Hastelloy C-22 vs C-276: Chemical Composition, Price

For mixed oxidizing and reducing chemical environments where the highest overall resistance to pitting, crevice attack, and stress-corrosion cracking is required, HASTELLOY® C-22 (UNS N06022) is usually the safer selection. For many strongly reducing acid services, for easier weldability with long industrial proven performance and slightly higher molybdenum content that helps in some acid media, HASTELLOY® C-276 (UNS N10276) often offers superior performance and cost-effectiveness. Final material choice depends on exact chemistry, temperature, mechanical demands, and life-cycle cost — the practical decision should reference real-world isocorrosion data, weld procedure qualifications, and site test data where available.

What is C-22 and C-276 mean?

Both C-22 and C-276 belong to the nickel-chromium-molybdenum family of corrosion-resistant alloys developed to handle aggressive chemical environments. The HASTELLOY® name is a registered trade name (Haynes / historic trademark family) often used in industry literature; the underlying standardized identifiers are UNS N06022 for C-22 and UNS N10276 for C-276. These alloys evolved from earlier “C” family compositions to solve real plant problems including pitting, crevice corrosion, stress-corrosion cracking, and weldability challenges.

Alloy Chemical Composition

Below is a concise composition overview based on manufacturer technical data. Small tolerances vary by producer and product form; always confirm with mill certificates.

Sources: Haynes technical sheets for both alloys provide official nominal numbers and commentary on composition limits.

Why these differences matter: Higher chromium in C-22 contributes to stronger resistance in oxidizing, chloride-bearing environments; higher molybdenum plus tungsten in C-276 boosts resistance in many reducing acid environments and helps with pitting resistance in some conditions.

Microstructure and metallurgy notes

Both alloys are austenitic, solid-solution nickel-base alloys with chemistry tuned to remain single-phase and avoid precipitate formation that could embrittle or degrade corrosion resistance. Low carbon levels were chosen to improve weldability and to reduce sensitization risk during thermal cycles. Tungsten additions provide solid solution strengthening and help with localized corrosion resistance. Manufacturers caution that heavy cold work will change formability and may require intermediate anneals. For welded systems, both alloys are commonly used in the “as-welded” state, though weld filler and procedure control matter greatly.

Corrosion behavior: oxidizing media, reducing media, and mixed chemistries

• Oxidizing acids and mixed oxidizing/chloride environments: C-22 was developed to give outstanding performance in oxidizing conditions, including mixtures with nitric acid and wet chlorine-containing streams. Its higher chromium content and the balanced chemistry provide excellent passivity and raise critical pitting and crevice temperatures in many chloride-bearing systems.

• Reducing acid environments (hydrochloric, some sulfuric scenarios): C-276, with somewhat higher molybdenum and tungsten, has demonstrated very good resistance in many reducing acid services and historically gained widespread use in hydrochloric acid and organic acid systems. Nickel Institute is among sources that show C-276 performing strongly in many sulfuric and hydrochloric conditions.

Practical rule: Where oxidizers (chlorine, nitric acid, chlorinated oxidants) are present or can form intermittently, C-22 tends to be more conservative. Where the environment is purely reducing and weldability plus general acid resistance are prime concerns, C-276 often works well.

Localized corrosion: pitting, crevice, and SCC

• Pitting and crevice corrosion: Testing using acidified ferric chloride (ASTM G48 family methods) yields critical pitting temperature (CPT) and critical crevice temperature (CCT) values; C-22 typically shows higher CPT/CCT values than C-276 in published manufacturer test matrices, which indicates stronger resistance to localized attack in chloride-bearing oxidizing solutions.

• Stress corrosion cracking (SCC): Both alloys were formulated to minimize susceptibility to chloride-induced SCC compared with standard austenitic stainless steels. C-22’s nominal formulation and control of impurities give it an edge for SCC resistance under many field conditions; however local service details (temperature, chloride activity, tensile stress level, and electrochemical environment) dominate the outcome. Refer to isocorrosion charts and test data for specific service envelopes.

Mechanical and thermal properties

Both alloys offer good tensile strength, ductility, and creep resistance up to moderately elevated temperatures. They are not intended for high strength structural duty at elevated temperatures in the range where precipitation-strengthened nickel alloys would be chosen; instead, their mechanical performance is typically sufficient for pressure containment and process piping/vessels where corrosion resistance is primary. Manufacturers publish temperature limits for continuous use; consult mill data and design codes for exact allowable stresses.

Fabrication, welding, and heat treatment

• Weldability: Both alloys were developed with weldability in mind. C-276’s low carbon and silicon contents historically made it easier to weld without degradation in corrosion performance around welds. C-22 is weldable but may require slightly more attention to filler selection and heat input control; manufactured guidance exists for welding procedures, pre/post heat treatment where required, and matching filler metals.

• Forming and cold work: Both alloys work harden quicker than typical austenitic stainless steels. Cold forming might call for multiple passes with intermediate anneals for tight radii. For thin-wall tubing and complex shapes, coordinate with supplier capabilities.

• Post-weld: In many cases, no post-weld heat treatment is necessary for corrosion performance. Nevertheless, where specific property requirements exist or where weld hydrogen cracking risk arises, follow qualified procedures referenced to codes or manufacturer literature.

Hastelloy C22 vs C276 — Price comparison

Below is a concise market price comparison table (USD) for common mill forms. Prices are approximate and highly variable by form (bar, plate, pipe), quantity, certification, and region — figures reflect supplier listings and market indexes as of Aug 25, 2025.

Key notes & sources

• Market indexes & industry data show Hastelloy C276 market-reference levels near ~$52/kg (Q1 2025 index), but finished products (e.g., certified seamless pipe FOB Shanghai) can be notably higher (~$67.8/kg). This explains why supplier quotes vary widely by product and certification.

• Online marketplace and Chinese supplier listings (Alibaba / trading catalogs) commonly show much lower per-kg headline prices for small-lot or non-certified stock (commonly $15–40/kg), which is valid for some sellers but often tied to MOQ, lead time, or looser spec/inspection. Use these only as ballpark starting points.

• C22 is often priced similarly or slightly higher than C276 for certain mill forms because C22’s chemistry and supply balance can push distributor prices higher for certified plate/stock. Example distributor pages list C22 plate in higher ranges (e.g., ~$48–80/kg).

Typical industrial applications

HASTELLOY® C-22 common uses: flue gas desulfurization (FGD) scrubbers and piping, chemical reactor vessels subject to mixed oxidizers/reducers, pharmaceutical reactors where nitric acid or chloride mixtures may occur, seawater/brine handling where crevice/bronze galvanic issues exist.

HASTELLOY® C-276 common uses: chemical process equipment handling hydrochloric acid, sulfuric acid at certain concentrations, waste treatment, organic acid processes and general industrial piping where reducing conditions are frequent and weldability is prioritized.

Selection strategy and life-cycle cost

Material choice should be driven by:

• Exact chemical composition of the process stream (including impurities and oxidizers)

• Operating temperature and pressure

• Expected duration and maintenance access (downtime cost)

• Welding or fabrication constraints on site

• Regulatory or code constraints (pressure vessel design rules, toxic service lines)

• Life-cycle cost modeling (replacement, downtime, and monitoring costs)

When in doubt, run coupon tests or pick the more conservative alloy when failure would create safety or environmental risk. Nickel Institute is a useful source for isocorrosion guidance when comparing alloy envelopes.

Quick-reference comparison table

(Manufacturer data and Nickel Institute charts inform these comparisons.)

Limitations, testing, and pitfalls

• Do not rely on “family names”: Two batches from different makers may show slight composition tolerances. Always require mill certificates and confirm UNS number.

• Service chemistry can change: A process upset can create oxidizing spikes that shift the preferred alloy. Plan for worst-case excursions.

• Localized crevice geometries matter: Gaskets, lap joints, and deposits change local chemistry significantly. Consider design that avoids stagnant crevices.

• Field testing: For novel chemistries, short-term coupon exposures and electrochemical testing are cost-effective risk reducers. Nickel Institute and Haynes provide isocorrosion and test data for reference.

FAQs

1. Which alloy resists pitting better?
   C-22 generally shows higher critical pitting and crevice temperatures in chloride-bearing oxidizing media; for those environments C-22 is preferred.

2. Which alloy handles hydrochloric acid better?
   C-276 has a long record in many hydrochloric and reducing acid services and often provides better general corrosion rates in such environments.

3. Can I weld both alloys without losing corrosion resistance?
   Yes, both alloys were designed with weldability in mind. Use recommended filler metals and qualified procedures; C-276 historically had advantage because of very low carbon and silicon.

4. Which is more expensive?
   Market prices fluctuate. Typically C-22 can be priced higher in some markets due to alloying content and demand, but shop quotes and form factor (tube, plate, pipe) control actual cost. Always request current mill quotes.

5. Are either of these alloys immune to corrosion?
   No metallic alloy is universally immune. Both are highly resistant in many environments but can fail under specific chemistries, temperatures, or geometric stressors. Field testing recommended for unique services.

6. Do either require post-weld heat treatment?
   In most corrosion services, post-weld heat treatment is not required. Follow qualified welding procedures and manufacturer guidance when specific mechanical properties or hydrogen concerns exist.

7. What standards or UNS numbers apply?
   C-22 = UNS N06022; C-276 = UNS N10276. Referencing these in procurement ensures correct chemistry.

8. Which to choose for FGD scrubbers?
   C-22 is widely used in flue gas desulfurization scrubbers due to mixed oxidizing/reducing chemistry including chlorides.

9. Do these alloys need monitoring in service?
   Yes. Periodic inspection, deposit control, and corrosion monitoring reduce risk. Coupons or electrical resistance probes help track degradation.

10. Where can I find authoritative curves or isocorrosion charts?
    The Nickel Institute and alloy manufacturer technical literature publish isocorrosion charts and corrosion rate data; consult those for specific acid concentration vs temperature boundaries.

Practical selection checklist for engineers

1. Collect full process sample chemistry including contaminants.

2. Note operating temperature range and maximum excursion conditions.

3. Confirm welding needs and fabrication constraints.

4. Request mill certificates and test data for the chosen heat.

5. If uncertainty remains, perform coupon tests under expected temperature and flow conditions.

6. Evaluate life-cycle cost including downtime and potential environmental liability.

Closing technical remark

Both HASTELLOY® C-22 and C-276 are premium nickel-base alloys engineered to handle severe corrosion challenges. C-22 is the conservative choice for oxidizing/chloride scenarios and where SCC is a prime concern. C-276 remains highly valuable for reducing acid services and where proven weldability and field history are deciding factors. The best practice is to pair manufacturer technical data with site-specific sampling and testing, and to document weld procedures and inspection plans for long-term reliability.

Official references

• HASTELLOY® C-22® alloy — Haynes International (technical brochure/PDF)
• HASTELLOY® C-276 alloy — Haynes International (technical brochure/PDF)