bluuebunny/crossref_metadata_2025 huggingface dataset:
Research on Failure Mechanism of Carbon Fiber Composite Materials Basing on Acoustic Emission
Authors: Liu Yan-Lei , Li Wei-Zhong , Xia Fu-Yong , Wang Bing , Han Shu-Xin , He Cheng-Dai , Yu Bing
Published: January 2014

Tensile process of carbon fiber composite laminate was monitored by acoustic emission technique. And the acoustic emission signals by tensile specimens of different winding angles were analyzed. The results show that carbon fiber released signals of different characteristics in different stages. So, the acoustic emission technique can effectively distinguish the different stages such as delaminating, detaching and fracture. Also, different angles in specimen’s layers of carbon fiber had different mechanical properties and failure mechanisms. Analysis on experimental data showed that acoustic emission testing technique can determine the process of different internal activities in carbon fiber composite laminate. Therefore, it can be used in the integrity evaluation for carbon fiber composite materials.
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.
Visual End-of-Life Criterion for Composite High Pressure Vessels for Hydrogen Storage
Authors: Chou Heng-Yi , Bunsell Anthony , Thionnet Alain
Published: January 2014

The storage of hydrogen at pressures clearly presents a challenge to designers of pressure vessels to ensure their utmost reliability. At present there is a paucity of information on the reliability of carbon fibre composite pressure vessels which are intended for use over periods of decades and those testing procedures which are mentioned in standards have been shown to be largely unsuitable as they are based on the failure of metal structures. This study deals with failure and failure prediction in advanced fibre reinforced composite pressure vessels. The aim of this study has been to evaluate the possibility of providing a simple, cost effective and unambiguous visual means of detecting approaching failure at a stage when the pressure vessel can be safely removed from service. It is proposed to benefit from the wide family of carbon fibres which is produced so as to add a layer of carbon fibre composite material, the fibres of which have the same stiffness as the carbon fibres in the bulk of the structure but which possess lower strength. The failure of this layer would provide advanced warning of progressive and unacceptable damage to the pressure vessel and would avoid any ambiguous interpretation.
Dynamic Stability of a Flexible Plate Moving in a Parallel Flow
Authors: Fujita Katsuhisa
Published: January 2014

The dynamic stability of a flexible plate subjected to a parallel flow is investigated when it moves in a flowing fluid. As the flexible flat plates, the papers in a high speed printing machine, the papers discharged by a paper machine, and the thin plastic and metal films, the fluttering flag and the oscillating doom roof caused by wind are enumerated. The fluid is assumed to be treated as an ideal fluid in a subsonic domain, and the fluid pressure is calculated using the velocity potential theory. The fluid-structure coupled equation of motion of a flexible flat plate supported simply at the both ends is derived into consideration with the added mass, added damping and added stiffness of a fluid, respectively. In addition, the effect of tension acting on a flexible plate, the influence of velocity of a moving plate and that of a fluid velocity, are also included into the coupled equation of motion respectively. The eigenvalue analysis is performed for the dynamic stability analysis. Changing the velocities of a plate and a fluid, and the specifications of a plate as parameter studies, the influences of these parameters on the dynamic stability of a plate are clarified. It is made clear that the plate moving in a still fluid becomes unstable at slightly lower velocity than the stationary plate subjected to a parallel flow. Moreover, it is found that the present solution shows a good agreement with the already reported experiments in which the flexible flat plate was a paper.
An Approach to Model Abstraction of Stress Corrosion Cracking Damage in Management of Spent Nuclear Fuel and High-Level Waste
Authors: Ahn Tae M.
Published: January 2014

This paper presents an approach to assess stress corrosion cracking (SCC) damage of a canister for use in confinement management (extended dry storage or geological disposal) of radionuclides from spent nuclear fuel and high-level (radioactive) waste. Localized corrosion, mainly in pitting form and fabrication flaws, were analyzed as a possible precursor to SCC using field/laboratory data. This paper assesses single crack propagation over long time periods and estimates the potential maximum opening area resulting from multiple cracks. This crack propagation model was developed by the Sandia National Laboratories (SNL) for disposal under seismic conditions, and it appears to be conservative with respect to radionuclide releases through the opening area. The SNL model could be applied to the weld and various metals for both management applications. The conservative SNL approach could be used to estimate consequences of radionuclides dispersals, if a canister failed as the confinement barrier.
Inverse Solution for Bolt Preload Using Joint Surface Deformation
Authors: Zaki Amro M. , Nassar Sayed A. , Shillor Meyer , Kruk Serge
Published: January 2014

In this paper, an inverse bi-harmonic axisymmetric elasticity problem is solved by invoking measured out-of-plane surface deformation values at discrete locations around a preloaded bolt head, in order to calculate the under head contact stress and joint clamp load that would have caused that out-of-plane surface deformation. Solution of this type of inverse problem promises to improve the automation process of bolted joint system assembly, especially in critical and safety related applications. For example, a real-time optically measured joint surface deformation can be utilized for automating process control of bolted joint assembly in a reliable fashion. This would be a significant reliability improvement as compared to the commonly used method in mass production using torque-only control method in which there is wide scatter in the torque-tension correlation due to the normal scatter in frictional variables. Finite Element Analysis (FEA) method is used to validate the inverse problem solution provided in this paper.
Effect of Upstream Edge Geometry on the Trapped Mode Resonance of Ducted Cavities
Authors: Bolduc Michael , Elsayed Manar , Ziada Samir
Published: January 2014

Gas flow over ducted cavities can excite strong acoustic resonances within the confined volumes housing the cavities. When the wavelength of the resonant acoustic modes is comparable to, or smaller than, the cavity dimensions, these modes are referred to as trapped acoustic modes. The excitation mechanism causing the resonance of these trapped modes in axisymmetric shallow cavities has been investigated experimentally in a series of papers by Aly & Ziada [1–3]. In this paper, the same experimental set-up is used to investigate the effect of the upstream edge geometry on the acoustic resonance of trapped modes. The investigated geometries include sharp and rounded cavity corners, chamfering the upstream edge, and spoilers of different types and sizes. Rounding off the cavity edges is found to increase the pulsation amplitude substantially, but the resonance lock-on range is delayed, i.e. it is shifted to higher flow velocities. Similarly, chamfering the upstream corner delays the onset of resonance, but does not increase its intensity. Spoilers, or vortex generators, added at the upstream edge have been found to be the most effective means to suppress the resonance. However, the minimum spoiler size which is needed to suppress the resonance increases as the cavity size becomes larger.
Numerical Method to Provide Cavitation Index for Control Valves
Authors: Malavasi Stefano , Rossi Marco M. A. , Messa Gianandrea V. , Ferrarese Giacomo
Published: January 2014

Cavitation is a harmful phenomenon for control valves. Starting from noise and vibration, cavitation can bring erosion and pitting of mechanical parts. Experimental costs for cavitation tests are high, not even considering the difficulties to test large-sized valves. For those reasons a CFD analysis could be an attractive solution to predict cavitation. However, a reliable numerical prediction of cavitation inception is hard to achieve and the computational cost of complex multi-phase models, necessary for a correct description of this phenomenon, is often very high. The purpose of this research is to overcome those difficulties by using a single-phase model to predict the onset of cavitation, in terms of the incipient cavitation index introduced in several technical standards. A method, based on the generalized pressure criterion reported in previous works, is applied to particularly complex control devices, namely the Cage Ball control valves, in which perforated plates are inserted to increase the energy dissipation with respect to a traditional Ball valve. Numerical results are compared with our own experimental data of acceleration induced by cavitation vibrations, showing good agreement. The final result is a simple and reliable method, with low computational cost, to evaluate the incipient cavitation index for control valves.
High Strain Rate Effects on Environment Assisted Fatigue for Austenitic Stainless Steels in PWR Environment
Authors: Fukuta Yuichi , Nomura Yuichiro , Saruwatari Toshiya , Asada Seiji
Published: January 2014

Current Japanese fatigue evaluations in the PWR environment are conducted using JSME S NF1 in which some parameters (temperature, strain rate, dissolved oxygen, etc.) are evaluated as influencing factors. However, it is assumed that the JSME Code would be conservative in high-strain-rate regions because the environmental factor (Fen) is evaluated by extrapolating experimental test results from a low strain rate (up to 0.4%/sec). In this study, experimental data are obtained additionally and Fen for high-strain-rate regions are reevaluated. As a result, it is confirmed that Fen at a strain rate of 1.0%/sec is about one half of that in the JSME Code. Further, marshaled experimental data obtained from the EFT project, which are classified according to stainless grade and material charge, indicated that the strain rate at Fen = 1 can be lower than 3%/sec for all austenitic stainless steels and similar to the current test result.
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).
A New Method for Measuring the Bond Strength of Electrofusion Joint
Authors: Zheng Jinyang , Hou Dongsheng , Shi Jun , Lu Shunli , Shi Jianfeng , Xu Ping
Published: January 2014

Electrofusion (EF) technique is very widely used in connecting polyethylene and its composite pipes. Safety of pipeline system depends on the quality of joints. For EF joints, the quality is characterized by the bond strength of welding interface. Peel test is a normal method for measuring the bond strength for EF joints. In our previous study (PVP2012-78655), we used the peel test to analyze the bond strength for EF joints with cold welding defects by calculating the bonding energy of fusion interface. However, in most well electrofused joints, test specimens fail in the pipe, rather than the fusion interface. As a result, it is difficult to determine the optimum welding conditions with the method of peel test. In this paper, a new method for measuring the bond strength of EF joint is proposed. A set of horizontal apparatus is designed and specific improved test means are introduced. Test results are then presented, which proves the effectiveness of the new method for high strength joints and in reducing pipe deformations. Finally, criteria to estimate the bond strength of joints are investigated. A comparison is made between the criterion of mean percentage decohesion presented in ISO 13954 and the criterion of normalized decohesion energy, which reveals that the latter one is more practical in statistics for peel tests, with better normality, a good concentration of data and facility to rank EF joints of different types.
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).
Constructing a Validated Deformation Mechanism Map Using Low Temperature Creep Strain Accommodation Processes for Waspaloy (A Nickel-Based Superalloy)
Authors: Asadi Mahyar , Guillot Dominic , Weck Arnaud , Koul Ashok K. , Chamanfar Ahmad , Jahazi Mohammad
Published: January 2014

A creep Deformation Mechanism Map (DMM) of an engineering alloy can be an effective tool for developing physics based prognostics systems. Many classical diffusion based rate equations have been developed for time dependent plastic flow where dislocation glide, dislocation glide-plus-climb and vacancy diffusion driven grain boundary migration (diffusion creep) are rate controlling. Long term creep testing and analysis of complex engineering alloys has shown that power law breakdown phenomenon is related to the dominance of Grain Boundary Sliding (GBS) as opposed to diffusion creep. Rate equations are now available for GBS in complex alloys and, in this paper, a DMM is constructed for Waspaloy (a Nickel-Based Superalloy) and validated by comparison with a collection of experimental data obtained from the literature. The GBS accommodated by wedge type cracking is considered dominant at low homologous temperatures (0.3 to 0.5Tm - temperature in Kelvin) whereas GBS accommodated by power-law or cavitations creep dominates above 0.55Tm.
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.
Optimization of Residual Stresses Induced by Multiple Laser Shock Processing
Authors: Wei Xinlong , Zhou Jianxin , Ling Xiang
Published: January 2014

Laser shock processing (LSP), also known as laser peening (LP), proves to be superior to conventional surface treatments such as shot peening, including deeper penetration of the residual stresses. The LSP treatment, which uses a very short pulse (ns) of intense (GW cm−2) laser beam to generate compressive residual stresses near the surface of the metallic samples, demonstrates a significant improvement of fatigue life and stress corrosion cracking resistance. In this paper, finite element analysis (FEA) combined with particle swarm optimization (PSO) method to predict the magnitude and distribution of optimized multiple LSP impacts on 304 stainless steel. The results of the simulation clearly show that optimized multiple LSP can mitigate residual stresses loss in the centre of the single impact zone and generate homogeneous compressive residual stresses at the surface. The results also reveal the optimized multiple LSP can lead to deeper penetration of the compressive residual stresses in the samples.
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.
Analytical Study on Effect of Failure of Pipe Support Structure on Seismic Response of Piping System
Authors: Takahashi Tsuneo , Maekawa Akira
Published: January 2014

This study discussed seismic response of a piping system when the pipe support structure was deformed plastically on being subjected to a much larger seismic load than the designed one. This case is expected as one of the conditions beyond seismic design that should be analyzed. To examine the effect of elastic-plastic deformation of the pipe support structure on seismic response, the effect of various shapes and failure mode of support structures was investigated. Difference of failure modes of the pipe support structure was modeled by change of initial stiffness and secondary stiffness of the load-displacement curve in this study. Seismic response analyses were conducted by using a typical small bore piping system shaped in a three-dimensional arrangement. The investigated change of seismic response behavior generated by plastic deformation of the pipe support structure was clarified based on comparison of seismic responses by using the elastic-fully plastic model and bi-linear model with various initial stiffness and secondary stiffness values. The results showed that the secondary stiffness of the load-displacement curve of the support structure did not affect the decreasing area of the response acceleration and the amount of the decrement significantly. It was concluded that the plastic deformation behavior of the pipe support structure could be modeled by using the elastic-fully plastic model when modeling plastic deformation characteristics of the pipe support structure.
A Response Spectrum Approach Using Model Order Reduction for Seismic Analysis
Authors: Oh Jinho , Choi Jinbok , Ryu Jeong-Soo
Published: January 2014

A response spectrum analysis (RSA) has been widely known as one of the methods used for the purpose of an earthquake-resistant design of a structure in the nuclear industry through evaluating the structural integrity during and after seismic events. Recently, as the structures, systems, and components for the design are massive, complex, and complicate, a considerable amount of computational resources and time is required for applying the RSA. Reduced methods have been considered as important technique to resolve computational resources and time problem. For a few decades, various approximate techniques have been developed to obtain the dynamic characteristic in a reduced manner. This paper adopts the model order reduction (MOR) technique known as the one of various reduction methods. The MOR for solving the large linear system in mathematics has been studied by a number of researchers. The MOR is achieved by applying a projection from a higher-order to a lower-order space using Krylov subspaces generated by the Arnoldi algorithm. It has been extended to engineering applications such as circuit analysis, structural analysis, and multi-scale analysis. However, it has not yet been applied in RSA. The aim of this study is to evaluate applicability of the MOR into RSA. Numerical examples demonstrate that the proposed method saves computational costs effectively with maintaining accuracy. Thus, it is confirmed that the proposed method is valid and applicable in predicting seismic responses.
Analysis of ASME Class 3 Buried HDPE Piping Systems Related to Code Case N-755-1
Authors: Kim Young Seok , Yoon Jung Kwang , Kim Young Ho
Published: January 2014

This paper proposes an analysis method for Section III, Division 1, Class 3 buried High Density polyethylene (HDPE) piping system in the nuclear power plants (NPP). Although HDPE pipe would yield at high temperature (limited to 140°F), it may be suitable for the areas prone to earthquakes; owing to its comparable ductility and flexibility. Thus, the buried HDPE piping may be applicable for the safety related Essential Service Water (ESW) system in the NPPs. Despite some limitations to buried HDPE piping, the piping could be designed based on ASME Code Case [1]. Generally, codes and standards including ASME Code Case [1] do not provide load combinations for the design of both buried steel piping and HDPE piping. Meanwhile, EPRI Report [4] provides load combinations including thermal expansion effects and seismic loads with detailed seismic criteria for polyethylene pipe. In this paper, load cases and load combinations for buried HDPE piping are suggested for implementation of reference documents and a buried HDPE piping system is analyzed referring to EPRI Report [4] to evaluate stress, force, and moment using a piping stress analysis program. Additionally, this paper will recommend the design procedure in accordance with ASME Code Case [1] using an example of buried HDPE piping analysis. An investigation of soil spring coefficients and the design considerations for hydrostatic tests are suggested for the enhanced analysis of buried HDPE piping.
Chronological Review of Manufacturing Technologies and Considerations to Maintenance/Inspection for Heavy Wall Hydroprocessing Reactors
Authors: Tahara Takayasu , Antalffy Leslie P. , Kayano Rinzo , Kikuchi Tsutomu
Published: January 2014

A great number of heavy wall hydroprocessing reactors for oil refining processes have been installed in the refineries all over the world in the past 50 years. These reactors are made from heavy wall Cr-Mo steel with stainless steel weld overlay cladding and are suitable for high pressure/high temperature hydrogen services. During past half century, manufacturing technologies such as those for design, materials, welding and NDE have seen remarkable advances based on feed back from operational experience. This paper summarizes the generation changes of manufacturing technologies and considerations for appropriate maintenance and inspection in order to provide for the safe operation of heavy wall hydroprocessing reactors.
Modelling of Micro-Plasticity Evolution in Crystalline Materials
Authors: Li Dong-Feng , Golden Brian , O’Dowd Noel P.
Published: January 2014

In this work, a micromechanical finite element model is presented to investigate micro-plasticity evolution in crystalline materials, with a comprehensive consideration of microstructural interactions, including morphology-based intragranular stress-strain response and the strain gradient induced scale effect. A dislocation-mechanics based crystal plasticity formulation has been employed to account for slip based inelastic deformation. A polycrystalline model has been constructed using the Voronoi tessellation technique to represent the microstructure of a martensitic power plant steel, P91. The model has been validated through a uniaxial tensile test. The effects of strain gradient have been examined at both macroscopic and microscopic levels and the importance of accounting for strain gradient effects in the prediction of local deformation states is discussed for P91.
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.
Influence of Variable Amplitude Fatigue Loading on AISI 304L Stainless Steel
Authors: Gloanec Anne-Lise , Anis Aqmal Syafiq , Courtin Stéphan
Published: January 2014

The aim of this work was to study the influence of variable amplitude loading on the fatigue crack initiation and propagation. Low Cycle Fatigue (LCF) tests are conducted, on an AISI type 304L austenitic stainless steel, at different total-strain-amplitudes, in laboratory air at room temperature and with a constant strain rate of 3.10−3 s−1. Two types of signal were used: a conventional signal and a complex signal. The first one was triangular in shape with a negative strain ratio (Rε = −1). The second one is still triangular in shape with Rε = −1, but between the maximum of the total-strain (εmax = +0.6%) and the minimum (εmin = −0.6%), several cycles with a smaller total-strain-amplitude are introduced (with values ranged from 0% to +/− 0.3%). From these tests, several conclusions can be drawn on Cyclic Stress Strain (CSS) behaviour, fatigue life and fracture characteristics.
A Hybrid Friction Model for Dynamic Modeling of Stick-Slip Behaviour
Authors: Azizian Reza , Mureithi Njuki
Published: January 2014

Fretting wear is a common problem in different industries especially when it comes to interactions between metallic components. In heat exchangers, the problem plays a destructive role due to long term interaction between tubes and supports which may consequently lead to tube failure. In the present work, the tube-support fretting wear problem was investigated by refining models for friction effects in the stick-slip regions. The Slip distance is the most important parameter for wear estimation. Using the tangential stress distribution in the contact area, a new hybrid spring-damper friction model was developed. The model is able to estimate elastic, plastic and partial slipping distances during relative motion. The ability of the model to reproduce experimental tests is investigated in the present work.
Existence Form of Boron in Dissimilar Weld Metals of Low Alloy Steel With Boron Bearing High Chromium Steel
Authors: Honma Yuta , Kayano Rinzo , Sakata Mikihiro , Yamashita Ken
Published: January 2014

Recently, boron bearing high chromium steel is applied to structural material of a fossil power generation plant. Dissimilar weld joints between this steel and low alloy steel are applied for various parts such as boiler or other equipments in this plant. In this weld joint, boron added to low alloy steel weld metals by the dilution from boron bearing base metal. However, the existence form of boron and the effect of boron on reheat cracking susceptibility during post weld heat treatment (PWHT) have not been surveyed in previous literature. So, reheat cracking test, precipitated carbide observation of boron bearing Cr-Mo low alloy steel weld metal was carried out in this study. From these test results, the reheat cracking susceptibility clearly increased by boron addition. Moreover, it decreased according to increasing chromium content. It was estimated that the structural form of boron was recognized in four kinds, such as BN, M2B, M23(C,B)6 and dissolved boron by thermo-dynamic calculation. The amount of M23C6 type carbide was increased with increasing chromium content. On the basis of these results, it was presumed that large amounts of dissolved boron existed in boron bearing low chromium steel weld metal compared with high chromium one during PWHT.
Development of JWES Standard WES7700 for Repair Welding of Pressure Equipment
Authors: Tahara Takayasu , Hoshika Takahisa , Yamamoto Eiichi , Murakami Takushi , Shiga Keisuke , Hirai Yukio , Ogayu Yasushi , Minami Fumiyoshi
Published: January 2014

The Japan Welding Engineering Society (JWES) published the guideline for repair welding of pressure equipment, CP-0902 in 2009. Considering the regal approval of each repair welding procedure for pressure equipment, JWES WES7700 has been also published in 2012. This paper summarizes the contents of WES7700 along with a verification of repair welding procedures such as minimum required grind out thickness for thermal removal of flaws, minimum required throat thickness of fillet welds for patched plates by experimental pressure tests and FEM analysis and some comparison of the requirements of several stamdards for repair weldings.
Characteristics of Corrosion Fatigue Crack Growth in Salt Water of Aluminum Alloys for Hydrogen Gas Containers
Authors: Ogawa Takeshi , Sugiyama Yuki , Kanezaki Toshihiko , Hayashi Noboru
Published: January 2014

A hydrogen gas container is one of the critical components for fuel cell vehicles (FCV), which is expected for CO2-free personal transportation. In the early stage of commercial FCV, the major container structure will be a compressed hydrogen gas cylinder, which consists of metal or plastic linear with metal boss and carbon fiber reinforced plastics (CFRP). In order to choose an appropriate material for the metal boss and metal liner, corrosion resistance should be evaluated for various aspects such as corrosion fatigue crack growth (CFCG) and stress corrosion cracking (SCC) in the high pressure hydrogen as well as in salt water environment for the purpose of vehicle use. In the present study, CFCG characteristics were evaluated for several aluminum alloys in air and in salt waters with various concentrations. The results showed that the crack growth rates were accelerated in salt water for all the materials and their environmental sensitivities were compared. The concentrations of the salt water exhibited minor effect on the fatigue crack growth rates. These CFCG characteristics were compared with the corrosion test results based on the ISO 7866 Annex A [1]. A basic idea was proposed for the evaluation of compressed hydrogen gas containers and the important material properties were suggested.
Effects of Fracture Toughness Curves of ASME Section XI: Appendix G on a Reactor Pressure Vessel Under Pressure–Temperature Limit Operation
Authors: Chou Hsoung-Wei , Huang Chin-Cheng , Huang Kuan-Rong , Liu Ru-Feng
Published: January 2014

After the Code Case N-640 was issued in 1999, the fracture toughness curve of reactor pressure vessel materials in ASME Section XI-Appendix G was amended to the KIC curve. In Taiwan, the present pressure-temperature limit curves of normal reactor startup (heat-up) and shut-down (cool-down) for the reactor pressure vessel is still calculated per KIA curve in 1998 or earlier editions. In this paper, the failure risks of a Taiwan domestic reactor pressure vessel under various pressure-temperature limit operations are analyzed. First, the pressure-temperature limit curves of the Taiwan domestic reactor pressure vessel based on KIA and KIC curves, and various levels of embrittlement, are calculated. Then, the ORNL’s probabilistic fracture mechanics code, FAVOR, and the PNNL’s flaw model are utilized to assess the failure probabilities of the reactor pressure vessel under such pressure-temperature limit transients. Further, the deterministic analyses of FAVOR code are also conducted. It is found that under the pressure-temperature limit transients based on KIC curves, the reactor pressure vessel presents higher failure probabilities, but are all below the allowable risk. The present results indicate that using the KIC curve the pressure-temperature limits can either increase the operational margin or still maintains the sufficient stability of the analyzed reactor pressure vessel.
PWR Steam Generator Tube and AVB Wear Under Perpendicular Impacting
Authors: Phalippou Christian , Ruffet Franck , Herms Emmanuel , Balestreri François
Published: January 2014

Flow-induced vibrations of steam generator tubes in nuclear power plants may result in wear damage at support locations. The steam generators in EPR power plants have a design life of 60 years; as wear is an identified ageing damage in steam generators, it is therefore important to collect experimental results on wear of tube and support due to dynamic interactions at EPR secondary side temperature. In this study, wear tests were performed between a steam generator tube (Alloy 690) and two flat opposite anti-vibration bars (AVB in 410s stainless steel) at different impact force levels. Tests were performed in pressurized water at 290°C in wear machines for long term repeated predominant impact motions. The worn surfaces were observed by SEM, the wear coefficients of tube and AVB were evaluated using the work rate approach. Significant scoring, due to the importance of sliding when impacts occur, was shown on wear scar patterns. There were greater wear volumes and depths on tubes than on AVBs, but dynamic forced conditions and rigid mounting of AVB in the rigs have prevailed for finally getting an upper bound of the wear rates. Alloy 690 for tubes and 410s for AVB remain a satisfactory material combination considering comparative wear results with other published data.
Aneurysm No-Linear Unsteady Dynamic: Mathematical Modeling
Authors: Hamadiche M.
Published: January 2014

A second order no-linear partial differential equation is worked out to describe the interaction of the flow with an elastic shell in large deformation domain. The model intends to describe the vibration of an aneurysm in arteries and veins. Two models are presented in this work. In the first one, the shell is inserted in otherwise rigid plane channel and in the second model the shell is inserted in otherwise rigid tube. In order to allow large displacement, the shell motion is described by Lagrangian variables. The steady version of the governing equation is a second order no-linear differential equation. A formal solution of the steady no-linear equation is obtained for plane channel model. It is shown that a steady solution exists only for some values of the dimensionless parameters ϕ and λ where ϕ is the ratio of transmural pressure to the elasticity coefficient and λ is the ratio of volume flux to the elasticity coefficient. The critical curve in the plan (ϕ,λ) for some control parameters are computed. Then, an unsteady solution of the no-linear unsteady equation is obtained numerically. It is found that the time signal prescribed by the unsteady no-linear solution depends strongly on the numerical values of the rheological parameters of the system. It is suggested that these signals could be used as a non invasive method in the diagnostic of the aneurysm when its vibration could be detected by a non invasive method. The linear analysis of the cylindrical geometry model shows that the aneurysm structure can be locked with heart pulse in a resonance frequency when the wall of the aneurysm becomes soft leading eventually to its rupture.
A Linear Model for the Onset of Whistling in Corrugated Pipe Segments: Influence of Geometry
Authors: Rudenko Oleksii , Meertens Dennis , Nakiboğlu Güneş , Hirschberg Avraham , Belfroid Stefan
Published: January 2014

Corrugated pipes combine small-scale rigidity and large-scale flexibility, which makes them very useful in industrial applications. The flow through such a pipe can induce strong undesirable whistling noises and even drive dangerous structural vibrations. Placing a short corrugated segment along a smooth pipe reduces the whistling, while this composite pipe still retains some global flexibility. The whistling is reduced by thermo-viscous damping in the smooth pipe segment. A linear semi-empirical model is proposed that allows to predict the critical Mach numbers at the onset of whistling for a composite pipe at moderately high Reynolds numbers. Experimental results for corrugated pipes of three different corrugations geometries are presented revealing fair agreement with the theory. In addition, the model indicates that even for a corrugated pipe segment with an anechoic termination, corresponding to a very long smooth pipe segment, there exists a finite critical Mach number above which the whistling occurs.
Modeling of Multiaxial Stress Effects on the Creep Resistance of High Chromium Steel
Authors: Esposito Luca , Bonora Nicola , Dichiaro Simone
Published: January 2014

Materials creep resistance is usually determined under uniaxial constant load condition while the state of stress in real components is multiaxial in general. How to correlate multiaxial creep behavior to uniaxial creep data is still an open issue. Most of the theories available in the literature are phenomenological in nature and limited to few classes of metals and stress triaxiality ranges. From the computational point of view, stress field relaxation depends on the creep model formulation. Therefore, it is necessary to use a refined creep model capable to reproduce the effective state of stress in the material. In the present work, a mechanism based creep model proposed by Bonora and Esposito [1] was used to predict creep life of P91 high chromium steel under multiaxial state of stress. This creep model is capable to reproduce all creep stages and was validated for different classes of metals and alloys. The performance of different reference stress definitions (i.e. the principal facet stress, skeletal stress and a new formulation) was investigated. Results were compared with available creep life data obtained on round notched samples at different temperatures.
Fracture Integrity Assessment of Flawed Bi-Metallic Girth Weld Joint
Authors: Bonora Nicola , Carlucci Antonio , Ruggiero Andrew , Iannitti Gianluca
Published: January 2014

The objective of the work is to establish, for a bi-metallic girth weld joint, up to which level of remote stress/strain is still conservative the use of the standard approach to perform an Engineering Criticality Assessment (ECA) considering the joint made of a single equivalent material. Several flaw types located at the interfaces between the joint materials were considered. Extensive finite element analysis was performed to derive the crack driving force using domain integral method. The possibility to use, with appropriate meshing, the CTOD as parameters to directly derive the J-integral in the numerical simulation is also demonstrated. Computational results indicate that the use of a material curve, obtained as the lower bound of all joint materials curves, lead to conservative results.