Study On Adjusting And Controlling For Welding Residual Stress Field Of Francis Turbine Runners

The turbine runner is the key part which effects efficiency and serving life of turbine units directly. In the large internal power station, working efficiency of hydropower station has been decreased greatly for cracking of large runners regarded highly by all concerned departments. Cracking problem has been approached by waterpower equipment manufacturers of all states, but it is not solved radically. Cracking problem has been one of the key technical difficult subjects in dire need of solving.Cracking reasons of the turbine runner are extensive. The fact shows that the leading reason induced cracking is exorbitant stress. Therefore one of efficiency means to solve cracking problem of runners is to change distribution of welding residual stress of blades, to decrease welding residual tensile stress in the dangerous area of blades or even turn to compressive stress.The welding technology of Francis turbine runners is optimized from the view of subsection welding and local heating by numerical simulation. The result shows that Welding residual tensile stress appears in the weld and its area nearby,and peak stress appears in the dangerous area of blades after practising quondam welding technology ;Welding residual tensile peak stress in the dangerous area of blades can be decreased by welding both ends earlier and then welding middle section later during subsection welding, and decreasing effect on welding residual stress of the subsection welding is related to the weld length of blade outlets and welding direction of each subsection; Decreasing effect on residual stress of the local heating is direct proportional to heating time, heating temperature, heating area, and inversely proportional to cooling area, and welding residual tensile peak stress in the dangerous area is decreasing trend earlier ,and then increasing trend later with heated location increased.On basis of numerical simulation, the optimized weling technological has been vadidated and adjusted by plane test, results show that residual stress of both ends welded in advance can be decreased by the interspace welded later, and decreasing effect is the most obvious in the 50mm range of the interspace;For local heating, it is 60mm from the edge of heated area to decrease residual stress...