Experimental Study of the Effects of Welding Depth and Heat Treatment on Residual Stresses in a Cracked Rotor

One of the important issues in power plants is the occurrence of cracks on the steam turbine rotor. Removing cracks by machining is a common repair method to prevent crack propagation and failure. However, excess machining and reducing the rotor radius is limited. Therefore, welding the machined zone is a good way to repair the rotor. In this paper, the effects of welding depth and heat treatment on residual stresses of a laboratory sample of a welded power plant rotor have been investigated. For this purpose, a minimized model of the turbine rotor made of VCN200 with two V-shaped grooves has been prepared and then the grooves have been, respectively, filled by 7- and 32-pass welding after preheating. Afterward, residual stresses in different rotor zones (welded and non-welded zones), before and after stress relieving heat treatment, have been measured by the hole drilling method. Results showed the presence of residual stresses in all areas of the rotor before heat treatment, i.e., tensile residual stresses in non-welded and 7-pass welded areas and compressive residual stresses in 32-pass welded area. The results also showed stress relieving heat treatment led to a significant reduction in residual stresses in all studied areas.