Deformation control during the welding of AP1000 main pump casing and steam generator

• The AP1000 main pump casing and SG outlet nozzle have strict requirements on alignment precision. • A special RCP bracket is needed for precise assembling. • The joint between pump casing and SG should be TIG welded with different alloy materials. • The first few layers of welding have great influences on the pitch angle and the angle change. The welding of the AP1000 Reactor Coolant Pump (RCP) casing and Steam Generator (SG) is an important issue to maintain the integrity of pressure boundary. The position tolerance of pump casing nozzles after welding will directly affect the internal components of the main pump, as well as the on-site assembling processes. This article investigated the method of controlling deformations during welding (such as assembly alignment, groove design, welding process control, etc), in order to prevent excessive welding deformation and therefore extra discrepancies during pump casing positioning. In this paper, we have developed a welding process, which can allow the installations of AP1000 pump casings to meet all nuclear grade requirements.