Hastelloy C-276 vs C-22 Pipe Fittings: Service and Welding

Key performance markers reported by Haynes International and downstream sources:

• C-22 critical pitting temperature: above 150 degC in standard test environments.
• C-22 critical crevice temperature: around 102 degC.
• C-22 is markedly more resistant to wet chlorine than C-276.
• C-276 has higher Mo + W and outperforms C-22 in many reducing-acid services such as concentrated HCl.

Decision matrix

Both grades are routinely used in the as-welded condition. C-276 is well known for resisting grain-boundary precipitation in HAZ. C-22 is also used as a filler metal because of its strong over-alloying margin and good weldability.

For seamless butt-welding pipe fittings in C-276 or C-22, the standard delivery condition is solution annealed (typically around 1120-1150 degC) followed by rapid quench, which dissolves intermetallic phases.

Common procurement mistakes

1. Specifying C-276 for hot wet chlorine service by default. C-22 is the better choice in this environment.
2. Substituting C-22 for C-276 in concentrated HCl without re-verifying corrosion data. The two alloys are not interchangeable in reducing acids.
3. Skipping ASTM G28 corrosion testing on the fittings. This is the standard intergranular attack test and should be on the MTC for critical service.
4. Mixing C-276 and C-22 in the same weld joint without filler qualification. Use ERNiCrMo-10 (for C-276) or ERNiCrMo-22 (for C-22) deliberately.
5. Ignoring the iron upper limit. Fe content above the spec ceiling indicates dilution and can change corrosion behaviour.

Buyer checklist

• Confirm UNS N10276 or N06022 on every MTC and via PMI.
• Require ASTM G28 Method A or B intergranular corrosion test on the supplied condition.
• Specify solution-annealed and water-quenched delivery state.
• For forged flanges and pipe bends, check that hot working has been followed by full re-solution annealing.
• Cross-reference our certificates for nickel alloy quality system records.
• Send your enquiry through our inquiry form with corrodent, concentration and temperature.

Sources

• https://www.csidesigns.com/blog/articles/hastelloy-c-22-or-hastelloy-c-276-which-is-right-for-your-processing-environment
• https://haynesintl.com/en/hastelloy-c-22-c-276-alloys-in-saturated-wet-chlorine/
• https://msestudent.com/hastelloy-c-276-composition-properties-and-applications/