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The side walls of the regeneration tank are now made of 304 stainless steel, primarily to withstand alkaline environments at higher temperatures or concentrations, and to prevent carbon steel (CS) from suffering from alkali embrittlement cracking at high temperatures. In an alkaline solution environment, when the temperature exceeds 46°C, post-weld heat treatment must be applied to carbon steel welds; otherwise, alkali embrittlement is highly likely to occur. Even after stress-relief treatment, carbon steel still faces a high risk of corrosion cracking in areas subjected to repeated evaporation and concentration. While 304 stainless steel can also suffer from alkali embrittlement in high-concentration, high-temperature alkaline solutions, its corrosion resistance is superior to that of carbon steel; especially at higher temperatures (above 80°C) or in conditions where the alkaline solution tends to concentrate, it offers better protection against alkali corrosion and stress corrosion cracking. Therefore, 304 is used for the side walls of the regeneration tank, usually because this area experiences uneven heating, local high temperatures, or a risk of evaporation and concentration, requiring an improved corrosion resistance from the material. Furthermore, side walls may present issues such as complex welding structures and stress concentration; the use of 304 material along with appropriate heat treatment can further reduce the risk of alkali embrittlement.