Hastelloy C22 and Hastelloy C276 are two highly corrosion-resistant nickel-based alloys widely used in chemical processing, marine environments, pollution control, and high-temperature corrosive systems. Although both alloys provide outstanding resistance to oxidizing and reducing media, they differ in chemical composition, corrosion performance, mechanical properties, and application suitability. Understanding the differences between Hastelloy C22 and C276 helps engineers select the correct alloy for demanding industrial conditions.
Chemical Composition Comparison
The chemical composition is the primary factor that differentiates Hastelloy C22 from C276. C22 contains higher chromium and molybdenum, giving it superior resistance to certain oxidizing chemicals.
| Element | Hastelloy C22 (%) | Hastelloy C276 (%) |
|---|---|---|
| Nickel (Ni) | Balance | Balance |
| Chromium (Cr) | 20–22.5 | 14.5–16.5 |
| Molybdenum (Mo) | 12.5–14.5 | 15–17 |
| Tungsten (W) | 2.5–3.5 | 3–4.5 |
| Iron (Fe) | 2–6 | 4–7 |
| Cobalt (Co) | ≤2.5 | ≤2.5 |
| Carbon (C) | ≤0.015 | ≤0.01 |
| Manganese (Mn) | ≤0.5 | ≤1 |
| Silicon (Si) | ≤0.08 | ≤0.08 |
Main Performance Differences
Both alloys deliver excellent corrosion resistance, but each performs differently depending on the chemical environment.
| Property | Hastelloy C22 | Hastelloy C276 |
|---|---|---|
| Resistance to Oxidizing Acids | Better due to higher chromium | Good, but lower than C22 |
| Resistance to Reducing Acids | Very high | Excellent, often better |
| Resistance to Chloride Stress Cracking | Excellent | Excellent |
| Weldability | Very good | Superior (lower risk of weld cracking) |
| Cost | Generally higher | Moderate |
| Temperature Resistance | Up to ~1250°C | Up to ~1100°C |
Corrosion Resistance Comparison
Hastelloy C22 is known for exceptional resistance to oxidizing environments, while C276 excels in mixed corrosive media and severely reducing environments.
| Environment | C22 Performance | C276 Performance |
|---|---|---|
| Wet Chlorine Gas | Superior | Excellent |
| Nitric Acid | Better | Good |
| Sulfuric Acid | Excellent | Excellent (slightly better) |
| Hydrochloric Acid | Good | Better |
| Seawater / Marine | Excellent | Excellent |
| Pollution Control Systems | Excellent | Best choice |
Mechanical Properties Comparison
| Property | C22 | C276 |
|---|---|---|
| Tensile Strength | 690–760 MPa | 690–785 MPa |
| Yield Strength | 310 MPa | 280–355 MPa |
| Elongation | 45–55% | 40–50% |
Applications of Hastelloy C22
| Industry | Typical Use |
|---|---|
| Chemical Processing | Strong oxidizing acid systems |
| Pharmaceutical | High-purity corrosive vessels |
| Waste Treatment | Oxidation reactors |
| Pollution Control | NOx scrubbers |
Applications of Hastelloy C276
| Industry | Typical Use |
|---|---|
| Oil & Gas | Downhole tools, sour gas environments |
| Marine | Pumps, valves, seawater systems |
| Chemical Processing | Mixed acids, reducing environments |
| Flue Gas Desulfurization | Absorber towers, ducting |
Which Alloy Should You Choose?
The choice between C22 and C276 depends on the chemical environment and required performance:
- Choose Hastelloy C22 for strong oxidizing conditions or when maximum corrosion resistance is necessary.
- Choose Hastelloy C276 for reducing or mixed-acid environments, high-temperature corrosive operations, and excellent weldability.
Related Questions
1. Is Hastelloy C22 more corrosion-resistant than C276?
Yes, C22 generally offers better resistance to oxidizing chemicals due to its higher chromium content.
2. Which alloy is better for welding, C22 or C276?
C276 is usually preferred for welding because it has lower weld cracking tendencies and more stable metallurgy.
3. Can C22 and C276 be used interchangeably?
In many applications they can, but for strong oxidizing environments C22 performs better, while C276 is superior in reducing or mixed corrosive media.
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