Accumulator middle tread run is welded by submerged arc welding for HL1000 nuclear plant in China. The welding is performed with the combination of sphere positioner and narrow gap submerged arc welding machine

and the automation welding of sphere arc-shaped curve welds of ACC middle tread run is realized. The influence factors for welding quality are discussed from material

welding current

voltage

rolling speed of the positioner and weld groove type. The measures are adopted from the design of groove

the selection of welding methods

the control of the size of middle tread run

the control of assembly size

the control of welding process

the welding sequence and so on

and the technology planning is done in all directions. Finally

the welding of three accumulator middle tread runs for HL1000 nuclear plant is accomplished.