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C22 alloy, created and produced by Haynes International in the United States, belongs to the Hastelloy alloy series. Its chemical name is UNS N06022. It is an advanced material that exhibits excellent performance in extremely corrosive environments. The alloy is widely used in chemical, petroleum, environmental protection, pharmaceutical, energy and other industrial fields. As an important model in the Hastelloy alloy series, it has excellent corrosion resistance and good mechanical properties, and is particularly suitable for harsh chemical environments.
Hastelloy C22 has better corrosion resistance than other Hastelloy alloys, including Hastelloy C276, C4 alloy and 625 alloy. JN is a Hastelloy C22 alloy supplier, providing C22 pipes, bars, plates, flanges, butt-welded pipe fittings, forgings, fasteners and other products. JN high-quality Hastelloy C22 products meet SGS and ISO international standards and are certified by ASTM, DIN, JIS, GOST, TÜV and other certifications. Global supply, one-stop service provider.
Property | Value |
UNS Number | N06022 |
Werkstoffnummer (W.Nr.) | 2.4602 |
JIS | NW 6022 |
EN Designation | NiCr21Mo14W |
Alloy Family | Ni-Cr-Mo (C-type Hastelloy) |
Nominal Ni | 56% (balance) |
Nominal Cr | 22% |
Nominal Mo | 13% |
PREN (pitting resistance) | 65–70 |
Density | 8.90 g/cm³ |
Melting Range | 1325–1370 °C (2417–2500 °F) |
Crystal Structure | Face-centered cubic (FCC) |
ASTM Product Specs | B574 (bar), B575 (plate/sheet), B622 (seamless pipe), B619 (welded pipe), B366 (fittings), SB-564 (flanges/forgings) |
Certification | EN 10204 3.1 standard; 3.2 on request |
Hastelloy C22 (UNS N06022/2.4602) Alloy C22 is a nickel-chromium-molybdenum solid solution strengthened super-alloy with a nominal chemical composition of 56% nickel, 22% chromium, and 13% molybdenum, with additions of iron, tungsten, and cobalt.
Grade | C≤ | Mn≤ | P≤ | S≤ | Si≤ | Cr | Mo | Fe | Co≤ | W | V≤ | Ni |
Hastelloy C22 | 0.01 | 1.0 | 0.04 | 0.03 | 0.08 | 20.0-22.5 | 12.5-14.5 | 2.0-6.0 | 2.5 | 2.5-3.5 | 0.35 | remainder |
Property | Value (Room Temp, Solution Annealed) | Standard Reference |
Tensile Strength (UTS), min | 690 MPa (100 ksi) | ASTM B574/B575 |
Yield Strength (0.2% offset), min | 310 MPa (45 ksi) | ASTM B574/B575 |
Elongation, min | 45% | ASTM B574/B575 |
Hardness, typical | HRB 89–95 (HBW 180–210) | — |
Elastic Modulus | 206 GPa (29.9 × 10⁶ psi) | — |
Poisson’s Ratio | 0.31 | — |
Elevated Temperature Tensile Properties (Typical, Plate)
Temperature | Tensile Strength | Yield Strength (0.2%) | Elongation |
RT (20°C) | 790 MPa | 405 MPa | 58% |
100°C (212°F) | 735 MPa | 350 MPa | 56% |
200°C (392°F) | 670 MPa | 305 MPa | 54% |
300°C (572°F) | 630 MPa | 275 MPa | 52% |
400°C (752°F) | 605 MPa | 260 MPa | 50% |
500°C (932°F) | 575 MPa | 245 MPa | 46% |
Note: Maximum recommended continuous service temperature is approximately 675°C (1250°F). Above this, oxidation scaling and carbide precipitation accelerate. Source: Haynes International data.
The physical properties of Hastelloy C22 include density and melting point. The following table shows the specific values:
Grade | Density | Melting point |
Hastelloy C22 | 8.90 g/cm3 | 1325-1370 ℃ |
STANDARD | WERKSTOFF NR. | UNS | JIS | EN |
Hastelloy C22 | 2.4602 | N06022 | NW 6022 | NiCr21Mo14W |
Product | Standards | Show |
Hastelloy C22 Bars
| ASTM B574 |  |
Hastelloy C22 Sheets
| ASTM B575 |  |
Hastelloy C22 Plates
| ASTM B575 |  |
Hastelloy C22 Forging
| ASME SB-564 |  |
Hastelloy C22 Pipes
| ASME B474 |  |
Hastelloy C22 BW Fittings
| ASME B366 |  |
Hastelloy C22 is engineered for environments where multiple corrosion mechanisms operate simultaneously. Its balanced chemistry enables it to handle oxidizing media (nitric acid, wet chlorine, ferric chloride), reducing media (hydrochloric acid, sulfuric acid), and mixed oxidizing-reducing environments—all without the selective attack patterns that plague single-purpose alloys.
C22 has one of the highest PREN values of any wrought corrosion-resistant alloy. PREN = %Cr + 3.3(%Mo + 0.5×%W) + 16%N = 65–70. In ASTM G48 Method C (crevice corrosion test in 6% FeCl₃), C22 exhibits a critical crevice temperature (CCT) of ≥ 60°C — approximately 35–40°C higher than 316L, 15–20°C higher than 2205 duplex, and comparable to or slightly better than C276.
With ≥ 56% nickel, C22 is virtually immune to chloride stress corrosion cracking (Cl-SCC) in boiling MgCl₂ environments that cause 304L and 316L to crack within hours. This immunity extends to sour service: C22 passes NACE TM0177 Method A testing at 90% of actual yield strength in NACE Level VII environments (highest severity). C22 is listed in NACE MR0175/ISO 15156-3 Table A.31 for H₂S service without environmental limits.
The ultra-low carbon content (≤ 0.015%) ensures C22 resists intergranular attack in the as-welded condition. ASTM G28 Method A testing (boiling 50% H₂SO₄ + Fe₂(SO₄)₃) typically yields corrosion rates of ≤ 0.5 mm/yr for properly solution-annealed C22—well within acceptance limits. No post-weld heat treatment is required for corrosion resistance.
Hastelloy C22 has a face-centered cubic lattice structure.
Choosing between C22 and C276 is one of the most frequent decisions in corrosion-resistant alloy selection. While both are Ni-Cr-Mo solid-solution alloys, their chemistry differs significantly. The rule of thumb: C22 wins in oxidizing and mixed environments; C276 has an edge in strongly reducing conditions.
Chemistry
Element | Hastelloy C22 | Hastelloy C276 | Difference & Impact |
Ni | ~56% (balance) | ~57% (balance) | Similar; both SCC-immune |
Cr | 20.0–22.5% | 14.5–16.5% | C22 has ~6% more Cr → superior oxidizing-acid resistance |
Mo | 12.5–14.5% | 15.0–17.0% | C276 has ~3% more Mo → slight edge in HCl, H₂SO₄ |
W | 2.5–3.5% | 3.0–4.5% | C276 has ~1% more W; C22’s W + higher Cr = better mixed-acid balance |
Fe | 2.0–6.0% | 4.0–7.0% | Minor; both controlled-residual |
C (max) | 0.015% | 0.010% | Both ultra-low; excellent as-welded IGC resistance |
PREN | 65–70 | 64–68 | C22 slightly higher due to Cr advantage |
Performance
Environment / Test | Hastelloy C22 | Hastelloy C276 | Winner |
10% HNO₃, boiling | Corrosion rate < 0.05 mm/yr | Corrosion rate ~0.15–0.25 mm/yr | C22 |
Wet chlorine gas, 25°C | Excellent; no attack | Good; minor pitting possible | C22 |
10% HCl, 25°C | Corrosion rate < 0.10 mm/yr | Corrosion rate < 0.05 mm/yr | C276 |
50% H₂SO₄, 50°C | Corrosion rate < 0.10 mm/yr | Corrosion rate < 0.05 mm/yr | C276 |
Mixed HNO₃ + HCl (oxidizing + reducing) | Excellent; stable passive film | Minor selective attack possible | C22 |
ASTM G48A pitting (6% FeCl₃) | CPT ≥ 85°C | CPT ≥ 80°C | C22 (marginal) |
ASTM G48C crevice (6% FeCl₃) | CCT ≥ 60°C | CCT ≥ 55°C | C22 (marginal) |
ASTM G28A IGC (50% H₂SO₄ + Fe₂(SO₄)₃) | < 0.5 mm/yr | < 0.5 mm/yr | Equal |
Cl-SCC (boiling 45% MgCl₂) | Immune | Immune | Equal |
NACE MR0175/ISO 15156 compliance | Table A.31 — no limits | Table A.34 — no limits | Equal |
FGD absorber (wet limestone) | 10–15 year life typical | 8–12 year life typical | C22 |
Pharmaceutical API reactor | Excellent; broad compatibility | Very good; more limited in oxidizing media | C22 |
Choose Hastelloy C22 when:
· Your process stream contains oxidizing species (HNO₃, Cl₂, FeCl₃, CuCl₂)
· The environment alternates between oxidizing and reducing conditions (mixed-acid synthesis)
· You need the broadest possible compatibility across multiple process steps (pharmaceutical, fine chemical)
· The application is FGD or waste incineration with variable gas composition
· You are specifying for a new plant and want one alloy that handles the widest range of future process changes
· Pitting resistance is the primary concern (elevated PREN over C276)
Choose Hastelloy C276 when:
· The primary corrosive is strong reducing acid (HCl, H₂SO₄) with minimal oxidizing species
· The application is deep sour gas well equipment where the higher Mo + W content provides an edge in elemental sulfur environments
· You have an existing qualified design basis for C276 and switching would require re-validation
· Cost sensitivity favours the slightly lower per-kg price of C276 (molybdenum is ~$45/kg vs Cr at ~$12/kg at 2025 prices)
Pharmaceutical manufacturing, particularly API synthesis, imposes some of the most demanding corrosion conditions in the process industries. Reaction mixtures routinely combine hot organic solvents, halogenated compounds, strong mineral acids (HCl, H₂SO₄, HNO₃), and chloride salts in the same vessel — often in alternating oxidizing and reducing environments as the batch progresses. This is precisely the scenario for which Hastelloy C22 was designed.
Typical Pharmaceutical Equipment in C22
· API synthesis reactors (glass-lined alternative where glass damage risk is unacceptable)
· Heat exchangers and condensers handling mixed acid vapours
· Centrifugal pump casings and impellers for corrosive solvent transfer
· Instrumentation (thermowells, pressure sensor diaphragms) exposed to reaction mass
· Piping systems carrying acid chlorides, brominating agents, and sulfonating mixtures
· Agitator shafts and blades in multi-purpose production vessels
· Spray dryer components for aggressive pharmaceutical intermediates
Regulatory Compliance
C22 meets the material-of-construction requirements for FDA cGMP (21 CFR Part 211 Subpart D) equipment: non-reactive, non-absorptive, non-additive to the product. The alloy is fully wetted-surface-compatible with pharmaceutical cleaning protocols including CIP (Clean-in-Place) with 1–2% NaOH at 80°C and acid passivation with 10% citric acid or 20% HNO₃. EN 10204 3.1 certification with full traceability supports pharmaceutical quality audit requirements.
Flue Gas Desulfurization (FGD) systems represent one of the largest installed bases for Hastelloy C22 globally. In wet limestone FGD, the flue gas is scrubbed with a limestone slurry, producing a condensate that contains H₂SO₄, HCl, HF, and dissolved heavy metals at pH 1–3 and temperatures of 50–80°C (122–176°F). Below the acid dewpoint, concentrated acid droplets form on vessel walls, creating severe pitting and crevice corrosion conditions that rapidly destroy 316L and duplex steels.
Where C22 Goes in an FGD System
FGD Component | Corrosion Challenge | Why C22 | Alternative Materials & Their Limitations |
Absorber vessel (wet zone) | H₂SO₄ + HCl condensate at pH 1–3, 50–80°C | C22 resists both acids; 10–15 yr life vs 3–5 yr for 316L | 316L (3–5 yr), 2205 (5–8 yr), C276 (8–12 yr) |
Inlet duct (dry/wet transition) | Acid dewpoint condensation + fly ash erosion | C22 wall-papering (2 mm sheet lining) on carbon steel | C276 liner (comparable), Alloy 625 (lower pitting resistance) |
Outlet duct / stack liner | Wet acidic gas below dewpoint | C22 sheet lining or solid C22 in lower stack section | C276, Alloy 59, titanium (gr.2) |
Mist eliminators | Acid droplet impingement + chloride concentration | C22 wire mesh; resists under-deposit crevice attack | 316L (fails rapidly), Alloy 20 (3–5 yr), C276 (comparable) |
Dampers / guillotines | Acid condensate + mechanical wear | C22-clad blades and seats | C276 (comparable), Alloy 625 (lower corrosion) |
Slurry pump casings | Erosion-corrosion from limestone slurry | Solid C22 casting or C22 weld overlay | CD4MCuN duplex (lower life), white iron (brittle) |
Quench / pre-scrubber | Rapid temperature drop → concentrated acid shock | C22 lining or solid construction | Graphite (brittle), PTFE-lined (temperature limit), C276 (comparable) |
C22 vs C276 in FGD — Why C22 Is Gaining Ground
Historically, C276 dominated the FGD market. However, the past 15 years have seen a steady shift toward C22 for two reasons:
(1) C22's higher chromium content provides measurably longer service life in the oxidizing conditions that prevail in the upper absorber and outlet duct where air in-leakage raises the redox potential
(2) the tungsten-modified chemistry gives C22 a wider operational window as coal sources change and flue gas composition varies. Major FGD OEMs including Babcock & Wilcox, Mitsubishi Hitachi Power Systems, and Ducon now specify C22 for absorber vessel wall-papering in new-build coal-fired and waste-to-energy plants.
Waste-to-Energy & Hazardous Waste Incineration
Waste incineration flue gas is significantly more aggressive than coal-fired FGD: PVC and halogenated plastics in the waste stream generate HCl and HF at concentrations 5–20× higher than coal. C22 is one of the few alloys that can handle the combined HCl + H₂SO₄ + heavy-metal chloride condensate in waste incinerator scrubbers without suffering pitting within the first 12–18 months. For medical waste incinerators (which burn PVC-rich hospital waste), C22 is the material of choice for quench sections and wet scrubber components.
Hastelloy C22 alloy has been widely used in chemical and petrochemical fields, such as components and catalytic systems in contact with chloride-containing organics. This material is especially suitable for use in high temperature, inorganic and organic acids mixed with impurities (such as formic acid and acetic acid), and seawater corrosive environments.
Chemical Processing
Food Processing
Pharmaceutical Industry
Oil & Gas
Power Generation
Pulp & Paper Industries
Marine Engineering
Case 1: Pharmaceutical API Reactor Retrofit (Switzerland, 2023)
A Swiss CDMO (Contract Development and Manufacturing Organization) was experiencing 316L reactor failure every 18–24 months in a multi-purpose API synthesis vessel. The process alternated between: (Step A) nitration in HNO₃/H₂SO₄ at 60°C (oxidizing), and (Step B) HCl quench with chlorinated solvent at 80°C (reducing). The 316L vessel suffered from end-grain pitting at agitator blade attachment welds and crevice corrosion under baffle mounting pads. Root cause: PREN 24–26 was inadequate for the mixed oxidizing-reducing cycle.
Solution:
Reactor replaced with solid Hastelloy C22 (12 mm wall). After 30 months in service, inspection showed zero pitting and zero measurable wall loss. ROI: The C22 vessel cost 3.2× the 316L vessel but eliminated two 14-day shutdowns per year for vessel replacement, saving an estimated CHF 1.8 million over 3 years in avoided downtime alone.
Case 2: FGD Absorber Retrofit (Coal Power Plant, India, 2022)
A 660 MW coal-fired unit in Gujarat had a rubber-lined carbon steel FGD absorber that was failing at lining seams after 4 years. Acid bypass had corroded the carbon steel shell to 50% of original thickness. The plant needed a retrofit solution that could be installed during a 45-day outage.
Solution:
C22 wall-papering (2 mm sheet, welded to carbon steel shell with C22 batten strips). JN Alloy supplied 14 tonnes of C22 sheet (ASTM B575) in 2.0 mm and 3.0 mm gauges, cut to size with CNC-profiled edges for butt-welding on site. Installation completed within 38 days. After 3 years of operation, UT thickness survey showed zero corrosion loss in the C22 lining. The plant operator has since specified C22 for a second unit.
Case 3: Medical Waste Incinerator Scrubber (Germany, 2024)
A medical waste incineration facility in Bavaria was experiencing rapid quench section failure. The flue gas composition (post-PVC-rich hospital waste) produced HCl concentrations of 800–1500 ppm in the condensate, with intermittent SO₂ peaks from rubber waste batches. 316Ti lasted 14 months; Alloy 31 lasted 22 months.
Solution:
Complete quench section replacement in Hastelloy C22 (6 mm plate + C22-clad nozzles). JN Alloy supplied 9 tonnes of C22 plate, pre-formed into quench vessel shell courses with weld preparation. After 24 months of operation, inspection found the C22 surface in "as-new" condition with no pitting, no crevice attack, and wall thickness within original mill tolerance. Facility now standardises on C22 for all wet-scrubber components.
What is the difference between Hastelloy C22 and C276?
Hastelloy C22 contains ~22% Cr and ~13% Mo, while C276 has ~16% Cr and ~16% Mo. C22’s higher chromium gives it superior resistance to oxidizing media (HNO₃, wet Cl₂, FeCl₃) and a slightly higher PREN (65–70 vs 64–68). C276’s higher Mo gives it a slight edge in strongly reducing acids (HCl, H₂SO₄). C22 is generally preferred for mixed oxidizing-reducing environments (pharmaceutical, FGD), while C276 remains strong in deep reducing acid service.
Is Hastelloy C22 suitable for pharmaceutical manufacturing?
Yes. C22 is extensively used in pharmaceutical API manufacturing for reactors, heat exchangers, and piping exposed to hot chloride solutions, mixed mineral acids, and halogenated organic compounds. Its PREN of 65–70 prevents pitting and metal ion leaching that would contaminate pharmaceutical products. C22 meets FDA cGMP material-of-construction requirements (21 CFR Part 211) and is compatible with standard CIP and acid passivation protocols.
Can Hastelloy C22 be used in FGD (Flue Gas Desulfurization) systems?
Yes. C22 is a premium material for FGD absorber vessels, inlet ducts, dampers, and mist eliminators. It resists the H₂SO₄/HCl condensate that forms below the acid dewpoint in wet FGD systems. C22 outlasts 316L by 3–5× and duplex stainless steels by 2–3× in FGD service. Major FGD OEMs specify C22 wall-papering as standard for new-build absorbers.
What is the PREN value of Hastelloy C22?
Hastelloy C22 has a PREN of 65–70 using the formula PREN = %Cr + 3.3(%Mo + 0.5×%W) + 16%N. This places C22 among the top tier of commercially available corrosion-resistant alloys, comparable to Alloy 59 (PREN ~66–72) and superior to Inconel 625 (PREN 48–52), 254SMO (PREN 43–45), and 2205 duplex (PREN 34–36).
What product forms are available for Hastelloy C22?
JN Alloy supplies C22 in: pipe (ASTM B622 seamless / B619 welded, 1/2″–24″ NPS), tube (ASTM B626, OD 6–50 mm), plate and sheet (ASTM B575, thickness 0.5–50 mm), bar and rod (ASTM B574, diameter 6–300 mm), butt-weld fittings (ASTM B366, 1/2″–24″, Sch 10S–Sch 160), flanges (ASME SB-564, 150#–2500#), forgings, fasteners, and welding consumables (ERNiCrMo-10). All with EN 10204 3.1 certification; 3.2 with third-party witness available on request.
How does Hastelloy C22 compare to Inconel 625?
C22 has significantly higher Mo (13% vs 9%) and W (3% vs 0%), giving it a PREN of 65–70 vs 625’s 48–52. This means C22 provides substantially better pitting and crevice corrosion resistance. Inconel 625, however, has higher strength (YS 415 MPa vs 310 MPa) due to niobium solid-solution strengthening and is preferred for elevated-temperature applications above 650°C. For room-temperature to moderate-temperature corrosion service with mixed acids, C22 is the superior choice.
Does Hastelloy C22 require post-weld heat treatment?
No. The ultra-low carbon content (≤ 0.015%) prevents chromium carbide precipitation at grain boundaries during welding, so C22 resists intergranular corrosion in the as-welded condition. PWHT is not required for corrosion resistance. Stress relief at 1120°C + rapid quench may be applied if required by the applicable pressure vessel code, but is not needed for corrosion performance.
Is Hastelloy C22 NACE MR0175 compliant?
Yes. C22 (UNS N06022) is listed in NACE MR0175/ISO 15156-3 Table A.31 for any equipment or component in H₂S-containing environments with no environmental restrictions on H₂S partial pressure, chloride concentration, pH, or temperature within the material’s mechanical design limits. Maximum hardness: HRC 37 in the solution-annealed condition per MR0175.
What is the maximum service temperature for Hastelloy C22?
For corrosion-resistant applications, continuous service up to 675°C (1250°F) is recommended. Above this temperature, accelerated oxidation scaling and carbide precipitation can reduce corrosion resistance. For purely structural applications without corrosion requirements, C22 can be used up to approximately 1000°C (1830°F), though creep strength declines significantly above 800°C.
What is the difference between Hastelloy C22 and Alloy 59?
Alloy 59 (UNS N06059, 2.4605) is another premium Ni-Cr-Mo alloy with ~23% Cr and ~16% Mo, giving a PREN of ~66–72, slightly higher than C22. Alloy 59 was specifically designed to avoid the micro-segregation issues of earlier C-type alloys and can have an even wider application window for extreme mixed-acid environments. In practice, C22 and Alloy 59 often compete directly in FGD and chemical processing. C22 has a larger installed base and broader availability; Alloy 59 can offer marginal performance gains in the most aggressive conditions. Contact JN Alloy for a detailed comparison specific to your process.
