Hastelloy C-276 vs Hastelloy C-22
Hastelloy C-276 and C-22 are Ni-Cr-Mo corrosion alloys. C-22 is the next-generation variant with higher Cr and lower impurities, giving it better resistance to oxidising media and localised corrosion.
Hastelloy C-276
UNS N10276
Composition (wt %)
| Element | Min | Max |
|---|---|---|
| Ni | 54.0 | 100.0 |
| Mo | 15.0 | 17.0 |
| Cr | 14.5 | 16.5 |
| Fe | 4.0 | 7.0 |
| W | 3.0 | 4.5 |
| Co | 0.0 | 2.5 |
Hastelloy C-22
UNS N06022
Composition (wt %)
| Element | Min | Max |
|---|---|---|
| Ni | 56.0 | 100.0 |
| Cr | 20.0 | 22.5 |
| Mo | 12.5 | 14.5 |
| W | 2.5 | 3.5 |
| Fe | 2.0 | 6.0 |
| Co | 0.0 | 2.5 |
Key differences
| Aspect | Hastelloy C-276 | Hastelloy C-22 | Engineering impact |
|---|---|---|---|
| Chromium content | 14.5-16.5% Cr | 20.0-22.5% Cr | Higher Cr in C-22 improves resistance to oxidising acids (nitric, hot concentrated sulphuric) and pitting. |
| PREN (pitting resistance) | ~65-70 | ~70-75 | Both are excellent; C-22 has a margin in hot chloride service and mixed-acid environments. |
| Best-in-class environments | Reducing acids (HCl, H2SO4), FGD | Oxidising acids + mixed media, hot chloride | Choose C-276 for known reducing service, C-22 when the process alternates between oxidising and reducing states. |
| Weldability | Excellent - matching filler standard | Excellent - matching filler standard | Both weld without filler substitution. C-22 has marginally lower HAZ precipitation risk due to reduced impurities. |
When to choose Hastelloy C-276
- Flue gas desulphurisation (FGD) absorbers
- Pulp and paper bleach plants
- Hydrochloric acid service
When to choose Hastelloy C-22
- Mixed-acid and changing-chemistry chemical plants
- Nuclear waste containers
- Hot seawater and brine service
Frequently asked questions
Is C-22 always better than C-276?
No. In pure reducing service (e.g. HCl), C-276 can outperform because Mo content matters more than Cr. C-22 wins in oxidising or swinging-redox service.
Are the two alloys interchangeable in piping specs?
Some specs (e.g. NACE MR0175) list both, but mill certs must match the specific UNS number called out (N10276 vs N06022).
What is PREN and why does it matter?
PREN = %Cr + 3.3 x %Mo + 16 x %N is an empirical index of pitting resistance. Higher is better for chloride service, though it is not a complete predictor on its own.