When screening corrosion-resistant materials, significant differences arise when they are placed in solutions under the same conditions

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This post was last edited by Wang Wei2 on 2023-12-25 at 09:57. When selecting corrosion-resistant materials, significant differences can occur when they are placed in solutions under the same conditions. To remove chlorides from a strong acid mixture containing some residual chlorine and numerous salts, it is necessary to heat the solution to 80–90°C in a container. Due to the high corrosivity of the medium, glass-lined steel containers can only be used for one to two years, and it is even more difficult to choose materials for the heating coils. To this end, specimen pieces of several alloy materials were immersed in the production solution in the laboratory to conduct material selection tests. The selected materials include nickel, Hastelloy, stainless steel, and titanium. The results show that only titanium is corrosion-resistant. However, the heating coil made of titanium suffered corrosion damage within two days, with a corrosion rate as high as 38 millimeters per year. The difference between the test results and the actual corrosion behavior of titanium is quite large. Analysis: According to the description, the testing was carried out by placing test specimens of several materials in the same container. This approach is clearly incorrect. Because interactions may occur between different materials, leading to incorrect results. In this case, the Fe2+ ions generated by the corrosion of the iron-based alloy specimen located near the titanium specimen are oxidized to Fe3+ ions in this halide solution, and Fe3+ ions act as an extremely effective corrosion inhibitor for titanium. Therefore, a basic principle of corrosion testing is that only test specimens made of one type of material should be placed in a test container, to ensure sufficient contact with the solution. Gaps should be avoided between the test piece and the container, as well as between the test piece and the support frame. No metal support frames are used. In short, it is necessary to avoid introducing corrosion factors that are difficult to estimate.