bluuebunny/crossref_metadata_2025 huggingface dataset:
Modified J Estimation by GE/EPRI Method for Circumferential Surface Cracked Pipes Under Bending or Combined Bending and Pressure Loads
Authors: Zhang Jing , Liu Chang-Jun , Xuan Fu-Zhen , Li Pei-Ning
Published: May 2012

In order to assess the structural integrity of the components in nuclear power plants, it is necessary to accurately evaluate the J-integral. EPRI J-integral estimation method has been widely used. However for the pipes with circumferential surface cracks, since the solutions of fully plastic factors H1 were few under the combined pressure and bending loading condition. In such a case, EPRI J-integral might be non-conservative in elastic-plastic transition zone. Considering the problems, detailed finite element analysis (FEA) were conducted in this work, and H1, shape factors F were provided for the pure pressure, pure bending, and combined pressure and bending conditions. The reasons for non-conservatism of EPRI method were discussed, and a modified J estimation method was developed. For validation, failure assessment curves (FACs) were employed to compare the proposed J-integral estimation, EPRI J-integral and FEA method. The results showed that FAC based on the proposed J-integral method agreed well with FEA result, which provided good confidence in the use of this method.
CFD Estimation of the Unsteady Fluid Force Along a Fuel Rod Downstream a Mixing Grid
Authors: Moussou P. , Benhamadouche S. , Bodel Ch.
Published: May 2012

Unsteady flow loading of fuel assemblies in Pressurised Water Reactors power plants is a potential cause of deformation and of fretting wear damage. Inside a fuel assembly, rods are arranged in 17 × 17 bundles. The rod diameter is equal to about 9 mm, and the gap between two rods is equal to about 2 mm. Each rod is several meters long, and mixing grids are arranged every 0.4 m. The axial flow velocity is equal to about 5 m/s, so that the Reynolds number reaches 5 × 105 in the reactor configuration. Due to the complexity of the turbulent flow pattern, an accurate description of the fluid-structure interaction is still a challenging task, and only a few data about this issue are available today in literature. Recent Computational Fluid Dynamics results are revisited from the point of view of classical axial turbulence-induced vibrations. The unsteady pressure force Power Spectral Densities are determined, a convective velocity is derived, and an estimation of the axial correlation length for the pressure force is given. The results agree reasonably well with the scientific literature.
Numerical Analysis of the Mesoscale Mechanical Field at the Intergranular Crack Tip
Authors: Tang Wei , Xue He , Shi Longbo , Fang Xiurong
Published: May 2012

Austenitic stainless steel components operated in the light-water reactor (LWR) environment are susceptible to intergranular corrosion cracking (IGSCC). It is well known that the environment and materials near the crack tip are the most important factors affecting the IGSCC crack growth rate in the high-temperature aqueous environments. An intergranular crack growth model based on the multi-scale method is proposed in this study to accurately capture the stress-strain state at the crack tip of IGSCC. This model is implemented in ABAQUS via a sub-model technique. The effect of the extension direction of the kinking cracks on IGSCC behavior is studied for better understanding the effect of stress-strain field at crack tip on the crack growth rate in LWR.
Study of Tank Acoustic Emission Testing Signals Analysis Method Based on Wavelet Neural Network
Authors: Li Wei , Dai Guang , Wang Yali , Long Feifei
Published: May 2012

Acoustic emission technology is mostly used in corrosion detection of the atmospheric vertical storage tank bottom, but the evaluation results are always affected by the complex sound sources. In this paper, wavelet neural network is used to identify the acoustic emission signals from different types of tanks. Using wavelet transform and threshold denoising to denoise the detection signals, after wavelet packet decomposition, each node’s energy distribution and the feature vectors of extracted corrosion signals of the tank floor are selected as the input. At last, the compact-type wavelet neural network is chosen to recognize different AE signals. The result of magnetic flux leakage test proves that this method can improve acoustic emission signal analysis precision and achieve the accurate corrosion evaluation based on AE technology.
Investigation on Fatigue Properties of Cold Stretched Austenitic Stainless Steel
Authors: Miao Cunjian , Zheng Jinyang , Ma Li , Ye Duyi
Published: May 2012

Cold stretched pressure vessels from austenitic stainless steel (ASS), which are sometimes subjected to alternative loads during operation, have been widely used for storage and transportation of liquefied gases. Understanding how the fatigue properties respond to cold stretching is the basis for establishing fatigue design method of such vessels. This paper involves in the fatigue properties of ASS with 9% plastic deformation by pre-stretching parallel to the rolling direction at room temperature. For this purpose, low-cycle fatigue tests at total strain amplitudes ranging from ±0.4 to 0.8% of cold stretched ASS EN 1.4301 (equivalents include UNS S30400, AISI 304) are performed, while the martensite contents are measured during the fatigue cycles. A comparison study of cyclic stress-strain behavior and fatigue lives is carried out for both cold stretched and solution annealed specimens. Based on the testing results, a S-N curve of cold stretched ASS is obtained, which is compared with the design curves given by the standards such as ASME BPVC VIII-2. These works may help to establish a favorable foundation for the development of fatigue design in cold stretched pressure vessel.
Embrittlement Issues in RPV Materials; Might They Be Used Beyond Their Current Fluence Range?
Authors: Blagoeva Darina T. , Debarberis Luigi , Hegeman Hans J. B. J. , Luzginova Natalia V.
Published: May 2012

Reactor Pressure Vessel (RPV) materials are well proven suitable materials for nuclear applications. Surveillance data from both pressurized Water Reactors (PWR) and Water-cooled Water-moderated Energy Reactor (WWER) up to 0.08–0.45 dpa and research data up to approx 1–2 dpa are available for irradiation temperature of 300°C. The response to radiation is very well understood as well as the effect of deleterious impurities. The data have been analysed in details, showing the strong role of impurities like copper and phosphorus besides basic matrix damage (MD). Reliable embrittlement models have been developed for the range of pressure vessel application. In fact, nowadays, very ‘clean’ materials with minimum radiation sensitivity are utilized. For ‘clean’ RPV steels, basic matrix damage is the main damage mechanism, described as a power function of the dose with exponents normally from 1/3 to 1/2. New advanced ferritic-martensitic (FM) materials have been designed for fusion and GEN IV applications, as for example Eurofer steel. Irradiation embrittlement data at high doses for this material are already available, also at 300°C. Both RPV and FM materials may be suitable also for GEN IV applications; in particular for the pressure vessel. In this study, the embrittlement curves of RPV and Eurofer are compared showing continuity and a common embrittlement trend till intermediate doses. For very high doses, over 1–2 dpa where only Eurofer data are available, damage rate saturation tendency is observed. The observed continuity and partial overlapping can be explained by a common damage underlying mechanism of the different steels, e.g. ferrite damage, in spite of different steel structures and content (e.g. from 1% Cr for PWR, 2.25% Cr for WWER and 9% Cr for Eurofer steel. Form the modeling point of view the matrix term need to be adjusted for doses far higher than those experienced for RPV applications; in fact the predictions are far too conservative and a new descriptive term need to be developed. In conclusion, clean RPV materials together with new developed steels can be conveniently utilised at 300°C also outside their envisaged dose range.
Experimental Study of a Full Scale Building Isolated With Multiple Friction Pendulum System With Multiple Sliding Interfaces
Authors: Tsai C. S. , Wang Y. M. , Su H. C.
Published: May 2012

Presented in this paper is the performance evaluation of the multiple friction pendulum system (MFPS) with multiple sliding interfaces on seismic mitigation through a series of shaking table tests of a full scale MFPS-isolated building. In the tests, a three-story steel building of 40 tons in total weight, 3m and 4.5m in two horizontal directions and 9m in height, was equipped with MFPS isolators each with 4 sliding interfaces and subjected to various types of earthquakes to examine the efficiency of the isolators in reducing seismic response of a structure. Experimental results from shaking table tests tells that the roof accelerations, base shears, column shear forces have been significantly lessened with negligible residual displacements in the isolators while compared to the responses of a fixed-base structure.
Uncertainties in Predictions by Complex System Codes
Authors: D’Auria Francesco , Petruzzi Alessandro
Published: May 2012

Uncertainty analysis aims at characterizing the errors associated with experiments and predictions of computer codes, in contradistinction with sensitivity analysis, which aims at determining the rate of change (i.e., derivative) in the predictions of codes when one or more (typically uncertain) input parameters varies within its range of interest. In the present paper the salient features of established approaches for estimating uncertainties associated with predictions of complex system codes are reviewed together with the reasons why uncertainty evaluation is mandatory in nuclear reactor safety and licensing.
Identification of Whistling Ability of a Single Hole Orifice From an Incompressible Flow Simulation
Authors: Lacombe Romain , Moussou Pierre , Aure´gan Yves
Published: May 2012

Pure tone noise from orifices in pipe result from vortex shedding with lock-in. Acoustic amplification at the orifice is coupled to resonant condition to create self-sustained oscillations. One key feature of this phenomenon is hence the ability of an orifice to amplify acoustic waves in a given range of frequencies. Here a numerical investigation of the linear response of an orifice is undertaken, with the support of experimental data for validation. The study deals with a sharp edge orifice. Its diameter equals to 0.015 m and its thickness to 0.005 m. The pipe diameter is 0.030 m. An air flow with a Mach number 0.026 and a Reynolds number 18000 in the main pipe is present. At such a low Mach number, the fluid behavior can reasonably be described as locally incompressible. The incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are solved with the help of a finite volume fluid mechanics software. The orifice is submitted to an average flow velocity, with superimposed small harmonic perturbations. The harmonic response of the orifice is the difference between the upstream and downstream pressures, and a straightforward calculation brings out the acoustic impedance of the orifice. Comparison with experiments shows that the main physical features of the whistling phenomenon are reasonably reproduced.
Development of Design Rules for Nozzles in Pressure Vessels for the ASME B&PV Code, Section VIII, Division 2
Authors: Cao Zhenning , Bildy Les , Osage David A. , Sowinski J. C.
Published: May 2012

The theory behind the pressure-area method that is incorporated in the ASME B&PV Code, Section VIII-2 is presented in this paper. Background and insight to the nozzle rules of ASME B&PV Code, Section VIII, Division 2, Part 4, paragraph 4.5 are also provided. Recommendations for modifying the current nozzles rules, those published in ASME B&PV Code, Section VIII, Division 2, 2010 Edition, is given based on continuing research and development efforts. A comparison between experimental results, results derived from detailed finite element analysis (FEA), the rules prior to the VIII-2 Rewrite (2004 Edition), and the rules in VIII-2 are provided in terms of a design margin and permissible maximum allowable working pressure (MAWP) computed with the design rules. A complete description of the theory including a commentary and comparison to experimental results is provided in WRC529 [1].
Predictive Simulation in Structural Health Monitoring With Piezoelectric Wafer Active Sensors for Risk-Informed In-Service Inspection
Authors: Giurgiutiu Victor
Published: May 2012

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive enablers for a large class of structural health monitoring (SHM) applications. The presentation will start with a brief review of PWAS physical principles and basic modeling. Then, the presentation will consider the several ways in which PWAS can be used for damage detection: (a) embedded guided-wave ultrasonics, i.e., pitch-catch, pulse-echo, phased arrays, thickness mode; (b) high-frequency modal sensing, i.e., the electro-mechanical (E/M) impedance method; (c) passive detection, i.e., acoustic emission and impact detection. Emphasis will be placed on recent developments. Special attention will be given to the mechatronics predictive modeling of the complete cycle from electrical excitation through piezoelectric transduction, ultrasonic acoustic waves, and finally reverse piezoelectric transduction to generate the received electric signal. Power and energy aspects of this process will be considered and discussed. The presentation will end with conclusions and suggestions for further work.
Steam and Feedwater Piping Assessment Outside the Containment at Metsamor NPP
Authors: Rydlova Jolana , Fetter Jiri
Published: May 2012

In this paper, experience and results of the Pipe integrity design project applied to Unit 2 of Armenian NPP in Metsamor are presented. The feedwater and steam piping lines, which were covered by the Project, are located in the turbine hall on the elevation of +14.7 m, outside the containment. Piping was assessed from point of view of both pipe rupture postulation criteria defined in SRP 3.6.2 [2] and in BTP 3.4 [4] and seismic margin requirements [5] based on the international practice for the NPPs in operation. Concerning hydrodynamic calculations, possible causes of steam and water hammer were assessed. To lower the stresses in critical locations and to solve the effects of steam/feedwater/emergency feedwater pipe whip, some measures have been proposed — installations of whip restraints, hydraulic snubbers, etc. Detailed design files have been prepared for the proposed measures. Within this project, ISI program was conducted, with application to the most loaded locations. Proposal of the first stage of inspections was given, taking into account the possibility that the inspections will be performed within one outage.
Plastic Amplification β of the Stress Intensity Factor for Underclad Defect in a Vessel Submitted to a Pressurised Thermal Shock
Authors: Marie S.
Published: May 2012

For the assessment of an under-clad defect in a vessel submitted to a pressurized thermal shock, the plasticity is considered through the amplification β of the elastic stress intensity factor KI in the ferritic part of the vessel. The current solution in the French RSE-M Code has been developed from a fitting of F.E. calculation results and specifies to keep constant the amplification (deduced from its value at the maximum loading point) when the stress intensity factor is decreasing. A more physical solution is proposed in this paper to deal with the initial increasing loading phase but also with the unloading phase. It takes into account two phenomena: the amplification of the elastic KI due to the plasticity in the cladding and a plastic zone correction in the ferritic part. The first amplification is determined assuming that the plasticity in the cladding could be represented as an imposed opening displacement on the crack lips. When the loading is decreasing, the model takes into account the initial elastic unloading of the cladding but also the plastic compression which leads to reduce the cladding influence on the loading of the crack tip located in the ferritic part.
Prediction of the Absence of Brittle Failure Risk for Ferritic Steel Piping Components in the Brittle-Ductile Region
Authors: Marie S. , Schwab J. , Vidard S.
Published: May 2012

This paper deals with the brittle fracture risk evaluation for a C-Mn piping component in the upper shelf of the brittle to ductile fracture transition temperature range, with the main objective to validate a predictive criteria, able to demonstrate the complete absence of brittle fracture risk. The criteria is based one a critical stress and the volume around the crack were the maximum principal stress exceed this critical stress. The model is calibrated on notched tensile specimens and CT specimens. A four-points bending pipe test has then been designed using this criterion to insure that no brittle fracture will occurs at a temperature that all CT specimens failed by cleavage. The material is a French secondary loop Tu42C ferritic steel and the pipe dimensions for the test are the same than the size of the principal secondary loop pipes. The results of the pipe test confirm the prediction with the model and the interpretation lead to define an equivalence between the loading conditions (based on the J parameter) of the pipe and the loading condition of a CT specimen.
Fast Three-Dimensional Finite Element Analysis of Weld Overlay Application on a Formed Feeder Elbow
Authors: Ku Francis H. , Riccardella Pete C.
Published: May 2012

This paper presents a fast finite element analysis (FEA) model to efficiently predict the residual stresses in a feeder elbow in a CANDU nuclear reactor coolant system throughout the various stages of the manufacturing and welding processes, including elbow forming, Grayloc hub weld, and weld overlay application. The finite element (FE) method employs optimized FEA procedure along with three-dimensional (3-D) elastic-plastic technology and large deformation capability to predict the residual stresses due to the feeder forming and various welding processes. The results demonstrate that the fast FEA method captures the residual stress trends with acceptable accuracy and, hence, provides an efficient and practical tool for performing complicated parametric 3-D weld residual stress studies.
Determination of Pipe Whip Restraint Location to Prevent Plastic Hinge Formation in High Energy Piping Systems
Authors: Vongmongkol Sivadol , Faal-Amiri Asgar , Srivastava Hari M.
Published: May 2012

The purpose of this study is to determine the Pipe Whip Restraint (PWR) location that would prevent the formation of a plastic hinge due to secondary effects of a postulated pipe break load in a high energy line(1). The prevention of a plastic hinge formation at the PWR location is important since its secondary effects could lead to additional interactions with safety related equipment, structure, and component that are essential to safely shutdown the nuclear power plants. The proper location of the PWR can be found by using the relationship between bending moment-carrying capacity of the pipe and the applied thrust force. Several closed-form solutions obtained from several literatures were studied and used to calculate bending moment-carrying capacities of a piping system and ultimately used to determine a plastic hinge length. The plastic hinge formation is also determined analytically by using the Finite Element Analysis (FEA) method. ANSYS LS-DYNA® [8] Explicit Finite Element code is used in modeling the pipe whip models, which includes the piping system and pipe whip restraint. Comparisons are made between the analytical (FEA) results and the results from several closed-form solutions.
Acoustic Fatigue Assessment of Piping System Components by Finite Element Analysis
Authors: Dweib Ahmed H.
Published: May 2012

High levels of acoustic energy can be produced at the downstream of pressure-reducing valves, pressure safety valves and control valves in piping systems. The presence of acoustic pressure waves and their coupling with the piping wall flexural modes of vibration can result in high levels of dynamic stresses, which cause acoustic fatigue failure at points of discontinuities on the pipe wall. This work presents a procedure for the assessment of the acoustic fatigue of different piping components by the application of finite element analysis. The piping system process data is used to generate the acoustic pressure and acoustic power spectrum at the downstream of the pressure-reducing valve. This acoustic power spectrum is taken to act at a finite element model of the piping system. Dynamic analysis, by use of power spectrum and harmonic analysis, is performed to obtain the response dynamic stresses, which are used for the fatigue evaluation of the piping component. The methodology presented can be applied during the engineering phase in the design and stress analysis of piping components in critical services subjected to acoustic fatigue as well as in the detailed evaluation of the different proposed acoustic fatigue design solutions.
ORNL Pre-Test Analyses of a Large-Scale Experiment in STYLE
Authors: Williams Paul T. , Yin Shengjun , Klasky Hilda B. , Bass B. Richard
Published: May 2012

Oak Ridge National Laboratory (ORNL) is conducting a series of numerical analyses to simulate a large scale mock-up experiment planned within the European Network for Structural Integrity for Lifetime Management – non-RPV Components (STYLE). STYLE is a European cooperative effort to assess the structural integrity of (non-reactor pressure vessel) reactor coolant pressure boundary components relevant to ageing and life-time management and to integrate the knowledge created in the project into mainstream nuclear industry assessment codes. ORNL contributes “work-in-kind” support to STYLE Work Package 2 (Numerical Analysis/Advanced Tools) and Work Package 3 (Engineering Assessment Methods/LBB Analyses). This paper summarizes the current status of ORNL analyses of the STYLE Mock-Up3 large-scale experiment to simulate and evaluate crack growth in a cladded ferritic pipe. The analyses are being performed in two parts. In the first part, advanced fracture mechanics models are being developed and performed to evaluate several experiment designs taking into account the capabilities of the test facility while satisfying the test objectives. Then these advanced fracture mechanics models will be utilized to simulate the crack growth in the large scale mock-up test. For the second part, the recently developed ORNL SIAM-PFM open-source, cross-platform, probabilistic computational tool will be used to generate an alternative assessment for comparison with the advanced fracture mechanics model results. The SIAM-PFM probabilistic analysis of the Mock-Up3 experiment will utilize fracture modules that are installed into a general probabilistic framework. The probabilistic results of the Mock-Up3 experiment obtained from SIAM-PFM will be compared to those results generated using the deterministic 3D nonlinear finite-element modeling approach. The objective of the probabilistic analysis is to provide uncertainty bounds that will assist in assessing the more detailed 3D finite-element solutions and to also assess the level of confidence that can be placed in the best-estimate finite-element solutions.
Experimental Investigation of a Tandem Cylinder System With a Yawed Upstream Cylinder
Authors: Wilkins Stephen J. , Hall Joseph W.
Published: May 2012

The unsteady flow field produced by a tandem cylinder system with the upstream cylinder yawed to the mean flow direction is investigated for upstream cylinder yaw angles from α = 60° to α = 90°. Multi-point fluctuating surface pressure and hotwire measurements were conducted at various spanwise positions on both the upstream and downstream cylinders. The results indicate that yawing the front cylinder to the mean flow direction causes the pressure and velocity spectra on the upstream and downstream cylinders to become more broadband than for a regular tandem cylinder system, and reduces the magnitude of the peak associated with the vortex-shedding. However, span-wise correlation and coherence measurements indicate that the vortex-shedding is still present and was being obscured by the enhanced three-dimensionality that the upstream yawed cylinder caused and was still present and correlated from front to back, at least for the larger yaw angles investigated. When the cylinder was yawed to α = 60°, the pressure fluctuations became extremely broadband and exhibited shorter spanwise correlation.
Predicting Macroscopic Dynamics in Large Distributed Systems: Part I
Authors: Mills K. L. , Filliben J. J. , Cho D.-Y. , Schwartz E. J.
Published: May 2012

Society increasingly depends on large distributed systems, such as the Internet and Web-based service-oriented architectures deployed over the Internet. Such systems constantly evolve as new software components are injected to provide increased functionality, better performance and enhanced security. Unfortunately, designers lack effective methods to predict how new components might influence macroscopic behavior. Lacking effective methods, designers rely on engineering techniques, such as: analysis of critical algorithms at small scale and under limiting assumptions; factor-at-a-time simulations conducted at modest scale; and empirical measurements in small test beds. Such engineering techniques enable designers to characterize selected properties of new components but reveal little about likely dynamics at global scale. In this paper, we outline an approach that can be used to predict macroscopic dynamics when new components are deployed in a large distributed system. Our approach combines two main methods: scale reduction and multidimensional data analysis techniques. Combining these methods, we can search a wide parameter space to identify factors likely to drive global system response and we can predict the resulting macroscopic dynamics of key system behaviors. We demonstrate our approach in the context of the Internet, where researchers, motivated by a desire to increase user performance, have proposed new algorithms to replace the standard congestion control mechanism. Previously, the proposed algorithms were studied in three ways: using analytical models of single data flows, using empirical measurements in test beds where a few data flows compete for bandwidth, and using simulations at modest scale with a few sequentially varied parameters. In contrast, by applying our approach, we simulated configurations covering four-tier network topologies, spanning continental and global distances, comprising routers operating at state-of-the-art speeds and transporting more than 105 simultaneous data flows with varying traffic patterns and temporary spatiotemporal congestion. Our findings identify the main factors influencing macroscopic dynamics of Internet congestion control, and define the specific combination of factors that must hold for users to realize improved performance. We also uncover potential for one proposed algorithm to cause widespread performance degradation. Previous engineering studies of the proposed congestion control algorithms were unable to reveal such essential information.
Load Recovery of a Bolted Joint With a Shape Memory Alloy Stud
Authors: Ould-Brahim Nazim , Bouzid Abdel-Hakim , Brailovski Vladimir
Published: May 2012

Creep is an important factor that contributes to the clamp load loss and tightness failure of bolted joints. Retightening of the joint can be expensive, time consuming and therefore is an undesirable solution. Currently, most efforts are put towards reducing load losses directly by tightening to yield, improving material creep properties or making joint less rigid. An alternative solution of current interest is the use of bolts in Shape Memory Alloys (SMA). However very few experimental studies are available that demonstrates its feasibility. The objective of this study is to exploit the benefit of the shape memory and superelasticity behaviors of a SMA stud to recover the load losses due to creep and thermal exposure of a gasket in a bolted joint assembly. This paper explores several venues to investigate and model the thermo-mechanical properties of a bolted joint with a nickel-titanium SMA stud. A stiffness-based analytical model which incorporates the Likhachev model of SMA is used as a representation of an experimental bolted joint assembly. Using this model, the rigidity of the experimental setup is optimized to make the best use of the SMA properties of the stud. This analytical model is compared with a Finite Element Model which also implements the Likhachev’s material law. Finally an experimental test bench with a relatively low stiffness representative of EN and JIS flanges is used, with and without gaskets to demonstrate the ability of the SMA stud to recover load losses due to gasket creep.
Criterion for Preventing Self-Loosening of Preloaded Countersunk Head Threaded Fasteners
Authors: Zaki Amro M. , Nassar Sayed A. , Yang Xianjie
Published: May 2012

This study develops an analytical formula for determining the minimum initial preload required to prevent the self-loosening of preloaded countersunk fasteners that are subjected to cyclic transverse loading. The formula is based on mathematical modeling of the self-loosening behavior of the fastener. The accurate prediction of the minimum bolt preload required for preventing loosening would reliably enable the use of that minimum threshold preload as a primary locking feature in critical bolted joint applications. An experimental setup and test procedure is established to compare the model prediction with the experimental data. The focus of this paper is to investigate the effect of thread pitch, excitation amplitude, as well as the bearing friction coefficient on the threshold value of the bolt preload that would prevent loosening.
Formulation of a Strain Hardening Model for Gasket Creep Relaxation
Authors: Abboud Antoine , Nassar Sayed A.
Published: May 2012

This paper proposes a novel strain hardening model for investigating gasket creep relaxation under compressive step-loading at room temperature. A closed form solution is developed for predicting the steady-state gasket pressure. Step-loading of the gasket may be directly achieved and controlled, or indirectly estimated through the bolt tightening and re-tightening torque. The effect of gasket material, time duration at each stress level, as well as the geometric parameters of the gasket is investigated. An experimental procedure and test set-up are used to validate the proposed gasket model.
The Background to Light Water Reactor Environment Fatigue Evaluation Methods for Austenitic Stainless Steel and Their Application to Sample Pressurised Water Reactor Components
Authors: Watson C. T.
Published: May 2012

There is now a large amount of small cylindrical specimen test data, which indicates that in a Light Water Reactor (LWR) environment, compared to that in air, the fatigue life of stainless steel is significantly reduced. The current ASME III design fatigue curve does not explicitly include factors to account for a LWR environment. Using the available cylindrical specimen test data, methods for accounting for a LWR environment in fatigue assessments have been proposed in NuReg/CR-6909 and in two American Society of Mechanical Engineers (ASME) code cases. One of the code cases (N-792) uses a penalty factor (Fen) approach, similar to that in NuReg/CR-6909, another (N-761) utilizes a set of environmentally corrected fatigue curves. A third code case, which is still under development, uses a flaw tolerance approach. In this paper the background to the methods for correcting for a LWR environment in fatigue calculations is presented. The safety margin present in the ASME fatigue design methodology is discussed and a short review of civil nuclear plant operating and geometrical features testing experience provided. The NuReg/CR-6909 and ASME code case N-761 methods are applied to a number of ASME III Class 1 austenitic stainless steel components, and the cumulative usage factors calculated compared with those obtained using the ASME 2007 design fatigue curve. An objective of the paper is to highlight some of the issues arising out of applying the newly proposed methods to reactor plant components.
Valve-Induced Piping Vibration
Authors: Porter Michael A. , Martens Dennis , Harrylal Ramesh , Henley Charles
Published: May 2012

While going through the startup process of a 600MMSCFD Gas Processing Plant, the piping downstream of a gas expander bypass valve and supporting structure was observed to be shaking abnormally. The shaking was significant enough that plant personnel limited the valve flow rate to well under the design capacity and at a level that limited the plant startup. The initial assumption was that the piping or the piping supports had been improperly designed. An investigation revealed no unusual looseness in the piping supports and no significant piping natural frequency at the observed vibration frequency. Further investigation revealed that the root cause of the problem was a flow-generated pulsation in the discharge of the bypass valve that excited the piping and structural supports. Changing the valve flow path and applied valve opening limits provided a temporary work-around that allowed the plant to operate at sufficient flow rates to complete the startup. Subsequent replacement of the valve with one using the same trim but with different gas flow path characteristics proved to be the ultimate solution to the problem.
Vortex-Induced Vibrations of a Cylinder at Subcritical Reynolds Number
Authors: Jus Yoann , Longatte Elisabeth , Chassaing Jean-Camille , Sagaut Pierre
Published: May 2012

The present work focusses on the numerical study of Vortex-Induced Vibrations (VIV) of an elastically mounted cylinder in a cross flow at moderate Reynolds numbers. Low mass-damping experimental studies show that the dynamic behavior of the cylinder exhibits a three-branch response model, depending on the range of the reduced velocity. However, few numerical simulations deal with accurate computations of the VIV amplitudes at the lock-in upper branch of the bifurcation diagram. In this work, the dynamic response of the cylinder is investigated by means of three-dimensional Large Eddy Simulation (LES). An Arbitrary Lagrangian Eulerian framework is employed to account for fluid solid interface boundary motion and grid deformation. Numerous numerical simulations are performed at a Reynolds number of 3900 for both no damping and low-mass damping ratio and various reduced velocities. A detailed physical analysis is conducted to show how the present methodology is able to capture the different VIV responses.
Synchrotron Radiation Study on Alloy 617 and Alloy 230 for VHTR Application
Authors: Mo Kun , Tung Hsiao-Ming , Chen Xiang , Chen Weiying , Hansen Jon B. , Stubbins James F. , Li Meimei , Almer Jonathon
Published: May 2012

High-energy synchrotron radiation has proven to be a powerful technique for investigating fundamental deformation processes for various materials, particularly metals and alloys. In this study, high-energy synchrotron X-ray diffraction (XRD) was used to evaluate Alloy 617 and Alloy 230, both of which are top candidate structural materials for the Very-High-Temperature Reactor (VHTR). Uniaxial tensile experiments using in-situ high-energy X-ray exposure showed the substantial advantages of this synchrotron technique. First, the small volume fractions of carbides, e.g. ∼6% of M6C in Alloy 230, which are difficult to observe using lab-based X-ray machines or neutron scattering facilities, were successfully examined using high-energy X-ray diffraction. Second, the loading processes of the austenitic matrix and carbides were separately studied by analyzing their respective lattice strain evolutions. In the present study, the focus was placed on Alloy 230. Although the Bragg reflections from the γ matrix behave differently, the lattice strain measured from these reflections responds linearly to external applied stress. In contrast, the lattice strain evolution for carbides is more complicated. During the transition from the elastic to the plastic regime, carbide particles experience a dramatic loading process, and their internal stress rapidly reaches the maximum value that can be withstood. The internal stress for the particles then decreases slowly with increasing applied stress. This indicates a continued particle fracture process during plastic deformations of the γ matrix. The study showed that high-energy synchrotron X-ray radiation, as a non-destructive technique for in-situ measurement, can be applied to ongoing material research for nuclear applications.
Analysis Techniques for Modeling the Pressure Wave Effects of Guillotine Ruptures of Steam Lines
Authors: Becht Charles , Moody Frederick J.
Published: May 2012

The rupture of a pipe containing gas or steam at high pressure will cause a shock wave. In order to assess the potential damage that such a shock wave may cause to the surrounding structures, systems and components, it is necessary to determine the amplitude and propagation properties of the shock. A CFD model has been developed for the purpose of predicting shock propagation transients resulting from a sudden pipe rupture in terms of the fluid properties, pipe geometry, and surroundings. A simplified shock propagation model also is included, which offers verification of the CFD model results.
A Lower-Bound Temperature and Strain-Rate Dependent Strength Model for AISI 304 SS
Authors: Follansbee Paul S. , Gross David J. , Minichiello John , Rodriguez Edward
Published: May 2012

The use of a material in a design where failure carries environmental or health and safety risk requires computational design using a conservative strength model. The materials design engineer must determine and be able to justify a lower-bound stress-strain curve. This paper uses the AISI 304 / 304L system to demonstrate how such a model might be derived. It addresses the question of variability in materials properties. Also discussed is the contribution of strain-rate dependence that is relevant to applications involving impact or explosive loading conditions. Designers and those reviewing and approving designs are more comfortable with the use of temperature dependent than strain-rate dependent material properties. Ignoring strain-rate dependence can lead to overly conservative designs, even when the objective is a conservative design. The Mechanical Threshold Stress model is used to demonstrate, in the 304 / 304L system, a lower-bound temperature and strain-rate dependent constitutive model. This model implements a state-variable approach and easily accounts for temperature and strain-rate dependent material properties as well as strain hardening. A wealth of literature data is used to benchmark and validate the model. Comparison of model predictions with applicable ASME and ASTM code standards is described.
Long-Term Creep Life Estimation for Manaurite XM Material, Using a Constrained Monkman-Grant Plot and Proportional Similitude
Authors: Voorhees Howard R. , Rhee H. Chong , Baker Michael K.
Published: May 2012

The present paper revisits a constrained use of Monkman-Grant coordinates, a relatively little employed or appreciated method for estimation of long-term creep life. This method is based on a logarithmic plot of remaining life versus the steady creep rate. A procedure, here called proportional similitude, is also discussed as a means to estimate the steady creep rate or time to rupture at an early stage of a test. Numerous studies as yet mostly unpublished increasingly demonstrate for many steel samples from prior creep service that a combination of these two methods permits extrapolations at least as soon, as accurate, and at overall cost similar to other popular procedures. One of the advantages of this procedure is that short term creep test results can be extrapolated to long-term creep life in a transparent manner without complex mathematical maneuvers or need for typical reference properties or initial behavior of the sample. Results now available for a variety of widely-employed materials suggest that these methods may have more-general validity for remaining creep life evaluations than industry has recognized. This paper presents remaining creep lives obtained though a combination of four procedures, i.e., Monkman-Grant, proportional similitude, Larson-Miller, and curve fit methods, for exposed hydrogen reformer tube samples. Results are compared with those of previous Omega analyses performed independently for the same sample.
Development of Prototype Valve to Separate Two-Phase Air-Water Flows
Authors: Harling Henry E.
Published: May 2012

A certain nuclear power plant uses a siphon to bring cooling water into the plant during emergency operations. This siphon was “hardened” by adding a nuclear grade vacuum system to the siphon high points. A float valve, sized for the required air flow rate, was used to prevent water carryover into the vacuum system. In order to pass the required flow rate, the valve’s orifice size would be the largest produced by any manufacturer to date. Initial system testing revealed that the valve was not fully opening due to the high vacuum and the design of the valve opening mechanism. Analysis and testing developed a solution to the opening problem. However, a new problem was introduced — excessive liquid carryover. The liquid carryover rate was estimated at 6 gallons per minute. The liquid carryover was postulated to be due to droplet entrainment as high velocity air bubbles entered the valve body, ruptured the air-water interface, and carried some of the resultant droplets through the valve outlet as the valve opened due to falling water level. Additionally, valve operating mechanism changes resulted in it responding slower. Using information learned from modifying the original valve, a new valve design was conceived that would be based on the following 3 principles: 1) liquid momentum must cause it to separate from the air upon entrance into the valve body; 2) enough distance and space must exist inside the body to allow gravity to act upon any liquid droplets to allow them to fall back into the liquid pool instead of being carried out of the valve toward the vacuum system; 3) valve operating mechanism must respond quickly enough to close the valve upon rapid liquid influx. The valve manufacturer reviewed the conceptual design and produced a prototype. The prototype valve was successfully tested with zero water carryover plus better flow versus pressure loss performance than the original valve. The valve also functioned acceptably during shaker table testing to simulate earthquake conditions.
Design of an Automatic Waterhammer Prevention System
Authors: Harling Henry E.
Published: May 2012

The Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 96-06 [1] which required utilities to evaluate the potential for waterhammers in cooling water systems serving containment following a Loss of Offsite Power (LOOP) concurrent with a Loss of Coolant Accident (LOCA) or Main Steam Line Break (MSLB). At Duke’s Oconee Nuclear Station, analysis and system testing in response to GL 96-06 concluded that waterhammers occur in the Low Pressure Service Water (LPSW) system during all LOOP events. Column Closure Waterhammers (CCWH) occur when the LPSW pumps restart following a LOOP and rapidly close vapor voids within the system, specifically, in the Reactor Building Cooling Unit (RBCU) and Reactor Coolant Pump (RCP) motor piping. Condensation Induced Waterhammers (CIWH) occur when heated steam voids interact with sub-cooled water in long horizontal piping sections, specifically in the RBCU and Reactor Building Auxiliary Coolers (RBAC) piping. These waterhammers were not expected to result in pipe failure, but resulted in piping code allowable stresses being exceeded. Piping code compliance was achieved by installing modifications that prevent all GL 96-06 related waterhammers inside containment. Two modifications were designed and implemented. These modifications were designed to isolate the piping inside containment, the high point in the open loop system, in order to maintain it in a water solid state. This was accomplished by a valve closure scheme that is actuated by low LPSW supply header pressure. Additionally, “controllable vacuum breakers” (pneumatic valves) open on low LPSW supply header pressure to eliminate void formation and collapse while the isolation valves are closing. The pneumatic isolation valve arrangement is single failure proof to open and to close. The Waterhammer Prevention System (WPS) circuitry closes the valves by one of two digital channels consisting of relays, which are triggered by two of four analog channels consisting of a pressure transmitter/current switch. The valves re-open on increasing supply header pressure. A “leakage accumulator” was provided in the supply header to make-up any boundary valve leakage that may occur when the system is isolated. This provides for a larger allowable aggregate boundary valve leakage rate. The system response was predicted by a model using the thermal-hydraulic code GOTHIC. Following installation, an integrated test was successfully conducted by inducing a LOOP into the LPSW system.
Finite Element Analysis for Nozzle With External Loads
Authors: Lee Hak-Sung , Ha Chang-Hoon , Park Tae-Jung
Published: May 2012

Various kinds of nozzles are attached to a pressure vessel including Steam Generator (SG) in a pressurized water reactor plant. The downcomer feedwater nozzle on the upper vessel shell and the economizer feedwater nozzle in the lower vessel shell of the SG are representative nozzles which have a non axi-symmetric shape. In most cases, external loads composed with forces and moments are imposed on those nozzles during the plant operation. In order to evaluate structural integrity of junctures between the nozzles and vessels in compliance with the ASME Boiler and Pressure Vessel Code, Section III, it is essential to find the maximum stress intensity resulting from those loads. Welding Research Council (WRC) Bulletin 297 has been used to find the maximum stress intensity since it is not straightforward to calculate the stress intensity with a non axi-symmetric two dimensional finite element model. However, the compatibility of adopting WRC Bulletin 297 to nozzles which have a variety of geometries shall be considered. Moreover, the applicability of the stress intensity resulting from the bulletin should be into consideration when interested lines where stress intensity linearization is to be performed are not exactly consistent with the line defined in the Bulletin. In this study, the nozzles in cylindrical vessel shells are developed as three dimensional finite element models, which are loaded with unit forces and moments. The stress intensities from finite element models are investigated through a comparison of WRC Bulletin 297. In addition, a methodology to apply the stress intensity results from WRC 297 to different lines is proposed.