, and -1.20 V, the corrosion rates were 124.39, 87.13, 54.56, and 1.45 μm/h, respectively. The effect of various cathodic protection pretreatment potentials on the corrosion behavior of X80 steel under HVDC interference was clarified based on the product surface membrane layer, polarization, and EIS results. For the cathodic protection pretreatment potential of -0.85 to -1.05 V, the sample products after HVDC interference mainly showed a mixture of green rust GR1, calcium, and magnesium deposits; the corrosion rate of the sample products decreased with the increasing negative cathodic protection pretreatment potential under DC interference due to the gradual increase in the quality of the calcium and magnesium deposited layer on the surface of the sample products. At -1.20 V cathodic protection polarization potential, the corrosion rate of the sample products was substantially lower than that at other potentials because passivation of the products occurred under the combined action of high cathodic protection potential and HVDC interference.
Fig.1 Schematics of cathodic protection system device (a) and high-voltage direct current (HVDC) interference simulation experiment device (b) (WE—working electrode, CE—counter electrode, RE—reference electrode, R—resistance)
Fig.2 Current density changes (a) and corrosion rates (b) with different cathodic protection potentials
Fig.3 Macroscopic morphologies of the specimen surface after cathodic protection with different cathodic protection potentials for 4 d (a) -0.85 V (b) -0.95 V (c) -1.05 V (d) -1.20 V
Fig.4 Macroscopic corrosion morphologies of samples with different cathodic protection potentials after DC interference before (a1-e1) and after (a2-e2) pickling (a1, a2) uncathodic protection (b1, b2) -0.85 V (c1, c2) -0.95 V (d1, d2) -1.05 V (e1, e2) -1.20 V
Fig.5 XRD spectra of corrosion products on the sample surface after interference (a) -0.85 V (b) -0.95 V (c) -1.05 V (d) -1.20 V
Fig.6 XPS of Fe element (a) and O element (b) in corrosion products of sample after -1.20 V cathodic protection for 4 d and 20 V DC inter-ference for 1 h
Fig.7 Nyquist (a) and Bode (b) plots of samples with different cathodic protection polarization poten-tials for 4 d (f—frequency, Z'—real part of the impedance, Z''—imaginary part of the imped-ance)
Table 1 EIS fitting results of samples after cathodic protection
Fig.9 EIS of samples with different cathodic protection polarization potentials after cathodic protection for 4 d and 20 V DC interference for 1 h (a) Nyquist plot (-0.85 V, -0.95 V, -1.05 V) (b) Nyquist plot (-1.20 V) (c) Bode plot
Potential (vs SCE)
V
RS
Ω·cm2
Rf
Ω·cm2
Qf
S·s n ·cm-2
nf
Rt
Ω·cm2
Qdl
S·s n ·cm-2
ndl
-0.85
30.88
12.90
2.915 × 10-3
0.688
44.59
3.055 × 10-3
0.855
-0.95
32.80
6.90
5.928 × 10-4
0.773
87.02
8.532 × 10-4
0.874
-1.05
62.74
97.09
1.021 × 10-3
0.747
112.10
1.856 × 10-3
0.935
-1.20
60.54
208.3
1.355 × 10-5
0.328
89850
8.894 × 10-4
0.807
Table 2 EIS fitting results after cathodic protection and interference
Fig.10 Surface micromorphologies (a1, a2, b1, c1, d1, d2) and corresponding EDS analyses (a3, b2, c2, d3) of samples after cathodic protection at different cathodic protection polarization poten-tials for 4 d (a1, a2, a3) -0.85 V (b1, b2) -0.95 V (c1, c2) -1.05 V (d1, d2, d3) -1.20 V
Fig.11 Surface micromorphologies (a1, a2, b1, b2, c1, c2, d1) of samples after cathodic protection with different cathodic protection polarization potentials for 4 d, and 20 V DC interference for 1 h and corresponding EDS analyses of rectangle areas in Figs.11a2-c2 and d1 (a3, b3, c3, d2) (a1, a2, a3) -0.85 V (b1, b2, b3) -0.95 V (c1, c2, c3) -1.05 V (d1, d2) -1.20 V
Fig.12 Variation curve of Cl- concentration on sample surface under cathodic protection of -1.20 V (a) and anode polarization curves of samples under different cathodic protection potentials (b) (i—current density)
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