bluuebunny/crossref_metadata_2025 huggingface dataset:
Reference Stresses for Cold-Tube-Bends Including Thickness Variation and Ovality Using Three-Dimensional Finite Element Method
Authors: Zarrabi Khosrow , Kwok Felix Kumiadi
Published: July 2010

Tube-bends are extensively used in the boilers of power plants. Tube-bends are manufactured by bending a straight tube section. During this process, the tube cross-section becomes oval and its thickness varies around the circumference of its cross-section. This study uses three-dimensional finite element analysis to establish practical and simple equations for predicting the plastic collapse pressures and the reference stresses of the oval and variable thickness boiler-tube-bends. Such equations are pertinent to the design and integrity assessment of the boiler tube-bends.
Stress Field Around a Large Opening in a Pressure Vessel During a Major Repair
Authors: Garrido Erik , Casanova Euro
Published: July 2010

It is a regular practice in the oil industry to modify mechanical equipment to incorporate new technologies and to optimize production. In the case of pressure vessels, it is occasionally required to cut large openings in their walls in order to have access to the interior part of the equipment for executing modifications. This cutting process produces temporary loads, which were obviously not considered in the original mechanical design. Up to now, there is not a general purpose specification for approaching the assessments of stress levels once a large opening in a vertical pressure vessel has been made. Therefore stress distributions around large openings are analyzed on a case-by-case basis without a reference scheme. This work studies the distribution of the von Mises equivalent stresses around a large opening in FCC Regenerators during internal cyclone replacement, which is a frequently required practice for this kind of equipment. A finite element parametric model was developed in ANSYS, and both numerical results and illustrating figures are presented.
Discrete Element Methods for Large Scale Particle/Fluid Simulations
Authors: Kruggel-Emden Harald , Stepanek Frantisek , Munjiza Ante
Published: July 2010

The time- and event-driven discrete element methods are more and more applied to realistic industrial scale applications. However, they are still computational very demanding. Realistic modeling is often limited or even impeded by the cost of the computational resources required. In this paper the time-driven and event-driven discrete element methods are reviewed addressing especially the available algorithms. Their options for simultaneously modeling an interstitial fluid are discussed. A potential extension of the time-driven method currently under development functioning as a link between event- and time-driven methods is suggested and shortly addressed.
Dynamic Behavior of the Five Storied Pagoda Under the Earthquake and the Wind
Authors: Mikoshiba Tadashi , Minowa Chikahiro , Chiba Toshio
Published: July 2010

Five storied pagoda is built of wood and is known as a high earthquake proof structure. The pagoda is composed of the frame and the center column. The center column is structurally independent of the frame structure. Many researchers have mainly been interested in its dynamic characteristics under the earthquake. They have focused on the acceleration response of the pagoda. This time, we observed not only its dynamic characteristics under seismic load but also under strong wind load. We focused on the displacement response of the pagoda. By integrating the acceleration data twice, the displacement of the structure was obtained. Under low level earthquake, the pagoda swayed about the central axis of the structure. On the other hand, the pagoda was statically deformed by the wind pressure and swayed in the deformed central axis of the structure. The dynamic behavior of the pagoda in the wind is distinctly different from that of the earthquake.
Development of Duplex Specimens for Potential Application in Testing of Highly Irradiated Weld Metals
Authors: Gundermann Arnulf , Keim Elisabeth , Hein Hieronymus , Schnabel Hilmar
Published: July 2010

According to the German Safety Standard 3201.2 [1] of the Nuclear Safety Standards Commission (KTA) it must be proven that for cracks which may have initiated crack arrest will occur in the wall (of the RPV). This importance of crack arrest for the fracture mechanics concept requires reliable experimental data, especially regarding irradiated materials and testing techniques with appropriate specimens. The recently finished CARISMA (Crack initiation and ARrest of Irradiated Steel MAterials) [2] program shows some limitations to use Compact Crack Arrest (CCA) specimens manufactured from highly irradiated weld metals. The welding process to generate the brittle zone at the tip of the starter notch causes annealing effects which influences the heat affected zone (HAZ) of the brittle weld. These effects lead to a crack arrest in the HAZ after unstable crack initiation. During further loading the limits of the test equipment were reached, but no unstable crack initiation event occurred. The use of so-called Duplex specimens with a pre-hardened specimen part instead of using CCA specimens is a promising alternative which still needs further investigation. This type of specimen was already used successfully at the Oak Ridge National Laboratory in the “Heavy-Section Steel Irradiation” (HSSI) [4] program for two irradiated high copper welds. It should be noticed, that the Duplex specimens used in the HSSI program were first produced, and afterwards irradiated in the Oak Ridge Research Reactor. In the case presented, the material is already irradiated, so the specimens must be manufactured in that condition. This situation complicates the development of a successful crack arrest test with Duplex specimens. The objectives of the experimental study, the test matrix and the approach to find an optimized specimen design for crack arrest testing are described.
Prediction of Ductile Fracture as a Process Controlled by Cavitation Instability
Authors: Novak Jiri
Published: July 2010

Recently, we applied criterion of initiation of deformation bands based on bifurcation analysis as a criterion of ductile fracture. Experience shows that this procedure yields realistic results if plastic behavior is described by deformation theory of plasticity, with corresponding stress-strain dependence — especially with transition between strain hardening stages III and IV. But it is generally known that under high stress triaxilities, fracture strain depends strongly on stress triaxiality. If deformation theory of plasticity is suitable for modeling of constitutive properties of polycrystalline metals, it should lead to good results in prediction of cavitation instability as a criterion of ductile fracture under high triaxialities as well. We present prediction of fracture strains for reactor pressure vessel steel, in comparison with experimental results. Criterion of cavitation instability based on deformation theory of plasticity predicts similar dependence of fracture strain on stress triaxiality as the classical Rice-Tracey void growth model does, but, moreover, in contrast to the Rice-Tracey model, it predicts absolute values of critical strains. Finally, important role of deformation theory of plasticity in other areas of material engineering and structural integrity analysis is shortly remembered.
Benchmark of Numerical Codes for Coupled CSD/CFD Computations on an Elementary Vortex Induced Vibration Problem
Authors: Pomarede Marie , Longatte Elisabeth , Sigrist Jean-Franc¸ois
Published: July 2010

Numerical simulation of vortex-induced-vibrations (VIV) of an elastically supported rigid circular cylinder in a fluid cross-flow has been thoroughly studied over the past years, both from the experimental and numerical points of view, because of its theoretical and practical interest in the understanding of flow-induced vibrations problems. In this context, the present paper aims at exposing a numerical study based on a coupled fluid-structure simulation, compared with previously published studies [34], [36]. The computational procedure relies on a partitioned method ensuring the coupling between fluid and structure solvers. The fluid solver involves a moving mesh formulation for simulation of the interface motion. Energy exchanges between both systems are ensured through convenient coupling schemes. The present study is devoted to a low Reynolds number configuration ( Re = 100). Cylinder motion magnitude, hydrodynamic forces, oscillation frequency and fluid vortex shedding modes are investigated with the intention to observe the “lock-in” phenomenon. These numerical simulations are proposed for code validation purposes prior to industrial applications to tube bundle configurations [4].
CARINA: A New Project to Extend the Data Base for Fracture Mechanical Characteristics of Irradiated German RPV Materials at High Neutron Fluences
Authors: Hein Hieronymus , Ganswind Jens , Gundermann Arnulf , Keim Elisabeth , Schnabel Hilmar
Published: July 2010

Within the recently finished project CARISMA “Determination of Fracture Mechanics Values on Irradiated Specimens of German PWR Plants” a data base was created for pre-irradiated original RPV steels of the four construction lines of German PWRs, which allowed to examine the consequences if the Master Curve (T0) approach instead of the RTNDT concept is applied for the RPV safety assessment. In the new research project CARINA the experimental data base for both the safety concepts RTNDT and Master Curve for the proof against RPV brittle fracture will be extended by additional representative materials irradiated under different conditions and with respect to the accumulated neutron fluences and specific impact parameters (neutron flux, chemical composition, manufacturing effects). The investigation of materials irradiated to higher neutron fluences and different irradiation conditions complements the representativeness of the conclusions for the applicability of safety concepts to RPVs with longer operation times and beyond EoL respectively in terms of “Upper Bound” coverage. The obtained results will be evaluated on the basis of the already elaborated approaches and will be represented by the aid of the Master Curve concept in an appropriate way. An overview on the objectives, the experimental program, and the current status of the project is given. Finally first test results are presented and evaluated.
Reliability and Safety of the Power Equipment in Respect of Properties Evaluation of Welded Joints Made From New Generation Creep-Resisting Steels
Authors: Dobrzanski Janusz , Pasternak Jerzy
Published: July 2010

The modernisation of power generation sector has involved the construction of new power units, having supercritical parameters e.g. 580/ 600°C with 280bar, and calculated efficiency of approx. 43%. The new boilers are supercritical ones of capacities 440MW and 840MW. Their investors expect that new creep-resistant steels to be used in order to comply with the operational requirements, as well as to assure the appropriate reliability and safety of the boiler equipment in operation. Authors describe a co-operating process has been made with RAFAKO S.A. the Institute for Ferrous Metallurgy in Gliwice, the Institute of Welding and the Silesian Technical University in Katowice, for several years now, initiating research and development programmes. This paper contains selected information, test results and their evaluation before implementation of the new creep-resistant steels, including evaluation of: - working parameters and temperature conditions of main boiler components, which influence reliability and safety procedures, - base material, welded joints and HAZ structure by means of LM and SEM methods in the welding technology implementation process, - the requested level of mechanical properties, including corrosion mechanisms, - corrosion and creep-resistance results, - loss of service life for selected evaporator and steam superheater components, as crucial elements in evaluation of reliability and safety of boiler equipment.
Thermal Analysis of Drum Type Radioactive Material (RAM) Packaging Arrays in Storage
Authors: Gupta Narendra K.
Published: July 2010

Drum type packages are routinely used to transport radioactive material (RAM) in the U.S. Department of Energy (DOE) complex. These packages are designed to meet the federal regulations described in 10 CFR 71. In recent years, there has been a greater need to use these packagings to store the excess fissile material, especially plutonium for long term storage. While the design requirements for safe transportation of these packagings are well defined, the requirements for safe long term storage are not well established. Since the RAM contents in the packagings produce decay heat, it is important that they are stored carefully to prevent overheating of the containment vessel (CV) seals to prevent any leakage and the impact limiter to maintain the package structural integrity. This paper analyzes different storage arrays for a typical 9977 packaging for thermal considerations and makes recommendations for their safe storage under normal operating conditions.
The Effect of Angle of Attack on the Fluidelastic Instability of Tube Bundle Subjected to Two-Phase Cross-Flow
Authors: Joly T. F. , Mureithi N. W. , Pettigrew M. J.
Published: July 2010

Tests were done to study the effect of angle of attack on the fluidelastic instability of a fully flexible tube bundle subjected to two-phase (Air-Water) cross-flow. A test array having nineteen flexible tubes in a rotated triangular configuration with a pitch-to-diameter ratio of 1.5 was tested. Four different angles of attack ranging for 0 degree (inline flexibility) through 30 and 60 degrees to 90 degrees (transverse flexibility) were studied. For each angle of attack several homogeneous void fractions have been tested (70%, 80%, 90%, and 95%). Stability test results show that the angle of attack strongly affect the tube bundle dynamic behavior. The different mechanisms underlying the fluidelastic instability are highlighted and the results compared to existing data on fluidelastic instability.
The Ultimate Strength of Cylindrical Liquid Storage Tanks Under Earthquakes: Evaluation of Dynamic Buckling Behavior of Tanks Used in PWR Plants
Authors: Iijima Toru , Suzuki Kenichi , Morita Hideyuki , Tai Koichi
Published: July 2010

The new seismic design guideline for nuclear power plants, which was established in September 2006 in Japan, requires the consideration of residual risk for earthquakes beyond the design base. Seismic Probabilistic Safety Assessment (PSA) is the current available method to evaluate the residual risk of the nuclear power plant. Since 2002, Japan Nuclear Energy Safety Organization (JNES) has been carrying out seismic capacity tests for several types of equipment whose malfunction would significantly affect core damage frequency. The primary purpose of those tests is to obtain seismic capacity data and use them to increase the reliability of the seismic PSA. In this study, some elastic-plastic analyses considering the dynamic buckling behavior were performed to evaluate previous seismic capacity test results. The study confirmed that response displacement, residual deformation of the elephant-foot bulge (EFB) and local strain of tank after the EFB occurred could be evaluated analytically. Besides, a 3D FEM elastic-plastic buckling analysis using kinematic hardening law could simulate the behavior in the early stage of the dynamic buckling. In addition to those analyses, dynamic response reduction factor (Ds) of the actual material tanks, and influence of different materials on the energy absorption and seismic capacity were evaluated by using previous seismic capacity tests results.
Prediction of Fracture Toughness for WWER RPV Integrity Assessment on the Basis of the Unified Curve Approach and Surveillance Specimens Testing
Authors: Margolin Boris , Shvetsova Victoria , Gulenko Alexander , Fomenko Valentin
Published: July 2010

For construction of the fracture toughness temperature curve that may be used for WWER RPV integrity assessment on the basis of tests of cracked surveillance specimens, the issues have to be solved as follows. First of all, it is important to determine how fracture toughness varies as a function of temperature, and how the fracture toughness vs. temperature dependence, KJC(T), changes with in-service material degradation due to neutron irradiation. These variations of KJC(T) curve are known to be the shift of KJC(T) curve to higher temperature range and change in the KJC(T) curve shape. At present, two advanced engineering methods are known that allow the prediction of KJC(T) curve on the basis of small-size fracture toughness specimens (for example, pre-cracked Charpy specimens), namely, the Master Curve and the Unified Curve methods. Procedures of test result treatment for the Master Curve and the Unified Curve are very similar. The Master Curve method uses the lateral temperature shift condition and, therefore, does not describe possible change in the KJC(T) curve shape. The Unified Curve method has an advantage as compared with the Master Curve as the Unified Curve describes a variation of the KJC(T) curve shape when degree of embrittlement increases. This advantage becomes important for RPV integrity assessment when the reference KJC(T) curve is recalculated to the crack front length of the postulated flaw that is considerable larger than thickness of surveillance specimens. Application of the KJC(T) curve determined from test results of cracked surveillance specimens to RPV integrity assessment requires also to introduce some margins. These margins have to take into account the type and number of tested specimens and the uncertainty connected with spatial non-homogeneity of RPV materials. Indeed, there is sufficient number of experimental data showing variability in fracture toughness for various parts of RPV. Therefore, situation is possible when the material properties near the postulated flaw will be worse than the properties of surveillance specimens. In the present report, advanced approaches are considered for prediction of fracture toughness for WWER RPV integrity assessment that allow one: • to construct the KJC(T) curve for irradiated RPV steels with any degree of embrittlement; • to provide transferability of fracture toughness data from cracked surveillance specimens to calculation of resistance to brittle fracture of RPV with a postulated flaw.
Prediction of Creep-Rupture Properties for Austenitic Steels Undergone Neutron Irradiation
Authors: Margolin B. Z. , Gulenko A. G. , Buchatsky A. A.
Published: July 2010

The paper presents the physical and mechanical model that allows predicting fracture of materials subjected to neutron irradiation under creep. The model is based on the equations of void nucleation and growth on grain boundaries that were proposed earlier. The equations are developed for the case of neutron irradiation of a material. The constitutive equations describing viscoplastic deformation of a material with regard to void evolution are formulated. The criterion of microplastic collapse of a unit cell is used as a fracture criterion. The creep-rupture strength and ductility of austenitic materials in the initial and irradiated conditions with different neutron flux levels are predicted on the basis of the model. The calculated results are compared with the available experimental data.
Creep Strength of Welds in Hydrogen Reformer Outlet Manifolds
Authors: Jaske Carl E.
Published: July 2010

This paper reviews the creep strength of welds of the type typically used in hot outlet manifolds of hydrogen reformers. These manifolds can be visualized as a high-temperature piping system that collects the reformed gas from the outlets of the catalyst tubes. The catalyst tube outlet usually is connected to the manifold by means of a flexible pigtail. The pigtail is connected to the manifold via welded fittings, and the components of the manifold assembly are connected by welded joints. These hot manifolds operate under internal pressures in the range of 2000 to 3500 kPa and at temperatures in the range of 800 to 900 °C. The components are typically made of wrought Alloy 800, 800H or 800HT or similar cast 20Cr-32Ni-1Nb alloys. The welds are made using filler metals or electrodes of similar compositions or high-nickel alloy compositions. Creep-rupture data that have been developed for weld metals are reviewed and compared. Problems that have been encountered with failures of welds in this application are discussed. The current recommended materials for welding these manifolds are outlined.
Seismic Qualification by Testing for Electrical and Active Mechanical Equipment to be Installed in Hard-Rock High Frequency Sites
Authors: Chen Pei-Ying , Ng Ching Hang
Published: July 2010

All electric and active mechanical equipment important to safety must be seismically qualified by either analysis, testing, or a combination of both. The general requirements for seismic qualification of electric and active mechanical equipment in nuclear power plants are delineated in Appendix S to Title 10, Part 50, of the Code of Federal Regulations (10 CFR Part 50), item 52.47(20) of 10 CFR 52.47, and Appendix A to 10 CFR Part 100. The staff at the US Nuclear Regulatory Commission (NRC) has recognized that the Certified Design Ground Motion may be exceeded by the site-specific ground motion. The exceedances are generally in the high-frequency range for the Central and Eastern US sites. For equipment seismic qualification consideration, the exceedances must be addressed at both the ground level and the floor level where the equipment is located. Thus, the in-structure response spectra at some locations may exceed those in-structure response spectra generated by the certified seismic design response spectra. The U.S. nuclear industry and the NRC have initiated activities to address this issue. Two scenarios that revealed themselves during the review activities of the design certification and combined license applications for new reactors will be expounded upon in the paper. In Case I, equipment seismic qualification has been approved for a certified design and equipment is to be installed at a hard-rock high frequency (HRHF) site with certified seismic design response spectra (CSDRS) exceeded by the Ground Motion Response Spectra (GMRS) of the hard-rock site. In Case II, equipment seismic qualification has not been approved for a design certification and there is an application with GMRS exceeding the not-yet-approved CSDRS. In the paper, the staff will begin the discussion with the regulatory requirements for seismic qualification of electric and mechanical equipment. The focus of the paper is to identify the staff concern and illustrate the resolution between the NRC staff and an applicant on the seismic qualification of equipment by testing, in particular for equipment to be installed in hard-rock high frequency sites, to meet the regulatory requirements.
A Whistling Criterion for Two Orifices in Series
Authors: Lacombe Romain , Aure´gan Yves , Moussou Pierre
Published: July 2010

Whistling phenomena in pipe power plants have been observed in the past years. It occurs at pressure drop devices where vortex shedding is established. It generates high noise levels and excessive vibrations. Aure´gan and Starobinsky [1] have developed an experimental criterion to predict whistling frequencies of pressure drop devices submitted to plane propagating pressure waves. This criterion estimates the net acoustic power, an acoustic exergy generation indicating that the device behaves as an acoustic amplifier. The corresponding frequencies are potential whistling frequencies. The application of the criterion only requires the determination of the scattering matrix of the device. In previous works, this criterion was applied to different single hole orifices. The purpose of the present study is to apply the criterion to two orifices in series and to verify that the behavior of this system can be predicted from the scattering matrix of each individual orifice and of the straight pipe in-between. Measurements are done on an air test rig with an inner diameter of 3 cm, a Mach number of 2.6 × 10−2 and a Reynolds number of 104. Different distances between orifices are characterized. The study of the influence of the second orifice on the whistling criterion shows an enhancement of the whistling potential and a shift of the main potential whistling frequency. A fair agreement is found between experimental and predicted results. Characterization of orifices in series is then possible from the coefficients of the scattering matrix of one orifice and an appropriate condition on the distance between the orifices.
Experimental Study of Ductile Fracture for Non-Aligned Multiple Flaws in a Plate
Authors: Miyazaki Katsumasa , Hasegawa Kunio , Saito Koichi , Bezensek Bostjan
Published: July 2010

The fitness-for-service code requires the characterization of non-aligned multiple flaws for the flaw evaluation, which is performed using a flaw proximity rule. Worldwide almost all codes provide own proximity rule, often with unclear technical bases of the application of proximity rule to ductile fracture. To clarify the appropriate proximity rule for non-aligned multiple flaws in fully plastic fracture, fracture tests on flat plate specimen with non-aligned multiple through wall flaws were conducted at ambient temperature. The emphasis of this study was put on the flaw alignment rule, which determines whether non-aligned flaws are treated as independent or aligned onto the same plane for the purpose of flaw evaluations. The effects of the flaw separation and flaw size on the maximum load were investigated. The experimental results were compared with the estimations of the collapse load using the alignment rules in the ASME Section XI, BS7910 and API 579-1 codes. A new estimation procedure specific to the fully plastic fracture was proposed and compared with the comparison with the experimental results.
A Generalization of the FAVOR Code to Include BWR Geometries and Heat-Up Transients
Authors: Dickson Terry , Yin Shengjun , Williams Paul
Published: July 2010

The FAVOR computer code, developed at the Oak Ridge National Laboratory (ORNL), under United States Nuclear Regulatory Commission (NRC) funding, has been and continues to be extensively applied by analysts from the nuclear industry and regulators at the NRC to apply established fracture mechanics and risk-informed methodologies to assess / update regulations designed to insure that the structural integrity of aging and increasingly radiation-embrittled nuclear reactor pressure vessels (RPVs) is maintained throughout the life of the reactor. Earlier versions of FAVOR were primarily developed to perform probabilistic fracture mechanics (PFM) analyses of RPVs subjected to thermal hydraulic transients associated with accidental pressurized thermal shock (PTS) conditions and therefore were limited to modeling internal surface breaking flaws and / or embedded flaws near the RPV internal (wetted) surface. For cool-down transients, these flaws are particularly vulnerable, because at the inner surface the temperature is at its minimum and the tensile stress and radiation-induced embrittlement are at their maximum. Tensile stresses tend to open existing cracks located on or near the internal surface of a reactor pressure vessel (RPV). These earlier versions of FAVOR did not have the capability to model external-surface breaking flaws and / or embedded flaws near the RPV outer surface which are the primary flaws of concern for heat-up transients, such as those associated with reactor start-up. Furthermore, earlier versions of FAVOR were limited to the calculation of applied stress intensity factors (applied KI) of internal surface breaking flaws in RPVs with an internal radius to wall thickness (Ri / t) ratio of approximately 10:1, characteristic of pressurized water reactors (PWRs). This limitation is because the stress intensity factor-influence coefficients (SIFICs), applied by FAVOR to calculate applied KI for surface breaking flaws, were applicable only to internal-surface breaking flaws in RPV geometries characteristics of PWRs. Most boiling water reactors (BWRs) have an (Ri / t) ratio of approximately 20:1, although a few BWRs in the United States have an (Ri / t) ratio of approximately 15. Work has recently been performed at ORNL to generalize the capabilities of the next version of FAVOR, and its successors, such that it will have the capability to perform deterministic and PFM analyses of cool-down and heat-up transients on all domestic commercial PWR and BWR RPV geometries. This paper provides an overview of this generalization of the FAVOR fracture mechanics computer code.
Changes in the Bauschinger Effect Level Post the Autofrettage Process
Authors: Perl M. , Perry J.
Published: July 2010

The favorable residual stress field generated by the autofrettage process is increasing the barrel’s capacity to withstand pressure during firing — defined as the re-loading phase. There are two principal autofrettage processes: swage autofrettage and hydraulic autofrettage. Both processes include two successive stages of loading and unloading followed by an additional reloading during firing. Reyielding during the firing phase of an autofrettaged barrel is strongly affected by the secondary Bauschinger effect that involves a reduction of the yield stress in tension due to previous plastic deformation in compression, occurring in the unloading phase of the autofrettage process. The level of the secondary Bauschinger effect can be reduced by introducing a low temperature heat treatment (LTHT) immediately after the autofrettage process, thus increasing the barrel’s safe maximum pressure (SMP). In the utmost case, the yield stress in tension may regain its initial value prior to the autofrettage process. The aim of the present work is to quantitatively analyze the effect of different levels of the yield stress in tension post the autofrettage process, on a gun barrel’s SMP, resulting from a low temperature heat treatment. The two autofrettage processes, the swage and the hydraulic, are numerically analyzed using the newly developed 3-D computer code. For the hydraulic autofrettage case five different Bauschinger effect levels were analyzed while for the swage autofrettage case, only two limiting cases were considered. The numerical results are indicating that the thermal treatment might partially or fully eliminate the influence of the secondary Bauschinger effect thus, increasing the barrel’s SMP. The swage autofrettage SMP, which is higher than the hydraulic one, is less sensitive to the LTHT thus, increasing barrel’s reliability.
Study on Requirements to be Fulfilled With Rules for Repair Replacement Activities in JSME Code on Fitness-for-Service
Authors: Nishikawa Akira , Dozaki Koji , Koyama Koji , Asada Kazuyuki
Published: July 2010

Rules on Repair Replacement Activities (RRA) have been incorporated in Japan Society of Mechanical Engineers (JSME) Code on Fitness-For-Service (FFS) since its 2004 edition. Since then, it has been a priority to clearly identify the RRA rules that should be endorsed by the regulatory authority, in addition to better organizing the relationship among inspection, flaw evaluation and RRA rules, especially inspection and flaw evaluation prior to RRA. A Task Group on development of RRA rules was organized under Subcommittee on JSME code on fitness-for-service to develop more organized RRA rules. In this paper, requirements for RRA rules, and related inspection and flaw evaluation rules that were studied in that Task Group (TG), are described. Discussion results of the TG contain two parts as follows. 1) Improving conformance of RRA rules to regulatory standard. Desirable conformance of some typical patterns of RRA to classified requirements of regulatory standards was discussed. Several cases of conformance were derived from this discussion. It was shown that individual RRA methods were classified into one or two of these conformance cases. 2) Identifying the relationship among RRA, inspection, and flaw evaluation rules. Desirable flow of inspection, flaw evaluation and RRA rules was illustrated at first. Based on a comparison between this flowchart and present RRA rules, pre-service/in-service inspection and flaw evaluation rules prior to RRA were picked out for development with the highest priority.
Numerical Simulation for Identification of Semi-Elliptical Crack on the Inner Surface of Pipe by Means of Direct-Current Electrical Potential Difference Method With Multiple-Probe Sensor
Authors: Tada Naoya , Uchida Makoto , Ishikawa Hiroki
Published: July 2010

The direct-current potential difference method (DC-PDM) is known as one of the promising non-destructive methods to evaluate the crack in the conductors. This method utilizes the change in the current path or the potential difference which is caused by the crack. In the previous study, a method of three-dimensional evaluation of semi-elliptical crack on the back surface of plate was proposed and its theoretical validity and practical utility were shown based on the results of numerical analyses and experiments. In this study, the method is extended to the identification of semi-elliptical crack on the inner surface of pipe and the related electric field analyses are carried out by the finite element method. The results show that the crack on the inner surface of pipe can be evaluated by the proposed method based on the distribution of potential difference measured on the outer surface of pipe. The present extension will be very useful for various practical cases which are often seen in the piping of power-generating and petrochemical plants.
Non Destructive Examination of Helium Implanted Fe-Cr Model Alloys
Authors: Krsjak V. , Sojak S. , Petriska M. , Veternikova J.
Published: July 2010

The helium implantation has been successfully used for the obtaining of radiation damage in different Fe-Cr ferritic/martensitic steels. Implanted doses within the range 6.24×1017 – 3.12×1018 cm−2 corresponding to local damage up to 90 DPA (Displacement per Atom) were acquired in a thin (<1 μm) region. For observing the dependence of vacancy-type defects on the load and the chromium content, positron annihilation lifetime spectroscopy (PALS) has been used. Experiments showed that chromium had a significant effect on the radiation treated microstructures of the materials. In particular, chromium influences the size and density of the implantation induced defects and specific Cr content should prevent the formation of vacancy clusters.
Strain-Based Acceptance Criteria for Energy-Limited Events
Authors: Snow Spencer D. , Morton Dana K. , Pleins Edward L. , Keating Robert
Published: July 2010

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code is primarily a stress-based acceptance criteria code. These criteria are applicable to force, displacement, and energy-controlled loadings and ensure a factor of safety against failure. However, stress-based acceptance criteria are often excessively conservative for one time energy-limited events such as accidental drops and impacts. For several years, the ASME Working Group on Design of Division 3 Containments has been developing the Design Articles for Section III, Division 3, “Containments for Transportation and Storage of Spent Nuclear Fuel and High-Level Radioactive Material and Waste,” and has wanted to expand the design articles to include strain-based acceptance criteria for accidental drops of containments. The Division 3 Working Group asked the Working Group on Design Methodology (WGDM) to assist in developing strain-based acceptance criteria. This paper discusses the current proposed strain-based acceptance criteria, associated limitations of use, its background development, and the current status.
Energy Dissipation Behavior of an Autonomous Controller for Semi-Active Control Device
Authors: Shih Ming-Hsiang , Sung Wen-Pei
Published: July 2010

In this research, autonomous controller is developed to provide the function of “Sensing-Computing-Transferring” for improving of energy dissipation capability of semi-active control device. This proposed controller has qualifications of detecting structural response under the excitation of earthquake; it depends on the control law to produce control order to adjust and control the action of semi-active control damper. The principle of this controller is: 1.) autonomous controller and damper-added stiffness element are parallel connection; 2.) the direction of pressure force and velocity moving direction of structure are changed simultaneously by this controller; 3.) the action of switching direction of damper has been finished when the tiny displacement of structure is happened by reverse process of moving direction of structure. Practically, this controller was simulated by connecting soft springs, damper and actuator in serial. The experimental results indicate that the function and energy-dissipating behavior of this proposed controller is similar to traditional semi-active controller except that this controller can switch the damper status at the right moment. This proposed controller can replace the detector, central control computer and damping controller included in original semi-active control system. The advantages of this developed autonomous controller are: 1.) low manufacturing cost; 2.) low requirement of system maintenance; 3) high reliability of control system.
Loads Applied to Clogged Steam Generators Internal Structures
Authors: Brunin Olivier , Deotto Geoffrey
Published: July 2010

During their commissioning, steam generators are clean, which means there is no fouling of the heat transfer surface of tubes and no clogging of the flow area on the secondary side. Then sludge appears steadily at a slow pace during operation. Sludge initiates a partial loss of cooling capacity which is modeled by a fouling factor and which mainly results in vapor pressure decrease. Sludge also initiates a reduction of the secondary side flow area, known as clogging. Four safety-related issues are dependant on clogging [1]: the secondary water mass balance, the thermohydraulics oscillations, the tube vibration risk and the resistance of internal structures. This paper focuses on the last of these issues. A numerical application, based on the modeling of a fictitious steam generator, is detailed in this presentation. The order of magnitude is an 8-times increase of the loads in normal operating conditions in case of a typical 60% clogging ratio of the upper tube support plate, and a 12-times increase in case of incidental depressurization transient. These theoretical results emphasize the need to take these loads properly into account in the checking of the mechanical behavior of the internal structure of the steam generators in operation in case of significant sludge deposits.
International Standards for Boilers and Pressure Vessels
Authors: Cameron Stuart , Feigel Richard Gene
Published: July 2010

This paper outlines the need for a single comprehensive International Standard for boilers and pressure vessels but also recognizes that the development of such a standard will be a lengthy process. The development of a performance based standard is seen as the best realistic approach to facilitating world trade and progress on this is described.
3D FE Analysis for Two-Gasket Sealing Structure Considering Hysteresis Effect of Gasket Material Under Pre-Tightening and Pressurized Loads
Authors: Ding Zhenyu , Liang Lihua , Gao Zengliang
Published: July 2010

Gaskets play an important role in the sealing performance of tube-shell joint, and their behavior is complex due to nonlinear material properties. A three-dimensional finite element analysis (FEA) of two-gasket sealing structure of tube-shell joint has been carried out. The loading and unloading characteristics of the gaskets were obtained by experiments. Several combinations of pre-tightening force and internal pressure were considered for finding the sealing and strength conditions simultaneously. After calculation and analysis, the appropriate pre-tightening force and the distribution contour of Von-Mises stress, axial displacement and the gasket pressure of the connect components were obtained. At last, a simplified method to find appropriate pre-tightening based on force analysis and diagrammatic method are presented and discussed.
Optimising Residual Stress Measurements and Predictions in a Welded Benchmark Specimen: A Review of Phase 2 of the NeT Task Group 1 Single Bead on Plate Round Robin
Authors: Smith Michael C. , Smith Ann C. , Wimpory Robert C. , Ohms Carsten , Nadri Brahim , Bouchard P. John
Published: July 2010

A single weld bead deposited on a flat plate is a deceptively simple problem that is in practice a challenge for both measurement and prediction of weld residual stresses. Task Group 1 of the NeT collaborative network has examined this problem in a two-phase programme extending from 2002 to 2008. Ten independent sets of residual stress measurements have been reported using diverse techniques, and over forty finite element simulations have been performed. This paper reviews Phase 2 of the Task Group 1 round robin. Here, the finite element simulations all made use of optimised thermal solutions, in which the global welding parameters, including efficiency, were fixed, and only the detailed heat source geometry was varied. These resulted in accurate far field welding temperature distributions, with significant variability only close to the weld bead itself. The subsequent mechanical analyses made use of kinematic, isotropic, and mixed isotropic-kinematic material constitutive models, and made a variety of assumptions about the introduction of weld filler material to the structure and the handling of high temperature inelastic strains. The large database of measurements allowed the derivation of statistical best estimates using a Bayesian “duff data” approach, and these best estimates were compared with the predictions to establish the most accurate material constitutive models. The most accurate predictions of residual stress were made using non-linear kinematic or mixed isotropic-kinematic constitutive models. The methods used to handle high-temperature inelastic strains influenced the predicted stresses only in regions where very high temperatures were predicted during welding. The results emphasise the importance and value of both well-characterised benchmark problems and international collaboration in the development of technologies to both measure and predict weld residual stresses.
Welding Residual Stress and Flaw Evaluation for Dissimilar Metal Welds With Alloy 52 Inlays
Authors: Rudland D. , Csontos A. , Brust F. , Zhang T.
Published: July 2010

With the recent occurrences of primary water stress corrosion cracking (PWSCC) at nickel-based dissimilar metal welds (specifically Alloy 82/182 welds) in the nation’s pressurized water reactors (PWRs), the commercial nuclear power industry has been proposing a number of mitigation strategies for dealing with the problem. Some of these methods include Mechanical Stress Improvement Process (MSIP), Full and Optimized Structural Weld Overlay (FSWOL, OWOL) and Inlay and Onlay welds. All of these methods provide either a reduction in the ID residual stress field, (MSIP and WOL) and/or apply a corrosion resistant layer to stop or retard a leak path from forming (WOL, Inlay, Onlay). For the larger bore pipe, i.e. hot leg outlet nozzle, methods such as FSWOL become cost prohibitive due to the amount of weld metal that must be deposited. Therefore, inlay welds are being proposed since only a small layer (3 weld beads) needs to be deposited on the inside surface of the pipe. Currently the ASME code is developing Code Case N-766 ‘Nickel Alloy Reactor Coolant Inlay and Cladding for Repair or Mitigation of PWR Full Penetration Circumferential Nickel Alloy Welds in Class 1 Items.’ This code case is documenting the procedures for applying these inlay welds. As part of a confirmatory analysis, the US NRC staff and its contractor, Engineering Mechanics Corporation of Columbus, (Emc2) have conducted both welding residual stress and flaw evaluation analyses to determine the effectiveness of inlay welds as a mitigative technique. This paper presents the ongoing results from this effort. Using several large bore geometries, detailed welding simulation analyses were conducted on the procedures set forth in draft Code Case N-766. Effects of weld repairs and temper bead welding are included. Using these residual stress results, PWSCC growth analyses were conducted using simulated crack growth rates as a function of chromium content to estimate the time to leakage and rupture for small initial flaws in the inlay. The paper concludes with discussions on the effectiveness of inlays based on these analyses.
Pseudodynamic Response to Impulsive Loading
Authors: Chang Shuenn-Yih , Huang Chiu-Li , Yang Ching-Hao
Published: July 2010

The application of a pseudodynamic technique to yield a shock response from an impulse might encounter a difficulty caused by a significant load discontinuity at the end of the impulse since this load discontinuity at the end of an impulse will result in an extra impulse and then an extra amplitude distortion. This extra impulse is linearly proportional to the step size and thus it is natural to consider the use of a very small time step for a whole pseudodynamic test to overcome the difficulty. However, a series of computer simulations reveal that this approach might not be feasible. This is because that the use of a small time step will lead to a very small displacement increment and it may be contaminated by experimental errors as its magnitude is less than or close to the magnitude of the experimental errors. Thus, an inaccurate test result is obtained. A technique is proposed to overcome this difficulty. This novel technique is to perform a single small time step immediately upon the termination of the applied impulse while the other time steps are conducted by using the time step determined from general considerations. This single small time step will not lead to a significant error propagation problem since only this time step is performed by using a very small step size for a complete pseudodynamic test. The feasibility of this technique was confirmed by a series of pseudodynamic tests.
Burst Pressure Predictions of Corroded Pipelines With Long Defects: Failure Criteria and Validation
Authors: Chiodo Mario S. G. , Ruggieri Claudio
Published: July 2010

This study examines the applicability of a stress-based criterion based upon plastic instability analysis to predict the failure pressure of corroded pipelines with axial defects. A central focus is to gain additional insight into effects of defect geometry and material properties on the attainment of a local limit load to support the development of stress-based burst strength criteria. A verification study conducted on burst testing of large-diameter pipe specimens with different defect length shows the effectiveness of a stress-based criterion using local ligament instability in burst pressure predictions, even though the adopted burst criterion exhibits a potential dependence on defect geometry and possibly on material’s strain hardening capacity. Overall, the results presented here suggests that use of stress-based criteria based upon plastic instability analysis of the defect ligament is a valid engineering tool for integrity assessments of pipelines with axial corroded defects.
Modeling Cohesive Cracks With Meshless Method
Authors: Wu S.
Published: July 2010

We present a discrete rotating crack method embedded in the elementfree Galerkin method. The crack is represented by discrete cohesive crack segments only passing through nodes. The discrete crack segments are introduced when the tensile strength in the material is exceeded and the crack segments are oriented perpendicular to the direction of the maximum principal stress. The orientation of the crack segments are rotated when directional changes in the maximum principal stress occur. It will be shown that fixed crack models lead to over-smearing the crack and too stiff responses of the system. The advantage of this method is that no representation of the crack surface is needed.