C-2000: The Pinnacle of C-Family Corrosion Breadth

Hastelloy C-2000 is the most versatile corrosion-resistant nickel alloy ever developed in the wrought C-family. Introduced in the 1990s by Haynes International, C-2000 was engineered to bridge the historical trade-off between oxidizing and reducing acid resistance — a limitation that had forced engineers to choose between alloys optimized for one environment or the other. By adding a deliberate 1.3–1.9% copper content to an already elevated Cr (22–24%) and Mo (15–17%) base, C-2000 achieves self-passivation in intermediate-concentration sulfuric acid while retaining best-in-class oxidizing and reducing acid resistance.

The Cu addition is the critical differentiator. In H‍₂SO‍₄, copper self-polarizes through cathodic hydrogen evolution, shifting the alloy’s corrosion potential into the passive range where a protective Cr‍₂O‍₃ film forms. This mechanism gives C-2000 resistance to intermediate-concentration sulfuric acid that no other C-family alloy can match. At the same time, the 22–24% Cr — the highest of any commercial C-grade — provides superior oxidizing acid resistance, while the 15–17% Mo provides reducing acid resistance comparable to C-276.

For multi-product chemical plants, batch reactors, and mixed-acid systems where the corrosive environment changes between production campaigns, C-2000 is the definitive single-material solution. It eliminates the need to stock multiple alloy grades, simplifies maintenance, and reduces the risk of catastrophic corrosion from unintended process chemistry excursions.

Five Defining Advantages of Hastelloy C-2000

Chemical Composition — ASTM B575 UNS N06200

The unique Cu addition + highest Cr of any C-family alloy defines C-2000’s unmatched corrosion breadth. Every element is precisely controlled:

★ Starred elements define C-2000’s unique corrosion performance — Cr, Mo, and Cu are the three pillars

Mechanical Properties — Room Temperature (Solution-Annealed)

C-2000 is a solid-solution strengthened alloy. There is no precipitation hardening mechanism. Properties are stable after solution annealing and do not degrade with moderate temperature exposure. The combination of high Cr, Mo, and Cu provides solid-solution strengthening above a pure nickel matrix.

Elastic Constants & Physical Constants (Solution-Annealed at 20°C)

Physical Properties — UNS N06200

C-2000’s physical properties are comparable to other C-family alloys. The slightly lower density (8.50 g/cm³ vs. 8.89 for C-276) reflects the higher chromium and lower tungsten content. Thermal conductivity is moderate for a nickel alloy, and the alloy is non-magnetic in all conditions.

Heat Treatment Procedures

C-2000 requires careful heat treatment control due to its complex multi-element chemistry. The solution anneal window is tighter than C-276 or C-22, demanding precise furnace control:

Do not exceed 1200°C — incipient melting risk. The melting range starts at 1340°C but localized melting can occur at grain boundaries above 1200°C due to solute segregation.
Solution anneal window is tight (±25°C). Precise furnace control (+/−14°C calibration) is essential. Overshooting dissolves beneficial carbides; undershooting leaves harmful phases.
Rapid quench is mandatory. Slow cooling through 800−500°C risks μ-phase and M‍₆C precipitation. Water quench from anneal temperature to below 400°C within 2 minutes for sections > 10 mm.

Corrosion Resistance — The Broadest Envelope

C-2000’s defining advantage is corrosion breadth — no other wrought nickel alloy handles such a wide range of chemical environments in a single material. The combination of high Cr (oxidizing protection), high Mo (reducing protection), and Cu (H‍₂SO‍₄ passivation) creates a corrosion resistance envelope that is both broad and deep.

Sulfuric Acid (H‍₂SO‍₄) ★ — DEFINING STRENGTH

This is C-2000’s signature capability and the reason for the deliberate Cu addition. C-2000 achieves <0.05 mm/yr corrosion rate in 50% H‍₂SO‍₄ boiling — a condition where C-276 and C-22 suffer unacceptably high rates (typically >0.5 mm/yr). The Cu self-polarization mechanism shifts the corrosion potential into the passive range where a protective Cr‍₂O‍₃ film is stable. Resistance extends across the full concentration range from dilute to ~70% at temperatures up to boiling, making C-2000 the definitive choice for sulfuric acid service in the C-family.

Hydrochloric Acid (HCl)

Very good resistance to 50°C at all concentrations. The high Mo content (15–17%) provides reducing-acid protection comparable to C-276. For pure HCl service at higher temperatures, Hastelloy B-3 is preferred, but C-2000 provides adequate resistance with the added benefit of oxidizing acid protection that B-3 lacks entirely.

Nitric Acid (HNO‍₃)

Excellent resistance at all concentrations and temperatures up to boiling. The 22–24% Cr — highest in the C-family — provides superior HNO‍₃ resistance compared to C-276 (14.5–16.5% Cr) and C-22 (20–22.5% Cr). For pure HNO‍₃ service, C-2000 offers best-in-class C-family performance.

Mixed Acids ★ — BEST-IN-CLASS

C-2000’s greatest value proposition. It handles HNO‍₃/HCl, HNO‍₃/HF, and H‍₂SO‍₄/HCl combinations that attack C-276 (insufficient oxidizing resistance) and C-22 (insufficient reducing resistance). In chemical plants running diverse batch chemistries, C-2000 is the safest single-material specification for mixed-acid reactors, heat exchangers, and piping. No other wrought alloy provides this combination of oxidizing and reducing mixed-acid resistance.

Pitting & Crevice Corrosion

Excellent pitting resistance with CPT (Critical Pitting Temperature) exceeding 100°C in ASTM G48 Method C (6% FeCl‍₃). PREN ≈ 75 (highest of any C-family alloy). The high Cr and Mo combination provides exceptional localized corrosion resistance — suitable for seawater, brine, bleach plant, and FGD scrubber environments.

Stress-Corrosion Cracking (SCC)

Immune to chloride SCC at all temperatures — a fundamental advantage over austenitic stainless steels (which crack above ~60°C in chloride service). The austenitic Ni matrix with high alloy content provides complete chloride SCC immunity.

Intergranular Corrosion (IGC)

Passes ASTM G28 Method A and B in the solution-annealed condition. As-welded: passes for most common environments thanks to ultra-low C (0.01% max) and Si (0.08% max). For the most aggressive environments requiring guaranteed as-welded IGC resistance, a full post-weld solution anneal is recommended.

Corrosion Rate Comparison — C-2000 vs C-22 vs C-276 (mm/yr)

Green = excellent; Red = unacceptable. Data from Haynes International published corrosion tables and independent lab reports. Values are typical — actual performance depends on specific process chemistry, aeration, velocity, and contaminants.

Hastelloy Grade Selection Guide — C-Family Comparison

C-2000 is the ultimate all-around choice when corrosion breadth is the priority. It earns 5-star ratings in three of five selection criteria and 4-star ratings in the remaining two, at a premium cost ($5-level):

Key Applications

C-2000 is the premium choice for multi-product chemical facilities and applications where the corrosive environment varies between campaigns or process steps. Its unique ability to handle oxidizing acids, reducing acids, and intermediate H‍₂SO‍₄ in a single material makes it irreplaceable in flexible chemical manufacturing:

Applicable Standards & Specifications

Available Product Forms from HT PIPE

We supply C-2000 in solution-annealed condition with EN 10204 3.1 certification on every shipment. ASTM G28 IGC testing per heat is available on specification. C-2000 is a premium-priced alloy and lead times vary by mill — contact us for current availability and project quotations.

HT PIPE Project Experience — C-2000

For additional project references matching your specific process chemistry, contact our technical sales team. We can provide anonymized case studies for mixed-acid, API, fine chemical, and sulfuric acid applications.

Frequently Asked Questions — Hastelloy C-2000