MATERIAL SELECTION FOR EQUIPMENT OPERATED IN SODIUM HYDROXIDE SOLUTIONS

Important aspects of the choice of material for the manufacture of equipment operated in caustic solutions at various temperatures are considered. The basic object of the study was the Nickel 201 alloy, from which the equipment of a number of enterprises specializing in the production of caustic soda was made. Due to its resistance to alkaline media, the material in question is ideally suited for use in sodium hydroxide solutions. However, the alloy has a low hardness, which significantly reduces its wear resistance. One of the significant limitations of the high-tonnage consumption of Nickel 201 alloy is its high cost. Samples of three corrosion-resistant materials (Nickel 201 alloy, high-alloy steel grades 10X23H18 and 06KHN28MDT) were tested at different temperatures (20, 80 and 100 °C) in solutions of sodium hydroxide of various concentrations (50, 60, 70 and 80 %). A special feature of these steels is the significant chromium and nickel content, which provides them with increased resistance to contact with caustic substances, as well as an acceptable cost in comparison with a nickel alloy. It was found that steel grade 10X23H18 has the highest corrosion resistance among the three materials at room temperature. This alloy can be recommended for the manufacture of equipment used in the early stages of caustic soda production at low temperatures. In hot alkaline solutions, Nickel 201 alloy is more resistant. For each material in the Statgraphics shell, an equation has been obtained that makes it possible to make a calculated prediction of their corrosion rate, including at elevated temperatures typical of caustic soda production processes. The use of this approach is designed to ensure not only a significant increase in the durability of metal equipment, but also significant savings in the material resources of the industry.

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