Showing papers in "Journal of Pressure Vessel Technology-transactions of The Asme in 2009"

Lower and Upper Bound Shakedown Analysis of Structures With Temperature-Dependent Yield Stress

Abstract: Based upon the kinematic theorem of Koiter, the Linear Matching Method (LMM) procedure has been proved to produce very accurate upper bound shakedown limits. This paper presents a recently developed LMM lower bound procedure for shakedown analysis of structures with temperature-dependent yield stress, which is implemented into ABAQUS using the same procedure as for upper bounds. According to the Melan's theorem, a direct algorithm has been carried out to determine the lower bound of shakedown limit using the best residual stress field calculated during the LMM upper bound procedure with displacement-based finite elements. By checking the yield condition at every integration point, the lower bound is calculated by the obtained static field at each iteration, with the upper bound given by the obtained kinematic field. A number of numerical examples confirm the applicability of this procedure and ensure that the upper and lower bounds are expected to converge to the theoretical solution after a number of iterations.

Structural Response of Piping to Internal Gas Detonation

Abstract: Detonation waves in gas-filled piping or tubing pose special challenges in analysis and prediction of structural response. The challenges arise due to the nature of the detonation process and the role of fluid-structure interaction in determining the propagation and arrest of fractures. Over the past 10 years, our laboratory has been engaged in studying this problem and developing methodologies for estimating structural response. A brief overview of detonation waves and some key issues relevant to structural waves is presented first. This is followed by a summary of our work on the elastic response of tubes and pipes to ideal detonation loading, highlighting the importance of detonation wave speed in determining, flexural wave excitation and possibility of resonant response leading to large deformations. Some issues in measurement technique and validation testing are then presented. The importance of wave reflection from bends, valves, and dead ends is discussed, as well as the differences between detonation, shock wave, and uniform internal pressure loading. Following this, we summarize our experimental findings on the fracture threshold of thin-walled tubes with pre-existing flaws. A particularly important issue for hazard analysis is the estimation of loads associated with flame acceleration and deflagration-to-detonation transition. We give some recent results on pressure and elastic strain measurements in the transition regime for a thick-wall piping, and some remarks about plastic deformation.

The Effects of Filler Metal Transformation Temperature on Residual Stresses in a High Strength Steel Weld

Abstract: Residual stress in the vicinity of a weld can have a large influence on structural integrity. Here the extent to which the martensite-start temperature of the weld filler metal can be adjusted to engineer the residual stress distribution in a bainitic-martensitic steel weld was investigated. Three single-pass groove welds were deposited by manual-metal-arc welding on 12 mm thick steel plates using filler metals designed to have different martensite-start temperatures. Their longitudinal, transverse, and normal residual stress distributions were then characterized across the weld cross section by neutron diffraction. It was found that tensile stresses along the welding direction can be reduced or even replaced with compressive stresses if the transformation temperature is lowered sufficiently. The results are interpreted in the context of designing better welding consumables.

Target Reliability Levels for Design and Assessment of Onshore Natural Gas Pipelines

Abstract: This paper proposes a set of reliability targets that can be used in the design and assessment of onshore natural gas pipelines. The targets were developed as part of a PRCI-sponsored project that aims to establish reliability-based methods as a viable alternative for pipeline design and assessment. The proposed targets are calibrated to meet risk levels that are considered widely acceptable. The proposed criteria are based on a detailed consideration of both societal and individual risk criteria. Two societal risk criteria were considered: the first based on a fixed expectation of the number of fatalities and the second based on a risk aversion function as characterized by a F /N relationship. Societal risk criteria were calibrated to match or exceed the average safety levels implied by current codes. Individual risk criteria were based on published tolerable levels. The target reliability levels corresponding to the three criteria are presented and a recommended set of targets is presented. DOI: 10.1115/1.3110017 In the last 30 years, reliability-based design principles have been used to develop limit states design codes in many industries e.g., nuclear containments, bridges, and buildings. These methods, which are still not used for pipelines, have been shown to have significant benefits over allowable stress design methods, including improved safety, cost savings, and an ability to address unique design situations. To establish reliability-based methods as a viable design alternative for the design and assessment of pipelines, the Pipeline Research Council International PRCI sponsored a multiyear project to develop the required technical information, communicate the approach to the industry and regulators, and facilitate its incorporation into relevant pipeline standards. The first step of this process was a technical project that was carried out by C-FER Technologies to develop a set of guidelines for reliability-based design and assessment RBDA of onshore natural gas pipelines. The reliability-based design and assessment process adopted in these guidelines was described in Ref. 1

A Review on Current Status of Alloys 617 and 230 for Gen IV Nuclear Reactor Internals and Heat Exchangers

Abstract: Alloys 617 and 230 are currently identified as two leading candidate metallic materials in the down selection for applications at temperatures above 760 C in the Gen IV Nuclear Reactor Systems. Qualifying the materials requires significant information related to Codification, mechanical behavior modeling, metallurgical stability, environmental resistance, and many other aspects. In the present paper, material requirements for the Gen IV Nuclear Reactor Systems are discussed; certain available information regarding the two alloys under consideration for the intended applications are reviewed and analyzed. Suggestions are presented for further R&D activities for the materials selection.

Systematic Evaluation of Creep-Fatigue Life Prediction Methods for Various Alloys

Abstract: Failure under creep-fatigue interaction is receiving increasing interest due to an increased number of start-up and shut-down in fossil power generation plants as well as development of newer nuclear power plants employing low-pressure coolant. These situations have promoted the development of various approaches for evaluating its significance. However, most of them are fragment and rather limited in terms of materials and test conditions they covered. Therefore applicability of the proposed approaches to different materials or even different temperatures is uncertain in many cases. The present work was conducted in order to evaluate and compare the representative approaches used in the prediction of failure life under creep-fatigue conditions as well as their modifications, by systematically applying them to available test data on a wide range of materials which have been used or are planned to be used in various types of power generation plants. The following observations have been made from this exercise. (i) Time fraction model has a tendency to be unconservative in general, especially at low temperature and small strain range. Because of the large scatter of the total damage, this shortcoming would be difficult to cover by the consideration of creep-fatigue interaction in a fixed manner. (ii) Classical ductility exhaustion model showed a common tendency to be overly conservative in many situations, especially at small strain ranges. (iii) The modified ductility exhaustion model based on the re-definition of creep damage showed improved predictability with a slightly unconservative tendency. (iv) Energy-based ductility exhaustion model developed in this study seems to show the best predictability among the four procedures in an overall sense although some dependency on strain range and materials was observed.Copyright © 2009 by ASME

Numerical Simulation of the Flow-Sound Interaction Mechanisms of a Single and Two-Tandem Cylinders in Cross-Flow

Abstract: A numerical simulation of the flow-excited acoustic resonance for the case of two-tandem cylinders in cross-flow is performed. The spacing ratio between the cylinders (L/D =2.5) is inside the proximity interference region. Similar simulation is performed for the case of a single cylinder. The unsteady flow field is simulated using a finite-volume method. This simulation is then coupled with a finite-element simulation of the resonant sound field, by means of Howe's theory of aerodynamics sound, to reveal the details of flow-sound interaction mechanisms, including the nature and the locations of the aeroacoustic sources in the flow field. For the case of a single cylinder, acoustic resonance is excited over a single range of flow velocity. The main aeroacoustic source, which causes a positive energy transfer from the flow field to the acoustic field, is found to be located just downstream of the cylinder. For the case of two-tandem cylinders, the acoustic resonance is excited over two different ranges of flow velocity: the precoincidence and the coincidence resonance ranges. For the coincidence resonance range, the main aeroacoustic source is found to be located just downstream of the downstream cylinder, and the excitation mechanism of this resonance range is found to be similar to that of a single cylinder. However, for the precoincidence resonance range, the primary acoustic source is found to be located in the gap between the cylinders. Moreover, flow visualization of the wake structure for the two-tandem cylinders during acoustic resonance shows that for the precoincidence resonance range there is a phase shift of about 90 deg between the vortex shedding from the upstream and the downstream cylinders, which is different from the coincidence resonance range, where the vortex shedding from both cylinders seems to be in-phase.

Thermal Stress Distribution in Thick Wall Cylinder Under Thermal Shock

Abstract: This paper presented the stress distribution in a thick walled cylinder under thermal shock. Dirac function was introduced to model thermal shock. An analytical solution of the temperature field was obtained by Laplace transform. Based on the temperature solution, the thermal stress response of the thick walled cylinder was solved. The time dependent variations of the temperature field-thermal stress field-were discussed, and the effect of cylinder radius ratio on the problem was given. The exploration in this paper will lay a theoretical reference to further study on the decrease in fatigue damage of the superhigh pressure tubular reactor under thermal shock.

On the Buckling of Functionally Graded Cylindrical Shells Under Combined External Pressure and Axial Compression

Abstract: The stability problem of a circular cylindrical shell composed of functionally graded materials with elasticity modulus varying continuously in the thickness direction under combined external pressure and axial compression loads is studied in this paper. The formulation is based on the first-order shear deformation theory. A load interaction parameter is defined to express the combination of applied axial compression and external pressure. The stability equations are derived by the adjacent equilibrium criterion method. These equations are employed to analyze the buckling behavior and obtain the critical buckling loads. A detailed numerical study is carried out to bring out the effects of the power law index of functionally graded material, load interaction parameter, thickness ratio, and aspect ratio on the critical buckling loads. The validity of the present analysis was checked by comparing the present results with those results available in literature.

Pipe Wall Damage Detection in Buried Pipes Using Guided Waves

Abstract: It is well known that cylindrical guided waves are very efficient for detecting pipe wall defects when pipes are open in the air. In this paper it is investigated how efficient the guided waves are for detecting pipe wall damage when the pipes are embedded in the soil. For this purpose guided waves were propagated through pipes that were buried in the soil by placing transmitters on one end of the embedded pipe and receivers on the other end. Received signals for both defect-free and defective pipes were recorded. Then the received signals were subjected to wavelet transforms. To investigate whether embedding the pipe in the soil makes it more difficult to detect the pipe wall defects, the same set of defective and defect-free pipes were studied before and after burying them in the soil. In both cases the defective pipes could be easily identified. Interestingly, contrary to the intuition, it was observed that under certain conditions defective pipes could be identified more easily in buried conditions. For example, the difference between the strengths of the initial parts of the received signal from defect-free and dented pipes was found to be greater for the buried pipes. Some qualitative justification for easier detection of buried dented pipes is provided.

Exact, Hierarchical Solutions for Localized Loadings in Isotropic, Laminated, and Sandwich Shells

Abstract: This paper presents closed form solutions for simply supported cylindrical and spherical shells subjected to uniform localized distributions of transverse pressure and bending moment. These distributions have been expanded in terms of Fourier's series for which Navier type "exact" solutions have been found for the governing differential equations of the employed shell theories. Shells made of isotropic materials, composites laminates, and sandwich have been analyzed. Carrera's unified formulation has been adopted in order to implement a large variety of two-dimensional theories. Classical, refined, zigzag, layerwise, and mixed theories are compared in order to evaluate the stress and deformation variables. Conclusions are drawn with respect to the accuracy of the various theories for the considered loadings and layouts. The importance of the refined shell models in order to describe accurately the three-dimensional stress state in the neighborhood of the localized loading application area is outlined.

Applicable Contact Force Models for the Discrete Element Method: The Single Particle Perspective

Abstract: Several processes in nature as well as many industrial applications involve static or dynamic granular materials. Granulates can adopt solid-, liquid-, or gaslike states and thereby reveal intriguing physical phenomena not observable in its versatility for any other form of matter. The frequent occurrence of phase transitions and the related characteristics thereby strongly affect their processing quality and economics. This situation demands for prediction methods for the behavior of granulates. In this context simulations provide a feasible alternative to experimental investigations. Several different simulation approaches are applicable to granular materials. The time-driven discrete element method turns out to be not only the most complex but also the most general simulation approach. Discrete element simulations have been used in a wide variety of scientific fields for more than 30 years. With the tremendous increase in available computer power, especially in the past years, the method is more and more developing to the state of the art simulation technique for granular materials not only in science but also in industrial applications. Several commercial software packages utilizing the time-driven discrete element method have emerged and are becoming more and more popular within the engineering community. Despite the long time of usage of the time-driven discrete element method, model advances derived and theoretical and experimental studies performed in the different branches of application lack harmonization. They thereby provide potential for improvements. Therefore, the scope of this paper is a review of methods and models for contact forces based on theoretical considerations and experimental data from literature. Particles considered are of spherical shape. Through model advances it is intended to contribute to a general enhancement of simulation techniques, which help improve products and the design of the related equipment.

Finite Element Analysis of Externally-Induced Sloshing in Horizontal-Cylindrical and Axisymmetric Liquid Vessels

Abstract: Motivated by the earthquake response of industrial pressure vessels, the present paper investigates externally-induced sloshing in horizontal-cylindrical and axisymmetric liquid containers. Assuming ideal and irrotational flow, small-amplitude free-sarface elevation, and considering appropriate trigonometric functions for the sloshing potential, a two-dimensional eigenvalue problem is obtained for zero external excitation, which is solved through a variational (Galerkin) formulation that uses triangular finite elements. Subsequently, based on an appropriate decomposition of the container-fluid motion, and considering the eigenmodes of the corresponding eigenvalue problem, an efficient methodology is proposed for externally-induced sloshing through the calculation of the corresponding sloshing (or convective) masses. Numerical results are obtained for sloshing frequencies and masses in horizontal circular cylindrical, spherical, and conical vessels. It is shown that, in those cases, consideration of only the first sloshing mass is adequate to represent the dynamic behavior of the liquid container quite accurately. For the case of a horizontal cylinder subjected to longitudinal external excitation, its equivalence with an appropriate rectangular container is demonstrated. The numerical results are in very good comparison with available semi-analytical or numerical solutions and available experimental data.

Instability of Pressure Relief Valves in Water Pipes

Abstract: Pressure relief valves in water pipes are known to sometimes chatter when the inlet pressure slightly exceeds the set pressure. While these devices are responsible for numerous fatigue issues in process industries, there is a relatively low number of technical publications covering their performance, especially in heavy fluid applications. The present study is intended as a contribution to the understanding of pressure relief valve dynamics, taking into account fluid-structure interactions. A series of tests were performed with a water relief valve in a test rig. Adjusting the set pressure of the valve to about 30 bars, an upstream pressure varying from 20 bars to 35 bars was imposed, so that the valve opened and the water flow varied from a few m 3 /h to about 80 m 3 /h. During the tests, the pipe was equipped upstream and downstream of the valve with static pressure sensors and a flowmeter, the disk lift was measured with a laser displacement sensor, and the spring force was recorded simultaneously. Several fluctuating pressure sensors were also installed in the inlet pipe. Static instability is investigated by comparing the spring force to the hydraulic force. Dynamic instability is observed and it is shown that the resonant behavior of the disk generates an apparent negative pressure drop coefficient at some frequencies. This negative pressure drop coefficient can trigger a dynamic instability in a manner similar to the negative damping effect in leakage-flow vibrations.

One-Dimensional Moving Heat Source in a Hollow FGM Cylinder

Abstract: This paper presents the analytical solution of one-dimensional mechanical and thermal stresses for a hollow cylinder made of functionally graded material. The material properties vary continuously across the thickness, according to the power functions of radial direction. Temperature distribution is symmetric and transient. The thermal boundary conditions may include conduction, flux, and convection for inside or outside of a hollow cylinder. The thermoelasticity equation is transient, including the moving heat source. The heat conduction and Navier equations are solved analytically, using the generalized Bessel function. A direct method of solution of Navier equation is presented.

Two-Phase Flow-Induced Forces on Bends in Small Scale Tubes

Abstract: Two-phase flow occurs in many situations in industry. Under certain circumstances, it can be a source of flow-induced vibrations. The forces generated can be sufficiently large to affect the performance or efficiency of an industrial device. In the worst-case scenario, the mechanical forces that arise may endanger structural integrity. Thus, it is important to take these forces into account in designing industrial machinery to avoid problems during operation. Although the occurrence of such forces is well known, not much is known about their magnitudes because, unfortunately, the amount of experimental data available in literature are rather limited. This paper describes the experiments performed to measure forces in 6 mm diameter tubing containing a bend. Experiments are performed on bends of different radii, with the bend positioned horizontally or vertically. The experimental results are analyzed based on flow regime and bend configuration. A comparison with available experimental results for bigger internal pipe diameter shows a general good agreement. To improve future predictions, a simple model based on momentum exchange is proposed to estimate the forces generated by multiphase flow. The proposed model shows a good agreement with the experimental data. Copyright © 2010 by ASME.

Approach for selection of rayleigh damping parameters used for time history analysis

Abstract: Nonlinearities, whether geometric or material, need to be addressed in seismic analysis. One good analysis method that can address these nonlinearities is direct time integration with Rayleigh damping. Modal damping is the damping typically specified in seismic analysis Codes and Standards. Modal damping is constant for all frequencies where Rayleigh damping varies with frequency. An approach is proposed here for selection of Rayleigh damping coefficients to be used in seismic analyses that are consistent with given Modal damping. The approach uses the difference between the modal damping response and the Rayleigh damping response along with effective mass properties of the model being evaluated to match overall system response levels. This paper provides a simple example problem to demonstrate the approach. It also provides results for a finite element model representing an existing piping system. Displacement, acceleration, and stress results are compared from model runs using modal damping and model runs using Rayleigh damping with coefficients selected using the proposed method.

Novel Formulation of Bolt Elastic Interaction in Gasketed Joints

Abstract: Novel formulation was proposed for studying bolt elastic interaction during the tightening of a group of fasteners in flat faced gasketed joints. The model was used for developing tightening strategies that would achieve a more uniform clamp load in the flange at initial assembly. Clamp load distribution is investigated for various tightening sequences and values for the gasket modulus of elasticity, gasket thickness, and grip length. An experimental setup and test procedure were developed to verify the numerical results produced by the elastic interaction model. Analytical and experimental results were presented and discussed.

Quantitative Estimation of the Growth of Environmentally Assisted Cracks at Flaws in Light Water Reactor Components

Abstract: Since environmentally assisted cracking (EAC) is an important degradation mechanism affecting the structural materials of nuclear power plants, numerous EAC experiments have been performed in the past three decades using standard specimens in simulated high temperature water environments to evaluate the various core materials used in light water reactors (LWRs). However, the environment, the condition of the material, and the mechanical properties near flaws in LWR components are not absolutely equivalent to those near the crack tip in standard specimens; thus, more research needs to be done before EAC growth in an actual LWR component can be accurately estimated using existing experimental EAC data. By combining the film slip-dissolution/oxidation model with the elastic-plastic finite element method and existing experimental EAC data, we have derived a method by which an estimation of EAC growth at flaws in actual LWR components can be made. In this paper we propose and discuss the use of this method. The results show that this new method basically concurs with the Fracture Research Institute (FRI) model in evaluating EAC growth across a semi-elliptic crack front under a simple tensile load and is also in approximate agreement with the experimental results obtained in evaluating EAC growth along a semi-elliptic crack front under complex loading conditions. The approach is expected to form a bridge between predicting EAC growth rate in core materials and evaluating EAC growth in key structural components in LWRs, and it is also expected that it can be used as a pre-analytical tool for EAC experiments using nonstandard specimens.

Effect of Precompression on Ovality of Pipe After Bending

Abstract: Ovality is a main defect in all pipe bending techniques. An objective of the work is to control ovality in pipe bending. A new concept is suggested for reducing the flattening or ovality. Based on the concept, a mechanism is developed for bending pipes. This mechanism has provisions for precompression of the pipe along the directrix of maximum deformation during bending. Experimentation is carried out on this mechanism and dimensions are measured at 13 discrete places along the length of the pipe. Percentage ovality is computed using experimental results. It is justified by using equations of radius and displacement functions. Minimization of potential energy by sequential search method is done. The methodical approach is presented in this paper. Results show that precompression reduces ovality of the pipe after bending.

A Parametric Study of the Resonance Mechanism of Two Tandem Cylinders in Cross-Flow

Abstract: A parametric study has been performed to investigate the effect of cylinder diameter on the acoustic resonance mechanism of two tandem cylinders exposed to cross-flow in a duct. Three spacing ratios corresponding to different flow regimes inside the "proximity interference" region are considered, LID =1.5, 1.75, and 2.5, where L is the spacing between the cylinders and D is the diameter. For each spacing ratio, six cylinder diameters in the range of D =7.6-27.5 mm have been tested. For small diameter cylinders, the acoustic resonance mechanism of the tandem cylinders seems to be similar to that observed for single cylinders; i.e., it occurs near frequency coincidence as the vortex shedding frequency approaches that of an acoustic resonance mode. However, for larger diameter cylinders, the resonance of a given acoustic mode occurs over two different ranges of flow velocity. The first resonance range, the precoincidence resonance, occurs at flow velocities much lower than that of frequency coincidence. The second resonance range, the coincidence resonance, is similar to that observed for single and small diameter tandem cylinders. Interestingly, the observed precoincidence resonance phenomenon is similar to the acoustic resonance mechanism of in-line tube bundles. It is shown that increasing the diameter of the tandem cylinders affects several flow parameters such that the system becomes more susceptible to the precoincidence resonance phenomenon. The occurrence and the intensity of the precoincidence resonance are therefore strongly dependent on the diameter of the cylinders.

High-Density Polyethylene Piping Butt-Fusion Joint Examination Using Ultrasonic Phased Array

Abstract: With the increasing use of high-density polyethylene (HDPE) piping for nuclear applications, nondestructive evaluation is an important tool for evaluation of the integrity in fused joints. This paper will discuss the method of using ultrasonic phased array for inspecting butt-fusion (BF) joints in HDPE piping. The benefit of phased array is the ability to perform a volumetric inspection using multiple angles, which greatly increases the probability of detection of defects and allows the data to be analyzed using a representative two-dimensional image of the joint. It has been determined that successfully producing BF joints is highly dependent on environmental and mating-surface conditions. The primary defects of concern are lack-of-fusion, an area of the joint where there is no bond, cold fusion, an area of partial bond, and inclusion. Phased array has successfully demonstrated the ability of detecting and characterizing these defects using low frequency ultrasound. Factors addressed include joint location, wall thickness, material temperature, transducer wedge material, and manual versus automated data acquisition.

An Experimental Study of the Crack Growth Behavior of 16MnR Pressure Vessel Steel

Abstract: An experimental investigation was conducted on the crack growth behavior of a pressure vessel steel, 16MnR, in ambient air. Standard compact tension specimens were subjected to Mode I loading with several R-ratios and loading amplitudes. Three circular notch sizes ranging from very sharp notch to blunt notch were used. In addition to constant amplitude loading, experiments were conducted to study the influences of overload and loading sequence on crack growth. The results show that the R-ratio has an insignificant influence on the crack growth of the material. The size of the notch together with the R-ratio and loading amplitude has a great influence on the early crack growth from the notch. A single tensile overload during a constant amplitude loading experiment retards the crack growth significantly. Right after the application of an overload, the crack growth rate is higher than that of the stable crack growth observed in the constant amplitude loading. The crack growth rate decreases and reaches a minimum value before it gradually increases and reaches the stable crack growth curve. In high-low sequence loading with the maximum load in the second step lower than that of the first loading step, the preceding higher constant amplitude loading results in a significant crack growth retardation in the second loading step. This phenomenon is similar to the effect of a single tensile overload on the constant amplitude loading. An existing model making use of the stress intensity factor is discussed with respect to its capability to describe the observed crack growth behavior with the influence of overload and sequence loading.

Interaction of Hydrogen Transport and Material Elastoplasticity in Pipeline Steels

Abstract: The technology of large scale hydrogen transmission from central production facilities to refueling stations and stationary power sites is at present undeveloped. Among the problems that confront the implementation of this technology is the deleterious effect of hydrogen on structural material properties, in particular, at gas pressures of the order of 15 MPa, which are the suggested magnitudes by economic studies for efficient transport. In order to understand the hydrogen embrittlement conditions of the pipeline materials, we simulate hydrogen diffusion through the surfaces of an axial crack on the internal wall of a vessel coupled with material deformation under plane strain small scale yielding conditions. The calculation of the hydrogen accumulation ahead of the crack tip accounts for stress-driven transient diffusion of hydrogen and trapping at microstructural defects whose density evolves dynamically with deformation. The results are analyzed to correlate for a given material system the time after which hydrogen transport takes place under steady state conditions with the level of load in terms of the applied stress intensity factor at the crack tip and the size of the domain used for the simulation of the diffusion.

A Review of the Effects of Coolant Environments on the Fatigue Life of LWR Structural Materials

Abstract: The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code specifies design curves for the fatigue life of structural materials in nuclear power plants. However, the effects of light water reactor (LWR) coolant environments were not explicitly considered in the development of the design curves. The existing fatigue-strain-versus-life ({var_epsilon}-N) data indicate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. Under certain environmental and loading conditions, fatigue lives in water relative to those in air can be a factor of 15 lower for austenitic stainless steels and a factor of {approx}30 lower for carbon and low-alloy steels. This paper reviews the current technical basis for the understanding of the fatigue of piping and pressure vessel steels in LWR environments. The existing fatigue {var_epsilon}-N data have been evaluated to identify the various material, environmental, and loading parameters that influence fatigue crack initiation and to establish the effects of key parameters on the fatigue life of these steels. Statistical models are presented for estimating fatigue life as a function of material, loading, and environmental conditions. An environmental fatigue correction factor for incorporating the effects of LWR environments into ASME Code fatigue evaluationsmore » is described. This paper also presents a critical review of the ASME Code fatigue design margins of 2 on stress (or strain) and 20 on life and assesses the possible conservatism in the current choice of design margins.« less

Rate Dependence and Short-Term Creep Behavior of a Thermoset Polymer at Elevated Temperature

Abstract: The inelastic deformation behavior of PMR-15 neat resin, a high-temperature thermoset polymer, was investigated at 288° C. The effect of loading rate on monotonic stress-strain behavior as well as the effect of prior stress rate on creep behavior were explored. Positive nonlinear rate sensitivity was observed in monotonic loading. Creep response was found to be significantly influenced by prior stress rate. The effect of loading history on creep was studied in stepwise creep tests, where specimens were subjected to a constant stress rate loading followed by unloading to zero stress with intermittent creep periods on both loading and unloading paths. The strain-time response was strongly influenced by prior deformation history. Negative creep was observed on the unloading path. In addition, the behavior of the material was characterized in terms of a nonlinear viscoelastic model by means of creep and recovery tests at 288°C. The model was employed to predict the response of the material under monotonic loading/unloading and multistep load histories.

A Reliability-Based Approach for the Design of Nuclear Piping for Internal Pressure

Abstract: Nuclear pipes are designed to withstand primary membrane stresses generated by internal pressure according to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code, Section III, Parts NB-3641, NC-3641, and ND-3641, which uses the allowable stress design (ASD) method. This paper presents limit states and equations for the design of nuclear pipes for internal pressure based on the load and resistance factor design (LRFD) method. The LRFD method is shown and explained to be more consistent than the ASD method. The paper presents the procedure for the derivation of the partial safety factors. Moreover, these factors are evaluated, example calculations are provided, and-comparisons with the present design are made.

Spatially Resolved Materials Property Data From a Uniaxial Cross-Weld Tensile Test

Abstract: Application of electronic speckle pattern interferometry (ESPI) is described to measure the spatial variation in monotonic tensile stress-strain properties along “cross-weld” specimens machined from a stainless steel three-pass welded plate. The technique, which could also be done with digital image correlation, was applied to quantify how the material 0.2%, 1%, 2%, 5%, 10%, and 20% proof stress varied with distance from the center-line of the weldment for parent and weld material associated with the first and final passes. The stress-strain curves measured by the ESPI method correlated closely with stress-strain data measured using conventional test specimens. The measured results are consistent with the hypothesis that thermo-mechanical cycles associated with the welding process work harden previously deposited (single-pass) weld metal and the surrounding parent material. The stress-strain response of the heat affected zone adjacent to the first weld pass is consistent with an accumulated (equivalent monotonic) plastic strain of 6.5% and that of the first pass weld bead was consistent with an accumulated plastic strain of approximately 4% greater than the state of the final pass weld metal

Numerical Simulation of Subcooled Flow Boiling Heat Transfer in Helical Tubes

Abstract: This paper addresses the numerical simulation of two-phase flow heat transfer in the helically coiled tubes of an integral type pressurized water reactor steam generator under normal operation using a computational fluid dynamics code. The shell-side flow field where a single-phase fluid flows in the downward direction is also calculated in conjunction with the tube-side two-phase flow characteristics. For the calculation of tube-side two-phase flow, the inhomogeneous two-fluid model is used. Both the Rensselaer Polytechnic Institute wall boiling model and the bulk boiling model are implemented for the numerical simulations of boiling-induced two-phase flow in a vertical straight pipe and channel, and the computed results are compared with the available measured data. The conjugate heat transfer analysis method is employed to calculate the conduction in the tube wall with finite thickness and the convections in the internal and external fluids simultaneously so as to match the fluid-wall-fluid interface conditions properly. Both the internal and external turbulent flows are simulated using the standard k-e model. From the results of the present numerical simulation, it is shown that the bulk boiling model can be applied to the simulation of two-phase flow in the helically coiled steam generator tubes. In addition, the present simulation method is considered to be physically plausible in the light of discussions on the computed results.