Formation mechanism of iron tubercles during corrosion of water supply pipes

• V.A. Chukhin and A.P. Andrianov

Moscow State University of Civil Engineering (National Research University), Yaroslavskoe shosse 26, 129337 Moscow, Russian Federation

Abstract: The literature data and own results of the study of corrosion mechanism and tubercle structures formation in steel and cast iron pipes are analyzed. Several possible ways for the nucleation and growth of tubercles are considered: local accumulation of corrosion products and the formation of a hemispherical membrane when the solubility limit of iron oxides is exceeded, the effect of redox processes on corrosion products under oxygen deficiency, and the participation of a template formed by hydrogen bubbles in the formation of tubular structures that subsequently form tubercles. It is shown that all mechanisms of tuberculation growth can take place in pipelines of water supply systems depending on the conditions (including hydrodynamic). At the initial stage the tuberculation corrosion proceeds with oxygen depolarization, and then, as denser layers of corrosion deposits are formed, the process begins to proceed with hydrogen depolarization. Long-term observation of the corrosion process of steel pipe in hot water showed the influence of the release of hydrogen gas on the growth of elongated tubercles and the validity of the third version of growth mechanism by analogy with ferrotubes. It is emphasized that hydrodynamic conditions along with the composition of water and the intensity of the initial stage affect the type of the formed tubercles (with or without liquid) and their integrity. Formation of large loose tubercles filled with liquid contributes to autocatalytic corrosion process inside the pitting with the appearance of through fistulas.

Keywords: pitting corrosion, corrosion tubercle formation, carbon steel, water supply systems

Int. J. Corros. Scale Inhib., 2022, 11, no. 2, 812-830
doi: 10.17675/2305-6894-2022-11-2-24

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