Study on Forging Technology of Integrated Topcover Forging for AP1000 Reactor Pressure Vessel

Abstract

AP1000 topcover forging, as a key component in the Reactor Pressure Vessel (RPV), is located at the top of the RPV and is an important reactor primary component within the pressure boundary of the primary circuit, and its integrity is of great significance to the safe operation of nuclear power equipment. The traditional topcover part is welded by three parts: the upper head, the topcover flange and the stacking tube socket. When the components are in service, the in-service inspection workload of the equipment is large, and the safety risk is high under complex working conditions. Therefore, the study of a large forging integrated top cover with a stacking tube socket is carried out to realize the upper head, the topcover flange and the stacking tube as integrated topcover. The integral forging of the integrated topcover is an urgent problem to be solved. This paper mainly studies the development of forging process for topcover forging of AP1000 RPV with SA508 III material. Based on the shape characteristics and forging rheological characteristics of the topcover forgings, the topcover tube seat was identified as the key point of forming, so the concave round cake preform was designed, and the final forging was formed by spinning the preform. The preform forming simulation and the final spinning forming simulation were carried out by DEFORM software respectively. The simulation results show that the metal filling is good, the forging allowance is sufficient, but the fracture factor of the bottom head is high. In order to more comprehensively verify the feasibility of the forming scheme, Trial production of 1:20 small scale simulation parts was carried out, and the forming results showed that the small scale parts of the integrated topcover were well filled after spinning. Through the manufacture of theoretical and practical simulation parts, the forging process scheme of spinning preforms through two sets of dies is verified, which effectively solves the problem that the size of the top cover forgings is difficult to guarantee. It was manufactured according to the designed forging process using the 300-ton series of steel ingots, and the final product size and non-destructive testing met the requirements, and the qualified product was delivered.