Hastelloy itself is a nickel-based alloy, but it is different from ordinary pure nickel (Ni200) and Monel. It uses chromium and molybdenum as the main alloying elements to improve its adaptability to various media and temperatures, and has been specially optimized for different industrial applications. At present, the chemical industry generally pursues high production capacity and constantly improves the process to increase the temperature and pressure to speed up the reaction, so that it is easy to have unpredictable situations in production and cause unplanned maintenance. Hastelloy is aimed at such a demand, adapting to all kinds of unpredictable harsh environments and minimizing unplanned maintenance. At the same time, it also has good processing and welding performance and is convenient for on-site maintenance. Classification of Hastelloy. At present, corrosion-resistant Hastelloy alloys are mainly divided into C series, B series, G series and D series alloys. Table 1 lists some commonly used Hastelloy alloys. C series alloy is nickel-chromium-molybdenum alloy. Because chromium can form a dense oxide film (passivation) on the alloy surface, it provides anti-oxidation environmental ability, while molybdenum mainly provides anti-reduction environmental ability. Therefore, C series alloys can be used in the environment with both oxidizing medium and reducing medium. C-series alloy is the most widely used alloy, especially C-276 alloy. After being invented in the 1960s, it still shows strong vitality after more than 40 years of tests. After development, C-4 mainly meets the needs of a small number of European users, and it can only be seen in older equipment at present. C-22 alloy has enhanced its corrosion resistance without increasing the cost, and its cost performance is particularly excellent. C-2000? As a new generation product, it provides a wider range of safe use, which is very suitable for users who want to improve the service life of equipment and test new technologies. At present, C series alloys have been used in quite a few industries in China. Such as fine chemical industry (TDI, PTA, acetic acid/anhydride, acrylic acid, etc.); Environmental engineering industry (FGD, sewage treatment); Plate heat exchanger industry. At present, Hastelloy has been applied in many industries abroad, but it is still in the experimental stage in China, such as pharmaceutical industry. B series alloy is nickel-molybdenum alloy, which provides the best corrosion resistance for completely reduced environment. Although B series alloys perform well in reducing environment, they are very sensitive to oxidizing media (iron and copper ions). 50ppm iron ion is enough to obviously reduce the corrosion resistance of B series alloys. Because of its special properties, B series alloys are relatively concentrated in application, the most important of which is acetic acid production (carbonyl synthesis), and some sulfuric acid recovery systems also use this series of alloys. At present, the widely used brand is B-3, and B-2 has gradually withdrawn from the market due to the lack of processing performance. G series alloy is Ni-Cr-Fe alloy (G-35? Except alloys). The high chromium content makes this series of alloys outstanding in oxidation resistance. At the same time, the new G series alloy (G-30? G-35? ) also has good pitting corrosion resistance, and with a small amount of copper content, it enhances the ability to resist sulfuric acid and hydrofluoric acid. Therefore, G series alloys are mainly used in strong oxidizing environment and complex environment of mixed acids, such as wet-process phosphoric acid and pickling line in steel mills. D series alloy is Ni-Cr-Si alloy. Because this series of alloys contain a certain amount of silicon, it can produce a fairly stable oxide film on the surface, which is very difficult to weld in extreme strong oxidizing environment. At present, D-205, the D-series alloy produced in batch, is applied to plate heat exchangers in high-temperature concentrated sulfuric acid environment. At present, the alloy is exclusively represented by Affara Law Company, and only finished plates are provided. Hastelloy has been developing continuously, and new alloy materials have been derived to promote the development of industry. It has excellent environmental adaptability and reliable corrosion resistance. For the special environment of various industries, there are targeted solutions. As a mature commercial product, Hastelloy has a variety of product forms, which can fully meet various needs.