What Is Hastelloy C276?
When to Specify Hastelloy C-276
Hastelloy C-276 (UNS N10276) is a nickel-molybdenum-chromium alloy with tungsten additions, engineered for the most aggressive chemical environments where other alloys fail. It resists both oxidizing and reducing media, handles wet chlorine gas, ferric chloride, and hot contaminated sulfuric acid. C-276 is the “universal” corrosion-resistant alloy; specified when no single corrosion mechanism dominates and the process fluid combines multiple aggressive species.
| Property | Value |
|---|---|
| UNS designation | N10276 |
| Common names | Hastelloy C-276, Alloy C-276 |
| Nickel | Balance (~57%) |
| Molybdenum | 15.0-17.0% |
| Chromium | 14.5-16.5% |
| Tungsten | 3.0-4.5% |
| Iron | 4.0-7.0% |
| Cobalt | 2.50% max |
| Carbon | 0.01% max |
| Tensile strength (min) | 690 MPa (100 ksi) |
| Yield strength (min) | 283 MPa (41 ksi) |
| Elongation (min) | 40% |
| Density | 8.89 g/cm3 |
| Max service temp | 1040°C (1900°F); in oxidizing atmospheres |
| Heat treatment | Solution anneal 1120°C, rapid water quench |
Corrosion Resistance
The very high molybdenum content (15-17%) provides resistance to reducing acids and localized attack. The chromium (14.5-16.5%) handles oxidizing environments. Tungsten enhances resistance to localized corrosion. This triple-defense chemistry makes C-276 uniquely versatile:
| Environment | C-276 Performance |
|---|---|
| Wet chlorine gas | Excellent |
| Ferric chloride | Excellent |
| Sulfuric acid (all concentrations) | Good to excellent |
| Hydrochloric acid (dilute) | Excellent |
| Phosphoric acid (impure) | Excellent |
| Acetic/formic acid | Excellent |
| Chloride SCC | Immune |
| Pitting (seawater) | Immune |
| Oxidizing + reducing mixed media | Superior to all other Ni alloys |
C-276 in the Hastelloy Family
| Alloy | UNS | Mo | Cr | W | Key Advantage |
|---|---|---|---|---|---|
| C-276 | N10276 | 16% | 16% | 3.5% | Best versatility |
| C-22 | N06022 | 13% | 22% | 3% | Better oxidizing resistance |
| C-4 | N06455 | 16% | 16% | - | Thermal stability |
| B-3 | N10675 | 28% | 1.5% | - | Pure reducing acids (HCl, H2SO4) |
C-276 remains the most widely specified grade for general aggressive service. C-22 is preferred when oxidizing conditions dominate.
ASTM Specifications
| Product Form | ASTM Specification |
|---|---|
| Forgings | B564 |
| Seamless pipe and tube | B622 |
| Welded pipe | B619 |
| Plate, sheet, strip | B575 |
| Castings | A494 CW-12MW |
Applications
- Chemical processing: reactor vessels, heat exchangers, and piping for mixed-acid environments
- Flue gas desulfurization: scrubber internals, outlet ducts, and reheater components
- Pharmaceutical: high-purity reactor piping with aggressive cleaning chemicals
- Waste treatment: incinerator off-gas scrubbing, hazardous waste handling
- Oil and gas: sour gas wellhead components, pipeline cladding in highly corrosive production environments
Testing
Mill test certificates per EN 10204 3.1 or 3.2 must report chemistry, mechanical properties, and heat treatment records. Intergranular corrosion testing per ASTM G28 is standard. NDT and hydrostatic testing follow the applicable piping or equipment standard. C-276 has excellent weldability in the solution-annealed condition; matching filler metal ERNiCrMo-4 is used for all welds.
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