Numerical investigation on welding residual stresses in a PWR pressurizer safety/relief nozzle

Abstract

A B S T R A C T This paper presents finite element simulation results of residual stresses in dissimilar metal welds of a PWR pressurizer safety/relief nozzle. The present results are believed to be significant in two aspects. The first one is to consider the effect of the presence of similar metal welds on resulting residual stresses. The second one is the mitigation effect of the overlay welding thickness on residual stresses. After dissimilar metal welding, tensile residual stresses are present both at the inner surface and at the outer surface of dissimilar metal welds. Adjacent similar metal welding, however, decreases residual stresses to compressive ones at the inner surface of dissimilar metal welds, possibly due to the bending mechanism caused radial contraction of the weld. At the outer surface of dissimilar metal welds, similar metal welding increases residual stresses. Overlay welding further decreases residual stresses at the inner surface of dissimilar and similar metal welds, but increases slightly residual stresses at the outer surface.Keywords finite element simulation; PWR pressurizer safety/relief nozzle; weld overlay; welding residual stress. I N T R O D U C T I O NRecently stress corrosion cracks were found in dissimilar metal welds of some pressurized water reactor (PWR) nuclear plants. [1][2][3][4][5] As a result, several mitigation methods have been discussed, 5-7 one of which is the weld overlay. 5,8-10 As the weld overlay method has been applied to piping systems in boiling water reactor components over some decades, 11,12 its effectiveness in mitigation is well appreciated. In addition, the weld overlay can also provide other benefits, for instance, improved inspectability and structural reinforcement effects due to an increasing thickness. 5,10,12 Although some guidelines on the weld overlay for dissimilar metal welds in pressurized water reactor nuclear plants are available, 13-15 numerical simulations are desirable to assess the weld overlay effect on residual stresses, as the weld overlay process is expensive. Furthermore such numerical simulations can be used to help optimise the weld overlay process.Welding residual stress simulation of stainless pipes using the finite element (FE) analysis is relatively well established, and accordingly many papers have been published Correspondence: Yun-Jae Kim.in the literature. [16][17][18][19][20] Some relevant works are briefly described here. Brickstad and Josefson 16 performed a parametric study for multipass circumferential butt-welding of stainless steel pipes to quantify residual stresses and their sensitivity to variation in weld parameters. Yaghi et al. 17 presented another parametric study on effects of the thickness and radius-to-thickness ratio on residual stresses in butt-welded stainless pipes. Related to repair welds and overlay welding for dissimilar metal welds in PWR plants, many works have been published in American Society of Mechanical Engineers, Pressure Vessel and Piping Division (ASME PVP) conferences. [4][5][6]8,9 One ...

Through-wall welding residual stress profiles for dissimilar metal nozzle butt welds in pressurized water reactors

“…To reflect the fabrication processes, DMWs and SMWs are simulated in order, and residual stresses will be given after each welding process, that is, after dissimilar metal welding and after similar metal welding. Simulations for the buttering weld and hydro‐test are not conducted, as possible welding residual stress induced by buttering is almost removed by post weld heat treatment, and the effect of hydro‐test on residual stresses is minimal for a thick nozzle with r i / t SE < 5 34–35 . Residual stresses in this section are reported along the centre line (path A; shown in Fig.…”

“…The buttering process was not simulated, as possible welding residual stress induced by the buttering weld could be almost removed by post weld heat treatment. The hydro‐test was also not simulated, as its effect on residual stresses is known to be minimal for thick nozzles with r i / t SE less than five 34–35 . The effect of kinematic boundary conditions imposed during welding simulation on residual stresses could be quite important.…”

“…The hydro-test was also not simulated, as its effect on residual stresses is known to be minimal for thick nozzles with r i /t SE less than five. [34][35] The effect of kinematic boundary conditions imposed during welding simulation on residual stresses could be quite important. In the present investigation, free boundary conditions were applied to both dissimilar and similar metal welding.…”

“…Simulations for the buttering weld and hydro-test are not conducted, as possible welding residual stress induced by buttering is almost removed by post weld heat treatment, and the effect of hydro-test on residual stresses is minimal for a thick nozzle with r i /t SE < 5. [34][35] Residual stresses in this section are reported along the centre line (path A; shown in Fig. 2b) within the DMW, as they are of main interest for stress corrosion cracking.…”

Investigation of residual stresses in a repair‐welded rail head considering solid‐state phase transformation

“…The other is very high temperature mechanical and thermal properties, which are crucial to build up a simulation model and are difficult to obtain. Of these reasons, practical modelling and welding simulation techniques with reasonable accuracy have been proposed to resolve time‐consuming and limited resource issues . As a part of optimized welding simulations, Song et al .…”