bluuebunny/crossref_metadata_2025 huggingface dataset:
Ring Winding Technology: Increased Process Efficiency and Effects on the Mechanical Properties of Ring Specimens
Authors: Paessler Michael , Miaris Angelos , Schledjewski Ralf , Mitschang Peter
Published: May 2012

For automotive applications high pressure storage of compressed hydrogen (CH2) becomes more and more important especially regarding the future sustainable mobility based on renewable energy. The filament winding technology is highly industrialized today to meet the requirements for a high-quantity production of lightweight fiber reinforced pressure vessels used for hydrogen-powered cars using fuel cells or combustion engines. However, the main disadvantage of the conventional wet winding process is the low lay-down rate. A decrease of the cycle time to increase the production rate can be realized by the simultaneous feed of a large number of rovings circumferentially arranged around the mandrel. A team of engineers at the Institut fuer Verbundwerkstoffe (Institute for Composite Materials) now further developed the ring winding technology to manufacture pressure tanks with a diameter up to 500 mm (20 inch) with fully wrapped dome sections. This large ring winding head with 12 radial movable arms and multiple payout eyes allows an accordingly higher material output and reduces the cycle time significantly. The profitability analysis considering ring winding head configurations with different number of feed-eyes show the optimization potential regarding the reduction of the production costs of FRP pressure cylinders. A critical review regarding reachable process efficiency is also given in this paper. A modified “tube siphon impregnation unit” is the most important component of the ring winding head due to its compact and modular design. This clean impregnation of 48 carbon fiber rovings near the winder minimizes possible resin leakages. In comparison to a conventional resin bath the amount of hazardous waste, for example contaminated acetone, can be reduced. FRP laminates (fiber reinforced plastic) with a reduced number of crossing points and less ondulation of fiber bundles result higher load bearing capacity and increased mechanical properties. Regarding the degree of interweaving the multi feed-eye configuration of a ring winding head makes it more challenging to define an optimized winding pattern with the given winding angle. The split disk test method was used for comparative investigations regarding the influence of undulations on the material properties of filament wound laminates.
Modeling the Impregnation Process of a Siphon Impregnation System During Filament Winding
Authors: Miaris Angelos , Paessler Michael , Schledjewski Ralf , Mitschang Peter
Published: May 2012

Filament winding is a well-established process for the production of high-end fully wrapped composite pressure vessels. This type of tanks can be designed for service pressures that exceed 700 bar and are ideal for storage of gas fuels like compressed hydrogen in automotive and lightweight applications. As the demand for composite pressure vessels increases, lower costs and better product quality become very important. Impregnation is one of the most important steps in the wet winding process. During this step the dry continuous fibers are combined with the liquid matrix in order to create a fully impregnated semi-finished product. The properties of the impregnated roving have a major effect on the laminate quality and the efficient processing of the liquid matrix has a big influence on the manufacturing costs. The present work is related to the development of a new impregnation method for the processing of carbon fiber rovings. The developed impregnation unit (siphon impregnation system) consists of a sinusoidal cavity without any moving parts. This combined with an automated resin mixing-dosing system this allows complete wet-out of the fibers, precise calibration of the resin fraction, and stable processing conditions. The paper focuses on the modeling of the impregnation process inside the siphon unit. Mathematical expressions for the fiber compaction, the gradual increase of the roving tension, the static pressure, the capillarity of the roving, and the fiber permeation are presented, discussed, and experimentally verified. These expressions were implemented in an algorithm which can model the impregnation process by taking input parameters into account like winding speed, resin dosing, viscosity, and roving tex. The model was solved and the processing parameters of winding tension, fiber volume fraction, and impregnation degree have been simulated. An experimental set-up based on a filament winding machine was used for the validation of the model. Trials with different processing parameters and long run tests have been performed. The results proved that the model can accurately simulate the impregnation process. The good impregnation degree of the wound samples confirmed the efficiency of the siphon impregnation unit.
An Evaluation Method for Plastic Buckling of Cantilever Type Pipes Controlled by Displacement Loads: Part 1—Proposal of the Estimation Method and the Criterion
Authors: Ando Masanori , Tezuka Taiji , Nakamura Toshio , Okawa Tomohiro , Enuma Yasuhiro , Kawasaki Nobuchika , Tsukimori Kazuyuki
Published: May 2012

In Fast Breeder Reactor, dominant stresses in the piping system are secondary, which are induced by constraint of the thermal expansion of components and pipes. Therefore, the structural design rule should essentially prevent the buckling caused by displacement controlled loads. In this study, the evaluation method of the buckling criterion of cantilever type pipes subjected to lateral displacements is proposed. We define the criterion of the deformation controlled buckling based on bending strain at local buckling portion. Then finite element analysis (FEA) is performed for estimating the displacement and bending strain at local buckling portion during the displacement controlled buckling. Those defined criterion and results of FEA are availed to investigate the evaluation method of the displacement controlled buckling criterion. In those FEA, material properties of Mod.9Cr-1Mo steel are applied, because the material is a candidate for primary and secondary heat transport system components of JSFR (Japan Sodium cooled Fast Reactor), and those of 316FR (type 316 stainless steel modified for FR) are also used to compare the FEA results of Mod.9Cr-1Mo steel. Results of FEA suggest that buckling behaviors strongly depend on the distribution of bending moment and strain hardening behavior of the material. Therefore, those features must be considered in construction of the evaluation method of displacement controlled buckling. To consider the distribution of bending moment, two indexes are defined. One indicates nonlinear bending displacement of a straight pipe. The other indicates the configuration of the pipe and material properties. Relationship between those indexes, which including criterion of displacement controlled buckling, is formulated by the enveloped line considering the effect of the strain hardening behavior of the material. As a result, an equation which represents the criterion for displacement controlled buckling of cantilever type pipes was proposed. This equation consists of two indexes as mentioned above, and can estimate criterion of displacement controlled buckling by material properties and pipe configuration. The proposed equation can be applied to the pipes made of Mod.9Cr-1Mo steel and 316FR.
Assessment of Local Approach Methods for Predicting End-of-Life Toughness of RPV Steels
Authors: Jivkov Andrey P. , Lidbury David P. G. , James Peter
Published: May 2012

Local approach methods are becoming increasingly popular as practical tools for cleavage fracture toughness prediction. Their application involves two distinct elements: calculation of ‘individual’ probabilities of failure, dictated by the local mechanical fields; and summation of these failure probabilities to predict the probability of component failure. In this work, we demonstrate that development of the local approach methods to date has been essentially focused on improving the criterion for predicting local failure as a function of the local mechanical fields. Yet, the existing methods fail to predict with sufficient accuracy the effects of irradiation and defect geometry on fracture toughness when the calculations are based on a common set of model parameters. A possible reason for this, common to all methods, is found in the calculation of the cumulative failure probability, which is based on the weakest-link argument. We discuss the implications of the weakest-link assumption, identify those situations where it needs to be reconsidered, and propose future work that will increase our understanding for improving the calculation of global failure probability.
An Evaluation Method for Plastic Buckling of Cantilever Type Pipes Controlled by Displacement Loads: Part 2—Verification of Proposal Method by Buckling Test
Authors: Ando Masanori , Tezuka Taiji , Nakamura Toshio , Okawa Tomohiro , Enuma Yasuhiro , Kawasaki Nobuchika , Tsukimori Kazuyuki
Published: May 2012

In Fast Breeder Reactors, dominant stresses in the system are secondary, which are induced by constraint of the thermal expansion of components and pipes. Therefore, the structural design rule should essentially prevent the buckling caused by displacement-controlled loads. In this paper the applicability of the estimation method of buckling criterion, which was proposed by the authors on the basis of a series of Finite Element Analysis (FEA), was confirmed by carrying out a series of buckling tests. The displacement-controlled buckling tests were performed with cantilever type pipes made of Mod.9Cr-1Mo steel at room temperature and at 550°C. A visual measurement using image processing was applied to clarify both deformation profile and strain distribution at the local buckling portion of pipes. FEA was used in advance for estimating the buckling behavior of tests, such as load-displacement relationship, deformation profile and longitudinal strain distribution. Comparison between test and FEA results showed that buckling behaviors in the tests are predictable by FEA. The estimation method of buckling criterion on the basis of FEA was found to conservatively cover the test results, and we can conclude that this estimation method can be adopted for designing the piping systems of Fast Breeder Reactors.
Study on Mechanism of Stress-Strain Redistribution by Elastic-Plastic-Creep Deformation
Authors: Sato Masakazu , Kikuchi Hiroki , Kasahara Naoto
Published: May 2012

Design of structures subjected to elevated temperature is substantial, especially at structural discontinuities where strain concentration induced by stress-strain redistribution causes a reduction of creep fatigue strength. In the design of those structures, it is needed to consider elastic-plastic-creep deformation. Methods to estimate elastic-plastic-creep deformation are categorized into inelastic FEM analyses and simple methods based on elastic FEM analyses. The latter methods provide the advantages of shorter calculation time and uniqueness of results. Stress Redistribution Locus (SRL) was proposed as one of the simplified methods. Previous analyses indicate that SRL depends on neither constitutive equations nor magnitude of loads. By clarifying the mechanism of stress-strain redistribution, and determining a condition where the SRL coincide, this method can be utilized as a rational analysis for inelastic structural design. The objective of this study is to clarify the mechanism which determines SRL in elastic-plastic-creep deformation. Firstly, elastic-plastic analyses were achieved in a pipe model. Considering an analogy based on the theoretical solution of a two bars model, the pipe model with fixed elastic core ratio was analyzed. In consequence, it was clarified that stress-strain redistribution by elastic-plastic deformation depends on the area of the elastic cores. Secondly, elastic-creep analyses and elastic-plastic-creep analyses were performed in the same model, and it was revealed that the elastic core is the main factor on stress-strain redistribution induced by elastic-plastic-creep deformation.
Assessment of Safety Integrity of LDPE Tubular Reactor With Emergency Pressure Relief Requirement Consideration
Authors: Zhu Jianxin , Chen Xuedong , Ai Zhibin , Guan Weihe , Zhuang Lijian , Fang Xiangrong
Published: May 2012

The production of low density polyethylene (LDPE) with tubular reactor process always involves ultra high pressure (up to 310 MPa (3059 atm)) and medium temperature (normally less than 310°C (590 F)). As polymerization is highly sensitive to temperature and pressure fluctuation, emergency relief valves are required to prevent the runaway of a reaction (C2H4 decomposition, a strongly exothermal reaction). The pressure increase during decomposition develops rapidly (normally in several second). The pressure relief speed plays an important role in the safety integrity of reactor. The purpose of this paper is to demonstrate the evaluation of safety integrity of tubular reactor by taking process deviation and pressure relief requirement into consideration, and to determine the safety requirement specification of the emergency relief. A state of the art analysis is proposed in this paper. The time-dependent pressure fluctuation and relief capacity, as well as various decomposition scenarios during emergency pressure relief are studied. The analysis is then used to determine the required redundancy of the emergency relief valves. The probability of failure on demand (PFD) of multi-valve relief operation is calculated with the classic reliability model. The pressure fluctuation due to emergency pressure relief is calculated with a proven-in-use relief model. Necessary assumptions are made about the relief operation. It is concluded that 2 out of 5 (2005) emergency relief valves are sufficient for the emergency pressure relief in order to prevent the overpressurization of the tubular reactor under a given condition that the emergency relief valve fully opens in less than 3 seconds.
The Influence of Winding Density in the Sealing Behavior of Spiral Wound Gaskets
Authors: Veiga Jose´ C. , Cipolatti Carlos F. , Kavanagh Nelson , Reeves David
Published: May 2012

Spiral wound gaskets are used worldwide in piping and equipment flanges and can be manufactured in several combinations of materials, and in a wide range of dimensions, winding densities and shapes. This paper shows the sealability influence of winding densities, which are not specified by the current Spiral Wound B16.20 gasket standards, including flexible graphite filler thickness, height and number of windings. The effect of the flange rotation is also shown.
Effect of Flaw Dimensions on Ductile Fracture Behavior of Non-Aligned Multiple Flaws in a Plate
Authors: Miyazaki Katsumasa , Hasegawa Kunio , Saito Koichi
Published: May 2012

The fitness-for-service codes require the characterization of non-aligned multiple flaws for flaw evaluation, which is performed using a flaw proximity rule. Worldwide, almost all such codes provide their own proximity rule, often with unclear technical bases of the application of proximity rule to ductile or fully plastic fracture. In particular, the effect of flaw dimensions of multiple surface flaws on fully plastic fracture of non-aligned multiple flaws had not been clear. To clarify the effect of the difference of part through-wall and through-wall flaws on the behavior of fully plastic fracture, the fracture tests of flat plate specimens with non-aligned multiple part through-wall flaws were conducted. When the flaw depth a was shallow with 0.4 in ratio of a to thickness t, the maximum load Pmax occurred at penetration of multiple flaws and the effect of vertical distance of non-aligned multiple flaws H on Pmax was not so significant. However, when flaw depth was deep with 0.8 in a/t, Pmax occurred after penetration of flaws and the effect of H on Pmax could be seen clearly. It was judged that the through-wall flaw tests were appropriate for discussion of the effect of H on Pmax and the alignment rule of multiple flaws. In addition, in order to clarify the appropriate length parameter to estimate Pmax of test specimens with dissimilar non-aligned through-wall multiple flaws, the fracture tests of plate specimens were also conducted. The effect of different flaw length on Pmax was discussed with maximum, minimum and averages of dissimilar non-aligned multiple flaw lengths. Experimental results showed that the maximum length lmax would be an appropriate length parameter to estimate Pmax, when the non-aligned multiple through-wall flaws were dissimilar.
Investigation of the Seismic Safety Capacity of Aged Piping System: Shake Table Test on Piping Systems With Wall Thinning by E-Defense
Authors: Nakamura Izumi , Otani Akihito , Sato Yuji , Takada Hajime , Takahashi Koji , Shibutani Tadahiro
Published: May 2012

In order to investigate the seismic safety capacity of the piping system with local wall thinning, shake table tests on 3-D piping system models were conducted using E-Defense. Two piping system models which were the same in appearance and different in degradation condition were arranged on the shake table of E-Defense. One of the models was put into degradation condition of about 50% wall thinning at four elbows and one tee. Modified seismic motions were applied to these models at the same time. As a result, the piping system model with wall thinning did not fail for the primary stress limit level of sound piping system model, though a ratchet deformation was observed on the thinned wall tee. The model with wall thinning finally failed at the thinned wall tee by over five times larger excitation than the limit level. From the experiment, it was found that the life of the piping system with wall thinning would be reduced compared with that of the piping system without wall thinning, but it was also found that the degraded piping system still had a certain seismic margin until the piping system failed by the seismic load.
The Development of Processing to Mechanical Property Relationships via Quantitative Microstructure Assessment in Low Alloy Steel Heavy Section Forging Materials
Authors: Cogswell Daniel J.
Published: May 2012

This paper provides details of an ongoing effort to characterise the microstructure of heavy section low alloy steel forgings used in high integrity applications and correlate these data to the mechanical properties of these materials. Current industry practice is to use chemical etching and visual assessment in acceptance standards to determine nominal averages for microstructure parameters. This work uses electron microscope techniques to provide information on a variety of grain and secondary-phase particle information allowing numerical comparison of key microstructure variables to mechanical properties. For instance, the transition toughness behaviour of low alloys steels is controlled by the combination of the largest grain and particle in the material, i.e. the most potent initiator for cleavage failure. Knowledge of only the average grain size is insufficient to correlate microstructure and transition toughness performance. The programme consists of three main stages: modelling key variables in the manufacturing process to predict microstructure from thermodynamic predictions, developing quantitative microstructure data on archive materials for which mechanical property data are known to allow empirical relationships to be constructed and, a final validation exercise of a complete model by production and assessment of trial forgings.
A Study on Thermal Stress Evaluation of Safety Injection System for NPPs Considering Leakage Effect
Authors: Sung Hee-Dong , Kim Sun-Hye , Kim Ik-Joong , Kim Young-Jin , Park Jeong-Soon , Choi Young-Hwan
Published: May 2012

Several piping failures caused by thermal stratification have been reported in some nuclear power plants since the early 1980s. However, this kind of thermal effect was not considered when the old vintage nuclear power plants were designed. Thermal stratification is usually generated by turbulent penetration from the RCS to branch line or leakage through damaged part of valve in branch line. In this paper, using the CFD analysis, characteristics of thermal stratification in a safety injection system of PWR plant were investigated and thermal stress evaluation was also conducted. First, CFD analyses were carried out on in-leakage model and out-leakage model according to operating condition. The case of out-leakage, the thermal stratification based on temperature distribution was generated a little at the rear of 1st valve. In contrast, significant thermal stratification was generated in front of 1st valve in in-leakage model because the effect of rapid flow velocity from RCS.
Multi-Disciplinary Design Optimization of Unmanned Aerial Vehicle
Authors: Kim Cheolwan , Lee Yung-Gyo
Published: May 2012

A general procedure of preliminary design of aircraft and one-way fluid-structure interaction (FSI) applied to aircraft design is introduced briefly. Then, FSI and optimization technique are implemented to optimize a wing shape of an unmanned aerial vehicle (UAV) for minimum cruise drag. FSI analysis and optimization processes for minimizing drag of UAV are explained. Design variables are wing taper ratio and dihedral angle, and objective function is the cruise drag of UAV. Fluid solution is generated with Euler solver and structural analysis is performed with FEM solver, Diamond. Sample points are selected by Design of Experiment (DOE) method and Kriging method is used for generation of an approximation model.
Determination of Material Degradation at Various Environmental Conditions
Authors: Wang Zhengdong , Liu Changjun , Xuan Fu-Zhen , Tu Shan-Tung
Published: May 2012

There are growing interests in materials and system degradation at various environmental conditions, especially for structures in fossil fuel power station, nuclear power plants and petrochemical industry. Several testing and simulation approaches have been developed to determine the degradation of material properties with the influence of corrosion environment. A simulation technology is introduced to investigate the effects of irradiation on mechanical properties for a degraded reactor pressure vessel steel. The degradation procedure combines the application of cold prestrain together with high temperature heat treatment. It is found from the results of Charpy impact tests for degraded material that there is an increase of ductile-brittle transition temperature and a trend to a decrease of upper shelf energy because of irradiation embrittlement. Evaluation procedures of temper embrittlement and hydrogen-embrittlement are described for reactor pressure vessel steel exposed to hydrogen environment. A regular coupon sample test is adopted to determine the material degradation of hydrogen processing reactors. Numerical analysis and experimental hydrogen charging technique are explored to simulate the process of hydrogen embrittlement. A critical parameter of hydrogen concentration is defined to evaluate the susceptibility of hydrogen induced cracking for reactor steels. A fatigue testing system is designed to obtain the degradation of fatigue strength for materials under the low oxygen steam environment. The system couples a steam chamber with an axial force-controlled fatigue testing machine. The fatigue tests are performed for a titanium alloy with tension-compression loading up to 107 cycles. Test results show that the fatigue strength is obviously influenced by the steam environment and the stress ratios.
An Engineering Method for Assessing the Effects of Neutron Irradiation on the Fracture Toughness of RPV Steels
Authors: Chen Zhong-An , Wang L. Y. , Chao Yuh-Jin , Lam Poh-Sang , Jin X. S.
Published: May 2012

Neutron irradiation degrades the reactor pressure vessel (RPV) steels. As the steel degrades, the mechanical properties of the material also change which affect the crack tip stress fields. In this article, we show that reduction of the “fracture toughness” of the RPV steels due to neutron irradiation can be interpreted by a change of an “equivalent constraint” due to material property changes. Using the J-A2 two-parameter fracture methodology to quantify the crack tip stress fields and a critical stress fracture criterion, the methodology is applied to the interpretation of fracture toughness test data from un-irradiated and irradiated RPV steels.
Outline and Activities of E-Defense, the Three-Dimensional Full-Scale Earthquake Testing Facility
Authors: Nakamura Izumi , Kajiwara Koichi
Published: May 2012

The 1995 South Hyogo Prefecture Earthquake (Kobe Earthquake) severely damaged many structures such as buildings, highways, and foundations. Over 6,000 fatalities were reported. In order to clarify the reason of such structural damage and then to mitigate the earthquake disaster, National Research Institute for Earth Science and Disaster Prevention (NIED) and the Science and Technology Agency of Japan (at that time, STA) decided to construct a three-dimensional full-scale earthquake testing facility so as to obtain the real data of structural response during an earthquake. The construction of the testing facility which is nicknamed E-Defense was completed in March 2005. The main component of E-Defense is a large shaking table. The table size is 20 meters by 15 meters in the plan, and the maximum payload that can be tested on E-Defense is 12MN. The maximum horizontal and vertical acceleration for the maximum payload are 9 m/s2 and 1.5 m/s2, respectively. The maximum velocity and displacement in horizontal are 2 m/s and 1m, respectively. Since the facility started operation, more than 40 experiments have been conducted. In this paper, the outline and the basic performance of the facilities, and research activities using E-Defense until 2010 are summarized.
A Comparison Study of Coupling Algorithms for Fluid-Structure Interaction Problems
Authors: Rajaomazava Tolotra Emerry , Benaouicha Mustapha , Astolfi Jacques-Andre´
Published: May 2012

The influence of numerical schemes for solving coupled problem in fluid-structure interaction is addressed. A non-linear Burgers equation in a bounded domain with moving interface is solved by finite element method (FEM). The implicit and explicit coupling algorithms are studied with interface equation solved at outside then inside of Newton iterative procedure (referred to as implicit-outer, implicit-inner, explicit and semi-implicit schemes respectively). Iteration numbers and computing time are compared for each algorithm. The interface position and energy conservation condition at the interface are discussed.
Fitness for Purpose Design of a Steel Cylinder for Hydrogen-Natural Gas Blends
Authors: Bortot P. , Bellingardi M. , Beretta S.
Published: May 2012

The present paper deals with a structural integrity assessment of a seamless steel cylinder for transportation of HCNG blend for a 200 bar pressure application with 30% H2 content. First a fracture mechanics approach with an estimation of expected number of cycles and failure mode is applied to a typical cylinder for CNG transportation designed with a traditional approach. The same approach is then used for an assessment of the same cylinder working in a HCNG environment. Fracture toughness was experimentally measured in HCNG blend according to a stepwise procedure and used as input for cylinder failure mode prediction. Fatigue crack growth rate was estimated based on comparison of two interrupted full scale tests carried out in oil and in the investigated HCNG environment. Acceleration of crack propagation, when using HCNG blend, suggests that a dedicated structural integrity assessment of the cylinder is needed to determine the proper design parameters for a safe product life.
Fluid Structure Interaction Modelling for the Vibration of Tube Bundles: Part I—Analysis of the Fluid Flow in a Tube Bundle
Authors: Desbonnets Quentin , Broc Daniel
Published: May 2012

It is well known that a fluid may strongly influence the dynamic behaviour of a structure. Many different physical phenomena may take place, depending on the conditions: fluid flow, fluid at rest, little or high displacements of the structure. Inertial effects can take place, with lower vibration frequencies, dissipative effects also, with damping, instabilities due to the fluid flow (Fluid Induced Vibration). In this last case the structure is excited by the fluid. Tube bundles structures are very common in the nuclear industry. The reactor cores and the steam generators are both structures immersed in a fluid which may be submitted to a seismic excitation or an impact. In this case the structure moves under an external excitation, and the movement is influence by the fluid. The main point in such system is that the geometry is complex, and could lead to very huge sizes for a numerical analysis. Homogenization models have been developed based on the Euler equations for the fluid. Only inertial effects are taken into account. A next step in the modelling is to build models based on the homogenization of the Navier-Stokes equations. The papers presents results on an important step in the development of such model: the analysis of the fluid flow in a oscillating tube bundle. The analysis are made from the results of simulations based on the Navier-Stokes equations for the fluid. Comparisons are made with the case of the oscillations of a single tube, for which a lot of results are available in the literature. Different fluid flow pattern may be found, depending in the Reynolds number (related to the velocity of the bundle) and the Keulegan-Carpenter number (related to the displacement of the bundle). A special attention is paid to the quantification of the inertial and dissipative effects, and to the forces exchanges between the bundle and the fluid. The results of such analysis will be used in the building of models based on the homogenization of the Navier-Stokes equations for the fluid.
Numerical Simulation of TIG Welding Distortions: Distortions of a Mock-Up Representative of ITER Vacuum Vessel
Authors: Pont Denis , Tisset Mathieu , Boitout Fre´de´ric , Gilles Philippe
Published: May 2012

Welding problems encountered in the nuclear industry have been mainly addressed by weldability tests and the analysis, development of new techniques or improvements through lesson learning. Since a decade, AREVA is developing a complementary approach based on numerical simulation. Residual stresses present in reactors do not constitute a major problem at the design stage; even though they may have a strong impact on some types of damage. Numerical welding simulation in the nuclear industry has focused mainly on residual stress prediction, which constitutes an issue for engineering. PWR components are usually massive; nevertheless distortion may also be a source of concern in component design: some structures are slender in spite of their thickness; narrow gap welding requires a close control of the groove width. AREVA, also working on a fast breeder project, the distortion problem gains in importance. In this prospect, AREVA, world energy expert, paid special attention on the numerical simulation of Gas Tungsten Arc Welding (GTAW) of a mock-up relative to the International Thermonuclear Experimental Reactor (ITER) Vacuum Vessel (VV). One of the challenges of manufacturing the ITER vacuum vessel is the low value of acceptance level of distortion (∼ 10 mm) compared to the global dimensions of the structure (∼ 10 m). Welding simulations of a representative mock-up of VV pattern of the made of austenitic steel plates (316L(N) ITER GRADE) are carried out. The aim of the numerical simulations is to check the quality of the distortion prediction. Multi pass welding simulation reproduces the deposit of each bead by thermo-metallurgical and mechanical calculations. Distortions induced by each weld are computed using a simplified approach (local global method). This method aims at modeling long and numerous welding operations with an acceptable calculation time. Moreover, this method is improved in order to respect welding sequence with partial filling of grooves. After welding sequences, distortions are measured at some representative points of the mock-up. The paper presents the methodology of the numerical simulations and the relevant results: • Residual stress and strain fields in and near the welds (local fields), • Distortion prediction for the global structure. The comparison with experimental distortions shows that the trends of the experimental deformed shape are well represented by the simulations. Moreover, displacement magnitudes are in good agreement with measurements.
Failure Analysis of Piping Systems With Thinned Elbows on Tri-Axial Shake Table Tests
Authors: Shibutani Tadahiro , Nakamura Izumi , Otani Akihito
Published: May 2012

This paper presents a computational failure analysis of piping systems with and without thinned elbows on tri-axial shake table tests. In a previous experimental study, two piping models, a sound piping system and a degraded piping system with thinned elbows, were assessed. The sound piping system was found to failed at the elbow flank due to in-plane cyclic bending, whereas the degraded system failed at the end of the elbow due to excessive pipe ovalization. In the present study, finite element (FE) models of elbows were developed in order to carry out fracture analysis. The measured displacements of seismic motions were used as the boundary conditions for FE models. In the sound piping system, plastic strain concentrated at the flank of the elbow due to in-plane bending. The cumulative damage factor was calculated from the fatigue curve and Miner’s rule. The effect of ratcheting was also considered. In the failed elbow, the calculated cumulative damage factor showed good agreement with experimental results. On the other hand, for the fracture analysis of the thinned elbow, the entire seismic loading history on the tri-axial shake table was considered, since the effect of pipe ovalization depends on loading history. The ovalization occurred at the elbow due to cumulative seismic loading. Consequently, the principal plastic strain began to concentrate at the end of the elbow. These FE results offer quantitative explanation for the observed failure modes in the degraded piping system.
Influences of Cyclic Pre-Overload on Low Cycle Fatigue Behaviours of Elbow Pipe
Authors: Matsuo Kazuya , Takahashi Koji , Sato Kyohei
Published: May 2012

Low cycle fatigue tests were conducted using sound elbows made of carbon steel (STPT410). The elbows were subjected to cyclic in-plane bending under displacement control with internal pressure of 9 MPa. The preliminary fatigue tests were conducted under constant cyclic displacements. Then, two test conditions were adopted to investigate the influence of cyclic pre-overload on low cycle behavior of elbow on the basis of the preliminary test results. The fatigue test results were evaluated by using the total usage factor UFTotal (= UFpre+UFpost), where the UFpre and UFpost correspond to usage factor for δpre and δpost, respectively. The fatigue lives of overloaded elbow pipes were estimated based on the cumulative fatigue damage rule basically from UFpre = 0.2 to UFpre = 0.6. In addition, three-dimensional elastic-plastic analyses were carried out using the finite element method. The crack penetration area and the crack growth direction were successfully predicted by the analyses.
Consideration of Thermally Induced Bending Load in Failure Assessment of Piping Components
Authors: Varfolomeev Igor , Mayinger Wolfgang
Published: May 2012

The primary goal of this paper is to demonstrate and validate the applicability of the failure assessment diagram (FAD) approach for predicting failure behavior of piping subjected to thermal loading caused by thermal stratification. The analysis is performed for an austenitic surge line of a PWR circuit where thermal gradients over both the pipe length and circumference produce high bending moments. For the most critical location, circumferential through-wall cracks of variable length are assumed and assessed with respect to their initiation and possible unstable propagation. The assessment result is shown to be decisively influenced by the modeling approach, which in effect depends on the categorization of the bending stresses as either primary or secondary loading. To achieve realistic fracture mechanics assessment, the whole surge line is described by a finite-element model, whereas thermal loading is imposed by mapping the temperature distribution measured under service conditions. Subsequently, elastic-plastic stress and fracture mechanics calculations are performed for the entire surge line model containing cracks of different size in the most stressed location. The analysis clearly confirms the LBB behavior. The numerical results are then compared to those based on the failure assessment diagram (FAD) approach, whereas the section bending moment determined from pipe calculations is categorized as either primary or secondary loading. It is concluded that most realistic analytical failure prediction is achieved when considering the bending moment as secondary loading. Even though the analytical approach is found in this case to produce conservative assessment results, its accuracy is concluded to be acceptable within a wide range of crack sizes considered.
Plastic Limit Loads for Slanted Circumferential Through-Wall Cracked Pipes Based on Finite Element Limit Analysis
Authors: Jang Hyun-Min , Cho Doo-Ho , Choi Jae-Boong , Kim Young-Jin , Huh Nam-Su , Shim Do-Jun , Choi Young-Hwan , Park Jeong-Soon
Published: May 2012

Based on detailed three-dimensional (3-D) finite element (FE) limit analyses, the plastic limit load solutions for pipes with slanted circumferential through-wall cracks (TWCs) subjected to axial tension, global bending and internal pressure are reported. The FE model and analysis procedure employed in the present numerical study were validated by comparing the present FE results with existing solutions for plastic limit loads of pipes with idealized TWCs. To quantify the effect of slanted crack on plastic limit load, the slant correction factors for calculating plastic limit loads of pipes with slanted TWCs from pipes with idealized TWCs were newly proposed via extensive 3-D FE calculations. These slant correction factors are presented in a tabulated form for practical ranges of geometry and each loading conditions. Moreover, the present FE plastic limit loads were also compared with the existing solutions of pipes with slanted TWCs. These FE plastic limit load solutions can be applied to estimate elastic-plastic fracture mechanics parameters and creep fracture mechanics parameters, such as elastic-plastic J–integral and crack opening displacement, creep C*-integral and creep crack opening displacement, based on the reference stress concept considering more realistic crack shape.
A Plastic Collapse Assessment Procedure for Multiple Cracks Under Internal Pressure
Authors: Kamaya Masayuki
Published: May 2012

The influence of the interaction between two surface cracks on the limit pressure was examined by finite element analysis. Longitudinal semi-elliptical surface cracks were assumed to be on a straight pipe that was subjected to internal pressure. The changes in limit pressure due to the relative spacing of cracks and the geometries of the cracks and pipe were investigated. The intensity of the interaction depended on the relative distance between the cracks as well as the pipe and crack geometries. In all cases, the maximum magnitude of the reduction in limit pressure was equivalent to twice the crack face area. Based on the results obtained, criteria for the combination rules the for plastic collapse analysis were proposed. Furthermore, it was concluded that the surface length of the combined cracks could be assumed to be equal to the sum of their lengths. The ligament length was not included.
Thermal Fatigue Analysis at a Mixing Tee by a Fluid-Structural Simulation
Authors: Kamaya Masayuki , Utanohara Yoichi , Nakamura Akira
Published: May 2012

In this study, the thermal stress at a mixing tee was calculated by the finite element method using temperature transients obtained by a fluid dynamics simulation. The simulation target was an experiment for a mixing tee, in which cold water flowed into the main pipe from a branch pipe. The cold water flowed along the main pipe wall and caused a cold spot, at which the membrane stress was relatively large. Based on the evaluated thermal stress, the magnitude of the fatigue damage was assessed according to the linear damage accumulation rule and the rain-flow procedure. Precise distributions of the thermal stress and fatigue damage could be identified. Relatively large axial stress occurred downstream from the branch pipe due to the cold spot. The position of the cold spot changed slowly in the circumferential direction, and this was the main cause of the fatigue damage. In the thermal stress analysis for fatigue damage assessment, it was concluded that the detailed three-dimensional structural analysis was not required. Namely, for the current case, a one-dimensional simplified analysis could be used for evaluating the fatigue damage without adopting the stress enhancement factor Kt quoted in the JSME guideline.
Fluid Structure Interaction Modelling for the Vibration of Tube Bundles: Part II—Homogenization Method Based on the Navier Stokes Equations
Authors: Broc Daniel , Desbonnets Quentin
Published: May 2012

It is well known that a fluid may strongly influence the dynamic behaviour of a structure. Many different physical phenomena may take place, depending on the conditions: fluid at rest, fluid flow, little or high displacements of the structure. Inertial effects can take place, with lower vibration frequencies, dissipative effects also, with damping, instabilities due to the fluid flow (Fluid Induced Vibration). In this last case the structure is excited by the fluid. The paper deals with the vibration of tube bundles in a fluid, under a seismic excitation or an impact. In this case the structure moves under an external excitation, and the movement is influenced by the fluid. The main point in such system is that the geometry is complex, and could lead to very huge sizes for a numerical analysis. Many works has been made in the last years to develop homogenization methods for the dynamic behaviour of tube bundles. The size of the problem is reduced, and it is possible to make numerical simulations on wide tubes bundles with reasonable computer times. These homogenization methods are valid for “little displacements” of the structure (the tubes), in a fluid at rest. The fluid movement is governed by the linear Euler equations (without the convective term). In this case, only “inertial effects” will take place, with globally lower frequencies. It is well known that dissipative effects due to the fluid may take place, even if the displacements of the tube are no so high, or if the fluid is not still. Such effects may be described in the homogenized models by using a Rayleigh damping, but the basic assumption of the model remains the “perfect fluid” hypothesis. It seem necessary, in order to get a best description of the physical phenomena, to build a more general model, based on the general Navier Stokes equation for the fluid. The homogenization of such system will be much more complex than for the Euler equations. The paper presents the first step in the building of a method based on the homogenization of the Navier Stokes equations.
Limit Load Determination and Material Characterization of Cracked Polyethylene Miter Pipe Bends
Authors: EL-Bagory Tarek M. A. A. , Younan Maher Y. A. , Sallam Hossam E. M.
Published: May 2012

The quality of Natural Gas Piping Systems, NGPS, must be ensured against manufacturing defects. The main purpose of the present paper is to investigate the effect of loading mode and load angle (30°,45°, and 60°) on the limit load of miter pipe bends, MPB, under different crack depths a/W = 0 to 0.4 at a crosshead speed 500 mm/min. The geometry of cracked and un-cracked multi miter pipe bends are: pipe bend angle, α = 90°, pipe bend factor, h = 0.844, standard dimension ratio, SDR = 11, and three junctions, m = 3. The material of the investigated pipe is a high-density polyethylene, HDPE, which is commonly used in natural gas piping systems. The welds at the miter pipe junction are produced by butt-fusion welding. For all loading modes the limit load is obtained by the tangent intersection method, TI, from the load deflection curves produced by the specially designed and constructed testing machine at the laboratory. Tensile tests are conducted on specimens longitudinally extruded from the pipe with thickness, T = 10, 30 mm, at different crosshead speeds (5–500 mm/min), and different gauge lengths (G = 20, 25, and 50 mm) to determine the mechanical properties of welded and un-welded specimens. The fracture toughness is determined on the basis of elastic plastic fracture mechanics, EPFM. Curved three-point bend specimens, CTPB, are used. All specimens are provided with artificially pre-crack at the crack tip, a/W = 0.5. The effect of specimen thickness variation (B = 10, 15, 22.5, 30, 37.5, and 45mm) for welded and un-welded specimens is studied at room temperature (Ta = 23°C) and at different crosshead speeds, VC.H, ranging from 5 to 500 mm/min. The study reveals that increasing the crack depth leads to a decrease in the stiffness and limit load of MPB for both in-plane, and out-of-plane bending moment. In case of combined load (out-of-plane and in-plane opening; mode) higher load angles lead to an increase in the limit load. The highest limit load value occurs at a loading angle, φ = 60°. In case of combined load (out-of-plane and in-plane closing; mode) the limit load decreases with increasing load angles. On the other hand, higher limit load values are proved at a load angle, φ = 30°. For combined load opening case; higher values of limit load are obtained. The crosshead speed has a significant effect on the mechanical behavior of both welded and un-welded specimens. The fracture toughness, JIC, is greater for un-welded than welded specimen.
Helical Steam Generator Tubes Containing Crack Under External Pressure: A Review of Applicability for Existing Integrity Evaluation Method
Authors: Ryu Tae-Young , Seo Han-Beom , Kim Jong-Min , Choi Jae-Boong , Kim Young-Jin , Chang Yoon-Suk , Kim Jong-Wook , Park Sang-Yun
Published: May 2012

For integrity assessment of structure containing crack, evaluation method based on fracture mechanics such as linear-elastic and elastic-plastic fracture mechanics has been relatively common method and becoming more widespread. However, it can be used only if the crack opening or tearing is occurred. If the crack exists on the piping components subjected to internal pressure, net-section stress is occurred in the direction on crack opening no matter where crack locate. On the contrary to this, if the external pressure is applied to piping components, net-section stress is occurred opposite direction and it is expected crack opening not to be occur. The subject of this study is SMART steam generator tube which is designed as helical geometrical feature and to be pressurized outside. Three dimensional finite element analyses are carried out to investigate crack behavior under external pressure considered various crack geometries and locations. Furthermore, the possibility of failure of SMART steam generator tube under design pressure is investigated.