bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and Thermal Analyses of Pressure Vessel Bottom Head With Penetration Holes
Authors: Wu David W. , Yee Raymond K.
Published: August 2008

The paper presents a three-dimensional (3-D) finite element (FE) model of a nuclear pressure vessel and the analyses results under typical loadings using ANSYS finite element code. Structural analyses of the vessel with internal pressure loading and thermal transient loading are described. The main focus of the analysis is on the bottom head shell with the Control Rod Drive (CRD) penetration holes. The vessel support skirt and selected CRD housing/welds that attached to the bottom head shell are included in the model. The objective of this study is to assess the bottom head stress distributions of a nuclear pressure vessel, especially the stress concentrations due to the CRD penetration openings. The calculated stresses around uphill oblique holes in the vessel are compared with those around the normal facing center penetration hole. The preliminary results and conclusions drawn from the study are presented in the paper.
Enhanced ASME Section XI Appendix L Flaw Tolerance Procedure
Authors: Gosselin S. R. , Simonen F. A. , Carter R. G. , Davis J. M. , Stevens G. L.
Published: August 2008

Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code has worked since the early 1990s to develop guidelines for the nuclear power industry to evaluate the serviceability of components that are adversely subjected to fatigue stresses. Results of this work formed the basis for a non-mandatory Appendix L that became part of the 1996 Addenda to the 1995 Edition of Section XI [1]. A key part of this appendix was the introduction of a damage tolerance based examination strategy designed to assure that the component will operate reliability between subsequent inspections. Since the issuance of Appendix L, new data on the flaw detection capabilities have become available, and these data show that ultrasonic inspections can detect flaws much smaller than assumed during the original development of Appendix L. This information allows for significantly smaller sizes for initial postulated flaws. Additionally, Appendix L did not address the potential for multiple fatigue crack initiation sites for a given location on the component. In 1999 the ASME Working Group on Operating Plant Criteria (WGOPC) re-established the Task Group on Operating Plant Fatigue Assessments (TGOPFA) to address these concerns. This paper summarizes the research results, supporting computations, and technical bases for TGOPFA recommended Appendix L improvements. A detailed sample calculation is presented for a PWR charging nozzle-to-pipe weld.
The Influence of Autofrettage With Bauschinger Effect on the SIFS of Multiple Longitudinal Coplanar Cracks in Pressurized Cylinders
Authors: Levy C. , Perl M. , Kotagiri S.
Published: August 2008

The influence of the Bauschinger Effect (BE) on the three dimensional, Mode I, Stress Intensity Factor (SIF) distributions for arrays of longitudinal coplanar, surface cracks emanating from the bore of a fully or partially autofrettaged thick-walled cylinder is investigated. The generation and comparison of the SIFs for a “realistic” - Bauschinger Effect Dependent Autofrettage (BEDA) and those for an “ideal” - Bauschinger Effect Independent Autofrettage (BEIA), which until now did not exist, is undertaken. The 3-D analysis is performed via the finite element (FE) method and the submodeling technique, employing singular elements along the crack front. Both autofrettage residual stress fields, BEDA and BEIA, are simulated using an equivalent temperature field. More than 250 different crack configurations are analyzed. SIFs for various crack densities (2c/d = 0.25–0.75), a wide range of crack depth to wall thickness ratios (a/t = 0.01–0.25), various ellipticities (a/c = 0.5–1.5), and different levels of autofrettage (ε = 30%–100%) are evaluated. The Bauschinger Effect (BE) is found to significantly lower the beneficial stress intensity factor due to autofrettage, KIA, by up to 52%, as compared to the case of “ideal” autofrettage. The reduction in KIA varies along the crack front with the maximum determined by the crack ellipticity, crack depth and crack separation distance. In some cases the maximum occurs at the deepest point of the crack and in others the maximum is at the point of intersection between the crack plane and the inner surface of the cylinder. In certain situations, the maximum transitions from one to the other as crack density increases. The detrimental influence of the BE increases as the crack density decreases and as crack depth decreases. For a partially autofrettaged cylinder, as the level of overstrain becomes smaller the influence of the BE is considerably reduced. As a result, the SIFs due to 100% BEDA differ by less than 15–17% when compared to 60% BEDA, and on the average the difference is only about 6%. Furthermore, the results indicate that crack density, and, in some cases, crack depth and crack ellipticity have opposing effects on the SIF of longitudinally coplanar crack arrays.
Load Development for Vessels With Skirts or Intermediate Supports Located in Structures
Authors: Bardia Kanhaiya L. , La Bounty Donald G. , Hathaitham Kanajett
Published: August 2008

Pressure vessels are sometimes supported in structures using skirts at the bottom tangent line, skirts on the shell, or intermediate supports such as lugs). Examples of pressure vessels with these kinds of support are coke drums and CCR reactors. In these cases some part of the shell and lower vessel head extend below the line of support such as the top of the skirt or lugs. The vessel can be separated into three sections: the first section (top) vessel shell and head above the support line; the second section (bottom) is the shell and head below the line of support; the third section is the combination of the top and bottom section. This paper presents a method to determine the design values of the shear and moment, of these three sections of the vessel and support in response to wind and seismic excitation to determine their loading of the support structure. It is important to assess the contribution of each section to the loading that is used to design the supporting structure. Direction is given as to which these three will govern the vessel design and which will govern the design of the structure. The loading which may govern the vessel design may not govern the design of the structure.
Development of an Improved Methodology for Predicting Airblast Pressure Relief on a Directly-Loaded Wall
Authors: Rickman Denis D. , Murrell Donald W.
Published: August 2008

The interaction of an airblast wave with a structure, and the blast wave propagation around and over the structure is of significant importance. In order to protect a structure from the airblast produced by such explosive threats as terrorist bombs, a facility designer must possess an adequate knowledge of the expected blast wave loading. Of greatest importance are pressures and impulses on the directly-loaded face of the structure, since it is typically subjected to the highest (reflected) pressures. It has long been recognized that reflected pressure time-histories can be strongly influenced by pressure relief from the free edges of the loaded wall. The relief wave can significantly reduce the magnitude of the late-time portion of the positive reflected pressure phase, resulting in a substantial decrease in the peak impulse load. Most current predictive methodologies attempt to account for the relief wave and its effect on impulse. Unfortunately, these methods tend to be rather inaccurate because the exact manner in which the relief wave is manifested is not accurately defined. The US Army Engineer Research and Development Center has developed an improved methodology to predict the effect of pressure relief. This paper presents the basis for the methodology, and its practical application.
Thermal Analysis of the SAFKEG Package for Long Term Storage
Authors: Gupta Narendra K. (Nick)
Published: August 2008

Interim plutonium storage for up to 10 years in the K-reactor building is currently being planned at Savannah River Site (SRS). SAFKEG package could be used to store Pu metal and oxide (PuO2) in the K-reactor complex with other packagings like 9975. The SAFKEG is designed for carrying Type-B materials across the DOE complex and meets the 10CFR71 requirements. Thermal analyses were performed to ensure that the temperatures of the SAFKEG components will not exceed their temperature limits under the K-reactor storage conditions. Thermal analyses of the SAFKEG packaging with three content configurations using BNFL 3013 outer container (Rocky Flats, SRS bagless transfer cans, and BNFL inner containers) were performed for storage of PuO2 and plutonium metal.
Experimental Investigation of Ductile Tearing Properties for API X70 and X80 Pipeline Steels
Authors: Silva Mauri´cio Carvalho , Hippert Eduardo , Ruggieri Claudio
Published: August 2008

This work presents an investigation of the ductile tearing properties for API 5L X70 and X80 pipeline steels using experimentally measured crack growth resistance curves (J-R curves). Testing of the pipeline steels employed compact tension (C(T)) fracture specimens to determine the J-R curves based upon the unloading compliance method using a single specimen technique in accordance with the ASTM E1820 standard procedure. Conventional tensile tests and Charpy V-Notch tests were also performed to determine the mechanical and impact properties for the tested materials. Severe splitting running parallel with the crack propagation path with varied lengths was observed in all tested fracture specimens, particularly for the API X80 material. The occurrence of splits makes the determination of JIc and resistance curves more difficult, as delamination of interfaces positioned normal to the crack front decreases the effective thickness of the test piece, inducing plane stress conditions deep inside the specimen. This experimental characterization provides additional toughness and mechanical data against which the general behavior of X70 and X80 class pipeline steel can be compared.
Bolted Flange Joints With Full Face Gaskets: An Analytical Approach Based on Flexibility
Authors: Bouzid Abdel-Hakim , Galai Hichem
Published: August 2008

The low leakage performance of flanges with full face gaskets is attributed to the reliability of the design method used in Appendix 2 and Appendix Y of the ASME code in assessing accurately the bolt and gasket load changes. The prediction of tightness of these bolted joints relies very much on the level of precision of the gasket contact stress during operation. The evaluation of this stress requires a flexibility analysis of the joint including the flange the gasket and bolt and the interaction between them. This paper analyses the distribution of gasket stress and the load change in bolted joints with full face gaskets. It proposes a simple analytical approach capable of predicting flange rotation and bolt load change during operation. The method is based on the gasket-bolt-flange elastic interaction, including flange rotational flexibility. The proposed model is supported by comparison with numerical FEA of different size flanges.
Impact of Particles on Ductile Substrate
Authors: Cheng Wing , Itoh Shigeru
Published: August 2008

The purpose of this research is to obtain a better understanding of the stress state in ductile substrate due to impact of hard particles. Impact dynamic finite element analyses were performed using a nonlinear transient finite element code. In this phase of the research, only rounded particle is considered. Other considerations include impact angles and velocities. Resulting stress state at various locations of the impact region was studied. Results provide insights into the mechanisms for erosion wear and are used to explain erosion wear behavior in ductile substrate. A wear relation was developed to include the fatigue wear mechanism.
Applications of Capacity Spectrum Method for Buildings With Metallic Yielding Dampers
Authors: Chen Bo-Jen , Tsai C. S. , Chung L. L. , Chiang Tsu-Cheng
Published: August 2008

The 921 Chi-Chi Earthquake was one of the most destructive earthquakes in Taiwan in the twentieth century. The earthquake caused severe damage or collapse to the residential and public structures. It is a sensible choice to utilize the metallic yielding dampers for retrofitting damaged structures and to enhance earthquake-resistant capacity of new structures. In this paper, in order to facilitate the designs of the metallic yielding dampers, an improved nonlinear static analysis iteration procedure based on the capacity spectrum method for buildings with metallic yielding dampers has been proposed. The numerical results of the buildings with the metallic yielding dampers through the nonlinear static analysis iteration procedure and the nonlinear dynamic analysis have been obtained, compared and verified in this study. Moreover, it is also illustrated that the proposed nonlinear static analysis iteration procedure based on the capacity spectrum method for structures with metallic yielding dampers can fairly predict the seismic responses of the buildings with metallic yielding dampers during the earthquakes.
Shaking Table Test of Structure With Reinforced Buckling Restrained Braces
Authors: Tsai C. S. , Chen Wen-Shin , Chen Kuei-Chi
Published: August 2008

The traditional brace elements will buckle when subjected to severe earthquakes. Many researchers have been trying to overcome this disadvantage of the traditional brace element since 1970’s. Many types of braces have been developed without buckling under large compressive forces called the buckling restrained brace BRB, or unbonded brace. This type brace includes a steel core, a case that encases the steel core and brace projection, and can enhance both the stiffness and hysteretic damping of a structure to resist seismic loadings. Recently, some investigators have carried out the researches focusing on the procedure of designing buckling restrained braces, quasi dynamic testing and the methods of the connection between the buckling restrained brace and main structure. But, these results can not reflect the effects of the structure with buckling restrained braces during earthquakes. Therefore, the shaking table testing should be done to examine the effects of new BRBs on the seismic responses of a structure. In this study, the reinforced buckling restrained braces were installed on a three-story scaled steel structure in Feng Chia University to perform a series of shaking table tests. The test results illustrate that the new unbond braces provide good protection for structures during earthquakes.
Stifling of Crevice Corrosion in Alloy 22 During Constant Potential Tests
Authors: Yilmaz Ahmet , Pasupathi Pasu , Rebak Rau´l B.
Published: August 2008

Artificially creviced Alloy 22 (N06022) is susceptible to crevice corrosion in presence of high chloride aqueous solution when high temperatures and high anodic potentials are applied. The presence of oxyanions in the electrolyte, especially nitrate, inhibits the nucleation and growth of crevice corrosion. Crevice corrosion may initiate when a constant potential above the crevice repassivation potential is applied. The occurrence of crevice corrosion can be divided into three characteristic domains: (1) nucleation, (2) growth and (3) stifling and arrest. That is, crevice corrosion reaches a critical stage after which growth stops and the specimens start to regain the passive behavior displayed before the nucleation of localized attack.
Validation of RTTo for German Reactor Pressure Vessel Steels
Authors: Keim Elisabeth , Siegele Dieter , Nagel Gerhard
Published: August 2008

For the introduction of the new reference temperature RTTo of the ASME Code Cases N-629 and N-631 into the German KTA rules the equation RTTo = T0 + 19,4 °C (35 °F) was validated by the re-evaluation of the existing fracture toughness data base of German RPV steels, including unirradiated and irradiated base material and weld metal data. The test temperatures of the data base were standardized to the reference temperature T0 of the Master Curve of the data sets and the data base was compared with the ASME KIc-curve as adjusted by RTTo. The KIc-curve adjusted by RTTo enveloped both, the 1T-size adjusted data base and also the as measured data base, corresponding with the definition of RTTo. Thus the results also prove the validity of the KIc(RTTo)-curve for allowable flaw sizes and up to the crack length spectrum of the ASME KIC-data base without size adjustment of T0. The results of both investigations confirmed the validity of RTTo for German RPV steels.
Integrity Assessment of Cracked Piping Components: Experimental, Analytical and Numerical Studies
Authors: Chattopadhyay J. , Pavankumar T. V. , Tomar A. K. S. , Dutta B. K. , Kushwaha H. S.
Published: August 2008

Integrity assessment of piping components is very essential for safe and reliable operation of power plants. Over the last several decades, considerable work has been done throughout the world to develop a methodology for integrity assessment of pipes and elbows, appropriate for the material involved. However, there is scope of further development/improvement of issues, particularly for pipe bends, that are important for accurate integrity assessment of piping. Considering this aspect, a comprehensive Component Integrity Test Program was initiated in 1998 at Bhabha Atomic Research Centre (BARC), India. In this program, both theoretical and experimental investigations were undertaken to address various issues related to the integrity assessment of pipes and elbows. Under the experimental investigations, fracture mechanics tests have been conducted on pipes and elbows of 200–400 mm nominal bore (NB) diameter with various crack configurations and sizes under different loading conditions. Tests on small tensile and three point bend specimens, machined from the tested pipes, have also been done to evaluate the actual stress-strain and fracture resistance properties of pipe/elbow material. The load-deflection curve and crack initiation loads predicted by non-linear finite element analysis matched well with the experimental results. The theoretical collapse moments of throughwall circumferentially cracked elbows, predicted by the recently developed equations, are found to be closer to the test data compared to the other existing equations. The role of stress triaxialities ahead of crack tip is also shown in the transferability of J-Resistance curve from specimen to the component.
Tests and Numerical Analysis of Cracked Rings Under Thermal Shock in the Brittle/Ductile Transition of a Pressure Vessel Steel
Authors: Reytier M. , Chapuliot S. , Ferry L. , Ne´de´lec M.
Published: August 2008

Thermal shocks and temperature gradients associated with large thickness constitute difficult loadings for structures integrity analysis. Moreover, at low temperature or because of irradiation effects, the pressure vessel steel 16MND5 undergoes a transition in fracture mode which may lead to cleavage initiation. The prevention of this fracture mode is generally ensured by first staying outside the brittle domain and secondly, by imposing a stress intensity factor below the fracture toughness which is determined from monotonic and isotherm standard tests. But, with various temperature-loading histories, this criterion is not faultless. Therefore, in order to study in detail rupture under thermal shocks, with several loading types (mechanical and/or thermal loadings), a specific-adapted cracked ring has been developed. It consists of a 50mm thick ring which has a crack on the external diameter and several holes through the specimen to locally heat the ring by injecting hot water which can lead to crack initiation. This particular test allows the study of crack initiation with only thermal loading or both thermal loading and external mechanical loading. This article describes in details several tests including one with cleavage rupture. Moreover, numerical calculations are presented to estimate the mechanical fields at the crack tip and the global fracture mechanics parameters as a function of the temperature. Several rupture criteria are then applied to predict the initiation.
Flow-Induced Vibration of a Large-Diameter Elbow Piping Based on Random Force Measurement Caused by Conveying Fluid: Visualization Test Results
Authors: Nakamura Tomomichi , Shiraishi Tadashi , Ishitani Yoshihide , Watakabe Hisato , Sago Hiromi , Fujii Tadashi , Yamaguchi Akira , Konomura Mamoru
Published: August 2008

A 1/3 scale flow-induced vibration test facility that simulates the hot-leg piping of the JNC sodium-cooled fast reactor (JSFR) is used to investigate the pressure fluctuations of the pipe, where the high velocity fluid flows inside the piping. By the measurement of the pressure drop in the elbow piping while changing the Reynolds number, the similarity law of this model is confirmed. To evaluate the flow-induced vibrations for the hot-leg and cold-leg pipes, the random force distributions along the pipe and their correlations are measured with pressure sensors in a water loop. It is found that a flow velocity-dependent periodic phenomenon in the rear region of the elbow, and the maximum flow-induced random vibration force in the pipe are observed in the region of flow separation downstream the elbow. Finally, a design method is proposed with power spectral densities of the pressure fluctuations classified into four sections, correlation lengths in the axial direction divided into three sections, and with correlation lengths in the tangential direction into four sections.
Significance of Finite Compliance of a Cracked Piping System on Fracture Integrity Assessment
Authors: Khan I. A. , Bhasin V. , Vaze K. K. , Ghosh A. K. , Kushwaha H. S.
Published: August 2008

One of the thrust areas in the integrity analysis of cracked nuclear piping system is concern with the reduction in moment, at the crack section due to combined effects of local and global residual compliance. However an important consideration in the design of piping system, which is generally not considered, is the re-distribution of load that occurs due to finite compliance of the piping system. The load at the crack section reduces while it increases generally at support/anchor locations, which may be high stressed locations. In case of stiff-piping system this re-distribution of load may be quite significant. Hence for the complete integrity of the piping system these un-cracked locations should also be re-assessed. A generalized procedure is suggested to take care of the reduction in load at the cracked section and corresponding increase in reactions at the support/anchor locations in a 3-D cracked piping system. Thus the stability of cracked section as well as other highly stressed locations can be simultaneously assessed. Here it is assumed that the remaining piping system behaves in a linear elastic manner and the plasticity remains confined to the cracked section only. Detailed finite element analyses are performed on circuitous (3-D) cracked piping system to validate the developed approach. Results presented in this article clearly show that due to reduction in moment the crack driving force, for the same external load, reduces significantly.
Advanced Design of Packing and Cylinders for Hyper-Compressors for LDPE Production
Authors: Giacomelli Enzo , Graziani Franco , Pratesi Simone , Zonfrillo Giovanni , Giovannetti Iacopo
Published: August 2008

The optimization of packing cup geometry is important for improving the reliability of hyper-compressors. The complex arrangement and the transmission of loads through the various components requires the use of FEA to properly determine the stress level. The need to reduce the sensitivity to external factors requires an investigation with more advanced simulations. The entire cylinder and associated components such as head flanges, cylinder chambers and tie rods, were modeled. This provided the characteristics of the interfaces and the boundary conditions necessary to simulate the packing cups. Considering the thickness, ring housing profile, lube-oil holes, mating surfaces, interference-fit and diameter make it possible to obtain the stresses at the most critical points. This new simulation approach shows the effect of the parameters that influence the stress level at critical points, thus optimizing the packing cup profile and its relevant features.
Pressure Vessel Design for Reciprocating Compressors Applied in Refinery and Petrochemical Plants
Authors: Giacomelli Enzo , Passeri Marco , Battagli Paolo , Euzzor Mario
Published: August 2008

The process gases (often at rather high pressure), used in refinery and petrochemical plants must be handled and contained in the most safe and reliable manner. All gas-bearing components therefore must be accurately designed to this purpose. Particularly, in reciprocating compressor plants pressure pulsations are unavoidable, however their occurrence and effects can be controlled through a proper design of pressure vessels, piping layout, supports etc. Proper sizing of pulsation bottles is in fact a key step in the definition of a reciprocating compressor plant system. Definition of volume, shape and type of the pulsation bottles is the first step of the design. Then the mechanical design, according to the required Code, is performed. Calculation of stresses occurring on the bottle internals, as well as a low cycle fatigue analysis may also be necessary in certain circumstances. Once the pulsation bottles are defined, it is possible to perform a vibration analysis by means of a FE model including the cylinders, the suction and discharge bottles and the relevant supports, using as an input the result of the piping pulsation and vibration analysis. This very accurate calculation is called the “cylinder manifold analysis”.
Square Root 3: Background to the New Design Margin for High Pressure Vessels
Authors: Keltjens Jan , Cornelissen Philip , Koerner Peter , Hiller Waldemar , Wink Rolf
Published: August 2008

The ASME Section VIII Division 3 Pressure Vessel Design Code adopted in its 2004 edition a significant change of the design margin against plastic collapse. There are several reasons and justifications for this code change, in particular the comparison with design margins used for high pressure equipment in Europe. Also, the ASME Pressure Vessel Code books themselves are not always consistent with respect to design margin. This paper discusses not only the background material for the code change, but also gives some practical information on when pressure vessels could be designed to a thinner wall.
Validation of an Estimation Procedure to Predict the Quasi-Static Brittle-to-Ductile Fracture Initiation Transition Temperature (FITT) for Ferritic Piping
Authors: Williams Craig , Brust Bud , Scott Paul , Rudland Dave , Wilkowski Gery
Published: August 2008

This work was conducted in order to validate the flaw evaluation criteria for class 2, 3, and balance of plant piping in nuclear power plants. A methodology was developed as part of the Battelle Integrity of Nuclear Piping (BINP) program for predicting fracture initiation transition temperature (FITT) for a surface crack in a pipe from the 85% shear area transition temperature from Charpy specimen data. The predictive relationship is described in a separate paper in this conference [1]. In order to validate this methodology a series of Charpy, dynamic tear test (DTT), compact (tension) (CT), single-edge-notch [tension] (SEN(T)), and full-scale circumferential surface-cracked pipe experiments were conducted at different temperatures. As part of this paper, the results from these tests, along with their potential impact on the validation procedure to predict the quasi-static brittle-to-ductile FITT will be discussed.
Buckling of Imperfect, Axisymmetric, Homogeneous Shells of Variable Thickness: Perturbation Solution
Authors: Williams Dennis
Published: August 2008

This paper presents the first of a series of solutions to the buckling of imperfect cylindrical shells subjected to an axial compressive load. In particular, the initial problem reviewed is the case of a homogeneous cylindrical shell of variable thickness that is of an axisymmetric nature. The equilibrium equations as first introduced by Donnell over seventy years ago are thoroughly presented as a basis for embarking upon a solution that makes use of perturbation methods. The ultimate objective of these calculations is to achieve a quantitative assessment of the critical buckling load considering the small axisymmetric deviations from the nominal shell wall thickness. Clearly in practice, large diameter, thin wall shells of revolution that form stacks (as found in flue gas desulphurization absorber assemblies) are never fabricated with constant diameters and thicknesses over the entire length of the assembly. As such, 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 Study of MFPS-Isolated Sensitive Equipment
Authors: Tsai C. S. , Cheng C. K. , Chen M. J. , Yu S. H.
Published: August 2008

After observations of many seismic disasters, let is found that many structures were just damaged slightly or even without any damage such as hospitals, high technology factories, computer generator rooms, but huge damage to internal installations was caused by earthquakes. Therefore, in addition to promoting the earthquake-resistant capacity of a structure, it is also important to ensure the safety of ancient objects and instruments in the structure. Structural control has been recognized as an effective and attractive method for preventing structural damage from earthquakes. In this study, shaking table tests of the high-end server equipment equipped with the multiple friction pendulum system (MFPS) were carried out to study the earthquake-proof benefit of the MFPS isolator. The MFPS isolator can not only shift the natural periods of high-end server equipments away from the rich period contents of earthquake motions, but also provide considerable hysteretic friction damping to absorb the input energy of earthquakes to insure the sensitive equipments unharmed during earthquakes.
Residual Stress Analysis of Tube Attachment Weld in Pressure Vessel Forging: Comparison of FE Predictions and Measurements
Authors: Hurrell P. R. , Leggatt N. A. , Dennis R. J.
Published: August 2008

Residual stresses were analysed in a partial penetration weld attaching a tube inside a thick pressure vessel forging, both made of SA508 steel. 2D finite element (FE) analyses methods were used to simulate this multi-pass manual TIG weld. The weld preps are buttered and the forging subsequently heat-treated prior to making the closure weld. Buttering of the forging J-prep and subsequent PWHT creep stress relaxation were modelled. Generally the buttering was found to have minimal influence on the final stress state, although some difference in local peak stress and stress gradients were calculated. Representative test blocks were manufactured, with and without buttered weld preps. Each test block contained two tube penetrations and attachment welds, in order to examine interaction effects. Welding details were captured and peak temperatures recorded by thermocouples were reasonably consistent with the FE model predictions. Surface stresses were measured both in the as-welded condition and after machining, using the hole drilling strain gauge method. Good agreement with FE results was achieved in surface stress levels in the vessel forging, buttering and tube wall. However the 2D model overestimates weld hoop stresses. Large yield magnitude tensile stresses in the vicinity of the joint are balanced by lower compressive stresses in the surrounding PV forging. Interaction effects between the stress fields produced by adjacent tube welds are negligible.
Improving the Reliability of Tube Hydroforming Process by the Taguchi Method
Authors: Li Bing , Nye T. J. , Metzger Don R.
Published: August 2008

The tube hydroforming process has undergone extremely rapid development, especially in applications for the automobile industry. In-process variation of forming parameters such as material properties, friction conditions and part geometries will directly affect the quality of forming response by causing variation in the process output. To ensure a reliable hydroforming process at the design stage, applying robust design methodologies becomes crucial to the success of the resulting process. The reliability of the tube hydroforming process based on the tube wall thickness thinning ratio is studied in this paper. In order to improve the reliability of the process, the Taguchi method, which is capable of evaluating the effects of process variables on both the mean and variance of process output, is used to determine the optimal forming parameters for minimizing the variation and average value of the thinning ratio. The Taguchi method is applied to design experimental arrays which incorporate design (i.e., controllable) parameters and noise (i.e., non-controllable) parameters. Finite element simulation is used to analyze the virtual experiments according to the experimental arrays. Through statistical analysis, the influence of each design parameter on both the mean and variance of the thinning ratio is obtained, and is used to find the optimal combination of design parameters for minimum thinning ratio, minimum variance of thinning ratio, and maximum expected process reliability. A cross-extrusion hydroformed tube is employed as an example to illustrate the effectiveness of this approach.
Stress Corrosion Cracking of Carbon Steel Weldments
Authors: Lam Poh-Sang , Cheng Changmin , Chao Yuh J. , Sindelar Robert L. , Stefek Tina M. , Elder James B.
Published: August 2008

An experiment was conducted to investigate the role of weld residual stress on stress corrosion cracking in welded carbon steel plates prototypic to those used for nuclear waste storage tanks. Carbon steel specimen plates were butt-joined with Gas Metal Arc Welding technique. Initial cracks (seed cracks) were machined across the weld and in the heat affected zone. These specimen plates were then submerged in a simulated high level radioactive waste chemistry environment. Stress corrosion cracking occurred in the as-welded plate but not in the stress-relieved duplicate. A detailed finite element analysis to simulate exactly the welding process was carried out, and the resulting temperature history was used to calculate the residual stress distribution in the plate for characterizing the observed stress corrosion cracking. It was shown that the cracking can be predicted for the through-thickness cracks perpendicular to the weld by comparing the experimental KISCC to the calculated stress intensity factors due to the welding residual stress. The predicted crack lengths agree reasonably well with the test data. The final crack lengths appear to be dependent on the details of welding and the sequence of machining the seed cracks, consistent with the prediction.
Flow Induced Vibration of a Steam Control Valve in Middle-Opening Condition
Authors: Morita Ryo , Inada Fumio , Mori Michitsugu , Tezuka Kenichi , Tsujimoto Yoshinobu
Published: August 2008

In some cases, a steam control valve in a power plant causes a large vibration of the piping system under partial valve opening. For rationalization of maintenance and management of a plant, it is favorable to optimize the valve geometry to prevent such vibration. However, it is difficult to understand the flow characteristics in detail only from experiments because the flow around a valve has a complex 3D structure and becomes supersonic (M>1). Therefore, it is useful to combine experiments and CFD (Computational Fluid Dynamics) for the clarification of the cause of vibration and optimization of valve geometry. In previous researches involving experiment and CFD calculation using “MATIS” code, we found that an asymmetric flow attached to the valve body (named “valve-attached flow”) occurs and pressure increases where the valve-attached flow collides with the flow from the opposite side under the middle opening condition. This high-pressure region rotates circumferentially (named “rotating pressure fluctuation”) and causes cyclic side load on the valve body. However, because we assumed the valve support is rigid, we cannot clarify the interaction between the rotating pressure fluctuation and the valve vibration when the valve stiffness is small. Thus, in this paper, we conducted flow-induced vibration experiments on a valve with a very weak support and investigated the characteristics of the vibration mode under the middle-opening condition. As a result, under the specific lift condition of the region where rotating pressure fluctuation occurs, lock-in phenomena between the rotating pressure fluctuation and the valve vibration occur and large-amplitude vibration can be seen.
Experimental Verification of the Theoretical Results for Annular Flows With Moving Boundaries
Authors: Mekanik Abolghasem
Published: August 2008

This paper describes three objectives: (a) experiments on the unsteady pressure fields generated in annular flow, made of two uniform concentric rigid cylinders, when the outer cylinder of the annulus is subjected to either lateral or rocking motion in the plane of oscillation; (b) calculations of the unsteady pressure for viscous laminar flows in the same annular configurations using the time-accurate integration of the full non-linear Navier-Stokes equations. For this purpose, the three-point backward implicit scheme with pseudo-time and artificial compressibility is used and the discretized equations are solved on stretched staggered grids to enhance the accuracy of the solution; (c) comparison of theoretical and experimental results, which shows that when the amplitude of oscillation of the outer cylinder is of the order of one-tenth of the annular gap excellent agreement between the measured and calculated unsteady pressures is obtained, thus validating the numerical procedure used. The results of this research can be used for flow-induced vibration analysis.
Failure Mode and Failure Strengths for Wall Thinning Straight Pipes and Elbows Subjected to Cyclic Loading
Authors: Hasegawa Kunio , Miyazaki Katsumasa , Nakamura Izumi
Published: August 2008

It is important to assess the failure strengths for pipes with wall thinning to maintain the integrity of the piping systems and to make codification of allowable wall thinning. Full-scale fracture experiments on cyclic loading under constant internal pressure were performed for 4-inch diameter straight pipes and 8-inch diameter elbow pipes at ambient temperature. The experiments were low cycle fatigue under displacement controlled condition. It is shown that dominant failure mode under cyclic loading for straight pipes and elbows is crack initiation/growth accompanying swelling by ratchet or buckling with crack initiation. When the thinning depth is large, burst occurs after swelling. In addition, it is shown that pipes with wall thinning less than 50% of wall thickness have sufficient margins against seismic event of the safety shut down earthquake (SSE).
Wear Measurements Using Electrochemical Methods
Authors: De´forge Damien , Lina Agne`s , Boursier Jean-Marie , Wenger Franc¸ois , Ponthiaux Pierre , Ambard Antoine
Published: August 2008

A research program dedicated on the interaction between motion and wear in aqueous environment was launched by “Electricite´ de France” (EDF). The influence of environmental parameters such as temperature, chemical composition and oxidative power will be tested. In primary water of nuclear reactors, contacts occur at high temperature (320°C) and corrosion effects are likely to be determining. The whole study will thus be performed from a corrosion-wear point of view. A wear simulator able to operate at high temperature and in high-pressurized water was thus electrochemically instrumented to perform in situ measurements. The results obtained at room temperature are presented. The oxidative power of the environment was varied using dissolved oxygen or hydrogen. It is shown that the oxidative power of the environment has a strong influence on corrosion and wear. Electrochemical experiments performed in situ prove that vibrations induced contacts lead to the removal of the passive film present on the steel. The extent of wear can be evaluated using electrochemical measurements. Prospects opened by this technique in studying wear in primary water at high temperature (320°C) are finally discussed.
Assessment and Extension of an Analytical Formulation for Prediction of Residual Stress in Autofrettaged Thick Cylinders
Authors: Parker Anthony P.
Published: August 2008

A recent formulation due to Huang and Cui provides an analytic method for calculating residual stresses in autofrettaged tubes exhibiting non-linear behavior (including Bauschinger effect) during manufacture. The formulation incorporates Von Mises criterion but is limited in its application to plane strain end conditions and an incompressible material (i.e. Poisson’s ratio 0.5) with a fixed unloading behavior. Comparisons indicate that, by selecting unloading behavior typical of that at the bore, the method produces reliable results for both A723 type steels and for steels which exhibit significant strain hardening and/or more dramatic Bauschinger effect. Numerical comparisons show that open-end, compressible conditions produce results which differ from the plane strain, incompressible case, but that these differences may be accurately corrected using a straightforward, pragmatic process. It is concluded that a simple modification of the Huang & Cui procedure may be used to perform extremely accurate straightforward spreadsheet calculations of residual stress in autofrettaged tubes manufactured from a wide range of steels under various end conditions. The Huang & Cui formulation also provides a reliable and highly accurate means for validating numerical formulations including Finite Element methods.
Dynamics of Multi-Connected Bodies Supported by Damper-Spring Systems Moving in a Narrow Passage
Authors: Fujita Katsuhisa , Shintani Atsuhiko , Hatae Fuminobu , Toyama Shingo
Published: August 2008

In this paper, the vibrational behavior and unstable phenomena of multi-connected bodies supported by damper-spring elements moving in a narrow flow passage are investigated. These vibrational phenomena have been often observed in high-speed trains running in tunnels, cleaning robots going through pipings, medical machines in human blood vessels and core internal structures in nuclear reactor vessels. The fluid forces acting on the multi-connected rigid bodies are obtained analytically on the basis of the Navier-Stokes equations applied to a narrow flow passage. After the equations of coupled motion of the multi-connected bodies and fluid are derived, a stability analysis is performed, taking physical dimensions such as gaps etc. as parameters.
Three Dimensional Seismic Isolation System for Next-Generation Nuclear Power Plant With Rolling Seal Type Air Spring and Hydraulic Rocking Suppression System
Authors: Shimada Takahiro , Suhara Junji , Inoue Kazuhiko
Published: August 2008

Three dimensional (3D) seismic isolation devices have been developed to use for the base isolation system of the heavy building like a nuclear reactor building. The developed seismic isolation system is composed of rolling seal type air springs and the hydraulic type springs with rocking suppression system for vertical base isolation device. In horizontal direction, the same laminated rubber bearings are used as horizontal isolation device for these systems. The performances and the applicability have already been evaluated by the technical feasibility tests and performance tests for each system. In this study, it was evaluated that the performance of the 3D base isolation system with rolling seal type air springs combined with hydraulic rocking suppression devices. A 1/7 scaled model of the 3D base isolation devices were manufactured and some performance test were executed for each device. For the rolling seal type air springs, dynamic loading test was executed with a vibration table, and pressure resistant ability test was executed for reinforced air springs. In the dynamic loading test, it is confirmed that the natural period and damping performance were verified. In the pressure resistant ability test, it is confirmed that the air springs had sufficient strength. For the hydraulic rocking suppression system, forced dynamic loading test was carried out in order to measure the frictional and oil flow resistance force on each cylinder. And the vibration table tests were carried out with supported weight of 228 MN in order to evaluate and to confirm the horizontal and vertical isolation performance, rocking suppression performance, and the applicability of the this seismic isolation system as the combined system. 4 rolling seal type air springs and 4 hydraulic load-carrying cylinders with rocking suppression devices supported the weight. As a result, the proposed system was verified that it could be applied to the actual nuclear power plant building to be target.
Development of Guidance for Leak-Before-Break Analysis for Complex Shaped Cracks
Authors: Yellowlees S. F. , Lynch K. M. , Warren A. P. , Sharples J. K. , Budden P. J.
Published: August 2008

Within the context of leak-before-break (LbB) methodology, this paper presents results from finite element (FE) analyses of a range of complex through-wall cracks in an infinite flat plate subject to combined primary membrane and secondary bending loads. The aim is to provide a simplified approach for the treatment of converging/diverging cracks in LbB assessments. Expressions have been derived from curve fits to FE results, which allow the calculation of the crack opening area (COA) for a complex crack. This expression is based on the crack mouth opening displacement for a straight fronted crack under membrane loading, with modification factors that take account of the crack shape, section thickness and the level of imposed bending stress. The variation of J through the plate thickness has also been studied. Some of the flat plate analyses have been repeated for a straight crack using elastic-plastic material properties. Elastic values of COA are always found to be conservative (i.e. an underestimate) compared to inelastic values. Elastic analyses of a cylinder containing a circumferential defect have also been carried out. These indicate that the crack opening on the inside wall is generally smaller than the crack opening from the corresponding flat plate analysis.
Comparison of Predicted and Observed Fretting-Wear Damage in Nuclear Steam Generators
Authors: Fisher N. J. , Han Y. , Gue´rout F. M. , Janzen V. P.
Published: August 2008

Fretting-wear of nuclear heat exchange equipment is addressed at the design stage to demonstrate that components will meet their design life. Atomic Energy of Canada Limited (AECL) has developed a methodology to predict the progression of fretting-wear damage using the combination of predicted work-rates from a finite element model and experimentally-derived wear coefficients. The predicted progression of fretting-wear damage in a recent steam generator design is compared to inspection results from steam generators in a mid-life plant. The predicted wear is similar to the maximum observed wear. Therefore, AECL’s methodology is shown to provide reasonable quantitative predictions of the progression of fretting-wear.