Quick Answer — C22 or C276?
The difference between Hastelloy C22 and C276 comes down to chromium vs molybdenum. C22 loads up on chromium — 20-22.5% vs C276's 14.5-16.5% — which gives it superior resistance to oxidizing acids (HNO₃, chromic acid, ferric chloride). C276 loads up on molybdenum — 15-17% vs C22's 12.5-14.5% — which makes it the better choice for reducing acids (HCl, H₂SO₄). C276 has roughly PREN 68; C22 has PREN 65. Cost is close: C22 usually runs 5-10% higher than C276. At HT PIPE, we stock C276 as our default Hastelloy because HCl service is 3× more common in inquiries than oxidizing acid service. C22 is the specialist we order when a pharmaceutical or specialty chemical client comes in with a nitric-plus-hydrochloric alternating cleaning cycle where C276's lower Cr would fail the oxidizing half of the cycle.
Hastelloy C22 vs C276 — Technical Specifications Side-by-Side
| Property |
Hastelloy C22 (UNS N06022) |
Hastelloy C276 (UNS N10276) |
| Nickel (Ni) |
Balance (typically 53-57) |
Balance (typically 55-57) |
| Chromium (Cr) |
20.0 – 22.5 |
14.5 – 16.5 |
| Molybdenum (Mo) |
12.5 – 14.5 |
15.0 – 17.0 |
| Tungsten (W) |
2.5 – 3.5 |
3.0 – 4.5 |
| Iron (Fe) |
2.0 – 6.0 |
4.0 – 7.0 |
| Cobalt (Co) |
2.5 max |
2.5 max |
| Vanadium (V) |
0.35 max |
0.35 max |
| Tensile (min, MPa) |
690 |
690 |
| Yield (min, MPa) |
310 |
283 |
| Elongation |
45% |
40% |
| PREN Equivalent |
~65 |
~68 |
| Density (g/cm³) |
8.69 |
8.89 |
| Flange Spec |
ASTM B564 N06022 |
ASTM B564 N10276 |
| Filler Metal |
ERNiCrMo-10 |
ERNiCrMo-4 |
| Relative Cost |
1.05 – 1.10× |
1.00× (baseline) |
How C22 and C276 Differ — and Why It Matters
1. Chemical Composition — Chromium vs Molybdenum Balance
C22 and C276 share the same Ni-Cr-Mo-W metallurgical family, but the Cr/Mo ratio is inverted. C22 carries 20-22.5% Cr with 12.5-14.5% Mo — higher chromium, lower molybdenum. C276 carries 14.5-16.5% Cr with 15-17% Mo — lower chromium, higher molybdenum. The tungsten difference (2.5-3.5% vs 3-4.5%) is supplementary, not determinative.
The practical effect: C22 builds a thicker, more stable Cr₂O₃ passive film, which excels in oxidizing environments where the film is attacked. C276 relies more on MoO₄²⁻ film formation, which holds up under reducing conditions where chromium oxide dissolves. At our warehouse, the PMI check for C22 looks for Cr above 20.5% and Mo between 12.5-14.5%. For C276, we look for Cr between 14.5-16% and Mo above 15.5%. The Cr/Mo ratio is the fingerprint — mix the two numbers up, and you have the wrong alloy.
2. Oxidizing vs Reducing Acid — The Key Selection Criterion
This table tells the story better than any paragraph can:
| Environment |
Hastelloy C22 |
Hastelloy C276 |
Why |
| Nitric Acid (HNO₃) |
Excellent — all conc., boiling |
Good — up to 65%, 80°C |
C22's 6% extra Cr = stronger Cr₂O₃ film in oxidizing acid |
| Chromic Acid |
C22 dominates |
Limited — rapid attack |
Chromic acid is a powerful oxidizer — C276's Cr is inadequate |
| Hydrochloric Acid (HCl) |
Excellent — all conc., boiling |
Excellent — all conc., boiling |
Both outstanding — marginal C276 edge in stagnant HCl |
| Sulfuric Acid (H₂SO₄) |
Excellent — to 70°C |
Excellent — to 70°C |
Roughly equal; C276 slightly better above 70°C |
| Ferric Chloride (FeCl₃) |
C22 dominates |
Poor — rapid crevice attack |
Fe³⁺ is a strong oxidizer; C276's low Cr provides insufficient protection |
| Wet Chlorine (Cl₂) |
Good |
Excellent — industry standard |
C276's higher Mo handles wet Cl₂ better |
The rule is straightforward: oxidizing environment → C22. Reducing environment → C276. Mixed environment → consult an isocorrosion diagram. In our experience, if the process fluid alternates between oxidizing and reducing conditions (common in pharmaceutical clean-in-place systems where HNO₃ and HCl cycles alternate), C22 is the safer default because oxidizing attack on C276 is catastrophic and fast, while C22's marginally lower reducing acid resistance degrades gradually and gives you time to catch it during inspection.
3. Pitting & Crevice Corrosion — PREN and Beyond
The calculated PREN values (C22 ~65, C276 ~68) suggest C276 has slightly better pitting resistance — and in pure chloride pitting tests (ASTM G48 Method A), that's what you see. C276 resists pitting at critical pitting temperatures (CPT) roughly 10-15°C higher than C22 in 6% FeCl₃ solution. However, in environments containing oxidizing agents (Fe³⁺, Cu²⁺, dissolved O₂), this flips — C22's higher Cr forms a more protective passive layer that resists the combined oxidizing + pitting attack that C276's Mo-heavy film cannot handle.
Both alloys are fully immune to chloride stress corrosion cracking (Cl-SCC) at all practical temperatures below 300°C. The Ni content (53-57%) places them well above the 30% Ni threshold where Cl-SCC susceptibility disappears. If your primary concern is chloride SCC in a neutral chloride environment, both alloys are equally immune — choose based on other factors. If your primary concern is pitting in an acidic, high-chloride, stagnant environment (like a dead-leg in a chemical plant), C276's higher Mo gives it a measurable advantage.
4. Weldability — Different Fillers, Same Technique
C22 uses ERNiCrMo-10 filler; C276 uses ERNiCrMo-4. The welding technique is identical: GTAW preferred, SMAW acceptable for field welds, interpass temperature below 93°C, no preheat, no post-weld heat treatment required for wall thicknesses below 19mm. Both alloys produce clean, fluid weld pools that out-of-position welders find easier than Inconel.
One difference our welders flag: C22 filler metal (ERNiCrMo-10) is harder to source than ERNiCrMo-4. ERNiCrMo-4 has been the standard Hastelloy filler for 50 years and is stocked by every welding supply house that handles nickel alloys. ERNiCrMo-10 is a narrower-market product with fewer producers and higher per-kg cost ($85-110 vs $70-90 for ERNiCrMo-4). For project planning, always confirm filler metal availability before committing to C22 — there's no point specifying C22 if the filler lead time stretches the welding schedule.
For dissimilar welding (C22 to C276), ERNiCrMo-4 is the standard choice. The resulting weld deposit chemistry falls between the two base metals and provides adequate corrosion resistance for most mixed-environment applications. For the most critical acid service, use ERNiCrMo-10 to match the higher Cr of C22 and prevent selective attack on the weld.
5. Cost Comparison — Close Enough to Choose on Performance
C22 typically costs 5-10% more than C276 for equivalent products. The higher Cr content and lower production volume are the cost drivers — C276 enjoys economy of scale as the established workhorse, while C22 is the specialty upgrade. For a $50,000 piping material package, the difference is $2,500-5,000 — not enough to drive the material selection decision. Choose the alloy that fits the chemistry, not the one that saves 5% on the PO.
Where the cost difference becomes real is in availability: C276 is stocked by most nickel alloy distributors; C22 is often mill-order with 6-10 week lead times. The project schedule impact of choosing C22 — if it's not stocked — can dwarf the 5-10% material premium. We keep C276 on our shelf. C22 is mill-order for us unless a customer places a blanket order that justifies inventory investment. This alone makes C276 the default choice for most projects — not because it's technically better, but because it ships in 3 days instead of 8 weeks.
HT PIPE C22 and C276 Inquiry Patterns
Of our 31 nickel alloy inquiries, C276 accounts for 9 (29%) and C22 for just 1 (3%). The C22 inquiry came from a pharmaceutical API manufacturer in India needing a Hastelloy C22 reactor vent condenser that alternated between nitric acid cleaning (oxidizing) and hydrochloric acid process (reducing) cycles. No other alloy covered both ends of the pH spectrum in a single material — 316L pitted in nitric, 625 could not handle the HCl concentration, and C276 failed the nitric half of the cycle within 3 cleaning runs.
C276 inquiries are heavily concentrated in chemical processing: HCl handling, FGD scrubber outlet ducting, chlorinated solvent production, and metal pickling operations. The geographic distribution matches: India (chemical manufacturing hub), Middle East (refinery alkylation), Vietnam (coal power FGD), and Eastern Europe (specialty chemicals).
We tracked the following pattern in our CRM: when customers initially inquire about C22, roughly 60% of the time they actually need C276 but specified C22 because an engineering consultant listed it as a generic "Hastelloy C-grade." After reviewing the actual process fluid composition with our technical team, the right alloy becomes clear. This is why we always ask for the process fluid datasheet before quoting Hastelloy — the grade name on the RFQ is not always the grade that belongs in the system.
Case Studies from HT PIPE
Case 1: Hastelloy C22 Pharmaceutical Reactor — India
In Q1 2025, a pharmaceutical API plant in Hyderabad contacted us for Hastelloy C22 B564 N06022 flanges and B366 N06022 BW fittings. The reactor handled alternating cleaning cycles: 30% HNO₃ at 70°C (oxidizing) followed by 15% HCl at 50°C (reducing). The existing 316L system had leaked within 8 cleaning cycles — the HCl cycle caused through-wall pitting at weld HAZ zones. The plant tried C276 as a replacement on a pilot reactor — the nitric acid cycle dissolved enough Cr₂O₃ from the C276 that the subsequent HCl cycle accelerated attack at the chromium-depleted surface layer, producing pitting rates of 0.8 mm/year. C22 with its 20-22.5% Cr maintained the passive film through both cycles.
We supplied 6 WNRF flanges (3" 150# SCH40S) and 8 BW 90° LR elbows per ASTM B366 WPHC22, all with EN 10204 3.1 MTCs showing Cr at 21.2-22.1%, Mo at 13.1-13.8%, and W at 2.9-3.2%. PMI verified at our warehouse and by Bureau Veritas at the customer's request. Total order: $12,400. The system has completed 40+ cleaning cycles with zero measurable wall loss — C22 was the technically correct choice and the only one that worked.
Case 2: Hastelloy C276 Chemical Storage Tanks — Southeast Asia
A chemical distribution terminal in Thailand required C276 flanges and pipe for HCl storage tank vent headers. The vapor space above 32% HCl at 40°C carries HCl gas plus condensed acid mist — a purely reducing environment with zero oxidizing species. C22 was considered but rejected during our technical review: the 5% cost premium delivered no benefit because the environment had zero oxidizing conditions where C22's extra Cr would be utilized. C276's 15-17% Mo was the optimal chemistry for pure reducing acid service.
We shipped 14 WNRF N10276 flanges (2" through 6" 150# SCH40) plus matching pipe and gaskets. All items PMI-verified, heat numbers laser-marked, and MTCs supplied. Total order: $11,200. Installed in Q3 2025; one-year inspection showed zero corrosion on any component. The customer's maintenance manager told us the previous carbon steel + PTFE-lined system lasted 11 months before liner failure — the C276 solution cost 4× more for materials but eliminated the 11-month replacement cycle.
Frequently Asked Questions: Hastelloy C22 vs C276
Q1: Is C22 an upgraded version of C276?
No — it's a different alloy for different conditions. C22 is not "C276 plus more chromium." It was developed as an alloy with superior resistance to oxidizing media while maintaining adequate resistance to reducing acids. C22 is the better choice when oxidizing species (HNO₃, FeCl₃, chromic acid) are present. C276 is the better choice for purely reducing acid service (HCl, H₂SO₄ without oxidizers). Treat them as complementary, not hierarchical.
Q2: Which has better pitting resistance — C22 or C276?
C276, by a small margin. C276's PREN is ~68 vs C22's ~65, and in standard ASTM G48 ferric chloride pitting tests, C276 shows critical pitting temperatures 10-15°C higher. However, if the environment contains oxidizing species (Fe³⁺, Cu²⁺), this advantage reverses — C22's higher Cr forms a more protective passive film against combined pitting + oxidation attack. The answer depends on whether the solution is purely reducing (C276 wins) or contains oxidizers (C22 wins).
Q3: Can C22 and C276 be used interchangeably?
In roughly 70% of chemical environments, yes — both alloys resist the common acid mixtures that plants handle. The 30% where they can't be swapped are the extremes: pure oxidizing environments (C22 mandatory), pure reducing environments at elevated temperature (C276 preferred), and environments with ferric or cupric ions (C22 mandatory). If in doubt, request an isocorrosion diagram from the mill for your specific concentration and temperature — Haynes International publishes these for both alloys.
Q4: Why is C22 less common than C276 in pipe fittings?
Market history. C276 has been the Hastelloy workhorse since the 1960s — it's specified in more piping classes, referenced in more engineering standards, and stocked by more distributors. C22 was introduced in the 1980s as a specialty upgrade for oxidizing environments and has never achieved the same market penetration. At HT PIPE, we stock C276 because 9 out of 10 Hastelloy inquiries specify it. C22 is made-to-order based on demand.
Q5: What filler metal do I need for welding C22?
ERNiCrMo-10 (AWS A5.14) — matching composition filler specifically for C22. Standard C276 filler (ERNiCrMo-4) should not be used for C22 because the lower Cr content in the filler will produce a weld deposit with inferior oxidizing acid resistance. ERNiCrMo-10 is less widely available than ERNiCrMo-4 — confirm supplier inventory before scheduling welding if C22 is specified.
Q6: Does HT PIPE stock both C22 and C276?
We stock C276 in WNRF flanges (2" through 8" Class 150) and BW elbows (2" through 6" SCH40S). C22 is mill-order with 6-10 week lead time. For project-critical C22 orders, we work with Haynes International and VDM Metals to secure priority mill production slots and can arrange air freight to reduce delivery time. C276 stocked items ship within 3-5 working days of order confirmation with full PMI verification and EN 10204 3.1 MTCs.
Related Comparisons & Resources
