bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigation of the Aeroacoustic Sources in a Tandem Cylinder Configuration
Authors: Finnegan Shane Leslie , Meskell Craig , Ziada Samir
Published: July 2010

The empirical investigation of the spatial distribution of resonant acoustic sources around a tandem cylinder configuration subject to cross flow in a duct and an imposed transverse acoustic wave is described. The imposed wave induced acoustic “lock-in” and the vortex shedding frequency from the cylinders became entrained to the frequency of the imposed wave near acoustic-Strouhal coincidence. Howe’s aeroacoustic theory was used to couple an acoustic field to a hydrodynamic flow field and the spatial distribution of the time-resolved acoustic power and net-acoustic energy throughout a complete acoustic wave cycle at two resonant conditions were calculated. The first resonant condition occurred at a low flow velocity before acoustic-Strouhal coincidence, whilst the second occurred at a higher flow velocity just after acoustic-Strouhal coincidence. The acoustic field was analysed using finite element analysis combined with microphone pressure measurements whilst the hydrodynamic flow field was extracted using particle image velocimetry from a field of view concentrated around the cylinders and roughly three diameters downstream of them. For both resonant conditions, the dominant individual sources were found to lie in the shear layers of the gap region between the cylinders, however, stronger individual sinks were found to be located there also. Thus, for the amplitude of the applied sound wave and for the available field of view, the gap shear layer region contributed an overall acoustic sink whilst the wake contributed an overall acoustic source.
Thermal Fatigue Analysis of a PWR NPP Steam Generator Injection Nozzle Model Subjected to the Thermal Stratification Phenomenon
Authors: da Silva Luiz Leite , Mansur Tanius Rodrigues , Cimini Carlos Alberto
Published: July 2010

This work is related to an experimental thermal stratification study aiming to quantify thermal fatigue damages in the pipe material. Thermal fatigue damages appear as a consequence of non-linear longitudinal and circumferential loads and thermal stripping present in pipes whit thermal stratified flows. In this work an experimental section, simulating the injection nozzle of a NPP steam generator, was subjected to the effects of thermal fatigue due to thermal stratification. The experimental section was made of stainless steel pipe type AISI 304L and its geometric characteristics allowed the same range of Froude numbers of a Pressurized Water Reactor (PWR) NPP. Temperatures were measured externally and internally in three positions and deformations just externally in seven positions. Up-and-down fatigue tests were done to assess the amount of damage induced in the material experimental section. Preliminary numerical simulations were done using a coupled analysis in the ANSYS code with temperatures and pressure inputs taken from thermo hydraulic experimental results. The objectives in this work are quantify the thermal fatigue intensity imposed to the pipe material by thermal stratification experiments, verify the agreement between numerical and experimental thermal stratification results and obtain the material fatigue limit testing specimens made of pipe experimental section and from the virgin pipe. In this work is possible to conclude that stratified flows could be developed in the experimental section, thermal stratification induces considerable thermal stresses and strains in the experimental section pipe material, thermal stratification reduces the material fatigue limit, numerical and experimental results agreed appropriately in some pipe region and disagreed in others.
Shaking Table Tests on a Passive Equipment Isolation System for Earthquake Protection
Authors: De Angelis Maurizio , Perno Salvatore , Reggio Anna , De Canio Gerardo , Ranieri Nicola
Published: July 2010

The present work refers to steel frame structures in industrial plants. A passive isolation system for seismic protection of a considerable equipment, already present on a frame support structure and rigidly constrained to it, is investigated through both numerical simulations (1+1 DOF system) and shaking table tests on a 1:5 scale two-story steel frame structure. The equipment (e.g. a pipeline, a compressor unit, ...) is modelled as a rigid mass. The optimal design is determined by minimizing the dynamic response of the isolated mass. In order to ensure strenght and serviceability, the response of the frame is also monitored.
Materials Aging Degradation of Reactor Vessel Internals: Part III—Structural Evaluation and Local Finite Element Models
Authors: Snyder Matthew D. , Liszkai Tama´s R. , Demma Anne
Published: July 2010

Pressurized water reactor (PWR) internals components can experience material aging and degradation due to irradiation. The purpose of the functionality analysis is to provide a best-estimate evaluation of the reactor internals core barrel assembly for materials degradation to see if the components retain their function. The evaluation uses an irradiated material-specific constitutive model for use in a finite element analysis [1] representing the current state of knowledge for plasticity, creep, stress relaxation, void swelling, and embrittlement. This constitutive model is a function of temperature and fluence. The analysis focuses on finding the integrated effects of material aging combined with steady-state operational characteristics of the reactor internals. In order to evaluate the potential failure mechanisms of the core barrel assembly, finite element models were developed capable of representing the complex interactions between the components. The goal of this specific analysis is to characterize the potential failure modes, spatial and chronological distribution of potential component failures for a representative model of the Babcock & Wilcox-type (B&W) designed plants. Evaluation of the reactor vessel internals for materials aging degradation involves three analytical calculations. Radiation calculations of the core provide essential information on radiation dose and heat rates of the internals. The computational fluid dynamics domain (CFD) allows evaluation of the internals temperatures through conjugate heat transfer (CHT) analysis coupled with coolant flow. Detailed structural analysis of the internals components and bolted connections is the third major physics field involved, which facilitates the development of operating stress fields within the internals. Structural analysis was performed as two parts. First, a global structural model of the core barrel assembly was used to represent the interaction of components of the core barrel assembly during 60 years of operation. The global model does not include detail of the areas of stress concentration within bolted connections. Therefore local models of selected bolts were developed. Results of both the global and local models were used as a basis for evaluating age-related effects. The description of the functionality analysis for the B&W designed RV internals is divided into three papers. Part I was presented in PVP-2008 [2] and included a description of the overall methodology with special attention to CFD-CHT evaluations. Part II, to be presented at PVP 2009 [2] describes global structural finite element models. Part III, presented in this paper, presents a description of local models of bolted connections, results, and conclusions.
Bend Flexibility Factors of Piping Elbows and Piping Elbows With Trunnion Attachments Using the Boundary Element Method
Authors: Martinez Manuel , Bracamonte Johane , Gonzalez Marco
Published: July 2010

Flexibility Factor is an important parameter for the design of piping system related to oil, gas and power industry. Elbows give a great flexibility to piping system, but where a trunnion is attached to an elbow in order to support vertical pipe sections, the piping flexibility is affected. Generally, determination of elbow flexibility factors has been performed by engineering codes such as ASME B31.3 or ASME B31.8, or using the Finite Element Method (FEM) and Finite Difference Method (FDM). In this work, bend flexibility factors for 3D models of piping elbows and piping elbows with trunnion attachments using the Boundary Element Method (BEM) are calculated. The BEM is a relatively new numerical method for this kind of analysis, for which only the surface of the problem needs to be discretized into elements reducing the dimensionality of the problem. This paper shows the simulation of 9 elbows with commercially available geometries and 29 geometries of elbows with trunnion attachments, 10 of them using commercial elbow dimensions, with applied in-plane and out-of-plane bending moments. Structured meshes are used for all surfaces, except the contact surface of elbow-trunnion joints, and no welded joints are simulated. The results show smaller values of flexibility factors of elbow and elbow–trunnion attachments in all loading cases if are compared to ASME B31.3 or correlations obtained from other works. The results also indicate that flexibility factor for elbow-trunnion attachment subjected to in-plane bending moment is greater than flexibility factor for out-of plane bending moment. Accuracy of BEM’s results were not good when flexibility characteristic values are lesser than 0.300, which confirm the problems of this numerical method with very thin-walled structures. The method of limit element could be used as tool of alternative analysis for the design of made high-pitched system, when the problem with very thin-walled structures is fixed.
The Effect of Gaps on the Impact Response of a Cask Closure Lid
Authors: Bjorkman Gordon S.
Published: July 2010

During an impact event, gaps between the various components of a spent fuel transportation cask may create secondary impacts that result in higher dynamic loads than would have occurred if the gaps had not been present. A condition of particular interest is the gap that may exist between the cask internal contents (fuel assemblies) and cask closure lid, and the effect this gap may have on amplifying the response of the closure lid during an impact. Through the use of a simple dynamic model this paper investigates the effect of a secondary impact due to a gap between the cask internals and the cask closure lid on the response of the closure lid during a 30 foot end drop. The dynamic model consists of five components: (1) The equivalent mass of the internal contents, (2) the gap between the contents and cask lid, (3) the stiffness of the cask lid, assumed to be a simply supported circular plate, (4) the equivalent mass of the lid and finally, (5) an impact limiter that applies a constant deceleration force to the cask overpack during impact. In addition, the dynamic model assumes elastic behavior. This is consistent with the Standard Review Plan (NUREG-1617), which recommends that the closure lid bolts and closure lid system within the region of the lid bolts remain elastic in order to demonstrate leak-tightness by finite element analysis. The response results are presented in terms of the Dynamic Load Factor (DLF) for the closure lid. Response is shown to be a nonlinear function of the impact limiter deceleration, gap size and closure lid diameter, thickness and inertial properties. These results provide valuable insights into the parameters that affect response and show the conditions under which gaps of sufficient size may significantly influence response.
Dynamic Interaction Between a Straight Tube and an Anti-Vibration Bar
Authors: Nowlan Isabelle , Ross Annie , Pettigrew Michel J.
Published: July 2010

Fretting-wear is a known problem in steam generator U-tubes. These tubes are supported by flat bars called anti-vibration bars (AVB) in the plane of the U-bend. Clearances between the tubes and the bars are designed to be minimal, but cumulative tolerances and manufacturing variations may lead to clearances larger than expected. Large clearances may result in ineffective support leading to in-plane and out-of-plane motion causing fretting-wear and impact abrasion. In the present work, the problem is investigated with a single two span tube, an anti-vibration bar at mid-span and a local excitation force. The dynamic behavior of a tube with simple supports at both ends and an anti-vibration bar at mid-span is characterized. The influence of clearance, preload and tilt of the support on the dynamics of the tube are investigated experimentally. The results indicate that the fretting-wear work-rate is very low with preloads, reaches a maximum around a zero clearance and diminish again for larger clearances. The tilt of the anti-vibration bar in our experiments seems to change the dynamic behavior of the tube.
Simulation of Ratcheting Responses of Elbow Piping Components
Authors: Hassan Tasnim , Rahman Syed M.
Published: July 2010

Ratcheting damage accumulation in piping components may occur under repeated reversals of loading induced by earthquakes, mechanical and thermal operating conditions, and other extreme loading conditions. Ratcheting damage accumulation can cause failure of structures through fatigue cracks or plastic collapse. A major challenge in structural mechanics is the prediction of ratcheting responses of structures under various cyclic loading conditions. Accurate prediction of ratcheting-fatigue and ratcheting-collapse of elbow components is imperative in order to incorporate the ratcheting related failures into the ASME design Code in a rational manner. This would require predictions of both local (stress-strain) and global (load-deflection) responses simultaneously. Towards achieving this goal, a set of experimental responses of elbow piping components is developed. Advanced cyclic plasticity models, such as, modified Chaboche, Ohno-Wang, modified Ohno-Wang and Abdel Karim-Ohno, are implemented into ANSYS for simulating the experimental responses. Results from the experimental and simulation studies are presented in order to demonstrate the state of structural ratcheting response simulation by these models.
Plastic Deformation and Vibration in a Fluid-Filled Tube Subject to Axial Impact
Authors: Inaba Kazuaki , Shepherd Joseph E.
Published: July 2010

The goal of the present study is to examine the coupling of large-amplitude (including plastic deformation) flexural waves and precursor waves in water-filled, thin-wall (1.6 mm) steel tubes. To do this, we have compared the coupling created by exciting the stress waves in water versus in the tube wall. To examine the case of coupling from water to the tube, we used projectile impact on the water surface to create pressure waves in the water propagating along the tube axis. We have tested mild steel tubes using a steel impactor accelerated to speeds of up to 80 m/s using an air cannon to strike a polycarbonate buffer placed on top of the water surface within the tube. Strain gages measure hoop and longitudinal stresses at selected locations and a pressure gage measures the reflected pressure at the bottom of the tube. To examine the coupling from the stress waves in the tube to pressure waves in the water, we excited stress waves by axial impact on the tube along using a Hopkinson bar coupled to the tube without making contact with the water. For direct impact on the water surface, propagating plastic deformation flexural waves with more than 2% hoop strain were obtained at an impact speed of 80 m/s. The maximum hoop strain was observed just below the bottom surface of the buffer as a bulge with 16% hoop strain. Hoop and longitudinal strains indicate a steep elastic front followed by a gradual plastic deformation. Initially, the plastic deformation is dominant but the peak amplitude decays as the wave propagates. Since the plastic deformation wave travels much slower than the elastic waves, the initial flexural wave fronts propagate at 1350 m/s and are close to the wave speed of the Korteweg’s elastic theory of water hammer. Stress waves propagated at 5400 m/s in the tube wall and caused a 1–2 MPa pressure fluctuation in the water. Comparing strain histories to those of tubes without water, we observe that the coupling to the water damps high frequency vibrations and reduced peak amplitudes while maintaining the ratio of hoop and longitudinal strains.
Applying Fractional Calculus Method to Evaluation of Damping in Testing Apparatus of Hard Drive Systems
Authors: Sakurada Akira , Sunakoda Katsuaki , Naganawa Akihiro , Shibuya Yotsugi , Mori Shigeki
Published: July 2010

Fractional Calculus Method is increasingly recognized as central to the interpretation and solution of nonlinear differential equation which is included time power domain [1]. Some of the authors have been engaging in the development of an nanometer positioning actuator (Hereinafter referred to as “Nano-Motion Actuator or N.M.A.”.) which is used for a spin-stand. The spin-stand is a testing apparatus for the hard disk drive system in computer hardware [2]. The N.M.A. needs a large working displacement range over 10 micrometers and its primary resonance frequency should be kept at as high a frequency domain as possible. Moreover, positioning resolution of the N.M.A. is required to be less than 0.5 nanometers (10−9 meters). A new damping mechanism which consists of visco-elastic material has recently been developed for the N.M.A. to improve vibration response characteristics [3]. However, the damping mechanism causes a new vibration problem and the characteristic of the visco-elastic material needs to be clarified. A response spectrum of the N.M.A. is examined by applying a sinusoidal sweep test. Fractional Calculus Differential Equation is introduced for curve fitting of the response spectrum of the N.M.A. Finally, the calculated results are compared with the experimental results, and both agree.
Weight Savings Using ASME Section VIII, Division 2, Design-by-Analysis Methods
Authors: Bardia Kanhaiya L. , LaBounty Donald G. , Basic Michael M. , Breig Timothy D.
Published: July 2010

The 2007 ASME Section VIII, Division 2, Part 5 Design-By-Analysis provides requirements for vessels and components using analytical methods. The authors have spent a considerable amount of time in studying and applying the requirements of the design by analysis methods in Part 5. As a result of this process, the authors have concluded that the main factor for weight savings is the stress criteria used to calculate the thickness by the design-by-analysis method. An example is provided to demonstrate the methods presented.
Flaw Evaluation for PWR and BWR Component Weld Joints Using Advanced FEA Modeling Techniques
Authors: Hayashi T. , Hankinson S. F. , Saito T. , Ng C. K. , Bamford W. H.
Published: July 2010

Primary Water Stress Corrosion Cracking (PWSCC) of Pressurized Water Reactor (PWR) primary loop piping/nozzle Dissimilar Metal Weld (DMW) joints and Inter Granular Stress Corrosion Cracking (IGSCC) of Boiling Water Reactor (BWR) weld joints is an ongoing issue in the nuclear power industry. Recent field experiences with PWSCC of various DMW joints in US plants led to the development and application of an Advanced Finite Element Analyses (AFEA) methodology that permits crack propagation with a natural flaw shape. Crack growth and fracture evaluations for both PWR and BWR components are generally performed based on a conservative, idealized crack shape model, e.g. semi-ellipse, rectangle, etc., depending on the geometry of the crack and the component. Conventional evaluation methodologies and/or assumptions of this kind, in some cases may provide excessive conservatisms. The use of natural flaw shape development with crack propagation might provide a more realistic assessment of crack growth and structural integrity. The prime purpose of this study is to demonstrate the conservatism/margins in the conventional “idealized crack shape” methodology. A comparison study of crack growth behavior between the applications of the idealized and natural crack shape methodologies has been performed in order to assess the level of conservatism/margins in the conventional crack growth evaluation methodology and the possible impacts on the structural integrity evaluation for both PWR and BWR components. Comparison studies on the impacts of the differences in crack growth law and loading condition used for crack growth evaluations have been performed as well.
Modelling of Hydrodynamic Forces on a Whirling Mixing Vessel Stirrer Including Fluid-Structure Interaction
Authors: Mohamed Khaled M. , Gerber Andrew G. , Holloway Gordon A. L.
Published: July 2010

In this paper, a modeling approach for strongly coupled Fluid-Structure Interaction (FSI) simulations of a mixing vessel stirrer is presented and discussed. A finite-volume Computational Fluid Dynamics (CFD) model is used to calculate the mixer flow field while the structural dynamics of the stirrer is based on a 2-DOF damped spring-mass oscillator system. The time integration of the stirrer response is carried out using the Newmark method, and is applied in conjunction with the implicit time integration of the fluid governing equations. The solution methodology employs a transient rotorstator interface to handle frame change between the rotor system and the baffles. Furthermore, mesh adaption around the rotor system is applied using an Arbitrary Lagrangian Eulerian (ALE) treatment of the fluid governing equations. The fluid forces acting on the impeller are analyzed and a method is proposed for extracting the added mass, damping, and stiffness coefficients, which are of significance in rotordynamic analysis. The computational results for the average stirrer deflections are in close agreement with experimental data, and the trends in the extracted rotordynamic coefficients align with other previously reported data for turbomachinery.
On the Role of Fracture Mechanics Assessment Within the Integrity Concept
Authors: Koenig Guenter , Bartonicek Jaroslav , Schoeckle Friedrich
Published: July 2010

In the EnBW nuclear power plant Neckarwestheim, the “Integrity Concept” is applied to important piping systems. As basis of this concept is an existing quality according to the requirements this has to be proven (e.g. during design and manufacturing) or verified (after a period of operation). This means for example that the material characteristics are as demanded, the construction is appropriate in detail and there is a fault free status. Possible causes of damage mechanisms in operation (loads, environment, degradation of material behavior) are either excluded or controlled, i.e. analyzed and assessed according to the requirements (standards). Within the scope of the “Integrity Concept” fracture mechanics analysis is a redundant measure. In the state of design, already, the assessment of a postulated crack is necessary to produce a “fault-tolerant” component and to determine effective non destructive test regions, methods and test intervals, so that possible consequences of damage mechanisms like cracks can be detected in an early stage. The size of the postulated crack envelopes the detectable crack depending on the resolution of the non destructive test method used during the manufacturing process and in operation. Using the operation loads the growth of the postulated crack is analyzed and assessed. Additionally, it is shown that the size of a through wall crack is safe below the critical crack size. Furthermore, it is demonstrated that the maximum loads in operation as well as in emergency and faulted conditions are below the collapse load. The high quality of the systems as produced has to be guaranteed in operation using redundant measures. Ageing phenomena have to be controlled concentrating on the relevant causes of possible damage. In most of the cases, damage mechanisms are caused by local effects; consequently, these local effects (like loads, water chemistry etc.) have to be monitored, evaluated and assessed regularly. Thus the knowledge about the system is permanently increased. Inservice inspection and testing are redundant measures to safeguard integrity. The efficiency of the entire procedure has to be assessed, periodically, taking into account the actual state of knowledge. Following this procedure the safety margin of the systems and components can be verified (and demonstrated) at every stage of operation. If the “Integrity Concept” is applied consequently there is no reason to restrict the application e.g. to certain systems or to nominal diameters > 200 mm. Furthermore, as fracture mechanics analysis is a tool to control a postulated extreme case (that can not occur if the analysis is correct) it is obvious that a special leak detection system is obsolete because it does not increase safety. Therefore it makes no sense to analyze leak rates etc.
Application of Instrumented Indentation Technique to Small-Scale Testing of Pressure Vessels and Piping Systems
Authors: Kim Kug-Hwan , Kang Seung-Kyun , Choi Min-Jae , Kim Kwang-Ho , Kwon Dongil
Published: July 2010

The instrumented indentation technique (IIT) is a powerful tool for measuring mechanical properties by analyzing the load-penetration depth curve. It differs from conventional test methods such as tensile testing, CTOD, etc., in being applicable to small samples and to localized sections where material properties change rapidly. It also has the significant advantage of simplicity in specimen preparation and experimental procedure. Analytic models and procedures are presented here for evaluating flow properties and stress state using IIT; the flow properties are treated by defining the representative stress and strain underneath a spherical indenter and the residual stress by using a stress-insensitive contact hardness model. Flow properties of 5 steel materials were measured by IIT and compared with those from uniaxial tensile tests. The residual stress states of a welded joint were evaluated and compared with those measured by mechanical saw cutting. Examples of the application of IIT to small-scale materials and localized sections of pressure vessel and piping systems in situ are also presented.
Overview of DCNS Methodology on Fluid-Structure Interaction Modelling in Nuclear Pressure Vessels
Authors: Sigrist Jean-Franc¸ois
Published: July 2010

The design of nuclear pressure vessel requires the description of various dynamic effects, among which fluid-structure interaction. The present paper gives on overview of DCNS R&D methodology for fluid-structure interaction modelling in nuclear pressure vessels: a global R&D program has been launched by DCNS within a collaborative framework, or the application of numerical methods in FSI to the dynamic analysis of nuclear propulsion systems (nuclear reactors and steam generators). Two applications are proposed in the paper as a conclusive example of this R&D program. 1) The dynamic analysis of a nuclear reactor with FSI is made possible by the implementation of the so-called (u, p, φ) formulation within the ANSYS code [J.F. Sigrist, S. Garreau, Dynamic Analysis of Fluid-Structure Interaction Problems with Spectral Method Using Pressure-Based Finite Elements, Finite Element Analysis in Design, 43 (4), 287–300, 2007] allowing the application of modal methods in the context of coupled fluid-structure systems; importance of FSI in the dynamic behaviour of a nuclear reactor are underlined by a fully coupled analysis. 2) The dynamic analysis of a steam generator with FSI is made possible by the implementation of an homogenisation technique within the CASTEM code [J.F. Sigrist, D. Broc, Dynamic Analysis of a Tube Bundle with Fluid-Structure Interaction Modelling Using a Homogenisation Method, Computer Methods in Applied Mechanics and Engineering, 197 (9–12), 1080–1099, 2008] allowing the description of the interactions between the confined fluid and inner structures and tube bundle in a straightforward manner.
Sensitivity of the Effective Seismic Support Damping in a Class I Piping System to Analysis Parameters
Authors: Zobeiry Nima
Published: July 2010

It is understood that the level of seismic damping in a piping system is strongly influenced by the supports. Put differently, the supports contribute to an effective damping that can be considered in the seismic analysis of the piping system. This paper investigates the issue for the feeder pipes of a CANDU™ reactor. Feeders are numerous class I pipes in parallel, which are separated by frictional spacer elements. The results of a time history analysis, taking into account different damping mechanisms, are compared to those from a response spectrum analysis to deduce the effective damping in the system. The sensitivity of the effective damping to different parameters, such as the coefficient of friction and the input frequency content, is investigated.
Constraint Analysis and Failure Prediction of Line Pipes
Authors: Wang Z. X. , Chao Y. J. , Lam P. S.
Published: July 2010

The crack tip stress fields in X80 pipeline steels were analyzed with the J-A2 constraint theory in fracture mechanics. The relationship between the constrain parameter, A2, and the ratio of crack length to specimen width (a/W) or pipe wall thickness (a/t) was obtained, respectively, for three-point bend, single edge-notched tension, and a part-through wall axial crack in a line pipe subject to internal pressure. For engineering purposes, the equivalent values of a/W (or a/t) between these geometries at the same constraint level can be calculated by a conversion formula based on curve fitting. In addition, an empirical factor, which is a function of a/t and is defined as the ratio of plastic limit load to the fracture load based on J-A2 theory, was shown to be an effective method to estimate the pipeline failure stress without complicated elastic-plastic stress analysis.
On-Line Monitoring System for Main Steam Piping of Power Plants
Authors: Wang Ning , Wang Zhengdong , Chen Yingqi
Published: July 2010

An on-line life prediction system is developed for remote monitoring of material aging in a main steam piping system. The stress analysis of piping system is performed by using the finite element method. A sensor network is established in the monitoring system. The creep damage is evaluated from strain gages and a relationship is given based on a database between the damage and residual life. Web technologies are used for remote monitoring to predict the residual life for every part of the piping system. This system is useful for safety assessment procedures in thermal power plant, nuclear power plant and petrochemical industries.
JSME Construction Standard for Superconducting Magnet of Fusion Facility “Procedure for Structural Design”
Authors: Takahashi Yukio , Tado Shigeru , Kitamura Kazunori , Nakahira Masataka , Ohmori Junji , Nakasone Yuji
Published: July 2010

Superconducting magnets are structures which have an important role in Tokamak-type fusion reactor plants. They are huge and complicated structures exposed to very low temperature, 4K and the methods for keeping their integrity need to be newly developed. To maintain their structural integrity during the plant operation, a procedure for structural design was developed as a part of JSME Construction Standard for Superconducting Magnet. General structures and requirements of this procedure basically follow those of class 1 and class 2 components in light water reactor plants as specified in Section III, Division 1 of the ASME Boiler and Pressure Vessel Code, and include the evaluation of primary stress, secondary stress and fatigue damage. However, various new aspects have been incorporated considering the features of superconducting magnet structures. They can be summarized as follows: (i) A new procedure to determine allowable stress intensity value was employed to take advantage of the excellent property of newly developed austenitic stainless steels. (ii) Allowable stress system was simplified considering that only austenitic stainless steels and a nickel-based alloy are planned to be used. (iii) A design fatigue curve at 4K was developed for austenitic stainless steels. (iv) In addition to the conventional fatigue assessment based on design fatigue curves, guidelines for fatigue assessment based on crack growth prediction were added as a non-mandatory appendix to provide a tool of assurance for welded joints which are difficult to evaluate nondestructively during the service.
Multi-Variable Engineering Model for Axial Delayed Hydride Cracking Growth Rate in Pre-Irradiated Zr-2.5%Nb
Authors: Gutkin Leonid , Scarth Douglas A.
Published: July 2010

The growth rate of postulated delayed hydride cracks in CANDU Zr-2.5%Nb pressure tubes is an important material property required for flaw evaluations and leak-before-break assessments. It is monitored using surveillance pressure tubes according to the requirements of the Canadian Standards Association (CSA) Standard N285.4 [1]. Radial growth rate and axial growth rate are used to calculate the propagation of delayed hydride cracks in the through-wall direction and along the pressure tube length, respectively. The axial delayed hydride cracking growth rate had been previously found to increase exponentially with inverse absolute test temperature. This dependence had been described by an Arrhenius-type regression model with one explanatory variable. As more experimental results were obtained from surveillance pressure tubes, it has become possible to assess whether there may be statistically significant effects of other variables, which should be incorporated into the representative relation for the axial delayed hydride cracking growth rate. In this paper, multi-variable regression analysis has been used to develop an improved representative model for the axial delayed hydride cracking growth rate of irradiated Zr-2.5%Nb pressure tube material. The developed model explains approximately 93% of overall observed variation in the experimental data, and therefore has better predictive capabilities than the reference regression model with test temperature as a sole predictor. The developed multi-variable model is proposed to be incorporated into the scheduled revision (2010 edition) of the CSA Standard N285.8 as the representative predictive model.
Simplified Stress Intensity Factor Equation for SCC Propagation in the Pipe Welds (Step 2)
Authors: Ochi Mayumi , Hojo Kiminobu , Ogawa Kazuo , Ogawa Naoki
Published: July 2010

Considering characteristics of PWSCC’s propagation behavior of the dissimilar welding joint of the safe end nozzles, an axial crack was modeled in a FE (Finite Element) model as a rectangular shape with larger aspect ratio. The stress intensity factors at the deepest point of the crack were calculated with change of crack depth. Using the influence coefficients, the simplified equation of stress intensity factor with parameters of radius/thickness and thickness/weld width was proposed. The contents of this paper is revised from the paper already presented [1] by further investigation for the shallow cracks with less than 20% thickness.
Computational Study of Flow Structure and Forces on a Cylinder Vibrating Transversely and In-Line to a Steady Stream: Effects of Sub-Harmonic Forcing
Authors: Perdikaris Paris G. , Kaiktsis Lambros , Triantafyllou George S.
Published: July 2010

In this work, we present a computational study of the flow structure and forces on a cylinder vibrating both transversely and in-line to a uniform stream. The in-line frequency is equal to twice the transverse frequency, while the ratio of the in-line to the transverse oscillation amplitude varies from zero (transverse vibration only) to infinity (in-line oscillation only). For all intermediate values, the cylinder thus follows an “eight”-like of trajectory, emulating the motion of real cylindrical structures undergoing vortex-induced vibrations. For a flow from left to right, we distinguish between a “counter-clockwise” mode (if the upper part of the trajectory is traversed counter-clockwise) and a “clockwise” mode (if the upper part of the trajectory is traversed clockwise). Here, we use a spectral element method, and perform simulations for a Reynolds number of 400. We focus on a value of the transverse oscillation frequency equal to half the natural frequency of the Ka´rma´n vortex street (sub-harmonic excitation). Results are compared against cases corresponding to resonant forcing, previously studied by the research team. In all cases, the flow properties are greatly influenced by the direction in which the cylinder is traversed. In particular, the “counter-clockwise” mode is characterized by higher values of the forces acting on the cylinder, as well as by higher values of the power transfer from the flow to the cylinder. The case of sub-harmonic excitation is unique, in that the power transfer remains negative for all values of the non-dimensional excitation amplitude, i.e. corresponds to damping. Flow visualization reveals a variety of vortex patterns in the wake, in particular regular patterns at sub-harmonic excitation, and complex vortex streets at high amplitude resonant forcing.
3D Modeling of Crack Arrest Experiment With a Local Approach
Authors: Dahl Anna , Moinereau Dominique , Berdin Clotilde , Meziere Yves
Published: July 2010

A local stress criterion based on the maximal principal stress is applied for 3D-modeling crack arrest experiments: thermal shock experiments on precracked disc. The crack front shape is simulated and compared to the experimental results. A scatter in critical stress for cleavage crack arrest is introduced through Monte-Carlo simulations with the Weibull distribution. As a result, for the thermal shock experiment on precracked disc, the scatter in critical stress has no influence on the crack length at arrest, but the regularity of the simulated crack arrest front depends on it. This result can be due to the mechanical aspect of the test rather than to the micro-mechanisms of cleavage crack arrest: the vibration of the disc induces the crack closure.
“Low Temperature” FAC
Authors: Crockett Harold M. , Horowitz Jeffrey S.
Published: July 2010

Flow-acceleration corrosion (FAC) is a degradation mechanism that impacts carbon steel under conditions often found in both nuclear and fossil power plants. FAC damage is normally found between about 90 – 230°C. However, damage at higher temperatures and occasionally lower temperatures has been reported. Although not common, low temperature degradation can result in shutdowns and costly maintenance activities. Described are reports of damage to piping and equipment in the condensate system and downstream of a blowdown demineralizer at several Pressurized Water Reactors (PWR). In all cases, the piping contained flowing deoxygenated, neutral water at about 120°F (∼ 50°C). Also, experience with non-FAC degradation was reported at one unit. This paper also describes damage to systems in two Boiling Water Reactors (BWR). In these cases, there was a low concentration of dissolved oxygen in neutral water. Damage to BWRs may be less common, but damage rates similar to those found in PWRs have been observed. Based on this work, it is recommended that plant operators perform susceptibility analyses and if necessary inspections in areas where there is neutral water with a low concentration of dissolved oxygen. PWR units that run their polishers full-time are especially vulnerable. Implications to system re-design will also be presented.
Fitness-for-Service Assessment for a Radioactive Waste Tank That Contains Stress Corrosion Cracks
Authors: Wiersma Bruce J. , Elder James B. , VandeKamp Rodney W. , McKeel Charles A.
Published: July 2010

Radioactive wastes are confined in 49 underground storage tanks at the Savannah River Site. The tanks are examined by ultrasonic (UT) methods for thinning, pitting, and stress corrosion cracking in order to assess fitness-for-service. During an inspection in 2002, ten cracks were identified on one of the tanks. Given the location of the cracks (i.e., adjacent to welds, weld attachments, and weld repairs), fabrication details (e.g., this tank was not stress-relieved), and the service history the degradation mechanism was stress corrosion cracking. Crack instability calculations utilizing API-579 guidance were performed to show that the combination of expected future service condition hydrostatic and tensile weld residual stresses do not drive any of the identified cracks to instability. The cracks were re-inspected in 2007 to determine if crack growth had occurred. During this re-examination, one indication that was initially reported as a “possible perpendicular crack <25% through wall” in 2002, was clearly shown not to be a crack. Additionally, examination of a new area immediately adjacent to other cracks along a vertical weld revealed three new cracks. It is not known when these new cracks formed as they could very well have been present in 2002 as well. Therefore, a total of twelve cracks were evaluated during the re-examination. Comparison of the crack lengths measured in 2002 and 2007 revealed that crack growth had occurred in four of the nine previously measured cracks. The crack length extension ranged from 0.25 to 1.8 inches. However, in all cases the cracks still remained within the tensile weld residual stress zone (i.e., within two to three inches of the weld). The impact of the cracks that grew on the future service of Tank 15 was reassessed. API-579 crack instability calculations were again performed based on expected future service conditions and trended crack growth rates for the future tank service cycle. The analysis showed that the combined hydrostatic and tensile weld residual stresses do not drive the identified cracks to instability. This tank expected to be decommissioned in the near future. However, if these plans are delayed, it was recommended that a third examination of selected cracks in the tank be performed in 2014.
Analytical Modeling of Dynamic Crack Propagation in DCB Specimens
Authors: Shahani Amir Reza , Amini Fasakhodi Mohammad Reza
Published: July 2010

An analytical solution via the beam theory considering shear deformation effects is developed to solve the static and dynamic fracture problem in a bounded medium such as DCB (Double Cantilever Beam) specimen. In the static case, the stress intensity factor (SIF) is derived at the crack tip through the compliance approach for fixed displacement conditions. In the dynamic case, the energy balance criterion is employed to obtain the equation of motion for a running crack and the problem is solved supposing quasi-static crack propagation. Finally, a closed form relation for the crack propagation velocity versus specimen parameters and crack growth resistance of the material is found. Therefore, the effects of various parameters are investigated on the crack growth velocity. It is shown that the reacceleration of crack growth appears when the crack tip approaches the end of specimen under fixed displacement loading. The predicted results are compared with those cited in the literature and a good agreement is observed. It is seen that shear deformation effects are more significant when the small values of a0/h is considered in the analysis.
Elevated Temperature Shakedown Concepts
Authors: Becht Charles
Published: July 2010

This paper is the first part of a two part paper. It describes concepts of shakedown at elevated temperatures that form the foundation for proposed rules described in the second paper for extension of fatigue design rules in Section VIII, Div 2 slightly into the creep range.
Identification of Stress Multiaxiallity Effect on Creep Damage by a Combination of Experiments and Numerical Analyses
Authors: Takahashi Yukio
Published: July 2010

Structural materials experience various stress states and their integrity under a wide variety of stress multiaxility needs to be evaluated in design and life management for various components. Especially creep rupture behavior is known to be quite sensitive to the stress multiaxiality. To systematically evaluate the multiaxial effect on creep rupture behavior of modified 9Cr-1Mo steel, a number of creep tests were conducted on round-bar specimens with circumferential notches. Strong effects of temperature and deformation rate on the reduction of area were observed and their synergetic effect was modeled by a simple expression. Then crack growth in compact tension specimens was simulated by finite element analysis to derive ductility under higher stress triaxiality. Finally, true rupture strain was expressed as a function of temperature, inelastic strain rate and triaxiality factor and its validity was demonstrated through finite element analyses on notched bar and compact tension specimens employing it as a local fracture criterion.
Tearing Resistance Properties of Stainless Steel Orbital TIG Narrow Gap Welds of Primary Piping in PWR Plants
Authors: Ould Pascal , Joly Pierre , Pillot Sylvain
Published: July 2010

The homogeneous butt welds of the main coolant lines of the French PWR plants have been done either by manual process with covered electrode (SMAW), automatic Orbital TIG process and, more recently for the EPR™ plants, automatic Orbital TIG Narrow Gap process (Orbital TIG NG). The primary piping is made of stainless steel, and the weld metal is an austenitic stainless steel grade Type AWS 316L for the three welding processes used. The safety analysis of the main coolant line requires the knowledge of the tearing resistance of these stainless steel butt welds consequently, tearing resistance tests have been performed recently on stainless steels Orbital TIG NG weld mock-ups. The characterizations have been done for the centreline of the weld, in the fusion Line and in the HAZ. This paper present the tearing resistance results obtained on Stainless steels Orbital TIG NG welds. The results are discussed, related to the mechanical properties and compared with the tearing resistance obtained by the other butt welding processes of the primary piping.
Effect of Pressurization on the Buckling Behavior of Thin-Walled Cylinders Under Bending Load
Authors: Limam Ali , Mathon Ce´dric
Published: July 2010

This study deals with the buckling of thin cylindrical shells submitted to combined loads such internal pressure, bending and axial compression. A large experimental investigation is conducted and some explanations on the behavior of such loaded structures and on the influence of distinct parameters are gauged. The parametrical studies show the stabilising effect of low internal pressure and a drop of the load capacity for high internal pressure due to the plasticity effect. Specific recommendations are finally established for the design.