【20090806 Focus Topic】Anti-halogen treatment
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This post was last edited by jothan on 2009-8-5 19:34. When the instruments manufactured by our company are exported to Europe, customers require that the stainless steel sealing containers be treated to resist halogens. The stainless steel sealed container functions as a reaction vessel; combustible materials such as coal or oil burn inside this oxygen-enriched stainless steel sealed container. The combustion products include nitrogen, carbon dioxide, nitric acid, sulfuric acid, water, and possibly halides as well. The material used for the stainless steel sealed container is 0Cr17Ni12Mo2. Since the customer believes that halide ions can also cause corrosion of the container, they have requested that we apply anti-halide treatment. We lack knowledge in this area and seek guidance from experts regarding anti-halogenation treatment processes, the equipment used in such processes, as well as the raw materials required for anti-halogenation treatment.
It is likely that the harm of chloride ions to stainless steel was taken into consideration; 316L stainless steel possesses excellent oxidation resistance, and by controlling the carbon content, it reduces the precipitation of chromium carbide at the grain boundaries after welding, thereby providing good corrosion resistance. However, 316L stainless steel is most susceptible to stress corrosion cracking in chloride environments and does not possess resistance to chloride corrosion. It has been proven that using standard grades of stainless steel, such as 316L stainless steel, in seawater systems is not successful. Furthermore, there is still a possibility of chromium depletion at the grain boundaries in the weld heat-affected zone after welding. Due to practical constraints, it is not possible to carry out acid pickling and passivation on the inner surface of the weld site after welding; as a result, the protective coating there is relatively poor. Additionally, the increased surface irregularity after welding creates conditions favorable for the formation of pitting nuclei.
Agree with the person above. Foreigners are quite cautious when choosing equipment; there are things we may not pay much attention to, but they take them quite seriously.
Thank you to the two people above for their advice. I would like to take this opportunity to learn about the theoretical basis of halide resistance treatment, as well as the methods used for such treatment.
Austenitic steel is likely to be susceptible to halogen corrosion; if there is no better alternative and foreign customers have such requirements. 1) Replace with better processing materials; of course, the increase in price must be explained ； 2) Maintain the status quo and increase the frequency of equipment replacement ；
Halides are generated during use, and a level of halide ions that does not exceed certain limits poses little threat. If the purpose of anti-halide treatment is to enable 316L stainless steel to resist corrosion caused by halides, then it is somewhat putting the cart before the horse.
However, the customer’s requirements are clear: 316L stainless steel can be used provided it is treated to resist halides, or another stainless steel alloy resistant to halide corrosion can be used. I searched for a long time but still couldn’t find a method for halide resistance treatment, nor any stainless steel material that is more resistant to halide corrosion than 316L stainless steel. But the customer is waiting for our results before placing an order.
May I ask what the special stainless steels of the Hastelloy family are? My knowledge is quite limited; I would appreciate any guidance you can provide!