bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analytical Study of Two-Phase Flow Instability in a Natural Circulation PWR Auxiliary Feedwater System
Authors: Jo Jong Chull , Moody Frederick J. , Do Kyu Sik 
Published: January 2014

A PWR incorporates a passive auxiliary feedwater system (PAFS), a closed natural circulation loop which is aligned to feed condensed water to its corresponding steam generator (SG). During its operation, saturated steam in the SG secondary side moves up due to buoyancy force and passes through a steam line, and then flows into a tube-tank type passive condensation heat exchanger where steam is condensed inside the tubes while the tube outer surfaces are cooled by the pool water. The condensate water is passively fed into the SG economizer by gravity. Because a natural circulation loop is susceptible to two-phase flow instability, it is requisite to confirm the system is designed adequately to avoid the potential challenges to its operational safety due to the instability.
This paper presents an analytical approach for assessing if the PAFS has possible thermal and fluid mechanical characteristics which could lead to an undesirable unstable or oscillating condensate water level in the vertical pipe section. Both steady and unsteady analytical solutions for a simplified natural circulation loop model of the PAFS were derived in terms of the condensate water level and velocity in the vertical pipe section. From the solutions, the criteria for determining a potential for two-phase instability in the system were obtained.
Evaluation of Mechanical Properties of the Reactor Pressure Vessel Materials Changes by Small Punch Test Application
Authors: Petzová Jana , Březina Martin , Kupča Ľudovít 
Published: January 2014

The reactor pressure vessel (RPV) is the most important component of nuclear power plants. RPV steel near the reactor core is subject of irradiation degradation due to the fast neutron flux. Irradiation processes are rather complex but after all the damage of the steel crystal lattice lead to the changes of RPV mechanical properties as well as the shift of the transition temperature to higher values.
Hence, monitoring of the RPV material irradiation changes must be proved during the all nuclear power plant (NPP) operation.
The new surveillance specimen programs (SSP) at all Slovak NPPs reactors included, among the standard mechanical tests, also new types of evaluation mechanical properties due to method Small Punch Test (SPT).
Bench-KJ: Benchmark on Analytical Calculation of Fracture Mechanics Parameters KI and J for Cracked Piping Components — Progress of the Work
Authors: Marie S. , Faidy C. 
Published: January 2014

For many design and ageing considerations fracture mechanics is needed to evaluate cracked components. The major parameters used are K and J. For that, the different codes (RSE-M appendix 5, RCC-MRx appendix A16, R6 rule, ASME B&PV Code Section XI, API, VERLIFE, Russian Code…) propose compendia of stress intensity factors, and for some of them compendia of limit loads for usual situations, in terms of component geometry, type of defect and loading conditions.
The benchmark bench-KJ, proposed in the frame of the OECD/IAGE Group, aims to compare these different estimation schemes by comparison to reference analyses done by Finite Element Method, for representative cases (pipes and elbows, mechanical or/and thermal loadings, different type and size of cracks). The objective is to have a global comparison of the procedures but also of all independent elements as stress intensity factor or reference stress.
The benchmark will cover simple cases with basic mechanical loads like pressure and bending up to complex load combinations and complex geometries (cylinders and elbows) including cladding or welds: these cases are classified into 6 tasks.
Twenty-nine partners are involved in this benchmark. This paper gives a short overview of the different tasks of the benchmark and presents the analysis of the results for the four first tasks, devoted on the elastic stress intensity factor calculation (task 1) and J calculation in cracked pipes (taks 2 and 3).
Effects of Nut Thinning on the Bolt Load Reduction in Bolted Flange Joints Under Internal Pressure and Bending Moments
Authors: Kikuchi Tsutomu , Sawa Toshiyuki 
Published: January 2014

In the depreciation evaluations for pressure equipment, it is important for engineers to evaluate the reduction in the sealing performance in bolted flange joints under external loading. In this study the effects of nut thinning due to corrosion on the bolt load reduction in 3 inch and 20 inch bolted flange joints under internal pressure and bending moments are investigated. The stress distributions in the bolted joints, in particular, in using bolts are examined with both FEM calculations and measurements. The obtained stress distributions in the bolts are discussed from the strength standpoint. The sealing performance of the joints with thinned nuts are measured and it is discussed concerning the effect of the thinned nuts on the sealing performance. The following results are obtained:
1) when the height of the nut was kept constant at the 2/3 height of the original dimensions according to the JPI standard, the sealing performance of the joints with the thinned nuts is the same as that with the original height nuts under internal pressure and bending moments.
2) when the height of the nut was reduced to 1/3 height of the original dimensions according to the JPI standard, the sealing performance of the joints could no longer be assured. Thus, it can be concluded that the reduction of the nuts should be checked.
Damage Modeling of the Load-Bearing Capacity of Damaged Steam Generator Tubes in Nuclear Power Plants
Authors: Schuler Xaver , Seidenfuss Michael , Gehrlicher Sarah , Mahlke Jan 
Published: January 2014

In austenitic steam generator (SG) tubes installed in nuclear power plants (NPP), wall thinning and crack formation caused by stress corrosion cracking have been observed. These cracks are manly orientated in longitudinal direction of the tube but also in a few cases circumferential oriented cracks nave been found. Because of the small crack depths and wall thickness, the application of fracture mechanics assessments of the load-bearing capacity of these cracks is very limited. Equally it is almost impossible to determine the necessary fracture mechanics parameters for such component geometries.
Damage mechanics models are able to describe the experimentally observed processes in smooth and cracked specimens. They have no restrictions like fracture mechanics models.
In this paper, the damage model of Rousselier was used to describe the failure behavior and load-bearing capacity of cracked steam generator tubes. The operation temperature of these tubes is about 300 °C. The Rousselier parameters for the austenitic steel X 2 NiCrAlTi 32-20 (1.4558) of the tubes were determined by using tensile tests and burst tests at temperatures of 20 °C and 300 °C. With this damage model it is possible to evaluate the existing limit values for burst pressures and necessary safety factors for the plugging of steam generator tubes in nuclear power plants. These results can also contribute to the safety evaluation of stress corrosion cracking in steam generator tubes.
FFS Assessment for Material Degradion due to Fire Damage of Pressure Equipment
Authors: Kikuchi Tsutomu , Kurihara Tomoyuki , Nishikawa Toru , Fujishiro Tomoyuki , Nagata Satoshi , Murata Hidenori 
Published: January 2014

The fire damage FFS assessment is based on the material degradation associated with heat exposure. The proposed identification of heat exposure zone will be provided in the API 579-1/ASME FFS-1 Standard. As the useful judgments, temper colors and mechanical properties such as tensile strength, hardness, impact energy, ductility and so on for the damaged materials.
However, the reference temper colors are shown only by the names of colors without photographic examples and the details of metallurgical analysis are not available in the Standard.
This paper presents the temper color reference shows by presenting several photographic examples of different exposed temperature, elapsed time and cooling rates for carbon steel and stainless steel.
The metallurgical analysis guide describes typical degradations in mechanical properties and appearances in microstructure observed in the materials exposed to fire, evaluation criteria, procedure for replica preparation, personnel qualification and so on.
Development of a Two-Way Fluid Structure Coupling for Studying Power Transformers Subjected to Internal Dynamic Over-Pressures
Authors: Landis Ben , Ahmed Omar , Yoon Sangpil , Goj Anne M. , Périgaud Guillaume 
Published: January 2014

Within the highly competitive electricity market, companies often reduce costs by using aging equipment and by overloading their transformers. These conditions substantially increase the risk of transformer explosions. These incidents are caused by electrical arcs occurring within oil filled transformers. The arc, within milliseconds, vaporizes the surrounding oil and the generated gas is pressurized because the liquid inertia prevents its expansion. The pressure difference between the gas bubble and the surrounding liquid oil generates a dynamic pressure peak, which interacts with the transformer. The reflections generate pressure waves that lead to transformer rupture since transformers are not designed to withstand these pressures. This results in dangerous explosions, expensive damages and possible environmental pollution. Despite all these risks, and contrary to usual pressure vessels, no specific standard has been set to protect sealed transformer tanks subjected to large dynamic overpressures.
In order to study transformer rupture and its prevention, experiments have been performed on transformers. However, safely carrying out live tests is difficult and expensive. In order to limit the costs, to reduce the risks and to gain insight on these phenomena numerical simulation tools are necessary. First a computational fluid dynamics solver was developed; it is based on an unsteady compressible two-phase flow model, the equations parameterizing the system are solved using a 3D finite volume method. Previous papers showed the ability of the hydrodynamic tool to study in detail (1) dynamic pressure wave propagation inside transformer oil that leads to transformer rupture and (2) depressurization induced by efficient protection means. Later, the hydrodynamic numerical tool has been one-way coupled with Code_ASTER, a dynamic structural analysis package, to create a fluid structure interaction (FSI). Preliminary results were shown and this strategy has been applied to the study of more complex electrical equipment.
The present paper’s goal is to illustrate the development and application of a two-way coupling for the aforementioned fluid structure interaction strategy. The methodology for the enhanced coupling is explained and the simulation results about the structural behavior caused by these dynamic pressures are presented.
Simulating Residual Stress Profiles of Welds With Re-Heat Cracking in an Ex-Serviced AISI 316H Weld Header
Authors: Zhou Haoliang , Biglari Farid , Davies Catrin M. , Nikbin Kamran 
Published: January 2014

In the current study, simulating residual stress distributions has been investigated for an AISI 316H austenitic stainless steels weld header and compared to actual measured residual stresses. These welds connect the outlet nozzle to the archetypal header 1B1/1 which was ex-serviced from Heysham power plant in UK. Finite element (FE) analyses of different load and boundary conditions have been performed to predict the optimum stress distribution around the cracking region to compare with available measured residual stress distributions in the literature. The FE predictions show that a remote displacement control tensile load on the nozzle with fixed vertical movement of cylinder can best fit the measured residual stress distribution.
Hardness profile across the weld cross section indicates that the hardness gradually decease from HV 210 in weld metal to HV 160 in base metal, however, in the fusion away from 3 mm, the hardness were over HV 240. The facts indicate that the primary crack is likely to initiate at high hardness boundary and propagate in the direction of the highest principal stress regardless of the material hardness. Hypothesis of mechanism to the crack propagation is considered and proposals to predict damage and cracking in the header using FEM are presented.
Flow-Induced Transverse Vibration of a Cantilevered Prism and Vibration-Generated Power Using Magnetostrictive Material
Authors: Kiwata Takahiro , Yamaguchi Makoto , Kono Takaaki , Ueno Toshiyuki 
Published: January 2014

Free-vibration tests of a cantilevered rectangular prism with a side ratio of less than D/H = 0.5 (D, depth of the rectangular prism in the flow direction; H, height of a rectangular prism) that experiences low-speed galloping at a lower reduced velocity than the resonant reduced velocity were conducted in a water tunnel. We also carried out a power generation experiment using an iron-gallium alloy, which is a magnetostrictive material, to investigate the possibility of harvesting energy from a flow-induced transverse vibration. The effects of the side ratio of the rectangular prism and the configuration of a fin that was fitted on the back of a rectangular prism to increase the flexural rigidity on the response amplitude were investigated. The vibration of a rectangular prism with D/H = 0.1 occurred at a lower reduced velocity than that of the other rectangular prisms. This prism has the largest increment rate of the non-dimensional response amplitude ηrms for reduced velocity Vr, and the vibration has an uniform amplitude for each reduced velocity. The reduced velocity at the 20% non-dimensional response amplitude of a rectangular prism Vr0.2 decreases linearly with decreasing side ratio D/H. The response amplitude of the rectangular prism with D/H = 0.2 is only slightly dampened for all values of the reduced mass-damping parameter Cn.
The values of Vr0.2 of the rectangular prism with a fin increased as the depth ratio of the fin increased. The response amplitude of the rectangular prism with/without a fin was found to be related to the second moment of area of the prism. The energy harvester using magnetostrictive material and a rectangular prism with D/H = 0.2 generates a maximum electric power of 8.8 mW.
Effect of Make-Up on the Structural Performance of Standard Buttress Connections Subjected to Tensile Loading
Authors: Galle Timothy , De Waele Wim , De Baets Patrick 
Published: January 2014

When establishing oil wells, pipe sections are connected by means of threaded couplings. In an effort to minimize the possibility of failure by jumpout, standard buttress connections were introduced. Part of their strength is directly acquired as a result of radial interference during make-up.
This paper discusses the results of a numerical study evaluating the effect of make-up on the performance of a standard 4.5 inch API buttress connection when axial tensile force is applied. In order to characterize the structural performance, the load distribution along the coupling length is evaluated, combined with a parameter defining thread separation. The latter is indicative for jumpout and the tendency of creating a leak path throughout the thread helix.
From the results it is clear that relative axial displacement within the coupling occurs, even when made up, because of an initial clearance among the load and stab flanks. This clearance may cause a connection to leak through the thread helix when available thread compound cannot heal this leak path. Despite undesirable effects on the sealability and rigidness of this joint, such a clearance is required to decrease frictional forces during make-up while maintaining the desired radial interference.
A CFX Simulation of the OECD/NEA T-Junction Benchmark
Authors: Gillis Jay C. , Belley Benoit P. , Romero Martin 
Published: January 2014

In response to a solicitation for Computational Fluid Dynamic (CFD) simulations of flow in a T-junction from the Nuclear Energy Agency of the Organization for Economic Co-operation and Development (OECD/NEA) [1], Structural Integrity (SI) Associates of San Jose, CA, USA has completed a simulation using the commercially available CFD code ANSYS-CFX. The simulation was carried out for geometry and flow conditions matching an experiment underway at Vattenfall Research and Development in Sweden where two streams of differing temperature mix in a T-junction. The benchmark was to be a blind test of CFD simulations. Experimental results were not released until after benchmark participants submitted the results of their simulation to the OECD/NEA.
The CFD simulation done by SI was carried out on an all hexahedral mesh of 1,881,504 elements generated using the ANSYS Mechanical Finite Element program. The mesh was then transferred into the CFX program and, after applying proper boundary conditions, a time-dependent simulation was done using the Large Scale Eddy Simulation (LES) turbulence model [2] with Wall Adjusting Local Eddy Viscosity (WALE) sub-grid scale (SGS) turbulence model [2, 3].
Comparisons of the CFD results to the Vattenfall data show close correspondence for mean and root-mean-square (rms) turbulent temperature fluctuations.
Fitness-For-Service Assessment of Pressure Equipments With Local Metal Loss Subjected to Seismic Loading
Authors: Yamamoto Takashi , Kaida Takuyo , Nagata Satoshi , Tsuji Hirokazu 
Published: January 2014

The concerns about Fitness-For-Service (FFS) assessment technique for pressure equipments with local metal loss have been growing from some characteristic damages, for example, many examples of the corrosion under insulation (CUI) of pressure equipment, have been reported from petroleum and petrochemical industries. FFS assessment procedure for the pressure equipments for metal loss has been validated by the results of various burst tests and FEM simulations for internal pressure loads.
There has, however, been little study to validate FFS assessment for pressure equipments subjected to seismic load. This paper suggests an FFS assessment procedure for pressure equipments with local metal loss subjected to both internal pressure and seismic loading. To ensure consistency to High Pressure Gas Law in Japan, allowable stress is based on the Japanese seismic design code. Developed stress on local metal loss from both internal pressure and seismic load is evaluated in accordance with API 579/ASME FFS-1.
The authors have verified safety margin and reliability of this method to toward to practical application. In order to verify, some cyclic bending load testings and finite element analysis were implemented under the conditions of ambient temperature and 300 degree C. The results of these validations show that the safety margins against low cycle fatigue are the range of 2.6 to 4.6. In addition, the test results at 300 degree C showed higher safety margin than that in ambient temperature.
Crack Propagation due to Movement or Size Change of Hot Spot in Pipe
Authors: Wirgart Jonas Erik , Terai Takayuki , Kasahara Naoto 
Published: January 2014

Thermal fatigue may occur downstream from mixing tee junctions where hot and cold water are turbulently mixed. Depending on the momentum of the incoming flows, different characteristic eddies are formed which create a local hot spot on the inner surface of the pipe. The hot spot have an unstable discrete boundary that spatially oscillates and this creates an oscillating multidimensional thermal load that induces high cycle thermal fatigue.
To predict the thermal fatigue lifetime of a pipe subject to this kind of thermal load, transient FEM simulations with an ideal hot spot in two and three dimensions were conducted. The crack lengths induced by the frequency of the oscillating boundary was analysed and it was found that the most harmful frequency for a pipe is in the nondimensional frequency of 0.01 to 1.0. Additionally, the simulation method was validated against data publications of FAT3D experiments.
The simulations have been compared to the current proposed Japanese design code for mixing tee junctions. The study shows that this multidimensional effect induces larger crack lengths than the current design code. The reason of this was analysed.
Towards a Smoothed Particle Hydrodynamics Algorithm for Shocks Through Layered Materials
Authors: Zisis Iason , van der Linden Bas , Giannopapa Christina 
Published: January 2014

Hypervelocity impacts (HVIs) are collisions at velocities greater than the target object’s speed of sound. Such impacts produce pressure waves that generate sharp and sudden changes in the density of the materials. These are propagated as shock waves. Previous computational research has given insight into this shock loading for the case of homogeneous materials. Shock-wave propagation through materials with discontinuous density distribution has not been considered in depth yet.
Smoothed Particle Hydrodynamics (SPH) is a numerical technique, which has been extensively used for the simulation of HVIs. It is especially suitable for this purpose as it describes both the solid and fluid-like behavior effectively as well as the violent breakup of the material under impact. In previous studies on SPH, impact loading of composite materials was modeled by homogenization of the material, or under assumption of being a so-called functionally graded material (FGM). Both these models neglect the reflection-transmission effects on the interface between materials of different density.
In this paper the shock loading of layered materials is studied. A modification to the standard SPH method is developed and tested, that incorporates materials with purely discontinuous density distribution. The developed method’s performance at simple shock loading cases is investigated; reflection-transmission patterns of shock-waves through layered materials are discussed, along with a parametric study of the governing parameters.
Assessment of Weld Overlay Defects in a Hydrocracking Unit Reactor
Authors: Robai Mohammed S. , Al-Sudairy Jarallah A. , Al-Harbi Abdullah M. , Joseph Joy 
Published: January 2014

Asset Performance Management is a key element of operational excellence. It refers to the management systems, strategies and activities aimed at maintaining the integrity of plant assets for their desired life. The safe operation of the assets is to be ensured at any cost. The objective of this paper is to offer one of the most critical assets in a refinery, namely the Hydrocracking Unit (HCU) reactor, as a case study addressing assessment of defects found in the weld overlay.
The reactor was built in 1978 according to ASME Sec. VIII Div. 2 and has been in operation since then. The reactor is constructed of Chromium-Molybdenum (Cr-Mo) base material (SA 336 F21) with thickness of 266 mm and corrosion resistant stainless steel (TP-347 with thickness of 3.2 mm) weld overlay. The very high operating temperature and pressure of the reactor in hydrogen rich hydrocarbon service and the resulting thermal stress and material degradation caused disbonding and cracks in the stainless steel weld overlay. This paper will address the approach that was used to alleviate such type of defects. Also, various considerations that go into the assessment are discussed and recommendations are suggested.