How to avoid alkali embrittlement of carbon steel storage tanks in high-temperature NaOH?
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This post was last edited by Wang Wei2 on 2019-1-8 at 09:07. Everyone had in-depth discussions regarding the tendency of carbon steel to suffer from stress corrosion cracking (alkaline embrittlement) at different temperatures in NaOH aqueous solutions, and answers were provided from various perspectives – which is great. There is currently a carbon steel storage tank with a NaOH concentration of 38%, operating at a temperature of 70 degrees Celsius. How can corrosion and alkali embrittlement be prevented?
1. Lower the temperature of sodium hydroxide by using a circulating water heat exchanger to exchange heat with the alkali, thereby reducing corrosivity； 2. The inner wall of carbon steel storage tanks is coated with anti-corrosion materials; currently, high-density coating materials are available that can provide protection against corrosion in acidic and alkaline environments
The reason for alkaline embrittlement is the concentration of alkali, the temperature of the metal, and the magnitude of stress； Additionally, if concentration increases, there may be (locally high concentrations). Heat treatment can be carried out after welding to eliminate stress, and the temperature of the liquid alkali should be kept below 66 degrees. The increase in concentration is due to the inability to control the process fluids...
May I ask what the lowest and highest temperatures for alkaline embrittlement in carbon steel are?
The conditions for alkali embrittlement in carbon steel are related to temperature and the concentration of the alkali; generally, lower alkali solution concentrations result in a higher temperature at which alkali embrittlement occurs. If the alkali solution is around 40%, its alkali embrittlement should occur at around 60 degrees Celsius.
My polyaniline should be fine; it can withstand this temperature of caustic soda and prevent contact between carbon steel and the caustic soda. Slip tests can be conducted.