Selection of low-temperature materials
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Our facility has a reaction vessel capable of operating at temperatures as low as -90 degrees Celsius, which is used for precision chemical synthesis at low temperatures. We are currently facing a problem: for a new type of product, both the reactions and the raw materials take place in an alkaline environment; however, there is one acidic raw material that needs to be added to the mixture. After using this vessel for 9 months, it was found that the upper part of the coiled tubes had corroded. The properties of this raw material are similar to those of benzyl chloroformate. We are seeking advice regarding the material suitable for making these coiled tubes – the liquid nitrogen flows through these tubes, and the preferred material for the tubes is SS30408
Coil material upgraded. I wonder what the CL-concentration is? But at least choose 316L, which offers both low-temperature resistance and resistance to chloride corrosion.
Corrosion should have nothing to do with chloride ions; there must not be even a trace of water in the reaction system, with the water content required to be below 50 ppm
Use 2205 duplex steel or 2507 super duplex steel, imported from Sweden; the latter is slightly more expensive.
Is it a bit luxurious? I don’t think it reaches that level yet
1: Use 316; it is superior to 304, but will fail due to chloride ions in the morning and evening. 2: The inside and outside of the coil are coated with PTFE for corrosion protection; importantly, coating the inside with PTFE is more difficult, and this depends on the length of the coil, its diameter, and the angle at which it is positioned. 3:2205 or 2507.
The coil is cooled by liquid nitrogen, so it’s not possible to apply tetrafluoroethylene coating. Additionally, my medium should be free of chloride ions, containing only chlorinated organic acids
You said it’s a chlorinated organic acid, so of course there will be chloride ion corrosion. Is it sodium hypochlorite?
Bro, do chlorinated organic acids necessarily contain chloride ions? This seems a bit far-fetched; if that’s the case, then dichloromethane is also corrosive
For dichloromethane, it depends on the environmental conditions under which it is stored and used, such as temperature and pressure; corrosivity is merely a matter of degree. It’s a simple principle: dichloromethane will stay in a carbon steel container for a longer time than in a stainless steel container. This is just my personal opinion; I hope experts can give me some guidance
To be honest, I’ve never really understood the corrosion mechanism of dichloromethane. The corrosion manuals state that 304 steel has better resistance to dichloromethane than 316 steel, but in actual use I find that 304 seems to suffer little corrosion at all. Could it be that the information in those manuals is misleading?