Nickel Alloy C‑22, commonly known as Hastelloy C‑22, is a high-performance austenitic nickel–chromium–molybdenum–tungsten alloy (UNS N06022). With outstanding resistance in both oxidizing and reducing environments, it is widely used in chemical processing, pollution control, oil & gas, pharmaceuticals, and marine applications.
This article dives into its composition, exceptional corrosion resistance, fabrication, applications, and the niche for recycling alk Nickel alloys like C‑22. We’ll also explore the market for reclaimed alloy, sustainable nickel recovery, and more affordable alternatives.
1. Composition & Metallurgical Characteristics
1.1 Chemical Composition
Typical composition (weight %):
1.2 Microstructure & Strength Mechanisms
C‑22 is a single-phase austenitic alloy with high solution-strengthening. The low carbon content and minimal impurities inhibit carbide or sigma-phase precipitation—even after welding—enabling robust as-welded performance .
2. Corrosion Resistance
2.1 Broad‑Spectrum Protection
C‑22 is considered one of the most corrosion-resistant commercial metals—resisting pitting, crevice corrosion, stress-corrosion cracking, general corrosion, and oxidation in both reducing and oxidizing environments.
It excels in harsh conditions like:
- Wet chlorine, nitric acid mixtures, oxidizing chlorides
- Sulfuric and hydrochloric acids, brines, seawater
- Ferric and cupric chlorides, formic/acetic acids mixed with organic.
2.2 Temperature Limits
Serviceable up to about 650 °C (1200 °F). Prolonged exposure above 650–700 °C (≈1250 °F) risks embrittlement due to sigma-phase formation .
2.3 Real‑World Insights
A Reddit metallurgy thread recounts a pipe tested as C‑22 failed prematurely in 18% HCl—possibly due to material misidentification or contamination. This underscores the importance of proper alloy verification and environment matching.
3. Mechanical & Physical Properties
3.1 Key Mechanical Properties (Annealed, Room Temp)
- Tensile Strength: ~690–800 MPa (~100–114 ksi)
- Yield Strength (0.2%): ~310–410 MPa (~45–60 ksi)
- Elongation: 45–62%
- Hardness: ~93 HB (~95 HRB)
3.2 Physical Properties
- Density: ~8.69 g/cm³ (~0.314 lb/in³)
- Elastic Modulus: ~205 GPa (≈29.9 × 10³ ksi)
- Thermal Expansion: 12–13.5 µm/m–°C (20–400 °C)
- Thermal Conductivity: ~13 W/m·K
3.3 Elevated Temp Behavior & Work Hardening
C‑22 is stable up to ~650°C. It work-hardens rapidly and may require intermediate annealing when cold-formed.
4. Fabrication & Welding
4.1 Hot & Cold Work
- Hot working should be done between ~2250–1750 °F (1230–950 °C).
- Cold forming is possible but requires intermittent anneals due to hardening.
4.2 Weldability
Fully weldable via TIG, MIG, SMAW. The alloy resists HAZ precipitation, preserving corrosion resistance without post-weld annealing.
5. Industrial Applications
C‑22 is chosen where mixed or aggressive environments are encountered and reliability is critical:
- Chemical & Petrochemical: Reactors, piping, HP vessels, distillation
- Pollution Control: Flue-gas scrubbers, incinerator components
- Oil & Gas: Sour service nodes, high chloride
- Pharma & Food: Seals, sterility-critical systems
- Marine & Power: Heat exchangers, condenser tubing
- Nuclear: Reprocessing, storage, handling aggressive solutions.
Examples like wire springs for flue-gas applications, fasteners, and medical devices exploit its corrosion resilience in narrow spaces and sterilization environments.
6. Recycling and Reclaimed Nickel
6.1 Challenges with C‑22 Scrap
- Scrap must be segregated to maintain alloy chemistry (Ni/Cr/Mo/W).
- Low-volume scrap often gets sold for base-metal recycling unless it’s verified and highly pure.
- Specialized alloy buyers or remelters (using VOD/AOD refining) manage corrections in composition.
6.2 Market Insights
The value of exotic alloys fluctuates based on scrap demand, tariffs, and recycling regulation. Reddit users highlight that recycled exotic scraps often fetch low offers unless handled by specialist buyers .
6.3 Nickel Recovery from Scraps & By‑products
- Recycling recovers nickel from electronics, tailings, industrial slags.
- Commodity-grade metal is partially recycled via energy-efficient pyro/hydro processing.
- Complete recovery of Mo, W, Cr is rare; alloys use scrap plus virgin elements to meet spec .
Regulatory factors (e.g. tariffs) can make scrap recovery more economically attractive .
7. Low‑Cost Nickel Alloys: Alternatives
Markets exist for lower-performance, lower-cost alloys where key C‑22-grade durability is unnecessary:
- Nickel Pig Iron (NPI): Basic, low-nickel, used in standard stainless steel.
- Recycled remelt alloys: Scraps of C‑276 or other Ni alloys blended with Cr/Mo drop-in.
- Budget Ni–Cr–Mo grades: Offer resistance in mid-range environments (C‑276, 625, 825, etc.).
These often afford 50–70% cost savings, at the expense of high-end corrosion protection.
8. Comparing C‑22 with Other Nickel Alloys
C‑22 remains unmatched in extreme chemical environments thanks to its balanced alloying.
9. Market & Sustainability Trends
9.1 Reduced Nickel Dependency
Transition to low-nickel and recycled feedstock is driven by cost and regulatory pressure. However, high-performance alloys like C‑22 still require virgin elements.
9.2 Scrap Segregation & Specialist Recyclers
Facilities with scrap scanning (e.g., XRF) can fetch premiums for C‑22, especially in Europe and North America .
9.3 Circular Economy & Tariffs
Trade policy shifts can prime the recycled market—making reclamation of exotic alloys more viable .
10. Case Study: Foundry Scrap
A Reddit user shared how their family foundry had 10 tons of high-temp nickel alloy revert (Waspaloy). Offers were low (~$2.75/lb) until they were connected with firms using VOD refining and matching quality needs —highlighting the value of scrap purity and buyer specialization.
11. Conclusions
- Hastelloy C‑22 is the pinnacle of corrosion-resistant nickel alloys—high specs and high cost.
- It retains structure and corrosion resistance across extreme environments, even when welded.
- Fabrication: weldable, forgeable, but work-hardens quickly and needs careful heat treatment.
- Recycling is viable but requires segregation, certification, and sometimes alloy correction.
- Cost‑effective alternatives can serve where ultra resistance isn’t needed.
- Industry trends favor greener processes, scrap-based alloys, and reduced critical metal dependency.
12. Recommended Next Steps
- Material selection: Use decision matrices comparing C‑22 to alternatives for given environments.
- Quality control: Validate C‑22 using XRF/optical methods in field scrap sorting.
- Recycling channels: Engage specialist alloy recyclers early.
- Eco‑innovation: Watch developments in low-nickel alloys and nickel-from-tails technology.
Appendix: Quick‑Reference Spec Table
