bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical/Experimental Modelling of a Fuel Tank Impact
Authors: Seddon Caroline M. , Moatamedi Moji , Cheng Wing
Published: August 2008

High speed projectile impacts of fuel tanks can cause catastrophic failure. The complex fluid structure interactions produce structural behaviour that is often difficult to predict. This particular event was highlighted following the accident involving the Air France Concorde in July 2000. In this incident, accident investigations suggested that during the impact, penetration of the projectile didn’t occur, however, vibration of the skin coupled with excessive hydraulic pressure caused the tank to rupture outwards. The work reported details experimental and numerical analysis of a metallic rectangular fuel tank impacted by a high speed projectile, representative of the Concorde accident. The experiments were performed by Health and Safety Laboratory (HSL), in which the fuel tank was impacted at various projectile speeds. Numerical modelling of the experiments was undertaken, in which full fluid structure interaction was incorporated. Comparisons are made between measured and numerical accelerations at several points on the tank. The numerical results were consistent with the experiment, showing that the numerical modelling methodology was both valid and accurate.
Protection of Underground Gas Pipelines From the Third Party Damage by On-Line Monitoring Using Piezoelectric Accelerometer
Authors: Cao Chengfan , Nam Jay-Young , Choi Jae-Boong , Kim Young-Jin
Published: August 2008

While it is difficult to detect target signals, on-line monitoring remains the most reliable method to protect underground pipelines from the third party damage. To distinguish signals from a variety of white noises during remote pipelines monitoring, it is necessary to filter signals from unanticipated noise and to find co-relation among signals. In this paper, an on-line monitoring system based on local area network (LAN) is developed not only to detect a damage occurrence but also to find its location along the pipelines. For this purpose, an acoustic wave propagation model is generated along the gas pipelines, and signals based on the model are compared with experimental data. In modeling the wave propagation, auto power spectral density (APSD) and cross power spectral density (CPSD) processing methods are applied to distinguish damage signals from noises. To locate the damage point on the pipelines, signals from three different piezoelectric accelerometers are monitored, and compared with those from the proposed model. From the experiments, the number of sensors should be determined in accordance with the attenuation coefficient of signal. Also, the proposed scheme which combines APSD and CPSD processing methods is proved to be powerful in practical applications.
Buckling Considerations for U-Shaped Bellows Utilized in Flexible Metal Hoses
Authors: Williams Dennis K.
Published: August 2008

This paper describes some of the considerations for evaluating the structural adequacy of flexible metal hoses utilized in a petro-chemical or process type environment. Specifically, the issues associated with the instability of the metal U-shaped bellows, from which the hose derives its overall flexibility and name, are reviewed and discussed in detail. In an effort to provide a comprehensive examination of the flexible hose’s use in the petro-chemical industry, a discussion of the applied mechanics associated with both column buckling of the bellows (also known as “squirm”) and in-plane buckling is presented. Results from a non-linear column buckling finite element analysis (FEA) of the U-shaped bellows are described and compared against previously published theoretical works on the instability of shells of revolution and most specifically, toroids. The applied loads in the finite element analyses include both internal pressure and transverse displacements (i.e., translations perpendicular to the longitudinal axis of the hose/bellows assembly). In addition, the guidance provided by the rules of the Expansion Joint Manufacturers Association Standards (EJMA) with regard to squirm are also reviewed and discussed. Finally, the results of both the theoretical and analytical investigations into the squirm phenomenon are utilized to identify some very practical solutions and recommendations to avoid the possibility of catastrophic failure of U-shaped bellows from column type instability.
Consequences of the German TA Luft for Bolted Flange Connections and Valves in Industrial Plants
Authors: Kockelmann Hans , Hahn Rolf
Published: August 2008

The high grade performance of gaskets for bolted flange connections in terms of TA Luft and VDI guideline 2440 assumes the fulfilment of the following requirements: Long-term suitability of the gasket particularly with regard to the exposure to the operating temperature and the medium; this requires the investigation of the long-term behaviour, e.g. according to DIN 28090-2 and DIN 28090-3 The design of flange connections (strength and tightness proof) on the basis of realistic gasket characteristics determined experimentally, e. g. according to DIN 28090-1 or prEN 13555 Compliance with the specific leakage rate of 10-4 mbar 1 / (s·m) in a type test at 1 bar test pressure. Similar requirements are effective for packings of stuffing boxes, in which the type test is carried out under more intensive boundary conditions compared to the flange connections: real operating pressure and stem strokes. In the frame of a research project sponsored by the German chemical industry a choice of gaskets were tested which cover all gasket types in the European gasket standard EN 1514 part 1 to 7. The gasket types were classified in view of their high grade performance potential. Similar investigations and analyses were carried out for standard packings for stuffing boxes. These results and their consequences are presented. In addition to the explicitly mentioned requirements in VDI 2440 further requirements should be seen as important in view of the assurance of high grade performance: Quality control during gasket production This can be ensured by manufacturers quality management and by compliance with requirements of corresponding quality standards, e.g. DIN 28091 (an European quality standard (prEN 14772) for gaskets is in preparation) Controlled assembly, which is necessary to realise the design assembly bolt load with limited scattering High grade performance proof of gaskets, more correctly of gasketed bolted flange connections has to be regarded as a complex matter in opposition to common interpretations and involves more than just the compliance with a certain leakage rate criterion of a special type test.
Field Tests and Simulation of Lion-Head River Bridge
Authors: Fang Yao-Min , Pu Jun-Ping
Published: August 2008

Lion-Head River Bridge is a parallel twin bridge. The East Bridge was designed and constructed as a traditional prestressed concrete box of bridge (Pot Bearings); and the West Bridge used seismic isolation devices (Lead Rubber Bearings). The behaviors of these two bridges are compared with each other through several field tests including the ambient vibration test, the force vibration test induced by shakers, and the free vibration test induced by push and fast release devices. During the period of this construction, the East and West bridges were strongly damaged by Chi-Chi and Chi-I earthquakes and had been retrofitted. The damage changed the natural frequencies of the bridges, which was explored from the ambient vibration test. The models of the two bridges are simulated by finite element method according to the original design and the soil-structure interaction was put into consideration in the models. Simulations were modified based on the results of the every test in the field. The dynamic parameters of the bridges are identified and compared with those from the theoretical simulation. The efficiency of isolated bridge is observed and verified.
Unsteady Fluid/Solid Numerical Simulations to Evaluate Thermal Solicitations in PWR Nuclear Plant Mixing Zones
Authors: Pasutto Thomas , Pe´niguel Christophe , Sakiz Marc , Ste´phan Jean-Michel
Published: August 2008

Thermal fatigue of the coolant circuits of PWR plants is a major issue for nuclear safety. The problem is especially accute in mixing zones, like T-junctions, where large differences in water temperature between the two inlets and high levels of turbulence can lead to large temperature fluctuations at the wall. Until recently, studies on the matter had been tackled at EDF using steady methods: the fluid flow was solved with a CFD code using an averaged turbulence model, which led to the knowledge of the mean temperature and temperature variance at each point of the wall. But, being based on averaged quantities, this method could not reproduce the unsteady and 3D effects of the problem, like phase lag in temperature oscillations between two points, which can generate important stresses. Benefiting from advances in computer power and turbulence modelling, a new methodology is now applied, that allows to take these effects into account. The CFD tool Code_Saturne, developped at EDF, is used to solve the fluid flow using an unsteady L.E.S. approach. It is coupled with the thermal code Syrthes, which propagates the temperature fluctuations into the wall thickness. The instantaneous temperature field inside the wall can then be extracted and used for structure mechanics computations (mainly with EDF thermomechanics tool Code_Aster, see joint paper [1]). The purpose of this paper is to present the application of this methodology to the simulation of a straight T-junction mockup, similar to the Residual Heat Remover (RHR) junction found in N4 type PWR nuclear plants, and designed to study thermal striping and cracks propagation. The results are generally in good agreement with the measurements; yet, in certain areas of the flow, progress is still needed in L.E.S. modelling and in the treatment of instantaneous heat transfer at the wall.
Development of Risk-Based Inspection Software for Petrochemical Plant
Authors: Lee Sang-Min , Park Sung-Ho , Chang Yoon-Suk , Choi Jae-Boong , Kim Young-Jin , Yoon Kee-Bong , Han Sang-In , Choi Song-Chun , Kim Ji-Yoon
Published: August 2008

Risk-based inspection (RBI) guideline based on API 581 provides a methodology for calculating the risks of equipments in refinery or petrochemical plants. However, there are limitations of such application to the petrochemical plant directly since only a representative material is considered in calculating the risk, especially the consequence of failure, even though the equipment is made up of numerous different materials. The objectives of this paper are to develop a proposed RBI software to resolve the above issue and to evaluate the risk of equipments in petrochemical plants using the software. In this respect, the mole fractions of materials were used to incorporate the characteristics of all materials. The proposed RBI software consists of qualitative, semiquantitative and quantitative risk evaluation modules in which toxic materials as well as representative materials were derived automatically for comparison with those in the current guideline. The developed RBI software has been applied to evaluate the risk of equipments in Naphtha Cracking Center (NCC) which is the typical facility of petrochemical plant. Thereby, promising evaluation results were obtained and applicability of the proposed RBI software was proven.
Stability and Accuracy for Nonlinear Systems
Authors: Chang Shuenn-Yih
Published: August 2008

Stability and accuracy of the Newmark method for solving nonlinear systems are analytically evaluated. It is proved that an unconditionally stable method for linear elastic systems is also unconditionally stable for nonlinear systems and a conditionally stable method for linear elastic systems remains conditionally stable for nonlinear systems except that the upper stability limit might vary with the step degree of nonlinearity and step degree of convergence. It is also found that numerical accuracy in the solution of nonlinear systems is highly related to the step degree of nonlinearity and the step degree of convergence although its general properties are similar to those of linear elastic systems. Analytical results are confirmed with numerical examples.
Sub-Scale Versus Full-Scale Testing of Jet Pump Vibration
Authors: Law J. C. , Moody F. J. , Laursen A. L.
Published: August 2008

Time-dependent fluid pressure forces on jet pump components have been observed to cause destructive mechanical vibrations at a number of BWR plants. A test has been proposed for the purpose of studying the fluid-structure interaction phenomena and to determine what design or operational modifications can be imposed to mitigate or remove the vibration problem. Due to multi-system interactions of this problem, a full-scale test of water flow through a jet pump at reactor conditions is recommended over a sub-scale test. Each system to be studied imposes additional constraints to the modeling laws. Acoustic effects, vortex shedding or shear layer instability, and the fundamental beam mode of the jet pump diffuser all have similar characteristics, or response times. The need to maintain the time scale ratios for all systems implies that a full size system at full size structural and fluid parameters is the most likely success path in obtaining accurate and relevant data.
Testing and Risk Analysis are Key Elements of Post Construction Problem Solving: A Case History of System Failure and Fire Hazards
Authors: Brown Samuel J. , Husband Eldon , Lyons Jerry L.
Published: August 2008

Hazardous thermal hydraulic loading conditions and unintended plant shut downs from turbine trips that are identified shortly after a plant start up may be the tip of the iceberg of even greater interrelated hazards and costly damages. This paper presents a case study to further illustrate (from ASME PVP2002-1124 paper) additional considerations for the testing and risk analysis to identify a systematic approach to reduce the hazards and risks of equipment failure from thermal hydraulic forces and secondary hazards (such as fires) to the plant and personnel. This paper examines problems of turbine trip caused by fuel computer controlled regulator valves that results in thermal hydraulic forces from compressor pressure wave surges in the process system that result in piping “Y” fitting (45° laterals) failures in the process piping from crack growth and brittle fracture which lead to process chemical release and fires.
Flow Induced Vibration of Large Deflection Filament in Viscous Flow
Authors: Pagwiwoko Cosmas P. , David Tim , Van Houten Elijah
Published: August 2008

This work presents a numerical simulation of fluid-structure interaction of a highly flexible filament in a flow. A finite element model of nonlinear/large deflection cantilever beam is developed to represent the filament. The flow of Newtonian fluid is considered laminar and two-dimensional. The coupling of fluid-structure is carried out by using the fictitious domain algorithm where the moving boundary conditions are imposed. A no-slip condition is applied to all boundary conditions included on the surface of the moving filament. The structural response is calculated at one time step behind the solution of the Navier-Stokes equations. The additional mass plays an important role in dynamic response especially when the density ratio between the fluid and the filament becomes considerably high. To prevent the numerical instability, the equation of motion needs to be represented in a non-dimensional form by keeping the similarities of flow and dynamic response. A ramp function model is applied to simulate the gradual growth of fluid dynamic loads. In the structural part, a Crank-Nicholson integration algorithm is used in calculating the simultaneous structural response. The validation of the method was carried out through the existing experimental results for low density ratio of flowing fluid and filament material in wind-tunnel test, and for high density ratio in flowing soap test as well.
Review and Consideration of Unsettled Problems on Evaluation of Fatigue Damage in LWR Water
Authors: Higuchi Makoto , Sakaguchi Katsumi
Published: August 2008

Reduction in the fatigue life reduction of structural materials of nuclear components in LWR water was initially detected and examined by the authors in the 1980s, who subsequently directed considerable effort to the development of a method for evaluating this reduction quantitatively. Following the establishment of equations to calculate environmental fatigue life reduction for carbon and low alloy steels in 1985 by Higuchi and Sakamoto [1], appeared based on numerous new fatigue data obtained under various environmental and mechanical test conditions. The latest models for evaluation using Fen of the environmental fatigue life correction factor were proposed for carbon and low alloy steels in the year 2000 and for austenitic stainless steel, in 2002. Fen depends on some essential variables such as material, strain rate, temperature, dissolved oxygen and sulfur concentration in steel. The equation for determining Fen is given by each parameter for each material. These models, having been developed three to five years ago, should be properly revised based on new test results. This paper reviews and discusses five major topics pertinent to such revision.
Buckling of Axisymmetric, Homogeneous Cylindrical Shells With Random Imperfections: Monte Carlo Method
Authors: Williams Dennis
Published: August 2008

This paper presents the second of a series of solutions to the buckling of imperfect cylindrical shells subjected to an axial compressive load. In particular, the current problem reviewed is the case of a homogeneous cylindrical shell with random axisymmetric imperfections. The problem solution for the determination of the critical buckling load utilizes a statistical approach to define the random imperfections as opposed to the deterministic methods most often employed in the pressure vessel industry. The imperfections are treated as a random function of the axial (i.e., longitudinal) position on the shell. The Monte Carlo technique is utilized to create a large sample of random shell geometries from which to eventually calculate a critical buckling load for each randomly generated shell geometry. Having matched or predefined the statistical parameters (including the co-variance) of interest as determined from actual manufacturing statistics to the Monte Carlo simulation of shell geometries, the reliability of the critical buckling load is then calculated for the set of cylindrical shells with the random axisymmetric imperfections. The ASME Boiler and Pressure Vessel Code Section VIII fabrication tolerances as supplemented by ASME Code Case 2286-1 are reviewed and addressed in light of the findings of the current study and resulting solutions with respect to the critical buckling loads. The method and results described herein are in stark contrast to the “knockdown factor” approach currently utilized in ASME Code Case 2286-1. Recommendations for further study of the imperfect cylindrical shell are also outlined in an effort to improve on the current design rules regarding column buckling of large diameter shells designed in accordance with ASME Section VIII, Divisions 1 and 2 and ASME STS-1 in combination with the suggestions contained within Code Case 2286-1.
Experimental Investigations on Effects of Simulated Seismic Loading on LBB Assessment of High Energy Piping
Authors: Gupta Suneel K. , Bhasin Vivek , Vaze K. K. , Ghosh A. K. , Kushwaha H. S.
Published: August 2008

The current Leak Before Break (LBB) assessment is based primarily on the monotonic fracture tearing instability. In it the maximum design accident load is compared with the fracture-tearing resistance load. The effect of cyclic loading has generally not been considered in the fracture assessment of nuclear power plant piping. It is a well-known fact that the reversible cyclic loading decreases the fracture resistance of the material, which leads to increased crack growth. Indian nuclear power reactors consider Operational-Basis-Earthquake (OBE) and Safe-Shutdown-Earthquake (SSE) event in the design of various structures, systems and components. Keeping this in view a series of cyclic tearing test have been conducted on straight pipes, made of ASTM SA333 Gr.6 carbon steel. This is the material of primary heat transport (PHT) piping material of Indian Pressurised Heavy Water Reactor (PHWR). In this series 13 tests have been carried out on circumferentially through wall cracked seamless and circumferential seam welded straight pipes under reversible cyclic bending loading. All the tests have been conducted under quasi-static i.e. slow loading rates and the dynamic effect is not considered. The cyclic test results have been compared with the corresponding monotonic pipe fracture test results. These test results and its comparison with corresponding monotonic tearing clearly illustrates the need of addressing the reduction in apparent fracture toughness of material under reversible cyclic loading and safe number of load cycles in the LBB assessment.
A Study on the Improvement of Pneumatic Braking Characteristics of Freight Train
Authors: Nam Seong Won
Published: August 2008

We have performed experimental studies for the improvements of pneumatic brake systems of freight trains. Currently, most of the freight trains operated by the Korean National Railroad have either empty-load or diaphragm type brake systems. In this study, the differences in the air pressure characteristics of both types of brake systems are investigated. Also, we have performed running tests using a 30 car-train set in order to design optimum capacity of a quick release valve. The test results show that the quick release valve is considerably effective in shortening the release time of the diaphragm type brake system. In the case of a normal brake application, the diaphragm type brake system with the quick release valve reduces the release time to 34% of that of the system without the quick release valve. This release time is almost equivalent to that of the empty-load type brake system. Proper performance of a brake system in a train set, preventing wheel flats and reducing maintenance costs, is very crucial.
Simplified Method to Evaluate Upper Limit Stress Intensity Factor Range of an Inner-Surface Circumferential Crack Under Steady State Thermal Striping
Authors: Meshii Toshiyuki , Shibata Kentaro , Watanabe Katsuhiko
Published: August 2008

The upper limit stress intensity factor (SIF) range of an inner-surface circumferential crack in a thin- to thick-walled cylinder under steady state thermal striping was considered in this paper. The edges of the cylinder were rotation-restrained and the outer surface was adiabatically insulated. The inner surface of the cylinder was heated by a fluid with constant heat transfer coefficient whose temperature fluctuated sinusoidally at constant amplitude ΔT. By combining our analytical temperature solution for the problem and our semi- analytical numerical SIF evaluation method for the crack, we showed that the desired maximum steady state SIF range can be evaluated with an engineering accuracy after ΔT, the mean radius to wall thickness ratio rm/W of the cylinder, the thermal expansion coefficient and Poisson’s ratio are specified. No transient SIF analysis nor sensitivity analysis of the striping frequency on the SIF range is necessary. Numerical results showed that our method is valid for cylinders in a range of rm/W = 10 to 1.
An Analysis of Structural-Acoustic Coupling in a Side Branch
Authors: Goyder H. G. D. , Every M. J. , Jee T. P. , Saunders C. P. , Swindell R. J.
Published: August 2008

Side branches are small diameter pipes attached to a main pipeline. If a high noise level is present in the pipeline then the side branch may suffer from damaging vibration or fatigue. The mechanics of the vibration involve an acoustic resonance of the fluid within the side branch which is coupled to a structural resonance. The particular conditions investigated in this paper are where the acoustic and structural natural frequencies coincide. It is shown that the resonant vibration amplitude is controlled by the following factors: (i) the degree of correlation of the acoustic wavelength with the distances between bends in the side branch, (ii) the structural and acoustic damping and (iii) the ratio of the structural mass to the mass of the internal fluid. Simple equations are presented for conditions that will result in coupling and for the maximum amplitude of the coupled vibration.
Analytical Research on Mechanism of Bolt Loosening Due to Lateral Loads
Authors: Shoji Yasumasa , Sawa Toshiyuki
Published: August 2008

It is well known that bolted joints are loosened when lateral loads are applied after they are tightened. This phenomenon is proved by experiments or by the real operations, but the mechanism is not yet elucidated why the bolts are loosened. In this paper several finite element analyses were performed and reproduced the phenomenon that the bolts are loosened, or the nut rotates, when the lateral loads are applied. Based on this result, the mechanism of the bolt loosening (the nut rotation) is investigated. Additionally, it is also examined that bolts are more difficult to be loosened when double nut procedure is used or that they are almost not loosened when the eccentric bolt/nut systems are used. As the result, the bolt loosening is caused by the shape of the thread that is the wedge inclined to the bolt axis. When lateral loads are applied, the bolt/nut threads slide relatively, which causes the relative nut rotation. When the loads are released, the bolt returns to the normal position keeping the relative slide to the nut. This nut rotation causes a reduction of the bolt tension, too. Although the magnitude of this rotation may be quite small, many times of repetition makes the bolt loosened.
Failure Behavior of Pipe Having Local Wall Thinning in Downstream Region of Orifice
Authors: Takahashi Koji , Ando Kotoji , Hisatsune Masakazu , Hasegawa Kunio
Published: August 2008

Monotonic four-point bending tests were conducted using pipe specimens having orifice undergoing local wall thinning. The effects of local wall thinning on the fracture behaviors of pipe were investigated. Local wall thinning was machined on the inside of pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area were l = 100 mm in eroded axial length, d/t = 0.5 and 0.8 in eroded ratio, and 2θ = 180° in eroded angle. The area undergoing local wall thinning was subjected to either tensile or compressive stress. Failure type could be classified into ovalization, local buckling, and crack initiation, depending on eroded ratio, and stress at the eroded area. Three-dimensional elasto-plastic analyses were also carried out using the finite element method, which is able to accurately simulate fracture behaviors. The crack initiation point could be successfully predicted by the criterion proposed by Miyazaki et al..
Case Study of Temperature Analysis Performed on a 45-inch Diameter Heat Exchanger Flange
Authors: Brown Warren , Brodzinski Richard
Published: August 2008

This paper presents an overview of thermal and mechanical analysis performed on the tubesheet joint of a 45 inch diameter feed/effluent heat exchanger to determine the effects of temperature on the joint operation. Two methods of analysis are used, a new analytical approach and Finite Element Analysis (FEA). The analysis determined a potential problem with the operation of the joint in the intended service and a method of improvement was proposed. Some pitfalls of the methods of analysis, for both the analytic method and FEA, are presented. The comparison between the analytic approach and FEA clearly outlined the advantages of each method in determining the operability of heat exchanger joints.
Improving and Simplifying Leakage Based Flange Design
Authors: Brown Warren
Published: August 2008

This paper outlines a new method of determining flange design information from gasket leakage test data. The method is intended to greatly reduce the complexity of leakage based flange design, whilst improving the accuracy. The basis of the method is the conversion of gasket leakage test results into the existing ASME “m” & “y” values. Commentary on the existing ASME and CEN leakage based design methods is provided and the advantage of the new method over both is clearly detailed. This paper guides the flange designer in the pitfalls of leakage based flange design from both a technical and practical perspective and, as such, is important reading for anyone involved in pressure vessel or piping design or operation.
Brittle Failure Assessment of a PWR-RPV for Normal-Anomalous Operation and Loss of Coolant Accident Loads
Authors: Siegele Dieter , Varfolomeyev Igor , Nagel Gerhard
Published: August 2008

The brittle failure assessment for the reactor pressure vessel (RPV) of a 1300 MW pressurized water reactor (PWR) was revised according to the advanced state of the art. The RPV steel is 22 NiMoCr 37 (A 508 Cl.2). The expected neutron fluence at End of License (EOL) after 32 years of full operation is Φ < 2.3·1018 cm−2. The assessment followed a multi-barrier concept to prove independently exclusion of crack initiation, crack arrest and exclusion of the load necessary to advance the arrested cracks through the RPV wall. For operational conditions, a combination of shut-down and anomalous operation was proven as the leading transient. This transient follows a load path decreasing with temperature and thus producing a warm pre-stressing for flaws in the RPV. Therefore, a warm pre-stress (WPS) effect is to be considered. For loss of coolant accident (LOCA) conditions, a leak size screening was performed to find the leading transients. Enveloping transients were determined and used for the brittle failure assessment. As covering crack postulates circumferential cracks in the flange joint to the vessel and axial cracks in the nozzle corner were investigated both under the assumption of a broken clad. For the LOCA loads, the leading leak size was determined by finite element analyses and fracture mechanics based assessment of different combinations of cold/hot leg leak position and cold/hot leg injection of emergency core cooling (ECC). Leading situations are in the flange joint for the cylinder and in the nozzle corner for the flange. In the nozzle corner, high thermal loading from cross corner cooling produces large plastic deformation and loss of constraint. In this situation, the fracture toughness KIC as determined from deeply cracked fracture mechanics specimens is not representative for the component. Thus, loss of constraint in the component was considered by the application of a constraint modified master curve to determine the constraint representative fracture toughness. For the investigated load cases the relevant part of the load paths is at upper shelf temperatures, with the exception of the anomalous operation starting at 50°C to lower temperatures. The results of the investigation demonstrate preclusion of initiation for normal and anomalous operation as well as for LOCA loads. For LOCA, two further barriers were proven with crack arrest for postulated crack extension well within allowable depth in the RPV wall and with the preclusion of the load necessary to advance the arrested crack through the wall.
Rotational Components of Seismic Motion Based on Surface Wave
Authors: Li Hong-Nan , Zhao Yan-Gang , Li Chen , Sun Li-Ye
Published: August 2008

In this paper, the appropriate methods are presented to obtain the seismic rotational components caused by the arrival of the surface waves applying the theory of elastic wave propagation. The rocking component around a horizontal axis and the torsional component around a vertical axis are generated respectively by the Rayleigh and Love waves. At the same time, the calculation formulations of phase velocities about these waves with frequent dispersion are derived and introduced to the rotational components, which may be more suitable for engineering practice. A procedure is developed to compute the time histories. Finally, numerical results have shown that the rotational motions have more energy than the translatonal motions in high frequent range by using the given methods.
Research on the Underwater Shock Wave Generated by Discharge of High Voltage Impulsive Current
Authors: Otsuka Masahiko , Inoue Kouhei , Itoh Shigeru
Published: August 2008

The high energy generated from electric pulsed power has various applications. We investigated the underwater shock wave generated by the metal wire explosion and the electric discharge of electrode using high voltage impulsive current. This investigation was performed using optical observation, pressure measurement and current measurement. In the case of metal wire explosion, the velocity, pressure and the current value of underwater shock wave obtained from the experimental data is proportional to the electric resistance rate. In the other case, the discharge from the electrode, the velocity of the underwater shock wave generated by the discharge of electrode with metal wire explosion is faster than the underwater shock wave generated by the discharge of the electrode without metal wire.
Application of Modern Weld Modelling Techniques in the Design of a Ring Weld Reheat Cracking Test Specimen
Authors: Dennis R. J. , Easterbrook L. E. , Leggatt N. A.
Published: August 2008

New test specimens to study initiation of reheat cracking in stainless steels have been developed using modern finite element (FE) weld modelling techniques. Residual stress simulations of two theoretical ring weld test specimens were conducted in order to optimise the specimen designs so that large zones of creep damage are predicted when subject to elevated temperatures. Each design was optimised to predict damage in the heat affected zone (HAZ) or weld metal region respectively. Fabrication of test components is proceeding on the basis of these studies. The general design is based on a thick disc of parent material with a multi-pass manual metal arc (MMA) ring weld on one surface. The overall objective was to design a specimen that produces macro cracks when soaked at temperatures of 600°C–650°C within several thousand hours. However, consideration was also given to the ease at which automated NDT procedures could be applied to monitor the development of creep damage, as well as the ability to measure residual stress levels by neutron diffraction and the contour method. The design analysis followed a pragmatic approach whereby an ‘appropriate’ geometry for the ring weld test specimen was analysed based upon a ‘baseline’ set of welding parameters, namely, heat input, lay-up sequence and inter-pass temperature. This ‘baseline’ design was then subject to a number of sensitivity studies to ascertain the performance of the specimen where key parameter’s were varied; these being lay-up sequence, number of capping passes, specimen thickness, radial weld position and weld fill. Also investigated was the introduction of an offset weld in order to control the location at which initiation occurred, either HAZ or weld metal. Residual stresses in this multi-pass MMA weld were predicted using a 2D axisymmetric model, simulating both the welding procedure, subsequent machining and furnace heat soak. The coupled thermal-mechanical analysis was performed using the FE code ABAQUS. A heat source modelling tool was employed to calculate welding fluxes, which were read into ABAQUS via a user subroutine. Fusion boundaries were assessed a correlation for total fused area.
Discrete Element Simulation (DEM) for Coupled Description of Material and Energy Flow Within Moving Granular Media
Authors: Kruggel-Emden Harald , Wirtz Siegmar , Simsek Erdem , Scherer Viktor
Published: August 2008

The discrete element method (DEM) can be used for modeling moving granular media in which heat and mass transport takes place. In this paper the concept of discrete element modeling with special emphasize on applicable force laws is introduced and the necessary equations for heat transport within particle assemblies are derived. Possible flow regimes in moving granular media are discussed. The developed discrete element model is applied to a new staged reforming process for biomass and waste utilization which employs a solid heat carrier. Results are presented for the flow regime and heat transport in substantial vessels of the process.
Stabilization of Annular Flow-Induced Vibration of Axisymmetric Elastic Beam With Piezoelectric-Type Actuators
Authors: Shintani Atsuhiko , Fujita Katsuhisa
Published: August 2008

Structures such as an elastic beam in an annular flow begin to vibrate due to the annular flow. Furthermore, the flow-induced vibration becomes larger. In this paper, the stabilization of an axisymmetric elastic beam subjected to an annular flow by acting the control input on the fluid-structure coupled system is investigated. The coupled equation, based on the Euler-Bernoulli type of partial differential equation and the Navier Stokes equation, is derived with control terms. In this paper, a piezoelectric actuator is used to control the coupled system. By applying the optimal control law to the coupled system, the unstable behavior is stabilized. Numerical studies are performed to investigate the efficiency of the proposed control method and the effect of the position of the actuator on the control performance.
A Re-Autofrettage Procedure for Mitigation of Bauschinger Effect in Thick Cylinders
Authors: Parker Anthony P.
Published: August 2008

A manufacturing procedure for enhancing residual stresses and thereby improving fatigue lifetime and fracture resistance of pressure vessels is proposed. The procedure involves initial autofrettage; one or more ‘heat soak plus autofrettage’ sequences and an optional final heat soak. Stresses are calculated numerically for traditional, single autofrettage and compared with those created by the new procedure. The loss of bore compressive hoop stress due to Bauschinger effect is predicted to be significantly reduced. Associated fatigue lifetime calculations indicate that life may be improved by a factor of between 2 and 30, depending upon tube geometry and the ratio of cyclic pressure to yield strength. Repeated overload plus heat soak cycles may also be of benefit in other engineering design scenarios.
Leak Before Break: Studies in Support of New R6 Guidance on Leak Rate Evaluation
Authors: Taggart J. P. , Budden P. J.
Published: August 2008

The concept of leak-before-break (LBB) is often used in safety cases for pressure systems, particularly in the nuclear industry. An important factor in making a LBB case is in the prediction of the leak rate of fluid through a crack. This paper presents a summary of a programme of work, which had the aim of improving guidance on leak rate evaluation for the LBB procedures in the R6 defect assessment methodology. Methods of calculating leak rates have been reviewed, and this has led to a crack morphology model being proposed, which represents single-phase isothermal compressible flow through a crack. In the crack morphology model, the flow is assumed by default to be fully rough turbulent, and the effective roughness to vary between a local roughness value for narrow cracks, to a global value (i.e. the overall crack contours) for wide cracks. The effect of pressure drops due to changes in the flow direction at crack turns has also been included. Calculations using the model show that the friction factor relation due to Spence et al. gives better agreement with measured flow rates than that due to Button et al., which tends to overestimate the flow rate for the examples studied. The inclusion of an inertial pressure term arising from changes in overall flow direction appears to be justified.
Canadian Nuclear Regulatory Perspective on Degradation of CANDU Feeder Piping
Authors: Jin John C. , Viglasky Tom , Blahoianu Andrei
Published: August 2008

As some CANDU plants in Canada are approaching the end of their design lives, various degradation mechanisms which were not anticipated during the design phase have been identified in the CANDU feeder piping and resulted in either actual structural failures or the early replacement of components. In particular, inter-granular stress corrosion cracking (IGSCC) and pipe wall thinning due to flow accelerated corrosion (FAC) are the most prominent degradation mechanisms in the CANDU feeder piping. The Canadian CANDU industry has developed and implemented programs to monitor and manage those unanticipated service-related degradations. Fitness for service guidelines are also developed to justify the structural integrity of the components until the next inspection. These programs include augmented periodic inspections that are targeted to specific components, thereby ensuring the early detection of cracks or excessive wall thinning. The inspection scope and frequency adopted in the degradation management programs exceed the requirements of ASME Section XI, “Inservice Inspection of Nuclear Reactor Coolant Systems” and CSA N285.4, “Periodic Inspection of CANDU Nuclear Power Plants Components”. However, those currently effective codes and standards do not specify requirements which are developed based on the consideration of the specific degradation mechanisms such as IGSCC and FAC wall thinning. Accordingly, it has been an issue for the nuclear regulator as well as in the industry to develop criteria for inspection and replacement/repair, which are based on the current level of understanding of degradation mechanisms and the inspection capability. Presented in this paper are the Canadian regulator’s perspective on the assurance of the safe operation of the CANDU feeder piping which endures degradations of IGSCC and FAC.
Acoustically Induced Vibration of Drums Excited by Rotating Machinery
Authors: Hayashi Itsuro , Guo Shijie
Published: August 2008

Rotating machinery generates pressure pulsations, and the pulsations may cause severe vibrations of drums in high frequency region, resulting in material fatigue failure under certain conditions. Experiments and numerical simulations were performed to investigate the mechanism of the high frequency vibrations of the drums downstream of compressors. The results show that fatigue failure occurs when acoustic diametral modes of a drum are excited by pressure loading. In order to establish practical countermeasures against the vibrations, three-dimensional sound-structural coupled analysis as well as one-dimensional pulsation analysis were conducted. As a result, practical measures such as changing diameter, or thickness of the drums, applying restriction orifice are confirmed effective by using the approach proposed in this study. The validity of the simulation methods incorporating the sensitivity to the fluid conditions is shown.
An Experimental Investigation on Metallic Plates Dynamic Cracking
Authors: Mosnier Martial , Mercier Fre´de´ric M. B. , Renard Je´roˆme , Bailly Patrice
Published: August 2008

Metallic pressure vessels are of common use in the industrial field. They can contain either gases or liquefied gases. If a sudden pressure rise happens inside one of these vessels for any reason (human mistake, uncontrolled chemical reaction, BLEVE, rise in mass, explosion...), it can result in the bursting of the vessel. Though a pressure rise is relatively frequent, the response of the vessel to that sort of load cannot be easily forecasted, since the phenomenon is dynamic. Moreover, except from statistical studies, few experimental data are available on the topic. Therefore, an experimental study can help to understand the behavior of a pressurized enclosure in relation to such a solicitation. This paper analyzes the results of a set of experiments, that have been achieved in order to identify the mechanisms of a vessel rupture. The experimental device consists in a two-parts shock tube between which the sample, viz. a metallic plate, is set. This shock tube is fitted out with pressure gages. The plates are equipped out with strain and crack propagation gages. These sensors, in addition to a high velocity camera make possible the study of dynamic crack formation and fracture propagation on samples submitted to an explosion. Various classes of material with different ductilities have been tested. Moreover, the plate thickness influence has also been investigated. Flaws have been machined as external axial surface notches to produce and control cracking. Various solicitations have also been browsed: the loads were different kinds of explosions produced by the deflagration or the detonation of a stoichiometric hydrogen-oxygen mixture. Preliminary tests have shown a good reproducibility of the experiments. The loading amplitude (the pressure curves) and the shape of the plates after the operation, and especially the crack opening, are almost identical. These experiments have allowed to have a first overview of the role of the different input parameters on the plate behavior under load, and the way cracking occurs. The input parameters that have been monitored are the material ductility, the thickness of the samples and the kind of loading that is applied to them (i.e. different velocities deflagrations, detonations and so on). Output parameters are the strain rate of the plates and their cracking. Cracking is characterized by the size and the shape of the crack, its fracture facies and propagation velocity. In this paper, fracture behavior has been discussed with regard to the above mentioned parameters.
The Significance of Nonlinear Characteristics on the Seismic Induced Pressures of Deeply Embedded NPP Structures
Authors: Xu J. , Miller C. , Hofmayer C. , Graves H.
Published: August 2008

The conventional approach for treating the soil-structure interaction (SSI) effect is to apply various linear methodologies (e.g., substructure and direct methods). In the absence of any major nonlinear effect, linear methodology is sufficient to capture the SSI response parameters. However, for situations where structures are deeply embedded and/or buried (DEB) below grade and a sizeable inertial effect must be considered, the nonlinearity induced by the interaction at the soil/structure interface may potentially influence the SSI response. This is especially true for the seismic induced soil pressures. The effect of such nonlinear characteristics on SSI methodologies should be assessed to determine the extent to which the nonlinearity associated with DEB structures needs to be modeled. Sponsored by the US Nuclear Regulatory Commission (NRC), Brookhaven National Laboratory (BNL) is carrying out a research program to develop a technical basis to support the safety evaluation of deeply embedded and/or buried (DEB) structures as proposed for advanced reactor designs. In this paper, a study of the effect of the soil/structure interface on seismic induced pressures is presented. The nonlinear effect considered includes separation or slipping along the side soil/wall interface. This paper describes various finite element models developed using the LS-DYNA computer code to study the nonlinear effect associated with the soil/structure interface interaction of DEB structures subjected to seismic motion. It is found, based on results to date, that the seismic response characteristics of DEB structures are considerably influenced by the modeling technique for soil/structure interfaces. One of the prominent effects found is the soil/structure interface separations, which modify the soil pressure distributions in both circumferential and vertical directions, as well as their frequency content.