bluuebunny/crossref_metadata_2025 huggingface dataset:
Is poor glycaemic control in diabetic patients a risk factor of myopia?
Authors: Jacobsen Nina , Jensen Hanne , Lund‐Andersen Henrik , Goldschmidt Ernst
Published: July 2008

Purpose: As a consequence of an increasing prevalence of short‐sightedness (myopia) in countries that have adopted western dietary patterns, it has been hypothesized that hyperglycaemia and hyperinsulinaemia induce myopia. The purpose of this study was to evaluate the relation between glycosylated haemoglobin (HbA1c), insulin dosage and myopia in diabetic patients.

Methods: All type 1 diabetic patients aged 16–26 years [mean age 22.0, standard deviation (SD) 2.9] attending the eye clinic at Steno Diabetes Center, Copenhagen, in 1995–1997 were included in the study (n = 393). The following data were collected from the medical records from baseline to 2005: age at diabetes onset, age at baseline, sex, weight, HbA1c, insulin dosage, refractive error, visual acuity and ocular diabetes complications.

Results: The prevalence of myopia [spherical equivalent (SE) ≤ −0.5 D] was 53.3% [95% confidence interval (CI) ± 5.29] at baseline. We followed 252 patients for 7.1 years (SD 2.2). In a logistic regression analysis, age at baseline [odds ratio (OR) 0.90 (95% CI 0.82; 0.99),P = 0.031], duration of diabetes at baseline [OR 0.95 (95% CI 0.91; 0.99),P = 0.047] and HbA1c[OR 1.26 (95% CI 1.03; 1.47),P = 0.022] were associated with myopia. The relative risk of a myopic shift was 1.7 (95% CI 1.28; 2.26) in patients aged 16–21 years and 1.6 (95% CI 1.19; 2.14) in patients with HbA1cabove 8.8%. Insulin dosage was not related to myopia.

Conclusion: The prevalence of myopia in diabetic patients is considerably higher than in the background Danish population. Poor metabolic control of glucose is a suggested risk factor of myopia. The study suggests that myopia may be regarded as a complication of hyperglycaemia in diabetes.
A prospective study on intravitreal bevacizumab (Avastin®) for neovascular age‐related macular degeneration of different durations
Authors: Algvere Peep V. , Steén Björn , Seregard Stefan , Kvanta Anders
Published: July 2008

Purpose:  Choroidal neovascularization (CNV) accounts for 85–90% of severe visual impairment in age‐related macular degeneration (AMD). Vascular endothelial growth factor (VEGF) is a major factor mediating angiogenesis, and VEGF inhibitors have become a new treatment modality. In this prospective study, we used bevacizumab (Avastin®), a recombinant monoclonal antibody to VEGF, to treat neovascular AMD.

Methods:  The case material comprised 36 subjects (26 females, 10 males) aged 65–88 years with subfoveal neovascular AMD with all subtypes of CNV. There were two categories of patients: category I, long‐standing CNV (12 months or more), preoperative visual acuity (VA) 0.16 (mean); category II, CNV (duration <12 months), preoperative VA 0.25 (mean). Evaluation protocol included the Early Treatment Diabetic Retinopathy Study (ETDRS) VA, clinical ophthalmological examination, fluorescein angiography and optical coherence tomography (OCT). Intravitreal injections of bevacizumab (Avastin®) (IVB), 1.25 mg (0.05 ml), were given under an operating microscope and aseptic conditions in a theatre for surgery with intervals of 4 or 6 weeks during the first 3 months and subsequently according to clinical assessment. The follow‐up was 6 months in all cases.

Results:  At 6 months, mean VA had improved by 4.6 ETDRS letters in the entire case material (P = 0.001), by 3.9 letters in category I (duration 12 months or more) and by 6.0 letters in category II (duration <12 months). A total of 148 IVB (mean 4.1 injections/eye) were delivered during 6 months, the first 3 months comprising 3.1 IVB (mean) and the last 3 months 1.0 IVB (mean). No eyes suffered visual decline of 15 ETDRS letters. Fluorescein angiograms displayed stabilization or regression of CNV activity; OCT showed resorption of intraretinal oedema and subretinal fluid. No severe complications occurred but recurrence was common, and repeated IVBs were necessary in most cases during the 6‐month period.

Conclusion:  When addressing the issue of frequency of IBV, we observed that 6‐week intervals were sufficient because VA and CNV lesions generally stabilized at 4 weeks. The gain in VA was promising in eyes with <12 months CNV duration. Even in eyes with a longer CNV duration, a slight visual improvement was observed when retinal oedema resorbed, although subretinal fibrosis and general cellular damage certainly limited recovery.
Integrating -algebras
Authors: Henriques André
Published: July 2008

Given a Lie n-algebra, we provide an explicit construction of its integrating Lie n-group. This extends work done by Getzler in the case of nilpotent $L_\infty $-algebras. When applied to an ordinary Lie algebra, our construction yields the simplicial classifying space of the corresponding simply connected Lie group. In the case of the string Lie 2-algebra of Baez and Crans, we obtain the simplicial nerve of their model of the string group.
Invariants of welded virtual knots via crossed module invariants of knotted surfaces
Authors: Kauffman Louis H. , Faria Martins João
Published: July 2008

We define an invariant of welded virtual knots from each finite crossed module by considering crossed module invariants of ribbon knotted surfaces which are naturally associated with them. We elucidate that the invariants obtained are non-trivial by calculating explicit examples. We define welded virtual graphs and consider invariants of them defined in a similar way.
p-adic confluence of q-difference equations
Authors: Pulita Andrea
Published: July 2008

We develop the theory of p-adic confluence of q-difference equations. The main result is the fact that, in the p-adic framework, a function is a (Taylor) solution of a differential equation if and only if it is a solution of a q-difference equation. This fact implies an equivalence, called confluence, between the category of differential equations and those of q-difference equations. We develop this theory by introducing a category of sheaves on the disk D−(1,1), for which the stalk at 1 is a differential equation, the stalk at q isa q-difference equation if q is not a root of unity, and the stalk at a root of unity ξ is a mixed object, formed by a differential equation and an action of σξ.
Moduli of toric vector bundles
Authors: Payne Sam
Published: July 2008

We give a presentation of the moduli stack of toric vector bundles with fixed equivariant total Chern class as a quotient of a fine moduli scheme of framed bundles by a linear group action. This fine moduli scheme is described explicitly as a locally closed subscheme of a product of partial flag varieties cut out by combinatorially specified rank conditions. We use this description to show that the moduli of rank three toric vector bundles satisfy Murphy’s law, in the sense of Vakil. The preliminary sections of the paper give a self-contained introduction to Klyachko’s classification of toric vector bundles.
Measurement of Velocities in Two-Phase Flow by Laser Velocimetry: Interaction Between Solid Particles’ Motion and Turbulence
Authors: Sad Chemloul N. , Benrabah O.
Published: July 2008

In this work, an experimental method based on laser anemometry with Doppller effects is developed. This allows the measurement of velocities and their fluctuations in a flow of solid-liquid suspension in an ascendant vertical pipe. In order to distinguish between the signals coming from the continuous phase, water, and those of the glass bead particles larger than the Kolmogorov length scale, an electronic logic circuit was incorporated in the measuring equipment. This enabled the study of both the slip velocity of the solid-liquid suspension and the influence of the large particles on turbulence. The results show that a fine particle suspension, which represents a tracer, behaves as a homogeneous fluid. For large particles, we confirmed the existence of a slip velocity and the effect of particle size on the turbulence. The use of two distinct measurement volumes produces good results for the direct measurement of the turbulent length scales. The results show that the presence of solid particles modifies the turbulence characteristics.
Particle Deposition Onto Rough Surfaces
Authors: Iacono Giovanni Lo , Reynolds Andy M. , Tucker Paul G.
Published: July 2008

Predictions for the number of particles depositing from fully developed turbulence onto a fully roughened k-type surface are obtained from the results of large-eddy simulations for a ribbed-channel flow. Simulation data are found to provide only partial support for the “mass-sink hypothesis,” i.e., the notion that all particles entering a mass sink, a volume of fluid extending vertically from the deposition surface, are captured and eventually deposited. The equality of the number of particles entering the mass sink and the number of particles depositing is attained, and a qualitative agreement with the empirical model of Wood (1981, “A Simple Method for the Calculation of Turbulent Deposition to Smooth and Rough Surfaces,” J. Aerosol Sci., 12(3), pp. 275–290) for the height of this mass sink is obtained. However, a significant proportion of particles escapes from the mass sink and the equality of numbers is attained only because many particles deposit onto rib surfaces above the mass sink, without first entering the mass sink.
Aerodynamics of Large-Scale Vortex Generator in Ground Effect
Authors: Katz Joseph , Morey Frederic
Published: July 2008

The aerodynamic performance of several vortex generators (VGs) of the type used on the lower surface of race cars was tested in a low-speed wind tunnel. In this particular application, the vortices emanating from the VGs create a suction force between the vehicle and the ground, thereby improving tire adhesion and the vehicle’s cornering∕traction performance. Since the size of these devices is much larger than the local boundary layer thickness, they are termed “large scale” in this study. Results of the wind tunnel tests indicate that the aerodynamic adhesion forces increase with reduced ground clearance while the corresponding drag increase is much smaller. The parameters investigated in this study are the VG length, shape, and the effect of incidence angle. Amongst the various shapes tested, the traditional rectangular VG created the largest forces while the simple triangular design was the most efficient in terms of the incremental lift to drag ratio.
Evaluation of the Mixing Performance of the Micromixers With Grooved or Obstructed Channels
Authors: Tsui Yeng-Yung , Yang Ching-Shiang , Hsieh Chung-Ming
Published: July 2008

The mixing flows in microchannels were examined using numerical methods. To speed up fluid mixing, it is essential to generate lateral transport of mass. In this study, the mixing flow is disrupted by either placing grooves or block obstacles on the walls of the channels. Since the grooves or the blocks appear in a periodic configuration, the velocity is solved only in a section of the channel. With the repeating cycle of flow velocity field, the fluid concentration can be calculated throughout the entire length of the channel. Good agreement with experiments in the mixing performance justifies the present methodology. Two different channel configurations are under consideration: grooved channels and obstructed channels. The results reveal that with straight grooves, a well organized vortex flow is formed in the vertical plane along the groove, which leads to a helical flow in the channel. The mixing performance can be enhanced by having grooves on both the top and the bottom walls arranged in a staggered manner, by which the transversal velocity is largely increased. It is seen that the strength of the secondary flow and, thus, the mixing can be improved by suitably choosing geometric parameters of the groove, such as the depth, the width, and the oblique angle. It is also shown that the efficient mixing for the staggered herringbone type groove is due to the fluid stratification caused by the exchange of position of the resulted counter-rotating vortices. As for the obstructed channels, the flows are in essence two dimensional. Very strong transversal velocity can be produced by narrowing down the flow passage in the channel. However, the efficient mixing is obtained at the cost of large pressure head loss.
Cavitation Structures in a Venturi Flow With Various Backward Facing Steps
Authors: An Hailing , Plesniak Michael W.
Published: July 2008

Cavitation inception and development caused by a backward facing step in a Venturi-type test section were studied experimentally for different step heights (0.8–4mm). High-speed cinematography and particle image velocimetry images were used to demonstrate the cloud shedding process and cavitation development stages. It was found that for small step height (0.8mm, h∕δ0=1.7) cavitation started in the reattachment region in the form of a reentrant jet, and caused cloud shedding in its developed stage. For high step height (4mm, h∕δ0=8.5) cavitation started midway downstream of the shear layer and resembled the spanwise vortices in the separated shear layer. This study contributes experimental results for better understanding of cavitation inception and development in the separated shear layer.
An Alternating Magnetic Field Driven Flow in a Spinning Cylindrical Container
Authors: Shatrov Victor , Gerbeth Gunter , Hermann Regina
Published: July 2008

This paper presents a numerical analysis of the free surface liquid metal flow driven by an alternating current magnetic field in a spinning cylindrical container. The axisymmetric flow structure is analyzed for various values of the magnetohydrodynamic interaction parameter and Ekman numbers. The governing hydrodynamic equations are solved by a spectral collocation method, and the alternating magnetic field distribution is found by a boundary-integral method. The electromagnetic and hydrodynamic fields are fully coupled via the shape of the liquid free surface. It is found that the container rotation may reduce the meridional flow significantly.
Engineering-Driven Factor Analysis for Variation Source Identification in Multistage Manufacturing Processes
Authors: Liu Jian , Shi Jianjun , Hu S. Jack
Published: July 2008

Variation source identification is an important task of quality assurance in multistage manufacturing processes (MMPs). However, existing approaches, including the quantitative engineering-model-based methods and the data-driven methods, provide limited capabilities in variation source identification. This paper proposes a new methodology that does not depend on accurate quantitative engineering models. Instead, engineering domain knowledge about the interactions between potential variation sources and product quality variables is represented as qualitative indicator vectors. These indicator vectors guide the rotation of the factor loading vectors that are derived from factor analysis of the multivariate measurement data. Based on this engineering-driven factor analysis, a procedure is presented to identify multiple variation sources that are present in a MMP. The effectiveness of the proposed methodology is demonstrated in a case study of a three-stage assembly process.
Multiobjective Optimization for Integrated Tolerance Allocation and Fixture Layout Design in Multistation Assembly
Authors: Li Z. , Izquierdo L. E. , Kokkolaras M. , Hu S. J. , Papalambros P. Y.
Published: July 2008

Cost and dimensional variation of products are significant attributes in multistation assembly processes. These attributes depend on product∕process tolerances and fixture layouts. Typically, tolerance allocation and fixture layout design are conducted separately without considering potential interrelations. In this work, we use multiobjective optimization for integrated tolerance allocation and fixture layout design to address interactions and to quantify tradeoffs among cost, product variation, and assembly process sensitivity. A nested optimization strategy is applied to a vehicle side frame assembly. Results demonstrate the presence and quantification of tradeoffs, based on which we introduce the concept of critical variation and critical budget requirements.
Computational and Experimental Studies of High Temperature Crack Growth in the Presence of Residual Stress
Authors: O’Dowd Noel P. , Nikbin Kamran M. , Wimpory Robert C. , Biglari Farid R. , O’Donnell Manus P.
Published: July 2008

Residual stresses have been introduced into a notched compact tension specimen of a 347 weld material by mechanical compression. The required level of compressive load has previously been determined from finite element studies. The residual stresses in the vicinity of the notch root have been measured using neutron diffraction and the results compared with those obtained from finite element analysis. The effect of stress redistribution due to creep has been examined and it is found that significant reduction in stress is measured after 1000 hours at 650 °C. The implications of these results with regard to the development of damage in the specimen due to creep relaxation are examined.
A Homogenization Method for the Modal Analysis of a Nuclear Reactor With Fluid-Structure Interaction
Authors: Sigrist Jean-Franc¸ois , Broc Daniel
Published: July 2008

The present paper exposes a homogenization method developed in order to perform the modal analysis of a nuclear reactor with fluid-structure interaction effects. The homogenization approach is used in order to take into account the presence of internal structures within the pressure vessel. A homogenization method is proposed in order to perform a numerical calculation of the frequencies and modal masses for the eigenmodes of the coupled fluid-structure problem. The technique allows the use of a simplified fluid-structure model that takes into account the presence of internal structures: the theory bases are first recalled, leading to a new formulation of the fluid-structure coupled problem. The finite element discretization of the coupled formulation leads to the modification of the classical fluid-structure interaction operators. The consistency of the formulation is established from a theoretical point of view by evaluating the total mass of the coupled system with the fluid and structure mass operator, and the modified added mass operator. The method is tested and validated on a 2D case (two concentric cylinders with periodical rigid inclusions within the annular space) and applied on the industrial case. A complete modal analysis (calculation of frequencies and modal masses) is performed on a simplified geometry of a nuclear reactor with and without internal structures. Numerical results are then compared and discussed, and the influence of the internal structures on the fluid-structure coupled phenomenon is highlighted.
Fluid Forces on a Moving Body at Low Amplitude in Fluid at Rest: Part 1 — A Review of Literature
Authors: Melot Vincent , Sigrist Jean Franc¸ois , Lane Christian , Auvity Bruno , Peerhossaini Hassan
Published: July 2008

The study of a interaction fluid-structure problem requires the calculation of fluid forces acting on moving boundaries. Since the first studies carried out by Stokes, a lot of work has been performed to derive various expressions of fluid forces, in particular for the case of simple geometry, such as infinite planes, spheres or circular cylinders. These bodies are subjected to elementary motions, namely harmonic motions or Dirac acceleration motions, (i.e. constant speed velocity motions). The present paper exposes a review of fluid forces exerted on accelerated rigid body in an incompressible viscous fluid initially at rest. The principal objective of this paper is to carry out a synthesis of the current literature and to develop a general analytical formulation of the fluid forces in order to deal with more general rigid body motions. The analytical formulation is exposed in the present paper for fluid forces acting on any moving body. This approach is limited to low displacements of the solid body, i.e. the non linear convective term of NS equation is not taken into account. The non-dimensional numbers is pointed out and detailed. The different solutions given in the literature are especially discussed with the influence of the viscosity compared to the irrotational model.
Blast Containment Chamber Development and Testing
Authors: King Kim W. , Waclawczyk Johnny H.
Published: July 2008

Explosive containment chambers are produced for a number of purposes. Some chambers are designed to protect personnel from a single accidental explosion, such as storage in a manufacturing process. Other chambers are designed for multiple intended detonations such as a chamber used for explosive research and testing. Several bomb containment vessels are produced that are used for explosives storage and transportation, as well as the destruction of conventional and chemical-biological improvised explosive devices (IED). Multiple spherical vessels exist that are rated for multiple detonations of explosives that range from 10-lbs TNT equivalent to more than 25-lbs TNT in what would be considered a venting mode of operation. Additionally, there are similar chambers designed to limit the risk of exposure to hazardous materials during the transportation and destruction of an IED that has an associated chemical or biological hazard. The charge rating for these chambers is typically less due to the nature of the threat. A new type of bomb containment vessel has emerged to contain the effects of a device found in luggage or smaller shipping packages. These chambers are typically intended to contain IEDs that do not have an associated chemical or biological hazard. Often times these units do not have the preferred geometrical shape of a sphere because of use and spatial restrictions. Additionally, these units are designed for a single detonation of the design charge weight (i.e., it is not reusable). It is expected to undergo severe permanent displacement during an event, but will not rupture. Other explosive containment chambers are used to destroy military munitions. Many of these chambers have survived hundreds or even thousands or detonations. Typically, these chambers are designed using a dynamic non-linear finite element analysis (FEA) during initial design. Following the design phase, these vessels are tested to confirm performance, and (in the case of a sealed chamber) characterize the leakage characteristics. Additionally, the test program is intended to identify and eliminate any physical weaknesses in the system, quantify structural response of the system under various explosive charge weights, and identify operational and maintenance problems. This paper describes the design and testing procedures for these programs and compares them based on similarities and differences.
Reconstitution of V-Notched Charpy Impact Specimen Made of Short Insert
Authors: Osaki Toru , Matsuzawa Hiroshi
Published: July 2008

Reconstitution in this paper means to constitute the original size V-notched Charpy impact specimen, which is made of the irradiated insert cut out from broken piece and un-irradiated tabs welded to the insert. It is a promising technique to secure an adequate number of surveillance specimens for long-term operation of nuclear power plants. Every Japanese nuclear power plant has its own surveillance test program, and is operated considering its unique surveillance test results along with the general reduction tendency of fracture toughness. This practice should be continued and enhanced if possible, after the full use of originally installed specimens, because its fracture toughness is lower than before. Reconstitution of V-notched Charpy impact specimens to the original shape by using a short insert was studied. Charpy absorption energy is generally shifted by reconstitution, if the insert length is as short as 10 mm. Reconstitution with a short insert is necessary when the transverse property of the original specimen is required although only the longitudinal surveillance specimen is installed as in some early constructed reactor pressure vessels in Japan. This case is important when the reactor pressure vessel is suspected to be a so-called low upper shelf toughness reactor pressure vessel. The minimum required insert length to avoid affect on the specimen properties depends on the Charpy absorption energy of the insert and reconstitution weld condition. Correlation between Charpy absorption energy and plastic deformation size, and short time annealing properties of irradiated pressure vessel steels were investigated. A method to evaluate the minimum required insert length was proposed, which depends on the expected Charpy absorption energy and thermal transient during reconstitution. It was demonstrated that the reconstituted specimens of 10 mm-long irradiated inserts, whose upper shelf absorption energy was 69J and required insert length was 9.5mm, showed little shift of upper shelf absorption energy.
Fracture Failure Risk Analysis of Pressure Pipeline Containing Defects on Pile Foundation Settlement
Authors: Li Xiang , Zheng Jinyang , Xie Yujun
Published: July 2008

Pile foundation settlement might cause a disastrous consequence to an in-service pressure pipeline. Flaws, which are unavoidable in the pipeline, lead to reduction of load-supporting capability and service life of the pipeline. So fracture failure risk analysis of in-service pressure pipeline is important in engineering. Failure probability of pipeline due to pile foundation settlement is computed by using the well-known safety assessment procedure R6. Three-moment equation is adopted to compute bending moment in the condition of n piles, where n is the number of piles. A numerical example was presented to illustrate the application of fracture failure risk analysis to determine the failure probability of the pressure pipeline, considering the uncertainties in various internal operating loadings and external forces, flaw sizes, material fracture toughness and flow stress. Furthermore, the failure probabilities of each defect and the whole pipeline were obtained.
Plastic Collapse Analysis of Pipe Bends Under Out-of-Plane Moment and Internal Pressure Loading
Authors: Li Hongjun , Mackenzie Donald
Published: July 2008

Two recently proposed Design by Analysis criteria of plastic collapse based on plastic work concepts, the Plastic Work criterion and the Plastic Work Curvature criterion, are applied to a strain hardening pipe bend arrangement subject to combined pressure and out-of-plane plane moment loading. Calculated plastic pressure-moment interaction surfaces are compared with limit surfaces, large deformation analysis instability surfaces and plastic load surfaces given by the ASME Twice Elastic Slope criterion. The results show that both large deformation theory and material strain hardening have a significant effect on the elastic-plastic response and calculated static strength of the component.
Global Buckling Investigation in Welding of a Thin Wall Aluminum T Joint
Authors: Asle Zaeem M. , Nami M. R. , Kadivar M. H.
Published: July 2008

In this paper global welding buckling distortion of a thin wall aluminum T joint is investigated. A thermo-elastoplastic model is employed to determine longitudinal residual stresses; analysis of thermal model and elastic-viscoplastic (Anand) model are decoupled. Molten puddle motion (speed of welding) is modeled by using birth and death element method and time dependent model. Three dimensional nonlinear-transient heat flow analysis has been used to obtain temperature distribution, and then by applying thermal results and using three dimensional Anand elastic-viscoplastic model, stress and deformation distributions are obtained. By applying residual stresses on a structural model and using eigenvalue methods, global buckling instability of the welded structure is determined.
Thermo-Mechanical Modelling for the Opening of Electron-Beam Welded Joints
Authors: Carin Muriel , Rogeon Philippe , Manach Pierre-Yves , Pilvin Philippe , Menes Olivier , Sigrist Jean-Franc¸ois
Published: July 2008

The aim of this study is to estimate residual stresses and distortions during the assembly of dissimilar metallic materials welded by Electron Beam Welding (EBW) technique. This work is motivated by a new welding procedure for the manufacture of large speed reduction gear. The gear consists of a central hub of S275 J2G3 steel and a toothed wheel of 32CrMoV13 steel, chosen for its high fatigue performances. Preliminary experimental welding tests have shown the opening of the joint plane during the circular welding of the gear leading to lack-of-fusion defects. To improve the joining technique, a thermomechanical model has been developed to predict the opening of the joint plane during welding. A two-dimensional finite element model has been applied on a simplified geometry of smaller size. The opening of the joint plane has been modelled by two different ways, the first one uses activation / deactivation elements and the second one uses specific contact elements. Both techniques have shown similar displacements. The assumptions of plane stress or generalized plane strain are discussed. Numerical results obtained with similar metals with or without metallurgical transformations are presented. Calculations carried out with dissimilar metals are compared with experiments in terms of fusion zone size and displacements.
Buckling of Pipelines With Inconstant Corrosion Subjected to External Hydrostatic Pressure
Authors: Xue Jianghong
Published: July 2008

Methodology to derive analytical solutions for the buckling of pipelines with inconstant corrosion subjected to external hydrostatic pressure is presented. The corroded pipeline is modeled as a non-uniform, infinitely long cylindrical shell with two regions: Region 1 of nominal thickness and Region 2 of reduced, inconstant thickness. Eigen-functions to determine the buckling pressure for the corroded pipeline are derived using asymptotic expansion. Symmetric and anti-symmetric buckling modes are found to occur for pipelines when the corrosion is symmetric about its centerline. In particular, solutions of the buckling mode and the eigenvalues for buckling pressure of the corroded pipeline are obtained when Region 2 has a reduced and constant thickness and are found to converge to the validated solutions obtained from equilibrium analysis.
Ligament Crack Growth in a Main Steam Superheater Outlet Header
Authors: Karstensen Annette , Guerra Jorge , Knowles David , Kwon Ohgeon
Published: July 2008

Ligament cracks were discovered during a cold survey in a main steam outlet header in a 250MW coal/gas fired unit following over 100,000 hours of service. Subsequent inspection revealed similar cracking in the same headers of two other units in the plant which had seen similar service. To ensure the safety of the headers a structural integrity programme was initiated by the operator, Genesis Energy, in order to determine their fitness for service. The maximum stress and stress range due to the temperature and pressure fluctuations during operation and starts was established by carrying out a detailed thermo-mechanical FE analysis, validated against detailed thermocouple measurements. The critical crack size was calculated and the time for the flaw to reach the critical flaw size was established by considering creep and fatigue crack growth mechanisms. Mechanical testing on material obtained during a repair of one of the headers was used to refine estimates of toughness and tensile properties. Moreover examination of the fracture face removed during the repair indicated that the crack growth was primarily due to fatigue. This was found to be due to frequent thermal cycling of the unit during nominally “steady state” operation. The crack growth rate established from the fracture surface analysis was compared with NDT measurements for validation of the fatigue crack growth model. The demonstrated predictability for the rate at which the ligament cracks are growing as a function of operation has provided Genesis with the opportunity develop a long term strategy for inspection, repair or replacement of their superheater headers.
Fluid-Structure Interaction: Numerical Validation of an Homogenization Method
Authors: Broc Daniel , Sigrist Jean-Franc¸ois
Published: July 2008

The considered structure is a nuclear reactor vessel, composed of two concentric inner and outer structures, with water in the annular space between. Previous dynamic analysis showed that this water lead to strong fluid structure interaction coupling the structures. The annular space is filled by regularly spaced cylinders, which are linked to the inner structure. Their influence was neglected in the first studies. Recent analyses, using homogenization methods, show that these cylinders increase the FSI coupling in the vessel. The homogenization methods is based on general principles developed in the study of tube bundles, and very well established, from a physical and numerical point of view. Even if it seems reasonable to have a high degree of confidence in the results obtained with this homogenization methods, it is still interesting to validate the results of the “homogenization analysis” with a comparison with “direct calculations”, taking into account the real geometry of the system. The paper presents the main results of the validation. The main limitation of the “direct calculations” is the size of the mesh and the computer time. The main limitation for the “homogenization analysis” is that the actual modeling does not take into account the anisotropy in the Fluid Structure Interaction in the annular space.
Characterization of Duplex Stainless Steel Weldments
Authors: El-Demellawy Mona A.
Published: July 2008

Duplex Stainless Steels (DSS) have found widespread use in a range of industries, because of their high strength with high resistance to stress corrosion cracking and resistance to sensitization-induced intergranular corrosion. The more high alloyed grades [super DSS] are resistant to oxygenated or chlorinated seawater. Consequently, due to the stable mechanical and corrosion properties after thermal aging for long term service at temperatures below 400°C, duplex stainless steel is used in pipes and components in the primary cooling systems in the PWRs (Pressurized Water Reactors). The investigated material was DSS of grade {UNS S31803 (ASTM A790, ASTM 2205)} in the form of pipe. Each weldment specimen was heat treated at one of the following temperatures: 475°C, 600°C, 700°C, 850°C, 1050°C and 1150°C for 1 hour. The ferrite content and hardness tests were performed along the weldment. The impact test was performed according to the ASTM E23 and the examination of intergranular corrosion susceptibility was performed (ASTM A262 - Practice B). The microstructure investigation was carried out by using the light optical microscopy for etched specimens. The SEM with EDAX was used to detect the microstructural changes due to the heat treatment and after corrosion as well as within the fracture surface of the impact specimens. Slight changes were observed at 475 and 600 °C/1 h conditions as compared to the as received condition, while a little loss in ferrite content was observed at 700°C aging condition. This may be the result of precipitation of different types of secondary phases such as χ-phase, ζ-phase, carbides and nitrides. At 850°C, the observed great loss in ferrite content may be attributed to precipitation of σ-phase with large volume fraction. The solution treatment at 1050 °C/1h condition improved the ferrite content values as a result of decomposition of σ-phase. But the ferrite % value does not return back to its original value at the as received condition. On the other hand, when the solution treatment was done at 1150 °C/1h condition, the ferrite content continued to increase to the as received condition as a result of recovery of δ-ferrite inside the structure.
Structural Evaluation for Repaired J-Weld Portion of Reactor Vessel Head Penetration
Authors: Asada Seiji , Hojo Kiminobu , Ochi Mayumi , Muroya Itaru , Ito Hajime
Published: July 2008

Leakage was found in a Reactor Vessel (RV) Head Penetration of Ohi unit 3 of the Kansai Electric Power Co., Inc. in May 4, 2004. Non-destructive examinations identified flaws in a J-weld portion of the Head Penetration. The J-weld portion was repaired by using Embedded Flaw Repair Technique [1] that performs welding of 52 weld metal on the J-weld surface remaining the flaws. In order to show the structural integrity of the J-weld portion, a fracture mechanics evaluation was performed in accordance with the Rules on Fitness-for-Service for Nuclear Power Plants of the JSME Codes for Nuclear Power Generation Facilities, JSME S NA1-2002 [2] (hereafter, the JSME Fitness-for-Service Rules) and literatures related. The flaw was characterized as both case of an embedded flaw and a surface flaw and KI for each flaw was directly calculated by using FE analysis. Fatigue crack growth analysis using KI calculated showed the amount of the crack growth was quite small. The fracture mechanics evaluation followed confirmed that the result satisfied the criteria. This paper explains the method and results for evaluation of the structural integrity of the J-weld portion.
Using Statistic Method to Calculating and Monitoring the Corrosion Rate of Petroleum Process Piping
Authors: Chien Chi-Hui , Chen Chun-Hung
Published: July 2008

In chemical plants and most refineries, some process piping is suffered from metal thinning. Take carbon steel piping for example, each component such as elbow, tee, direct piping, branches, reducers are suffered thinning no matter the piping is still in using or not. So, with an eye to personal safety and smooth operation held in the chemical plants and refineries, every effort put in the inspections should be correctly getting knowledge about the deterioration conditions. Normally, to check the piping thinning condition is to perform the ultrasonic thickness spot gauging at each component of the piping. Through the thickness reading, inspectors could get the information about the piping remaining thickness, calculate the corrosion rate, and evaluate the remaining life at each part of the piping spools. However, when one puts an eye on the piping inspection management and deterioration conditions about the piping system in the operating unit, the variation condition of the inspection thickness data, in some view points, always play an important part as corrosion information hidden in the thickness data group. Besides, by considering the variation condition of the thickness data, the inspectors can get a more conservative and satisfactory corrosion rate data about the whole piping spool. By plotting the histogram of the corrosion data; inspectors can get a more clear idea about the deterioration condition of the whole operating unit. In this paper, the ultrasonic thickness survey is reported from the pre-selected susceptible areas of deterioration such as the injection points, elbow, tee etc. (as suggested by the API 570 Code and the API recommended practice 574). After collecting the thickness readings, the statistic skill is used to evaluate the corrosion rate of each piping spool in the operating unit. After the statistic calculations, the inspectors can analyze the evaluated corrosion rate data by plotting the histogram of the evaluated upper bound corrosion rate values. With the trend shown in the histogram, the inspectors can easily get knowledge about the deteriorating condition of the operating unit. Finally, in order to discuss the feasibility of the proposed method, the inspection data of two piping spools will be used as the examples. Also, a site survey result performed in the lubricant rerun unit shows the effectiveness of this statistic calculation method.
Code Case for Extension Use of 2-1/4Cr-1Mo-1/4V Steels for Vessels in ASME Section VIII Division 3
Authors: Terada Susumu
Published: July 2008

2-1/4Cr-1Mo-1/4V steels have been used extensively as materials for reactors in high temperature and high pressure hydrogeneration service. The design temperature of these reactors is 850F to 900F. These reactors have been designed per ASME Sec. VIII Division 2. If these reactors can be designed per ASME Sec. VIII Division 3, thickness of shell and head for these reactors in case of design temperature of 850F can be reduced by about 15% compared with that per Division 2 even if the membrane abjustment factors based on creep allowable stress are applied. However yield strength in Division 3 is limited less than 700F. In this paper, the additional requirements and background for extension use of 2-1/4Cr-1Mo-1/4V steels are presented.
Assessment of Steam Line Dynamic Pressures Using External Strain Gage Measurements
Authors: Szasz Gyorgy , Fujikawa Karen K. , DeBoo Guy
Published: July 2008

Dynamic pressure measurements have been made at a number of power plants using externally mounted strain gages on piping in order to characterize structural loading of upstream piping and pressure vessel components. The pressure fluctuations are derived from the ‘breathing’ mode of the piping therefore this indirect technique must be robust enough to reject the effects of other shell modes and/or bending. Several factors influence the ability to ensure that the breathing mode response can be measured; these factors include strain gage configuration options and data processing methods. The tested strain gage configurations utilized up to eight strain gages per location in an axisymmetric manner to facilitate the handling of any shell mode responses that may exist. Data processing strategies utilizing channel combination and filtering techniques were designed to extract pure breathing mode data for conversion to dynamic pressure. This paper will evaluate the various approaches and identify the most reliable one for plant implementation.
Determination of J-R Curves for A285 Carbon Steel Using Normalization Method
Authors: Zhu X. K. , Chao Y. J. , Lam P. S.
Published: July 2008

The normalization method is adopted and extended in this paper to develop J-R curves for standard and nonstandard specimens directly from load versus load-line displacement test data without the need for online crack length measurement. A set of single edge notched bend (SENB) specimens with different crack lengths for an A285 carbon steel are tested according to the guideline of ASTM standard E1820, and the ability of normalization method is then demonstrated in determination of crack-tip constraint-dependent J-R curves for the SENB specimens. The results show that the normalization method can be used to determine J-R curves for the standard as well as nonstandard specimens. The resistance curve procedure and the basic procedure specified in ASTM E1820 are evaluated, and a modified basic procedure is also presented for determining the J-integral. Comparisons of the resulting J-R curves indicate that the modified basic procedure can be equivalent to the resistance curve procedure. To validate the normalization method, the conventional electric potential drop method is used to monitor crack growth and to determine the J-R curves for the A285 steel. Two equations used in the potential drop method, i.e. linear and nonlinear relationships between the crack length and the electric potential, are employed to determine the crack length during the fracture testing. It shows that the J-R curves determined with the normalization method are in good agreement with those based on the potential drop methods for all specimens considered.
Study of Shield Design for Shock Mitigation
Authors: Cheng Wing , Hokamoto Kazuyuki , Itoh Shigeru
Published: July 2008

Detonation of high explosive due to impact of fragments and flyer plates was modeled using hydrodynamic computer code. Included in the model were the warhead consisting of casing and high explosive (which is H-6 in this case). An 80-gram fragment simulated projectile (FSP) was used as the projectile. Flyer plates considered are single- and multi-layer structures. A reactive flow model which is able to capture the initiation, propagation and complete detonation or deflagration of detonation was used to predict the occurrence of complete detonation. Analyses were performed with several impact velocities to obtain the velocity beyond which complete detonation would occur. Shields have been used to mitigate mechanical shocks. It has been well established that shields with multi-layered materials with impedance mismatch would reduce shock levels significantly. A numerical study was conducted to derive an optimum shield design with this concept. The model used encompasses a warhead-canister system. It was assumed that one of the two adjacent warheads would detonate. The canister wall was made of multi-layered materials consisting of layers of materials made of metal and lucite. This material combination represents a medium degree of mismatch while still exhibiting certain amount of strength. The model determines the pressure level at explosive in the neighboring warhead. The pressure level was used to determine if detonation would occur, and provided a measure of effectiveness on the shields for shock mitigation.
A Constraint-Based FAD Procedure for Defect Assessments of Pipelines
Authors: Cravero Sebastian , Ruggieri Claudio
Published: July 2008

This study explores applications of the failure assessment diagram methodology to predict the failure pressure for high pressure pipelines with planar defects having different geometries (i.e., crack depth and crack length). One purpose of this investigation is to assess the capability of FAD procedures in integrity analyses of high pressure pipelines with varying crack configurations. Another is to address the effectiveness of constraint-corrected FADs to predict burst pressure of low-constraint cracked pipelines. The FAD curves are corrected for effects of constraint based on the Lr-Q trajectories for pin-loaded SE(T) specimens. Full scale burst testing of end-capped pipe specimens with axial surface flaws provides the data needed to compare the failure predictions derived from the FAD procedures. The analyses reveal that the degree of agreement between predicted pressures and experimentally measured values depends rather markedly on the crack size for the tested pipes. Moreover, the analyses also show a potential weak dependence of the predicted pressures on the constraint-based correction scheme. Overall, the results validate the use of FAD-based methodologies for defect assessments of axially cracked pipelines.
Buckling of Externally Pressurised Prolate Ellipsoidal Domes
Authors: Smith P. , Blachut J.
Published: July 2008

Details are given of a numerical and experimental study into buckling of steel ellipsoidal domes loaded by static external pressure. A range of geometries and thicknesses of domes is examined, as is the influence of different boundary conditions. Shells are examined on the basis of having the same mass. The main focus of the study is on prolate domes, i.e., those taller than a hemisphere of the same base radius. Numerical predictions are confirmed by pressurising six laboratory scale prolate domes to destruction. Details are given of the manufacture and test procedure for the domes. The adverse effects of variations in shape, and wall thickness are discussed, and FE predictions are made for geometrically imperfect domes. Correlation between the two sets of results is good. Numerical and experimentally obtained results are related to the current design codes: ASME Boiler & Pressure Vessel Code, Section VIII, Division 2 (described hereon as ASME VIII), PD5500, and ECCS recommendations [1–3], which at present make no provision for prolate domes. Suggestions are made for the possible inclusion of such domes into the standards.
Development on High Pressure Material ASTM SA 723: Design and Economic Consequences
Authors: Po¨lzl Manfred , Schedelmaier Johannes , Zand Johann
Published: July 2008

Due to the continuous increase of production capacity in the last years for new polyethylene-high pressure plants, the licensors and plant operators take care to optimize the process efficiency and the complete manufacturing costs. Significant is the trend for big capacities of LDPE-plants in recent years. Figure 1 shows the increasing trend of nominal size for high pressure reactor tubes.