bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical Evaluation of Local Stress by Three-Dimensional Polycrystalline Material at Elevated Temperature
Authors: Watanabe Osamu
Published: July 2010

The present paper presents the Voronoi tessellation algorithm in the three dimensional geometry together with the mesh subdivision algorithm using first order tetrahedron element (4 nodes) and second order tetrahedron element (10 nodes). The elasticity tensors are assumed to include isotropic material and anisotropic material of FCC or BCC crystal. The employed finite element formulation is based on the updated Lagrange type, and the selective numerical integration scheme is used in the present analysis. The obtained numerical examples includes the effects of employed finite elements on local stress, and also the statistical variation around mean value is investigated for the isotropic material and the anisotropic materials having different anisotropy ratio A in elastic range. The inelastic analysis at elevated temperature is also carried out for the anisotropic materials in order to investigate ability of modeling.
Experimental Investigation on Flow Characteristics of Hydrogen in Pipelines
Authors: Zheng Jinyang , Chen Honggang , Xu Ping , Zhao Yongzhi , Zhang Lifang , Liu Yanlei
Published: July 2010

The design of high pressure pipeline is one of key technical problems facing the realization of hydrogen refueling stations and fuel cell automobiles. Currently, hydrogen velocity restrictions in pipeline are considered in reference to natural gas, which leads to some difficulties in design of pipelines for hydrogen supply systems. Considering the different characteristics of hydrogen, this paper establishes an analytical model and carries out a series of experimental tests to investigate the flow characteristics of hydrogen in pipelines. The effects of the pressure in the pipeline on the hydrogen flow velocity and mass flow are studied, and the corresponding relationships are also obtained. The results may provide references for the design of hydrogen pipelines and the development of standards in hydrogen refueling stations and hydrogen supply systems.
Microstructure and Properties of Heat-Affected Zones in X100 Steel Grade Line Pipes
Authors: Zhuang Chuanjing , Li Na , Wang Shipeng , Lin Weiping , Ren Jicheng
Published: July 2010

The relationship between microstructure and properties of weld heat-affected zones in X100 grade pipeline steels was studied. It was found that the intercritically reheated coarse-grained heat-affected zone (IRCGHAZ) of experimental steels has the lowest toughness values when the second peak temperature is at the intercritical (α + γ) region during multi-pass welding. The local embrittlement is attributed to the morphology, amount, and size of the M-A constituent. It is also found that the microstructural inheritance at IRCGHAZ has a deleterious effect on toughness. On the basis of the experimental results, it is suggested that the local embrittlement could be prevented by using pre-heating or post-heating thermal cycle. Pre-heating thermal cycle would eliminate the microstructural inheritance and meliorate M-A constituent. Furthermore, the use of a post-heating thermal cycle will improve the morphology, amount and size of the M-A constituent, and improve the conformation of ferrite matrix.
Stress Analysis of Pressurized Micro-Channel Passages
Authors: Zhou Guo-Yan , Tu Shan-Tung , Xuan Fu-Zhen , Wang Zhengdong
Published: July 2010

To enhance the heat transfer intensification effect, a micro heat exchanger is generally composed of a number of rectangular passages with multiple fin elements. It has been extremely difficult to determine its reliability and durability due to the complicated structures and the stress distributions up to now. In the present paper, the small deformation thin plate bending theory is introduced to analyze the deflection and stress distribution in a pressurized rectangular passage. Analytical formulae are firstly derived for a single-layer micro-channel passage with multiple support fins. The results obtained from the current analytical model are compared with those from the numerical analysis, which verify that the proposed method gives better feasibility and accuracy.
Numerical Investigation of Flow Structure in Pipe Elbow With Large Eddy Simulation Approach
Authors: Tanaka Masa-aki , Ohshima Hiroyuki , Monji Hideaki
Published: July 2010

At the JAEA (Japan Atomic Energy Agency), the simulation code “MUGTHES (MUlti Geometry simulation code for THErmal-hydraulic and Structure heat conduction analysis in boundary fitted coordinate)” has been developed. MUGTHES employs LES (Large Eddy Simulation) approach to calculate unsteady thermal-hydraulic phenomena and the BFC (Boundary Fitted Coordinate) system to simulate complex geometry in the system. In this study, numerical simulations for pipe elbow flows in various curvature radius ratio (Rc/D) conditions at several Reynolds number conditions. By the numerical simulation in pipe elbow at a laminar flow condition of Re = 700, the numerical schemes and the evaluation method of metrics in BFC system are verified and an appropriate mesh arrangement for elbow pipe is considered. By the numerical simulations in pipe elbow with the ratio of Rc/D = 2 under turbulent flow condition of Re = 60,000, the LES approach using standard Smagorinsky model with wall function law is examined in comparison with the experimental results. Moreover, numerical simulation for the 1/3-scaled water experiment at Re = 3.7×106 which simulates the primary cooling system of the JSFR (Japan Sodium-cooled Fast Reactor) is conducted. From comparisons of axial velocity profiles, applicability of MUGTHES to the elbow pipe flow is confirmed and the characteristic of three-dimensional flow structure relating to the structural integrity of the elbow pipe is discussed.
Comparison of the Strength Design and Prevention Method of Elephant Foot Buckling Among Countries’ Standards of Oil Tanks
Authors: Chen Zhiping , Sun Bo , Yu Chulin , Fang Zhou , Zeng Ming
Published: July 2010

In China a large number of tanks whose volumes are greater than 100000 m3 are necessary to be built for establishing the oil reserves system with four levels, which include national strategic oil reserve, commercial oil reserves in the three major oil companies, oil reserves in local governments and general enterprises. Oil tanks built in China were mostly welded tanks and on the ground. The difference among the methods of the strength design of the tank side plate designed by countries’ standards such as API 650, JIS B 8501, BS EN 14015 and GB 50341 is discussed. And the reason why API 650 is used by China engineering company is given. Then kinds of prevention methods about the tank wall elephant foot buckling by earthquake which were designed according to different national standards are compared. It is pointed out that the calculation methods of the tank wall’s allowable compressive stresses and longititude compressive stresses designed by national standards are different. At last the existing problems and the appropriate solutions are analyzed briefly.
Analytical Modeling of the Transverse Load-Displacement Relation of a Bolted Joint With Consideration of the Mechanical Behavior on Contact Surfaces
Authors: Yokoyama Takashi , Izumi Satoshi , Sakai Shinsuke
Published: July 2010

An analytical model for the mechanical behavior of bolted joints subjected to transverse load has been theoretically formulated. It has been shown that transverse displacement of the cramped component can be separated into five factors: (a) bolt bending due to transverse force acting on the thread surface, (b) bolt bending due to thread surface reaction moment, (c) inclination of bolt head, (d) thread surface slip, and (e) bearing surface slip. In order to calculate the factors (d) and (e), contact force and slip displacement induced on the contact surfaces are modeled while factors (a) to (c) are formulated according to previous theories. In addition, it has been shown that variation in reaction moment induced on the contact surfaces, which affects (b) to (e), depends on contact state. Then, the relation between the reaction moment and transverse load is formulated. We have applied our analytical model to an M16 bolted joint and confirmed that the model shows good agreement on the load-displacement relation with FEM result.
Influence of Different Strikers on Charpy Impact Absorbed Energies of High Strength Pipeline Steels
Authors: Lin Weiping , Zhuang Chuanjing , Li Na , Wang Xiaoyan , Bai Xiaoliang
Published: July 2010

Charpy impact tests at different temperatures were carried out with both API X80 and X70 linepipes. The influence of different strikers on impact absorbed energies of API X80 and X70 longitudinal seam submerged-arc welded (LSAW) line pipes were studied. The results indicate that impact absorbed energies tested with American Society for Testing and Materials (ASTM) standard striker (8mm radius) are higher than those with Chinese standard striker (2mm radius). The higher the impact absorbed energies, the bigger the difference between them. In addition, the difference between impact absorbed energies gradually decreased as test temperature reduced. It was found that the impact absorbed energies of specimens tested with ASTM standard striker were more susceptible to change of test temperatures than those with Chinese standard striker. The Charpy impact energy curves of samples tested with ASTM striker presented part of transition zone and the upper shelf energy (USE), but the curves for tests using Chinese standard striker showed only the USE.
Time of Flight Diffraction Technique (TOFD-T) as an Alternative to X-Ray Examination for Thick Welds: A Literature Review
Authors: Bleuze Alexandre , Banchet Julien , Glass S. W. , Tchilian Jean-Michel , Thomas Andre´ , Jambon Michel , Godefroy Vanessa
Published: July 2010

In the nuclear industry, and in particular, regarding large steel components including the nuclear steam supply system, weld integrity must be assessed and confirmed during the fabrication process, for the initial field-welds and periodically during in-service follow-up of some critical assembly welds. In France, this quality control is prescriptively carried out via nondestructive inspections in accordance with the RCCM code primarily via X-Ray Radiography or Gammagraphy (RT) coupled to conventional ultrasound (C-UT). These two techniques are integrated into code inspection requirements since the industry has good evidence that RT and C-UT are able to detect and characterize defects, and are well suited to the large weld thickness of the reactor pressure vessel, pressurizer or stream generators. C-UT is frequently used where it may be shown equivalent to RT. Use of RT however becomes more and more problematic because of the trend of regulatory restrictions to limit radiological source transport, extension of radiological exclusion zones to limit the dose to which workers are exposed, and pressure to increase production for new component fabrication and on-site assembly to support aggressive new-build schedules. Replacement of RT by another dose free technique such as the Time of Flight Diffraction Technique (TOFD-T) would be desirable. In this context, AREVA conducted a study of other industries and other countries management of RT particularly focusing on replacement of radiography by TOFD-T. Interviews were conducted surveying industries manufacturing pressure vessels and making similar welds to those within the nuclear industries, i.e. the oil and gas and the submarine industry. In addition, a literature review on the TOFD-T performances, existing codes and standards, and past approaches to justify the replacement of radiography by the TOFD-T was performed. For all this study, European, American and Japanese industries were surveyed or considered. This study showed that TOFD-T is widely used in the US oil and gas industry thanks to ASME code case, but the global nuclear industry has been reluctant to accept TOFD-T due to the lack of specific acceptance criteria. Follow-on work must be performed for TOFD-T to be proposed and accepted as an alternative to RT in France.
Linear Stability Analysis and Buckling of Two-Layered Shells Under External Circumferential Loading: A Numerical Investigation
Authors: Papadakis George
Published: July 2010

The aim of the paper is the numerical investigation of the stability of two-layered shells under the action of imposed azimuthal strain on the external surface. Although this type of loading is not common in engineering practice, it appears often in biomedicine (for example buckling of esophagus, asthmatic airways, gastrointestinal tract etc). The differential stability equations are discretised using the finite volume method and the resulting generalised eigenvalue problem is solved using the QZ decomposition technique. The results show that the buckling behaviour under circumferential loading is entirely different compared to hydrostatic pressure loading. More specifically, it is well known that in the latter case the number of folds with the smallest critical load is equal to 2. In the former case however it depends on the thickness of each layer and their moduli of elasticity. Comparison with experimental measurements shows good agreement. The thickness of the inner layer significantly affects the number of folds and the critical load (it was found that the number of folds is reduced with increasing layer thickness). Comparison of the eigenfunctions of radial and azimuthal displacements also shows more complex behavior compared to pressure loading.
Effect of Welding Residual Stress and Plastic Constraint on Brittle Fracture of a High Strength Steel
Authors: Torigoe Masaki , Yamashita Yoichi , Yamada Takehisa
Published: July 2010

This paper investigates the effect of welding residual stress and plastic constraint on brittle fracture of a 780 MPa class high-strength steel (HT780). In order to investigate the effect of welding residual stress, three point bend (3PB) fracture toughness tests were conducted using the parent-material specimens and groove-welded specimens which were prepared to have the same cross-sectional proportion; i.e., a ratio of thickness to width of 0.5. Crack length was determined so that the crack tip was located in the base-metal zone far from the heat-affected zone of the welded specimen to eliminate the effect of any degradation of the parent-material property on fracture resistance. Also, in order to investigate the effect of constraint, tensile loading tests in which the plastic constraint was expected to be less than 3PB were conducted using welded specimens as the same as employed in the 3PB test. Three dimensional finite element (FE) analyses were performed to evaluate the stress state near the crack tip at the point of brittle fracture initiation for each test condition. From the results of experiments and FE analyses, it is confirmed that the fracture test results can be evaluated using J or KJ – Q theory, by considering enhancement or reduction due to residual stress.
Experimental and Analytical Studies on the Effect of Excessive Loading on Fatigue Crack Propagation in Piping Materials
Authors: Yamaguchi Yoshihito , Katsuyama Jinya , Onizawa Kunio , Sugino Hideharu , Li Yinsheng , Yagawa Genki
Published: July 2010

The seismic regulatory guide was revised in September 2006 and the Niigata-ken Chuetsu-oki earthquake, whose magnitude was beyond the design base seismic motion, occurred in July 2007. Due to these events, attention is being drawn to the evaluation of the effects of large scale earthquakes for some piping systems in which SCC and/or fatigue cracks may potentially occur. Many papers have been already published about the retardation effect that excessive loading has on fatigue crack growth. The retardation effect is treated qualitatively in regard to the plastic strain generated by excessive loading. In this work, crack growth after excessive loading is evaluated for carbon steel and austenitic stainless steel. Some cyclic excessive loading patterns such as stepwise increases or decreases were applied to fatigue crack growth experiments. The FEM analyses were conducted to evaluate the plastic region size during these loading conditions. PFM analyses were performed to evaluate the extent to which the retardation of crack growth influences the probability of failure.
The Effect of Strength Mis-Match and Residual Stress in ECA of Girth Welds With Internal Circumferential Cracks
Authors: Sisan Ali Mirzaee , Motarjemi Afshin
Published: July 2010

A numerical study was carried out to quantify the effect of a residual stress field on subsequent fracture behaviour of a girth welded pipe with an internal circumferential long crack when subjected to high applied strain loading. In order to introduce an initial residual stress field similar to a welding process in a pipe, a quenching process was numerically simulated and associated residual stress profiles were modified and mapped into the finite element (FE) models. A detailed comparison between the crack driving force for various cases with and without residual stress and weld strength mismatch was carried out for cases under a high plastic deformation regime. The BS7910 procedure was also used to predict crack driving forces using its current assumption of interaction of residual stress with primary loads. The results obtained from the FE analyses were compared with the BS7910 predictions.
Analysis of Spacer Grid Spring Load-Deflection Characteristic for PWR Fuel Assembly
Authors: Eom Kyong-Bo , Park Joon-Kyoo , Kim Kyoung-Joo , Suh Jung-Min , Jeon Kyeong-Lak
Published: July 2010

Spacer grid springs support fuel rods so that the rods keep the position laterally and axially in pressurized water reactor fuel assemblies. The spring load-deflection characteristic, i.e. spring force and stiffness, is needed to evaluate the rod support conditions in the case of fuel assembly manufacturing, shipping and handling. In general, the load-deflection characteristic of grid spring is obtained by mechanical test, but it takes long time to get the new designed grid specimen because the grid manufacturing process comprises strip material manufacturing, stamping die and punch preparation, heat treatment and welding, etc. Therefore the analytic method such as finite element method (FEM) is tried to predict the nonlinear load-deflection characteristic of new designed grid. The spring characteristic mechanical test is simulated with unit cell model and analyzed by FEM tool. Comparing the results between test and analysis shows that more details are needed in the modeling because the boundary conditions of the spring are very complicated and the spring material thickness is changed by the stamping process. The analysis of modified model including expanded cells and thickness changed springs is performed. Using the analytic method of the work to obtain the load-deflection characteristic of spacer grid spring is expected to be useful in the prediction of the characteristic of new designed grids.
Creep-Fatigue Life Determination of Grade 91 Steel Using a Strain-Range Separation Method
Authors: Hoffelner Wolfgang
Published: July 2010

The method of strain range partitioning developed by Manson offers a possibility for treatment of creep-fatigue interactions. It partitions the strain-range of a complex hysteresis loop into four elementary strain range types. Although the method has its merits it is difficult to apply because of lacking experimental data and difficult loop reconstructions. The paper describes an approach which separates the inelastic strain range only into a fatigue portion and a creep portion following both a power law Coffin-Manson relationship. Coefficients and exponents were determined by a simple least square fitting procedure from a set of literature data. The plastic part agreed very well with the experimentally determined fatigue curve. The creep part could, however, only be understood using fatigue-modified stress rupture data accounting for cyclic softening. With this approach it was possible to determine number of cycles to creep failure as a function of the pure creep strain range. This procedure was applied to a set of literature data of grade 91 steel which covered a temperature range of 500°C, 550°C, 600°C with stress controlled and strain controlled hold-times. Life-times were predicted in a range corresponding with the scatter of pure fatigue or creep curves, which means that a very good agreement was obtained. The paper will give a thorough description of the procedure and demonstrate its applicability to design codes.
Microstructure and Mechanical Properties of G17CrMoV5 – 10 Cast Steel After Regenerative Heat Treatment
Authors: Golan´ski Grzegorz
Published: July 2010

The paper presents results of research on the influence of regenerative heat treatment on microstructure and properties of a cast steel after long term operation at the elevated temperature. The material under investigation was G17CrMoV5 – 10 cast steel taken out (in the form of a section) from an internal frame of steam turbine serviced for about 250 000 hours. Performed research has proved that, through the structure degradation, long-term service contributes to an increase of brittleness and decrease of mechanical properties — higher in the case of yield strength than tensile strength. The heat treatment, however, contributes to an increase of impact energy, regardless of the applied parameters. Is has also been proved that the optimum combination of mechanical properties and impact energy is ensured by the structure of high tempered bainite. Low mechanical properties and impact energy, however, were obtained for the structure which was slowly cooled from the austenitizing temperature, i.e. the ferritic – bainitic – ferritic structure.
PWSCC Assessment of Dissimilar Weld on Steam Generator Drain Nozzle in PWR
Authors: Kim Jong-Sung , Hwang Seong-Sik , Kim Hong-Pyo
Published: July 2010

Recently, it is reported that axial and circumferential PWSCCs (primary water stress corrosion crackings) occurred on the dissimilar welds of steam generator drain nozzles in PWR. In this study, the PWSCC is assessed via residual stress analysis, PWSCC initiation review and growth assessment. The residual and operating stress distributions are calculated by finite element method. Based on the stress analysis results, PWSCC initiation locations are predicted by comparing between the stresses and PWSCC threshold stress value. The predicted locations are compared with the examination results by using penetration, eddy current and destructive tests. It is found that the PWSCC initiation prediction has good agreement with the examination results. Also, PWSCC growth is assessed by using the PWSCC growth analysis procedure presented in ASME B&PV Code, Sec.XI. Finally, it is identified that the penetration time via growth assessment has reasonable agreement with the real one.
Simulation and Applications of NDT Ultrasonic Array Techniques
Authors: Benoist Philippe , Poidevin Clarisse , Roy Olivier
Published: July 2010

More and more, phased arrays play an increasing role in ultrasonic non destructive testing, as they provide improved versatility, adaptability to complex configurations and efficiency compared to conventional techniques. The possibilities offered by arrays are numerous, involving electronic commutation, applications of electronic delays in the aim of beam forming, signal processing, etc... Besides the most standard techniques based on 2D beam steering and focusing, more sophisticated techniques are emerging involving matrix arrays and 3D beam forming. Flexible arrays are now available which allow to overcome problems due to complex and varying geometries of the inspected part (elbow, nozzles, butt weld...). The conception and optimization of the techniques, the design of the arrays, as well as the imaging and interpretation of the data requires dedicated simulation tools. Such tools based on an accurate modelling of ultrasound propagation in the part and dedicated to the conception and optimization of the techniques, the design of the arrays, as well as the imaging and interpretation of the data have been developed and implemented in the CIVA software plat-form. They allow to fully exploit electronic commutation over linear or matrix arrays, to compute adapted delay laws which take into account the whole complexity of the inspection, to predict transmitted beams in the part as well as echoes arising for prescribed flaws. In this communication the efficiency of array techniques and the capabilities of related simulation are illustrated on various complex applications such as nozzles, welds, and pipes inspection.
Vibration of Standard Pitched Blade Impellers in Baffled Mixing Vessels
Authors: Kippers Noel , Holloway Gordon
Published: July 2010

This paper presents an experimental investigation of the vibration of standard 45° pitched-blade impellers (PBI) in a baffled mixing vessel. Test conditions include different blade configurations, impeller sizes and rotational speeds. Experiments were conducted in mixtures of water and glycerol, with and without baffles. Three different impellers were used: two, 4-blade PBI with diameter to tank diameter ratios of D/T = 1/2 and D/T = 5/7 and a 6 blade PBI with D/T = 5/7. Impeller orbits were measured directly using high speed imaging and from shaft root strain measurements. The results indicated that the baffles had a strong effect on the vibration characteristics for small tip clearances but less so at large tip clearances.
Metal to Metal Flanges Leakage Analysis
Authors: Bertini L. , Beghini M. , Santus C. , Mariotti G.
Published: July 2010

The use of a gasket made in soft material is not recommended for large size centrifugal compressor case flange. The two case halves are assembled with bolted flanges and leakage is prevented by the metal–to–metal contact under pressure. The prediction of the leakage condition is an important engineering issue for this technology. In the paper an original model able to predict the leakage condition, based on a Fracture Mechanics approach, is presented. The flange surfaces interface is regarded as a crack which can be partially open. As the flanges can not transfer tensile traction, the extension of the open zone, i.e. the crack length, is obtained by the condition that the Stress Intensity Factor K is zero. An analytical model, based on the Weight Function technique, was applied to find the stress intensity K, and then to predict the leakage condition. The paper illustrates a validation of the proposed model by the comparison with a nonlinear Finite Element analysis and the results of a full scale experimental test series obtained by a research collaboration between industry and academia. The leakage pressure predicted by the model is in good agreement with the numerical prediction and the experimental results.
A Parametric Study on the Whistling of Multiple Side Branch System as a Model for Corrugated Pipes
Authors: Nakiboglu Gunes , Belfroid Stefan P. C. , Tonon Devis , Willems Johannes F. H. , Hirschberg Avraham
Published: July 2010

Corrugated pipes are widely used in industry due to their inherent character of being globally flexible and locally rigid. Under certain conditions flow through the corrugated pipes causes severe noise and vibration problems. Thus, to understand the phenomenon and parameters that play role is a real asset for industry. This study is a continuation of a research based on multiple side branch system and presented together with results of an investigation performed on corrugated pipes. Many similarities between the corrugated pipes and multiple side branch system have been observed. A Strouhal number which uses as characteristic length the cavity width plus the upstream edge radius yields the best collapse of the data for both corrugated pipes and multiple side branch system. For both systems the upstream edge radius of the cavity has significant effect on pressure fluctuation amplitudes. It can increase the amplitude of the pressure fluctuation by an order of magnitude compared to sharp edges. The radius of the downstream edge has a less pronounced effect on the sound production. Strouhal numbers display two hydrodynamic modes the first with a Strouhal number around 0.1 and the second one varying in the range between 0.4 and 0.6. The variation in critical Strouhal number for the second hydrodynamic mode correlates with the relative corrugation volume compared to the pipe volume. Experiments with corrugated pipes reveal that 1st hydrodynamic mode is limited to configuration with small relative corrugation volume. The first hydrodynamic mode was not yet observed in the multiple side-branch systems.
Non-Linear Contact Analysis of an API Line Pipe Coupling
Authors: Van Wittenberghe Jeroen , De Baets Patrick , De Waele Wim
Published: July 2010

In this study, the finite element model of an API Line Pipe threaded pipe connection is presented. The non-linearities in material properties and contact behaviour are discussed. A series of modifications of the standard connection are simulated to gain a better understanding in the influence of geometrical and material parameters on the connection’s performance. Finally, test results obtained from a four-point bending fatigue experiment are presented and compared with numerical simulations.
Some Aspects of the Spring Hanger Design Procedure for Piping Flexibility Analysis
Authors: Berkovsky Alexey , Kireev Oleg
Published: July 2010

Influence of the spring hanger design on the piping flexibility and stress analysis is considered in the presented paper. Three aspects of this procedure are discussed and illustrated by the numerical examples: - load variation criteria: different interpretations of load variability could lead to different sizes and even types of selected springs. The key issue of this problem is definition of the cold load (theoretical installed load vs. actual cold load); - influence of the different nonlinearities (hanger’s side forces due to short rod length and support’s friction) on the values of calculated piping thermal movements and hence on the type of selected springs; - modeling and interpretation of spring hanger loads within calculation of sustained stresses. Being differently realized in the commercially available programs for piping flexibility analysis these effects are significant for flexible hot pipes and could introduce a big scattering of results.
Use of Large Databases to Identify Trends in the Behavior of Ferritic Steels
Authors: EricksonKirk Mark T. , EricksonKirk MarjorieAnn , Rose Charles , Zhang Xian J.
Published: July 2010

In this paper we explore the crucial role played by the use of large databases in the identification, development, and refinement of models that describe the toughness behavior of ferritic steels. Specifically, we seek to emphasize and illustrate the point that when physical models are calibrated using large databases this process can reveal trends not previously seen, or foreseen. In support of this idea two examples are cited. First, the evidence for a CVE master curve in fracture mode transition is reviewed, as a counterpoint to the commonly held belief that each Charpy tanh transition curve is unique, with little commonality even within specific alloys, let alone across all ferritic steels. Second, new evidence is presented that the degree of prior hardening experienced by a ferritic steel has a systematic effect on the scatter exhibited by KJc data. This evidence suggests that the KJc Master Curve model, in which the scatter of KJc follows a Weibull distribution having a Kmin = 20 MPa√m and a slope (scatter magnitude) of 4, requires refinement, especially for the higher To values characteristic of steels that have been hardened by, for example, neutron irradiation damage.
Constitutive Modeling for Simulating a Broad Set of Uniaxial and Multiaxial Cyclic and Ratcheting Responses
Authors: Krishna Shree , Hassan Tasnim
Published: July 2010

A set of cyclic and ratcheting experimental responses obtained under proportional to various degrees of nonproportional loading cycles are simulated using the modified Chaboche model in its rate-independent and rate-dependent forms. Features of the modified Chaboche nonlinear-kinematic hardening model needed for simulating cyclic hardening-softening, cyclic relaxation and ratcheting responses under uniaxial and multiaxial loading are elaborated. Significance of “rate-dependent” and novel “back stress shift” modeling features in improving the hysteresis loop and ratcheting rate simulations are demonstrated. Influence of the isotropic and kinematic hardening parameters in improving the multiaxial ratcheting response simulation by the modified Chaboche model are illustrated.
Analysis of FCC Expansion Joints Movement Test
Authors: Medeiros Jorivaldo , Veiga Jordana Luiza B. da C. , Veiga Jose´ Carlos C.
Published: July 2010

The Turboexpander is an equipment that works under very critical conditions requiring very low allowable nozzle forces and moments. A solution to minimize the piping loads transmitted to the equipment is the use of expansion joints. A usual piping stress analysis normally is not enough to guarantee the turboexpander reliability. This paper shows the results obtained in a movement test realized on metallic bellows expansion joints (EJ) used in a turboexpander piping system. The EJ were designed according to the expansion joints manufacturer association code (EJMA), the diameters range from 457 to 2,898 mm, the material of the bellows is Inconel 625 LCF and the shell materials are “killed” carbon steel, for refractory lined EJ or stainless steel 304H. A special test device was developed to apply the design movements on the EJ at the factory. A digital dynamometer was used for data acquisition and the tests were performed on 16 expansion joints of two distinct types: hinged and gimbal. The EJ were pressurized with water during the test. The reactions and corresponding displacements for each step of the test were recorded during loading and unloading.
Effect of Interface Wedge Angle in Ceramic Side on Tensile Bonding Strength in Ceramic to Metal Joint
Authors: Tateno Masayoshi , Morikawa Hiroki , Kokubo Kunio
Published: July 2010

This study was performed to clarify the dependence of ceramic-to-metal joint bonding strength on the interface wedge angle on the ceramic side. Plate Si3N4-to-Ni joints with a plane interface were produced by electric discharge machining. The geometric interface shape at the edge of the interface is characterized by wedge angle on both sides of the ceramic and metal defined as a configuration angle between the free surface of each material and the interface. As the wedge angle of Ni is a right angle, the wedge angle of Si3N4 is set from 30° to 180°. Joints were bonded at high temperature using thin braze metal under vacuum and cooled slowly. The tensile bonding strength of the ceramic-to-metal joint was evaluated to determine the optimum interface shape. The highest bonding strength appeared under identical interface conditions where the fracture pattern changed. The optimum wedge angle to obtain the greatest bonding strength appears to depend on bonding temperature. This study provided a useful geometric interface shape to improve the tensile bonding strength of ceramic-to-metal joints.
Non-Linear Numerical Analysis of Large-Sized Double-Cone Sealing Process
Authors: Sheng Shui-ping , Han Shu-xin , Zheng Jin-yang , Gao Yong-jian , Zhou Ning
Published: July 2010

An integral FEA model and a nonlinear contact algorithm were emplyed for the double-cone seal structure, which were applied on the large-sized double-cone seal structure under internal pressure. The stress distribution of double-cone ring and gasket under pre-tightening and working conditions, as well as the influence of pre-tightening force and internal pressure on the gasket stress, double-cone ring strain and radial clearance, were obtained. If the radial clearance was designed according to g⩾0.1% D1, the material of double-cone ring would yield globally. Meanwhile, If the radial clearance was designed according to g⩽0.05%D1, the sealing performance in the pressurizing process would not be ensured. A radial clearance g=(0.075%∼0.1%)D1 is recommended.
Use of Design-by-Analysis for Designing Shear Key Structure
Authors: Naruse Tomohiro , Kuwano Tetsuya , Narita Mitsuhiro , Hashimoto Taiji , Miura Haruo
Published: July 2010

In many vessels with container, such as those involving rotating machinery, barrel casings are closed with disc shaped end covers on both axial sides. The end covers are fixed to the barrel casing with bolted joints or retaining devices. A shear key structure is often applied to pressurized vessels as a retaining device, because it can endure higher pressure than bolted joints can. Stress distribution in the shear key and the casing depends on the contact condition between the shear key and the casing. Thus, it is difficult to design a shear key structure merely by using Design-by-Formula procedures. We designed the shear key structure according to Design-by-Analysis procedures based on finite element (FE) analysis. By taking the contact condition between shear key and casing into consideration in an FE model and carrying out elastic and inelastic analyses, we developed a new shear key structure configuration. We will confirm the validity of the new shear key structure by means of pressure tests that will be conducted in May of 2009.
Failure Assessment of Nuclear Piping Components Due to Combined Degradation Mechanisms by an Advanced Probabilistic Fracture Mechanics Code
Authors: Datta Debashis , Jang Changheui
Published: July 2010

Probabilistic failure analysis of nuclear piping components due to a combined degradation mechanisms is a challenging issue. At present the majority of analyses were done by assuming a single failure mechanism for a specific location of a piping system. But in reality, this might not be an accurate approach. A tiny crack might be present in a weld location due to fabrication defect or initiated due to fatigue after a short incubation time of plant’s start up. This pre-existing or initiated crack then may be further matured by the synergistic effect of different probable degradation mechanisms e.g. fatigue, stress corrosion cracking, etc. In this study the development process of an advanced probabilistic fracture mechanics code has been described which can handle this combined failure mechanisms. Numerical examples are also presented to rationalize the use of such methodology.
Numerical Optimisation of Blowing Glass Parison Shapes
Authors: Groot J. A. W. M. , Giannopapa C. G. , Mattheij R. M. M.
Published: July 2010

Industrial glass blowing is an essential stage of manufacturing glass containers, i.e. bottles or jars. An initial glass preform is brought into a mould and subsequently blown into the mould shape. Over the last few decades, a wide range of numerical models for forward glass blow process simulation have been developed. A considerable challenge is the inverse problem: to determine an optimal preform from the desired container shape. A simulation model for blowing glass containers based on finite element methods has previously been developed [1, 2]. This model uses level set methods to track the glass-air interfaces. In previous work of the authors [3] a numerical method was introduced for optimising the shape of the preform. The optimisation method aims at minimising the error in the level set representing the inner container surface. The objective of this paper is to analyse the inverse problem by means of an analytical approximation of the flow problem and to improve the performance of the optimisation method previously introduced. In particular an initial guess of the preform for the iterative optimisation algorithm is constructed from the approximate solution of the inverse problem. The main goals of this work are the analysis of the inverse problem and the development of the optimisation method in consideration of the application to containers of industrial relevance.
Revised Weld Residual Stress and Creep Damage Assessments
Authors: Price A. , Smith M. C. , Dennis R. , Spindler M. W.
Published: July 2010

Reheat cracking is a brittle inter-granular type of cracking that occurs in some types of stainless steel welds that have not been post-weld heat treated. It is caused by the accumulation of small creep strains that accompany the relaxation of the weld induced residual stresses. Because relaxation processes produce small creep strains, reheat cracking can occur only if creep ductility is low. Sufficiently low ductilities arise if there is a combination of three factors, susceptible material, operation in the susceptible temperature range and stress triaxiality. The current method used to predict the extent of the zone where reheat cracking can initiate in Type 316H steel weldments is based on continuum damage mechanisms using specially developed material models. In this work more advanced methods have been developed. These methods have been applied to welded specimens manufactured from Esshete 1250. These specimens are described as ‘Borland’ specimens and have been used to study reheat cracking in stainless steel welds. The advanced methods include an improved plasticity model that incorporates combined isotropic and kinematic hardening as well as a two phase annealing function. A number of simulated thermal soak conditions were performed, with a reheat cracking initiation model employed to predict the development of creep damage. This paper details the methodology of the improved welding simulation, its influence on the prediction of reheat cracking and a comparison to previous simulations using existing methods.
The Effect of Multiaxial States of Stress on Creep Failure of Type 316H Under Displacement Control
Authors: Spindler Michael W. , Smith Michael C.
Published: July 2010

Reheat cracking in the heat affected zones (HAZ) of Type 316H welds has been observed in the UK’s Advanced Gas cooled Reactors after 15–50k hours service at 490 to 520°C. These cracks are caused by creep damage from the relaxation of a triaxial residual stress. To validate a model for multiaxial creep damage under triaxial states of stress, notch bar specimens have been tested under displacement control. The test programme included the effects of different notch geometries, test temperatures (475 to 550°C) and both Type 316H parent and HAZ materials. Finite element analysis was used to develop a simplified method to calculate creep damage in the test specimens and this simplified method was then used to analyse the results of the notched bar stress relaxation tests. It was found that the multiaxial creep damage model gave a good prediction of failure in the tests particularly for the levels of triaxiality relevant to welds and at temperatures relevant to service.
Crack-Opening Displacement and Leak-Rate Calculations for Full Structural Weld Overlays
Authors: Shim D.-J. , Kurth E. , Brust F. , Wilkowski G. , Csontos A. , Rudland D.
Published: July 2010

Full structural weld overlays have been used in the U.S. nuclear power industry for over twenty years in boiling water reactors (BWRs). Primary water stress corrosion cracking (PWSCC) in nickel-based dissimilar metal welds (DMWs) has been experienced in pressurized water reactors (PWRs) since the early 1990s. As a result, the nuclear industry is implementing full structural weld overlays (FSWOL) as a PWSCC mitigation technique that may be used on primary coolant lines previously approved for Leak-Before-Break (LBB). This work investigates the effect of the FSWOL on the leakage behavior of these lines with postulated defects. In this paper, finite element (FE) based crack-opening displacements (CODs) were developed for pipes with a FSWOL with postulated complex cracks. The COD solutions were then employed in standard leak-rate calculations, where equivalent crack morphology parameters were developed to consider a flow through two different crack morphologies, i.e., PWSCC through the DMW and corrosion fatigue through the weld overlay. The results of the sensitivity study and a discussion on the impact of the weld overlay on the leakage behavior concludes this paper.
Effects of Axial and Radial Distortion on Residual Stress of HSAW Pipe
Authors: Xiong Qingren , Zhao Wenzhen , Zheng Maosheng , Feng Yaorong , Ji Lingkang , Hu Feng
Published: July 2010

The complex distortion often occur when the pipe sections of HSAW pipe are cut along the axis. The residual stress caused by the axial and radial distortion in the cut-ring test of HSAW pipe is studied by elastic mechanics theory in this paper, and the effects of the axial and radial distortion on the residual stress of HSAW pipe are analyzed according to the results of the cut-ring test of HSAW pipe section and the mechanical status during the forming of HSAW pipe. The research indicates that the larger axial and radial displacement shows that the larger torsion and shearing stress exist during the strip forming, and which will result in the larger residual stress. It is suggested that the axial and radial displacement in the cut-ring test shall be limited in the technical specification of HSAW line pipe for pipeline project, especially for the key pipeline project.
Efficient Computation of Three-Dimensional Flow in Helically Corrugated Hoses Including Swirl
Authors: van der Linden Bas J. , Ory Emmanuel , Dam Jacques , Tijsseling Arris S. , Pisarenco Maxim
Published: July 2010

In this article we propose an efficient method to compute the friction factor of helically corrugated hoses carrying flow at high Reynolds numbers. A comparison between computations of several turbulence models is made with experimental results for corrugation sizes that fall outside the range of validity of the Moody diagram. To do this efficiently we implement quasi-periodicity. Using the appropriate boundary conditions and matching body force, we only need to simulate a single period of the corrugation to find the friction factor for fully developed flow. A second technique is introduced by the construction of an appropriately twisted wedge, which allows us to furthermore reduce the problem by a further dimension while accounting for the Beltrami symmetry that is present in the full three-dimensional problem. We make a detailed analysis of the accuracy and time-saving that this novelty introduces. We show that the swirl inside the flow, which is introduced by the helical boundary, has a positive effect on the friction factor. Furthermore, we give a prediction for which corrugation angles the assumption of axisymmetry is no longer valid. It then has to make place for Beltrami-symmetry if accurate results are required.
Assessment of a Corrosion Under Insulation (CUI) Using DNV RP-F101 Procedure
Authors: Motarjemi Afshin
Published: July 2010

Corrosion under insulation is a typical type of localised corrosion in oil and gas industry especially when water penetrates into a damaged thermal insulation/coating. An area of corrosion under insulation (CUI) was observed on the external surface of a pipe on topside of an offshore platform after removing the insulation. Surveys of depth measurements of the corroded area in both longitudinal and circumferential directions (with respect to the pipe axial direction) using a depth micrometer tool were performed and then converted to a river-bottom profile following the procedure of DNV RP-F101 Part A. A best estimate of the failure pressure safe working pressure (maximum operating pressure) of the pipe were calculated. The former was then compared against the finite element analysis (FEA) results which showed good agreement when axial stresses were excluded. The effect of assumptions such as confidence level and inspection sizing accuracy are also discussed.