bluuebunny/crossref_metadata_2025 huggingface dataset:
Implementation of the EPRI Guidelines to Fatigue Analyses of Primary Circuit Components: Challenges and Recommendations in the Framework of Practical Application
Authors: Reese Sven H. , Seichter Johannes , Klucke Dietmar , Karabaki H. Ertugrul , Mayinger Wolfgang
Published: November 2014

The influence of LWR coolant environment to the lifetime of materials has been discussed recent years. Nowadays the environmentally assisted fatigue (EAF) is under consideration in Codes and Standards like ASME by formula calculation and in the German KTA Rules (e.g. KTA No. 3201.2 and 3201.4) in addition by means of so called attention thresholds.

Basic calculation procedures in terms of quantifying the influence of LWR coolant environment by the so called Fen-factor were proposed in NUREG CR-6909 in 2007. Since this report the set of formulas have been adapted several times (e.g. in ANL-LWRS47-2011) and further changes in set of formulas are likely to occur. Subsequently a revision of the NUREG CR-6909 report is taking place incorporating recent changes.

Within the EPRI 2012 Technical Report “Guidelines for Addressing Environmental Effects in Fatigue Usage Calculations” some practical recommendations for the application of the EAF to real components are stated. In this report EPRI presented the calculation of sample problems in combination with sample transients carried out by the participants and verifying the applicability of the proposed approaches. However, the EPRI guideline provides a set of tools taking environmentally assisted fatigue into account. This guidance figures out to be quite helpful on one hand, but incorporates some challenges in terms of practical application on the other hand. Additionally, the EPRI Report gives no clear advice which specific combination of calculation methods to apply finally.

Within this publication the procedures proposed in the EPRI guideline will be applied to existing numerical approaches being published. Challenges when applying the methods defined in the EPRI guideline will be identified and solutions will be given. Additionally, recommendations will be stated based on the proposed procedures in terms of practical application especially in context of calculations for fatigue relevant primary circuit components.
Effects of Soil-Structure Interaction, Damping and Higher Modes on the Response of a Mid-Story-Isolated Structure Founded on Multiple Soil Layers
Authors: Tsai Chong-Shien , Su Hui-Chen
Published: November 2014

This paper focuses on investigating the effects of soil-structure interaction (SSI), higher modes, and damping on the response of a mid-story-isolated structure founded on multiple soil layers overlying bedrock. Closed-form solutions were obtained for the entire system, which consists of a shear beam type superstructure, seismic isolator, and multiple soil layers overlying bedrock, while subjected to ground motion. The proposed formulations simplify the problem in terms of well-known frequency and mechanical impedance ratios that can take into account the effects of SSI, higher modes, and damping in the entire system, and be capable of explicitly interpreting the major dynamic behavior of a mid-story-isolated structure interacting with the multiple soil layers overlying bed rock. The SSI effects on the dynamic response of a mid-story-isolated structure as a result of multiple soil layers overlying bedrock were extensively investigated through a series of parametric studies and physically explained by virtue of derived formulations. In addition, the results of numerical exercises show that higher damping provided by the isolator may provoke higher mode response of the superstructure; that the lower structure below the isolator may have significantly larger deformations compared to those of the upper structure above the isolator; and that isolator displacements may be amplified by the SSI effects while compared to those of mid-story-isolated structures with fixed-base.
Experimental Determination of the Static Equivalent Pressures of Detonative Decompositions of Acetylene in Long Pipes and Chapman-Jouguet Pressure Ratio
Authors: Schildberg Hans-Peter
Published: November 2014

Gaseous acetylene (C2H2), which is used in industry in large quantities, is well known for being prone to detonative decomposition. Existing guidelines provide advice for a safe handling but are still deficient with regard to quantifying the static equivalent pressures experienced by the wall of a pipe when exposed to an internal detonative decomposition reaction. By applying the pipe wall deformation method we determined the static equivalent pressures occurring in long pipes. Once the static equivalent pressure is known, the well-established pressure vessel design guidelines, which can cope with static loads, can be applied for detonation pressure proof pipe design in all cases where the detonation speed is not close to the propagation speed of the flexural waves in the pipe.

The tests revealed further important new details characterizing the detonative decomposition of C2H2: 1) The static equivalent pressure at the location of the occurrence of the deflagration to detonation transition (DDT) turned out to decrease relatively with increasing initial pressure. 2) When exceeding an initial pressure of approximately 12 bar abs there was no longer a stage of instable detonation after the occurrence of the deflagration to detonation transition, but the reaction front immediately propagated as a stable detonation. 3) It was found that the Chapman-Jouguet theory, which provides reasonably precise predictions for the propagation speed of the stable detonation and the Chapman-Jouguet pressure ratio in the case of common stoichiometric combustible/oxidant mixtures, seems to fail in the case of the decomposition of C2H2. A possible reason for this could be the fact that the decomposition reaction, in contrast to all other combustion reactions, generates both gaseous and solid reaction products. 4) By combining the results of recent work on detonations in ethylene/O2/N2-mixtures published in PVP2013-97677 and the present tests, a good estimate for the Chapman-Jouguet pressure ratio of the detonative decomposition reaction of C2H2 could be derived.
European Contributions to Environmental Fatigue Issues Experimental Research in France, Germany and Finland
Authors: Métais Thomas , Karabaki Ertugrul , De Baglion Laurent , Solin Jussi , Le Roux Jean-Christophe , Reese Sven , Courtin Stéphan
Published: November 2014

Environmentally assisted fatigue (EAF) is at the centre of numerous discussions and conferences on fatigue around the world. The methodology proposed in NUREG/CR-6909 [1] is being applied in the USA for new builds and for license renewal per the RG 1.207 [2], but there is still room for a better understanding of all the effects involved and for fine-tuning of the methodology. A roadmap by EPRI lists areas where testing is recommended [3].

In Europe, research is going on and the accumulated results show that NUREG/CR-6909 is very conservative [4]–[10]. Applicability of the proposed design curve and the Fen factors were questioned in previous papers and alternative approaches have been developed [11]–[14].

This paper summarizes different experimental, analytical and practical approaches taken by four main players in the European nuclear industry and compares results with the NUREG/CR-6909 methodology. This joint discussion demonstrates that, although the approaches have been different, a common conclusion is reached: the NUREG/CR-6909 methodology can be improved.
License Renewal and Subsequent License Renewal in the U.S.
Authors: Young Garry G.
Published: November 2014

As of February 2014, the NRC has renewed the operating licenses for 73 nuclear units, allowing for up to 60 years of safe operation. In addition, the NRC has license renewal applications under review for 18 units and 9 additional units have announced plans to submit applications over the next few years [1]. This brings the total of renewed licenses and plans for renewal to 100% of the operating nuclear units in the U.S.

By the end of 2014, there will be 38 nuclear plants that will have operated for more than 40 years and will be eligible to seek a subsequent license renewal (or almost 40% of the nuclear units expected to be operating at the end of 2014). In 2013, nuclear plant owners of 5 units shutdown operation or announced plans to shutdown by the end of 2014. However, most of the remaining operating plant owners are keeping the option open for long term operation beyond 60 years. NRC and the U.S. nuclear industry have made significant progress in preparing the way for subsequent license renewal applications. This paper presents the status of the U.S. license renewal process and issues being addressed for possible applications for subsequent renewals for up to 80 years of operation.
Initiation and Growth of Small Fatigue Cracks of Steels Used for Nuclear Power Plants Under Low Cycle Regime
Authors: Hasunuma Shota , Ogawa Takeshi
Published: November 2014

Low cycle fatigue tests were conducted for carbon steel, STS410, low alloy steel, SFVQ1A, and austenitic stainless steel, SUS316NG, which were used for nuclear power plants, in order to investigate the mechanism of fatigue damage when the plants were subjected to huge seismic loads. In these tests, the surface behavior of fatigue crack initiation and growth was observed in detail using cellulose acetate replicas, while the interior behavior was detected in terms of fracture surface morphology developed by multiple two-step strain amplitude variations with periodical surface removals. Fatigue crack growth rates were evaluated by elasto-plastic fracture mechanics approach. For SFVQ1A and SUS316NG, the fracture mechanics approach is available in order to predict the crack growth life from the metallurgical crack initiation size to the final crack length of the specimens. For STS410, numerous small cracks initiated, grew and coalesced each other on the specimen surface under low cycle fatigue regime.
Evaluation of Specific Mechanical Behavior of Fine Screw Threads by Finite Element Analysis and Experiments
Authors: Fukuoka Toshimichi , Nomura Masataka , Sasai Misato
Published: November 2014

Fine screw threads are widely used for the bolted joints under severe running conditions. It is well known that they are effective to prevent thread loosening due to fine pitch. As for other mechanical characteristics, it has been reported in the previous paper using complex stress functions that the stress concentration at bolt thread root is higher than coarse screw threads and the fatigue strength of threaded fasteners shows a minimum value for varying pitch. However, the latter is questionable since the calculations were conducted under lots of hypotheses. In this study, stress concentration and stress amplitude along thread root are evaluated by three-dimensional finite element analysis, in which numerical models of the bolted joints are constructed so as to accurately represent the effect of thread helical geometry. It is shown that the stress concentration at thread root of fine screw threads is higher than that of coarse screw threads, and the maximum stress amplitude is likely to be lower on the contrary. Meanwhile, it is sometimes recognized that clamping forces of fine screw threads are smaller comparing to those of coarse screw threads when tightened with same torque. To clarify this contradictory phenomenon, tightening experiments are conducted, and it is found that the difference of the energy needed for tightening screw threads is found to be the major cause.
Study on Power Generation Using Unstable Energy by In-Flow Fluidelastic Vibration
Authors: Sumitani Takuya , Hagiwara Shinichiro , Nakamura Tomomichi
Published: November 2014

In-flow instability of tube arrays is one of recent major issues to be examined in the heat exchanger design since the event at a nuclear power plant in California [1]. In our previous tests [2], the effect of the pitch-diameter ratio in triangular arrays is reported. This is one of the present major issues in the nuclear industry.

On the other hand, there are some trials [3] to produce the electric power by the phenomenon of the flow-induced vibration. They are mainly using the vortex shedding, but in this report the power generation by the unstable vibration is investigated. It is spotlighted the combination between the unstable vibration and the power generation whether the limit cycle exists or not. This report introduces the result on the existence of the limit cycle.

Many engineers have attempted to produce electric power using semi-conductor devices, but they could not obtain enough power. Then, the device using the electro-magnetic system is used here. The in-flow instability has a small effect on the fluid flow compared with the usual fluidelastic vibration in the transverse direction, because the in-flow movement does not disturb the flow path compared to the transverse fluidelastic vibration.

The coil-magnet system is set on the top of the flexible cylinder cantilevered from the bottom. A three by three array of cylinders in a triangular pattern is set in a small wind tunnel. When the flow velocity increases, the cylinder array becomes unstable in the in-flow direction as similarly to the transverse direction, and it produces the electricity in the coil. However, as the power generation means energy dissipation, resulting in increase of the system damping, the effect on the instability is examined.

At the end of this report, an analytical solution is introduced to explain the measured results. It is successfully completed to show the existence of the limit cycle.
Residual Stress Profiles of Pipe Girth Weld Using a Stress Decomposition Method
Authors: Teng Huaguo , Bate Steve
Published: November 2014

The application of procedures such as R6 or BS7910 for the structural assessment of defects in pressurised components containing residual stresses requires knowledge of the through-wall residual stress profile. Currently there is much interest in improving the residual stress profiles that are provided in the procedures. In this paper we present an improved analysis of residual stresses of the pipe girth welds by applying the developed heuristic method to one set of extended residual stress measurement data. The through-thickness residual stress is decomposed into three stress components: membrane, bending and self-equilibrating. The heuristic method was applied to the three components separately, so that the residual stress profile was a combination of the three stress components. This form provides not only a clear physical basis for the residual stress profile, but is also convenient for defect assessment where only the membrane and bending stress components are important.
Experimental Study of All-Steel Buckling Restrained Brace With Windowed Lateral Support Elements
Authors: Tsai Chong-Shien , Wang Yan-Ming
Published: November 2014

The buckling restrained brace (BRB) that has been worldwide adopted as a structural control device possesses excellent energy dissipation mechanism and can overcome the disadvantages of the traditional brace. However, the traditional BRB is a fully close design, it is therefore impossible to inspect the condition of the internal components during manufacturing and after earthquakes. This study proposed an all-steel buckling restrained brace with windowed lateral support elements that allow inspecting the internal condition of the BRB. We also studied the optimization in selecting the sizes and positions of the windows in the internal components without affecting its strength to provide an economically feasible all-steel BRB that is convenient for manufacturing and installation and meets the rigorous testing protocols. The all-steel BRB consists of the steel core, lateral support and constraining elements. In this study, scaled all-steel BRBs were tested under cyclic loadings by using an MTS 250 kN test machine. Test results showed that the mechanical behavior of the BRB with windows on the sides of lateral support elements is stable and that damage always occurred at the energy dissipation sections after low cycle fatigue tests. The difference between tensile and compressive forces was small under identical strain, and the accumulated inelastic deformation exceeded the requirement of test protocols. These test results confirm that the windows opened on the proposed BRB have insignificant effects on the strength of the device and that the proposed device meets the design requirement and is thus considered as a stable energy dissipative apparatus.
Horizontal Aerodynamic Derivatives in Bridge Flutter Analysis
Authors: Larsen Allan
Published: November 2014

Inclusion of a horizontal degree of freedom along with the vertical and twisting degrees of freedom has been an active area of research in bridge flutter predictions for the past three decades. While much work has been published on theoretical aspects, limited experience as to the importance of the horizontal degree of freedom is available in the literature. Three cases of actual long span bridge designs are examined with respect to the critical wind speed for onset of classical flutter. For the tree cases examined inclusion of the horizontal modes of motion had almost negligible influence on the flutter wind speed.
FP7 Project STYLE: Implications and Recommendations, Discussion
Authors: Keim Elisabeth , Sharples John , Nicak Tomas
Published: November 2014

The European collaborative project STYLE is one of the NUGENIA umbrella projects. The STYLE project was completed by the end of 2013 and during an external workshop in October 2013, the implications of the STYLE results were discussed and recommendations for future challenges outlined. Several technical issues have been addressed in STYLE. These include Dissimilar Metal Weld Integrity, Effect of Weld Residual Stress on fracture and damage modeling, Weld Residual Stress simulation and measurement with and without weld repairs, Transferability of material properties, Stress Corrosion Cracking, Thermal fatigue through turbulent mixing, Dynamic Impact Testing and FE Analysis, Benchmarking of Engineering Assessment Methods and Leak-Before-Break approaches.
Synthesis of a Rotor Noise Controller by Parallel Blade-Vortex Interaction Aeroelastic Modelling
Authors: Modini S. , Graziani G. , Bernardini G. , Gennaretti M.
Published: November 2014

The aim of this paper is the presentation and application of a methodology for the identification of a multi-cyclic, higher harmonic blade pitch actuation controller suited for alleviating impulsive noise induced by Blade-Vortex Interactions (BVI). The blade pitch actuation is driven by a feedback control law derived by an optimal linear-quadratic regulator control formulation based on simulations provided by an equivalent two-dimensional, multi-vortex, parallel BVI problem that describes the aerodynamic response of elastic rotor blade cross sections in BVI conditions. This control law identification process is particularly efficient in that exploits two-dimensional simulations, instead of using three-dimensional, time-consuming predictions. In order to examine the effectiveness of the proposed controller in alleviating BVI noise, it is applied to the analysis of a realistic helicopter main rotor in descent flight.
On the Cyclic J-Integral of a 3D Semi Elliptical Surface Crack
Authors: Beesley Ross , Chen Haofeng , Hughes Martin
Published: November 2014

This paper investigates an approach for calculating the cyclic J-Integral (ΔJ) through a new industrial application. A previously proposed method is investigated further with the extension of this technique through a new application of a practical 3D notched component containing a semi-elliptical surface crack.

Current methods of calculating the cyclic J-Integral are identified and their limitations discussed. A modified monotonic loading method is adapted to calculate the cyclic J-integral of this 3D Semi Elliptical Surface Crack under cyclic loading conditions. Both the finite element method (FEM) and the Extended Finite Element Method (XFEM) are discussed as possible methods of calculating the cyclic J-Integral in this investigation. Different loading conditions including uni-axial tension and out of plane shear are applied, and the relationships between the applied loads and the cyclic J-integral are established. In addition, the variations of the cyclic J-integral along the crack front are investigated. This allows the critical load that can be applied before crack propagation occurs to be determined as well as the identification of the critical crack direction once propagation does occur.

These calculations display the applicability of the method to practical examples and illustrate an accurate method of estimating the cyclic J-integral.
Experimental Evaluation of the Markl Fatigue Methods and ASME Piping Stress Intensification Factors: Part II
Authors: Hinnant Chris , Paulin Tony , Becht Charles , Becht Charles , Lock William Santiago
Published: November 2014

Part 1 of this paper was presented by Mr. Chris Hinnant at the 2008 PVP Conference in Chicago. Since 2008 additional fatigue test data has become available to the Paulin Research Group (PRG) which includes tests on unreinforced fabricated tees intended to support the fatigue curve approach established in the 2008 paper, and twenty-five additional straight pipe cantilever fatigue tests on carbon, stainless, duplex, CuNi, P91, X42 and X65 materials. These more recent experimental results confirm the fatigue slope recommended for cantilevers in the 2008 paper, but suggest that the original Markl slope may be more suited for some configurations of branch connections. Comparisons of the B31 Code allowable with failure data, tests, reviews of ratcheting behavior in pipe systems, and crack growth monitoring help draw conclusions about design equations in the B31 Codes and fatigue test procedures.
A Survey Method to Optimize Bolted Flanged Joint Assembly Torques for ASME B16.5 Flanges
Authors: Bausman Anita R. , Waterland A. Fitzgerald (Jerry)
Published: November 2014

The three critical components within a bolted, flanged connection are the flanges, gasket, and bolts. Until recently, simplified flange assembly target torque values for ASME B16.5 flanges were routinely determined by considering just one or two of these primary components.

One approach considers only the gasket. Gasket-based target torque values are selected to optimize the gasket’s sealing performance by ensuring compression between minimum and maximum seating stress ranges, or based upon achieving specific levels of gasket Tightness (Tp). Another approach, fastener-based torque values, simply targets a specific bolt preload during assembly, typically some percentage of bolt material yield stress. A third approach optimizes gasket seating stress or tightness within the specific preload stress range of particular grades of fasteners. None of these approaches consider the physical limitations and capabilities of the flange itself, which can result in flange damage due to excessive bolt preload or the lost opportunity to gain fatigue resistance and reliability when low fastener preloads are selected [1].

While detailed Finite Element Analysis (FEA) could meet this objective, cost and time constraints limit the number, size, and materials to be considered. The objective of this method to optimize target assembly torques for B16.5 flanges is to identify the likely maximum safe assembly bolt load not exceeding the compression, yield, or tensile limits of any of the three flange components. It is recognized that some localized yielding does occur. Existing industry efforts to study and optimize target torques are surveyed, reviewed, combined, and extrapolated to determine acceptable torque values that conform to selected component limits. The limits are chosen consistent with normal practice in the chemical, process, and power industries.
Reference Stress Based Assessment for Creep-Fatigue Life Under Multiaxial Condition
Authors: Tokuda Kenji , Yoshida Kimiaki , Yatomi Masataka
Published: November 2014

The reference stress method has been developed to assess the service life for many components under creep condition. However, in order to use the reference stress as a representative stress to assess the creep fatigue life, some modifications are needed. The σd approach based on reference stress, used in RCC-MR, is one of the most common method to assess creep fatigue crack incubation. The aim of this paper is to develop a novel model based on reference stress and the σd approach to estimate the life subjected to creep-fatigue interaction under multiaxial condition for defect free structures. Three kinds of circumferentially notched bar specimens were used in order to examine the creep-fatigue interaction under multiaxial conditions. Finite element analyses were conducted to develop a simplified life assessment method and to calculate the creep fatigue damage in the test specimens. The predicted creep fatigue lives are in good agreement with the experimental results using notched bar specimens of 316H stainless steel.
Linear and Nonlinear Dynamics of Cantilevered Cylinders in Axial Flow
Authors: Jamal Ahmad , Païdoussis Michael P. , Mongeau Luc G.
Published: November 2014

Understanding and prediction of the dynamics of slender flexible cylinders in axial flow is of interest for the design and safe operation of heat exchangers and nuclear reactors, specifically that of heat exchanger tubes, nuclear fuel elements, control rods, and monitoring tubes. In such fluid-structure interaction problems, the fluid forces acting on the flexible structure play a vital role in defining its dynamics. Therefore, a precise calculation of the coefficients associated to these forces, such as the longitudinal and normal viscous force coefficients, and base drag coefficient in the equation of motion is imperative. The present work is aimed at (i) calculating these force coefficients for a cantilevered slender flexible cylinder, fitted with an ogival end-piece, in axial flow and (ii) conducting experiments on the same system. In the calculation of these force coefficients, the parameters of the experimental system are used, so that the theoretically predicted dynamics would be representative of the actual physical system. These calculated force coefficients are then incorporated in the linear and nonlinear equations of motion and the predicted dynamics are compared with those of the experiments. The comparison shows good agreement between the theoretical and experimental results.
Basic Study on Vibrational Behavior of Piping Systems Supported by Elasto-Plastic Damper With Gap Support
Authors: Tsujita Keishi , Shintani Atsuhiko , Ito Tomohiro , Nakagawa Chihiro
Published: November 2014

In this study, the vibrational behavior of piping systems supported by elasto-plastic dampers with gap supports was considered. First, an analytical model of L-type piping systems subjected to sinusoidal input was derived, including nonlinear characteristics of the elasto-plastic dampers and gap supports. Next, a numerical simulation was performed to verify the effect of the gap support on the piping system. The effect of the input characteristics on the response behavior of the piping system was investigated.
Crack Initiation and Propagation Under Hydrogen-Enhanced Fatigue of a Cr-Mo Steel for Gaseous Hydrogen Storage
Authors: Briottet Laurent , Escot Marielle , Moro Isabelle , Tamponi Gian Marco , Furtado Jader , Solin Jussi , Bortot Paolo
Published: November 2014

The current international standards and codes dedicated to the design of pressure vessels do not properly ensure fitness for service of such vessel used for gaseous hydrogen storage and subjected to hydrogen enhanced fatigue. Yet, hydrogen can reduce the fatigue life in two ways: by decreasing the crack initiation period and by increasing the fatigue crack growth rate. The European project MATHRYCE aims are to propose an easy to implement vessel design methodology based on lab-scale tests and taking into account hydrogen enhanced fatigue.

The study is focused on a low alloy Cr-Mo steel, exhibiting a tempered bainitic and martensitic microstructure, and classically used to store hydrogen gas up to 45 MPa. Due to hydrogen diffusion at room temperature in such steel, tests have to be performed under hydrogen pressure to avoid outgassing.

In the present work, experimental procedures have been developed to study both crack initiation and crack growth. The specimens and tests instrumentation have been specifically designed to quantitatively measure in-situ these two stages under high hydrogen pressure. We developed and tested crack gages located close to a small drilled notch. This notch simulates the presence of steel nonmetallic inclusions and other microstructural features that can affect fatigue crack initiation and propagation. The experimental results addressing the effects of the testing conditions, such as stress ratio, frequency and hydrogen pressure will be compared to the local strain and stress fields obtained by Finite Element Method and correlated to the possible hydrogen enhanced fatigue mechanisms involved.
Extending Replacement Intervals of Elastomeric Components by Evaluating Samples Removed From Service
Authors: Marchesi Jenifer T. , McBrine William J. , Roy Vincent
Published: November 2014

Elastomers play an essential role in pressure vessels as seals, hoses, gaskets, diaphragms, liners and other critical components [1]. Some polymeric materials used for non-pressure applications such as electric power cable insulation have received much attention with respect to the effects of aging and life management, but many critical elastomeric pressure vessel components such as seals have not. Performance of these seals depends upon the effects of both time- and event-dependent aging. Understanding and addressing aging and degradation are fundamental to effective preventative maintenance and life-cycle management programs.

Proper management of elastomers is necessary for performance requirements and for cost containment. In one of the case studies presented synthetic seals in engines were quite costly to change on the suggested OEM maintenance schedule where replacement intervals were based on assumed operating conditions applicable to other industries. When the actual service for these engines is as emergency diesel generators (EDGs, e.g., in nuclear power plants) the use is primarily in stand-by mode, and the usage is far different than that of the manufacturer’s target application. In this investigation the assessment of pressure seal performance was based on situation-specific operation and environmental parameters. This resulted in much longer replacement intervals. In another case study alternate materials were identified which are expected to improve performance over the original material.
Acoustically Induced Instabilities in Pipes by the Nyquist Criterion
Authors: Moussou Pierre
Published: November 2014

In process pipes, orifices and pressure relief valves are sometimes prone to self-sustained oscillations in the presence of acoustic reverberating conditions. Former studies have shown that this kind of instability can be adequately described by a linear approach inspired by control theory, where the pressure drop device behaves like an acoustic amplifier and the surrounding pipe as an acoustic feedback. In order to better understand the instability conditions, a simplified model of a device and its surroundings is elaborated: in harmonic regime, the device is assumed to amplify propagating plane pressure waves in a range of Strouhal numbers close to 0.2, whereas acoustic waves are reverberated by acoustic obstacles located several diameters upstream and downstream. The application of the Bode-Nyquist criterion brings out several features of actual acoustically-induced instabilities: first, the unstable frequencies are close to a series of discrete values equal to the acoustic natural frequencies of the pipe. Second, the unstable frequencies depend slightly on the flow velocity, because of the phase shift generated by the pressure drop device. Third, the instability is enhanced by the amplitude of the acoustic reflection coefficients and the proximity of the device to a pressure node. In dimensionless representation, the whistling frequencies exhibit successive branches, depending on the flow velocity. Comparisons with actual cases support this simplified representation. Former acoustic data obtained with a single hole orifice are revisited, and plotted in the dimensionless representation; the successive branches appear quite similar to the ones of the ideal model. Fluctuating pressures obtained with a safety relief valve experiencing chatter are processed, and bring out two branches in the same dimensionless representation. The results suggest that acoustically-induced instabilities are dominated by the acoustic response of the surrounding pipe, and that a gain/feedback representation is adequate for predicting the flow velocities associated with these instabilities.
Fluid Damping in an Oscillating Array of Cylinders Submitted to Axial Flow
Authors: Divaret Lise , Depaix Fanny , Moussou Pierre , Cadot Olivier , Doaré Olivier , de Buretel de Chassey Nicolas
Published: November 2014

Axial flows are known to generate a high level of damping with respect to the lateral oscillations of cylinder arrays. The evaluation of these dissipative forces is crucial for seismic design of fuel assemblies. The present study is focused on the case of an array of 40 cylinders oscillating laterally in an axial flow.

An experiment is performed in a water tunnel with an rectangular array of 8 × 5 cylinders. The cylinder diameters are D = 10mm, and their length to diameter ratio is L/D = 56. The cylinders are equally spaced with a gap of 3 mm. The distance from the array of cylinders to the wall of the water tunnel is equal to 14mm in the lateral direction and 24.5mm in the direction of the oscillations. The axial flow velocity varies between 0.5m/s and 4.5m/s. The array of cylinders is rigidly clamped to a rod connected to a motoreductor system which enforces a sine-like displacement. The oscillation frequency ranges from 3Hz to 7Hz and the amplitude from 5.4mm to 16mm. An impedance head and an optical micrometer are used to measure the lateral force and the displacement.

The added mass and damping coefficients are estimated from the lateral force signal for different axial flow velocities, oscillation amplitudes and frequencies. Results show that the added mass coefficient is almost constant and equal to the potential value proposed by Chen. The damping coefficient depends on only one non dimensional parameter which is the ratio between the oscillation velocity and the axial flow velocity. Two force regimes are also observed: for very low oscillation velocities to axial flow velocity ratios, the damping force is proportional to the oscillation velocity and quadratic otherwise.
Vibration Analysis of Curved Pipes Conveying Fluid
Authors: Liu Gongmin , Li Shuaijun , Karney Bryan W.
Published: November 2014

The partial differential equations for curved pipes with fluid structure interaction, including the effects of fluid pressure and Coriolis force, Centrifugal force and migration force caused by flow velocity, etc., were derived. These equations were then solved numerically utilizing the transfer matrix method (TMM) in the frequency domain because of its computational efficiency. The results were compared with those predicted by the finite element method and a discrete model. It is demonstrated that the TMM has high precision in the vibration analysis of fluid-filled curved pipes. Furthermore, the influence laws of geometrical properties on the natural frequencies and frequency responses of pipeline are discussed, which show that the natural frequencies of the fluid do not change with the varying of curvature angle when curved pipe filled with steam. But the resonance frequencies of the out-of-plane vibration and vibration amplitudes of the fluid pressure waves are strongly influenced by the variation of curvature angle.
Evaluation of the Numerical Validity of the J Parameter for a Crack Located on a Multi-Material Interface
Authors: Blouin A. , Chapuliot S. , Hamouche W.
Published: November 2014

In the primary circuit of PWR, main components composed of ferritic steel, such as the pressure vessel or the pressurizer, are connected to the piping system made of austenitic steel with weld joints. In this paper, we are considering a narrow gap weld made of Inconel 52, typical of the new EPR™ design. Thus, there are two interfaces between the different materials, that is to say Ferritic steel/Inconel 52 and Inconel 52/austenitic steel. For safety purposes, the demonstration of the fracture resistance of this area is necessary. In that frame, a conventional defect is postulated at one of the interfaces and the fracture resistance of the structure is evaluated. To do so, the J parameter is determined and then compared to the material toughness. However, calculation of the J parameter for a crack located at an interface is usually difficult to evaluate depending on the Finite Element (F.E.) code used. As a matter of fact, this configuration is close to the limit of validity of the J formulation since the crack is surrounded by different materials. In general, most of studies are conducted with a conventional defect parallel and close to the interface. This configuration is usually used because the domain of validity of the J parameter is well known in that case. Nevertheless, it is important to be able to evaluate the J parameter for a crack located on the interface since it is more representative of a defect due to the welding process and also easier to mesh. This paper focuses on that particular case and evaluates the validity of the J parameter for such a location of the conventional defect. Using F.E.M. with Systus® and Castem®, the J parameter is calculated for a piping structure containing a narrow gap weld and a defect at the ferritic steel/Inconel 52 interface and around this area. The structure is submitted to different types of loading such as internal pressure, axial force, or thermal shocks. All the different results allow concluding about the continuity of the J parameter through the interface and its numerical validity. Also, it gives interesting information about the size of the integration path to use and the adapted mesh size around the crack.
Structural Reliability Evaluation on the Pressurized Water Reactor Pressure Vessel Under Pressurized Thermal Shock Events
Authors: Chou Hsoung-Wei , Huang Chin-Cheng
Published: November 2014

The failure probability of the pressurized water reactor pressure vessel for a domestic nuclear power plant in Taiwan has been evaluated according to the technical basis of the USNRC’s new pressurized thermal shock (PTS) screening criteria. The ORNL’s FAVOR code and the PNNL’s flaw models are employed to perform the probabilistic fracture mechanics analysis based on the plant specific parameters of the domestic reactor pressure vessel. Meanwhile, the PTS thermal hydraulic and the probabilistic risk assessment data analyzed from a similar nuclear power plant in the United States for establishing the new PTS rule are applied as the loading condition. Besides, an RT-based regression formula derived by the USNRC is also utilized to verify the through-wall cracking frequencies. It is found that the through-wall cracking of the analyzed reactor pressure vessel only occurs during the PTS events resulted from the stuck-open primary safety relief valves that later reclose, but with only an insignificant failure risk. The results indicate that the Taiwan domestic PWR reactor pressure vessel has sufficient structural margin for the PTS attack until either the end-of-license or for the proposed extended operation.
Effect of Fastener Under Head Contact on the Early Stage of Self-Loosening of Preloaded Countersunk Fasteners Subjected to Cyclic Shear Loading
Authors: Zaki Amro M. , Nassar Sayed A.
Published: November 2014

Three dimensional Finite Element model is used to investigate the loosening behavior of countersunk threaded fasteners subjected to cyclic shear loading applied through prescribed transverse excitation to the fastener head. Fasteners with conical head profile require precision machining of both the fastener head and the mating joint hole. Any mismatch between the head and the joint conical angles affects the torque tension relationship as well as the loosening performance. Investigation focuses on the loosening behavior in its early stages. Factors investigated include the effect of the bolt head/joint hole contact location, joint elastic modulus, and tapped hole clearance for different combinations of thread fit, on the loosening performance of preloaded countersunk-head bolts. The FEA model prediction of the self-loosening behavior is experimentally validated.
The Effects of In-Plane and Out-of-Plane Dimensions of a Curved Wide-Plate on Crack-Tip Constraint for Pipeline Fracture Assessment
Authors: Lee Hwee-Seung , Huh Nam-Su , Kim Ki-Seok
Published: November 2014

One important element of fracture mechanics assessment in pipelines is how to determine the relevant fracture toughness (J-resistance or CTOD-resistance (crack-tip opening displacement)) for nonlinear fracture mechanics analysis. The general practice using a standard fracture mechanics specimen is known to often provide conservative estimates of toughness due to differences in crack-tip constraints between standard specimens and actual components.

To improve the accuracy of predicting pipeline failure, various non-standard fracture mechanics specimens have been suggested over the past few decades. Among the several non-standard test specimens, a curved wide-plate in tension is often employed to predict fracture behavior of cracked components, for instance, in gas transportation pipelines.

In order to show validity of a curved wide-plate in tension, the fracture toughness values from a full-scale pipeline test have been compared with those from a curved wide-plate in tension, and crack-tip constraints of a curved wide-plate in tension have also been compared with those of actual pipelines or other specimens during last decades. It is well known that a crack-tip constraint of test specimens, including curved wide-plates in tension, depends on many geometric and material parameters, for instance, crack length, thickness and width of specimen and material’s hardening characteristic. Thus, in order to obtain relevant fracture resistance from a curved wide-plate in tension representing accurate crack-tip constraint of pipeline of interest, variations of crack-tip constraints of curved wide-plates in tension according to various in-plane and out-of-plane constraint conditions should systematically be quantified.

In the present study, systematic 3-dimensional finite element analyses attempt to investigate the effect of in-plane and out-of-plane parameters on crack-tip constraints of a curved wide-plate in tension.
RCC-MRx Edition 2012: Bolt Design Rules Criteria
Authors: Borazzo C. , Pétesch C. , Lebarbé T. , Ancelet O.
Published: November 2014

This paper describes and explains the contents of bolt and bolted connection design rules included in the present 2012 edition of the French RCC-MRx code ([1], applicable to nuclear installation components). The aim of this work is to describe the rules and their technical and historical background, owing to the widespread fields of application in a NPP and to the relative complexity of methods; bolted connections have often a major safety-related role.

The domain of the RCC-MRx covers high temperature sodium reactors, experimental nuclear facilities (Jules Horowitz Reactor, research reactor under construction in France), and fusion reactor components (ITER Vacuum Vessel). The first major application is at present for ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration).

The bolt connection usual domain varies in a wide range, from very complex configurations, like high temperature, pressure retaining under cyclic load, to simpler flanges for low temperature piping.

In order to fulfill such different needs in design, several sets of rules are included at present in RCC-MRx code, issued from the historical development of previous RCC-MR and RCC-MX codes, from which the “RCC-MRx” version is derived.

In the following, the existing four configurations of bolted connections are identified, the respective rules are summarized, and, finally, a short comparison with other nuclear codes and industrial standards is provided. Available rules to-date concern respectively:

1) Preloaded bolts assuring leaktightness (type “B1”)

2) Preloaded bolts not assuring leaktightness (“B2”)

3) Non-preloaded bolts (“B3”)

4) Flange bolts
Application of Advanced Fatigue Damage Parameters in Comparison With Fatigue Analysis Included in Codes and Standards
Authors: Rettenmeier Philipp , Herter Karl-Heinz , Schuler Xaver , Fesich Thomas Markus
Published: November 2014

Technical components are subjected to cyclic loading conditions that can be arbitrarily complex in the most general case. For analytical fatigue strength verifications in the finite life regime both the uniaxial material characteristics by means of Wöhler curves as well as a representative equivalent fatigue damage parameter (FDP) for multiaxial cyclic loadings have to be determined. For simple loading conditions, the fatigue assessment can be performed using well-known and verified strength hypotheses for quasi-static loading conditions. However, for complex non-proportional cyclic loading conditions with rotating principle stress directions the application of these hypotheses is not sufficiently verified. Hence, advanced stress, strain or energy based strength hypotheses in critical plane formulation are used. These hypotheses require considerable numerical efforts.

The fatigue concept (MPA AIM-Life) enables an assessment of complex fatigue loading conditions with different advanced strength hypotheses. An interface to the finite element code ABAQUS allows the fatigue assessment of complex component geometries. Based on fatigue tests of specimens made from ferritic and austenitic materials under uniaxial and multiaxial loading conditions (tension/torsion) the accuracy of different strength hypotheses is demonstrated. Therefore the fatigue analysis assessment included in codes and standards is compared to different advanced fatigue damage parameters.
Fatigue Crack Propagation Experimental Evaluation and Modeling in an Austenitic Steel Elbow From a LMFBR Primary System Piping
Authors: Garcia-Rodriguez Daniel , Sakakibara Yasuhide
Published: November 2014

In this work the behavior of high temperature (400C) low-cycle fatigue crack propagation during in-plane bending of an elbow from Monju Liquid Metal Fast Breeder Reactor (LMFBR) is presented in three stages. First, experimental measurements made in a real-size laboratory specimen are presented. This test was carried out under displacement-controlled conditions, with artificial defects introduced in the crown parts, where the maximum stress arises. Second, the experimental setup is simulated making use of Finite Element Analysis (FEA), in order to obtain the actual stress distribution through the loaded elbow. Finally, based on the FEA data, deterministic fatigue crack propagation based on the J-integral criterion is compared with the experimental data.

Overall a good agreement was observed between experimental and analysis results, highlighting our capacity to evaluate such phenomena without necessarily incurring into extensive experimental work. In the future these tools will keep supporting the cost-efficient acceleration and improvement of LMFBR design and inspection criteria.