bluuebunny/crossref_metadata_2025 huggingface dataset:
In-Service Inspection Strategy for Alloy X-750 BWR Jet Pump Beams Based Upon Linear Elastic Fracture Mechanics Analysis
Authors: Sommerville Daniel V. , Mehta Hardayal , Carter Robert , Kubiak Jonathon
Published: July 2010

Jet pumps in a boiling water reactor (BWR) are located in the annulus region between the core shroud and the reactor vessel wall and provide core flow to control reactor power. Between 16 and 24 jet pumps are included in BWR/3 through BWR/6 plants, depending on the plant rating. The inlet mixer assembly of the jet pump is secured in place with a hold down mechanism called a jet pump beam. This beam is fabricated of alloy X-750 and tensioned to 58–74% of the yield stress of the material, depending on the beam design. In recent years, more attention has been placed upon inter-granular stress corrosion cracking (IGSCC) of alloy X-750 BWR internal components as a result of in-service cracking and failures. BWR plant owners have implemented actions to manage IGSCC of jet pump beams and assemblies through increased inspections and changes to process specifications for X-750. However, a thorough understanding of the flaw tolerance of the jet pump beam was not available to guide the periodicity of inspections as well as to define critical flaw sizes needed to validate the capability of inspection techniques. This paper describes a linear elastic fracture mechanics (LEFM) evaluation in which the flaw tolerance of the existing jet pump beam designs is established and used to recommend inspection frequencies for the jet pump beam. Industry operating experience is used to assess the credibility of the results obtained from this evaluation. This work illustrates an example of the use of LEFM to develop a technically defensible basis for the required inspection regions and the frequency of inspection for an alloy X-750 BWR internal component and helps to establish the necessary sensitivity of non-destructive examination technology to be used to examine the component.
Effects of a Gyroscope in Reducing Rocking Motion of a Rigid Vessel Coupled With Inner Structure Subjected to a Base Excitation
Authors: Furuta Kazuhisa , Ito Tomohiro , Shintani Atsuhiko
Published: July 2010

Many spent fuels coming out of the nuclear power station are planned to be stored in the special site in Japan until they are reprocessed. In this site, the spent fuels are installed in a cylindrical container called canister. The canister, in tern, will be installed in the outer cylinder called cask that is a free-standing structure. When this system is subjected to strong seismic excitations, sliding or rocking motion will be induced. And, in the worst case, the cask may collide to each other or overturn. Therefore, it is very important to reduce sliding and rocking motions of the cask in order to avoid the consequent contamination of radio active substances. The authors have already reported the studies on the sliding and rocking motions of the cask subjected to a seismic excitation that contains a vibration system in it, and clarified the effects of the vibration of the inner canister. It was shown that the inner canister gives very large influences on the sliding and rocking motions of the outer cask. In this study, we applied a gyroscope at the top of the outer cask for reducing rocking motion of the cask. The effects of the gyroscope are studied for various excitation frequencies, excitation amplitudes and the structural dimensions of the gyroscope such as weight and rotational frequency. It is found that the gyroscope is very effective for reducing rocking motions of the cask-canister system subjected to seismic excitations.
A First Investigation on Cumulative Fatigue Life for a Type 304-L Stainless Steel Used for Pressure Water Reactor
Authors: Fissolo A. , Stelmaszyk J. M.
Published: July 2010

In order to estimate the crack initiation damage, and also the water leakage conditions on PWR pipes, uniaxial fatigue curves are often used. They were deduced from strain or stress load control tests using normalised cylindrical specimens. However, severe thermo-mechanical loading fluctuations are observed in operating conditions. Components may also be submitted to transient loadings. The purpose of the present work is to start investigation on the fatigue life with a variable loading, in order to examine cumulative damage effect in fatigue. In this frame, multilevel strain controlled fatigue tests have been performed on a Type 304-L stainless steel (elaborated in accordance with the RCC-M specifications). The experimental results show that linear Miner’s rule is not verified in our conditions. When the strains are applied in a decreasing order (High-Low strain sequence), the summation of cycle ratios is smaller than unity, whatever the number of applied levels, whereas this summation is higher than one for an increasing order (Low-High strain sequence). A loading sequence effect is clearly evidenced. Different cumulative fatigue damage theories, proposed in literature, have been also tested. Some of them have been given better estimation than the Miner’s rule. That is the case of the so-called “Hybrid Theory” proposed and tested before by Bui Quoc on a Type 304-L steel. Extension of a model proposed by S. Taheri would seem also promising. At this stage, final conclusion cannot be yet deduced, additional investigations are needed.
Meshless Simulation of Fracture in Thin-Walled Pipe Structures
Authors: Liu S. J.
Published: July 2010

A meshless shell method for dynamic fracture problems based on normalized Smoothed Particle Hydrodynamics (SPH) is presented. The SPH method is corrected by a normalization in order to fulfill completeness requirement. Instability are controlled by stress-point integration. The method is modified for Mindlin-Reissner shell analysis. Stress based fracture criterion is incorporated based on the visibility method. The method is applied to two dynamic fracture problems in thin-walled pipes including fluid-structure interaction. The results are compared to experimental data and they are very promising.
Analysis of Fracture Mechanics Specimens Made of Inconel 600 Based on Assessment Methods of Different Complexity
Authors: Nicak Tomas , Schendzielorz Herbert , Keim Elisabeth
Published: July 2010

Fracture mechanics analysis plays an important role in the frame of the safety assessment of nuclear components. Usually the goal of such an analysis is to decide if a given flaw size in the piping (or any component of the primary circuit) is acceptable or not. The word “acceptable” means that structural integrity of the component is guaranteed with sufficient safety margins up to the end of service life or up to the next in-service inspection (considering the worst case loads and lower bound material properties). To fulfil this high-responsible task in practice some useful Engineering Assessment methods (EAM) have been established i.e. Local flow stress concept (Germany), assessment based on J-Integral (France RSE-M), Limit load calculation according to (ASME XI, USA) or Two criteria approach (R6, UK). These EAM are verified by a large number of testscarried out in the past. On a higher level, more advanced assessment methods have been developed during the last years, based on micromechanical models of void nucleation and growth. These advanced micromechanical models are used within the Finite Element Analysis (FEA) and allow to study the whole crack growth process from initiation to final failure in more detail. In the ductile regime, which is the typical case for application of aforementioned methods, the crack growth can be divided into three phases: crack initiation, stable crack growth and unstable crack growth. In this paper methods of different complexity will be applied to analyse fracture mechanics specimens made of Inconel 600. Special focus will be placed on the crack growth modelling based on the Gurson’s porous metal plasticity theory. All performed calculations will be compared with experiments.
Extending the Internal Examination Intervals for Pressure Vessels Using an RBI Approach
Authors: Moore Philippa , Wintle John
Published: July 2010

For pressure equipment containing clean, dry and non corrosive products under stable and benign conditions, there may not be any degradation mechanisms affecting the containment material over a considerable length of time. Taking account of the low risk of failure, it may then be possible to justify a longer interval between shutdowns for internal examination. Nonetheless, it is important that this judgement has been made carefully and correctly, and that adequate safeguards are in place so appropriate action may be taken if the expected conditions are subject to change. This is the theme of a recent report by TWI [1] commissioned by the UK Health and Safety Executive (HSE), which has outlined a six-step approach for assessing and justifying internal examination requirements for process plant at high hazard sites. The work has been developed partly through consultation with leading UK petrochemical companies and inspection bodies that are proactive in developing risk-based inspection methodologies.
Development of Alternate Methods for Establishing Design Margins for ASME Section VIII Division 3: Part 2
Authors: Terada Susumu
Published: July 2010

The design margin against collapse for Division 3 is based on Nadal’s equation. For high strength material this method is adequate. However for material with a lower ratio of Sy/Su this method has additional margin from yielding through the thickness to final collapse or burst. The experimental burst test results for closed-end cylinder show the excessive margin for these materials as stated in former paper. Therefore the development of alternate methods for establishing design margin for all materials is desirable. The design margin of 1.5 in equation for open-end cylindrical shell and spherical shell in current code is different from that of 1.732 for closed-end cylindrical shell. The design margin of elastic-plastic analysis is 1.732. Therefore the consistent design margins of equations and elastic-plastic analysis for open-end cylindrical shells and spherical shells are also desirable. In this paper new equations for design pressure of cylindrical shell and spherical shell are proposed by investigation of burst test results and case studies of various methods.
Implementation of PLIM and AMPs in Czech NPPs
Authors: Krivanek Robert
Published: July 2010

Since 2003 CEZ is preparing and implementing new Plant Life Management (PLIM) Programme. It includes also detailed Ageing Management Review of all already implemented Ageing Management Programmes. It was necessary to develop and approve the Plant Life Management Conception in connection with an implementation of Plant Life Management Programme in CEZ power plants. This Conception became a basis for formation of the “CEZ Plant Life Management Standard” which provides basic fundamentals and goals during PLIM implementation in power plants. This article describes main ideas of these documents, work done in past years and plans for following years.
Investigation on the Flow Induced Erosion-Corrosion Failure of Hydrocracking Air Cooler Systems and Optimization Study
Authors: Ou Guofu , Zheng Zhijian , Jin Haozhe , Bao Jinzhe
Published: July 2010

The flow induced erosion-corrosion of a hydrocracking reactor effluent air cooler (REAC) system normally occurs locally and abruptly, which leads to the high risk of unplanned shutdown and even catastrophic accidents. To study the typical failure cases induced by the high-sulfur and chloride-containing raw oil in the process of refining, numerical simulation of technical process and fluid dynamics parameters are performed on softwares of HYSYS and CFD, and the rules of multiphase flow erosion and ammonium salts deposition are analyzed. Analytical results are in good agreement with actual failure instance and thus the reliability of the predictive method is validated. A corrosion-control research system, consisting of mechanism research, numerical simulation, experimental verification and similarity theory correction, is established. The critical characteristics of multiphase flow deposition and erosion are obtained. And the system to control the flow induced erosion-corrosion, which can be widely applied in various conditions, is formed on the basis of “avoiding blockage and controlling erosion” conception. Moreover, this paper proposes an optimum design based on the degree of unbalancedness and a frame of the REAC Real-time Diagnosis Expert Software for guiding the optimum design. The method above will be beneficial to the promotion and modification of related criteria and regulations in the future.
Risk Informed In-Service-Inspection Activities of the ENIQ Task Group on Risk
Authors: Gandossi L. , Simola K. , Toft Adam
Published: July 2010

The European Network for Inspection Qualification (ENIQ) was established in 1992 in response to increasing recognition of the importance of qualification of non-destructive inspection systems used in in-service inspection programmes for nuclear power plants. Driven by European Nuclear utilities and managed by the European Commission Joint Research Centre (JRC), ENIQ represents a network in which the available resources and expertise can be pooled at European level. ENIQ has recognized the importance of addressing, at European level, the issue of optimizing inspection strategies on the basis of risk by establishing a Task Group on Risk (TGR). Membership of TGR is drawn from European nuclear utilities and consultants. ENIQ TGR is focused on Risk-Informed In-Service Inspection (RI-ISI) methodologies. Its work is directed towards harmonisation in the field of codes, standards and best practice for RI-ISI methodologies, with the objective of increasing the safety of European nuclear power plants. In March 2005 TGR published a European Framework Document for RI-ISI. This publication provides guidance for both developing new RI-ISI approaches and using or adapting established approaches to a European environment, taking into account utility-specific characteristics and national regulatory requirements. More recently, ENIQ TGR has been working at producing more detailed recommended practices and discussion documents on several RI-ISI related issues, such as the role of ISI within the philosophy of defence-in-depth, the verification and validation of structural reliability models (SRMs) to be used in RI-ISI programmes, the use of expert panels and the applicability of RI-ISI to the reactor pressure vessel. Work is ongoing to develop a discussion document on updating of RI-ISI programmes, and new initiatives were launched to study topics such as what magnitude of risk reduction is reasonable to achieve through ISI, and how to set inspection targets, following the selection of ISI sites. In addition, TGR has been active in initiating international projects linked closely to its work, such as the JRC-OECD/NEA co-ordinated RI-ISI benchmark exercise (RISMET), and the project on the relation between inspection qualification and RI-ISI. This paper describes the key activities and publications of TGR to date.
Numerical Evaluation of Ratchetting Effects on the Deformation and Failure Behaviour of Components
Authors: Roos Eberhard , Schuler Xaver , Stumpfrock Ludwig
Published: July 2010

Within a recent project of German reactor safety research an existing phenomenological material model was improved and verified. The material model allows to simulate numerically the complex procedures during multiaxial and cyclic load in a component. The model makes the simulation for in-phase and out-of-phase loads possible. Parallel to the theoretical work experimental investigations were accomplished. With the experimental data on the one hand the parameter necessary for the material model are determined. On the other hand experiments supply a database from thin-walled hollow cylinders with multiaxial load for the verification of the implementation of the material model to a finite element programme. Good coincidence between measured data and simulation could be achieved in most cases. In some cases the simulation overestimates the measured data. With respect to a safety assessment of components, therefore, the simulation gives conservative results.
Unstable Crack Propagation Under Severe Accident Scenario Conditions in a Pressurized Water Reactor
Authors: Tardif Nicolas , Coret Michel , Combesure Alain
Published: July 2010

In the case of a severe accident scenario of a pressurized water reactor which includes cracking of the vessel bottom head, it is crucial to predict the leak rate and hence the crack size for the ex-vessel accident management. We present an experimental framework to analyze the crack propagation under such severe conditions for different 16MND5 French nuclear steel grades. An original experimental setup has been designed in order to perform bi-axial tests (tensile load independent of internal pressure) at high temperatures (1180K – 1280K) on tubular test specimens. The temperature loading and the mechanical loading can be set to reproduce the stress distribution of the hemispherical vessel bottom head submitted to an internal pressure. Moreover, the test was designed to be easily transposable to the real structure in terms of crack propagation and depressurization thanks to an energy based scaling methodology. We observed the crack initiation and propagation with two high speed digital cameras. Force, internal pressure, displacement and temperature fields were also measured and synchronized with the optical measurements. The different creep stages are observed and characterized. The crack propagation and opening history have been measured. During crack initiation and propagation stages, the depressurization can be correlated with the crack geometry. Finally, the setup has been designed in order to validate future numerical analysis.
Component Mode Synthesis Based SSI Analysis of Complex Structural Systems Using SASSI
Authors: Tabatabaie Mansour , Sumodobila Basilio
Published: July 2010

Three-dimensional seismic soil-structure interaction (SSI) analysis of nuclear power plants (NPP) is often performed in frequency domain using the computer program SASSI [1]. This enables the analyst to properly a) address the effects of wave radiation in an unbounded soil media, b) incorporate strain-compatible soil shear modulus and damping properties and c) specify input motion in the free field using de-convolution method and/or spatially variable ground motions. For large, complex structural systems with multi-million degrees of freedom (DOF) and large foundation impedance matrices associated with deeply embedded foundations, the conventional sub-structuring analysis approach employed in SASSI often results in a coefficient matrix that is too large to solve with currently available computer resources. To address this problem, the method of component mode synthesis (CMS) is employed in the SSI analysis. This involves partitioning the structure into several interconnected components, calculating the reduced-order model of each component, and then assembling the reduced-order component models into a global model of the total SSI system. This technique has been implemented in MTR/SASSI® [2] utilizing the super-element capability. After the component boundary and foundation motions of the synthesized SSI model are determined, these motions are substituted back into the structural component model to compute the response of the structure. This paper presents the formulation of component mode models, and their implementation into the global SSI model. To check out this procedure, an example of seismic SSI analysis of a simplified NPP model on flexible basemat subject to horizontal and vertical excitations is considered. The total SSI system is first analyzed with SASSI using the conventional approach to compute the baseline (target) solution. The structure is then partitioned from the basemat and analyzed separately using the ANSYS® [3] program to compute the component mode properties that are used to form the boundary super-elements. These super-elements are input into the foundation/soil model and analyzed by MTR/SASSI® to calculate the basemat response. The response of the flexible basemat is checked against the baseline solution. In the final step, the foundation basemat response that includes the SSI effects is imposed onto the structural component to calculate the response of the structure. Comparison of the responses show excellent agreement between the baseline solution and those obtained using CMS method.
Dynamical and Thermal Testing of a FW Panel Attachment System for the ITER Vessel
Authors: Va´clavi´k Jaroslav , Oliva Vladislav , Materna Alesˇ , Lorenzetto Patrick
Published: July 2010

The objective of this paper is to describe and evaluate mechanical tests of the First Wall (FW) panel Attachment System (AS) for the blanket system of the fusion reactor ITER according to the 2001 design. The tests were performed in SˇKODA VY´ZKUM, Ltd. with FE simulation support from Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering. The goal of the tests was to check the stiffness, strength limit, and fatigue behavior of the bolted joint under loads simulating conditions during off-normal plasma operations in the reactor. The FW panels are attached to a bottom thick shield block by means of ten special studs located on a shaped key-way on a shield block surface. A special device for a long-lasting test of stud tensile pre-load relaxation over of 30 000 temperature cycles between 100° and 200°C was developed. Two methods were used to determine the real stud pre-load force drop during such temperature cycling. An optimum procedure for pre-loading of the AS studs has been developed. Four panel mock-ups (1080×250×50 mm) and one massive shield block having all the features of the real AS were fabricated from 316L stainless steel at VI´TKOVICE Research and Development, Ltd. The panel screwed to the shield with stud preload from 45 to 100 kN and was then loaded alternatively by 2500 cycles of radial moment (±24.5 kN·m), poloidal (longitudinal to panel axis) force (±108 kN), or poloidal moment (±53 kN·m) at room temperature. The stud bending stresses, stud pre-load relaxation, cyclic deformation leading to undesirable radial gap opening at the key-way and a possible plastic deformations of AS were studied. Additional FE simulations were used for better interpretation of measurements. The experimental results have shown that thermal cycling leads to a stud pre-load drop from 100 to 60 kN, whereas the dynamic cycling itself does not cause an additional loss of the pre-load. The individual loads applied do not cause a loss of radial contact in the keyway or a damage of AS even under a low stud’s pre-load of only 54 kN. A small radial gap in the key way was observed only under maximum poloidal moment with an extremely low stud pre-load of 45 kN.
Assessment of the Temperature Field of the Viscous Damper GERB Type VES 40/40/40
Authors: Pecinka Ladislav , Zakovec Pavel , Barutzki Frank
Published: July 2010

GERB pipework viscous dampers are highly effective viscous – elastic elements. The stiffness and damping coefficients of these ones are strongly dependent on the working temperature of the fluid. It is a crucial problem of nuclear power plants if viscous dampers are installed inside the hermetic zone. Circulation of the air due to ventilation system represents either heating or cooling of the damper surface and finally can influenced, the damper reliability. This problem has been solved for the Armenian NPP Metsamor. Results are presented.
A Study on Estimation of Internal Pressure Creep Life Using Small Punch Creep (SPC) Tests for Boiler Pipes
Authors: Kobayashi Toshimi , Izaki Toru , Kusumoto Junichi , Kanaya Akihiro
Published: July 2010

The small punch creep (SPC) test is possible to predict residual creep life at a high accuracy. But, the results of SPC tests cannot be compared with uniaxial creep or internal pressure creep results directly. In this report, the relationship between SPC test results and uniaxial creep test results in ASME A335 P11 (1.25Cr-0.5Mo Steel) was studied. The obtained relationship between SPC load and equivalent uniaxial creep stress formed a simple linear equation under the wide range of test temperature and test period. Then, the SPC results can be compared with uniaxial results by converting SPC loads to the equivalent uniaxial creep stresses. The relationship between SPC test results and internal pressure creep tests results was also studied. The internal creep life of as-received P11 pipe was almost same as SPC result when the hoop stress was converted to the SPC load. The creep lives of internal pressure creep influenced materials also showed good correspondence with SPC results. Therefore SPC can estimate the residual life of internal pressure creep influenced materials.
Proposal of Rational Determination of Fracture Toughness Lower-Bound Curves by Master Curve Approach
Authors: Miura Naoki , Soneda Naoki , Sawai Shu , Sakai Shinsuke
Published: July 2010

The Master Curve gives the relation between the median of fracture toughness and temperature in ductile-brittle transition temperature region. The procedure to determine the Master Curve is provided in the current ASTM E1921 standard. Considering the substitution of the alternative lower-bound curves based on the Master Curve approach for the recursive KIc curves in the present codes, the statistical characteristic should be well incorporated into the determination of the lower-bound curves. The appendix in the ASTM standard provides the procedure to derive the lower-bound curves, however, it seems to be addressed without sufficient consideration on statistical reliability. In this study, we proposed a rational determination method of fracture toughness lower-bound curves based on the Master Curve approach. The method took account of the effect of sample size in the determination of the tolerance bound curve. The adequacy of the proposed method was then verified by comparing with a fracture toughness database for RPV steels. The method allows the application of the Master Curve using fewer specimens, which can coexist with the present surveillance program.
Crack Tip Constraint for a Surface Crack Under Fully Plastic Conditions
Authors: Terfas Osama A.
Published: July 2010

The development of the crack shape in a thick wall pressure vessel is important in fitness-for-service evaluations such as leak-before-break. In this work the crack tip stress field for surface cracks in a thick plate is investigated using 3-D finite element analyses. The mean stress around the crack from the deepest point to the free surface is investigated for a semi-circular surface breaking crack. A new empirical procedure is developed that allows ductile crack growth to be modelled on the basis of standard deep and shallow cracked fracture toughness test data. In conjunction with this procedure the results show that the crack growth will be suppressed at the deepest segments and the crack will preferentially grow in direction of 45°–70° measured from the deepest point in full plasticity.
Effect of Adjacent Safe End to Piping Weld and Preemptive Weld Overlay Repair on Residual Stresses on Nozzle to Safe End Weld
Authors: Song Tae-Kwang , Kim Yun-Jae , Chun Yun-Bae , Oh Chang-Yong , Bae Hong-Yeol , Lee Kyoung-Soo , Park Chi-Yong
Published: July 2010

In this study, simplified nozzle geometry was proposed to quantify the effects of adjacent similar metal weld and weld overlay on residual stresses in dissimilar metal weld. Finite element analyses were conducted with various thickness ratios and safe end lengths and corresponding residual stresses were provided. According to the results, residual stresses in dissimilar metal weld were improved after adjacent similar metal welding. The effect of similar metal welding is more evident with shorter length of safe end. Thus, short length of safe end was recommended for new design of nozzle. Appropriate thickness of preemptive weld overlay reduces the conservative thickness recommended by ASME Code.
Remaining Lifetime Evaluation of High Temperature Components of Power Plant Steam Boilers: Case Studies
Authors: Mentl Vaclav , Lisˇka Va´clav , Koc Jaroslav , Chocholousˇek Michal
Published: July 2010

The energy producing power plants are designed for operational period of 20, 30 years. During this period, inspections are realized to investigate the operational capability of the respective components and the plant as a whole, and when the designed time is approaching its limit, the crucial questions are raised with respect to the following possible operation, its safety and risks that stem from the fact that the continuous degradation of material properties occured during the longtime service as a result of service conditions, e.g. high temperatures, fatigue loading etc. The inspection of the boiler and the assessment of its future operational capability should ensure the safe operation and minimazing the failure risks. In comparison with the more sofisticated and much more expensive methods that use numbers of variables that enter the evaluation process of the lifetime exhaustion, or the metallographic non-destructive or even destructive methods that do not result often in a quantitative lifetime assessment, a relatively simple assessment method was used to evaluate the remaining lifetime of the high temperature components. On the basis of accelerated creep test data performed on the degraded materials, the remaining lifetime hours were calculated for the three “safety” situations: 1. “ZERO SAFETY” (neither recommended k = 1, 5 safety coefficient for working stress nor +70deg Celsius increase of working temperature were taken into consideration). 2. “STRESS SAFETY” (1, 5 safety coefficient for working stress and working temperature were taken into consideration). 3. “FULL SAFETY” (1, 5 safety coefficient for working stress and working temperature +70 deg Celsius were taken into consideration). This paper summarizes the results of remaining lifetime calculation for three different cases of steam boilers inspected after longtime service by Skoda Research ltd. Recently. On the basis of performed examination, the results provided the customer the recommendations relating the future safe and reliable operation.
Investigation of Pressure Stress Concentration Factors for Intersecting Elliptic Bores With Circular Bores in Blocks
Authors: Badr Elie A. , Yousef Nataly
Published: July 2010

Stress concentration factors due to intersecting elliptic bores as well as circular bores in blocks have been thoroughly investigated by Badr [1] and Sorem et al [2]. Results of these investigations indicated that intersecting elliptic crossbores generate lower stress concentration factors than those due to intersecting circular crossbores. In this study, we investigate stress concentration factors for crossbores in blocks (cubical and rectangular) emanating from intersecting elliptic with circular holes. Comparing these results with those generated by Badr [1] for elliptic hole intersections; it was found that crossbores due to intersecting elliptic with circular bores generate higher hoop stress concentration factors. A regression analysis was also performed to determine a relationship between the stress concentration factors, the bore ratio (a2/a1) and the tilt angle θ.
ASME Code Needs for Very High Temperature Generation IV Reactors
Authors: O’Donnell William J. , Griffin Donald S.
Published: July 2010

Subsection NH “Components in Elevated Temperature Service” of Section III was originally developed to provide structural design criteria and limits for elevated-temperature design of Liquid-Metal Fast Breeder Reactor (LMFBR) systems and some gas-cooled systems. The U.S. Nuclear Regulatory Commission (NRC) and its Advisory Committee for Reactor Safeguards (ACRS) reviewed the design limits and procedures in the process of reviewing the Clinch River Breeder Reactor (CRBR) for a construction permit in the late 1970s and early 1980s, and identified issues that needed resolution. In the years since then, the NRC, DOE and various contractors have evaluated the applicability of the ASME Code and Code Cases to high-temperature reactor designs such as the VHTGRs, and identified issues that need to be resolved to provide a regulatory basis for licensing. Since the 1980s, the ASME Code has made numerous improvements in elevated-temperature structural integrity technology. These advances have been incorporated into Section II, Section VIII, Code Cases, and particularly Subsection NH of Section III of the Code. The current need for designs for very high temperature and for Gen IV systems requires the extension of operating temperatures from about 1400°F (760°C) to about 1742°F (950°C) where creep effects limit structural integrity, safe allowable operating conditions, and design life. This paper (1)identifies the structural integrity issues in the ASME Boiler and Pressure Vessel Code, including Section II, Section VIII, Section III, Subsection NH (Class 1 Components in Elevated Temperature Service) and Code Cases that must be resolved in order to support licensing of Generation IV Nuclear Reactors, particularly Very High Temperature Gas-Cooled Reactors (VHTRs); (2) describes how the Code addresses these issues; and (3) identifies the needs for additional criteria to cover unresolved structural integrity concerns for very-high-temperature service.
Stress Corrosion Cracking in Tear Drop Specimens
Authors: Lam P. S. , Zapp P. E. , Duffey J. M. , Dunn K. A.
Published: July 2010

Laboratory tests were conducted to investigate the stress corrosion cracking (SCC) of 304L stainless steel used to construct the containment vessels for the storage of plutonium-bearing materials. The tear drop corrosion specimens each with an autogenous weld in the center were placed in contact with moist plutonium oxide and chloride salt mixtures. Cracking was found in two of the specimens in the heat affected zone (HAZ) at the apex area. Finite element analysis was performed to simulate the specimen fabrication for determining the internal stress which caused SCC to occur. It was found that the tensile stress at the crack initiation site was about 30% lower than the highest stress which had been shifted to the shoulders of the specimen due to the specimen fabrication process. This finding appears to indicate that the SCC initiation took place in favor of the possibly weaker weld/base metal interface at a sufficiently high level of background stress. The base material, even subject to a higher tensile stress, was not cracked. The relieving of tensile stress due to SCC initiation and growth in the HAZ and the weld might have foreclosed the potential for cracking at the specimen shoulders where higher stress was found.
Sudden and Gradual Alteration of Amplitude During the Computation for Flow Around a Cylinder Oscillating in Transverse or In-Line Direction
Authors: Baranyi La´szlo´
Published: July 2010

This study investigates the effect of altering oscillation amplitude on time-mean and root-mean-square values of force coefficients when plotted against amplitude of oscillation. The cylinder is placed in a uniform flow and is oscillated mechanically in transverse or in-line direction. The two-dimensional numerical computations are carried out at Re = 140 and 160, at 90% of the natural vortex shedding frequency. For in-line oscillation, jumps were found in the time-mean values of lift and torque. Both abrupt and gradual alteration of amplitude in the course of a computation had the effect of keeping the solution in one state curve, i.e., of conserving state, or inhibiting changes in vortex structure. Transverse oscillation displayed no jumps, and alteration of amplitude had no effect on the solution.
Finite Element Simulation for Bolted Flange Joints Assembly With Misalignment
Authors: Konnai Takashi , Tsuji Hirokazu , Shoji Yasumasa
Published: July 2010

JIS B 2251 (former HPIS Z 103 TR) is published as the assembly guidelines for bolted flanged joints with ring-type gasket, which employs the rotational clockwise tightening sequence in the main tightening step. Actual flanged joints have misalignment, and when the flanged joints are assembled, the bending moment to modify the influence of the misalignment acts on the flange faces. There is risk that the uniformity of gasket stress distribution is affected by the bending moment of the misalignment. So, the influence of the misalignment on the uniformity of the gasket stress distribution is investigated using finite element analysis. Consequently, setting the acceptance criteria of the misalignment to get the uniformity of gasket stress distribution. The influence of the uniformity of the gasket stress distribution in case of changing the starting tightening bolt against the direction of the misalignment is also investigated.
Current Status of NIMS Structural Materials Database
Authors: Yamazaki Masayoshi , Xu Yibin
Published: July 2010

The NIMS Materials Database has been open to public on the Internet from National Institute for Materials science April, 2003. In this paper, the present status of on-line version of the creep and fatigue datasheet, the microstructure for crept materials database, and the CCT Diagram for welding are introduced. Furthermore, collaboration with the database of an external organization and the search method of a database are explained.
Residual Stress Measurements in a Three-Bead Slot Weld in a 20 mm Carbon Steel Plate
Authors: Ohms C. , Wimpory R. C. , Neov D. , Hofmann M. , Turski M. , Haigh R. , Fitzpatrick M. , Edwards L.
Published: July 2010

Residual stresses have been measured by different techniques in a 3-bead slot weld in a carbon steel plate. Neutron diffraction has been applied at two different facilities, the High Flux Reactor of the Joint Research Centre in the Netherlands and the new research reactor FRM-II in Germany. Furthermore, measurements by surface hole drilling and by the contour method have been obtained by the Open University in the UK. The neutron measurements have been executed with different settings of the instruments and employing different crystallographic reflection planes of the bcc-lattice of the low-alloy steel. The results were found to be in remarkably good agreement in the base material, away from the fusion zone. Closer to and within the fusion zone, differences of significant magnitude between the measurements have been found. It has to be noted that the differences found were only in the absolute stress values, and not in the general trends of the stress distributions. The comparison between neutron diffraction and contour data is limited to common measurement locations and directions, e.g. through thickness measurements at the weld centre line and the start and stop ends, in the welding transverse direction, which is the direction of the contour measurements. A reasonable qualitative agreement has been obtained, but no exact quantitative agreement. The paper makes an attempt to explain the similarities and the differences between the measurements, and provides an outlook to additional work done in this context within the NeT European Network, also with a view to establishing methods to obtain better agreement of the stresses found in measurements at different facilities and/or by different methods.
Ultrasonic Guided Wave Testing System for Piping
Authors: Imagawa Yukihisa , Wada Hideki , Wakibe Yasuhiko , Kitagawa Hideaki , Kusumoto Junichi , Kanaya Akihiro
Published: July 2010

In the operation of electric power plant, it is necessary to understand the condition of the pipe quantitatively. The purpose is to prevent the accident caused of the wall thinning portion due to erosion or corrosion. The thickness of the pipe is partially measured with the ultrasonic thickness gage now. However, it is difficult to investigate the wall thinning portion in the pipe quantitatively without confirming it beforehand. In this study, for the purpose to identify the location of thinning, we have developed the ultrasonic testing system using the guided wave that was able to investigate partially the wall thinning portion of all aspects of pipe to be inspected at a time. This system propagates guided wave by using an electro-magnetic acoustic transducer. We understand the extensive condition of the pipe by using this system. Therefore, the efficient investigation of the pipe is available. For that reason, it is expected to contribute to the reliability improvement of facilities and the reduction of maintenance and repairs.
Creep Fatigue Behavior and Life Prediction Including the Load History Effect Under High Temperature
Authors: Dong Jie , Chen Xuedong , Fan Zhichao , Jiang Huifeng , Jiang Heng
Published: July 2010

Creep fatigue interaction is one of the main failure modes for high temperature pressurized equipment. In practice, the amplitude of load on structure often changes which results in the load history effect on cyclic behavior and life of material. Therefore, 316L stainless steel 1-step and 2-step creep fatigue test under high temperature was conducted, the influence of two kinds of load history on material behavior was analyzed. The results showed the first step load with different amplitude and life fraction would lead to different hardness or softness of material and affect the cyclic behavior under the second step load. There is also much difference of material behavior at the time of load change for high-low and low-high load case. A uniform nonlinear creep fatigue damage model based on “disorder” and a modified failure rule coupled with the load history effect were presented in the paper. The creep fatigue life under 2-step load at high temperature was evaluated by the damage model and the modified rule. The predicted results were in good agreement with the experimental data.
Proposal for Determination of Strain Rate in Environmental Fatigue Correction Evaluation
Authors: Asada Seiji
Published: July 2010

To calculate an accurate environmental fatigue life correction factor (Fen) for evaluation of environmental fatigue, a detailed strain time history is needed. The strain history is determined by dividing the stress difference history with the Young’s modulus. ASME B&PV Code, Section III, NB-3216 has two methods of derivation of stress differences. One is NB-3216.1, “Constant Principal Stress Direction.” The other is NB-3216.2 “Varying Principal Stress Direction.” Determination methods for strain rates for two kinds of calculation methods of stress differences are proposed by applying the JSME Code for Environmental Fatigue Evaluation Method for Nuclear Power Plants. Also a sample calculation is performed for a typical nozzle to verify the proposed methods.
Capability for Growth in Nonlinear Response of SDOF With Bilinear Hysteresis
Authors: Taniguchi Tomoyo
Published: July 2010

To approximate nonlinear response of structures subjected to an earthquake excitation, the displacement method in U.S. or the energy method in Japan has been practically used. However, unless these methods include the nature of dynamics of nonlinear structure well, the nonlinear response is not adequately calculated. Applying the equivalent linearization technique to a Single Degree Of Freedom (SDOF) system with bilinear hysteresis subjected to white noise base acceleration, this paper mathematically quantifies deterioration in a spring constant and increase in a damping coefficient with the progress of nonlinearity in the restoring force system as a function of the ensemble ductility ratio. As the nonlinearity progresses, the spring constant rapidly deteriorates and the damping substantially increases. Increments of damping of the lightly damped linear SDOF system are more than that of the moderately damped one. A comparison of the response of the equivalently linearized system to that of the corresponding linear system reveals the capability for growth in the nonlinear response. The nonlinear response predicable by either method is identified by values of the ensemble ductility ratio and damping ratio of the linear SDOF system. In addition, in a range of the ensemble ductility ratio where the bulk of the engineered structures are included, neither method can properly evaluate the nonlinear response. Although the results presented herein give the mean nature of the nonlinear response and phase and amplitude characteristics of accelerograms make the nonlinear response vary around the mean, uniform application of either displacement method or energy method to approximating the nonlinear response may be reconsidered.
Analysis of the Mechanical Behavior of Pipe Flange Connections by Taking Account of Gasket Compression Characteristics at Elevated Temperature
Authors: Fukuoka Toshimichi , Nomura Masataka , Nishikawa Takashi
Published: July 2010

Sealing of contained fluids is the primary performance required for pipe flange connections. It is well known that the leakage is likely to occur when contained fluids at high temperature are concerned. Due to the differential thermal expansion of each part, bolt preloads that tighten a pair of pipe flanges tend to decrease. Therefore, it is significantly important for the joint safety to estimate the amount of bolt preload reduction at the design stage. In this paper, a finite element approach is proposed to analyze thermal and mechanical behavior of pipe flange connections at elevated temperature, by incorporating the stress-strain curves of sheet gaskets measured in the previous paper. Then, the reduction rate of bolt preloads at elevated temperature is systematically evaluated. The analytical objects are pipe flange connections tightened with aramid sheet gaskets. When a pipe flange connection is subjected to thermal load, the gasket stress usually decreases along unloading curves. The temperature dependency of gasket stiffness is considered by defining Young’s modulus in unloading E*, which can be introduced into FE formulation using ordinary solid elements. Numerical results show that bolt preloads are decreased by as much as 30% of the initial value when using aramid sheet gaskets of 3mm thickness. The effectiveness of the proposed numerical method has been confirmed by comparing the numerical results of bolt preload reduction to experimental ones.
Modeling Stress Corrosion Cracking Growth Rates Based Upon the Effect of Stress/Strain on Crack Tip Interface Degradation and Oxidation Reaction Kinetics
Authors: Shoji Tetsuo , Lu Zhanpeng , Das Nishith Kumar , Murakami Hiroyoshi , Takeda Yoichi , Ismail Tirtom
Published: July 2010

Quantitative prediction of environmentally assisted cracking such as stress corrosion cracking is one of the greatest concerns in lifetime management and consequent lifetime extension of light water reactors. Continuum mechanics has been applied to quantify the effect of crack tip mechanics on crack tip film degradation and its physical interaction with the oxidation kinetics. Besides such an effect, it has been realized that crack tip stress/strain can significantly affect the oxidation kinetics by a physical-chemical mode. The present paper focuses on optimizing crack tip asymptotic fields, oxidation kinetics laws, and their interaction modes for modeling stress corrosion cracking growth rates. Meanwhile, the physical-chemical effect of stress/strain on solid state oxidation kinetics at the stress corrosion crack tip is emphasized. The criteria for formulating stress corrosion cracking and optimizing input parameters are also discussed.