Effect of Sulfides on the Hydrogen Overvoltage and Hydrogenation of U8 Steel in Chloride-Hydrogen-Sulfide Media
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EFFECT OF SULFIDES ON THE HYDROGEN OVERVOLTAGE AND HYDROGENATION OF U8 STEEL IN CHLORIDE-HYDROGEN-SULFIDE MEDIA М. S. Khoma,1 S. А. Holovei,1 V. R. Ivashkiv,1 and Kh. B. Vasyliv1,2 We study the effect of FeS, FeS2 , and Fe 9S8 sulfide films on the corrosion rate and hydrogenation of U8 steel with different structures in chloride-acetate solutions. It is shown that these parameters increase with changes in the nonequilibrium structure of steel. Sulfide films formed on steel decelerate the anodic processes and accelerate the cathodic processes. The formation of kansite films on the steel surface is accompanied by a significant decrease in the overvoltage of hydrogen depolarization and makes the process of hydrogenation about five times more intense. The effect of sulfide films on the electrode processes and hydrogenation in chloride-acetate solutions depends on the structure of the metal on the surface of which they are formed. Keywords: U8 steel, corrosion, hydrogenation, sulfides, chloride-acetate solutions, stress-corrosion defects.
In the course of interaction between metals and acid electrolytes and in the presence of hydrogen sulfide, their corrosion proceeds under the conditions of hydrogen depolarization. Hydrogen atoms appear on the metal surface as a result of the reactions of hydrogen reduction. Then these atoms are adsorbed and can diffuse deeper into the metal, accumulate in its surface layers and in the bulk, and finally, lead to the hydrogen embrittlement and accelerated fracture of the metal. In the crystal lattice of metals, hydrogen can be in different states (proton, ion, molecule, or compound) characterized by different energies of Ме–Н bonds depending on their location: between grains, in the defects, traps, collectors, etc. This may affect the development of stress corrosion defects in the metals in different ways [1–4].
In hydrogen-sulfide media, the insoluble corrosion products formed on the metal surface (sulfides, oxidehydroxide iron compounds, etc.) can accelerate or decelerate the subsequent corrosion processes [5–8]. Depending on the conditions of formation of hydrogen sulfide and its concentration in aqueous solutions, we observe the formation of FeS troilite, FeS 2 pyrite, and Fe 9S8 kansite films on the surfaces of iron and steels. These films may affect the cathodic and anodic processes in different ways depending on their defectiveness, structure, and chemical composition of the metal [9]. Structural steels always contain carbides, which decrease hydrogen overvoltage and, together with surface sulfides, change the character of the electrode processes [10].
The aim of the present work is to study the influence of sulfide films on the surface of U8 steel with the pearlite, sorbite, troostite, and cementite structures on the characteristics of corrosion and hydrogenation in chloride-acetate solutions, which serves as a basis of the standard NACE solution [11]. 1 2
Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, Ukraine. Corresponding author; e-mail:
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