Nickel Alloy 625 vs C-276 Selection Guide: Complete Comparison for Corrosive Service 2026
When engineering components for highly corrosive environments, two nickel-based alloys dominate the specification sheets: Inconel 625 (UNS N06625) and Hastelloy C-276 (UNS N10276). Both offer exceptional corrosion resistance, but their compositions, mechanisms, and cost profiles differ significantly.
This guide provides a side-by-side comparison to help engineers, procurement managers, and project teams select the right alloy for demanding applications in chemical processing, oil & gas, marine, and pollution control.
Chemical Composition Comparison
| Element | Inconel 625 (%) | Hastelloy C-276 (%) |
|---|---|---|
| Nickel (Ni) | 58.0 min | Balance (57-63) |
| Chromium (Cr) | 20.0 – 23.0 | 14.5 – 16.5 |
| Molybdenum (Mo) | 8.0 – 10.0 | 15.0 – 17.0 |
| Iron (Fe) | 5.0 max | 4.0 – 7.0 |
| Columbium (Cb/Nb) | 3.15 – 4.15 | — |
| Tungsten (W) | — | 3.0 – 4.5 |
| Cobalt (Co) | 1.0 max | 2.5 max |
| Carbon (C) | 0.10 max | 0.01 max |
| Manganese (Mn) | 0.50 max | 1.0 max |
| Silicon (Si) | 0.50 max | 0.08 max |
| Phosphorus (P) | 0.015 max | 0.04 max |
| Sulfur (S) | 0.015 max | 0.03 max |
Key Compositional Differences
- C-276 has much more Mo (15-17% vs 8-10%) → Superior pitting and crevice corrosion resistance in chloride environments
- C-276 has extremely low carbon (0.01% max) → Minimal sensitization risk, better weldability without post-weld heat treatment
- 625 has Cb/Nb (3.15-4.15%) → Strength through solid solution + precipitation strengthening
- 625 has higher Cr (20-23% vs 14.5-16.5%) → Better oxidation resistance at high temperatures
- C-276 contains W (3-4.5%) → Additional solid solution strengthening and localized corrosion resistance
Mechanical Properties Comparison
| Property | Inconel 625 | Hastelloy C-276 |
|---|---|---|
| Tensile Strength (min, MPa) | 896 (annealed) / 1034 (cold-worked) | 790 (annealed) |
| Yield Strength (min, MPa) | 448 (annealed) / 690 (cold-worked) | 365 (annealed) |
| Elongation (min, %) | 30 | 40 |
| Hardness (HB) | 220-340 | 200-230 |
| Max Service Temperature (°C) | 980°C (continuous) / 1095°C (intermittent) | 400°C (recommended max for corrosion) |
| Density (g/cm³) | 8.44 | 8.89 |
Corrosion Resistance Comparison
General Corrosion
- 625: Excellent in oxidizing environments (nitric acid, chromic acid)
- C-276: Superior in reducing environments (sulfuric acid, hydrochloric acid, phosphoric acid)
Pitting and Crevice Corrosion
| Parameter | Inconel 625 | Hastelloy C-276 |
|---|---|---|
| PREN | 50 | 69 |
| Critical Pitting Temperature (CPT) in 6% FeCl₃ | 50°C | ≥85°C |
| Critical Crevice Corrosion Temperature (CCT) | 25-35°C | >40°C |
C-276 is clearly superior for pitting/crevice corrosion due to its higher Mo content and higher PREN value.
Stress Corrosion Cracking (SCC)
- 625: Excellent resistance to chloride SCC
- C-276: Excellent resistance to chloride SCC and additionally resistant to polythionic acid SCC
High-Temperature Corrosion
- 625: Superior oxidation resistance up to 980°C; excellent resistance to carburization
- C-276: Not recommended for continuous service above 400°C in corrosive environments; forms detrimental phases (sigma, mu) at 540-870°C during prolonged exposure
Application-Specific Selection Guide
| Application | Recommended Alloy | Reason |
|---|---|---|
| Flue gas desulfurization (FGD) systems | C-276 | Superior resistance to chloride-containing acidic condensates |
| Chemical reactor vessels (H₂SO₄ service) | C-276 | Best resistance to reducing acids across all concentrations |
| Subsea piping and risers | 625 | Excellent SCC resistance, high strength, proven track record |
| Exhaust ducting and expansion joints | 625 | High-temperature oxidation resistance |
| Offshore platform firewalls | 625 | Fire resistance + corrosion resistance combination |
| Pickling tanks and heating coils | C-276 | Resistance to HCl and HNO₃ at all concentrations |
| Heat exchanger tubing (high-temp) | 625 | Superior high-temperature strength and oxidation resistance |
| Pharmaceutical process equipment | 625 or C-276 | Both acceptable; C-276 for aggressive cleaning chemicals |
Welding Comparison
| Factor | Inconel 625 | Hastelloy C-276 |
|---|---|---|
| Weldability | Good — may require PWHT for thick sections | Excellent — low carbon minimizes sensitization |
| Filler Metal | ERNiCrMo-3 (Alloy 625) | ERNiCrMo-4 (Alloy C-276) |
| Hot Cracking Susceptibility | Moderate (higher Cb content) | Low (very low carbon) |
| Post-Weld Heat Treatment | Not required for most services | Not required |
Cost Comparison
As a general guide (prices fluctuate with nickel, molybdenum, and tungsten markets):
- Hastelloy C-276 is typically 15-25% more expensive than Inconel 625
- The price premium comes from higher Mo content (15-17% vs 8-10%) and tungsten addition (3-4.5%)
- Molybdenum prices are typically 2-3× the price of nickel per kilogram
- Total installed cost should be evaluated — C-276’s longer service life in severely corrosive service may justify the premium
Availability and Product Forms
Both alloys are available in:
- Plate, sheet, and strip
- Seamless pipe and tube
- Welded pipe and tube
- Bar, rod, and wire
- Fittings (elbows, tees, flanges, forgings)
- Fasteners
Inconel 625 generally has shorter lead times due to higher production volume and more mill sources worldwide.
Standards and Specifications
| Product Form | Inconel 625 | Hastelloy C-276 |
|---|---|---|
| Plate/Sheet/Strip | ASTM B443, B906 | ASTM B574, B906 |
| Seamless Pipe/Tube | ASTM B444, B704, B705 | ASTM B622, B619, B626 |
| Bar/Rod | ASTM B446 | ASTM B574 |
| Fittings | ASTM B366 | ASTM B366 |
| Forgings | ASTM B564 | ASTM B564 |
Sourcing Nickel Alloys
When procuring nickel alloy products:
- Always request Mill Test Certificates (MTC EN 10204 3.1)
- Verify chemical composition meets specification limits
- For critical services, specify supplementary requirements (PMI testing, NDE)
- Confirm the heat treatment condition (solution annealed per the relevant standard)
CoreMetal Steel supplies Inconel 625 and Hastelloy C-276 in all product forms including pipe, tube, plate, fittings, and fasteners, with full material traceability and competitive pricing.
Conclusion
The choice between Inconel 625 and Hastelloy C-276 depends on your specific service environment: choose C-276 for severe localized corrosion in reducing acids and chloride-containing media; choose 625 for high-temperature applications, superior strength requirements, and oxidizing environments. In many cases, a life-cycle cost analysis — considering both material cost and expected service life — provides the best basis for selection.