bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Extended Element-Free Galerkin Method to Multiple Flaws Under Brittle Fracture Conditions
Authors: Rabczuk T. , Bezensek B. , Bordas S.
Published: July 2009

The extended element-free Galerkin (XEFG) method incorporates cracks through partition of unity enrichment of the standard basis functions. Discontinuous functions are added to capture the jump through the crack faces and near-front enrichment is added to capture the asymptotic behaviour in the vicinity of the crack fronts. Depending on the material behaviour, these functions can be of various type. The method can treat initiation, growth and coalescence of cracks seamlessly in both linear elastic and non-linear settings. The method is a powerful tool for modelling and studying crack paths, which are a central feature in the assessment of multiple flaws. The method is applied to the problem of multiple non-aligned flaws in a ferritic plate under cleavage failure. Fracture paths from two non-aligned notches in a plate are modelled. Based on the observations of crack paths the critical flaw alignment distance is established for non-aligned through-wall flaws.
FKM Guideline “Fracture Mechanics Proof of Strength for Engineering Components”: Procedures, Compendiums, Examples
Authors: Varfolomeyev Igor , Pyttel Brita
Published: July 2009

The German guideline “Fracture Mechanics Proof of Strength for Engineering Components” has been released in 2001 as a result of activities sponsored by the Research Committee on Mechanical Engineering (FKM), task group “Component Strength”. The guideline compiles basics for the integrity assessment of cracked components subjected to static or cyclic loading and provides a step-by-step computational procedure for the use in engineering practice. The paper gives an overview of the guideline, describes its specific features, contents and some new topics included in the last 3rd edition (2006).
NDE and Failure Prevention: Past, Present, and Future
Authors: Hedden Owen F.
Published: July 2009

The history and development of many aspects of our subject were explored in the 2007 Conference Symposium honoring Dr. Spencer H. Bush, and these have suggested several aspects that will be developed further in this Symposium. These include introduction of fracture mechanics and risk analysis concepts into the Boiler Code, improved NDE reproducibility and reliability through both domestic and international programs, and application of failure databases. In addition, discussion will include introduction of statistical analysis of failure data and integration of prevention methodology with maintenance engineering.
Weld-Overlay Analyses: An Investigation of the Effect of Weld Sequencing
Authors: Zhang T. , Wilkowski G. , Rudland D. , Brust F. , Mehta H. S. , Sommerville D. V. , Chen Y.
Published: July 2009

The weld overlay process has been developed and applied to repair of nuclear reactor pipe girth welds for many years in BWR plants. The objectives of such repairs were to induce compressive axial residual stresses on the pipe inside surface, as well as increase the pipe thickness with a weld material that is not susceptible to stress-corrosion cracking. Hence, understanding the residual stress distribution is important to evaluate the reliability of pipe joints with weld overlay repairs. In this paper, a six-inch diameter Schedule 120 stainless steel pipe with an overlay thickness of 7.87 mm (0.31 inch) was picked as a validation case. Weld sequencing effects were thoroughly studied. The residual stresses were calculated by using thermal elasto-plastic finite-element analysis (FEA). After comparing results using different weld sequences, it was found that the calculated weld residual stresses on ID surface were very sensitive to weld sequencing in FE analyses as well as internal cooling rate. The influence of the weld sequencing was relatively secondary to the pipe distortion. An optimum (producing compressive residual stress on the ID surface) weld sequencing was obtained and applied to a 711.2 mm (28-inch) diameter pipe-to-elbow girth weld with an overlay thickness of 24.9 mm (0.98 inch) and a pipe thickness of 29.5 mm (1.16 inch).
Analytical Solutions and Tools for Assessment of Surface Cracks in Cylindrical Components
Authors: Varfolomeyev Igor , Beukelmann Dieter
Published: July 2009

The paper reviews some advanced stress intensity factor solutions derived for analyses of axial and circumferential surface cracks in cylindrical components subjected to variable stress fields. The solutions are examined considering their validity ranges with respect to the crack and cylinder geometry, ability to account for a complex stress distribution in the pipe wall, as well as their accuracy. A method for estimating errors in numerical stress intensity factor solutions is introduced and applied to a particular set of data. Examples of a leak-before-break assessment and crack growth calculations under thermal fatigue loading are included to demonstrate the solutions performance. The considered analytical stress intensity factor solutions yield close results provided that the stress field in the prospective crack plane is described by a smooth function of the radial coordinate. For two-dimensional stress profiles as well as for variable ratios of the cylinder wall thickness to the inner radius, a selective use of the solutions is recommended considering their specific features and validity ranges.
Continuous NDE Monitoring via Web Technology
Authors: Marcal Pedro V. , Fong Jeffrey T.
Published: July 2009

For safe operation of high-consequence structures such as airplanes, ships, trains, chemical plants, electricity-generating units, nuclear reactors, oil and gas pipelines, and pressure vessels, periodic inspection using nondestructive evaluation (NDE) technology and a deterministic approach to modeling fatigue crack growth has been mandated by government in the energy and transportation sectors of the nation’s economy since the 1970s. Recent advances in web-based computing, direct measurement-based NDE, and a stochastic approach to remaining fatigue life cycle prediction model have made it possible to not only enhance the credibility of fatigue life prediction but also shorten the turn-around time between field-based NDE and office-based modeling, analysis, verification and integrity assessment back to the field for decision making. To illustrate this new concept in preventing structural failure and extending useful life of high-consequence systems, we first recount a lesson learned in the history of the deployment of the U.S. nuclear submarine fleet, where the emphasis was on the continuous monitoring of 100% of pipe and vessel welds from their initial placement to the discovery of tangible signs of fatigue damage way before the onset of service disruption. Using two crack length vs. fatigue life cycle plots, one being based on the deterministic and the other a stochastic model, we summarize the contrast between the two models in their ability to deliver a credible prediction of the remaining fatigue life cycle based on a periodic or continuous inspection mode. In conjunction with that summary, we answer an important question in designing an NDE-based inspection strategy, namely, whether the inspection should be periodic or continuous. We show in this paper that the key to the success of a continuous monitoring system for aging structure is an NDE capability in measuring not only the initial crack length and the initial crack growth rate, but also their standard deviations. We conclude with a remark that a continuous direct-measurement-based NDE inspection system, when coupled with a finite element modeling and analysis capability, is capable of monitoring not only surface but also subsurface cracks.
Status of Code Development for ASME B&PV Code, Section III, Division 3
Authors: Morton D. Keith , Foster Gerald M. , Smith R. Howard , Cannell Gary R.
Published: July 2009

Current activities of the American Society of Mechanical Engineers (ASME), Section III Subgroup on Containment Systems for Spent Fuel and High-Level Waste Transport Packagings (also known as Subgroup NUPACK) are reviewed with emphasis on the recent revision of Subsection WB (transportation containments). Also, brief insights on new proposals for the development of rules for internal support structures (e.g., spent fuel baskets) and for a strain-based acceptance criteria are provided.
Analysis of the Effective Seismic Support Damping in a Class I Piping System
Authors: Zobeiry Nima , Reinhardt Wolf
Published: July 2009

Based in the existing literature, it is understood that the supports strongly influence the behaviour of piping during earthquake. Given that the level of seismic dissipation depends on the specific support system, the subject of effective damping provided by seismic supports has not been widely explored. This paper investigates this issue for the feeder pipes of a CANDU® reactor. Feeders are numerous class I pipes in parallel, which are separated by frictional spacer elements. The piping system is analyzed using the time history method, taking into account the different damping mechanisms present. By comparing this and a response spectrum analysis of piping, the effective damping in the system is deduced. The effect of specific parameters on the results and the relationship between linear and nonlinear analyses are discussed.
CFD Simulations of an 8×8 Rod Array Inside of an Isothermal Enclosure Filled With a Rarified Gas
Authors: Araya Pablo E. , Greiner Miles
Published: July 2009

Numerical simulations of an experimental apparatus consisting of an 8×8 square array of heater rods within an aluminum enclosure are used to model a Boiling Water Reactor (BWR) fuel assembly. The total heat generation rate is varied from 100W to 500W and the enclosure wall temperature is set at 325°C. The void is filled with air and simulations are run at atmospheric pressure, low pressure (500 Pa) and without cover gas (total vacuum). Low pressure simulations at 500 Pa are run with two models, the first assumes a continuum heat transfer regime in the cover gas, and the second includes a non-continuum temperature jump on the surfaces of the rods and enclosure wall. A contact resistance is used to simulate a temperature jump on all inner surfaces of the model. Simulations show that natural convection does not have significant effects on heat transfer when the pressure is lowered to 500 Pa. In general, radiative heat transfer dominates over the conduction in the cover gas at a wall temperature of 325°C. Results show that a model using a total vacuum with only radiative heat transfer at the wall, predicts maximum rod to wall temperature difference as much as 19.1% higher than a model at atmospheric pressure, whereas a model at 500 Pa, that considers a slip flow regime with temperature jump at the wall, predicts temperatures that are 7.0% higher. A low pressure model at 500 Pa without a temperature jump does not result in any significant increase in temperatures. Temperatures from these simulations will be compared to future experiments at low pressures.
A Practical Approach to Evaluating Fastener Preload Retention With Elastomeric Gaskets
Authors: Reid Daniel F. , Frew James E. B. , Benet Steve
Published: July 2009

Fastener preload retention is critical to ensuring overall long term joint integrity. The range of allowable gasket stress in conjunction with the acceptable bolt preloading can pose a challenge to engineers recommending proper assembly procedures. Users of PTFE based gasket materials are often encouraged to re-torque flange bolts within 24 hours of flange assembly in order to re-establish gasket stress and bolt load loss due to creep relaxation, however little is known regarding this behavior with elastomeric gaskets. This paper explores the characteristics of various elastomeric materials in raised face (non-confined) and tongue & groove (confined) flanges, benchmarked against graphite materials, and the impact that they have on sustained flanged connection reliability.
License Renewal: Status of Long Term Operation in the U.S.
Authors: Young Garry G.
Published: July 2009

As of February 2008, the NRC has approved renewal of the operating licenses for 48 nuclear units and has applications under review for 15 more units. In addition, nuclear plant owners for at least 25 more units have announced plans to submit license renewal applications over the next few years. This brings the total of renewed licenses and announced plans for license renewal to over 80% of the 104 currently operating nuclear units in the U.S. This paper presents some of the factors that have made the U.S. license renewal process so successful. These factors include (1) the successful regulatory process and on-going continuous improvement of that process, (2) long-term safe plant operation trends, (3) stable low-cost generation of electricity, (4) high levels of plant reliability, and (5) improving public opinion trends.
ASME NDE Engineering Division: 25 Years of Excellence
Authors: Springer William T. , Hedden Owen F.
Published: July 2009

Since its beginnings in 1982, the NDE Engineering Division has worked to emphasize the need to integrate analysis, design, materials, manufacturing, and inspection into the overall pressure vessel design, fabrication, installation, and evaluation process so that not only are quality products put into service, but also that the condition of those products can be accurately assessed over their lifetimes. Recently, the division has begun exploring avenues that will allow it to interact with other elements within ASME where synergy clearly exists, e.g. the Pipeline Systems Division and the Petroleum Institute, as well as other organizations such as ASNT. The goal is to work on ways in which the knowledge base and past successes of the division can be used to support activity outside of the pressure vessel area while continuing to work on expanding the interaction already taking place between the NDE Engineering and Pressure Vessel and Piping Divisions.
Application of Time Synchronous Averaging, Spectral Kurtosis and Support Vector Machines for Bearing Fault Identification
Authors: Komgom Christian N. , Mureithi Njuki W. , Lakis Aouni A.
Published: July 2009

Condition monitoring of rolling elements bearings is investigated in this paper. Recently [12, 13], we have developed a diagnosis procedure that combines a signal processing tool, i.e. Time Synchronous Averaging (TSA), and a pattern recognition method, i.e. Support Vector Machines (SVM), for bearing fault detection and prediction. As the generalization performance of the SVM-boundaries was strongly affected by the signal transmission path, this paper is then concerned with the integration of Spectral Kurtosis (SK) analysis in the diagnosis procedure to improve efficiency in such cases. We validate the use of both Time Synchronous Averaging and Spectral Kurtosis analysis, as signal processing tools that will automatically highlight bearing defect frequencies in the envelope spectrum. Twenty-one features (rms, peak, crest factor, band spectral energy, etc...) are extracted from the envelope of signals obtained from these two analyses and are used in the learning scheme. Results show that the generalization performance is less affected by the signal transmission path and the faulty bearing location, thus demonstrating that the modified diagnosis procedure can actually find some underlying patterns that are common to each type of bearing failure. The case-dependency of the support decision tool can therefore be reduced.
Multi-Objective Optimal Design of Sandwich Composite Laminates Using Simulated Annealing and FEM
Authors: Sarhadi A. , Tahani M. , Kolahan F. , Sarhadi M.
Published: July 2009

Multi-objective optimal design of sandwich composite laminates consisting of high stiffness and expensive surface layers and low-stiffness and inexpensive core layer is addressed in this paper. The object is to determine ply angles and number of surface layers and core thickness in such way that natural frequency is maximized with minimal material cost and weight. A simulated annealing algorithm with finite element method is used for simultaneous cost and weight minimization and frequency maximization. The proposed procedure is applied to Graphite-Epoxy/Glass-Epoxy and Graphite-epoxy/Aluminum sandwich laminates and results are obtained for various boundary conditions and aspect ratios. Results show that this technique is useful in designing of effective, competitive and light composite structures.
Structural Aging Monitoring via Web-Based Nondestructive Evaluation (NDE) Technology
Authors: Fong Jeffrey T. , Ranson William F. , Vachon Reginald I. , Marcal Pedro V.
Published: July 2009

To assist owners and operators in real-time on-site monitoring and damage assessment of aging structures, we propose an “aging structure monitoring system” using direct measurements and web-based transmission technology. Such a system from field detection of surface or subsurface cracks to computer modeling/analysis/verification of simulated fatigue crack growth with ultimate delivery of remaining life prediction, is designed to have four major components: (1) The system is capable of transmitting from the field via internet to the office computer direct measurement data that are being collected in the field by personnel using handheld optical scanners to read bar-code-like strain gages either laser bonded (permanent marking) or adhesively bonded to selected critical high stress areas of the surface of a structure. (2) The office computer has a customized database that stores not only relevant geometric and material property data with variability information, but also a history of prior loadings, cumulated strain (plastic) measurements and fatigue crack length or crack tip opening displacement measurements. Such database is constantly being updated and enhanced with variability estimates subsequent to an event on a continouus or periodic inspection basis. (3) Using a minimum of four commercially-available finite-element method (FEM) packages, e.g., ABAQUS, ANSYS, LS-DYNA, and MPAVE, a numerical simulation experiment is conducted on real time using a fracture mechanics and fatigue damage theory-based deterministic model and the direct measurement data. This model is capable of predicting remaining lives for selected future loading scenarios. (4) The results of the FEM simulations are verified via a web-based statistically designed experiment using DATAPLOT where an uncertainty-bounded estimate of the remaining lives of the structure for selected loadings is delivered in real time to the field for decision making. Significance and limitations of this web-based direct-measurement approach to fatigue modeling are discussed.
Effect of Internal Bubbly Flow on Channel Vibration: Comparison Between Experiment and Model
Authors: Zhang Ming Ming , Katz Joseph , Prosperetti Andrea
Published: July 2009

The effect of an internal turbulent bubbly flow on vibrations of a channel wall is investigated in this paper both experimentally and theoretically. Vibrations of an isolated channel wall and associated wall pressure fluctuations are measured using several accelerometers and pressure transducers along streamwise direction under various gas void fractions and characteristic bubble diameters. A waveguide theory based mathematical model, i.e. a solution to the 3D Helmholtz Equation in an infinite long channel, and the physical properties of bubbles is developed to predict the spectral frequencies of the vibration and the wall pressure fluctuation, the corresponding attenuation coefficients of spectral peak and propagated phase speeds. Results show that compared with the same flow without bubbles, the presence of bubbles substantially enhances the power spectral density of the channel wall vibrations and pressure wall fluctuations in the 250–1200 Hz by up to 27 dB and 26 dB, respectively, and increases their overall rms values by up to 14.1 times and 12.7 times, respectively. In the lower frequency range than the resonant frequency of individual bubble, i.e. 250–1200 Hz range, both vibrations and spectral frequencies increase substantially with increasing void fraction and slightly with increasing bubble diameter. The origin for enhanced vibrations and wall pressure fluctuations is demonstrated to be the excitation of the streamwise propagated acoustic pressure waves, which are created by the initial energy generated during bubble formations. The measured magnitudes and trends of the frequency of the spectral peaks, their attenuation coefficients and phase velocities are well predicated by the model. All the three variables decrease as the void fraction or bubble diameter increase. But the effect of void fraction is much stronger than that of bubble diameter. For the same void fraction and bubble diameter, the peaks at higher spectral frequencies decay faster.
CFD Analysis and Optimization of an Inlet Manifold for a Large TGU Reactor
Authors: McGuffie Sean , Porter Mike
Published: July 2009

This paper will discuss the use of Computational Fluid Dynamics (CFD) to study the flow characteristics of inlet manifolds into a large TGU reactor. The design parameters for the operation of the reactor required a very minimal system pressure drop, outside of the pressure drop across the reactor bed. For this reason several alternative designs were considered for the inlet manifolds and distribution into the reactor. Detailed CFD models were constructed of each proposed variant and analyzed to determine their pressure drop and distribution characteristics. The results of these analyses were then used to choose the best candidate for optimization as well as in providing guidance in system changes that would improve pressure drop and flow distribution characteristics. A discussion of how the results’ guidance was used in optimizing the flow path will be provided. The paper will conclude with a brief overview of other considerations in the complete analysis of the reactor system.
A Fast-Running Finite Element Based Method for Evaluating the Blast Performance of Laminated Insulated Glazing
Authors: McArthur Chad , Tennant Darren , Weeks Jim
Published: July 2009

The current state of practice in the design and assessment of Insulated Glazing Units to resist blast loading utilizes calculation methods to estimate the performance. The most prevalent methods used for calculating the window’s performance have been developed from a single degree of freedom (SDOF) approach. This paper presents an alternative, finite element based, approach to analyzing the blast performance of laminated insulated glazing units. The modeling approach is described for each of the primary components represented in the analysis and the results of an indicative model are compared against an equivalent analysis calculated using SDOF methods.
Integral Mean of Yield Criterion in Design and Fitness for Service Assessment
Authors: Adibi-Asl R. , Seshadri R.
Published: July 2009

Mura’s variational formulation for determining limit loads, originally developed as an alternative to classical methods, is extended further by allowing the pseudo-elastic distributions of stresses to lie outside the yield surface provided they satisfy the “integral mean of yield” criterion. Consequently, improved lower-bound and upper-bound values for limit loads are obtained. The mα estimation limit load method, reference volume method and the fitness for service assessment procedure (including corrosion damage and thermal hot spot damage), are all applications and extensions of the “integral mean of yield” criterion.
Theoretical and Experimental Investigation of Pipe Wall Thinning Detection Using Guided Waves
Authors: Nishiguchi Isoharu , Sakata Fumitoshi , Hamada Seiichi
Published: July 2009

A method to investigate pipe wall thinning using guided waves has been developed for pipes in thermal power generation facilities. In this paper, the reflection coefficient and the transmission coefficient are derived for the torsional waves which propagate along a pipe and a simplified method to predict the waveform is proposed. The predictions of the waveforms by the FEM and a simplified method based on the reflection of torsional waves are also examined by comparing with experimental data.
Basic Study on Pre-Processing by the Shock Wave for Freeze-Drying
Authors: Watanabe Toshiaki , Maehara Hironori , Takemoto Ayumi , Itoh Shigeru
Published: July 2009

In the food industry, it is hoping high value-aided product and the increase in efficiency of food processing. On the other hand, we get an experimental result that the load of the shock wave improves an extraction of food, and soften food. We tried to examine the effectivity of the shock wave as pre-processing for freeze-drying from the result in permeation character seen in the radish and so on. In the case of freeze-drying, the object tends to be limited to the small or thin one with size, from the sublimability in processing, the performance in case of the restoration and the viewpoint of the cost performance ratio. We report the result that shock wave loading was done to various food as pre-processing of freeze-drying.
Creep Damage Analysis of High Pressurized Steam Pipelines Using Omega Method
Authors: Jung Gong H. , Prashant Parikh , Penso Jorge , Kim Dong S.
Published: July 2009

Cracks, bulges and leaks have been found in weld-o-let connections that were installed in high-pressure steam lines. Creep has been known as one of failure mechanisms associated with cracks on the weld-o-let connections. A success of weld repairing of the creep-damaged connections strongly relies on how well the creep-damaged material is removed. The FE (finite element) model was developed to predict the creep damage on the weld-o-let connections. Omega creep model and time fraction damage model were incorporated. The developed FE model successfully explained why cracks were found on the outer surface of saddle point in most of the connections. The results of creep analyses were successfully incorporated into development of a weld repair plan of the creep damaged connections.
Flexural Waves in Fluid-Filled Tubes Subject to Axial Impact
Authors: Inaba Kazuaki , Shepherd Joseph E.
Published: July 2009

We experimentally studied the propagation of coupled fluid stress waves and tube flexural waves generated through projectile impact along the axis of a water-filled tube. We tested mild steel tubes, 38–40 mm inner diameter and wall thickness of 0.8, 6.4, and 12.7 mm. A steel impactor was accelerated using an air cannon and struck a polycarbonate buffer placed on the top water surface within the tube. Elastic flexural waves were observed for impact speeds of 5–10 m/s and plastic waves appeared for impact speeds approaching 20 m/s for a 0.8 mm thickness tube. We observed primary wave speeds of 1100 m/s in a 0.8 mm thickness tube, increasing to the water sound speed with 6.4 and 12.7 mm thickness tubes. Comparison of our measurements in the 0.8 mm thickness tube with Skalak’s water hammer theory indicates reasonable agreement between predicted and measured peak strains as a function of the impact buffer speed. For thick-wall tubes, the correlation between experimentally determined peak pressures and strains reveals the importance of corrections for the through-wall stress distribution.
Model Tests on Sloshing of a Floating Roof in a Cylindrical Liquid Storage Tank Under Seismic Excitation
Authors: Nagaya Takashi , Matsui Tetsuya , Wakasa Takuo
Published: July 2009

Shaking table tests are carried out to validate the analytical solutions for the sloshing of a floating roof in a cylindrical liquid storage tank under seismic excitation. The experimental tank is a 1/100 scaled model of typical oil-storage tank of 100,000m3 capacity, made of acrylic tube of 800mm in diameter. The tests are performed using three types of floating roof model: (1) a roof composed of a pontoon ring only, (2) a roof composed of uniform isotropic plate, and (3) a single-deck type roof composed of an inner deck and an outer pontoon. The motion capture system using high-speed micro cameras is employed to measure the roof displacement over the whole roof surface. The test results are compared with the analytical solutions based on linear potential theory. Overall agreement is confirmed between theory and experiment, while nonlinear bi-harmonic resonance oscillation is observed to occur in certain cases.
New Italian Standards for Creep-Operated Pressure Equipment
Authors: Grisolia Ottaviano , Delle Site Corrado , Tonti Andrea
Published: July 2009

ISPESL is preparing new guidelines for pressure equipment designed to operate in the creep range according to time dependent mechanical properties. During the years, the results of infield examinations have improved and sharpened the original procedure through a series of new routes and methods. Now new entire standardization covers new subjects and it is set as an advanced means of investigation for equipment working in the creep range. It goes by the name of 2007 ISPESL & CTI Recommendations. The elaborating of the guideline in matter has benefited from the previous experience, the indications of users and the European and international standards.
Wind Effects on Sloshing of a Floating Roof in a Cylindrical Liquid Storage Tank
Authors: Matsui Tetsuya , Uematsu Yasushi , Kondo Koji , Wakasa Takuo , Nagaya Takashi
Published: July 2009

Sloshing of a floating roof in an open-topped cylindrical liquid storage tank under wind loads is investigated analytically. Wind tunnel test in a turbulent boundary layer is carried out to measure the wind pressure distributing over the roof surface. The measured data for the wind pressure is then utilized to predict the wind-induced dynamic response of the floating roof, which is idealized herein as an isotropic elastic plate of uniform stiffness and mass. The dynamic interaction between the liquid and the floating roof is taken into account exactly within the framework of linear potential theory. Numerical results are presented which illustrate the significant effect of wind loads on the sloshing response of the floating roof.
EBSD Analysis of Fracture Separation in X80 Line Pipe Steel
Authors: Li Yang , Meng Li , Lin Guanfa , Han Xinli , Huo Chunyong , Zhu Lixia , Feng Yaorong
Published: July 2009

During testing pipe and steel for 2nd china west-east gas pipeline (WEGP), fracture separation was found in X80 line pipe steel plates in tensile tests, charpy impact tests and DWTT tests. In this paper, fracture separation is investigated by using EBSD technique to analyze microstructure and to compare it with microstructure of the material after annealing. Results show that there are obvious texture of {111} <110> and {110} <001> in hot rolling plate, but a reduction of this two textures and a new texture of {110} <111> are found after annealing at 700°C for 2 hours. It is found in charpy impact tests that the {111} <110> micro-texture, as a main factor leading to fracture separation was eliminated in annealed specimens. The average grain size of specimen changed from 2.2687μm to 2.8362μm comparing with hot rolling plate because of the decomposition of Bainite. The results of Orientation Imaging displayed that the proportion of substructure and the distribution of misorientation of grain boundary of annealed specimens did not changed remarkably in contrast to the original ones. It is concluded that, X80 steel has well heat stability.
On Leak Detection of Pipelines Using Computational Pipeline Monitoring
Authors: Moustafa Kamal A. F. , Nawara Gamal M. , Elawady Hesham , Fouad Mohsen
Published: July 2009

The unintentional release of fluid from pipelines is considered as a leak. Leaks contribute to the environmental pollution, promote corrosion and equipment failures and produce instabilities in the pipeline operation and control. There is a need, therefore, to develop an effective leak diagnosis scheme in pipeline systems that can detect the occurrence of any leak in the system. One objective of this paper is to develop a mathematical model that accounts for the behavior of pressure and flow-rate profiles in pipeline systems with multi leaks. Such a mathematical model is needed to better understand the dynamic behavior of the pipeline and its characteristics and for the detection the leaks. The paper also involves computer simulation of pipeline conditions using the developed mathematical model. A leak detection scheme is developed that is based on a computational pipeline monitoring method. This method evaluates the mismatch between the actual variables and those of the healthy pipeline system. The pipeline conditions during normal operation were simulated and the system state variables were computed in real time based on simulated measurements collected at few selected locations along the pipeline. The underlying pipeline variables are estimated by applying Kalman filtering technique.
Modeling and Optimization of Ultra High Pressure Vessel With Self-Protective Flat Steel Ribbons Wound and Tooth-Locked Quick-Actuating End Closure
Authors: Ma Xin , Ning Zhongpei , Chen Honggang , Zheng Jinyang
Published: July 2009

Ultra-High Pressure Vessel (UHPV) with self-protective Flat Steel Ribbons (FSR) wound and Tooth-Locked Quick-Actuating (TLQA) end closure is a new type of vessel developed in recent years. When the structural parameters of its TLQA and Buttress Thread (BT) end closure are determined using the ordinary engineering design method, Design by Analysis (DBA) shows that the requirement on fatigue life of this unique UHPV could hardly be satisfied. To solve the above problem, an integrated FE modeling method has been proposed in this paper. To investigate the fatigue life of TLQA and BT end closures of a full-scale unique UHPV, a three-dimensional (3-D) Finite Element (FE) solid model and a two-dimensional (2-D) FE axisymmetric model are built in FE software ANSYS, respectively., Nonlinear FE analysis and orthogonal testing are both conducted to obtain the optimum structure strength, in which the peak stress in the TLQA or BT end closure of the unique UHPV is taken as an optimal target. The important parameters, such as root structure of teeth, contact pressure between the pre-stressed collar and the cylinder end, the knuckle radius, the buttress thread profile and the local structure of the cylinder, are optimized. As a result, both the stress distribution at the root of teeth and the axial load carried by each thread are improved. Therefore, the load-carrying capacity of the end closure has been reinforced and the fatigue life of unique UHPV has been extended.
Failure Criterion for Steel Explosive Containment Vessel Design
Authors: Vaught Chris R. , King Kim W.
Published: July 2009

Steel explosive containment vessels that are intended for a single internal detonation (one-time use) should not be designed using elastic, or near elastic design criteria. Single detonation chambers can be economized by taking advantage of strain energy capacity beyond the elastic region. Classical designs that limit response to nearly elastic limits can result in conservative designs that do not take into account the ductile nature of steel material. While ductile steel materials can exhibit large deformations before rupture, the full ductile capacity of the material cannot be realized due to limiting factors such as material imperfections, the heat affected zone near welds, and geometric discontinuities that limit strain development. There is little criterion available to help establish a reasonable strain limit for one-time use explosive containment vessels due to the complex nature of the dynamic loading, large deformations of the unit, and plastic response of the material. This paper will explore two failure criteria for steel explosive containment vessels. Dynamic analysis methods and data from blast containment vessel test programs will be analyzed and compared to help establish the adequacy of the failure criteria.
Investigation on the Strength of Ultra High Pressure Vessel Cylinder With Self-Protective Flat Steel Ribbons Wound
Authors: Ma Xin , Zheng Jinyang , Ning Zhongpei , Chen Honggang
Published: July 2009

A unique type of self-protective Ultra-High Pressure Vessel (UHPV) cylinder with helically wound Flat Steel Ribbons (FSR) is proposed. The shielding properties of its self-protection in the hoop and axial directions of a FSR cylinder in the case of fracture failure, as well as quick-actuating of the tooth-locked end closure of this new vessel structure are both expounded. Based on its axial strength, a formula of the ultimate load-carrying capability of FSR layers is derived. The shielding function and self-protective capability of FSR layers to the UHPV cylinder are analyzed quantitatively in detail, and a design criterion is also defined. According to the formula and the design criterion defined in this paper, the predicted ultimate load-carrying capability of the FSR layers is 48.3% higher than that in previous references. Results from burst tests of 6 model vessels show that the brittle failure morphology of UHPV cylinders are changed with FSR layers and the potential hazard of failure of the UHPV is reduced. In addition, the cross fracture of the UHPV cylinder is shielded effectively and the derived formulation on the ultimate load-carrying capability of FSR layers is reasonable. UHPV cylinders designed according to the formula and the criterion can use much fewer FSR layers with the same shielding capability.
Strain-Based Acceptance Criteria for Inelastic Analysis
Authors: Ammerman Douglas J. , Bjorkman Gordon S.
Published: July 2009

Modern finite element codes used in the design of nuclear material transportation and storage casks can readily calculate the response of the packages beyond the elastic regime. These packages are designed to protect workers, the public, and the environment from the harmful effects of the transported radioactive material following a sequence of hypothetical accident conditions. Hypothetical accidents considered for transport packages include a 9-meter free drop onto an essentially unyielding target and a 1-meter free fall onto a 30-cm diameter puncture spike. For storage casks, accident conditions can include drops, tip-over, and aircraft impact. All of these accident events are energy-limited rather than load-limited, as is typically the case for boilers and pressure vessels. Therefore, it makes sense to have analysis acceptance criteria that are more closely related to absorbed energy than to applied load. Strain-based acceptance criteria are the best way to meet this objective. As cask vendors’ ability to perform non-linear impact analysis has improved, the need for a code-based method to interpret the results of this type of analysis has increased. The ASME Section III Working Group on Design of Division 3 Containments is working with Section III Working Group Design Methodology to develop strain-based acceptance criteria to use within the ASME Code for energy-limited events. This paper will briefly discuss the efforts within the ASME, detail the advantages of using strain-based criteria, discuss the problem areas associated with establishing strain-based criteria, and provide insights into inelastic analyses as applied to radioactive material transportation and storage casks in general. The views expressed represent those of the authors and not necessarily those of their respective organizations or the ASME.
Methods for Design of Explosion Containment Vessels
Authors: Chen Yongjun , Zheng Jinyang , Deng Guide , Ma Yuanyuan , Sun Guoyou
Published: July 2009

Explosion containment vessels (ECVs), which can be generally classified into three categories, i.e., multiple use ECVs and one-time use ECVs, single-layered ECVs and multi-layered ECVs, metallic ECVs and composite ECVs according to the usage, structural form and the bearing unit, respectively, are widely used to completely contain the effects of explosions. There are fundamental differences between statically-loaded pressure vessels and ECVs that operate under extremely fast loading conditions. Conventional pressure design codes, such as ASME Section VIII, EN13445 etc., can not be directly used to design ECVs. So far, a lot of investigations have been conducted to establish design method for ECVs. Several predominant effects involved in the design of ECVs such as scale effect, failure mode and failure criteria are extensively reviewed. For multiple use single-layered metallic ECVs, dynamic load factor method and AWE method are discussed. For multiple use composite ECVs, a minimum strain criteria based on explosion experiments is examined. For one-time use ECVs, a strain limit method proposed by LANL and a maximum strain criteria obtained by Russia are discussed for metallic vessel and composite vessel, respectively. Some improvements and possible future work in developing design criterion for ECVs are recommended as a conclusion.
Stress Classification Lines Straight Through Singularities
Authors: Kalnins Arturs
Published: July 2009

The paper considers geometries of pressure vessels and components for which the theoretical models contain sharp corners, representing singularities. The idea is proposed that a stress classification line passed straight through the singularity can yield linearized stresses that are applicable in pressure vessel design. Using elastic finite element analysis, details of the procedures by which this result can be achieved are given for two examples. One is a sharp corner at the toe of a fillet weld. Membrane and bending stresses are calculated directly in the toe plane, showing little or no dependence on mesh size. The other is an axisymmetric shell with a flat head and a sharp corner at the joint. The objective is to determine the primary-plus-secondary stress intensity on a Stress Classification Line (SCL) through the joint. Two methods are used. One is by determining the zone of valid SCLs and extrapolating the linearized stresses to the joint. The other is by calculating the linearized stresses directly on the SCL through the joint. Conditions for the use of the SCL through the joint for the shell/flat head model are established.
Optimization of Hydrogen Utilization Ratio in Hydrogen Filling Stations
Authors: Chen Honggang , Zheng Jinyang , Liu Yanlei , Xu Ping , Li Lei , Liu Pengfei , Bie Haiyan
Published: July 2009

High pressure hydrogen storage is widely used in hydrogen filling stations and fuel cell automobiles. Currently, single filling is the main method for hydrogen transfer from stationary storage tanks to cylinders of fuel cell automobiles. Along with the wide application of hydrogen the multistage filling will be adopted in hydrogen filling stations due to its high hydrogen utilization ratio. The hydrogen utilization ratio of single or multistage filling can be determined by various parameters such as the pressure and volume of the stationary tanks and cylinders of fuel cell automobiles. In this research, the utilization ratios of hydrogen in different filling methods are analyzed using the algorithm established in this article based on the real gas law of hydrogen and the corresponding hydrogen utilization ratios are obtained. The results show that it can be significantly improved using multistage filling method and reaches a maximum as the ratio of the volume of higher-pressure stationary tank to the lower one is 0.5.
Nonlinear Analysis of Pressure Strengthening for Austenitic Stainless Steel Pressure Vessel
Authors: Ma Li , Zheng Jinyang , Miao Cunjian , Qin Yongquan , Sheng Shuiping , Han Shuxin , Shi Caixing
Published: July 2009

Austenitic stainless steel exhibits excellent ductility and high strain hardening. When the steel is loaded in tension to a stress σk above its proof strength and then unloaded a permanent plastic elongation will result. If the steel is loaded again it will remain elastic up to this higher stress. This characteristic of the strain hardening offers the space to increase the allowable stress of the steel by pressure strengthening. In practice the finished vessel was loaded by internal pressure to the strengthening stress of σk, which is well above the proof strength of the material and greatly improves the bearing capacity of the vessel. The strain energy function-based principle accompanied with a constraint condition was presented according to the true stress-strain curve of material to determine the strengthening stress of σk. Using this principle, the finite element analysis of pressure strengthening was performed where material and geometrical nonlinearity were considered in the large deformation computation of pressure vessel. Also, the strain under the load steps of the vessel was studied in strengthening operation process, which was coincident with numerical results. For the strengthened pressure vessels, the strength margin was evaluated by the comparison of the measured plastic collapse pressure with the design pressure.
Application of a Reliability Method to Maintenance Strategy for Mechanical Components
Authors: Park Young Ho , Hijazi Iyad , Tang Jun
Published: July 2009

This paper presents a maintenance decision-making strategy in the general area of replacement and reliability of mechanical components. The decision-making strategy involves the optimization of replacement interval based on fatigue failure of mechanical components. This new approach is based on the cumulative damage distribution function for evaluating mean fatigue life. By using the approach, the analytical expressions for the mean and the variance of the cumulative damage distribution under both stationary narrow-band and stationary wide-band random process are provided. The mean value and variance of the fatigue life distribution are thus evaluated to determine the optimal replacement intervals under fatigue failure. To evaluate probability function and the expected length of a failure cycle, approximated function forms were used.
PBMR Reactor Unit Seismic Response Including Impact Damping
Authors: du Plooy N. F.
Published: July 2009

The Pebble Bed Modular Reactor (PBMR) is a High Temperature Reactor (HTR), with a closed-cycle, gas turbine power conversion system. The PBMR essentially comprises a steel pressure vessel which holds the enriched uranium dioxide fuel encapsulated in graphite spheres. The fuel is supported by a graphite block reflector and a steel core barrel. It is clear that the Reactor Unit consists of parts with very different damping properties. Additionally a large number of gapped supports are used to satisfy the support requirements for both thermal and seismic load cases. In this paper a method to account for the energy dissipation through impact of the gapped supports is investigated. It is found that the inclusion of viscous impact damping results in significant reductions of the impact force.
A Generalized Anisotropic Hardening Rule Based on the Mroz Multi-Yield-Surface Model
Authors: Choi K. S. , Pan J.
Published: July 2009

In this paper, a generalized anisotropic hardening rule based on the Mroz multi-yield-surface model is derived. The evolution equation for the active yield surface is obtained by considering the continuous expansion of the active yield surface during the unloading/reloading process. The incremental constitutive relation based on the associated flow rule is then derived for a general yield function. As a special case, detailed incremental constitutive relations are derived for the Mises yield function. The closed-form solutions for one-dimensional stress-plastic strain curves are also derived and plotted for the Mises materials under cyclic loading conditions. The stress-plastic strain curves show closed hysteresis loops under uniaxial cyclic loading conditions and the Masing hypothesis is applicable. A user material subroutine based on the Mises yield function, the anisotropic hardening rule and the constitutive relations was then written and implemented into ABAQUS. Computations were conducted for a simple plane strain finite element model under uniaxial monotonic and cyclic loading conditions based on the anisotropic hardening rule and the isotropic and nonlinear kinematic hardening rules of ABAQUS. The results indicate that the plastic response of the material follows the intended input stress-strain data for the anisotropic hardening rule whereas the plastic response depends upon the input strain ranges of the stress-strain data for the nonlinear kinematic hardening rule.