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.

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.

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.

Summary of Weld Residual Stress Analyses for Dissimilar Metal Weld Nozzles

2010 ◽  
Author(s):  
F. W. Brust ◽  
Tao Zhang ◽  
Do-Jun Shim ◽  
Sureshkumar Kalyanam ◽  
Gery Wilkowski ◽  
...  
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Residual Stresses ◽  
Weld Metal ◽  
Crack Growth ◽  
Steam Generator ◽  
Deep Hole ◽  
Pressurized Water ◽  
Dissimilar Metal ◽  
Weld Residual Stress

Flaw indications have been found in some dissimilar metal nozzle to stainless steel piping welds in pressurized water reactors (PWR) throughout the world. The nozzle welds usually involve welding ferritic (often A508) nozzles to 304/316 stainless steel pipe using Alloy 182/82 weld metal. Due to an unexpected aging issue with the weld metal, the weld becomes susceptible to a form of corrosion cracking referred to as primary water stress corrosion cracking (PWSCC). It can occur if the temperature is high enough (usually >300C) and the water chemistry in the PWR is typical of operating plants. This paper represents one of a series of papers which examine the propensity for cracking in a particular operating PWR in the UK. This paper represents an examination of the weld residual stress distributions which occur in four different size nozzles in the plant. Companion papers in this conference examine crack growth and PWSCC mitigation efforts related to this plant. British Energy (BE) has developed a work program to assess the possible impact of PWSCC on dissimilar metal welds in the primary circuit of the Sizewell ‘B’ pressurized water reactor. This effort has included the design and manufacture of representative PWR safety/relief valve nozzle welds both with and without a full structural weld overlay, multiple residual stress measurements on both mock-ups using the deep hole and incremental deep hole methods, and a number of finite element weld residual stress simulations of both the mock-ups and equivalent plant welds. This work is summarized in companion papers [1–3]. Here, the detailed weld residual stress predictions for these nozzles are summarized. The weld residual stresses in a PWR spray nozzle, safety/relief nozzle, surge nozzle, and finally a steam generator hot-leg nozzle are predicted here using an axis-symmetric computational weld solution process. The residual stresses are documented and these feed into a natural crack growth analysis provided in a companion PVP 2010-25162 paper [1]. The solutions are made using several different constitutive models: kinematic hardening, isotropic hardening, and a mixed hardening model. Discussion will be provided as to the appropriateness of the constitutive model for multi-pass DM weld modeling. In addition, the effect of including or neglecting the post-weld heat treatment process, which typically occurs after the buttering process in a DM weld, is presented. During operation the DM welds in a PWR experience temperatures in excess of 300°C. The coefficient of thermal expansion (CTE) mismatch between the three materials, particularly the higher CTE in the stainless steel, affects the stresses at operating temperature. The K-weld geometry used in the steam generator nozzles in this plant combines with CTE mis-match effects to result in service stresses somewhat different from V-weld groove cases.

Finite Element Simulation and Experimental Investigation of Welding Residual Stress for PWR Safe-End

2016 ◽  
Author(s):  
Guodong Zhang ◽  
Fei Xue ◽  
Yanfen Zhao ◽  
Lu Zhang
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Weld Metal ◽  
Welded Joint ◽  
Welding Residual Stress ◽  
Chemical Compositions ◽  
Dissimilar Metal ◽  
Element Simulation ◽  
Dissimilar Metal Weld ◽  
Metal Weld

A 3-D sequential coupling finite element simulation is performed to investigate the temperature field and residual stress in the dissimilar metal weld of a PWR safe-end and nozzle. Chemical compositions and welding residual stress of the dissimilar metal weld are measured. And residual stress of the welded joint of nozzle and safe-end has been studied, aiming to provide a reference for the fabrication and operation of safe-end and nozzle. The testing results show that the experiment results are consistent with FE results. The FE simulation method can be used for the welding residual analysis of the welded joint. And, the calculating results show that large hoop (S33) and axial (S22) of welding residual stresses are generated in the weld metal. The maximum tensile and compressive stresses of S22 and S33 are all in the weld metal or at the interface of the nozzle and weld metal. Due to the difference in mechanical properties and chemical compositions between the base metal and weld metal, a discontinuous stress distribution is generated across the interface between the weld metal and nozzle.

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.

NRC/EPRI Welding Residual Stress Validation Program: Phase III Details and Findings

2011 ◽  
Author(s):  
Lee F. Fredette ◽  
Matthew Kerr ◽  
Howard J. Rathbun ◽  
John E. Broussard
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Plant Material ◽  
Welding Residual Stress ◽  
Phase Iii ◽  
Pressurized Water ◽  
Dissimilar Metal

The US Nuclear Regulatory Commission (NRC) and the Electric Power Research Institute (EPRI) are working cooperatively under a memorandum of understanding to validate welding residual stress predictions in pressurized water reactor primary cooling loop components containing dissimilar metal (DM) welds. These stresses are of interest as DM welds in pressurized water reactors are susceptible to primary water stress corrosion cracking (PWSCC) and tensile weld residual stresses are one of the primary drivers of this stress corrosion cracking mechanism. The NRC/EPRI welding residual stress (WRS) program currently consists of four phases, with each phase increasing in complexity from lab size specimens to component mock-ups and ex-plant material. This paper discusses Phase III of the WRS characterization program, comparing measured and predicted weld residual stresses profiles through the dissimilar metal weld region of pressurizer safety and relief nozzles removed from a cancelled plant in the United States. The DM weld had already been completed on all of the plant nozzles before use in the mock-up program. One of the nozzles was completed with the application of the stainless steel safe-end weld to a section of stainless steel pipe. Measurements were taken on the nozzles with and without the welded pipe section. Several independent finite element analysis predictions were made of the stress state in the DM weld. This paper compares the predicted stresses to those found by through-thickness measurement techniques (Deep Hole Drilling and Contour Method). Comparisons of analysis results with experimental data will allow the NRC staff to develop unbiased measures of uncertainties in weld residual stress predictions with the goal of developing assurances that the analysis predictions are defensible through the blind validation provided using well controlled mock-ups and ex-plant material in this program.

Residual Stress Prediction in Dissimilar Metal Weld Pipe Joints Using the Finite Element Method

2005 ◽  
Vol 490-491 ◽  
pp. 53-61 ◽  
Author(s):  
Dimitrios Elias Katsareas ◽  
Anastasius Youtsos
Keyword(s):  
Finite Element Method ◽  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
The Finite Element Method ◽  
Dissimilar Metal ◽  
Stress Prediction ◽  
Dissimilar Metal Weld ◽  
Metal Weld ◽  
Element Method

Dissimilar metal welds are commonly found in the primary piping of pressurized water nuclear reactor power plants. The safety assessment practice for such welds requires residual stresses to be taken into consideration. In the present paper the finite element method is utilized for the simulation of the welding process and prediction of the residual stress field in a dissimilar metal weld pipe joint. Although it is common practice to develop in-house finite element codes for weld simulation, the ANSYS commercial finite element code is selected. This is mainly due to the fact that industry focuses on commercial software, since residual stress analysis procedures based on them can be readily transferred to industrial applications. A simplified 2-D axi-symmetric model, in which residual stresses are produced due to the thermo-mechanical properties mismatch during cooling of the weld, is compared with a detailed model in which the complete multi-pass welding procedure is simulated. The latter incorporates the “birth & death of elements” technique, temperature dependant material properties and kinematic hardening material behavior. The aim of this comparison is to establish the degree of model detail and complexity, necessary to obtain satisfactory results and consequently to define a golden rule between computational cost and practically accurate predictions. Identifying the specific simulation parameters and variables, that have the highest impact on the accuracy of the computed results, is also important. It is concluded that, a bead-by-bead or lump-by-lump detailed simulation is necessary in order to obtain reasonably accurate residual stresses that cannot be predicted by a simplified model. A general conclusion is that the proposed method, being simple in implementation and cost effective concerning model complexity and analysis time, is a potential weld residual stress prediction tool.

Residual Stress Analysis in a Thick Dissimilar Metal Weld Based on Neutron Diffraction

2004 ◽  
Author(s):  
Carsten Ohms ◽  
Dimitrios E. Katsareas ◽  
Robert C. Wimpory ◽  
Peter Hornak ◽  
Anastasius G. Youtsos
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Residual Stresses ◽  
Stress Analysis ◽  
Test Procedure ◽  
Diffraction Method ◽  
Research Centre ◽  
Dissimilar Metal ◽  
Dissimilar Metal Weld ◽  
Metal Weld

Residual stresses in welded structural components can significantly compromise their performance and lifetime. Non-destructive measurement of such stresses remains a challenging task and neutron diffraction, in principle similar to X-ray diffraction, is used in this study. At the High Flux Reactor (HFR) of the Joint Research Centre (JRC), Petten, the Netherlands, a facility is available to investigate residual stresses in components of up to 1000 kg — the Large Component Neutron Diffraction Facility (LCNDF). Residual stress measurements in a dissimilar metal weld are presented. The specimen investigated is a full-scale mock-up of a pressure vessel to primary piping bi-metallic weld. The specimen wall thickness is 51 mm. A key issue in applying neutron diffraction to welds is the reliable estimation of the stress-free lattice spacing in the heat affected zones and weld pool. The description of the test procedure and the resulting strain/stress data are presented in this paper. Based on this a predictive FEM model has been calibrated. Comparison of test data and numerical results clearly shows that the neutron diffraction method as applied at the HFR, although touching its limits in this study, is still capable of yielding 3-D stress analysis data in steel specimens of more than 50 mm thickness.

Effectiveness of Excavate and Weld Repair on a Large Diameter Piping Dissimilar Metal Weld by Finite Element Analysis

2012 ◽  
Author(s):  
Francis H. Ku ◽  
Pete C. Riccardella ◽  
Aparna Alleshwaram ◽  
Eric Willis
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Large Diameter ◽  
Weld Repair ◽  
Element Analysis ◽  
Dissimilar Metal ◽  
Primary Water ◽  
Dissimilar Metal Weld ◽  
Metal Weld

Finite element weld residual stress analyses are performed to investigate the effectiveness of a newly proposed repair option for primary water stress corrosion cracking (PWSCC) in dissimilar metal welds in PWRs: Excavate and Weld Repair (EWR). Analyses are performed on a 30″ (762mm) outside diameter (OD) and 3″ (76mm) thick stainless steel pipe connected to a low alloy steel nozzle with a dissimilar metal weld (DMW). Eight EWR cases are analyzed to evaluate the sensitivities in weld residual stresses due to variations in the width and depth of the EWR, including cases with and without a thin weld cap on top of the DMW. The results demonstrate that a wide EWR that extends beyond the original width of the DMW provides the maximum residual stress benefits to the DMW, in terms of reducing the as-welded residual stresses. It is also found that the presence of the weld cap yields only marginal residual stress benefits.

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