Choice of welding consumable and procedure qualification for welding of 304HCu austenitic stainless steel boiler tubes for Indian Advanced Ultra Super Critical power plant

India has embarked on a mission programme for setting-up a coal-fired 800 MWe Advanced Ultra Super Critical (AUSC) power plant with steam parameters of 710/720 degrees C temperature and 30,400 kPa pressure. To implement this programme, India-specific version of 304HCu austenitic stainless steel (SS) and nickel-base Alloy 617M boiler tubes has been developed in collaboration with Indian manufacturers. The objective of the present study is to choose the appropriate gas tungsten arc (GTA) welding consumable for welding of 304HCu SS/304HCu SS and 304HCu SS/Alloy 617M dissimilar weld joints. Welding procedure specification (WPS) was prepared by using three types of filler wires, viz. ER304HCu, ERNiCrMo-3 and ERNiCrCoMo-1, for the 304HCu SS tube weld joints and ERNiCrCoMo-1 for the 304HCu SS/Alloy 617M dissimilar tube weld joints. Welding procedure qualification (WPQ) was carried out as per ASME Sec. IX requirements. Tube weld joints were also fabricated for evaluation of mechanical properties and for microstructural characterisation. Based on the detailed evaluation of mechanical properties, including creep, ER304HCu has been chosen for the similar welding of 304HCu SS and ERNiCrCoMo-1 for the dissimilar metal welding between 304HCu SS and Alloy 617M.