Abstract: The structure features of 1000 MW ultra-supercritical turbine produced by Siemens, the type of LP (low pressure) outer cylinder structure and its assemble welding procedures were introduced. The field-assembly and welding are the heavy work because the outer casing has large volume, many and long welding seams. The low quality of assembly and the large welding deformation would cause the clearance occurring in horizontal split, vacuum leakage and dislocation of bolt hole. The assemble welding technology was adopted in welding of top half and lower half of LP outer cylinder, so its deformation could be controlled in field-assembly. The main control points of melding in LP outer cylinder were described according to the control requirement.

Key words: 1000 MW ultra-supercritical turbine, LP outer cylinder, assemble welding, deformation control, main control points