Zbytková napětí heterogenních svarových spojů

Abstract

The subject of the dissertation is the study of residual stresses in the heterogeneous weld of the reactor pressure vessel using the cutting and drilling method. In pressurised water reactors, the welds of the reactor pressure vessel between the nozzle and the safe end are made of a nickel-based alloy. This material is known to be prone to primary circuit water stress corrosion cracking (PWSCC) if the stress is at a sufficient level. For this reason, it is of utmost importance to accurately evaluate the residual stress field created by welding technology. For this purpose, residual stress measurements are performed on a heterogeneous joint of a decommissioned nuclear power plant using the tensometric method of drilling holes according to ASTM E837. The sample between the nozzle and the safe end is gradually cut externally (machined) to derive the residual stress profile across the weld thickness. These residual stress profiles are useful for assessing the acceptability of defects that might eventually be detected during in-service inspection work and for defining reasonable inspection intervals. Residual stress data can be used to plan and verify the residual life of power plant welds. The knowledge of the residual stresses in the heterogeneous weld can thus enable optimisation of the welding technology and thereby reduce the overall tension of the circuit system. Residual stress is not the only quantity that affects service life, but it plays a significant role. The aim of this work will be to gain knowledge about the course of residual stresses in the weld between the reactor pressure vessel and the nozzle. The basic methods for determining residual stresses will be discussed in the thesis. Part of the work will be devoted to the analysis of the drilling method, which will be applied subsequently. Local residual stresses are determined by the drilling method, and the profiles of residual stresses across the thickness of the weld are compiled by subsequent analysis and applied correction methodology.