Hastelloy C-276 Vs C-22: Which Is Better For Harsh Environments?
Aug 14, 2026
Introduction
When engineers face highly corrosive environments, Hastelloy C-276 (UNS N10276) and Hastelloy C-22 (UNS N06022) are two of the most frequently shortlisted nickel-chromium-molybdenum alloys. Both belong to the same C-series family and offer exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking. Yet their subtle compositional differences create distinct performance profiles that can make or break your project.
The real question is: which alloy is better for your specific corrosive environment? This comparison breaks down chemical composition, mechanical properties, corrosion resistance, weldability, and cost - giving you the data-driven clarity needed for an informed procurement decision.
Product Overview
Hastelloy C-276 (UNS N10276, W.Nr 2.4819)
Hastelloy C-276 is a nickel-molybdenum-chromium alloy with tungsten addition, widely regarded as the benchmark for severe corrosive environments. Its high molybdenum content (15–17%) makes it exceptionally resistant to reducing acids such as hydrochloric and sulfuric acid, while chromium (14.5–16.5%) provides adequate protection in oxidizing media. C-276 has been the workhorse of the chemical processing industry for decades, with extensive track record in flue gas desulfurization, pulp and paper bleach plants, and pharmaceutical reactors.
Hastelloy C-22 (UNS N06022, W.Nr 2.4602)
Hastelloy C-22 features a significantly higher chromium content (20–22.5%) and rebalanced molybdenum (12.5–14.5%). This makes C-22 superior in oxidizing environments - particularly those containing wet chlorine, ferric chloride, and mixed acids. C-22 also demonstrates better overall corrosion resistance across a broader range of media, earning it the informal designation of "the upgraded C-276" in many engineering circles.
Chemical Composition Comparison
The performance divergence originates directly from chemical composition. The table below presents the elemental breakdown per ASTM B575:
| Element | Hastelloy C-276 (N10276) | Hastelloy C-22 (N06022) | Key Difference |
|---|---|---|---|
| Nickel (Ni) | Bal. | Bal. | Matrix element in both |
| Chromium (Cr) | 14.5–16.5% | 20.0–22.5% | C-22 is ~5% higher |
| Molybdenum (Mo) | 15.0–17.0% | 12.5–14.5% | C-276 is ~2.5% higher |
| Tungsten (W) | 3.0–4.5% | 2.5–3.5% | C-276 slightly higher |
| Iron (Fe) | 4.0–7.0% | 2.0–6.0% | C-276 allows more Fe |
| Carbon (C) | ≤0.01% | ≤0.015% | Both extremely low |
Composition logic: C-22 trades molybdenum for chromium - strengthening oxidizing-media resistance while reducing its reducing-media edge. C-276 retains higher Mo+W for reducing acids and wet chlorine.
Mechanical and Physical Properties Comparison
Both alloys share similar ASTM mechanical minimums with subtle differences:
| Property | Hastelloy C-276 | Hastelloy C-22 |
|---|---|---|
| Tensile Strength (min) | 690 MPa | 690 MPa |
| Yield Strength 0.2% (min) | 283 MPa | 283 MPa |
| Elongation (min) | 40% | 45% |
| Density | 8.89 g/cm³ | 8.69 g/cm³ |
| Melting Range | 1325–1370°C | 1359–1399°C |
Key takeaway: C-22 offers higher elongation (45% vs 40%) for better formability. Both alloys machine similarly - gummy and work-hardening, requiring sharp tooling.
Corrosion Resistance Performance Analysis
Oxidizing Media: C-22 Wins
The 5-percentage-point chromium advantage gives C-22 a significantly stronger passive oxide film in oxidizing environments. C-22 outperforms C-276 in wet chlorine gas, hypochlorite solutions, ferric and cupric chlorides, nitric acid, mixed acid pickling baths, acetic acid, and contaminated organic/inorganic acids.
Reducing Media: C-276 Wins
The higher molybdenum content makes C-276 the preferred choice in reducing environments: hydrochloric acid at low to mid concentrations, dilute sulfuric acid at elevated temperatures, wet hydrogen chloride gas, wet-process phosphoric acid, and reducing acid mixtures with chloride contamination.
Localized Corrosion Resistance
Both alloys excel in resisting pitting, crevice corrosion, and chloride SCC - far surpassing 316L stainless steel. C-22 demonstrates a measurable advantage in Critical Pitting and Crevice Temperatures per ASTM G48:
| Corrosion Test | Hastelloy C-276 | Hastelloy C-22 |
|---|---|---|
| CPT (ASTM G48 Method C) | ≥90°C | ≥120°C |
| CCT (ASTM G48 Method D) | ≥70°C | ≥100°C |
| PREW Index* | ~74 | ~73 |
*PREW = %Cr + 3.3 × (%Mo + 0.5 × %W). Both alloys have very high PREW values, confirming superior localized corrosion resistance.
Welding and Fabrication Comparison
Weldability
Both alloys are designed for excellent weld-zone corrosion resistance. Very low carbon minimizes HAZ carbide precipitation, allowing as-welded use. Both work-harden rapidly; solution annealing at 1121°C with rapid quench is required after severe cold forming. C-22's lower density (8.69 vs 8.89 g/cm³) yields ~2% more surface area per unit weight.
Welding Filler Metals - Critical: Do Not Mix
| Parameter | Hastelloy C-276 | Hastelloy C-22 |
|---|---|---|
| GTAW/GMAW Filler Metal | ERNiCrMo-4 | ERNiCrMo-10 |
| SMAW Electrode | ENiCrMo-4 | ENiCrMo-10 |
Warning: Using the wrong filler metal will compromise weld-zone corrosion resistance. C-276 filler on C-22 base metal (or vice versa) is never acceptable. Some fabricators use C-22 filler to weld C-276 base metal for over-alloyed welds in oxidizing service, but the reverse is not recommended.
Pickling requires mixed acid (HNO₃ + HF); standard stainless pickling is insufficient.
Application Selection Guide
Choose Hastelloy C-276 When:
- Primary media is reducing (HCl, dilute H₂SO₄, H₃PO₄)
- Wet chlorine gas service
- FGD scrubbers, pharmaceutical reactors
- Oil and gas sour service (NACE MR0175)
Choose Hastelloy C-22 When:
- Primary media is oxidizing (chlorides with Fe³⁺/Cu²⁺)
- Mixed acid pickling, seawater exchangers
- Chlorine dioxide bleach plants
- When broadest corrosion resistance is desired
Cost Consideration
C-276 is typically 5–10% less expensive than C-22. In sheet form, C-22's lower density partially offsets the per-kg premium. In most projects, the cost difference is negligible compared to correct alloy selection.
Internal Linking & Image ALT Tags
- FeCrAl vs NiCr Resistance Wire - heating element applications
- Inconel 600 vs 601 vs 625 - high-temperature nickel alloy alternatives
- Hastelloy vs Inconel - broader nickel alloy family comparison
- Welding Hastelloy Best Practices - detailed welding procedures
- Corrosion-Resistant Alloys for CPI - chemical processing applications
Image ALT tags: Hastelloy C-276 vs C-22 composition chart, corrosion resistance comparison graph, C-22 welded pipe for chemical processing
FAQ
Q1: Is Hastelloy C-22 an upgraded version of C-276?
Not exactly. C-22 has broader overall corrosion resistance from higher chromium, but C-276 remains superior in reducing environments (e.g., hydrochloric acid). They are complementary, not substitutes - always select based on your specific media.
Q2: Can I weld C-276 and C-22 together?
Technically yes, but you must use ERNiCrMo-10 (C-22 filler) for the joint - never ERNiCrMo-4. The C-22 filler's higher chromium provides over-alloyed weld metal. However, dissimilar welds always carry some performance compromise and should only be used when unavoidable.
Q3: Which alloy is better for seawater applications?
C-22 is generally preferred for seawater service due to its higher Critical Pitting and Crevice Temperatures. The elevated chromium provides a more robust passive film against chloride-induced localized corrosion, particularly in stagnant zones where crevice corrosion initiates.
Q4: What standards cover both alloys?
Both alloys share the same ASTM/ASME specs: B575/B574 (plate/bar), B619/B622 (pipe), B366 (fittings), B564 (forgings). Always specify the UNS number (N10276 or N06022) when ordering.
Q5: Are there newer alternatives to C-276 and C-22?
Yes. Hastelloy C-2000 (UNS N06200) adds copper for enhanced sulfuric acid resistance, and Inconel 686 (UNS N06686) offers even higher localized corrosion resistance. However, C-276 and C-22 remain the industry standards due to their proven track record and widespread availability.
Conclusion
The choice between Hastelloy C-276 and C-22 comes down to one question: is your corrosive environment primarily oxidizing or reducing? For oxidizing media with chlorides, C-22's higher chromium delivers superior protection. For reducing acids and wet chlorine, C-276's higher molybdenum remains the proven choice. Both alloys offer outstanding weld-zone corrosion resistance and decades of field-proven reliability.
For procurement teams, Taizhou Aoyuan Alloy Material Co., Ltd. supplies both alloys in wire, bar, sheet, and plate forms with full mill test certificates per EN 10204-3.1. Contact us at +8615952661350 or [email protected].
Further Reading: Hastelloy product line and Special Metal Welding Materials.
