Hydrochloric acid is one of the most aggressive corrosive reducing acids, and its corrosion to metal materials was a major technical problem that the corrosion resistant structure was difficult to solve. The corrosion rate of industrial pure nickel 200,201 and nickel-copper alloy Monel 400 in room-temperature air-free hydrochloric acid with a concentration of 10% or less is less than 0.25mm/a. Only in hydrochloric acid without oxidizing agent whose concentration is lower than 0.5%, they can be used. At 200 degrees Celsius, however, the presence of oxidants such as Fe3+, Cu2+, CrO42+, and air in hydrochloric acid will greatly accelerate the corrosion of these alloys, so their use is extremely limited.
Among nickel-based corrosion-resistant alloys, only Ni-Mo alloys B-2, B-3, and B-4 have the best resistance to hydrochloric acid corrosion in unstained hydrochloric acid. When oxidative impurities in hydrochloric acid are contaminated, Accelerate the corrosion of Ni-Mo alloys. Corrosion resistance of Ni-Cr-Mo corrosion-resistant alloy series such as alloyC-276,alloyC-22,alloy686,alloy625,alloy59 in hydrochloric acid is insensitive to the presence of oxidizing impurities, and has suitable corrosion resistance in high-temperature dilute hydrochloric acid and all concentrations of hydrochloric acid at room temperature. In the hydrochloric acid concentration greater than 5%, the highest molybdenum-containing Ni-Cr-Mo alloy C-276 can only be used below 50 degrees Celsius. The iron-nickel base corrosion-resistant alloy Ni-Fe-Cr-Mo-Cu does not have sufficient resistance to hydrochloric acid corrosion, and can only be taken into consideration in the case of a very dilute hydrochloric acid concentration. Obviously, B-2 alloy has the best corrosion resistance to hydrochloric acid, and this alloy has been successfully applied to the process equipment for hydrochlorination to produce hydrochloric acid. At high temperatures, the oxygen has a low dissolution bottom and therefore has a low corrosion rate, whereas at low temperatures, the solubility of oxygen is higher thereby accelerating the corrosion of the alloy. The iron-nickel-based corrosion-resistant alloys containing higher amounts of Mo are safer to use at temperatures below room temperature in hydrochloric acid, and can only be used at higher temperatures in hydrochloric acid concentrations less than 5%. The corrosion resistance of alloy 59 in hydrochloric acid is lower than that of alloy C-276, indicating that tungsten in the alloy is beneficial to its resistance to hydrochloric acid corrosion. If the corrosion rate is 0.51mm/a, some nickel-based corrosion-resistant alloys containing Cr and Mo alloys have good corrosion resistance in hydrochloric acid, while iron-nickel-based alloys and stainless steels have the limitation of applications in hydrochloric acid.
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Post time: May-11-2018