bluuebunny/crossref_metadata_2025 huggingface dataset:
Creep Rupture of Anisotropic Pipes
Authors: Shesterikov S. A. , Lokochtchenko A. M. , Mjakotin E. A.
Published: February 2008

The problem of creep rupture of pipes from an anisotropic material is studied. The authors suggest a method describing the results of creep rupture tests on thin-walled pipes under complex stress state by taking the strength anisotropy of material into account. A coefficient of strength anisotropy has been determined from the results of creep rupture testing, and a method is given for calculation under various modes of complex stress state. This procedure is based on evaluating the values of the statistical spread from the experimental data. The anisotropy coefficient corresponding to the minimum spread is adopted. The suggested method of calculating the strength anisotropy coefficient is confirmed experimentally.
Mechanical Behaviors of Bolted Joint in Various Clamping Configurations
Authors: Fukuoka T. , Takaki T.
Published: February 2008

In a bolted joint, failures usually initiate at the first root of the bolt thread. However, rupture around the bolt head is sometimes reported for a tap bolt because of high stresses produced by tightening torque applied to the bolt head. It is also well known that manufacturing errors of internal threads in a tapped hole are generally much larger than those of external threads, thus leading to the failures concerned. In this paper, mechanical behaviors of bolted joints in various clamping configurations are analyzed using FEM as multi-body elastic contact problem, and the effects of nominal diameter, friction and pitch error upon stress concentrations are evaluated for through bolts, studs, and tap bolts. It is then quantitatively estimated on the effectiveness of “recessed internal threads” for reducing the stress concentration occurred around the far end of bolt hole. In addition, the tightening process and strength of a bottoming stud, which have seldom been studied despite favorable performance in preventing stress concentration at the runout of threads, are also investigated.
The Support of Horizontal Vessels Containing High-Temperature Fluids—A Design Study
Authors: Tooth A. S. , Cheung J. S. T. , Ong L. S. , Ng H. W. , Nadarajah C.
Published: February 2008

This paper investigates the behavior of horizontal cylindrical vessels, subjected to thermal loading by high-temperature fluid, where the saddles are fixed to the supporting structure. In order to determine an optimum saddle design, three widely used saddle configurations, with differing saddle heights and top saddle plate extensions, are explored. Thereafter, one of the saddle designs is selected to illustrate a decoupling procedure, for the radial and axial expansions, whereby design charts are obtained to derive the maximum stress values for a range of vessel geometries. The finite element approach, using linear elastic, small displacement analysis, is used throughout.
Reliability Assessment of Mechanical Components Using Fuzzy-Set Theory
Authors: Tang J.
Published: February 2008

An approach to assessing the reliability of mechanical components, especially for pressure vessels and piping, is proposed in which the vagueness and fuzziness in variables have been considered. In this method, a fuzzy-random reliability model is developed by using a fuzzy-set theory. This particular theory can be described as a generalization of the classical set theory. Using a fuzzy-set theory, a failure event is defined in a more flexible form than usual. In particular, the concept of nonfuzzy probability of fuzzy events is used to derive a reliability approach which includes the subjectivity of human judgement. Meanwhile, a constructive way for generating a membership function of a fuzzy set is also provided in the paper.
Centrifugal Compressor Modifications and Their Effect on High-Frequency Pipe Wall Vibration
Authors: Motriuk R. W. , Harvey D. P.
Published: February 2008

High-frequency pulsation generated by centrifugal compressors, with pressure wavelengths much smaller than the attached pipe diameter, can cause fatigue failures of the compressor internals, impair compressor performance, and damage the attached compressor piping. There are numerous sources producing pulsation in centrifugal compressors. Some of them are discussed in literature at large (Japikse, 1995; Niese, 1976). NGTL has experienced extreme high-frequency discharge pulsation and pipe wall vibration on many of its radial inlet high-flow centrifugal gas compressor facilities. These pulsations led to several piping attachment failures and compressor internal component failures while the compressor operated within the design envelope. This paper considers severe pulsation conditions at an NGTL compression facility which resulted in unacceptable piping vibration. Significant vibration attenuation was achieved by modifying the compressor (pulsation source) through removal of the diffuser vanes and partial removal of the inlet guide vanes (IGV). Direct comparison of the changes in vibration, pulsation, and performance are made for each of the modifications. The vibration problem, probable causes, options available to address the problem, and the results of implementation are reviewed. The effects of diffuser vane removal on discharge pipe wall vibration as well as changes in compressor performance are described.
Vibration Damping in Multispan Heat Exchanger Tubes
Authors: Taylor C. E. , Pettigrew M. J. , Dickinson T. J. , Currie I. G. , Vidalou P.
Published: February 2008

Heat exchanger tubes can be damaged or fail if subjected to excessive flow-induced vibration, either from fatigue or fretting-wear. Good heat exchanger design requires that the designer understands and accounts for the vibration mechanisms that might occur, such as vortex shedding, turbulent excitation or fluidelastic instability. To incorporate these phenomena into a flow-induced vibration analysis of a heat exchanger requires information about damping. Damping in multispan heat exchanger tubes largely consists of three components: viscous damping along the tube, and friction and squeeze-film damping at the supports. Unlike viscous damping, squeeze-film damping and friction damping are poorly understood and difficult to measure. In addition, the effect of temperature-dependent fluid viscosity on tube damping has not been verified. To investigate these problems, a single vertical heat exchanger tube with multiple spans was excited by random vibration. Tests were conducted in air and in water at three different temperatures (25, 60, and 90°C). At room temperature, tests were carried out at five different preloads. Frequency response spectra and resonant peak-fitted damping ratios were calculated for all tests. Energy dissipation rates at the supports and the rate of excitation energy input were also measured. Results indicate that damping does not change over the range of temperatures tested and friction damping is very dependent on preload.
The Response of a Partially Confined Detonation Facility to Blast Loading
Authors: Lind C. A. , Boris J. P. , Oran E. S. , Mitchell W. J. , Wilcox J. L.
Published: February 2008

It is estimated that more than 500,000 tons of obsolete and unwanted conventional weapons exist in the United States. The disposal of these unexploded ordnances, in an environmentally sound and cost-effective way, is of paramount importance. Open-air burning and open-air detonation (OB/OD) are two of the most widely used methods to dispose of these unwanted energetic materials. This paper describes our efforts to improve OB/OD operations through the design and testing of a new, large-scale, partially confined facility that minimizes the adverse affects of far-field noise and maximizes the afterburn of explosive by-products. Several designs were evaluated by a series of axisymmetric, time-dependent numerical simulations using FAST3D, a flux-corrected transport-based code optimized for parallel processing. The simulations are used to test various facility geometries and placements and sizes of charges to determine combinations that result in acceptable environmental impact. Comparisons of the pressure and structural analyses for 50 and 100 lb of spherically shaped RDX charges show that the 50-lb spherically shaped charge placed at a height of approximately 2.0 m resulted in an efficient detonation and maintained the structural integrity of the detonation facility.
Life Prediction in High-Temperature Structural Materials
Authors: Jaske C. E.
Published: February 2008

Life prediction methods are required to assess the performance and safety of the structural materials used in engineering systems and components that operate at high temperatures. At high temperatures, materials are subject to time-dependent creep environmental degradation, as well as cycle-dependent fatigue degradation. The life prediction methods must account for all of these degradation mechanisms and their possible interactions. The purpose of this paper is to review the methods that are used predict the creep and fatigue life of structural materials. Traditional methods that have been used to predict the life of structural materials are based on the initiation of a significant crack; whereas more recent methods employ fracture mechanics to predict life based on the growth of crack from some initial size to a critical size. Crack-growth-based life prediction methods are emphasized in this review.
Buckling of Unbalanced, Sandwich Panels With Titanium and GRP Skins
Authors: Kwon Y. W. , Murphy M. C. , Castelli V.
Published: February 2008

An unbalanced and asymmetric sandwich composite structure consisting of Titanium 6-4 and glass-reinforced plastic (GRP) skins with a phenolic honeycomb core is being considered for construction of a surface ship mast which will enclose critical shipboard equipment. Stability of the structure is one of the major concerns in the design process. This research focuses on analytical and experimental studies of an unbalanced composite sandwich beam subjected to a compressive axial load. The failure load (i.e., peak load) and failure mode of each skin material and the sandwich construction were measured at the laboratory. An analytical model was developed for predicting the failure load of the unbalanced and asymmetric sandwich composite configuration, including the transverse shear energy of the core material. The experimental data agreed very well with analytical prediction. Postbuckling failure, as well as residual strength after initial failure, were also studied.
Stress Analysis in Composite Hollow Cylinders due to an Asymmetric Temperature Distribution
Authors: Zibdeh H. S. , Al Farran J. M.
Published: February 2008

A solution is presented for the stresses and displacements in an orthotropic, hollow, circular cylinder subjected to asymmetric temperature distribution at the outer surface and heat convection into a medium at zero reference temperature at the inner surface. Assuming temperature-independent material properties, the heat conduction equation in cylindrical coordinates is solved for a single and multilayer cylinders. Results of temperature analysis along with linear elasticity theory are used to obtain the required thermal stresses and displacements. Numerical results are given for a typical fiber-reinforced composite material where fibers in each layer are oriented axially or circumferentially. The results show that the response of the cylinder is sensitive to changes in thickness, orientation of fibers in each layer, number of layers, and stacking sequence.
J Estimation Method for a Semi-Elliptical Surface
Flaw in a Cylinder
Authors: Yoon K. K. , Killian D. E.
Published: February 2008

With the emergence of readily available simple J solutions for various types of structures through J estimation techniques, J-integral-based elastic-plastic fracture mechanics has become a common tool for analyzing ductile materials. This paper presents elastic-plastic solutions for semi-elliptical surface flaws of four different crack depths. Solutions are developed from a series of finite element analyses using the ABAQUS computer program with a deformation plasticity material constitutive law. Although the solutions are directly applicable to a single set of Ramberg-Osgood material parameters, they may be extended to include various amounts of strain hardening by a ratioing technique utilizing calibration functions from the EPRI handbook for continuous flaws. This paper addresses cylindrical structures loaded by internal pressure, and excludes any consideration of thermal loadings. Elasticplastic J solutions, determined for pressures up to 5000 psi (12700 Pa), or twice the design pressure, depart from plastic-zone-corrected linear elastic predictions at approximately 3000 psi (7620 Pa) pressure. The h1 plastic calibration functions derived in this paper are limited to the point of greatest crack depth in 6:1 aspect ratio semi-elliptical inside surface flaws in cylindrical pressure vessels.
Study on Life Extension of Aged RPV Material Based on Probabilistic Fracture Mechanics: Japanese Round Robin
Authors: Yagawa G. , Yoshimura S. , Handa N. , Uno T. , Watashi K. , Fujioka T. , Ueda H. , Uno M. , Hojo K. , Ueda S.
Published: February 2008

This paper is concerned with round-robin analyses of probabilistic fracture mechanics (PFM) problems of aged RPV material. Analyzed here is a plate with a semi-elliptical surface crack subjected to various cyclic tensile and bending stresses. A depth and an aspect ratio of the surface crack are assumed to be probabilistic variables. Failure probabilities are calculated using the Monte Carlo methods with the importance sampling or the stratified sampling techniques. Material properties are chosen from the Marshall report, the ASME Code Section XI, and the experiments on a Japanese RPV material carried out by the Life Evaluation (LE) subcommittee of the Japan Welding Engineering Society (JWES), while loads are determined referring to design loading conditions of pressurized water reactors (PWR). Seven organizations participate in this study. At first, the procedures for obtaining reliable PFM solutions with low failure probabilities are examined by solving a unique problem with seven computer programs. The seven solutions agree very well with one another, i.e., by a factor of 2 to 5 in failure probabilities. Next, sensitivity analyses are performed by varying fracture toughness values, loading conditions, and pre and in-service inspections. Finally, life extension simulations based on the PFM analyses are performed. It is clearly demonstrated from these analyses that failure probabilities are so sensitive to the change of fracture toughness values that the degree of neutron irradiation significantly influences the judgment of plant life extension.
Normal Mode Theory as a Tool in Finite Element
Substructuring
Authors: Sebert K. A. , Scavuzzo R. J.
Published: February 2008

Two methods of substructuring finite element models are examined. Each method uses normal mode theory as the basis for selecting the appropriate modes for the substructure and the properties of the modes. One of the substructuring procedures uses component mode synthesis to attach the substructure to the residual structure, while the other method uses direct connection. The resulting combined models are evaluated for shock input using NASTRAN, and the results are compared to the analysis of the original model in each case.
A Technique to Distinguish the Primary and Secondary
Stresses
Authors: Eslami M. R. , Shariyat M.
Published: February 2008

A technique is developed which can be used to distinguish the primary and secondary stresses in pressure vessels. The general definition of the two types of stresses stated by the ASME Code is used; a simple viscoelastic model is proposed for each stress category. The proposed model can be extended to elastic as well as plastic regions of strain-hardening materials and can include the mechanical as well as thermal loads. The proposed viscoelastic models are used to judge the nature of elastic stresses and the effective stress-strain curve is used to simulate the state of stress at any stage of loading and the percentage of primary to secondary stresses at any radius of the vessel. It is found that thermal stresses cannot always be categorized as secondary stress, and in the case of thermoplastically loaded vessels they can contribute partly to the primary stress in the vessel.
Experiment of Chaotic Vibration of Loosely Supported Tube Rows in
Cross-Flow
Authors: Chen S. S. , Zhu S. , Cai Y.
Published: February 2008

A tube array supported by baffle plates in cross-flow may be subjected to fluidelastic instability in the tube-support-plate-inactive mode. An experimental study is presented to characterize the tube motion. Three series of tests were performed to measure tube displacements as a function of flow velocity for differing clearances. The motion was examined by root-mean-square values of tube displacements, power spectral densities, phase planes, Poincare´ maps, and Lyapunov exponents. The experimental data agree reasonably well with an analytical model based on the unsteady flow theory.
Fatigue Life Analyses and Tests for Thick-Wall Cylinders Including
Effects of Overstrain and Axial Grooves
Authors: Underwood J. H. , Parker A. P.
Published: February 2008

A fracture mechanics-based fatigue life analysis was developed for overstrained, pressurized thick-wall cylinders with one or several semi-elliptical-shaped axial grooves at the inner diameter. The fatigue life for a crack initiating at the root of the groove was calculated for various cylinder, groove, and crack configurations and for different material yielding conditions. Comparisons were made with fatigue crack growth and laboratory life results from A723 thick-wall cylinders, in which cannon firing tests were first performed to produce axial erosion grooves, followed by cyclic hydraulic pressurization to failure in the laboratory. The life analysis, with an initial crack size based on the expected preexisting defects, gave a good description of the crack growth and fatigue life of the tests for cylinders with and without grooves. General fatigue life calculations summarized important material and configurational effects on the fatigue life design of overstrained cylinders, including effects of material yield strength, cylinder diameter ratio, stress concentration factor, and initial crack size.
The Effect of Water Flow Rate Upon the Environmentally Assisted
Cracking Response of a Low-Alloy Steel
Authors: James L. A. , Wire G. L. , Cullen W. H.
Published: February 2008

The effect of water flow rate upon the environmentally assisted cracking (EAC) response of a high-sulfur ferritic steel was studied at a temperature of 243°C. In contrast to earlier studies which employed compact-type specimens, this study employed relatively large tight semi-elliptical surface cracks tested under generally linear-elastic conditions. Flow velocities parallel to the crack as low as 1.58–1.84 m/s were effective in mitigating EAC.
Stress-Strain and Failure Analyses of Composite Pipe Under
Torsion
Authors: Zhao Y. , Pang S. S.
Published: February 2008

An analytical and experimental study was conducted to investigate the elastic and failure behavior of composite laminated pipe under torsion. The analytical model was developed based on the mechanics of composite materials and the maximum strain failure criterion. Five composite pipe samples were tested on a specially designed pipe torsional tester. A finite element analysis was also performed to be compared with the analytical and experimental results. The relationship between applied torque and shear strain and between torque and torsional angles was obtained by all three methods. The effects of fiber angle and its deviation were also studied.
B31.3 Appendix X Rules for Expansion Joints
Authors: Becht C.
Published: February 2008

In 1988, ASME B31.3 added Appendix X containing requirements for Metallic Bellows Expansion Joints into the Chemical Plant and Petroleum Refinery Piping Code. These have been revised and improved in subsequent addenda to the Code. This paper describes some of the salient features of this Appendix, as well as the revisions and the background behind them.
Experimental Fretting-Wear Studies of Steam Generator
Materials
Authors: Fisher N. J. , Chow A. B. , Weckwerth M. K.
Published: February 2008

Flow-induced vibration of steam generator tubes results in fretting-wear damage due to impacting and rubbing of the tubes against their supports. This damage can be predicted by computing tube response to flow-induced excitation forces using analytical techniques, and then relating this response to resultant wear damage using experimentally derived wear coefficients. Fretting-wear of steam generator materials has been studied experimentally at Chalk River Laboratories for two decades. Tests are conducted in machines that simulate steam generator environmental conditions and tube-to-support dynamic interactions. Different tube and support materials, tube-to-support clearances, and tube support geometries have been studied. The effect of environmental conditions, such as temperature, oxygen content, pH and chemistry control additive, have been investigated as well. Early studies showed that damage was related to contact force as long as other parameters, such as geometry and motion, were held constant. Later studies have shown that damage is related to a parameter called work-rate, which combines both contact force and sliding distance. Results of short and long-term fretting-wear tests for CANDU steam generator materials at realistic environmental conditions are presented. These results demonstrate that work-rate is an appropriate correlating parameter for impact-sliding interaction.
A Practical Method Based on Stress Evaluation
(σd Criterion) to Predict Initiation of
Crack Under Creep and Creep-Fatigue Conditions
Authors: Moulin D. , Drubay B. , Acker D. , Laiarinandrasana L.
Published: February 2008

The behavior of defects like cracks in nuclear components operating at high temperature, where creep is significant, must be under control. There exists the need to have a practical method of analysis, which can be used by engineers, to calculate the time of initiation for defects existing at the start of life of nuclear components. This study presents the background, the development, the application, and results concerning validation work made for a simplified method named σd of prediction of initiation for nuclear structures made of 316L austenitic steel and operating at temperature where creep is significant. This method relies on the evaluation of real stress-strain history on a small distance d (d = 0.05 mm) close to the crack front and material characteristics (limiting stresses) that are available in nuclear codes like ASME Code cases or RCC-MR.
Ramberg-Osgood Strain-Hardening Characterization of an ASTM A302-B
Steel
Authors: James L. A.
Published: February 2008

The Ramberg-Osgood strain-hardening exponents and coefficients are characterized for an unirradiated ASTM A302-B steel over a wide range of temperatures from −129 to 260°C. The strain-hardening exponent increases only slightly with temperature over this range, while the coefficient decreases with increasing temperature. Tensile specimens irradiated to 0.002, 0.029, and 0.046 dpa exhibited significant increases in the strain-hardening exponent with increasing neutron irradiation level.
Alternative Method of RTNDT Determination
for Some Reactor Vessel Weld Metals Validated by Fracture Toughness
Data
Authors: Yoon K. K.
Published: February 2008

The fracture toughness curves used for nuclear power plant operation pressure-temperature limits and for pressurized thermal shock evaluations are dependent on the reference temperature for nil-ductility transition (RTNDT). The original method to determine the RTNDT was formulated more than 20 yr ago when Section III of the ASME Code was adopted. At that time, there were insufficient data to judge whether some of the weld metals used in reactor vessel fabrication were unsuitable for this procedure. Presently, this causes a compliance problem for some weld metals used in nuclear reactor vessels, whereas there is no technical problem in meeting required safety margins. The RTNDT is a parameter to index degrees of irradiation embrittlement to adjust the Code reference fracture toughness curves to represent the actual degraded fracture toughness at a given fluence of a reactor vessel beltline region. When there is a problem determining RTNDT value for unirradiated material where Charpy transition temperature is the dominating criterion, an alternative RTNDT based solely on a drop-weight test was investigated for some of the weld metals. Using a new test method for fracture toughness in the transition range (ASTM, 1993), a fracture toughness curve was directly generated from a set of compact tension test data and used for validating the nil-ductility temperature (TNDT) from drop-weight test data as the sole mean for determining initial RTNDT value.
Elastoplastic Analysis of Layered Metal Matrix Composite Cylinders—Part I: Theory
Authors: Salzar R. S. , Pindera M.-J. , Barton F. W.
Published: February 2008

An exact elastic-plastic analytical solution for an arbitrarily laminated metal matrix composite tube subjected to axisymmetric thermo-mechanical and torsional loading is presented. First, exact solutions for transversely isotropic and monoclinic (off-axis) elastoplastic cylindrical shells are developed which are then reformulated in terms of the interfacial displacements as the fundamental unknowns by constructing a local stiffness matrix for the shell. Assembly of the local stiffness matrices into a global stiffness matrix in a particular manner ensures satisfaction of interfacial traction and displacement continuity conditions, as well as the external boundary conditions. Due to the lack of a general macroscopic constitutive theory for the elastic-plastic response of unidirectional metal matrix composites, the micromechanics method of cells model is employed to calculate the effective elastic-plastic properties of the individual layers used in determining the elements of the local and thus global stiffness matrices. The resulting system of equations is then solved using Mendelson’s iterative method of successive elastic solutions developed for elastoplastic boundary-value problems. Part I of the paper outlines the aforementioned solution strategy. In Part II (Salzar et al., 1996) this solution strategy is first validated by comparison with available closed-form solutions as well as with results obtained using the finite-element approach. Subsequently, examples are presented that illustrate the utility of the developed solution methodology in predicting the elastic-plastic response of arbitrarily laminated metal matrix composite tubes. In particular, optimization of the response of composite tubes under internal pressure is considered through the use of functionally graded architectures.
Nonlinear Effects on the Stresses and Deformations of Bolted Joints
Authors: Lehnhoff T. F. , Wistehuff W. E.
Published: February 2008

Axisymmetric finite element modeling of bolted joints was performed to show the effects of the magnitude as well as the radial location of the externally applied load on the member separation radius and the stress on the surface between the two members. The separation radius was found to be nonlinearly related to changes in the magnitude as well as position of the external load. A 27-percent decrease for 24-mm bolts to 39-percent decrease for 8-mm bolts in the separation radius resulted with changes in the load magnitude. The external load varied from zero to the maximum that could be sustained before joint separation for steel members. The change in separation radius for the aluminum members, cast iron members, and a combination of the two materials was on the order of 2–10 percent. For the minimum and maximum external load, the separation radius decreased by 5 and 12 percent, respectively, with an increase in radial position of one to five bolt diameters for the 24-mm bolt models. Changes in the stress on the surface between the members also occurred with changes in magnitude as well as radial position of the external load. The stress was found to be higher near the bolt for larger external loads and also when the radial location of the external load was increased.
Using Aural (Audible) Information Generated Directly From Conventional NDE Technology Signals to Aid the Inspector in Defect Detection and Discrimination
Authors: Holt A. E. , Light G. M. , Polk K. D. , Clayton W. T.
Published: February 2008

During nondestructive evaluation (NDE) of a material, an NDE instrument typically is used to receive the inspection signals and display them for visual interpretation. Work has been underway to convert these signals to a range of aural (audible) signals with the intent to enhance the accuracy of evaluation through the use of two senses (ears and eyes) instead of one. This paper describes auralization of ultrasonic NDE testing signals to improve characterization and evaluation of materials.
Plane Strain Crack Growth Models for Fatigue Crack Growth Life Predictions
Authors: Bloom J. M. , Daniewicz S. R. , Hechmer J. L
Published: February 2008

Experimental data and analytical models have shown that a growing fatigue crack produces a plastic wake. This, in turn, leads to residual compressive stresses acting over the crack faces during the unloading portion of the fatigue cycle. This crack closure effect results in an applied stress intensity factor during unloading which is greater than that associated with the Kmin, thus producing a crack-driving force which is less than ΔK = Kmax − Kmin. Life predictions which do not account for this crack closure effect give inaccurate life estimates, especially for fully reversed loadings. This paper discusses the development of a crack closure expression for the 4- point bend specimen using numerical results obtained from a modified strip-yield model. Data from tests of eight 4-point bend specimens were used to estimate the specimen constraint factor (stress triaxiality effect). The constraint factor was then used in the estimation of the crack opening stresses for each of the bend tests. The numerically estimated crack opening stresses were used to develop an effective stress intensity factor range, ΔKeff The resulting crack growth rate data when plotted versus ΔKeff resulted in a material fatigue crack growth rate property curve independent of test specimen type, stress level, and R-ratio. Fatigue crack growth rate data from center-cracked panels using Newman's crack closure model, from compact specimens using Eason 's R-ratio expression, and from bend specimens using the model discussed in this paper are all shown to fall along the same straight line (on log-log paper) when plotted versus ΔKeff, even though crack closure differs for each specimen type.
Proof-Test-Based Life Prediction of High-Toughness Pressure Vessels
Authors: Panontin T. L. , Hill M. R.
Published: February 2008

The paper examines the problems associated with applying proof-test-based life prediction to vessels made of high-toughness metals. Two A106 Gr B pipe specimens containing long, through-wall, circumferential flaws were tested. One failed during hydrostatic testing and the other during tension-tension cycling following a hydrostatic test. Quantitative fractography was used to verify experimentally obtained fatigue crack growth rates and a variety of LEFM and EPFM techniques were used to analyze the experimental results. The results show that: plastic collapse analysis provides accurate predictions of screened (initial) crack size when the flow stress is determined experimentally; LEFM analysis underestimates the crack size screened by the proof test and overpredicts the subsequent fatigue life of the vessel when retardation effects are small (i.e., low proof levels); and, at a high proof-test level 2.4 × operating pressure), the large retardation effect on fatigue crack growth due to the overload overwhelmed the deleterious effect on fatigue life from stable tearing during the proof test and alleviated the problem of screening only long cracks due to the high toughness of the metal.
Impact Damper With Granular Materials for Multibody System
Authors: Yokomichi I. , Araki Y. , Jinnouchi Y. , Inoue J.
Published: February 2008

An efficient impact damper consists of a bed of granular materials moving in a container mounted on a multibody vibrating system. This paper deals with the damping characteristics of a multidegree-of-freedom (MDOF) system that is provided with the impact damper when the damper may be applied to any point of the system. In the theoretical analysis, the particle bed is assumed to be a mass which moves unidirectionally in a container, and collides plastically with its end. Equations of motion are developed for an equivalent single-degree-of-freedom (SDOF) system and attached damper mass with use made of the normal mode approach. The modal mass is estimated such that it represents the equivalent mass on the point of maximum displacement in each of the vibrating modes. The mass ratio is modified with the modal vector to include the effect of impact interactions. Results of the analysis are applied to the special case of a three-degree-of-freedom (3DOF) system, and the effects of the damper parameteres including mode shapes and damper locations are determined. A digital model is also formulated to simulate the damped motion of the physical system.
Simulative Analyses of Dynamic Buckling of Bellows
Authors: Ooka Y. , Ogawa H. , Ohno K. , Dozaki K.
Published: February 2008

Simulative analyses of dynamic buckling have been performed for bellows of piping expansion joints for FBR plants using an explicit finite element computer code “RADIOSS.” Deformation modes were well simulated in comparison with the associated test results. As for critical buckling pressures, values obtained in the analyses were about 50 percent higher than test values, and further improvement is needed. This paper presents these analytical results and discussion. The associated test results are also reviewed for the arrangement of validation of the analyses.
Reliability Factors and Tightness of Tube-to-Tubesheet Joints
Authors: Sang Z. F. , Zhu Y. Z. , Widera G. E. O.
Published: February 2008

The main purpose of this paper is to provide an applicable method to establish reliability factors for expanded tube-to-tubesheet joints. The paper also reports on the results of a preliminary study to validate experimentally the reliability efficiencies listed in Table A-2 of Appendix A of Section VIII, Division 1, of the Boiler and Pressure Vessel Code (ASME, 1986), and tightness of expanded tube-tubesheet joints. A comparison between the actual reliability factors fr determined from testing the damage strength of the joint and calculated according to Appendix A-4 of the ASME Code and those of Table A-2 is carried out. The results are discussed in light of the restrictions inherent in Table A-2. It is confirmed that some existing values of fr are conservative, while others are less so.
Further Investigations in Tubesheet Design for a U-Tube Heat Exchanger
Authors: Paliwal D. N. , Moulick S. K.
Published: February 2008

A tubesheet for U-tubesheet heat exchanger is analyzed as an equivalent solid circular plate having complete isotropy in the plane of the tubesheet with usual effective elastic constants. However, the tubesheet is expected to have different values of modulus of elasticity, modulus of rigidity, and Poisson’s ratio in the thickness direction. This anisotropic behavior of the tubesheet in thickness direction is taken into account by using the anisotropic theory of plates. When performing theoretical analysis, normal stress in thickness direction is also not assumed equal to zero. Hence, the resulting expressions for deflection and bending stresses are closer to those of a thick plate. Expression for radial stress is compared with that of an isotropic thin circular plate. Based on this comparison, certain modifications in the existing code formulas are proposed. Some design aspects related to ligament efficiency, effective elastic constants, and tubesheet edge conditions are also discussed. Proposed modifications in the design procedure may lead to six to ten percent saving in the material cost.
Biaxial Ratcheting and Cyclic Plasticity for Bree-Type Loading—Part I: Finite Element Analysis
Authors: Ng H. W. , Nadarajah C.
Published: February 2008

The Bree diagram has been incorporated in the ASME B&PV Code in the elevated temperature Code Case N47 as a design approach for limiting strain accumulation in cylinders subjected to cyclic thermal loadings under sustained primary stress. Since the Bree diagram is based upon uniaxial-stress model, it is pertinent to examine the influence of biaxial stresses on strain growth and cyclic stress-strain hysteresis response. The results of inelastic analyses presented in this paper showed that ratcheting and hysteresis behavior may also occur in the axial direction in addition to the hoop direction. Results of almost 100 load cases were presented to clarify the influence of biaxial membrane and thermal bending stresses on the structural behavior. A design approach for the assessment of this type of problem was suggested which utilizes these results.
Further Experimental Verification of Warm Prestressing Effect Under Pressurized Thermal Shock (PTS)
Authors: Okamura H. , Yagawa G. , Hidaka T. , Urabe Y. , Satoh M. , Tomimatsu M. , Koyama K. , Iida M.
Published: February 2008

Fracture tests for the verification of WPS (warm prestressing) effect were carried out by using large flat specimens with very low toughness. Tensile and bending loads and thermal shock were applied simultaneously to the specimens with the realistically postulated flaw and the two times larger one in order to make the maximum KI cross the lower bound of KIC data. During the tests, loading was controlled to simulate the shape of KI versus temperature curve for the postulated PTS transient. Both the specimens did not break within the scatter band of KIC when KI was decreasing during cooling. KI values at fracture by reloading were beyond the upper bound of KIC. That is, the effectiveness of WPS was directly demonstrated for the PTS transients. Also, KI values at fracture can be predicted by Chell’s theory. As the test results, Japanese PWRs have sufficient temperature margin against PTS.
Estimation of Creep Buckling Deformation Under External Pressure at Elevated Temperature
Authors: Kaji Y. , Ioka I. , Nishiguchi I. , Miyamoto Y.
Published: February 2008

The effect of the initial ovality, wall thickness, and pressure level on the collapse time of a heat transfer tube subjected to both constant and cycled external pressure at elevated temperature was examined experimentally and analytically. The creep deformation of the tube obtained by FEM code and the simplified method was a good approximation. The simplified method proposed by Nishiguchi et al. is an effectual method in the estimation of the creep buckling deformation and the collapse time of the tube under external pressure at elevated temperature as compared with the experimental results and the FEM. Though many cracks initiated by creep collapse were observed on the outer surface of a few test tubes, the cracks did not pass through the tube thickness, and leak tightness was maintained despite a collapse for all tubes tested.
Prediction of Acoustic Vibration in Steam Generator and Heat Exchanger Tube Banks
Authors: Eisinger F. L. , Francis J. T. , Sullivan R. E.
Published: February 2008

Criteria are formulated for the development of acoustic vibration in transverse acoustic modes in steam generator tube banks, based on flow and acoustic parameters. Theoretical predictions are validated against available in-service data for nonvibrating and vibrating tube banks and published laboratory experimental data. The criteria can be used for the prediction of acoustic vibration in steam generator and heat exchanger tube banks both, in-line and staggered.
Generation and Use of Simplified Uplift Shape Functions in Unanchored Cylindrical Tanks
Authors: Lau D. T. , Zeng X.
Published: February 2008

This paper presents a simplified mathematical model for modeling the flexible bottom plate in an unanchored cylindrical liquid storage tank partially uplifted under the static tilt condition. In this model, the cylindrical tank is divided into substructures according to the deformation-resistant mechanisms involved. The modeling of each substructure is based on the Ritz formulation. Numerical results are presented and compared with reported experimental measurements. The results show that the simplified mathematical model is efficient. Practical and accurate results can be obtained using the model leading to a better understanding of the uplift mechanism. The relationship of the uplift behavior with the static tilt angle is also presented and discussed.
Detection and Sizing of Defects in Control Rod Drive Mechanism Penetrations Using Eddy Current and Ultrasonics
Authors: Light G. M. , Fisher J. L , Tennis R. F. , Stolte J. S. , Hendrix G. J.
Published: February 2008

Over the last two years, concern has been generated about the capabilities of performing nondestructive evaluation (NDE) of the closure-head penetrations in nuclear-reactor pressure vessels. These penetrations are primarily for instrumentation and control rod drive mechanisms (CRDMs) and are usually thick-walled Inconel tubes, which are shrink-fttted into the steel closure head. The penetrations are then welded between the outside surface of the penetration and the inside surface of the closure head. Stress corrosion cracks initiating at the inner surface of the penetration have been reported at several plants. Through-wall cracks in the CRDM penetration or CRDM weld could lead to loss of coolant in the reactor vessel. The CRDM penetration presents a complex inspection geometry for conventional NDE techniques. A thermal sleeve, through which pass the mechanical linkages for operating the control rods, is inserted into the penetration in such a way that only a small annulus (nominally 3 mm) exists between the thermal sleeve and inside surface of the penetration. Ultrasonic (UT) and eddy current testing (ET) techniques that could be used to provide defect detection and sizing capability were investigated. NDE techniques that could be applied inside and outside the annulus were investigated, but the major goal was to provide high defect-detection sensitivity without requiring removal of the thermal sleeve. As a result of this investigation, both ET and UT techniques for the CRDM penetrations have been developed and evaluated. Long, thin probes were designed to fit into the annulus to carry both eddy current coils and irrigated ultrasonic transducers into the region of interest. The eddy current probes were used primarily to detect cracks in the penetration while the ultrasonic transducers were used to provide an estimate of the remaining wall thickness. This paper describes the ET and UT techniques, the probes developed, and the results obtained using these probes and techniques on CRDM penetration mock-ups.
Transient Pressure Analysis in Piping Networks due to Valve Closing and Outlet Pressure Pulsation
Authors: Choy F. K. , Braun M. J. , Wang H. S.
Published: February 2008

This paper investigates the transient flow and pressure developments in a piping network due to design parametric and operational variations. Numerical simulations using both the method of characteristics and the finite difference formulation are performed and compared. The transient fluid pressure pulsations in the pipes are examined in both the time and frequency domains using a Fast Fourier Transform (FFT) algorithm. The parametric studies consider changes in i) the main pipe size, ii) the valve closing time at the branch outlet, iii) the piping system configuration (both single and multiple branched systems), and iv) the frequency of pressure pulsation at the branch outlet (manifold effect). The paper discusses the sensitivity of the transient fluid pressure and the excitability of the piping natural frequencies at various locations of the pipes, due to valve closing and manifold effects at the branch outlet. The effects of resonance due to pressurefrequency variation at the branch outlet are also studied and general conclusions are drawn from these results.
Frangible Roof Joint Behavior of Cylindrical Oil Storage Tanks Designed to API 650 Rules
Authors: Lu Z. , Swenson D. V. , Fenton D. L
Published: February 2008

This paper presents the results of an investigation into the frangible joint behavior of tanks designed to API 650 rules. In such tanks, the roof-to-shell joint is intended to fail in the event of overpressurization, venting the tank and containing any remaining fluid. The reasoning behind present API design formulas is reviewed. Combustion analyses, structural analyses, and the results of testing are presented. Results show that higher pressures are reached before frangible joint failure than predicted by the present API 650 calculation. One consequence is that (for empty tanks) uplift of the bottom can be expected to occur more frequently than predicted using API 650. However, uplift does not necessarily mean bottom failure. Instead, the relative strength of the shell-to-bottom and roof-to-shell joints will determine failure. This ratio is larger for larger tanks. Recommendations are made as to possible changes in the design approach of API 650.
Stress Intensity, Stress Concentration, and Fatigue Crack Growth Along Evacuator Holes of Pressurized, Autofrettaged Tubes
Authors: Parker A. P. , Underwood J. H.
Published: February 2008

The geometry analyzed consists of a thick-walled cylinder having a small-diameter evacuator hole penetrating radially through the wall. The loading involves pressure acting on the i.d. of the tube and all or part of this pressure acting on the evacuator hole. In addition, the tube may be fully or partially autofrettaged. Total hoop stress concentrations are determined for a range of radial locations along the evacuator, as are stress intensity factors along a crack emanating from the evacuator hole. Fatigue crack growth rates, and hence crack profiles, are predicted at each of the radial locations. These predictions indicate that the critical location for the crack in a nonautofrettaged tube is at the i.d., whereas in a fully autofrettaged tube it is located approximately halfway through the wall thickness. Taking account of the influence of strees ratio, σmin/σmax, has a significant influence on crack shape in autofrettaged tubes, but a limited effect upon lifetime. The effect upon fatigue lifetime of axialresidual stresses due to the autofrettage process is described and it is demonstrated that an insignificant reduction in lifetime results from the presence of such stresses. Finally, the predicted profiles are compared with experimental observations of fatigue cracked evacuator holes and a limited comparison of predicted and actual lifetimes is presented. Agreement is considered good.