ASTM A790 UNS S31803/S32205 duplex stainless steel pipe coupons feature a balanced two-phase microstructure of approximately 50% ferrite and 50% austenite. This dual-phase structure provides roughly twice the yield strength of austenitic grades while maintaining superior corrosion resistance, particularly against chloride-induced stress corrosion cracking.

Type 2205 duplex stainless contains approximately 22% chromium, 5% nickel, 3% molybdenum, and nitrogen additions that stabilize the austenite phase and enhance pitting resistance. The PREN (Pitting Resistance Equivalent Number) exceeds 35, indicating excellent resistance to localized corrosion in chloride environments.

Performance Advantages

The balanced microstructure delivers yield strength typically 65-80 ksi, approximately double that of 316L stainless steel. This higher strength allows for thinner wall construction, reducing material costs and installation weight. Duplex 2205 provides exceptional resistance to chloride stress corrosion cracking, a failure mode that plagues austenitic stainless steels in hot chloride service.

Target Applications

Offshore oil and gas production platforms, chemical tankers and process piping, pulp and paper digesters and bleach plants, desalination systems, heat exchangers in brackish or seawater service, and geothermal piping systems leverage the unique properties of duplex 2205. The material performs well in both oxidizing and reducing environments.

Critical Welding Considerations

Welding duplex stainless requires careful heat input control to maintain balanced microstructure. Excessive heat input promotes ferrite formation and reduces toughness and corrosion resistance. Filler metal ER2209 is overalloyed with nickel to compensate for preferential ferrite formation during solidification. Heat input should range from 0.5 to 2.5 kJ/mm. Interpass temperature must not exceed 300°F. Root pass back purging with nitrogen-enhanced argon mixtures improves corrosion resistance and aids austenite formation.

Post-weld solution annealing is generally not required but may be specified for critical corrosion service to optimize phase balance and dissolve any detrimental secondary phases.