Hot Radial Upset-Extruding Process for Tube Structure with a Nozzle of 316LN Stainless Steel

Abstract

AP1000 nuclear power main pipe, a type of complicated thick-walled tube structure with both high and thick-walled nozzles, is one of the key parts in nuclear island. It is required to be manufactured by integral plastic forming technique. Up to now, no economical and efficient plastic forming process for AP1000 main pipe has been reported. To aim for forming the tube structure with a nozzle such as AP1000 main pipe, a radial upset-extruding (RUE) process was developed, in which the initial billet is an extruded tube with a hole. RUE process is an extrusion method which realizes radial outflow of the metal around the hole of tube billet through an axial upsetting force and restriction of dies. Thick-walled tube structure with a nozzle derived from AP1000 main pipe was simplified to be a thick-walled three-way pipe, on which RUE process was analyzed based. Combined with reduced scale model experiments, thermomechanical coupled finite element analysis integrated with recrystallization models of 316LN was performed to investigate RUE process. Metal flow, deformation distribution, recrystallization distribution, and extrusion load and clamping load in RUE process was analyzed. The experimental workpiece of pure lead based on reduced scale model validate metal flow behavior predicted by using numerical simulation. The results indicate that the essence of RUE process is to deflect the flow of the material around the orifice of the tube billet. The loads of dies are significantly sensitive to the initial forming temperature and the friction coefficient, while the impact of the extrusion velocity is negligible. RUE process could be used to form thick-walled tube structure with a nozzle, and it has a potential for solving the manufacture of AP1000 main pipe.