For nuclear reactor applications, AREVA NP has to perform junctions between ferritic low alloy steel heavy section components and austenitic stainless steel piping systems. For Gas Tungsten Arc Welding (GTAW) of dissimilar metal weld (DMW) narrow gap, AREVA NP has developed special manufacturing procedures guaranteeing high quality standards and resistance in service. Since a decade, AREVA NP is developing the numerical simulation of welding to have a better understanding of involved physical phenomena and to predict residual stresses. In spite of the large thickness of Pressurized Water Reactor (PWR) components, the distortion issue may also be important. Narrow gap welding requires indeed a close control of the groove width. This paper presents numerical simulations performed by AREVA NP on 14″ narrow gap DMW mock-ups as part of a research project carried out internally. The simulations focus on the predictions of microstructure and residual stress distribution. The analysis simulates the main steps of the mock-up manufacturing procedure. Multi pass welding simulation reproduces the deposit of each bead by thermo-metallurgical and mechanical calculations. A special attention has been paid on the buttering of the ferritic side. Generally a post weld heat treatment (PWHT) is carried out after the buttering of the ferritic side in order to relieve residual stresses. For some repair operations, a PWHT is not feasible. Thus a temper bead process can be used. During this process, a large part of the previous heat affected zone is tempered to guarantee a limited hardness and to reduce the risk of cold cracking. The results in terms of microstructure and stress obtained with the two techniques are compared. With the temper bead process, the final level of hoop stresses in the heat affected zone (HAZ) of the buttering remains significant as stresses are not relieved by viscous effects implied during PWHT. Nevertheless the temper bead process has a positive effect on the material hardness as the proportion of tempered phase is higher. One of the objectives of this task is to compare the numerical results with measurements. This comparison is not only a validation of numerical simulation of welding but also a way to investigate the relevance of residual stress measurement by Deep Hole Drilling (DHD). Calculated stresses are globally in good agreement with measurements made by DHD. A comparison with axial shrinkage is also made for validation of the modelling methodology.
Welding problems encountered in the nuclear industry have been mainly addressed by weldability tests and the analysis, development of new techniques or improvements through lesson learning. Since a decade, AREVA is developing a complementary approach based on numerical simulation. Residual stresses present in reactors do not constitute a major problem at the design stage; even though they may have a strong impact on some types of damage. Numerical welding simulation in the nuclear industry has focused mainly on residual stress prediction, which constitutes an issue for engineering. PWR components are usually massive; nevertheless distortion may also be a source of concern in component design: some structures are slender in spite of their thickness; narrow gap welding requires a close control of the groove width. AREVA, also working on a fast breeder project, the distortion problem gains in importance. In this prospect, AREVA, world energy expert, paid special attention on the numerical simulation of Gas Tungsten Arc Welding (GTAW) of a mock-up relative to the International Thermonuclear Experimental Reactor (ITER) Vacuum Vessel (VV). One of the challenges of manufacturing the ITER vacuum vessel is the low value of acceptance level of distortion (∼ 10 mm) compared to the global dimensions of the structure (∼ 10 m). Welding simulations of a representative mock-up of VV pattern of the made of austenitic steel plates (316L(N) ITER GRADE) are carried out. The aim of the numerical simulations is to check the quality of the distortion prediction. Multi pass welding simulation reproduces the deposit of each bead by thermo-metallurgical and mechanical calculations. Distortions induced by each weld are computed using a simplified approach (local global method). This method aims at modeling long and numerous welding operations with an acceptable calculation time. Moreover, this method is improved in order to respect welding sequence with partial filling of grooves. After welding sequences, distortions are measured at some representative points of the mock-up. The paper presents the methodology of the numerical simulations and the relevant results: • Residual stress and strain fields in and near the welds (local fields), • Distortion prediction for the global structure. The comparison with experimental distortions shows that the trends of the experimental deformed shape are well represented by the simulations. Moreover, displacement magnitudes are in good agreement with measurements.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.