A Numerical Study on Mock-Up Downsizing to Predict Residual Stresses at CRDM Welds

2010 ◽  
Author(s):  
Ik-Joong Kim ◽  
Jae-Uk Jeong ◽  
Jae-Boong Choi ◽  
Young-Jin Kim ◽  
Sung-Woo Kim ◽  
...  
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Nuclear Power ◽  
Power Plants ◽  
Numerical Study ◽  
Welding Process ◽  
Piping System ◽  
Experimental Conditions ◽  
Control Rod ◽  
Set Up

Since several defects caused by PWSCC (Primary Water Stress Corrosion Cracking) have been observed at the piping system of nuclear power plants, during the last two decades, lots of analytical and experimental researches have been performed to find out the relationship between the residual stress and PWSCC initiations. The present research deals with prediction of the residual stress at welding parts of CRDM (Control Rod Drive Mechanism). Especially, numerical investigations are carried out to support relevant experimental set-up because it is not easy to prepare large-sized mock-ups comparable to real geometry. First, preliminary examination was performed to establish an optimized welding process simulation procedure to accurately predict weld residual stresses. Then, detailed parametric FE analyses were carried out to examine effects of varying geometries and experimental conditions. Key findings were obtained from the FE analyses, which were used for finalizing the configuration of mock-up, are fully discussed in this manuscript.

Finite Element Simulation of Laser Welding in a P91 Steel Plate

2013 ◽  
Author(s):  
Kiranmayi Abburi Venkata ◽  
Christopher E. Truman
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Laser Welding ◽  
Nuclear Power ◽  
Power Plants ◽  
Welding Process ◽  
P91 Steel ◽  
Modelling Techniques ◽  
Materials Used ◽  
Steel Welds

New methods for joining materials used in advanced nuclear power plants are of interest to increase the efficiency and productivity. Optimised joints require narrow heat affected zones, low residual stress, strain and distortion. This requires research into a large range of aspects including the nature of the joining processes, characterisation of the joint materials and the integrity of joints in manufacture and service. Of particular interest is the laser welding of the P91 steel used extensively in the power plants. The objective of this paper is to fully characterise the laser welding process using numerical modelling techniques and compare the measured residual stresses for P91 steel welds induced by the welding process with the predicted residual stresses by numerical simulation. The FE simulation consists of thermal analysis and a sequentially coupled structural analysis. Solid state phase transformation is included in the analysis to account for the volumetric changes due to martensitic transformation during cooling. The neutron diffraction technique is used to measure the residual stresses in the welded plate. The measurements are compared with the simulation results and the characteristics of the residual stress distribution and the influence of phase transformations are discussed.

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.

Strategies for Treating Weld Residual Stresses in Probabilistic Fracture Mechanics Codes

2011 ◽  
Author(s):  
Frederick W. Brust ◽  
R. E. Kurth ◽  
D. J. Shim ◽  
David Rudland
Keyword(s):  
Fracture Mechanics ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Nuclear Power ◽  
Power Plants ◽  
Degradation Mechanism ◽  
Welding Process ◽  
Corrosion Cracking ◽  
Uncertainty Sources

Risk based treatment of degradation and fracture in nuclear power plants has emerged as an important topic in recent years. One degradation mechanism of concern is stress corrosion cracking. Stress corrosion cracking is strongly driven by the weld residual stresses (WRS) which develop in nozzles and piping from the welding process. The weld residual stresses can have a large uncertainty associated with them. This uncertainty is caused by many sources including material property variations of base and welds metal, weld sequencing, weld repairs, weld process method, and heat inputs. Moreover, often mitigation procedures are used to correct a problem in an existing plant, which also leads to uncertainty in the WRS fields. The WRS fields are often input to probabilistic codes from weld modeling analyses. Thus another source of uncertainty is represented by the accuracy of the predictions compared with a limited set of measurements. Within the framework of a probabilistic degradation and fracture mechanics code these uncertainties must all be accounted for properly. Here we summarize several possibilities for properly accounting for the uncertainty inherent in the WRS fields. Several examples are shown which illustrate ranges where these treatments work well and ranges where improvement is needed. In addition, we propose a new method for consideration. This method consists of including the uncertainty sources within the WRS fields and tabulating them within tables which are then sampled during the probabilistic realization. Several variations of this process are also discussed. Several examples illustrating the procedures are presented.

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.

Welding Residual Stress Solutions for Dissimilar Metal Surge Line Nozzle Welds

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
D. Rudland ◽  
A. Csontos ◽  
T. Zhang ◽  
G. Wilkowski
Keyword(s):  
Residual Stress ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Industry ◽  
Welding Residual Stress ◽  
Nozzle Geometry ◽  
Material Strength ◽  
Piping System ◽  
Dissimilar Metal ◽  
Weld Material

At the end of 2006, defects were identified using ultrasonic testing in three of the pressurizer nozzle dissimilar metal (DM) welds at the Wolf Creek nuclear power plant. Understanding welding residual stress is important in the evaluation of why and how these defects occur, which in turn helps to determine the reliability of nuclear power plants. This paper presents analytical predictions of welding residual stress in the surge nozzle geometry identified at Wolf Creek. The analysis procedure in this paper includes not only the pass-by-pass welding steps, but also other essential fabrication steps of pressurizer surge nozzles. Detailed welding simulation analyses have been conducted to predict the magnitude of these stresses in the weld material. Case studies were carried out to investigate the change in the DM main weld stress fields resulting from different boundary conditions, material strength, weld sequencing, as well as simulation of the remaining piping system stiffness. A direct comparison of these analysis methodologies and results has been made in this paper. Weld residual stress results are compared directly to those calculated by the nuclear industry.

The Application of the Hole Drilling Method to Define the Residual Stress of Dissimilar Laser Welded Components

2007 ◽  
Vol 7-8 ◽  
pp. 133-138 ◽  
Author(s):  
E.M. Anawa ◽  
Abdul Ghani Olabi
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Laser Welding ◽  
Power Plants ◽  
Welding Process ◽  
Hole Drilling ◽  
Welding Parameters ◽  
Heating Process ◽  
Hole Drilling Method ◽  
Drilling Method

Dissimilar metal welds between Ferritic steel and Austenitic steel (F/A)are commonly used in power plants, food industry, pharmaceutical industry and many other applications. There are many issues/problems associated with the joining of dissimilar materials, depending on the materials being joined and the process selected. During the laser welding process, residual stresses are introduced by a rise in temperature during the melting or heating process followed by a very quick cooling of the weld and the surrounding material. In this study, CO2 continuous laser welding has been successfully applied for joining 316 stainless steel with AISI 1009 low carbon steel F/A. Design of Experiment techniques (DOE) has been used for some of the selected welding parameters (laser power, welding speed, and focus position) to model the dissimilar F/A joints in terms of its residual stresses. The Hole-Drilling Method technique was use for measuring the residual stress of dissimilar welded components. Taguchi approach for selected welding parameters was applied and the output response was the residual stresses. The results were analysed using analysis of variance (ANOVA) and signal-tonoise (S/N) ratios for the effective parameters combination.

FE Simulation of Welding Residual Stresses in Reactor Vessel Head Penetrations

2009 ◽  
Author(s):  
Anne Teughels ◽  
Christian Malekian
Keyword(s):  
Residual Stresses ◽  
Nuclear Power ◽  
Power Plants ◽  
Element Model ◽  
Mechanical Analysis ◽  
Alloy 600 ◽  
Finite Elements Analysis ◽  
Pressurized Water ◽  
Water Reactors ◽  
Set Up

The penetrations in the early Pressurized Water Reactors Vessels are characterized by Alloy 600 tubes, welded by Alloy 182/82. The Alloy 600 tubes have been shown to be susceptible to PWSCC (Primary Water Stress Corrosion Cracking) which may lead to crack forming. The cracking mechanism is driven mainly by the welding residual stresses and, in a second place, by the operational stresses in the weld region. It is therefore of big interest to quantify the weld residual stresses correctly. In order to determine the welding residual stresses, the weld procedure is simulated numerically by finite elements analysis. In the article, central as well as eccentric sidehill nozzles on the vessel head are analyzed. For the former a 2-dimensional axisymmetrical finite element model is used, whereas for the latter a 3-dimensional model is set up. A nonlinear transient thermo-mechanical analysis is performed, which is preceded by a transient thermal analysis simulating the heating during the multipass welding. Weld beads are deposited “all-at-once”. Different positions on the vessel head are compared and the influence of the sidehill effect is illustrated. The methodology is applied to the reactor vessels of the Belgian nuclear power plants by Tractebel Engineering (Belgium). The results are compared with literature. The global approach in both cases is very similar but is applied to different configurations, specific for each plant.

Evaluation of through-thickness residual stresses and microstructure in SA516 Gr. 70 steel welds

2021 ◽  
pp. 095440542199012
Author(s):  
Pradeeptta Kumar Taraphdar ◽  
Manas Mohan Mahapatra ◽  
Arun Kumar Pradhan ◽  
Pavan Kumar Singh ◽  
Kamal Sharma ◽  
...  
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Nuclear Power ◽  
Three Dimensional ◽  
Welding Process ◽  
Influential Factors ◽  
Stress Fields ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Steel Welds

The critical working condition of nuclear power plant equipment necessitates meticulous determination of the welding process and parameters. In this work, some major influential factors of welding were investigated to observe their effects on the through-thickness residual stress distribution in multipass pressure vessel steel welds. In this regard, experiments were conducted to find the characteristics of residual stresses dispersed in SA516 Grade 70 steel welds of different groove geometries with distinct welding conditions. Three-dimensional finite element models of the weldments were developed considering a moving heat source with temperature-dependent material properties to simulate the welding thermal cycles and corresponding residual stress fields. Effects of weld groove geometry, number of weld passes, external constraints, and preheating on the through-thickness residual stress fields were studied. Additional attention was given to the evaluation of the heterogeneous microstructure and microhardness across the weld cross-section associated with their weld thermal history. Finally, the evolution of the through-thickness residual stresses attributed to subsequent weld passes was elaborated.

Part Repair and Start/Stop Effects and Three Dimensional Residual Stress in Dissimilar Metal Welds

2015 ◽  
Author(s):  
F. W. Brust ◽  
E. Punch ◽  
E. Kurth
Keyword(s):  
Residual Stress ◽  
Stress State ◽  
Nuclear Power ◽  
Power Plants ◽  
Three Dimensional ◽  
Filler Materials ◽  
Piping System ◽  
Dissimilar Metal ◽  
Residual Stress State ◽  
Weld Residual Stress

PWR nuclear power plants have dissimilar metal (DM) welds at many junctions between the vessels and the piping. The DM welds are made with Alloy 82 filler materials between carbon steel and stainless steel. These are potentially susceptible to Primary Water Stress Corrosion Cracking (PWSCC). PWSCC is mainly driven by the tensile weld residual stresses (WRS) that develop during fabrication of the piping system. In particular, weld repairs that often occur during the weld fabrication process also play a strong role in the development of the weld residual stress state in and near the DM welds. Most weld residual stress analyses performed to date in order to characterize the weld residual stress state in DM welds for PWSCC crack growth, leakage, and subsequent failure used axis-symmetric assessments. The purpose of this work is to provide direct assessment of the appropriateness of this axis-symmetric assumption on the WRS by comparison with full three dimensional analyses of several nozzles. In particular, weld start stop effects on the original weld will be assessed. In addition, the effect of partial arc weld repairs will be included. Repair cases considered include 15% and 50% deep repairs of length 48-degree and 96-degree of the circumference, along with the baseline case with no repair. The more complex three dimensional WRS state from the three dimensional analyses are compared to the corresponding axis-symmetric solutions and guidelines regarding the appropriateness of 2D solutions are discussed. Finally, some limited calculations of stress intensity factors at locations along the repair are presented.

Assessment of J-Integrals for Surface Cracks in a Weld Metal

2012 ◽  
Author(s):  
Young-Chul Park ◽  
Jae-Uk Jeong ◽  
Jae-Boong Choi ◽  
Yoon-Suk Chang ◽  
Sung-Woo Kim ◽  
...  
Keyword(s):  
Residual Stress ◽  
Water Stress ◽  
Stress Corrosion ◽  
Nuclear Power ◽  
Power Plants ◽  
Driving Mechanism ◽  
Surface Cracks ◽  
Stress Distributions ◽  
Control Rod ◽  
Primary Water

Lots of defects due to primary water stress corrosion cracking have been observed at diverse penetration locations of major components in nuclear power plants. To resolve this issue, during the past couple of decades, numerous analytical and experimental researches have been carried out to determine residual stress distributions in dissimilar metal welds that are plausible to crack initiation caused by the primary water stress corrosion. The present research deals with prediction of J-integrals for axial inner surface cracks in a mock-up that is to resemble upper head of reactor pressure vessel with penetrations of control rod driving mechanism. At first, representative residual stress distributions at J-groove welded region of the mock-up were calculated through finite element analyses of un-cracked models according to practical welding procedure. Then, J-integrals were calculated by mapping the residual stress distributions to the cracked models with different shapes. Based on these parametric analyses, effects of varying crack geometries were investigated of which are fully discussed in the manuscript.

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