Residual Stress Evaluation of Dissimilar Weld Joint Using Reactor Vessel Outlet Nozzle Mock-Up Model: Report 2

Abstract

In recent years, the occurrence of primary water stress corrosion cracking (PWSCC) in Alloy 600 weld regions of PWR plants has increased. In order to evaluate the crack propagation of PWSCC, it is required to estimate stress distribution including residual stress and operational stress through the wall thickness of the Alloy 600 weld region. In a national project in Japan for the purpose of establishing residual stress evaluation method, a test model was produced using the same fabrication process in Japanese PWR plants in order to measure stress distribution change of the Alloy 132 weld region during fabrication process such as a hydrostatic test, welding a main coolant pipe to the stainless steel safe end and operation condition test. For the mock up test model, the stress distribution of selected fabrication processes was measured using the Deep Hole Drilling (DHD) method. From the measurement results, it was found that the stress distribution in thickness direction at the center of the Alloy 132 weld line was hardly varied with the hydrostatic test at site and operating condition test history. FE analysis was performed to calculate the stress distributions for each fabrication process. Comparing with measurement results, the validity of the FE analysis was confirmed. From the validation procedure, a standard residual stress evaluation method was established.

Influence of Material Randomness on Welding Residual Stress in Dissimilar Metal Welded Joints of Nuclear Power Plants

“…As is well known, the welding residual stress is affected by many factors and varied complicated, and it is very expensive and time-consuming to investigate the welding residual stress, and sometime is impossible [7] . Therefore, welding residual stress simulation using finite element method (FEM) analysis has become increasingly common in crack analysis combined with experiments [8,9] . It has been found that the distribution of welding residual stress depends on several main factors such as structural dimensions, material properties, restraint conditions, heat input, number of welding pass and welding sequence [10] .…”

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

“…This is in contrast to pipe butt welds which typically involve a single weld. Recent works reveal that the presence of the SMW can affect welding residual stresses in the DMW, depending on the safe‐end length 20–23 . In addition, the length of the safe‐end varies, depending on design and on manufacturer.…”

“…Finally, nozzle components consist of several materials, for instance low alloy steels, Ni‐based alloys and stainless steels. Due to these complexities, according to our knowledge, no systematic results have yet been presented, and existing works have been focused on specific nozzles 20–22,24–26 …”

“…Recent works reveal that the presence of the SMW can affect welding residual stresses in the DMW, depending on the safe-end length. [20][21][22][23] In addition, the length of the safe-end varies, depending on design and on manufacturer. The second issue is the complexities associated with geometry.…”

“…Due to these complexities, according to our knowledge, no systematic results have yet been presented, and existing works have been focused on specific nozzles. [20][21][22][24][25][26] The present work attempts to propose generally applicable through-wall welding residual stress profiles for dissimilar metal nozzle butt welds. The proposed profiles are based on parametric FE welding residual stress simulations.…”