Is 316L material suitable for 32% NaOH solution?
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There is a plate heat exchanger that has been in use for just over a year, and it has started to leak. Upon disassembly, it was found that at the inlet side, where a 32% NaOH solution (at 85°C) flows, the gasket area had been corroded. Is it possible that the 316L material is not suitable for use with 32% NaOH hot solutions?
As a supplementary point, the temperature of the NaOH solution in this plate exchanger dropped to around 65°C, while that in another unit dropped below 40°C; both have been in use for over 4 years without such issues occurring.
High temperatures won’t work, and high concentrations either. At high temperatures, the alkali concentration in areas with poor flow can increase, leading to corrosion
At a solution concentration of 35%, the maximum operating temperature for carbon steel in NAOH is 50 degrees; stainless steel performs slightly better than carbon steel. You can check the diagram for details
Could you clarify the source of the graph? It’s worth checking when selecting materials these days
The concentration should be above 32%, and the temperature is best kept below 65 degrees; otherwise, pitting will occur in the equipment. This is based on personal experience. For more details, simply search for “NAOH CORRISION” on the website
For conditions involving a 32% NaOH solution at 85°C, 316L is not recommended; the plates used in heat exchangers are already thin and lack corrosion resistance, so it is advisable to use materials of grade 904 or higher.