bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiphysics Inverse Analysis Method for Reducing Transient Thermal Stress in a Thick-Walled Pipe
Authors: Ishizaka Takuya , Kubo Shiro , Ioka Seiji
Published: July 2010

When high temperature fluid flows into a pipe, a temperature distribution in the pipe induces a thermal stress. It is important to reduce the thermal stress for managing and extending the lives of plants. In this problem heat conduction, elastic deformation, heat transfer, liquid flow should be considered, and therefore the problem is of multidisciplinary nature. In a previous paper the present authors proposed an inverse method for determining the optimum thermal load history which reduces the transient thermal stress considering the multidisciplinary physics. The optimum temperature history of inlet fluid may be useful for designing and operating plants. Analytical solutions of the temperature and stress distributions for a thin-walled pipe were used in the analysis. In the present study the reduction of transient thermal stress in a thick-walled pipe is considered. The finite element techniques are employed in the optimization for obtaining the temperature distribution and the thermal stress in the thick-walled pipe. The maximum hoop tensile stress is minimized for the case where inner surface temperature is expressed in terms of a polynomial function of time. The effect of the ratio of inner radius to outer radius on the optimum temperature history is examined. It is found that when the ratio of inner radius to outer radius is larger than 0.8 the optimum temperature history for the thin-walled pipe gives a good estimate. For thicker pipes the optimum temperature history for the thin-walled pipe can be an initial guess for searching the optimum temperature history.
A Simple Analysis and Design Method of Bolted Pipe Flange Connections With Gaskets Under Internal Pressure
Authors: Oyama Yasuro , Sawa Toshiyuki , Kobayashi Takashi , Nagata Satoshi
Published: July 2010

In designing pipe flange connections, it is important to examine the hub stress, bolt load and the gasket stress distribution which governs the sealing performance. However, actually a simpler calculation method is needed for designing a pipe flange connection. In the present paper, a simpler calculation method is proposed using shell-ring theory which is modified Kohmura method. In the present calculation method, a separation point at the gasket interfaces can be estimated accurately, in addition to the rigidity of flange and the bolt preload for a given allowable amount of gas leakage. In addition, a design method taking account the leakage is demonstrated and calculation examples are also shown for better understanding.
Discussion on a Comparative Study Among FFS Rules
Authors: Oyamada Kenji , Konosu Shinji , Ohno Takashi
Published: July 2010

Remaining Strength Factor (RSF) approach in Part 5 of API 579-1/ASME FFS-1 is an assessment method for a cylindrical component with a local metal loss based on surface correction factors. Also, reference stress solutions that are applied in the Failure Assessment Diagram (FAD) method for a cylindrical component with a crack-like flaw are provided in Annex D using surface correction factors. In the p-M diagram method that has been recently developed, reference stress solution for local metal loss evaluation in a cylindrical component is derived using bulging factors, which are similar but not identical to the surface correction factors used in API 579-1/ASME FFS-1. This paper describes the results of a comparative study among the RSF approach, reference stress solutions for the FAD method, and the p-M diagram method, in terms of plastic collapse evaluation of a cylindrical component. These results were compared with the FEA and experimental results to confirm how those estimated stresses could be validated. The results of the study also contain proposals for prospective modifications of API 579-1/ASME FFS-1.
Triggering of Vortex Shedding by Cylinder Oscillation for Reynolds Number Under 47
Authors: Baranyi La´szlo´
Published: July 2010

This study investigates the triggering of vortex shedding by transverse and in-line forced oscillation of a circular cylinder placed in a uniform stream below the critical Reynolds number 47. The effect of Reynolds number, frequency and amplitude of cylinder oscillation is investigated numerically. The effect of Reynolds number, amplitude of oscillation, and frequency of oscillation is investigated. Time-mean and rms values of lift, drag, base pressure, and torque coefficients, as well as mechanical energy transfer, are plotted against Reynolds number and amplitude of oscillation. Periodic vortex shedding is more easily triggered for a cylinder oscillated transversely than for in-line oscillation. Lower Reynolds number, amplitude of oscillation, and time is needed to reach periodic vortex shedding for the transversely oscillated cylinder.
Weld Residual Stress and Distortion by Considering Process Mechanics
Authors: Mochizuki Masahito
Published: July 2010

Welding residual stress and distortion are directly subjected to welding process conditions. Residual stress induced by welding is often the cause of failure in pressure vessels and pipings, thus their understanding, prediction and mitigation is essential for ensuring structural integrity. High precision fabrication is being demanded recently thus distortion control becomes very important. Highly precise fabrication of welded materials is in great demand, and so microstructure and distortion controls are essential. Furthermore, consideration of process mechanics is important for intelligent fabrication. In this study, the microstructure and hardness distribution in multi-pass weld metal are evaluated by computational simulations under the conditions of multiple heat cycles and phase transformation. Because conventional CCT diagrams of weld metal are not available even for single-pass weld metal, new diagrams for multi-pass weld metals are created. The weld microstructure and hardness distribution are precisely predicted when using the created CCT diagram for multi-pass weld metal and for calculating the weld thermal cycle. Weld distortion is also investigated by using numerical simulation with a thermal elastic-plastic analysis. In conventional evaluations of weld distortion, the average heat input has been used as the dominant parameter; however, it is difficult to consider the effect of molten pool configurations on weld distortion based only on the heat input. Thus, the effect of welding process conditions on weld distortion is studied by considering molten pool configurations, determined by temperature distribution and history.
Locally Delaminating Stress Corrosion Cracking Growth of Strain-Hardened Austenitic Alloys in Hydrogenated High Temperature Water Environments
Authors: Lu Zhanpeng , Xue He , Murakami Hiroyoshi , Shoji Tetsuo
Published: July 2010

Locally delaminating cracks, i.e. cracks that grow along the plane that is parallel to the principal applied loading direction, are observed on the fracture surfaces of heavily strain-hardened austenitic alloys after stress corrosion cracking tests in hydrogenated high temperature water environments. These delaminating cracks often occur locally on mixed intergranular-transgranular stress corrosion cracking fracture surfaces. The crack tip stress field is analyzed by finite element analysis. The physical-chemical degradation effect of stress on oxidation kinetics is formulated. The combinations of local oxidation penetration, relatively slow crack growth on the principal plane, and locally high crack tip stress are favorable for the growth of delaminating cracks. These conditions can be satisfied in stress corrosion cracking for austenitic alloys with heavily deformed microstructures and high strengths in hydrogenated high temperature water environments.
Numerical Simulation of Irradiation-Induced Grain-Boundary Phosphorous Segregation in Reactor Pressure Vessel Steels Using Rate Theory Model With First-Principles Calculations
Authors: Ebihara Ken-ichi , Yamaguchi Masatake , Nishiyama Yutaka , Onizawa Kunio , Matsuzawa Hiroshi
Published: July 2010

The experimental results on neutron-irradiated reactor pressure vessel (RPV) steels have revealed grain boundary segregation of phosphorous (P) due to neutron irradiation, which may lead to intergranular fracture. Because of the lack of experimental database, however, the dependence of the segregation on variables such as dose, dose-rate, and temperature is not clear. Here, we incorporate the parameters determined by first-principles calculations into the rate theory model which was developed for bcc lattice on the basis of the fcc lattice model proposed by Murphy and Perks [1], and apply it to the simulation of irradiation-induced P segregation in bcc iron. We evaluate the grain boundary P coverage and discuss its dependence on dose-rate and irradiation temperature by comparing our results with previously reported results and experimental data. As results, we find that dose-rate does not affect the grain boundary P coverage within the range of our simulation condition and that the dependence on irradiation temperature differs remarkably from the previous results.
Dynamic Analysis of Supported Pipes Conveying Fluid Using Precise Time Step Integration Method
Authors: Liu Long , Xuan Fu-zhen
Published: July 2010

In this study, dynamic analysis of supported pipes conveying fluid is investigated in Hamiltonian system using precise time step integration method (PTSIM). Firstly, vibration equations of supported pipes are discretized using the state variable vectors composed of displacement and momentum. Then, PTSIM is introduced briefly and used to solve nonlinear symplectic canonical equations with linear approximation formula. Finally, the precision of this approach is testified by numerical examples of pinned-pinned pipes with different fluid parameters. The results show that PTSIM is an efficient and stable approach for vibration analysis of fluid-conveying pipes.
Fatigue Studies of Stainless Steel Pipes Subject to High Cycle Domain Sinusoidal Thermal Loads
Authors: Paffumi Elena , Radu Vasile , Nilsson Karl-Fredrik , Taylor Nigel
Published: July 2010

The assessment of fatigue crack growth due to turbulent mixing of hot and cold coolants presents significant challenges, in particular to determine the thermal loading spectrum. A simplified approach in which the entire spectrum is replaced by a sine-wave variation of the temperature at the inner pipe surface has been applied in this study. Particular attention is given to the evaluation of the maximum allowable surface temperature variation before the growth of a given defect occurs in relation to different frequencies of loading. A critical frequency defined as that which gives the shortest crack initiation and growth life will be investigated for different semi-elliptical crack shapes. The application of the method is described for the pipe geometry and loadings conditions reported for the Civaux 1 case.
Study on the Heating Process and Properties of X80 Induction Heated Bending Pipe
Authors: Chi Qiang , Liu Yinglai , Ji Lingkang , Wang Peng
Published: July 2010

Induction heated bending pipe is an important connecting piece widely used in natural gas pipeline. As the persistent development of natural gas pipeline project, the X80 induction heated bending pipe needed to be developed and studied. The local induction quenching process and the wholly induction quenching process were adopted to develop the Φ1219mm×22mm X80 bending pipe in this paper. The effects of different technologies on the bending pipe property were studied. Based on the pipe-bending machine that can not apply the continuous wholly induction quenching process, a multiple-step wholly induction quenching process was proposed and realized. The study results show that for the X80 bending pipe manufactured via the local induction quenching process, the strength of straight part is higher than the bend part. The toughness of welding seam and heat-affected zone at straight part is lower. The match of property between the straight part and the bend part is not perfect. The continuous wholly induction quenching process improve effectively the toughness of bending pipe, reduce the strength and yield ratio to a certain extent, so the match of property between the straight part and the bend part is reasonable. The multiple-step wholly induction quenching process can also improve the property of the straight part in bending pipe. The property of intermediate zone by double quenching has no clear changes. This kind of process is suitable for the pipe-bending machine that can not provide continuous wholly induction quenching process.
Experimental Measurement of the Permeability of Die-Formed Exfoliated Graphite Compression Packings
Authors: Lasseux Didier , Jolly Pascal , Jannot Yves , Sauger Emmanuel , Omnes Benoit
Published: July 2010

In this work, we address the issue of sealing performance of ring-shape valves compression packings. Our analysis is focused on the characterization of the permeabilty of the rings made of die-formed exfoliated graphite. Because of the tight character of the material, significant Klinkenberg effects are expected. In addition, due to the manufacturing process, permeabilities kz and kr as well as Klinkenberg coefficients bz and br in the respective axial and radial directions are markedly different and strongly dependent upon the applied stress. A specific experimental device, based on pressure pulse relaxation of nitrogen through the material, was designed for the measurement in each direction under a controlled axial compression. Determination of kz, kr and bz, br is performed on the basis of a non-stationary gas-flow model in the radial and axial directions using an inverse procedure applied to the pressure decay signal. Our results confirm the efficiency of the method developed here. They clearly show the anisotropic character of the material (kz is roughly one order of magnitude larger than kr) and the dependence upon axial compression. The present analysis is the key step before further quantification of the leak rate which may result from the permeation through the material as envisaged here as well as through interfaces between the housing, the packings and the stem.
The Effect of Pre-Strain on Ductile Fracture Toughness of Reeled Pipeline Steels
Authors: Tkaczyk Tomasz , O’Dowd Noel P. , Nikbin Kamran , Howard Brett P.
Published: July 2010

The reel-lay method is a cost efficient alternative to the S-lay and J-lay methods for small to medium size steel offshore pipelines. The quality of the pipeline construction is enhanced by on-shore welding and inspection under controlled conditions. However, reeled pipelines are subject to at least two symmetrical plastic strain cycles during installation. The plastic straining associated with reeled installation modifies the axial tensile response of the pipe material. Also, it has been suggested that plastic straining may reduce the fracture toughness. In this work small scale tests, representative of conditions experienced under reeling of steel pipelines, have been carried out. The fracture resistance curves obtained for the material in the as-received and strained conditions have been compared. No significant effect of the reeling strain cycle on the fracture toughness during subsequent straining was observed.
Seismic Performance of Vibration Control Device That Generates Power
Authors: Matsuoka Taichi , Sunakoda Katsuaki , Hiramoto Kazuhiko , Yamazaki Issei , Fukukita Akira , Roschke Paul N. , Loh Chin-Hsiung , Lin Pei-Yang
Published: July 2010

In a previous paper the authors proposed a semi-active vibration control device (VCD) that generates power. The device utilizes a ball screw, and has inertial and damping forces. The damping coefficient is adjusted by altering resistance at the terminal of the power generator. A small-scale VCD was manufactured for experimental testing. Frequency responses of a small-scale spring mass structure were measured in order to confirm the effects of vibration suppression within a wide range of frequencies. In this paper, as the next step, vibration tests using a benchmark structure with an installed VCD that has a 30 kN capacity are carried out at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan. The benchmark structure has three stories with a 3 m height and a mass of 6 tons at each floor level for a total height and weight of 9 m and 18 tons, respectively. The VCDs are installed between adjacent floors with steel chevron braces. A simple control law that is based on a minimized Lyapunov function and employs bang-bang operation is used as a variable current controller instead of the modifying the resistance level of the VCD. Scaled earthquake motions including the Imperial Valley El Centro north-south component that is normalized to be a peak level of 0.5 m/s2, are applied to the base of the steel framed structure in the horizontal direction by a shaking table. Experimental responses of each floor for the uncontrolled and controlled cases are compared with analytical responses, and effects of vibration suppression for the large-scale model are discussed quantitatively.
Numerical Analysis of a MDOF Structure Protected With TMD Techniques
Authors: Moretti Vincenzo , De Angelis Maurizio , Ranieri Nicola , Roselli Ivan
Published: July 2010

In the present paper a complete numerical study of a 1:5 scaled four-storey steel-frame structure with the application of Tuned Mass Dampers (TMD) is reported. In particular, Passive Tuned Mass Dampers (PTMD), Semi-Active Tuned Mass Dampers (SATMD), and Hybrid Tuned Mass Dampers (HTMD) were considered and compared. The initial aim of this work was to define a Simplified Equivalent Model to be conveniently utilized for simulations instead of a realistic Prototype Numerical Model in order to estimate the designing parameters of the devices with good approximation and sensible time calculation saving. Subsequently, the feasibility, the reliability and the effectiveness of the considered seismic control techniques were also assessed. The results of the numerical analysis showed how the use of a simplified model allows to estimate the designing parameters with accuracy. More importantly, the numerical results showed to what extent the several TMD techniques revealed to be effective for the seismic response reduction.
Effects of Gaseous Hydrogen on Fatigue Crack Growth Behavior of Low Carbon Steel
Authors: Lee Dongsun , Nishikawa Hide-aki , Oda Yasuji , Noguchi Hiroshi
Published: July 2010

In order to investigate the effects of hydrogen on the fatigue crack growth behavior of low carbon steel JIS S10C, bending fatigue tests were carried out using a specimen with a small blind artificial hole in a low pressure pure hydrogen gas atmosphere. The results show that the fatigue crack growth rate in hydrogen gas is higher than that in nitrogen gas, moreover, the degree of acceleration is greater in the high strain range. In fractography, intergranular facets mixed with ductile fracture and quasi-cleavage fracture with brittle striations appear in a hydrogen gas environment, while only ductile fracture mainly appears in nitrogen gas. In the low growth rate range, many intergranular facets are seen on the ductile fracture surface, and in the higher growth rate range, quasi-cleavage facets increase as the growth rate increases. The growth rate of a small crack in nitrogen gas can be expressed by dl/dN ∝ Δεpnl in the wide range of applied total strain range Δεt. The same type equation is also satisfied in hydrogen gas, but in the narrow range roughly from Δεt = 0.25% to Δεt = 0.37%. The fracture surface in this range shows only intergranular facets and a ductile morphology, but no quasi-cleavage fracture. Although the crack growth mechanism in hydrogen is different from that in nitrogen, observation of the mechanism of intergranular facet formation shows a similarity to the mechanism in nitrogen in which the slip-off mechanism of crack growth is valid. The formation of intergranular facets is also closely related to the slip behavior influenced by hydrogen. This means that there exists a high possibility for the application of the small crack growth law inhydrogen to not only S10C, but also to other carbon steels in which the intergranular facet appears.
Accounting for Crack Propagation in a Model to Predict Fracture Toughness in Ferritic Steels
Authors: EricksonKirk Marjorie A. , Wagenhofer Matthew , Williams Paul T. , Yin Shengjun
Published: July 2010

A program was undertaken to develop a predictive model of the scatter in toughness of a structural steel across the wide temperature range of ductile-to-brittle transition based on physical understanding of deformation and fracture behaviors. The initial model was focused on microcrack initiation and includes criteria to describe the propagation of particle-sized microcracks into the surrounding ferritic matrix. Parametric studies using this model found that the temperature dependence for fracture toughness, derived from microcrack, was insufficient to describe the temperature dependence observed in measured KJc toughness values. A microcrack propagation model was developed to account for additional barriers associated with transgranular crack propagation to failure. This propagation model accounts for the temperature dependence of crack propagation across grain boundaries and is therefore expected to increase the degree of temperature dependence. This paper summarizes the initiation model and discusses the approach taken in developing a microcrack propagation model component and discusses preliminary results from a Monte Carlo simulation.
Integrity and Life Assessment of Cast Duplex Stainless Steel Elbows Used in the Primary Loops of PWRs
Authors: Ligneau N. , Page`s C. , Akamatsu M. , Pokor C. , Calonne-Chatelee V.
Published: July 2010

Type CF8M cast duplex stainless steels used in the primary loop elbows of PWRs can be affected by thermal aging embrittlement at service temperature, which is around 300°C. This mechanism, resulting from the microstructural evolution of the ferrite, can reduce their fracture toughness properties. In addition, it is necessary to consider manufacturing quality and the possible occurrence of casting defects, such as shrinkage cavities. In a context of life extension, it is important to assess the margins for crack initiation and crack propagation instability. This paper reports the present integrity and life expectancy assessment methodologies as carried out by EDF. The French approach is based on engineering code RSE-M guidelines and French regulation requirements on NPPs in operation. This work is supported by an extensive R&D program on one hand and on field experience analysis on the other hand. It is shown how R&D and engineering tools complement each other. This paper details the three main topics of the life assessment methodology: - Fracture toughness estimates are made with predictive formulae based on chemical composition and aging conditions. These formulae are supported by a data base which is regularly up-dated with new measurements. - An inventory of manufacturing quality is drawn up and the most severe defects are characterized regarding mechanical concerns. - Fracture mechanics analyses are performed using both engineering simplified methods and classical finite element analysis. The calculated J parameter is then compared with the estimated fracture toughness of the material. Margin coefficients are included in the calculation process as required by the French regulation and code. Finally, this evaluation enables the utility to: - Identify the sensitive parts regarding the aging of cast components, - Perform a monitoring and a maintenance program as necessary.
Assessment of the Fatigue Life of a PWR Surge Line Including the Effect of Coolant Environment
Authors: Ko¨nig Gu¨nter , Bartonicek Jaroslav , Rothenho¨fer Horst
Published: July 2010

In Germany, the integrity concept is applied to important piping systems in most of the nuclear power plants. Regarding the framework of this concept, those damage mechanisms that cannot be controlled by analysis have to be excluded using appropriate measures. In most of the cases, these damage mechanisms are a result of local effects (like loads, medium, material characteristics) that cannot be determined exactly in advance and thus cannot be controlled by analysis, reliably. Examples are strain induced corrosion (LCF area) and corrosion fatigue (HCF area). For cases like these and given medium, suitable materials have to be chosen in combination with optimized design, appropriate manufacturing procedures (incl. welding), construction and operation. The loads and the water chemistry in operation have to be monitored and the effectiveness of the measures has to be verified, regularly, taking into account the actual state of knowledge. Regarding these boundary conditions the fatigue evaluations that have been performed until today seem to be sufficient, as experience shows with piping systems where this procedure has been applied. There are usually no significant failures (indication of failures); failures detected have been attributed to violation of the boundary conditions. With this background, there seems to be no need to change this procedure to safeguard the effect of environment. In this paper, the measures to guarantee integrity in design and operation state are discussed, first. Using the example of a surge line and the comprehensive monitoring results of this system the evaluation of fatigue usage and the assessment of the effect of coolant environment is discussed with reference to the ANL approach. Where the ANL approach is meant to be applied only in the design phase of a new reactor its relevance for the operation phase is cross-checked with real life measurement data. The conclusion summarizes where the effect of coolant environment has to be taken into account and gives advice how to find realistic transients for the design phase of new reactors.
Special Design Considerations for Buried HDPE Piping in Nuclear Safety Related Applications
Authors: Basavaraju Chakrapani , Manoly Kamal A.
Published: July 2010

Due to its recognized resistance against galvanic corrosion, microbiological induced corrosion (MIC), and fouling compared to carbon steel, high density polyethylene (HDPE) piping material has recently been proposed for replacement of carbon steel piping in nuclear safety related class 3 service water buried piping applications. However, there are some unique challenges requiring special design considerations due to HDPE’s visco-elastic nature, need for relatively thicker pipe walls, and very low material allowable stress. This paper examines special design considerations such as design factor, minimum required wall thickness for pressure, thermal gradient effects, and cumulative effect from loads of different duration. Useful guidelines from design and analysis perspective are provided.
Application of Diffraction Methods for the Residual Stress Determination in Welded Joints
Authors: Nitschke-Pagel Thomas
Published: July 2010

The paper gives an overview about the most important diffraction methods for the determination of residual stresses in welded joints. The basic principles and the particular advantages and limitations of the methods are shown as well as the applicability for lab size samples and welded components.
UK Technical Advisory Group on the Structural Integrity of High Integrity Plant: Overview of Recent Activities
Authors: Burdekin F. M. , Ainsworth R. A. , Lidbury D. P. G.
Published: July 2010

TAGSI is an acronym for The UK Technical Advisory Group on the Structural Integrity of High Integrity Plant. The purpose of TAGSI is to address and make recommendations on issues raised by its sponsoring organisations in discussion with independent advisors. Collectively, these sponsoring organisations operate, maintain, assess and regulate nuclear power producing and chemical plant. Against this background, an overview is presented of the recent work of TAGSI in terms of structural integrity issues addressed, symposia organised, and output appearing in the open literature. Other papers at this conference describe some of the technical work of TAGSI in more detail.
Ratcheting Predictive Methods in RCC-MR Code
Authors: Gelineau Odile , Sperandio Morello , Berton Marie-Noe¨l
Published: July 2010

The structures belonging to Gen IV reactors such as Sodium Fast Reactors (SFRs) and High Temperature Gas Reactors (HTGRs) are submitted to high temperatures and high thermal gradients and must be designed against the risk of ratcheting. RCC-MR code has been developing for several years original methods to deal with this damage mode. The last edition of the code has been issued in French and English versions on October 2007 by AFCEN. It constitutes the result of a continuous and important work to develop and improve design and construction rules. To deal with ratcheting damage mode, the “efficiency diagram” method is used. This method has been improved with time as a function of experience and R&D work and it is able to get a good prediction of ratcheting in all specific phenomena occurring in high temperature reactors: - Cases where high thermal membrane stresses are present. Such problems appear particularly at the free level zone of shells in SFRs for which ratcheting risk has been proved. - Cases involving short-term overloads, representative of seismic cycles and pipe draining operations, for which ratcheting appears to be less damaging than permanent overloads of same amplitude. The objective of this paper is to describe the original methods used in RCC-MR code, the process of development and improvement, helped by the R&D work, leading to the present 2007 edition.
Numerical Study of Tube Array Vibrations Under Cross Flow
Authors: Bra¨ndle de Motta J. C. , Baj F.
Published: July 2010

Tube array vibration in heat exchangers has been treated thoroughly. One part of the vibration is induced by the cross flow. The vibration of a free tube, surrounded by rigid tubes, is a common model used to simplify the problem. In this paper, a numerical simulation of this experiment is carried out and a database of the results is created. Some assumptions have been introduced in the simulation. The flow is considered incompressible, monophasic and non-turbulent. The tubes are fixed, except for the central one, which has a mass, a damping ratio and a frequency in vacuum. At the initial time, it is displaced from its static equilibrium. Variables of the simulation include the parameters of the tube in vacuum, the water velocity, the separation between tubes and their diameters. The results are the frequency and the damping ratio that enable the characterization of the the dimensionless mass-damping parameter. Many results have been collected, by changing these parameters. The results include a Rogers’ formula review. This formula is used to obtain the mass and damping factor from the tubes’ diameter-pitch ratio, when there is no flow. In this manuscript the influence of the water velocity on those factors is explained. When water velocity grows, the damping ratio of the central tube becomes negative, therefore, the tube becomes instable. Increasing the velocity further makes this instability disappear, generating a new zone of stability. This initial instability is compared to other authors experimental results.
Modeling of Thermal Shock Effects on a Globe Valve Body-Bonnet Bolted Flange Joint
Authors: Mathieu Jean-Philippe , Ferrari Je´roˆme , Rit Jean-Franc¸ois , Hersant David
Published: July 2010

Advances in computational mechanics allow to improve safety and reliability of many components used in nuclear applications. Although valves are numerous and critical for safety considerations, many difficulties arise that highly complicate the use of numerical methods for qualification and testing. Thus, valves are mainly tested by experimental simulation in representative conditions, which is sufficient to prevent failures, but do not help to comprehensively analyze mechanisms of failure. This paper attends to demonstrate efforts made at EDF R&D to improve comprehension of valve parts loadings during operation. Thermal shock in a globe valve is represented and modeled using EDF R&D Finite Element Analysis (FEA) code (Code_Aster). Since the globe valve representation implies several parts, attention is first focused on Boundary Conditions (BC) and meshing refinements to allow calculation on a standard engineering workstation. Materials characteristics are mainly given by standard industrial codes and modeling hypothesis relies on elastic behavior of materials. Thermal BC consists in a thermal field beforehand calculated with a coupled approach between EDF computational fluid dynamics code (Code_Saturne) and its thermal code (Syrthes). Simulation results are presented. Attention is then focused on the evolution of the body-bonnet bolted flange joint tightening forces which are simulated during the thermal shock. Choices of modeling are addressed: for example, it is shown in this paper that the contact modeling hypothesis have to be discussed in order to allow good parts behavior description during transient.
Decompression Pressure Wave Loads in a Boiling Water Reactor (BWR) Due to Recirculation Pipe Break
Authors: Molyneux John , Ananth Raju , Gillis Jay
Published: July 2010

This paper presents a theoretical and numerical investigation of one of the postulated accidents for Boiling Water Reactors (BWRs), namely, a double-ended guillotine break of recirculation outlet line that leads to a sudden depressurization locally at the recirculation outlet nozzle. The depressurization wave front thus formed will propagate inside the reactor leading to transient loads on the internals. The paper discusses the solution to this wave propagation problem.
Seismic Evaluation of Large Server Computer Structure
Authors: Notohardjono Budy D. , Canfield Shawn , Cooke James A.
Published: July 2010

This paper discusses the analysis and verification of a finite element model which simulates the robustness of a high end computer server structure during a severe seismic event. The server consists of the frame which is the structure that components are installed into, such as processor units, input-output units and power components. The finite element modeling of this server frame is presented here not only to inform on creating an accurate model for simulation purposes, but also to provide guidelines as to the critical factors in setting up a large assembly finite element model (FEM) and to establish the optimum methodology for modeling this complex assembly with the available analysis software tools. For verification, the simulated modal data is compared to both modal data measured from an instrumented impact hammer, and to measured swept sine data. The simulated results compare favorably with the measured data, and it has been determined that location and integrity of the welded connections are critical for an accurate vibration response of the finite element model. The analysis frame model was subjected to loads and environmental conditions similar to those endured under horizontal table vibration tests and seismic events. The results of the experimental testing and simulations were compared and proved to be in a good correlation. Based on this verified finite element model, any additional redesign of the frame structure and its stiffening members can proceed very efficiently. This design study builds toward the objective of constructing a verified model of the server frame and components which will lead to a guideline for implementing stiffener designs on high-end server systems.
The Buckling of Fuel Rods Under Inertia Loading
Authors: Bjorkman Gordon S.
Published: July 2010

The buckling analysis of fuel rods during an end drop impact of a spent fuel transportation cask has traditionally been performed to demonstrate the structural integrity of the fuel rod cladding or the integrity of the fuel geometry in criticality evaluations for a cask drop event. The actual calculation of the fuel rod buckling load, however, has been the subject of some controversy, with estimates of the critical buckling load differing by as much as a factor of 5. Typically, in the buckling analysis of a fuel rod, assumptions are made regarding the percentage of fuel mass that is bonded to or that participates with the cladding during the buckling process, with estimates ranging from 0 to 100%. The greater the percentage of fuel mass that is assumed to be bonded to the cladding the higher the inertia loads on the cladding, and, therefore, the lower the “g” value at which buckling occurs. However, these solutions do not consider displacement compatibility between the fuel and the cladding during the buckling process. By invoking displacement compatibility between the fuel column and the cladding column, this paper presents an exact solution for the buckling of fuel rods under inertia loading. The results show that the critical inertia load magnitude for the buckling of a fuel rod depends on the weight of the cladding and the total weight of the fuel, regardless of the percentage of fuel mass that is assumed to be attached to or participate with the cladding in the buckling process. Therefore, 100% of the fuel always participates in the buckling of a fuel rod under inertia loading.
Influence of Specimen Type, Crack Length and Evaluation Method on Quasi-Static and Dynamic Fracture Toughness Properties
Authors: Zurbuchen Conrad
Published: July 2010

This paper provides a comparison of the influence of specimen type (single edge bend (SE(B)) specimen vs. compact tension C(T) specimen), specimen dimensions (crack length ratio a/W, thickness B) and the effect of the loading rate on fracture toughness properties. In the lower ductile-brittle transition region the quasi-static Master Curve (MC) reference temperature T0 is evaluated according to ASTM E 1921-08ae1 and the dynamic MC T0 according to the Swiss guideline HSK-AN-425, which is compared with a modified ASTM E 1921-08ae1 approach. The ductile behaviour was evaluated by quasi-static JR curve testing in which the applicability of several evaluation standards are compared (ASTM E 1820-08, ISO 12135, ESIS-P2). Quasi-static and dynamic MC temperatures T0 deviate by up to 68 K. SE(B) specimens with shorter crack lengths (a/W = 0.3) than prescribed by ASTM E 1921 yield the same T0 as specimens with a/W = 0.5. Thus, such short crack surveillance specimens are also suitable for fracture mechanical assessments. SE(B) specimens of B = 0.4T (1T = 1 inch) up to 3.2T show comparable T0, proving the transferability of fracture mechanical test results of small surveillance specimens to heavy-walled RPV structures.
Experimental Study and Numerical Simulation of Domes Under Wind Load
Authors: Al-Hashimi H. , Seibi A. C. , Molki A.
Published: July 2010

Dome structures are of architectural significance in many applications ranging from building decorations to fluid confinement usage such as pressure vessels and storage tanks in the petrochemical industry. Most domes are subjected to severe external loads caused by wind flow. Therefore, careful material selection and structural design of domes is imperative to avoid any unexpected failure. This paper presents the design of an experimental set-up to study the flow behavior around ABS dome models of hemispherical and elliptical shapes and their structural integrity under wind loads. The objective of this paper is to determine the dome’s wall thickness for various geometrical shapes. The domes were placed inside a wind tunnel where the wind speed was varied from 60 to 100 km/hr and pressure distribution on the surface of the dome roof was measured. Pressure measurements were carried out for various attack angles with respect to its centerline using a data acquisition system programmed in LabVIEW™. In addition, flow visualization of the air flow around the dome was carried out using a smoke generator. The experimental study was supplemented by a numerical simulation of the air flow around domes to mimic experiments using Computational Fluid Dynamics (CFD) techniques. The effect of wind on the dome structural integrity was studied using finite element analysis. The experimental results were used to validate the CFD models from which pressure distribution around domes were obtained. Results related to the pressure distribution around domes obtained from the CFD analysis were used as loading conditions to study the structural integrity of the domes using ANSYS™. Preliminary experimental results of wind speed effect on a hemispherical/elliptical dome revealed pressure variations for various angles of attack and height inclination along the dome roof surface.
An Experimental Investigation of High Level Vibration on the Residual Heat Removal Line of a Pressurized Water Reactor
Authors: Brown Jeffrey A. , Blevins Robert D. , Fernando H. Joseph
Published: July 2010

This paper presents the results of a scaled aero acoustic test that modeled a side branch resonance observed in the residual heat removal suction line of a large pressurized water reactor. Resolution of the acoustic resonance was sought by detuning the eddy shedding frequency from the fundamental side branch acoustic mode. The specific physical modifications and their ability to detune the coupled system are presented.
Factors Affecting High Temperature Relaxation Behaviors of Expanded PTFE Gaskets
Authors: Lee Walter , Bouzid Abdel-Hakim , Huang James
Published: July 2010

High temperature behaviors of expanded PTFE gaskets have been studied using the hot blow-out test (HOBT) method. The results suggest that the operating stress and temperature measurements of a tested gasket form a linear relationship on a logarithmic plot, and that higher assembly stress causes proportionally larger degrees of stress relaxation. In contrast, the cooling curve follows a linear relationship in a semi-logarithmic plot (only stress converted). The new formulation and methodology so derived has permitted a better understanding of external and internal factors on relaxation behaviors of expanded PTFE-based gaskets. For example, for a gasket design incorporating a corrugated metal insert, the relaxation curve stays relatively flat until the temperature reaches about 90–100°F, where the stress reduction starts to follow a linear trend parallel to, but above the relaxation curve of the expanded PTFE gasket without the insert. Essentially, the metal insert “delays” the effect of temperature on relaxation, and produces an “effective assembly stress” that is about 13% higher than the actual assembly stress. The use of Belleville washers has shown a similar phenomenon, but with a longer delay and higher effective assembly stress. Finally, the effect of in-process retightening, or hot retorquing, is quantitatively assessed. The contrasting relaxation behaviors of the material by different retightening methods (hot retorque versus post-process retorque in a cooled state) will be discussed.
Potential Effects of Historic Rail Accidents on the Integrity of Spent Nuclear Fuel Transportation Packages
Authors: Bajwa Christopher S. , Easton Earl P.
Published: July 2010

The US Nuclear Regulatory Commission (NRC) completed an analysis of historical rail accidents (from 1975 to 2005) involving hazardous materials and long duration fires in the United States. The analysis was initiated to determine what types of accidents had occurred and what impact those types of accidents could have on the rail transport of spent nuclear fuel. The NRC found that almost 21 billion miles of freight rail shipments over a 30 year period had resulted in a small number of accidents involving the release of hazardous materials, eight of which involved long duration fires. All eight of the accidents analyzed resulted in fires that were less severe than the “fully engulfing fire” described as a hypothetical accident condition in the NRC regulations for radioactive material transport found in Title 10 of the Code of Federal Regulations, Part 71, Section 73. None of the eight accidents involved a release of radioactive material. This paper describes the eight accidents in detail and examines the potential effects on spent nuclear fuel transportation packages exposed to the fires that resulted from these accidents.
Eliminating Conservatism in the Piping System Analysis Process Through Application of a Suite of Locally Appropriate Seismic Input Motions
Authors: Crawford Anthony L. , Spears Robert E. , Russell Mark J.
Published: July 2010

Seismic analysis is of great importance in the evaluation of nuclear systems due to the heavy influence such loading has on their designs. Current Department of Energy seismic analysis techniques for a nuclear safety-related piping system typically involve application of a single conservative seismic input applied to the entire system [1]. A significant portion of this conservatism comes from the need to address the overlapping uncertainties in the seismic input and in the building response that transmits that input motion to the piping system. The approach presented in this paper addresses these two sources of uncertainty through the application of a suite of 32 earthquake realizations with equal probability of occurrence whose collective performance addresses the total uncertainty while each individual motion represents a single variation of it. It represents an extension of the soil-structure interaction analysis methodology of SEI/ASCE 43-05 [2] from the structure to individual piping components. Because this approach is computationally intensive, automation and other measures have been developed to make such an analysis efficient. These measures are detailed in this paper.
JSME Construction Standard for Superconducting Magnet of Fusion Facility “MATERIAL”
Authors: Nishimura Arata , Nakajima Hideo
Published: July 2010

A construction standard for a large superconducting magnet for a fusion device has been established by Japan Society of Mechanical Engineers in Japan. This paper describes the outline of the part of “Material” and interprets some special features provided in the standard. The standard was composed based on Japan Industrial Standard. The materials used for the superconducting magnet structure was limited and divided into two groups. The first group is for the materials of which cryogenic strength are not limited and will be used under the design with the strength at room temperature. The other group composes of the materials of which cryogenic strength are provided. The former group includes forged austenitic stainless steel, Inconel 718, Ni and Ni alloy, Cu and Cu alloy and welding wires for these materials. The latter group holds cryogenic structural materials, such as JJ1 and 316LN steels. The design strength of these materials is given in a quadratic function from room temperature to cryogenic temperature when the material is used in an as-solution heat treated condition. The standard also equips the process to register the new materials. One shall be able to prepare the data set necessary to make registration, and submit to the JSME Code Committee to register the materials with the standard.
Evaluation of Sealing Behavior of Gaskets at Elevated Temperature Based on the Test Method HPIS Z105 Proposed in Japan
Authors: Tsuji Hirokazu , Honda Takashi , Yamaguchi Atsushi , Kobayashi Takashi , Sawa Toshiyuki
Published: July 2010

A method to test the sealing performance of gaskets at elevated-temperatures, HPIS Z105, will be published soon in Japan. This paper discusses the gasket testing procedure to obtain the sealing behavior of gasket at elevated-temperatures. This testing procedure extends the room-temperature gasket testing procedure HPIS Z104 to the elevated-temperatures. The purpose of this testing procedure is to evaluate the effect of a moderate exposure at the elevated-temperature on the sealing performance of the non-asbestos gasket. This testing procedure consists of 4 parts; pre-exposure room-temperature tightness test, aging exposure of gasket at elevated-temperature, stress cycling disturbances, and post-exposure room-temperature tightness test. In order to demonstrate the validity of the testing procedure, measurements of leak rates of several types of sheet gaskets and spiral wound gaskets are carried out. It has shown that the sealing behavior can be well characterized using the proposed testing procedure.