bluuebunny/crossref_metadata_2025 huggingface dataset:
Defect Assessments at Elevated Temperature
Authors: Ainsworth R. A. , Goodall I. W.
Published: November 2009

Methods are described for assessing acceptable defect sizes for plant in high temperature service. At one extreme of behavior, that of creep ductile response, failure is governed by continuum damage mechanics which may be analyzed using finite element methods or more approximately by reference stress techniques. In less ductile cases failure can occur through the initiation and growth of a dominant creep crack. For this case the paper outlines how the assessment requirements may be based on an estimate of the initiation time and a method for calculating this initiation time is given. When the initiation time is small, the assessment also requires an estimate of the time taken in the creep crack growth stage and both empirical correlation and statistical approaches for analyzing this stage are described. Finally the paper outlines how fast fracture and ductile instability can be included in determining repair criteria for use with the various assessment methods.
Stress Intensity Factor Solutions for Internal Longitudinal Semi-Circular Surface Flaws in a Cylinder Under Arbitrary Loading
Authors: Lee Y. S. , Raymund M.
Published: November 2009

The behavior of semi-circular surface flaws in cylinders is of interest in the technology of pressure vessels. The object of this study is to determine the stress intensity factor distribution around the crack front under arbitrary loading conditions for a longitudinal semi-circular flaw with Ri/t = 10; where Ri is the inside radius of the cylinder, and t is the cylinder thickness. Six crack depths are studied under various loading conditions: a/t = 0.10, 0.25, 0.50, 0.65, 0.80, and 0.90, where a is the circular flaw radius. In general, the finite element method is used to determine the displacement solution. Parks’ stiffness derivative method is used to find the stress intensity factor distribution around the semi-circle. The immediate crack tip geometry is modeled by use of a “macro-element” containing over 1600 degrees of freedom. Four separate loadings are considered: 1) constant, 2) linear, 3) quadratic, and 4) cubic crack surface pressure. From these loadings, nondimensional magnification factors are derived to represent the resulting stress intensity factors. Comparisons are made with other investigators and results agree within 5 percent of published results.
Added Mass for Beam Mode Response
Authors: Fisher H. D.
Published: November 2009

In 1972 a method was presented for evaluating the added mass of fluid contained between two long co-axial cylinders. The resulting equations have been widely quoted in the literature, and the resistive forces obtained from these expressions have been utilized extensively in seismic and LOCA studies to demonstrate design integrity. The present study extends the analysis to less idealized design configurations in which a finite annular geometry is subjected to a velocity that is a function of the axial coordinate. The theory includes the capability to model the effect of any combination of closed-open axial boundary conditions on the fluid and to compute the added mass associated with motion of either or both of the radial boundaries.
Experimental Buckling Investigation of Ring-Stiffened Cylindrical Shells Under Unsymmetrical Axial Loads
Authors: Baker W. E. , Bennett J. G. , Babcock C. D.
Published: November 2009

Six steel shells having nuclear containmentlike features were fabricated and loaded to failure with an offset axial load. The shells (R/t = 500) buckled plastically. Four of the shells had reinforced circular cutouts. These penetrations were sized to cut no ring-stiffener, a single, two- or three-ring stiffeners. Reinforcing and framing around the penetrations were based upon the area-replacement rule of the applicable portion of the ASME Boiler and Pressure Vessel Code and were of a design to simulate actual practice for nuclear steel containments. Prior to testing, imperfections were measured and strain gages were applied to determine information on load distribution at the ends of the cylinder and strain fields at areas likely to buckle. Buckling loads were determined for an axial load applied with an eccentricity of R/2 where R is the cylinder radius. The results showed that the buckling load and mode for the shell having a penetration that did not cut a ring stiffener were essentially the same as those for the unpenetrated shell. The buckling loads for the penetrated shells in which stiffeners were interrupted were less than that for the unpenetrated shells. Results of all tests are compared to numerical solutions carried out using a nonlinear collapse analysis and to the predictions of ASME Code Case N-284.
Membrane Theory for Layered Ellipsoidal Shells
Authors: Logan D. L. , Hourani M.
Published: November 2009

The stress analysis of a laminated anisotropic ellipsoidal membrane shell of revolution is considered. A system of equations which is appropriate to the elastic behavior of anisotropic membrane shells of revolution is used as a basis. These equations are applied to the specific geometry of an ellipsoidal shell to develop the particular equations used in the analysis. Closed-form solutions are derived for the stresses and displacements. Methods for determining the extremely cumbersome integrals in the equations for the displacements are discussed as well. To illustrate the equations, solutions are presented for an ellipsoidal shell simply supported on one edge and subjected to internal pressure loading. Numerical results are presented for glass-epoxy and boron-epoxy material systems.
A Parametric Approach for the Stress Analysis of Orthogonally Stiffened Rectangular Plates
Authors: Dohrmann R. J. , Wu J. N. , Beckett R. E.
Published: November 2009

This report describes a parametric approach for the stress analysis of orthogonally stiffened rectangular plates. The analysis assumes that the deflection of an orthogonally stiffened plate is approximated by a homogeneous orthotropic plate of a uniform thickness. Polynomial expressions for maximum deflection for two sets of boundary conditions (all edges clamped and two edges clamped–two edges simply supported) are presented in terms of plate geometry and loading (normal pressure and in-plane forces). A method for computing the stress is presented that permits stresses in the actual orthogonally stiffened plate (that generally does not have a uniform plate thickness) to be determined.
A Theoretical Evaluation of the Backfill Effect in Fracture of Gas Pressurized Pipelines
Authors: Alpa G. , Bozzo E. , Gambarotta L.
Published: November 2009

The constraining action exerted by the soil surrounding pipelines, when an axial fracture propagates, has been analyzed through a simplified model. In order to avoid large-scale numerical computations, two main hypotheses have been assumed: (a) the deformed configuration of the fractured pipe has been considered as defined by two geometrical parameters; (b) the soil has been schematized as a cohesionless medium composed of rigid particles with friction. The energy absorption rate by soil during fracture propagation and the constraining forces on the pipe walls has been obtained as a function of the fracture speed and acceleration, of kinematic and geometric parameters and of the soil properties. Available experimental data give factors supporting the engineering evaluation of the backfill effect developed in the paper.
Suitability of Synthesized Waveforms for Seismic Qualification of Equipment
Authors: Kana D. D. , Pomerening D. J.
Published: November 2009

Qualification of nuclear plant equipment and components can be performed by analysis, test, or a combination of both. It is often required to synthesize artificial time histories which represent earthquake excitation at either ground level, or some elevated level of a structure. A set of parameters appropriate for the synthesis of acceleration time histories is developed. The parameters are based on a study of six typical earthquake accelerograms, and include general characteristics of the motion, a definition of strong ground motion, frequency content, stationarity, coherence between orthogonal components, and amplitude probability density. It is concluded that the strong ground motion can be approximated by a stationary Gaussian random process, whose frequency content depends on the ground or elevated position of concern. Coherence between orthogonal components is low at ground level, but can become high at elevated structural levels due to coupled responses. Some examples are given for application of the parameters to qualification by testing, as a means of achieving better satisfaction of existing criteria.
Thermal Stratification in Steam Generator Feedwater Lines
Authors: Braschel R. , Miksch M. , Schu¨cktanz G.
Published: November 2009

In recent years cracks have been found in the inlet nozzles of feedwater lines of steam generators. These cracks occur as a result of material fatigue. Thermal stratification in the feedwater is probably one of the factors primarily responsible for the fatigue. This paper describes methods of calculating the stress intensity ranges occurring as a result of the stratification. In addition, a design modification (a diversion tank) is proposed which effectively prevents the occurrence of this load case.
On the Determination of the Propagation Pressure of Long Circular Tubes
Authors: Kyriakides S. , Yeh M.-K. , Roach D.
Published: November 2009

A propagating buckle can be initiated in tubes under external pressure from localized imperfections. Once initiated a buckle will propagate with the result of flattening the tube behind it. The lowest pressure at which it can propagate is known as the propagation pressure, and it represents a characteristic pressure of the tube. The paper attempts to model quasistatic steady-state propagation through a plane strain large deflection, inelastic analysis of the collapse of a circular ring. An energy balance type of argument is used to obtain a lower-bound estimate of the propagation pressure from the ring response. The results are compared with experimental results obtained from stainless steel and aluminum tubes having diameter-to-thickness ratios ranging between 100 and 10. It was found that for these two materials the estimated value for the propagation pressure was in good agreement with experimental results for D/t > 20.
The Effect of Length: Diameter Ratio on Collapse of Casing
Authors: Huang N. C. , Pattillo P. D.
Published: November 2009

This paper presents an analysis of the cross-sectional collapse of a cylinder of finite length loaded simultaneously by an axial tension (which may be zero) and external pressure. The calculation is based on Sanders’ nonlinear shell equations with plasticity introduced via the concept of effective stress from a uniaxial tension test. The finite cylinder is an appropriate model of oil well casing as it undergoes quality control testing in the steel mill where the edges of the cylinder are usually fixed in the case of nonzero axial load and free in the case of zero axial load. However, in field application, the length: diameter ratio of casing is such that the cylinder may be considered infinite. Guidelines contained herein permit prediction of the collapse resistance of field casing from the results of mill tests performed on short samples.
Development of B1 and C1 Stress Indices for Trunnion Elbow Supports
Authors: Williams D. K. , Lewis G. D.
Published: November 2009

A finite element analysis of a trunnion elbow support is presented for the case of a long radius elbow subjected to an internal pressure loading. The stress results are categorized as average and linearly varying (through the thickness) stresses. The resulting stresses are then interpreted per Section III of the ASME Boiler and Pressure Vessel Code from which the primary and secondary (B1 and C1) pressure stress indices are developed. Several analysis were performed on various structural geometries in order to determine empirical relationships for the stress indices as a function of dimensionless ratios.
Limits of Linear Elastic Fracture Mechanics
Authors: Bloom J. M. , Hechmer J. L.
Published: November 2009

This paper presents a simple procedure for determining the validity limits of linear elastic fracture mechanics (LEFM) calculations for low alloy steel (ferritic) structures. The procedure is limited to structures with flaws whose depths are 50 percent or less of the wall thickness of the component at the flaw location and to components which can be considered to be in a plane strain state. Typical yield and ultimate strengths are assumed to be 60 and 80 ksi (414 and 552 MPa), respectively. The procedure is based upon failure assessment curves derived for typical nuclear vessels and components. Calculations of the ratios of the linear elastic stress intensity factor to the plane strain fracture toughness and the applied load to the plastic collapse load are used in conjunction with these curves to determine the validity limits of LEFM. The procedure is limited to the consideration of primary loading. When the load calculated by LEFM deviates significantly from the load calculated assuming elastic-plastic behavior, LEFM is deemed to be invalid and an elastic-plastic calculation procedure is recommended. Example problems are given which demonstrate the applicability of LEFM analysis in one case and the inapplicability in another case. The paper is an extension of the ideas and work generated from the Electric Power Research Institute research project RP 1237-2.
Comparison of Different Methods for the Determination of Stress Intensity Factors of Cracks in Pipes With Stress Gradients
Authors: Mattheck C. , Morawietz P. , Munz D. , Stamm H.
Published: November 2009

Stress intensity factors for long longitudinal and complete circumferential cracks under stress gradients were calculated using a weight function method. The weight functions were obtained by a method proposed by Petroski and Achenbach [3] and by a finite element fit procedure. Excellent agreement was obtained with finite element results of Labbens, et al. [7].
Stochastic Simulation of PWR Vessel Integrity for Pressurized Thermal Shock Conditions
Authors: Jackson P. S. , Moelling D. S.
Published: November 2009

A stochastic simulation methodology is presented for performing probabilistic analyses of Pressurized Water Reactor vessel integrity. Application of the methodology to vessel-specific integrity analyses is described in the context of Pressurized Thermal Shock (PTS) conditions. A Bayesian method is described for developing vessel-specific models of the density of undetected volumetric flaws from ultrasonic inservice inspection results. Uncertainty limits on the probabilistic results due to sampling errors are determined from the results of the stochastic simulation. An example is provided to illustrate the methodology.
Accurate Treatment of Material Interface Dynamics in the Calculation of One-Dimensional Two-Phase Flows by the Integral Method of Characteristics
Authors: Shin Y. W. , Wiedermann A. H.
Published: November 2009

Accurate numerical methods for treating the junction and boundary conditions needed in the transient two-phase flows of a piping network were published earlier by us; the same methods are used to formulate the treatment of the material interface as a moving boundary. The method formulated is used in a computer program to calculate sample problems designed to test the numerical methods as to their ability and the accuracy limits for calculation of the transient two-phase flows in the piping network downstream of a PWR pressurizer. Independent exact analytical solutions for the sample problems are used as the basis of a critical evaluation of the proposed numerical methods. The evaluation revealed that the proposed boundary scheme indeed generates very accurate numerical results. However, in some extreme flow conditions, numerical difficulties were experienced that eventually led to numerical instability. This paper discusses further a special technique to overcome the difficulty.
Pipe Whip Considerations for Design of Nozzles
Authors: Kumar R.
Published: November 2009

Effects of pipe breaks on nozzle design have been considered in this paper. Simple methods have been used for estimating the maximum possible pipe whip loads for design of nozzles and other components. The required minimum thickness for nozzles has been established to account for pipe whip loads in the design. For typical nozzle and pipe materials, this thickness within reinforcement limit of nozzles should be approximately two and a half (2 1/2) times the attached pipe thickness.
Tubesheet Thicknesses and Tube Loads for Floatinghead and Fixed-Tubesheet Heat Exchangers
Authors: Soehrens J. E.
Published: November 2009

This paper presents procedures for computing tubesheet thicknesses and tube loads for floatinghead and fixed-tubesheet heat exchangers. It was prepared in connection with the activities of the Special Working Group on Heat Transfer Equipment of the ASME Boiler and Pressure Vessel Code Committee, for their use and consideration in the drafting of code rules for these items. The mathematical procedures are closely associated with the publications of Mr. K. A. Gardner. These are references [1 and 2] of the attached bibliography. As far as practicable, the symbols in this paper are those used by Gardner. Some differing symbols are used to be consistent with currently used Code symbols.
Plastic Strain Energy in Fatigue Failure
Authors: Ellyin F. , Kujawski D.
Published: November 2009

In this paper the cyclic plastic strain energy of the A-516 Gr. 70 carbon low-alloy steel during fully reversed constant strain or stress-controlled cycles is discussed. A relationship is proposed which can be used to determine the plastic strain energy per cycle for a non-Masing material for various stress ranges during the entire life cycle. Predictions of the proposed method are in good agreement with the experimental data. The variation of the plastic strain energy per cycle and cyclic creep during the life of fully reversed stress-controlled tests is also presented. It is shown that the cyclic creep strain affects the fatigue crack initiation period and consequently the amount of the total absorbed plastic strain energy to failure.
Curvatures and Membrane Stresses in Pressure Vessel Heads
Authors: Shang H. M. , Hsu T. C.
Published: November 2009

In this paper, the membrane stresses induced in axisymmetrical shells subjected to internal loading are analyzed in the light of curvatures. This approach enables a deeper understanding of the subtle relationships of the generator, the shape of the surface thus generated, and the membrane stresses. Some common pressure vessel heads are used to demonstrate the present analysis.
The Velocity of Missiles Generated by the Disintegration of Gas-Pressurized Vessels and Pipes
Authors: Baum M. R.
Published: November 2009

A theoretical model is developed to describe the velocity of fragments generated when a gas-pressurized vessel disintegrates. The predictions are compared with new and existing experimental data for spherical and cylindrical vessels and are shown to be an improvement over the widely used empirical correlation developed by Moore. It is also shown that, by an appropriate definition of the energy available for doing work on the fragments, the velocity of the fragments from the disintegration of a section of gas pipeline may be predicted by the same model.
A Method for In Situ Test and Analysis of Nuclear Plant Equipment
Authors: Unruh J. F. , Polch E. Z. , Kana D. D.
Published: November 2009

Requalification of equipment in operating nuclear power plants to present-day criteria can be an expensive undertaking; however in situ measurements and data analysis procedures can be used to significantly reduce these costs. The procedures necessary to develop a required response spectrum for an instrument located at an elevated position within a base-fixed enclosure from modal analysis parameter measurements on the enclosure while installed in operating nuclear plant is addressed. Several examples are given to demonstate the ability of the procedures to develop the parameters necessary to predict component elevated responses from postulated enclosure base motion without recourse to analytical structural modeling of the base-fixed structure.
Ductile Fracture of Circumferentially Cracked Type-304 Stainless Steel Pipes in Tension
Authors: Zahoor A. , Norris D. M.
Published: November 2009

Circumferentially cracked pipes subjected to tensile load were analyzed for finite length and constant depth part-through cracks located at the inside of the pipe wall. The analysis postulated loads sufficient to cause net-section yielding of the flawed section. It was demonstrated that a propensity for predominantly radial growth exists for part-through cracks loaded in tension. This result is similar to the result for bend loading, except that bend loading causes more favorable conditions for wall breakthrough than tension loading. Numerical results were developed for 4-in. and 24-in-dia pipes. Safety margins for displacement controlled loads were described by a safety assessment diagram. This diagram defines a curve delineating leak from fracture in a space of nondimensional crack length and crack depth. 4-in-dia schedule 80 Type-304 stainless steel pipes with length to radius ratio (L/R) of up to 100 exhibited leak-before-break behavior.
Stable Growth and Instability of Circumferential Cracks in Type 304 Stainless Steel Pipes Under Tensile Load
Authors: Yagawa G. , Takahashi Y. , Kashima K. , Hasegawa K. , Saito M. , Umemoto T. , Sasaki N.
Published: November 2009

Flaws due to stress corrosion cracking have frequently been found in Type 304 stainless steel piping of some boiling water reactor (BWR) plants. In this work, in order to quantitatively examine the integrity under the presence of such cracks, pipe fracture tests and related finite element analyses were conducted. The unstable fractures were observed under the quasi-static and the dynamic tensile loading conditions with a high-compliance test machine. The finite element methods were used to demonstrate the effectiveness of the J-integral and the crack tip opening angle (CTOA) as criteria for stable crack extension, and that of the total displacement stationariness condition as a criterion for the onset of instability.
Thermal Stresses in U-Tubes Versus Bend Radius and Baffle Spacings
Authors: Le´ N. V.
Published: November 2009

Analytical and explicit formulas are developed to give maximum rotation, bending moment and stress in heat exchanger U-tubes due to the difference between thermal expansions of hot leg and cold leg. The formula for maximum axial plus bending stress is given in the form of an ordinary uniaxial thermal stress multiplied by a factor f which is a function of geometric details of the tube. These formulas are intended for designers to quickly check secondary stresses in heat exchanger U-tubes and to study a possibility of improving the lifetime of small bends against Stress Corrosion Cracking by minimizing the stress in function of design details of U-tubes.
The Impact of NDE Unreliability on Pressure Vessel Fracture Predictions
Authors: Simonen F. A.
Published: November 2009

This paper reviews the significant variables of flaw depth, length, location and orientation required for fracture mechanics evaluations of pressure vessel integrity. Results of calculations emphasize pressurized thermal shock (PTS) and the significance of flaws located at or near the inside surface of the vessel. For PTS conditions, previous studies have shown that vessel failure probability is relatively insensitive to flaw depth. In this study the impact of flaw length is also evaluated. Results of other evaluation show the importance of accurately locating flaws by NDE. The influence of vessel cladding is emphasized, with the relative significance of flaws through the clad and at various depths below the clad being addressed.
Study on Underclad Cracking in Nuclear Reactor Vessel Steels
Authors: Horiya T. , Takeda T. , Yamato K.
Published: November 2009

Susceptibility to underclad cracking in nuclear reactor vessel steels, such as SA533 Grade B Class 1 and SA508 Class 2, was studied in detail. A convenient simulation test method using simulated HAZ specimens of small size has been developed for quantitative evaluation of susceptibility to underclad cracks. The method can predict precisely the cracking behavior in weldments of steels with relative low crack susceptibility. The effect of chemical compositions on susceptibility to the cracking was examined systematically using the developed simulation test method and the following index was obtained from the test results: U=20[V]+7[C]+4[Mo]+[Cr]+[Cu]−0.5[Mn]+1.5log[X]X=Al…..Al/2N≦1X=2N…..Al/2N>1 It was confirmed that the new index (U) is useful for the prediction of crack susceptibility of the nuclear vessel steels; i.e., no crack initiation is detected in weldments in the roller bend test for steels having U value below 0.90.
Load-Carrying Capacity of Welded Slip Joints
Authors: Tawfik M. S. , O’Rourke T. D.
Published: November 2009

Welded slip joints, which are used in many high-pressure water transmission pipelines, are vulnerable during earthquakes to axial compressive loads generated by ground movements. This paper analyzes two failure modes associated with: 1) yielding in the vicinity of welded connections, and 2) plastic flow in the curvilinear, belled ends of the joints. The analyses indicate that the axial load causing plastic deformation is from three to five times smaller than that causing yield in straight sections of pipe. Typical slip-joint dimensions are studied, and recommendations are made for improving the axial load-carrying capacity by 50 to 100 percent.
Dynamic Response of a Buried Pipeline at Low Frequencies
Authors: O’Leary P. M. , Datta S. K.
Published: November 2009

A long wavelength and low-frequency analysis is presented here for the dynamic behavior of a long continuous pipeline embedded in an elastic medium. Using a shell model for the pipe, it is shown that the dynamic amplification of axial and hoop stresses induced in the pipe due to traveling plane waves (longitudinal and shear) depends crucially on the ratio of the rigidities of the surrounding soil and the pipe. Results are presented showing the dependence of the induced stresses on the direction of propagation of the incident waves, the Poisson’s ratios and rigidities of the ground and pipe materials.
Minimum Mass Design of Boiler Drums by Nonlinear Programming
Authors: Kowalski J.
Published: November 2009

Based on the systems approach to mathematical modeling, the paper shows the method for selecting the optimum design features of boiler drums with a given structure for minimum mass. The optimization problem is reduced to finding the minimum of the objective function in a 10-dimensional space bounded by 11 constraints. The numerical example has been presented.
Alternate Designs for Piping Integral Attachments
Authors: Ghosn A. H. , Bersu Z. J.
Published: November 2009

Axisymmetric discontinuity elastic analyses for two designs of piping integral attachments are presented. The proposed designs are partial and full penetration welded shear rings. The analytical approach used is that of interaction between finite structural elastic elements. The mid-surface displacements and the discontinuity loads at the interfaces are generated.
The Uniformly Valid Asymptotic Solution of Ellipsoidal Shell Heads in Pressure Vessels
Authors: Guodong C.
Published: November 2009

In this paper, the complex equation is derived for the ellipsoidal shell heads in pressure vessels and uniformly valid asymptotic solution is given.
Safety Valve Dynamic Instability: An Analysis of Chatter
Authors: MacLeod G.
Published: November 2009

Safety valve chatter, which is characterized by violent oscillation of the disk or closure member, is a dynamical phenomenon representable by differential rather than algebraic equations. It is shown that the conditions necessary for avoiding chatter may be determined from the behavior of the differential equations in the region of certain critical points. The paper demonstrates how to determine these points and establish conditions necessary for avoiding chatter. The method is illustrated using a simple, but representative, gas-filled system. The results and their implications for safety valve design and selection are discussed, and a numerical example is given.
Power/Response Spectrum Transformations in Equipment Qualification
Authors: Unruh J. F. , Kana D. D.
Published: November 2009

Since its introduction a few years ago the use of the power/response spectrum transformation has gained considerable interest and acceptance, and a number of new applications of the transformation have been developed in the equipment qualification area. A brief review of the power/response spectrum transformation is given with a discussion of the input/output relationships for linear systems required for elevated power spectrum generation. Frequency content of earthquakelike signals is discussed with emphasis on the resolution given by the PSD. The problem of excessive ZPA due to inconsistent spectra enveloping and mechanical nonlinearities is also discussed. The PSD/RS transformation is applied to the problems of combining various dynamic load events, developing bounding spectra, and developing damping consistent test spectra. Development of elevated component spectra corrected for base overtest and generation from in-situ measurements is reviewed.
Closed Form Expressions for Fracture Mechanics Analysis of Cracked Pipes
Authors: Zahoor A.
Published: November 2009

Closed form stress intensity factor (K1) expressions are presented for cracks in pipes subjected to a variety of loading conditions. The loadings considered are: 1) axial tension, 2) remotely applied bending moment, and 3) internal pressure. Expressions are presented for circumferential and axial cracks, and include both part-through and through-wall crack geometries. The closed form K1 expressions are valid for pipe radius to wall thickness ratio between 5 and 20.
Stresses in Spherical Shells Due to Local Loadings Over a Rectangular Area
Authors: Chao T. L.
Published: November 2009

Analytical solutions for displacements, membrane stresses, and bending stresses in spherical shells due to local loadings over a rectangular area were developed. The three types of loading considered are radial load, overturning moment load, and tangential shear load.
Prediction of the Remaining Life of High-Temperature/Pressure Reactors Made of Cr-Mo Steels
Authors: Iwadate T. , Watanabe J. , Tanaka Y.
Published: November 2009

The Cr-Mo steels widely used for pressure vessels have a potential for temper embrittlement. Therefore, embrittlement during long-term service is expected, and it leads to the decrease of the critical flaw size of brittle fracture and/or to the reduction of the remaining life of a pressure vessel. In this paper, the concept of a remaining life prediction model is presented. And also, experimental data on the temper embrittlement and fracture toughness after long-term exposure and sub-critical crack growth rate, such as creep crack growth rate, were collected, and the data were analyzed for use in the remaining life prediction model. Examples of the remaining life prediction of a 2 1/4 Cr-1Mo steel hydrogenation reactor and a 1 1/4Cr-1/2Mo steel catalytic reforming reactor were calculated from the statistical data base.
A Computational Model for Predicting the Life of Tubes Used in Petrochemical Heater Service
Authors: Simonen F. A. , Jaske C. E.
Published: November 2009

This paper describes a model developed for computer simulation of stresses in heater tubes used in petrochemical service. The model predicts the damage to the tube material and thus provides an assessment of both tube design life and residual-life of tubes that have been subjected to service exposure. The analysis procedure has been incorporated into a computer code (TUBE), which has been applied to a number of applications for heat-resistant alloys. The focus of these applications has been to address the effect of sustained and cyclic loadings on the predicted service lives of tubes used in elevated temperature service. The model was originally developed at Battelle-Columbus in the 1970s, as part of an industrial group research program on “Materials for Steam Reformer Furnaces.” The computer model uses conventional numerical approaches [1–4] to solve finite element models of two-dimensional creep problems. This paper addresses the practical difficulties of applying such models to real service conditions and real commercial alloys.
Performance of Dissimilar Welds in Service
Authors: Roberts D. I. , Ryder R. H. , Viswanathan R.
Published: November 2009

Dissimilar metal welds (DMWs) between austenitic and ferritic steel tubing and piping are commonly employed in high-temperature applications in energy conversion systems. Differences in coefficient of thermal expansion between the two types of steel induce thermal stresses at the welds and local metallurgical changes near the low alloy steel/weld metal interface due to prolonged service at an elevated temperature. These phenomena, together with the differences in creep behavior of the materials joined, render the DMWs more prone to failure than welds between similar steels. This has been reflected in relatively high failure rates in DMWs in certain service applications (e.g., in utility power plant boiler tubing). Typically these welds fail by low ductility cracking in the low alloy steel at, or very close to, the fusion line. A project, sponsored by the Electric Power Research Institute (EPRI) and managed by the Metal Properties Council (MPC), has made significant headway over the last three years in understanding the failure modes and causes involved and in developing methods to assess residual life of DMWs. Welds from service in superheaters and reheater tubes and from laboratory simulation tests were examined to establish metallurgical characteristics and failure modes. Three failure modes were identified: (i) Prior austenite grain boundary cracking in the ferritic steel, one or two grains away from the fusion line; this mode was mainly observed in DMWs made with stainless steel filler metal. (ii) Cracking along the weld interface, which occurred in DMWs made with nickel-base filler metal. (iii) Propagation of cracks initiating from oxide notches formed at the weld outside surface; this mode occurred mainly in thin-walled tubes. Creep damage induced by steady and cyclic loading was found to be the predominant mechanism for damage and failure; therefore a dependence of damage on loading levels and service temperature was established. It was also determined that failure susceptibility in DMWs made with nickel-base filler was strongly influenced by the type of microstructure that formed at the low alloy steel/weld metal interface. The technique developed for estimating the condition and remaining life of DMWs in service involves detailed assessment of loading histories to which the welds are subjected, along with the use of empirical quantitative relationships established from both laboratory and service data. The methodology assumes that damage results from the combined effects of self damage (caused by thermal cycling of materials of different expansion coefficients) and service loadings, including both primary loads (e.g., pressure and deadweight) and secondary, or cyclic, loads due to the constrained thermal expansion of the system as a whole. The technique, Prediction Of Damage In Service (designated PODIS), has been found to adequately predict levels of damage in stainless-based DMWs in service. It is currently being developed further to embrace nickel-based DMWs.
Vibration of Tube Bundles Subjected to Two-Phase Cross-Flow
Authors: Pettigrew M. J. , Tromp J. H. , Mastorakos J.
Published: November 2009

Two-phase cross-flow exists in many shell-and-tube heat exchangers such as condensers, reboilers and nuclear steam generators. Thus we are conducting a comprehensive program to study tube bundle vibrations subjected to two-phase cross-flow. This paper presents the results of experiments on a normal-triangular and a normal-square tube bundle, both of p/d = 1.47. The bundles were subjected to air-water mixtures to simulate realistic vapor qualities and mass fluxes. Vibration excitation mechanisms were deduced from vibration response measurements. Results on damping, hydrodynamic mass, fluid-elastic instability and random turbulence excitation in two-phase cross-flow are presented.
Damping in LMFBR Pipe Systems
Authors: Anderson M. J. , Barta D. A. , Lindquist M. R. , Renkey E. J. , Ryan J. A.
Published: November 2009

Liquid Metal Fast Breeder Reactor pipe systems typically utilize a thicker insulation package than that used on water plant pipe systems. They are supported with special insulated pipe clamps. Mechanical snubbers are employed to resist seismic loads. Recent laboratory testing has indicated that these features provide significantly more damping than presently allowed by Regulatory Guide 1.61 for water plant pipe systems. This paper presents results of additional in-situ vibration tests conducted on Fast Flux Test Facility pipe systems. Pipe damping values obtained at various excitation levels are presented. Effects of filtering data to provide damping values at discrete frequencies and the alternate use of a single equivalent modal damping value are discussed. These tests further confirm that damping in typical LMFBR pipe systems is larger than presently used in pipe design. Although some increase in damping occurred with increased excitation amplitude, the effect was not significant. Recommendations are made to use increased damping values for seismic events in design of heavily insulated pipe systems.
Time Interval Damage Potential of Seismic Testing Waveforms
Authors: Tang D. T. , Li D.
Published: November 2009

The concept of time interval response spectrum is introduced for characterizing the damage potential or the likelihood of a waveform to cause multiple mode response. By modifying slightly a typical response spectrum calculation routine the Weighted Spectrum Mean (WSM) is determined by evaluating the area under a normalized spectrum curve. A more detailed delineation of the response peaks statistics of simple oscillators results in the development of a Damage Potential Index (DPI). Both WSM and DPI are utilized to quantify damage potential for a variety of waveforms including free field motion and recorded testing motions. The results suggest that a useful tool has been established with only a small added effort to help design, predict, or analyze the damage potential of testing waveforms for seismic operability qualification of equipment.
Analysis of Elastic Surface Cracks in Cylinders Using the Line-Spring Model and Shell Finite Element Method
Authors: Kumar V. , German M. D. , Schumacher B. I.
Published: November 2009

This paper presents elastic analysis of axial and circumferential semielliptical surface flaws in cylinders using the line-spring model of Rice and Levy [1-3] and a shell finite element method. Results for the stress intensity factor are obtained at various points along the crack front, and are compared in some cases against published literature solutions. A broad range of values for the cylinder radius-to-wall thickness ratio, flaw depth and aspect ratio are considered including surface flaws with very large aspect ratios. The critical values of aspect ratio at which the surface flaws can be treated as 2-dimensional cracks are determined. Effect flaw location (internal or external) and flaw shape (semielliptical, circular or rectangular) are also investigated. Finally, the significance of these results in the elastic-plastic fracture analysis procedures is discussed.
An Improved Multiaxial Creep-Rupture Strength Criterion
Authors: Huddleston R. L.
Published: November 2009

An improved strength model is developed for predicting creep rupture under multiaxial stress states. The new model incorporates three independent stress parameters and distinguishes between life under tensile versus compressive stress states. Assessments of the new model based on experimental biaxial creep-rupture data for type 304 stainless steel tested at 593°C show the new model to be significantly more accurate than the classical criteria of von Mises, Tresca, or Rankine.
Stress Corrosion Cracking Susceptibility of Low Alloy Steels Used for Reactor Pressure Vessel in High Temperature Oxygenated Water
Authors: Kuniya J. , Masaoka I. , Sasaki R. , Itoh H. , Okazaki T.
Published: November 2009

Studies have been done on stress corrosion cracking (SCC) susceptibility of low alloy steels in water containing dissolved oxygen. The fundamental factors which affect the SCC susceptibility were clarified, and the integrity of the reactor pressure vessel (RPV), in which these steels are used, was assessed from the standpoint of SCC initiation. The effects of applied stress, strain rate, dissolved oxygen concentration, and test temperatures, on the SCC susceptibility was examined utilizing uniaxial constant load tensile tests (UCL), and slow strain rate tests (SSRT).
Estimation of Energy Release Rates and Instability Analysis for a Pipe With a Circumferential Surface Crack Subjected to Bending
Authors: Pan J.
Published: November 2009

An estimation of the energy release rate J for a three-dimensional nonlinear elastic solid containing a two-dimensional plane crack is presented. Special attention is focused on a pipe with a circumferential surface crack subjected to bending. The present analysis gives an estimation of the distribution of J along the crack front of a circumferential surface crack. Fracture instability of the cracked solid is also discussed. Based on the deformation theory of plasticity and a postulated criterion for crack growth, wall-breakthrough instability of the circumferential surface crack is examined. The predictions of the present analysis are in agreement with experimental observations, and indicate that a longer circumferential surface flaw is more susceptible to radial instability. Implications of this study on “leak before break” conditions are also discussed.
Dynamic Analysis of Fluid-Filled Piping Systems Using Finite Element Techniques
Authors: Everstine G. C.
Published: November 2009

Two finite element procedures are described for predicting the dynamic response of general 3-D fluid-filled elastic piping systems. The first approach, a low-frequency procedure, models each straight pipe or elbow as a sequence of beams. The contained fluid is modeled as a separate coincident sequence of axial members (rods) which are tied to the pipe in the lateral direction. The model includes the pipe hoop strain correction to the fluid sound speed and the flexibility factor correction to the elbow flexibility. The second modeling approach, an intermediate frequency procedure, follows generally the original Zienkiewicz-Newton scheme for coupled fluid-structure problems except that the velocity potential is used as the fundamental fluid unknown to symmetrize the coefficient matrices. From comparisons of the beam model predictions to both experimental data and the 3-D model, the beam model is validated for frequencies up to about two-thirds of the lowest fluid-filled lobar pipe mode. Accurate elbow flexibility factors are seen to be important for effective beam modeling of piping systems.
An Experimental Stability Analysis of a Single Flexible Cylinder Positioned in an Array of Rigid Cylinders and Subject to Cross-Flow
Authors: Price S. J. , Mark B. , Paidoussis M. P.
Published: November 2009

The fluidelastic response of a single flexible cylinder in an array of rigid cylinders, subject to cross-flow, has been investigated. Experiments were done in two wind tunnels on three different types of array: (i) a double row in-line (square) array, with pitch-to-diameter ratio P/d = 1.5; (ii) a triple row staggered (rotated-square) array, with P/d = 1.5 2; (iii) a double row version of (ii). The modal damping logarithmic decrement was varied in the range 0.01 to 0.46. Measurements of vibration were made in both the in-flow and cross-flow directions, taking not only the vibration amplitudes, but also the power spectral density of the response over a wide frequency range and over a broad range of flow velocities. This permitted a more detailed examination of system behavior, prior to, at, and beyond the threshold of fluidelastic instabilities, as well as a better definition of the onset of instability. Fluidelastic instability was observed for downstream cylinders of both the in-line and staggered arrays, the motion in both cases being predominantly in the cross-flow direction. However, in the in-line array, further increase in flow velocity tended to shift the instability to one involving mainly in-flow motion.
Modal Combination in Response Spectrum Analysis of Piping Systems
Authors: Gupta A. K. , Jaw J.-W.
Published: November 2009

Modal combination methods in the response spectrum analysis of piping systems have been investiaged. Two particular effects are identified, viz, (i) the residual rigid response, also known as the higher modes effect (HME); (ii) the correlation between the modal response and the rigid response. Gupta’s method accounts for both these effects. It is shown that Gupta’s method gives results which are much closer to the direct integration analysis results than are the results obtained from any other modal combination rules which ignore either one or both of the foregoing effects.
Stress Redistribution During Local Annealing of a Multi-Pass Butt-Welded Pipe
Authors: Josefson B. L.
Published: November 2009

Stress redistributions during local Post Weld Heat Treatments (PWHT) are numerically studied for a multi-pass butt-welded pipe with mechanically unrestrained ends. The pipe material is a micro-alloyed C-Mn steel. Temperature and stress fields developed during welding and PWHT are determined from a FE-analysis where rotational symmetry is assumed. Use of heaters with a total axial width less than four times the pipe wall thickness is found to result in substantially different final stress fields than those obtained after a uniform (furnace) heat treatment. The tensile axial and hoop stresses on the inner pipe surface near the centre section of the weldment are considerably higher after a local PWHT. The differences were found to arise mainly during the cooling periods of the PWHTs.
Experimental Tests on Buckling of Torispherical Heads and Methods of Plastic Bifurcation Analysis
Authors: Roche R. L. , Autrusson B.
Published: November 2009

Sixteen torispherical heads were tested under internal pressure. These heads, which were 500 mm in diameter, had diameter/thickness ratios ranging from 330 to 1000. They were all prepared by spinning mild steel plates. Deflections along the axis and in the knuckle area were recorded. The most practical result is the buckling pressure and this can be exceeded without fracturing the head. The tests show that the buckling pressure is relatively unaffected by geometric imperfections. These experimental results are used to assess the validity of the different plastic bifurcation analysis methods. Five different methods were employed using the CASTEM general-purpose computer program. The method based on the incremental theory of plasticity proved to be incapable of correctly predicting head buckling. If this method is modified by replacing the elastic shear modulus by the secant modulus, the results obtained show good agreement with experimental results.