bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical Studies of Blowdown Thrust Force and Elastic-Plastic Behavior of Pipe at Pipe Rupture Accident
Authors: Miyazaki N. , Ueda S.
Published: November 2009

When high-temperature and high-pressure water is ejected from pipe, a blowdown thrust force will act on the pipe and it will cause pipe movement. The analytical methods of blowdown thrust force and pipe movement are presented in the paper. The equation of momentum conservation is used to calculate the blowdown thrust force, together with the results of the thermal-hydraulic analysis code RELAP4/MOD6. The finite element method is used to calculate the dynamic movement of pipe. The equations for calculating the maximum strain at the outer surface of pipe are derived by assuming the static equilibrium condition. The analytical results are compared with experimental ones to verify the analytical methods presented here.
Evaluation and Prediction of Critical Overhang Length Under Pipe Whip Accident
Authors: Yano T. , Miyazaki N. , Miyazono S.
Published: November 2009

When the pipe length between break exit and restraint is long in the pipe whip accident, the pipe will undergo a plastic collapse as the moment increases. The length at which plastic collapse may occur is called the critical overhang length, (OH)cr. The experimental results of (OH)cr show good agreement with the prediction by a static simplified estimation method for (OH)cr although the pipe whipping is a dynamic phenomenon. The diagrams of (OH)cr are also described for a range of sizes of stainless steel pipe under the loss of coolant accident conditions of light water reactors.
Acoustic Resonances in Cylinder Bundles Oscillating in a Compressible Fluid
Authors: Lin W. H. , Raptis A. C.
Published: November 2009

This paper deals with an analytical study on acoustic resonances of elastic oscillations of a group of parallel, circular, thin cylinders in an unbounded volume of barotropic, compressible, inviscid fluid. The perturbed motion of the fluid is assumed due entirely to the flexural oscillations of the cylinders. The motion of the fluid disturbances is first formulated in a three-dimensional wave form and then casted into a two-dimensional Helmholtz equation for the harmonic motion in time and in axial space. The acoustic motion in the fluid and the elastic motion in the cylinders are solved simultaneously. Acoustic resonances were approximately determined from the secular (eigenvalue) equation by the method of successive iteration with the use of digital computers for a given set of the fluid properties and the cylinders’ geometry and properties. Effects of the flexural wavenumber and the configuration of and the spacing between the cylinders on the acoustic resonances were thoroughly investigated.
Seismic Design of Buried Pipeline for Fault Movement Effects
Authors: Wang L. R. , Yeh Y.-H.
Published: November 2009

This paper presents a design procedure for buried pipelines subjected to both strikeslip and reverse strike-slip faults after modifying some of the assumptions used previously. Based on the analysis results, this paper also discusses the design criteria for buried pipelines subjected to various fault movement effects. Parametric responses of buried pipeline for various fault movements, angles of crossing, buried depths and pipe diameters are presented.
Micro-Crack Initiation, Propagation and Threshold in Elevated Temperature Inelastic Fatigue
Authors: Usami S. , Fukuda Y. , Shida S.
Published: November 2009

Micro-crack initiation, propagation and threshold behavior in plain, short crack, weld defect and notch specimens of 304 stainless steel are observed under elevated temperature strain-controlled inelastic fatigue conditions. The effects of temperature, strain rate, wave shape and strain gradient are analyzed and methods for estimating fatigue life and fatigue limit are postulated on the basis of the behavior of the micro-cracks.
Fluid-Structure Interaction in Waterhammer Response of Flexible
Piping
Authors: Belytschko T. , Karabin M. , Lin J. I.
Published: November 2009

In the waterhammer analysis of piping systems, incompressible (or added mass) representations are generally used in computing the response of the piping. It is shown that this procedure is not necessarily conservative, particularly for thin-walled, flexible piping systems, and that fully coupled fluid-structure solutions can predict higher loads and stresses. A modal recovery procedure which easily permits the representation on the acoustic effects of the fluid to be included in a structural model is also presented. Results are given for both simple models and a piping system from an LMFBR design.
Flow-Induced Vibration in Safety Relief Valves
Authors: Baldwin R. M. , Simmons H. R.
Published: November 2009

Flow-induced vibration in safety relief valves (SRV’s) in high-energy piping systems such as power plants is identified as the source of many SRV failures. The mechanism is an unstable coupling of vortex shedding at the mouth of the valve with the side branch acoustic resonance. Characteristics of the problem and computerized methods of acquiring data lead to positive identification of flow-induced vibration. Pulsation and vibration data recorded from several valves in power plant steam service are presented for comparison of stable and unstable configurations. Based on this data, a rational design procedure utilizing the relationship among Strouhal number, Mach number, and stub dimensions has been developed to eliminate an existing problem or to prevent one in a new piping system. Proper side branch sizing coupled with flow stabilization techniques provide for the design of a main pipe to safety valve transition piece which has been shown to be successful in several applications.
An Analysis of the Fatigue/Creep Behavior of 304 Stainless Steel
Using a Continuous Damage Approach
Authors: Gomuc R. , Bui-Quoc T.
Published: November 2009

A recently suggested procedure for estimating the life of a material subjected to fatigue-creep loading is applied to analyze the behavior of Type 304 stainless steel on the basis of the experimental data already available in the literature. The predictive technique is based on a combination of the two separate damage functions for fatigue and for creep. The effect of the tension hold time in interspersed creep-fatigue loading on the material life is taken into account by considering the relaxation stress characteristics during the hold period. The technique also permits the evaluation of damage (or healing) due to a compression hold time. The correlation between predictions and available experimental results obtained on Type 304 SS from 538 to 649° C under various loading conditions is discussed.
Shakedown and Cold Creep of Stainless Steel Type 316 Torispherical
Drumheads Subjected to Internal Pressure
Authors: Brookfield D. J. , Moreton D. N. , Moffat D. G.
Published: November 2009

The results from cyclic internal pressure tests on two nominally identical stainless steel type 316 torispherical drumheads are presented. The effect of cold creep is investigated and is shown to contribute most of the accumulated strain during pressure cycling. The experimental shakedown pressure is compared with the design pressures from BS 5500 and the effect of over-pressure testing on subsequent cyclic behavior is discussed.
Three-Dimensional Finite Element Analysis of a Scale Model Nuclear
Containment Vessel
Authors: Derbalian G. , Fowler G. , Thomas J.
Published: November 2009

Current design procedures for nuclear containment vessels are based on elastic analyses. Though such techniques are adequate under normal operating conditions, if the potential risks associated with extreme environments or accident conditions are to be assessed, knowledge of the ultimate capacity of the containment structure is essential. A key technical question is whether penetrations, such as personnel hatches, weaken the containment structure. In this paper, the maximum pressure sustained by a scale model, steel, nuclear containment vessel with a penetration is determined using a three-dimensional finite element analysis. To assess containment strength, a clean shell is analyzed in closed form for its ultimate strength, and the solution is then compared with finite element results for a structure that has a penetration. The comparison shows that the personnel hatch penetration does not reduce the ultimate strength of the containment structure. In this paper, it is assumed that the materials have no flaws and welded joints are perfectly bonded. Cracks in the structure, which would degrade its strength, are not considered.
Evaluation of Flaws in Austenitic Steel Piping
Authors: Section XI Task Group for Piping Flaw Evaluation, ASME
                            Code
Published: November 2009

This report summarizes the methods and bases used by the Task Group for Piping Flaw Evaluation to develop allowable flaw sizes for the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section XI, IWB-3640, “Evaluation Procedures and Acceptance Criteria for Austenitic Piping.” Because the Task Group identified two flaw-related failure mechanisms for light water reactor (LWR) austenitic steel piping, two sets of allowable flaw size tables were developed. One set is presented for base metal and nonflux welds, which have high flaw tolerance; a second set is provided for flux welds that can have lower relative toughness and flaw tolerance. Application of the flaw evaluation procedures for cast austenitic piping requires material classification on a case by case basis. Allowable flaw sizes are presented in tabular form, with the allowable part-through flaw depth defined as a function of load and flaw length. Tables are presented for both longitudinal and circumferential flaws, and normal/upset and emergency/faulted conditions. This report also recommends crack growth rate and weld residual stress data needed to perform subcritical crack growth analyses in accordance with Section XI, Appendix C, “Evaluation of Flaws in Austenitic Piping.” These data and the allowable flaw size tables provide the means to determine the acceptabiality for continued service of austenitic piping containing flaws whose sizes exceed the standards specified in Section XI, IWB-3514.3, “Allowable Indication Standards for Austenitic Piping.”
Stiffness of Pipe Straps for Computer Modeling—A Simplified
Approach
Authors: Tewfik W. A.
Published: November 2009

This paper includes a methodology and calculated results for the stiffness of two (2) types of pipe straps. The calculated results are then compared to two (2) other sources of data: finite element analysis (FEA) computer-generated results, and test results for some of strap sizes as listed in Table 1. All calculated, FEA and test results are tabulated in Table 1. A home computer has been utilized to generate all calculated figures for different pipe sizes and straps. Graphs 1 and 2 represent all results for equations generated in this paper and can be utilized to extract the stiffness values required when appropriate width and inside radii of straps are known.
A Review of Flow-Induced Vibration of Two Circular Cylinders in
Crossflow
Authors: Chen S. S.
Published: November 2009

The flow field around a pair of rigid circular cylinders is very complex and has been studied extensively. When either one or both cylinders vibrate, the flow field becomes significantly more complicated because of the interaction of the fluid flow and the cylinder motion. This paper presents an overview of the problem including different flow regimes, vortex-excited vibration, and fluidelastic instability for two cylinders in tandem, two cylinders side by side and two cylinders in staggered arrangement. A general formulation to study dynamic response under different conditions is outlined and future research needs are discussed.
Quantitative Assessment of Mass Discretization in Structural Dynamic
Modeling
Authors: Vashi K. M.
Published: November 2009

For dynamic analysis of majority of structures, a dynamic model is developed by discretizing the distributed mass and elastic properties. For assessing the adequacy of mass discretization, several procedures are used. These procedures include a comparison of analysis with test, parametric studies using finer mass discretizations, and lump mass spacing according to a frequency-controlled span length of a simply supported beam. This paper presents a quantitative assessment of mass discretization by utilizing exact analytical solution to the discrete problem of beam and bar vibrations. The assessment examines the effect of mass discretization on the accuracy of natural frequencies, modes and participation factors. In one modeling rule, the total number of dynamic degrees of freedom is taken to be twice the number of lower frequencies to be computed with a reasonable amount of accuracy. The assessment in this paper provides support for this rule.
An Efficient Computational Approach for a Large Opening in a
Cylindrical Vessel
Authors: Steele C. R. , Steele M. L. , Khathlan A.
Published: November 2009

In our previous work, solutions of the shallow shell equations have provided the basis for efficient computer calculation for a reinforced opening in a cylindrical vessel. However, solutions are restricted to smaller nozzles and openings (d/D≤0.5). In the present effort, an approach for the large opening has been developed which retains computational efficiency and minimum user time. The total solution can be divided into “high” harmonics around the intersection curve, which are obtained from asymptotic analysis, and particular solutions and low harmonics of self-equilibrating loads, which are obtained as “cut” solutions. By this, the vessel is considered to be cut along the portion of the circumference inside the intersection curve. Appropriate discontinuities of stress and displacement on the cut provide the necessary solutions. Results for a rigid nozzle with external loadings show good agreement with the previous shallow shell calculations for d/D≤0.5 with a substantial divergence for larger values of d/D. The behavior at the limit of d/D = 1 remains to be clarified.
Interaction of External Moment Loads With Internal Pressure on an
Equal Diameter Branch Pipe Intersection
Authors: Moffat D. G. , Mistry J.
Published: November 2009

Maximum stress intensities are presented for an equal diameter unreinforced cylinder/cylinder pipe intersection of mean diameter/thickness ratio 24.7, when subjected to the complete set of six individual moment loadings and also internal pressure. Stresses arising from combinations of the moment loadings are considered, and moment/moment and moment/pressure interaction diagrams are presented. From these diagrams the magnitudes of the various load combinations required to cause yielding can be determined. The significance of the results is discussed in the light of British and American piping design codes.
A Simple Fracture Mechanics-Based Method for Fatigue Life Prediction
in Thick-Walled Cylinders
Authors: Kendall D. P.
Published: November 2009

A method is proposed for predicting the fatigue life of thick-walled cylinders subjected to repeated internal pressure based on numerical integration of the fatigue crack growth curve as determined from fracture mechanics analysis. The effects of autofrettage residual stresses, crack shape, and of the compressive portion of the stress intensity factor range are accounted for. A method for correcting the residual stresses for the Bauschinger effect, based on recent analytical results by P. C. T. Chen [8], is also included. A simple computational scheme for calculating the fatigue life is presented. Results of this calculation are compared with experimental results of Davidson et al. [16] and of Throop and Fujczak [17].
J-Integral and Tearing Modulus Estimates for
Circumferentially Cracked Pipes in Torsion
Authors: Zahoor A.
Published: November 2009

J-integral and tearing modulus analyses are developed for full circumference part-through cracks in pipes under torsion. The approach is based on the psuedo-potential energy interpretation of the J-integral. The paper develops estimation formula for the plastic component of the J-integral for the condition of net-section yielding in the cracked section of the pipe. The applied tearing modulus estimates are derived for deformation-controlled loading. Numerical results are presented for crack initiation and tearing instability that provide quantitative results for inferring safety of cracked nuclear piping.
Comparison of Theoretical Estimates and Experimental Measurements of
Fatigue Crack Growth Under Severe Thermal Shock Conditions—Part I: Experimental
Observations
Authors: Marsh D. , Green D. , Parker R.
Published: November 2009

This paper reports the results of an experiment in which a severe thermal cycle comprising of alternate upshocks and downshocks has been applied to an axisymmetric feature with an internal, partial penetration weld and crevice. The direction of cracking and crack growth rate were observed experimentally and detailed records made of the thermal cycle. A second part of the paper, reported separately, compares a linear elastic fracture mechanics assessment of the cracking to the experimental observations.
Fatigue Crack Growth Rate Testing of Gun Steels
Authors: Morrison J. , Laforce C. H.
Published: November 2009

The experimental measurement of fatigue crack growth rates is an integral part of the fracture mechanics approach to safe life estimation in structures subjected to cyclical loading. To assess the variation in crack growth properties, data has been collected from five different gun steels from various sources. The experimental, analytical and statistical techniques are described, and an assessment is made of the applicability of a single growth rate expression. There are significant differences in strength, toughness and extent of autofrettage between these gun steels, and a correspondingly wide range of fatigue crack growth rates has been encountered.
On the Asymptotic Solutions of Dished Shell Heads in Pressure
Vessels
Authors: Guodong C.
Published: November 2009

In this paper, the basic equation is derived for dished thin shell heads in pressure vessels and the uniformly valid asymptotic solutions are given.
Impact-Induced Temperature Rise in a Thermovisco-Plastic
Rod
Authors: Nicholson D. W.
Published: November 2009

A solution is presented for stress, strain and temperature rise in a long rod subject to axial impact by a small rigid mass. The rod material is described by a bilinear thermoviscoplastic constitutive model. The rod response is assumed to be adiabatic, so that inelastic work is completely converted into heat. The general solution is derived using Laplace transforms, and a numerical inversion technique is formulated. Calculations are presented in a case typical of commercially pure titanium. It is hoped that this solution will serve as a "benchmark" for validating general purpose impact codes such as EPIC-II.
Notch Fatigue Crack Initiation in High Temperature Water Environments: Experiments and Life Prediction
Authors: Prater T. A. , Coffin L. F.
Published: November 2009

Test results, experimental techniques and analytical interpretations are reported from notched compact type (CT) tests of SA 333 Gr. 6 carbon steel to determine quantitatively fatigue initiation lives in high temperature oxygenated water. Parameters explored include environments of air, 0.2 ppm O2 and 8 ppm O2-water at 10.3 MPa (1500 psi), temperatures of 149, 232 and 288° C, frequencies of 0.00021, 0.0021 and 0.021 Hz, notch radii of 0.051 and 0.51 mm and R-values of 0.2, 0.5 and 0.8. Pseudostress amplitudes were calculated elastically and by Neuber notch analysis procedures using a worst case notch concept. Results were compared to ASME Section III fatigue data curves. Test results showed that the fatigue initiation life of carbon steel is substantially lowered as oxygen level is raised, as frequency is lowered or as temperature is raised. No frequency or temperature effect occurred in air. To a lesser extent, a decreasing notch radius or an increased R-value degrade the initiation life. Results compare favorably with interpretations based on environmental fatigue crack growth of this material.
Fatigue Life Estimates for a Notched Member in a Corrosive Environment
Authors: Kurath P. , Khan Z. , Socie D. F.
Published: November 2009

It is often assumed that the effects of an aggressive environment can be included in fatigue life estimation procedures by determining the material properties in the environment and at the frequency of interest. An analytical and experimental program was conducted to confirm or refute this assumption. Automotive grade aluminum alloy, 5454-H32, in 3 percent NaCl solution and laboratory environment was selected for this study. A simple model where the total fatigue life is the summation of the portion where fatigue damage is best described by the notch strain field, and the portion where nominal stress and crack length dominate damage assessment, was used to estimate fatigue lives for center notched plates. Smooth cylindrical specimens were employed to determine the material properties for initiation. The environment had a large influence on the initiation resistance of this material at long fatigue lives, whereas at shorter fatigue lives (i.e., <104 cycles) there was little effect. Center cracked plates were used to determine the crack growth rates. Linear elastic fracture mechanics concepts were employed to estimate crack propagation lives. Approximately a factor of three reduction in crack propagation life was attributable to the hostile environment. Center notched plate specimens with Kt = 2.4 and Kt=5.1 were tested in both environments to examine the model. The accuracy of the fatigue life predictions in relation to the experimental data were comparable in 3 percent NaCl solution to the results obtained in laboratory air.
Statistical Methods Applied to Fuel Rod Bow Analysis
Authors: Heller A. S. , Farnsworth D. A. , McGuinn E. J.
Published: November 2009

An extensive data base was used to arrive at an empirical “best estimate” model for predicting fuel rod bow as a function of burnup. The best estimate rod bow predictions were bounded (accounting for uncertainties) at an upper 95 percent value. This global bound or tolerance value was subsequently revised to be representative of the bow value at reactor operating conditions. Conservative predictions for bow were finally implemented at several high burnups in a statistically derived Departure from Nucleate Boil Ratio (DNBR) penalty function. It was found that penalties for DNBR due to bowing are insignificant even at higher burnups and, therefore, do not seriously impact the design thermal margin.
J-Integral Analysis for Notched Round Bar in Tension
Authors: Zahoor A.
Published: November 2009

J-integral and crack-associated displacement formulas are derived for a notched round bar in tension. The formulas are applicable for a wide range of flaw length to bar radius ratio. The formulas are particularly useful for calculating J from single load-displacement record obtained as part of fracture toughness test.
Evaluation of Tube-to-Tubesheet Junctions
Authors: Jawad M. H. , Clarkin E. J. , Schuessler R. E.
Published: November 2009

The strength of tube-to-tubesheet joints is influenced by many factors such as method of attachment, details of construction, and material property. In this report three methods of attachment are investigated. They are uniform expansion, mechanical rolling, and welding. Details of construction studied in this report are: the finish of tubesheet hole surface; grooved versus ungrooved tubesheets; and groove geometry. The effect of material property on the joint strength was investigated for carbon steel and titanium tubes attached to carbon steel tubesheet. The results indicate that a theoretical prediction of the behavior of joints is feasible for various materials, methods of attachment, and details of construction.
A Design Procedure for Evaluating the Tube Axial Load due to Thermal Effects in Multi-Pass Fixed Tubesheet Exchangers
Authors: Singh K. P. , Soler A. I.
Published: November 2009

The unequal length change of the tubes in various tube passes of a multi-tube pass fixed or floating head tubular exchanger produces axial tube loads which may be substantial in some operating units. This paper provides a rational analysis method, heretofore unavailable to the design community, to quantify the effect of multi-pass thermal expansion on the tube axial load. A numerical example is used to illustrate the solution procedure.
Validation of Inelastic Analysis by Full-Scale Component Testing
Authors: Griffin D. S. , Dhalla A. K. , Woodward W. S.
Published: November 2009

This paper compares theoretical and experimental results for full-scale, prototypical components tested at elevated-temperatures to provide validation for inelastic analysis methods, material models, and design limits. Results are discussed for piping elbow plastic and creep buckling, creep ratcheting, and creep relaxation; nozzle creep ratcheting and weld cracking; and thermal striping fatigue. Comparisons between theory and test confirm the adequacy of components to meet design requirements, but identify specific areas where life prediction methods could be made more precise.
Experimental Studies on Earthquake Response Behavior of Cylindrical Tanks
Authors: Zui H. , Shinke T. , Nishimura A.
Published: November 2009

A series of dynamic tests for the seismic behavior of ground-supported liquid storage tanks are evaluated and compared with previous theoretical studies. Two model tanks were subjected to shaking table tests with particular attention to the influence of base fixity and geometric imperfections in the tank walls. Test results support numerical calculations which show that base fixity conditions strongly influence the seismic response of tanks. Although high radial accelerations are induced by the imperfections, they are not found to be significant factors in tank failure.
Three-Dimensional Seismic Response Analysis of Buried Continuous or Jointed Pipelines
Authors: Takada S. , Tanabe K.
Published: November 2009

This paper presents a three-dimensional quasi-static analysis of continuous or jointed pipelines. Transfer Matrix Method was applied to the analysis providing for nonlinear behaviors of joints and soil frictions. An improved computer program ERAUL-II (Earthquake Response Analysis of Underground Lifelines-II) was developed for numerical computations. First, numerical response analyses were carried out for three-dimensional pipe systems with steel or cast iron pipe materials subject to large ground deformations or seismic ground motions. Analytical results show that torsional properties of pipes are also important factors for seismic behavior, which cannot be known by two-dimensional analyses. Second, experimental test data of three-dimensional steel pipe systems were simulated by using the ERAUL-II program. Simulated results agree well with the experimental values.
A New Model on Transient Wave Propagation in Fluid-Filled Tubes
Authors: Joung II-bok , Shin Y. S.
Published: November 2009

A new theory was developed for the fluid-filled semi-infinite tube model subjected to pressure impulse. The new model takes into account the shear and flexural waves of the elastic tube. The tube displacement field is axisymmetric. Axial deformations are based on the uniform extensional symmetric mode, and antisymmetric flexural mode along the tube thickness. Radial deformation is based on the uniform symmetric mode about the tube axis. Walker-Phillips’ theory can be recovered as a special, limiting case.
Experimental Study on Impact/Fretting Wear in Heat Exchanger Tubes
Authors: Cha J. H. , Wambsganss M. W. , Jendrzejczyk J. A.
Published: November 2009

The objective of this study is to provide qualitative impact/fretting wear information for heat exchanger tubes through the performance of a series of tests involving the pertinent parameters: force between the tube and its support; tube to support plate hole clearance; tube support plate thickness; preload; and tube vibration frequency. The characteristics of impact/fretting wear relative to material combinations and fluid environment were also investigated. The test apparatus consists of a cantilevered tube with a simulated tube support plate at the “free end.” Tube vibration is induced by an electromagnetic exciter to simulate the flow-induced tube motion occurring in a real heat exchanger at the tube/tube support plate interface. Tests are conducted in air, water, and oil, all at room temperature. Removable wear rings are attached to the tube free end and simulated support fixture. Wear ring materials include carbon steel, 304 stainless steel, Inconel 600 and brass. Wear is measured by a weight loss technique and wear rates are calculated and reported as functions of the various pertinent parameters. Based on the test results, general conclusions are drawn.
A Model for Fixed-Tubesheet Heat Exchanger
Authors: Cascales D. H. , Militello C.
Published: November 2009

A model for a fixed-tubesheet heat exchanger was developed under the assumption that the outer rim of the tubesheet behaves as a circular plate. The tubesheet is conceived as made up of two parts; an inner drilled plate with uniform tube pattern and an external circular rim. Previous models assumed the outer rim to behave as a rigid plate. Under our more realistic model, a more accurate and economic design is possible. Four examples are brought to bear in order to show the procedure as well as to compare the stress distributions for a previous model assuming a rigid ring and our flexible counterpart.
Pressure-Plus-Moment Limit-Load Analysis for a Cylindrical Shell Nozzle
Authors: Tabone C. J. , Mallett R. H.
Published: November 2009

A finite element model of a nozzle in a cylindrical shell is analyzed for three cases; pressure, out-of-plane moment and combined pressure plus out-of-plane moment. The model uses three-dimensional finite elements and the analysis considers inelastic behavior at small displacements. Load versus displacement behavior is given for the three cases. Estimates of limit loads are obtained based upon extrapolation of load versus inverse displacement data curves. An interaction expression is used to show the effect of the combined loading for a case in which an internal pressure reduces the moment capability of the nozzle by 35 percent.
Application of the Ritz Averaging Method in the Analysis of the Seismic Performance of Piping Systems
Authors: Pickett M. A. , Cunningham D. J. , Sinha S. K. , Madia J.
Published: November 2009

The Ritz averaging method is utilized to reduce the nonlinear characteristics of piping system supports (snubbers) to equivalent linear support stiffnesses during seismic excitation. The equivalent snubber support stiffnesses are used in seismic modal analyses of two piping systems. The analyses are performed in order to determine the effect that high snubber lockup velocities have on piping system stresses. The results show that the lockup velocity of snubbers in the systems analyzed can be safely allowed to increase above normal limits without any significant increase in nodal stresses.
Fatigue Life of Seamless Steel Pressure Vessels
Authors: Brockenbrough R. L.
Published: November 2009

Cyclic-pressure fatigue tests of three seamless steel pressure vessels show that typical production vessels should have a fatigue life at least equal to the allowable life calculated by code procedures. Stresses from finite-element models and strain-gage measurements are correlated and used in a simplified fracture mechanics approach for a conservative estimate of fatigue life.
Dynamic Stability of Pipes Under Jet Forces From a Circumferential Through-Crack
Authors: Keskinen R. P.
Published: November 2009

An investigation is made into the dynamic stability of a pipe with a postulated circumferential through-crack. The dynamic deformation of the pipe is found to control the ensuing jet force in such a manner that positive or negative damping results, depending on the local mode shape geometry. The leak is governed by quasi-steady fluid dynamics, which permits a simple closed-form evaluation of the damping energy for a crack geometry idealized from existing LEFM solutions. Energy losses develop via structural damping and plastic dissipation at the crack tip; the latter is estimated using the Irwin’s plastic zone correction approach. Application to a PWR plant primary circuit piping suggests that structural damping in practice rules out the instability.
Further Development of a Model for Predicting Corrosion Fatigue Crack Growth in Reactor Pressure Vessel Steels
Authors: Gilman J. D.
Published: November 2009

Analysis of fatigue crack growth data for low-alloy steel shows that the influence of cyclic frequency in simulated LWR environments can be interpreted as the superposition of a time-dependent, corrosion-assisted crack growth rate upon an increment predicted by a Paris law. The time-dependent component increases monotonically to a maximum of about 6×10−5 mm/s as stress cycling becomes more aggressive. A useful measure of aggressiveness is the average time rate of crack advance due to the Paris law component alone; i.e., AΔKn × frequency. The result suggests that current ASME Code methods for flaw assessment are highly conservative in some regimes of stress and frequency, but there is a possibility of growth rates well above the ASME XI, Appendix A curves in a very low-frequency, high-stress regime. An upper bound to the time rate of corrosion-assisted crack growth in low-alloy steel is well supported by the data. The threshold conditions for the onset of this high rate are less well defined and require further investigation.
Elastic-Plastic Plane Strain Analysis of Compressible Materials
Authors: Fan Hui , Widera G. E. O.
Published: November 2009

The analysis of elastic, perfectly plastic compressible materials under the assumption of plane strain is a statically indeterminate problem. In the present paper, by introducing a perturbation parameter ε = 1/2−ν, the problem can be changed into a series of statically determinate ones. The first-order approximation yields the solution for the incompressible material. In order to show the details of this method, the second-order approximation for the problem of the thick-walled cylinder under internal pressure is obtained.
Assessment of Current High-Temperature Design Methodology Based on Structural Failure Tests
Authors: Corum J. M. , Sartory W. K.
Published: November 2009

A mature design methodology, consisting of inelastic analysis methods provided in U.S. Department of Energy guidelines and failure criteria contained in ASME Code Case N-47, exists in the United States for high-temperature reactor components. The objective of this paper is to assess the adequacy of that overall methodology by comparing predicted inelastic deformations and lifetimes with observed results from structural failure tests and from an actual service failure. Comparisons are presented for three structural cases: 1) nozzle-to-spherical shell specimens, emphasizing stresses at structural discontinuities; 2) welded structures, emphasizing metallurgical discontinuities; and 3) thermally loaded cylinders and pipes, emphasizing thermal discontinuities. The comparisons between predicted and measured inelastic responses are generally reasonable; quantities are sometimes overpredicted somewhat and sometimes underpredicted. However, even seemingly small discrepancies in predicted stresses and strains can have a significant effect on life, which is thus not always as closely predicted. For a few cases, the lifetimes are substantially overpredicted, which raises questions regarding the methodology and/or the adequacy of the current design margins.
The Impact of Tube Plugging on Closed Feedwater Heater Operation and Maintenance
Authors: Linley F. H.
Published: November 2009

Failures of tubes in closed feedwater heaters are due to localized thermal, mechanical and chemical processes, in combination with the susceptibility of the tube material involved. Experience has demonstrated that changes in operating practice such as feedwater chemistry, frequency of exposure to atmosphere on shutdown and other factors often modify the environmental conditions and introduce unanticipated causes of tube failure. Good practice calls for immediate corrective action, whenever tubes fail, to arrest extension of the problem. Such corrective action is based on an accurate determination of the location of each failure with respect to the tube pass, position in the tube field and distance from the face of the tubesheet. Nondestructive examination and individual tube hydro test of adjacent and other suspect tubes for incipience of failure is required, including the examination of failure specimens, if they can be recovered. More than one failure mechanism may be in process in a heater and no problem potential should be treated casually. Analysis of tube plugging should consider the affect of each failure on heater performance and other equipment in the system, the probability of chronic, continuing failures and the ultimate number of tubes that can be plugged before plant capacity is curtailed. Once the tubes that should be plugged have been determined, plugging systems and installation techniques must also be addressed, with emphasis on preventing secondary damage from failed tubes and the avoidance of any failure caused by the plugs themselves.
Subspace Iteration for Eigen-Solution of Fluid-Structure Interaction Problems
Authors: Yu I.-W.
Published: November 2009

The subspace iteration method, commonly used for solving symmetric eigenvalue problems in structural dynamics, can be extended to solve nonsymmetric fluid-structure interaction problems in terms of fluid pressure and structural displacement. The two cornerstones for such extension are a nonsymmetric equation solver for the inverse iteration and a nonsymmetric eigen-procedure for subspace eigen-solution. The implementation of a nonsymmetric equation solver can easily be obtained by modifying the existing symmetric procedure; however, the nonsymmetric eigen-solver requires a new procedure such as the real form of the LZ-algorithm. With these extensions the subspace iteration method can solve large fluid-structure interaction problems by extracting a group of eigenpairs at a time. The method can generally be applied to compressible and incompressible fluid-structure interaction problems.
Buckling of Oil Storage Tanks in SPPL Tank Farm During the 1979 Imperial Valley Earthquake
Authors: Shih C.-F. , Babcock C. D.
Published: November 2009

An oil storage tank that suffered damage during the 1979 Imperial Valley earthquake is studied using a laboratory model. The tank is unanchored and includes a floating roof. The tank is subjected to a single horizontal axis base excitation. Buckling is studied under both harmonic and simulated earthquake base motion. The model buckling results are in reasonable agreement with the field observations. It was also found that the floating roof has no effect on the buckling behavior. Comparison with the API design provisions shows that the empirical model used as the basis of the code for both tip-over and buckling have little resemblance to the actual tank behavior.
Development of Design Criteria for a High Pressure Vessel Construction Code
Authors: Mraz G. J.
Published: November 2009

Out of concern for public safety, most legal jurisdictions now require unfired pressure vessel construction to comply with the ASME Boiler and Pressure Vessel Code. Because the present two divisions of Section VIII of that Code are not well suited for high pressure design, a new division is needed [1]. The currently anticipated main design criteria of the proposed division are full plastic flow or full overstrain pressure, stress intensity in the bore, fatigue, and fracture mechanics. The rules are expected to allow better utilization of high strength steels already included in the present Section VIII. At the same time materials of even higher strength are introduced. The benefits of compressive prestress are recognized. Construction methods allowing it’s achievement, such as autofrettage, shrink fitting and wire winding are included. Reasons for selection of the criteria are given.
A Rational Design of Thin-Walled Pressure Vessel Ends
Authors: Szyszkowski W. , Glockner P. G.
Published: November 2009

Optimal contours for heads of cylindrical pressure vessels are discussed. As opposed to the common method of preventing buckling in pressure vessel ends by means of increased wall thickness or local reinforcements, this paper proposes a design for “buckle-free” shapes in which the contour is established/adjusted so as to ensure stable behavior. A previous analysis by the authors, in which compressive stresses were eliminated, is extended so as to take into account the actual flexural rigidity of the wall. The shapes obtained from such buckle-free designs appear to be similar to standard ellipsoidal and torispherical ends and should be acceptable from various design and aesthetic viewpoints.
Buckling at the Top of a Fluid-Filled Tank During Base Excitation
Authors: Natsiavas S. , Babcock C. D.
Published: November 2009

An explanation is provided for the earthquake-induced damage observed at the top of liquid storage tanks. An analysis is developed and the results are compared with experimental work. The basic steps of the analysis, which is developed for the general dynamic response of fluid-filled tanks under horizontal ground excitation, are first presented. In this analysis, the structural displacements are expanded in appropriate series forms which involve both rigid body and flexible components. The latter components are expressed as linear combinations of terms, each of which is a product of a function with assumed spatial dependence and an unknown time-dependent function. These time functions are then determined from the solution of the fluid/structure system equations, which are set up by employing Hamilton’s principle. In the present work, results are obtained and compared with model tests carried out at Caltech, during which buckling was observed at the top of the tank under a known base excitation history. Computing analytically the corresponding pressure distribution and using the BOSOR computer code for the buckling computations, a value for the amplitude of the ground acceleration which results in buckling at the top of the tank is calculated. Good correlation with the test work is obtained.
A Finite Element Model to Analyze Cylinder-Cylinder Intersections
Authors: Natarajan R. , Widera G. E. O. , Afshari P.
Published: November 2009

A finite element model is proposed to study the stresses in the neighborhood of a cylinder-cylinder intersection. In particular, diameter ratios greater than 0.5 are focused upon since little information is available in the ASME Boiler and Pressure Vessel Code or in the literature about the stress concentration for these geometries. The aim of the present work is to validate such a model for internal pressure loading. To accomplish this, various parametric finite element studies were conducted. The selected model is then validated by applying it to various available cylinder intersection models and comparing the results. The finite element results are further compared with a solution obtained using a shell theory.
Comparison of Theoretical Estimates and Experimental Measurements of Fatigue Crack Growth Under Severe Thermal Shock Conditions—Part II: Theoretical Assessment and Comparison With Experiment
Authors: Green D. , Parker R. , Marsh D.
Published: November 2009

This paper reports the theoretical assessment of cracking which may occur when a severe cycle comprising alternate upshocks and downshocks is applied to an axisymmetric feature with an internal, partial penetration weld and crevice. The experimental observations of cracking are reported separately. A good agreement was noted even though extensive cycle plasticity occurred at the location of cracking. It is concluded that the LEFM solution has correlated with the experiment mainly because of the axisymmetric geometry which allows a large hydrostatic stress to exist at the internal weld crevice end. Thus the stress at the crevice can approach the singular solution required for LEFM correlations without contributing to yielding.
Modeling of 316 Stainless Steel (17.12 Sph.) Mechanical Properties Using Biaxial Experiments—Part I: Experiments and Basis of the Model
Authors: Delobelle P. , Oytana C.
Published: November 2009

Experimental results aimed at establishing the relationship existing between plastic instantaneous and creep strains are reported. They are chiefly tensile at constant strain rates and tensile or tensile-torsion creep experiments. Recovery and hardening are also measured. It is shown that two types of viscous behavior may occur according to whether the loading path is an active loading or an unloading. The features of these two types of viscoplastic behavior are such that they can be modeled with the same plastic state equation using a single internal variable. But according to a criterion based on internal variables, the single internal variable of the plastic state equation may split into the sum of an isotropic and a kinematical variable with small strain hardening (case of large viscoplastic strains) or remain a single kinematical variable with very high hardening (case of unloadings). The bases of the model are described.
Creep Relaxation in Multilayer Wrapped Vessels
Authors: Dalton M. , Sabbaghian M.
Published: November 2009

One of the common methods of construction of vessels for high to ultra-high pressure applications is the wrapping technique. In this method, relatively thin plates (normally in the range of 6 mm) are rolled to proper curvature, wrapped around the core or the preceding layers and then welded. In this fashion, a prestress is gradually built in the cylinder wall which would compensate and moderate the extreme stresses due to internal pressure. Relying on such prestress, however, should be done only with careful consideration of stress relaxation that will take place while the vessel is in service, especially in high temperature services. In this paper, the initial stresses due to wrapping are obtained. These stresses are due to shrinkage of the weld as well as the plate affected by the heat of welding. The power function stress-creep strain rate is employed to predict the relaxation of interface pressure between any two adjacent layers. The creep stress distribution based on relaxing interface pressures are given as a function of time. In such vessels, in order to maintain the same safety factor as existed when the vessel was constructed, the internal pressure must be decreased with time. A relationship between the internal pressure and time, based on a constant safety factor, is obtained. Alternately, for the case of internal pressure being kept at the same level, a relationship is obtained that would give the decreasing safety factor or the vessel as a function of time.
Modes of Failure—Primary and Secondary Stresses
Authors: Roche R. L.
Published: November 2009

The paper begins with a reminder that the purpose of stress classification is to ensure suitable margins with respect to failure modes. The distinction between primary stresses and secondary stress is then examined and a method is given for assessing the degree of spring effect (elastic follow-up) in the elastic plastic field. The importance of the spring effect is then highlighted by an examination of the effect of primary and secondary stresses on instability and on crack behavior.