A Study of Redistribution of Residual Stress and Hardness Due to Welding and Surface-Machining at Girth Welded Joint

2009 ◽  
Author(s):  
Masahito Mochizuki ◽  
Jinya Katsuyama ◽  
Ryohei Ihara ◽  
Hiroaki Mori ◽  
Yoshiki Mikami ◽  
...  
Keyword(s):  
Residual Stress ◽  
Nuclear Power ◽  
Power Plants ◽  
Crack Growth Behavior ◽  
Internal Diameter ◽  
Butt Weld ◽  
Butt Welding ◽  
Surface Machining ◽  
Inner Surface ◽  
Before And After

Stress corrosion cracking (SCC) near the welded zone of core internals and recirculation piping of Type 316L stainless steel in BWR nuclear power plants has been observed at the surface where tensile residual stress exists due to welding and/or surface-machining. It is well-known that butt-welding of austenitic piping causes the tensile stress in the inner surface of the pipe and that surface-machining is usually conducted before and after piping butt-welding to match the internal diameter (ID) of pipes and to provide a smooth surface finish but some amount of hardening. The SCCs near the welds of Ni-based alloys have been observed in the environment of primary water coolant, which is so called PWSCC. In this case, both residual stress and hardening are also the most important factors induced by welding as well as surface-machining in the regions of interest. In this work, therefore, Vickers hardness and residual stress distributions at work hardened layer such as inner surface of piping butt-weld by surface-machining before and after welding were experimentally evaluated. A simulation using a local micron-scale finite element method (FEM) model has been performed to support the understanding of experimental data by a model which was proposed in previous paper (PVP2006 and 2008 [1, 2]). Redistribution behavior of residual stress by welding after surface-machining will be discussed based on experimental and analytical results with regard to crack growth behavior.

Effect of Welding Conditions on Residual Stress and SCC Behavior at Butt-Welding Joints of Recirculation Pipes

2008 ◽  
Author(s):  
Jinya Katsuyama ◽  
Tohru Tobita ◽  
Hiroto Itoh ◽  
Kunio Onizawa
Keyword(s):  
Residual Stress ◽  
Crack Growth ◽  
Welding Speed ◽  
Heat Input ◽  
Welding Parameters ◽  
Crack Growth Behavior ◽  
Butt Weld ◽  
Butt Welding ◽  
Type 316L ◽  
Welding Joints

Stress corrosion cracking (SCC) in recirculation pipes made of low carbon austenitic stainless steel (Type 316L) has been observed near butt-welding joints. The recent SCC grows near the welding zone mainly due to high tensile residual stress by welding since the effect of the other contributing factors of material and environment decreases due to the countermeasures. Therefore, the residual stress analysis due to welding of austenitic stainless piping is important and has been already conducted by many researchers. In present work, scatters of welding conditions such as heat input and welding speed were measured experimentally by producing a series of butt-weld specimens of Type 316L pipes. Distribution and its scattering of residual stress were also measured by non-destructive and destructive methods. The effects of welding conditions on residual stress have been evaluated by parametric FEM analyses considering the variation of some parameters based on the welding experiments. The effects of welding conditions on crack growth behavior have been also evaluated by SCC growth simulations using calculated residual stress distributions and a procedure in the fitness-for-service code. Welding parameters such as heat input and welding speed have a strong influence on crack growth rate since residual stress is also affected by scatter of these welding parameters.

Analytical Study of the Relaxation of Welding Residual Stress by Excessive Loading for Austenitic Stainless Steel Piping Welds

2009 ◽  
Author(s):  
Jinya Katsuyama ◽  
Kunio Onizawa
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Nuclear Power ◽  
Power Plants ◽  
Three Dimensional ◽  
Welding Residual Stress ◽  
Low Carbon ◽  
Three Dimensional Model ◽  
Butt Weld

Welding residual stress is one of the most important factors of stress corrosion cracking (SCC) for austenitic stainless steel in pressure boundary piping in nuclear power plants. The effect of excessive loading, such as an earthquake, on the residual stress was evaluated by three-dimensional analyses based on finite element method (FEM). The FEM analyses were performed using three-dimensional model for a 250A piping butt weld of low carbon stainless steel of Type 316L. A welding simulation method used in this work is based on the moving heat source with the double ellipsoid model and was confirmed by comparing with the experimental measurements. After conducting welding residual stress simulation, several loading patterns of bending moment and uni-axial displacements have been applied to a model by varying amount of moment and displacement. The analyses indicated that higher loading to bending and axial stresses caused higher relaxation of welding residual stress near piping welds. The difference in the effect of loading direction was observed for both cases. It is concluded that the SCC growth rate might be decreased as loading level increased.

SCC Assessment Based on Probability Fracture Mechanics Considering SCC Initiation and Propagation Under Residual Stress Fields Generated by Machining and Welding Process of Pipes

2013 ◽  
Author(s):  
Masahito Mochizuki ◽  
Ryohei Ihara ◽  
Jinya Katsuyama ◽  
Makoto Udagawa
Keyword(s):  
Residual Stress ◽  
Stress Distribution ◽  
Crack Growth ◽  
Welding Process ◽  
Residual Stress Distribution ◽  
Initiation Time ◽  
Butt Welding ◽  
Surface Machining ◽  
Inner Surface ◽  
Growth Analyses

Stress corrosion cracking (SCC) has been observed near the welded zones of pipes made of austenitic stainless steel type 316L. Residual stress is an important factor for SCC. In the joining processes of pipes, butt welding is conducted after surface machining. Residual stress is generated by both processes, and the residual stress distribution by surface machining is varied by the subsequent butt-welding process. In this study, numerical analysis of the residual stress distribution by butt welding after surface machining was performed by the finite element method. The SCC initiation time was estimated by the residual stress obtained at the inner surface. SCC growth analyses based on probability fracture mechanics were performed by using the SCC initiation time and the residual stress distribution. As a result, the residual stress distribution in the axial direction due to butt welding after surface machining has high tensile stress exceeding 1000 MPa at the inner surface. The effect of SCC initiation on leakage probability is not as significant as the effect of plastic strain on the crack growth rate. However, to perform crack growth analyses considering SCC initiation, evaluation of the residual stress due to surface machining and welding is important.

Simplified Computation of the Welding Process on a Steam-Generator Divider Plate

2013 ◽  
Author(s):  
Frédérique Rossillon ◽  
Lionel Depradeux
Keyword(s):  
Residual Stress ◽  
Steam Generator ◽  
Nuclear Power ◽  
Power Plants ◽  
Welding Process ◽  
Computation Time ◽  
Stress Fields ◽  
Residual Stress Field ◽  
Butt Weld ◽  
2D Simulation

The integrity of structures in nuclear power plants has to be assessed to meet given safety criteria. For a better understanding of the in-service loads in welded areas of PWRs components, the residual stresses resulting from the welding process have to be estimated. For that purpose, numerical simulations of welding have proved efficient but still require some improvement in terms of computation time reduction to be widely used in an industrial context. This paper focuses on the residual stress fields in a double V butt weld on a steam generator divider plate. To set a reference, a 2D simulation of multi-pass welding was performed taking into account the whole non-linear thermo-mechanical history. Two simplified method were then carried out to estimate the residual stress field. The first method consists of modeling macro-beads by merging passes together. The second considers only a reduced number of appropriately selected passes in the analysis. Both methods are confronted to the full multi-pass simulation, set as a reference simulation, and their respective efficiency and robustness are discussed. The main feature of this work, the RNP method, based on a reduced number of appropriately selected passes, gives a good reproduction of the stress fields and strongly reduce the computation time. A significant improvement is observed: CPU time is divided by 10 times with this predictive method.

Finite Element Analyses of Residual Stresses in Typical Welded Joints Used in Nuclear Power Plants and Comparisons With Experiments

2010 ◽  
Author(s):  
Dean Deng ◽  
Kazuo Ogawa ◽  
Nobuyoshi Yanagida ◽  
Koichi Saito
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Residual Stresses ◽  
Welded Joints ◽  
Nuclear Power ◽  
Power Plants ◽  
Butt Joint ◽  
Welding Residual Stress ◽  
Dissimilar Metal ◽  
Water Reactors

Recent discoveries of stress corrosion cracking (SCC) at nickel-based metals in pressurized water reactors (PWRs) and boiling water reactors (BWRs) have raised concerns about safety and integrity of plant components. It has been recognized that welding residual stress is an important factor causing the issue of SCC in a weldment. In this study, both numerical simulation technology and experimental method were employed to investigate the characteristics of welding residual stress distribution in several typical welded joints, which are used in nuclear power plants. These joints include a thick plate butt-welded Alloy 600 joint, a dissimilar metal J-groove set-in joint and a dissimilar metal girth-butt joint. First of all, numerical simulation technology was used to predict welding residual stresses in these three joints, and the influence of heat source model on welding residual stress was examined. Meanwhile, the influence of other thermal processes such as cladding, buttering and heat treatment on the final residual stresses in the dissimilar metal girth-butt joint was also clarified. Secondly, we also measured the residual stresses in three corresponding mock-ups. Finally, the comparisons of the simulation results and the measured data have shed light on how to effectively simulate welding residual stress in these typical joints.

An Analysis of Residual Stress Improvement for a Dissimilar Metal Nozzle-to-Pipe Weld by Using the Heat Sink Method

2008 ◽  
Author(s):  
J.-S. Park ◽  
J.-M. Kim ◽  
G.-H. Sohn ◽  
Y.-H. Kim
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Heat Sink ◽  
Nuclear Power ◽  
Power Plants ◽  
Base Alloy ◽  
Fatigue Cracking ◽  
Hole Drilling ◽  
Fe Model ◽  
Dissimilar Metal

This study is concerned with the mechanics analysis of residual stress improvement by the heat sink method applied to a dissimilar metal weld (DMW) for the use in nuclear power plants. The DMW joint considered here is composed of ferritic low-alloy steel nozzle, austenitic stainless steel safe-end, and nickel-base alloy A52 weld metal. To prepare the DMW joint with a narrow-gap, the gas tungsten arc welding (GTAW) process is utilized, and the heat sink method is employed to control thermal gradients developed in the critical region of work pieces during welding. Weld residual stresses are computed by the non-linear thermal elasto-plastic analysis using the axisymmetric finite element (FE) model, for which temperature-dependent thermal and mechanical properties of the materials are considered. A full-scale mock-up test is conducted to validate analytical solution for the DMW joint, and residual stresses are measured by using the hole-drilling method. Results of the FE modeling and mock-up test for the DMW joint are compared and effects of the heat sink method are discussed. It is found that a significant amount of residual compressive stresses can be developed on the inner surface of the DMW joint by using the heat sink method, which can effectively reduce the susceptibility of the welded materials to stress corrosion or fatigue cracking.

Crack Growth Analyses of SCC Under Various Residual Stress Distributions Near the Piping Butt-Welding

2007 ◽  
Author(s):  
Jinya Katsuyama ◽  
Wataru Asano ◽  
Kunio Onizawa ◽  
Masahito Mochizuki ◽  
Masao Toyoda
Keyword(s):  
Residual Stress ◽  
Crack Growth ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Stress Distributions ◽  
Contributing Factors ◽  
Butt Welding ◽  
Type 316L ◽  
Growth Analyses ◽  
Reactor Internals

Stress corrosion cracking (SCC) of core internals and/or recirculation pipes of austenite stainless steel (Type 316L) has been observed. When a SCC is detected at the reactor internals or pipes, it is necessary to calculate crack growth behavior of the crack for a certain operational period. The SCC initiates and grows near the welding zone because of high tensile residual stress by welding relative to the other contributing factors of material and environment. Therefore, the residual stress analysis due to welds of austenitic stainless piping is becoming important and has been already conducted by many researchers. In present work, the through-thickness residual stress distributions near multi-pass butt-welds of Type 316L pipes have been calculated by thermo-elastic-plastic analyses with the geometric and welding conditions changed and collected from literatures. Then crack growth simulations were performed using calculated and collected residual stress distributions. The effects of geometric and welding conditions on crack growth behavior were also discussed.

scholarly journals Crack Growth Behavior in a Residual Stress Field for Vessel Type Structures

2003 ◽  
Author(s):  
P. Dong ◽  
G. Rawls
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Crack Growth ◽  
Surface Crack ◽  
Growth Behavior ◽  
Welding Parameters ◽  
Crack Growth Behavior ◽  
Butt Weld ◽  
Small Surface ◽  
Longitudinal Residual Stress

Detailed residual stress analysis was performed for a multi-pass butt weld, representing the middle butt-girth weld of a storage tank. The analysis procedures addressed welding parameters, joint detail, weld pass deposition sequence, and temperature-dependent properties. The predicted residual stresses were then considered in stress intensity factor calculations using a three-dimensional finite element alternating model (FEAM) for investigating crack growth behavior for both small elliptical surface and through-wall cracks. Two crack orientations were considered: one is parallel to the vessel girth weld and the other is perpendicular to the girth weld. Since the longitudinal (parallel to weld) and transverse (perpendicular to weld) residual stresses exhibit drastically different distributions, a different crack growth behavior is predicted. For a small surface crack parallel to the weld, the crack tends to grow more quickly at the surface along the weld rather than into the thickness. The self-equilibrating nature of the transverse residual stress distribution suggests that a through-wall crack parallel to crack cannot be fully developed solely due to residual stress actions. For a crack that is perpendicular to the weld, a small surface crack exhibit a rapid increase in K at the deepest position, suggesting that a small surface crack has the propensity to become a through-wall crack. Once the through crack is fully developed, a significant re-distribution in longitudinal residual stress can be seen. As a result, in the absence of external loads there exists a limiting crack length beyond which further crack growth is deemed unlikely.

scholarly journals The Effect of Welding-Pass Grouping on the Prediction Accuracy of Residual Stress in Multipass Butt Welding

2017 ◽  
Vol 2017 ◽  
pp. 1-13
Author(s):  
Jeongung Park ◽  
Gyubaek An ◽  
Sunghoon Kim
Keyword(s):  
Residual Stress ◽  
Diffraction Method ◽  
Fe Analysis ◽  
Computer Memory ◽  
Butt Weld ◽  
Butt Welding ◽  
Welded Structure ◽  
Welding Sequence ◽  
Grouping Method ◽  
Neutron Diffraction Method

The residual stress analysis of a thick welded structure requires a lot of time and computer memory, which are different from those in thin welded structure analysis. This study investigated the effect of residual stress due to welding-pass grouping as a way to reduce the analysis time in multipass thick butt welding joint. For this purpose, the parametric analysis which changes the number of grouping passes was conducted in the multipass butt weld of a structure with a thickness of 25 mm and 70 mm. In addition, the residual stress by thermal elastoplastic FE analysis is compared with the results by the neutron diffraction method for verifying the reliability of the FE analysis. The welding sequence is considered in order to predict the residual stress more accurately when using welding-pass grouping method. The results of the welding-pass grouping model and half model occurred between the results of the left/right of the full model. If the total number of welding-pass grouping is less than half of that of welding pass, a large difference with real residual stress is found. Therefore, the total number of the welding-pass grouping should not be reduced to more than half.

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