Temperature profile optimization in a new robotic local induction heat treatment process

Abstract Post-weld heat treatment (PWHT) restores mechanical properties and relieves internal stress present in hydraulic turbine runners assembled by welding. For many aging turbines, PWHT is needed to ensure high-quality repairs. It is impossible, however, to dismantle large runners or other such steel equipment and take it to a furnace. A new robotic process was thus developed to perform local induction heat treatment in situ. Heat is generated by moving an induction coil back and forth over a specific area. The critical factor in this process is to maintain a uniform temperature profile within a precise range. A method combining finite element analysis and optimization is proposed to set heating parameters. Through a series of stationary and transient thermal analyses, the heating path and parameters are optimized to achieve a uniform temperature profile. The method was tested by performing robotic PWHT in the laboratory. Results show good agreement between simulations and measurements.