Hastelloy C‑22 (UNS N06022) and Hastelloy C‑276 (UNS N10276) are widely‑used nickel‑molybdenum‑chromium corrosion‑resistant alloys for grounding rings and electrodes of electromagnetic flowmeters. Both alloys resist oxidizing and reducing corrosive media. Due to different chemical compositions, C‑276 features higher molybdenum‑tungsten content while C‑22 contains higher chromium content, resulting in clear differences in corrosion resistance, weld performance and service suitability, especially for flange‑gap structures prone to crevice corrosion such as grounding rings.
Hastelloy C‑276 (UNS N10276)
Advantages
Superior performance in pure reducing‑acid environments such as dilute hydrochloric acid and dilute sulfuric acid with low oxidizing impurities. Well‑proven industrial grade, abundant stock and competitive cost. Suitable for flue‑gas desulfurization slurry and hydrometallurgical wastewater dominated by reduction reactions.
Limitations
Corrosion rate rises rapidly in media containing nitric acid, wet chlorine, hypochlorite or ferric ions. Corrosion resistance degrades in the weld‑affected zone; post‑weld solution heat‑treatment is recommended. Lower critical crevice‑corrosion temperature, higher risk of local pitting under high‑chloride high‑temperature conditions.
Recommended applications: Desulfurization systems, hydrometallurgy, normal‑temperature reducing wastewater with few oxidizing impurities, cost‑sensitive projects.
Not recommended: Conditions with nitric acid, wet chlorine, ferric/copper ions, high‑temperature high‑chloride fluids and variable‑composition process media.
Hastelloy C‑22 (UNS N06022)
Advantages
Higher chromium content delivers outstanding resistance to oxidizing media including nitric acid, mixed acids, wet chlorine and ferric‑ion‑contaminated acids. Excellent as‑welded performance, no post‑weld heat‑treatment required. Higher critical pitting & crevice‑corrosion temperature, greatly mitigating flange‑gap crevice‑corrosion risks. High tolerance for fluctuating oxidizing‑reducing mixed wastewater.
Limitations：Slightly inferior corrosion resistance compared with C‑276 in pure low‑temperature reducing acid. Higher material cost and less available spot stock.
Recommended applications: Fine‑chemical and pharmaceutical wastewater with variable compositions, media containing nitric acid / wet‑chlorine / hypochlorite, high‑temperature high‑chloride pipelines, instrument components unable to receive post‑weld heat‑treatment, long‑life maintenance‑free equipment.
Not recommended: Simple low‑temperature dilute‑acid projects with tight‑budget constraints.
Conclusion
- Select C‑276 for clean reducing‑acid service without oxidizing impurities when cost‑efficiency is prioritized.
- Select C‑22 for complex media, oxidizing contaminants, high‑temperature service and as‑welded instrument parts requiring long‑term reliability.
Crevice corrosion is the dominant failure mode for grounding‑ring assemblies. For complicated chemical processes and unstable process fluids, Hastelloy C‑22 provides superior comprehensive stability and is the preferred premium grade for anti‑corrosion flow‑meter components.
