bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Element Analysis of a Gasketed Flange Joint Under Combined Internal Pressure and Thermal Transient Loading
Authors: Abid Muhammad , Chattha Javed A. , Khan Kamran A.
Published: August 2009

Performance of a bolted flange joint is characterized mainly by its ‘strength’ and ‘sealing capability’. A number of analytical and experimental studies have been conducted to study these characteristics only under internal pressure loading. In the available published work, thermal behavior of the pipe flange joints is discussed under steady state loading with and without internal pressure and under transient loading condition without internal pressure. The present design codes also do not address the effects of steady state and thermal transient loading on the structural integrity and sealing ability. It is realized that due to the ignorance of any applied transient thermal loading, the optimized performance of the bolted flange joint can not be achieved. In this paper, in order to investigate gasketed joint’s performance i.e. joint strength and sealing capability under combined internal pressure and transient thermal loading, an extensive nonlinear finite element analysis is carried out and its behavior is discussed.
Spatially Resolved Materials Property Data From a Cross-Weld Tensile Test
Authors: Turski M. , Bouchard P. J. , Smith M. , Edwards L. , Withers P. J.
Published: August 2009

This work involves the determination of uniaxial stress-strain data from ‘cross-weld’ specimens machined from across a 3 pass welded generic 316 type austenitic stainless steel grooved plate test specimen, using Electronic Speckle Pattern Interferometry (ESPI). ESPI has been applied as a novel surface strain mapping tool for measuring the mechanical properties of uniaxial tensile test specimens with heterogenous microstructures. Using this technique, proof stresses have been measured at different distances from the centre of a manual metal arc (MMA) weld, using a single cross-weld specimen. Mechanical properties were measured using cross-weld specimens taken across a first pass and third pass weld bead, thus allowing the effect of subsequent weld passes on a single weld bead to be quantified. Measurements indicate 0.2% proof stress values more than 100 MPa higher in the first pass weld bead compared to the third pass. This is due to the higher levels of accumulated plastic strain in the first pass weld bead, as a result of thermo-mechanical cycling associated with subsequently deposited weld passes.
Fatigue Testing of Welded Flat Head Pressure Vessel Joints
Authors: Hinnant Chris
Published: August 2009

Experimental results for the fatigue testing of several welded flat head geometries are reported. These tests are similar to those previously reported by Hinnant (2006) [1] and focus on the fatigue behavior of full penetration welds with cover fillet welds. Fatigue calculations according to several fatigue design methods are compared against the experimental results, as are the mean fatigue curves of several of the design methods. Of particular interest for these new tests is the effect of plate thickness, testing environment, and geometric effects. Nominal plate thickness values ranging from 0.0625" (1.59 mm) to 0.1875" (4.76 mm) have been tested and correlated. Four additional fatigue tests were conducted using air to determine if previous testing in room temperature tap water resulted in decreased fatigue life.
Determination of Residual Stresses in Autofrettaged Compound Tubes for Different Geometries
Authors: Mohammadi M. , Farrahi G. H. , Hoseini S. H.
Published: August 2009

In this paper, using numerical solutions of bore and outer radius hoop residual stresses in various tube geometries for autofrettage prior to shrink fit and shrink fit prior to autofrettage design are investigated, and the results are compared with monobloc autofrettaged and shrunk fit tubes. Both of the former compound tubes induce more compressive bore hoop residual stresses than a monobloc autofrettage and shrunk fit case. Furthermore, in geometries in which maximum bore hoop residual stresses are induced, the outer radius experiences acceptably low tensile residual stresses. Bore hoop residual stresses increase with increase of tube outer radius; however the rate of increasing decreases.
Simulations of Valve Operation in High Pressure Facilities
Authors: Ahuja Vineet , Hosangadi Ashvin , Cavallo Peter , Shipman Jeremy
Published: August 2009

An innovative technique for simulating moving valve problems in liquid rocket testing facilities using cryogenic working fluids has been developed. This strategy uses a novel library grid approach in conjunction with an elasticity based grid movement solver with a multi-element unstructured CFD framework. The numerical formulation is based on a compressible gas-liquid framework that accurately models cavitation and multi-phase mixture acoustics while accounting for real fluids property variation. Demonstration of transient moving valve simulations for valve configurations operated at NASA SSC have been carried out for two different valves with very different plug operating profiles. The results are in good agreement with testing data for variable displacement plug motion as well as quasi-steady simulations for slow operating valves. Valve response to varying operating conditions such as plug speed can be predicted using the developed tool. This technique can also serve to analyze problems of valve stall, valve timing/scheduling and can reduce need for expensive activation runs at test facilities.
Time-Frequency Analysis of Pressure Fluctuations on a Hydrofoil Undergoing a Transient Pitching Motion Using Hilbert-Huang and Teager-Huang Transforms
Authors: Benramdane S. , Cexus J. C. , Boudraa A. O. , Astolfi J.-A.
Published: August 2009

In this paper, time-frequency analysis of wall pressure signals of a hydrofoil’s suction side undergoing a forced transient pitching motion with incoming flow is conducted. A novel method recently introduced by Huang et al., the Empirical Mode Decomposition (EMD), is first used to decompose resulting non-stationary signals into frequency sub-band components called Intrinsic Mode Functions (IMFs). EMD-filtered pressure coefficient signals are then reconstructed from few selected IMFs from low frequency modes and time-frequency analysis performed on high frequency modes. For this latter purpose, two analysis methods are used. The first one consists in demodulating IMFs into their Instantaneous Amplitude (IA) and Instantaneous Frequency (IF) using the Hilbert transform and the second one is based on the Teager energy tracking operator (TEO). The transition occurrence is analyzed using IA and IF of extracted IMFs from chordwise pressure transducer’s signals. This transition occurrence is then described in time-frequency domain.
Bauschinger Effect Investigation of an Aluminum Alloy, and Its Application in Autofrettaged and Compound Tubes
Authors: Mohammadi M. , Farrahi G. H. , Hoseini S. H.
Published: August 2009

For characterizing Bauschinger effect factor (BEF) and Bauschinger modulus reduction of an A5083 aluminum alloy experimentally, several uniaxial tension-compression tests carried out in different pre-strain levels using INSTRON testing machine. BEF was investigated using both Welter and Milligan’s definitions for various offset values. It was observed that Milligan’s definition predicts BEF less than Welter’s definition for all offset values. In addition, real loading-unloading behavior of such alloy was recorded to predict residual stresses resulting from autofrettage and shrink fit processes. Variable material properties (VMP) method, which is capable of incorporating real unloading behavior of materials, was used as an accurate way to estimate residual stresses. Hoop residual stresses were calculated using real unloading behavior and isotropic hardening rule. Results showed that, isotropic hardening rule in comparison with real unloading behavior overestimates bore hoop residual stresses up to 12%.
Effect of Size of Butt Weld Repairs on Weld Overlay Residual Stresses
Authors: Limpus Carl R. , Dijamco David G. , Bax Richard , Cofie Nathaniel G.
Published: August 2009

Weld overlays have been used to provide repair and mitigation to stress corrosion cracking (SCC) susceptible butt welds in nuclear power plant piping. Among the several advantages associated with weld overlays are the beneficial compressive residual stresses that are developed in the inner portion of the component after application of the overlay. These compressive stresses can provide significant mitigation against SCC in these welds. To determine the residual stresses resulting from the weld overlay process in analytical modeling, a weld repair during original fabrication of the butt weld is typically assumed before application of the weld overlay. If the fabrication records are available, the details of the weld repair can be simulated in the analysis. However, in most cases, the weld records are not easily accessible and in instances where they are available, the quality and completeness of the information are questionable. As such, various conservative assumptions are made on the extent of the weld repair to be simulated in the analytical modeling. In this paper, the residual stress results of an axisymmetric finite element simulation of a bimetallic weld subjected to an inside surface weld repair followed by a weld overlay repair are presented. Three through-wall weld repair sizes (25%, 50% and 75% of the wall thickness without the overlay) assumed to be full 360° around the circumference were considered in the study. The results indicate that for all three weld repair cases, the inside of the configuration is very tensile after the weld repair indicating that regardless of the size of the weld repair, SCC is a possibility. The post weld repair stress distribution of the 50% and the 75% repair cases are similar indicating that an assumed 50% repair is fairly representative of repairs that can be assumed for analysis purposes. The application of the overlay resulted in favorable compressive stresses on the inside portion of the configuration for all the three weld repair cases indicating that regardless of the size of the initial weld repair, the application of the weld overlay provides mitigation against SCC.
Flaw Evaluations Using Master Curve Methodology
Authors: Sham T.-L. , Mahmoud Samer H. , Gunawardane Heshan P. , Hawileh Rami A.
Published: August 2009

The Master Curve (MC) reference temperature, T0, characterizes the fracture performance of pressure vessel steels in the ductile-brittle transition region. An MC-based flaw-evaluation analysis procedure that accounts for the variations of stress intensity factor, temperature, constraint, and material conditions is presented. The analysis procedure is applied to an example problem of pressure-temperature curve construction for a Section XI, Appendix G, internal, axial, semi-elliptical surface flaw subjected to a simple cool-down transient. The results show that the enhancement in the fracture toughness due to constraint loss in the ductile-brittle transition region as seen in data from test specimen geometries does not always translate to similar benefits in structural applications. Analyses such as those carried out in this work are necessary to quantify the potential benefit for each application.
A Review of Haynes® 230 and Haynes 617 Alloys for High Temperature Gas Cooled Reactors
Authors: Katcher Michael , Klarstrom Dwaine L.
Published: August 2009

HAYNES 230 and 617 alloys are competing for use on Generation IV, high temperature gas cooled reactor components because of their good high temperature creep strength in the temperature range of 760°C and 982°C and resistance to attack in the gas cooled reactor environment. A review of the metallurgy affecting the properties in each alloy is provided. It is shown that the grain size and carbide precipitation developed during manufacture affect short term and long term ductility, fatigue life, and creep strength. For example, 230 alloy has a finer grained structure which promotes fatigue strength with a slight sacrifice in creep strength. The 617 alloy has a coarser grain structure which provides slightly higher creep resistance while sacrificing some fatigue strength. Thermal aging also introduces gamma prime precipitation to 617 alloy in addition to grain boundary carbides. This, along with grain boundary oxidation, reduces the low cycle fatigue strength of 617 alloy compared to 230 alloy. Independent studies have shown that 230 alloy possesses higher resistance to thermal fatigue than 617 alloy. However, welds of both base metals with similar weld composition have about the same thermal fatigue life. Cooling rates from solution annealing temperatures during processing affect the ductility and creep strength of these alloys with the highest cooling rates preferred for retention of ductility and creep strength. Slow cooling rates promote carbide precipitation in the grain boundaries which reduces ductility and creep strength.
Development and Application of Materials Properties for Flaw Stability Analysis in Extreme Environment Service
Authors: Sindelar Robert L. , Lam Poh-Sang , Duncan Andrew J. , Wiersma Bruce J. , Subramanian Karthik H. , Elder James B.
Published: August 2009

Discovery of aging phenomena in the materials of a structure may arise after its design and construction that impact its structural integrity. This condition can be addressed through a demonstration of integrity with the material-specific degraded conditions. Two case studies of development of fracture and crack growth property data, and their application in development of in-service inspection programs for nuclear structures in the defense complex are presented. The first case study covers the development of fracture toughness properties in the form of J-R curves for rolled plate Type 304 stainless steel with Type 308 stainless steel filler in the application to demonstrate the integrity of the reactor tanks of the heavy water production reactors at the Savannah River Site. The fracture properties for the base, weld, and heat-affected zone of the weldments irradiated at low temperatures (110°–150°C) up to 6.4 dpaNRT and 275 appm helium were developed. An expert group provided consensus for application of the irradiated properties for material input to acceptance criteria for ultrasonic examination of the reactor tanks. Dr. Spencer H. Bush played a lead advisory role in this work. The second case study covers the development of fracture toughness for A285 carbon steel in high level radioactive waste tanks. The approach in this case study incorporated a statistical experimental design for material testing to address metallurgical factors important to fracture toughness. Tolerance intervals were constructed to identify the lower bound fracture toughness for material input to flaw disposition through acceptance by analysis.
Initial Investigation on Joining ODS Alloy Using Friction Stir Welding for Gen IV Nuclear Reactor Heat Exchanger Applications
Authors: Feng Zhili , Ren Weiju
Published: August 2009

To investigate the possibility of joining oxide-dispersion-strengthened (ODS) alloys while preserving the dispersion for high temperature strength in potential applications to Gen IV nuclear reactor compact heat exchanger, solid-state welding of ODS alloy sheets using friction stir welding (FSW) was studied. Butt weld was successfully produced, and the weld and base metals were characterized using optical, scanning electronic, and transmission electronic microscopes, as well as energy dispersion x-ray spectrum. Microhardness mapping was also conducted over the weld region. Analyses indicate that the distribution of the strengthening oxides was preserved in the weld. Decrease in microhardness of the weld was observed but was insignificant. The preliminary results seem to confirm the envisioned feasibility of FSW application to ODS alloy joining. Further investigation activities are suggested for providing better mechanistic understanding and processing control for applications to Gen IV nuclear reactor systems.
Applicability of Simplified Methods to Alloy 617 in Excess of 649°C
Authors: McGreevy Timothy E. , Abou-Hanna Jeries
Published: August 2009

The Alloy 617 draft Code case does not permit the use of simplified methods to assess ratcheting when temperatures exceed 649°C. This restriction was placed due to an apparent difficulty in distinguishing between creep and plastic deformation at various strain rates for this material. A numerical evaluation of the B-1 and B-2 Tests for a tube under constant pressure and cyclic thermal gradients (linear and nonlinear) was made. Analysis results indicate that simplified methods currently in Appendix T of ASME-NH are applicable for Alloy 617 in excess of 649°C.
Numerical Simulation of Small Amplitude Oscillatory Cylinder Under Incompressible Laminar 2D Fluid Flow: ALE, ARF and Transpiration Methods
Authors: de Morais Marcus Vinicius G. , Gibert Rene-Jean , Baj Franck , Magnaud Jean-Paul
Published: August 2009

In this paper, we compare the performances of ALE and Transpiration methods aided by an third method in non-inertial referential: ARF — Accelerated Reference Frame —. The approach ALE (Donea and Hughes finite element approach) is a powerful tool to treat coupled problems. However, the ALE performance for determining fluid-elastic forces to small vibrations amplitudes is still ignored. The Transpiration method is a simplified approach for calculation of fluid-elastic forces to relatively small vibrations amplitudes. Based on a first order development of velocity boundary conditions, this method allows the use of a fluid domain fixed in time during a dynamic computation, by avoiding hence the problems due to the mesh distortions. We aim to provide a numerical fluid-elastic forces estimate of a moving tube under 2D transverse fluid flow. At first, we carried out a numerical validation on vortex wake characteristic behind an isolated rigid cylinder 2D with Re = 200: Strouhal number Sh and lift’s and drag’s coefficients, CL and CD respectively. These values were useful for following simulations. Finally, a harmonic movement perpendicular to flow is imposed on the cylinder, having a frequency ratio fo/fk and a reduced amplitude So/D. We compare ALE and Transpiration methods, with aid of ARF method, considering the temporal lift signals and their power spectra. The test parameters of vibrating cylinder with Re = 200 are the frequency ratios fo/fk ∈ [0.85–1.20] and the reduced amplitudes of So/D = 0.01 and 0.05. Simulations were compared with Sonneville’s and Gibert’s experimental results. In order to obtain satisfactory converged results, simulations were continued for 100 periods of vibrations. These methods are implemented in Cast3M, a numerical platform of French Nuclear Agency CEA/Saclay.
Hypothesis of Plastic Adaptation in Metal Fatigue: Physical Bases, Mechanisms and Application to Data Analyses
Authors: Matsuno Hiroshi
Published: August 2009

Author has proposed a new idea of an equivalent stress ratio as the parameter for correspondence between cyclic stress conditions of a notched and unnotched specimen. The equivalent stress ratio is formulated as a function of a nominal stress ratio and a theoretical stress concentration factor of a notched specimen. Derivation of the equivalent stress ratio is based on the hypothesis of plastic adaptation in metal fatigue. In the present paper, physical bases of the hypothesis of plastic adaptation and its mechanisms are discussed from a viewpoint of micromechanics. As a result, it is found that the hypothesis is applicable to analyses of metal fatigue characteristics themselve as well as notch problems. The fatigue strength diagrams of ferrous metals are rearranged from JSMS database and other literature by using the equivalent stress ratios (REQ-parameter method). Fatigue strength is discriminated into the two types: critical stresses to form and propagate mode I fatigue cracks, i.e., σw1 and σw2. According to the critical stresses, the fatigue strength diagrams are categorized into three groups, i.e., (1) σw1/σw2-transition types, (2) σw2-dominant types and (3) σw1/σw2-mixed types. Such discrimination depends on kinds of metals, especially, conditions of dispersed precipitates.
Neutron and Synchrotron Diffraction Measurements of Residual Stress in Steel Weldments
Authors: Paradowska Anna M. , Price John W. H. , Ibrahim Raafat
Published: August 2009

This paper explores the use of state-of-the-art instruments such as neutron and synchrotron diffraction for evaluation of residual stress in carbon steel welded components. The study shows significant variation in transverse residual strain/stress distribution across the length of the weld. Measurements before and after post weld heat treatment are reported together with traditional mechanical tests. The changes in residual stress distribution as weld beads are added in multi-bead welds are also presented. Important practical results are: i) The start and end of the weld are the most critical parts of the weldment. Implementations of run-in and run-out (which are subsequently ground off) can minimize the residual stress at the start and end of the weld. ii) Manipulation of the sequence especially around the weld toes can minimize the value of the residual stress in that region. iii) Post weld heat treatment is very effective at reducing residual stresses.
A Modelling Approach for Inter-Linked Feeder Pipes in CANDU Reactors
Authors: Zobeiry Nima , Reinhardt Wolf
Published: August 2009

The feeder pipes of a typical CANDU reactor supply each of 380 fuel channels with coolant and are individually connected to the large bore primary piping. In some designs the longer pipes are interlinked with spacer rods, which mitigate vibrations and prevent contact between adjacent feeder pipes. Under severe loading conditions, the spacer rods will yield, which prevents overstressing the pipes as the strength of the coupling gets reduced. Spacer yielding also provides increased damping for dynamic loads. It has recently become practicable to model the entire interlinked system in a single model. This paper presents the modelling approach for seismic analysis and for fuel channel creep (a radiation induced slow unidirectional anchor motion). Results with and without spacer bars are compared to illustrate the effect of spacers. The importance of representing spacer yielding in the model is discussed.
Experimental Study of Ratcheting for SUS304 Stainless Steel and A1070 Aluminum Alloy
Authors: Sakane Masao , Inoue Akihiko , Chen Xu , Kim Kwang Soo
Published: August 2009

This paper studies the cyclic ratcheting for two materials under multiaxial stress state. The two materials are SUS304 austenitic stainless steel and A1070 pure aluminum. The former material is known as a material that gives strong additional hardening and the latter material shows little additional hardening under nonproportional cyclic loading. The ratcheting behavior under 12 stress-strain waveforms was extensively studied using hollow cylinder specimen. Ratcheting strain depended on the material and stress-strain waveform. Anisotropic ratcheting was found in A1070 but isotropic ratcheting was observed in SUS304 steel.
Tensile Testing of Carbon Steel in High Pressure Hydrogen
Authors: Duncan Andrew , Lam Poh-Sang , Adams Thad
Published: August 2009

An infrastructure of new and existing pipelines and systems will be required to carry and to deliver hydrogen as an alternative energy source under the hydrogen economy. Carbon and low alloy steels of moderate strength are currently used in hydrogen delivery systems as well as in the existing natural gas systems. It is critical to understand the material response of these standard pipeline materials when they are subjected to pressurized hydrogen environments. The methods and results from a testing program to quantify hydrogen effects on mechanical properties of carbon steel pipeline and pipeline weld materials are provided. Tensile properties of one type of steel (A106 Grade B) in base metal, welded and heat affected zone conditions were tested at room temperature in air and high pressure (10.34 MPa or 1500 psig) hydrogen. A general reduction in the materials ability to plastically deform was noted in this material when specimens were tested in hydrogen. Furthermore, the primary mode of fracture was changed from ductile rupture in air to cleavage with secondary tearing in hydrogen. The mechanical test results will be applied in future analyses to evaluate service life of the pipelines. The results are also envisioned to be part of the bases for construction codes and structural integrity demonstrations for hydrogen service pipeline and vessels.
Influence of Load Ratio, Rise Time and Waveform on the Corrosion Fatigue Crack Growth of Austenitic Stainless Steel in a PWR Primary Coolant Environment
Authors: Platts Norman , Tice David , Rigby Keith , Stairmand John
Published: August 2009

The rate of growth of flaws in reactor circuit components by fatigue is usually determined using the reference crack growth curves in Section XI of the ASME Boiler and Pressure Vessel Code. These curves describe the rate of crack propagation per cycle (da/dN) as a function of the applied stress intensity factor range (ΔK). No reference curves for water-wetted defects in austenitic stainless steels are currently available. This paper describes the results of testing of austenitic stainless steel and weld metal in simulated PWR primary coolant over a range of temperatures and mechanical loading conditions. Previous data presented by the authors on wrought stainless steel demonstrated that crack growth rates can be significantly enhanced by the PWR primary environment at temperatures between 150°C and 300°C. The current study extends these data to weld metal and also investigates the impact of other loading waveforms (e.g. trapezoidal loading) on the degree of environmental enhancement. The environmental enhancement increases significantly with reducing loading frequency and decreases with decreasing water temperature. The environmental influence on fatigue is shown to be independent of load ratio over the range R = 0.1 to R = 0.8. The level of enhancement is frequently smaller at very high R ratio (≥0.85) with the enhanced rates of fatigue frequently being unsustained at these high load ratios. There is a strong correlation between the rise time and the level of enhancement of crack growth rate over inert crack growth rates at all temperatures tested. Weld metal has been shown to exhibit similar behavior to wrought material over the whole temperature range studied although the apparent rates of enhancement relative to average inert crack growth rates are lower than found for wrought material. For complex loading waveforms (e.g. trapezoidal loading with hold periods at maximum or minimum load) it is possible predict the level of enhancement on the basis of the test data generated using simpler saw tooth loading regimes.
Computer Piping Analysis, ASME B31.3 Appendix S: Example S3 — Moment Reversal
Authors: Edwards Don R.
Published: August 2009

The American Standards Association (ASA) B31.3-1959 Petroleum Refinery Piping Code [1] grew out of an ASA document that addressed all manner of fluid conveying piping systems. ASA B31.3 was created long before widespread engineering use of computer “mainframes” or even before the inception of piping stress analysis software. From its inception until recent times, the B31.3 Process Piping Code [2] (hereafter referred to as the “Code”) has remained ambiguous in several areas. This paper describes some of these subtle concepts that are included in the Code 2006 Edition for Appendix S Example S3. This paper discusses: • the effect of moment reversal in determining the largest Displacement Stress Range, • the impact of the average axial stress caused by displacement strains on the Example S3 piping system and the augmenting of the Code Eq. (17) thereto, • a brief comparison of Example S3 results to that of the operating stress range evaluated in accordance with the 2006 Code Appendix P Alternative Requirements.
The “Spectrum Dip”: Dynamic Interaction of System Components
Authors: Scavuzzo Rudolph J. , Hill George D. , Saxe Peter
Published: August 2009

In the early 1960s, many full sized surface combatants, submarines and structural models were tested with underwater explosive in order to evaluate the shock load to the ship and internal equipment and structures. Initially, shock spectra were calculated from base motion measurements of internal equipment and components. Attempts were made to envelop these spectra to develop shock design spectra inputs. At that time, earthquake engineers were using this enveloping method to develop design procedures from ground motion measurements to protect structures from earthquakes. However, for the measurements on ships, this procedure resulted in calculated loads that would have caused catastrophic failure of the equipment; yet the equipment had not failed on the ship tests. As a result, the data was reanalyzed over a period of over a year. It was concluded that the dynamic interaction of each component or structure reduced the measured spectral motion at the fixed-base frequencies of the structure by about an order of magnitude. In many cases, there was a dip in the shock spectra at the fixed-base frequencies: the “spectrum dip” phenomenon. This reanalysis led to shock spectra design curves for navy ships. This paper will present a review of an experimental study and an analytical model to explain the effect of dynamic interaction on the shock or response spectrum. In addition, a practical example of interaction of four single mass dynamic systems mounted on a realistic deck and subjected to a high impact shock input was studied by the authors.
Materials, Fabrication, Installation, and Applied Mechanics Considerations in the Catastrophic Failure of a Flex Hose Bellows
Authors: Deegan Dennis C. , Williams Dennis K.
Published: August 2009

This paper is the third in a series that describes the materials, fabrication, installation, and applied mechanics considerations surrounding the catastrophic failure of a bellows component within a metallic flexible hose. The subject flexible hose was utilized in a compressor piping system attachment juncture to a petro-chemical piping system designed in accordance with the ASME B31.3 Process Piping Code. Specifically, the ultimate failure mode issues related to the instability of the metal u-shaped bellows, from which the hose derives its overall flexibility and name, are reviewed and discussed in detail. In an effort to provide a comprehensive examination of the use of the flexible hose in the petrochemical industry, a discussion of the materials, fabrication methods, installation, and, applied mechanics associated with column buckling of the bellows (also known as “squirm”) are presented. A metallurgical failure analysis is presented to identify and document the mode of failure and metallurgical condition of the wire braid and bellows components of the hose. In addition, material examination results, including the discovery of inherent flaws from the fabrication process, are presented and the significance of the findings is presented. The selection process for this particular type of flexible hose (and bellows component) for eventual installation in a vibratory service environment is reviewed in light of the published recommendations provided by the rules of the Expansion Joint Manufacturers Association Standards (EJMA) with regard to squirm are also reviewed and discussed. Finally, a summary of the elastic-plastic finite element analysis of the u-shaped bellows is briefly described and compared against previously published theoretical works on the instability of shells of revolution and most specifically, toroids. The results of the theoretical, empirical, and analytical forensic investigations into the squirm phenomenon are utilized to identify some very practical recommendations in an effort to minimize the probability of catastrophic failures of u-shaped bellows from column type instability.
Analysis of a PHWR Outlet Feeder Vibration Due to Random Turbulence-Induced Excitation
Authors: Han Y. , Janzen V. P. , Smith B. A. W. , Godet T.
Published: August 2009

A nuclear-reactor feeder pipe has been analyzed to assess its vibration and stresses due to internal coolant random turbulence-induced excitation. The structural models were created from both isoparametric beam elements and continuum elements in the finite-element code H3DMAP, a general three-dimensional mechanics analysis package developed to solve a wide variety of problems encountered in the nuclear industry. The feeder was also modelled with beam elements in VIBIC, a finite-element code designed for the vibration assessment of beam-like structures. The excitation forces were based on recent experimental results obtained from piping-vibration tests that used two-phase air/water flow, performed at E´cole Polytechnique at Montreal. Feeder vibration levels, in terms of normalized response amplitude and velocity, and normalized vibratory stresses along the feeder are predicted for the as-designed feeder and for feeders thinned by flow-accelerated corrosion.
Evaluation of Load Damage in Steel Using the LCR Ultrasonic Technique
Authors: Bray Don E.
Published: August 2009

Piping and pressure vessels are on occasion subjected to overload that may affect their ability to perform the role for which they were designed. A combination of velocity change and frequency analysis for near surface longitudinal (LCR) waves is used to evaluate load damage past the yield point in 4140 steel. Prior work has shown that loading past the yield point affects the velocity in the bar. Further, frequency analysis has been shown to predict the fracture toughness in AISI 4137 steel used in offshore drilling. The present project joins these two approaches and uses velocity measurement and frequency analysis at different locations in the steel bar. Some locations were subjected to post-yield loading and others were not. Discussion on applying the technique to detecting hydrogen attack is included.
Flow-Induced Vibration Responses of U-Tube Bundle in Air-Water Flow
Authors: Chu In-Cheol , Chung Heung June , Lee Chang Hee , Byun Hyung Hyun , Kim Moo Yong
Published: August 2009

In the present study, a series of experiments have been performed to investigate a fluid-elastic instability of a nuclear steam generator U-tube bundle in an air-water two-phase flow condition. A total of 39 U-tubes are arranged in a rotated square array with a pitch-to-diameter ratio of 1.633. The diameter and other geometrical parameters of U-bend region are the same to those of an actual steam generator, but the vertical length of U-tubes are reduced to 2-span in contrast to 9-span of an actual steam generator. The following parameters were experimentally measured to evaluate a fluid-elastic instability of U-tube bundles in a two-phase flow: a general tube vibration response, a critical gap velocity, a damping ratio and a hydrodynamic mass. Based on the experimental measurements, the instability factor, K, of Connors’ relation was preliminary assessed with some assumptions on the velocity and density profiles of the two-phase flow.
Numerical Simulation of Flow Field in a Quench Oil Tower
Authors: Zheng Shuihua , Zhang Shengchang , Gao Zengliang
Published: August 2009

Towers are applied in the wide range of the petrochemical industry. The flow condition and the temperature distribution in the tower are the focus of the people’s attention, which would affect function of the tower and could result in unstable operation of the tower. In this paper, the flow field in a quench oil tower is simulated based on CFD method. The DPM (Discrete Phase Model) is used to calculate and analyze flow distribution and heat transfer between gas and liquid. The numerical results such as temperature and velocity distributions below lower tray in tower are obtained. According to CFD results, modification method of improving the flow distribution is proposed.
Research on the Vibratory Stress Relief Used to Reduce Residual Stress of Mismatch Butt Welds of a Cylinder
Authors: Ren Xin , Tian Yuan , Gao Zengliang , Zhang Kangda
Published: August 2009

The residual stresses of mismatch butt welds of a cylinder were measured by the blind-hole method before and after a vibratory residual stress relief treatment. The results show that this treatment could greatly reduce the maximal butt weld residual stress of dissimilar steel from 540MPa to 119MPa. The concentrated distributions of the first and the second principal residual stresses became gentle after the vibratory residual stress relief treatment.
Ex-Vessel Neutron Dosimetry Results in the Vicinity of RPV Supports
Authors: Hopkins Daniel N. , Hayes Eugene T. , Ferro Arnold H.
Published: August 2009

Neutron-induced embrittlement of the reactor pressure vessel has been a long standing concern for pressurized water reactors (PWR). To date, the beltline region of the pressure vessel, defined as the portion of the pressure vessel experiencing fast neutron fluence (E > 1.0 MeV) equal to or greater than 1017 n/cm2, has been the primary focus of evaluations assessing this embrittlement. These evaluations typically include a calculation of the neutron flux incident on the reactor pressure vessel beltline region, which is in part validated by direct comparison with dosimetry measurements. Two general types of measurements are commonly used, those being dosimetry sets that are included as part of the in-vessel surveillance capsules, and at some plants, those that are included in supplemental surveillance programs such as Ex-Vessel Neutron Dosimetry. In the context of life extension, the beltline region as defined above is getting larger. Present fluence calculations for a number of plants indicate that beltline region at the end of the 60 years of operation will extend to the bottom of the reactor pressure vessel nozzle welds. This extended beltline creates a new problem in terms of validating the neutron fluence calculations in this region well above the top of the active fuel, in that there are no measurements available to confirm calculated results in this new region of interest. Prior to the start-up of Cycle 11 at Comanche Peak Unit 1, an Ex-Vessel Neutron Dosimetry Program was initiated. This program included placement of neutron dosimetry sensor sets in the vicinity of the reactor pressure vessel supports. At the conclusion of Cycle 11, the first set of dosimetry was replaced and the irradiated set analyzed. The Ex-Vessel Neutron Dosimetry set from Cycle 11 was analyzed using a 2D/1D flux synthesis technique using the two dimensional discrete ordinates transport theory calculations (DORT) along with the BUGLE 96 cross-section library and the SNLRML neutron dosimetry cross-section library. The measurements in the vicinity of the vessel supports compare well with the transport calculations, thus confirming that the expected fast neutron fluence (E > 1.0 MeV) in the vicinity of the reactor vessel supports is below the 1018 n/cm2.
Fuzzy Meshfree Method for Fracture Analysis of Cracks
Authors: Rao B. N. , Balu A. S.
Published: August 2009

Uncertainty in loading has been treated by probabilistic methods and by fuzzy set methods. Fuzzy finite element method (FFEM) that calculates, given possible bounds of the applied loads, sharp bounds on displacements and stresses are available in the literature. However, FFEM requires a structured mesh to perform the underlying finite element analysis. It is generally recognized that the creation of workable meshes for complex geometric configurations can be difficult, time consuming, and expensive. This discrepancy is further exacerbated when solving solid mechanics problems characterized by a continuous change in the geometry of the domain under analysis. The underlying structures of these methods, which rely on a mesh, are cumbersome in treating moving cracks or mesh distortion. Consequently, the only viable option when applying FEM is to remesh during each discrete step of the model’s evolution. This creates numerical difficulties, even for deterministic analysis, and often leads to degradation in solution accuracy, complexity in computer programming, and a computationally intensive environment. Consequently, there is considerable interest in eliminating or greatly simplifying the meshing task. In recent years, a class of Galerkin-based meshfree or meshless methods have been developed that do not require a structured mesh to discretize the problem, such as the element-free Galerkin method, and the reproducing kernel particle method. These methods employ a moving least-squares approximation method that allows resultant shape functions to be constructed entirely in terms of arbitrarily placed nodes. Meshless discretization presents significant advantages for modeling fracture propagation. By sidestepping remeshing requirements, crack-propagation analysis can be dramatically simplified. Since mesh generation of complex structures can be far more time-consuming and costly than the solution of a discrete set of linear equations, the meshless method provides an attractive alternative to FEM. However, most of the development in meshless methods to date has focused on deterministic problems. Research into fuzzy meshless analysis has not been widespread and is only now gaining attention. Due to inherent uncertainties in loads, material properties and geometry, a fuzzy meshless model is ultimately necessary. Hence, there is considerable interest in developing fuzzy meshless methods capable of addressing uncertainties in loads, material properties and geometry, and of predicting the probabilistic response. This paper presents a new fuzzy meshless method for interval of the fracture parameters due to variability in the mechanical and load properties using fuzzy set approach.
Efficient Reliability Analysis Using Multipoint Response Surface Method
Authors: Rao B. N. , Chowdhury Rajib , Prasad A. Meher
Published: August 2009

In the reliability analysis of complex structural system, to approximate the performance function accurately, the most common approach is Response Surface Method. Response surface is usually constructed around the design point, for better approximation of the performance function. Existence of multiple design points accelerates the difficulty of approximating the performance function. This paper presents i) a simplified approach for identifying the existence of multiple design points/or regions on the limit surface which have significant contributions to the failure probability and ii) a newly developed concept of multipoint response surface. Identification of multiple design points is based on a weight function, which can provide the weighting index of sampling points. Failure probability can be estimated by constructing multipoint response surface around the identified pints. In addition to the effort of identifying the region of importance, the method requires a small number of exact or numerical evaluations of the performance function at selected inputs. Numerical examples show the accuracy and efficiency of the proposed approach.
Autofrettaged Spherical Pressure Vessels Design
Authors: Adibi-Asl R.
Published: August 2009

Autofrettage process, adopted by the pressure vessel industry, enhances the static limit pressure of components. In addition, a significant increase in the fatigue life autofrettage components is also observed due to the inhibition of crack initiation and propagation. The application of autofrettage treated vessels can be extended to the power generation industry (fossil and nuclear), the petrochemical industry, the food industry (bacterial eradication container), and automotive applications (injection pump), among many others. In particular, spherical pressure vessels, due to their inherent stress and strain distributions require thinner walls compared to cylindrical vessels; therefore, they are extensively used in gas-cooled nuclear reactors, gas or liquid containers rather than heads of close-ended cylindrical vessels. In this paper analytical expressions have been derived for stress and strain during autofrettage process of spherical vessels with different material models. These formulas have been applied to evaluate the residual stresses, and optimized design in monotonic and cyclic loading conditions.
Prediction of Fracture Resistance Behaviour Using Nonlocal Damage Model
Authors: Samal M. K. , Seidenfuss M. , Roos E. , Dutta B. K. , Kushwaha H. S.
Published: August 2009

Prevention of failure of pressurised and high-energy components and systems has been an important issue in design of all types of power and process plants. Each individual component of these systems must be dimensioned such that it can resist the forces or moments to which it will be subjected during normal service and upset conditions. Design by analysis is an important philosophy of modern design. The ability of now-a-days computers to numerically handle complex mathematical problems has inspired the use highly nonlinear material behaviour (including material softening) instead of classical linear constitutive theory for the materials. Under the influence of these developments, a fundamentally different type of modelling has emerged, in which fracture is considered as the ultimate consequence of a material degradation process. Crack initiation and growth then follow naturally from the standard continuum mechanics theory (called continuum damage mechanics). Numerical analyses based on these so-called local damage models, however, are often found to depend on the spatial discretisation (i.e., mesh size of the numerical method used). The growth of damage tends to localise in the smallest band that can be captured by the spatial discretisation. As a consequence, increasingly finer discretisation grids can lead to crack initiation earlier in the loading history and to faster crack growth. This non-physical behaviour is caused by the fact that the localisation of damage in a vanishing volume is no longer consistent with the concept of a continuous damage field, which forms the basis of the continuum damage mechanics approach. In this work, the Rousellier’s damage model has been extended to its nonlocal form using damage parameter ‘d’ as a degree of freedom. The finite element (FE) equations have been derived using the weak form of the governing equations for both mechanical force equilibrium and the damage equilibrium. As an example, a standard fracture mechanics specimen [SE(B)] made up of a German low alloy steel has been analysed in 2D plane strain condition using different mesh sizes near the crack tip. The results of the nonlocal model has been compared with experimental results as well as with those predicted by the local model. It was observed that the fracture resistance predicted by the local damage model goes on decreasing when the mesh size near the crack tip is refined whereas the nonlocal model predicts a converged fracture resistance behaviour which compares well with the experimentally determined behaviour.
Impact Mitigation for Buried Structures: Demolition of the New Haven Veterans Memorial Coliseum
Authors: Woelke Pawel , Tang Margaret , McClennan Scott , Abboud Najib , Tennant Darren , Hapij Adam , Ettouney Mohammed
Published: August 2009

We present an overview of the analysis and design of mitigation schemes for buried structures subjected to impact loading, with a focus on the hazard evaluation to underground utilities from the demolition by implosion of the Veterans Memorial Coliseum in New Haven, CT, due to implosion. We discuss analytical and numerical investigations validated by field testing conducted prior to the implosion and leading to the design of the mitigation schemes aimed at protecting the utilities buried under the roadway. The mitigation schemes were successful during the January 2007 implosion of the Veterans Memorial Coliseum.