bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscoplastic Characterization of A533B Steel at High Strain
Rates
Authors: Dexter R. J. , Chan K. S.
Published: June 2008

The yield strength of A533 grade B class 1 steel is relatively low. Dynamic fracture in test specimens and pressure vessels made with this material is generally accompanied by significant plastic flow over a large range of strain rates. Therefore, it is imperative to use viscoplastic constitutive equations in the analysis of dynamic fracture in A533B steel. This paper describes the characterization and modeling of the viscoplastic behavior of A533B steel using the Bodner-Partom model. Tensile tests were performed from −60°C to 175°C at strain rates ranging from 10−3 to 103. The tensile data were used to obtain material constants in the Bodner-Partom constitutive equations over this range of temperatures. Comparison of calculated and measured stress-strain curves showed good agreement, validating the model and the procedures for determining the model constants. The use of the Bodner-Partom model for dynamic fracture modeling is then discussed.
Creep Deflection of Thick-Walled Piping due to Combined Bending and
Internal Pressure
Authors: Finnie I. , Shirmohamadi M.
Published: June 2008

A closed-form solution is derived for the creep deflection in thick-walled piping subjected to combined internal pressure and bending moment. The solution is limited to the situation usually encountered in practice with sustained gravity loads and support forces in which the additional stresses due to bending are small compared to those due to internal pressure. For this case, it is shown that a simple correction factor may be applied to an elastic computation of pipe deflections to include the effect of creep. Predictions using this factor show satisfactory agreement with observations on a thick-walled piping system which had been in service for 20 years.
Effect of Creep Relaxation of Prestress on the Integrity of
Axisymmetric Wire-Wound Cylindrical Pressure Vessel
Authors: Sabbaghian M. , Baroud M. H.
Published: June 2008

The creep relaxation of prestress in a wire-wound cylindrical vessel based on power function creep law is obtained. In this analysis, it is assumed that the wire is wrapped perpendicular to the axis of the cylinder. The relaxed stress at each layer of wire at any time t is then employed to determine the capability of the cylinder to safely contain an internal pressure. The maximum allowable pressure is obtained as a function of time.
Seismic Pressure Surges in Liquid-Filled Pipelines
Authors: Hatfield F. J. , Wiggert D. C.
Published: June 2008

Observed damage and analytic studies indicate that earthquakes may cause destructive pressure surges in liquid-filled piping. Most studies have concerned buried piping that could be assumed to move with the ground. However, pressure surges also would be expected in above-ground piping, where they would affect the displacement response and, hence, the amplitude of flexural stress in the piping. Current aseismic design practice is to simplify this effect by treating the contained liquid as incompressible mass. This paper describes a technique for computing pressure and relative displacement that incorporates elasticity of both the piping and the liquid. Seismic responses of an example pipeline are predicted. It was found that assuming the piping to be rigid produced an upper-bound estimate of pressure, but assuming the liquid to be incompressible resulted in underestimating displacement of the piping.
A Weight Function Technique for Estimating Stress Intensity Factors for Cracks in High Pressure Vessels
Authors: Desjardins J. L. , Burns D. J. , Thompson J. C.
Published: June 2008

This paper describes a computationally efficient weight function technique which can be used to estimate the opening-mode stress intensity factor around the perimeter of planar surface or embedded cracks. The accuracy of the weight function itself and of the numerical quadrature schemes adopted are verified for elliptical cracks with a wide range of aspect ratios. The technique is then applied to longitudinal-radial cracks at the inner surface, including crossbores, of thick-walled pressure vessels. The results obtained for a wide range of crack depths, aspect ratios and vessel diameter ratios agree well with the predictions obtained by others using finite element, boundary element and modified mapping collocation methods, as well as with previously unpublished experimental data. The paper also considers the applicability of the ASME Boiler and Pressure Vessel Code procedures for estimating K1 for these defects.
State-of-the-Art Review of Pressure Relief Valve Design, Testing and Modeling
Authors: Petherick P. M. , Birk A. M.
Published: June 2008

It is well known that the response of a rail tank car to exterior heating (e.g., fire engulfment) is significantly affected by the operating characteristics of the pressure relief valve (PRV). If the valve jams or fails in some way, it can lead to a violent vessel rupture; therefore, PRV failure modes and mechanisms must be understood. This paper investigates the studies which have been conducted in the area of PRV technology. The original focus of the paper was to conduct a literature search to find the state-of-the-art for the PRV’s which are presently installed on railway tank cars, highway tankers, and stationary LPG storage vessels. When few papers were found which had concentrated on this particular topic, the authors continued the search by considering both the nuclear power and chemical processing industries, where similar technologies are found. The results of the literature search suggest that the PRV’s currently installed on tank cars and highway tankers are based on designs more than 30 yr old. Controlled fire tests and industry’s maintenance programs suggest that PRV’s could be improved. Most experimental studies of PRV’s have concentrated on flow visualization techniques and have not considered PRV dynamic characteristics. The lack of understanding of valve dynamic characteristics has slowed the development of improved PRV dynamic computer models.
Developments in Ferrous Alloy Technology for High-Temperature Service
Authors: Swindeman R. W. , Gold M.
Published: June 2008

Developments during the past twenty-five years are outlined for the technology of ferrous alloys needed in elevated temperature service. These developments include new alloys with improved strength and corrosion resistance for use in nuclear, fossil, and petrochemical applications. Specific groups of alloys that are addressed include vanadium-modified low alloy steels, 9Cr-1Mo-V steel, niobium-modified lean stainless steels, and high chrome-nickel iron alloys. A brief description of coating and claddings for improved corrosion resistance is also provided.
Overview of the ASME Section XI Code Relating to NDE and Ultrasonic
Examination Performance Demonstration
Authors: Cowfer C. D. , Hedden O. F.
Published: June 2008

Nondestructive examination (NDE) in Section XI of the ASME Boiler and Pressure Vessel Code has been an evolving process. The Code’s use of NDE for in-service inspection (ISI) to establish fitness for duty has brought about major changes in applied NDE philosophy and practice. The publication in Section XI, 1989 Addenda, of mandatory Appendix VIII, “Performance Demonstration for Ultrasonic Examination System,” sets a precedent for both NDE performance and recognition of the total NDE system (personnel, equipment and procedures). This paper highlights appropriate portions of Appendix VIII. Performance values such as probability of detection (POD) and flaw sizing accuracy are addressed. The use of flawed specimens for performance demonstration qualifies personnel, equipment and procedures, hence the “Ultrasonic System” qualification. Appendix VIII provides the opportunity for technique performance demonstration for assessment of material aging and qualification of components and systems for continued service. This article provides the background and justification for Code action to publish Appendix VIII.
The History of Allowable Damping Values for U.S. Nuclear Plant Piping
Authors: Ware A. G.
Published: June 2008

Prior to 1982, pipe damping values in nuclear plants were prescribed by Regulatory Guide 1.61 and Appendix N to Section III of the ASME Boiler and Pressure Vessel Code. In the early 1980s, it became clear that piping design was too conservative resulting in systems that had far too many supports, particularly snubbers. These supports were costly to design, install, and inspect; contributed to increased worker radiation exposure; and since snubbers sometimes lock when unloaded causing higher fatigue usage in piping, the safety margin of the systems was reduced. A series of steps was undertaken by the Pressure Vessel Research Committee (PVRC) to propose new damping limits, which culminated in alternate damping allowable values, called PVRC damping. This damping was later adopted as Code Case N-411 to the ASME Code. Code Case N-411 has enabled several utilities to make significant reductions in the number of snubbers on their plants, resulting in lower maintenance costs, lower worker radiation exposure, and greater reliability (since the consequences of snubber malfunction are reduced). More recently, the Electric Power Research Institute sponsored a project by Bechtel to review the damping data, perform a regression analysis, and recommend a permanent change to the ASME Code to replace Code Case N-411.
Recent Advances in Dynamic Buckling Analysis of Liquid-Filled Shells
Authors: Liu W. K. , Chen Y.-J. , Tsukimori K. , Uras R. A.
Published: June 2008

The dynamic buckling of liquid-filled shells is reviewed. Comparison of the analysis with experimental results is presented. The governing equations of dynamic buckling of liquid-filled imperfect shells are then derived. A simple imperfection pattern is chosen to explain the additional buckling modes encountered in the experiments.
Effect of Cyclic Loading on Ductile Fracture Resistance
Authors: Marschall C. W. , Wilkowski G. M.
Published: June 2008

The influence of cyclic loading on ductile fracture toughness was examined from limited experimental data available in the literature. The review indicated that, in the absence of global compressive loads during the unloading cycle (R ≥ 0), the total crack extension generally is the sum of the monotonic component (Δamono) and the cyclic component (Δacyclic). The former can be obtained from the monotonic J-R curve and the latter from a fatigue-crack-growth curve. When large global compressive loads are developed during unloading (R<0), the review indicated that simply summing Δamono and Δacyclic gives an under prediction of the actual crack extension in load cycling tests. Thus, it appears that the local compressive strains lower a material’s normal monotonic fracture resistance in a region immediately ahead of the crack following the load reversal. Although few data are available in this regime of cyclic loading, it is likely that the magnitude of the loss of monotonic toughness depends on frequency of unloadings, R-ratio, and material. For ferritic steels susceptible to strain aging, temperature and strain rate also are likely to be important. The review also examined the applicability of various fracture mechanics parameters, including those based on deformation plasticity and those based on incremental plasticity, in quantifying cyclic-loading effects. While incremental plasticity parameters (for example T*) appear promising, they may be time-consuming and costly to develop. Until such advanced parameters are available, it is likely that empirical correlations involving deformation J will have to be developed to handle cyclic loading effects. Finally, the significance of the findings reported herein relative to the performance of flawed nuclear piping subjected to cyclic loading is discussed. It appears that circumferential cracks are of greater concern in seismic events than are axial cracks because the former may experience negative R-ratios.
Finite Element Analysis of Residual Stresses in Threaded End Closures
Authors: Chaaban A. , Muzzo U.
Published: June 2008

Due to the high stress concentration at the root of the first active thread in threaded end closures of high pressure vessels, yielding may occur in this region during the application of the first pressure cycle or proof testing. This overstraining introduces residual stresses that influence the fatigue performance of the vessel. This paper presents a parametric analysis of threaded end closures using elastic and elasto-plastic finite element solutions. The results are used to discuss the influence of these residuals on the estimated fatigue life when the vessel is subjected to repeated internal pressure. A simple empirical method to allow for the Bauschinger effect of the material is also proposed.
Experimental Studies on Damping Characteristics of Bolted Joints for
Plates and Shells
Authors: Shin Y. S. , Iverson J. C. , Kim K. S.
Published: June 2008

Reducing the contact force in bolted structural connections can reduce system vibration amplitudes by enhancing joint damping capacity. A test model consisting of two concentric circular cylindrical shells and four vanes connected by groups of bolts was tested and analyzed to investigate the relationship between the bolt preload and the system damping. A viscoelastic material was then introduced between the contacting surfaces at bolted joints and its effect on system damping was again investigated.
Buckling of Force-Excited Liquid-Filled Shells
Authors: Uras R. A. , Liu W. K.
Published: June 2008

The matrix equation of motion for liquid-filled shells with a particular reference to the influence of ground excitation are derived through a Galerkin/finite element discretization procedure. The modal coupling among the various combinations of axial and circumferential modes are identified. The equations for the dynamic buckling analysis of liquid-filled shells are presented. The buckling criteria of liquid-filled shells subjected to horizontal ground excitation are established. A comparison to available experimental results gives strikingly good agreement. The importance of modal interaction in the axial as well as circumferential directions is also demonstrated. This provides guidelines for a better understanding of dynamic buckling of liquid-filled shells.
Application of the Discrete Vortex Method to Fluid-Structure Interaction
Authors: Blevins R. D.
Published: June 2008

The discrete vortex method for numerical simulation of two-dimensional flows is applied to six problems in fluid-structure interaction: steady flow over bluff and streamlined sections, flow with transverse oscillations of the free stream, oscillation in otherwise still reservoir, vibration induced by steady flow, flow-induced vibration in oscillating flow, and impulsively started flow. Direct comparison is made with various formulations and with experimental data.
A Global Model for Flow-Induced Vibration of Tube Bundles in Cross-Flow
Authors: Granger S.
Published: June 2008

This paper presents an approximate model which can be used for predictive analysis of industrial tube bundles subjected to cross-flow. A tube bundle in cross-flow is locally approximated, in a global sense, by a single-degree-of-freedom system, called the global system. The critical flow velocity can be predicted by computing the velocity at which the damping ratio of the global system becomes zero. In the stable region, tube response amplitude can be approximated by the amplitude of the global system response. In this approach, the knowledge of four fluid force coefficients is required to solve the problem. They are determined experimentally by dynamic response measurements. The global model so defined is compared with the simplified method usually used for industrial predictive analysis purposes. It is shown that the conventional method can be considered as a particular simplified case of the present model. Practical examples concerning square-in-line tube bundles are given. They show that the first results obtained with the global model are promising.
Stress Classification for Elevated Temperature Service
Authors: Dhalla A. K.
Published: June 2008

The paper presents two procedures which can be used to classify the stresses originating at the structural discontinuities of pressure vessel and piping components designed for elevated temperature service. The stress classification is based upon the definitions of primary and secondary stress intensities which are provided in the ASME Boiler and Pressure Vessel Code, Sections III and VIII. The intent is not to reclassify primary stresses, but to provide a designer with practical guidance in evaluating the primary characteristics of thermal and structural discontinuity pressure stresses. Two objectives for an appropriate classification of stresses are: (a) to reduce undue conservatism in elevated temperature Code Case N-47 design rules when primary stress is only a small fraction of secondary stress, and (b) to provide a sufficient margin of safety for extreme (Level D) loadings when the primary local and general membrane stress levels are close to the yield point of the material at structural discontinuities.
A Simple Model for Fatigue Crack Growth Near Stress Concentrations
Authors: McClung R. C.
Published: June 2008

Fatigue crack growth rates are often difficult to predict for short cracks growing near stress concentrations. This paper presents a simple model to predict those growth rates which incorporates the phenomenon of crack closure. Crack opening stresses are shown to change significantly as cracks grow away from notches, and the simple model is designed to describe those changes. The effective stress range ratio, U, is assumed to be dependent on the local stress at the crack tip location in a corresponding uncracked body. The value of U changes with the normalized maximum stress in unnotched bodies, and this dependence can be quantified with elastic-plastic finite element models or simpler modified-Dugdale crack analyses. The local stress distribution is estimated with a Neuber analysis. A semi-empirical stress intensity factor solution is constructed and calibrated with known exact solutions. The crack growth rate is then calculated with the modified Paris law, taking crack growth constants from long crack data. The model is illustrated with a specific case study, the growth of cracks from center notches in an SAE 1026 steel. Experimental crack growth data for notches of different sizes and shapes compare favorably with the calculations. The scheme is contrasted with previous models for notch fatigue cracks. The implications of the simple model for other fatigue design problems are explored, highlighting the simplicity and generality of the model.
Effect of Composite Damage on the Fatigue Behavior of the Metal-Lined Hoop-Wrapped Cylinders
Authors: Bhuyan G. S.
Published: June 2008

Effects of an axial defect in the composite of hoop-wrapped steel and aluminum cylinders on the hoop stress as well as on the bulging of the liners were investigated through the numerical and experimental stress analysis. Comparison with the experimental results (reported in reference [5]) suggests that relative fatigue performance of the cylinders, containing damages to the composite wrapping, can be assessed without conducting prototype tests.
Methods Used for Calculating Seismic Response of Multiply Supported Piping Systems
Authors: Singh M. P. , Burdisso R. A. , Maldonado G. O.
Published: June 2008

The paper describes the response spectrum methods which are being used currently in the industry for the calculation of seismic design response of piping systems supported at several points of primary structures. In actual practice, the seismic input motions at the piping supports are correlated to varying degrees. To include the effect of this correlation between different support motions in the calculation of piping response, several methodologies with different simplifying assumptions have been proposed. This paper evaluates the effect of these assumptions on the accuracy of the calculated piping response. For this evaluation the results obtained by some of the currently used approximate approaches have been compared with the results obtained by an analytically rational and a more accurate approach. The comparison shows large differences in the two sets of results. For the example problem, the response values calculated by the approximate approaches are rather on the overly conservative side. This conservatism is, however, neither uniform nor assured. The use of these approximate approaches is, therefore, not recommended.
Expanded, and Welded-and-Expanded Tube-to-Tubesheet Joints
Authors: Yokell S.
Published: June 2008

This paper discusses some practical aspects of expanded and welded-and-expanded tube-to-tubesheet joints. It reviews elastic-plastic tube expanding theory, which it uses as the basis for setting pressures for uniform-pressure expanding and for estimating residual interfacial stress at the tube-hole interface. It addresses uniform-pressure-expanded tube joint strength and the problem of correlating of roller-expanded joint strength with wall reduction and rolling torque. It advocates two-stage expanding: 1) applying just sufficient pressure or torque to create firm tube-hole contact over substantially the tubesheet thickness; and 2) re-expanding at full pressure or torque. It points out the advantages of segregating heats of tubing and mapping the tube-heat locations. It recommends non-TEMA Standard (and non-HEI Power Plant Standard) grooves for grooved-hole joints made by roller-expanding, when the tubes are thin-walled, high-strength, low-elastic-modulus, and for joints made by uniform-pressure expanding [1, 2]. It states what to examine when considering grooves for small-diameter tubes. It reviews tube-to-tubesheet welding requirements and discusses welding before and after expanding. It suggests TEMA revise its standards to define strength and seal welds and urges the ASME Boiler and Pressure Vessel Code Committee (the Code Committee) to incorporate the TEMA definition in Section VIII of the ASME Boiler and Pressure Vessel Code (the Code) [3]. It makes recommendations for pressure and leak-testing. The work shows why welded-and-expanded joints should be full-strength expanded and why expansion length should equal the tubesheet thickness minus 1/8 in. (approximately 3 mm) rather than the lengths the TEMA and HEI Standards permit.
Limit Loads of Mechanical Components and Structures Using the GLOSS R-Node Method
Authors: Seshadri R. , Fernando C. P. D.
Published: June 2008

A method for determining plastic collapse loads of mechanical components and structures on the basis of two linear elastic finite element analysis is presented in this paper. The r-nodes, which are essentially statically determinate locations, are obtained by GLOSS analysis. The plastic collapse loads are determined for statically determinate and indeterminate components and structures by using the single-bar and the multibar models, respectively. The paper also attempts to unify the concepts of load-control, limit load, reference stress and stress-classification. The GLOSS R-Node method is applied to several component configurations of practical interest.
The Elastic-Plastic Analysis of Tubes—I: General Theory
Authors: Jiang W.
Published: June 2008

A study is made in this paper of the elastic-plastic analysis of tubes subjected to various loads and temperatures. The kinematic hardening rule is used in the analysis and constitutive equations are developed for the tube problems. By piecing several elastic and plastic solutions together, various tube problems can be solved in closed forms.
Ratcheting of Pressurized Piping Subjected to Seismic Loading
Authors: Scavuzzo R. J. , Lam P. C. , Gau J. S.
Published: June 2008

The ABAQUS finite element code was used to model a pressurized pipe and subjected to cyclic bending loads to investigate ratcheting. A 1-in. schedule 40 pipe was loaded with a slow (static) cyclic load. The pipe internal pressure was varied from 0 to 6000 psi. Two types of materials were considered: an elastic perfectly plastic and a bilinear elastic-plastic material. Two types of finite elements of the ABAQUS program were compared to analytical solutions to evaluate the element accuracy in the plastic regime. Depending upon loading conditions and specified material properties, three different responses were observed from the finite element analyses: cyclic plasticity, ratcheting of the hoop strain, or shakedown. These analytical results are compared to some experimental measurements.
A Study of Cyclic Thermal Straining in a Welded Joint, Using a Closed-Loop, Servo-Controlled Testing Machine
Authors: Itoh Y. Z. , Kashiwaya H.
Published: June 2008

For investigating the origin of residual stresses in welded joints, the transient thermal stresses in a carbon-manganese-silicon steel (JIS SM41B), a cast martensitic stainless steel (JIS SCS5), an austenitic stainless steel (JIS SUS304), and a titanium alloy (Ti-6Al-4V) were investigated by subjecting round bar specimens, in which both ends were fixed, to thermal of cycles. The specimens were heated in air by high-frequency induction. The cyclic thermal straining tests were conducted for the case of a single thermal cycle and the case of multiple thermal cycles, using a closed loop, servo-controlled testing machine. The experimental results made clear that the transient thermal stress behavior was dependent on metallurgical effects, such as phase transformations, strain hardening, the Bauschinger effect, etc. The effects on phase transformation on the transient thermal stress behavior of SCS5 and SM41B were especially remarkable. However, the effects of phase transformations on the residual stresses due to the thermal straining cycle were negligible in SM41B and not observed in both SUS304 and Ti-6Al-4V. The residual stresses tended to increase with increase of the peak temperature of thermal cycles in SM41B, SUS304 and Ti-6Al-4V. However, when the peak temperature increased above 600°C in SCS5, the residual stress rapidly decreased and became compressive because of the expansion due to the martensite transformation. This study led to the conclusion that the transient thermal stresses for various peak temperatures could easily be obtained by an incremental step test using a single specimen and that this incremental step test could simply estimate the residual stress character of butt-welded joints.
An Improved Flange Bolt-Up Procedure Using Experimentally Determined Elastic Interaction Coefficients
Authors: Bibel G. D. , Ezell R. M.
Published: June 2008

Uniform bolt stress (±2 percent) was obtained in a one-pass, tension-controlled, bolt-up procedure. This was done by experimentally determining elastic interaction coefficients. The coefficients were then used to solve for the required initial bolt loads that gave the desired final stresses. The procedure worked on two similar pairs of 16-in. class 300 flanges. Each flange set had different interaction, apparently due to surface gaps and misalignment. The procedure was repeated several times with a flat sheet gasket and without a gasket. The procedure and experimental results are described in detail.
Study on the Vibrational Characteristics of a Tube Array Caused by Two-Phase Flow—Part 1: Random Vibration
Authors: Nakamura T. , Fujita K. , Kawanishi K. , Yamaguchi N. , Tsuge A.
Published: June 2008

There are few published papers about the flow-induced vibration caused by two-phase flow. Especially, the experimental data at high-pressure and high-temperature conditions which corresponds to the practical phenomenon, are extremely few, and the mechanism of the two-phase flow-induced load acting on a tube in tube array has not yet been explained. This paper shows the experimental results about the turbulent buffeting force both by air-water two-phase flow and by steam-water flow of extreme conditions up to 5.8 MPa in pressure and 272°C in temperature, the explanation of the mechanism of this force, and the method to evaluate the response of the tube caused by two-phase flow. Here, the main source of the buffeting force by two-phase flow in slug or froth flow pattern is recognized to be the impact force caused by the intermittently rising liquid slug. The slug speed and the fluid force acting on a tube are estimated, combined with the estimation of the intermittence of the occurrence of the liquid slug rising.
On the Collapse of Long, Thick-Walled Tubes Under External Pressure and Axial Tension
Authors: Madhavan R. , Babcock C. D. , Singer J.
Published: June 2008

The paper presents the results from a combined experimental and analytic study on the collapse of long, thick-walled tubes subjected to external pressure and axial tension. The experiments involved tubes of diameter-to-thickness ratio (Dm/t) 10 to 40. Collapse envelopes were obtained for two different pressure-tension loading paths. Collapse tests involving initially ovalized tubes were also carried out. The collapse strength predicted with a two-dimensional elasto-plastic model applying J2 flow rule was in good agreement with the experiments. The results show that the collapse strength under combined loading is strongly influenced by initial ovality and that the shape of the stress-strain curve has a significant influence on the tension-pressure collapse envelope.
Study of the Fluid Flow in the Elliptical Duct by the Method of Characteristics
Authors: Huang Yuan Mao , Ho C. H.
Published: June 2008

This study develops a mathematical model to determine the properties of laminar flow in the elliptical duct. With some assumptions, the nonlinear governing equations of the air in the elliptical duct are transformed into the hyperbolic type. The method of characteristics is then applied. Numerical results are obtained by using the finite difference method and the uniform interval scheme. The air properties in the elliptical duct are analyzed. The local Nusselt number and the heat transfer coefficient along the duct are studied. The numerical results are compared and show good agreement with the available data.
The Design of Test Equipment for Safety and Safety-Relief Valves
Authors: Sievert P. R.
Published: June 2008

A design method for safety and safety-relief valve test equipment is presented which is applicable to compressible media. A test stand pressure vessel is sized for an assumed ideal valve operation. In this way, a minimum size is determined which will allow the measured safety valve performance to be characteristic of the valve and not the test equipment.
Assessment of Life of Inner Vessel for a Pool-Type Fast Breeder Reactor Based on Inelastic and Viscoplastic Deformations
Authors: Alwar R. S. , Chellapandi P. , Bhoje S. B.
Published: June 2008

Towards assessing the creep-fatigue damage for the inner vessel of a pool-type fast reactor, 3-D elastic and axisymmetric inelastic analysis with classical kinematic hardening model, ORNL material model and more realistic CHABOCHE visco-plastic model have been performed. The material properties of stainless steel type 316 LN at various temperatures are used in the analysis. Using the results of this analysis, the creep-fatigue damage and ratcheting are assessed as per the rules of RCC-MR and results have been compared for the various constitutive models used. Inelastic analysis has been performed only at highly stressed local regions. Computations with the ORNL material model is found to be satisfactory in terms of conservatism and computer cost involved, and hence recommended for use in the design stage. Further, conservatism in estimating the creep fatigue-damage of the component associated with the elastic route of RCC-MR has been quantified. The inelastic and viscoplastic analysis tool has been validated using experimental benchmark problems.
Static Analysis of Thick Laminated Circular Cylindrical Shells
Authors: Chandrashekhara K. , Kumar B. S.
Published: June 2008

An approximate solution for a thick laminated simply supported circular cylindrical shell of revolution and shell panel subjected to asymmetric load has been obtained using elasticity approach. The results obtained from this analysis have been compared with the exact solution. Numerical results have been presented for 3-ply hybrid laminates and (0/90/0) laminates subjected to patch loads. The results have also been compared with some available classical and shear deformation theories to assess the accuracy of these theories.
On the Applicability of Local Approaches for the Determination of the Failure Behavior of Ductile Steels
Authors: Kussmaul K. , Eisele U. , Seidenfuss M.
Published: June 2008

The strength and deformation behavior of specimens and components is, on the one hand, influenced by the local state of stress and strain, and on the other hand, by the chemical composition and the microstructure of the material used. Using two different steels, it was investigated how far it is possible to predict the failure behavior of specimens and components qualitatively and quantitatively by means of local approaches. For this purpose, two methods differing considerably from the basic idea were chosen. For the description of the failure behavior, so-called damage models were used. These damage models try to describe numerically the process developing microscopically and finally leading to fracture by means of continuum mechanical approaches in order to calculate the macroscopical failure behavior. The results show that for ductile materials, the damage models allow a very accurate calculation of smooth and notched specimens and components. The efforts presently required for the calculation are, however, still very high. Analyses using fracure mechanics approaches (J-integral) in combination with the local stress states (multiaxiality) were performed to describe the failure behavior. With this approach, it was attempted to calculate crack initiation and maximum load of pre-cracked specimens and components. The fracture mechanics methods are preferred for cracked components if an engineering estimation of crack initiation and maximum load only is required since the calculation efforts of the fracture mechanics methods are much lower than those of the damage models.
Bifurcation Buckling of Circular Cylindrical Shells Subjected to Axial Compression During Creep Deformation
Authors: Miyazaki N. , Hagihara S.
Published: June 2008

In the present work, analytical and experimental investigations were performed on creep buckling. Special attention was focussed on bifurcation behavior during creep deformation. The finite element method was used to analyze creep buckling of circular cylindrical shells without initial imperfection. The number of circumferential waves obtained from the analyses agrees well with those of the experiments. The present experimental investigation shows that the circumferential waves are suddenly caused near a bulge. It is also found that there is no correlation between the wavelength of the circumferential waves observed at creep buckling and that of the circumferential initial imperfection. Deformation patterns at the bifurcation creep buckling obtained from the analyses are analogous to those of the experiments. It is concluded from the analyses and the experiments that the circumferential waves observed in creep buckling experiments are due to bifurcation buckling during creep deformation.
The Elastic-Plastic Response of Thin-Walled Tubes Under Combined Axial and Torsional Loads: Part I—Monotonic Loading
Authors: Jiang W.
Published: June 2008

This paper investigates the elastic-plastic response of thin-walled tubes subjected to combined axial and torsional loads. The kinematic hardening model is used and exact closed-form solutions are obtained for linear loading paths. The characteristics of the stress-strain relationships are discussed and the corresponding movements of the yield center are illustrated. The response of the material under nonproportional loading is proved to be path-dependent, and the hardening behavior is shown to be different from that under proportional loading. The investigation then shows that such a difference will finally disappear when the stresses tend to infinity.
The Elastic-Plastic Response of Thin-Walled Tubes Under Combined Axial and Torsional Loads: Part II—Variable Loading
Authors: Jiang W.
Published: June 2008

This paper continues the investigation of the elastic-plastic response of thin-walled tubes subjected to combined axial and torsional loads. The stress-strain loop under arbitrary variable loading is first discussed. It is then shown that due to the kinematic hardening, a steady state, either one of the reversed plasticity or one of the elastic shakedown, can always be reached under cyclic loadings, with a hysteresis loop in the form of a parallelogram or a straight line. As a result, the difference in response between nonproportional and proportional loading will finally disappear. The investigation indicates that the simple kinematic hardening rule is able to describe, at least qualitatively, certain basic characteristics of the material behavior observed in nonproportional tests.
Finite Element Analysis of History-Dependent Damage in Time-Dependent Fracture Mechanics
Authors: Krishnaswamy P. , Brust F. W. , Ghadiali N. D.
Published: June 2008

The demands for structural systems to perform reliably under both severe and changing operating conditions continue to increase. Under these conditions time-dependent straining and history-dependent damage become extremely important. This work focuses on studying creep crack growth using finite element (FE) analysis. Two important issues, namely, (i) the use of history-dependent constitutive laws, and (ii) the use of various fracture parameters in predicting creep crack growth, have both been addressed in this work. The constitutive model used here is the one developed by Murakami and Ohno and is based on the concept of a creep hardening surface. An implicit FE algorithm for this model was first developed and verified for simple geometries and loading configurations. The numerical methodology developed here has been used to model stationary and growing cracks in CT specimens. Various fracture parameters such as the C1, C*, T*, J were used to compare the numerical predictions with experimental results available in the literature. A comparison of the values of these parameters as a function of time has been made for both stationary and growing cracks. The merit of using each of these parameters has also been discussed.
Mixed-Mode Fracture in Plastically Deforming Materials
Authors: Cordes J. , Yazici R. , Seo M.
Published: June 2008

A finite element method was developed for evaluating an angled crack in a thin plate. In the spirit of the Dugdale and Barenbaltt damage zone models, the method superposes cohesive stresses in a damage zone onto a linear elastic fracture analysis. The method uses incremental changes in the boundary conditions along the damage zone to model loss in stiffness due to yielding and stable crack growth. A crack tip opening displacement criterion is used for predicting stable crack growth and unstable crack growth. The resulting nonlinear analysis is used to predict the applied loads at failure. Numerical results compared favorably with experimental values.
Sizing Swing Check Valves for Stability and Minimum Velocity Limits
Authors: Rahmeyer W. J.
Published: June 2008

Unexpected wear and failure of swing check valves cost power plants and water treatment facilities millions of dollars each year. Operating swing check valves at too low flow velocities can cause the check valve internals to rapidly wear and suddenly fail. Many of the swing check valve failures could have been avoided by the use of a minimum velocity limit or a numerical model to predict the limit of minimum velocity. The following equations and methodology can be used to predict a minimum velocity limit or VMIN for swing check valves. The limit of VMIN is defined as the minimum flow velocity in which the valve disk is fully open and stable without motion. The procedures and equations can also be used to predict the velocity (VOPEN) to just open the disk to any position or angle. The equations presented in this paper are also unique in that they can be applied to swing check valves that have large degrees of disk position or valve opening. The equations are not limited to swing check valves that must have a portion of the valve disk protruding into the flow through the check valve. Although the methodology was developed primarily for horizontal liquid flows, limited testing has shown that the equations can be applied for installations with inclined slopes and for applications with compressible fluids. The following equations were derived from a large data base of tests of different sizes and types of swing check valves. Tables and figures are presented to support the suggested equations.
Application of Ultrasonics to Nonintrusive Vibration Measurement
Authors: Au-Yang M. K.
Published: June 2008

This paper outlines a nonintrusive vibration measurement method using standard, off-the-shelf commercial ultrasonic instruments designed for flaw detections, together with digital signal analysis techniques. This method was incorporated into a commercial package designed for nonintrusive check valve monitoring and has been extensively tested in both the laboratory and the field. It can detect valve disk flutter as small as 0.02-in. (0.50 mm) peak-to-peak, without disassembly of the valve. In simulated tests, it quantitatively measured, remotely and nonintrusively, stationary vibration amplitudes as small as 0.0001 in. (0.0025 mm). Other potential applications include in-service vibration monitoring of internal components of nuclear reactors, steam generators, heat exchangers, pumps and valves, and in the laboratory or in the field, when the vibration frequency is too low for accelerometers and the strain is too low for strain gages.
Life Assessment of Superheater/Reheater Tubes in Fossil Boilers
Authors: Viswanathan R. , Paterson S. R. , Grunloh H. , Gehl S.
Published: June 2008

Creep rupture failure of superheater (SH)/reheater(RH) tubes is a major cause of forced outages of power boilers. A methodology developed recently by EPRI and its contractors has helped utilities make more informed run/replace decisions for tubes by judiciously combining calculational, nondestructive, and destructive evaluations. In this methodology, the tubes/tube assemblies at risk are identified by ultrasonically measuring the thickest steamside oxide scale and thinnest wall thickness in the tubes. The remaining life of each tube/tube assembly is predicted using a computer code known as TUBELIFE, thus achieving a further level of focus on the tubes/assemblies in the “highest risk” category. Sacrificial tube samples are then removed from the select locations and subjected to laboratory metallurgical evaluation and isostress rupture testing to refine the remaining life estimates. Research has further refined this methodology by validating the ultrasonic technique for scale measurement, identifying the appropriate stress formula and oxide growth laws and evaluating the limitations of creep damage summation rules and isostress rupture test procedures. This paper provides an overview of the research in the field, and establishes a road map for assessing the remaining life of SH/RH tubes.
Random Thermal Stress Oscillations and Fatigue Life Estimation for Steam Generator Tubes
Authors: Klevtsov I. , Crane R.
Published: June 2008

A one-dimensional computation model was used to determine the temperature and stress fields under conditions corresponding to those found in once-through steam generator tubes. The random oscillatory nature of the water/steam convective boundary conditions in the transition boiling zone was simulated by postulating random variations in heat transfer coefficients or flow temperatures. Statistical parameters describing the tube temperatures and thermal stress oscillatory history are determined allowing appropriate fatigue life estimations to be made. The results indicate that the tube wall temperature oscillation parameter provides a strong influence on thermal stress and the predicted fatigue life. In contrast, Biot number variations provide only a relatively small effect. An improved method of determining the allowable thermal stress limitations due to certain wall temperature oscillations is proposed.
The Effect of Temperature and Cyclic Frequency Upon Fatigue Crack Growth Behavior of Several Steels in an Elevated Temperature Aqueous Environment
Authors: James L. A.
Published: June 2008

The fatigue crack propagation (FCP) behavior of several ASTM A302-B and A508-2 steels was characterized in deaerated elevated temperature aqueous environment. FCP behavior was determined over the range 121°C to 343°C at a constant value of ΔK, stress ratio, and load rise time. A complex response of FCP rates as a function of temperature was observed, and this is discussed in the light of similar results developed by others within the nuclear industry. Corrosion potentials (referenced to the standard hydrogen electrode) were measured for each of the steels over the above temperature range and comparisons are made to the observed FCP behavior. Cyclic frequency effects were studied at two temperatures, 149°C and 243°C, and these are analyzed within the “time domain” format first suggested by Shoji et al. The results, when expressed in the time domain format, clearly show regions where environmentally assisted cracking (EAC) occurs, and regions where EAC does not occur. A “threshold” for EAC was noted at 149°C, and the possibility of an EAC threshold was observed at 243°C.
Application of the Finite Element Method to the Quasi-Static
Thermoelastic Analysis of Prestress in Multilayer Pressure
Vessels
Authors: Rasty J. , Tamhane P.
Published: June 2008

Multilayered wrapped vessel technology utilizes the compressive prestress induced during construction process to gain a considerable advantage over the monoblock vessels. The compressive prestress allows for more efficient use of construction material and more uniform distribution of stress throughout the vessel’s cross section. Analysis of the magnitude of prestress throughout the vessel’s thickness has been previously reported (Rasty, 1988). However, one major idealization in such analysis has been the assumption that the magnitude of induced prestress is constant around the circumference of the vessel. In this research, thermoelastic finite element method was utilized to simulate the construction process of one layer of the vessel. It was concluded that the compressive residual stress induced by the weld shrinkage varies through the circumference of the vessel by as much as 13.5 percent. Circumferential distributions of the prestress are presented and compared to the closed-form solutions (constant prestress assumption) in earlier works.
Interpretation of Probabilistic Structural Analysis of an Aging
Passive Component
Authors: Phillips J. H. , Atwood C. L. , Magleby H. L. , Khericha S. T.
Published: June 2008

This article describes a technique to calculate the risk from failure of passive components over time, and demonstrates the technique by applying it to a weld in the auxiliary feedwater (AFW) system. It uses a modified version of the PRAISE computer code to perform a probabilistic structural analysis to calculate the probability that crack growth due to aging would cause the weld to rupture. It then uses the weld rupture probability as input to a modified existing PRA to calculate the change in plant risk with time. The results show an insignificant effect on plant risk because of the low calculated rupture rate of the weld in this particular calculation over 48 yr of service. A decreasing yearly rupture rate for this weld is calculated. This results from infant mortality; that is, most of those initial flaws that will eventually lead to rupture will do so early in life.