bluuebunny/crossref_metadata_2025 huggingface dataset:
Ice Management in Scandinavian Ports
Authors: Hu¨ffmeier Johannes , Sandkvist Jim , Forsman Bjo¨rn
Published: July 2009

Scandinavian ports, especially the ports in the northern Baltic Sea, face a regular challenge every year — ice. In an INTERREG-project led by the Lulea˚ University of Technology, SSPA Sweden AB conducted a study to gain insight into the problems related to winter traffic in Swedish ports. This research is intended to lead to the identification of technical solutions to ease winter navigation in the ports. The state icebreakers have been making navigation possible all year round since the nineteen seventies by assisting ships sailing in ice-covered waters. In Sweden, the local port owner is responsible for breaking channels and assisting arriving and departing vessels. All port owners along the east coast of Sweden have been interviewed to get an overview of the local ice conditions and their impact on the traffic. Specific emphasis was put on the collection and analysis of different ice-reducing measures currently used in the ports. These include mechanical (e.g., ice breaking) and thermal (e.g., waste water discharge) measures. The distribution and range of applications and most importantly the experiences gained from the different measures have been described and summarised. The efficiency of the different measures has been investigated and compared to predictions of theoretical calculations. In the analyses of the ice-reducing measures, the effects of different measures have been studied, a cost-benefit assessment for different ice-reducing measures has been included and the environmental impact studied. Most of the ports base their ice management only on the utilization of an icebreaking tug boat even though other measures could play a decisive roll in ice handling. High pressure on quay structures occurs as a consequence of the berthing of ships in ice-covered ports. This pressure represents a regular source of damage. Manoeuvring and reversing in ice can further lead to damages of the propeller and rudder of the ice-going vessels. In addition other problems like icing on ships and equipment was looked at. Repairs and other extra costs due to winter navigation for the port and — indirectly — the ship owners can be seen as a commercial disadvantage. Identification of costs caused by the winter conditions was therefore an important part of our analysis. The results of the research have been compared with a similar study performed in Finland and a further literature study was conducted to recommend efficient improvements for the port owners.
Stress Analysis of Bulk Carrier Hatch Corners
Authors: Boote Dario , Cecchini Francesco
Published: July 2009

Owing to the hull structure complexity and severe load conditions, bulk carrier ships are the subject of an intense research activity by Classification Societies and research centres. Many problems affecting this kind of vessel derive from loading and unloading operations, corrosion and fatigue phenomena and, sometimes, the age of the ship. For what the structural strength is concerned, one of the typical failure causes for bulk carriers is represented by high stress concentrations occurring in deck plating close to hatch corners in way of coaming stay. The aim of this work, performed in cooperation by the Registro Italiano Navale (RINA) and the Department of Naval Architecture and Ship Construction of the University of Genova, is to investigate the stress distribution close to hatch corners in a systematic way, in order to determine and quantify the influence of the selected parameters on this phenomenon.
Assessment of the Uncertainty in Corrosion Models for Ship Steels
Authors: Jiang Xiaoli , Soares C. Guedes
Published: July 2009

The corrosion model proposed by Melchers (2003) is compared with the one of Guedes Soares and Garbatov (1999) for a range of parameters that is considered representative of the situations to occur in corrosion of ships and offshore platforms. The differences in the model predictions are represented by a model uncertainty variable and the bias and uncertainty is determined for representative corrosion periods of 7, 15 and 25 years. Is concluded that the average bias is generally within 10% and the standard deviation is of the order of 10% for periods of the order up to 15 years. For shorter durations even better correlations are obtained. For durations of the order of 25 years the mean bias can go up to 20% in limit conditions although in the most common situations it is within 12%.
Alternative Approaches to Storm Statistics in the Ocean
Authors: Bernardino Mariana , Boukhanovsky Alexander , Guedes Soares C.
Published: July 2009

The classical approach to storm statistics in the ocean is an Eulerian analysis of wave time series at a given location, in which the wave data can be observations or results of wave models. The information obtained from this approach is storm frequency, duration and intensity, from which extremes at the particular location can be estimated. The availability of spatial information of wave characteristics at successive time intervals, which is available from large scale forecasts or hindcast allows the follow-up of storm evolution in space and time. Using this data it is possible to study the spatial evolution of storms, i.e to provide a Lagrangean description of storm characteristics. In this paper the principles for spatio-temporal identification and statistical analysis of storm variability are formulated. Using ten years of wave data the HIPOCAS North Atlantic hindcast data, storms were identified using both approaches and two different sets of storm characteristics were obtained. The enhanced information that is possible to obtain from the Lagrangean approach in comparison to the Eulerian is illustrated.
Rules on Transforming Embedded Flaws to Surface Flaws
Authors: Hasegawa Kunio , Kikuchi Masaaki
Published: July 2009

If embedded flaws are located near the component surfaces, proximity rules are used to determine whether the flaws should be treated as embedded flaws as is, or transformed to surface flaws. This is because failures at ligaments are expected to occur for embedded flaws. The proximity rules are widely adopted in fitness-for-service codes and standards. This paper introduces the proximity rules in the world, and stress intensity factors for embedded and transformed surface flaws are calculated and compared among the proximity rules.
Experience With Extended Power Uprate at Leibstadt Nuclear Power Plant
Authors: Engel Robert , Zichanowicz Karl
Published: July 2009

Since the 1970s power uprates have been employed to enhance the electricity output of nuclear power plants. Extended power uprate is defined as an increase of reactor thermal power in excess of 7% up to about 20% of the original plant licensed thermal power. Such power uprates generally require significant modification of major plant equipment and were initially implemented at boiling water reactor plants approximately 15 years ago. The early experience with extended power uprates was very positive. However, in recent years an increased number of failures of nuclear power plant components totally or partly caused by those power uprates have been reported. This paper presents the issues and operating experience with extended power uprate at the Leibstadt Boiling Water Reactor Nuclear Power Plant in Switzerland concerning the mechanical and electrical equipment. Failures such as fretting-wear and fatigue damage due to an increased vibration level, structural damage due to thermal overheating as well as shortened maintenance intervals due to elevated temperature and increased pump speed are reported. As a summary, the failures of mechanical and electrical components caused by extended power uprate experienced at the plant during the last years are related to plant reliability and have not adversely impacted plant safety.
A Mesh Independent GTN Damage Model and Its Application in Simulation of Ductile Fracture Behaviour
Authors: Samal M. K. , Seidenfuss M. , Roos E. , Dutta B. K. , Kushwaha H. S.
Published: July 2009

Ductile fracture process involves the typical stages of nucleation, growth and coalescence of voids in the micro-scale. In order to take the effects of these voids on the stress carrying capability of a mechanical continuum during simulation, damage mechanics models, such as those of Rousselier and Gurson-Tvergaard-Needleman (GTN) are widely used. These have been highly successful in simulating the fracture resistance behaviour of different specimens and components made of a wide spectrum of engineering steels. However, apart from the material parameters, a characteristic length parameter has to be used as a measure of the size of the discretisation in the zone of crack propagation. This inherent limitation of these local damage models prevents them from simulating the stress distribution near the sharp stress gradients satisfactorily, especially at transition temperature regime. There have been efforts in literature to overcome the effect of mesh-dependency by development of nonlocal and gradient damage models. A nonlocal measure (weighted average of a quantity over a characteristics volume) of damage is usually used in the material constitutive equation. In this paper, the authors have extended the GTN model to its nonlocal form using damage parameter ‘d’ as a degree of freedom in the finite element (FE) formulation. The evolution of the nonlocal damage is related to the actual void volume faction ‘f’ in ductile fracture using a diffusion type equation. The coupled mechanical equilibrium and damage diffusion equations have been discretised using FE method. In order to demonstrate the mesh independent nature of the new formulation, a standard fracture mechanics specimen (i.e., 1T compact tension) has been analysed using different mesh sizes near the crack tip and the results have been compared with those of experiment. The results of the nonlocal model have also been compared with those of the local model. The effect of different GTN parameters on the fracture resistance behaviour of this specimen has been studied for the nonlocal model and these results have been compared with those of experiment.
Elastic-Plastic Solutions for Open-End Thick Walled Cylinders Subjected to Internal and External Pressures
Authors: Dixon R. D. , Perez E. H.
Published: July 2009

Available theoretical solutions for the collapse pressure of open-end thick walled cylinders based on the Vo n Misses yield criterion are very limited. The known elastic-plastic theoretical solutions are primarily based on the Tresca yield criterion. So far, little study has been devoted to fairly thick open-end cylinders under external pressure. This can be performed by finite element analysis that considers material plasticity. In this paper the authors propose the use of simple formulae for the solution of the collapse internal and external pressures of open-end cylinders. The proposed formulae provide excellent agreement with finite element results obtained by the authors. Also criterion is provided for the interaction of elastic instability and plastic collapse of open-end cylinders subjected to external pressure.
Material Modeling for Autofrettage Stress Analysis Including the “Single Effective Material”
Authors: Parker Anthony P. , Gibson Michael C. , Hameed Amer , Troiano Edward , Hetherington John G.
Published: July 2009

Analytical and numerical stress analysis of the autofrettage process has made great strides in the last few years. The major challenge is no longer the stress analysis process but the incorporation of ‘real’ material behavior, including Bauschinger effect. This means that material properties may vary at every radial location within the tube. In this paper it is demonstrated that Finite Element Analysis (FEA) may be accomplished using a ‘user programmable feature’ within a non-linear FEA or, more simply using an elastic modulus and Poisson’s ratio adjustment procedure within a linear-elastic FEA. The results of these two methods are shown to be in agreement with each other and with an independent numerical analysis. It is further demonstrated that numerical solutions may be obtained using a single ‘fictitious’ material. This is called a ‘single equivalent material’ (SEMAT). Whilst this requires a very small number of iterations for accurate convergence, it dramatically reduces the material-modeling challenges. Furthermore, SEMAT may be implemented into an analytical procedure thereby permitting highly accurate modeling of a real material whose unloading behavior varies with radius. Comparisons indicate that this is a robust, accurate procedure.
A Numerical Study on the Sensitivity of the Discrete Element Method: The Multi Particle Perspective
Authors: Kruggel-Emden Harald , Rickelt Stefan , Wirtz Siegmar , Scherer Viktor
Published: July 2009

Based on the time-driven Discrete Element Method, granular flow within a hopper is investigated. Contacts are assumed as linear viscoelastic in normal and frictional-elastic in tangential direction. The hopper geometry is chosen according to Yang and Hsiau [1] who performed both experimental and numerical investigations. The considered setup is attractive, because it involves only a small number of particles enabling fast modeling. However, results on the experimental flow rates reported are contradictory and are afflicted with errors. By a visual analysis of the hopper fill levels at different points of time the correct average discharge times and flow rates are obtained. Own simulation results are in good agreement with the experimental flow rates and discharge times determined. Based on the thereby defined set of simulation parameters, a sensitivity analysis of parameters like friction coefficients, stiffnesses and time steps is performed. As flow properties, besides the overall discharge times, the time averaged axial and radial velocity distributions within the hopper are considered. Results show a strong connection of the friction coefficients with the discharge times and the velocity distributions. Other parameters only reveal a weak often indifferent influence on the studied flow properties.
Selection of Optimal Models for the Discrete Element Method: The Single Particle Perspective
Authors: Kruggel-Emden Harald , Wirtz Siegmar , Scherer Viktor
Published: July 2009

Several processes in nature as well as many industrial applications involve static or dynamic granular materials. Granulates can adopt solid, liquid or gas like states and thereby reveal intriguing physical phenomena not observable in its versatility for any other form of matter. The frequent occurrence of phase transitions and the related characteristics thereby strongly affect their processing quality and economics. This situation demands for prediction methods for the behavior of granulates. In this context simulations provide a feasible alternative to experimental investigations. Several different simulation approaches are applicable to granular materials. The time-driven Discrete Element Method turns out to be the most complex but also as the most general method. The method has been used in a wide variety of scientific fields for more than thirty years. With the tremendous increase in available computer power, especially in the last years, the method is more and more developing to the state of the art simulation technique for granular materials. Despite of the long time of usage, model advances and theoretical and experimental studies are not harmonized in the different branches of application, providing potential for improvements. Therefore, the scope of this paper is a review of methods and models based on theoretical considerations and experimental data from literature. Through model advances it is intended to contribute to a general enhancement of techniques, which are then directly available for simulations.
The Stress Distribution Ahead of a Tapered Crack
Authors: Smith E.
Published: July 2009

The paper is concerned with the stress distribution ahead of a tapered crack; this type of crack features in the fracture behaviour of some materials and structures. When the expression for the stress is described in terms of an expansion to the first two terms in increasing powers of the distance ahead of the crack, the first term has a power −1/2 for both Mode 1 and Mode 3 scenarios just as with a linear crack. However with regard to the second term, though the power is +1/2 for the Mode 1 tapered crack and linear crack scenarios, it is zero for the Mode 3 tapered crack scenario. Consequently, caution must be exercised in using results from Mode 3 analyses to quantify Mode 1 loading situations, where tapered cracks are concerned.
UK Research Programme on Fracture Mechanics: Latest Review of Progress
Authors: Sharples J. K. , Watson C. T.
Published: July 2009

A long-term research programme was launched in the UK in late 2004, a significant part of which is aimed at developing and improving fracture mechanics based methods for assessing the structural integrity of metallic engineering structures and components. The research includes: • Deriving alternative methods for the treatment of combined primary and secondary stresses in fracture mechanics evaluations. • Assessing the effects that cyclic loading and crack growth have on crack driving force parameters so that the significance of ignoring these aspects (as in conventional fracture mechanics methodologies) can be evaluated. • Assessing the validity of the characterisation rules for multiple defects, particularly in view of the fact that previous work has indicated that there may be non-conservatisms in the current rules when applying them to cleavage fracture situations. • Develop guidance on the most relevant way of dealing with weld residual stress profiles in fracture mechanics calculations. This paper presents an overview of the research work being undertaken and provides examples of the outcome of some of the studies obtained to-date.
Recent Developments to Improve Crack Opening Areas for R6 Leak-Before-Break Procedures
Authors: Sharples J. K. , Hooton D. G. , Charles R. , Dodia H. , Budden P. J.
Published: July 2009

This paper provides an overview of developments that have been undertaken in recent years in order to extend the Crack Opening Area (COA) solutions for Leak-Before-Break (LBB) within the R6 Flaw Evaluation Procedures. For high temperature operations, the effect of creep strains on COA has been studied using finite element (FE) models of a centre-cracked plate with combined primary and secondary stresses. Primary creep, as well as secondary creep, has been included in the studies. The ultimate aim of this work is to further develop and validate by FE analysis, simplified expressions for the prediction of COA under realistic loading conditions for high temperature operations. For COA evaluations in general, work has been undertaken by FE modelling of the following aspects: • Straight-fronted cracks under combined loading. • Converging/diverging cracks whereby the length on one surface is different to that on the other surface (i.e. cases where there is a through-wall variation in crack length). • Weld strength mis-match effects. • Component features effects.
Design and Analysis of an Ash Collector Hopper
Authors: Antaal Bikramjit S. , Hari Yogeshwar
Published: July 2009

This paper addresses the design and analysis of a hopper for ash collection in a Boiler Plant. The hopper collects the ash blown from the boiler soot blowers. The objective is to establish the design load. The design load is decided on the basis of the two cases. Case 1 Hopper full of ash Case 2 Hopper full of water. Based on the two cases the maximum pressure is considered as the design load. Also the hopper has a static head of gas pressure. The combinations of these are considered as design pressure. A typical hopper is taken. The thickness of the plate is decided. Then a procedure is developed to size the spacing and size of the stiffeners. The stiffeners used are Wide Flange I-beams. The hopper is modeled using STAAD III Finite Element Software. Two models are considered. First with one side of hopper. Second, complete model of the hopper. The stresses obtained are compared with the design values. The design of the hopper with analytical means is verified with Finite Element modeling of the two models considered.
Application of Direct Cyclic Analysis to the Prediction of Plastic Shakedown of Nuclear Power Plant Components
Authors: Martin Michael
Published: July 2009

The majority of shakedown prediction methods available, amenable to practical engineering application, are based on Melan’s lower bound theorem and are capable only of predicting elastic shakedown. Structural discontinuities and the severe thermal transients typical of nuclear power plant operating scenarios may lead to local, elastically bounded, alternating plasticity. Consequently, Melan’s theorem is not satisfied, often leading to cycle-by-cycle finite element analysis which for large problems may be impractical. In contrast, direct methods lead to reduced data storage and analysis time. Direct methods capable of predicting alternating plasticity are now available, developed to a level applicable to the complex thermo-mechanical loading experienced in real structures. This paper compares the stress-strain response and solution times obtained from the Fourier based direct cyclic approach formulated within the finite element code Abaqus with the cycle-by-cycle method and a superposition implementation of Melan’s theorem. The approaches are applied to the Bree problem and a more complex case representative of a real plant load scenario. Automated application of the direct cyclic approach has resulted in the rapid generation of interaction diagrams, providing the pressure vessel designer with a tool to assess the shakedown sensitivity of structures to changes in the design domain.
The Role of Displacement-Controlled Stresses in Critical Flaw Size Determination for Piping Systems
Authors: Riccardella Peter C. , Hirschberg Paul , Anderson Ted , Thorwald Greg , Scheibler Eric
Published: July 2009

A debate has long ensued in ASME Subcommittee XI regarding the need to include displacement-controlled (secondary) stresses in critical flaw size calculations for austenitic weldments. There is general agreement that inclusion of secondary stresses is not necessary for highly ductile piping materials such as wrought stainless steel and high nickel alloys. However, some stainless steel weldments are classified as “low-toughness” because, although not considered brittle, they exhibit lower toughness than wrought stainless steel. The Code requires the inclusion of global secondary stresses, such as piping thermal expansion loads, in critical flaw size calculations for such weldments, albeit at reduced safety factors. The Code requirements are less clear for dissimilar metal weldments, such as Alloy 82/182, which were often used for ferritic nozzle to safe-end welds in nuclear power plants, and which have proven in service to be susceptible to a form of stress corrosion cracking. Analyses are presented in this paper that shed additional light on the subject. Finite element analyses (FEA) of a straight pipe with a through-thickness crack were used to determine the effect on bending moment and crack driving force due to an imposed end rotation. Moment and J-integral knock-down factors are computed for a range of crack sizes for two different pipe lengths. Piping analyses are also presented for two typical PWR surge lines, which are among the highest secondary stress locations in U.S. nuclear plants. These analyses predict the maximum rotation at the surge nozzle that could be produced by the secondary loads (anchor movement + thermal expansion + stratification), and compare that to rotations that were sustained in full scale pipe tests containing large complex cracks. The analyses demonstrate that secondary loads would be substantially reduced prior to fracture of a cracked weldment, and that they are therefore of reduced significance in critical flaw size calculations. A general method for estimating the effect of secondary loads on pipe fracture as a function of relative piping system and crack section stiffness is suggested.
Experimental Investigations for Reducing Effect of Sensitization in Tungsten Inert Gas Welding
Authors: Singh Rupinder , Singh Sehijpal
Published: July 2009

Stainless steels are considered to have very good resistance to general and localized corrosion due to their chromium content. This property of corrosion resistance constitutes the main criterion for selecting austenitic grades of steels for service in the chemical, nuclear and aerospace industries although their mechanical properties are relatively modest. However, this resistance can degrade when structural components manufactured from these steels are used in a chemically aggressive environment, especially when service involves exposure to high temperatures like in welding. This exposure gives rise to precipitation of chromium carbides producing chromium depletion at grain boundaries that brings about the inter-granular corrosion or sensitization of these materials. Austenitic stainless steel (316L) is one of the corrosion resistance material used extensively in the oil production, chemical and power generation industries for transportation and reservoir of corrosive products. In spite of its corrosion resistance property there exist severe problems of sensitization. In the present work an effort has been made to reduce the effect of sensitization in Tungsten Inert Gas welding of Austenitic stainless steel (316L). Three welding procedures (namely conventional, back step and skip welding) in Tungsten Inert Gas welding have been used to control exposure time of the weld pool to higher temperatures, in order to study the effect of sensitization on mechanical properties (such as tensile strength, yield strength, percentage elongation and hardness). The results of this study suggested that the better mechanical properties were attained by the skip welding procedure and recommended welding parameters are 90 Amp current and 10 L/min of gas flow rate for a 5 mm thick work piece. Noticeable change in amount/extent of sensitization was observed using a scanning electron microscope (SEM) analysis within the various welding specimens prepared using the various procedures. Further mechanical properties (like strength and hardness) have been correlated with the extent of sensitization, which show remarkable decreases when the amount/extent of sensitization increases.
Comparison of Environmental Fatigue Evaluation Methods in LWR Water
Authors: Higuchi Makoto
Published: July 2009

Many studies on the environmental fatigue of structural materials in LWR (Light Water Reactor) water have been carried out over the past 30 years. Early environmental fatigue tests were mainly carried out in Japan in the 1980s, and these results were reported to the ASME in 1988. After that, O. Chopra and W. Shack of ANL (Argonne National Laboratory) also carried out similar fatigue tests and reported that their data corresponded well to Japanese data. In the US, the PVRC (Pressure Vessel Research Council) started the CLEE Committee (Cyclic Life and Environmental Effect, Chair: Sumio Yukawa) for developing the environmental fatigue evaluation method in LWR water under the request from the ASME in 1991. This committee continued for 13 years and closed in 2004 after publishing the final report as WRC (Welding Research Council) Bulletin 487. After 1990 in Japan, the EFD Project (1993–1995) and the EFT Project (1994–2006) were carried out under the collaboration of electric utilities, plant vendors and government. A large number of environmental fatigue data have been generated in these projects, and these were offered to the US through the CLEE Committee. Based on Japanese and US fatigue data, environmental fatigue evaluation methods have been established in both countries that assess the effects of some parameters on fatigue life reduction in LWR water environments. This paper introduces the history of studies on the environmental fatigue in LWR water and the contributions of Sumio Yukawa to these activities. After that, the comparison of three major methods of environmental fatigue evaluation such as PVRC, JSME and MJREG/CR-6909 are reported.
Nonlinear Cycling Analysis of Pipe Bends With Initial Ovality
Authors: Vlaicu Dan
Published: July 2009

The paper presents the nonlinear shakedown analysis using finite element method for piping bends taking account of the maximum ovality tolerance. In the ASME Code, Section III NB-4223.2, it is required that the ovality tolerance of piping after bending shall be considered when the pipe structure is subjected to any combination of cyclic thermal and pressure loads. Parametric studies are carried out to assess the progressive strain accumulation induced by various finite element analyses employing different types of boundary conditions and cycling loading. The resulting strain state of the stabilized cycle for the pipe bend including the maximum ovality tolerance is compared with the strain state for the perfectly round pipe bend. This paper also discusses the choice of the global shakedown related to the global in-plane strain and the local shakedown defined as the radial strain on the side of the elbows. Furthermore, the strain range is taken as the representative parameter for fatigue calculations.
Interaction Between Wind Loading and Japanese Slates: Effect on Vibration and Scattering
Authors: Okamoto Satoru
Published: July 2009

A series of wind tunnel tests was conducted on the vibration and scattering behavior of full-sized model of roof tiles, which were used widely for roofings of Japanese wooden dwellings. This study has investigated the nature and source of the vibrating and scattering behavior of roof tiles with the aim of providing a better insight to the mechanism. The roof tiles were set up on the pitched roof in the downstream of the flow from the wind tunnel. The vibrations for the roof tiles were measured by the Laser Doppler Vibrometry and the accelerometer, and the practical natural frequencies of the roof tiles were analyzed by the impulse force hammer test method. The motions of the vibration and scattering were observed by the high-speed video camera. Based on the consideration on the results of the measurements, there is a basic mechanism which can lead to flow-induced vibrations of the roof tiles. This mechanism is similar to that of the so-called fluttering instability, which appears as the self-excited oscillation in the natural mode of the structure at the certain critical flow speed. The values of the frequencies for the oscillating relate to the values of natural frequencies of the vibration.
Fracture Toughness Evaluation of High Strength Steel Pipe
Authors: Shen G. , Bouchard R. , Gianetto J. A. , Tyson W. R.
Published: July 2009

Stress fields and constraint parameters (Q and A2) of circumferentially-cracked high strength pipe in displacement-controlled tension are compared with those of small-scale single-edge notched samples tested in tension (SE(T)) and bending (SE(B)). The factors affecting transferability of fracture toughness (J-resistance) data from small-scale laboratory tests to cracked high strength pipe are discussed. The crack-tip stress field is of similar form for a circumferential crack in a pipe and a SE(T) test specimen, while for a SE(B) specimen there is a significant gradient in the crack-tip stress field. Hence, the fracture toughness can be characterized by only two parameters (J and Q or J and A2) for tension-loaded pipe and SE(T) tests, but for SE(B) tests one more parameter is needed to describe the bending term. It is concluded that the constraint in a SE(T) test with ratio of span between load points to width H/W = 10 provides a reasonable match to that for a circumferential crack in a pipe subjected to tensile loading.
TIMES: Application of a Local Approach Model Within a Case Study
Authors: Hu¨mmer Matthias , Keim Elisabeth , Hoffmann Harald
Published: July 2009

During the last decades the research within the field of local approach (LA) models lead to an increase of the predictive capabilities of these models and thus extended the range of applicability. Since these LA models were originally developed for cleavage fracture, they had to be adopted to account also for ductile fracture events in order to assess fracture behavior in the ductile-to-brittle transition (DBT) region. This article presents a case study, where a recently developed and validated LA model is applied to predict failure of a RPV under a realistic transient loading situation. Within this case study a loss of coolant accident is considered, where a postulated subclad flaw with 20mm depth in the nozzle corner is examined. Because the RPV steel in the nozzle corner region is ductile during a LOCA event, no failure would be predicted using original material properties. Therefore the base metal is simulated using unrealistic high embrittled material properties, i.e. irradiated at a fluence of 3.5E19n/cm2 and an irradiation temperature of TIRR = 150°C., which is to be a very conservative material condition. The reason to use this conservative material condition is to obtain a large shift in transition temperature and the necessary brittle material condition to allow the application of the LA model. The outcome of the LA simulation is compared to other constraint correction methods, like the T-Stress correction. It can be stated that: • the conventional method, which uses no constraint corrections, leads to very conservative results. • T-Stress and T0-corrections are less conservative than the conventional method. • the prediction results attained by means of the LA model describes the failure behavior well; a large safety margin between the different concepts can be shown.
Development of Z-Factor for Circumferential Part-Through Surface Cracks in Dissimilar Metal Welds
Authors: Shim D.-J. , Wilkowski G. M. , Rudland D. L. , Brust F. W. , Ogawa Kazuo
Published: July 2009

Section XI of the ASME Code allows the users to conduct flaw evaluation analyses by using limit-load equations with a simple correction factor to account elastic-plastic fracture conditions. This correction factor is called a Z-factor, and is simply the ratio of the limit-load to elastic-plastic fracture mechanics (EPFM) maximum-load predictions for a flaw in a pipe. The past ASME Section XI Z-factors were based on a circumferential through-wall crack in a pipe rather than a surface crack. Past analyses and pipe tests with circumferential through-wall cracks in monolithic welds showed that the simplified EPFM analyses (called J-estimation schemes) could give good predictions by using the toughness, i.e., J-R curve, of the weld metal and the strength of the base metal. The determination of the Z-factor for a dissimilar metal weld (DMW) is more complicated because of the different strength base metals on either side of the weld. This strength difference can affect the maximum load-carrying capacity of the flawed pipe by more than the weld toughness. Recent work by the authors for circumferential through-wall cracks in DMWs has shown that an equivalent stress-strain curve is needed in order for the typical J-estimation schemes to correctly predict the load carrying capacity in a cracked DMW. In this paper, the Z-factors for circumferential surface cracks in DMW were determined. For this purpose, a material property correction factor was determined by comparing the crack driving force calculated from the J-estimation schemes to detailed finite element (FE) analyses. The effect of crack size and pipe geometry on the material correction factor was investigated. Using the determined crack-driving force and the appropriate toughness of the weld metal, the Z-factors were calculated for various crack sizes and pipe geometries. In these calculations, a ‘reference’ limit-load was determined by using the lower strength base metal flow stress. Furthermore, the effect of J-R curve on the Z-factor was investigated. Finally, the Z-factors developed in the present work were compared to those developed earlier for through-wall cracks in DMWs.
Explicit Nonlinear Dynamic Analysis of Cylindrical Water Storage Tanks Concerning Coupled Vibration Between Fluid and Structure
Authors: Maekawa Akira , Fujita Katsuhisa
Published: July 2009

This study describes a nonlinear vibration analysis for a cylindrical water storage tank considering oval-type vibration, which is a higher-order vibration mode (axial wave number m ≥ 1 and circumferential wave number n ≥ 2). Oval-type vibration occurs in the side wall of cylindrical tanks when a coupled vibration system forms between the sidewall and the contained liquid. Recently, it was found that oval-type vibration causes the nonlinear vibration response of the tanks. Hence, it would be useful for future seismic design methods to conduct a nonlinear dynamic analysis of water storage tanks considering the influence of oval-type vibration. This study proposes a nonlinear dynamic analysis method concerning the coupled vibration between fluid and structure using an explicit method. The proposed method uses a shell element which can take into account the geometric nonlinearity characteristics and a solid element which follows Euler’s equation. The ALE method is applied to the coupling analysis between fluid and structure, and the explicit time integration method is used for the time-history response analysis. Next, the proposed method is used to conduct a numerical simulation of the dynamic response of oval-type vibration and the nonlinear vibration behavior of the tank, and the analytical results are compared with the experimental ones. Both results are in good agreement concerning the occurrence and modes of oval-type vibration in addition to the nonlinear vibration response of the tank. Regarding the dynamic fluid pressure, the local pressure by oval-type vibration as well as the main pressure by beam-type vibration can be calculated accurately. These results confirm that the proposed method achieves a more accurate analysis for the nonlinear vibration response of the tank considering the influence of oval-type vibration.
Residual Stress Modeling of Warm-Bent Tight-Radius CANDU Feeder Bends
Authors: Ding Y. , Yetisir M.
Published: July 2009

In one CANDU® nuclear station, a few feeder piping failures have occurred because of stress corrosion cracking. All the cracks were located in tight-radius bends. Root cause analyses indicated that the residual stress played a significant role in these failures. Residual stress measurements using the neutron diffraction technique have been performed to quantify the residual stresses for a large number of feeder bends. Numerical simulations have also been performed to supplement the measurement data. This paper presents the modeling work carried out for 2.5” warm-bent tight-radius feeder bends using LS-DYNA®. The warm-bending process was divided into heating, bending, springback and cooling stages. The simulation results were compared to the measurement data using the neutron diffraction technique. Good agreement was achieved between the trends of simulation results and the measured residual stresses in feeder bends. Additionally, it was found that the predicted cross-sectional shape and wall thickness distribution agreed well with the measurements. Limitations of the simulation work were summarized and recommendations for future research were made based on this study.
Recent Developments in Methods to Study Creep Strain Variations in Power Station Steam Plant
Authors: Morris Andy , Maharaj Chris , Puri Amit , Kourmpetis Miltiadis , Dear John
Published: July 2009

In power station steam plant, experience has shown that portable monitoring equipment is ideal for reliable point-to point measurement of creep strain and also acquisition of strain mapping information. On going laboratory tests have shown positive initial results in that direction; the results being validated against metrology standards. In addition to the monitoring of in-service strain in steam pipes, the study of the effects of strain distribution across welded pipe sections and other known early failure locations on steam pipes and other plant components is growing in interest. An existing strain monitoring method employs the E.ON UK ARCMAC gauge system with a capability of both uniaxial and biaxial strain measurements. For strain mapping, digital image correlation (DIC) is also incorporated and integrated with the ARCMAC system. In an effort to further improve the ARMAC system portability, the use of a digital single-lens reflex (DSLR) camera system is investigated. The scope of a combined ARCMAC/DIC system to provide for both point-to-point and strain mapping of piping features is studied. Identification of a feature using a combination of ARCMAC and DIC techniques is presented here. Additionally, the investigation of an edge-finding technique which can complement the existing ARCMAC system is presented.
Online Software Tool for Predicting Weld Residual Stress and Distortion
Authors: Yang Yu-Ping , Zhang Wei , Gan Wei , Khurana Shuchi , Xu Junde , Babu Sudarsanam Suresh
Published: July 2009

Weld residual stress and distortion are inevitable during welding due to rapid local heating and cooling, high-temperature material reactions and weld-fixture effects. To predict weld residual stress and distortion, an engineer has to understand welding processes and the finite element analysis method. It is difficult for an engineer without finite element background to calculate the weld residual stress and distortion. With the development of weld modeling technology, automatic meshing generation, and high performance computation, a web-based analysis tool (E-Weld Predictor), was developed to predict weld residual stress and distortion. This allows an engineer to calculate the weld residual stress and distortion on line. The engineer does not need to have finite element analysis knowledge to perform the calculation. By providing welding parameters, defining a weld joint, giving geometry dimensions, and specifying a material, weld residual stress and distortion are automatically calculated in a remote high performance computer. A report will then be sent to the engineer to review. This paper introduces the development of E-Weld Predictor. The software structure, the theory, the implementation, and the validation of E-Weld Predictor are discussed in detail. It also shows the simulation process of applying this software in predicting temperature, microstructure, residual stress and distortion.
Model 9975 Shipping Package Fabrication Problems and Solutions
Authors: May Cecil G. , Smith Allen C.
Published: July 2009

The Model 9975 Shipping Package is the latest in a series (9965, 9968, etc.) of radioactive material shipping packages that have been the mainstay for shipping radioactive materials for several years. The double containment vessels are relatively simple designs using pipe and pipe cap in conjunction with the Chalfont closure to provide a leak-tight vessel. The fabrication appears simple in nature, but the history of fabrication tells us there are pitfalls in the different fabrication methods and sequences. This paper will review the problems that have arisen during fabrication and precautions that should be taken to meet specifications and tolerances. The problems and precautions can also be applied to the Models 9977 and 9978 Shipping Packages.
The Stress Corrosion Cracking Behavior of Alloys 690 and 152 Weld in a PWR Environment
Authors: Alexandreanu B. , Chopra O. K. , Shack W. J.
Published: July 2009

Alloys 690 and 152 are the replacement materials of choice for Alloys 600 and 182, respectively. The latter two alloys are used as structural materials in pressurized water reactors (PWRs) and have been found to undergo stress corrosion cracking (SCC). The objective of this work is to determine the crack growth rates (CGRs) in a simulated PWR water environment for the replacement alloys. The study involved Alloy 690 cold-rolled by 26% and a laboratory-prepared Alloy 152 double-J weld in the as-welded condition. The experimental approach involved pre-cracking in a primary water environment and monitoring the cyclic CGRs to determine the optimum conditions for transitioning from the fatigue transgranular to intergranular SCC fracture mode. The cyclic CGRs of cold-rolled Alloy 690 showed significant environmental enhancement, while those for Alloy 152 were minimal. Both materials exhibited SCC of 10−11 m/s under constant loading at moderate stress intensity factors. The paper also presents tensile property data for Alloy 690TT and Alloy 152 weld in the temperature range 25–870°C.
Fatigue Evaluation in Mixing Zones: Comparison of Different Criteria of Fatigue
Authors: Stephan J. M. , Gourdin C. , Angles J. , Quilici S. , Jeanfaivre L.
Published: July 2009

The distribution of unsteady temperatures in the wall of the 6" FATHER mixing tee mock-up is calculated for a loading configuration: The results seem realistic even if they are not still very accurate (see paper PVP2005-71592 [11]). On this basis, thermal stresses are evaluated for elastic and elastic-plastic material behavior. Then, different types of fatigue criteria are used to evaluate the fatigue damage. The paper develops a brief description of the criteria, the corresponding fatigue damage evaluation and attempts to explain the differences.
Development of Alternate Methods for Establishing Design Margins for ASME Section VIII Division 3
Authors: Terada Susumu
Published: July 2009

The design margin against collapse for Division 3 is based on Nadai’s equation. For high strength materials (the ratio of Sy/Su is more than 0.9) this method is adequate. However for the material with lower ratio of Sy/Su than 0.9 this method has additional margin from entire yielding through the thickness to collapse. The experimental burst test results for closed-end cylinder show the excessive margin for these materials. Therefore the development of alternate methods for establishing design margins for all materials is desirable. In this paper the experimental burst test results, case study of various methods (Div.2 rewrite, current Div.3 and proposed method) for design pressure are investigated.
Implementation of Load Reducing Bushings for Valves in a High Vibration Environment
Authors: Reich Alton , Doherty Steve , Williams Keith
Published: July 2009

The Arnold Engineering Development Center (AEDC) testing complex includes more than 50 wind tunnels, test cells, arc heaters, and other specialized test facilities. Of these, 27 units have capabilities that are unmatched in the United States, and 14 are unmatched in the world. These unique facilities create equally unique operating environments for instrumentation used for monitoring and control of test conditions. Several high flow-rate, supersonic wind tunnels utilize off-the-shelf angular displacement transducers (ADTs) for monitoring the position of 90° valves (i.e. butterfly valves) used to control the air flow-rate, operating pressure, and temperature during testing. There are significant structural vibrations in the wind tunnels to which the ADTs are subjected. These ADTs have experienced an unacceptably high rate of failure during testing. These failures increase maintenance costs, and in some cases can require test operations be suspended while the faulty ADT is replaced; leading to significant cost and schedule impacts associated with the down-time. This paper discusses the final phase of a multi-year effort to develop and field a vibration reducing bushing assembly for use on quarter turn valves used for flow control on wind tunnels at Arnold Enginnering Development Center. The focus of the final phase was on adapting the solution that was tested in the laboratory and field to fit the various valve geometries and conditions found in the installations. Design challenges and solutions are discussed.