Abstract
Cast iron is primarily used in buried piping to transport water in the fire protection system of nuclear power plants; ductile cast iron is generally used for domestic nuclear power plants. In general, the fluid used as fire-extinguishing water in such fire protection systems is tap water, and corrosion inhibitors are not currently added. In this study, the synergistic effect of an adsorption barrier (monoethanolamine) and oxidized film in an environment with a corrosion inhibitor (tungstate) is examined, and the corresponding passivation properties are presented. An immersion corrosion test and electrochemical test in tap water to which only tungstate was added showed suppression of corrosion compared to molybdate at the same concentration. The polarization resistance value of a passivation film in tap water mixed with monoethanolamine and tungstate showed better results than that of the molybdate control. A surface analysis in mixed addition tap water also demonstrated that oxygen ions were sufficiently distributed, including at some spheroidized graphite sites, when tungstate was added compared to molybdate. In addition, the amount of tungsten ions adsorbed on the surface was larger than that of molybdenum ions, and it was confirmed that tungsten ions were evenly distributed over the entire surface.
Highlights
Corrosion can be described as a mechanism by which a metal gradually loses its original function and deteriorates through contact with gas or liquid owing to a chemical, biochemical, and/or electrochemical reaction according to changes in the surrounding environment [1]
ductile cast iron (DCI) wasof inhibited the concentration of 100 k ppm
Can the be results of an inhibited immersion test electrochemical confirmed that corrosion completely by corrosion co-addition of and a 2 kanppm test solution experiment confirmed that corrosion can be completely inhibited by co-addition of a ppm test obtained by mixing tungstate and monoethanolamine
Summary
Corrosion can be described as a mechanism by which a metal gradually loses its original function and deteriorates through contact with gas or liquid owing to a chemical, biochemical, and/or electrochemical reaction according to changes in the surrounding environment [1]. As the operating time of buried piping in a closed system increases, the prolongation of physical and chemical contact between the inner metal and water increases the likelihood of corrosion. The possibility of such corrosion is determined by temperature, flow rate inside the pipe, etc. It varies depending on factors including the passivation characteristics of the electrochemical reaction [2]. Depending on access restrictions (because some pipes have a small diameter), the risk of occurrence of corrosion defects increases preferentially according to the electrochemical reactivity at the interface between the base metal and the internal fluid [3].
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