Is Alloy 22 the Same as C22?

Nickel-based alloys play a vital role in industries that demand outstanding corrosion resistance and durability. Among them, Alloy 22 and Hastelloy C22 are frequently mentioned, sometimes interchangeably. This has led to a common question in procurement, engineering, and materials selection: Is Alloy 22 the same as C22?

The short answer is yes. Alloy 22 and Hastelloy C22 are two names for the same nickel-chromium-molybdenum alloy, designed to resist some of the harshest chemical environments. However, understanding why the same material is referred to with different names, along with its properties and applications, is critical for making the right decisions in engineering projects.

This article provides a comprehensive guide on Alloy 22 (C22), covering its composition, properties, applications, standards, and how it compares to similar materials.

1. The Naming of Alloy 22 and Hastelloy C22

• Alloy 22 is the generic designation often used in industry and standards.

• Hastelloy C22 is the trade name under the Hastelloy family of corrosion-resistant alloys produced by Haynes International.

In practice, both refer to the same material: a nickel-chromium-molybdenum alloy with tungsten additions for enhanced corrosion resistance.

2. Chemical Composition of Alloy 22 (C22)

The chemical balance of Alloy 22 is carefully designed to resist multiple forms of corrosion. Typical composition:

• Nickel (Ni): ~56%

• Chromium (Cr): ~22%

• Molybdenum (Mo): ~13%

• Iron (Fe): 3–6%

• Tungsten (W): ~3%

• Cobalt (Co): ≤2.5%

• Carbon (C): ≤0.01%

The combination of chromium, molybdenum, and tungsten makes C22 highly resistant to oxidizing, reducing, and mixed chemical environments.

3. Key Properties of Alloy 22 (C22)

Corrosion Resistance

• Outstanding resistance to pitting and crevice corrosion.

• Excellent performance in oxidizing agents like nitric acid and reducing agents like hydrochloric acid.

• Resistant to chloride-induced stress corrosion cracking.

Mechanical Strength

• Maintains high strength across a wide temperature range.

• Suitable for both cryogenic and elevated temperature applications.

Fabrication

• Readily fabricated using standard methods such as welding, machining, and forming.

• Compatible with other nickel alloys and stainless steels.

Longevity

• Prolonged service life in harsh chemical environments reduces maintenance and downtime.

4. Applications of Alloy 22 (C22)

Alloy 22 is a preferred material in industries where chemical resistance is critical.

Chemical Processing

• Reactors, heat exchangers, evaporators.

• Handling of mixed acid environments.

Pharmaceutical Industry

• Equipment exposed to sterilization and cleaning chemicals.

• Ensures contamination-free processes.

Environmental Engineering

• Flue gas scrubbers and pollution control systems.

• Waste treatment plants dealing with aggressive chemicals.

Power Generation

• Heat exchangers in nuclear and conventional power plants.

• Resistant to high-temperature oxidizing conditions.

Marine and Offshore

• Components exposed to seawater and brines.

• Long service life in offshore oil and gas equipment.

5. Standards and Specifications

Alloy 22 (C22) is recognized under multiple international standards:

• ASTM B575: Plate, sheet, and strip.

• ASTM B574: Bars and rods.

• ASTM B622: Seamless pipe and tube.

• ASTM B619: Welded pipe.

• ASTM B626: Welded tube.

• UNS Number: N06022.

Reliable suppliers like sasaalloy ensure Alloy 22 products meet these stringent standards.

6. Comparison with Other Alloys

Alloy 22 (C22) vs. C276

• Both belong to the Hastelloy family.

• C276: Better resistance to strong oxidizers such as ferric and cupric chlorides.

• C22: More versatile in handling both oxidizing and reducing environments.

Alloy 22 (C22) vs. 625 (Inconel 625)

• 625: Excellent strength and oxidation resistance but less resistant to chemical attack compared to C22.

• C22: Superior chemical resistance, especially in mixed acid conditions.

Alloy 22 (C22) vs. Stainless Steel 316L

• 316L: Economical but limited resistance in aggressive chemicals.

• C22: Chosen for critical processes where stainless steel fails.

7. Benefits of Using Alloy 22 (C22)

• Versatility: Works well in environments where conditions may shift between oxidizing and reducing.

• Safety: Reduces risk of leaks and equipment failure in chemical plants.

• Cost-effectiveness: Higher initial investment, but savings in long-term maintenance and replacement.

• Compliance: Meets international standards for use in chemical, pharmaceutical, and environmental industries.

8. Challenges and Considerations

• High Cost: More expensive than stainless steels and some nickel alloys due to alloying elements.

• Fabrication Skill: Requires experienced welders to avoid contamination.

• Material Availability: May require longer lead times depending on product form and dimensions.

9. Future Trends for Alloy 22 (C22)

• Green Chemistry: Increasing use in eco-friendly chemical processing plants.

• Energy Transition: Expected demand in hydrogen and renewable energy sectors.

• Advanced Coatings: Research into combining Alloy 22 with protective coatings for even longer lifespans.

• Additive Manufacturing: Potential application of C22 in 3D printing of chemical-resistant components.

10. Common Mistakes to Avoid

• Assuming Alloy 22 and Alloy 625 are interchangeable — they serve different purposes.

• Using stainless steel instead of Alloy 22 in highly aggressive environments, leading to premature failure.

• Overlooking welding expertise — improper technique can cause contamination and weaken the joint.

• Ignoring supplier certification — always verify compliance with ASTM and UNS standards from trusted suppliers like sasaalloy.

Conclusion

So, is Alloy 22 the same as C22? The answer is yes. Alloy 22 is the generic designation, while Hastelloy C22 is the branded name for the same nickel-chromium-molybdenum alloy. This high-performance material stands out for its unmatched resistance to a wide range of corrosive environments, making it invaluable in chemical processing, pharmaceuticals, pollution control, marine, and power generation.

Although more costly than traditional stainless steels, Alloy 22’s durability, safety, and long-term efficiency justify the investment. By sourcing from reliable and certified suppliers such as sasaalloy, industries can ensure access to high-quality materials that meet international standards.

Whether you refer to it as Alloy 22 or Hastelloy C22, this alloy remains a cornerstone in critical applications where corrosion resistance and reliability cannot be compromised.