bluuebunny/crossref_metadata_2025 huggingface dataset:
Low‐grade or benign intestinal tumours contribute to intussusception: a report on one feline and two canine cases
Authors: Schwandt C. S.
Published: August 2008

Three adult patients were presented with sudden onset of intestinal signs. An intestinal intussusception was diagnosed in all three cases by ultrasound and exploratory celiotomy. Three different benign intraluminal tumours were the eliciting cause of intussusception. The tumours had equal macroscopic appearance consisting of a stalk attached to the intestinal wall with the bulk of the tumour floating in the chyme. Enterectomy without enteroplication of the concerned intestinal part cured the animals.
Liver X receptor in cooperation with SREBP‐1c is a major lipid synthesis regulator in nonalcoholic fatty liver disease
Authors: Higuchi Nobito , Kato Masaki , Shundo Yuki , Tajiri Hirotaka , Tanaka Masatake , Yamashita Naoki , Kohjima Motoyuki , Kotoh Kazuhiro , Nakamuta Makoto , Takayanagi Ryoichi , Enjoji Munechika
Published: August 2008

Aim:  Nonalcoholic fatty liver disease (NAFLD) is one of the most frequent causes of liver dysfunction and its incidence has increased markedly. However, the mechanisms involved in the pathogenesis of NAFLD in humans have not been thoroughly investigated. Sterol regulatory element binding protein (SREBP)‐1c and carbohydrate responsive element binding protein (ChREBP) are transcriptional factors that regulate the expression of lipogenic genes, including acetyl‐CoA carboxylases (ACCs) and fatty acid synthase (FAS). SREBP‐1c and ChREBP are transactivated by liver X receptor (LXR), a nuclear receptor that regulates the metabolism of cholesterol and fatty acids. To understand the mechanisms involved in the pathogenesis of NAFLD, we investigated the transcriptional factors and lipogenic genes activated in the liver with NAFLD.

Methods:  Real‐time PCR was carried out on liver biopsy samples from 20 NAFLD patients. The target genes studied were: ACC1, FAS, SREBP‐1c, ChREBP, AMP‐activated protein kinase (AMPK), and LXRα.

Results:  LXRα, SREBP‐1c, ACC1, and FAS were upregulated in NAFLD patients. Expression levels of LXR were four times greater than those of the controls and correlated significantly with SREBP‐1c, but not with ChREBP, levels.

Conclusions:  These findings suggest that LXR acts as one of the main regulators of lipid metabolism by regulating SREBP‐1c expression in NAFLD.
Recent role of splenectomy in chronic hepatic disorders
Authors: Ikegami Toru , Shimada Mitsuo , Imura Satoru
Published: August 2008

For years splenectomy in hepatic disorders has been indicated only for the treatment of gastro‐esophageal varices. However, with recent advances in medical and surgical treatments for chronic hepatic disorders, the use of splenectomy has been greatly expanded, such that splenectomy is used for reversing hypersplenism, for applying interferon treatment for hepatitis C, for treating hyperdynamic portal circulation associated with intractable ascites, and for controlling portal pressure during small grafts in living donor liver transplantation. Such experiences have shown the importance of portal hemodynamics, even in cirrhotic livers. Recent advances in surgical techniques have enabled surgeons to perform splenectomy more safely and less invasively, but the procedure still has considerable clinical outcomes. Splenectomy in hepatic disorders may become a more common procedure with expanded indications. However, it should also be noted that the long‐term effects of splenectomy, in terms of improved hematological or hepatic function, is still not guaranteed. Moreover, the impact of splenectomy on immunologic status remains unclear and needs to be elucidated in both experimental and clinical settings.
Expression of galectin‐3 involved in prognosis of patients with hepatocellular carcinoma
Authors: Matsuda Yasunori , Yamagiwa Yoko , Fukushima Koji , Ueno Yoshiyuki , Shimosegawa Tooru
Published: August 2008

Aims: Galectins are multifunctional lectins binding to the β‐galactoside of glycoproteins that affect diverse physiological and pathophysiological processes such as development, inflammation and tumor growth. In hepatocellular carcinoma (HCC), the over‐expression of galectin‐1, 3, and 4 has been reported, although their function and correlation with tumor progression remain unknown. Thus, we aimed to assess the role of galectin‐3 during HCC progression.

Methods: Specimens were obtained during curative operations and used for immunohistochemical analysis of galectin‐3 (n = 52), and statistically assessed for correlations with the clinical profiles and the prognoses of the patients. The serum galectin‐3 levels from the patients with liver diseases including HCC were assessed by ELISA.

Results: In total, galectin‐3 expression was found in 34 of 52 tumors (65%) and was statistically correlated with histological differentiation and vascular invasion. Kaplan‐Meier's analysis showed that patients with galectin‐3 expression tended to relapse in the earlier phase and had worse overall survival. In particular, a higher expression rate of nuclear galectin‐3 showed a markedly worse prognosis, and it was independent in the multivariate analysis for overall survival. Serum galectin‐3 levels were significantly increased in HCC compared with chronic liver disease. The sensitivity and specificity of galectin‐3 were equivalent to alpha‐fetoprotein and Vitamin K absence or antagonist II, and the combination of HCC biomarkers with galectin‐3 improved the diagnostic performance.

Conclusions: Galectin‐3 expression was involved in the tumor progression and related to the prognosis of HCC. Our observations suggested that galectin‐3 could be a novel tumor marker and therapeutic target.
Effects of Regular and Random Roughness on the Heat Transfer and Skin Friction Coefficient on the Suction Side of a Gas Turbine Vane
Authors: Dees Jason E. , Bogard David G.
Published: August 2008

Skin friction coefficients and heat transfer coefficients are measured for a range of regular and random roughnesses on the suction side of a simulated gas turbine vane. The skin friction coefficients are calculated using boundary layer data and the momentum integral method. High resolution surface temperature data measured with an IR camera yield local heat transfer values. 80 grit, 50 grit, 36 grit, and 20 grit sandpapers along with a regular array of conical roughness elements are tested. Measured skin friction coefficient data show that the conical roughness array behaves very similar to the 50 grit, 36 grit, and 20 grit sandpapers in terms of the effect of the roughness on the hydrodynamic boundary layer. In terms of heat transfer, the conical roughness array is most similar to the 80 grit sandpaper, which are both lower than the roughest sandpapers tested. These data show that the particular regular array of roughness elements tested has fundamentally different behavior than randomly rough surfaces for this position on the simulated turbine vane. In addition, this difference is in the opposite direction as seen in previous experimental studies. In order to draw a more general conclusion about the nature of random and regular roughness, a parametric study of regular roughness arrays should be performed.
The Effect of Combustor-Turbine Interface Gap Leakage on the Endwall Heat Transfer for a Nozzle Guide Vane
Authors: Lynch S. P. , Thole K. A.
Published: August 2008

To enable turbine components to withstand high combustion temperatures, they are cooled by air routed from the compressor, which can leak through gaps between components. These gaps vary in size from thermal expansions that take place. The leakage flow between the interface of the combustor and the turbine, in particular, interacts with the flowfield along the endwall. This study presents measurements of adiabatic cooling effectiveness and heat transfer coefficients on the endwall of a first vane, with the presence of leakage flow through a flush slot upstream of the vane. The effect of axial contraction of the slot width due to thermal expansion of the engine was tested for two blowing rates. Contracting the slot width, while maintaining the slot mass flow, resulted in a larger coolant coverage area and higher effectiveness values, as well as slightly lower heat transfer coefficients. Matching the momentum flux ratio of the leakage flow from the nominal and contracted slot widths lowered both cooling effectiveness and heat transfer coefficients for the contracted slot flow. Comparison of the coolant coverage pattern to the measured endwall shear stress topology indicated that the trajectory of the slot coolant was dictated by the complex endwall flow.
Friction and the Inverted Pendulum Stabilization Problem
Authors: Campbell Sue Ann , Crawford Stephanie , Morris Kirsten
Published: August 2008

We consider an experimental system consisting of a pendulum, which is free to rotate 360deg, attached to a cart. The cart can move in one dimension. We study the effect of friction on the design and performance of a feedback controller, a linear quadratic regulator, that aims to stabilize the pendulum in the upright position. We show that a controller designed using a simple viscous friction model has poor performance—small amplitude oscillations occur when the controller is implemented. We consider various models for stick slip friction between the cart and the track and measure the friction parameters experimentally. We give strong evidence that stick slip friction is the source of the small amplitude oscillations. A controller designed using a stick slip friction model stabilizes the system, and the small amplitude oscillations are eliminated.
Minimax Input Shaper Design Using Linear Programming
Authors: Singh Tarunraj
Published: August 2008

The focus of this paper is on the design of robust input shapers where the maximum value of the cost function over the domain of uncertainty is minimized. This nonlinear programming problem is reformulated as a linear programming problem by approximating a n-dimensional hypersphere with multiple hyperplanes (as in a geodesic dome). A recursive technique to approximate a hypersphere to any level of accuracy is developed using barycentric coordinates. The proposed technique is illustrated on the spring-mass-dashpot and the benchmark floating oscillator problem undergoing a rest-to-rest maneuver. It is shown that the results of the linear programming problem are nearly identical to that of the nonlinear programming problem.
Command Shaping for Flexible Systems Subject to Constant Acceleration Limits
Authors: Danielson Jon , Lawrence Jason , Singhose William
Published: August 2008

Input shaping is an effective means of eliminating vibration in many types of flexible systems. This paper discusses how input shaper performance is affected by a fixed acceleration limit. This type of limit is a common occurrence in many mechanical drive systems because it corresponds to a constant force or torque input. It is shown that some input shapers are not affected by an acceleration limit under certain conditions. A test criterion is developed to determine what types of input shapers are negatively affected, and a method is proposed to compensate for the detrimental effects of the constant acceleration limit. Experimental results from an industrial crane support the main theoretical results.
Initial Development of a Numerical Methodology to Simulate the Roller Expansion Forming Process
Authors: Manu Corneliu , Babu Suresh , Baset Saleh , Millard Julian
Published: August 2008

A distinguishing design feature of CANDU® nuclear reactors is the use of horizontal fuel channels housed in a horizontal vessel called a calandria, which is made of stainless steel 304L. Each channel consists of a Zr-2.5%Nb alloy pressure tube and an externally concentric Zr-2 calandria tube. The calandria tubes are joined to the end plates (tubesheets) of the calandria vessel by joints formed by roller expansion. The bores in the tubesheets are grooved. Roller expanded joints provide a cost effective means of joining dissimilar materials, require minimal space and no maintenance. The quality of these roller expanded joints is important from a sealing, strength and stress corrosion point of view. The roller expansion process consists of expanding the calandria tubes to deform them plastically against the bores and into the grooves of the tubesheets. Therefore, understanding the effect of the number, geometry and the pitch of the grooves on the quality of a roller expanded joint is very important. The objective of this paper is to present a numerical methodology developed to optimize the design of such roller expanded joints with particular interest on the effect of the grooves. This numerical analysis was used as an adjunct to assist the related design test program. The numerical techniques required to simulate the behaviour of calandria tubes during roller expansion involve the evaluation of large deformations, large plastic strains and stresses and rapidly changing contacts. The LS-DYNA general-purpose finite element computer code was selected for such simulations. A three-dimensional finite element model was developed so that the sweeping of the rollers while under outward radial movement is properly modelled and the plastic deformation and flow of the calandria tube material into the tubesheet grooves are accurately simulated. The paper discusses this numerical methodology, presents results of general interest, and makes comparisons with associated experimental data and other available results.
New Weld Joint Strength Reduction Factors in the Creep Regime in ASME B31.3 Piping
Authors: Becht Charles
Published: August 2008

The 2004 edition of ASME B31.3, Process Piping, includes strength reduction factors that apply to welds operating in the creep regime for the material. These factors apply to allowable stresses for sustained loads such as weight and pressure. This paper describes the background for the rules.
New Piping Flexibility Rules in ASME B31.3, Appendix P
Authors: Becht Charles , Diehl David W.
Published: August 2008

Alternative rules for performing flexibility analysis were added, as Appendix P, in ASME B31.3, the Process Piping Code, 2004 edition. These rules are considered to be more comprehensive; they were designed around computer flexibility analysis. To compute stress range, the difference in stress states, considering all loads, is computed. This paper describes the new rules, their intent, and provides several example piping stress analyses, comparing the results of an analysis using the Appendix P rules with that using the rules in the base Code.
Simulation of Structural Deformations of Flexible Piping Systems by Acoustic Excitation Using Modal Controllabilities
Authors: Maess Matthias K. , Gaul Lothar
Published: August 2008

Valve action and pump fluctuation in piping systems can lead to undesired excitation of structural components by propagating sound waves in the fluid path. This vibro-acoustic problem is addressed by studying the dynamics as well as excitation mechanism. Fluid-structure interaction has a significant influence on both hydroacoustics and on structural deformation. Therefore, pipe models are generated in three dimensions by using Finite Elements to include higher-order deflection modes and fluid modes. The acoustic wave equation in the fluid is hereby fully coupled to the structural domain at the fluid-structure interface. These models are used for simulating transient response and for performing numerical modal analysis. Unfortunately, such 3D models are large and simulation runs turn out to be very time consuming. To overcome this limitation, reduced pipe models are needed for efficient simulations. The proposed model reduction is hereby based on a series of modal transformations and modal truncations, where focus is placed on the treatment of the nonsymmetric system matrices due to the coupling. Afterwards, dominant modes are selected based on controllability and observability considerations. Furthermore, modal controllabilities are used to quantify the excitation of vibration modes by white noise at the pipe inlet representing acoustic sources. The excitation of structural elements connected to the piping system can therefore be predicted without performing transient simulations. Numerical results are presented for spatially arranged complex piping systems including elbow pipes and joints connected to target structures to demonstrate the usefulness of the presented method for vibro-acoustic investigations. The method is to support the design and the analysis of fluid-filled elastic piping systems and its environment in the presence of acoustic sources such as in hydraulic systems.
Description of Rules of Section XII Transport Tank Code
Authors: Rana Mahendra D. , Staniszewski Stanley , Voorhees Stephen V.
Published: August 2008

ASME Section XII Transport Tank Code was published in July 2004. This newly developed Code which provides rules for construction and continued service of pressure vessels used in transportation of dangerous goods via highway, rail or water. This paper presents a broad overview of Section XII. The main topics included in the paper are: scope and general requirements, materials and design, and fabrication, inspection and testing requirements.
On a Process of Rapid Estimation of Seismic Demands for Generic Steel Frame Structures
Authors: Lin Chiung-Yueh , Chen Wei-Zhi , Jan Tysh-Shang
Published: August 2008

The seismic demands of tall buildings can be evaluated by nonlinear response history analysis with some more representative, site-dependent, earthquakes, or by pushover analysis. However, the process of the evaluation is tedious and time consuming. Therefore, it is desirable to have a simplified process that provides quick and reasonable estimates of seismic demands, especially in the stage of conceptual (preliminary) design. Gupta & Krawinkler (2000) has reached on a process in the estimation of roof and story drift demands for frame structures from the spectral displacement at the first period of the structure, through a series of modification factors, accounting for MDOF effects, inelasticity effects, and P-delta effects. It is found that this process can estimate seismic demands reasonably, provided that no negative post-yield story stiffness exists. Also, the modification factors are uniform or with reasonable dispersion, except for structures dominated by higher mode effects. This study has conducted a similar research by performing simulations on Taiwan code–compliant structures of different heights (2,5,10,20 and 30 stories), located in different seismic zones and subjected to sets of local ground motions. The feature of this study is that the seismic demands are estimated from the SRSS of the elastic, modal roof displacements of the structure, instead of the first mode spectral displacement. The simulation results have shown that the modification factors are more promising — uniform or with more reasonable dispersion — even the structure is dominated by high mode effects. Therefore, it is concluded that the process proposed in this study is a feasible method and the modification factors obtained in this study are useful for local engineer in engineering applications.
Design and Qualification of AL-R8 2040 Sealed Insert Container
Authors: Black Michael , Addington Jeff , Hoff Tommy
Published: August 2008

The end of the Cold War, coupled with weapons reduction agreements, resulted in large numbers of nuclear weapons that are required to be dismantled. After the weapons are dismantled, certain radioactive components must be stored and maintained in a controlled environment. A graded approach is used in selecting the baseline criteria. Site-specific conditions, operating procedures/practices, National Design Agency weapon specific requirements, and DOE requirements are first evaluated to establish a baseline. Additionally, the design criteria provided in 10CFR71 are adopted as-is or modified to reflect the site-specific conditions. To accomplish this controlled storage environment, containers have been designed so that the internal atmosphere may be kept consistent throughout a minimum design life of 30 years. The most recent storage container design is the AL-R8 2040 Sealed Insert. This report will summarize the design and qualification activities associated with this container.
Piping Local Stresses for Solid Versus Hollow Attachments
Authors: Basavaraju C. , Fox R. C.
Published: August 2008

The simple and most commonly used WRC-107 (Welding Research Bulletin #107) Bijlaard methodology for local stress evaluation addresses cylindrical shells and pipes with solid circular, rectangular, and square attachments only. Hollow circular, square, or rectangular tubular shaped attachments on cylindrical shells, though commonly used, are not addressed in WRC-107. ASME Code Case N-392 addresses hollow circular attachments on pipes but is known to be conservative. This paper studies commonly encountered sizes of hollow circular, hollow square, and hollow rectangular attachments of various wall thicknesses on piping utilizing rigorous finite element analysis (FEA) method to obtain the local stresses at the pipe/attachment interface due to mechanical loads. A total of fifty (50) finite element models were analyzed to study the most frequently used configurations. The impact of attachment wall thickness including solid attachment will be addressed. A comparison of finite element results with WRC-107 solid attachment results, when applicable, will be made. Recommendations and guidelines are provided based on the results of the FEA study. The objective is to reduce conservatism, and hence the associated cost in piping and pipe support design by optimizing the round attachment’s wall thickness.
Assessment of Long-Term Creep Strength and Review of Allowable Stress of High Cr Ferritic Creep Resistant Steels
Authors: Kimura Kazuhiro
Published: August 2008

Large drop in creep rupture strength in the long-term is a noticeable phenomenon for high Cr ferritic creep resistant steels, and the neglecting this phenomenon may result in overestimation of 100,000h creep rupture strength, and allowable stress. A committee at Japan Power Engineering and Inspection Corporation was organized to evaluate long-term creep strength and to review current allowable stresses of high Cr ferritic creep resistant steels. Life prediction method for high Cr ferritic creep resistant steels with tempered martensite microstructure is discussed. Appropriateness of current allowable tensile stress regulated in METI (Ministry of Economy, Trade and Industry) Thermal Power Standard Code has been assessed on a modified 9Cr-1Mo steel (ASME Gr.91) and KA-SUS410J3 type steels. KA-SUS410J3 is a material specification in METI Thermal Power Standard Code and corresponds to ASME Gr.122. The validity of existing allowable stress was shown on a modified 9Cr-1Mo steel. Those for KA-SUS410J3 type steels, however, have been revised to the lower values.
Fitness for Service Assessment of Circumferential Cracks at Pipe Penetrations
Authors: Ellis Fred V.
Published: August 2008

An engineering study of the main steam line pressure tap cracking was performed. The failure mechanism was thermal fatigue and the circumferential cracks initiate at the pipe penetration on the inside surface of the pipe. Based on the results, a parametric fitness for service study was performed to develop a flaw tolerance graph to be used for the evaluation and disposition of detected defects. The parameters are pipe diameter, penetration diameter, and inspection interval. The objective is to determine the value of the current crack size when weld repair is needed. The fatigue crack growth calculations used the NASGRO computer program. The crack geometries were a single corner crack from a hole in a plate and a corner crack from a hole in a plate with two cracks. The analysis used the properties for Grade 22 plate material given in the program and applied a correction factor (69 cycles for Grade 22 at room temperature equals 1 fatigue cycle with hold time of 12 hours for P11) to account for the pipe material of P11, 1-1/4Cr-1/2Mo and the nominal operating temperature of 482°C. There were approximately 40 cold starts and 210 hot starts per year for the unit. The magnitude of the remote stress depended on the temperature range for the hot and cold starts. The applied stress consisted of tension and bending stresses and was estimated by the observed failure life of approximately 20 years for the 3/4 penetration in the pipe size 18 pipe.
Fatigue and Corrosion Fatigue Failures
Authors: Ellis Fred V.
Published: August 2008

A metallurgical failure analysis was performed for a hanger rod and a waterwall tube sample. The hanger is a rigid type and supports a long vertical run of piping. The fracture is in one of the threaded ends and the fracture surface consists of three regions. The outermost portion adjacent to the thread root has ratchet marks that are an indication of fatigue crack initiation. The center portion has concentric, oval shaped beachmarks. The oval shape is consistent with an applied loading due to two bending moments. The inner portion is the final fracture and is approximately 1/4 of the thread root area indicating relatively low remote stresses. The failure mechanism is fatigue based on the beachmarks on the fracture surface and the transgranular cracking. The lower slope waterwall tube failure had a window opening fracture appearance. The axial fractures forming the window are located at the edge of the membrane welds on the cold or backside. There are shallow toe cracks at the membrane weld on the tube outside surface. The fracture surface had multiple, thumbnail-shaped fatigue cracks connected to the inside surface. These fatigue cracks are due to the corrosion fatigue mechanism based on two factors: (1) the stress responsible for their growth is related to the unit thermal cycling and the welded panel geometry near the corner of the boiler, and (2) they are oxidized indicating a corrosion contribution.
Thermoelastic Stresses in Thick-Walled Vessels Under an Arbitrary Thermal Transient via the Inverse Route
Authors: Segall A. E.
Published: August 2008

A common threat to thick-walled vessels and pipes is thermal shock from operational steady-state or transient thermoelastic stresses. As such, boundary conditions must be known or determined in order to reveal the underlying thermal state. For direct problems where all boundary conditions are known, the procedure is relatively straightforward and mathematically tractable as shown by recent studies. Although more practical from a measurement standpoint, the inverse problem where boundary conditions must be determined from remotely determined temperature and/or flux data is ill-posed and inherently sensitive to errors in the data. As a result, the inverse route is rarely used to determine thermal-stresses. Moreover, most analytical solutions to the inverse problem rely on a host of assumptions that usually restrict their utility to timeframes before the thermal wave reaches the natural boundaries of the structure. To help offset these limitations and at the same time solve for the useful case of a thick-walled cylinder exposed to thermal loading on the ID, the inverse problem was solved using a least-squares determination of polynomial coefficients based on a generalized direct-solution to the Heat Equation. Once the inverse problem was solved in this fashion and the unknown boundary-condition on the ID determined, the resulting polynomial was used with the generalized direct solution to estimate the internal temperature and stress distributions as a function of time and radial position. For a thick-walled cylinder under an internal transient with external convection, excellent agreement was seen with various measured temperature histories. Given the versatility of the polynomial solutions advocated, the method appears well suited for many thermal scenarios provided the analysis is restricted to the time interval used to determine the polynomial and the thermophysical properties that do not vary with temperature.
Triaxial Stress Analysis of Cylindrical Pressure Vessels Composed of Two Layers of Orthotropic Elasto-Plastic Materials
Authors: Okamoto S. , Omura Y.
Published: August 2008

A triaxial stress analysis method for pressure vessels composed of two layers of orthotropic elasto-plastic materials is presented. The validity of the formulation and the corresponding computer program is examined by comparing the results of the program with the numerical results of a finite-element analysis. A simulation of the self-constriction process is also performed for a pressure vessel composed of an inner layer of aluminum alloy (A6061BE-T6) and an outer layer of fiber-reinforced plastic (FRP).
Thermal Elastic-Plastic Stress Analysis of Structural Elements With Creep
Authors: Sarala R. , Sutharson B. , Jaya Kanth D.
Published: August 2008

Finite element analysis of thermo-mechanical problems is reported here. From the literature, it may be seen that the thermal-elastic plastic analysis of structural elements has continued to remain a research topic for a couple of decades. No one computationally verified the thermal elastic plastic stress analysis with creep using triangular elements or quadrilateral elements. Finite element analysis code TSAP (Thermal Structural Analysis Programme) was developed in FORTRAN to handle the elastic-plastic stress analysis on two-dimensional planar or three dimensional axisymmetry structures subjected to combined thermal and mechanical loads. In this work, thermo elastic plastic analysis is extended to creep support. A triangular or quadrilateral element has been used to analysis of structures with inclusion of creep. The formulation is based on isotropic or kinematic hardening rule. The validation checks on the program are carried out using results available in the literature. The parameters are considered while analyses are (1.) Type of materials used (2.) Type of elements used (3.) Structure geometry (axisymmetry, plane stress or plane strain) (3.) Type of analysis (steady state or transient state) (4.) Type of loading (5.) Various boundary conditions (conductive or heat flux boundary) (6.) Effect of creep inclusion.
Design Formulas of Blind End Closures for High Pressure Vessels
Authors: Dixon R. D. , Perez E. H.
Published: August 2008

The available design formulas for flat heads and blind end closures in the ASME Code, Section VIII, Divisions 1 and 2 are based on bending theory and do not apply to the design of thick flat heads used in the design of high pressure vessels. This paper presents new design formulas for thickness requirements and determination of peak stresses and stress distributions for fatigue and fracture mechanics analyses in thick blind ends. The use of these proposed design formulas provide a more accurate determination of the required thickness and fatigue life of blind ends. The proposed design formulas are given in terms of the yield strength of the material and address the fatigue strength at the location of the maximum stress concentration factor. Introduction of these new formulas in a non-mandatory appendix of Section VIII, Division 3 is recommended after committee approval.
Simulations of Heat Transfer Within the Fuel Assembly/Backfill Gas Region of Transport Packages
Authors: Araya Go´mez Pablo E. , Greiner Miles
Published: August 2008

A two-dimensional computational model of a spent 7×7 Boiling Water Reactor assembly in a horizontal support basket was developed using the Fluent computational fluid dynamics package. Heat transfer simulations were performed to predict the maximum cladding temperature for assembly heat generation rates between 100 and 600W, uniform basket wall temperatures of 25 and 400°C, and with helium and nitrogen backfill gases. Different sets of simulations modeled conduction/radiation and natural convection/radiation transport across the gas filled regions to assess the importance of different transport processes. Simulations that included natural convection exhibited measurably lower cladding temperatures than those that did not only for nitrogen, at the lower basket wall temperature, and within an intermediate range of heat generation rates. Outside these conditions and for helium, conduction and radiation transport are sufficiently large so that natural convection has no measurable effect. Finally, the maximum cladding temperature is more sensitive to the assumed value of the fuel cladding emissivities when nitrogen is the backfill gas than when helium is used.
Geometric Non Linear Analysis of Composite Shells Under Thermomechanical Loading
Authors: Sutharson B. , Sarala R. , Thangarathanam R. Kari
Published: August 2008

A Geometric non-linear analysis of composite shells under thermomechanical loading has been discussed here. From the literature, it may be seen that the thermal stress analysis of structural elements has continued to remain a research topic for a couple of decades. No one computationally verified the geometric non-linear buckling of composite shells under thermomechanical loading using semiloof element. In this work, linear buckling analysis of Kari Thangaratnam (2) is extended to geometric non-linear analysis of composite shells under thermomechanical loading. A general shell element called the semiloof shell element has been extended to thermal stress analysis of laminated shells. The formulation is based on nonlinear theory and the finite element method using semiloof element. The validation checks on the program are carried out using results on homogeneous isotropic shells available in the literature. The parameters considered in analysis are (1) number of layers in the laminate, (2) Lay-up sequence (symmetry, antisymmetry, cross-ply etc.), (3) Fibre orientation angle, (4) Different aspect ratios, (5) Orthotrophy ratio, (6) Boundary conditions (simply supported, clamped and combination of boundary conditions).
Effects of Weld Geometry on Residual Stress and Crack Driving Force for Centerhole Control Rod Drive Mechanism Nozzles: Part I — Weld Residual Stress
Authors: Cheng Wentao , Rudland David L. , Wilkowski Gery , Norris Wallace
Published: August 2008

The U.S. Nuclear Regulatory Commission (NRC) has undertaken a program to assess the integrity of control rod drive mechanism (CRDM) nozzles in existing plants that are not immediately replacing their RPV heads. This two-part paper summarizes some of the efforts undertaken on the behalf of the U.S.NRC for the development of detailed residual stress and circumferential crack-driving force solutions to be used in probabilistic determinations of the time from detectable leakage to failure. In this first paper, the finite element (FE) simulations were conducted to investigate the effects of weld geometry on the residual stresses in the J-weld for a centerhole CRDM nozzle. The variables of weld geometry included three weld heights (weld sizes) and three groove angles for each weld height while keeping the same weld size. The analysis results indicate that the overall weld residual stress decreases as the groove angle increases and higher residual stress magnitude is associated with certain weld height. The results also reveal that the axial residual stresses in the Alloy 600 tube are very sensitive to the weld height, and that the tube hoop stresses above the J-weld root increase with the increasing weld height.
Effects of Weld Geometry on Residual Stress and Crack Driving Force for Centerhole Control Rod Drive Mechanism Nozzles: Part II — Circumferential Cracked K-Solutions
Authors: Rudland David L. , Cheng Wentao , Wilkowski Gery , Norris Wallace
Published: August 2008

The U.S.NRC has undertaken a program to assess the integrity of CRDM nozzles in existing plants that are not immediately replacing their RPV heads. This two-part paper summarizes some of the efforts undertaken on the behalf of the U.S.NRC for the development of detailed residual stress and circumferential crack-driving force solutions to be used in probabilistic determinations of the time from detectable leakage to failure. In this second paper, the weld residual stresses from the first paper were mapped onto detailed fracture mechanics finite element models that contained different length circumferential cracks in the CRDM centerhole nozzle. In each case, the cracks were unpinned after application of the operating pressure and temperatures and the K-solutions extracted. The results from these analyses suggest that the crack-driving force for a circumferential crack at the root of the J-weld slightly increases with increasing weld height but appears to be insensitive to bevel angle.
Heat Exchanger Bolt Stress Measurements
Authors: Guillot Michael W. , Findlay Matthew , Grimsley Corey T.
Published: August 2008

During a new plant startup a high pressure heat exchanger was subjected to significant thermal gradients and experienced a leak. The joint was modified and a new type of gasket was selected to eliminate the leakage. Several studs were instrumented with strain gages to gain a better understanding of the loading experienced during torquing and due to the gradients occurring during startup and normal operation. In addition to the strain gages, the temperature gradients in the flange were measured using 26 thermocouples. This paper presents the data obtained from the instrumented studs and thermocouples over a span of five months and summarizes the lessons learned. These included an assessment of the error in various bolting techniques, the benefit of bolting techniques such as multiple jack bolt tensioners, and the nature and effect of thermal gradients in flanges, the effects of spring washers on the magnitude of thermally induced loads, and problems arising from gasket quality control. Recommendations to improve the leak tightness of large diameter heat exchanger joints experiencing thermal gradients are presented.
Fatigue Evaluation Incorporating Multiaxiality of Stress States
Authors: Chattopadhyay Somnath
Published: August 2008

In this work the effects of multiaxiality on the fatigue evaluation by the ASME Boiler and Pressure Vessel Code procedures have been assessed. The conservatism associated with the Ke factor has been critically appraised for fatigue evaluation using a design example of a feed water nozzle subjected to pressure and thermal fluctuations. A fictitious stress concentrator is applied to account for the ratio of the peak stress to the stress linearized through the thickness of the section under consideration. The effect of the traxiality of the stress distribution has also been assessed using the same design example for fatigue evaluations. Additional analytical and experimental studies have been recommended to study these important critical factors for fatigue assessment.
An Approach for Analysing Boiler Tubes Ultrasonic Inspection Data to Support Decision Making
Authors: Noori Soudabeh A. , Price John W. H.
Published: August 2008

There is now much interest in the development of risk based strategies for maintenance planning including assessing appropriate inspection strategies and making economic life estimates of critical components. This study examines this problem from a practical point of view by studying a significant body of tube thickness inspection data collected in a power station. This data naturally has all sorts of difficulties. For example there are issues related to the accuracy and correctness of the measurements. Then there is the issue of how to use the data to determine deterioration rates and life expectancy. This paper examines this data using: • a method developed by the authors: a procedure based on a “warning level” approach, and • a suggested interpretation of the American Petroleum Institute’s technique of “risk based inspection”.
Wear Testing of Bushings During the Cyclic Process
Authors: Campbell Judd , Gray Nathan N. , Wiley Tim , Shields Elvin B.
Published: August 2008

Excessively worn bushings and shafts lead to the destruction of machines and pose safety hazards. In particular, mining machines can have twenty or more articulating joints and are subject to extremely harsh conditions. It is desirable to use a bushing-shaft combination that will yield the longest life with minimal maintenance. This study provides accelerated test cases using different shaft and bushing materials subjected to a variety of environments typically seen in underground mining. Through the use of Design of Experiments (DOE), nine initial combinations of bushings, shafts, and environments were subjected to testing. The tests simulated the loads and articulation of a shear jack on a Joy 12CM miner. The DOE computer program predicted the results of many variables while at the same time decreasing the number of physical tests that had to be done. The goal of the physical testing was to find the bushing with the best wear characteristics to provide the longest life on a mining machine. This data can be used to facilitate maintenance and replace bushings before total failure. This will save wear and tear on machines and reduce downtime.
Residual Stresses Evaluation in Welds and Implications for Design for Pressure Vessel Applications
Authors: Price John W. H. , Paradowska Anna , Finlayson Trevor
Published: August 2008

Welding residual stresses have important consequences on the performance of engineering components. High residual stresses lead to loss of performance in corrosion, fatigue and fracture but as yet these consequences are poorly quantified. The major cause of this is that residual stress often remains the single largest unknown in industrial damage situations since they are difficult to measure or estimate theoretically. One of the key issues in the study of residual stress is that the detail of the stress distribution on a small scale (in the order of millimetres) can be important. In this paper, the neutron diffraction technique is used which while it is a very expensive technique, is capable of non-destructively measuring residual stresses at this scale up to a depth of 35mm. The investigation reported compares the residual stress characteristics due to various restraints for a single bead and in fully restrained samples with different numbers of beads. The findings have important consequences with respect to design of welding procedures and fitness for purpose assessments.
Thermal Shock Cracking: Design and Assessment Guidelines
Authors: Price John W. H.
Published: August 2008

Repeated thermal shock cracking is common in the operation of pressure equipment where water and steam are present. Surprisingly it is not directly covered in the ASME Boiler and Pressure Vessel code nor in fitness-for-purpose recommended practice such as API 579. An example of thermal shock stresses occurs when hot surfaces exposed to splashing of cold water. This eventually may lead to crack nucleation and crack growth. However not all thermal shock cracks lead to failures (such as rupture, leak or in more brittle material fragmentation), indeed the most frequent situation is that the cracking arrests at a depth of a few millimeters. This paper presents a unique experimental study and analysis the information being gained from this study in terms of design guidelines and crack growth mechanisms. In the experiments, cracks are initiated and then grown in low carbon steel specimens exposed to repeated thermal shock. The test-rigs achieve large thermal shocks through the repeated water quenching of heated flat plate specimens. The effect of steady state loads on the growth and environmental effects due to the aqueous nature of the testing environment are found to be major contributors to the crack growth kinetics. The most important findings are that are that the conditions leading to both the initiation and the arrest of cracks can be identified and that the depth of a starter notch contributes little to the crack propagation.
The Mode III Elastic Stress Distribution in the Immediate Vicinity of an Inclusion
Authors: Smith E.
Published: August 2008

As part of a wide ranging research programme aimed at developing a fracture mechanics methodology for blunt notches, earlier work for a general two-dimensional blunt notch Mode III model has shown that the stress at a distance × ≪ ρ (notch root radius of curvature) ahead of the notch root only depends on x, ρ and the peak stress σp, irrespective of the notch shape and the loading characteristics. This uniqueness has been confirmed for various notch profiles and loading scenarios. In this paper we show that the uniqueness of the local stress distribution is peculiar to a notch and does not apply to an inclusion.
Justification of the Small Process Zone Case of the Two Extremes Procedure for Quantifying Fracture Initiation at a Blunt Flaw
Authors: Smith E.
Published: August 2008

With the cohesive process zone representation of the micro-mechanistic processes that are associated with fracture as a basis, the author is involved in a wide-ranging research programme, the objective being to extend the sharp crack fracture mechanics methodology to blunt flaws, so as to take credit for the blunt flaw geometry. In earlier work, a blunt flaw fracture initiation relation has been derived, subject to the restriction that the process zone size s is small compared with the flaw depth (length) or any characteristic dimension of a configuration other than the root radius ρ. This relation gives the critical elastic flaw-tip peak stress σpcr, and has been derived using a two extremes procedure, whereby the separate solutions for small and large s/ρ are blended together so as to give a single relation that is valid for the complete spectrum of s/ρ values. The small s/ρ solution was obtained by inputting the stress field in the immediate vicinity of the flaw root into an analysis of the behaviour of a process zone at a planar surface. This paper provides formal justification for this small s/ρ procedure.
Butane Storage Bullet Calculation and FEA Verification
Authors: Wang Zhanghai , Bast Daryl , Shen David
Published: August 2008

This paper presents a comparative study of FEA with the Zick’s method of analysis for a two saddles-supported horizontal cylindrical tank. Zick’s method is an analytical method commonly used in horizontal vessel support design. We used two methods to calculate local stresses in selected areas with the findings that the results of these two methods produced very agreement. These results are used to verify the FEA for this application. We then used FEA to get more detailed information about stress distribution, which cannot be obtained using the Zick’s method. FEA was further used to study the buckling behavior of the object and to determine some critical parameters of the object, e.g., the vacuum ring weld size with consideration of both external and internal loads.