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Use of UNS S32906 versus UNS N02200 on the first effect evaporator in NaOH production

The production of sodium hydroxide (NaOH) can be carried out by the membrane, diaphragm or mercury process. The biggest difference between these processes, with regard to fluid composition, is that the caustic soda (NaOH) produced by the diaphragm process has a higher chloride content during its production process.

Such aggressiveness in the environment generally calls for the use of special materials to increase the useful life of the equipment and avoid unscheduled shutdowns in the production unit.

Product Number: 51323-19487-SG
Author: Renata Mota, Felipe Beluche, Karen Picker
Publication Date: 2023
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Caustic soda (NaOH) production is related to a very aggressive environment. The use of special alloys is essential, such as UNS N02200 and duplex UNS S2906 in the first evaporator effect through diaphragm route. A similar environment compared both different materials and concluded that UNS S32906 had performed better than UNS N02200 under boiling 50%NaOH and addition of NaCl and ClO3-. This present study referred to 45%NaOH and 5%NaCl at 141,3°C in the tube side. After six months, UNS S32906 sample was intact while UNS N02200 showed general corrosion attack. It consequently represented a cost-effective solution to implement the duplex stainless steel after several evidence of its equipment life cycle improvement.

Caustic soda (NaOH) production is related to a very aggressive environment. The use of special alloys is essential, such as UNS N02200 and duplex UNS S2906 in the first evaporator effect through diaphragm route. A similar environment compared both different materials and concluded that UNS S32906 had performed better than UNS N02200 under boiling 50%NaOH and addition of NaCl and ClO3-. This present study referred to 45%NaOH and 5%NaCl at 141,3°C in the tube side. After six months, UNS S32906 sample was intact while UNS N02200 showed general corrosion attack. It consequently represented a cost-effective solution to implement the duplex stainless steel after several evidence of its equipment life cycle improvement.