The nickel and nickel-based alloy family is extensive and diverse, offering a wide range of options for various industrial needs. These alloys are available in multiple forms, including plates, sheets, strips, pipes, joints, forgings, and matching welding wires and electrodes.

Nickel-based alloys are typically categorized based on their primary alloy components. Here's a concise overview of some widely used nickel-based alloys in chemical equipment:

Ø Pure Nickel (201 UNS N02201)

Pure nickel boasts exceptional corrosion resistance against various reducing acids and salts, although it's not suited for highly oxidizing media like nitric acid. Its hallmark trait is its unmatched resistance to caustic alkali corrosion, even in molten form. While it exhibits remarkable corrosion resistance in dry halogen environments, its effectiveness diminishes below the water dew point. For applications under 600°F, Alloy 201’s high-carbon sibling, Nickel 200 (UNS N02200), is also an option.

Ø Nickel-Copper Alloy 400 UNS N04400

Similar to nickel, Nickel-Copper Alloy 400 excels in corrosion resistance under reducing conditions, while aeration and oxidizing agents can compromise its effectiveness. Alloy 400 demonstrates outstanding resistance to hydrohalic acids and halide corrosion, especially against hydrofluoric acid and high-temperature gases containing fluorine or hydrogen fluoride. Developed in 1905, Monel 400 is a pioneer among nickel alloys, widely used in treating sulfuric acid solutions, seawater, and brine. For high-strength applications like valves and pump parts, Alloy K-500 (NO5500), a precipitation-hardening derivative, is preferred.

Ø Nickel-Chromium-Iron Alloy 600 UNS N06600

The addition of chromium to nickel broadens Alloy 600's utility in oxidative environments. While its resistance to inorganic acids is moderate, it fares well against organic acids, making it ideal for fatty acid processing. Alloy 600 finds extensive use in producing, storing, and transporting hydroxides and alkaline chemicals. It also excels in high-temperature applications requiring both heat and corrosion resistance. Its performance in high-temperature halogen environments makes it suitable for organic chlorination processes. Additionally, it exhibits excellent resistance to high-temperature degradation, such as oxidation, carburization, and nitriding.

Ø Nickel-Chromium-Molybdenum Alloy 625 UNS N06625

Molybdenum addition enhances nickel-chromium alloys' corrosion resistance against oxidative and reductive inorganic acids and salts. Alloy 625 is a high-strength material with excellent fatigue resistance. Its derivative, Alloy 625LCF, is specialized for bellows, offering exceptional low-cycle fatigue and thermal fatigue resistance. Like Alloy 600, Alloy 625 serves as both a corrosion-resistant and heat-resistant material, making it ideal for chemical and petrochemical equipment operating in harsh high-temperature environments.

Ø Conclusion

Nickel and nickel-based alloys play vital roles across industries, offering unmatched corrosion resistance, mechanical properties, and versatility. From pure nickel's resilience against caustic alkalis to Alloy 625's performance in high-temperature corrosive environments, these alloys continue to drive innovation and progress in various applications.