bluuebunny/crossref_metadata_2025 huggingface dataset:
A Flaw Proximity Rule for Interacting Surface Cracks Based on Elastic-Plastic Fracture Analysis
Authors: Kamaya Masayuki
Published: July 2010

When multiple cracks approach one another, the stress intensity factor and J-integral value of cracks are likely to change due to the interaction of the stress field. Since the changes in these parameters are not always conservative in structural reliability evaluations, the interaction between multiple cracks should be taken into account. Section XI of the ASME Boiler and Pressure Vessel Code provides a flaw characterization rule for interacting multiple cracks. In Section XI, adjacent cracks are replaced with a coalesced single crack when the distance between the cracks is less than half of the crack depth. However, the criterion for the offset distance is given as an absolute value, although the magnitude of the interaction depends on the crack size. In the current study, an alternative criterion for the offset distance was examined. Elastic-plastic analyses were performed for interacting semicircular and semi-elliptical surface cracks by the finite element method under a tensile and bending load. The change in the J-integral values due to the relative spacing of cracks was investigated. Based on the relationship between the magnitude of the interaction and the relative position of the cracks, the allowable condition for the offset distance was discussed.
Stress Corrosion Cracking in Welds of Reactor Vessel Nozzle at Ohi-3 and of Other Vessel’s Nozzle at Japan’s PWR Plants
Authors: Nakamura Takao , Taniguchi Keiji , Hirano Shinro , Marekazu Narita , Sato Tomonobu
Published: July 2010

During the 13th periodic inspection, which started in February 2008, KEPCO’s Ohi unit 3 (1,180MWe PWR) implemented voluntary ECT in addition to the visual inspection of the RV hot and cold leg nozzle welds to confirm the integrity of the concerned section. As a result of inspection, in March 2008, a flaw extending in the depth direction along dendritic grain boundaries of the weld metal was found in the RV A-loop hot leg nozzle. With traces of machining, which could cause residual tensile stresses, it was suspected that SCC initiated and grew at the concerned section. After grinding the section to remove the entire flaw, WJP was applied as the corrective action. Ohi-3 restarted operation on November 2008. It is planned to apply repair welding to the ground out section with alloy 690 during the next periodic inspection [1]. Several Japan’s PWR plants have experienced similar incidents in the nozzle welds. This paper presents the details of repair technologies, which have been developed to address PWSCC found in Ohi-3 RV hot leg nozzle and previous similar incidents in the RV and other vessel’s nozzle welds at Japan’s PWR plants.
A Study on AWJ Trimming of Composite Aircraft Stringers
Authors: Hashish Mohamed
Published: July 2010

A study was undertaken to develop AWJ processes and tools for trimming carbon fiber composite stringers used in several structural air frame components. The cutting strategy was to trim the stringers flanges from the inside out to allow beveling and to minimize cutting risks. Specially designed small size side fire cutting heads were developed to meet this requirement, and they were first used to cut flat composite material samples with thicknesses up to 1 inch. These cutting tests focused on identifying the cutting speeds for producing high quality surfaces without any frayed edges or delamination and meet the Boeing BAC 5578 specifications. For example, tests were performed to determine the effects of pressure, abrasive flow rate, orifice size, and cutting speed on the taper and surface finish of the produced surface walls. It was shown that cutting stringer material with AWJ is highly feasible both qualitatively and quantitatively. An example cutting rate of 18 inch/min was determined to cut 0.65-inch thick composite to produce better than 400 micro inch surface finish with less than 1 degree taper. Trimming tests were then performed for both 90 and 45 degrees to produce straight and beveled surfaces using sample stringers. This new AWJ process is now being used for production at aircraft subcontractor facilities for the Boeing 787.
Diagnosis of Modern Economy Using Repetitive Identification Approach for the Prediction of GDP Per Capita
Authors: Lin Jeng-Wen , Huang Chih-Wei
Published: July 2010

System identification for economic health monitoring in modern economy is moving to the forefront of worldwide research activities. Such monitoring for economic development and management is important for the public welfare related to technological breakthrough such as the Industrial Revolution, leading to new construction technology. In economy practice, however, there are many situations in which a feedback identification system is given model uncertainties and uncertainty of measurement. Aiming for accurate economy model updating, this paper presents the diagnosis of the GDP per capita trend through an automatic repetitive sifting process. It shows how a statistical confidence interval based model updating approach can be applied to the health evaluation of economic development via prediction of GDP per capita over time. The model updating approach uses the confidence interval of the estimated economic parameters to determine their statistical significance in order to mitigate the model uncertainties and measurement errors. If the parameters’ confidence interval covers the “null” value, it is statistically sustainable to truncate such parameters. The remaining parameters will repetitively undergo such parameter sifting process until all the parameters’ statistical significance cannot be further improved. Consequently, the proposed repetitive identification approach promotes the accuracy of the prediction of GDP per capita, assisting the assessment of modern economic trend.
Numerical Validation of a Strain-Based Failure Assessment Diagram Approach to Fracture
Authors: Budden Peter J. , Smith Michael C.
Published: July 2010

The basic approaches in defect assessment procedures such as R6 consider the stresses on the section containing the flaw. Such approaches can be overly conservative and lead to unacceptably small estimates of limiting defect sizes for cases where the applied loads are due to displacements or strains well in excess of yield, when significant plastic relaxation of stress occurs. The potential for over-conservative assessments has led to a renewed interest in recent years in strain-based assessment methods, in both the power and pipeline industries. Significant levels of plastic strain can be imposed across the flawed section in some cases. Recently, the present author has published a general approach to strain-based fracture that uses a strain-based failure assessment diagram (SB-FAD). This includes a range of Options similar to that of the basic R6 approach. The present paper describes some validation of the SB-FAD approach based on elastic-plastic cracked-body finite element data for plates and cylinders.
Evaluation of Fatigue Damage by X-Ray Diffraction Technique of Steam Turbine Rotor Steels at Elevated Temperatures
Authors: Fiala Jaroslav , Mentl Vaclav , Kolarik Vladislav , Chocholousek Michal
Published: July 2010

In many industrial applications materials are subjected to degradation of mechanical properties as a result of real service conditions. The assessment of the remaining lifetime of components and structures is commonly based on correlated procedures including numerous destructive, non-destructive and mathematical techniques that should guarantee reasonable precise assessment of the current damage extent of materials in question and the remnant lifetime assessment. The assessment of the remaining lifetime by X-ray diffraction technique is based on the fact that mechanical properties of the most materials depend strongly on crystallite size and orientation of ingredients, which are the crucial parameters for the determination of the ageing state and the prediction of residual lifetime of the components. X-ray diffraction technique proved to be useful as a tool for the assessment of material degradation extent after a long-time service. Framework 5 project “XPECTION” [1] was dealing with this task with respect to high temperature creep degradation of boiler tube steels. In this presentation, the X-ray diffraction technique was applied to reveal subtle details of the microstructural changes induced by fatigue. Several steam turbine rotor steels were fatigue tested at elevated temperatures up to 600°C at strain control regime. After the tests, the X-ray diffraction method was used to correlate the extent of fatigue damage with the X-Ray diffraction patterns to be able to assume the life-time exhaustion caused by fatigue loading in service.
Detection of Foreign Bodies in Closed Food Containers Supported With Fluid-Solid-Interaction Analysis
Authors: Schmidt Tobias R. H. , Nesme Anuhar O. , Forstner Judith K. , Beronov Kamen N. , Benning Rainer M. , Delgado Antonio R.
Published: July 2010

The unwanted inclusions in food and beverages pose a threat to both consumer health and the business, including producer image and liability. Detection of such inclusions, in particular metal and glass particles of millimetre size, is an important element of quality control in such industries. Specific solutions usually are limited in their detection range or are investment and space intensive. The presented project investigates a principally new detection method for foreign particles in fluid media of different densities and transparencies. Proof of concept is provided for the important case of glass containers, but the method is applicable to other materials.
A Numerical Study of the Alignment of Surface Flaws in a Pipe
Authors: Bezensek Bostjan , Miyazaki Katsumasa , Hasegawa Kunio , Saito Koichi
Published: July 2010

Flaw evaluations require guidance on the alignment and combination of multiple crack-like indications to provide a conservative assessment. This paper presents ongoing work on the alignment of twin non-aligned flaws (i.e. flaws on parallel offset planes normal to the principal loading direction). The experimental data on bending of austenitic stainless steel pipes with non-aligned flaws is briefly presented, followed by a parametric study using detailed finite element analyses with damage modelling. These are used to determine the load capacity of a pipe containing non-aligned flaws as a function of the flaw size and flaw separation. The experimental and FEA results suggest no significant effect of the alignment distance on the load capacity of the pipe with twin non-aligned surface flaws.
PTS Benchmark Performed Within IAEA Coordinated Research Project 9
Authors: Pistora Vladislav , Brumovsky Milan
Published: July 2010

During the period 2005 – 2008, the Coordinated Research Project 9 (CRP 9) “Review and Benchmark of Calculation Methods for Structural Integrity Assessment of RPVs During PTS” was organised by the IAEA. The overall objective of this Coordinated Research Project was to perform benchmark deterministic calculations of a typical pressurised thermal shock (PTS) regime and finally to recommend the best practice for PTS assessment. The benchmark concerns the assessment of the reactor pressure vessel (RPV) resistance against fast fracture for events in the NPP leading to PTS. This assessment is based on the stress intensity factors KI for a postulated crack. The aim of the benchmark was to compare the results obtained by individual participants for well-defined task, to compare the results obtained when applying national codes requirements, and to assess the influence of individual parameters entering the analysis when performing a large set of sensitivity studies. Further aim of this benchmark was to create data which can be used for training of young specialists and for validation of their approach. The benchmark phase of CRP 9 comprised: • Definition of two separate benchmarks for generic WWER-440/213 and PWR-900 (3 Loop) designs, considering the Participants’ own experience and the results of previous international studies. • Basic case analysis of the benchmark problems and application of national code approaches. • Sensitivity studies to assess the impact of individual parameters on the assessment results. The basic (mandatory) case was defined uniquely (all input parameters precisely defined) to enable comparison of the results. Only effect of different models, methods of solving the problems or user effect can be source of the differences in the results, but not the difference in the input data (e.g. material properties, crack geometry, safety margins etc.). The extent and format of output data to be used for comparison were also well-specified. This paper describes the definition of the PTS benchmarks and some examples of the comparative results, like: • variation of temperature through the RPV wall thickness, • variation of stress through the RPV wall thickness, • KI and KIC in dependence on temperature, • variation of KI along crack front, • resulting maximum allowable transition temperature. Finally, it was concluded that the differences among the results were reasonably low and that the methods and models used by the participants can be used for integrity assessment of real RPVs.
Analysis of the Compression Behavior of Spiral Wound Gaskets
Authors: Waterland A. Fitzgerald Jerry , Bouzid Abdel-Hakim
Published: July 2010

Recent updates to the ASME B16.20 standard for spiral wound gaskets now require inner rings on all flexible graphite and PTFE filler spiral wound gaskets [1]. This new requirement is intended to prevent the occurrence of inward buckling; however the addition of an inner ring can have significant impact on the spiral wound gasket compression behavior and possibly its sealing performance. This paper explores the compression behavior and sealing performance of spiral wound gaskets, with and without inner rings, and thus provides a better understanding of their performance capabilities in ASME B16.5 flanges, as well as their design and performance within ASME Boiler & Pressure Vessel Code Appendix 2 flanges [2].
Numerical Simulation of Transient Temperature in SMAW
Authors: Panwala M. Sohel M. , Channiwala S. A. , Srinivasan K. N.
Published: July 2010

Welding is the most commonly used and one of the most important material-joining processes widely used in industries. Low carbon steel plates with thickness 8 mm and above with 45° V and 60° V single pass and multipass weld geometry are widely used in fabrication of pressure vessels and other components. The residual stress developed due to welding is largely depends on the distribution of heat in weldment. In present work, experimental work has been carried out to find out the temperature distribution during welding of the above weld geometry with single pass and double pass welding on 8 mm thick plates. Non-linear transient thermal analysis has been also performed using commercially available finite element code ANSYS. ‘Tsai’ model is used for modeling heat input in ANSYS. Temperature curves obtained from analysis have been validated with experimental temperature data. The temperature distribution curves obtained from experiments and from numerical simulations are presented in the study. This temperature data can be used as an input for residual stress calculation in any Finite Element Analysis software like ANSYS, ABAQUS and SYSWELD etc. Also from this data, the better weld geometry can be selected for same amount of heat input and thickness.
Creep-Fatigue Interaction in Coke Drums: An Approach Based on API 579-1/ASME FFS-1 2007
Authors: Panwala M. Sohel M. , Srinivasan K. N. , Mehta S. L.
Published: July 2010

Coke Drums are critical equipment in refineries due to variable temperature and pressure. The temperature is also very high and coke drums work in the creep range for some duration of one full cycle. The phenomenon of creep along with fatigue plays a very crucial role in failure of coke drums. In the present study, a coke drum is subjected to pressure–temperature reversal with each cycle of 48 hours duration. Temperature and pressure varies from 65 to 495 °C and 1.72 to 4.62 bar, respectively. The material of construction is 1.25Cr-0.5Mo. This material is in the creep range beyond 454 °C as defined by ASME Section II, Part D. This coke drum is in creep range for 23 hours of one full cycle. The skirt to shell and cone junction is a critical portion of coke drum because it is highly susceptible to creep and fatigue simultaneously. In addition to this, the skirt is provided with slots at specific pitch all around circumference to induce flexibility. This has great influence on creep and fatigue due to localized stress. API 579-1/ASME FFS-1 2007 is used for the creep fatigue interaction in the present case. Non-linear transient thermal analysis is coupled with the elastic-plastic structural analysis for calculation of stresses and strains. These stresses are further used in deducing a creep damage factor and strains are used for deducing permissible cycles for fatigue as per the approach based on API 579-1. A macro is developed in the commercially available Finite Element Code ANSYS 11 for calculation of the creep damage factor and permissible cycles for fatigue. The creep damage factor works out to be 0.01 and this has been used for deducing a fatigue damage factor from creep-fatigue interaction curve. The fatigue damage factor is found to be 0.9. The macro results are validated with theoretical calculations.
Evaluation of Hydraulic Factors Affecting Flow Accelerated Corrosion and Its Verification With Power Plant Data
Authors: Yoneda Kimitoshi , Ohira Taku , Tanji Kazuhiro , Akiba Shinji , Niiyama Koichi , Morita Ryo , Inada Fumio
Published: July 2010

Flow Accelerated Corrosion (FAC) is well known as a complex phenomana of hyraulics and electro-chemicals. Among the two, this study focused on the hydraulic factors affecting FAC. FAC experiments with small rectangular flow duct were conducted in PWR condensate condition. Flow field for the experiment was calculated with numerical simulation using LES (Large Eddy Simulation) turbulence model. From both experimental and numerical results, new model of mass transfer coefficient, as the essential parameters of hydraulics, was proposed considering local turbulent velocity, so as to evaluate the effect of eccentric flow on FAC. To verify the applicability of the model, FAC plant data of actual PWR (Pressurized Water Reactor) condensate line (146 degC) and BWR (Boiling Water Reactor) condensate line (35 degC) were referred. Mass transfer coefficients for each pipe lines were calculated from flow numerical analysis. The new proposed model showed good correlation with the data of FAC thinnng rate, and its applicability was confirmed. In addtion, comparing the two plant cases, electro-chemical effect could be estimated as a similar level, which suggests the possibility of low-temperature FAC in BWR condensate lines.
Evaluation of Sealing Performance of Pipe Flange Connection Subjected to External Bending Moments
Authors: Takagi Yoshio , Torii Hiroyasu , Sawa Toshiyuki , Funada Kensuke
Published: July 2010

The sealing performance of pipe flange connection subjected to an external bending moment was evaluated with the FEM and the experiments. The experimental leakage test using water revealed that the bending moment had an important effect on the sealing performance. The FE analyses suggested that the contact gasket stress, which was a function of the bolt preload, determines the leakage. The changes in contact gasket stress at tension side and compression side when the external bending moment applied were not symmetrical. The reduction in the contact gasket stress of tension side was larger than that of compression side due to the non-linear stress-strain behavior of the gasket. In addition, the hub stress of the flange when external bending moment applied, was evaluated from FE result and the discussion for optimizing the flange design subjected to external bending moment was done in this paper.
Non-Destructive Analysis of Wind Turbine Blade Structural Integrity
Authors: Puri Amit , McGugan Malcolm , Jensen Find M.
Published: July 2010

The hollow profile of a wind turbine blade is subject to high levels of deformation when under the crushing pressure that is induced by flapwise loading. The load bearing box girder will ovalize under the pressure like forces and the shear sandwich webs and monolithic composite flanges are critical components whose failure may cause overall blade failure. This paper addresses the underlying causes of failure for these two parts by performing individual representative mechanical testing on them, and using digital image correlation (DIC) and acoustic emissions (AE) monitoring. Results show that the strength of the flange is primarily determined by the tensile strength of a relatively thin biaxial layer in this complex design. The buckling tests performed on sandwich material show that DIC is useful in determining the causes of failure, whilst AE monitoring has potential for in-situ monitoring of these structures, and is able to provide important data about the damage inside a blade.
Failure Analysis and Structure Optimization of Hydrogenation Air-Cooler System Based on Imbalanced Degree
Authors: Jin Haozhe , Ou Guofu , Wang Yanping , Cao Jing
Published: July 2010

Due to the prevalent leakage and rupture of a hydrocracking reactor effluent air cooler (REAC) pipes, the corrosion mechanism is studied based on the REAC operation mode and conditions. The mathematic model of imbalance degree is constructed according to the REAC structural property. The multiphase flow characteristics are obtained by a universal petrochemical software HYSYS; and the systemic imbalance of dynamic parameters, such as flux and volume fraction, is simulated using Computational Fluid Dynamics (CFD). Comparing with actual anatomical instances, failure analysis based on the imbalance criterion is achieved. Moreover, the optimum measures to enhance the running reliability are proposed.
Stress Intensity Factors for Closely and Densely Packed Cracks in Partially Autofrettaged Pressurized Thick-Walled Cylinders
Authors: Ma Q. , Levy C. , Perl M.
Published: July 2010

Due to acute temperature gradients and repetitive high-pressure impulses, extremely dense internal surface cracks can be practically developed in highly pressurized thick-walled vessels, typically in gun barrels. In our previous studies, networks of typical radial and longitudinal-coplanar, semi-elliptical, internal surface cracks have been investigated with an ideal or realistic autofrettage level of 100 percent. We have shown that the combined SIFs are considerably influenced by the three-dimensionality of the problem and the Bauschinger effect (BE) along with dependence on other parameters, such as radial crack density, longitudinal crack spacing, crack depth, crack ellipticity, and the autofrettage level. When pressure is considered solely, radial crack density and longitudinal crack spacing were found to have opposing effects on the prevailing stress intensity factor, KIP. Furthermore, the addition of the negative stress intensity factor (SIF), KIA, resulting from the residual stress field due to autofrettage, whether ideal or realistic, tended to decrease the combined SIF KIN = KIP − |KIA|. Therefore, to assess the fracture endurance and the fatigue life of a cylindrical, autofrettaged, pressure vessel containing such a network of cracks, it is necessary to determine the KIA’s and the KIN’s. However, to assess the SIFs accurately, significant computational efforts and strategies are necessary, especially for networks with closely and packed cracks. In this study, our effort will focus on the KIA and the KIN distribution for numerous configurations of closely and densely packed semi-circular and semi-elliptical networked cracks affected by pressure and partial-to-full autofrettage levels of 30–100%, which is practically seen in autofrettaged thick-walled pressure vessels. The 3-D analysis will be performed via the finite element (FE) method and the submodeling technique employing singular elements along the crack front and the various symmetries of the problem. The network cracks will include up to 128 equally spaced cracks in the radial direction; with relative, longitudinal crack spacing, 2c/d, from 0.1 to 0.99; autofrettage level of 30–100 percent; crack depth to wall thickness ratios, a/t, from 0.01 to 0.4; and, cracks with various ellipticities of crack depth to semi-crack length, a/c, from 0.2 to 2.
High Deposition Pulse Current GMAW Can Change Current Scenario of Thick Wall Pipe Welding
Authors: Ghosh P. K. , Kulkarni Shrirang G. , Agarwal Banshi Prasad
Published: July 2010

The high deposition pulse current gas metal arc welding (P-GMAW) with multiple drop transfer per pulse has been used to weld thick wall austenitic stainless steel pipe. Welding of the pipe was also carried by the commonly used shielded metal arc welding (SMAW) and conventional gas metal arc welding (GMAW) processes and compared. Utility of the P-GMAW to facilitate narrow gap welding of the thick wall pipe by appropriate control of pulse parameters has been discussed in reference to produce superior quality weld. The superiority of weld quality has been justified through the microstructure, mechanical properties, residual stresses and fracture mechanics properties of weld joints. Basic characteristics of the P-GMAW process changing the scenario of thick wall pipe welding have been closely studied with respect to its arc characteristics and behaviour of metal transfer. A precise control of the process in order to achieve desired thermal, mechanical and microstructural effects in the narrow gap welding has been achieved by regulation of summarised influence of pulse parameters, mean current (Im) and arc voltage. The summarised influence of pulse parameters is defined by a hypothetically defined dimensionless factor φ = [(Ib/Ip) f.tb] where, the Ib, Ip, f and tb are the base current, peak current, pulse frequency and pulse off (base) time respectively.
Performance Evaluation on Jointed Pipes Used Underground for Fire Protection at a Nuclear Power Plant as a Response to the Effects of the 2007 Niigata-Ken Chuetsu-Oki Earthquake
Authors: Sato Yusuke , Toyoda Yukihiro , Matsuura Shinichi , Sakai Michiya
Published: July 2010

This study discusses the strength of jointed pipes used underground for fire protection at a nuclear power plant and their capacity to accommodate ground displacement. For this purpose, bending tests, a finite element analysis and an elastic beam theory analysis were conducted. The bending tests were conducted for four types of joints previously subjected to actual use, including welded, flange, screw and coupling types. The welded and flange joints demonstrated significantly higher load capacity; five times that of the coupled joint. The bending test results for the flange, screw and coupling joints were applied to identify the bending moment and rotation angle at the moment the internal pressure reached the level of the atmospheric pressure due to leakage. The limit state of the welded joint was not obtained in the experiment but was estimated by nonlinear finite element analysis. The bending moment and rotation angle of the welded joint were identified at the moment the welded joint reached the limit state. Finally, the test results and finite element analysis were applied to estimate the capacity of each joint to accommodate ground displacement. The elastic beam theory was used by modeling the pipe as an elastic beam and idealizing the joint as an elastic rotational spring. Consequently, the ground displacement capacity of the welded joint exceeded that of the coupling and screw joints by more than 500 per cent.
Fundamental Study on Shape Dependency of Input Energy for Failure
Authors: Minagawa Keisuke , Fujita Satoshi , Kitamura Seiji , Okamura Shigeki
Published: July 2010

This paper describes a comparison of input energy for failure between experimental models. Recently, understanding ultimate fatigue endurance in strong earthquakes is strongly required in order to improve seismic safety reliability. We have dealt with this issue from the viewpoint of the energy balance equation, and already confirmed relations between input energy and fatigue failure by a previous paper. However the confirmed relations were qualitative, so that a quantitative investigation is required. Therefore this paper deals with another experimental model that has 4 times as big width as the previous model. Input energy for failure is investigated by vibration experiment using random wave. As a result, same relations as the previous paper are confirmed. Then relations are expressed by power function, and are compared with the previous model. Consequently the rectangle model requires input energy which is about 4 times bigger than the square model.
Real-Time Prediction of Liquid Sloshing of Oil Storage Tank Based on Earthquake Early Warning
Authors: Zama Shinsaku , Nishi Haruki , Yamada Minoru , Hirokawa Yoshihiro
Published: July 2010

For an efficient patrol to prevent and/or minimize secondary disaster such as fire breakout, diffusion of oil just after an earthquake, we investigated the possibility of real-time prediction of liquid sloshing of oil storage tank based on Earthquake Early Warning (EEW), and also investigated the estimation of volume of overflowed oil from a tank due to large liquid sloshing. As to velocity response spectrum prediction used in predicting liquid sloshing, we constructed the attenuation equation of spectral amplitude for far-field surface waves considering both the seismotectonics and the scaling law of the source characteristics. For estimation of the amount of overflowed oil, we executed experimental studies using a model tank of 7 m in diameter and proposed an empirical equation based on the velocity response spectrum and verified the validity of the formula for the past earthquakes. We applied these equations to the EEW in the 2008 Iwate/Miyagi inland earthquake (M7.2) for Sendai Oil Industrial Complex District, and obtained a good agreement between the predicted and the observed spectrum. Thus, it is expected that the information about the predicted sloshing behavior in a very early stage after a large earthquake using EEW, will be disseminated to person responsible for disaster countermeasures prior to communication congestion.
Isolation Performance of Intelligent Seismic Isolation System Using Air Bearing
Authors: Fujita Satoshi , Minagawa Keisuke , Miyazaki Mitsuru , Tanaka Go , Omi Toshio , Shimosaka Haruo
Published: July 2010

This paper describes three-dimensional isolation performance of seismic isolation system using air bearings. Long period seismic waves having predominant period of from a few seconds to a few ten seconds have recently been observed in various earthquakes. Also resonances of high-rise buildings and sloshing of petroleum tanks in consequence of long period seismic waves have been reported. Therefore the isolation systems having very long natural period or no natural period are required. In a previous paper [1], we proposed an isolation system having no natural period by using air bearings. Additionally we have already reported an introduction of the system, and have investigated horizontal motion during earthquake in the previous paper. It was confirmed by horizontal vibration experiment and simulation in the previous paper that the proposed system had good performance of isolation. However vertical motion should be investigated, because vertical motion varies horizontal frictional force. Therefore this paper describes investigation regarding vertical motion of the proposed system by experiment. At first, a vertical excitation test of the system is carried out so as to investigate vertical dynamic property. Then a three-dimensional vibration test using seismic waves is carried out so as to investigate performance of isolation against three-dimensional seismic waves.
Shaking Table Tests With Large Test Specimens of Seismically Isolated FBR Plants: Part 2—Damage Test of Reinforced Concrete Wall Structure
Authors: Inaba Satoru , Anabuki Takuya , Shirai Kazutaka , Yabana Shuichi , Kitamura Seiji
Published: July 2010

This paper describes the dynamic damage test of a reinforced concrete (RC) wall structure with seismic isolation sysytem. It has been expected that seismically isolated structures are damaged in sudden when the accelerations of the structures exceed a certain level by hardening of the rubber bearings. However, the response behavior and the damage mode have not been observed by experimental test yet. So, shaking table tests were carried out at “E-Defense”, equipping the world’s largest shaking table, located at Miki City, Hyogo prefecture, Japan. The specimen was composed of an upper structure of 600 ton by weight and six lead-rubber bearings (LRBs) of 505 mm in diameter which provide both stiffness and hysteretic damping. The upper structure consisted of a RC mass and four RC walls with counter weight. The RC wall structure was designed so that the damage of the RC wall occurred between the shear force at the hardening of the rubber bearings and that at their breaking. The dimensions of the RC wall were 1600 × 800 × 100 mm (B × H × t). The reinforcement ratios were 2.46% in vertical by D13 (deformed reinforcing bar, 13 mm in diameter) and 1.0% in horizontal by D10. The shaking table test was conducted consecutively by increasing the levels up to 225% of tentative design earthquake motion. Consequently, because of the increase of the structural response by the hardening of the rubber bearings, the damage of the wall structure with seismic isolation system suddenly happened. In addition, the preliminary finite element analysis simulated the test results fairly well, which were the restoring force characteristics, the crack patterns of the RC wall structure and such.
Internal Reversible Hydrogen Embrittlement and Hydrogen Gas Embrittlement of Austenitic Stainless Steels Based on Type 316
Authors: Imade Masaaki , Zhang Lin , Wen Mao , Iijima Takashi , Fukuyama Seiji , Yokogawa Kiyoshi
Published: July 2010

The internal reversible hydrogen embrittlement (IRHE) of austenitic Fe(10–20)Ni17Cr2Mo alloys based on type 316 stainless steel was investigated by tests using the slow strain rate technique from 80 to 300 K in comparison with its effect on the hydrogen gas embrittlement (HGE) of the alloys in hydrogen at a pressure of 1 MPa. The IRHE and HGE of the alloys in 70 MPa hydrogen at room temperature was also investigated. At low temperatures, IRHE occurred below a Ni content of 15% (Ni equivalent (Nieq):29%), increased with decreasing temperature, reached a maximum at 200 K, and decreased with further decreasing temperature, similarly to the temperature dependence of HGE. At room temperature, IRHE and HGE were observed below a Ni content of 14% (Nieq:28%) and decreased with increasing Ni content (Nieq). The dependence of HGE on hydrogen pressure increased with decreasing Ni content (Nieq). Hydrogen-induced fracture closely related to the strain-induced α′ martensite structure and twin boundaries mainly occurred for both IRHE and HGE. Dimple ruptures caused by hydrogen segregation occurred in only IRHE at 150 K. The content of strain-induced α′ martensite increased with decreasing temperature and Ni content (Nieq). Thus, the susceptibility to IRHE and HGE depended on Ni content (Nieq). It was concluded that both IRHE and HGE were controlled by the amount of strain-induced α′ martensite above 200 K, whereas they were controlled by the hydrogen transport below 200 K.
JSME Construction Standard for Superconducting Magnet of Fusion Facility “Fabrication, Installation, NDE and Testing”
Authors: Nakahira Masataka , Niimi Kenichiro , Irie Hirosada
Published: July 2010

For construction of TF coil, a “Fabrication and Installation” standard FM-4000, accompanying a mandatory Appendix 41 “Welded Joint” and a “Nondestructive Examination” standard FM-5000 accompanying a mandatory Appendix 51 for “Ultrasonic Examination Method” and a “Pressure and Leak Testing” standard FM-6000 have been developed, based on other JSME standards for nuclear power plant (JSME S NB1) and also ASME Sec. III ND, NF or Sec. VIII-div.2 Since TF coil structure does not include radioactive materials but is operated under high stress produced by high magnetic field, it is not safety-relevant-barrier. The requirements to construction should be relaxed in comparison with a fission reactor. The TF coil structure is mainly classified into two divisions; (1) Jacket and helium cooling pipe that is required for leak tightness, and (2) The general structure which is stressed only by the electromagnetic force. For the welded joint in the structure part (1), more severe requirements for nondestructive examination are prescribed in addition to the requirement for pressure and leak testing, based on JSME S NB1 and ASME Sec. III ND, NF or Sec. VIII-div.2. All of weld joints are classified into 6 categories depending on strength and direction of the stress induced by the magnetic field. Approved weld joint configuration and welding processes, nondestructive examinations, pressure and leak testing required and also acceptance criteria of discontinuity are defined in each category. Qualification of welding personnel and inspector are also defined, but its final responsibility is to the owner of TF coil.
Analysis of Large-Scale Fracture Experiments Addressing the Behaviour of Sub-Clad Flaws in Reactor Pressure Vessel Steel
Authors: Minnebo Philip , Paffumi Elena , Taylor Nigel , Nilsson Karl-Fredrik , Palyza J. , Pistora V.
Published: July 2010

To investigate transferability of the Master Curve methodology to shallow, sub-clad flaws in reactor pressure vessel applications, a series of six fracture tests was performed on large-scale specimens, which were fabricated from grade A533 steel and contained simulated sub-surface defects. First of all, the paper briefly describes this four-point bend test programme. Further an in-depth analysis of the experiments is presented. Detailed finite element calculations are used to compare the fracture behaviour of the large-scale bend beams with the test material’s standard Master Curve. The latter is obtained from dedicated laboratory experiments, also checking through-wall variation of brittle-to-ductile transition behaviour. This study confirms a significant constraint-loss effect related to the sub-clad defects, which is in line with findings from previous research projects.
Methodology for the Determination of a Set of Safety Factors That are Consistent for Design Code and Fitness-for-Service Code: Case Study for Fast Breeder Reactors
Authors: Asayama Tai
Published: July 2010

This paper proposes a method for determining a set of safety factors taking account of multiple failure modes and their interactions. The purpose of the work is to materialize the System Based Code concept for the applications to fast breeder reactors. Current structural codes prevent failure by limiting primary stress, excessive strain, buckling and fatigue damage. However, the relationships between safety factors in these criterion and failure modes are not necessarily clear. For example, safety factors in the limitation of primary stress are considered to cover not only ductile fracture but also fracture due to crack like defects. When the System Based Code concepts, one of the most important of which is designing to target reliability, it is essential to determine safety factors so that they explicitly correspond to particular failure modes. This paper deals with the most important two failure modes to be prevented in fast breeder reactors (FBRs), that is, primary stress due to seismic load and secondary stress due to creep-fatigue. Safety factors that are consistent for design code and fitness-for-service code are derived by the following steps: 1) Formulations of continuous evaluation of reliability are derived for both fracture by primary stress and creep-fatigue crack initiation and propagation due to secondary stress, with their interaction taken into account, 2) Reliability is calculated for various combinations of loading conditions, 3) Safety factors corresponding to various levels of target reliabilities are investigated and compared with currently used ones. The safety factors thus determined not only have firm physical basis but also contribute to enlarge design windows for fast breeder reactor components. Items to be further investigated for the methodology to be implemented in current code are also discussed.
Three Dimensional Elastic-Plastic Finite Element Simulation on Bolt Tightening Beyond Yield
Authors: Nagata Satoshi , Kaneda Shinobu , Tsuji Hirokazu , Sawa Toshiyuki
Published: July 2010

This paper presents 3-dimensional elastic-plastic finite element stress analysis simulating the behaviors of bolt and nut during the tightening process beyond the bolt yield so called plastic region tightening. The finite element model has the shape of helical threads as it is shown in the actual M16 stud bolt and heavy hex nut. The stress analysis is solved as contact problem among the engaged threads and the nut bearing surface to the clamped body. Tightening torque, thread torque, bearing surface torque and bolt axial force are calculated. They are compared with the experimental test results and show a fairly good agreement. Stress distribution as well as the development of plastic zone in the bolt and nut during the tightening are also demonstrated by this simulation. In addition, the load distribution in the engaged threads are computed and clarified the difference from those based on elastic analysis.
Solving U-RANS k-ω SST Equations and Post-Processing Motion Independent Fluid Forces in a Tube Bundle
Authors: Jusserand Franc¸ois , Adobes Andre´ , Randrianarivelo Tseheno N.
Published: July 2010

The computation of the dynamic response of a structure subjected to a fluid flow requires the knowledge of the fluid forces acting on the structure. At least three classes of these forces can be distinguished: - fluid-elastic forces due to the coupling between fluid flow and structure displacement; - random forces due to the turbulent nature of the flow. In cases of two-phase fluid configurations, such as those occurring in steam generators of nuclear power plants, forces due to the two-phase nature of the fluid are also assumed to be part of this type of excitations; - fluid forces due to coherent structures in the flow, such as Von Karman vortex-streets downstream of a single tube in cross-flow. In this paper we focus on the numerical study of this last class of excitations. We propose here a method to compute the dimensionless spectrum of those forces as a function of a scaled parameter called “reduced frequency” [1]. We perform CFD (Computational Fluid Dynamics) calculations with the EDF (Electricite´ De France) CFD software Code_Saturne® [2], using a U-RANS (Unsteady-Reynolds Averaged Navier Stokes) approach, and a k-ω SST (Shear Stress Transport) model. Tube wall fluid stresses are derived and post-processed into spectra. This numerical methodology allows one to distinguish the drag from the lift component in overall fluid force. The paper includes three parts: - In the first part, the numerical method of our study is presented: the k-ω SST model developed to solve U-RANS equations [2] is described. We then detail the post-processing used to compute the dimensionless spectrum starting from fluid stresses at tube walls. - In the second part, k-ω SST model’s implementation is validated on the case of a single rigid tube in an upwards cross-flow of water. CFD results are compared to experimental measurements [3]. - Eventually the study of a 2D rigid tube bundle subjected to a two-phase cross-flow modeled by an equivalent single phase flow is presented. A sensitivity analysis is carried out to study the influence of bundle’s bulk and the Reynolds number. Wall pressures are post-processed to derive the dimensionless spectrum associated with fluid forces due to coherent structures.
Testing of the High-Velocity Water Jetting on Concrete Samples Inside the Overpressure Vessel
Authors: Hlava´cˇ Libor M. , Bodna´rova´ Lenka , Ma´dr Vile´m , Hela Rudolf , Kalicˇinsky´ Jirˇi´ , Janurova´ Eva , Pustelni´k Jan , Hlava´cˇova´ Irena M.
Published: July 2010

The concrete samples with various erosion states were disintegrated inside the overpressure vessel using high-velocity water jet. Their erosion states were prepared by application of several laboratory techniques simulating the concrete aging under the natural conditions due to the real applications in practice. The influence of the erosion state on the disintegration rate was tested and the surface topography was studied both prior the application of water jet and post it. The water jet was applied in the overpressure vessel used for simulation of pressures equivalent to the submersion to several depths under the water level. Usual experimental scale responsive to the national practical application range was from the depth of submersion close to the water level up to the depth about 100 meters with the 20 meters step. Nevertheless, the data were obtained for overpressures equivalent to the submersion levels up to 140 meters enlarging so the range of results useful for regression analysis of the physical trend. Several samples were tested even in overpressures simulating depth of submersion equal to 160 meters and more. Few samples of special decorative concretes were also studied and special techniques of their working up were prepared and tested. All results are discussed regarding their application in practice and further development of special routings.
Evaluation of Fracture Characteristics of Ni-Base Weld Metal for BWR Components
Authors: Itatani Masao , Saito Toshiyuki , Hayashi Takahiro , Narazaki Chihiro , Ogawa Kazuo , Kikuchi Masaaki
Published: July 2010

Fracture behavior of Ni-base weld metals used for boiling water reactor (BWR) was investigated. The elastic-plastic fracture toughness (JIc) tests were conducted for Alloys 182 and 82 in room temperature (R.T.) and 300°C air using 2TCT specimen. It was found that the ductile crack growth resistance of Alloy 82 is higher than that of Alloy 182, and also the ductile crack growth resistances at 300°C are higher than those at R.T. for both Alloys 182 and 82. The fracture loads of CT specimen were predicted using existing limit load equations. The estimated limit load Pc using flow stress which is defined as the average of 0.2% proof stress and tensile strength coincided well with the experimental maximum load Pmax. It was confirmed that the conservative limit load estimation is possible when using 2.7Sm as the effective yield stress in the limit load equation.
Water Hammer Simulation Capabilities With CATHENA
Authors: Beuthe Thomas
Published: July 2010

This paper summarizes the current water hammer simulation capabilities of the CATHENA one-dimensional two-fluid network thermalhydraulics simulation code. The single-phase and one- and two-component two-phase capabilities for simulating void collapse water hammer and water hammer in the presence of noncondensables is discussed. Recent successful efforts to resolve nodalization-dependence observed in the simulation of condensation-induced water hammer are presented along with efforts to develop condensation relationships for simulating condensation-induced water hammer. A summary of current code coupling capabilities is also presented. Possible future efforts to simulate water hammer at supercritical pressures as well as the coupling of CATHENA to piping stress codes are discussed.