This TIP contains guidelines for the open root joint welding of 6% molybdenum austenitic stainless steel pipe with the gas tungsten arc welding (GTAW) process and hand-fed filler metal. These guidelines include welding procedure specification elements designed to provide root pass welds enriched in molybdenum. The higher molybdenum content filler metal compensates for molybdenum segregation in the cast weld metal. The standard filler metal for 6% Mo stainless steel is a nickel-base alloy with a nominal 9% or greater molybdenum content. The guidelines describe welding joint designs, weld fit-up, and tacking practices that allow adequate filler metal addition in the root pass. Other elements of typical root pass welding procedure are also described.
The guidelines may be used as a basis for developing welding procedures agreeable to the owner and piping fabricator. The agreement should cover the quality control measures and any standards that may be involved. All welding procedures, welder, and welding operators should be qualified in accordance with Section IX of the ASME Boiler and Pressure Vessel Code or other applicable jurisdictional code requirements.
