Development of integral type forgings for steam generator of nuclear power plant

The use of integral type steel forgings for the construction of pressure vessel enhances the structural integrity of components and makes the fabrication of components and the execution of in-service inspection (ISI) easier than those fabrication from plate and casting materials. Such steel forgings have been realized for steam generator (SG) for nuclear power plant as follows : (1) Forged shell ring : change from welding fabrication of formed plates to forging ; (2) Forged conical shell ring : ditto ; (3) Forged head integral with nozzles (s) : (i) Primary head : change from casting to forging ; (ii) Secondary head : change from welding fabrication of formed plates to forging. These steel forgings have been realized by recent development in manufacturing technologies, such as steel making, forging processes and heat treatment which are vital to the quality of steel forgings. Some examples of recent typical high quality steel forgings developed by the Japan Steel Works, Ltd. (JSW) are introduced, and the main points of the manufacturing technique and the quality attained are also described. (author)