bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Hydride Morphology and Test Temperature on Fracture Toughness of Zr-2.5Nb Pressure Tube Material
Authors: Cui Jun , Shek Gordon K.
Published: July 2010

CANDU® reactor uses Zr-2.5Nb alloy pressure tubes as the primary coolant containment. Fracture toughness properties of the pressure tubes are required for evaluation of fracture initiation and leak-before-break. This paper presents an experimental study on the effects of hydride morphology and test temperature on axial fracture toughness of a cold-worked, unirradiated Zr-2.5Nb pressure tube. Compact tension specimens were prepared from one tube section which contained as-received hydrogen concentration and another section which was electrolytically hydrided to 70 ppm hydrogen. Reoriented hydrides were formed in the hydrided tube section in ten thermal cycles under an applied tensile hoop stress of 160 MPa. The hydride morphologies were characterized by a parameter referred to as the hydride continuity coefficient (HCC), which provided a measure of the extent to which the hydrides were reoriented with respect to the applied stress direction. Partially reoriented hydrides with HCC between 0.3–0.4 were formed under the stress and temperature cycles used to precipitate the hydrides. J-R curves were generated to characterize the fracture behavior of the specimens tested at five different temperatures: 25°C (room temperature), 100°C, 150°C, 200°C and 250°C. Test results indicate that, for the as-received specimens, the fracture toughness is relatively high at room temperature and not significantly affected by the test temperature between room temperature and 250°C. For the 70 ppm hydrided specimens containing partially reoriented hydrides, the fracture toughness is significantly lower than that of the as-received specimens at room temperature. At 100°C, the fracture toughness is higher than that at room temperature but the average value is still lower than that of the as-received specimens. The specimens exhibit either brittle or ductile fracture behavior with a sharp transition to an upper-shelf toughness value. At 150°C, the specimens achieve an upper-shelf toughness level. Between 150°C and 250°C, the fracture toughness is similar to that of the as-received specimens and not affected by the reoriented hydrides.
Burn Behavior of a Polyurethane Foam Impact Limiter
Authors: Li Jie , Tam Shiu-Wing , Liu Yung Y.
Published: July 2010

We recently studied the burn behavior of a polyurethane (PU) foam-filled impact limiter — a design for both the Mixed-Oxide Fresh Fuel Package and the Hanford Unirradiated Fuel Package (HUFP) that have been certified for shipment of their authorized contents by the U.S. Nuclear Regulatory Commission and the U.S. Department of Energy, respectively. In this paper, we examined the mechanisms of thermal degradation of PU foam by reaction type and flame temperature. Evidence suggests that, for an air-tight impact limiter, the pyrolysis reaction dominates initially in the limiter enclosure. The pyrolysis generates a large amount of highly flammable gases, creating the conditions necessary for a subsequent combustion reaction near the vent holes where air is abundant. The coupled heat release from the combustion of these flammable gases and oxygen drives the jet flames to burn at a very high temperature. The three-dimensional finite-element analysis code, ANSYS Mechanical, was used to model the HUFP package (with the PU foam-filled impact limiters) and compute the temperatures near the seal region of the containment boundary of the package. We examined the effects of various parameters — including fire duration, chimney flow, foam thickness loss, and jet flame temperature — on the thermal performance of the package. The results indicate that, under the simulated conditions, the O-ring seal temperature near the packaging containment boundary rose to varying degrees, but it did not exceed the seal temperature limit of 400°F (204°C). The remaining foam thickness is critical to maintain package safety.
Residual Stress Evaluation of Dissimilar Weld Joint Using Reactor Vessel Outlet Nozzle Mock-Up Model: Report 2
Authors: Ogawa Naoki , Muroya Itaru , Iwamoto Youichi , Hojo Kiminobu , Ogawa Kazuo , Kingston Ed , Smith David J.
Published: July 2010

In recent years, the occurrence of primary water stress corrosion cracking (PWSCC) in Alloy 600 weld regions of PWR plants has increased. In order to evaluate the crack propagation of PWSCC, it is required to estimate stress distribution including residual stress and operational stress through the wall thickness of the Alloy 600 weld region. In a national project in Japan for the purpose of establishing residual stress evaluation method, a test model was produced using the same fabrication process in Japanese PWR plants in order to measure stress distribution change of the Alloy 132 weld region during fabrication process such as a hydrostatic test, welding a main coolant pipe to the stainless steel safe end and operation condition test. For the mock up test model, the stress distribution of selected fabrication processes was measured using the Deep Hole Drilling (DHD) method. From the measurement results, it was found that the stress distribution in thickness direction at the center of the Alloy 132 weld line was hardly varied with the hydrostatic test at site and operating condition test history. FE analysis was performed to calculate the stress distributions for each fabrication process. Comparing with measurement results, the validity of the FE analysis was confirmed. From the validation procedure, a standard residual stress evaluation method was established.
Study on Collapse Characteristics of Cylinder-to-Cylinder Intersections by Inelastic Finite Element Analysis
Authors: Kataoka Shunji , Miyakawa Asako , Sato Takuya
Published: July 2010

It is known that the collapse strength of complex three-dimensional structures cannot be evaluated accurately with elastic analysis, and more accurate results require the use of inelastic analysis. A typical example is cylinder-to-cylinder intersection. In this paper, the relationship of collapse loads and local primary membrane stresses of cylinder-to-cylinder intersections was examined. First, elastic analysis of the cylinder-to-cylinder intersections with various combinations of diameter and thickness under internal pressure was conducted. The local primary membrane stress (PL) obtained from the analysis was normalized by the general primary membrane stress (Pm) the ratio of PL/Pm defining the Stress Intensification Factor (SIF). The results revealed that SIF was directly influenced by the geometries. Secondly, limit load analysis was conducted on the same structures and the collapse pressure was obtained. The Collapse Strength Reduction Factor (CSRF) defined as the ratio of the run pipe collapse pressure to the cylinder-to-cylinder collapse pressure was proposed. The CSRF was also found to be influenced by the geometries. Comparing the result of SIF with CSRF, it is clear that the evaluation by SIF is overly-conservative and the proposed concept of CSRF provides more accurate evaluation of the cylinder-to-cylinder intersections. Furthermore, the basic data for the intersections with uniform thickness can also be applied to the reinforced intersections.
IASCC Evaluation Method of Irradiated Cold Worked 316SS Baffle Former Bolt in PWR Primary Water
Authors: Takakura Kenichi , Nakata Kiyotomo , Kubo Noboru , Fujimoto Koji , Sakima Kimihisa
Published: July 2010

Irradiation Assisted Stress Corrosion Cracking (IASCC) is a matter of great concern as degradation of core internal components in light water nuclear reactor. To clarify the IASCC initiation conditions of baffle former bolt (BFB), constant load stress corrosion cracking (SCC) tests were carried out in simulated PWR primary water (290, 320, 340°C) using C-ring type specimens. Based on the SCC test results, IASCC initiation time becomes shorter with increasing fluence and increasing applied stress, IASCC initiation threshold stress becomes lower with increasing fluence. A test temperature effect was observed in SCC initiation time, but it was not clear the effect of test temperature for SCC initiation threshold stress. These results suggest that IASCC initiation threshold criteria can be described with stress in specimen and fluence. This paper describes the whole evaluation procedure to secure structural integrity of irradiated baffle structure in PWR primary environments, including the threshold stress diagram of IASCC initiation and the irradiation creep formula.
Analysis of Bolted Flange Joints for Lids of Packages for Radioactive Materials
Authors: Sterthaus Jens , Ballheimer Viktor , Droste Bernhard , Koch Frank , Probst Ulrich , Vo¨lzke Holger , Wille Frank
Published: July 2010

The design of bolted flange joints for the German double barrier closure system of spent fuel and high-level waste transport and storage casks is described. Additionally, the basic load assumptions are presented for service conditions and for hypothetical accident scenarios. The modelling details and the results of numerical analyses are discussed with respect to those of experiments. The treatment of the numerical results for the bolts is presented considering safety factors derived by nominal stress concepts. The lids of the double barrier system are designed for a specified helium leak tightness. In addition to interior pressure, the accelerations during usual service and in particular during accidental drop tests are considered. The sliding and the gap formation at the gasket surfaces is analysed with respect to drop test loads. The consequences for the containment analysis are discussed on basis of the tightness characteristics. Concerning the bolts, the transfer of local stresses provided by numerical analysis to nominal stress values is presented. This transfer enables the use of safety factors based on nominal stress concepts for the local stresses given by numerical analysis.
On the Analysis of Critical Flow Discharged From a Pressurized Pipe System Using a HEM
Authors: Chung Moon-Sun , Lee Sung-Jae
Published: July 2010

An accurate prediction of a critical flow discharged from a pressurized pipe system is of most importance in such a safety analysis of nuclear power plants, since it provides the transient boundary conditions during the depressurization transients initiated by a pipe break in primary or secondary systems and during the over-pressurization transients resulting in a relief of coolant through valves. Mass and energy discharge through the opening of pressure boundary affects the system thermal hydraulic responses, that is, phase changes and flow distribution in the system, and the mass inventory remaining in the system necessary to remove core decay heat of a nuclear reactor. Therefore, the safety significance relating to the critical flow led to a development of various empirical and mechanistic critical flow models. However, the accuracies of these models are still in question especially during two-phase critical flow condition. A good example of that is a homogeneous equilibrium model (HEM). The HEM is the basis of several system codes, such as early versions of RELAP, for nuclear loss-of-coolant accident (LOCA). The major non-equilibrium phenomena that are ignored in the HEM are vapor bubble nucleation and interface heat, mass, and momentum transfer. Henry & Fauske empirically handled non-equilibrium vapor generation by introducing a non-equilibrium parameter that allows only a fraction of the equilibrium vapor generation to occur. This approach boils down in essence to a correlation of the deviation between the measured flow rate and the prediction from the HEM: The details of the flow path do not have to be worked out and only needs to know the upstream conditions. However, if we treat non-equilibrium phenomena with this model, it requires an empirical database of the non-equilibrium parameters or their correlations that are so far unknown. Further, because the coefficients have not been applied separately to the subcooled liquid and two-phase mixture, we have not been able to treat the non-equilibrium phenomena with the phase change properly. For this reason, we propose the non-equilibrium parameters for subcooled liquid and two-phase mixture, respectively, and then we adopt their combinations according to the flow conditions through the phase change process using the RELAP5/MOD3 code. In addition, we discuss the assessment results of Marviken LBLOCA tests using these non-equilibrium parameter sets with those from the non-equilibrium model by Trapp & Ransom and Chung et al.
Multiple Yield and Bounding Surfaces Model for Analysis of Multiple Friction Pendulum System
Authors: Tsai C. S. , Lin Yung-Chang , Su H.-C.
Published: July 2010

In order to systematically investigate the mechanical characteristic of a multiple friction pendulum system with more than two concave sliding interfaces and one articulated slider located between these concave sliding interfaces, on the basis of the plasticity theory, a plasticity model called the multiple yield and bounding surfaces model is proposed in addition to analytical formulations derived from the proposed concept of subsystems in this study. The proposed model has two separate groups of multiple yield and bounding surfaces. The first group is adopted to describe the mechanical behavior of the subsystem including the concave sliding interfaces above the articulated slider and the second group is used for modeling the sliding characteristic of the subsystem representing the concave sliding interfaces below the articulated slider. The connection of these two subsystems in series forms the mechanical characteristic of the entire MFPS isolation system. By virtue of the proposed model, the phenomena of the sliding motions of the MFPS isolator with multiple concave sliding interfaces under cyclical loadings can be clearly understood. Analytical results infer that the natural frequency and damping effect of the MFPS isolator with multiple concave sliding interfaces change continually during earthquakes and are controllable through appropriate designs.
Case Study: Effect of Soil-Structure Interaction and Ground Motion Incoherency on Nuclear Power Plant Structures
Authors: Xu Jim , Samaddar Sujit
Published: July 2010

The soil-structure interaction (SSI) has a significant impact on nuclear power plant (NPP) structures, especially for massive and rigid structures founded on soils, such as containments. The U.S. Nuclear Regulatory Commission’s (NRC) Standard Review Plan (SRP) provides the requirement and acceptance criteria for incorporating the SSI effect in the seismic design and analyses of NPP structures. The NRC staff uses the SRP for safety review of license applications. Recent studies have indicated that ground motions in recorded real earthquake events have exhibited spatial incoherency in high-frequency contents. Several techniques have been developed to incorporate the incoherency effect in the seismic response analyses. Section 3.7.2 of Revision 3 of the SRP also provided guidance for use in the safety evaluation of seismic analyses considering ground motion spatial incoherency effect. This paper describes a case study of the SSI and incoherency effects on seismic response analyses of NPP structures. The study selected a typical containment structure. The SSI model is generated based on the typical industry practice for SSI computation of containment structures. Specifically, a commercial version of SASSI was used for the study, which considered a surface-founded structure. The SSI model includes the foundation, represented with brick elements, and the superstructure, represented using lumped mass and beams. The study considered various soil conditions and ground motion coherency functions to investigate the effect of the range of soil stiffness and the ground motion incoherency effect on SSI in determining the seismic response of the structures. This paper describes the SSI model development and presents the analysis results as well as insights into the manner in which the SSI and incoherency effects are related to different soil conditions.
An Analytical Evaluation of the Effect of Weld Material Thickness on Residual Stresses Produced by Structural Weld Overlays on Pressurized Water Reactor Primary Cooling Piping
Authors: Fredette L. F. , Scott Paul M. , Brust F. W. , Csontos A.
Published: July 2010

Full Structural Weld Overlay (FSWOL) has been used successfully to mitigate intergranular stress corrosion cracking in boiling water reactor (BWR) welded stainless steel piping for many years. The FSWOL technique adds structural reinforcement, can add crack resistant material, and can create compressive residual stresses at the inside surface of the welded joint which reduces the possibility of further stress corrosion cracking. Recently, the FSWOL has been applied as a preemptive measure to prevent primary water stress corrosion cracking (PWSCC) in pressurized water reactors (PWR) on susceptible welded pipes with dissimilar metal welds common to PWR primary cooling piping. This study uses finite element models to evaluate the likely residual and operating stress profiles remaining after FSWOL and describes the results of sensitivity studies which were performed to examine the effect of weld overlay thickness on the residual stresses for typical dissimilar metal weld configurations.
JSME Construction Standard for Superconducting Magnet of Fusion Facility ”Quality Assurance”
Authors: Suzuki Tetsuya , Nishimura Arata , Nakajima Hideo
Published: July 2010

This standard was developed to be applied the superconducting magnet structure of ITER, Tokamak type fusion facility. The standard for the conformity assessment and quality assurance was decided as a subsection of the standard, to ensure the quality of the superconducting magnet structure for fusion energy. Conformity assessment is indispensable as well as quality assurance for the products to perform their function satisfactorily. Most of Japanese voluntary consensus standards in nuclear field limited their contents to technical requirements only, so conformity assessment has been performed by regulatory authority. Ensuring conformance to the standard is necessary to satisfy Japanese responsibility for in-kind contribution to ITER. For this purpose, fundamental requirements for conformity assessment were defined. Role and responsibility of Owner, Manufacturer, Installer, Qualified Inspector, Standard-Expert Engineer were defined. The requirements of certification for Design Specification, Design Report, Fabrication Specification, Installation Specification, Data Report were defined as well. In conformity assessment, realistic Qualified Inspection and Design Certification were pursued, considering the legislation, infrastructure and prospective user of standard in Japan. These procedures of certification and qualified inspection specific to national system were separated from main body as appendix for international user to adopt their own alternative system. The quality assurance requirements consists of 18 articles, such as organization, quality assurance program, design control, document control etc. were used. Each article was designed to constitute simplified performance based requirement. In addition, guidance was given in non-mandatory appendix for the users to apply performance-based requirements effectively.
Finite Element Analysis of the Fatigue Strength of Threaded Fasteners Using Helical Thread Models
Authors: Fukuoka Toshimichi , Nomura Masataka , Fuchikami Takashi
Published: July 2010

Fatigue failures of bolted joints frequently lead to serious accidents of machines and structures. It is well known that fatigue failure is likely to occur around the first thread root of bolt adjacent to the nut loaded surface and the run-out of bolt thread. That is because high stress amplitudes are generated there due to alternating external forces. Accordingly, it is significantly important to evaluate the stress amplitudes along the thread root in order to better define the fatigue failure mechanism of bolted joints. In this study, stress amplitude distributions along the thread helix including the thread run-out are analyzed by three-dimensional finite element analysis, where the numerical models of bolted joints are constructed so as to accurately take account of the effect of thread helical geometry, using the modeling scheme proposed in the previous paper. The analytical objectives are bolted joints with axi-symmetric geometry except for the helical-shaped threaded portions, and are subjected to axi-symmetric external forces. It has been substantiated, based on the stress amplitude distributions along the thread helix, that the fatigue failures are likely to originate from the first bolt thread, as in the case of the maximum stress, and the run-out of threads. Also shown is that the fatigue failure location varies depending on the distance between the target bolt and the loading position and whether or not there is a separation at the plate interface.
Postbuckling Analyses of Elastic Cylindrical Shells Under Axial Compression
Authors: Kobayashi Takaya , Mihara Yasuko
Published: July 2010

In designing a modern lightweight structure, it is of technical importance to assure its safety against buckling under the applied loading conditions. For this issue, the determination of the critical load in an ideal condition is not sufficient, but it is further required to clarify the postbuckling behavior, that is, the behavior of the structure after passing through the critical load. One of the reasons is to estimate the effect of practically unavoidable imperfections on the critical load, and the second reason is to evaluate the ultimate strength to exploit the load-carrying capacity of the structure. For the buckling problem of circular cylindrical shells under axial compression, a number of experimental and theoretical studies have been made by many researchers. In the case of the very thin shell that exhibits elastic buckling, experimental results show that after the primary buckling, secondary buckling takes place accompanying successive reductions in the number of circumferential waves at every mode shift on systematic (one-by-one) basis. In this paper, we traced this successive buckling of circular cylindrical shells using the latest in general-purpose FEM technology. We carried out our studies with three approaches: the arc-length method (the modified Riks method); the static stabilizing method with the aid of (artificial) damping especially, for the local instability; and the explicit dynamic procedure. The studies accomplished the simulation of successive buckling following unstable paths, and showed agreement with the experimental results.
Estimation of V Factor Under Combined Thermal and Mechanical Stress for Circumferential Cracked Pipes
Authors: Song Tae-Kwang , Kim Yun-Jae , Oh Chang-Kyun , Nikbin Kamran , Ainsworth Robert A.
Published: July 2010

This paper provides V-factor estimation under combined mechanical and thermal load for circumferential cracked pipes. In this study, the effects of types and magnitudes of the thermal stress, mechanical loading mode, crack geometry, and plastic strain hardening on variations of V-factor are estimated. The results of finite element analyses are compared with R6 values. As a result, it is shown that R6 gives generally conservative results. The conservatism is especially increased for the combination of large mechanical and thermal load. As a result, new estimation equation which uses failure assessment curve in R6 is proposed for V-factor and gives less conservative results.
Validity of the Master Curve Temperature Dependence Assumption for Highly Embrittled RPV Materials: Results From the IAEA Coordinated Research Project (CRP-8)
Authors: Planman Tapio , Onizawa Kunio , Server William
Published: July 2010

The fracture toughness temperature dependence (transition curve shape) has been discussed almost since the original empirical definition of the curve in 1991. The data sets showing anomalous fracture behaviour of highly irradiated VVER-1000 pressure vessel steels presented in 2000’s have further enhanced this discussion and even a special model has been proposed for highly irradiated steels, including a mathematical definition of the curve shape change. Although in most cases the standard Master Curve (MC) approach, assuming a constant transition curve shape, has proven to give a realistic description for also highly irradiated ferritic steels, there are grades which show for example abnormally weak temperature dependence. In these cases, however, an obvious reason for the behaviour may be that the material does not fail by the mechanism assumed in the MC model. The fracture toughness data collected and analysed in the CRP-8 Topic Area 3 supports the validity of the curve shape assumption of ASTM E1921 also in case of irradiated steels and gives no rise to change the present definition. The Master Curve C-parameter (the shape parameter) estimation is proposed as an appropriate analysis method when there is need to estimate also the temperature dependence, whereas the SINTAP procedure is recommended for ensuring conservative lower bound estimates when material inhomogeneity is suspected. The results show that irradiation may slightly lower the fracture toughness in the upper transition region in relation to that predicted by ASTM E1921, but the effect after moderate T0 shift values (up to about 100°C) seems to be negligible. The investigated steels exhibit no or very weak correlation between the C-parameter and T0.
A Fully Elastic Model for Studying Submerged Circular Cylindrical Shells Subjected to a Weak Shock Wave
Authors: Leblond Ce´dric , Iakovlev Serguei , Sigrist Jean-Francois
Published: July 2010

The transient dynamics of evacuated and fluid-filled circular elastic shells, submerged in an infinite fluid medium and subjected to an external weak shock wave, is considered in this paper. This circular shell/acoustic medium interaction problem has already been tackled with simplified thin shell models, based on the Love-Kirchhoff hypotheses for the structural dynamics. In this case, the resulting radiated pressure field displays some discrepancies related to the A0/S0 waves when compared to the experimental data available in the literature for the evacuated case. These drawbacks are overcome here by the use of an isotropic elastic model for the structural dynamics and an inviscid acoustic flow for the fluid dynamics, in a two-dimensional framework. It is assumed that the shell displacements are small compared to both its radius and thickness. The approach is based on the methods of Laplace transform in time, Fourier series expansions and separation of variables in space. For the fluid-filled case, the transient thick shell-weak shock wave interaction problem is explored and the radiated acoustic field described.
Prevention of Transformer Tank Explosion: Part 3—Design of Efficient Protections Using Numerical Simulations
Authors: Brady Ryan , Muller Sebastien , Petrovan-Boiarciuc Margareta , Perigaud Guillaume , Landis Benjamin
Published: July 2010

Electricity markets are very competitive and in order to limit costs, companies often reduce their investments by using aging equipment and by overloading their transformers. For these reasons, oil-filled transformer explosions are becoming more and more frequent. They are caused by electrical arcs occurring in transformer tanks. Within milliseconds, arcs vaporize 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 propagates and interacts with the tank. Then, the reflections generate pressure waves that build up the static pressure, leading to tank rupture since tanks are not designed to withstand such levels of static pressure. This results in dangerous explosions, expensive damages and possible environmental pollution. Despite all these risks, and contrarily to usual pressure vessels, no specific standard has been set to protect sealed transformer tanks subjected to large dynamic overpressures. To limit the consequences of an explosion, protective walls surrounding transformers can contain the explosion while sprinklers may extinguish the induced fire. In order to extend this chain of protections to the transformer itself, a strategy to avoid transformer tank rupture was developed and presented at the previous PVP08 Conference (PVP2008-61526 - Prevention of Transformer Tank Explosion: Part 1). The concept of this strategy is based on the direct mechanical response of a depressurization set to the inner dynamic pressure induced by electrical faults. In the same paper, the efficiency of this depressurization strategy was experimentally shown: if the oil evacuation through the depressurization set is activated within milliseconds by the first dynamic pressure peak before static pressure increases, the explosion can be prevented. The use of these protections eliminates the need to design transformer tanks as pressure vessels, which by application of the ASME standard would require a significant increase of the the shell thickness. Complementarily, a compressible two-phase flow numerical simulation tool based on a 3D finite volume method was developed to study transformer explosions and possible strategies for their prevention. Its theoretical bases were detailed in the PVP08 ASME Conference (PVP2008-61453 - Prevention of Transformer Tank Explosion: Part 2). The current paper shows the applications of this simulation software as a decision making tool, especially toward improving the design of real mechanical transformer protections. Some guidelines to optimize the efficiency of transformer protections are suggested thus contributing to a possible standard setting.
Prevention of Transformer Tank Explosion: Part 4—Development of a Fluid Structure Interaction Numerical Tool
Authors: Landis Ben , Muller Se´bastien , Petrovan-Boiarciuc Margareta , Brady Ryan , Pe´rigaud Guillaume
Published: July 2010

Oil filled transformer explosions and their prevention is a complex industrial issue. Experimental tests showed that when an electrical fault occurs in a transformer, it generates dynamic pressure waves that propagate in the oil. Reflections of these waves on the walls build up high static pressure which transformer tanks cannot withstand. The tank’s ability to withstand this pressure is thus one of the key parameters of transformer explosion prevention, and a numerical tool was developed to simulate the phenomena highlighted during the tests, especially the pressure wave propagation. The present paper’s aim is thus to complete this numerical tool so that the mechanical behavior of the tank can be accurately studied. The hydrodynamic numerical tool was subsequently coupled with a dynamic structure analysis package: the open source software Code_ASTER. A weak coupling strategy was first developed by applying the simulated pressures to the structure geometry in order to evaluate stresses and deformations. This strategy has evolved with the development of a strong coupling strategy which required establishing a moving mesh technique for the hydrodynamic code to accept displacement data from the structure code and complete the exchange between hydrodynamic and structure codes. First encouraging results are shown.
Research on Metal Atmospheric Storage Tank Inspection Method for Standard in China
Authors: Wang Yadong , Xu Yanting , Wang Bing , Ding Shoubao , Xu Jiele , Zheng Mulin
Published: July 2010

In China, the management and inspection of metal atmospheric storage tanks are still in a self-discipline or post-mortem mode. Therefore, the effective inspection is not carried out for most metal atmospheric storage tanks especially those being on service for more than 20 years. The potential leakage risk and environmental pollution are serious. In order to reduce the operating risk of metal storage tanks, effective inspection for metal atmospheric storage tanks is needed. Based on the practical situation of their management in China and the development process of the standard, an effective inspection method is proposed in this paper in which magnetic flux leakage testing and acoustic emission testing technologies are adopted. The method is used to verify the inspection results and the treatment for inspected defect is also put forward. The inspection results show that this method can be adopted in practical application.
Research on Microstructure Dependence of Near-Threshold Fatigue Crack Propagation by Combined Analyses of Fracture Surface and Fatigue Crack Growth Path
Authors: Zhu Ming-Liang , Xuan Fu-Zhen , Wang Guo-Zhen , Wang Zheng-Dong
Published: July 2010

Near-threshold fatigue crack growth behavior was investigated in a newly developed steel 25Cr2NiMo1V with different heat treatments to meet different property requirements of high-pressure (HP) and low-pressure (LP) parts in the combined steam turbine rotor. The load-shedding method was adopted in the near-threshold fatigue crack growth experiment at room temperature with a constant load ratio of 0.1. Combined analyses of crack surface and fatigue crack growth path were carried out to identify the dominant crack growth mechanisms in both HP and LP. Results show that in the threshold regime, fatigue crack growth resistance of the HP is clearly superior to that of LP and hence shows strongly dependence on the microstructure of 25Cr2NiMo1V. The distributed bainitic microstructures and larger prior austenite grain size in HP result in more tortuous crack propagation path than that in LP. Compared with ferritic blocks in HP, the tempered martensitic laths in LP do not play a dominate role in stopping the fatigue crack advance.
Fatigue Assessment of Nuclear Power Plant Components Subjected to Thermal Cyclic Loading
Authors: Bauerbach Kai , Vormwald Michael , Rudolph Ju¨rgen
Published: July 2010

Thermal loading conditions of nuclear power plant components cause local stress-strain hystereses. For the fatigue life prediction of nuclear power plant components under thermal cyclic and structural loading a new method based on the local strain approach is to be presented. This method involves finite-element simulations as well as the experience gathered from lifetime assessment methods based on short crack models. The local stresses and strains are obtained from coupled-field FE-analyses. The calculation of the hysteresis-loops relies on appropriate material models and experimentally verified temperature-dependent material parameters in order to describe the elasto-plastic behavior of the material as realistically as necessary. Due to the temperature dependence of the material parameters the resulting hysteresis loops are of non-conventional shapes and similar to those observed under multiaxial nonproportional structural loading. Hence, fatigue methodologies developed for non-proportional loading conditions during the past years bear good prospects for successful application under non-isothermal loading conditions.
Superheated Steam Test Rig for Compressed Non-Asbestos Gaskets Evaluation
Authors: Veiga Jose´ C. , Cipolatti Carlos F. , Furtado Ana M.
Published: July 2010

This paper presents a Superheated Steam Test Rig and a Test Procedure for Compressed Non-Asbestos (CNA) Gaskets qualification. The Test Rig is a versatile assembly that can use different flange sizes and heating systems. It simulates a Superheated Steam Boiler with a water feed pump, pressurized water tank, pressure relief valve, condenser and the flange pair acting as the Steam generation unit. Heating can be provided by an oven or heating element bands. The Test Protocol enables the evaluation of the gasket performance in Superheated Steam in severe operational conditions like high pressure and temperature with thermal cycling. Different types of non-asbestos compressed gaskets were tested monitoring the leak rate and bolt load at each thermal cycle.
Numerical Estimation of Fluidelastic Instability in Staggered Tube Arrays
Authors: Omar H. , Hassan M. , Gerber A.
Published: July 2010

This study investigates the unsteady flow and the resulting fluidelastic forces in a tube bundle. Numerical simulations are presented for normal triangle tube arrays with pitch-to-diameter (P/d) ratios of 1.35, 1.75, and 2.5 utilizing a 2-dimensional model. In this model a single tube was forced to oscillate within an otherwise rigid array. Fluid forces acting on the oscillating tube and the surrounding tubes were estimated. The predicted forces were utilized to calculate fluid force coefficients for all tubes. The numerical model solves the Reynolds-Average Navier-Stokes (RANS) equations for unsteady turbulent flow, and is cast in an Arbitrary Lagrangian-Eulerian (ALE) form to handle mesh the motion associated with a moving boundary. The fluidelastic instability (FEI) was predicted for both single and fully flexible tube arrays over a mass damping parameter (MDP) range of 0.1 to 200. The effect of the P/d ratio and the Reynolds number on the FEI threshold was investigated in this work.
Effect of Seawater Pressure on the Static and Fatigue Strength of Subsea Production Equipment Used in Deepwater Oil and Gas Fields
Authors: Urthaler Yetzirah , McFarlane Rod , Brookes David
Published: July 2010

Static and fatigue assessments of subsea production equipment used in deepwater oil and gas applications are presented in this paper. Membrane, axial and radial stresses are calculated on a thick-walled cylinder subjected to internal and external pressure loads using the Lame` solution. The fatigue life cycles of the pressure component are calculated per the linear elastic fracture mechanics (LEFM) approach of the American standard ASME Section VIII Division 3 Article KD-4 and per the British standard BS 7910. The results discussed in this paper provide new insight into the much debated issue of increasing the service pressure of subsea equipment above the nameplate rating by taking credit for the ambient seawater pressure at depth.
Strain Rate Dependence of Yield Strength and Long-Term Creep Strength Evaluation of ASME Grade 91 Steel
Authors: Kimura Kazuhiro , Sawada Kota , Kushima Hideaki
Published: July 2010

Accuracy of long-term creep life prediction of creep strength enhanced ferritic steels is improved by region splitting analysis method in consideration of 50% of the 0.2% offset yield stress. According to JIS and ASTM standards for tensile test, however, specified strain rates for evaluation of yield strength are slightly different from each other. The conditions specified in JIS G0567 and ASTM E21-03a are 0.3 ± 0.2%/min and 0.5 ± 0.2%/min, respectively. Strain rate influences on yield strength and 0.2% offset yield stress of ASME T91 at 600 and 650°C under strain rate of 0.5%/min was about 10% higher than that under strain rate of 0.3%/min. Influence of difference in strain rate between JIS and ASTM regulations on the long-term creep rupture life prediction by region splitting analysis method was insignificant. With decrease in stress, magnitude of creep strain at the onset of accelerating creep stage decreased from about 2% in the short-term to less than 1% in the long-term. Life fraction of the time to 1% total strain tended to increase with decrease in stress. It was indicated that the initiation of tertiary creep should be a more important parameter for the stress intensity limit, St, than time to a total strain of 1%, since 80% of the minimum stress to cause initiation of tertiary creep was definitely smaller than 100% of the average stress required to obtain a total strain of 1% in the long-term.
Theoretical and Experimental Study on Flow-Induced Vibration of an Overflow Pipe Due to Discharged Fluid Flow
Authors: Watanabe Masahiro , Hara Kensuke
Published: July 2010

This paper deals with an experimental study and a theoretical stability analysis on unstable vibration of an overflow pipe due to discharged fluid flow. In the system, the overflow pipe consists of vertical and horizontal pipes and an elbow, which is attached at the bottom of the vertical pipe, and the discharged fluid falls along the inner surface of the vertical pipe and changes the flow direction at the elbow. First, the vibration characteristics and instability region of the unstable vibration are examined by the experiments. The instability region in which the unstable vibration occurs is examined with changing flow rate, vertical pipe length and inlet shape of the overflow pipe. Next, the theoretical stability analysis is conducted. In the theoretical analysis, a theoretical model of the unstable vibration in the vertical direction is developed, and the instability region is shown by the stability analysis.
Study on Expansion of a Silicon Tube by Underwater Shock Wave
Authors: Iyama Hirofumi , Hamashima Hideki , Nishi Keijirou , Itoh Shigeru
Published: July 2010

Many studies about the behavior of the structure by shock wave have been researched until now. On those researches, some metals, resin, glass, concrete, wood were handled as a structure, and on many studies it was clarified about processing and behavior by the shock wave. On the other hand, recently, bio-materials have attracted attention on the material dynamics. It is impotant to recognition the behavior of these materials by the shock loading. Therefore, we have investigated the deformation of bio-material by shock wave. As the first approach, the expansion behavior of a silicon tube by underwater shock wave has been investigated and some numerical simulations and experiment have been performed.
Simulation of Tube Bundle Vibrations: A Numerical 3D-Method
Authors: Reichel Christoph , Strohmeier Klaus
Published: July 2010

The shell-side cross-flow in tubular heat exchangers may cause vibrations leading to failure within hours or in long term. Design is still based on half-empirical correlation, based on the equation of Connors (1978). Overdesign (Kassera 1996) and singular cases of damage (Fischer and Strohmeier, 2002) are the result. Therefore a structural model for the tube motions has been developed further and coupled to the commercial flow simulation code ANSYS CFX. The predictive capability of such coupled methods is limited by the flow simulation. Still simplifications or modeling are needed, especially for turbulence. The paper starts with an overview of modeling assumptions used so far. In addition to simulations of flow around rigid circular cylinders (Reichel and Strohmeier, 2008) LDA-measurements of flow through rigid glass-bundles have been compared to flow simulations. The sample of results presented below demonstrates that, besides level of fluctuations is predicted far too low, the overall velocity distribution on the shell side is predicted well by the SST turbulence model (Menter 1994), making URANS models like SST worth a try, if mainly flow forces are needed. To capture the tube dynamics an Euler-Bernoulli beam model of Fischer (2001), discretized by central differences in space and Newmark’s method (1959) in time, has been extended and implemented into ANSYS CFX. Calculations will be presented, showing that simulations of initially deflected tubes almost perfectly match analytic predictions. To adapt the numerical grid for the flow calculations to the tube displacements, the code inherent standard methods at large displacements resulted in negative volumes and solver failure. Therefore the standard methods have been replaced by own routines for grid deformation. Even for grids with fine near wall resolution, this method is able to cope with large displacements. Finally, coupled simulations are conducted of a single cylinder and of a cantilevered tube bundle in cross flow. For the single cylinder amplitudes are extremely overpredicted as long as 2D-modeling is used. 3D-modeling shows a phase shift of vortex shedding along the cylinder, which results in noticeably lower tube deflections. But, using the SST-model, amplitudes are still higher than measured. A model extension for laminar to turbulent transition leads to further improvement. The same holds for the tube bundle. Onset velocity of instability is predicted too low, amplitudes are too high. Modeling transition and large scale 3D-effects moves results closer to experimental observations. Further improvements are expected taking small scale 3D-effects into account by introducing more grid layers along the tubes.
Development of Weld Modelling Guidelines in the UK
Authors: Hurrell P. , Watson C. , Bouchard J. , Smith M. , Dennis R. , Leggatt N. , Bate S. , Warren A.
Published: July 2010

This paper describes the development of finite element modelling guidelines for the calculation of welding residual stresses. These guidelines form a new section in the R6 procedure, used in the UK nuclear power industry for the assessment of integrity structures containing defects. The intention is to improve the consistency of weld modelling procedures, the accuracy of predicted residual stress profiles and confidence in their use for defect tolerance assessments. The first issue of these guidelines is applicable to austenitic stainless steel joints produced using arc welding processes. The components of interest are mainly thick section nuclear pressure vessels and pipe welds where distortion is not the key issue. Recommendations made in the guidelines are largely based on residual stress analysis methods, validated by measurements on a range of weld mock-ups, developed over several years in support of British Energy projects. Advice is included on the use of 2D and 3D models, welding heat sources, material properties requirements, cyclic hardening and annealing assumptions. The modelling and computational requirements depend on the level of accuracy and degree of validation required. This is likely to be a function of the defect tolerance in the structure. In future issues, the R6 modelling guidelines will be supported by weld validation benchmarks. This will provide a detailed manufacturing record and measurement data from controlled weld mock-ups (including specimen design, welding parameters, thermo-mechanical properties, thermocouple data and stress measurements). It is also planned to develop these guidelines to include ferritic steel and dissimilar metal welds. The metallurgical behaviour in ferritic steel welds is more complex, since micro-structural phase transformations occur. Guidance will be provided on modelling post-weld heat treatment (PWHT) applied to pressure vessel welds and stress relaxation by creep. In modelling dissimilar metal welds, it is necessary to provide advice on dealing with the structural discontinuity at material interfaces and overcome FE solution convergence problems.
Statistical Analysis of Pipe Girth Weld Experimental Residual Stress Data
Authors: Nadri Brahim , Smith Mike C. , Truman Christopher E. , Smith David J. , Bouchard P. John
Published: July 2010

Thermal and mechanical processes during welding introduce complex three-dimensional distributions of residual stress. Management of residual stresses represents a major challenge for engineers in order to achieve safe and reliable operation of existing engineering plants. Consideration of how such stresses vary through the wall within welded components is critical in structural integrity assessments. Development of more accurate and realistic weld residual stress profiles through statistical analysis of high quality measured data is highly desirable. This cannot be achieved without adequate interpretation of measured weld residual stress data through the development of an appropriate framework. At previous PVP conferences such a framework was detailed. However, the framework was used to analyse and interpret welding residual stresses measured in highly controlled test specimens of simple geometry. This paper represents the extension of the framework to interpret real plant weld residual stress data. Specifically, the results of residual stress measurements on nine pipe girth welds are analysed statistically with the objective of providing a justifiable residual stress profile. The measurement results were obtained using different measurement techniques from different laboratories. The extension to real life data, unsurprisingly, reveals some unanticipated difficulties compared to the simple test specimen previously considered.