Current steel forgings for steam generator (SG) of PWR plant are reviewed in the aspect of design and material improvement. The following three items are introduced.
1. The use of integral type steel forgings for the fabrication of steam generator enhances the structural integrity and makes easier fabrication and inspection including in-service inspection . The following examples of current integral type forgings developed by the Japan Steel Works, Ltd. (JSW) are introduced (1)Primary head integrated with nozzles, manways and supports (2)Steam drum head integrated with nozzle and handhole (3)Conical shell integrated with cylindrical sections and handholes
2. In order to decrease the weight of steam generator, the high strength materials such as SA508, C1.3a steel have been adopted in some cases. The properties of this steel are introduced and the chemistry and heat treatment condition are discussed.
3. As one of the methods to minimize the macro- and micro-segregations, the use of vacuum carbon deoxidization (VCD), i.e. deoxidization of steel by gaseous CO reaction, with addition of Al for grain refining was investigated. The properties of SA508, C1.3 steels with Low Si content are compared with those of conventional one.