Weld Procedure Specification (WPS) Addendum for Super Duplex Stainless Steels

Super duplex stainless steels (SDSS) exhibit exceptional strength and corrosion resistance due to their approximately 50:50 austenite–ferrite microstructure and high chromium, molybdenum, and nitrogen content. However, this microstructure is highly sensitive to thermal cycles during welding; excessive heat input or slow cooling can precipitate brittle intermetallic phases (e.g., sigma phase above 600–1000°C) or Cr₂N nitrides in the ferrite-rich regions, severely degrading toughness and localized corrosion resistance. The WPS Addendum therefore serves as a domain-specific technical safeguard—building upon ASME Section IX, ISO 15614-1, and ASTM A923 test requirements—to codify empirically validated welding parameters that maintain phase balance (typically 35–65% ferrite), minimize time-at-temperature in critical ranges, and ensure adequate nitrogen retention through controlled shielding gas composition (e.g., N₂ additions to Ar/He mixtures). It also integrates mandatory verification protocols such as ferritoscope measurements, intergranular corrosion testing (ASTM A923 Method C), and microstructural examination (ISO 17638) to confirm conformance. In practice, the addendum functions as both a qualification boundary document and a field execution guide—used by welding engineers, inspectors, and fabricators in offshore oil & gas, desalination plants, and chemical processing systems where SDSS integrity is mission-critical.