Study of the Stress State of a Dissimilar Metal Weld Due to Manufacturing and Operational Conditions

Bernadett Spisák,Szabolcs Szávai,Zoltán Bézi

doi:10.3311/ppme.19063

Abstract

Welding is accompanied by the presence of weld residual stresses, which in case of dissimilar metal welds even with post weld heat treatment cannot be removed completely therefore they should be considered when assessing possible welding defects. The measurement of residual stress in metal weld is a very complex procedure and also in the investigated case could not be carried out as it is the part of a working plant. However, by modelling these processes, the residual stresses and deformation of the components caused by this manufacturing method can be determined. It is important to calculate these values as accurately as possible to determine the maximum load capacity of the structure. The structure under examination was the dissimilar metal weld of a VVER-440 steam generator. 2D simulations were performed, where temperature and phase-dependent material properties were implemented. Different loading scenarios were considered in the numerical analysis. The results can be useful to determine the real loading conditions of a given component and can be used to predict stress corrosion crack initiation locations, as well as to evaluate the lifetime and failure mode prediction of welded joints.

Highlights

In several nuclear power plants, the dissimilar metal welds have proved to be a sensitive part of the structure
As in case of dissimilar metal weld (DMW) the impact of thermal sensitization, residual stress and galvanic effects are combined they are more sensitive to stress corrosion cracking (SCC), heat affected zones (HAZs) along the fusion lines of the DMWs are more susceptible to SCC [6]
The welding simulation was omitted and only the operational loads were applied, in the second case the welding of the joint was considered in addition to the design conditions, hereafter the complete welding process was simulated with the buttering layers

Summary

Introduction

In several nuclear power plants, the dissimilar metal welds have proved to be a sensitive part of the structure. The chemical compositions of the first and second buttering layers were examined by electron diffraction method, which revealed the dilution of the alloying elements [9] These results show that the analysis of the DMWs is very important and necessary to determine the residual stresses due to the manufacturing processes. It should be mentioned that ff + fr = 2, and the power density distribution inside the rear quadrant is lower than that in the front quadrant, the factor fr is smaller than ff From these equations it can be seen that for the simulation of welding the front length ( af ), the rear length ( ar ), the width (b) and the depth (c) of the heat source has to be known. The time-dependent creep behavior can be divided into three parts: primary creep, secondary creep and

DCEN DCEP

End of the primary collector

Conclusion