Robotic post-weld heat treatment for in situ repair of stainless steel turbine runners

This paper presents a new robotic heat treatment process designed to performed in situ interventions in hydroelectric turbine runners. Considering the down-time required to dismantle a turbine unit, most utilities perform in-situ inspections and interventions to address issues such as cavitation and cracking. Repairs are primarily done by welding. Lacking a solution to perform in situ heat treatment, quality repair are impossible on modern martensitic stainless steel turbine runner. To perform on site local short duration post weld heat treatment, an induction heating system is coupled to a portable robot that can access the confined space between runner blades. The robot moves a pancake coil to inject heat and control temperature distribution to satisfy heat treatment requirements. A simulator using thermal finite element analysis is used for path planning. The system is validated on a full size Francis turbine runner blade.