Abstract: The low pressure cylinder of ultra supercritical unit in Yuhuan Power Plant of China Huaneng Group has larger contour structure size.By adopting rationale method and scientific welding process: CO2 gasshield welding + synchronous section backwards welding process, the deformation in assembling and welding of low pressure cylinder was controlled effectively, the deformation values were smaller than the design values. This experience could be a useful reference for the assembling and welding of other ultra supercritical unit.

Key words: low pressure cylinder assembling, metal gas-shield welding, deformation control