RFQ Today
Certifications: EN 10204 3.1 / 3.2 material test certificates, PMI verification, and complete export documentation packages.
Hastelloy
C-22
(UNS N06022)
A world-class technical reference for EPC contractors, chemical process engineers, procurement heads, and TPI inspection agencies specifying Hastelloy C-22 nickel-chromium-molybdenum alloy — covering alloy metallurgy, its higher-chromium compositional shift from C-276 and the resulting improved localized corrosion and oxidizing-environment performance, and the QC and documentation discipline required for critical chemical process and pollution control equipment supply.
Key Properties
& Selection Logic
Hastelloy C-22 (UNS N06022) is a nickel-chromium-molybdenum- tungsten alloy developed as a compositional refinement of the C-276 alloy family (discussed in RR Hydraulic’s dedicated Hastelloy C-276 reference) — shifting the chromium-to-molybdenum ratio to deliver improved resistance to oxidizing environments and localized pitting/crevice corrosion while retaining strong reducing-acid performance.
1.1 — What Hastelloy C-22 (UNS N06022) Is and How It Differs from C-276
Hastelloy C-22 is a nickel-chromium-molybdenum-tungsten alloy with a nominal composition of approximately 56% nickel, 20–22.5% chromium, 12.5–14.5% molybdenum, 2.5–3.5% tungsten, and 2–6% iron, with the balance comprising minor elements including deliberately low carbon (≤0.010%) and low silicon (≤0.08%) content — sharing the same fundamental low-carbon/low-silicon weldability advantage discussed in detail in RR Hydraulic’s Hastelloy C-276 reference. The key compositional distinction from C-276 is the shift toward higher chromium content (20–22.5% vs. C-276’s 14.5–16.5%) and correspondingly lower molybdenum content (12.5–14.5% vs. C-276’s 15–17%) — this rebalancing gives C-22 measurably improved resistance to oxidizing environments and localized pitting/crevice corrosion in oxidizing chloride media compared to C-276, while retaining strong, though slightly reduced relative to C-276, performance in strongly reducing (non-oxidizing) acid environments where C-276’s higher molybdenum content provides a specific advantage.
1.2 — Key Engineering Properties
Superior Resistance to Oxidizing Environments
C-22’s higher chromium content provides notably better resistance than C-276 in oxidizing acid environments — ferric chloride, cupric chloride, wet chlorine gas, and mixed acid environments with an oxidizing component (such as nitric-hydrofluoric acid mixtures used in metal pickling and cleaning) — making C-22 the preferred choice where the process environment includes a meaningful oxidizing character.
Outstanding Localized Corrosion (Pitting/Crevice) Resistance
C-22 is widely regarded as offering among the best pitting and crevice corrosion resistance of any commercial nickel alloy in oxidizing chloride environments — a critical property for equipment with inherent crevice geometry (flanged joints, gasket contact areas, heat exchanger tube-to-tubesheet joints) exposed to hot chloride-bearing process fluids with any oxidizing character.
Strong General Versatility Across Both Oxidizing and Reducing Media
While C-276 is often cited as the more “reducing-environment-optimised” alloy of the Hastelloy family, C-22 is frequently described in industry literature as the more generally versatile alloy overall — performing well across an unusually broad combination of oxidizing and reducing conditions, and specifically outperforming C-276 in mixed-acid and variable-chemistry process streams with any oxidizing component.
Good Resistance to Reducing Acids (Slightly Reduced vs. C-276)
C-22 retains good resistance to hydrochloric acid and other strongly reducing acid environments, though C-276’s higher molybdenum content generally provides a measurable performance edge in the most aggressive, purely reducing acid conditions — the specific choice between C-22 and C-276 for reducing-acid-dominant service should be verified against documented corrosion data for the exact process conditions.
1.3 — Selecting Between C-22 and C-276
Product Forms
& Composition Reference
Hastelloy C-22 is manufactured across tube, pipe, bar, and plate product forms, each governed by a specific ASTM/ASME standard. Full detail on related nickel alloys is available across our standards reference library.
Submit form, size, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — Governing Standards
ASTM B575 / ASME SB-575 — Plate, Sheet, and Strip
Governs flat-rolled Hastelloy C-22 product — plate for pressure vessel fabrication, sheet and strip for general fabrication requiring the alloy’s corrosion performance.
ASTM B619 / B622 / B626 — Pipe and Tube
B619 governs welded pipe, B622 seamless pipe, and B626 welded tube — the specification family for C-22 pipe and tube across both seamless and welded construction, shared in general format with the C-276 specifications discussed in RR Hydraulic’s dedicated reference.
ASTM B574 — Rod
Governs rod stock for machined components and fastener manufacture in C-22 and related nickel-chromium-molybdenum alloys.
ASTM B564 / B366 — Forgings and Forged Fittings
B564 governs forgings; B366 governs forged fittings — the specifications for forged flanges, fittings, and valve bodies in C-22 where forged construction is specified for critical pressure-boundary components.
NACE MR0175 / ISO 15156
Provides the material qualification framework for sour service use of Hastelloy C-22, relevant where the alloy is specified for oil and gas process equipment with sour service exposure alongside its primary chemical process application.
2.2 — Chemical Composition and Mechanical Properties
| Element / Property | Value / Range |
|---|---|
| Nickel | Balance (~56%) |
| Chromium | 20.0–22.5% |
| Molybdenum | 12.5–14.5% |
| Tungsten | 2.5–3.5% |
| Iron | 2.0–6.0% |
| Carbon (max.) | 0.010% |
| Silicon (max.) | 0.08% |
| Tensile Strength | 760–900 MPa (typical, min. 690 MPa per spec) |
| Yield Strength | 350–420 MPa (typical, min. 283 MPa per spec) |
| Elongation | 45–65% |
2.3 — Comparison Across the Hastelloy C Family and Related Alloys
| Alloy | Cr / Mo Balance | Best Suited For |
|---|---|---|
| Hastelloy C-22 (N06022) | Higher Cr (20–22.5%) / Lower Mo (12.5–14.5%) | Oxidizing environments, superior pitting/crevice resistance, mixed oxidizing/reducing streams |
| Hastelloy C-276 (N10276) | Lower Cr (14.5–16.5%) / Higher Mo (15–17%) | Predominantly reducing environments, broadest “unknown chemistry” safety margin |
| Hastelloy C-2000 (N06200) | Similar Cr to C-22, added copper | Sulphuric acid-dominant environments specifically |
| Incoloy 825 (N08825) | Lower Cr and Mo than both C-22/C-276, added copper | Sulphuric/phosphoric acid and sour service at lower cost than full Hastelloy family |
Weld Practice
& Fabrication Guidance
Correct heat treatment and welding practice preserve Hastelloy C-22’s designed corrosion resistance — sharing the same weldability advantage from low carbon and silicon content discussed in detail in RR Hydraulic’s Hastelloy C-276 reference.
3.1 — Solution Annealing Heat Treatment
Hastelloy C-22 is supplied in the solution-annealed condition — heated to approximately 1120–1150°C and rapidly cooled (typically water quenched for tube and pipe) to dissolve secondary phases into solid solution and establish the single-phase austenitic microstructure that provides the alloy’s designed corrosion resistance. As with C-276, this annealed condition is the standard, as-supplied condition for the large majority of applications, since the alloy’s intended engineering value is corrosion resistance rather than maximum achievable mechanical strength.
3.2 — Weld Practice
As-Welded Service Without Mandatory PWHT
Like C-276, C-22’s low carbon and silicon content allows the alloy to be welded and placed into service without mandatory post-weld solution annealing for the majority of applications — a significant practical fabrication advantage over higher-carbon nickel alloy alternatives and older alloy generations.
Matching Filler Metal Selection
Welding consumables matched to C-22 (ERNiCrMo-10 type filler metal, per AWS A5.14) are used to maintain corrosion resistance and mechanical property matching in the weld deposit — using a mismatched filler metal, including inadvertently using C-276-matched filler on C-22 base metal, compromises the weld’s specific corrosion resistance profile even if both alloys are broadly similar in family.
Heat Input Control
Controlled heat input (avoiding excessive interpass temperature and heat accumulation) remains good practice to minimise any secondary-phase precipitation tendency and maintain optimal weld zone properties, particularly for multi-pass welds on thicker sections.
Cleanliness and Contamination Control
Strict cleanliness control (removing oils, grease, marking materials, and avoiding contact with carbon steel tools or grinding debris) before and during welding is essential to avoid weld defects and localized corrosion susceptibility in the completed weld.
3.3 — General Fabrication Considerations
Hastelloy C-22 machines and forms similarly to C-276 and other high-nickel alloys — work-hardening during machining requires appropriate tooling and cutting parameters, and standard nickel-alloy fabrication discipline (clean, controlled machining environments avoiding cross-contamination with lower-alloy materials) applies throughout component manufacture. There is no significant machining characteristic distinguishing C-22 from C-276 — the practical differences between the two alloys are corrosion-performance-related rather than fabrication-related.
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from certified nickel alloy heat to finished, tested, and packed Hastelloy C-22 component shipment. Chemical composition, mechanical, and PMI verification are standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 / Documentation Requirements
| Certificate | Content | EPC Requirement | When Mandatory |
|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Not acceptable for critical process supply | Never for critical chemical process equipment supply |
| 3.1 (EN 10204) | Heat-traceable chemical + mechanical test report | Mandatory — all EPC supply | All chemical process and pollution control component supply |
| 3.2 (EN 10204) | 3.1 + TPI countersign | Critical / owner-specified critical items | High-consequence chemical process pressure equipment |
4.3 — Applications by Industry
Waste Incineration and Flue Gas Equipment
Hastelloy C-22 components for waste incineration flue gas ductwork and scrubber systems exposed to hot, acidic, chloride-bearing, and oxidizing combustion byproduct condensate — leveraging the alloy’s superior oxidizing-environment and localized corrosion resistance in this specific demanding combination of conditions.
Metal Pickling and Cleaning Equipment
C-22 tanks and piping for metal pickling and cleaning operations using nitric-hydrofluoric acid mixtures and other oxidizing acid cleaning chemistries where the alloy’s specific oxidizing acid resistance advantage over C-276 provides meaningfully improved service life.
PVC and Chlor-Alkali Production
C-22 equipment for chlor-alkali and PVC production processes involving wet chlorine, hypochlorite, and oxidizing chloride process streams — a demanding combination of chloride exposure and oxidizing character where C-22’s specific property balance provides reliable performance.
4.4 — Export Packaging Specification
- Tube and pipe ends capped and bore-protected to prevent contamination and moisture ingress during transit, particularly important given the alloy’s typical use in high-integrity chemical process service
- Heat/lot number stamped or tagged on each item, cross-referenced to the accompanying material test certificate — with clear alloy grade marking (C-22 vs. C-276) to prevent confusion at site receiving inspection given the alloys’ compositional similarity
- Components segregated from carbon steel and other dissimilar materials during packing to avoid surface contamination affecting the alloy’s corrosion performance
- Documentation in a waterproof pocket: EN 10204 3.1/3.2 MTC, chemical composition report, mechanical properties report, PMI report, NDT reports, and packing list with form/size breakdown per item
- ISPM-15 timber or export cartons for international shipment, with country of origin and HS tariff code documentation matched to the nickel alloy product category
Submit your form, size, and quantity to RR Hydraulic for a complete, certified commercial offer.