bluuebunny/crossref_metadata_2025 huggingface dataset:
Main Steam Piping Creep Life Consumption in Circumferential Welds
Authors: Cohn Marvin J.
Published: May 2012

A high energy piping (HEP) asset integrity management program is important for the safety of power plant personnel and reliability of the generating units. HEP weldment failures have resulted in extensive damage of components and significant lost generation. The main steam (MS) piping system is one of the most critical HEP systems. Creep damage assessment in MS piping systems should include the evaluation of multiaxial stresses associated with the field conditions. Typical creep life assessment stress parameters and estimated failure times are evaluated and compared with those of three MS piping system girth weld creep failures. This paper presents empirical data indicating that lead-the-fleet girth welds of MS piping systems have creep failures which can be successfully predicted by a multiaxial stress parameter, such as maximum principal stress. The calibration study indicates that the parent metal maximum principal stress should be increased by more than 20% to predict reasonable circumferential weldment lives in 2-1/4Cr-1Mo material. The correlation of other stress parameters, such as hoop stress, longitudinal membrane stress, and the standard as-designed ASME B31.1 sustained load stress do not provide an adequate ranking of the most critical girth welds subject to creep. In some piping systems, it is possible that spool-to-spool and circumferential variations in pipe wall thicknesses may influence the weldment life consumption estimates. Therefore, field wall thickness measurements should be taken at the most critical stress locations and applied to the life consumption evaluations.
Finite Element Modelling of 5- and 8-Pass Ferritic Steel Welds Using Phase Transformation Material Models
Authors: Hodgson David Z. L. , Gill Christopher M. , Pellereau Benjamin M. E. , Hurrell Paul R. , Francis John
Published: May 2012

The modelling of welds is desirable to predict the distortion of components during manufacture, the position and magnitude of peak residual stresses and to predict metallurgical effects in specific regions. Welds are a complex modelling problem requiring both thermal and structural solutions. This has lead to the development of several weld-specific simulation packages and codes for finite element (FE) analysis. This paper describes the application of phase transformation material models to ferritic groove weld test specimens. These specimens were manufactured from SA508 Grade 3 Class 1 pressure vessel steel plates 200×150×20 mm with SD3 1Ni 1/4Mo weld metal deposited in a groove 10 mm deep. The fifth weld pass in both specimens had two stop-starts introduced to investigate their effect on the residual stress field. The first stop linearly ramped the torch power down before backtracking and continuing the bead. The second stop had the torch abruptly switched off before restarting in the same location. The residual stresses in these specimens were measured using Neutron Diffraction (ND) which has been compared with the FE predictions. The FE modelling used a decoupled thermo-mechanical approach. The VFT-CTSP weld simulation package was used for the thermal analysis and Abaqus 6.8-3 for the mechanical analysis using the VFT UMAT-WELD user subroutine with phase transformation material properties. The thermal results appear to be consistent with the thermocouple traces recorded during manufacture of the plates. The simulated thermocouple temperature peaks are within 10% of manufacturing peaks. The simulated heating and cooling rates closely follow the manufacturing heating and cooling rates. The stresses calculated appear to be similar to the ND results measured on the specimen plates though some suspected errors have to be taken into account. The predicted stress field in the weld bead has a discontinuity as the material within the model changes from SA508 to SD3. This is to be expected due to the slightly different Young’s modulii of the two materials. This effect is present in the FE results due to the inability to model the metal mixing that occurs at the fusion boundary. The ND results were continuous across the fusion zone (FZ) and heat-affected zone (HAZ). The phases predicted appear to be similar to those expected for welds of this type. The martensite formation in the weld metal is consistent with the cooling rates experienced at the stop-start locations. The ramped stop-start had the lower cooling rate and therefore less martensite forms while the abrupt stop-start had a higher cooling rate which produces a larger amount of martensite. The subsequent remelting caused by passes six-eight removes the effects of the stop-start features in the eight-pass plate in the FE predictions.
Simulation and Evaluation of Thermal Stratification in a Sloped Surge Nozzle Correlated With Plant Measurements
Authors: Meikle T. L. , Johnson E. D. , Gray M. A. , Glunt N. L. , Burr J. D.
Published: May 2012

Thermal stratification is a common phenomenon in the surge lines of Pressurized Water Reactors (PWR). The stratification temperature difference (ΔT) and cyclic action severities are most prevalent during the heatup and cooldown operations of a PWR, when the system ΔT between the pressurizer and the Reactor Coolant System (RCS) hot leg is the greatest and system inventory fluctuations are highest. This paper describes the computer simulation of thermal stratification loading in a surge line nozzle connected to the RCS hot leg to correlate to unusual behavior of plant sensor data in the hot leg and the subsequent development of a monitoring model to account for thermal stratification effects in the transient and fatigue evaluation performed in the online monitoring system. What makes this particular investigation unique is the geometry of the nozzle of interest. In many PWRs, the surge line and the surge line hot leg nozzle are horizontal at the hot leg connection. This particular nozzle is oriented at an upward angle before the attached surge line piping bends into a horizontal configuration. This orientation required a more detailed treatment of the stratification effects than has been typically developed for horizontal nozzles, with respect to both the orientation and the potentially detrimental effects of increased cyclic behavior indicated by nearby temperature sensors. This investigation combined Computational Fluid Dynamics (CFD) modeling of the system to correlate the plant data with a detailed stress model that will enable the fatigue usage factor calculation in the plant’s online transient and fatigue monitoring system.
Fatigue Crack Growth of Structural Metals for Hydrogen Service
Authors: San Marchi Chris , Somerday Brian P.
Published: May 2012

As hydrogen fuel cell technologies achieve market penetration, there is a growing need to characterize a range of structural metals that are used in the hydrogen environments that are encountered in gaseous hydrogen fuel systems. A review of existing data show that hydrogen can significantly accelerate fatigue crack growth of many common structural metals; however, comprehensive characterization of the effects of hydrogen on fatigue properties is generally lacking from the literature, even for structural metals that have been used extensively in high-pressure gaseous hydrogen environments. This report provides new testing data on the effects of hydrogen on fatigue of structural metals that are commonly employed in high-pressure gaseous hydrogen.
Evaluation of Filler Metal 52M (ERNiCrFe-7A) Hot Cracking When Welding on Cast Austenitic Stainless Steel Base Materials
Authors: McCracken Steven L. , Smith Richard E.
Published: May 2012

Dissimilar metal welds of filler metal 182 (ENiCrFe-3) in the primary loop of pressurized water reactor (PWR) nuclear plants are susceptible to primary water stress corrosion cracking (PWSCC) after decades of service. Repair or mitigation has been routinely accomplished by installing a structural weld overlay (SWOL) on the filler metal 182 weld joint with the more PWSCC resistant filler metal 52M (ERNiCrFe-7A). The typical dissimilar metal joint consists of a low alloy steel vessel nozzle welded to an austenitic stainless steel safe end. The SWOL extends from the low alloy steel nozzle over the safe end and most often onto the adjoining wrought or cast stainless steel pipe. Field experience shows that filler metal 52M is susceptible to hot cracking when welding on certain heats of centrifugally cast stainless steel piping. This report evaluates 52M hot cracking when welding on CASS piping and provides the likely cause and mechanism for the cracking. The synergistic influence of silicon (Si) and sulfur (S) elements on the weld bead shape and dilution that leads to hot cracking is investigated. In addition, studies on the influence and use of the gas tungsten arc welding (GTAW) power ratio parameter for 52M overlays are presented.
Mesh Convergence Studies for Thin Shell Elements Developed by the ASME Task Group on Computational Modeling
Authors: Bjorkman Gordon S. , Molitoris David P.
Published: May 2012

The ASME Task Group on Computational Modeling for Explicit Dynamics was founded in August 2008 for the purpose of creating a quantitative guidance document for the development of finite element models used to analyze energy-limited events using explicit dynamics software. This document will be referenced in the ASME Code Section III, Division 3 and the next revision of NRC Regulatory Guide 7.6 as a means by which the quality of a finite element model may be judged. One portion of the document will be devoted to a series of element convergence studies that can aid designers in establishing the mesh refinement requirements necessary to achieve accurate results for a variety of different elements types in regions of high plastic strain. These convergence studies will also aid reviewers in evaluating the quality of a finite element model and the apparent accuracy of its results. In this paper the authors present the results of a convergence study for an impulsively loaded propped cantilever beam constructed of LS-DYNA thin shell elements using both reduced and full integration. Three loading levels are considered; the first maintains strains within the elastic range, the second induces moderate plastic strains, and the third produces large deformations and large plastic strains.
Fatigue Analysis of Preloaded Threaded Fasteners
Authors: Nassar Sayed A. , Ali Rania A.
Published: May 2012

This study investigates the fatigue performance of a preloaded threaded fastener under two scenarios of axial cyclic in-service loading. Since the fastener mean stress level would naturally affect the fatigue performance, various methods are investigated for their suitability for use to generate mean-stress adjusted S´-N´ fatigue curves. The maximum in-service cyclic tensile load that may externally be applied to the joint for a desired fatigue performance is also investigated. Limited fatigue test data set-up is generated for comparison with various methodologies for generating the mean stress-adjusted fatigue strength curves of A286 fasteners. Cumulative damage analysis is also performed in accordance with commonly used damage theories.
Large Scale Dynamic Response Analysis of Rod Bundles in Fluid Using Partitioned Coupling Technique
Authors: Kataoka Shunji , Minami Satsuki , Kawai Hiroshi , Yoshimura Shinobu
Published: May 2012

Dynamic responses considering fluid structure interaction (FSI) is important in many engineering fields and some of the FSI phenomena are treated as an acoustic fluid and structure interaction (AFSI) problem. The dynamic interactions between the fluid and structure can change dynamic characteristics of structures and their responses to external excitation such as seismic loading. The authors have developed a coupled simulation system for the large scale AFSI problems using an iterative partitioned coupling technique. In the system, the authors employed ADVENTURE system which adopted an efficient preconditioned iterative linear algebraic solver, and ADVENTURE Coupler is used to handle interface variable efficiently on various parallel computational environments. The authors employ Broyden method for updating interface accelerations to obtain the robust and fast convergence property of fixed point iterations. This paper presents the overview of the coupled analysis system and the results of its application to several AFSI problems are shown. The system runs efficiently in a parallel environment and it is capable for analyses of complex shaped three dimensional structures with more than 20 million degrees of freedom model.
Present Status of Inspection Technology and Standards for Large-Sized In-Service Vertical Storage Tanks
Authors: Guan Weihe , Tao Yuanhong , Cheng Huayun , Ma Chuanjin , Guo Pengju
Published: May 2012

In order to assure reliable and safe operation of large-sized vertical storage tanks and find the hazardous defects during the operation, it is needed to regularly inspect and test the storage tanks. Current inspection technology for in-service storage tanks can be divided into online inspection technology and post-shutdown internal inspection technology. Online inspection technology mainly includes acoustic emission technique, guided ultrasonic wave technique, spot ultrasonic thickness measurement technique and ultrasonic thickness measurement technique using auto wall-climbing robot, etc., and post-shutdown internal inspection technology mainly includes magnetic flux leakage inspection technique, ultrasonic inspection technique, surface inspection technique and vacuum leak detection technique, etc. This paper introduces the inspection methods for large-sized vertical petroleum storage tanks adopted currently in China in order to judge the status of the storage tank according to the online inspection results, decide whether to cut down or extend post-shutdown internal inspection cycle or not and develop inspection and maintenance plan; and conduct post-shutdown internal inspection according to the cycle specified in the enterprise standard. This paper also introduces the development situation of codes for design, construction and erection, repair and retrofitting and inspection standards for large-sized vertical petroleum storage tanks.
A High-Risk High-Reward Approach to Public-Private Collaborative Research in Predictive Modeling and Control of Complex Systems
Authors: Swanson David , Fong Jeffrey T.
Published: May 2012

In this paper, we propose an approach to public-private collaborative research in predictive modeling and control of complex engineered systems. Society depends intimately on complex systems. The behavior of a simple system can be modeled and the model can be validated by experimental observations, if the behavior of each component and its interface with other components are known and well-defined. In contrast, a complex system cannot be modeled accurately enough to effectively predict and control the behaviors of the overall system. One example of an engineered complex system network (CSN) is the electricity power grid, which encompasses power generation, transmission, distribution, and consumption, as one giant system that includes electric generators, transformers, substation switchyards, transmission lines, consumer devices, and a multitude of new evolving components. The electricity power grid depends on other complex systems, e.g., climate systems that govern wind current for wind turbines, river water levels for thermoelectric cooling, and economic systems for service demand, pricing, revenue collection, and for business capital supply. Operational robustness, reliability, and efficiency of CSN’s are in the interest of all the subsystem owners, end users, and the public welfare of the nation. Conundrum? Who is responsible for the overall CSN’s operational robustness, reliability and efficiency, when so many parts of the system reside in so many different hands with the ultimate beneficiaries of the systems being the general public? Which entities are responsible for funding critical high-risk research, whose ultimate benefits do not reside with any one subset of stakeholders? These questions characterize the challenge of sourcing R&D funds that can be focused on modeling, understanding, and management of CSNs in general. To address such needs for innovative collaborative research, Congress established the Technology Innovation Program (TIP) at the National Institute of Standards and Technology (NIST) as part of the 2007 America COMPETES Act. Its purpose is to “assist United States businesses and institutions of higher education or other organizations, such as national laboratories and nonprofit research institutions, to support, promote, and accelerate innovation in the United States through high-risk, high-reward research in areas of critical national need.” Ongoing efforts by TIP to identify and qualify societal challenges in the critical national need area of Complex System Networks are introduced.
Elastic-Plastic Constraint Analysis of Semi-Elliptic Surface Cracks in X100 Pipeline Steel
Authors: Wang Z. X. , Zhang R. F. , Chao Y. J. , Lam P. S.
Published: May 2012

In the framework of the J-A2 fracture theory, the crack driving force J and the crack tip constraint parameter A2 are used to describe the near crack tip stress and deformation fields. These two parameters, J and A2, were calculated from three-dimensional finite element results for semi-elliptic surface cracks with various lengths and depths in X100 pipeline steel. It was found that, under a uniform far field tensile loading, A2 increases rapidly to a nearly constant value along the crack front from the free surface to the deepest part of the crack. A similar trend was found for the J-integral distribution except in the case of a semi-circular crack. In addition, for a given elliptic crack configuration, A2 showed significant J-integral dependence when the crack front approached the free surface, where a strong three-dimensional effect is apparent. On the other hand, at the deepest part of the crack, A2 converged to a constant value. Two-dimensional plane strain calculations were also performed for single edge-notched tension specimens (SENT), where the crack length corresponds to the depth of the surface crack. The constraint of these two configurations (semi-elliptic crack and SENT) were compared under the same crack driving force (J-integral). In general, the constraint at the deepest crack front of an elliptic crack is higher than that of the corresponding SENT, especially in mid- to large scale yielding condition where J-integral is relatively large. It can be concluded that using fracture toughness determined from SENT specimens to predict surface flaw stability may lead to non-conservative result.
The Seismic Response Analysis of LNG Storage Tank Isolated by Multiple Friction Pendulum System
Authors: Weng Dagen , Zhang Ruifu , Ren Xiaosong
Published: May 2012

The seismic response of extra-large Liquefied Natural Gas (LNG) tank isolated vertically by multiple friction pendulum system (MFPS) is analyzed. The fundamental frequency of the extra-large LNG tank is usually the range of dominant frequency of most earthquake ground motions. It is an effective way to decrease the response for an isolation system being used for extra-large LNG storage tanks under the strong earthquake. However, it is rather difficult to implement in practice using common bearings because of low temperature, soft site and other severe environment factors. The extra-large LNG tank isolated by MFPS is presented in this study to solve these problems. MFPS is appropriate for large displacements induced by earthquakes with long predominant periods. A simplified finite element model by Malhotra and Dunkerly methods is used to judge the utility of the isolation system. Data reported and statistically sorted include pile shear, wave height, impulsive acceleration, convective acceleration and outer tank acceleration. The results show that the isolation system has excellent adaptability for different liquid levels and is very effective to control seismic response of the extra-large LNG tank.
Analytical Modeling of the Mechanics of Re-Torque
Authors: Gordon Ali P. , Williams James , De Santiago Maricela
Published: May 2012

A secondary torque, i.e., re-torque, is generally applied in order to confer long term bolt tightness of certain gasketed-flange configurations that have undergone a primary torque with some relaxation. In some sense, the initial torque conditions the viscoelastic gasket material for long term performance under service loading. While prior research has been carried out to analytically model the mechanical response of gasket materials under either creep, stress relaxation, or creep relaxation, the mechanics of gasket re-torque has received much less attention. In the current study, a candidate fiber-glass reinforced gasket material is subjected to creep relaxation after a series of primary and secondary torques. Test variables considered here include values of either torque, dwell period, or gasket thickness. The over-arching goal addressed in this study is the identification of the conditions that confer the minimal initial dwell period without loss of long term load retention. In all cases, specimen-sized samples were used on a raised-face, serrated flange assembly. Based on the experimental test data and observations from scanning electron microscopy, an viscoelasticity model is developed to analytically predict the response of the time-dependent solid.
Measurement of Welding Residual Stress in Dissimilar Metal Welds Using the Contour Method
Authors: DeWald Adrian T. , Hill Michael R. , Willis Eric
Published: May 2012

Welding residual stresses can significantly impact the performance of structural components. Tensile residual stresses are of particular concern due to their ability to cause significant degradation to the PWSCC resistance of structural materials. The contour method is a residual stress measurement technique capable of generating two dimensional maps of residual stress, which is particularly useful when applied to welds due to the complex residual stress distributions that generally result. The two-dimensional capability of the contour method enables detailed visualization of complex weld residual stress fields. This data can be used to identify locations and magnitude of tensile residual stress hot-spots. This paper provides a summary of the contour method and presents detailed results of contour method measurements made on the dissimilar metal weld region of pressurizer relief nozzles removed from the cancelled WNP-3 plant in the United States as part of the NRC/EPRI weld residual stress (WRS) program [1].
Effect of Creep of Non-Asbestos Sheet Gaskets at Elevated Temperature on Relaxation Behavior of Bolted Flange Joints
Authors: Yamaguchi Atsushi , Honda Takashi , Hagihara Masahiro , Tsuji Hirokazu
Published: May 2012

Gaskets in bolted flange joints experience creep when used for long periods of time. Since gaskets are often used at elevated temperatures, the clarification of their high-temperature creep behavior is essential. Relaxation of bolted flange joints is caused by creep in the gaskets, and may result in leakage of internal fluids. Therefore, the ability to predict relaxation in bolted flange joints due to the effects of creep in gaskets would allow the lifetime of the gaskets to be estimated and thus prevent leakage of internal fluid. In the present study, the creep behavior of non-asbestos sheet gaskets and the relaxation behavior of these gaskets in bolted flange joints at room/elevated temperature were investigated using four-inch flanges. The test conditions were 180 °C for 360 hours (approximately 2 weeks). The test samples were four types of non-asbestos sheet gaskets, two types of compressed fiber sheet gaskets and two types of PTFE sheet gaskets. The differences in creep behavior between the two types of compressed fiber sheet gaskets and between the two types of PTFE sheet gaskets were clarified. The creep strain at the end of the test was always larger than that just after reaching the test temperature for all gasket materials. On the other hand, the creep strain in the PTFE sheet gaskets just after reaching the elevated temperature was approximately equivalent to the total creep strain after the test has been completed. Thus, the creep behavior of each test gaskets was clarified under aging. In addition, the time for replacement of gaskets was estimated using the relaxation behavior in bolted flange joints by defining the time to reach the minimum design seating stress of the test gasket.
Development of an ASME QME-1-2007 Program for Safety Related Active Valve Assemblies for Advanced Plants
Authors: Ezekoye L. Ike , Drake Edward W.
Published: May 2012

ASME QME-1 “Qualification of Active Mechanical Equipment Used in Nuclear Power Plants” sets forth the requirements and guidelines which could be used to assure that active mechanical equipment is qualified for specified service conditions [1]. As determined by federal regulators and/or nuclear power plant licensees, this Standard could be applied to future nuclear power plants, or existing operating nuclear power plant component replacements, modifications, or additions. Over the years, the standard has gone through various revisions to both clarify and extend the requirements. However, the ASME QME-1-2007 standard significantly altered the qualification process for Active Valve Assemblies. For new nuclear plants, such as the Westinghouse AP1000, the change required a redevelopment of the valve assembly qualification program. This paper examines how the ASME QME-1-2007 valve assembly qualification requirements changed, how this has affected new plant valve assemblies and overall equipment qualification program, and the lessons that have been learned during the redevelopment and implementation of the standard. Specific issues covered in this paper include selecting the qualified valves and adjusting valve actuator qualifications to provide the right inputs to the ASME QME-1-2007 program.
Cyclic Deformation and Buckling Behavior of Pipe With Local Metal Loss Subjected to Seismic Ground Motion
Authors: Mitsuya Masaki , Yatabe Hiroshi
Published: May 2012

Buried pipelines may be deformed due to earthquakes and also corrode despite corrosion control measures such as protective coatings and cathodic protection. In such cases, it is necessary to ensure the integrity of the corroded pipelines against earthquakes. This study developed a method to evaluate the earthquake resistance of corroded pipelines subjected to seismic ground motions. Axial cyclic loading experiments were carried out on line pipes subjected to seismic motion to clarify the cyclic deformation behavior until buckling occurs. The test pipes were machined so that each one would have a different degree of local metal loss. As the cyclic loading progressed, displacement shifted to the compression side due to the formation of a bulge. The pipe buckled after several cycles. To evaluate the earthquake resistance of different pipelines, with varying degrees of local metal loss, a finite-element analysis method was developed that simulates the cyclic deformation behavior. A combination of kinematic and isotropic hardening components was used to model the material properties. These components were obtained from small specimen tests that consisted of a monotonic tensile test and a low cycle fatigue test under a specific strain amplitude. This method enabled the successful prediction of the cyclic deformation behavior, including the number of cycles required for the buckling of pipes with varying degrees of metal loss. In addition, the effect of each dimension (depth, longitudinal length and circumferential width) of local metal loss on the cyclic buckling was studied. Furthermore, the kinematic hardening component was investigated for the different materials by the low cycle fatigue tests. The kinematic hardening components could be regarded as the same for all the materials when using this component as the material property for the finite-element analyses simulating the cyclic deformation behavior. This indicates that the cyclic deformation behavior of various line pipes can be evaluated only based on their respective tensile properties and common kinematic hardening component.
The Parameter Study of the Seismically Isolated Bridge System by Lead Rubber Bearing Based on Energy Analysis
Authors: Zhong Tieyi , Zhang Changyong , Yang Fengli
Published: May 2012

The energy response equations of the seismically isolated bridge system are established based On the energy equilibrium theory. Bilinear analysis model of the energy response of the seismically isolated bridge is constructed by series connecting the bridge piers and the Lead rubber bearings. According to the applicable Code of Seismic Design for Railway Engineering, forty strong ground motion records are appropriately selected as the seismic input and the nonlinear time history analyses for the seismic energy responses of the bilinear SDOF seismically isolated bridge systems with different natural periods are carried out. The influences of peak ground accelerations, principal dynamic parameters of isolated bridge system on input energy and their distributions are studied.
Cyclic Crack Growth Rate of Irradiated Austenitic Stainless Steel Welds in Simulated BWR Environment
Authors: Chen Y. , Alexandreanu B. , Shack W. J. , Natesan K. , Rao A. S.
Published: May 2012

Reactor core internal components in light water reactors are subjected to neutron irradiation. It has been shown that the austenitic stainless steels used in reactor core internals are susceptible to stress corrosion cracking after extended neutron exposure. This form of material degradation is a complex phenomenon that involves concomitant conditions of irradiation, stress, and corrosion. Interacting with fatigue damage, irradiation-enhanced environmental effects could also contribute to cyclic crack growth. In this paper, the effects of neutron irradiation on cyclic cracking behavior were investigated for austenitic stainless steel welds. Post-irradiation cracking growth tests were performed on weld heat-affected zone specimens in a simulated boiling water reactor environment, and cyclic crack growth rates were obtained at two doses. Environmentally enhanced cracking was readily established in irradiated specimens. Crack growth rates of irradiated specimens were significantly higher than those of nonirradiated specimens. The impact of neutron irradiation on environmentally enhanced cyclic cracking behavior is discussed for different load ratios.
Characterization of Short Basalt Fiber Reinforced Syntactic Foams
Authors: Vijay Morampudi , Ouyang Zhenyu , Ji Gefu , Li Guoqiang , Jerro H. Dwayne
Published: May 2012

Sandwiched structures with syntactic foam core and fiber reinforced composite skins may have a great potential in pipe and pressure vessel structures due to the lightweight, competitive material cost, and it thermal and acoustic insulation effects. One concern of the syntactic foam as core materials is its brittleness (low toughness). In the current study, short basalt fibers are considered as a reinforcing phase to toughen the syntactic foam material. A compressive test and a notched three-point bending test were conducted to characterize the mechanical properties of the basalt fiber reinforced syntactic foam. In order to measure the fracture toughness, in the notched three-point bending test, two inclinometers were applied to record the rotation of the notched beam. Based on a moment-rotation based formulation, the J-integral was calculated. The compressive test results showed that the compressive strength slightly decreased with the inclusion of short basalt fibers. The three point bending test indicated that with a very low fiber volume fraction (0.25% and 0.5%), there was a dramatic increase in the syntactic foam’s tensile strength, ductility and toughness.
Effects of Bending Moment and Torsion on the Internal Pressure Limit Load of Locally Thinned Pipes
Authors: Hoang Phuong H. , Hasegawa Kunio , Bezensek Bostjan , Li Yinsheng
Published: May 2012

The pipe wall thinning stress evaluation procedures in Code-Case N-597-2 [1] of the ASME Boiler and Pressure Vessel (B&PV) Code are essentially based on Construction Code [2] stress evaluation. Stresses in the hoop and the axial directions are evaluated separately to meet the Construction Code allowable stress. Using Construction Code rules for local pipe wall thinning stress evaluation in Class 2 & 3 piping may be too restrictive. An alternative approach is to use the limit loads of locally wall thinned pipe in conjunction with an appropriate Z-Factor and the structural factors of the ASME B&PV Section XI, Appendix C [3]. Such approach may require a combined effect of pressure, bending, axial load and torsion loads on locally thinned pipe. In this paper, the effects of bending moment and torsion on the internal pressure limit load of locally thinned straight pipes are investigated. Large strain finite element limit load analysis with elastic - perfectly plastic materials are performed for a parametric matrix of piping models with various pipe R/t ratios, flaw depths, axial and transverse flaw extents. Based on the results, the allowable pressure for axial flaws in C-5420 of the ASME B&PV Section XI, Appendix C [3] may be used for piping local wall thinning as an alternative evaluation procedure to the current minimum pipe wall thickness evaluation procedure in the Code Case N-597-2 [1].
Fatigue Design and Evaluation of Head to Skirt Welded Joint of a Pressure Swing Adsorber Vessel
Authors: Zhao Mingxin
Published: May 2012

For pressure vessels and other welded structures subjected to cyclic loading conditions, fatigue failure of welded joints has been a major concern in design and operation. ASME Boiler and Pressure Vessel Code Section VIII Division 2 [1] provides different methods for fatigue evaluation on welded joints with various geometries, which facilitates the design and evaluation of welded joints subjected to cyclic loading. The selection of fatigue evaluation method will affect accuracy and outcome. This study attempts to demonstrate the design and evaluation process of a welded joint. Two major different fatigue evaluation methods have been used and results are analyzed and compared against operation data. The intention of this study is simply to present a practical case, through which proper selection of fatigue evaluation method for the specific welded joint could be suggested to achieve a safe, and yet, economical design.
Finite Element Stress Analysis for Leak Tests of Pipe Flange Connections Subject to Internal Pressure and Bending Moment
Authors: Nagata Satoshi , Sawa Toshiyuki , Kobayashi Takashi , Tsuji Hirokazu
Published: May 2012

This paper reports the results of finite element analysis representing the sealing performance tests on the slip-on type pipe flange connections for 8 inch and 16 inch. The flange connections are subjected to internal pressure and bending moment. Internal pressure is applied by helium gas and the bending moment is loaded through 4 points bending equipment. Gas leak rates are measured by pressure decay method. During the test, the variations in the axial bolt force are monitored for all the bolts by strain gages. The pipe stress at the junction of pipe and flange is also measured. Finite element analysis simulates the tests and the simulated results are compared with the measured data. Then the behaviors of the slip-on type flange connections under internal pressure and bending moment as well as the sealing performance are clarified by the experiment and the finite element simulation.
Leak Tightness Based Design Procedure for Gasketed Pipe Flange Connections
Authors: Sawa Toshiyuki , Kobayashi Takashi , Tsuji Hirokazu , Nagata Satoshi
Published: May 2012

A design procedure for bolted gasketed pipe flange connections has been developed by the Sealing Technology Of Pressure-equipments (STOP) Committee organized in the High Pressure Institute of Technology Japan. This paper explains not only the design procedure itself but also the technical background of the leak tightness of gasket basis for the procedure. The point to be highlighted is that the design procedure has adopted a flexibility analysis of the flange connection based on the Oyama method, which is the modification of the Koumura method calculating the interaction among pipe, hub and flange ring including gasket stiffness, in order to determine the required bolt preload achieving the specified leak tightness. The Oyama method can calculate the variations of axial bolt force, the flange rotation, and the gasket stress distribution in the radial direction due to internal pressure using relatively simple formulas.
Reliability of LBB Evaluation Considering Randomness in Design Parameters
Authors: Chakraborty Arindam , Qian Haiyang , Miessi Angah
Published: May 2012

In US, definition of the Leak-Before-Break (LBB) approach and criteria for its use are provided in NUREG-1061. Volume 3 of NUREG-1061 defines LBB as “…the application of fracture mechanics technology to demonstrate that high energy fluid piping is very unlikely to experience double-ended ruptures or their equivalent as longitudinal or diagonal splits.” Current LBB evaluation uses a factor of safety of two (2) on critical flaw size and a factor of safety of ten (10) on detectable leakage to deterministically analyze, that for a given set of input those factors are achieved. Typical input for LBB evaluation consists of pipe geometry, material properties (both elastic and plastic), crack morphology, loads, and operating pressure and temperature. Since LBB has recently been applied for pipes with weld overlays (WOL), thickness, material properties, and crack morphology of WOL also becomes important. However, in real structure all the design parameters (input) for LBB evaluation are inherently random in nature. The current work includes randomness in the critical design input parameters for LBB evaluation. Based on the result of this study reliability (or its compliment, probability of failure) curves are obtained based on the randomness in the critical input parameters. A piping system is considered to fail the LBB evaluation if the actual leakage through the pipe is less than the required leak rate which is calculated as ten times the plant minimum leak detection capability. Separate reliability curves are obtained for various minimum plant leak detection capability piping (e.g.,…, 1, 0.5,…, 0.1 GPMs) and for various piping systems (large diameter pipes such as reactor coolant loop hot leg and cold leg; and small diameter pipes such as pressurizer surge line, etc.). The reliability curves give an insight into the likelihood for a deterministic design input based LBB evaluation to remain valid in view of the in-situ variations.
An Investigation of the Adequacy of a Simplified Boundary Integral Equation / Influence Function Equation Linear Elastic Fracture Mechanics Solution for Nozzle Corner Cracking
Authors: Sommerville Daniel , Qin Minghao , Houston Eric
Published: May 2012

As plants pursue operation for longer periods (i.e. 60 years) the region of the reactor pressure vessel (RPV) which must be considered as the beltline region for generation of pressure-temperature (P-T) curves and satisfaction of 10CFR50 Appendix G requirements for prevention of brittle fracture has increased in size as the region of the vessel with a cumulative fluence greater than 1E17 n/cm has increased with plant age. In recent years nozzles have been identified as being located inside the beltline region of Boiling Water Reactors (BWRs). Consequently fracture mechanics evaluations of the nozzles in the beltline must be performed when developing beltline P-T curves. This paper evaluates adequacy of an existing simplified method for performing a Linear Elastic Fracture Mechanics (LEFM) analysis of a corner cracked, partial penetration, nozzle present in the beltline region of many BWRs. The nozzle design considered in this paper is representative of the BWR water level instrument nozzle. The results of this investigation are intended to provide a technical basis for the adequacy of the simplified nozzle solution considered in this paper for performing ASME Section XI, Appendix G evaluations of the instrument nozzle design.
Boiling Water Reactor Core Shroud Acoustic Loads Resulting From a Recirculation Outlet Line Break Loss of Coolant Accident: A Case Study
Authors: Sommerville Daniel , Karpanan Kumar
Published: May 2012

Acoustic loads caused by a postulated Recirculation Line Break Loss of Coolant Accident are one of the required design basis events that must be considered for stress analyses of Boiling Water Reactor internal components such as Jet Pumps and Core Shrouds. These acoustic loads must also be considered for fracture mechanics evaluations performed to assess allowable operating periods for flaws detected during in-service inspections. Acoustic loads methods generally utilized in the past have been 1-D or simplified 2-D models of the domain of interest. In some cases sophisticated nuclear thermal-hydraulic codes are used to obtain the acoustic response to the LOCA event. The present paper summarizes a case study of a RLB LOCA acoustic loads analysis of a BWR core shroud using 3-D linear acoustic finite element analysis. Representative loads are presented at each circumferential shroud weld location. The results presented in this paper can be used to assess the general order of magnitude of the loads which can be expected for similar BWR designs.
Alternating Slant Mode of the Crack Propagation in Ductile Flat Plates
Authors: Xue Liang
Published: May 2012

Cracks in flat plates are often found to be about 45° to the plate plane for some metals and alloys. There are two identical 45° directions to the plate plane and the choice of crack direction seems to be random. Experiments have shown that, for large flat panels, the long ductile crack propagation exhibits a regular alternating pattern, i.e. the crack switches to the other direction after propagates some distance regularly. In this paper, a numerical examination of the details of the formation of the alternating crack pattern is presented. Relevant material parameters and their influencing factors to the alternating behavior of cracks are discussed.
Equilibrium and Equivalency (E2) Linear Surface Fitting Method for Data With Two Independent Variables
Authors: Wei Zhigang , Yang Fulun , Nikbin Kamran
Published: May 2012

A recently developed equilibrium and equivalency (E2) mechanisms based curve fitting method is extended to surface fitting for linear function z = f (x, y) = a + bx + cy with two independent variables x and y. The concept of equilibrium of ‘force’ and ‘moment’ is adopted to derive surface fitting formulae, which are exactly the same as that obtained with traditional least squares (LS) method for the linear function. However, E2 method has obvious physical meaning and therefore is more intuitive in quickly and correctly identifying data pattern and subsequent data analysis. Furthermore, the formula based on perpendicular offsets method in terms of data variation along surface normal direction is derived and the results are compared with the traditional methods. Finally, the application of these methods to data of fatigue and creep lives is presented.
Ground State Structure of Cu Nanoclusters
Authors: Park Y. H. , Hijazi I.
Published: May 2012

The study of metal clusters has attracted much attention in recent years. Noble metal nanoparticles are of particular interest since their chemical, thermodynamic, electronic, and optical properties make them interesting candidates as building blocks of nanostructure materials. Delineation of these properties requires a complete and definitive characterization of the cluster’s geometrical structure. To find the ground state structure for a cluster, the potential-energy surface (PES) needs to be searched. In this paper, we proposed an efficient hierarchical search method to determine a ground state structure of copper clusters using an effective Monte Carlo simulated annealing method, which employs the Aggregate-Volume-Bias Monte Carlo (AVBMC) algorithm. Incorporated in the Monte Carlo method, is an efficient Embedded Atom Method (EAM) potential developed by the authors.
The Influence on the Stuffing Box of the Forces Generated by Packing Thermal Expansion
Authors: Veiga Jose´ C. , Carmo Andre´ S. , Gira˜o Carlos D. , Cipolatti Carlos
Published: May 2012

This paper introduces a test device and a protocol that simulates a stuffing box to evaluate the packing expansion under different temperatures. This test device enables the measurement of axial forces at the bottom of the stuffing box and at the gland follower, the torque generated upon shaft turning and the influence of the thermal expansion on these measurements. It also enables comparisons between different braiding yarns materials such as e-PTFE, e-PTFE with fillers, Flexible Graphite and others. Test results showing these comparisons and correlations are reported.
High Temperature Design and Damage Evaluation of Mod.9Cr-1Mo Steel Heat Exchanger
Authors: Lee Hyeong-Yeon , Kim Jong-Bum , Eoh Jae-Hyuk , Lee Yong-Bum , Park Hong-Yune
Published: May 2012

High temperature design and evaluation of creep-fatigue damage for sodium-sodium heat exchanger, DHX (Decay heat exchanger) in a sodium test loop have been conducted. The DHX is a shell- and tube-type heat exchanger with outer diameter of 21.7mm, thickness of 1.65mm and effective length of 1.73m. The DHX shell and tube materials were Mod.9Cr-1Mo steel. The temperatures of shell inlet and shell outlet in the DHX are 510°C and 308°C, respectively, while the temperatures of tube inlet and outlet are 254°C and 475°C, respectively. Three dimensional finite element analysis was conducted for the DHX and evaluation of creep-fatigue damage at several critical locations of the heat exchanger was carried out according to the elevated temperature design codes of the ASME Section III Subsection NH and RCC-MR. Evaluations on the integrity of the DHX and code comparisons were carried out for the critical locations of the DHX.