Welding duplex stainless steel is more sensitive than austenitic grades. The core objective is to control the ferrite/austenite balance in the weld and HAZ (typically 35%–65% ferrite).

Key controls:

1) Heat input: typically 0.5–2.5 kJ/mm depending on thickness and procedure qualification. Too high causes coarse grains and nitride precipitation; too low leaves insufficient austenite and lower corrosion resistance. 2) Interpass temperature: usually below 150°C to avoid overheating. 3) Shielding gas: Ar + N₂ mixtures or nitrogen backing gas help austenite formation. 4) Filler metal: use matching duplex consumables (e.g. ER2209), not 316L. 5) Post-weld: solution annealing is usually not required, but pickle and passivate to restore surface corrosion resistance. 6) Inspection: ferrite content measurement (magnetic/metallographic), pitting and bend tests per code.

Purchasing and construction advice: require WPS/PQR and ferrite test reports; control heat input and interpass temperature on site instead of rushing continuous welding.