bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Modelling Guidelines for Stress Analysis of Pressure Vessel Bolted Closures
Authors: Towse A. , Mills A. , Griffin D. , Hurrell P. , Rowe D. , Pellereau B.
Published: January 2011

This paper describes some of the outcomes of the development of finite element modelling guidelines for the stress analysis of bolted joints in pressure vessels and piping. The modelling methods originally developed at Rolls-Royce typically used 2D axisymmetric models as this was deemed adequate at the time. However, computing software and hardware improvements have subsequently been made which enable more realistic 3D bolted joint models to be solved where a greater level of geometric detail is required. For example the bolts, nuts and perforated flanges can now be represented more realistically reducing the degree of geometric abstraction that is required. Also, modern finite element codes such as ABAQUS and ANSYS now offer gasket elements which enable the initial compression, in-service performance and unloading of the joint to be modelled more realistically. Additionally, contact techniques can also be used to simulate the axial and radial distribution of thread load in the joint which will affect the stress distribution remote from the threaded region. Consequently, the modelling guidelines have been updated and provide guidance for stress engineers to decide which degree of model complexity is warranted.
Characteristic and Modeling of Multiple Direction Optimized-Friction Pendulum System With Numerous Sliding Interfaces Subjected to Multi-Directional Excitations
Authors: Tsai C. S. , Lin Yung-Chang , Su H.-C.
Published: January 2011

In this paper, a base isolator call the multiple direction optimized-friction pendulum system (Multiple DO-FPS) with numerous sliding interfaces is proposed. For understanding the mechanical behavior of the Multiple DO-PFS isolator under multi-directional excitations, an analytical model called the multiple yield and bounding surfaces model is also proposed. On the basis of the derived mathematical formulations for the simulation of the characteristic of the Multiple DO-FPS isolation bearing, it is revealed that the natural period and damping effect for a Multiple DO-FPS is a function of the sliding displacement and sliding direction. By virtue of the proposed model, the phenomena of the sliding motions of the Multiple DO-FPS isolator with numerous sliding interfaces subjected to multi-directional excitations can be simply understood. Analytical results infer that the natural frequency and damping effect of the Multiple DO-PFS isolator with numerous concave sliding interfaces change continually during earthquakes and are controllable through appropriate designs.
Current Status of New Reactor Regulations in Korea
Authors: Paek Yong Lak , Song Seon Ho , Oh Seong Hun
Published: January 2011

This paper describes an overview of the nuclear regulatory framework of Korea such as licensing process and preoperational inspection program for the new reactor, etc. In addition, this paper has been prepared to share the information on the regulatory issues in new reactors that have been granted construction permit lately in Korea.
Advanced Methods for Vibration Reduction at a Piping
Authors: Kerkhof Klaus , Schwenkkros Joachim , Barutzki Frank , Gurr-Beyer Christa
Published: January 2011

Safe operation, availability and lifetime assessment of piping are of utmost concern for plant operators. This paper presents the first results of the European research project IRIS (Integrated European Industrial Risk Reduction System) [1]. One important IRIS goal is to identify risk reduction methods to avoid high cycle fatigue at a large vertical pipe system. The piping system is supported by a tall structure fixed at the base. As a result, the steel building stiffness decreases with height. Furthermore large piping-elbow forces act at the top of the building, which lead to large vibration amplitudes. Since both piping system and supporting structure exhibited these large vibration amplitudes, dampers or shock absorbers placed between them would prove ineffective. Therefore, special vibration absorbers were developed for such piping systems. The paper presents the design process, starting with an extensive system investigation up to the passive multi-axial vibration absorber design parameters. The aim was to establish a good basis for the risk reduction of vibration induced emergency conditions by use of vibration absorbers. This included: • Laboratory tests with a mock-up pipe system, where the first design ideas for new passive vibration absorbers were investigated. • Vibration measurements were carried-out to investigate the current state of the vibration behavior. • The piping system was inspected; strain gauges were used to identify stress concentrations at welds and other notches due to ovalization. • Finite element calculations were performed, first as a combined beam and shell model for the pipe without the support structure. • A detailed model for the combined steel construction and pipe system was created. • Modal-updating was done to fit the calculated model to the experimental modal analysis data. • Load simulations were created to describe the mass flow excitation. • Harmonic frequency analysis was performed. • On the basis of these calculations design parameters for the passive vibration absorber were determined. Finally, a solution for the design of the two passive vibration absorbers will be presented.
Assessment of Interaction Effect Between Two Aligned Surface Cracks in Elbows Subjected to Internal Pressure
Authors: Seo Han-Beom , Choi Jae-Boong , Kim Young-Jin , Chang Yoon-Suk , Kim Hyun-Su
Published: January 2011

Adjacent multiple cracks can be found in power plant components such as pressure vessel, piping and so forth. If multiple cracks are detected, it can be affected significant effect to structure integrity due to high interaction effect of the multiple cracks. Therefore general fitness-for-service (FFS) codes and standards propose assessment method for the multiple cracks. The Section XI of ASME Code suggests crack coalescence method for multiple cracks. It employs the approach combining neighbored cracks as single crack if the distance between them is close. In some cases, since this combined rule can be considered as a conservative approach, more accurate investigation of the interaction effect between multiple cracks is needed. In this study, the interaction effect between two aligned coplanar circumferential surface cracks in elbows subjected to internal pressure was investigated. Since most previous studies dealt with only plates or straight pipes, the present research was centered on cracked elbow. FE (Finite element) limit analyses were carried out by changing elbow geometries and crack shapes. Also, applicability of the current criterion for the multiple cracks was discussed.
Measurement of Pressure Loss Throughout a Clogged Steam Generator Tube Support Plate in Single Phase Flow
Authors: Brunin Olivier , Deotto Geoffrey , David Franck , Pillet Joe¨l , Dague Gilles , Nicoli Alexandre
Published: January 2011

After a period of several years of operation, steam generators can be affected by fouling and clogging. Fouling means that deposits of sludge accumulate on tubes or tube support plates (TSP). That results in a reduction of heat exchange capabilities and can be modelled by means of a fouling factor. Clogging is a reduction of flow free area due to an accumulation of sludge in the space between TSP and tubes. The increase of the clogging ratio results in an increase of the overall TSP pressure loss coefficient. The link between the clogging ratio and the overall TSP pressure loss coefficient is the most important aspect of our capability to accurately calculate the thermal-hydraulics of clogged steam generators. The aim of the paper is to detail the experimental approach chosen by EDF and AREVA NP to address the calculation uncertainties. The calculation method is classically based on the computation of a single-phase (liquid-only) pressure loss coefficient, which is multiplied by a two-phase flow factor. Both parameters are well documented and can be derived on the basis of state of the art methods such as IDEL’CIK diagrams and CHISHOLM formula. The experimental approach consists of a validation of the correlations by performing tests on a mock-up section with an upward flow throughout a vertical array of tubes. A mixture of water and vapour refrigerant R116 is used to represent two-phase flows. The tube bundle is composed of a 25 tubes array in a square arrangement. The overall height of the mock-up is 2 m. Eight test TSPs were manufactured, considering eight different clogging configurations: six plates with a typical clogging profile at six clogging ratios (0, 44%, 58%, 72%, 86%, 95%), and two plates with a clogging ratio of 72% associated with two different clogging profiles (large bending radius profile and rectangular profile). A series of tests were performed in 2009 in single-phase flow conditions. Two-phase flow tests with a mixture of liquid water and vapour refrigerant R116 will be performed in 2010. The paper illustrates the main results obtained during the single-phase tests performed in 2009.
Numerical Analysis on Convection Heat Transfer of Pulsating Flow in a Corrugated Tube
Authors: Yu Jiuyang , Wang Wei , Yang Xia , Xu Jianmin , Lin Wei , Zhang Jie , Gao Jiuyang , Wang Xin
Published: January 2011

Heat transfer enhancement of corrugated tube in Laminar flow was studied using CFD. Numerical calculation performed with grids of increasing density confirms that the grids are independent. In order to get the optimal numerical calculation the boundary layer was refined. The final grid consisted of 146,000 computational cells. The fluid inlet was defined as a velocity inlet with a sinuaoidal pulasating flow input. The outlet was modeled as a pressure-outlet. By numerical simulation, the distribution of velocity and temperature of the corrugated tube of different conditions in different Reynolds number (380–1900) of steady flow, and the vibration frequency (50–200HZ)and the vibration amplitude of sinusoidal (0.1–0.9) pulsating flow is analysed, thus the characteristics of distribution of velocity and temperature are demonstrated. The simulation result indicates that by comparing with the steady flow, the pulsating flow increases the heat transfer efficiency of the corrugated tube in Laminar flow by 83% for most. The enhancement is due to the pulsating flow increating vortex. The vortex result in increasrs disturbance, decreasing the thermal boundary layer thickness, enhancing heat transfer of the corrugated tube. The result also shows that enhancement of heat transfer coefficient inceases as the velocity rises in a certain range, and it also increases as the frequency rises before reaching the peak point and then decreases as the vibration frequency rises in a certain range. Under the condition of none-backflow, the velocity of increasing enhancement of heat transfer coefficient becomes slower and slower as the vibration amplitude rises. In our study, the best dimensionless pulsating frequencies of the corrugated tube are 100∼200 Hz and the amplitudes are 0.4∼0.6, when condition that the Reynolds number is ranged from 380 to 1900.
ARCMAC Optical Creep Monitoring: Developments in Image Analysis Techniques and Creep Measurement Validation
Authors: Morris Andy , Palmer Iain , Maharaj Chris , Dear John
Published: January 2011

Power station steam pipes operate at high temperatures (approximately 570°C) and pressures, and estimation of remaining life is critical in avoiding pipe failure. In estimating remaining life, creep rate for both parent pipe material and weldments is an important metric. A number of optical strain methods have been investigated to measure creep strain, including digital image correlation (DIC) and E.ON’s auto-reference creep management and control (ARCMAC) system. The ARCMAC system measures point to point strain by capturing and analysing images of a pair of inconel gauges. Recently, a modified ARCMAC image capture system has been developed using a DSLR camera, providing higher resolution images and lower costs compared to the existing system. Experimental results from the modified ARCMAC system show reduced accuracy compared to the existing system, likely due to distortion caused by lower quality lens components. However, by calculating and applying a correction for this distortion during image processing, it has been shown that accuracy of the modified system becomes significantly better than the existing system. The processing of ARCMAC images has previously been carried out manually by the user. In order to improve the repeatability and a speed of ARCMAC image processing, a computational code has been developed to carry out the procedure automatically. As well as reducing processing time substantially, the selection of image processing parameters has been standardised, improving accuracy significantly. ARCMAC results from creep tests carried out to simulate in-service conditions and measure creep under controlled conditions are also presented. These creep experiments form part of efforts to develop the ARCMAC system to be used to measure strain on-load rather than during the outage, allowing for more regular readings and more accurate creep rate estimation.
Long Term Operation and Surveillance Specimen Program of WWER RPVs
Authors: Brumovsky Milan , Kytka Milos
Published: January 2011

Long Term Operation (LTO) to 60 or 80 years of operation also requires a reliable information about the potential irradiation embrittlement (and also thermal ageing) of reactor pressure vessel materials. Such information is usually obtained from testing specimens within the surveillance specimen program that is designed for the design RPV life, regularly for 40 years only. Life extension requires modification of such program (if there is still time to perform it) or a design of a new – extended one. Such program should have to contain RPV archive materials that are not in every case available. Thus, combination of archive materials and possible surrogate materials must be taken into account for this program. Some complication can be expected with thermal ageing data as some laboratory tests at higher temperatures must be realized. The paper describes such program for NPP Dukovany, Czech Republic with WWER-440 type reactors that are now more than 20 years of operation.
Welding Procedure Establishment for Tubular Joints Welded by Single Station, Solid State Welding Machine
Authors: Marimuthu Ganesan S. , Moe Per Thomas , Salberg Bjarne , Liu Junyan , Valberg Henry , Burnell-Gray James S. , Rudd Wayne
Published: January 2011

Forge welding is an efficient welding method for tubular joints applicable in oil and gas industries due to its simplicity in carrying out the welding, absence of molten metal and filler metals, small heat-affected zone and high process flexibility. Prior to forging, the ends (bevels) of the joining tubes can be heated by torch or electromagnetic (EM) techniques, such as induction or high frequency resistance heating. The hot bevels are subsequently pressed together to establish the weld. The entire welding process can be completed within seconds and consistently produces superior quality joints of very high strength and adequate ductility. Industrial forge welding of tubes in the field is relatively expensive compared to laboratory testing. Moreover, at the initial stages of a new project sufficient quantities of pipe material may not be available for weldability testing. For these and several other reasons we have developed a highly efficient single station, solid state welding machine that carefully replicates the thermomechanical conditions of full-scale Shielded Active Gas Forge Welding Machines (SAG-FWM) for pipeline and casing applications. This representative laboratory machine can be used to weld tubular goods, perform material characterization and/or simulate welding and heat treatment procedures. The bevel shapes at mating ends of the tubes are optimized by ABAQUS® simulations to fine tune temperature distribution. The main aim of this paper is to establish a welding procedure for welding the tubular joints by the representative laboratory machine. The quality of the welded tubular joint was analyzed by macro/micro analyses, as well as hardness and bend tests. The challenges in optimizing the bevel shape and process parameters to weld high quality tubular joints are thoroughly discussed. Finally a welding procedure specification was established to weld the tubular joints in the representative laboratory machine.
Analytical Solutions for the Study of Immersed Unanchored Structures Under Seismic Loading
Authors: Mege Romain , Jobert Nicolas
Published: January 2011

In nuclear power plants, some structures are not anchored and lay directly on the ground. This is the case for fuel storage racks. As a safety issue, one has to evaluate precisely the behavior of this sliding structure, and in particular, the cumulated sliding displacement during a seismic event in order to prevent any impact with other components. During a seismic event, the unanchored structure can slide, rotate and tilt. The aim of this paper is to present analytical solutions to estimate the sliding amplitudes of different simplified systems which represent a given dynamic behavior. These simplified models are: a sliding mass, a sliding spring-masses system and a complex sliding structure defined by its eigenmodes. Each simplified system corresponds to a different set of assumptions made on the flexibility of the structure. Two analytical solutions are presented in this article: single sliding mass and a sliding spring-masses system. The analytical solutions are obtained considering the different phases of the movement and the continuity between each phase. The results are then compared to the values computed with the commercial Finite Element package ANSYS™. The analytical curves show a good fit of the computational results.
Use of API 579-1/ASME FFS-1 Limit-Load Criteria for Establishing Load Limits for Pressure Vessel Internals
Authors: Macejko Brian R.
Published: January 2011

The 2007 edition of ASME Boiler & Pressure Vessel Code Section VIII Division 2 and the 2007 edition of Fitness-For-Service API 579-1/ASME FFS-1 provide the option to use the limit-load method to assess protection against plastic collapse for components of pressurized process equipment. Per the methodology presented therein, the allowable load on a component is established by applying design factors to the elastic-perfectly plastic limit-load such that the onset of gross plastic deformation (plastic collapse) will not occur. Typically, the design limitations of pressure vessel internal components have been assessed through closed form solutions with conservative assumptions. It has been found that the maximum pressure delta across vessel internals established through closed form solutions can become limiting in determination of time between equipment shutdowns. This paper will outline a practical example of industry applied use of the limit-load method to qualify extended limits on mechanical loads applied to pressure vessel internals.
Influence of Hydrogen-Charging on Oxidation of SUSF316L in Simulated BWR Environment
Authors: Nakajima Motoki , Hosokawa Masayuki , Sugimura Takanori , Komazaki Shin-ichi
Published: January 2011

In order to clarify the effect of hydrogen on oxidation, the austenitic stainless steel SUSF316L was charged with hydrogen by the means of cathodic electrolysis and then the hydrogen-charged steel was subjected to the oxidation test in simulated BWR environment. Experimental results revealed that the size of oxide particle formed on the outer layer increased with increasing hydrogen content, resulting in the hydrogen accelerated oxidation (HAO). Additionally, the oxide of the hydrogen-charged steel was mainly NiFe2O4, whereas Fe3O4 was predominantly formed on the non-charged one. The effect of hydrogen on the oxidation was almost equivalent to that of applied stress.
Microstructural Changes Related to Through-Wall Attenuation of Neutron Irradiation Embrittlement
Authors: Soneda Naoki , Nishida Kenji , Dohi Kenji , Nomoto Akiyoshi , Server William L. , Brumovsky Milan , Kytka Milos , Spanner Jack
Published: January 2011

The through-wall attenuation of neutron fluence of reactor pressure vessel (RPV) steels is often expressed using an exponential decay function based on some estimate of displacements per atom (dpa). In order to verify this function, an irradiation project was performed in which 18 layers of Charpy specimens and one central temperatue control layer were stacked in a block to simulate a 190 mm thick RPV wall. Three western-type RPV steels (medium and low copper plates and a high copper Linde 80 flux weld) were irradiated in this project. Mechanical property tests of these materials have been performed under a consortium of EPRI, CRIEPI, NRI-Rez and ATI Consulting to fully characterize the mechanical properties in terms of Charpy transition temperature and upper-shelf energy, as well as reference fracture toughness using the Master Curve. Some results have been reported at previous PVP conferences. In this paper, we report the results of microstructural characterization using three-dimensional atom probe tomography (APT) of the medium copper plate and the high copper weld metal. The microstructures obtained by APT reasonably explain the changes in mechanical properties of these materials, and the difference in the response of these materials to irradiation was also identified. The mixed effect of fluence/flux/spectrum is discussed from the microstructural point of view.
Application of Elastic-Plastic Design Data in the New ASME B&PV Code Section VIII Division 2
Authors: Dewees David J.
Published: January 2011

The updating and re-writing of the ASME Boiler and Pressure Vessel Code, Section VIII Division 2 (2007) [1] has introduced several new and unique features. One of these features is the inclusion of specific materials data for use in elastic-plastic analysis of pressure vessel components. Both monotonic and cyclic stress strain curve models are provided, with supporting constants for a range of materials and temperatures. The elastic-perfectly plastic material model has been used in commercial Finite Element (FE) codes for many years to perform limit load and ratcheting analyses. The new material models and data of Section VIII Division 2 (S8D2) include strain hardening and are intended for use in deformation assessments, and for determining cyclic plastic strain ranges in fatigue evaluations. This paper presents one possible implementation of the Code models and data into a standard cyclic hardening model; the multiple backstress, nonlinear kinematic-hardening model of Chaboche, as implemented in the commercial Finite Element program Abaqus, versions 6.8 and later.
CFD Tools for Assessment of the Reactor Pressure Vessel Integrity in Pressure Thermal Shock Conditions: Thermalhydraulic Benchmark on the Validation Test Case UPTF
Authors: Martin A. , Huvelin F. , Balard G. , Bellet S. , Durand B. , Martinez P.
Published: January 2011

The Reactor Pressure Vessel (RPV) assessment and lifetime evaluation of the nuclear plants leads EDF and AREVA to use CFD tools for the demonstration of the Reactor Pressure Vessel (RPV) integrity. French PWR plants have been studied for a long time and so a large number of computations have been performed in three steps: System — CFD — Mechanical Analysis. This paper focuses on the CFD aspects and especially on the two different CFD tools imposed by the physical phenomena of the transient scenarii. Indeed, the results of the system code analysis (CATHARE computations) of the PTS transient induce two kinds of scenarii: single phase and two-phase flows in the cold leg. According to the approach considered, it was interesting to carry out a global benchmark with the different thermalhydraulic tools. In this frame, Code_Saturne and Star CD CFD tools used for single phase flow scenario configuration and NEPTUNE_CFD used for two phase flow configuration were confronted with UPTF (Upper Plenum Test Facility) experiment results in a single phase scenario. The choice to perform this benchmark on UPTF test case was retained because this integral test was very representative of the main physical phenomenon that is well suited for the validation of the CFD tools used to study the Pressurised Thermal Shock for the RPV integrity.
Finite Element Modelling and Measurements of Residual Stress and Phase Composition in Ferritic Welds
Authors: Pellereau Benjamin M. E. , Gill Christopher M. , Dawson Matthew , Hurrell Paul R. , Francis John , Mark Alison
Published: January 2011

This paper describes finite element (FE) modelling and neutron diffraction (ND) measurements to investigate the development of residual stresses in two different geometries of ferritic weld. All specimens were produced using SA508 Grade 3 steel plates, depositing a low carbon SD3 weld filler by mechanised TIG welding. The FE analyses were carried out using Abaqus/VFT and the behaviour of the SA508 steel was modelled using a simplified (Leblond) phase transformation model with isotropic hardening using VFT’s UMAT-WELD subroutine, which includes the change in volume due to phase transformation. Single bead-on-plate specimens were manufactured using a range of mechanised TIG welding parameters. One pass and three pass groove welds were also produced, in order to investigate the cyclic hardening behaviour of the materials, as well as phase transformation effects in a multi-pass weld. FE analyses were then performed to determine how accurately these effects could be modelled. During manufacture, a number of thermocouples were attached to each of the specimens in order to calibrate the heat input to the FE models. The residual stresses in each of the bead on plate welds, as well as the groove weld after the first and the third passes, were then measured using ND at the middle of the plate. The ND measurements for the three pass weld showed no significant cyclic hardening behaviour although some was predicted by the FE analysis. Another key finding of the FE modelling that was seen in all of the models was that the phase transformation acts to reduce the stress levels in the deposited weld metal leaving the largest tensile stresses in a ring at the outer edge of the full heat affected zone (HAZ). There are plans to refine the FE studies using improved material properties when material testing of SA508 and SD3 are completed in the near future.
Development of a New Measurement System for Tensile Testing
Authors: Ancelet O. , Matheron Ph.
Published: January 2011

The aluminum alloy 6061-T6 is a material used for some part of experimental reactor for its interesting physical and mechanical proprieties. To respect the European rules on pressure equipments, a material must present some minimal characteristics for toughness and ductility. In this frame, a new measurement system for tensile testing was developed in the LISN laboratory of the CEA (French atomic commission), in order to characterize the local behavior of the material during a whole tensile testing. Indeed, with the conventional measurement system (typically an extensometer), the local behavior of the material can only be determinate during the stable step of the testing. So, usually the behavior of the material during the necking step of the step is unknown. This new measurement is based on the use of some laser micrometers which allow measuring the minimum diameter of the specimen and the curvature radius during the necking phase with a great precision. Thanks to the Bridgman formula, we can evaluate the local behavior of the material until the failure of the specimen. For example, the application of this new measurement system on tensile test allow to determine the behavior of the Mod.9Cr-1Mo until a strain of 130% while the conventional method can not determine the behavior up to 10% corresponding to the initiation of necking.
Development of Pressure Vessel for Food Processing
Authors: Hamashima Hideki , Shibuta Manabu , Nishimura Yosuke , Itoh Shigeru
Published: January 2011

On the food processing using the shock wave, we have developed the pressure vessel with the device generating the shock wave. By using the silicone rubber as a medium for the shock waves transported to the foods, the processing system that established the health and safety was constructed. The food processing was performed using the shock wave generated by the high power spark. In this research, in order to confirm the mechanism for the shock propagation on the food processing, the experiments and numerical calculations about the underwater explosion using an explosive were performed. In the experiment, the process of the propagation of shock wave and the bubble gas generated by the explosion was observed by the high-speed video camera. The numerical calculations for the shock propagation on the food processing were performed by using the general-purpose software LS-DYNA using the Finite Element Method. The experimental and numerical results were examined. According to the results, some points of the mechanism of the shock propagation and the bubble gas on the food processing were clarified.
Probabilistic Leak-Before-Break Assessment of a Main Coolant Line
Authors: Varfolomeev Igor , Ivanov Denis , Siegele Dieter , Nagel Gerhard
Published: January 2011

The paper presents results of a probabilistic leak-before-break (LBB) assessment of a ferritic main coolant line of a pressurized water reactor representative for German nuclear power plants. The analysis approach is based on the elastic-plastic fracture mechanics methodology, incorporating the failure assessment diagram to calculate the critical through-thickness crack size, as well as fatigue crack growth calculations to determine the flaw length at wall penetration. An essential part of this study is the collation and statistical treatment of material data, such as strength properties, crack resistance and fatigue crack growth curves, and their incorporation in the probabilistic assessment. The analysis yields negligible break probabilities, thus demonstrating the LBB behavior of the piping. This conclusion is validated by results of a sensitivity study with additional conservative assumptions and simplifications with respect to the initial crack size and material state. For the sake of simplicity, the blocking effect of the intact austenitic cladding on the crack extension, as well as the conditional probability of crack penetration through the wall during the service life are neglected in this investigation. Through an additional treatment of these issues a more realistic assessment is achieved, resulting in even smaller failure probabilities.
Status Report on ASME Section III Subgroup on Design Plan for Code Changes to Implement Environmental Fatigue Evaluation Methods
Authors: Cole Jack R. , Minichiello John C.
Published: January 2011

This paper provides a status report on the ASME Section III Subgroup on Design Environmental Fatigue Action Plan. The plan will direct development of ASME Section III Code [1] changes to provide guidance on acceptable methods for evaluating reactor water environment effects on reactor coolant pressure boundary components. Section III provides indication to the user that special consideration should be given for the environment to which a component is exposed, but does not provide guidance in addressing these effects. Discussions on needed ASME Code changes to address reactor water environmental effects have been under consideration by ASME Code bodies for many years. Due to the renaissance of the nuclear industry it is now apparent that Section III should be up-dated to address the missing guidance. The action plan was developed by the Subgroup on Design to coordinate activities necessary for Code bodies to act on proposed Code changes that will provide the user with the necessary tools to evaluate the effect of reactor water environment on fatigue life of components. The action plan lays out a strategy for a staged implementation of analysis methodologies, needed research, analysis guides, sample problems, and an assessment of the impact of the new rules upon the industry. The ultimate goal of the Subgroup on Design is to develop a new non-mandatory appendix that provides guidance to the user when evaluating reactor water environmental fatigue effects on Class 1 components.
A Rapid Convex Hull Algorithm for Implementing Path-Dependent Multi-Axial Fatigue
Authors: Wei Zhigang , Dong Pingsha , Forte Thomas P.
Published: January 2011

The Path-Dependent Maximum Range (PDMR) is a general-purpose multi-axial fatigue life assessment tool recently developed by Battelle researchers. The PDMR has been successfully applied to fatigue analysis of engineering components under variable amplitude, non-proportional, multiaxial fatigue loading histories. PDMR begins by seeking the maximum possible distance (or range) between any two points in the equivalent stress/strain space over a given fatigue loading history, while also identifying the associated loading path-length. The process continues recursively until each loading path has been counted. PDMR then collects the cycles calculated and the associated path-lengths for subsequent calculations of the fatigue damage. The effectiveness of the PDMR method has been validated by its ability to correlate a large amount of fatigue data. In a computerized PDMR calculation, most of the central processor unit’s (CPU) time is spent searching for the maximum range. While a brute-force search is the simplest to implement, and will always find a solution if it exists, its cost, in many practical problems, tends to grow very quickly as the size of the loading spectrum increases with O(n2) time complexity, where n is the number of spectrum data points. In this paper, Andrew’s monotone chain algorithm, a sophisticated and reliable convex hull algorithm is implemented into the PDMR to reduce the solution time. Like the widely used angular Graham Scan sort, Andrew’s monotone chain runs in O(n log n) time due to the merge-sort approach. The Rotating Caliper algorithm, which is another computational algorithm for quickly determining all antipodal pairs of vertices on a predetermined convex hull, is also introduced. Several examples have clearly demonstrated that these algorithms can be used in combination to significantly decrease the execution time for the PDMR in engineering fatigue analysis and design.
Multi-Axial Cycle Counting and Fatigue Life Assessment Based on Nominal and Battelle Structural Stresses
Authors: Wei Zhigang , Dong Pingsha , Hong Jeong K. , Forte Thomas P.
Published: January 2011

In this paper, a path-dependent maximum range (PDMR) multi-axial cycle counting method is presented for performing fatigue life assessment of engineering components under general variable-amplitude multi-axial loading conditions. The PDMR method has two distinct features: (a) multi-axial cycle counting, in which the cycle counting is conducted in an equivalent stress or strain space, and (b) explicit loading path dependency. For uniaxial loading data, the PDMR and the ASTM standard Rainflow methods both generate the same counting results. The path-length, a function of both normal and shear stress components on a critical crack plane, is proposed as a fatigue damage parameter for ductile materials. PDMR can be applied to welded structures, in which the crack plane is usually known in advance, as well as to non-welded structures, in which the critical plane approach can be implemented into PDMR to determine both the fatigue crack orientation and the associated fatigue damage. The effectiveness and robustness of the PDMR method have been validated by its ability to correlate nominal stress and Battelle structural stress fatigue data including pure-bending, pure-torsion, in-phase, and out-of-phase loading conditions for welded tube-to-flange steel structures. The relationship between the data correlations based on nominal stress and Battelle structural stress for these loading conditions is illustrated. Finally, one-parameter and two-parameter equivalency approaches for PDMR operation are also introduced and discussed.
Asset Management Methodology: A Probabilistic Approach to Optimize Investments for Coal-Fired Power Plants Reheaters
Authors: Benetrix Ludovic , Bertrand Pierre
Published: January 2011

Despite electricity generation in France is mainly performed by nuclear power plants, the fossil-fired fleet plays a significant role for the French main utility EDF: indeed it is used as a complementary energy to cope with load variations depending on time of the day or weather. Thus it is essential for EDF to ensure a sufficient level of availability and performance for its fossil-fired plants. In addition EDF has recently implemented new air pollution control systems for its 600 MWe coal-fired fleet to cope with the regulatory constraints which are becoming more and more severe. This is why EDF wants to optimize the investments for these plants in a long-term operation perspective. Consequently the reliability of the main components of these plants is a fundamental issue for EDF. The reheaters are some of the key components of a plant boiler; they are subject to severe temperature and pressure conditions which cause several degradations and failures and significantly reduce the availability of the plant. We will describe in this paper the application of the French main utility’s asset management methodology to optimize the investments for the coal-fired reheaters: (1) Qualitative analysis of the experience feedback data to identify the mains risks and mitigation actions, (2) Elaboration of investment strategies and quantification of data including probabilities of failure and (3) Scenario modelling to perform the technical and economic analysis.
Multiphase Fluid Structure Interaction in Bends and T-Joints
Authors: Cargnelutti Marcos F. , Belfroid Stefan P. C. , Schiferli Wouter , van Osch Marlies
Published: January 2011

Air-water experiments were carried out in a horizontal 1″ pipe system to measure the magnitude of the forces induced by the multiphase flow. Forces and accelerations were measured on a number of bends and T-joint configurations for a wide range of operating conditions. Five different configurations were measured: a baseline case consisting of straight pipe only, a sharp edged bend, a large radius bend, a symmetric T-joint and a T-joint with one of the arms closed off. The gas flow was varied from a superficial velocity of 0.1 to 30 m/s and the liquid flow was varied from 0.05 to 2 m/s. This operating range ensures that the experiment encompasses all possible flow regimes. In general, the slug velocity and frequency presented a reasonable agreement with classical models. However, for high mixture velocity the measured frequency deviated from literature models. The magnitude of the measured forces was found to vary over a wide range depending on the flow regime. For slug flow conditions very high force levels were measured, up to 4 orders of magnitude higher than in single phase flow for comparable velocities. The annular flow regime resulted in the (relative) lowest forces, although the absolute amplitude is of the same order as in the case of slug flow. These results from a one inch pipe were compared to data obtained previously from similar experiments on a 6mm setup, to evaluate the scaling effects. The results for the one inch rig experiments agreed with the model proposed by Riverin, with the same scaling factor. A modification of this scaling factor is needed for the model to predict the forces measured on the 6mm rig. The validity of the theories developed based on the 6mm experiments were tested for validity at larger scales. In case of slug flow, the measured results can be described assuming a simple slug unit model. In annular and stratified flow a different model is required, since no slug unit is present. Instead, excitation force can be estimated using mixture properties. This mixture approach also describes the forces for the slug regime relatively well. Only the single phase flow is not described properly with this mixture model, as would be expected.
The Role of Research in Standards Development
Authors: Andrei Dan
Published: January 2011

ASME’s approach to standards development for piping codes recognizes the important role of technically relevant standards in advancing the commercialization of new technology, enhancing consumer confidence, and protecting public health and safety. ASME standards are developed in a collaborative, voluntary consensus environment that can support the development of government regulations. Research and development (R&D) projects are underway that strive to bridge the gaps between technology advancement and standards development. ASME’s involvement in R&D projects helps produce results that respond to the needs of voluntary consensus committees in developing technically relevant codes and standards. ASME identifies and prioritizes R&D needs to help focus the use of limited resources in these priority areas. Collaboration in R&D projects helps to minimize individual investment while maximizing benefits.
Prediction of Welding Residual Stresses, Crack Initiation and Creep Crack Driving Forces C(t) Within a Continuous Finite Element Solution
Authors: Bray D. P. , Dennis R. J. , Smith M. C.
Published: January 2011

The work reported in this paper investigates the manufacture, through-life operation and cracked behaviour of an attachment weld in a UK AGR boiler. A structural assessment of the attachment weld was performed to demonstrate its integrity. This assessment made use of complex finite element analysis of both the welding process and postulated defects. A simulation of the welding process was performed in order to predict the residual stresses and hardened material state throughout the attachment weld. The welding simulation was performed in two stages since a butter weld was deposited prior to the attachment weld itself. The accumulation of creep damage was predicted during steady normal operating conditions for the lifetime of the component. A contour map of creep damage was used to postulate the location and size of hypothetical single and double edge surface cracks within the weld. These postulated cracks were then explicitly introduced into the finite element model. The crack tip stress parameter C(t) was evaluated in order to predict the creep crack driving forces. The results from a cracked body simulation suggested that the creep crack driving force C(t) reduces as the crack grows, due to relief of the dominant welding residual stresses. The residual stress, creep damage and cracked body simulations have been brought together into a novel continuous finite element solution. The results can be used to support a safety case for continued operation of existing plant.
3D Simulation of a Peripheral Adapter J-Groove Attachment Weld in a Vessel Head
Authors: Lhachemi Dounia , Robin Vincent , Gilles Philippe , Mourge Philippe , Zemmouri Mehdi
Published: January 2011

In Pressurized Water Reactors, most of components have large thicknesses and their manufacturing processes often require multipass welding. In spite of the stiffness of these components, the distortion issue may be important for operational requirements (e.g. misalignment) or controllability reasons (Non Destructive Examinations have to be feasible). These requirements may be difficult to meet by adjusting welding processes. Indeed because of the complexity of mechanisms involved during a welding operation and the high number of influencing parameters, this process is still essentially based on the experience of the welder. Furthermore the experimental estimation of the stress and distortion level in the component remains a difficult task that is subject to errors even if techniques are currently improved to become more accurate. That is the reason why AREVA NP has put many efforts into developing welding numerical simulations, in order to have a better understanding of the involved physical phenomena and also to predict the residual state allowing a qualification of the manufacturing processes in the very early phase of the welded components design. Within the framework of a R&D program whose main objective was to improve tools for numerical simulation of industrial cases of welding, AREVA NP has decided to validate new methodologies based on 3D computation by comparison with measurements. For this validation task the chosen test case concerns a peripheral adapter J-groove attachment weld on a vessel head. For such an application, operations of post-joining straightening have to be limited, if not prohibited, because of their cost or the impossibility to use them in front of a steel giant. The control of distortions during welding operations constitutes an important stake for which simulation can be of great help. Regarding distortions issues, an accurate metal deposit sequence modeling is mandatory, especially for multipass welding on such a complex geometry. The aim of this paper is to present, through a peripheral adapter J-groove attachment weld mock-up, the capabilities AREVA NP has in order to predict, in an efficient way the consequences of complex welding operations requiring 3D transient numerical simulations.
Characterizing the Stability of Carbon Nanotube Enhanced Water as a Heat Transfer Nanofluid
Authors: Ryglowski Brian K. , Pollak Randall D. , Kwon Young W.
Published: January 2011

Heat dissipation is a major challenge for many technologies. Possible solutions include thermal energy transfer via coolant fluid to a phase change material (PCM), with higher thermal conductivity a design goal. In recent years, heat transfer nanofluids (fluids with suspended nanoparticles) have received attention based on their potential for improving thermal conductivity. Carbon nanotubes (CNTs) are an attractive additive due to their enhanced thermal conductivity and ability to remain suspended over long times. However, characterizing their potential is difficult due to the many design variables and the need for repeated thermal conductivity tests for comparison. Since thermal conductivity enhancement is dependent on a dispersed nanotube network, the electrical conductivity of CNTs can be exploited to monitor the stability of such nanofluids, as such testing is quick and simple. The aim of this research was to evaluate electrical conductivity testing as a means to monitor stability of CNT-enhanced distilled water as a PCM, with varying CNT size, type, and concentration; and various other processing variables. The prepared nanofluids were tested after repeated phase change cycles. Results indicate that electrical conductivity testing is a practical means of monitoring the nanofluid stability, and CNT-based nanofluids show both promise and limitations as a PCM.