If you are buying nickel alloy pipe for a chemical plant, offshore platform, or refinery upgrade, the Hastelloy C276 vs C22 decision usually arrives after 316L, 904L, and even duplex 2507 have been ruled out. Both alloys belong to the nickel-chromium-molybdenum family and both solve problems that stainless steels cannot. But they are not interchangeable. The wrong choice shows up as preferential weld attack in eighteen months, or as unexpected pitting in an oxidizing chloride loop that the material was never optimized for.
Product Forms
Bar & Rod
Plate & Sheet
Coil & Strip
Pipe & Tube
Fitting: Flange, Tee, Elbow, Reducer etc.
Forging: Ring, Shaft, Circle, Block etc.
What the Standards Say: UNS N10276 vs N06022
Both alloys are covered by the same ASTM product specifications for pipe, tube, fittings, forgings, and plate. The difference is the UNS designation and the chemistry limits.
| Product Form | ASTM Specification | C276 (UNS N10276) | C22 (UNS N06022) |
|---|---|---|---|
| Seamless pipe & tube | ASTM B622 / ASME SB622 | UNS N10276 | UNS N06022 |
| Welded pipe | ASTM B619 / ASME SB619 | UNS N10276 | UNS N06022 |
| Welded tube | ASTM B626 / ASME SB626 | UNS N10276 | UNS N06022 |
| Fittings | ASTM B366 / ASME SB366 | WPHC276 | WPHC22 |
| Forgings | ASTM B564 / ASME SB564 | N10276 | N06022 |
| Plate/sheet/strip | ASTM B575 / ASME SB575 | N10276 | N06022 |
| Rod/bar | ASTM B574 / ASME SB574 | N10276 | N06022 |
Chemical Composition and Why It Matters
| Element | C276 (UNS N10276) | C22 (UNS N06022) | Engineering Effect |
|---|---|---|---|
| Nickel (Ni) | Balance (~57%) | Balance (~56%) | Base matrix; ductility and SCC resistance |
| Chromium (Cr) | 14.5 – 16.5% | 20.0 – 22.5% | Oxidizing acid resistance; passive film stability |
| Molybdenum (Mo) | 15.0 – 17.0% | 12.5 – 14.5% | Reducing acid resistance; pitting resistance |
| Tungsten (W) | 3.0 – 4.5% | 2.5 – 3.5% | Localized corrosion resistance in reducing acids |
| Iron (Fe) | 4.0 – 7.0% | 2.0 – 6.0% | Lower Fe in C22 improves some acid performance |
| Carbon (C) max | 0.010% | 0.015% | Both ultra-low carbon; no sensitization risk |
| Silicon (Si) max | 0.08% | 0.08% | Weldability control |
| PREN (approx.) | ~69 | ~65 | Both extremely high; C22 slightly lower |
Pitting and Crevice Resistance (ASTM G48)
ASTM G48 is the standard ferric chloride test used to rank alloys for chloride service. The numbers below are representative laboratory ranges, not guaranteed minima, but they separate the two alloys clearly:
| Alloy | PREN | CPT (°C) Method A | CCT (°C) Method B | Seawater Pitting Index |
|---|---|---|---|---|
| 316L | 24 | 25 – 30 | < 0 | Limited |
| 2205 duplex | 35 | 45 – 55 | 20 – 25 | Good |
| 2507 super duplex | 42 | 70 – 80 | 45 – 55 | Excellent |
| Hastelloy C276 | ~69 | ~115 – 125 | ~70 – 80 | Outstanding |
| Hastelloy C22 | ~65 | ~105 – 115 | ~75 – 85 | Outstanding |
Both alloys outperform every stainless and duplex grade in chloride service. C276 has a slightly higher critical pitting temperature because of its higher molybdenum and tungsten. C22 has a slightly better critical crevice temperature because of its higher chromium. For most pipe systems, either alloy is over-engineered from a pitting standpoint; the real selection driver is the chemical environment.
Intergranular Corrosion in the As-Welded Condition (ASTM G28)
C22 was developed partly to resist preferential attack in the weld heat-affected zone and fusion line. In ASTM G28 Method A testing on welded specimens:
C276 as-welded: corrosion rate typically < 1.0 mm/year, but can show localized attack in strongly oxidizing environments if not solution annealed.
C22 as-welded: corrosion rate typically < 0.5 mm/year, with better resistance to HAZ attack in mixed oxidizing/reducing service.
For pipe spools that will be field-welded and not post-weld solution annealed - which is most of them - C22 provides a larger safety margin against weld-zone corrosion. This is one reason C22 has become the default for multipurpose chemical plants and pharmaceutical piping systems.
Environment-by-Environment Selection
| Service Environment | Better Choice | Reason |
|---|---|---|
| Concentrated hydrochloric acid (reducing) | C276 | Higher Mo + W content |
| Wet chlorine gas / hypochlorite (oxidizing) | C22 | Higher Cr content stabilizes passive film |
| Ferric chloride / cupric chloride | C22 | Oxidizing chloride service |
| Mixed nitric/hydrochloric acid (aqua regia type) | C22 | Broader versatility |
| Sulfuric acid, reducing, >90°C | C276 | Proven lower corrosion rate |
| Seawater / brine / chloride cooling water | Either | Both outstanding; C22 slightly better crevice margin |
| Flue gas desulfurization (FGD) absorber | C22 | Oxidizing chloride levels in slurry |
| Sour service with H2S (NACE MR0175) | C276 or C22 | Both listed; hardness control required |
Three Real Project Scenarios
Scenario 1 - Saudi Aramco Acid Gas Field Injection Line
Service: Sour wet gas, 8% H2S, 50,000 ppm chlorides, 80°C, NPS 3 process line. Decision: Hastelloy C276 seamless pipe per ASTM B622, Sch 40S, solution annealed, NACE MR0175 dual-certified, hardness ≤ 23 HRC. Why: Strongly reducing sour environment with high chlorides favors C276's Mo + W content. Full EN 10204 3.2 MTC with SGS inspection for Aramco approval.
Scenario 2 - Rotterdam Chemical Plant Chlor-Alkali Bleach Line
Service: Wet chlorine gas and sodium hypochlorite, 60°C, NPS 2 instrument loop, field-welded spools with no post-weld anneal. Decision: Hastelloy C22 seamless pipe per ASTM B622, Sch 40S, ERNiCrMo-10 filler, PED CE marking, EN 10204 3.1. Why: Oxidizing chloride service favors C22's higher chromium. As-welded HAZ corrosion resistance is critical because post-weld solution annealing is impractical in the existing plant.
Scenario 3 - QatarEnergy Offshore Seawater Lift Pump Column
Service: Raw seawater, ambient temperature, NPS 8 column pipe, welded construction. Decision: Either C276 or C22 welded pipe per ASTM B619; final choice driven by availability and total installed cost. Why: Both alloys are massively over-specified for seawater from a corrosion standpoint. The decision here is procurement economics and lead time, not metallurgy.
Quick-Reference Selection Table
| Parameter | Hastelloy C276 (UNS N10276) | Hastelloy C22 (UNS N06022) |
|---|---|---|
| Best for | Strongly reducing acids, high chlorides, sour service | Oxidizing acids, mixed oxidizing/reducing, weld-critical service |
| Cr content | 14.5 – 16.5% | 20.0 – 22.5% |
| Mo + W content | 18 – 21% combined | 15 – 18% combined |
| PREN | ~69 | ~65 |
| CPT (ASTM G48 A) | ~115 – 125°C | ~105 – 115°C |
| CCT (ASTM G48 B) | ~70 – 80°C | ~75 – 85°C |
| ASTM pipe spec | B622 / B619 / B626 | B622 / B619 / B626 |
| Filler metal | ERNiCrMo-4 | ERNiCrMo-10 |
| NACE MR0175 | Acceptable, hardness ≤ 23 HRC | Acceptable, hardness ≤ 23 HRC |
| PED / AD 2000 | Accepted with CE marking | Accepted with CE marking |
| Typical cost | Slightly lower | 10 – 15% premium in small sizes |
FAQ
Can Hastelloy C22 replace C276 in my project?
Often yes, but not automatically. C22 is the safer replacement when the service contains oxidizing acids, mixed oxidizing/reducing conditions, or when field welding without post-weld annealing is required. C276 remains the better choice for concentrated hydrochloric acid, high-chloride reducing environments, and sour service where the highest pitting resistance is needed. Always re-qualify the WPS/PQR and confirm the MTR chemistry before substituting.
Which alloy is better for seawater service?
Both are outstanding in seawater. C22 has a marginally better critical crevice temperature, which matters in creviced connections, under deposits, or in slow-flowing brine. C276 has a marginally better critical pitting temperature. For most seawater pipe applications, the choice is driven by the secondary chemical environment (e.g., chlor-alkali vs. FGD) and availability, not by seawater corrosion alone.
Do I need post-weld heat treatment for C276 or C22 pipe?
For C276, solution annealing after welding is recommended for the most aggressive services, although the alloy performs well in the as-welded condition for many applications. For C22, post-weld annealing is less frequently required because the alloy was specifically designed to resist HAZ attack in the as-welded state. The final decision belongs in the project WPS/PQR and corrosion engineering review.
What documentation should I request for a Middle East oil and gas project?
Request: EN 10204 3.1 or 3.2 Mill Test Certificate with full heat traceability, PMI report, hydrostatic test record, dimensional inspection report, NACE MR0175/ISO 15156 declaration, and third-party inspection certificate (SGS, Bureau Veritas, TÜV, or DNV) when required by the owner. For Saudi Aramco and ADNOC contracts, also confirm the supplier is on the approved vendor list or can pass the pre-qualification audit.
What is the PED requirement for Hastelloy pipe in Europe?
Both C276 and C22 pipe used in European pressure equipment carrying Group 1 hazardous fluids must carry CE marking under PED 2014/68/EU. Categories II–IV require Notified Body involvement. The MTC should reference EN 10204 3.1 or 3.2, and the DoC must list the applicable harmonized standard or material manufacturer approval.
Still deciding between Hastelloy C276 and C22 for your next project?
HUITONG supplies seamless and welded nickel alloy pipe in both grades per ASTM B622/B619/B626, with full NACE MR0175 compliance, PED CE marking for European shipments, and EN 10204 3.1/3.2 certification. Send your process conditions or MTO to market@htpipe.com or WhatsApp +86-19339900201 for a same-week alloy selection and pricing response.
