bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermo-Hydraulic Analysis in a Assembly Representative of a Feedwater Nozzle
Authors: Boissiere Xavier , Laine Christian , Doubliez Louis
Published: August 2008

One of the ways to reduce costs in modern nuclear power stations is to increase the life time of the steam generator. Much research is being carried out to gain a better understanding of the mechanical and thermal loads, which are generally overestimated in the interest of safety. One of the main technical problems is the feedwater of the reactor at a relatively cold (40 °C) temperature into the hot steam generator (270 °C). The connection zone, i.e. where the cold pipe is connected to the steam generator, is protected by an annulus inside the feedwater nozzle to reduce the thermal stresses. We have to identify the thermo-hydraulic behavior in that zone in order to accurately assess thermal information. This will give reliable boundary conditions for thermo-mechanical calculations. The configuration of the flows is a superposition of well known elementary fluid mechanic problems which interact strongly. No databases are available for this typical configuration, so we need to qualify the flow before using CFD modelisations. Therefore, a specific experimental testing bench was developed. In this paper, we focus our attention on the understanding of the flow in the one eyed cavity. PIV measurements allows us to identify the flow behavior. Our hypothesizes are demonstrated by a frequencies analysis, and finally confirmed with a numerical model. We also present and discuss the impact on a low thermal loading.
Methods for the Evaluation of Creep Relaxation and the Amplitude of Reverse Plastic Strain for Bodies Subjected to Cyclic Loading
Authors: Chen Haofeng , Ponter Alan R. S.
Published: August 2008

An extension of the upper bound shakedown theorem to load histories in excess of shakedown has been applied in previous papers [1, 2] to the evaluation of a ratchet limit and the varying plastic strain magnitudes associated with a varying residual stress field by the Linear Matching Method. In the present paper, this technique is further applied to the evaluation of creep-reverse plasticity mechanism for bodies subjected to cyclic loading including creep effects. The accumulated creep strain, the varying flow stress and the corresponding varying residual stress field during a creep dwell time are evaluated. The elastic follow-up factors are calculated thereafter. In order to verify the applicability of the proposed method, a monotonic creep computation method based upon the rapid cycle solutions is introduced for comparison. A holed plate subjected to cyclic thermal load and constant mechanical load is assessed in detail as a typical example. The consistent solutions of the accumulated creep strains, the varying flow stresses and the elastic follow-up factors with creep dwell time by these different methods confirm the applicability of the proposed new methods.
Numerical Simulation of Stirrer Oscillations in Consideration of Fluid-Structure-Interaction and Flexible Restraint Systems
Authors: Berger Thomas , Strohmeier Klaus
Published: August 2008

Stirrers are subjected to severe damages when the rotational speed n approaches the critical rotational speed nkrit (eigenfrequency). Appearing resonant vibrations result in huge stirrer shaft bending deformations and possible stirrer damages (see Figure 1). The possibilities of an accurate stirrer design (regarding the shaft vibrations) with analytical calculations [Fischer and Strohmeier (2000)] are often very unsatisfactional: The fluid dynamic effects on the structure and the real, often flexible, restraint systems cannot be considered. Both aspects, however, have an important influence, both on the critical rotational speed nkrit, and the oscillation amplitudes of the stirrer. As a method of solution, a fully coupled interaction of flow field and structural dynamic response of the stirrer is implemented in a commercial CFD-Code. The simulated results are compared to experimental data and show good agreement.
Calculation of Flow Induced Vibration Amplitudes of Radial Sewage Water Pumps
Authors: Benra Friedrich-Karl , Dohmen Hans Josef , Schneider Oliver
Published: August 2008

The extreme vibrations of sewage water pumps with single-blade impellers are induced mainly by interaction of the flow in the impeller and the casing. The resulting periodically unsteady forces affect the impeller and produce radial deflections of the pump shaft. These oscillations of the rotor are transferred to the pump casing and attached pipes. They can be recognized as vibrations at the bearing blocks or at the pump casing. The present contribution describes the investigation of the transient flow in a sewage water pump. The three-dimensional, viscous, unsteady flow in a pump with a single blade impeller is determined by numerical simulation. After that the hydrodynamic stimulation forces are calculated from the so known transient flow field. The forces can be classified into pressure and friction forces. The pressure forces usually exceed the friction forces on several orders of magnitude. A separate view on the fluid-wetted impeller surfaces shows that the pressure forces acting on the blade are clearly larger than the forces at the hub and at the shroud. So they are decisive for the vibration amplitudes of single-blade sewage water pumps. By a following dynamic analysis of the pump rotor using a commercial Finite-Element-Method (FEM) the resulting vibration amplitudes are determined for several operating points. With the known pressure field and the calculated vibration amplitudes the vibration behavior of sewage water pumps can be influenced during the design by changing the relevant construction parameters.
Effects of Flow-Pipe Interaction on Drill Pipe Buckling and Dynamics
Authors: Zhang Qun , Miska Stefan
Published: August 2008

A theoretical study has been performed on the buckling and lateral vibration of drillpipe interacted with incompressible fluid in vertical holes. Particular attention is paid to the flow-pipe interaction near drillpipe neutral zone. A new theoretical model has been established. The flow-pipe interaction forces are characterized in this model. Dimensional analysis has been conducted to generalize this model. An innovative numerical method has been developed to solve the eigensystem. Several numerical examples are provided to show the effects of flow-pipe interaction on drillpipe buckling and dynamics. Results show that drilling fluid has significant hydrodynamic influence on drillpipe statics and dynamics.
The Germano Large Eddy Simulation Model Used for the Simulation of Separated Flow
Authors: Cetindogan Engin , de With Govert , Holdo̸ Arne E.
Published: August 2008

A computational study of unsteady, separated fluid flow was made using the Large Eddy Simulation (LES). As flow problem the turbulent flow past a circular cylinder at a Reynolds number of Re = 3900 was chosen. The objective of this work was to study the numerical and modelling aspects of the dynamic Germano-LES turbulence model. Before LES can be used for applications of practical relevance, such as the flow around a complete aircraft or automobile, extensive tests must be carried out on simpler configurations to understand the quality of LES. Also, the influence of different grid resolutions was examined. Due to the fact of a low Reynolds number, no-slip boundary conditions were used at solid walls. Two different subgrid scale models were applied. In recent years several simulations were carried out using the Smagorinsky-LES model but there is still a lack of experience using the dynamic Germano-LES model, which takes the local flow parameters into account. Several simulations with different parameters and grid-models were carried out both with the Germano-LES model and the Smagorinsky-LES model. Comparisons were made between these two models as well as with several experimental data taken from literature.
Computational Fluid Dynamic Modelling of High Aspect Ratio Cross-Sectional Jets I: The Effect of Orifice Shape on Jet Behaviour
Authors: Wakes Sarah J.
Published: August 2008

High aspect ratio cross-sectional jets (HAR jets) are significant for many industrial applications including offshore hydrocarbon production safety, manufacturing processes, aeronautics and others. Little interest has been paid to such jets as the common belief was that within an acceptable distance from the jet orifice the behaviour emulates that of an axisymmetric jet. Previous experimental and preliminary numerical work [1–4] has shown that this is not necessarily correct. Work has been done to investigate numerically the effect the orifice shape has on the behaviour of the jets. This will be in terms of the curvature of the orifice in comparison to the same aspect ratio with a straight rectangular shape. Simulations have been carried out relating to experimental work [1] as comparison and verification. The spreading of the jet will be assessed as it can have significance in terms of safety, performance and effectiveness. This work enhances previous work [3] and allows an assessment of whether such a curvature in the inlet significantly effects the jet behaviour for two pipe pressures. The choice of turbulence model will also be assessed in terms of the standard two-equation k-ε model and it’s variants the RNG and Realisable models. Later work will investigate the use of Large Eddy Simulation within the context of the geometry used here. This important information will allow for greater understanding for the modelling of such jets in a CFD simulation within a complex industrial problem such as gas dispersion with a hydrocarbon production area. It is realized that the fluid does not emerge as a single velocity from the pipe into the flange and hence to form the inlet for the jet. Therefore the effect of the flow within the pipe and how this effects the emerging jet behaviour is investigated in part II of this paper [5].
Simplified Formulae of Dynamic Liquid Pressure in Rectangular Containers
Authors: Li Hong-Nan , Jia Ying , Wang Su-Yan
Published: August 2008

In this paper, the N-S equation of fluid is solved by the Method of Volume of Fluid (VOF) to obtain the dynamic liquid pressure in a rectangle container. The fluid is incompressible, viscous and changeful with a free surface. The simplified simulating calculation formulae are given in order to apply the method to engineering on the basis of calculation results and analysis. Numerical simulations have shown that the formulae presented here are effective.
Dynamic Fracture Parameters and Calculations for 3-D Cracks
Authors: Cheng Wing , Itoh Shigeru
Published: August 2008

Welded structures such as armor fighting vehicles, shipboard structures or munitions systems are required to sustain intense and rapidly applied dynamic loading due to gun firings, impact of enemy munitions and extreme loading from accident scenarios. Flaws are normally found in various extents in welds depending on quality control of the welding process. It is important to determine critical flaw sizes of three-dimensional cracks in a welded joint under dynamic loading introduced by the above scenarios. Calculation of dynamic fracture parameters of the three-dimensional cracks of various geometrical factors at different locations is important for use the crack growth evaluation, flacture and structural integrity assessment. This paper summarizes the methodologies and results of the dynamic fracture parameter calculations for stationary three-dimensional cracks in cracked structures subjected to both static and dynamic loads.
Three-Dimensional Nonlinear Modeling of Rubber Bushing Subjected to Complex Loading
Authors: Cheng Wing
Published: August 2008

A finite element procedure was used to analyze rubber components on track links of military vehicles for improving their life. The procedure includes consideration of material nonlinearity with the use of a hyper-elastic material model, geometric nonlinearities utilizing surface-to-surface contact interface, large deformation and large strain nonlinear solutions. The procedure was validated with available experimental data. Very good correlation was obtained. The procedure was then applied to analyze a two-lobe rubber bushing using a 3-D model and applying a complex loading sequence including installation of the bushing onto the track links, operative loading of a combined steady-state vertical and torsional load. Results provided detailed insight to the deformation and locations of highly stressed areas at which failure initiation and limiting life might occur.
Fluid-Structure Interaction Analysis of the Adaptive Finger Seal Assembly Using CFD-ACE+/FemStress
Authors: Kudriavtsev Vladimir , Braun M. Jack , Hendricks Robert C.
Published: August 2008

This paper presents base approach and methodology for computational fluid dynamics (CFD) analysis of adaptive finger seals. Finger seals can be utilized to separate high (HP) and low pressure (LP) zones in high speed rotating shaft environment. Seal reduces axial leakage and typically consists of first and second rows of bristles (sticks), which are packed in the staggered arrangement. First row faces high pressure side and second row faces low pressure side. First row of sticks is used to close circumferential gaps between the bristles of the second row, thus forming air tight package. Second row sticks are made with pads, which ride on the thin layer of film and are (in theory) capable of adjusting radial clearance (film thickness) in response to shaft radial movements or to axial pressure fluctuations. Seal adaptivity will depend on its solid structural stiffness, and on fluid film damping and stiffness characteristics. These characteristics are calculated implicitly during the coupled FSI (fluid-structure interactions) simulations.
Qualitative Experimental Study About the Safety Injection in the Cold Leg of a Reactor Pressure Vessel
Authors: Bichet Th. , Martin A. , Beaud F.
Published: August 2008

This paper presents the experimental results of a qualitative study concerning the physical phenomena present in a cold leg and the downcomer of a reactor pressure vessel during a safety injection scenario. This project contributes to the plant life time project. Single-phase and two-phase scenarios have been studied according to the thermal-hydraulic behavior obtained by system codes. This paper shows different physical phenomena visualisations concerning the behavior of the fluid flow at different location in downcomer and in cold leg and physical phenomena in a uncovered cold leg.
Steam Generator Tube Vibrations: Experimental Determination Versus ALE Computation of Fluidelastic Forces
Authors: Bendjeddou Z. , Longatte E. , Adobes A. , Souli M.
Published: August 2008

In heat exchanger tube bundles like in many others industrial applications, fluid structure interaction is a crucial problem to overcome. Flow-induced tube vibration in tube bundles is due to two main kinds of physical effects: (1) fluid-elastic forces caused by structure motion; (2) turbulent forces due to vortex generation at high Reynolds numbers. The second component, turbulent excitation, is independent on structure motion and may generate wear and fatigue damage while the first component may lead to fluid-elastic instability inducing high amplitude displacement and possible tube short term failure. In this context many studies are carried out in order to develop methods for the identification of critical flow velocity in tube arrays. In the present work two methods are presented: (1) the first one relies on experimental measurements, it is fitted with analytical modeling and provides fluid-elastic coefficients; (2) the second one relies on numerical simulation using Computational Fluid Dynamics Codes (CFD) involving moving boundary techniques; it provides fluid force estimates and in some cases it makes it possible to simulate tube vibrations. The first part is devoted to experimental determination of fluid-elastic forces. A numerical method for prediction of fluid-elastic effects in fluid at rest is presented in the second section. Results of both methods are compared in the third part.
Fluid-Structure Interaction in LS-DYNA: Industrial Applications
Authors: Souli M’hamed , Sofiane A. , Olovson Lars
Published: August 2008

A new Fluid Sructure coulping algorithms basesd on the penalty method is dpresented in thi spaper. The coupling algorithm and improved multi-material ALE-capabilities have made LS-DYNA an efficient tool for analyzing large deformation processes, such as bird strike events, forging operations and penetration problems and airbag simumations. This paper contains five example problems that illustrate the current features of the code.
High Explosive Impact Analysis Using LS-DYNA
Authors: Mahmadi K. , Aquelet N. , Souli M.
Published: August 2008

In order to realize numerical simulation of fast transient events, some wave propagation codes, which allow studying the time resolved development of shock wave propagation due to penetration, and detonation, were developed. In this article, Eulerian Multi-material and Arbitrary Lagrangian Eulerian formulations are used. Both formulations have already been used with success in the simulation of fluid with large motion such as the tank sloshing modeling, the overdriven detonation or the simulation of metal cutting processes. This article describes an air-blast simulation using an explicit finite elements code LS-DYNA. The main aim of this investigation is to compare numerical results with experimental results in order to prove the abilities of Eulerian Multi-Material and ALE formulations to treat air-blast problem using an explicit finite element method.
Flow-Induced Vibration in Spiral Finned Gas Tube Bundle Heat Exchangers
Authors: Fischer Michael
Published: August 2008

In the past finned tube bundle heat exchangers were often subject of severe damages due to flow-induced vibration followed by high amounts of loss for the operator. A case of practical importance is the design of spiral finned gas tube bundle heat exchangers that still have been investigated in literature only seldom. Both acoustic resonance and fluidelastic instability can lead to tube rupture within a short period of operation. In this paper analytic calculation methods for tube Eigenfrequencies are extended to spiral finned tubes. The results are in agreement with static and vibrational experiments. Stability criteria for fluidelastic instability are derived by flow channel experiments extending Connor’s equation to the design of spiral finned tube bundles. A number of cases of damage is described. The importance of correct damping values is demonstrated. The scheme reported in this paper is able to avoid damages in spiral finned tube bundle heat exchangers due to fluidelastic instability.
Shock Wave and Biotechnology
Authors: Itoh Shigeru
Published: August 2008

In order to clarify relation between chemical character and physical power, the test of shock wave loading for a living thing was carried out. In case of foraminifera, breeding from a fragment was confirmed in the observation test, after shock wave loading. And, as for the bivalve, the shell was very easy separated from organics. In the experiment of the underwater shock wave loading to a wood, alternative destruction of pit membrane realized improvement in moisture permeability. Furthermore, when the super-criticality disassembly experiment was conducted using the wood after shock wave load, the very good result was obtained.
Basic Study for Crushing of Frozen Soil by Underwater Shock Wave
Authors: Watanabe Toshiaki , Itoh Shigeru , Hamada Toru , Kiyama Osamu , Kuroyama Yutaka , Nakachi Akira
Published: August 2008

The final aim of study is confirm a new technique that can crush frozen soil and/or ice on the farm by underwater shock wave generated underwater explosion of explosive. In the cold region, for example, North Japan, Russia, Norway, and Sweden, etc., this technique can makes carry out early sowing and having large harvest. Especially, in Hokkaido prefecture Japan, if sowing is carried out in April, we may be expected to have a 150% of harvest of ordinary season due to the total of the sunshine hours. At first, we carried out experiments, which use detonating cord and ice block for the case of shock wave that collides aslant to ice. We obtained result that strength of the ice strongly depends on existence of bubble in the ice. So, we carried out experiments, which use explosive and ice block for the case of shock wave that collides verticality to ice. And, as the first step of pressure measurement, we experimented using the plate device that can detect shock wave. The process of breaking of ice was observed by using of the high-speed camera.
Numerical Simulation for the Multiple Cylindrical High Pressure Device
Authors: Itoh Shigeru , Kiyama Osamu , Morimoto Hideyuki , Kakimoto Etsuji
Published: August 2008

It is economically that we actually examine with the condition, which was chosen by numerical analysis. Therefore, the necessity for numerical analysis has been increasing and more realistic numerical analysis is called for. In this paper, in order to perform more realistic numerical analysis for explosion in a pipe, sliding boundary condition of Mark L.Wilkins was applied to the treatment of the boundary which different materials, such as an explosive and its container. Applying this sliding boundary condition is able to prevent cell destructions. And this leads the successful simulation and more realistic numerical analysis. The feature of the explosive applications is to obtain the high energy, super-high pressure and extreme temperature that are difficult to obtain by the static methods. In this paper, the numerical simulation for powder compaction was carried out in order to evaluate the performance of a numerical analysis and the characteristic of the device. This device was so called cylindrical method, and the powder, which filled up into the cylindrical container, was compressed toward the central part from the outer wall side of a pipe by the super-high pressure generated by the detonation of the surrounding explosive. In this devise, water is set between the explosive part and powder part to change the pressure that acts on the powder part, and paraffin is set at the central part of this device in preventing the extreme pressure raise. Additionally, many boundaries were formed with the explosive, water, powder, and paraffin part and each container in this device. Therefore, sliding boundary condition was very important to apply for all boundaries. From numerical analysis results, it was found that pressure which acts on the powder part does not change so much if the radial direction thickness of the explosive part is 20mm or more. Moreover, it was also confirmed that the pressure of the powder part was made high by setting the water part, and that the extreme pressure raise was prevented by setting the paraffin part.
Shock Consolidation System of Metallic Powder Using Concentric Double Cylindrical High Explosive
Authors: Hamada Toru , Nakamura Yuichi , Murata Kenji , Kato Yukio , Itoh Shigeru
Published: August 2008

Concentric double cylindrical high explosive [1] was caused Over Driven Detonation (O.D.D.) phenomenon [2], and it was found that this method was suitable for the shock consolidation system of the metallic powder by the numerical analysis [3] [4] [5] [6] and the pressure measurement [7] [8]. Therefore the shock consolidation [9] of the metallic powder that was one of the techniques of material development was made by using the concentric double cylindrical high explosive. As a result, the good sample of Tungsten Carbide was obtained.
The Performance of Pressure Vessel Using Concentric Double Cylindrical High Explosive
Authors: Hamada Toru , Nakamura Yuichi , Murata Kenji , Kato Yukio , Itoh Shigeru
Published: August 2008

In recent year, it has been hoped to develop a device that generate high pressure in the field of the material consolidation. Therefore a phenomenon of over driven detonation (O.D.D.) [1] that was one of the detonation phenomenons has been researched. The detonation velocity and pressure that is higher than Chapman-Jouguet state generate in the state of O.D.D.. But, in the method of using the flyer plate that has been investigated, it is difficult to apply to the material consolidation since the region where O.D.D. phenomenon generates is very small. Therefore, as a new method of effectively generating O.D.D., the method of combining two kinds of the high explosives was developed. This method is a technique that is generated O.D.D. in the low velocity explosive by making a double cylindrical explosive of the high velocity explosive and low velocity explosive. The detonation pressure of low velocity explosive in a double cylinder was measured by Manganin gauge. The detonation pressure was 2.0 times over higher than the Chapman-Jouguet pressure.
Quasi-Static Loading Rate Effect on the Master Curve Reference Temperature of Ferritic Steels and Implications
Authors: Hall J. B. , Yoon K. K.
Published: August 2008

It has long been recognized that there is a considerable difference between the dynamic and quasi-static fracture toughness reference temperature. However, it has not been clear whether this loading rate effect extends into the quasistatic loading regime. The current fracture toughness reference temperature test standard for ferritic steels (ASTM E1921) specifies an allowable quasi-static loading rate range spanning 100 fold. Recently obtained data from the IAEA JRQ material suggests that the same loading rate effect extends throughout this allowable quasi-static loading rate range. The loading rate effect could amount to a difference in the measured reference temperature of 23°C (41°F) between the extremes of the specified range. This paper presents the data demonstrating this effect, examines different ways of calculating the loading rate, suggests changes to related to the test standard, and discusses the use of applying the loading rate effect on reference temperature.
Effect of Boundary Conditions of Failure Pressure Models on Reliability Estimation of Buried Pipelines
Authors: Lee Ouk Sub , Pyun Jang Sik , Kim Dong Hyeok
Published: August 2008

This paper presents the effect of boundary conditions of various failure pressure models published for the estimation of failure pressure. Furthermore, this approach is extended to the failure prediction with the help of a failure probability model. The first order Taylor series expansion of the limit state function is used in order to estimate the probability of failure associated with each corrosion defect in buried pipelines for long exposure period with unit of years. A failure probability model based on the von-Mises failure criterion is adapted. The log-normal and standard normal probability functions for varying random variables are adapted. The effects of random variables such as defect depth, pipe diameter, defect length, fluid pressure, corrosion rate, material yield stress, material ultimate tensile strength and pipe thickness on the failure probability of the buried pipelines are systematically investigated for the corrosion pipeline by using an adapted failure probability model and varying failure pressure model.
An Analytical Method to Evaluate J Values in Elbows Submitted to Mechanical Loading
Authors: Marie Ste´phane , Kayser Yann
Published: August 2008

Regarding of structures behaviour which can be found in nuclear reactor, most of assessment method are based on the valuation of parameter J. This paper deals with the J calculation in cracked elbows submitted to internal pressure and various bending moments. Recent works on elbows including a semi-elliptical defect performed in the frome of the A16 guideline improvements are presented. The A16 methodology is based on the reference stress concept (named CEP method): It consists in an amplification of the elastic value of J by a plastic correction deduced from the reference stress. The elastic value of J is deduced from the influence factors of the pipe and from analytical relations for elastic nominal stresses. The reference stress estimation is performed using two equivalent stresses corresponding to the elastic and plastic behaviours of the cracked component. The analytical relations for the elastic value J and the reference stress determinations are presented and validated using 3D FE calculations.
Mechanical Analysis of Underclad Cracks in Reactor Pressure Vessel Nozzles
Authors: Verdiere Nicolas , Churier-Bossennec Henriette , Champigny Franc¸ois
Published: August 2008

During the in-service inspection in 1999 in Tricastin 1 Nuclear Plant, underclad cracks had been discovered in the core shell. Following specific justification of these defects, other parts of the reactor vessel also sensitive to this kind of defects have been re-examined, and particularly RPV nozzles, which are classified as “concerned by fast fracture”. Recent assessments with large defects, superior to maximum realistic ones, have been conducted in different sections in the reactor vessel inlet and outlet nozzles: circular cracks of 10 mm in the inner radius, and 20 mm depth in the straight section. Theses assessments highlighted the verification of acceptance criteria in various, normal and emergency conditions with large margins. Fatigue analysis has also been conducted. For underclad cracks located in the inner radius of RPV inlet nozzles, a small propagation in the austenitic cladding is demonstrated but would not lead to any cladding perforation within 40 years.
Elastic-Plastic Fracture Mechanics Assessment of Test Data for Circumferential Cracked Pipes
Authors: Huh Nam-Su , Shim Do-Jun , Kim Yun-Jae , Kim Young-Jin
Published: August 2008

This paper presents experimental validation of two reference stress based methods for circumferential cracked pipes. One is the R6 method where the reference stress is defined by the plastic limit load. The other is the enhanced reference stress method, recently proposed by the authors, where the reference stress is defined by the optimized reference load. Using thirty-eight published pipe test data, the predicted maximum instability loads according to both methods are compared with the experimental ones for pipes with circumferential through-thickness cracks and with part circumferential surface cracks. It is found that the R6 method gives conservative estimates of the maximum loads for all cases. Ratios of the experimental maximum load to the predicted load range from 0.54 to 0.98. On the other hand, the proposed method gives overall closer maximum loads than R6, compared to the experimental data. However, for part through-thickness surface cracks, the estimated loads were slightly non-conservative for four cases, and possible reasons were fully discussed.
An Analytical Model for Thermal Fatigue Crack Initiation and Propagation in Mixing Zones of Piping Systems
Authors: Musi Ste´phanie , Beaud Fre´de´ric
Published: August 2008

Nuclear power plants piping systems necessarily include connections of branches conveying fluids at different temperatures. Thermal-hydraulic fluctuations arising from the turbulent mixing of the flows possibly affect the inner wall of the pipes and lead to fatigue damage. This paper aims at presenting an analytical model for the mixing zone thermal-mechanical problem and consecutive crack initiation and propagation analyses.
Thermal Fatigue in Mixing Tees: On-Going Program to Support Code Rule Improvements
Authors: Faidy Claude
Published: August 2008

Following the CIVAUX 1 incident of a leak on RHR system, EDF has developed a step by step procedure to screen and analyse similar locations: mixing tees with long duration at high ΔT between the 2 fluids. The paper summarise the procedure, the background and some R&D results that support this procedure. The procedure is based on: • screening criteria without any duration consideration, only ΔT and material; • a simplified and conservative estimation of usage factor; • a detailed analyses of usage factor and crack growth rate, based on specific data collection of operating transients and fabrication parameters. Around that procedure, EDF launched an R&D program on fatigue curves and different fatigue reduction factors; thermal fatigue test on structures and review the agreement of predictions with French RHR system field experience. The major results confirm that, to-day, present Code rules (RCCM or ASME) are not totally in agreement with our results. Proposals and suggestions of future works are discussed in the paper.
The Application of Fracture Mechanics to Predict the Critical Initial Crack Length for Inspection
Authors: Liu C. T.
Published: August 2008

In this study, a method is developed based on fracture mechanics, for predicting the equivalent critical initial crack size, aic in a particulate composite material. The predicted aic is the crack size that should be used to develop an inspection criterion to determine the reliability of a structure made of the particulate composite material.
Computational Modelling of High Temperature Steady State Crack Growth Using a Damage-Based Approach
Authors: Yatomi Masataka , O’Dowd Noel P. , Nikbin Kamran M.
Published: August 2008

In this work a computational study of creep crack growth in a carbon manganese steel is presented. The constitutive behaviour of the steel is described by a power law creep model and the accumulation of creep damage is accounted for through the use of a well-established model for void growth in creeping materials. Two dimensional finite element analyses have been performed for a compact tension specimen and it has been found that the predicted crack growth rate under plane strain conditions approaches that under plane stress conditions at high C* levels. Furthermore it has been shown, both experimentally and numerically, that an increase in test temperature causes the convergence of the cracking rate to occur at higher values of C*. This trend may be explained by the influence of crack-tip plasticity, which reduces the relative difference in constraint between plane stress and plane strain conditions. The constraint effect has been quantified through the use of a two-parameter characterisation of the crack tip fields under creep conditions.
C-Specimen Fracture Toughness Testing: Effect of Side Grooves and η Factor
Authors: Kim Y. , Chao Y. J. , Pechersky M. J. , Morgan M. J.
Published: August 2008

Elastic-plastic crack front fields in arc-shaped tension specimens (C-specimens) were analyzed by a three-dimensional finite element method. The effect of side grooves on the ductile fracture behavior was investigated by studying the J-integral distribution, plane-strain constraint parameter, and development of plastic zones and comparing to experimental data. The applicability of the η factor (derived for use with compact tension specimens) for the calculation of J-integral values for the C-specimen was also investigated. The results show that side grooves promote and establish near plane strain conditions at the crack front in sub-size specimens. It was also found that a two-dimensional plane-strain analysis in conjunction with the standard American Society for Testing and Materials (ASTM) tests was sufficient to determine the fracture toughness values from side-grooved C-specimen. The results indicate the η factor for compact tension specimen as specified in the ASTM standards appears to produce reliable results for the calculation of J of C-specimens.
A Simplified Evaluation of Stress Intensity Factors for a Small Diameter Pipe Penetrating a Thick Plate
Authors: Emery John M. , Miyazaki Katsumasa , Ingraffea Anthony R.
Published: August 2008

Recent trouble with stress corrosion cracking in the internal parts of boiling water reactors and similar issues found in pressurized water reactors has prompted interest in developing simplified methods to determine stress intensity factors for such cracks. Currently, there are many practical and accurate simplified methods to calculate stress intensity factors for a surface crack in plates and pipes. However, there are none that deal with the complex geometry that can arise within the reactors. The complex geometry found within the vessels often entails reentrant comers, welds, holes, and other stress amplifiers. This paper sets forth a means by which some commonly known and accepted simplified solutions to cracks in pipes and plates can be modified to improve the accuracy of stress intensity factors when applied to this complex geometry. The effort to do so included axisymmetric and fully three-dimensional numerical modeling of both the cracked and uncracked body with a variety of assumed surface flaws. It was confirmed that the simplified methods lead to exceedingly conservative estimates for the stress intensity factors of the complex geometry. Finally, a correction factor based on the axisymmetric analyses was applied to the three-dimensional results to improve the accuracy of the simplified solutions.
Application of Master Curve Data for Reactor Vessel Steels
Authors: Server William L. , Griesbach Timothy J. , Rosinski Stan T.
Published: August 2008

The Master Curve method has been developed to determine fracture toughness of a specific material in the brittle-to-ductile transition range. This method is technically more descriptive of actual material behavior and accounts for the statistical nature of fracture toughness properties as an alternative to the current ASME Code reference toughness curves. The Master Curve method uses a single temperature, To, as an index of the Master Curve fracture toughness transition temperature. This method has been successfully applied to numerous fracture toughness data sets of pressure vessel steels contained in the Master Curve database, including the beltline materials for the Kewaunee reactor pressure vessel. The database currently contains over 5,500 toughness data records for vessel weld, plate and forging materials, and it is currently being updated to include more recent fracture toughness data. Application of Master Curve fracture toughness data to reactor pressure vessel (RPV) integrity evaluations requires some assumptions relative to the degree of constraint in the fracture toughness test specimens versus the actual assumed RPV flaw. An excessive degree of conservatism can be introduced if the constraint levels are substantially different. In performing a Master Curve evaluation, the analysis may be restricted by the type of fracture toughness data available. Any excess conservatism should be appropriately considered when the overall safety margin is applied. For example, the precracked Charpy three-point bend specimen actually has some advantages over the compact tension specimen when the application involves a shallow surface flaw in a RPV wall. This paper analyzes some key fracture toughness results from several weld data sets containing both unirradiated and irradiated data to evaluate constraint effects in fracture toughness and pre-cracked Charpy specimens. The evaluated To values were compared to determine if there is any difference in bias from specimen geometry between the unirradiated and irradiated data.
Validation of Constraint Based Methodology in Structural Integrity: VOCALIST — Analytical Programme
Authors: Keim Elisabeth , Ludwig Michael , Bass Richard , McAfee Wallace , Yin Sean , Williams Paul , Wadier Yves , Keina¨nen Heikki , Wallin Kim , Lidbury David , Sherry Andrew , Marie Ste´phane , Chapuliot Ste´phane , Gilles Philippe , Eisele Ulrich
Published: August 2008

The aim of the European Community (EC) project VOCALIST (Validation of Constraint-Based Assessment Methodology in Structural Integrity) is to develop and validate innovative procedures for assessing the level of, and possible changes to, constraint-based safety margins in ageing nuclear pressure boundary components. An iterative process of experiment and analysis will address this overall objective. The analytical investigations within VOCALIST cover all three ferritic materials used in the experimental program. Two of the three materials are investigated in the ductile to brittle transition regime and the third material will be tested in the ductile regime. The main effort is to predict the results of the large-scale tests in terms of constraint effects. All participants use constraint based methods, which as a first step are calibrated to the behaviour of standard specimens and then applied to the structural features and (or) large scale tests of each material. In this contribution the progress since last year of the analytical program of VOCALIST will be reported. The analyses of the specimens and components under investigation are highlighted with respect to modelling aspects and the first results are presented.
First Ductile Tearing Test of the VOCALIST Project on a Cracked Ferritic Pipe Submitted to a Four-Point-Bending Moment: Experiment and Modelling
Authors: Marie S.
Published: August 2008

The aim of the European Community project VOCALIST (Validation of Constraint-Based Assessment Methodology in Structural Integrity) is to develop and validate innovative procedures for assessing the level of stress-based safety margins in ageing pressure boundary components. This project includes ductile tearing experiments on cracked pipes submitted to a four-point bending moment. The first test have been performed on a circumferential through-wall defect at room temperature. This paper describes the first pipe test and presents experimental results. Then various finite element analyses have been performed to check the validity and the numerical stability of the models. Predictions from the classical J-Δa approach, the Ji-Gfr approach of the Rousselier model are compared and discussed.
Programme VOCALIST: The Energy Approach of Elastic-Plastic Fracture Mechanics Applied to the Analysis of the Constraint Effect
Authors: Wadier Yves , Bonnamy M.
Published: August 2008

In the context of the programme VOCALIST, different tests have been performed on SENB specimens made of an high toughness ferritic steel and containing deep and shallow cracks, at different temperatures, in order to analyse the shallow crack effect with different approaches. At EDF, an energy approach has been developed and an energy release rate, called Gp, has been defined. Conversely to the J-approach, this energy approach is, in principle, valid in all situations, and can be used in particular to study the constraint effect. The results obtained with this approach on the specimens used in VOCALIST cannot be compared to experimental results, which are not available at the present time, but they are consistent with the numerous results obtained in different experimental programs. In particular, the shallow crack effect is clearly obtained if we assume that the critical value of the parameter Gp is a material characteristic.
Flaw Evaluation Procedures and Acceptance Criteria for Nuclear Components in ASME Code Section XI
Authors: Cipolla Russell C. , DeBoo Guy H. , Bamford Warren H. , Yoon Kenneth K. , Hasegawa Kunio K.
Published: August 2008

The primary objective of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section XI is to provide the rules and requirements for maintaining pressure boundary integrity of components, piping, and equipment during the life of a nuclear power plant. Pressure boundary integrity in terms of assuring resistance to sudden and catastrophic failure has been an essential objective of the ASME Code since its inception in 1914. These objectives are especially important in ASME Section XI since maintaining pressure boundary integrity of components has a crucial role in ensuring safe and reliable operation in nuclear operating plants. The purpose of this paper is to describe the evaluation procedures, methods, and acceptance criteria for flaws detected in plant components during implementation of in-service inspection surveillance program. For nuclear plant components, pressure boundary integrity includes both leak integrity (no leakage from the reactor coolant system) and structural integrity (no rupture or burst of the pressure boundary). The evaluation requirements in ASME Section XI provide specific rules for assessing the acceptance limits for flaw indications that may be detected during the service life of a nuclear component. In addition to describing current flaw evaluation procedures, details of recent Code developments and improvements are discussed.
General Presentation of French Codified Flaw Evaluation Procedure: RSE-M
Authors: Faidy Claude
Published: August 2008

The RSE-M Code “Rules for In-service Inspection of Nuclear Power Plant Components” defines the requirements for in-service inspection of French Pressurized Water Reactor’s. The scope covered by the RSE-M is all the surveillance and in-service inspection program for safety class components with a special attention to class 1 components. A large concern for this code is the flaw evaluation procedure for an in-service inspection defect. Generally the defect has to be repaired, but in order to postpone the repair or to accept some small defect a complete procedure is proposed for safety class components: fatigue crack initiation, fatigue crack growth, brittle and ductile rupture. All the details and the validation limits are included in non-mandatory appendices. The methods are usable for nuclear and non-nuclear pressure equipment. Partial safety factors and material properties are more PWR oriented. The paper presents the different parts of the procedure, their validations and major on-going developments.
Flaw Evaluation and Allowable Flaw Sizes of Nuclear Piping in JSME Code
Authors: Hasegawa Kunio , Kobayashi Hideo , Kashima Koichi
Published: August 2008

A flaw evaluation code for nuclear power plants has been developed at the Japan Society of Mechanical Engineers (JSME) in 2000 and revised adding inspection rules in 2002. Then the code consists of inspection for nuclear components and evaluation procedures of flaws in Class 1 components detected during in-service inspection. This paper introduces the summary of the JSME Code and describes two kinds of allowable flaw sizes, Acceptance Standards and Acceptance Criteria, for Class 1 pipes in the flaw evaluation procedures. In addition, these allowable flaws are compared with those in the ASME (American Society of Mechanical Engineers) Code Section XI.
Flaw Evaluation Procedures and Acceptance Criteria for Nuclear Piping in ASME Code Section XI
Authors: Scarth Douglas A. , Wilkowski Gery M. , Cipolla Russell C. , Daftuar Sushil K. , Kashima Koichi K.
Published: August 2008

Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code provides rules and requirements for maintaining pressure boundary integrity of components, piping, and equipment during the life of a nuclear power plant. Evaluation procedures and acceptance criteria for the evaluation of flaws in nuclear piping in Section XI of the ASME Code were first published in 1983 and have been under revision for the past several years. This paper provides an overview of the procedures and acceptance criteria for pipe flaw evaluation in Section XI. Both planar and nonplanar flaws are addressed by Section XI. The evaluation procedures and acceptance criteria cover: failure by plastic collapse as characterized by limit load analysis; fracture due to ductile tearing prior to attainment of limit load, as characterized by elastic-plastic fracture mechanics (EPFM) analysis; and brittle fracture as characterized by linear elastic fracture mechanics (LEFM) analysis. A major revision to the evaluation procedures and acceptance criteria was published in the 2002 Addenda to Section XI. Evaluation procedures and acceptance criteria in the 2001 Edition, as well as the revisions in the 2002 Addenda, are described in this paper. Code Cases that address evaluation of wall thinning in piping systems, as well as temporary acceptance of flaws in moderate energy piping systems, are also described.