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.

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.

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.

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.

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.

FE Residual Stress Analysis in a Narrow Gap Dissimilar Metal Weld

2012 ◽  
Author(s):  
Florian Obermeier ◽  
Stéphan Courtin ◽  
Tomas Nicak ◽  
Elisabeth Keim
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Nuclear Industry ◽  
Narrow Gap ◽  
Dissimilar Metal ◽  
Piping Systems ◽  
Dissimilar Metal Weld ◽  
Residual Stress Analysis ◽  
Metal Weld

In the nuclear industry narrow gap welding techniques are used to perform junctions between ferritic low alloy steel heavy section components and austenitic stainless steel piping systems. The residual stresses in Dissimilar Metals Welds (DMW) may influence the lifetime and functionality of the welded components. In Pressurized Water Reactor (PWR) piping systems, weld residual stresses in particular increased the susceptibility to primary water stress corrosion cracking (PWSCC) in the past. It is therefore necessary to develop and validate methods for a reliable residual stress and distortion prediction. Numerical welding simulations for predicting residual stresses are commonly used in nuclear industry and their development is progressing fast during the recent years. As part of the European project STYLE — Structural Integrity for Lifetime Management — a case study was launched to assess the capability of such simulations. The mock-up in this case study is provided by AREVA NP SAS. It is a pipe with a narrow gap dissimilar metal weld. The pipe thickness is about 40 mm and the outer diameter is 352 mm after final machining. In this assembly a 316L austenitic pipe is welded to an A508 Class 3 ferritic pipe by means of Alloy 52 Gas Tungsten Arc (GTA) narrow gap weld which is representative for PWR primary circuit piping. This mock-up is in the scope of a continuation of the ADIMEW – Assessment of Aged Piping Dissimilar Metal Weld Integrity - project and deals with the improvement of the assessment for DMW and Leak-before-break (LBB) procedures. The fracture test on this mock-up is planed to be performed at 300 °C with an initial through-wall defect. Apart from the LBB demonstration this mock-up is also dedicated for the validation of the applied fracture mechanics approach, extension of material data basis and validation of the weld simulation procedures applied within AREVA. This paper presents the results of the finite element residual stress analysis related to this STYLE narrow gap weld case study. The two finite element codes ABAQUS and SYSWELD were used to predict the weld residual stresses and the shrinkage in axial direction. The major difference between the here presented methods is that SYSWELD accounts for phase transformation and the method used with ABAQUS does not. The results are compared between each other and with data obtained by deep-hole drilling techniques (DHD) at several locations.

ADIMEW Test: Assessment of a Cracked Dissimilar Metal Weld Assembly

2004 ◽  
Author(s):  
John B. Wintle ◽  
Bridget Hayes ◽  
Martin R. Goldthorpe
Keyword(s):  
Residual Stresses ◽  
Material Properties ◽  
Nuclear Power ◽  
Large Scale ◽  
Research Programme ◽  
Element Analysis ◽  
Dissimilar Metal ◽  
Four Point Bending ◽  
Dissimilar Metal Weld ◽  
Metal Weld

ADIMEW (Assessment of Aged Piping Dissimilar Metal Weld Integrity) was a three-year collaborative research programme carried out under the EC 5th Framework Programme. The objective of the study was to advance the understanding of the behaviour and safety assessment of defects in dissimilar metal welds between pipes representative of those found in nuclear power plant. ADIMEW studied and compared different methods for predicting the behaviour of defects located near the fusion boundaries of dissimilar metal welds typically used to join sections of austentic and ferritic piping operating at high temperature. Assessment of such defects is complicated by issues that include: severe mis-match of yield strength of the constituent parent and weld metals, strong gradients of material properties, the presence of welding residual stresses and mixed mode loading of the defect. The study includes the measurement of material properties and residual stresses, predictive engineering analysis and validation by means of a large-scale test. The particular component studies was a 453mm diameter pipe that joins a section of type A508 Class 3 ferritic pipe to a section of type 316L austentic pipe by means of a type 308 austentic weld with type 308/309L buttering laid on the ferritic pipe. A circumferential, surface-breaking defect was cut using electro discharge machining into the 308L/309L weld buttering layer parallel to the fusion line. The test pipe was subjected to four-point bending to promote ductile tearing of the defect. This paper presents the results of TWI contributions to ADIMEW including: fracture toughness testing, residual stress measurements and assessments of the ADIMEW test using elastic-plastic, cracked body, finite element analysis.

The Impact of Axi-Symmetric Boundary Conditions on Predicted Residual Stress and Shrinkage in a PWR Nozzle Dissimilar Metal Weld

2012 ◽  
Author(s):  
Philip J. Bendeich ◽  
Ondrej Muránsky ◽  
Cory J. Hamelin ◽  
Mike C. Smith ◽  
Lyndon Edwards
Keyword(s):  
Residual Stresses ◽  
Control Method ◽  
Axial Direction ◽  
3D Analysis ◽  
Computationally Efficient ◽  
Dissimilar Metal ◽  
Dissimilar Metal Weld ◽  
Set Up ◽  
The Impact ◽  
Metal Weld

Simulation of a dissimilar metal weld (DMW) in a pressurised water reactor (PWR) nozzle was performed to predict both axial distortion and hoop residual stresses in the weld. For this work a computationally efficient axi-symmetric finite element (FE) simulation was carried out rather than a full 3D analysis. Due to the 2-dimensional nature of the analysis it was necessary to examine the effect of structural restraint during welding of the main dissimilar metal weld (DMW). Traditionally this type of analysis is set up to allow one end of the structure, in this case the safe-end forging, to be unrestrained in the axial direction during welding. In reality axial expansion and subsequent contraction of deposited weld metal at the current torch position is restrained by solidified material both ahead and behind the torch. Thus the conventional axi-symmetric analysis is under-restrained in the axial direction at least during the early weld passes. The significance of this was examined by repeating the current simulation with the safe-end forging fixed to limit expansion during the heat up cycle. Contraction was however, allowed during cooling cycle. This modified boundary control method provided a significantly improved prediction of the axial distortion across the weld as well as improved prediction of through wall axial and hoop residual stresses.

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