Effect of Size of Butt Weld Repairs on Weld Overlay Residual Stresses

2007 ◽  
Author(s):  
Carl R. Limpus ◽  
David G. Dijamco ◽  
Richard Bax ◽  
Nathaniel G. Cofie
Keyword(s):  
Residual Stresses ◽  
Nuclear Power ◽  
Analytical Modeling ◽  
Weld Repair ◽  
Butt Weld ◽  
Weld Overlay ◽  
Compressive Stresses ◽  
Element Simulation ◽  
Weld Overlays ◽  
Compressive Residual Stresses

Weld overlays have been used to provide repair and mitigation to stress corrosion cracking (SCC) susceptible butt welds in nuclear power plant piping. Among the several advantages associated with weld overlays are the beneficial compressive residual stresses that are developed in the inner portion of the component after application of the overlay. These compressive stresses can provide significant mitigation against SCC in these welds. To determine the residual stresses resulting from the weld overlay process in analytical modeling, a weld repair during original fabrication of the butt weld is typically assumed before application of the weld overlay. If the fabrication records are available, the details of the weld repair can be simulated in the analysis. However, in most cases, the weld records are not easily accessible and in instances where they are available, the quality and completeness of the information are questionable. As such, various conservative assumptions are made on the extent of the weld repair to be simulated in the analytical modeling. In this paper, the residual stress results of an axisymmetric finite element simulation of a bimetallic weld subjected to an inside surface weld repair followed by a weld overlay repair are presented. Three through-wall weld repair sizes (25%, 50% and 75% of the wall thickness without the overlay) assumed to be full 360° around the circumference were considered in the study. The results indicate that for all three weld repair cases, the inside of the configuration is very tensile after the weld repair indicating that regardless of the size of the weld repair, SCC is a possibility. The post weld repair stress distribution of the 50% and the 75% repair cases are similar indicating that an assumed 50% repair is fairly representative of repairs that can be assumed for analysis purposes. The application of the overlay resulted in favorable compressive stresses on the inside portion of the configuration for all the three weld repair cases indicating that regardless of the size of the initial weld repair, the application of the weld overlay provides mitigation against SCC.

Technical Basis for Code Case N-847: Excavate and Weld Repair (EWR) for SCC Mitigation

2016 ◽  
Author(s):  
Steven McCracken ◽  
Jonathan Tatman ◽  
Pete Riccardella
Keyword(s):  
Nuclear Power ◽  
Outer Part ◽  
Nuclear Power Reactor ◽  
Preparation Time ◽  
Weld Repair ◽  
Butt Weld ◽  
Weld Overlay ◽  
New Strategy ◽  
Asme Code ◽  
Technical Basis

Stress corrosion cracking (SCC), though infrequent, is often detected in nuclear power reactor system piping and components. A number of approaches have been developed and successfully deployed for SCC repair and mitigation such as full structural weld overlay (FSWOL), optimized weld overlay (OWOL), and mechanical stress improvement process (MSIP). While these approaches are proven technologies and have served the industry well, a new strategy, excavate and weld repair (EWR), provides yet another option for repair or mitigation of SCC. The EWR approach excavates a portion of the outer part of the butt weld. The excavation is then filled with a weld metal with demonstrated SCC resistance. The EWR approach would require less welding compared to a weld overlay and may be the best option for large bore butt welds where restricted access may make FSWOL, OWOL, or MSIP impractical. For the situation where a flaw is detected and removal or reduction of the flaw to acceptable size is necessary for continued service, the approach would permit a local partial arc EWR where only a portion of the butt weld circumference is removed and repaired. While the partial arc EWR is not a full mitigation, it would provide the needed preparation time for a more permanent repair during a subsequent refueling or maintenance outage. ASME Code Case N-847 was developed to provide examination, design, installation, and preservice/inservice inspection requirements for the EWR repair and mitigation approach. This paper provides a background, description and the technical bases for the EWR case case.

Post Weld Overlay Residual Stresses in Dissimilar Metal Welds Considering Various Butt Weld and Weld Repair Fabrication Sequences

2009 ◽  
Author(s):  
Francis H. Ku ◽  
Christopher S. Lohse ◽  
David G. Dijamco ◽  
Charles J. Fourcade ◽  
Richard L. Bax ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Welding Process ◽  
Reasonable Assumption ◽  
Weld Repair ◽  
Pressurized Water ◽  
Butt Weld ◽  
Weld Overlay ◽  
Water Reactor ◽  
Dissimilar Metal ◽  
Pipe Size

Weld overlays have been used to repair or mitigate stress corrosion cracking (SCC) in both boiling water reactor (BWR) and pressurized water reactor (PWR) nozzle-to-pipe dissimilar metal welds (DMW). One of the contributing factors to SCC is the high tensile residual stresses produced during the fabrication of the original butt weld, especially when local weld repairs were present during the welding process. In analytical simulations to determine the post weld overlay residual stresses, complete simulation of the original butt weld, weld repair and the overlay is desired. However, to reduce the computational effort, it is commonly assumed that the weld repair stresses overwhelm the original butt weld residual stresses such that the original butt weld need not be simulated and only the weld repair is simulated before the application of the overlay. Questions have also been raised as to why the butt weld and/or the weld repair need to be simulated since it is assumed that both of these fabrication processes would be overcome by the weld overlay process. This paper investigates three fabrication sequences in order to determine their effect on the post weld overlay residual stresses: (1) the butt weld is simulated followed by a weld repair and then the weld overlay is applied; (2) the butt weld is simulated followed by the weld overlay with no consideration of a weld repair; (3) the butt weld is not simulated but a weld repair is assumed and the weld overlay is applied. Five different nozzle-to-pipe size configurations were used in the study to determine the effect of pipe size on the three fabrication sequences described above. The investigation indicates that the post weld overlay residual stresses for Cases 1 and 3 are similar and hence simulation of the weld repair alone (without the butt weld simulation) prior to simulating the weld overlay is a reasonable assumption. However, not simulating the weld repair (corresponding to Case 2) may provide different residual stress distribution.

scholarly journals Thermal Effects on Surface and Subsurface Modifications in Laser-Combined Deep Rolling

2021 ◽  
Vol 5 (2) ◽  
pp. 55
Author(s):  
Robert Zmich ◽  
Daniel Meyer
Keyword(s):  
Surface Layer ◽  
Residual Stresses ◽  
Thermal Loads ◽  
Deep Rolling ◽  
Mechanical Loads ◽  
Thermomechanical Process ◽  
Compressive Stresses ◽  
New Process ◽  
Negative Effect ◽  
Compressive Residual Stresses

Knowledge of the relationships between thermomechanical process loads and the resulting modifications in the surface layer enables targeted adjustments of the required surface integrity independent of the manufacturing process. In various processes with thermomechanical impact, thermal and mechanical loads act simultaneously and affect each other. Thus, the effects on the modifications are interdependent. To gain a better understanding of the interactions of the two loads, it is necessary to vary thermal and mechanical loads independently. A new process of laser-combined deep rolling can fulfil exactly this requirement. The presented findings demonstrate that thermal loads can support the generation of residual compressive stresses to a certain extent. If the thermal loads are increased further, this has a negative effect on the surface layer and the residual stresses are shifted in the direction of tension. The results show the optimum range of thermal loads to further increase the compressive residual stresses in the surface layer and allow to gain a better understanding of the interactions between thermal and mechanical loads.

Simplified FEA Models in the Analysis of the Redistribution of Beneficial Compressive Stresses in Welds During Cyclic Loading

2018 ◽  
Author(s):  
B. L. Josefson ◽  
J. Alm ◽  
J. M. J. McDill
Keyword(s):  
Cyclic Loading ◽  
Residual Stresses ◽  
Compressive Stress ◽  
Welding Process ◽  
Plastic Behavior ◽  
Element Analysis ◽  
Compressive Stresses ◽  
Static Contact ◽  
Weld Toe ◽  
Compressive Residual Stresses

The fatigue life of welded joints can be improved by modifying the weld toe geometry or by inducing beneficial compressive residual stresses in the weld. However, in the second case, the induced compressive residual stresses may relax when the welded joint is subjected to cyclic loading containing high tensile or compressive stress peaks. The stability of induced compressive stresses is investigated for a longitudinal gusset made of a S355 steel. Two methods are considered; either carrying out a high frequency mechanical impact (HFMI) treatment after welding or alternatively using low transformation temperature (LTT) electrodes during welding. The specimen is then subjected to a cyclic loading case with one cycle with a tensile peak (with magnitude reaching the local yield stress level) followed by cycles with constant amplitude. A sequential finite element analysis (FEA) is performed thereby preserving the history of the elasto-plastic behavior. Both the welding process and the HFMI treatment are simulated using simplified approaches, i.e., the welding process is simulated by applying a simplified thermal cycle while the HFMI treatment is simulated by a quasi-static contact analysis. It is shown that using the simplified approaches to modelling both the welding process and HFMI treatment gives results that correlate qualitatively well with the experimental and FEA data available in the literature. Thus, for comparison purposes, simplified models may be sufficient. Both the use of the HFMI treatment and LTT electrodes give approximately the same compressive stress at the weld toe but the extent of the compressive stress zone is deeper for HFMI case. During cyclic loading it is shown that the beneficial effect of both methods will be substantially reduced if the test specimen is subjected to unexpected peak loads. For the chosen load sequence, with the same maximum local stress at the weld toe, the differences in stress curves of the HFMI-treated specimen and that with LTT electrodes remain. While the LTT electrode gives the lowest (compressive) stress right at the well toe, it is shown that the overall effect of the HFMI treatment is more beneficial.

Fracture of Ceramics with Near Surface Gradient Residual Stresses

2007 ◽  
Vol 333 ◽  
pp. 97-106
Author(s):  
Marc Anglada
Keyword(s):  
Fracture Toughness ◽  
Residual Stresses ◽  
Graded Materials ◽  
Near Surface ◽  
Apparent Fracture Toughness ◽  
Surface Gradient ◽  
Compressive Stresses ◽  
Small Cracks ◽  
Monolithic Ceramics ◽  
Compressive Residual Stresses

The fracture toughness and strength of ceramics can be improved with respect to monolithic ceramics by developing graded materials as laminates composed of periodic alternating layers of one material separated by layers of a second material. The second layer must contain residual compressive stresses which are induced during densification because of differential thermal contraction of the layers. The overall residual stresses increase the apparent fracture toughness of the laminate. However, most deleterious natural flaws and most of the damage induced in service by the environment, contact loading, wear, etc, are small cracks on the surface of the outer layer, so that the effect of the laminate residual stresses on these cracks should be rationalised to understand their behaviour. This work presents an analysis of the influence of the gradient residual stresses on the behaviour of surface cracks under bending and indentation in materials with outer layers either with tensile or compressive residual stresses.

3D Residual Stress Simulation of an Excavate and Weld Repair Mockup

2016 ◽  
Author(s):  
Francis H. Ku ◽  
Pete C. Riccardella ◽  
Steven L. McCracken
Keyword(s):  
Residual Stresses ◽  
Weld Metal ◽  
Nuclear Power ◽  
Three Dimensional ◽  
Weld Repair ◽  
Element Analysis ◽  
Pressurized Water ◽  
Piping Systems ◽  
Asme Code ◽  
Original Construction

This paper presents predictions of weld residual stresses in a mockup with a partial arc excavate and weld repair (EWR) utilizing finite element analysis (FEA). The partial arc EWR is a mitigation option to address stress corrosion cracking (SCC) in nuclear power plant piping systems. The mockup is a dissimilar metal weld (DMW) consisting of an SA-508 Class 3 low alloy steel forging buttered with Alloy 182 welded to a Type 316L stainless steel plate with Alloy 82/182 weld metal. This material configuration represents a typical DMW of original construction in a pressurized water reactor (PWR). After simulating the original construction piping joint, the outer half of the DMW is excavated and repaired with Alloy 52M weld metal to simulate a partial arc EWR. The FEA performed simulates the EWR weld bead sequence and applies three-dimensional (3D) modeling to evaluate the weld residual stresses. Bi-directional weld residual stresses are also assessed for impacts on the original construction DMW. The FEA predicted residual stresses follow expected trends and compare favorably to the results of experimental measurements performed on the mockup. The 3D FEA process presented herein represents a validated method to evaluate weld residual stresses as required by ASME Code Case N-847 for implementing a partial arc EWR, which is currently being considered via letter ballot at ASME BPV Standards Committee XI.

scholarly journals Long-Term Stability of Residual Stress Improvement by Water Jet Peening Considering Working Processes

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Tadafumi Hashimoto ◽  
Yusuke Osawa ◽  
Shinsuke Itoh ◽  
Masahito Mochizuki ◽  
Kazutoshi Nishimoto
Keyword(s):  
Stress Relaxation ◽  
Residual Stresses ◽  
Microstructure Evolution ◽  
Elevated Temperatures ◽  
Water Jet ◽  
Term Stability ◽  
Long Term Stability ◽  
Compressive Stresses ◽  
Compressive Residual Stresses

To prevent primary water stress corrosion cracking (PWSCC), water jet peening (WJP) has been used on the welds of Ni-based alloys in pressurized water reactors (PWRs). Before WJP, the welds are machined and buffed in order to conduct a penetrant test (PT) to verify the weld qualities to access, and microstructure evolution takes place in the target area due to the severe plastic deformation. The compressive residual stresses induced by WJP might be unstable under elevated temperatures because of the high dislocation density in the compressive stress layer. Therefore, the stability of the compressive residual stresses caused by WJP was investigated during long-term operation by considering the microstructure evolution due to the working processes. The following conclusions were made: The compressive residual stresses were slightly relaxed in the surface layers of the thermally aged specimens. There were no differences in the magnitude of the relaxation based on temperature or time. The compressive residual stresses induced by WJP were confirmed to remain stable under elevated temperatures. The stress relaxation at the surface followed the Johnson–Mehl equation, which states that stress relaxation can occur due to the recovery of severe plastic strain, since the estimated activation energy agrees very well with the self-diffusion energy for Ni. By utilizing the additivity rule, it was indicated that stress relaxation due to recovery is completed during the startup process. It was proposed that the long-term stability of WJP under elevated temperatures must be assessed based on compressive stresses with respect to the yield stress. Thermal elastic–plastic creep analysis was performed to predict the effect of creep strain. After 100 yr of simulated continuous operation at 80% capacity, there was little change in the WJP compressive stresses under an actual operating temperature of 623 K. Therefore, the long-term stability of WJP during actual operation was analytically predicted.

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.

Weld Overlay Size Sensitivity on Residual Stresses in a Welded Pipe

2008 ◽  
Author(s):  
Aparna Chintapalli ◽  
G. Angah Miessi ◽  
Francis H. Ku ◽  
Raymond K. Yee
Keyword(s):  
Residual Stresses ◽  
Element Model ◽  
Sensitivity Study ◽  
Nuclear Industry ◽  
Operating Conditions ◽  
Normal Operation ◽  
Butt Weld ◽  
Weld Overlay ◽  
Overlay Technique ◽  
Welded Pipe

Weld overlay technique can be used on a welded pipe with a flaw in the butt weld to prevent it from cracking further. Due to the application of weld overlay on top of the weld, compressive stresses are developed in the pipe wall and the weld. These stresses counteract the effect of the residual stresses from the butt weld and tensile stresses produced in the pipe during normal operation. Existing guidelines in the nuclear industry specify minimum dimensions (length & thickness) of the weld overlay. However, there is no guideline regarding the optimum repair dimensions that should be used to obtain minimum residual stresses induced by the weld overlay technique. The optimum dimensions in this study refer to the minimum material that can be used for the weld overlay. This results in reduced cost, time and exposure to radiation. Hence a size sensitivity study is performed by varying three parameters, the width and thickness of the weld overlay, and the size of the pipe being repaired. The repaired pipe is assumed to be subjected to typical pressurizer water reactor (PWR) operating conditions. The weld overlay process is simulated using an axisymmetric finite element model. The axial and hoop stresses in the region of the butt weld after the weld overlay are compared. The results from this study will be analyzed to establish optimum dimensions of the weld overlay for various pipe sizes to mitigate axial and circumferential crack initiation at the butt weld.

Influence of Residual Stresses on the Interfacial Toughness Measurement by Cross-Sectional Nanoindentation

2007 ◽  
Vol 353-358 ◽  
pp. 400-403
Author(s):  
Pu Lin Nie ◽  
Yao Shen ◽  
Jie Yang ◽  
Qiu Long Chen ◽  
Xun Cai
Keyword(s):  
Thin Films ◽  
Finite Element ◽  
Residual Stresses ◽  
Interfacial Adhesion ◽  
Geometrical Parameters ◽  
Cross Sectional ◽  
Interfacial Toughness ◽  
Compressive Stresses ◽  
Element Simulation ◽  
Toughness Measurement

Cross-sectional nanoindentation (CSN) is a new method for measuring interface adhesion of thin films. The interfacial energy release rate (G), characterizing interfacial adhesion, is calculated from the material and geometrical parameters relevant to the test. Effects of residual stresses on G and crack tip phase angle Ψ, have been studied by finite element simulation in this study. The results show tensile residual stresses increase G and compressive stresses reduce it, and they have similar effects on the magnitude of Ψ.

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