Influence of Seawater Flow Characteristics Inside Pipelines on Cathodic Protection of Carbon Steel Pipelines-Experiment and Numerical Simulation

doi:10.11902/1005.4537.2025.291

Journal of Chinese Society for Corrosion and protection

2026, Vol. 46

Issue (4): 1081-1094 DOI: 10.11902/1005.4537.2025.291

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Influence of Seawater Flow Characteristics Inside Pipelines on Cathodic Protection of Carbon Steel Pipelines-Experiment and Numerical Simulation

WU Fangyun¹, QIAO Ruixin², LI Xuning¹, SHANG Haojie¹, LU Fenghua¹, ZHOU Cheng¹, WANG Xin¹, DONG Liang²(

)

^1.CNNC Nuclear Power Operations Management Co. Ltd., Jiaxing 314000, China
^2.School of Petroleum and Natural Gas Engineering, Changzhou University, Changzhou 213164, China

Cite this article:

WU Fangyun, QIAO Ruixin, LI Xuning, SHANG Haojie, LU Fenghua, ZHOU Cheng, WANG Xin, DONG Liang. Influence of Seawater Flow Characteristics Inside Pipelines on Cathodic Protection of Carbon Steel Pipelines-Experiment and Numerical Simulation. Journal of Chinese Society for Corrosion and protection, 2026, 46(4): 1081-1094.

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Abstract

The influence of seawater flowing inside the pipeline on the cathodic polarization behavior of carbon steel pipelines was studied viaa home-made closed-loop circulation system with electrochemical tests, meanwhile, the electrochemical behavior of different locations on the inner side of the pipeline by varying polarization potentials was analyzed by computational fluid dynamics simulation. The results show that as the polarization potential varies, the current density trends at elbows and straight sections are consistent; however, the middle region of the elbow is the most susceptible to corrosion, with the outer bend requiring a significantly higher protective current density than the inner bend. The capacitive arc radius at the elbow first increases and then decreases along the flow direction, consistent with the variation in current density. Surface morphology and XPS analyses reveal that at a polarization potential of -1.2 V, a compact Mg(OH)₂ deposit forms, which enhances protection but increases current consumption due to the cathodic reaction shifting toward hydrogen evolution. Numerical simulations further demonstrate that near-wall radial velocity is highly correlated with current density and can serve as a key parameter for evaluating the influence of seawter flow on the cathodic protection effectiveness. Based on this, a relationship model between current density and radial velocity was established, providing valuable reference for the design and assessment of cathodic protection systems in flowing seawater environments.

Key words: FAC cathodic Protection CFD hydrodynamics elbow carbon steel

Received: 17 September 2025 32134.14.1005.4537.2025.291

ZTFLH:

TG174

Corresponding Authors: DONG Liang, E-mail: dongliang@cczu.edu.cn

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	WU Fangyun
	QIAO Ruixin
	LI Xuning
	SHANG Haojie
	LU Fenghua
	ZHOU Cheng
	WANG Xin
	DONG Liang

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https://www.jcscp.org/EN/10.11902/1005.4537.2025.291 OR https://www.jcscp.org/EN/Y2026/V46/I4/1081

Fig.1 Position numbering of test points (a) and diagram of the recirculating flow system (b)

Fig.2 Geometric model schematic (a) and schematic diagram of the mesh at different sections of the pipe segment (b)

Fig.3 Current density curves at C1 (a), C2 (b), C3 (c), B1 (d), B2 (e) and B3 (f) measurement points

Fig.4 Comparison of current density at different positions (a) and different polarization potentials (b)

Fig.5 Current density curves at downstream of the elbow of 2D (a) and 4D (b)

Fig.6 Comparison of current density at different positions (a) and different polarization potentials (b)

Fig.7 Nyquist diagrams at B1 (a), B2 (b), B3 (c), C1 (d), C2 (e) and C3 (f) test points

Fig.8 Equivalent circuits compatible with experimental impedance data

Table 1 20# carbon steel impedance data at different positions of the elbow

Fig.9 Variation curves of the charge transfer resistance of 20# carbon steel at different positions of the elbow with cathodic polarization potential

Fig.10 Surface morphologies of the specimens at positions C1 (a1), C2 (a2), and C3 (a3) on the inner side of the elbow and at positions B1 (b1), B2 (b2), and B3 (b3) on the outside of the elbow (Magnification: 100 times)

Fig.11 Nyquist diagrams of 20# carbon steel at 2D (a) and 4D (b) positiens downstream of the elbow

Fig.12 Surface morphology of 20# carbon steel at 2D (a) and 4D (b) positions downstream of the elbow (Magnification: 100 times)

Table 2 XPS quantitative analysis

Fig.13 Elbow test segment annotation

Fig.14 Velocity distribution at each section of the pipeline (a), velocity distribution at the elbow and its upstream and downstream sections (b) and turbulent kinetic energy distribution at the elbow and its upstream and downstream sections (c)

Fig.15 Comparison of surface shear force and current density at different positions of outside of the elbow (a) and inner side of the elbow (b)

Fig.16 Comparison of TKE and current density at different positions of outside of the elbow (a) and inner side of the elbow (b)

Fig.17 Comparison of voriex intensity and current density at different positions of outside of the elbow (a) and inner side of the elbow (b)

Fig.18 Comparison of axial velocity and current density at different positions of outside of the elbow (a) and inner side of the elbow (b)

Fig.19 Comparison of near-wall radial and current density near the wall at different positions of outside of the elbow (a) and inner side of the elbow (b)

Fig.20 Fitting relationship between current density and radial rate at -0.7 V (a), -0.8 V (b), -0.9 V (c), -1.0 V (d), -1.1 V (e) and -1.2 V (f) polarization potentials

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