Distortion and residual stresses in electron beam-welded hydroelectric turbine materials

Heavy-section assembly of hydroelectric turbine runner materials using single-pass, autogenous EBW was demonstrated to penetrate a 90-mm-thick butt joint. The welding-induced distortions and residual stresses were characterised to understand the impact of the materials and process conditions (e.g. preheating and/or PWHT). Using 3D optical measurements, the angular distortions of EB-welded UNS S41500 and CA6NM steels were determined to be 0.13° and 0.38°, respectively. The longitudinal residual stresses, measured through the contour method, had a M-shaped distribution throughout the thickness with minimum (∼−500 MPa) compressive stresses in the FZ and maximum (∼600 MPa) tensile stresses in the HAZ. After PWHT, the tensile and compressive stresses reduced to ∼100 MPa.