Effect of Adjacent Safe End to Piping Weld and Preemptive Weld Overlay Repair on Residual Stresses on Nozzle to Safe End Weld

2009 ◽  
Author(s):  
Tae-Kwang Song ◽  
Yun-Jae Kim ◽  
Yun-Bae Chun ◽  
Chang-Yong Oh ◽  
Hong-Yeol Bae ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Short Length ◽  
Nozzle Geometry ◽  
Finite Element Analyses ◽  
Weld Overlay ◽  
Dissimilar Metal ◽  
Asme Code ◽  
Dissimilar Metal Weld ◽  
Metal Welding ◽  
Metal Weld

In this study, simplified nozzle geometry was proposed to quantify the effects of adjacent similar metal weld and weld overlay on residual stresses in dissimilar metal weld. Finite element analyses were conducted with various thickness ratios and safe end lengths and corresponding residual stresses were provided. According to the results, residual stresses in dissimilar metal weld were improved after adjacent similar metal welding. The effect of similar metal welding is more evident with shorter length of safe end. Thus, short length of safe end was recommended for new design of nozzle. Appropriate thickness of preemptive weld overlay reduces the conservative thickness recommended by ASME Code.

Design of a Weld Overlay for a Large Bore Pipe Nozzle to Optimize Residual Stress

2010 ◽  
Author(s):  
Douglas E. Killian
Keyword(s):  
Residual Stress ◽  
Compressive Residual Stress ◽  
Reactor Vessel ◽  
Inside Surface ◽  
Weld Overlay ◽  
Dissimilar Metal ◽  
Surface Flaws ◽  
Asme Code ◽  
Dissimilar Metal Weld ◽  
Metal Weld

Full Structural Weld Overlays (FSWOL) have been used successfully in the nuclear power industry for a number of years to mitigate and repair small (4″) to medium (10″) bore welded piping components susceptible to primary water stress corrosion cracking (PWSCC). Mitigation is provided by the creation of compressive residual stress on the inside surface of the pipe as layers of weld overlay are deposited over the outside surface of the pipe. ASME Code Case N-740-2 requires that these overlay designs provide adequate structural integrity considering the growth of postulated 75% through-wall inside surface flaws by PWSCC and cyclic fatigue. Application of this repair procedure to larger diameters components such as 30 inch reactor vessel nozzles is not practical due to the large amount of weld metal (overlay thickness) which would be required to satisfy the design requirements of a FSWOL and the associated demands on implementation schedule and exposure to radiation. An alternate procedure is currently being considered for these larger components which utilizes an Optimized Weld Overlay (OWOL) design based on a reduced thickness and smaller postulated flaw. In particular, ASME Code Case 754 specifies, in part, that 50% through-wall inside surface flaws be shown to be acceptable. Furthermore, an OWOL would continue to provide mitigation of materials susceptible to PWSCC by requiring that the thickness of the overlay be sufficient to induce compressive residual stress on the inside surface. This paper presents results of finite element analysis for an optimized weld overlay on a large bore (30″) reactor vessel coolant nozzle dissimilar metal weld, with particular attention to the incremental development of residual stress with each layer of weld metal. Through numerical simulation of the complete fabrication history, including repair of the original dissimilar metal weld, hydrostatic testing, and completion of the nozzle safe end-to-pipe joint prior to implementation of the overlay, the pre-overlay state of stress is defined for use as the basis for evaluating the stress improvement provisions of the weld overlay process. Results are obtained for both kinematic and isotropic hardening rules to study the effect of these two extreme measures of material characterization on the development of residual stress. Additional results are presented to study the sensitivity of the welding simulations to material yield strength and mesh refinement. Predicted stresses are also compared to measured data from a full scale mockup of a large bore reactor vessel nozzle with an optimized weld overlay.

scholarly journals Experimental Characterisation and Numerical Modelling of Residual Stresses in a Nuclear Safe-End Dissimilar Metal Weld Joint

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1298
Author(s):  
Shuyan Zhang ◽  
Zhuozhi Fan ◽  
Jun Li ◽  
Shuwen Wen ◽  
Sanjooram Paddea ◽  
...  
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Residual Stresses ◽  
Weld Joint ◽  
Steel Tube ◽  
Contour Method ◽  
Fe Modelling ◽  
Dissimilar Metal ◽  
Dissimilar Metal Weld ◽  
Metal Weld

In this study, a mock-up of a nuclear safe-end dissimilar metal weld (DMW) joint (SA508-3/316L) was manufactured. The manufacturing process involved cladding and buttering of the ferritic steel tube (SA508-3). It was then subjected to a stress relief heat treatment before being girth welded together with the stainless steel tube (316L). The finished mock-up was subsequently machined to its final dimension. The weld residual stresses were thoroughly characterised using neutron diffraction and the contour method. A detailed finite element (FE) modelling exercise was also carried out for the prediction of the weld residual stresses resulting from the manufacturing processes of the DMW joint. Both the experimental and numerical results showed high levels of tensile residual stresses predominantly in the hoop direction of the weld joint in its final machined condition, tending towards the OD surface. The maximum hoop residual stress determined by the contour method was 500 MPa, which compared very well with the FE prediction of 467.7 Mpa. Along the neutron scan line at the OD subsurface across the weld joint, both the contour method and the FE modelling gave maximum hoop residual stress near the weld fusion line on the 316L side at 388.2 and 453.2 Mpa respectively, whereas the neutron diffraction measured a similar value of 480.6 Mpa in the buttering zone near the SA508-3 side. The results of this research thus demonstrated the reasonable consistency of the three techniques employed in revealing the level and distribution of the residual stresses in the DMW joint for nuclear applications.

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

2022 ◽  
Author(s):  
Bernadett Spisák ◽  
Zoltán Bézi ◽  
Szabolcs Szávai
Keyword(s):  
Residual Stresses ◽  
Load Capacity ◽  
Maximum Load ◽  
Operational Conditions ◽  
Manufacturing Method ◽  
Dissimilar Metal ◽  
Welding Defects ◽  
Complex Procedure ◽  
Dissimilar Metal Weld ◽  
Metal Weld

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.

High-Temperature Constitutive Behavior of Austenitic Stainless Steel for Weld Residual Stress Modeling

2012 ◽  
Author(s):  
Dongxiao Qiao ◽  
Wei Zhang ◽  
Zhili Feng
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stainless Steel ◽  
High Temperature ◽  
Residual Stresses ◽  
Constitutive Rule ◽  
Dissimilar Metal ◽  
Weld Residual Stress ◽  
Dissimilar Metal Weld ◽  
Metal Weld

Weld residual stress is a major driving force for initiation and growth of primary water stress corrosion cracking (PWSCC), which is a critical challenge for weld integrity of reactor pressure vessel nozzles in nuclear industry. Predicting weld residual stresses for the purpose of understanding and mitigating PWSCC requires the knowledge of material constitutive rule especially strain hardening behavior over a wide range of temperatures. Though it is adequate for describing deformation at low temperature, the conventional, rate-independent, elastic-plastic constitutive rule falls short in predicting the strong microstructure-mechanical interaction such as the softening due to recovery (dislocation annihilation and realignment) and recrystallization at elevated temperature in welding. To quantify the extent of softening under temperature and strain conditions relevant to welding, a framework has been developed by combining advanced experimental techniques and finite element modeling. First, physical simulation in a Gleeble testing machine is used to simulate the temperature transients typical of dissimilar metal weld by subjecting round tensile bar shaped specimens to rapid heating and cooling. Second, the digital image correlation (DIC) technique is used to map the non-uniform strain field and extract local strain history needed for accurately determining the true stress vs. true strain curve of softened material. Third, the thermally-mechanically processed specimens are characterized metallographically to correlate the microstructure changes to the measured stress-strain behavior. Finally, a thermal-stress finite element model of three-bar frame is used to study the effect of softening on the predicted weld residual stresses. As a first step toward developing the much-needed, comprehensive material constitutive relation database for dissimilar metal weld, the framework has been applied to study AISI 304L austenitic stainless steel. The extent of softening due to different duration of high-temperature exposure is studied and its influence on final residual stresses is discussed.

Important Residual Stress Features in Reactor Nozzle Dissimilar Metal Welds

2011 ◽  
Author(s):  
Jinmiao Zhang ◽  
Shaopin Song ◽  
Pingsha Dong
Keyword(s):  
Residual Stress ◽  
Stress Distribution ◽  
Nuclear Reactor ◽  
Residual Stress Distribution ◽  
Stress Distributions ◽  
Weld Overlay ◽  
Dissimilar Metal ◽  
Nozzle Length ◽  
Dissimilar Metal Weld ◽  
Metal Weld

This paper is focused on the study of residual stress distribution at a dissimilar metal weld (DMW) of nuclear reactor nozzle. The paper extends some of the recent research on this subject by investigating the effect of weld sequence and nozzle length design on the residual stress distributions. It also investigates the effect of a partial excavation repair and a weld overlay on the residual stress distribution. As a result, some of the important residual stress features at DMW are revealed and these features are discussed and summarized in the paper.

Validation of Welding Residual Stress Model Using Results From a Pressurizer Surge Nozzle Mockup

2011 ◽  
Author(s):  
Doug Killian
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Residual Stresses ◽  
Crack Growth ◽  
Material Properties ◽  
Welding Residual Stress ◽  
Stress Model ◽  
Dissimilar Metal ◽  
Dissimilar Metal Weld ◽  
Metal Weld

Although numerical welding simulation is now commonly used in the nuclear industry to predict residual stresses in reactor vessels and associated piping components, there are currently no universally accepted guidelines for performing such analysis. Moreover, due to the complexity of the calculations and varying analytical procedures among analysts, there remains a need to validate predictions of residual stress against benchmark studies. As part of an industry initiative to manage the degradation of dissimilar metal welds in pressurized water reactor piping that are susceptible to primary water stress corrosion cracking, the U.S Nuclear Regulatory Commission embarked on a multi-phased program to validate welding residual stress models. The aim of Phase II of this program is to obtain measured residual stresses from a pressurizer surge nozzle dissimilar metal weld mockup for use in comparisons with numerically predicted stresses. This paper presents results of finite element analysis for various stages during the fabrication of a 14–inch pressurizer surge nozzle mockup, including an Alloy 82 dissimilar metal weld between a stainless steel safe end and carbon steel nozzle, an inside surface weld repair (back weld) and fill-in weld (weld build-up), and a stainless steel “field” weld attaching a section of straight pipe to the safe end. The NRC validation program was structured to allow participants to first calculate results using their own material properties, and then tune their welding simulations to thermocouple data. This was followed by reanalysis using NRC-supplied material properties. The program was conducted as a round robin analysis among an international group of participants and formatted as a blind validation project wherein results were submitted to the NRC prior to receipt of thermocouple and material property data. Results were obtained for both kinematic and isotropic hardening rules to study the effect of these two extreme measures of material characterization on the development of residual stress. Predicted stresses are then compared to measured stress data obtained by the deep-hole drilling technique at multiple locations through the thickness of the weld. The NRC residual stress model validation project serves as a valuable contribution to the understanding of how residual stresses are developed in dissimilar metal welds. The correlation of calculated residual stresses with measured data from a relevant mockup also serves to increase confidence in predicting crack growth in these primary pressure boundary welds by removing much of the uncertainty previously associated with residual stress input to crack growth analysis.

Development and Validation of Analysis Method for Simulating Residual Stresses in Dissimilar Metal Pipe Butt Welds

2008 ◽  
Author(s):  
Douglas E. Killian ◽  
Samer H. Mahmoud
Keyword(s):  
Residual Stresses ◽  
Fabrication Process ◽  
Research Centre ◽  
Analysis Method ◽  
Weld Repair ◽  
Butt Weld ◽  
Dissimilar Metal ◽  
Dissimilar Metal Weld ◽  
Temperature And Pressure ◽  
Metal Weld

It is now accepted practice in the commercial nuclear power industry to numerically simulate the residual stresses developed during welding of bimetallic piping components. A common example is the Alloy 82/182 shop weld between a low alloy steel nozzle and a stainless steel safe end. Piping is attached to the nozzle safe end by a separate girth butt weld in the field. The safe end to pipe weld influences stresses in the nozzle to safe end weld only for relatively short safe ends. Alloy 600 base metal material and its associated welds are susceptible to primary water stress corrosion cracking (PWSCC) at elevated levels of stress. It is therefore necessary to model each step of the fabrication process to capture the path dependent accumulation of stress and strain in the welded components, and to simulate the pre-service test loads and operating temperature and pressure loads. The fabrication process includes the build up of butter material on the nozzle prior to heat treatment and the deposition of weld metal in a single V-groove between the butter and safe end. This is followed by one or more repair welds to remove welding defects. The welded component is then subjected to a shop hydrostatic test pressure equal to 125 percent of the design pressure. Following several heatup and cooldown cycles to simulate “shakedown” of pre-service stresses, stresses in the vicinity of the weld are determined at operating conditions of temperature and pressure in order to access the susceptibility of the weld and butter to PWSCC. This paper discusses the analytical methodology used to numerically simulate welding residual stresses using the ANSYS general purpose computer code. The method is then applied to two-dimensional axisymmetric welding simulations, which are adequate to investigate most girth butt weld piping components, although it may be necessary to make conservative assumptions regarding weld repair configurations. Numerical results are used to characterize the effects of weld repair, pre-service loads, and cyclic loading on the final state of operating stresses for sustained loading conditions. The analysis method is validated using results from large scale tests performed by the European Commission Joint Research Centre as part of its Assessment of Aged Piping Dissimilar Metal Weld (ADIMEW) project. Residual stresses are predicted for a ferritic-to-austenitic dissimilar metal weld mockup and compared against results from neutron diffraction measurements.

Effects of Initial Crack Location on Failure Assessment Curves in Dissimilar Metal Weld Joints in Nuclear Power Plants

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
N. Gong ◽  
G. Z. Wang ◽  
F. Z. Xuan ◽  
S. T. Tu
Keyword(s):  
Three Dimensional ◽  
Initial Crack ◽  
Finite Element Analyses ◽  
Crack Location ◽  
Dissimilar Metal ◽  
Failure Assessment ◽  
Dimensional Finite Element ◽  
Dissimilar Metal Weld ◽  
Three Dimensional Finite Element ◽  
Metal Weld

Based on detailed three-dimensional finite element analyses, accurate, option 3, failure assessment curves (FACs) based on the R6 are constructed for a dissimilar metal weld joint (DMWJ) connecting the safe end to the pipe-nozzle of a reactor pressure vessel. The effects of initial crack location in the DMWJ structure on FACs are investigated. The results show that the plastic collapse of the DMWJ structure and the limit moment ML is mainly dominated by the plastic yield of the 316L material with lowest yield stress, and the crack locations in the DMWJ structure have less effect on the ML. When the load ratio Lr is less than 0.8, the crack locations have almost no effect on the FACs; while after the Lr is larger than 0.8, the crack locations have significant effect on the FACs. With the crack location moving from the safe end through the DMWJ toward the thickness transition in the pipe-nozzle, the FACs shift upward, which leads to a enlargement of the safe region in the failure assessment diagrams (FADs). This is mainly caused by the different properties of the materials in the DMWJ structure. To accurately assess the integrity of the DMWJ structure, the R6 option 3 FACs based on three-dimensional finite element analyses should be constructed and used for the cracks with different positions.

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