bluuebunny/crossref_metadata_2025 huggingface dataset:
Method to Evaluate Fatigue Life of Carbon Steel Under Simulated Synchronously Changing BWR Condition
Authors: Hirano Akihiko , Uchida Kazunari , Sakaguchi Katsumi
Published: August 2009

The environmental fatigue life of carbon steel is influenced by BWR conditions such as water temperature, dissolved oxygen concentration, water flow rate and so on. These parameters change inconstantly during operation of BWR plants and strain rate changes in the structural components due to the temperature change. In general, fatigue life evaluation equations have been formulated based on the fatigue data obtained under constant conditions. To apply these equations to evaluate the fatigue life of actual components, a study is necessary to confirm the applicability of the proposed equations to the changing conditions. In this study, fatigue tests were performed under changing conditions of strain amplitude, strain rate, temperature, dissolved oxygen concentration and water flow rate. It was confirmed that the proposed fatigue life equation could predict the fatigue life under changing conditions.
Elastic-Plastic Modeling of Hardening Materials Using a Corotational Rate Based on the Plastic Spin Tensor
Authors: Ghavam Kamyar , Naghdabadi Reza
Published: August 2009

In this paper based on the multiplicative decomposition of the deformation gradient, the plastic spin tensor and the plastic spin corotational rate are introduced. Using this rate (and also log-rate), an elastic-plastic constitutive model for hardening materials are proposed. In this model, the Armstrong-Frederick kinematic hardening and the isotropic hardening equations are used. The proposed model is solved for the simple shear problem with the material properties of the stainless steel SUS 304. The results are compared with those obtained experimentally by Ishikawa [1]. This comparison shows a good agreement between the results of proposed theoretical model and the experimental data. As another example, the Prager kinematic hardening equation is used. In this case, the stress results are compared with those obtained by Bruhns et al. [2], in which they used the additive decomposition of the strain rate tensor.
Basic Study on the Crushing of Frozen Soil by Shock Loading
Authors: Watanabe Toshiaki , Maehara Hironori , Otsuka Masahiko , Itoh Shigeru
Published: August 2009

The aim of study is to confirm a new technique that can crush the frozen soil and/or ice block using underwater shock wave generated by the underwater explosion of explosive. This technique can lead to the earlier sowing, which can have the larger harvest because the duration of sunshine increases. Especially, in Hokkaido prefecture, Japan, if the sowing is carried out in April, we can expect to have 150% of harvest in the ordinary season. This technique is effective against the cold regions. For example, Korea, China, Mongolia, Russia, Norway, and Sweden, etc. At first, we carried out experiments usung a detonating fuse and ice block. The process of ice breaking was observed by means of a high-speed camera. In order to check about that influence we tried to give an actual frozen soil a shock wave.
Application of Plastic Region Tightening Bolt to Flange Joint Assembly: Behavior of Bolt Preload in Flange Joint Subjected to Internal Pressure
Authors: Kaneda Shinobu , Tsuji Hirokazu
Published: August 2009

Elastic region tightening by means of the torque control method is a conventional method to tighten bolts. The bolt axial force is controlled by a torque wrench; however, it is not easy to achieve constant bolt axial force. When the torque control method is applied to the flange joint assembly, the scatter of the bolt axial force is significant with respect to the joint reliability, such that it may cause leakage of the internal fluid from the flange joint. Recently, plastic region tightening has received considerable attention, which provides good uniformity in the bolt axial force. In a previous study, plastic region tightening was applied to a flange joint assembly, and the superior uniformity of the bolt axial force was demonstrated. The present paper describes the behavior of the plastic region tightening bolt in a flange joint subjected to internal pressure. First, the flange joint is tightened to the plastic region using a downsized bolt. The internal pressure is then applied to the flange joint, and the behavior of the additional bolt axial force is investigated. Application of plastic region tightening to the flange joint assembly is found to be effective for obtaining leak-free joints and for downsizing of the nominal diameter of the bolt. The behavior of the bolt axial force in a flange joint subjected to internal pressure was clarified. The additional bolt axial force has a sufficient margin for the allowable limit.
Pressure Fluctuations Around Steam Control Valve: Steam Experiments and CFD Calculations
Authors: Morita Ryo , Inada Fumio
Published: August 2009

In some cases, a steam control valve (figure 1) in a power plant causes large vibrations in piping systems that can be attributed to pressure fluctuations generated in the valve under the partial-valve-opening (middle-opening) condition. For the maintenance and the management of the plant, the valve system needs to be improved to prevent the onset of hydrodynamic instabilities. However, in the case of the steam control valve, it is difficult to understand the flow characteristics in detail experimentally because the flow around the valve has a complex 3D structure and becomes supersonic (M>1). For these reasons, the details of the flow around the valve are not fully understood before, and CFD simulations are required to understand the underlying complex flow structure associated with the valve. In our previous researches, a mechanism of the pressure fluctuations in the middle opening condition, named “rotating pressure fluctuations”, were clarified and a suppression shape were developed by experiments and CFD calculations. However, as we used air as a working fluid in our previous researches instead of steam that is used in the power plant, we couldn’t consider effects of condensation and difference of change of the state quantities between air and steam. In this report, we have conducted steam experiments and CFD calculations by original code to clarify the effects of the difference of the fluids. As a result, in the middle opening condition, we have observed spike-type pressure fluctuations and their rotation in the experiment, and valve-attached flow and local high-pressure region in the CFD result. These results indicate the pressure fluctuations observed in steam experiments and CFDs are the same as rotating pressure fluctuations observced in air researches.
Comparison of Flange Stress Calculated by ASME Design Code and Finite Element Analysis
Authors: Nagata Satoshi , Sawa Toshiyuki
Published: August 2009

A flange strength calculation method for flange joints based on the researches carried out by Waters at el. is adopted in ASME B&PV Code and has been used with many good practices in several decades. However, it is also the fact that there are some cases like that the code calculation gives over conservative results or a leakage trouble occurs even if the calculation meets the code requirements. Discrepancy is pointed out between the calculation condition and the actual condition, too. This paper clarifies the difference of flange stresses calculated by ASME design code and finite element analysis. Furthermore, using the ASME Code formulas proposed by Waters with the bolt load and the gasket load obtained by finite element analysis, flange stresses are calculated and compared with the results of finite element analysis. Finally, the paper discusses the adequacy of flange stress calculation formulas and shows the point to be modified in ASME design method.
Study on Thickness and Actual Stress Measurement of Steel Structures Using Electromagnetic Acoustic Transducer
Authors: Mitani Kinya , Mochizuki Masahito , Toyoda Masao
Published: August 2009

Since an electromagnetic acoustic method could generate ultrasonic waves in the material surface non-contacting, high-precision wave velocity measurements were possible and application to steel structures is expected increasingly. On the other hand, from the aspect of the maintenance and control of steel structures, it is very important to measure quantitatively the wall-thinning and the actual stress of damaged and depleted materials by a non-destructive method. In this study, various examinations were performed to the wall-thinning measurement technique using an electromagnetic acoustic resonance method in which thickness and stress measurements are possible and the measurement method was established. Furthermore, as basic examination of actual stress measurements, a tensile testing was conducted by sensors of the shear wave and the longitudinal wave. As a result, it turned out that stress could be measured in a sufficient precision, and that the simultaneous measurement of thickness and stress became possible.
Occurrence of Nonlinear Oval-Type Vibration Under Large Sinusoidal Excitation: Experiment
Authors: Maekawa Akira , Fujita Katsuhisa
Published: August 2009

This study describes the vibration experiment which examines the vibration characteristics of a cylindrical water storage tank caused by the coupling between the beam-type and the oval-type vibrations in detail. A small or large acceleration excitation test is performed by a shaking table using a 1/10 reduced scale model of a large-scale tank. The sinusoidal waves with the resonance frequency of the beam-type vibration are used as the input. By using accelerometers, displacement sensors and strain gauges, the vibration characteristics and the vibration modes of the tank model are investigated. The beam-type and the oval-type vibrations are excited simultaneously and the oval-type vibration of fundamental harmonics is excited in the small or large acceleration excitation test. In the large acceleration excitation test, however, the oval-type vibration of subharmonics of order one-half appears suddenly and grows rapidly when the amplitude of the oval-type vibration of fundamental harmonics increases to some magnitude. At the same time, the response of the beam-type vibration of the tank is reduced rapidly. This result shows that the occurrence of the oval-type vibration of subharmonics of order one-half and the response reduction of the beam-type vibration are in close relationship.
Tensile Deformation of Alloy-22 at Ambient and Elevated Temperatures
Authors: Koripelli Rama S. , Roy Ajit K.
Published: August 2009

Significant efforts are in progress to identify and characterize the tensile properties of structural materials for application in hydrogen generation using a thermochemical process known as the sulfur-iodine cycle. Austenitic Alloy-22 has been evaluated for its tensile properties at temperatures ranging from ambient to 1000°C. As expected, the tensile strength was gradually decreased with increasing temperature due to the ease of plastic deformation at these temperatures. However, the failure strain gradually decreased from room temperature to 600°C, possibly due to the occurrence of a phenomenon known as dynamic strain aging. Transmission electron microscopy revealed maximum dislocation density at 600°C. Fractographic evaluation of the tested specimens by scanning electron microscopy showed dimpled microstructures at the primary fracture surface indicating ductile failures. However, at higher temperatures intergranular brittle failures were observed.
Seismic Response Reduction Caused by Coupling Between Beam-Type and Oval-Type Vibrations of a Cylindrical Water Storage Tank Under Large Excitation
Authors: Maekawa Akira , Fujita Katsuhisa , Suzuki Michiaki
Published: August 2009

This study describes the response reduction caused by coupling between the beam-type and the oval-type vibrations of a cylindrical water storage tank under seismic excitation. In this study, the seismic response experiment is performed by using a 1/10 reduced scale model of an actual tank and then numerical simulation is performed by the simplified model. The authors conducted the sinusoidal response experiment for the tank and reported that the coupling between the beam-type and the oval-type vibrations causes the resonance frequency of the beam-type vibration to shift to the lower frequency and the response in the beam-type vibration (the response of the tank) to reduce. The seismic response experiment of the tank model filled with water up to 95% is performed by a shaking table. The El Centro 1940 NS and the improved standard seismic wave for Japanese LWR are used as the input seismic wave. The experimental results show that the maximum response acceleration does not enlarge linearly as the maximum input acceleration increases. The dominant resonance frequency slightly shifts to the lower frequency as the maximum input acceleration increases. It is concluded that the coupling between the beam-type and the oval-type vibrations make an influence on the beam-type vibration in seismic excitation. In the meantime, the authors propose the nonlinear single-degree-of-freedom system model to explain that the vibration response of the tank reduces. This model is based on geometric nonlinearity due to the out-of-plane deformation of the side-wall of the tank caused by the oval-type vibration. The numerical simulation of the seismic response is conducted using the nonlinear single-degree-of-freedom system model proposed by the authors. The analytical results agree with the experimental results as a general trend. Therefore, it is concluded that the response reduction of the tank is generated by coupling between the beam-type and the oval-type vibrations in the seismic excitation as well as the sinusoidal excitation. In addition, the response reduction rate of the tank under much larger seismic excitation can be estimated by using the nonlinear single-degree-of-freedom system model.
Online AE Inspection and Safety Assessment of Vertical Storage Tank
Authors: Guan Weihe , Tao Yuanhong , Chen Xuedong , Yuan Rong , Chen Yingfeng
Published: August 2009

With the rapid growth of the global petroleum industry and continuous increase of energy demand, the crude oil and product oil reserve has been given a general concern in every country, and the requirements for the reserve capacity of various types of petroleum storage depots become higher and higher, therefore, the quantity of various types of storage tanks is increasing dramatically. At present, 100,000m3 storage tank has become the primary structure for construction of crude oil storage tanks for Chinese petrochemical industry. Large vertical metal storage tank features large capacity, central distribution, storage of inflammable, explosive and toxic media etc., leakage or explosion accident, once happens, often results in disastrous consequence and severe environmental pollution, which brings a huge loss and hazard to social economy, production and people’s living. The major cause for the accidents of storage tanks is corrosion and leakage, the external corrosion is mainly the soil corrosion and moist atmospheric corrosion of outer wall of oil tank baseplate; the internal corrosion is the corrosion of tank bottom, tank wall and tank top. Among the above corrosions, the most hard to treat is the corrosion of tank baseplate. In this paper through laboratory simulation of AE tests of leakage of storage tank and corrosion of baseplate and comparison between online AE inspection of more than 30 large vertical storage tanks and shutdown inspection of part of storage tanks, the matters about online AE inspection techniques for corrosion and leakage of storage tank baseplate and safety assessment of vertical storage tank are discussed, online AE inspection technique and assessment standard fit for China’s present condition are proposed, the safety class and corresponding shutdown inspection cycle of vertical storage tank are determined, the storage tanks where no problems are found by online AE inspection continue their service, whereas the storage tanks where severe problems are found are shut down for inspection, thus the contradiction between shutdown inspection and safe production is basically solved.
Structural Analysis for Ethylene Oxide Reactor
Authors: Woo Hee-Suk , Hong Yun-Seok , Lim Young-Soon , Park Jung-Yean , Ahn Hee-Jae , Lee Choong-Dong
Published: August 2009

The structural safety of the Ethylene Oxide (EO) reactor of an ethylene glycol plant project should be verified by computational analysis. The heat transfer analysis has been performed using the finite volume method program, Fluent and the stress analysis has been performed using the finite element program, ANSYS. The applied loads are dead weight, internal pressure, nozzle load, earthquake load, wind load and thermal load. The analysis results for the main load conditions are presented. In addition, abnormal operating conditions such as runaway, pre-ignition and post-ignition are analyzed. The structural integrity of an EO reactor is investigated in accordance with the ASME Boiler and Pressure Vessel Code, Section VIII, Div. 2. It is concluded that the design of the EO reactor complies with the design criteria for all design load conditions.
Assessment of Residual Stress and Determination of Stress Directionality by Instrumented Indentation Technique
Authors: Kwon Dongil , Choi Min-Jae , Kim Kug-Hwan , Lee Kyung-Woo , Kim Kwang-Ho
Published: August 2009

The instrumented indentation technique has taken the limelight as a promising alternative to conventional residual stress measurement methods for welds with rapid microstructural gradients because of its easy and nondestructive testing procedure. The technique is based on the key concept that the deviatoric-stress part of residual stress affects the indentation load-depth curve. By analyzing the difference between the residual stress-induced curve and residual stress-free curve, the quantitative residual stress of the target region can be evaluated. To determine the stress-free curve of the target region, we take into consideration microstructural changes that accommodate strength differences. In addition, we determine the ratio of the non-equibiaxial residual stress by using an asymmetric Knoop indenter, which has an elongated four-sided pyramidal geometry. We find that the load-depth curve is changed on penetration direction of the long diagonal for Knoop indenter, and derive a quantitative relation between the stress ratio and the load difference through both theoretical analysis and experiments. Finally, indentation tests and conventional tests were performed on the welded zone to verify the applicability of the technique. The estimated residual stress values obtained from instrumented indentation technique agreed well with those from conventional tests.
Finite Element Formulations and Experimental Study for Direction Optimized-Friction Pendulum System
Authors: Tsai C. S. , Chiang T. C. , Chen Wen-Shin , Yang Chen-Tsung , Lin Jian-Liang
Published: August 2009

The Friction Pendulum System (FPS) invented by V. A. Zayas in 1987 has been widely used in the seismic engineering all over the world. The efficiency for upgrading the earthquake-proof capability of a fixed base structure has been proved either from theoretical studies or experimental efforts. However, the seismic responses of the FPS-isolated structure are always significant as subjected to near fault earthquakes and strong ground motions with long predominant periods. In order to overcome the drawback of the FPS, a new base isolator named as the Direction Optimized Friction Pendulum System (DO-FPS) has been proposed in this study. The proposed device is mainly composed of a spherical sliding surface, a trench concave surface and an articulated slider. By using the special design, the isolation period is a function of the angle between the directions of the resultant displacement. Therefore, the undesirable phenomenon of resonance could always be prevented. In order to verify the functionality of the proposed device, the shaking table tests of a three story steel structure with DOFPS base isolators have been performed. The test results reveal that the proposed device can effectively upgrade the seismic resistibility of a conventionally fixed base structure. Furthermore, the comparisons between the numerical and the experimental results show that the theory proposed in this study could predict the nonlinear behavior of the DO-FPS with good accuracy.
Probabilistic Analysis of Cracking Phenomenon in a Mixing Tee Under Thermal Fatigue
Authors: Varfolomeyev Igor
Published: August 2009

The paper provides a feasibility study of crack initiation and propagation in a mixing zone of an austenitic piping subjected to thermal fatigue loading. The analysis employs input data generated within the European research project THERFAT. A deterministic analysis performed using conservatively selected boundary conditions revealed high stresses in a mixing tee giving rise to fatigue damage. To account for the uncertainties, scatter and randomness of the thermal-hydraulic data and material properties, statistical data treatment and probabilistic methods are applied. Experimental measurements of temperature fluctuations obtained on austenitic thin-walled models are first employed to estimate the heat transfer coefficient. Then temperature and stress calculations are performed for a realistic piping geometry, and time to crack initiation is evaluated based on the fatigue design curves. The derived distribution function for the component life-time is compared with a deterministic assessment obtained using conservative assumptions on heat transfer conditions and material data. A possibility of crack propagation into the pipe wall is analyzed.
Seismic Responses of a Full-Scale Steel Structure Using Multi-Curved Buckling Restrained Braces
Authors: Tsai C. S. , Chen Wen-Shin , Lin Yung-Chang , Yang Chen-Tsung , Tsou Ching-Pei
Published: August 2009

Since 1970’s, many types of braces have been developed without buckling under large compressive forces called the buckling restrained brace BRB, or unbonded brace. Recently, many investigators have made a lot of efforts to look into the behaviors of the buckling restrained brace under quasi-static forces, but few experimental results about shaking table tests of a structure with buckling restrained braces have been published. Therefore, in this study, a series of shaking table tests were carried out in the National Center for Research on Earthquake Engineering, and the issue is focused on observing the seismic responses of a full-scale three-story steel structure with multi-curved reinforced buckling restrained braces subjected to earthquake ground motions. Experimental results show that most column shear forces and displacements had been reduced by the RBRB devices. In addition, the absolute accelerations had also been favorably diminished during earthquakes. It can be proven that the proposed device is suitable for applications of seismic mitigation for structures.
Numerical Simulation of Residual Stresses Due to Cladding Process
Authors: Siegele Dieter , Brand Marcus
Published: August 2009

The inner surface of reactor pressure vessels is protected against corrosion by an austenitic cladding. Generally, the cladding is welded on the ferritic base metal with two layers to avoid sub-clad cracks and to improve the microstructure of the cladding material. On the other hand, due to the cladding process and the difference of the thermal expansion coefficient of the austenitic cladding and the ferritic base material residual stresses act in the component. This residual stress field is important for assessing crack postulates in the cladding or subclad flaws in the base metal. For the determination of the residual stress field, plates of RPV steel were cladded and heat treated representative to the RPV relevant conditions. During the cladding process the temperature and distortion were measured as basis for the validation of the finite element simulations. The numerical simulation was performed with the finite element code SYSWELD. The heat source of the model was calibrated on the measured temperature profile. In the analysis, the temperature dependent material properties as well as the transformation behavior of the ferritic base metal were taken into account. The calculated residual stresses show tensile stresses in the cladding followed by compressive stresses in the base metal that are in agreement with measurements with X-ray diffraction technique.
Data Analysis for RPV Life Management Studies of Temperature Measurements From Monitoring of Safety Injection Fluid in Refueling Water Storage Tank
Authors: Cagnac Albannie , Turato Silvia , Lestang Fre´de´ric , Planckeel Franc¸ois
Published: August 2009

In Electricite´ de France (EDF), it’s used to taking as a conservative constant value for the temperature of Refueling Water Storage Tank (RWST) in the deterministic and probabilistic analyses for Reactor Pressure Vessel (RPV) life management. The water contained in this storage tank supplies Security Injection during accidental conditions, such as loss-of-coolant accident (LOCA), so the temperature of this water is a very important input parameter for fracture mechanics analyses. In the continuation of [1], the aim of our study is to evaluate the variability of this temperature. Since 1999, EDF has been collecting the RWST temperature for several sites and several nuclear plant units. Using statistical analyses, this study aims at first to identify the most important RPV exploitation life events that influence this temperature and, at secondly, to obtain statistical density distributions in order to describe its variability in the most realistic way possible.
Application of Entry-Time Processes Within Probabilistic Risk Assessment (PRA) and Generation Risk Assessment (GRA)
Authors: Wang Shuwen , Nelson Paul , Kee Ernie J.
Published: August 2009

Aging has become a more important consideration since nuclear power plants have been in operation for decades. However, the current probabilistic risk assessment (PRA) and generation risk assessment (GRA) models are based on the assumption of constant failure rate. The consistent treatment of the dynamics of the evolution of aging and maintenance is critical to system reliability. The entry-time approach to dynamic reliability is based upon computational solution of the Chapman-Kolmogorov (generalized state-transition) equations underlying a certain class of marked point processes. Previous work has verified a particular finite-difference approach to computational solution of these equations. The objective of this work is to illustrate the potential application of the entry-time approach to PRA and GRA regarding maintenance or replacement of major systems within a plant. Results are presented in the form of plots, with replacement/maintenance period as a parameter, of associated risks and probabilities. Further recommendations for application of the entry-time approach to dynamic PRA/GRA are given at the end of the article.
Simulations of Cavitation in Orifice and Venturis
Authors: Ahuja Vineet , Hosangadi Ashvin
Published: August 2009

Computational simulations can play an integral role in supporting testing and developmental activities by identifying and characterizing flow instabilities. However, the diversity of flow regimes and instability mechanisms place very stringent requirements on any computational framework that could be used for such analyses. For example, the identification of dominant frequencies associated with flow instabilities in such systems requires high order numerics, advanced turbulence modeling capabilities, sophisticated grid topologies to resolve local physics in complex geometries, embedded models for unsteady cavitation, capture thermal effects in cryogenic fluids, and dynamic motion of feed system components such as valves. In this paper, we discuss simulations of cavitating instabilities in feed system components and control elements used in the E-1 test facility at NASA Stennis Space Center (SSC). The two different feed system components considered here are: (a) orifice and (b) flow control venturi that is attached to a 90 degree turning duct. These two components represent the two disparate regimes of cavitating flows: the orifice is representative of traveling cavitation class of flows commonly observed in tip vortices of propeller blades, whereas the venturi represents a sheet cavitation type problem with periodic shedding of vaporous clouds from this well developed cavity. The simulations are performed with a well validated cryogenic cavitation model that takes into account evaporative cooling and other associated thermal effects.
An Update on Improved Flange Design Methods
Authors: Brown Warren
Published: August 2009

This paper details further progress made in the PVRC project “Development of Improved Flange Design Method for the ASME VIII, Div.2 Rewrite Project” presented during the panel session on flange design at the 2006 PVP conference in Vancouver. The major areas of flange design improvement indicated by that project are examined and the suggested solutions for implementing the improved methods into the Code are discussed. Further analysis on aspects such as gasket creep and the use of leakage-based design has been conducted. Shortcomings in the proposed ASME flange design method (ASME BFJ) and current CEN flange design methods (EN-1591) are highlighted and methods for resolution of these issues are suggested.
Modeling of Fluidelastic Instability Forces in Fully Flexible Tube Arrays
Authors: Mahmood Faisal , Hassan Marwan
Published: August 2009

Fluidelastic instability remains the most devastating phenomenon in tube bundles subjected to cross-flow. Models have been developed to estimate the threshold of instability. Moreover, several time-domain models of fluidelastic instability have been developed to determine tube/support interaction parameters of tubes with loose supports. The present work deals with time domain modeling of fluid-elastic instability forces in a fully flexible tube array subjected to cross-flow. The model is based on the flow redistribution theory proposed initially by Lever and Weaver [1]. The proposed model utilizes fewer input parameters and can model various tube bundle geometries with any pitch-to-diameter ratio. Finite element method is used for solving the system response. The flow field inside the tube array is discretized into flow subdomains, each of which is surrounded by 4 tubes. The perturbation in the flow field, within each subdomain, is obtained by superimposing the effects of neighboring tube motions. The model has been applied to assess the response of a single flexible tube as well as multiple flexible tubes. It is shown that the single flexible model overestimates the stability threshold compared to the multiple flexible tube counterpart, especially at high mass-damping parameters. The results show a good agreement between the predicted and the experimental results. The proposed model does not assume any predetermined tube response or any tube motion pattern.
Vibration Behavior of a Channel Subjected to an Internal Two-Phase Flow
Authors: Zhang Ming Ming , Katz Joseph
Published: August 2009

Vibrations of a channel wall subjected to an external two-phase flow have been widely investigated in the past. However, there is very little information on the effect of internal two-phase flows on the vibrations. To this end, this paper presents results of an experimental investigation of changes to wall vibrations in a vertical square channel, which are caused by introducing a uniform bubble cloud into the flow. The effects of void fraction, characteristic bubble size and flow velocity on wall vibrations are measured. Results show that wall vibrations are greatly enhanced, by up to 25 dB, compared with the same flow without bubbles. The enhancement and spectra of the vibration are mainly dependent on the bubble void fraction. To understand the physics behind the results, evolution of the spectra along the streamwise direction are examined. The primary mechanisms for increased vibrations are: the lateral fundamental acoustic mode excitation of a bubble cloud whose frequency decreases due to change in sonic speed and normal modes of the bubble cloud. The fundamental mode of a bubble cloud persists along the entire channel and its harmonics enhance the vibrations over a broad frequency range. The cloud normal modes are generated due to the process of bubble formation, and they decay with increasing distance from the source.
Interpreting Surge Analysis Results
Authors: McGuffie S. M. , Porter M. A.
Published: August 2009

This paper details methods of interpreting maximum surge pressures in LNG pipelines due to valve closures and other transient events. The standard methodology for determining the onset of surge events and the pressure transients involved uses explicit integration; this method of analysis produces inherent “noise” in the solution results due to the integration method. The paper discusses methods of filtering data obtained through explicit integration and demonstrates which filters provide the best results for these analyses. Filtered and unfiltered results are presented for an actual LNG unloading facility subjected to a number of transient events, with discussion provided on determining the maximum peak pressures, their duration and the frequency content of secondary pressure waves.
Heavy-Section Steel Technology and Irradiation Programs: Retrospective and Prospective Views
Authors: Nanstad Randy K. , Bass B. Richard , Rosseel Thomas M. , Merkle John G. , Sokolov Mikhail A.
Published: August 2009

In 1965, the Atomic Energy Commission (AEC), at the advice of the Advisory Committee on Reactor Safeguards (ACRS), initiated the process that resulted in the establishment of the Heavy Section Steel Technology (HSST) Program at Oak Ridge National Laboratory (ORNL). Dr. Spencer H. Bush of Battelle Northwest Laboratory, the man being honored by this symposium, representing the ACRS, was one of the Staff Advisors for the program and helped to guide its technical direction. In 1989, the Heavy-Section Steel Irradiation (HSSI) Program, formerly the HSST task on irradiation effects, was formed as a separate program, and this year the HSST/HSSI Programs, sponsored by the U.S. Nuclear Regulatory Commission (USNRC), celebrate 40 years of continuous research oriented toward the safety of light-water nuclear reactor pressure vessels. This paper presents a summary of results from those programs with a view to future activities. The HSST Program was established in 1967 and initially included extensive investigations of heavy-section low-alloy steel plates, forgings, and welds, including metallurgical studies, mechanical properties, fracture toughness (quasi-static and dynamic), fatigue crack-growth, and crack arrest toughness. Also included were irradiation effects studies, thermal shock analyses, testing of thick-section tensile and fracture specimens, and non-destructive testing. In the subsequent decades, the HSST Program conducted extensive large-scale experiments with intermediate-size vessels (with varying size flaws) pressurized to failure, similar experiments under conditions of thermal shock and even pressurized thermal shock (PTS), wide-plate crack arrest tests, and biaxial tests with cruciform-shaped specimens. Extensive analytical and numerical studies accompanied these experiments, including the development of computer codes such as the recent Fracture Analysis of Vessels Oak Ridge (FAVOR) code currently being used for PTS evaluations. In the absence of radiation damage to the RPV, fracture of the vessel is improbable. However, exposure to high energy neutrons can result in embrittlement of radiation-sensitive RPV materials. The HSSI Program has conducted a series of experiments to assess the effects of neutron irradiation on RPV material behavior, especially fracture toughness. These studies have included RPV plates and welds, varying chemical compositions, and fracture toughness specimens up to 4 in. thickness. The results of these investigations, in conjunction with results from commercial reactor surveillance programs, are used to develop a methodology for the prediction of radiation effects on RPV materials. Results from the HSST and HSSI Program are used by the USNRC in the evaluation of RPV integrity and regulation of overall nuclear plant safety.
Use of Regular Rod Arrays to Model Heat Transfer From BWR Fuel Assemblies Inside Transport Casks
Authors: Araya Pablo E. , Greiner Miles
Published: August 2009

The current work is a scoping study to determine which heat transfer effects are significant in the fuel/backfill gas region of spent nuclear fuel transport casks. A two-dimensional finite volume mesh that accurately models the geometry of a 7×7 Boiling Water Reactor (BWR) assembly with its channel in a square isothermal enclosure is constructed. The peak cladding temperature is determined using computational fluid dynamics (CFD) simulations for a range of enclosure temperatures, fuel heat generation rates, cladding surface emissivities, and for both nitrogen and helium backfill gases. This work quantifies both the effect of buoyancy induced gas motion in the fuel/backfill gas region and the conditions when it does not significantly affect heat transfer. Future cask design simulations that neglect gas motion will require less computational resources than ones that do not. This work also quantifies the sensitivity of the maximum cladding temperature to fuel cladding emissivity. This helps quantify the uncertainty of temperature predictions if the emissivity is not known. The current CFD technique must be experimentally benchmarked before it may be used with confidence to predict peak cladding temperatures in transport casks. This work indicates that the thermal resistance between a BWR assembly’s channel and the basket walls may be modeled analytically. This will reduce the effort required for benchmark experiments because they will not need to include the channel.
Structural Capability of Austenitic Piping and Shells With Parallel Offset Cracks
Authors: Ranganath Sam , Carter Robert
Published: August 2009

Boiling water reactor (BWR) components made of austenitic stainless steel are exposed to the high temperature water environment. Under the combination of susceptible material condition (sensitization due to welding or cold work), weld residual stresses and the oxygenated high temperature water environment, reactor internals such as the core shroud and internal core spray piping experience stress corrosion cracking. The cracking is typically in the weld heat affected zone on both sides of the weld and is parallel to the weld direction. The determination of the structural capability of the component with parallel offset cracks is the subject of this paper. The Section XI, ASME code position on parallel planar flaws states that there is no interaction (i.e. no change in load capability due to multiple parallel cracks) for cracks that are separated by 12.5 mm (1/2 inch) or more. While this is reasonable under linear elastic fracture mechanics conditions, it is not conservative for ductile failure under limit load conditions. Alternatively, assuming that the parallel cracks are in a single plane for the purpose of determining the load capability is over-conservative and underestimates the structural capability. This paper is an extension of earlier work on the interaction of parallel flaws and considers the combines load capability as a function the crack separation. The interaction rules developed here were based on analysis and validated by comparison with extensive test data from different sources. For cracks in two parallel planes, the proposed rules for ductile materials (where limit load is the governing failure mechanism) allow them to be considered as separate cracks if the distance between the two planes is greater than 3t (where t is the shell thickness) and the limit load for cracking in each plane is determined separately. For planes separated by less than t, they are combined and assumed to be in one plane and the limit load is calculated for the combined crack. Linear interpolation is used when the separation distance, d is such that t≤d ≤3t.
Elastic-Plastic Shakedown Assessment of Piping Using a Non-Cyclic Method
Authors: Reinhardt Wolf
Published: August 2009

The analysis for shakedown in nuclear Class 1 piping following NB-3600 of the ASME Boiler and Pressure Vessel Code contains several simplifications and can be overly conservative in some cases and potentially non-conservative in some others. A detailed elastic-plastic analysis following NB-3228.4, on the other hand, is computationally expensive and time consuming because an elastic-plastic model needs to be cycled to stabilization. A non-cyclic method to assess elastic plastic shakedown (absence of ratcheting) has been proposed and is applied to the analysis of some simple straight piping scenarios. Interaction diagrams similar to the Bree diagram are derived for other loading situations, such as thermal bending in conjunction with primary bending. The effect of piping boundary conditions on the ratchet boundary is explored.
Fitness-for-Service Evaluation of Thermal Hot Spots and Corrosion Damage in Cylindrical Pressure Components
Authors: Tantichattanont P. , Adluri Seshu M. R. , Seshadri R.
Published: August 2009

Thermal hot spots and corrosion damage are typical of damages occurring in pressure vessels and piping. Structural integrity of such components needs to be evaluated periodically to determine “fitness-for-service” of the components. In the present paper, three alternative methods for Level 2 FFS assessments (as defined by API 579) are proposed. They are based on variational principles in plasticity, the limit load multiplier m-alpha method, reference volume and the concept of decay lengths in shells. Decay lengths in the axial and circumferential directions for cylindrical shells are derived based on elastic shell theories. They are used to specify the reference volume participating in plastic action and the limit of what can be called “local” damage. Interaction between longitudinal and circumferential effects is investigated. A linear interaction curve is shown to give good estimations of “remaining strength factor” for damages of practical aspect ratios. The stretching and bulging effects due to the damage are also studied. The limit defining the threshold to dominance of stretching action is proposed by using an approximate equilibrium calculation based on yield-line analysis. The effectiveness of the proposed assessments are demonstrated through an example and verified by Level 3 inelastic finite element analysis.
Derivations for Hoop Stresses Due to Shock Waves in a Tube
Authors: Leishear Robert A.
Published: August 2009

Equations describing the hoop stresses in a pipe due to water hammer have been presented in the literature in a series of papers, and this paper discusses the complete derivation of the pertinent equations. The derivation considers the pipe wall response to a water hammer induced shock wave moving along the inner wall of the pipe. Factors such as fluid properties, pipe wall materials, pipe dimensions, and damping are considered. These factors are combined to present a single, albeit rather complicated, equation to describe the pipe wall vibrations and hoop stresses as a function of time. This equation is also compared to another theoretical prediction for hoop stresses, which is also derived herein. Specifically, the two theories predict different maximum stresses, and the differences between these predictions are graphically displayed.
Development of Engineering Formula for Welding Residual Stress Distributions of Dissimilar Welds on Nozzle in Nuclear Component
Authors: Kim Jong-Sung , Jin Tae-Eun
Published: August 2009

The purpose of this study is to develop robust engineering formulae of residual stress distributions in the dissimilar welds by using finite element analysis. First, finite element analysis procedure is validated by comparing the residual stresses of a mock-up dissimilar weld calculated by finite element analysis with hole drilling measurement results. Second, parametric study based on the finite element analysis procedure is performed adequately considering the effect of geometric variables and mismatch on real dissimilar welds. Third, engineering formulae are developed based on the parametric study results. Last, the formulae are verified by comparing with the previous results such as PVRC JIP and API 579.
Literature Survey of Gaseous Hydrogen Effects on the Mechanical Properties of Carbon and Low Alloy Steels
Authors: Lam P. S. , Sindelar R. L. , Adams T. M.
Published: August 2009

Literature survey has been performed for a compendium of mechanical properties of carbon and low alloy steels following hydrogen exposure. The property sets include yield strength, ultimate tensile strength, uniform elongation, reduction of area, threshold stress intensity factor, fracture toughness, and fatigue crack growth. These properties are drawn from literature sources under a variety of test methods and conditions. However, the collection of literature data is by no means complete, but the diversity of data and dependency of results in test method is sufficient to warrant a design and implementation of a thorough test program. The program would be needed to enable a defensible demonstration of structural integrity of a pressurized hydrogen system. It is essential that the environmental variables be well-defined (e.g., the applicable hydrogen gas pressure range and the test strain rate) and the specimen preparation be realistically consistent (such as the techniques to charge hydrogen and to maintain the hydrogen concentration in the specimens).
3D Finite Element Modeling of the Swage Autofrettage Process Including the Bauschinger Effect
Authors: Troiano E. , Underwood J. H. , de Swardt R. R. , Venter A. M. , Parker A. P. , Mossey C.
Published: August 2009

The autofrettage process is a method that produces tensile plastic deformation during the overloading of a pressure vessel which reverses and becomes compressive during unloading. This process produces favorable compressive residual hoop stresses at the bore of the pressure vessel, and results in an increase in the life of the component. In thick walled pressure vessels this process can be accomplished with either a hydraulic or mechanical overloading process. These processes produce different residual stress fields by their inherent nature. The Bauschinger effect, which is observed in most of the materials used in thick walled pressure vessels, is a phenomenon which results in lower reverse loading stresses than those predicted with the classic techniques of Hill and others. The phenomenon is a strong function of the amount of plastic strain during the initial loading of the pressure vessel and results in losses of reverse loading strength of up to 40% in A723 and HB7 steels. A quasi-static three dimensional axi-symmetric finite element model of the swage mandrel autofrettage process of a thick walled pressure vessel is presented in this work. It includes the results of several methodologies for predicting the reduced reverse loading stresses resulting from the Bauschinger effect. The FE results are then shown to compare favorably with neutron diffraction residual stress measurements and yield pressure tests.
Anatomy of the Calandria Tube Rolled Joint
Authors: Metzger D. , Araujo E. , Brown D.
Published: August 2009

In CANDU™ (Canadian Deuterium Uranium) Reactors, the joint between the Calandria tubes to the Calandria tubesheets is achieved by roller expanded joints. This paper models a detailed account of the Calandria tube joint fabrication and deformation. Numerical simulation illustrates the mechanisms of bending and compression that cause the plastic deformation in the joint. Results show that the insert deformation must pinch the Calandria tube both axially and radially at groove edges to create leak tightness. Predicted rolling forces have been used to quantify the elastic deformation in the rollers and mandrel, and the final tool setting is seen to account for this springback as well as springback in the joint components.