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Potential in microroughness domain of metal surface employed in cathodic protection mode

V.Lukovich,
 
V.Kartuzov*
 

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Kyiv
vvk@ipms.kiev.ua
Usp. materialozn. 2021, 3:48-54
https://doi.org/10.15407/materials2021.03.048

Abstract

This effort presents the results of investigation of cathodic protection process of a section of the main pipeline, which has been operating in cathodic protection mode for a long time and which insulation has completely exfoliated from metal surface, and a cavity between is filled with water and salt impurities. In this case, a decisive factor is a fact that a metal surface is covered with microroughnesses in the form of protrusions with almost conical shape. The surface is immersed in electrolyte. At the electrolyte-metal interface, a potential difference is formed — a corrosion potential, which creates an unstable equilibrium among the potentials of metal and electrolyte. A mathematical model is designed and implemented into a numerical algorithm and computer program. A computational experiment has been carried out to calculate the potential around microroughness. The model describes a change in potential in this area at incomplete and complete cathodic protection of metal surface. The basis of computational model is a selection of one of metal protrusions of material microheterogeneity and placing it in a cylinder, which diameter coincides with that one of the lower base of this protrusion, and its upper part passes through the apex of the protrusion. Mathematical model equations with corresponding boundary conditions and their discrete implementation are presented. The solution of problems is obtained by iterative procedures based on reference values of protective potential taken from practice. The results of computational experiment are presented in the form of graphs: 1) potential distribution in the field of electrolytes; 2) changes in electrolyte potential at the border with protrusion at different values of polarization potential; 3) changes in polarization resistance in the area (calculated). The geometry of computational domain was also varied, and the values of protective potential were determined to ensure the absence of corrosion.


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CATHODIC PROTECTION, MICROROUGHNESS, PROTECTIVE POTENTIAL

References

1. Lukovych, V. V. (2020). On the pipeline polarization in the case of insulation delamination from its surface. Uspikhy materialoznavstva, Iss, 1, pp. 40—45 [in Ukrainian]. https://doi.org/10.15407/materials2020.01.040

2. Lukovich, V., Kartuzov, V. (2019). Potential in the area of metal surface microroughness. Matematicheskie modeli i vychislitel’nyj jeksperiment v materialovedenii. Kyiv: In-t probl. materialovedenija NAN Ukrainy, Iss. 21, pp. 36—41.

3. Shvets, V. A. Physico-chemical properties of ACCM tread alloy and structural steels X70, ST3: Avtoref. dys. ... kand. khim. nauk. Kyiv, 1993. 21 p.

4. Frantsevich, I. N., Lyashenko, M. E., Grimaylovskiy, V. A. (1968). Experience in protecting the Dashava—Kiev gas pipeline against soil corrosion and stray currents. Zaschita metallov, № 5, pp. 597—603.

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