Hastelloy C276 vs Inconel 625:
Which Alloy for Your Application?
Two of the most widely used nickel alloys in chemical, offshore, and refinery applications — but they are not interchangeable. Selecting the wrong one can mean premature failure, or paying 30-50% more than necessary. This guide breaks down the real differences.
Quick Summary
Choose C276 when your primary enemy is corrosion — especially reducing acids (HCl, H₂SO₄), wet chlorine, and chloride pitting.
Choose 625 when you need strength at temperature — above 500°C, pressure vessels, and seawater service where crevice corrosion is the concern.
Chemical Composition
| Element | C276 (%) | 625 (%) | Impact |
|---|---|---|---|
| Ni | Bal (57) | Bal (62) | Both nickel-based |
| Mo | 15–17 | 8–10 | C276: superior reducing acid resistance |
| Cr | 14.5–16.5 | 20–23 | 625: better oxidation resistance |
| W | 3–4.5 | — | C276: tungsten boosts crevice corrosion resistance |
| Nb+Ta | — | 3.15–4.15 | 625: niobium provides precipitation hardening |
| Fe | 4–7 | 5 max | — |
Key takeaway: C276 has nearly double the molybdenum + tungsten. This is what makes it the king of reducing-environment corrosion. 625 has more chromium + niobium, giving it high-temperature strength.
Corrosion Resistance Head-to-Head
| Environment | C276 | 625 | Winner |
|---|---|---|---|
| Hydrochloric acid (all conc.) | Excellent | Good (dilute only) | C276 |
| Sulfuric acid (50–70%) | Excellent | Good below 40% | C276 |
| Wet chlorine / hypochlorite | Excellent | Fair | C276 |
| Seawater (ambient) | Excellent | Excellent | Tie |
| Seawater (crevice, 60°C+) | Excellent | Good | C276 |
| Oxidizing acids (HNO₃) | Fair | Good | 625 |
| High-temp oxidation (800°C+) | Poor | Good | 625 |
Mechanical Properties
| Property (RT) | C276 | 625 |
|---|---|---|
| Tensile Strength (MPa) | 690 | 827 |
| Yield Strength (MPa) | 283 | 414 |
| Elongation (%) | 40 | 30 |
| Hardness (HRB) | 90 | 95 |
| Max Service Temp | ~400°C | ~700°C (precipitation hardened) |
625 is significantly stronger — 46% higher yield strength at room temperature, and retains strength at elevated temperatures where C276 softens. If your design is stress-controlled above 500°C, 625 is often the only choice.
Weldability
C276: Excellent weldability with matching filler (ERNiCrMo-4). Low carbon means minimal sensitization. Can be welded in all positions. No post-weld heat treatment required.
625: Good weldability with ERNiCrMo-3 filler. Niobium can cause microfissuring in highly restrained joints. Solution anneal after welding recommended for critical service.
Price Comparison (2026)
| Form | C276 ($/kg) | 625 ($/kg) | Premium |
|---|---|---|---|
| Sheet 2mm | 42–48 | 32–38 | C276 ~35% higher |
| Bar 50mm | 38–44 | 28–34 | C276 ~35% higher |
| Pipe 2" SCH40 | 55–65 | 42–50 | C276 ~30% higher |
C276 is consistently 30-35% more expensive due to higher molybdenum and tungsten content. Don't overspecify C276 when 625 is sufficient — the cost savings on a large project can be substantial.
Decision Flowchart
Step 1: Is reducing acid (HCl, H₂SO₄, wet Cl₂) the primary corrosion mechanism? → Yes = C276
Step 2: Is service temperature above 500°C? → Yes = 625
Step 3: Is high mechanical strength required (pressure vessel, shaft)? → Yes = 625
Step 4: Seawater service below 60°C? → Either works, 625 is cheaper
Step 5: Crevice corrosion risk in hot chloride? → C276
Common Applications Summary
| Application | Recommended | Why |
|---|---|---|
| FGD scrubber internals | C276 | Wet SO₂ + chloride pitting |
| Sour gas piping (NACE) | C276 | H₂S + chloride resistance |
| Heat exchanger (seawater) | 625 | Strength + adequate corrosion |
| Offshore fasteners | 625 | High strength + seawater |
| Chlor-alkali equipment | C276 | Wet chlorine resistance |
| Gas turbine components | 625 | High-temp strength |
| Pharmaceutical reactors | C276 | Universal acid resistance |
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