bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluid Pressure on Rectangular Tank Consisting of Rigid Side Walls and Rectilinearly Deforming Bottom Plate Due to Uplift Motion
Authors: Taniguchi Tomoyo , Segawa Toru
Published: July 2009

Although the uplift motion of flat bottom cylindrical shell tanks has been considered to contribute toward various damage to tanks, the mechanics were not fully understood. As well as computing uplift displacement of the tanks, accurate prediction of fluid pressure accompanied with uplift motion is indispensable to prevent the tanks from severe damage. This paper mathematically derives the fluid pressure on a rectangular tank with unit depth consisting of rigid walls and rectilinearly deforming bottom plate accompanied with the uplift motion. Assuming perfect fluid and velocity potential, the continuity equation is given by Laplace equation. The fluid velocity imparted by motion of rigid walls, immobile bottom plate and rectilinearly deformed bottom plate of tank accompanied with uplift of the tank constitutes boundary conditions. Since this problem is set as the parabolic partial differential equation of Neumann problem, the velocity potential is solved with Fourier-cosine expansion. Derivatives of the velocity potential with respect to time give the fluid pressure at arbitrary point inside the tank. The proposed mathematical solution well converges with a first few terms of Fourier series. Diagrams that depict the fluid pressure normalized by product of angular acceleration and diagonals of the tank are presented.
FEM Stress Analysis and Sealing Performance Evaluation in Pipe Flange Connections With Spiral Wound Gaskets Subjected to External Bending Moments: Case Where Internal Fluid is Liquid
Authors: Sawa Toshiyuki , Iwamoto Takeshi , Funada Kensuke , Omiya Yuya
Published: July 2009

The leakage evaluation when gas is used is more severe than that when liquid is used in pipe flange connections. In a practical design, it is also necessary to examine the leakage in the connections under liquid internal pressure application. The contact gasket stress distribution in the connection with a spiral wound gasket subjected to internal pressure and bending moments were analyzed using elasto-plastic (EP) finite element method (FEM) taking account hysteresis and nonlinearity in the stress-strain curve of the gasket. The effects of initial clamping bolt force (bolt preload), the nominal pressure and the nominal diameter of pipe flange and the equivalent pressure when the leakage occurs on the contact gasket stress distributions were examined. The leakage tests for the connections under the bending moments and the internal pressure were also conducted by using liquid (water). By using the results of the leakage tests and the calculated contact gasket stress distributions, the sealing performance of the connections was evaluated. It was found that the sealing performance of the connection can be estimated when liquid (water) was used, that is, when the contact gasket stress becomes zero, the leakage occurs. In addition, a method for determining the bolt preload in the connections under the bending moments was proposed for the reliable design.
Fatigue and Crack Growth Analysis of a Thick Instrumentation Ring Subjected to Thermal Fatigue Cycling
Authors: Piehler R. S. , Damiani T. M.
Published: July 2009

In the 2007 ASME PVP conference, a presentation was given on the testing and subsequent fatigue initiation analysis of 304 Stainless Steel (304SS) instrumentation spacer rings that had cracked while installed in a thermal fatigue test loop [1]. The instrumentation spacers contain ports radially machined through-wall for monitoring temperature and pressure. Routine flow-surface inspections revealed actively growing cracks emanating from each port. In this work, three dimensional finite element models (FEM) were constructed from the available test measurements and used to obtain, via elastic Finite Element Analysis (FEA), representative stress histories for each machined port of the spacer ring. The FEA stress results were used to perform fatigue usage and crack growth curves using 304SS material models adjusted for low-oxygen water environments to determine the fatigue initiation and crack growth characteristics of the spacer ring cracks. Destructive examination and metallographic results of the spacer rings are compared to the analytical fatigue initiation and crack growth results.
Development of a New Method for “Full Face” Gasketed Bolted Flange Connections Based on European Standard EN1591
Authors: Lejeune Hubert
Published: July 2009

The new analytical calculation method for gasketed circular flange connections NF EN1591-1 [3], has been issued in Europe in 2001. It is an alternative to the existing TAYLOR FORGE gasketed flange connections calculation rules. This standard, based on tightness criteria, gives a more detailed analytical modelling of the behaviour of the connection. However, the “full face” gaskets, located on each side of the bolt circle, are out of the scope of NF EN1591-1 [3], whereas a method partly based on the TAYLOR FORGE rules is proposed in the NF EN 13445-3 [6] and CODAP® [10]. A proposal for the calculation of “full face” gasketed joints, based on [3] is presented here.
Flow Accelerated Corrosion: The Entrance Effect
Authors: Barth Andy , Crockett Harold M. , Goyette Lee F. , Horowitz Jeffrey S. , Montgomery Robert
Published: July 2009

Flow-accelerated corrosion (FAC) is a degradation process that attacks carbon and low-alloy steels. The process has been studied extensively for the last thirty years. Nevertheless piping leaks and ruptures continue to occur. Recent fatal accidents at the Mihama nuclear station in Japan and at the Iatan fossil unit in Missouri demonstrate that plant operators must continue to maintain mitigation programs in order to maintain a high degree of confidence against unanticipated pipe rupture caused by FAC. While FAC is a complex phenomenon, most of its controlling elements are fairly well understood with U.S. nuclear plants using well-developed analytical methods to increase the efficacy of their inspection programs. However, there remains one particular controlling element — described 10 years ago — that is still not widely included in plant inspection programs. This is the entrance effect (or leading-edge effect), which refers to the accelerated attack downstream of a FAC resistant material to FAC susceptible material joint (e.g., a butt weld). This paper provides an update to the previous PVP Conference paper on this subject [1]. Recent plant experience, developments in analysis and the implications to existing plant programs will be discussed.
A Probabilistic Approach to Leak Before Break Demonstration
Authors: Dillstro¨m Peter
Published: July 2009

Recently, the Swedish Nuclear Power Inspectorate has developed guidelines on how to demonstrate the existence of Leak Before Break (LBB). The guidelines define the steps that must be fulfilled to get a conservative assessment of LBB acceptability. In this paper, a complementary probabilistic LBB approach is defined and implemented into the software ProLBB. The main conclusions, from the study presented in this paper, are summarized below. • The probabilistic approach developed in this study was applied to different piping systems in both Boiler Water and Pressurised Water Reactors. The present study shows that the conditional probability of fracture is in general small for the larger diameter pipes when evaluated as function of leak flow rate. However, when evaluated as function of fraction of crack length around the circumference, then the larger diameter pipes will belong to the ones with the highest conditional fracture probabilities. • The total failure probability, corresponding to the product between the leak probability and the conditional fracture probability, will be very small for all pipe geometries. • The influence from an off-center crack position on the conditional probability of fracture is not important when assuming a uniform distribution. This is because the result is dominated totally by the center crack position. However, if the crack position is treated as a deterministic parameter, the conditional probability of fracture is strongly dependent on the position of the crack, especially for large off-center cracks. • The weld residual stresses have quite an impact on the resulting fracture probabilities, especially for smaller cracks. The influence from the weld residual stresses on the calculation of leakage flow rate is largest for a thin-walled pipe. The influence from the weld residual stresses on the calculation of fracture probability is largest for one of the thick-walled pipes. • In the formal sensitivity analyses, it is shown that the standard deviation of the yield strength has the strongest influence on the conditional fracture probability. • This study has given an indication of the relation between the deterministic LBB-criteria and the corresponding conditional fracture probability. As expected, it is easier to fulfil the deterministic LBB-margins for a large diameter pipe compared to a small diameter pipe.
Mixed Mode Brittle Crack Propagation Modelling in a PWR Vessel Steel
Authors: Prabel B. , Marie S. , Combescure A.
Published: July 2009

R&D activities and some development are performed at CEA on the brittle crack propagation and arrest. Phenomena occurring after the initiation of a brittle crack are not yet well understood. Absence of model able to predict the rapid growth of a brittle crack motivates this study. Due to the rapid growth of the crack, inertial effects and dynamic fracture should be considered. Assumption of a linear elastic solid are often preferred, but when plasticity of the material become non negligible (which is the case in the vicinity of the transition zone), these models become more limited. That’s why the paper presented here deals with dynamic crack propagation in elastic-viscoplastic material and aims at proposing a model able to predict the brittle crack propagation and arrest. To this end, experimental work is carried out for different geometries made of french RPV ferritic steel. Compact Tension specimens with different thickness, isothermal rings under compression with different positions of the initial defect to study also a mixed mode configuration. The test conditions and mains results (crack initiation, crack velocity measurements, ...) are collected and presented in a first part of the paper. To model efficiently the crack propagation in the Finite Element calculation, the eXtended Finite Element Method (X-FEM) implemented in the CEA F.E. software CAST3M is described in the second part of the paper. Thanks to this numerical technique, the crack path does not need to follow the element edges and the crack progress is directly incorporated in the degrees of freedom of the elements crossed by the crack. A two-steps methodology is presented in the third and fourth parts of this paper. The first step consider only the CT specimen, experimental crack speed evolution with time is imposed in numerical simulations. Energy terms and stress field at the crack tip are evaluated and discussed to build up a criterion. Then, the criterion identified on CT specimen is used in a second step as a predictive model to simulate crack propagation for each geometry studied (CT, ring in both mode I and mixed mode). In particular, crack propagation models based on the stress field evaluated at the crack tip and on a critical cleavage stress dependent on the strain rate, exhibit very good agreement with experimental data in term of crack speed, crack path and crack length at arrest. The mixed mode case is discussed in detail because to be pertinent, a model of brittle crack propagation should not only give the crack speed, but also its preferred direction of evolution.
Case Studies of Pulsed Eddy Current to Measure Wall Loss in Feedwater Piping and Heater Shells
Authors: Cohn Marvin J. , Norton Jordan W.
Published: July 2009

There have been several feedwater piping and heater shell failures in power plants caused by flow-accelerated corrosion (FAC). This failure mechanism may be one of the most important types of damage to find proactively because FAC damage has occasionally resulted in catastrophic failures and human fatalities. Predicting, detecting, and resolving significant FAC damage can significantly reduce future forced outages and increase personnel safety. This paper describes the implementation of recent developments to perform cost-effective FAC examinations. These advances include the use of specialized pulsed eddy current (PEC) hardware and software to scan for wall thinning without removing insulation. Recent results are based on the current version, MK II, of this equipment. The authors have performed more than 200 power plant projects with this PEC equipment, examining numerous pipes and shells. This work consists of more than 70 projects of wall loss examinations for the nuclear industry, including examinations of feedwater heater shells inside the condenser. Results of wall loss measurements regarding PEC average wall thickness (AWT) measurements, ultrasonic thickness examinations (UTTH), and the PEC evaluated Defect Algorithm are compared in this study.
Correlation of Fracture Behavior in Circumferentially Cracked Pipes Under Combined Load Conditions Using SENT Specimens: Effects on J-R Resistance Curves
Authors: Cravero Sebastian , Bravo Richard E. , Ernst Hugo A.
Published: July 2009

Single edge cracked under tension (SENT) specimens appear as an alternative to conventional fracture specimens to characterize fracture toughness of circumferentially cracked pipes. The similarities of stress and strains fields between SENT specimens and cracked pipes are now well known. However, these similarities are not so well established for the case of circumferentially cracked pipes under combined loading conditions (i.e. internal pressure plus bending). This work presents a numerical analysis of crack-tip constraint of circumferentially surface cracked pipes and SENT specimens using full 3D nonlinear computations. The objective is to examine combined loading effects on the correlation of fracture behavior for the analyzed crack configurations. The constraint study using the J-Q methodology and the h parameter gives information about the fracture specimen that best represents the crack-tip conditions on circumferentially flawed pipes under combined loads. Additionally, simulations of ductile tearing in a surface cracked plate under biaxial loading using the computational cell methodology demonstrate the negligible effect of biaxial loadings on resistance curves.
Development of Nonlinear Ultrasound System Using PMN-PT Piezoelectric Crystal
Authors: Mihara T. , Ohara Y. , Yamanaka K.
Published: July 2009

After the basic researches about the cause and the mechanism of nonlinear ultrasound, industrial applications of nonlinear ultrasound have been also expected. Since nonlinear ultrasound requires higher amplitude ultrasound incidence to the crack, we believe that the efficient and reliable transducer must be the key technique to extend nonlinear ultrasound to the industrial crack estimation. In this study, we focused on a new transducer made by PMN-PT single crystal piezoelectric-element that recently developed as an efficient material for an actuator. Furthermore, we tried to use the low-cost burst square pulser to nonlinear ultrasound measurement to spread nonlinear ultrasound technique to many applications by combining with the new efficient transducer.
A Flaw Proximity Rule for Circumferential Surface Cracks on Pipe Under Tensile Loading Based on Limit Load Analysis
Authors: Kamaya Masayuki
Published: July 2009

The influence of interaction between two surface cracks on the limit load (LL) was examined by finite element analysis. Cicumferential surface cracks were assumed to be on a straight pipe that was subjected to a uniform tensile load. The results obtained under vaiours relative spacings of cracks and pipe geometries revealed that the magnitude of LL depends on the offset distance of the cracks and ratio Rm/t, where Rm is mean radius of pipe and t is thickness of pipe. Furthermore, regardless of pipe geometry, LL is almost equivalent to that of a coalesced crack when the offset and horizontal distance are the same. Based on these results, criteria were proposed for the combination rule, which is appliciable to the procedure of modeling multiple cracks in integrity analysis of flawed components.
Finite Element Modelling of Transgranular Chloride Stress Corrosion Cracking in 304L Austenitic Stainless Steel
Authors: Wenman Mark , Barton James , Trethewey Kenneth , Jarman Sean , Chard-Tuckey Paul
Published: July 2009

Austenitic stainless steels (ASS) have excellent resistance to general corrosion. However, these steels can be susceptible to localised corrosion such as pitting and crevice corrosion. In the presence of a tensile stress they can also exhibit stress corrosion cracking (SCC). In pressurised water reactor (PWR) nuclear plant incidents of SCC, especially chloride-induced SCC (CISCC), have been observed. Chloride ions which can lead to CiSCC of even low carbon austenitic grades can be introduced from many sources including the atmosphere and materials introduced into the reactor environment. Stress can result from primary loading or introduced as secondary stresses, such as residual stress, through machining or welding processes. Residual stresses are internal self-balancing stresses that can act alone or together with a primary stress to cause premature failure of a component. 15 mm lengths of 304L ASS tube were subjected to an in-plane compression of between 1–10 mm before unloading. This created regions of plasticity and on relaxation the specimen contains a complex state of residual stresses that can be modelled by finite element (FE) methods. The tube specimens were then boiled in MgCl2 for 14 days before metallographic examination. A FE model of transgranular CISCC has been created by writing a VUMAT user subroutine implemented into the commercial FE code ABAQUS. The model is based on simple rules which include the initiation of surface corrosion pits from which, under mechanical control, SCC cracks may propagate. The model includes rules for SCC growth, based on hydrostatic stress state, and can incorporate the idea of grain orientation effects. Cracks created interact with and modify the residual stress field in the tube. Test results were then compared with model outputs. Crack morphologies and to a certain extent crack positions matched well with experiment. Attempts were made to calculate the crack tip driving forces from the model. The results also highlight the need to consider the importance of triaxial stress states, created by pits and cracks, and stress as a tensor rather than a scalar property. The effect of grain misorientation is also investigated, but so far, found to be of more limited importance for modelling transgranular CISCC.
The Long-Term Environmental Degradation of Zirconium Alloys in Contact With Spent Nuclear Fuel: A Review
Authors: Rebak Raul B.
Published: July 2009

Zirconium (Zr) alloys were mostly developed for nuclear power applications. The most common commercial alloys are Zircaloy, which are used as cladding for fuel pellets in water-cooled reactors. These alloys have adequate corrosion resistance in service under irradiation in presence of high-purity water at approximately 300–350°C but in a few cases they may suffer environmental degradation. The most common types of degradation are hydriding, shadow corrosion and nodular corrosion. After the fuel rod bundles are removed from the reactors they are temporarily stored in water pools until their permanent disposition nuclear waste repositories. Simulated laboratory testing and modeling show that the long-term storage in the sealed containers would not cause further damage to the cladding material until the waste containers are breached by corrosion many thousands of years later. And even after water incursion, since the temperature will be low, it is predicted that the cladding material would survive for many thousands of years more, thus delaying the release of the radionuclides to the atmosphere.
A Real-Time DSPI System for Measuring Surface Deformation in Clamped Bolted Joints
Authors: Meng Aidong , Nassar Sayed A.
Published: July 2009

A Digital Speckle Pattern Interferometry (DSPI) system is developed for the real-time measuring and monitoring the out-of-plane surface deformation around tightened threaded fasteners that are used to clamp bolted assemblies. Spatial phase shifting is employed to quantitatively determine the distribution of phase data by introducing a spatial carrier fringe pattern to the speckle interferogram. This is achieved by leading the object and reference beams to two separate apertures. The configuration is also suitable for collecting the real-time deformation during bolt tightening. The experimental DSPI system is set-up with optical components on a vibration-isolation table. A Matlab software is developed for the image acquisition and phase data calculation, which yields the out-of-plane surface deformation caused by the bolt preload. An aluminum joint is used with an M12 steel fastener. For miniature screw application, however, a plastic joint is used for collecting data.
Seismic Fragility Tests of Motor Operated Valve Assemblies With Safety-Related Function
Authors: Hirose Jiro , Suzuki Kenichi , Ueki Takashi , Yoshika Naoki
Published: July 2009

Active valve assemblies in important systems to safety are required to maintain the operability during or following earthquakes. Motor operated valve assemblies have been designed to a validated response capacity 60m/s2 at the actuator in accordance with “JEAG4601-supplement 1991” in Japan. The Regulatory Guide for Reviewing Seismic Design of Nuclear Power Reactor Facilities issued in September 2006 defines Design Basis Earthquake Ground Motion and requires that residual risk for large earthquakes should be considered. It is needed to acquire seismic capacity data for a variety of active valve assemblies. JNES has performed fragility tests for motor operated valves: globe valve, gate valve and butterfly valve. An experimental test program is developed to ensure operating requirements for valve assemblies whose safety-related function is to open, close, or regulate fluid flow, and structural requirements for pressure boundary integrity. A series of vibration tests has been performed using shaking tables at varied acceleration levels up to target acceleration levels by sinusoidal waves. As a result of the vibration tests, the operability of valve assemblies for each type of motor operated valve has been verified at the target acceleration levels. The yoke of a motor operated gate valve connecting the actuator and the valve body was identified to be vulnerable for low cycle fatigue depending on the postulated load conditions in terms of intensity and frequency. The resulting seismic capacity data of actual valves will be applied for a fragility analysis of Seismic PSA.
Assessment and Test of the Creep-Fatigue Crack Behaviour for a High Temperature Component
Authors: Lee Hyeong-Yeon , Lee Jae-Han , Nikbin Kamran
Published: July 2009

Creep-fatigue crack behaviour has been investigated for a welded component with 316L stainless steel and Mod. 9Cr-1Mo steel through an assessment and test. The evaluation of creep-fatigue crack initiation and propagation was carried out for 316L stainless steel according to the French RCC-MR A16 guide, and evaluation on creep-fatigue crack initiation for Mod.9Cr-1Mo steel in a specimen was carried out with an extended A16 method. A test for a structural specimen with a diameter of 500mm, height of 440mm and thickness of 6.3mm was performed to compare its results with that by assessment according to the A16 guide. The specimen was subjected to creep-fatigue loads with two hours of a dwell time at 600°C and variable primary loads. The creep-fatigue crack behaviours for the two materials were assessed, observed and compared. The results showed that the A16 guide for the austenitic stainless steel was overly conservative for the assessment of creep-fatigue crack initiation while it was reasonably conservative for creep-fatigue crack growth for the present specimen.
Experimental and Numerical Investigation of Sub-Clad and Surface Cracks in Cladded Components
Authors: Hohe Jo¨rg , Brand Marcus , Siegele Dieter
Published: July 2009

The present study is concerned with the fracture behavior of sub-clad and surface cracks in components consisting of ferritic steels with an austenitic welded cladding. For this purpose, two tests on large scale specimens have been performed. The residual stress field has been determined by means of a numerical simulation of the welding and heat treatment processes. Based on the results, a numerical simulation of the component tests was performed in order to enable a fracture mechanics assessment of the conditions leading to crack initiation and arrest in the ferritic and austenitic regions. It was observed that in the present tests failure was initiated in the ferritic material whereas the austenitic cladding remained stable even in the case of a limited crack extension in the ferritic base metal.
Application of Plastic Region Tightening Bolt to Flange Joint Assembly: Downsizing of Flange Joint and Behavior of Bolt Force Under Internal Pressure
Authors: Kaneda Shinobu , Tsuji Hirokazu
Published: July 2009

The present paper describes the behavior of plastic region tightening of a bolt in a downsized flange joint subjected to internal pressure. An API 4-inch flange joint is downsized for plastic region tightening. The bolt is reduced from M16 to M8, and the bolt pitch circle diameter and the outer diameter of the flange are decreased by 11%. The flange rigidity and the stresses of the compact flange joint are calculated and are superior to the original API flange joint. The bolt spacing is also examined, and the correction factor for bolt spacing is acceptable. Internal pressure is applied to a compact flange joint, and the behavior of additional bolt force is demonstrated. Load factor depends on the type of gasket, such that the load factor is positive for a flexible graphite sheet gasket. The load factor is in agreement with the value calculated by the Load Factor Method (LFM). When the external force is applied to the bolted joint under plastic region tightening, the allowable limit of the additional bolt force is approximately 10% of the bolt yield force. In the present experiment, the additional bolt force is as small as 1% of the bolt yield force. Therefore, the additional bolt force has sufficient margin for the allowable limit.
Residual Stress Measurement Simulation in a Type 316 Stainless Steel Girth-Butt Weld Joint
Authors: Hossain S. , Truman C. E. , Smith D. J. , Ogawa K.
Published: July 2009

Several techniques exist to measure residual stresses, but most only work close to the surface of a component. The deep-hole drilling (DHD) method [1] provides complete, through-thickness, measurements of residual stress with high spatial resolution which can be used to validate numerical models. In common with all mechanical strain release methods of residual stress measurement, extra care must be taken when making measurements on components containing highly triaxial residual stress fields which are close to yield. This is because the introduction of a free surface, created as part of the measurement procedure, can lead to plastic redistribution of the residual stress field which is not accounted for in the elastic inversion algorithms of the experimental procedure. This paper seeks to demonstrate the usefulness and accuracy of the DHD method in a component predicted to contain a triaxial residual stress field by comparing measurements and the results of a DHD simulation on a type 316 stainless steel pipe with girth-butt weld joint. Step 1, results are presented from three-dimensional finite element (FE) simulations of the original girth weld. Step 2, the residual stresses predicted from these simulations are mapped onto a new mesh, designed in order to permit a simulation of the DHD measurement method detailed above. Step 3, an FE simulation of the DHD procedure was undertaken, and the predictions of the radial distortion of the initial reference hole were used in the usual experimental inversion algorithm. This permitted a simulation of the DHD measured residual stresses to be obtained and compared with the predictions of the initial FE model. The effects of different material models as well as the measurement paths were also considered. Finally, step 4, FE predicted residual stresses, DHD simulated residual stresses and actual DHD measured residual stresses were compared and conclusions concerning the accuracy of the DHD measurement procedure were made.
Layered Vessel Construction for Hydroprocessing Reactors
Authors: Andersson Jan , Stefanovic Radoslav , Kristensen Steven
Published: July 2009

The demand for hydroprocessing reactors has increased dramatically in recent years. In addition, reactor size and thickness has also increased. New materials with higher allowable stresses have been introduced. Lead times and prices for vessels have increased for many reasons, one of which is because of the limited number of mills that are capable of producing advanced materials for the higher thicknesses required. For many years, layered design was successfully used for high pressure vessels including hydroprocessing reactors, including some that have 40 years of service history. Yet, recent history shows that hydroprocessing reactors are exclusively built using solid wall design. This paper discusses the advantages and disadvantages of using layered construction for hydroprocessing reactors. Consideration is given to mechanical properties, venting of diffused hydrogen, thermal conductivity differences between the layered parts and solid sections, and non-destructive examination. Specific design issues related to bed support design, nozzle to shell, and head to shell connection construction are discussed. As a part of the evaluation, finite element analysis has been recommended to study critical areas for layered design assessment. An industry survey of layered reactor service is suggested as well.
Simulation of Reactor Pressure Vessel Internals Thermal Stress Due to Internal Heat Generation and Environmental Boundary Conditions Using Stress Transfer Functions
Authors: Gray Mark A. , Cranford E. Lyles , Gilmore Charles B. , Guillot Ste´phane G. , Yang Chuang Y.
Published: July 2009

The internal heating rates from the capture and scatter of neutrons and primary gamma radiation represent one of the most significant loadings acting on the reactor pressure vessel internal structures. The nuclear heating effects on the internal structures are mitigated by the flow of the primary coolant removing heat energy from these structures. This paper discusses the use of transfer functions to predict the time-dependent thermal stresses in the lower core plate of reactor vessel internals. Numerous stress analysis applications have employed the transfer function approach to obtain thermal stresses from fluid transients in reactor pressure vessel and piping locations. These solutions have been utilized in both design analysis applications and in stress and fatigue monitoring roles for evaluation of pressure vessels subjected to fluid transients and mechanical loads such as pressure and piping loads. This paper presents a further extension of the technology to address heat generation loads. The evaluation of stress and fatigue produced in a reactor vessel internals lower core plate due to multiple loadings, including heat generation, using the stress transfer function approach was investigated for reducing analysis process time and conservatism when compared to conventional analysis methods. Reduced conservatism provides margin that may be beneficial in life extension studies.
Crack Initiation Process for Semi-Circular Notched Plate in Creep-Fatigue Test at Elevated Temperature
Authors: Watanabe Osamu , Bubphachot Bopit , Kawasaki Nobuchika , Kasahara Naoto
Published: July 2009

Crack initiation and propagation in creep-fatigue test were observed on semi-circular notched plates at elevated temperature by the CCD video camera. Test specimens are made of SUS304 stainless steel, and temperature is kept to be 550°C, and geometry of the semi-circular plate specimens are changed by diameter size of the hole. Photographs of all cycles were recorded to investigate crack initiation process in structural component having stress concentration and obtain number of cycle of crack initiation (Nc). The test results were compared with predictions by the Stress Redistribution Locus (SRL) method and the Neuber’s rule’s method.
Fastener Preload Guidance Methodology for ASME B16.5 Welding Neck Flanges
Authors: Wacker Randy
Published: July 2009

Various resources have long been available from which bolted flange connection (BFC) preload guidance can be chosen. These range from Rules of Thumb gleaned from experience, to tables and charts based on average gasket stress, to parametric generalizations derived from the results of limited finite element analyses. Because the primary components of a BFC (flange, fastener and gasket) interact with one another to respond as a single system, and the system is unique to the conditions that define it, guidance based on these specific conditions will improve the accuracy of preload solutions and generate data to show the relative strengths and weaknesses of a given BFC. This paper presents a methodology that sets practical stress limits on a collection of commonly used ASME B16.5 welding neck flange components and then uses finite element analysis to solve the condition of preload that results in one or more limits being satisfied. Each preload solution is unique to the properties and geometries that define it and includes the effects of three design conditions. Fastener stress solutions include both the tension and bending components. This shows that yielding can initiate at relatively low values of preload when flange rotation is significant. Charts are created to show solution trends. This simplifies the task of identifying the component that sets the upper bound for a given solution. It also provides the basis to compare similar component combinations.
Finite Element Analysis of Al-Carbon Fiber/Epoxy Composite Laminates
Authors: Liu Pengfei , Zheng Jinyang
Published: July 2009

Carbon fiber/epoxy composites have been increasingly used to develop the lightweight high pressure hydrogen storage vessel in areas of the fuel cell vehicle. In this research, a numerical method is proposed to predict the progressive failure properties of the Al-carbon fiber/epoxy composite cylindrical laminates. A 3D finite element technique and the solution algorithm are proposed to investigate the real-time structural failure and damage properties with increasing internal pressure and the instant 3D stress state can be determined efficiently and accurately. The Tsai-Wu laminate failure criterion, three independent failure criteria including fiber break, matrix cracking and shear failure as well as the limited stiffness discount method are commonly employed as individual subroutines and incorporated into the numerical method. Parametric studies in terms of the effects of different stiffness reduction coefficients are conducted and the final failure strengths are also compared with the experimental results. This work provides a progressive understanding of the damage initiation and propagation behaviors of composite laminated structures above and the proposed numerical method can further serve as a guide for other laminated applications.
Evaluation of Structural Integrity for a Dry Storage System With Spacer Disks in a Scale Model Drop Test
Authors: Choi Woo-Seok , Nam Kyoung-O , Bang Kyoung-Sik , Lee Ju-Chan , Seo Ki-Seog
Published: July 2009

A new type of dry storage system has been developed in Korea. The dry storage cask under development consists of a cask body, a canister, and an in-canister structure. The in-canister structure is a complicated structure with many baskets and spacer disks. The spacer disks are originally designed to dissipate the heat from the baskets but they also influence the structural behavior. To evaluate a spacer disks’ influence on the overall structure behavior, especially on the characteristics when it is under a drop test, analyses and tests were conducted. Based on the analysis result, the sensor location and type is determined. Test result is utilized to validate the analysis result. After the drop tests, some strain gauges were detached from the original positions since the relative displacement between a basket and a disk removed the cable from the sensor. Thus, careful attention has to be paid when installing the sensors and cabling inside the in-canister structure. By means of these analyses and tests, the availability of the sensor and cabling arrangement is evaluated and a test procedure is established.
The Standard Pressure Test in EN 13445
Authors: Baylac Guy , Roberts Ian , Gawlick Ruediger , Kiesewetter Norbert
Published: July 2009

This paper details the determination of the test pressure of the standard hydrotest after fabrication, as provided in the 2008 edition of EN 13445.
Fuzzy Risk Analysis for the Urban Buried Gas Pipeline
Authors: Miao Chunsheng , Zhao Jianping
Published: July 2009

Based on the statistical analysis from a great deal of failure cases, generally, the failure causes of buried pipeline can be classified into four factors, namely, third-party damage, erosion-corrosion damage, design error, and incorrect operation. The factors influencing the failure of pipeline are complicated, varied and fuzzy. Especially, the influence factors of third-party damage of buried pipeline are of the character of fuzziness, which are difficult to express with the accurate mathematic models. In this paper the failure factors of buried gas pipeline are firstly analyzed by fault tree analysis (FTA) method. Then the failure likelihood and failure consequence, two parts of the risk, are evaluated with fuzzy comprehensive assessment method respectively. Finally, the in-service risk of the buried gas pipeline for a certain city is expressed by the risk matrix, which is established with the failure likelihood as vertical ordinate and the failure consequence as horizontal ordinate. It is concluded that there are two pipeline units belong to High risk category, 24 pipeline units belong to Medium-High risk category, 160 pipeline units belong to Medium risk category, and 392 pipeline units belong to Low risk category.
Evaluating Potential Acceleration Tests on Temper Embrittlement of 2.25Cr1Mo Steel for Hydro-Cracking Reactor
Authors: Zhao Jianping
Published: July 2009

Hydro-cracking reactors are the key facilities in hydrogenation units, which were exposed to the action of hydrogen and high pressure and temperature. In this case, hydro-cracking reactor made of 2.25Cr1Mo steel with austenite steel lining at the inner was service for 11 years. Impact energy curve of 2.25Cr1Mo steel will be shifted towards right direction and the material will be damaged. In theory, the value of VTr54.2 is the function of service time and operating temperature and hydrogen partial pressure. In order to assess the damage of 2.25Cr1Mo steel quantitatively, chemical composition examination and step cooling heat-treatment tests were carried out in this paper. After impact tests were performed for material from the test block which was removed from the hydro-cracking reactor with 11 years service, it was found that the continual step cooling curve can not be applicable for exposed material. Therefore, four modified temperature curves as acceleration tests were performed to obtain an embrittled material’s susceptibility for further embrittling. The results show that it is difficult to further embrittle the exposed material with continual step cooling test at 524°C. To accelerate the extent of temper embrittlement in laboratory, it should be prolonged the heat-treatment time or decreased the experimental temperature based on the traditionally step cooling curves.
CFD Numerical Simulation of the Submarine Pipeline With Spoiler
Authors: Zhao Jianping , Wang Xuechao
Published: July 2009

Submarine pipeline is one of the most important oil transportation components, pipeline failure due to over-span is the most serious failure mechanism. There are four reasons of pipeline span formation, including erosion of seabed, bumpy seabed, submarine pipeline climbing slope, and pipeline ascending to offshore platform. The Hangzhou Bay submarine pipeline is the most important subproject of the Yong-Hu-Ning network, and it is also the biggest long-distance pipeline for crude oil in China. Due to the dynamic nature of Hangzhou Bay, including high tides and high current amplified by the shallow waters, a self-burial method was selected as the best solution. By increasing the velocity of the stream between the pipeline and the seabed, shear stress on the seabed was enhanced. This localized increase in shear stress causes the seabed under the pipe to erode more quickly and facilitates self-burial of the pipe. To facilitate self-burial, a non-metallic vertical fin is fastened to the top of the pipeline. In this paper flow around a pipeline with and without a spoiler near a smooth wall is simulated with FLUENT version 6.1. The influences of the spoiler on pressure coefficient, lift coefficient, shear stress on the wall, as well as velocity profile are investigated. It is indicated that the coefficients for Drag and Inertia are increased with the application of the spoiler. The lift coefficient is reversed with the application of the spoiler increases the stability of the pipeline resulting in the reduction of the required coating weight.
Residual Stress Measurements in Autogenous SA508 Steel Welds
Authors: Francis J. A. , Turski M. , Withers P. J.
Published: July 2009

Engineering integrity assessments for power plant components need to account for the primary loads that arise during service as well as any residual stresses that may be associated with materials processing or fabrication. Welding operations come under particular scrutiny because they introduce substantial residual stresses. These stresses, however, are often either difficult or impractical to measure, so a heavy reliance is placed on obtaining estimates from numerical models. In ferritic steels, the prediction of weld residual stresses is particularly challenging, owing to the solid-state phase transformations that occur upon heating and cooling. Thus there is a great need to validate modeling strategies by comparing predicted stresses with those that are measured on well-defined test cases. In this article, we present the results of neutron diffraction measurements for two configurations that may serve as suitable test cases for weld models; an autogenous edge-welded beam and an autogenous bead on a plate.
Residual Stress and Constraint Effects on Fracture in the Transition Temperature Regime
Authors: Lee K. S. , Sherry A. H. , Goldthorpe M. R.
Published: July 2009

This paper presents the results of a combined experimental and numerical study aimed at quantifying the influence of self-balancing residual stresses on the fracture toughness constraint benefit of a ferritic pressure vessel steel tested in the cleavage fracture regime. Tests were performed on standard and pre-compressed, high constraint, compact-tension (CT) and low constraint, single-edge-notched tension (SENT) specimens at a temperature close to the Master Curve reference temperature T0. Pre-compression is undertaken prior to pre-cracking to establish a residual stress across the uncracked ligament, which is highly tensile at the pre-crack notch root and balanced by compressive stresses further ahead of the notch. The pre-crack is subsequently introduced into material ahead of the notch, within the tensile residual stress region, specimen by electro-discharge machining and fatigue. The tests demonstrate an influence of tensile residual stresses on the apparent fracture toughness properties for both CT and SENT specimens. The tests on low constraint specimens illustrate the constraint benefit on cleavage toughness for this material, and the influence of residual stresses in reducing this benefit. The paper shows how the observed behaviour can be quantified through using two parameter fracture mechanics. Here, the J-integral is determined by taking full account of the influence of preloading on the crack driving force. Both the elastic-T-stress and the elastic-plastic Q-stress are calculated and demonstrated as constraint indexing parameters. The results demonstrate a reduction in constraint benefit for cracks located within highly bending residual stress fields. Thus, when exploring any possible benefit in fracture toughness due to crack tip constraint, it is critical that the combined influence of the primary and secondary stresses on crack tip constraint be taken fully into account.
On the Material Modeling of the Autofrettaged Pressure Vessel Steels
Authors: Farrahi G. H. , Hosseinian E. , Assempour A.
Published: July 2009

Material modeling of the high strength steels plays an important role in accurate analysis of autofrettaged tubes. Although, the loading behavior of such materials is nearly elastic-perfectly plastic, their unloading behavior due to Bauschinger effect is very complicated. DIN1.6959 steel is frequently used for construction of autofrettaged tubes in some countries such as Germany and Switzerland. In spite of similarity between chemical compositions of this steel with A723 steel, due to different material processing, two steels have unlikely behavior. In this paper material behavior of DIN1.6959 has been accurately modeled by uniaxial tension-compression test results. Both 6 mm and 12.5 mm diameter specimens were used and compared. Also various functions for modeling of autofrettaged steels were investigated and new function was introduced for accurate modeling. Moreover, two test methods, i.e. uniaxial tension-compression and torsion tests, which used for modeling of autofrettage steels, were analyzed. As well, material models of three important autofrettage steels, i.e. A723, HB7 and Din1.6959 were compared.
Large Scale Fracture Mechanics Testing
Authors: Brumovsky Milan
Published: July 2009

This paper gives a short overview of experimental programs using large scale models/experiments realized in the Czech Republic with the aim to support the reactor pressure components of WWER type reactors. One part of the program was concentrated on reactor pressure vessel components only. It contained flat specimens with defects on one side and models with stress concentrators (nozzles, bolting joints) on the other side. Second part of the program was a part of the LBB (Leak-before-break) project applied to all WWER safety related pipings. Large scale models with defects, located in heterogenous (safe-end) as well as homogenous welds are described.
Numerical Investigation to Examine the Effect of Introducing a Crack in a Residual Stress Field
Authors: Kamel Simon , O’Dowd Noel P. , Nikbin Kamran M.
Published: July 2009

This paper presents a detailed two dimensional finite-element study to examine the effect of introducing a crack either progressively or instantaneously into a residual stress field. A progressive crack is defined as a crack which is introduced in fixed increments of crack extension until the desired crack length is achieved. An instantaneous crack is one in which a crack of the required length is introduced instantaneously into the finite-element mesh. Inspection is made of the crack tip fields and the crack opening displacements. A modified definition of the J-integral, which accounts for the initial plastic strain due to residual stress, is assessed, in order to examine its ability to characterise the intensity of the near crack tip fields. The implications of the results on fracture assessment of structural components are discussed.