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This post was last edited by Shaobin Fluid on 2026-4-1 09:10. It explains that in the complex environment of the Chemical Process Industry (CPI), engineers frequently face challenges posed by extreme operating conditions and highly corrosive media. These conditions, including high temperatures and pressures as well as the use of corrosive substances such as strong acids, alkali metal hydroxides, and molten salts, place extremely high demands on building materials. Therefore, selecting materials that can withstand harsh operating conditions while being cost-effective has become a key issue in the design of CPI plants. Although stainless steel, especially high-quality corrosion-resistant materials such as AISI 316L, is widely used, it is not an absolute barrier against corrosion; under certain conditions, slow corrosion can still occur, affecting product quality and catalyst efficiency and potentially leading to environmental problems. Taking AISI 316L stainless steel as an example, even if its annual corrosion rate is as low as 50 micrometers (2 mils), it can still result in the loss of hundreds of grams of metal components per day on equipment with a surface area of 1,000 square meters. These metal components include iron, chromium, nickel, molybdenum, and manganese. This undoubtedly poses a threat to the purity of products such as fine chemicals and pharmaceuticals, while also increasing the environmental burden. Generally speaking, when the corrosion rate is kept below 100 micrometers (4 mils) per year, the material’s corrosion resistance can be considered satisfactory; however, close monitoring is still required to prevent potential long-term damage. In light of this, various strategies are employed in the design of current CPI devices to effectively mitigate severe corrosion issues, with the key lying in making informed choices regarding the materials that come into contact with corrosive agents. This includes, but is not limited to, the use of more advanced corrosion-resistant alloys and surface treatment techniques to enhance the corrosion resistance of material surfaces, optimizing equipment design to reduce corrosion hotspots, using corrosion inhibitors to adjust the medium environment, implementing strict monitoring and maintenance programs to detect signs of corrosion early, and, when necessary, employing linings or double-layer structures as additional anti-corrosion measures. Through these comprehensive measures, the CPI industry is committed to reducing its environmental impact while ensuring production safety and product quality. Anti-corrosion materials for CPI; common industrial solutions for highly corrosive media. Depending on the level of corrosiveness of the medium, the metal materials used in CPI equipment range widely from steel to non-ferrous metal alloys. The main corrosive agents commonly encountered in chemical processes are sulfuric acid, nitric acid, hydrochloric acid, and strong bases. Therefore, to provide a simplified method, acid (especially sulfuric acid) is used as an example. Such arbitrary selection allows one to assign an order of magnitude to the corrosion rate of each material in this medium. Table 1 lists the corrosion resistance of several metal materials. Other criteria for selecting metal materials are mechanical, electrical, and thermal properties as well as cost. Therefore, these standards are listed in the table. Examinations of various categories of metals and alloys have shown that only precious metals and refractory metals are suitable for corrosion resistance under harsh operating conditions, but it is only the latter that offer a long service life under such conditions, along with good mechanical properties and moderate costs. Table 1. Classification of the corrosion resistance of metal materials used for CPI. Table 1. contd. Refractory metals in the CPI are transition metal subgroups in the periodic table, such as IVB (Ti, Zr, Hf), VB (V, Nb, Ta), and VIB (Cr, Mo, W), which are widely used in industrial applications. These metals are notable for their heat-resistant properties, with melting points higher than that of iron, ranging from 1660°C for titanium to 3410°C for tungsten. They also exhibit an activity to strongly bind with non-metals such as oxygen, nitrogen, and carbon, as well as a high sensitivity to the type of atom. Furthermore, these metals possess valve action (VA) properties, meaning that they allow current to pass when acting as a cathode, but prevent current from passing when acting as an anode due to the formation of an oxide protective layer. Refractory metals are widely used in various fields, such as nuclear power, pharmaceutical and chemical processing, the food industry, and ocean engineering, as well as in cathodic current protection systems in civil engineering. These metals are used in specific applications based on their chemical inertness. Tantalum possesses extensive chemical resistance, especially due to its enhanced valve-like properties; its protective passivation layer, Ta2O5, exhibits excellent dielectric characteristics, which makes tantalum a key material for the commercial development of high-performance electronic capacitors. However, tantalum corrodes rapidly when exposed to reagents such as hydrofluoric acid, fluoride ions, sulfur trioxide, fuming sulfuric acid, strong alkaline hydroxides, and molten carbonates. Overall, as an important material, tantalum holds an irreplaceable position in terms of heat resistance and resistance to highly corrosive chemicals, although its tolerance to certain specific chemicals is relatively low. Table 2. “Corrosion resistance of Ti, Zr, Hf, Nb, Ta, and Ir”, expressed in pm/year (converted from μm/year by dividing mpy by 25.4). The important physicochemical properties of pure chemical elements can be found in Table 3; more detailed information is available in specialized books. Table 3 shows that, in addition to its excellent corrosion resistance, tantalum metal possesses many physical properties that are attractive to chemical engineers, making it suitable for industrial applications in CPI devices. These additional properties enable tantalum to compete with other high-performance metals and alloys in industrial applications. In particular, compared to other refractory metals such as titanium and zirconium, tantalum’s excellent electrical conductivity makes it the preferred material for platinum-plated anodes. It is also widely used as a substitute for titanium in seawater cathodic protection systems, suitable for large surface facilities and vessels such as oil tankers and oil drilling rigs. Tantalum is also used as the base metal for DSA-type electrodes in certain electrochemical processes under harsh conditions. Combined with its good thermal conductivity, tantalum makes it an ideal material for heat transfer devices operating in highly acidic media (such as plate-and-tube heat exchangers, spike heaters, and heat exchanger casings). Its high tensile strength is also a necessary requirement for manufacturing devices such as rupture disks and impellers. For example, the internal structure of some distillation columns used for concentrating strong inorganic acids is made of solid tantalum (such as Ta-Intalox). Generally speaking, tantalum is used in harsh working conditions and corrosion-resistant products due to its unique properties. It is commonly used in the pharmaceutical, biotechnology, and food processing industries. Under special conditions, some tantalum alloys provided by Ains Company (such as KEV-6, -10, 47-40) are selected; these alloys contain 2% W, 10% W, and 40% Nb, and sometimes exhibit better mechanical properties than pure tantalum, but at a higher cost. They are used to manufacture fittings and internal components of valves. Finally, due to their chemical resistance similar to that of glass, they are sometimes also used in assembling pipes with glass linings. Table 3. Miscellaneous properties of the chemical element tantalum – Tantalum films. Nowadays, most industrial tantalum equipment is supplied by specialized manufacturers in the United States, Japan, and Germany, and such equipment is usually made from solid tantalum plates. As we mentioned earlier, although tantalum has unique properties, it also has two main drawbacks: high density and high cost. According to corrosion research conducted by international chemical research institutions, a thin layer of tantalum coating (100 microns) can provide good corrosion resistance to ordinary metals. Therefore, it is economical to use a thin layer of tantalum on ordinary base metals. Today, some composite containers used for CPIs are made of ordinary metals coated with tantalum (such as steel and copper). Table 4 provides a price comparison of several protective solid metals included in a 100-micron-thick thin metal layer. Checklist 4 shows first that, in harsh corrosive media such as boiling water and concentrated sulfuric acid, coatings that are more economical than tantalum (such as titanium, zirconium, niobium) are not satisfactory. Secondly, among high-quality corrosion-resistant metal protective coatings, the tantalum coating is the cheapest. Table 4 compares the costs of thin coatings for corrosion protection in harsh media. Tantalum thin coating technology: General properties of thin coatings. Metal coating technology involves applying a thin layer of metal onto the surface of ordinary metals, thereby combining the advantages of solid metals such as corrosion resistance and hardness, while reducing costs at the same time. This technology not only increases the diversity of materials but also expands their range of applications. Metals suitable for coating include carbon steel, stainless steel, aluminum, etc. Metal coatings serve not only for corrosion protection; they can also be classified into several categories based on physical or chemical principles, including mechanical, physical, chemical, and electrochemical methods. When selecting an appropriate coating technique, it is necessary to consider the preparation of the base metal, the deposition rate, the properties and limitations of the base metal, as well as economic factors such as equipment costs and maintenance expenses. The formation of a metal coating generally involves three steps: the generation of the material, its transport to the surface of the base metal, and its deposition and crystalline growth on that surface. Due to its cost-effectiveness and efficiency, this technology is widely used in various fields, including automotive, aviation, and electronics. Tantalum metal surface alloying technology: The CVI chemical vapor tantalum evaporation surface alloying technology developed by Ains develops an extremely strong, uniform, inert, and corrosion-resistant pure tantalum surface layer on existing equipment. Tantalum atoms actually grow into the nickel-based material to form an excess layer, thereby creating an inseparable nanoscale surface layer of pure tantalum. This layer conforms to complex geometric shapes. The thickness of the deposited film can be precisely controlled; thicknesses ranging from 5 to 200 μm can be achieved. Without the need for annealing, a tantalum metal deposition layer with an α-phase body-centered cubic crystal structure is obtained, which features high hardness as well as good wear and corrosion resistance. This approach improves the properties of the material, reduces the amount of material required, and also allows the excellent properties of tantalum metal to be fully utilized. Advantages of surface alloying technology for tantalum metal: The CVI chemical vapor deposition technique is used to perform atomic deposition on the surface of the workpiece. Compared with methods such as physical sputtering and coating, this approach results in a shorter production cycle, reduced energy consumption, and represents an advanced green manufacturing process. This process features good coating uniformity, enabling the deposition of large, complex-shaped parts with dense coatings. It allows for the deposition of multiple alloy layers as well as multi-layer coatings; it can also solve the problem of being unable to deposit tantalum metal on many workpieces that are not resistant to high temperatures. The CVI chemical vapor tantalum evaporation surface alloying process provides excellent corrosion resistance and pitting resistance, thereby extending the service life in the presence of chlorides, hot acids, and other corrosive chemicals. A robust pure tantalum surface layer can withstand high pressures and corrosive conditions in pipes, containers, and pressure equipment. The alternative advantage is that valves made from special alloys such as Hastelloy, Monel, zirconium, and titanium offer an economical alternative with shorter delivery times. Conclusion In the chemical processing industry (CPI), engineering and technical personnel face significant challenges when selecting building materials, especially when dealing with highly corrosive chemicals. Due to its extremely high corrosion resistance, tantalum is an ideal choice for harsh working conditions, as it can withstand the attack of highly corrosive acidic media. Tantalum has an extremely low corrosion rate, not exceeding 254 micrometers per year, which ensures the long-lasting durability of equipment. Tantalum not only possesses excellent chemical inertness, but also outstanding mechanical properties, thermal stability, and electrical properties, which make it particularly valuable for industrial applications. Although the high cost of tantalum limits its use in solid forms, we can still achieve effective corrosion protection for base metals by using tantalum films to manufacture composite equipment and containers. This solution achieves a good balance between economic efficiency and protective performance, which is why it has attracted much attention.