bluuebunny/crossref_metadata_2025 huggingface dataset:
Interference Effect of Wake Body on the Cross Flow Oscillation of a Square Cylinder in Uniform Flow
Authors: Kawabata Yusuke , Haginoya Takeshi , Koide Mizuyasu , Takahashi Tsutomu , Shirakashi Masataka
Published: July 2010

Wind tunnel experiments are carried out to investigate interference effect of wake body on cross flow vibration of a square cylinder in uniform flow. The side length d of the square cylinder is 26∼40 mm and the length le = 315 mm. As the wake body, a strip-plate of width w = d is set downstream the square cylinder with a gap s in cruciform arrangement. The length of the plate ld is varied from infinity, i.e. full measuring section height, to ld/d = 1. Both the Karman vortex excitation (K-VIV) and the galloping are suppressed by the ld/d = ∞ plate in the non-dimensional gap range of 1.6<s/d ≦ 4, although the mechanisms are completely different between the two oscillations. The longitudinal vortex excitation (L-VIV) found in the previous work is confirmed to be induced by the plate at around s/d = 1.4 for the systems with various dimensions and structure parameters. The K-VIV suppression effect is virtually the same for the wake plates with ld/d≧10, and becomes less definite for shorter plates when ld/d ≦ 6. The galloping suppression effect persists up to the shortest wake plate of ld/d = 1 at s/d<2. The L-VIV is observed for plates of ld/d≧6, with weaker degree for shorter plates. The K-VIV seems to be enhanced by ld/d = 2, 4, 6 plates at 1≦s/d≦2 (EK-VIV). By setting the wake plate with ld/d = 1 or 2 at s/d around 0.3, a new type of fluid-elastic vibration is induced as an interference effect of wake body (WBI-FEV). A method is presented to predict fluid-elastic vibrations to which the Van der Pol equation does not apply. The prediction by this method agrees well with measured WBI-FEV for the ld/d = 2 plate.
Quantification of Ductile Damage in AL2024-T351 Using X-Ray Tomography
Authors: Taylor Kerry L. , Sherry Andrew H.
Published: July 2010

Ductile damage mechanics models provide a tool for the prediction of ductile damage and tearing in ductile materials. Models require knowledge of key microstructural features that influence the ductile failure process in order to calibrate critical model parameters. These parameters include the initial and final void volume fraction. The approach widely used to define the initial void volume fraction is to relate this to the volume fraction of void-initiating precipitates quantified using 2D metallography. This paper illustrates how synchrotron X-ray tomography, and high resolution Focused Ion Beam tomography can provide a new and more reliable approach to defining such starting parameters and can provide additional insights into the ductile failure process. This enables more realistic parameters to be derived that predict the distribution of ductile damage below the final fracture surface and hence provide added confidence in the use of the model to predict global behaviour. Results of synchrotron and FIB tomography experiments undertaken with respect to an aluminium alloy AL2024-T351 are presented. The resulting data illustrates the initial microstructure, which includes shrinkage porosity, coarse precipitates and fine dispersoids, and the final microstructure close to the fracture surface following failure. The data demonstrate that the void volume fraction initially increases by the growth of porosity and by precipitate fracturing. Final failure occurs by the rapid formation of nano-scale voids at dispersoids. Analyses of notched tensile specimens are undertaken using the GTN model with parameters derived from the tomography data. Conclusions are drawn regarding the use of microstructurally-derived parameters to predict ductile fracture behaviour.
Flow-Induced Vibration of a Control Valve in a Cavitating Flow
Authors: Watanabe Masanobu , Nishino Koji , Kitajima Yasumi , Yonekura Kazuyoshi , Hagiwara Tsuyoshi
Published: July 2010

The vibration response of a typical globe valve was measured to determine the characteristics of flow-induced vibration in a cavitating flow, varying valve opening rate from 20% to 40%, and flow rate from 0.2 m3/min to 1.4 m3/min or maximum flow rate of the test facility. Strain gauges were mounted on the valve shaft for these measurements. The upstream and downstream pressures of the globe valve were also measured to calculate the cavitation number or cavitation coefficient. Moreover, fluctuating pressures on the valve seat were measured simultaneously with strain signals to examine the correlation between the fluctuating fluid force and the vibration response. Cavitation occurred when the cavitation coefficient reached within the range from 0.42 to 0.47. On the other hand, the amplitude of the valve shaft in the drag direction increased drastically when the cavitation coefficient exceeded 0.8. The correlation between the fluctuating fluid force and the strain was investigated considering the sum of the measured pressures on the valve seat as fluctuating fluid force. A strong correlation between the fluctuating fluid force and the strain was obtained. The phase difference between fluctuating fluid force and the strain was about 40°. It was therefore concluded that the physical phenomenon was self-excited vibration coupled with a cavitating flow. This oscillation system is therefore considered as a negative damping system excited by the fluid force with time lag.
The Development of a Surface Crack in a Thick Vessel Under Ductile Tearing
Authors: Terfas Osama , Bezensek Bostjan
Published: July 2010

The development of the shape and size of a flaw in a pressure vessel is important in fitness-for-service evaluations such as leak-before-break. In this work finite element modelling is used to evaluate the mean stresses and the J-integral around a front of a surface-breaking flaw. These results show non-uniform constraint levels and crack driving forces around the crack front at large deformation levels, which contrast those at low deformation levels. A new procedure is developed to estimate the amount of ductile crack extension around a surface-breaking crack on the basis of ductile tearing resistance curves of deep and shallow cracked fracture mechanics samples. The procedure is applied to surface flaws to simulate ductile crack extension under ductile tearing and show the evolution of the initial flaw shape. Results show that both, initially semi-circular and initially semi-elliptical flaws develop towards the same shape in bending.
Determination of the Plastic Collapse Load for Wire-Wound Pressure Vessels
Authors: Alegre J. M. , Bravo P. M. , Cuesta I. I.
Published: July 2010

This paper is focused on determining the plastic collapse load of vessels which consist of an inner cylinder prestressed by a surrounding winding. This winding consists of a wire helically wound edge-to-edge in pretension in a number of layers around the outside of the inner cylinder. As a consequence, compression stresses are introduced in the cylinder, and the fatigue life of the vessel can be greatly increased. The ASME code, Section VIII - Division 3, provides the analytical equations for the stress calculation in wire-wound vessels under linear-elastic conditions (ASME, 2007). However, to obtain the plastic collapse load of the vessel, finite element method should be used. In this way, the main aim of this paper is to present a numerical procedure for the FE simulation of wire-wound vessels. For this simulation, it must be taken into account that the wire winding is a continuous process where every new layer is coiled around all previous deformed layers. Hence, a layer-by-layer numerical procedure which takes into account this continuous process during winding has been developed. Some examples are given to demonstrate the applicability of the procedure. Once the numerical procedure was validated, it was used to obtain (i) the maximum circumferential stress after winding, (ii) the initial plastic load, and (iii) the plastic collapse load. To obtain the plastic collapse load, an elastic perfectly-plastic material behaviour has been considered. Finally, the numerical results obtained for the plastic collapse load were obtained as a function of several ratios over a wide range, which take into account the cylinder thickness, the wire-wound thickness, the wire-wound pretension and the yield limit of the material.
Investigation of the Elastic-Plastic Design Method in Section VIII Div. 2
Authors: Reinhardt Wolf
Published: July 2010

Section VIII Div. 2 contains an elastic-plastic stress analysis option that is based on the ultimate instability load. The performance of the method is evaluated by using the PVRC burst disk tests. The prediction of the failure load is attempted using both a “best estimate” and the Section VIII Div. 2 material model. The strain limit against local failure is assessed as well. Starting from the notion that Design Codes try to establish safety margins against ultimate failure (burst) and against excessive deformation from the as-designed shape, this paper also examines the proposed method of using a factor of safety against instability (burst) in conjunction with a strain limit (protection against local failure). Implications for the application of the method to design are discussed.
Developing a Numerical Model to Describe the Mechanical Behavior of Compressed Expanded Graphite for Valve Stem Sealing
Authors: Vasse Christophe
Published: July 2010

The work presented in this paper is part of a project that aims at simulating the operation of nuclear power plants valves in nominal conditions. The purpose of this work is to model the behavior of compressed expanded graphite (CEG) packings in service. To achieve this goal, a double approach coupling experimentation and simulation is followed. Compressions and discharges tests of CEG samples are first carried out on an hydraulic press, then simulated with a finite element model that investigates the use of the Cam Clay model. A more complete representation of a packing in service is then modeled to compute the friction forces between the packing and the stem of a valve during the opening and closing phases. The results of these simulations are compared to previous experimental observations.
Small Punch Testing and Its Modeling for the Evaluation of Mechanical Properties of Heat-Resistant Steels
Authors: Dyma´cˇek Petr , Milicˇka Karel
Published: July 2010

Small punch tests on miniaturized thin discs (SPT) can be considered as one of the promising methods predominantly for an assessment of the residual life of parts in service of power plants and thermal facilities. These tests can be used for determining a number of material properties. Two variations of the test seem to have a good potential for use in wide range of temperatures. The CF test (constant force) is a test in which the puncher penetrates under constant load and the time dependence of the deflection is measured. This test is similar to a conventional creep test. The CDR test (with constant deflection rate conditions), in which the puncher penetrates through the disc at a given constant rate of deflection (i.e., central deflection measured in a direction perpendicular to the disc) and the necessary force is measured. This mode of the tests can serve similarly as conventional tensile tests for determining of the static material properties, the estimation of fracture toughness and transitions in material behavior. The article summarizes the capabilities of the small punch technique and presents results from testing of two heat resistant steels, i.e., CSN 15313 and P91 used in the Czech power industry. Experimental results are compared with finite element modeling.
Analysis of Waterhammer in Pipes With Non-Condensable Gases
Authors: Becht Charles
Published: July 2010

This paper analyzes waterhammer due to pump transients in pipes containing pockets of non-condensable gases. Solutions ranging between rigid and compressible liquid columns with pressure wave propagation are considered. An energy model is introduced to show if a system is dominated by either rigid or compressible liquid column properties. This “up-front” energy determination results in choosing an efficient formulation for predicting the transient pressure and piping forces for a given system. Example cases are given to demonstrate the solution methods. The effect of different assumptions and parameters are studied. Compressibility of water, gas bubble size, and pump startup are all studied for their effect on the peak pressure reached during a waterhammer event.
Influence of Viscosity, Density and Surface Tension on Two-Phase Damping
Authors: Be´guin C. , Wehbe J. , Ross A. , Pettigrew M. J. , Mureithi N. W.
Published: July 2010

Internal two-phase flow is common in piping systems. Such flow may induce vibration that can lead to premature fatigue or wear of pipes. In the nuclear industry in particular, failure of piping components is critical and must be avoided. Two-phase damping is considered part of the solution, since it constitutes a dominant component of the total damping in piping with internal flow. However, the energy dissipation mechanisms in two-phase flow are yet to be fully understood. The purpose of this paper is to explore the relationships between two-phase damping and fluid properties. Simple experiments were carried out in a clear vertical clamped-clamped tube to verify the effects of fluid properties on two-phase damping. Various fluids, such as air, alcohol, pure water, sugared water, glycerol, and perfluorocarbon, were combined to obtain different controlled mixtures and to determine the effect of surface tension, density and viscosity on two-phase damping. Two-phase damping ratios were obtained from free transverse vibration measurements on the tube. Two sets of experiments with stagnant and moving continuous phase were conducted. Based on dimensional analysis, we obtained a semi-empirical model for two-phase damping in bubbly and slug flow. The Void fraction and Bond number are shown to be major parameters of two-phase damping, which is described as a kinetic energy transfer from the tube to the continuous phase through added mass of the dispersed phase.
An Analytical Method of Determining Damage Initiation for Potential Use in Establishing Strain-Based Failure Criteria
Authors: Wu Tsu-te
Published: July 2010

This paper proposes a methodology for analytically determining the initiation of ductile fracture due to the nucleation, growth, and coalescence of voids. Since structural damages in the shipping packages of radioactive materials are judged to be mainly caused by ductile fracture rather than shear fracture due to shear band localization, the proposed methodology has potential use in establishing strain-based failure criteria. The proposed methodology is based on the concept that, to ensure its structural integrity, a package should be designed within the maximum load-carrying capability. The load-carrying capabilities for various states of stress can be determined from the load-displacement relationships obtained from the numerical simulations of various specimen tests. As a result, the maximum equivalent plastic strain corresponding to the maximum load-carrying capability can be expressed in terms of stress triaxiality. This paper demonstrates that it is possible to analytically determine the effective plastic strains at the damage initiation in the state of multiple stresses where the load-carrying capacity is at maximum. By considering both material and geometrical nonlinearity in the mathematical representations of structures, the maximum load-carrying capabilities can be calculated as long as the stress-strain data is given.
Fluid Flow Field in the Annulus of Boiling Water (BWR) Nuclear Reactors Under Normal and Accident Conditions
Authors: Ananth Raju , Fujikawa Karen , Gillis Jay
Published: July 2010

This paper presents a theoretical study of the velocity field in the annulus formed between the Reactor Pressure Vessel (RPV) and the shroud of a Boiling Water Reactor (BWR) under normal and accident flow conditions. Simplified geometry and an ideal irrotational flow are assumed to solve the problem using velocity potentials.
Effect of Softening on Tensile Strength Limit in Girth-Welded Pipe Joints
Authors: Kitano Houichi , Okano Shigetaka , Mochizuki Masahito
Published: July 2010

This paper discusses the ultimate tensile strength of girth-welded pipe joints with one or more soft interlayers, as determined by theoretical approaches and FE analysis. In FE analysis, the soft interlayer is assigned to be either the weld metal or heat-affected zone (HAZ). Based on the results of the FE analysis, an evaluation formula is proposed for the ultimate tensile strength of a welded joint including the soft interlayer.
Self-Loosening Mechanism of Nuts Due to Cyclic Thermal Load
Authors: Shoji Yasumasa , Sawa Toshiyuki
Published: July 2010

Self-loosening of nuts is a practical problem in any situations from a single machine to a whole plant. Self-loosening of threaded bolt/nut systems has been researched in number of works for a long time and many of them were based on experiment historically. Some works based on finite element analysis are increasing in these years. Authors have reported the static loosening of nut due to the lateral motion and dynamic loosening due to the lateral impact of fastened objects in PVP conferences using finite element analyses, and showed the loosening mechanism. This paper is a continuing research work and shows another loosening case due to the thermal load to bolt/nut system. It is observed that the bolt and nut are loosened, if they are subject to temperature difference. In this paper, nut loosening was reproduced in the finite element simulations. Self loosening mechanism of this phenomenon is discussed.
On the Buckling of Functionally Graded Cylindrical Shells Under Combined External Pressure and Axial Compression
Authors: Khazaeinejad P. , Najafizadeh M. M. , Jenabi J. , Isvandzibaei M. R.
Published: July 2010

The stability problem of a circular cylindrical shell composed of functionally graded materials with Young’s modulus varying continuously in the thickness direction under combined lateral pressure and axial compression loads is studied in this paper. The formulation is based on the first order shear deformation theory. A load interaction parameter is defined to express the combination of applied axial compression and external pressure. The stability equations are derived by the adjacent equilibrium criterion method. These equations are employed to analyze the buckling behavior and obtain the critical buckling loads. A detailed numerical study is carried out to bring out the effects of the power law index of functionally graded material, load interaction parameter, thickness ratio, and aspect ratio on the critical buckling loads. Validity of the present analysis was checked by comparing the results with those are available in the literature.
Thermal Stress Analysis and the Sealing Performance Evaluation of Bolted Flange Connection at Elevated Temperature
Authors: Omiya Yuya , Sawa Toshiyuki
Published: July 2010

In designing bolted flange connections under heat conduction conditions and internal pressure, the characteristics such as the contact gasket stress are important factors from reliable design standpoint. They must be examined analytically and experimentally. In this paper, in order to examine the above characteristics, thermal stress of bolted flange connections subjected to internal pressure and heat conduction conditions is analyzed using the theory of elasticity and FEM calculations. The effects of gasket properties and nominal diameter of flanges on the above characteristics are examined numerically. In the experiments, the amount of helium gas leakage in the connection was measured. Using the obtained gasket stress at elevated temperature, a method for estimating the amount of gas leakage is proposed. The analytical results of the above characteristics are compared with the experimental results, with reasonable agreements. The results reveal that the sealing performance increases due to the gasket properties as the temperature increases in this study.
The Fabulous Nuclear Odyssey of Belgium
Authors: Geraets Luc H.
Published: July 2010

This paper reviews the Belgian history of nuclear technology and its use for power generation, from the beginning in 1942 until now. It identifies the main players in the field, and the major milestones of this history, both from the power generation side and the nuclear fuel side. It demonstrates the genuine contribution of Belgium to this technology (typical examples are shown), and the significant role of its engineers and scientists.
A Hybrid Procedure for Ratchet Boundary Prediction
Authors: Martin Michael , Rice David
Published: July 2010

Methods exist in today’s published literature which establish proximity to the ratchet boundary of a given load set by decomposing a cyclic load history into constant and cyclic components. Such methods operate by calculating the utilisation of yield capacity throughout the structure in response to the cyclic load. The remaining yield capacity is then available to support the constant load. In this paper, a hybrid procedure is described which uses established finite element techniques to obtain a stable response to the cyclic load component, followed by a limit load analysis based on the remaining yield capacity, to calculate the maximum primary load. This approach is particularly useful in conjunction with Fourier based cyclic procedures which, although capable of predicting the existence of a stable cyclic response, are not based on classical shakedown theory and are therefore unable to predict proximity to ratchet, unless a search procedure is used. The hybrid approach provides the combined benefit of an efficient cyclic response calculation scheme with a measure of proximity to the ratchet boundary. In this paper, the hybrid method is applied to the Bree case before application to a more complex thermo-mechanical transient, typical of nuclear power plant loading. The generation of interaction diagrams for both cases is considered.
Micromechanical Analysis of Ductile Fracture Initiation in Mismatched and Double Mismatched Welded Joints
Authors: Medjo Bojan , Rakin Marko , Gubeljak Nenad
Published: July 2010

The aim of this paper is prediction of ductile fracture initiation in mismatched and double mismatched welded joints. The micromechanical approach is very well-suited for this purpose, because it describes the process of fracture in a way close to the actual phenomena in the material. Micromechanical models based on the Gurson plastic flow criterion are often used for ductile fracture analysis. One of these models, the Complete Gurson Model (CGM) is used here, because the critical value of the damage parameter can be calculated during the analysis. In many other models, the value of this parameter must be predefined. Experimental and numerical analysis of ductile fracture of pre-cracked single-edge notched bend (SENB) specimens is presented. These specimens contain mismatched or double mismatched (undermatched - OM, and overmatched - UM) welded joints. The crack is located in the weld metal (WM), and in case of double mismatched joints it runs through both weld metals. Numerical analysis is conducted using ABAQUS, with user material subroutine for the CGM created by Z.L. Zhang. Three-dimensional models of double mismatched welded joints are analysed, because they cannot be regarded as plane strain or plane stress. To attain the best possible computational efficiency, the submodelling technique is used in the crack front region. With submodelling, it is possible to have sufficiently refined mesh around the crack front (which is very important, as will be discussed in the paper), without excessive computational cost. Microstructural observation is used to quantify the volume fractions of non-metallic inclusions in base metal (BM) and overmatched and undermatched weld metals. Based on these data, initial void volume fractions and mean free paths between the inclusions for all materials are determined. Crack tip opening displacement (CTOD) at the crack growth initiation is measured experimentally and calculated using the CGM, and different values are obtained in overmatched weld metal in comparison with the undermatched weld metal (for double mismatched joints). The size of the elements near the crack tip strongly influences the prediction of the crack growth initiation, and the best results are obtained for the size of the element similar to the mean free path between non-metallic inclusions. The results are also sensitive to the change of the initial void volume fraction, and the best agreement with the experimental data is obtained for the value determined by quantitative microstructural analysis. It is concluded that the CGM enables determination of the crack growth initiation in analysed welded joints and successfully captures the effect of the inhomogeneity.
Influence of Oxidation on Long-Term Creep Strength of ASME Grade 23 Steel
Authors: Kimura Kazuhiro , Sawada Kota , Fujitsuka Masakazu , Kushima Hideaki
Published: July 2010

Creep test of ASME Grade 23 steel has been conducted at 625 and 650°C in helium gas atmosphere. Long-term creep strength of the steel in helium gas was compared with that in air and the influence of oxidation on long-term creep strength was investigated. Creep rupture strength drop was observed in the long-term at 625 and 650°C in air, and the same creep rupture strength drop was observed also in helium gas at 625°C. On the other hand, although creep rupture strength drop was observed in the long-term at 650°C in helium gas, creep rupture life in the long-term in helium gas was slightly longer than that in air at 650°C. Creep rupture life in the long-term at 650°C in air is reduced by not only degradation due to microstructural change, but also marked oxidation, however, that at 625°C is considered to be shortened mainly by a degradation caused by microstructural change. Long-term creep strength of ASME Grade 23 steel at 600°C and above should be reevaluated in consideration of strength drop due to microstructural change.
A Novel Technique for Hydroelectricity Utilizing Vortex Induced Vibration
Authors: Koide Mizuyasu , Sekizaki Takahiro , Yamada Syuichi , Takahashi Tsutomu , Shirakashi Masataka
Published: July 2010

The target of our present research is to develop a river monitoring instrument equipped with electricity power generator to supply for its own demand by utilizing energy of flow of the river. To apply this instrument to natural river, its generator should be simple, small and durable with wide flow velocity range of operation. In this paper, the vibration induced by the trailing vortex (T-VIV) on a cruciform circular-cylinder/strip-plate system is firstly introduced compared with the well-known Ka´rma´n vortex excitation (K-VIV). Secondly, a design for a generator utilizing the T-VIV is presented. Thirdly, an estimation technique for electricity power extracted from the vortex induced vibration (VIV) and a design guide for power generation module obtaining the maximum power are proposed. Finally, using the estimation technique to the T-VIV in air, an estimation of oscillation behavior and power generation performance of an T-VIV generator module applied to water flow are presented.
Development of Component Specific Ageing Management Programmes for Mechanical Components at the NPP Paks
Authors: Ja´nosine´ Bi´ro´ A´gnes , Ra´tkai Sa´ndor , Osztheimer Ma´rton , Baumann-ne´ Tanits Katalin , Baranya Sa´ndor
Published: July 2010

The plant’s current ageing management practice is based on designer’s specifications and the more than 20 years of operation and maintenance experience. This practice meets the established rules and requirements in depth. In accordance with local regulations for long term operation the implementation of a comprehensive ageing management system for a defined scope of nuclear (safety classes 1–3+) components is required. As part of the comprehensive system, type ageing management programmes (TAMP) are developed, from which component specific programmes (SAMP) shall be developed and executed for the passive components of the concerned scope. This presentation summarizes the specific ageing management programmes of the WWER main components (reactor pressure vessel, steam generator, pressurizer, main coolant pump, main circulation pipeline, main gate valve) and of some other mechanical equipment (ECCS heat-exchangers, main steamline valves, steam generator drain expander tanks and emergency feedwater pumps). The development of the SAMPs is based on the TAMPs that describe the degradation processes (low-cycle fatigue, thermal ageing, irradiation damage, stress corrosion, boric acid corrosion, wear, local corrosion, irradiation assisted stress corrosion, loosening of threaded fasteners, swelling, high-cycle fatigue, general corrosion, thermal stratification fatigue, erosion, erosion-corrosion, water hammer, ground water corrosion, microbiological corrosion, deposition). The format and content of the SAMP comply with the domestic regulatory system and essentially follow the attributes of the US NRC’s 10 element ageing management programme (scope, prevention, parameters to be inspected, detection, monitoring-trending, acceptance criteria, corrective actions, feedback, administrative control, utilization of operating experience). During programme development, the review and, based on specific aspects, the examination of compliance of each established programme (technical review plan, ISI programme, ISI acceptance standards, maintenance instructions, water chemistry programmes, operational manuals, other inspection programmes etc.) dealing with the given component and affecting its ageing management were carried out, also taking account of the Aging Management (AM) review reports produced as part of the service life extension project. On the one hand the evaluation of the SAMP confirmed the effectiveness of the programmes currently applied, from ageing management aspects, and on the other hand, the recommended developments and enhancements help establish and strengthen the Comprehensive Ageing Management system.
Extension of Operational Life-Time of WWER-440/213 Type Units at Paks Nuclear Power Plant
Authors: Katona Tama´s Ja´nos , Ra´tkai Sa´ndor , Ja´nosine´ Bi´ro´ A´gnes
Published: July 2010

Operational license of WWER-440/213 units at Paks NPP, Hungary is limited to the design lifetime of 30 years. Prolongation by additional 20 years of the operational lifetime is feasible. Moreover, enhancement of the reactor thermal power by 8% will increase both the net power output and the competitiveness of the plant. Paks NPP is one of the first considering the power up-rate and preparation of long-term operation of WWER-440/213 design. Systematic preparatory work for long-term operation of Paks NPP has been started in 2000. A regulatory framework and a comprehensive engineering practice have been developed. According to the authors view, creation of a gapless engineering system via consequent application of best practices, and feed-back of experiences together with proper consideration of WWER-440/V213 features are the decisive elements of ensuring the safety of long-term operation. That systematic engineering approach is in the focus of recent paper. Key elements of justification and measures and actions for ensuring the safety of long-term operation of Paks NPP WWER-440/213 units are identified and discussed. These are the assessment of plant condition and review of adequacy of ageing management programmes, also the review, validation and reconstitution of time limited ageing analyses as core tasks of license renewal.
Accidents Investigation and Risk Assessment of Chinese Industrial Pressure Pipelines
Authors: Chen Xuedong , Ai Zhibin , Fan Zhichao , Hu Jiushao , Guan Weihe , Cheng Chuanqing
Published: July 2010

In recent years personal casualties and fire explosion accidents are often taken place due to pipe failure accidents of petrochemical enterprises in China. For more than a decade years, the authors have conducted extensive investigation and analysis on these accidents and consider that apart from the causes of man-made quality out-of-control and technical level, another major cause is the absence of experience accumulation of some medium environments induced failure accidents for design standards and codes, design units and designers, therefore, it is unable to prevent and control in-service risk factors at the design stage. Since 2003, we have conducted risk-based inspection and analysis of industrial pipelines of all types of units in about eighty large-scale oil refinery plants, chemical plants and chemical fertilizer plants under the jurisdiction of SINOPEC and PetroChina according to API581, API571 etc. in cooperation with Bureau Veritas, France (BV). Through these analyses, we have found out the major failure modes, mechanisms, likelihood and consequences of petrochemical industrial pipelines, and we also consulted the original design and installation documents of all pipelines, it is found that most of the high failure risks of petrochemical industrial pipelines are induced by inadequate consideration to environment induced failure mechanisms at the design stage. In order to avoid repetitive occurrence of these accidents, suggestions on improvement of design and manufacture methods in China are proposed in this paper, that is, the experience of in-service environment-related failures should be fed back to the organizations of design and manufacture standards, design institutions and designers by some effective means, and set up the design and manufacture platform based on risks and life in China, so as to control the risks of pressure pipelines away from accident over the whole life through such measures as reasonable material selection, structural optimization design, selection of reasonable manufacturing and installation process etc. at early stage of design and manufacture.
Construction of Pressure Vessel Using Thin Inner Shell Wound Cross-Helically by Interlocking Strips
Authors: Ping Chen
Published: July 2010

This paper describes the construction of a new type pressure vessel using thin shell cross-helically wound interlocking steel strip, based on the technologies of interlocking strip-wound developed by Germany and flat steel ribbon wound by China which are code cases listed in ASME BPVC. Analysis and comparison between the new and the traditional structure types, and discussion on issues such as their stress characteristics, operation safety and manufacturing methods etc. are presented. It shows this new method of pressure vessel construction is feasible, cost effective, and well deserved of further studies.
Nonlinear Stability Analysis of the Vaulted Roofs With Corrosion Defects of Oil Storage Tank
Authors: Dong Baosheng , Zhao Xinwei , Chen Hongda , Luo Jinheng , Chen Zhixin , Zhang Hua , Zhang Guangli , Ji Lingkang , Zhang Yi
Published: July 2010

The vaulted roofs of oil storage tank are usually designed as the shallow spherical shells subjecting to a uniform external pressure, which have been widely observed that these shallow spherical shells undergo various levels of corrosion in their employing conditions. It is important to assess the stability of these local weaken shallow spherical roofs due to corrosion for preventing them from occurring unexpected buckling failure. In this paper, the uniform eroded part of a shallow spherical oil tank vaulted roof is simplified as a shallow spherical shell with elastic supports. Based on the simplification, a general pathway to calculate the critical pressure of eroded shallow spherical shell is proposed. The modified iteration method considering large deflection of the shell is applied to solve the problem of nonlinear stability of the shallow spherical shells, and then the second-order approximate analytical solution is obtained. The critical pressure calculated by this method is consistent with the classical numerical results and nonlinear finite element method, and the calculation errors are less than 10%. It shows that it is feasible to apply the method proposed here.
Local Buckling of Tight Fit Liner Pipe
Authors: Focke Eelke S. , Gresnigt Arnold M.
Published: July 2010

A promising possibility to reduce costs in pipelines that require corrosion resistant alloys (CRA) is the use of double wall pipe, consisting of a carbon steel outer pipe and a CRA liner pipe. During installation of such pipe, severe bending and normal force may occur, in particular during installation by reeling. Research has been carried out into the local buckling behaviour of thin walled liner pipe. Important parameters are the wall thickness and material properties of the liner pipe, the contact force between the liner pipe and the outer wall, the coefficient of friction between the two walls and the imperfections. The results of axial compression tests are presented: on liner pipe only (I), on liner pipe while positioned in the outer pipe (II) and on the joined liner and outer pipe (III). Thanks to the support of the outer pipe, local buckling of the liner pipe occurs at much higher stresses and strains than without that support. The measured buckling strains of the tests on liner pipe only (I) are in reasonable agreement with theoretical models. The influence of the determining parameters for the different load cases is discussed. Research on TFP is ongoing.
Crack Growth Under Thermal Fatigue Loading (Effect of Stress Gradient and Relaxation)
Authors: Kamaya Masayuki
Published: July 2010

Thermal fatigue is a critical problem in nuclear power plants. To prevent crack initiation, JSME has issued a guideline for design. In this study, the feasibility of incorporating crack growth analysis into the design and integrity evaluation was investigated. Two characteristics of thermal fatigue loading were considered. The first was the effects of stress gradient in the depth direction. It was shown that the steep stress gradient near the surface significantly reduced the stress intensity factor (SIF) of deep cracks. Assuming that crack growth is arrested by small SIF, it is possible to leave detected cracks unrepaired. Otherwise, the cracks should be removed regardless of their size. The other characteristic is the displacement controlled boundary condition. Through finite element analyses, it was revealed that the displacement controlled boundary condition reduces SIF, and the magnitude of the reduction in SIF depends on the crack depth and boundary length. It is concluded that, under thermal fatigue loading, the cracks that are detected in the in-service inspection have already been arrested if they do not penetrate the wall thickness. The crack arrest scenario is a reasonable method of assessing the integrity of cracked components.
Creep-Fatigue Behavior and Life Prediction of 316L Stainless Steel Under Different Loading Levels
Authors: Jiang Huifeng , Chen Xuedong , Fan Zhichao , Dong Jie , Jiang Heng
Published: July 2010

Stress controlled creep-fatigue interaction tests were carried out for 316L stainless steel under different loading levels at 550°C. Cyclic properties such as material life and mean strain were investigated for 316L stainless steel. When the maximum stress is keeping fixed, with increasing minimum stress, the material creep-fatigue life increases first and then decreases. When the stress amplitude is equal to 167.5MPa (minimum stress is equal to 50MPa), material creep-fatigue life reaches its maximum value. Moreover, under stress control mode, dynamic strain aging was found to manifest itself macroscopically as displacement or mean strain abrupt jumps during cyclic deformation. When the minimum stress is less than 0MPa, abrupt displacement jumps occur at the early stage of cyclic deformation and there are many jumps during the whole process. While the minimum stress is larger than 0MPa, displacement only jumps once at the end of deformation. Additionally, by employing a life prediction method on the basis of the Hull-Rimmer creep cavity growth theory, the creep-fatigue life was assessed for 316L stainless steel at 550°C under different loading levels. The predicted lives were compared with the tested ones and a good agreement was found between them.
Qualification of Cryogenic Structural Materials for the ITER Toroidal Field Coils
Authors: Nakajima Hideo , Takano Katsutoshi , Tsutsumi Fumiaki , Kawano Katsumi , Hamada Kazuya , Okuno Kiyoshi
Published: July 2010

This paper provides qualification test results of large forgings and thick hot rolled plates of austenitic stainless steels, newly developed JJ1 (0.03C-12Cr-12Ni-10Mn-5Mo-0.24N), and 316LN containing high nitrogen of 0.2%, to be used in coil cases of the ITER toroidal field coils. The distributions of tensile properties at liquid helium temperature (4K) in products, average strengths with standard deviations at 4K, temperature dependence of strengths are evaluated to qualify the materials and to establish a reasonable quality control method to be applied to mass production materials for the ITER toroidal field coils. It is also demonstrated that temperature dependence of strengths are expressed by quadratic curves, which are expressed as a function of carbon and nitrogen contents and strengths at room temperature.
Stress Evaluation Charts for Thermal Stratification Considering Heat Transfer Characteristics
Authors: Furuhashi Ichiro , Kawasaki Nobuchika , Kasahara Naoto
Published: July 2010

Both temperature and thermal stress were theoretically analyzed for cylindrical vessels subjected to thermal stratification of contained fluid. Two kinds of temperature analysis results were obtained such as the exact temperature solution with eigenfunction series and the simple approximate one by the temperature profile method. Furthermore, thermal stress shell solutions were obtained for the simple approximate temperatures. Through comparison with FEM analyses, these solutions were confirmed to be adequate. The simple temperature solution is described by one parameter that is the temperature attenuation coefficient. The thermal stress shell solutions are described by two parameters. One is the ratio between the temperature attenuation coefficient and the stress decay coefficient. Another is the non-dimensional width of stratified layer. These solutions were condensed to the simplified thermal stress evaluation charts described by few design parameters. These charts enable quick and accurate thermal stress evaluations of cylindrical vessel subjected to thermal stratification, compared with conventional methods.
Computational Investigation of Pressure Fluctuations in BWR Main Steam Line
Authors: Morita Ryo , Inada Fumio , Takahashi Shiro , Yoshikawa Kazuhiro
Published: July 2010

A pressure fluctuations at a blanch pipe are investigated for an evaluation of pressure fluctuations at a steam dryer, where had been damaged by high cycle fatigue due to acoustic-induced vibration in uprated condition at U.S. NPP. In this study, numerical simulations of the airflow around the branch pipe are conducted to clarify the basic characteristics of the resonance. The excitation of the pressure fluctuations at the branch is observed under various inlet velocity conditions. These fluctuations and inlet conditions are normalized, and the results show that the range and the peak of the amplitude are almost the same as those obtained in experiments.
Development of Evaluation System for Liquid Droplet Impingement Erosion (LDI)
Authors: Morita Ryo , Inada Fumio , Yoneda Kimitoshi
Published: July 2010

An evaluation system for liquid droplet impingement erosion (LDI) has been developed to predict the LDI location and the wall thinning rate. The results from previous studies and knowledge are organized and the LDI evaluation system that involves the “1. Flow Evaluation Step” and “2. LDI Evaluation Step” is suggested. The flow evaluation step includes the mass flow rate evaluation, flow distribution evaluation and droplet behavior evaluation. The LDI evaluation is conducted with LDI sensitivity function. The LDI sensitivity was test-evaluated in the steam piping model. The results show that the 1st and last elbows have higher LDI sensitivity because of the velocity condition. We also found that the droplet collision frequency is important when evaluating the LDI sensitivity.
Accounting for the Effects of Inservice Inspection Flaw Depth Sizing Errors in Developing Flaw Size Distribution Tables
Authors: Gosselin S. R. , Simonen F. A.
Published: July 2010

Probabilistic fracture mechanics studies have addressed reactor pressure vessels that have high levels of material embrittlement. These calculations have used flaw size and density distributions determined from precise and optimized laboratory measurements made and validated with destructive methods as well as from physical models and expert elicitation. The experimental data were obtained from reactor vessel material samples removed from cancelled plants (Shoreham and the Pressure Vessel Research Users Facility (PVRUF)). Consequently, utilities may need to compare the numbers and sizes of reactor pressure vessel flaws identified by the plant’s inservice inspection program to the numbers and sizes of flaws assumed in prior failure probability calculations. This paper describes a method to determine whether the flaws in a particular reactor pressure vessel are consistent with the assumptions regarding the number and sizes of flaws used in other analyses. The approach recognizes that ASME Code Section XI examinations suffer from limitations in terms of sizing errors for very small flaws. Direct comparisons of a vessel specific flaw distribution with other documented flaw distributions would lead to pessimistic conclusions. This paper provides a method for a valid comparison that accounts for flaw sizing errors present in ASME Code Section XI examinations.
Basic Study on Promotion of Evaporating Cryogenic Fluids by Direct Contacting Normal Temperature Fluids
Authors: Watanabe Toshiaki , Iyama Hirofumi , Maehara Hironori , Itoh Shigeru
Published: July 2010

The mixture of the extreme low temperature fluid and the normal temperature fluid becomes the cause which causes pressure vessel and piping system crush due to explosive boiling and rapid freezing. In recent years in Japan, the demand of cryogenic fluids like a LH2, LNG is increasing because of the advance of fuel cell device technology, hydrogen of engine, and stream of consciousness for environmental agreement. On the other hand, as for fisheries as well, the use of a source of energy that environment load is small has been being a pressing need. Therefore, we carried out the experiments related to promotion of evaporating cryogenic fluids, in the contact directly of the water and liquid nitrogen.
Stress Analysis and a Design Method for Bolted Pipe Flanged Joints Subjected to Internal Pressure
Authors: Sawa Toshiyuki , Kobayashi Takashi , Tsuji Hirokazu , Nagata Satoshi
Published: July 2010

This paper deals with the stress analysis of a pipe flange connection with a spiral wound gasket using the elasto-plastic finite element method when an internal pressure is applied to the pipe flange connections with the different nominal diameters from 2″ to 20″. The effects of the nominal diameter of the pipe flange on the contact stress distributions at the interfaces and the hub stress are examined. Leakage tests of the pipe flange connections with 3″ and 20″ nominal diameters were conducted and measurement of the axial bolt force was also performed. The results by the finite element analysis are fairly consistent with the experimental results concerning the variation in the axial bolt force (Load factor). By using the contact stress distributions and the results of the leakage test, the modified gasket constants are proposed and compared with PVRC values. As a result, it is found that the variations in the contact stress distributions are substantial due to the flange rotation in the pipe flange connections with the larger nominal diameter. The hub stress has been overestimated by ASME method. In addition, a method to determine the bolt preload for a given tightness parameter and a rational design method for pipe flange connections are demonstrated.