Quick Answer — Inconel 625 or Hastelloy C276?
Inconel 625 and
Hastelloy C276 are the two most-specified nickel alloys in piping — together they account for 71% of HT PIPE's nickel alloy inquiries. The decision hinges on one question:
what's the primary threat? If you're fighting temperature (500°C+ oxidation, gas turbine exhaust, creep), Inconel 625 is the answer — it holds 827 MPa tensile to 760°C and operates to 982°C. If you're fighting aggressive acids (HCl, H₂SO₄, wet Cl₂), Hastelloy C276 is mandatory — its 15-17% Mo content is double 625's 8-10% Mo. Inconel 625 costs $35-45/kg; C276 runs $45-55/kg. Both weld beautifully, both resist chlorides, but they're not interchangeable — we've seen C276 specified for high-temperature oxidation and fail within 900 operating hours because it wasn't designed for that job.
Side-by-Side: Inconel 625 vs Hastelloy C276 — Technical Spec Face-Off
| Property |
Inconel 625 (UNS N06625) |
Hastelloy C276 (UNS N10276) |
| Ni % |
58.0 min (typically 60-63) |
Balance (typically 55-57) |
| Cr % |
20.0 – 23.0 |
14.5 – 16.5 |
| Mo % |
8.0 – 10.0 |
15.0 – 17.0 |
| W % |
— |
3.0 – 4.5 |
| Nb % |
3.15 – 4.15 |
— |
| Fe % |
5.0 max |
4.0 – 7.0 |
| Co % |
1.0 max |
2.5 max |
| Tensile Strength (min) |
827 MPa (120 ksi) |
690 MPa (100 ksi) |
| Yield Strength (min) |
414 MPa (60 ksi) |
283 MPa (41 ksi) |
| Elongation (min) |
30% |
40% |
| Max Operating Temp |
982°C (1800°F) |
1038°C (1900°F) oxidizing only |
| PREN * |
50+ |
60+ |
| Density (g/cm³) |
8.44 |
8.89 |
| Flange Spec |
ASTM B564 N06625 |
ASTM B564 N10276 |
| Filler Metal (GTAW) |
ERNiCrMo-3 |
ERNiCrMo-4 |
| Material Cost ($/kg) |
$35 – 45 |
$45 – 55 |
* PREN for nickel alloys is an approximation since the standard PREN formula was developed for stainless steels. Nickel alloy PREN uses Cr + 1.5(Mo+W+0.5Nb) per industry practice.
Detailed Comparison: 5 Critical Differences Engineers Need to Know
1. Chemical Composition & Element Impact — Cr, Mo, and Nb Define the Difference
The chemistry difference is straightforward once you understand what each element does. Inconel 625 packs 20-23% chromium — 6 percentage points more than C276's 14.5-16.5%. That extra Cr is what builds the dense Cr₂O₃ oxide scale that protects 625 at 1800°F. It also makes 625 the better choice in oxidizing environments: nitric acid, aerated solutions, and high-temperature air.
Hastelloy C276 loads up on molybdenum instead — 15-17% vs 625's 8-10%. Mo is the workhorse for reducing acid resistance. In HCl, H₂SO₄, and H₃PO₄, Cr₂O₃ dissolves, and MoO₄²⁻ is what forms the stable passive film. C276 also adds 3-4.5% tungsten, which works synergistically with Mo to resist localized corrosion — crevice and pitting initiation in stagnant acid conditions.
Inconel 625 contains 3.15-4.15% niobium (Nb) — a deliberate strengthening addition that forms gamma-double-prime (γ″) precipitates during hot working. This is why 625 delivers 827 MPa tensile strength vs C276's 690 MPa. Nb has zero corrosion function — it's purely structural. In our QC lab, when PMI shows Nb below 3.0%, the material is rejected regardless of whether it meets every other element — we've had heats where low Nb cut yield strength by 18% and the customer's pressure vessel failed hydrotest.
2. Corrosion Resistance — Reducing vs Oxidizing Acid Showdown
This is where the material selection decision gets made. The corrosion behavior splits sharply along acid type:
| Corrosive Environment |
Inconel 625 Performance |
Hastelloy C276 Performance |
Winner |
| Hydrochloric Acid (HCl), all conc. |
Limited — attack above 5% at RT |
Excellent — <0.13 mm/y at 10% boiling |
C276 dominates |
| Sulfuric Acid (H₂SO₄) |
Good to 40% at 50°C |
Excellent — all concentrations to 70°C |
C276 |
| Nitric Acid (HNO₃) |
Excellent — all conc. to boiling |
Good to 65% at 80°C |
625 dominates |
| Wet Chlorine (Cl₂, moist) |
Poor — rapid pitting |
Excellent — industry standard |
C276 |
| Phosphoric Acid (H₃PO₄) |
Good — industry standard for wet process |
Excellent — especially with fluoride impurities |
C276 (by narrow margin) |
| Seawater (flowing, ambient) |
Excellent — no pitting |
Excellent — no pitting |
Tie — both overkill |
| H₂S (Sour Gas) + Chlorides |
NACE MR0175 Level VII — proven |
NACE MR0175 Level VII — proven |
Tie — 625 preferred for higher strength |
| Chloride SCC |
Immune up to 300°C |
Immune up to 300°C |
Tie — both immune |
Workshop reality: We've shipped both alloys to chemical plants in India and the Middle East. The pattern is consistent — C276 buyers are running HCl or chlorinated solvents; 625 buyers are pushing temperature limits in oxidizing environments. The one call we dread is the buyer who says "just quote me whichever is cheaper." There's no "cheaper" when the wrong choice puts a chemical reactor down for 3 weeks at $80,000/day in lost production.
3. Temperature Performance — 625 Owns High Heat, C276 Handles the Acid Bench
Inconel 625 holds mechanical properties at temperatures where C276 softens. At 650°C (1200°F), 625 retains roughly 65% of its room-temperature yield strength; C276 falls below 50%. The difference is the niobium — gamma-double-prime (γ″) precipitates that pin dislocations and resist creep under sustained load. C276 was never designed for high-temperature strength; its metallurgy is optimized for wet corrosion at temperatures below 400°C.
C276's maximum continuous service temperature is technically higher (1038°C vs 982°C) in clean, oxidizing air — because the Cr₂O₃ + MoO₃ scale is stable at that range. But in any application where strength matters — pressure vessels, bolted flanges, valve bodies — 625's retained strength makes it the practical high-temperature choice. Above 650°C, both alloys require derating per ASME Boiler & Pressure Vessel Code Section II Part D, but 625 starts from a higher baseline.
One temperature consideration our engineers flag: sensitization. C276 is more resistant to intergranular attack in the weld HAZ than 625 because its lower Cr content is compensated by Mo+W that don't form grain-boundary chromium carbides as readily. In applications with repeated welding (field fabrication of complex pipe spools), C276 welds hold their corrosion resistance without the post-weld solution anneal that 625 sometimes needs for critical acid service.
4. Weldability & Fabrication — Both Excellent, Different Fillers, Different Habits
Both alloys weld with GTAW (TIG) and SMAW (stick) using matching composition filler metals. Inconel 625 uses ERNiCrMo-3 (AWS A5.14); Hastelloy C276 uses ERNiCrMo-4. The key difference in the weld pool: C276 is more fluid at welding temperature because the Mo and W lower the melting range slightly and reduce surface tension. 625 is stiffer — the weld bead stays where you put it, which out-of-position welders prefer.
Interpass temperature control is critical for both, but for different reasons. 625 above 150°C interpass risks gamma-double-prime precipitation that embrittles the HAZ and reduces corrosion resistance. C276 above 93°C interpass in some fabrication codes requires an intermediate solution anneal at 1121°C followed by water quenching — expensive and often impractical on-site. Our WPS for both alloys specifies 65-93°C maximum interpass with forced cooling between passes.
For dissimilar welding (625 to C276), ERNiCrMo-3 is the standard filler — it bridges the chemistry gap adequately, but the resulting weld deposit won't match either base metal's corrosion resistance exactly. If the weld will see the worst-case fluid (HCl at elevated temperature), we recommend ERNiCrMo-4 filler and a full solution anneal if geometry permits.
5. Cost Comparison & Total Cost of Ownership
C276 costs 25-30% more than 625 as raw material, but the true cost comparison depends entirely on the application:
| Cost Factor |
Inconel 625 |
Hastelloy C276 |
Impact on TCO |
| Raw material ($/kg) |
$35-45 |
$45-55 |
C276 +25% on material line item |
| Filler metal ($/kg) |
$65-85 |
$70-90 |
Roughly equal — filler is 2-3% of total project welding cost |
| Welding labor |
Standard nickel alloy rate |
Standard nickel alloy rate |
Equal — both require nickel alloy-qualified welders |
| Mill lead time |
4-6 weeks (stocked sizes 3 days) |
5-8 weeks (stocked sizes 3 days) |
625 slightly faster due to larger mill production runs |
| Replacement cost (wrong alloy) |
3-5× material cost |
3-5× material cost |
This is why the right choice matters. Shutdown + teardown + reinstallation dwarfs the material premium. |
HT PIPE's Experience: 625 vs C276 in the Real World
Across 31 nickel alloy inquiries in our CRM, Inconel 625 and Hastelloy C276 together account for 22 inquiries — 71% of the total. 625 leads with 13 (42%) to C276's 9 (29%). The average order value tells a different story: C276 orders average $24,300 vs 625's $18,500. C276 buyers are typically chemical plants buying larger-bore flanges and heavy-wall fittings for severe acid service — higher per-item value, higher total order.
Geographic patterns:
- Middle East / India: 60% C276, 40% 625. Chemical processing and refinery alkylation units dominate C276 demand; oil & gas wellhead equipment drives 625.
- Southeast Asia: 70% 625, 30% C276. Gas turbine exhaust, heat exchangers, and offshore platforms favor 625's high-temperature capability.
- Brazil / South America: 75% 625, 25% C276. Oil & gas upstream and power generation bias toward 625.
- Eastern Europe / CIS: 50/50 split. Chemical and oil & gas roughly balanced.
We stock both alloys in our Zhengzhou warehouse: 625 WNRF flanges 1/2" through 12" Class 150 and 300, plus BW elbows 2" through 8" SCH40S. C276 stocked in WNRF flanges 2" through 8" Class 150, elbows 2" through 6". Non-stock sizes are mill-order with 4-8 week lead time depending on the mill's production schedule.
Project Case Studies from HT PIPE Files
Case 1: Brazil Gas Turbine Exhaust — Inconel 625 Pipe & B564 Fittings
A Brazilian power generation contractor approached us in Q2 2025 for Tubo Inconel 625 (seamless pipe) and B564 N06625 socket weld fittings. The application was a gas turbine exhaust transition duct cycling between 300°F and 1650°F every 12 hours — thermal fatigue and high-temperature oxidation were the primary failure mechanisms. They had previously used 310S stainless steel, which oxidized through 3mm wall thickness in under 2,000 operating hours.
We supplied 18 meters of 6" SCH40S Inconel 625 seamless pipe (VDM Metals heat) plus 22 B564 socket weld tees, elbows, and unions. All items underwent PMI at our factory and were re-inspected by the customer's third-party inspector (SGS) at Shanghai port before loading. Total order: $32,600 FOB. After 18 months of operation with 500+ thermal cycles, the 625 components showed less than 0.05mm of surface oxidation — no measurable wall loss. The client re-ordered an additional 12-meter run for the adjacent turbine unit in Q4 2025.
Case 2: Indian Chemical Plant — Hastelloy C276 for HCl Recovery System
A chemical plant in Gujarat, India, needed Hastelloy C276 WNRF flanges and tees for an HCl recovery system handling 20% hydrochloric acid at 85°C with trace organic chlorides. The existing 316L system had developed through-wall pitting in 11 locations within 16 months — inspection found pit depths exceeding 6mm in 6.35mm wall fittings.
We shipped 8 WNRF N10276 flanges (6" 150# SCH40) and 6 BW tees, all with EN 10204 3.1 MTCs showing actual Mo at 15.8-16.2% and W at 3.9-4.1%. The MTCs included Charpy impact at -196°C (all exceeded 60J) as the client required cryogenic toughness for a planned future process expansion. Total order: $14,800. The plant reports zero corrosion after 10 months of continuous HCl service — C276 paid for itself in avoided downtime within the first year.
Frequently Asked Questions: Inconel 625 vs Hastelloy C276
Q1: Which is better for hydrochloric acid — Inconel 625 or Hastelloy C276?
Hastelloy C276, without question. C276 resists HCl at all concentrations up to boiling point with corrosion rates below 0.13 mm/year. Inconel 625 begins to suffer pitting above 5% HCl at room temperature. The 15-17% Mo in C276 vs 8-10% in 625 is the reason — Mo forms a stable passive film in reducing acid environments where Cr₂O₃ dissolves. If your process fluid includes HCl at any concentration above trace levels, C276 is the correct choice.
Q2: Can Inconel 625 replace Hastelloy C276 to save cost?
Only if the environment is oxidizing and temperature is the main concern. In nitric acid, high-temperature air, or gas turbine exhaust, 625 outperforms C276 and costs 25-30% less. In reducing acids (HCl, H₂SO₄), substituting 625 for C276 will cause rapid failure. We've seen buyers try this substitution on HCl systems and end up re-ordering C276 within 12 months — the "savings" become a 3× loss when you factor in teardown, production downtime, and reinstallation.
Q3: What filler metal is needed for welding 625 to C276?
ERNiCrMo-3 (Inconel 625 filler) is the standard choice for dissimilar welding. It provides adequate corrosion resistance for most mixed-environment applications. If the weld will see HCl or severe reducing acid service, switch to ERNiCrMo-4 (C276 filler) to match the more demanding chemistry. The weld deposit chemistry will never perfectly match either base metal — plan the weld placement so that critical corrosion exposure hits the base metal, not the weld.
Q4: Does Hastelloy C276 have better pitting resistance than Inconel 625?
Yes. C276's PREN equivalent is roughly 60+ vs 625's 50+. The higher Mo (15-17% vs 8-10%) and the addition of 3-4.5% W both contribute to pitting and crevice corrosion resistance. In stagnant chlorides, C276 resists pitting initiation at temperatures 30-40°C higher than 625. For flowing seawater, both are effectively immune — the PREN advantage only manifests in extreme chloride concentrations (50,000+ ppm) and low-flow/dead-leg conditions.
Q5: Why is Inconel 625 stronger than Hastelloy C276?
Niobium. 625 contains 3.15-4.15% Nb, which forms gamma-double-prime (Ni₃Nb) precipitates during hot working. These precipitates pin dislocations and increase yield strength from the solid-solution baseline (~350 MPa) to 414+ MPa. C276 is strictly a solid-solution strengthened alloy — no precipitation hardening — so its strength comes only from Mo and W atoms distorting the nickel lattice. At temperatures above 650°C, 625's Nb-derived strength retention becomes the decisive advantage for pressure-containing applications.
Q6: How does HT PIPE verify the alloy grade before shipping?
Three-layer verification. First, every incoming heat from the mill comes with an EN 10204 3.1 MTC showing full chemical analysis and mechanical properties. Second, our QC team runs PMI (handheld XRF) on 100% of nickel alloy material — we check Cr, Mo, Nb (for 625), and W (for C276). Third, for critical orders, we have a third-party inspector (SGS, Bureau Veritas, or the customer's appointed inspector) witness the PMI and review the MTC. Material that fails PMI at any stage is quarantined, marked REJECT, and returned to the mill.
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