ASTM B622 UNS N10276 Hastelloy C-276 pipe coupons provide universal corrosion resistance in both strongly oxidizing and reducing environments, making this nickel-molybdenum-chromium alloy the material of choice for the most aggressive chemical processing applications. C-276 resists the formation of grain boundary precipitates in the weld heat-affected zone, maintaining corrosion resistance as-welded.

Hastelloy C-276 contains approximately 57% nickel, 16% chromium, 16% molybdenum, and 4% tungsten. This chemistry provides resistance to localized corrosion, stress corrosion cracking, and general corrosion in oxidizing acids, reducing acids, chloride solutions, and mixed acid environments where conventional materials fail.

Chemical Processing Excellence

C-276 handles sulfuric acid across all concentrations and temperatures, hydrochloric acid, phosphoric acid, acetic acid and acetic anhydride, chlorine and chlorine-contaminated media, formic acid, hypochlorite and chlorine dioxide solutions, and wet chlorine gas. The alloy serves in pollution control scrubbers, pulp and paper digesters, pesticide production, and pharmaceutical synthesis where material versatility is paramount.

Performance in Extreme Environments

The high molybdenum and tungsten content provides exceptional resistance to reducing environments, while chromium content ensures performance in oxidizing conditions. This balanced chemistry allows C-276 to handle process upsets and varying conditions without material failure. Resistance to pitting and crevice corrosion in hot contaminated mineral acids exceeds that of more common nickel alloys.

Flue Gas Desulfurization

Hastelloy C-276 has become the standard material for flue gas desulfurization systems in coal-fired power plants, where it must resist hot sulfuric acid condensate, chlorides from coal combustion, and oxidizing conditions. The material’s longevity in these demanding applications justifies the premium cost through reduced maintenance and downtime.

Welding Considerations

Welding requires ERNiCrMo-4 filler metal and meticulous cleanliness. GTAW is standard for critical applications. Heat input should be minimized to prevent excessive grain growth. No preheat is required or desired. Interpass temperature should not exceed 200°F. Back purging with argon prevents oxidation. The low carbon content prevents sensitization, and post-weld heat treatment is generally not required.