bluuebunny/crossref_metadata_2025 huggingface dataset:
A Flaw Tolerance Concept for Plant Maintenance Using Virtual Fatigue Crack Growth Curve
Authors: Kamaya Masayuki , Nakamura Takao
Published: January 2014

Incorporation of the flaw tolerance concept in plant design and maintenance is discussed in order to consider the reduction in fatigue life due to the high-temperature water environment of class 1 components of NPPs. The flaw tolerance concept has been included in Section XI of the ASME BPVC. The structural factor (safety factor) for the flaw evaluation is considered in the stress, whereas it was considered in the design fatigue curve in Section III of the ASME BPVC. In order to apply the flaw tolerance concept to plant design and maintenance, it is necessary to assume the crack initiation and growth behavior. In this study, first, crack initiation and growth behavior during fatigue tests was reviewed and a relationship between the crack growth and fatigue life was quantified. Then, the safety factor was considered in the crack growth curve. It was shown that the crack size could be correlated to the usage factor and the flaw tolerance concept was reasonably considered in the plant maintenance by using the proposed virtual fatigue crack growth curve.
Cemented Carbide Plungers for LDPE Hyper Compressors: Properties, Defects and Reconditioning
Authors: van Loon Luc
Published: January 2014

Cemented carbide plungers are used in hyper compressors to compress ethylene gas to the reactor pressure between 160 and 350 MPa. Since cemented carbide is a brittle material, the failure load is determined by the nature and distribution of defects. This makes the plunger one of the most critical components in the LDPE production plant. Plunger failure can lead to very high costs because of damage on the compressor and production loss and in the worst case it can cause very high gas leakages that can lead to an explosion and fire.

Typical defects on plungers have been analyzed and related to their origin. Corrosion and thermo-mechanical fatigue cracks are discussed in detail because they are most frequently found. Causes of these defects can be process or component related, but also the influence of reconditioning techniques has been analyzed. Since most of plunger fractures are directly initiated by fatigue cracks, external factors that can lead to these cracks are analyzed.
Assembly of Gasketed Bolted Flange Joints Using Torque Control of Preload Method: FEA Approach
Authors: Abid Muhammad , Khan Yasir Mehmood , Nash David H.
Published: January 2014

This paper presents the results of the assembly of a gasketed bolted flange joint employing the torque control of preload method using nonlinear finite element analysis. It has been observed that bolt preload scatter due to elastic interactions, flange stress variation, bolt bending due to flange rotation and gasket contact stress variation are very difficult to eliminate when using the torque control method. The behaviour of a gasketed joint using two different target torque values is discussed in detail.
Residual Stress Evaluation of Dissimilar Weld Joint Using Mock-Up Models of Bottom Mounted Instrument Nozzle
Authors: Ogawa Naoki , Hojo Kiminobu , Shirako Hiroaki , Sera Takehiko
Published: January 2014

In this paper benchmark analyses was performed to evaluate the accuracy of the FE analysis method for estimating residual stress of a dissimilar weld joint of a bottom mounted instrument (BMI) nozzle. The analyses simulated each fabrication and operational process of the weld joint nozzle. For confirmation of calculation accuracy a mock-up models of BMI nozzle were produced using the same fabrication process in Japanese PWR plants and the stress distribution of the model was measured using inherent strain method. From the limitation of the geometry of the BMI nozzle smaller strain gauges were applied to decrease the measurement error. As a result a better agreement between the calculation and measurement was obtained than that of the former investigation and the circumferential stress is confirmed dominant component in the weld region.
Optimal Placement of Viscous Dampers in the Water Pipeline Networks Subjected to Near-Fault Earthquakes Using Genetic Algorithm
Authors: Sadat Shokouhi Seyed Kazem , Dolatshah Azam , Vosoughifar Hamid Reza , Rahnavard Yousef
Published: January 2014

Experiences of previous earthquakes demonstrate that lifelines have no proper performance exposed to Near-Fault (NF) earthquakes. Due to considerable effects of NF earthquakes and recommendation of the related design codes such as FEMA, evaluating the effects of these earthquakes on the pipelines is so important. In this research, the optimal placement of the viscous dampers in the water pipeline network subjected to NF earthquakes has been studied using Genetic Algorithm (GA). For this purpose, the water pipeline network of a zone in Tehran city was selected as a case study and was modeled using the Finite Element Method (FEM). Then, the nonlinear time-history analysis was undertaken via seismic scaled records of NF earthquakes. The obtained results indicated the critical points of network which were failed due to applied seismic waves. However, due to economical and technical issues, the optimal damper placement at critical points is necessary; all of the mentioned points were considered for optimization procedure using GA. Then, the viscous dampers were installed in the acquired optimal points. Eventually, a statistical test demonstrated optimum performance of the water pipelines network equipped with viscous dampers under NF earthquakes.
Pressurized Flanged Joints Subjected to Bending Cyclic Loading: Tests and Finite Element Analyses
Authors: Ferino Jan , Lucci Antonio , Demofonti Giuseppe
Published: January 2014

Temporary ground deformations produced by strong seismic activity can result in severe cyclic loading applied to piping, fittings and components such as flanges, elbows, tee joints etc. The integrity of the piping system in such condition is of critical importance for the safety of petro-chemical plants or refineries. Among various reasons of failures under earthquakes, the accumulation of plastic strains due to cyclic bending loading of pressurized piping sections containing bolted flanged joints, have to be carefully considered. This paper reports the results of the experimental full scale tests performed within the RFCS INDUSE Project [1] on PN40 and PN63 piping sections containing bolted flanged joints subjected to monotonic and cyclic bending load, in presence of internal pressure. On the basis of the experimental results, a FE model adopting Lemaitre-Chaboche nonlinear kinematic hardening rule for the pipe material has been developed, allowing to extend the results of the tests by performing a study on the main parameters affecting resistance of the joint.
Development of a Protocol to Determine the Minimum Operating Stress of Compressed Non-Asbestos Gaskets
Authors: Silva Ana C. , Rodrigues Gabriele , Xavier Lucas
Published: January 2014

The ASME PCC-1-2010 Guidelines for Pressure Boundary Bolted Flange Joint Assembly [1] introduced a new method for an appropriate assembly bolt stress determination across bolted flange connections. The method introduced in APPENDIX O of the ASME PCC-1-2010 has recently received substantial attention by several gasket researchers. In this new method, calculation is based in a complex approach that considers the integrity of each joint component. However, almost no information is found about some essential parameters. Therefore, the intent of the present study is to introduce a protocol for the determination of one of these factors: the minimum gasket operating stress (Sgmin-o). This value is defined as “the gasket stress that should be maintained on the gasket during operation in order to assure the leakage does not occur”. This paper will show a detailed study for a protocol to determine the minimum gasket operating stress and actual test results for compressed non-asbestos gaskets. Furthermore, the device used in the research will be defined in detail afterwards.
Simplified Prediction of Creep Void Density in Heat-Affected Zone of Grade 122 Steel Considering Multiaxial Stress State
Authors: Murakami Eiji , Hashimoto Masamitsu , Kikuhara Seiji
Published: January 2014

This paper deals with a simplified method for approximately predicting creep void growth in heat-affected zone (HAZ) of ASME grade 122 (11Cr-2W-0.4Mo-Cu-Nb-V) steel weldments. Authors have proposed a simplified prediction method based on the relationship between creep void density increasing rate and multiaxial stress state. This method has been applied to prediction of creep void growth behavior for grade 91 (9Cr-1Mo-Nb-V) tubular specimens with longitudinal weldments. In this study, the method has been also applied to grade 122 steel to clarify the applicability of the method.

Internal pressure creep tests of grade 122 tubular specimens with longitudinal weldments subjected to several internal pressures have been conducted to reveal creep void growth behavior in HAZ. In addition, finite element creep analyses for the specimens at different creep strain rates in base metal, weld metal and HAZ have been carried out to investigate distribution of stresses and stress triaxiality factor in HAZ. A comparison between stress distributions and creep void distributions revealed that stress triaxiality factor affects growth behavior of creep voids. From the result, the relationship between creep void density increasing rate and the parameter as a function of principal stress and triaxiality factor was established. It was found that the slope of this relationship for 122 steel has a tendency to be slightly small compared with grade 91 steel.

To demonstrate the applicability of the proposed simplified prediction method, the method was applied to the internal pressure creep test specimens at different experimental conditions. As a result, the predicted void distribution and void density increasing rates for grade 122 steel were in good agreement with the experimental results.
Low Cycle Fatigue Tests and Simulations on Steel Elbows
Authors: Pappa Patricia , Varelis George E. , Karamanos Spyros A. , Gresnigt Arnold M.
Published: January 2014

In this paper the low cycle fatigue behaviour of steel elbows under strong cyclic loading conditions (in-plane and out-of-plane) is examined. The investigation is conducted through advanced finite element analysis tools, supported by real-scale test data for in-plane bending. The numerical results are successfully compared with the experimental measurements. In addition, a parametric study is conducted, which is aimed at investigating the effects of the diameter-to-thickness ratio on the low-cycle fatigue of elbows, focusing on the stress and strain variations. Strain gauge measurements are compared with finite element models. Upon calculation of local strain variation at the critical location, the number of cycles to fracture can be estimated.
Development of Plastic Collapse Assessment Procedure for Cylindrical Vessels With a Local Thin Area Near a Nozzle Under Internal Pressure
Authors: Oyamada Kenji , Konosu Shinji , Horibe Tadashi , Ogasawara Kenta , Miyashita Tetsuji , Ohno Takashi
Published: January 2014

There are numerous cases where a local thin area has found near a nozzle attachment in cylindrical pressure vessels. Since the stress concentration due to a nozzle hole under internal pressure significantly affect to the stress state of the vessel near the nozzle, it must be taken into account in its plastic collapse assessment. In this paper, a new plastic collapse assessment procedure for cylindrical vessels with a local thin area near a nozzle attachment under internal pressure was proposed. This proposal utilizes the existing reference stresses to estimate the plastic collapse load under three-axial condition derived in accordance with the Tresca theory. The distribution of stress concentrations in vessel wall due to a nozzle attachment depends on its reinforcement condition for the nozzle hole, so the stress state should be computed by linear FEA in advance. The stress concentration factors are provided with normalizing of generated stresses in vessels near a nozzle attachment for the similar type of dimensions, orientations and projections of the nozzle attachment by the computed stresses with already-proposed equations for no reinforcement conditions.

The plastic collapse loads predicted by the proposed reference stress are ascertained with the results of experiments and non-linear FEA.
Advanced Assessment of the Ductile Fracture Mechanism in A508 Class 3 Reactor Pressure Vessel Steel Using Laboratory X-Ray Tomography
Authors: Daly Michael , Leonard Fabien , Sharples John K. , Sherry Andrew H.
Published: January 2014

Ductile damage is characterised by the nucleation, growth and coalescence of voids at initiating particles within the volume of high triaxial stresses and plastic strain ahead of a crack-tip or stress concentrator. To establish a more detailed understanding of the mechanism of ductile fracture in the A508 Class 3 ferritic RPV steels and to improve fracture models, the ductile damage was quantified below the fracture surface of tested compact test specimens using laboratory X-ray tomography imaging with sufficient resolution to image voids of approximately 10μm in diameter. The average distribution of void volume fraction as a function of distance below the fracture surface was quantified, and the initiating and coalescence mechanisms were characterised. The highest void volume fraction was observed at the fracture surface and this tends to decrease as a function of distance below the fracture surface. This decrease is periodically perturbed by large voids associated with inclusions which are distributed throughout the microstructure and act as further nucleating sites at low strains.

This distribution of voids was correlated with the local variations in stress triaxiality and plastic strain derived from finite element analyses to provide a relationship between experimental observations and the Rice and Tracey model. These correlations aim to provide new data and understanding with which to calibrate mechanistically based models such as the Gurson-Tvergaard-Needleman (GTN) model.
Numerical Simulation of Three-Dimensional Flow Past an Oscillating Cylinder
Authors: Peppa Sofia , Kaiktsis Lambros , Triantafyllou George
Published: January 2014

The paper presents computational results of three-dimensional flow past a cylinder forced to oscillate: (a) transversely with respect to a uniform stream, and (b) both transversely and in-line with respect to a uniform stream, following a figure-eight trajectory. For a flow from left to right the figure-eight is traversed counter-clockwise in the upper half-plane. DNS of the Navier-Stokes equations for three–dimensional flow is performed using a spectral element code. Computations are carried out for a Reynolds number equal to 400, at a transverse oscillation frequency equal to the natural frequency of the Kármán vortex street. For both oscillation modes, the transverse oscillation amplitude is varied from zero to 0.60 cylinder diameters. The forces on the cylinder are calculated and related to flow structure in the wake. The results indicate that, in general, the presence of in-line oscillation increases the magnitude of forces acting on the cylinder, as well as the power transfer from the flow to the structure. Flow visualizations indicate that, for the figure-eight mode, low-amplitude forcing tends to reduce the wake three-dimensionality. However, at high oscillation amplitudes, the wake structure is found to become more complex at increasing amplitude.
The Role of Computational Weld Mechanics in the Weld Repair of Canada’s NRU Nuclear Reactor
Authors: Goldak John A. , Yetisir Metin , Pistor Rob
Published: January 2014

The NRU reactor at Chalk River Laboratories is one of the largest and oldest research reactors in the world. It has been the world’s largest producer of medical isotopes, which are used in cancer treatments, nuclear medicine and other diagnostic procedures. The NRU reactor was shut down in May 2009 when a heavy water leak was detected in the reactor building. Subsequent inspections indicated that the reactors aluminum vessel corroded at various locations resulting in heavy water seeping through the reactor vessel.

The extent of the damage required a complex pattern of internally applied weld overlays in numerous areas. Weld repair was further complicated by concerns over the effect of radiation hardening of the aluminum and compositional changes (irradiation induced transmutation of aluminum to silicon). Considering the deformation and stress associated with welding aluminum plate (Figure 1) and the aggressive return to service schedule, Atomic Energy of Canada (AECL) commissioned an extensive Computational Weld Mechanics (CWM) campaign to guide the repair design and optimize structural integrity. This paper describes the technical issues encountered in the design of the weld repair processes and how CWM was used in selecting welding strategies. Traditionally, welding pattern, progression and sequence are determined through a combination of trial and error on mock ups along with welders experience and analyzed by computer after the fact. To the authors knowledge, this is the first weld repair that used CWM to assess proposed designs of welds.
Working Bolts Near to Yield: Theory, Experience and Recommended Practice
Authors: Noble Robert
Published: January 2014

For many years 50% yield was a favored generic level for bolted flanged joints, however in pursuit of leak free performance this is no longer the case. In line with the guidance given in modern documents such as Appendix O of ASME PCC-1-2010 Guidelines for Pressure Boundary Bolted Flange Assembly [1] and with the increasing number of joints requiring corrosion resistant alloys often it is necessary and desirable to take bolts to values closer to their yield point or more accurately their 0.2% proof stress. The paper will examine the issues associated with tightening bolts to values well in excess of 50% of their 0.2% proof stress and analyze the effects on the during tightening and subsequent re-tightening. The analysis will include results of actual testing of bolts tightened to high stresses and give recommendations on a sound engineering approach to this practice which considers the risks and benefits. Analysis will also include a statistical evaluation of the effects of torque and tension scatter at high levels of target bolt stress.
Triaxial Residual Stresses in Thermomechanically Rolled Seamless Tubes Characterized by High-Energy Synchrotron X-Ray Diffraction
Authors: Winter Gerald , Stefenelli Mario , Klarner Juergen , Staron Peter , Fischer Torben , Keckes Jozef , Buchmayr Bruno
Published: January 2014

Residual stresses in seamless steel tubes have a significant influence on the mechanical stability and reliability of industrial constructions. In this contribution, triaxial residual stresses in seamless rolled tubes with an outer diameter of 82 mm and a wall thickness of 9.8 mm were analyzed at synchrotron source PETRA III at DESY in Hamburg using the HZG beamline HEMS (P07) with a photon energy of 75 keV. The position-resolved measurements were performed using a conical-slit measurement technique with a spatial resolution in the direction of the X-ray beam of 0.8 mm. The tubes were produced under dedicated thermal conditions resulting in complex microstructure and residual stress profiles across the tube walls. The (experimental) measurements allowed determining axial, tangential and radial residual stress profiles. The results reveal tensile stresses up to 150 MPa on the outer wall side and compressive stress of about −120 MPa on inner wall side. The measurements document the importance of the cooling process control during the thermo-mechanical rolling, which represents a key factor for the design of dedicated microstructure and residual stress levels in the tubes.
Effect of Hydrostatic Pressure on Buckling Behavior of Storage Tanks Under Local Support Settlement
Authors: Gong Jianguo , Zeng Sheng , Jin Tao
Published: January 2014

In practical engineering, local settlement is a typical differential settlement under structures. It has drawn the attention of many researchers. This is because this kind of settlement has an important effect on tank structure. From research, the buckling behavior caused by local settlement has been reported. In most research, the local settlement is usually considered alone and the influence of hydrostatic pressure has not been reported. This work studies the effect of hydrostatic pressure on the buckling strength of conical roof tanks under local settlement. The results show that the pressure has a stiffening effect on buckling strength, preventing the shell from buckling. In addition, for small uplift half angles, buckling may not occur for liquid heights larger than the critical liquid height; while for large uplift half angles buckling may occur with full tanks. It is also shown that the critical local settlement for a small uplift half angle is more sensitive to the liquid height and hydrostatic pressure than the critical load for large uplift half angles. Finally, the relationship between the critical liquid height and uplift half angle is reported.
Methodology for the Experimental Assessment of True Stress-Strain Curves After Necking Employing Cylindrical Tensile Specimens: Experiments and Parameters Calibration
Authors: Donato Gustavo Henrique B. , Ganharul Grace Kelly Q.
Published: January 2014

Simulations and structural integrity evaluations including severe plasticity have undergone significant expansion during recent years (e.g. fracture mechanics FE models including ductile tearing and/or generalized yielding), which demand accurate true stress-strain data until fracture. This is a consequence of the use of high toughness ductile materials subjected to severe loadings and high levels of operational efficiency and optimization. However, tensile tests present one inconvenience when providing such data, since the occurrence of plastic instability (necking) complicates the direct assessment of true stress-strain curves until final fracture. Two main difficulties can be pointed out: i) the nonuniform geometry assumed by the cross sections along its length and; ii) the imposition of a complex triaxial stress state. The first occurrence can only be overcome by real-time physical measurements. The second occurrence demands a correction model to provide an equivalent stress including triaxial effects. Current authors recently demonstrated that even the well-known Bridgman’s correction presents limitations, particularly for strains greater than ∼ 0.50–0.60, which motivated proposals to better describe the geometrical evolution of necking minimizing the need for real-time physical measurements [1]. As a new step in this direction, this work presents three key contributions: i) first, experiments regarding the geometrical evolution of necking were largely extended incorporating 10 materials to corroborate the validity of the recently proposed model (including Carbon, stainless steels and copper); ii) second, and for the same materials, the necking region was investigated in more details to verify to which extent an osculating circle well describes the high deformation region. A new model could be proposed to better support future solid mechanics analyses regarding equilibrium and stress/strain fields; iii) finally, a modified Bridgman’s model is proposed, followed by recommended practices for testing. The results provide further support to σ-ε assessment considering severe plasticity and demanding less physical measurements.
Hourglass Control Convergence Studies for Hexahedral Elements Developed by the ASME Special Working Group on Computational Modeling
Authors: Molitoris David P. , Bjorkman Gordon S. , Tso Chi-Fung , Yaksh Michael
Published: January 2014

The ASME Special Working Group on Computational Modeling for Explicit Dynamics was founded in August 2008 for the purpose of creating a quantitative guidance document for the development of finite element models used to analyze energy-limited events using explicit dynamics software. This document will be referenced in the ASME Code Section III, Division 3 and the next revision of NRC Regulatory Guide 7.6 as a means by which the quality of a finite element model may be judged. One portion of the document will be devoted to a series of convergence studies that demonstrates the effect of hourglass control settings on solution convergence for reduced integration elements. These convergence studies will demonstrate the importance of selecting an appropriate hourglass control setting to achieve accurate results for large deformation simulations using reduced integration elements.

In this paper, the authors present the results of a convergence study for an impulsively loaded propped cantilever beam constructed of LS-DYNA reduced integration hexahedral elements using different hourglass control settings. A large load is applied to produce large deformations and large plastic strains in the beam.
The Influence of Inelastic Damage on Tensile Deformation and Creep Crack Growth Behaviour of Type 316H Stainless Steel
Authors: Mehmanparast A. , Davies C. M. , Dean D. W. , Nikbin K. M.
Published: January 2014

Inelastic deformation (combined plastic and creep strain) is known to have significant effects on the tensile and creep deformation behaviour of Type 316H stainless steel. In this work the influence of inelastic strain on the room temperature tensile behaviour of 316H has been examined. Plastic strain was introduced into the material by uniform pre-compression (PC) to 8% plastic strain at room temperature. In addition, creep strain was subsequently introduced into samples by performing uniaxial creep tests on the pre-compressed material. These creep tests were interrupted at various stages of life so that the influence of inelastic damage on the tensile response of the material could be examined. In addition, creep crack growth (CCG) tests have been performed on compact tension C(T) specimens made of 8% pre-compressed material at 550 °C and the results are compared to the existing data on PC material. The results from these tests have been discussed in terms of specimen constraint, initial crack length and loading effects on the CCG behaviour of the PC material.
Benchmarking PRAISE-CANDU 1.0 With xLPR 1.0
Authors: Wang Min , Duan Xinjian , Kozluk Michael J.
Published: January 2014

A probabilistic fracture mechanics code, PRAISE-CANDU 1.0, has been developed under a software quality assurance program in full compliance with CSA N286.7-99, and was initially released in 2012 June. Extensive verification and validation has been performed on PRAISE-CANDU 1.0 for the purpose of software quality assurance. This paper presents the benchmarking performed between PRAISE-CANDU 1.0 and xLPR (eXtremely Low Probability of Rupture) version 1.0 using the cases from the xLPR pilot study. The xLPR code was developed in a configuration management and quality assured manner. Both codes adopted a state-of-art code architecture for the treatment of the uncertainties. Inputs to the PRAISE-CANDU were established as close as possible to those used in corresponding xLPR cases. Excellent agreement has been observed among the results obtained from the two PFM codes in spite of some differences between the codes. This benchmarking is considered to be an important element of the validation of PRAISE-CANDU.
Brittle Fracture Assessments on Offshore Piping Systems
Authors: Subramanian Kannan , Penso Jorge , McVinnie Graham , Garic Greg
Published: January 2014

Offshore piping systems may be subject to low temperatures due to operation related scenarios and are cause for brittle fracture concern. The analyses included in this work consider probable events leading to low temperature conditions such as auto-refrigeration. In such circumstances, brittle fracture assessments of piping are typically carried out using API 579-1/ASME FFS-1, latest referred as API 579, procedures. The assessment of piping systems are in many cases very involved, requiring extended piping system information followed by stress analysis and MAT calculations depending on the material type, thickness of the piping analyzed, and stress levels. In addition, the component-by-component assessment approach recommended in API 579 leads to tedious calculations.

In this paper, approaches used for static and dynamic low temperature scenarios are presented. Static cases involve constant pressures and temperatures. Dynamic cases involve varying pressures and temperatures as the low temperature events unfold (e.g., blowdown of a valve or a vessel). Dynamic cases warrant the requirement of a safe operating envelope or MAT curve similar to those developed for pressure vessels. Case studies involving the influence of the extent of the system analyzed and the restraint conditions on the results are also presented. In addition, the importance of separately assessing the rated components such as flanges and valves away from the stress analysis is discussed. Based on the assessments carried out, a discussion on the toughness rules defined in ASME Section VIII Divisions 1, 2, and the original piping code of construction is provided.
Phase Transformation Properties Sensitivity Study in a Ferritic Groove Weld
Authors: Pellereau Benjamin , Hurrell Paul , Gill Christopher , Francis John , Bate Steve
Published: January 2014

A previous paper (PVP2010-25649) presented work carried out to model a three pass groove weld in an SA508 plate using Abaqus with the VFT material model. The model used the SA508 physical and mechanical properties for both parent and weld metal, with phase transformation properties for a slightly different material as these were the only properties available at the time. A material properties testing programme has since been completed allowing the analysis to be rerun using a complete set of properties for both the parent metal (SA508) and the weld metal (SD3). Properties to describe the phase transformations on cooling from austenite were derived for a range of austenite grain sizes. This paper presents a sensitivity study comparing the predicted stresses and phase proportions when using the different properties, and the effects of using different properties for the two materials. With the updated material properties and by using separate properties for the parent and weld, the results have been improved significantly. The results show that, while changing the phase properties affected the predicted phase proportions and the stresses in the weld metal, the residual stress distribution in the parent metal, where the peak tensile stresses occur, did not change significantly.
Fatigue Monitoring of BWR Feedwater Nozzles
Authors: Evon Keith , Gilman Tim , Walter Matthew
Published: January 2014

Implementing a stress based fatigue monitoring system, including all six stress terms per NB-3200 methodology, can help to reduce conservatism associated with design basis fatigue calculations. The boiling water reactor (BWR) feedwater nozzle is a perfect example of a location that has been analyzed in detail, but can still have many conservative assumptions in the design basis fatigue calculations or when using a single stress term Green’s function. The BWR feedwater nozzle is also typically subjected to operational changes such as transient ramp time and cycle count changes. Some important differences between the simplified single stress term methodology and the advanced six stress term methodology will be briefly outlined. Furthermore, a stress based fatigue monitoring system can automatically take into account operational changes that might affect fatigue calculations. This paper will explore the implementation and benefits for using a stress based fatigue monitoring system to monitor locations associated with a BWR feedwater nozzle.
Simple Benchmark Problems for Finite Element Weld Residual Stress Simulation
Authors: Smith Mike C. , Bate Steve , Bouchard P. John
Published: January 2014

Finite element methods are used increasingly to predict weld residual stresses. This is a relatively complex use of the finite element method, and it is important that its practitioners are able to demonstrate their ability to produce accurate predictions. Extensively characterised benchmark problems are a vital tool in achieving this. However, existing benchmarks are relatively complex and not suitable for analysis by novice weld modellers. This paper describes two benchmarks based upon a simple beam specimen with a single autogenous weld bead laid along its top edge. This geometry may be analysed using either 3D or 2D FE models and employing either block-dumped or moving heat source techniques. The first, simpler, benchmark is manufactured from AISI 316 steel, which does not undergo solid state phase transformation, while the second, more complex, benchmark is manufactured from SA508 Cl 3 steel, which undergoes solid state phase transformation during welding. A number of such beams were manufactured using an automated TIG process, and instrumented with thermocouples and strain gauges to record the transient temperature and strain response during welding. The resulting residual stresses were measured using diverse techniques, and showed markedly different distributions in the austenitic and ferritic beams. The paper presents the information necessary to perform and validate finite element weld residual stress simulations in both the simple austenitic beam and the more complex ferritic beam, and provides performance measures for the austenitic beam problem.
Strain Rate Sensitivity of Alloys 800H and 617
Authors: Wright J. K. , Simpson J. A. , Wright R. N. , Carroll L. J. , Sham T. L.
Published: January 2014

The flow stress of many materials is a function of the applied strain rate at elevated temperature. The magnitude of this effect is captured by the strain rate sensitivity parameter “m”. The strain rate sensitivity of two face–center cubic solid solution alloys that are proposed for use in high temperature heat exchanger or steam generator applications, Alloys 800H and 617, has been determined as a function of temperature over that range of temperatures relevant for these applications. In addition to determining the strain rate sensitivity, it is important for nuclear design within Section III of the ASME Boiler and Pressure Vessel Code to determine temperature below which the flow stress is not affected by the strain rate. This temperature has been determined for both Alloy 800H and Alloy 617. At high temperature the strain rate sensitivity of the two alloys is significant and they have similar m values. For Alloy 617 the temperature limit below which little or no strain rate sensitivity is observed is approximately 700°C. For Alloy 800H this temperature is approximately 650°C.
Determination of J-R Curves for Dissimilar Metal Welds Using Normalization Method and Compact Tension Specimens
Authors: Zhu Xian-Kui , Shim Do-Jun , Scott Paul , Rudland David
Published: January 2014

Normalization method is adopted in this paper to determine fracture resistance curves, i.e. J-R curves for dissimilar metal (DM) welds involved in nuclear reactor pressure vessels. Due to the restriction of material availability, three compact tension (CT) specimens containing a DM weld with a crack were utilized and tested under the guideline of ASTM fracture toughness test standard E1820 [1]. The test data of load versus load-line displacement were recorded during the tests, and directly applied to estimate crack extension using the normalization procedures. The J-R curves are then developed without the need of online crack extension measurement.

Three J-R curves of DM welds were obtained using the standard 1T CT specimens and the normalization method. These resistance curves were evaluated through comparison with those obtained from small sized ½T CT specimens via ASTM E1820 standard procedures and those obtained from the electrical potential drop method. The results showed that the normalization method, ASTM E1820 standard procedures, and the electrical potential drop method can determine similar fracture resistance curves for DM welds in a good agreement. Among the three methods, the normalization method is of most attractive because it is the only one that does not need crack extension measurements, and thus test costs are saved.
Weld Residual Stress Analysis and Axial PWSCC Predictions in a Double Vee Groove Large Diameter Nozzle
Authors: Brust Frederick W. , Punch E. , Shim D. J. , Rudland David , Rathbun Howard
Published: January 2014

Flaw indications have been found in some dissimilar metal (DM) nozzle to stainless steel piping welds and reactor pressure vessel heads (RPVH) 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. The welds may become 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 greater than 300°C) and the water chemistry in the PWR is typical of operating plants. The weld residual stresses (WRS) induced by the welds are a main driver of PWSCC.

The purpose of this paper is to determine the weld residual stresses in a double-vee groove welded nozzle and then to model the natural crack growth in the weld. The double vee groove geometry has not been modeled much to date especially in such a large nozzle. This leads to a rather unique weld residual stress pattern which changes as the throat of the double vee is approached. Axial crack growth is modeled using a natural crack growth procedure. This was challenging since the crack shape necked down in the region where the tips of the vee grooves meet making the mesh development during this process challenging. This analysis provides information regarding crack growth evolution versus time. In addition, some comments regarding idealized growth are presented.
Mitigation of Welding-Induced Tensile Residual Stress at Surface of Heavy Section Plate by In-Process Control Welding With Trailing Heat Sink
Authors: Okano Shigetaka , Mochizuki Masahito
Published: January 2014

In this study, in-process control welding with a trailing heat sink was applied to mitigate the weld tensile residual stress at the surface of a heavy section plate of low-carbon austenitic stainless steel. The distribution of the weld residual stress at the surface of the plate was evaluated by X-ray stress measurement and finite element analysis. As the results, it was experimentally and analytically confirmed that the welding-induced tensile residual stress at the welded surface was mitigated by welding with a trailing heat sink. Also, the measurement and simulation results were in good agreement. Based on the simulation results, the mechanisms of mitigation of the residual stress by welding with a trailing heat sink were discussed. It was concluded that the mitigation of the weld residual stress is due to the inverted gradient of temperature from the welded surface to the deepest parts of the plate.
A Unified Approach for Comparison of Multiaxial Fatigue Models
Authors: Noban M. , Adibi-Asl R.
Published: January 2014

There are several methods of estimating fatigue crack initiation life under multiaxial loading including strain and energy based methods.

This paper investigates a unified approach that enables comparison of these different models. The various fatigue models are mapped into a specific domain, i.e., stress, strain or energy domain. Three sets of experimental results available from literature are used for this comparison.

Under simultaneous axial and torsional loadings, the fatigue life predictions of investigated fatigue models are in a better agreement when the axial load is more dominant than torsional loading. The differences in the predictions increase when torsional loading increases. This is mostly due to the fact that fatigue parameters are generally determined and calibrated under uniaxial cyclic loading.
Mismatch Effect of Creep Properties on Steady-State Stresses for Welded Straight Pipes: Quantification and Application
Authors: Han Jae-Jun , Kim Sang-Hyun , Kim Yun-Jae , Nikbin Kamran , Dean David
Published: January 2014

This paper describes steady-state stresses on welded straight pipes with the heat-affected zone (HAZ) using detailed two dimensional elastic creep finite element analyses. In our previous studies [9,10], it was found that the mis-match effect in creep on steady-state stresses within the weld metal for a various branch junction could be uniquely quantified by the mis-match factor, defined as a function of creep exponent and constants. The present study expands the findings to be applicable for welded straight pipes, not only the most widely used but also relatively simple compared to branch junctions. To see the effects of mis-match in creep properties and weld configuration, the parametric studies have been performed for various mismatched creep properties and three different groove angles, respectively. Internal pressure, tension and its combined cases are applied to investigate the effect of the loading mode. It is found that steady-state creep stresses can be quantified as mis-match factor and creep exponent. In conclusion, validation of the findings is presented and discussed through an application to the CMV pipe.
Preliminary Evaluation of the Flooding Effects on an Existing PWR
Authors: Baudanza Vincenzo , Lo Frano Rosa , Forasassi Giuseppe
Published: January 2014

The aim of the study is the evaluation of the structural effects induced by a severe flooding or tsunami (which is one of the external events to be considered for the safety margin reassessment purpose according to the International requirements, after the Fukushima accident) in an outer containment walls of a typical PWR.

The hydrodynamic forces exerted by the breaking waves, characterizing the inundation phase of tsunami/flooding phenomenon, are calculated in agreement with ASME rules.

Therefore to evaluate the consequences and damages, if any, induced by the breaking water waves which have arisen on an existing PWR containment building, non linear analyses (by using an adequate FEM code) were performed simulating the impact forces of the water waves in terms of pressure. Moreover a FSI analysis was carried out in order to verify the adequacy (and consistency) of the methodology adopted in the evaluation of the pressure forces mentioned above.

To analyze the performances of the containment building suitable reinforced concrete material properties and damage phenomena features were considered.

The results obtained highlighted that the tsunami effects are strongly dependent on the wave height, flow velocity, hydrodynamic phenomena and on the geometry and material behaviour of the analyzed structures.

Finally they showed that the containment building considered seemed capable to withstand the flooding/tsunami effects without loss of the integrity of PWR containment structure.
Recent Developments in the R5 Volume 2/3 Procedures for Assessing Creep-Fatigue Initiation in Defect-Free Components Operating at High Temperatures
Authors: Dean David W. , Spindler Michael W. , Chevalier Marc , Smith N. Godfrey
Published: January 2014

The R5 procedures have been developed within the UK power generation industry to assess the integrity of nuclear and conventional plant operating at high temperatures. Within R5, there are specific procedures for assessing creep-fatigue crack initiation in initially defect-free components (Volume 2/3) and procedures for assessing components containing defects (Volume 4/5).

Recent developments in the R5 Volume 2/3 procedure for assessing creep-fatigue initiation in defect-free components include improved methods for predicting creep damage and a new approach for assessing weldments. The improved methods for predicting creep damage include the option of using the stress-modified ductility exhaustion (SMDE) approach as an alternative to the existing ductility exhaustion approach, together with improved methods for assessing compressive dwells. The new approach for assessing weldments involves splitting the existing Fatigue Strength Reduction Factor (FSRF) into a Weldment Endurance Reduction (WER), which accounts for reduced fatigue endurance due to weld imperfections, and a Weldment Strain Enhancement Factor (WSEF), which accounts for material mismatch and local geometry effects.

This paper briefly outlines the current R5 Volume 2/3 procedures and then focuses on these two significant recent developments in the procedures.
SCC Assessment Based on Probability Fracture Mechanics Considering SCC Initiation and Propagation Under Residual Stress Fields Generated by Machining and Welding Process of Pipes
Authors: Mochizuki Masahito , Ihara Ryohei , Katsuyama Jinya , Udagawa Makoto
Published: January 2014

Stress corrosion cracking (SCC) has been observed near the welded zones of pipes made of austenitic stainless steel type 316L. Residual stress is an important factor for SCC. In the joining processes of pipes, butt welding is conducted after surface machining. Residual stress is generated by both processes, and the residual stress distribution by surface machining is varied by the subsequent butt-welding process. In this study, numerical analysis of the residual stress distribution by butt welding after surface machining was performed by the finite element method. The SCC initiation time was estimated by the residual stress obtained at the inner surface. SCC growth analyses based on probability fracture mechanics were performed by using the SCC initiation time and the residual stress distribution. As a result, the residual stress distribution in the axial direction due to butt welding after surface machining has high tensile stress exceeding 1000 MPa at the inner surface. The effect of SCC initiation on leakage probability is not as significant as the effect of plastic strain on the crack growth rate. However, to perform crack growth analyses considering SCC initiation, evaluation of the residual stress due to surface machining and welding is important.
Numerical Simulation of Hot Cracking Tests
Authors: Le Minh , Asserin Olivier , Forest Laurent , Fandeur Olivier , Pilvin Philippe
Published: January 2014

One of the main nuclear materials is the austenitic stainless steels, which have good ductility and toughness, high thermal expansion coefficients and a thermal conductivity lower than that of martensitic or ferritic steels. The 316L(N) austenitic stainless steel (X2CrNiMo17-12-2 with controlled nitrogen) is evaluated for structures such as the vessels, which are steel enclosures surrounding the reactor core and its assemblies, in fourth generation nuclear systems.

The RCC-MR code, which is used as a frame of reference in the manufacture of SFR (Sodium Fast Reactor concept), recommends the use of austenoferritic filler material for the welding of 316L(N) steel. These recommendations derive from past experience of working with fast neutron reactors (Phenix and Superphenix). In order to guarantee long-term properties at high temperatures, an austenoferritic and an austenitic filler metals are evaluated as filler metals.

However, these materials are susceptible to hot cracking. Therefore, a study is conducted to ensure their weldability. The purpose of this work is to evaluate the susceptibility to hot cracking of the studied materials and to present a methodology applied to define a criterion called “laboratory” for each material and its transfer to a structure test.

The relative susceptibility to hot cracking of these materials was evaluated using four tests: the Varestraint, the Gleeble, the trapezoid and the skew tests. Numerical simulation using Cast3M code and Sidolo software of these four tests were investigated in order to survey behavior laws of each studied material and solidification cracking thermomechanical criteria intrinsic to the materials. Some test and simulation results as well as hot cracking susceptibility ranking are presented and the transferability to real component welds of hot cracking criteria is discussed.