bluuebunny/crossref_metadata_2025 huggingface dataset:
Preliminary Pulsation Analysis for High Pressure Piping Size Evaluation for Hyper-Compressors for LDPE Plants
Authors: Giacomelli Enzo , Passeri Marco , Bassani Simone , Zagli Fabrizio , Pieraccini Michele
Published: July 2008

The development of the market for large scale plants, driven by their greater economic return requires processing equipment with increasingly larger capacities. This includes the reciprocating compressors used in Low Density Polyethylene Plants. The design of the high pressure piping associated with hyper-compressors, particularly for reactors and intercoolers, requires careful analysis. Due to the lengthy delivery times for such components, decisions regarding the diameter of high pressure piping usually have to be made at an early stage. Because of the importance of pressure pulsations that occur during operation, an analysis has to be made based on preliminary information available. Such a simulation can be made using reasonable assumptions about the length of the piping involved, and the configuration of both the compressor and the cylinders. At this point, the piping diameter can be confirmed and later, when the plant arrangement has been finalized, a more detailed analysis can be performed which may result in minor adjustments to the piping design.
Effect of Interface Edge Shape on Bonding Strength in Ceramic to Metal Joint
Authors: Tateno Masayoshi , Hatano Yohei , Kokubo Kunio
Published: July 2008

Selection of the optimum shape for interface edge can produce significant increases in the strength of bonded dissimilar materials such as ceramic to metal joints. The focus of this study is to clarify an effect of interface edge shape on bonding strength of ceramic to metal joint. Each plate Si3N4 to Ni joint with arc interface of convexity or concavity is produced by Electric Discharge machining. The arc interface is characterized by edge angle defined as a configuration angle between tangential line at the edge of the interface and the free surface of the ceramic. Each joint is bonded at high temperature by using thin braze metal under vacuum and slowly cooled. A good fit on each bonded face is achieved in this process. The dependence of the bonding strength on the edge angle is experimentally clarified. The result shows that changing the edge angle from the right angle improves the bonding strength since it decreases the residual stress near edge of the interface. The highest bonding strength always appears at the identical interface condition where fracture pattern changes. It appears that the optimum edge angle for obtaining the highest bonding strength depends on bonding temperature.
Meso-Scale Mechanical Model for Intergranular Stress Corrosion Cracking and Implications for Microstructure Engineering
Authors: Jivkov Andrey P. , Stevens Nicholas P. C. , Marrow Thomas J.
Published: July 2008

The microstructure determines the resistance of polycrystalline materials to intergranular stress corrosion cracking to a large extent. The random grain boundaries are prone to sensitisation and form paths of low resistance for intergranular cracks to follow. The non-sensitised special grain boundaries, such as twin boundaries, are observed to encourage crack bridging ligament formation. Computational models of intergranular cracking have been developed to investigate crack bridging and its effects on crack propagation in microstructures with different fractions of special boundaries. Grain refinement has been shown to be beneficial through experimental studies, but was not described by the model. This work introduces a two-dimensional model and presents results for microstructures with grain sizes that differ by a factor of two. A synergetic effect of grain size and special boundaries fraction is demonstrated. It is shown that the crack bridging zone size depends on the grain size, and the shielding contribution depends on the relative size of the bridging zone compared to the crack length. It is concluded that both grain refinement and increase in the fraction of special boundaries are important for improving microstructure resistance. These observations are consistent with the effects of grain boundary engineering on stress corrosion cracking resistance.
Predicting Tritium and Decay Helium Effects on Burst Properties of Pressure Vessels
Authors: Lam P. S. , Morgan M. J. , Imrich K. J. , Chapman G. K.
Published: July 2008

Burst testing is used to assess the performance of stainless steel pressure vessels designed to contain tritium, a radioactive isotope of hydrogen. Burst ductility of tritium-exposed vessels is reduced in time as a result of the combined embrittlement effects from tritium that has diffused into the microstructure and its radioactive decay product, helium-3. A materials system model and finite element procedure were developed to predict burst pressure and the vessel volume change (ductility) during burst testing. The model is used to predict changes in burst pressure and ductility from the tritium service history, known values of tritium diffusivity, and published data on the effects of tritium and helium on the tensile properties of stainless steel. Good agreement has been achieved with actual burst test data for unexposed vessels. It is shown that the service history could be used to derive values of tritium concentration in the metal and the depth of penetration in the vessel sidewall. These values could be used in the finite element model to predict values of burst pressure and burst ductility for tritium-exposed vessels.
Shakedown Limits of a 90-Degree Pipe Bend Using Small and Large Displacement Formulations
Authors: Abdalla Hany F. , Megahed Mohammad M. , Younan Maher Y. A.
Published: July 2008

In this paper the shakedown limit load is determined for a long radius 90-degree pipe bend using two different techniques. The first technique is a simplified technique which utilizes small displacement formulation and elastic-perfectly-plastic material model. The second technique is an iterative based technique which uses the same elastic-perfectly-plastic material model, but incorporates large displacement effects accounting for geometric non-linearity. Both techniques use the finite element method for analysis. The pipe bend is subjected to constant internal pressure magnitudes and cyclic bending moments. The cyclic bending loading includes three different loading patterns namely; in-plane closing, in-plane opening, and out-of-plane bending. The simplified technique determines the shakedown limit load (moment) without the need to perform full cyclic loading simulations or conventional iterative elastic techniques. Instead, the shakedown limit moment is determined by performing two analyses namely; an elastic analysis and an elastic-plastic analysis. By extracting the results of the two analyses, the shakedown limit moment is determined through the calculation of the residual stresses developed in the pipe bend. The iterative large displacement technique determines the shakedown limit moment in an iterative manner by performing a series of full elastic-plastic cyclic loading simulations. The shakedown limit moment output by the simplified technique (small displacement) is used by the iterative large displacement technique as an initial iterative value. The iterations proceed until an applied moment guarantees a structure developed residual stress, at load removal, equals or slightly less than the material yield strength. The shakedown limit moments output by both techniques are used to generate shakedown diagrams of the pipe bend for a spectrum of constant internal pressure magnitudes for the three loading patterns stated earlier. The maximum moment carrying capacity (limit moment) the pipe bend can withstand and the elastic limit are also determined and imposed on the shakedown diagram of the pipe bend. Comparison between the shakedown diagrams generated by the two techniques, for the three loading patterns, is presented.
Multiaxial Time-Dependent Cyclic Deformation of Stainless Steel at High Temperatures
Authors: Gao Qing , Shi Zhi , Kang Guozheng , Liu Yujie
Published: July 2008

The multiaxial time-dependent cyclic deformation behavior of stainless steel (i.e., 1Cr18Ni9) was studied experimentally at 250 °C and 700 °C. In the tests, the strain cyclic characteristics and ratcheting behavior of the material were observed under multiaxial cyclic straining/stressing at different loading rates and with various hold-times and non-proportional loading paths. The results show that the cyclic deformation behavior of the material is significantly influenced by the non-proportional loading paths and present apparent time dependence, especially at 700°C. Some significant conclusions useful for the design and assessment of pipe structures in nuclear engineering are obtained.
Minimum Pressurization Temperature and Pressure-Temperature Envelope of a 1-1/4Cr-1/2Mo Steel Heavy Wall Vessel
Authors: Seijas Antonio J. , Munsterman Tim , Parr Kevin
Published: July 2008

An aged heavy wall pressure vessel for high temperature-high pressure service was to be reused in a new service. The vessel was built in the late sixties with 1-1/4Cr-1/2Mo alloy steel. The integrity of “old vintage” Cr-Mo steel vessels for high pressure service depends heavily on whether the material of construction has sufficient toughness and if they have remained crack free. Cracks or discontinuities may trigger brittle fracture. Because brittle fracture is more likely to occur when the vessel is cold, the planned hydrotest for future conditions as well as the normal start-up and shutdown procedures needed to be established to reduce the risk of brittle fracture by unstable crack propagation. A fracture mechanics and current engineering practice assessment was performed to determine the recommended hydrotest temperature and Minimum Pressurization Temperature (MPT) to avoid brittle fracture. A safe pressure-temperature envelope for future start-up and shutdown procedures was also developed. The evaluation was based on removal of actual test samples using LR Capstone’s proprietary device, the Scoop SamplerSM. Results showed that methods based on chemistry, while conservative, can be overly restrictive.
Delayed Hydride Cracking Initiation at Simulated Debris Fretting Flaws in Zr-2.5Nb Alloys
Authors: Cui Jun , Shek Gordon K. , Scarth Douglas A. , Wang Zhirui
Published: July 2008

Flaws in Zr-2.5Nb alloy pressure tubes in CANDU nuclear reactors are susceptible to a crack initiation and growth mechanism known as Delayed Hydride Cracking (DHC), which is a repetitive process that involves hydrogen diffusion, hydride precipitation, growth and fracture of the hydrided region at the flaw-tip. In-service flaw evaluation requires an analysis to demonstrate DHC will not initiate from the flaw. The work presented in this paper examines DHC initiation behavior from simulated debris fretting flaws. Groups of cantilever beam specimens containing V-notches with root radii of 15, 30 and 100 μm were prepared from two unirradiated pressure tubes hydrided to a nominal hydrogen concentration of 57 wt. ppm. The specimens were loaded to different stress levels that straddled the threshold value predicted by an engineering model, and subjected to multiple thermal cycles relevant to reactor operating conditions to form hydrides at the flaw-tip. Threshold conditions for DHC initiation were established for the flaw geometries and thermal cycling conditions used in this program. Test results indicate that the susceptibility to DHC initiation was affected by material variability and notch root radius. The results are also compared with model predictions.
2D Natural Convection and Radiation Heat Transfer Simulations of a PWR Fuel Assembly Within a Constant Temperature Support Structure
Authors: Araya Go´mez Pablo E. , Greiner Miles
Published: July 2008

Two-dimensional simulations of steady natural convection and radiation heat transfer for a 14×14 pressurized water reactor (PWR) spent nuclear fuel assembly within a square basket tube of a typical transport package were conducted using a commercial computational fluid dynamics package. The assembly is composed of 176 heat generating fuel rods and 5 larger guide tubes. The maximum cladding temperature was determined for a range of assembly heat generation rates and uniform basket wall temperatures, with both helium and nitrogen backfill gases. The results are compared with those from earlier simulations of a 7×7 boiling water reactor (BWR). Natural convection/radiation simulations exhibited measurably lower cladding temperatures only when nitrogen is the backfill gas and the wall temperature is below 100°C. The reduction in temperature is larger for the PWR assembly than it was for the BWR. For nitrogen backfill, a ten percent increase in the cladding emissivity (whose value is not well characterized) causes a 4.7% reduction in the maximum cladding to wall temperature difference in the PWR, compared to 4.3% in the BWR at a basket wall temperature of 400°C. Helium backfill exhibits reductions of 2.8% and 3.1% for PWR and BWR respectively. Simulations were performed in which each guide tube was replaced with four heat generating fuel rods, to give a homogeneous array. They show that the maximum cladding to wall temperature difference versus total heat generation within the assembly is not sensitive to this geometric variation.
Evaluation and Analysis of High Frequency Vibration on the Cavitating Venturi Downstream Piping
Authors: Jeon Chang-Bin , Chun Woochie H. , Lee Ju-Yeoul
Published: July 2008

During hot functional test (HFT) of the auxiliary feedwater (AFW) system of a nuclear power plant, high vibration and noise occurred in the downstream of the cavitating venturi (CV), which caused severe damages, such as the disengagement of internal parts, failure of threaded connection to the temperature gauge located nearby downstream piping, relaxation of fastening nuts for pipe clamp and damaged socket weld connection. The objective of this paper is to evaluate the venturi downstream piping vibration in accordance with the ASME OM 3 requirements and identify the characteristics of the high frequency piping vibration. The vibration test was performed for the steam generator-operating pressure range to confirm whether the amplitudes of the vibration are within the acceptable limits to assure that no piping failures would occur due to cyclic loads. In addition to the vibration evaluation from the fatigue standpoint, the root cause of piping vibration is investigated. From the test results, the characteristics of vibration are acoustically coupled with vortex-shedding and cavitations, which results in a frequency range from 2,000 to 5,000 Hz. During the test, the vibration and noise were severer at the steam generator pressure of 40 kg/cm2 rather than at the atmospheric pressure, or even at 82 kg/cm2. It was also detected that degrees of cavitation and locations where the collapse occurred varied depending on operating conditions. Due to the high frequency characteristics, the shell mode vibration was more dominant than the lateral beam mode vibration.
Probabilistic Prediction of Crack Depth Distributions Observed in Structures Subjected to Thermal Fatigue
Authors: Asayama Tai , Takasho Hideki , Kato Takehiko
Published: July 2008

The application of risk-based technologies not only to inservice inspections but also to the design of components and systems, encompassing a plant life-cycle, is the way to be pursued for the improvement of design of new reactors such as fast breeder reactors. When doing so it is necessary to develop an analytical method that is capable of estimating failure probabilities without a failure database that can only be established on the long-time accumulation of operational experiences. The prediction method should estimate failure probabilities based on actual mechanisms that cause failure. For this purpose, this study developed a probabilistic structural reliability evaluation method for fatigue which is a representative failure mode to be prevented in components of nuclear plants. This method is an extension of probabilistic fracture mechanics approach but is capable of modeling crack initiation, crack propagation, as well as crack depth density distribution at a given cycle. To verify the methodology, crack depth distribution observed in thermal fatigue test specimens were evaluated, and it was shown that the method could reproduce the observed crack depth distributions fairly well. This is considered to explore the possibility that probabilistic fracture mechanics approach can be verified by experiments, which was deemed impossible so far. Further improvement such as explicit implementation of interaction mechanisms between adjacent cracks will allow this methodology to be applied to the procedure of optimization of inservice inspection planning, as well as to the optimization of safety factors in component design of nuclear plants.
Research and Development of Earthquake Isolation System Using Vertically Utilized Coiled Spring
Authors: Fukasawa Tsuyoshi , Fujita Satoshi
Published: July 2008

This paper describes the research and development of new type of the isolation systems suitable for various structures. Basic concept of the new isolation system is to realize cost effective design without any reduction in the isolation performance. This paper presents results obtained from experimental and analytical studies to evaluate isolation performances of newly developed the isolation system. In the experiment, static tests were first carried out using a 0.20 scale model (55 kg mass, and 0.50 m × 0.50 m × 0.27 m size) for isolated-light-weight-structures model which was supported by two linear ball bearings and, restoring force was provided to superstructure by transversal stiffness of a coiled spring, so as to examine restoring force characteristic of the coiled spring. Second, dynamic tests were implemented in order to investigate the isolation performance of the isolation system against several actual seismic inputs. In analysis, seismic response analyses for the scale model, regarding the vibration tests using the actual seismic wave, were carried out to evaluate the response analytical method for the isolation system using the coiled spring. From these results, the followings are clarified. (1) Analytical results for the isolated light-weight-structures model agree well with experiment results. (2) The newly developed seismic isolation system using the coiled spring reduced response accelerations of the light-weight-structures sufficiently.
Study on Type-IV Damage Prevention in High-Temperature Welded Structures of Next-Generation Reactor Plants: Part II — Effect of Boron on Creep Properties and Microstructures of HAZ for High Cr Steels
Authors: Tabuchi Masaaki , Hongo Hiromichi , Takahashi Yukio
Published: July 2008

Creep strength of welded joints for high Cr ferritic steels is decreased for long-term services at high temperatures due to Type IV creep damages that occur in heat affected zone (HAZ). Aiming at improving the creep strength of HAZ, we have investigated the effect of boron and nitrogen content on the microstructures and creep strength of HAZ for the 9Cr and 12Cr steels produced based on the P91 and P122 steel. It was found that the effect of boron appeared remarkably for the 12Cr steel. By increasing boron and decreasing nitrogen, the formation of fine-grained HAZ structure during weld thermal cycle could be suppressed and the creep strength of HAZ was considerably improved. For the 9Cr steel, while the formation of fine-grained HAZ structure could be inevitable independent of boron and nitrogen contents, the creep strength of fine-grained HAZ was improved by grain boundary strengthening effect of boron.
Residual Life Assessment of 2.25Cr-1Mo Boiler Pipe by Small Punch Creep Test
Authors: Kusumoto Junichi , Kanaya Akihiro , Kobayashi Toshimi
Published: July 2008

The non-destructive techniques such as the microstructural assessment are usually performed for residual creep life assessment of plant components. Since these techniques have limited accuracy, destructive assessment techniques such as uniaxial creep tests are required to improve the accuracy of the assessment. However, if this type of destructive assessment technique are applied, the sampling and the weld repair damages the material, and also the assessment will become expensive. On the other hand, small punch creep (SPC) test [1,2], which uses miniature-sized specimens, does not cause any serious sampling damages, and its assessment accuracy is high since it is a mechanical assessment technique. However, in applying the SPC test to the residual creep life assessment of the boiler in service, there are some issues to be studied [1,3,4]. In order to apply SPC test to the residual creep life assessment of the 2.25Cr-1Mo steel boiler pipe, the relationship between uniaxial creep stress and the SPC test load has been studied. And the Omega method [5] by SPC test was also studied.
Three-Dimensional Identification of Semi-Elliptical Crack on the Back Surface by Means of Direct-Current Electrical Potential Difference Method With Multiple-Probe Sensor
Authors: Tada Naoya , Funakoshi Akira
Published: July 2008

A method of three-dimensional identification of a semi-elliptical crack existing on the back surface of a conductive plate by direct-current electrical potential difference method with a multiple-probe sensor was proposed. The geometrical condition of the crack was specified by six parameters, the surface and inward angles of the crack plane, θsur and θin, the length and depth of the crack, c and a, and the two-dimensional location of the crack center, (yc, zc), on the back surface, respectively. Identification was carried out based on the distribution of electrical potential difference on the surface of the plate measured with a sensor composed of grid-arranged multiple probes called the “multiple-probe sensor.” As an approximate cracked body and a quick analysis method were used, a number of repeated electrical potential field analyses necessary for the identification of the crack became possible within a practical time. The validity of the method was numerically confirmed by carrying out the identification based on the result by the finite element analysis.
Combined Effect of Temper and Hydrogen Embrittlement on Impact Properties of Cr-Mo Steels
Authors: Tanaka Yoichi , Aihara Shuji , Konosu Shinji , Hayashi Kenji , Yuga Masao , Yamamoto Hiroshi , Ohtsuka Naotake , Mimura Hiroshi
Published: July 2008

This paper presents the research activity of the subcommittee on Hydrogen Embrittlement of the Japan Pressure Vessel Research Council (JPVRC). It describes the superposition effect of hydrogen embrittlement and temper embrittlement in Cr-Mo steels which are used in high temperature and high pressure hydrogen environment like petroleum refining equipments. Three kinds of 2.25Cr-1Mo steels which have different temper embrittlement factors (J-factor) and 2.25Cr-1Mo-0.25V steel were investigated. These steels were prepared with normalizing, tempering and post weld heat treatment (PWHT) which simulated an actual PWHT condition for vessel fabrication. The temper embrittlement was evaluated by step-cooling heat treatment (SCHT). Hydrogen charging was performed by exposure to pressurized hydrogen gas (15MPa) for 48 hours at elevated temperature (550°C). The toughness of the materials in the as-PWHT condition deteriorated with increase of J-factor, and the toughness after SCHT showed the same tendency. 2.25Cr-1Mo-0.25V steel showed no hydrogen embrittlement and no temper embrittlement but the 2.25Cr-1Mo steels showed both types of embrittlements. The degree of hydrogen embrittlement was different between as-PWHT and SCHT conditions and the material toughness after either of the heat treatment followed by hydrogen charging was almost the same. The results mean that the effects of temper and hydrogen embrittlement are nonadditive. SEM observation of fracture surfaces showed increase of intergranular facets both after-SCHT and hydrogen charging. By considering that both the temper embrittlement and hydrogen embrittlement encourage intergranular fracture, it is understandable that both types of the embrittlement are nonadditive and the deterioration of toughness becomes saturated.
Stress Intensity Factor Error Index for Finite Element Analysis With Non-Singular Elements
Authors: Meshii Toshiyuki , Kageyama Kyohei
Published: July 2008

In this paper, it is shown that Meshii et al.’s stress intensity factor (SIF) error index called the DCE index [1], that was developed for a finite element analysis (FEA) with singular elements, can be also applied to FEA with non-singular elements. The DCE index has a dimension of a SIF and, thus, has an advantage to the conventional error indexes (e.g., Zienkiewicz and Zhu’s) on the point that it does not require mesh refinement iteration process to obtain an accurate SIF solution. Then the validity of the DCE index for non-singular crack tip elements was shown for elastic crack problems, whose analytical SIF solutions are known.
Improvements to PFM Analysis Code PASCAL and Some Case Studies on RPV Integrity During Pressurized Thermal Shock
Authors: Onizawa Kunio , Shibata Katsuyuki , Osakabe Kazuya , Tanaka Kazuhisa
Published: July 2008

The probabilistic fracture mechanics (PFM) analysis code PASCAL (PFM Analysis of Structural Components in Aging LWR) has been developed at JAEA to evaluate the conditional failure probability of a reactor pressure vessel (RPV) containing a flaw under transient conditions such as pressurized thermal shock (PTS). Some functions of PASCAL have been improved such as the Monte Carlo method, the probability of crack detection (POD) by inspection and the graphical user interface (GUI). Using the improved PASCAL, case studies on some parameters for some typical PTS transients have been performed. When the crack existence probability for the Marshall- and PNNL-type distributions is considered, the failure probabilities are approximately the same order of magnitude. The effect of chemical composition of the vessel material was studied through a comparison of conditional failure probabilities for some transients. The effect of POD for inspection was also compared and evaluated in terms of the inspection effectiveness and frequency.
Seismic Evaluation of the Oak Ridge National Laboratory High Flux Isotope Reactor Support Assembly
Authors: Aramayo Gustavo A.
Published: July 2008

The support assembly of the Oak Ridge National Laboratory High Flux Isotope Reactor (HFIR) was modeled to determine the assembly’s response to a seismic excitation. The compliance of this structural component to established U. S. Department of Energy (USDOE) standards [1, 2] is evaluated.
Review of Residual Stress Mitigation Methods for Application in Nuclear Power Plant
Authors: Hurrell P. R. , Everett D. , Gregg A. , Bate S.
Published: July 2008

A research project has recently been launched in the UK investigating residual stress (RS) in nuclear power plant [1]. At the outset there is a need to review techniques available for modifying/relieving residual stress levels in weldments, since it is well known that large tensile RS levels generated in welds can be detrimental in terms of fatigue, fracture resistance and environmentally assisted cracking (EAC). Therefore current RS mitigation methods have been reviewed. Mitigation methods can be categorised into three main groups as follows: a) Surface treatment to induce compressive skin stress; b) Stress relief through thickness; c) Weld design optimisation to produce low/favourable RS levels and minimize distortion. A brief description is provided of how each method works, together with the capability and potential benefit in terms of RS reduction, as well as references for further information. Metallurgical effects of treatment are also an important consideration. The practicality of application to nuclear plant is considered, both in manufacture and in-service, together with any limitations and risks. Several techniques are identified that are likely to be beneficial and warrant funding for further development. RS mitigation should be targeted at key/critical weld locations in the plant, where loadings and degradation mechanisms (such as corrosion, fatigue, EAC or fracture) are most significant. Treatment would be carried out in order to improve plant integrity and reliability (eg safety margins). There are potentially substantial cost savings since through-life inspection/maintenance work could be reduced and expensive repairs and shutdowns avoided. Note that it is important to understand whether the benefits in terms of RS improvement are likely to be long term. In certain systems large thermal transients are applied that might generate additional surface plastic strains, thereby modifying RS magnitudes and distributions.
The Effect of Modelling Simplifications on the Prediction of Residual Stresses in Thin-Walled Pipe Butt Welds
Authors: Warren A. P. , Bate S. K. , Charles R. , O’Gara D. M. , Wood P. M. , Gregg A.
Published: July 2008

The inherent complexity of modelling welding processes and the lack of computational power available to analysts has resulted in simplified methods being commonly utilised when predicting residual stresses. Despite considerable advances in computational power, it is still often not possible to run detailed 3D analyses of complex welded geometries within practical timescales. Against this background, a programme of work has been undertaken to develop a weld modelling procedure which can be followed by analysts. This procedure will account for how various modelling simplifications affect the predicted values of residual stress. One common geometry, which it is often necessary to analyse using modelling simplifications is that of a thin-walled pipe butt weld. Typically this geometry is simulated using a 2D axisymmetric analysis. Despite the popularity of this modelling simplification the effects of its use are not fully understood. In order to feed into this procedure, work has therefore been conducted to better understand the effects modelling simplifications will have on the residual stress levels that are predicted when simulating multi-pass pipe butt welds. The geometry considered in this study is the thin walled austenitic pipe butt weld specimen originally studied in VORSAC 5th Framework European Union project. This paper presents the results of a number of finite element analyses conducted of this geometry. These analyses have been conducted using a combination of the finite element codes SYSWELD and ABAQUS. The aim of this study was to understand the effect that the use of 2D axisymmetric analyses, and other modelling simplifications, namely block dumping and bead lumping will have on the predicted values of residual stress.
Low Frequency Phased Array Application for Crack Detection in Cast Austenitic Piping
Authors: Anderson Michael T. , Cumblidge Stephen E. , Doctor Steven R.
Published: July 2008

As part of a multi-year program funded by the United States Nuclear Regulatory Commission (US NRC) to address nondestructive examination (NDE) reliability of inservice inspection (ISI) programs, studies conducted at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington, have focused on assessing novel NDE approaches for the inspection of coarse-grained, cast austenitic stainless steel reactor components. The primary objective of this work is to provide information to the US NRC on the utility, effectiveness and reliability of ultrasonic testing (UT) as related to the ISI of primary piping components in US commercial nuclear power plants. This paper describes progress, recent developments and results from an assessment of a portion of the work relating to the ultrasonic low frequency phased array inspection technique. Westinghouse Owner’s Group (WOG) cast stainless steel pipe segments with thermal and mechanical fatigue cracks, PNNL samples containing thermal fatigue cracks and several blank vintage specimens having very coarse grains that are representative of early centrifugally cast piping installed in PWRs, were used for assessing the inspection method. The phased array approach was implemented using an R/D Tech Tomoscan III system operating at 1.0 MHz and 500 kHz, providing composite volumetric images of the samples. Several dual, transmit-receive, custom designed low-frequency arrays were employed in laboratory trials. Results from laboratory studies for assessing detection and localization are discussed.
FEM Simulation of Extreme Thermal and Mechanical Accident Loads on Screwed Spent Fuel Cask Lid Structures
Authors: Wieser Gu¨nter , Qiao Linan
Published: July 2008

The complex analysis of screwed spent fuel cask lid structures under extreme thermal and mechanical loads is very important for the evaluation of cask integrity and leak tightness under such conditions. The interest of such problems has been increasing since the terrorist attacks from September 11, 2001. Due to extension experiences of BAM in calculation and experimental testing of transport and storage casks for radioactive materials, BAM in this context has developed new methods to estimate the safety margins of transport and storage spent fuel and high-level waste casks under extreme thermal and mechanical loads resulting from aircraft crashes. In case of thermal loads, a thermal heat transfer analysis has to be made, which gives the time-dependent temperature distribution of the casks. But this is not enough, while the extreme kerosene fire scenario creates a strong transient heating of the cask body and its lid system. This causes elastic and plastic deformation of the cask body, the decrease of screw forces and especially great relative displacements between the seals and its contacting flanges. This results in an elevated leak rate. To cover this case so-called thermo-mechanical analyses had been carried out. One of the most critical mechanical loads on the cask is a central impact onto the lid-seal-system. This can be caused by direct aircraft crash or its engine as well as by a following impact of building structures of a nuclear facility like a storage hall. In this situation dynamical analyses had been carried out. Although it is currently not possible to calculate the leakage rates from deformation analysis directly, for the present it is possible to estimate the behaviour of the seal based on the calculated relative displacements at its place and the behaviour of the lid bolts under the thermal and mechanical impact loads respectively, in combination with experiments where the leakage rate of the seals had been measured after radial and axial shifting of the flanges. Except of the lid bolts, the geometry of the cask and the thermal/mechanical loads are axial-symmetric, which simplified the analysis considerably by using two dimensional finite element models and parameter studies are possible. The lid bolts had been “smeared” with a special technique as two-dimensional plane-stress bolt model, which has been verified with three dimensional bolt calculations. Experiments and calculation studies show that the German transport and storage casks for radioactive material have sufficient safety margins even by extreme thermal/mechanical loads. This paper will present the methodologies developed for the studies. Some of the calculation results will be presented.
Single-Phase Transient in Single-Elbow Pipe
Authors: Gale Janez , Tiselj Iztok
Published: July 2008

Mathematical and numerical model needed for description of single-elbow pipe movement in horizontal Z-Y plane coupled with one-dimensional single-phase fluid dynamics is described and discussed. The governing phenomenon is also known as two-way Fluid-Structure Interaction. Standard Skalak’s four-equation model was improved with additional four Timoshenko’s beam equations for description of flexural displacements and rotations. The applied model was solved with improved second-order accurate numerical method that is based on Godounov’s upwind first-order accurate method. The model was successfully used for simulation of the rod impact induced transient and conventional instantaneous valve closure induced transient in the tank-pipe-valve system. Special attention was made to the applicability of the applied numerical method.
Leakage Predictions for Static Gasket Based on the Porous Media Theory
Authors: Jolly Pascal , Marchand Luc
Published: July 2008

In the present work, the annular static gaskets are considered as porous media and the Darcy’s law is written for a steady radial flow of a compressible gas with a first order slip boundary conditions. From this, a simple equation is obtained that includes the Klinkenberg’s intrinsic permeability factor kv of the gasket and the Knudsen number Kn′o defined with a characteristic length l. The parameters kv and l of the porous gasket are calculated from experimental results obtained with a reference gas at several gasket stress levels. Then, with kv and l, the inverse procedure is performed to predict the leakage rate for three different gases. It is shown that the porous media model predicts leak rates with the same accuracy as the laminar-molecular flow model (LMF) of Marchand, Derenne and Masi. However, the new model has the advantage of furnishing phenomenological information on the evolution of the intrinsic permeability and the gas flow regimes with the gasket compressive stress. It also enables quick identification of the part of leakage that occurs at the flange-gasket interface at low gasket stresses. At low gas pressure, the behavior of the apparent permeability diverges from that of Klinkenberg’s, indicating that the rarefaction effect becomes preponderant on the leak. Finally, it is demonstrated that the porous media model could be very useful in predicting gasket leakage with liquids.
Microscale Fluid Flow at Rough Metallic Surfaces: A Lattice Boltzmann Study
Authors: Varnik F. , Raabe D.
Published: July 2008

In contradiction with common assumptions of a laminar lubricant flow, it is shown that high Reynolds number lubricant flows may occur in usual metal forming processes even at scales as small as the surface roughness asperities. This enhances the sensitivity of the flow to perturbations arising e.g. from the surface roughness and brings about the possibility of a roughness-induced transition toward an unsteady flow/turbulence. Via lattice Boltzmann simulations, it is shown that, under these circumstances, a qualitative change in flow properties may indeed be triggered by a variation of the wall roughness alone. We focus on the impact of various roughness parameters on the transition showing that it is not the roughness height alone which determines the onset of flow instability. Rather, it is the combined effect of the roughness height- and wave length which is essential. In particular, by an increase of the roughness wave length, it is possible to trigger flow instability even if the roughness slope is reduced. These findings are in line with experimental results on rough wall turbulence which indicate that a local Reynolds number based on the roughness height alone does not capture the roughness effects on the flow characteristics.
Residual Stresses in CANDU Feeder Bends: Effect of Bend Radius
Authors: Yetisir M. , Donaberger R. , Rogge R.
Published: July 2008

Since 1997, sections of nine feeder pipes have been removed at the Point Lepreau Generating Station (PLGS) because of cracking. All PLGS feeder cracks are axial in orientation and are located in the feeder bends. In all cases, cracks were either at the inside surface of the bend flanks (approximately 60° from the intrados symmetry plane) or at the outside surface of the bend extrados. Root cause analyses indicated that the residual stress has a significant role in these failures. In a typical feeder, there are a number of bends and welds, which are potential locations of high residual stresses. To reduce inspection scope, or to identify the highest risk components, a relative ranking of crack susceptibility is needed. This can be achieved using the residual stress data of these components. This paper compares the measured residual stress data in tight-radius and large-radius CANDU feeder bends. It was found that residual stresses are significantly higher for the bends with small bend radius (r) over diameter (D) ratios (for example, r/D = 1.5) as compared to those bends with large r/D ratios (r/D > 4). The differences in the magnitude of residual stress are consistent with the measured and calculated level of cold work in the two types of bends. It was concluded that the likelihood of cracking in large-radius bends is significantly smaller than that in tight-radius bends.
Finite-Element Modeling of the Thermal/Structural Response of a Rifled Silicon-Nitride Barrel Subjected to Thermal and Pressure Transients
Authors: Segall A. E. , Carter R.
Published: July 2008

A 3-D finite-element model was used to simulate the severe and localized thermal/pressure transients and the resulting stresses experienced by a rifled ceramic liner with a steel sheath. The focus of the simulations was on the influence of the rifling fillets on the heat transfer and resulting thermoelastic stresses (including pressure transients) generated during a single firing event. Since the modeling was primarily concerned with the effects of the rifling groove, a small, twisted segment of the barrel length based on rotational symmetry was employed. Using this simplification, the model utilized uniform heating and pressure across the inner surface via a time-dependent convective coefficient and pressure generated by the propellant gasses. Results indicated that the inner fillet radius of the rifling groove (rf2) had the greatest influence on the maximum circumferential (hoop) stresses and temperatures experience by the rifled barrel. Based on these simulations, it is recommended that rf2 be kept as large as possible in order to reduce the tensile hoop-stresses. Moreover, it appears to be permissible to keep the outer fillet radius of the groove (rf1) relatively small so as to help ensure that the rifling will adequately engrave the projectile and transmit rifling torque.
Effect of Constraint on the Shift of Ductile-Brittle Transition Curve of Reactor Pressure Vessel Steels
Authors: Chen Zhong-An , Zeng Zhen , Chao Yuh J.
Published: July 2008

Nuclear reactor pressure vessel (RPV) steels degrade due to neutron irradiation during normal operation. As a result, the ductile-brittle transition curve of the steel shifts to higher temperature which decreases operation margins in both the temperature and pressure. The loss of these margins however can be offset somewhat by appealing to arguments based on constraint of potential/postulated shallow cracks. In this paper, we demonstrate that the fracture toughness values for ASME postulated shallow flaws are higher than those determined from high constraint, standard deep cracked test specimens. The J-A2 three-term solution is used to characterize the crack-tip stress field where J represents the level of loading and A2 quantifies the level of constraint. It is shown that shallow (deep) flaws have lower (higher) constraint and A2. Based on the RKR cleavage model, procedures to quantify the temperature shift between specimens with different constraint levels are developed. The experimental data by Sherry et al. [1] for the A533B RPV steel are used to demonstrate the procedure and it is shown that the ductile-brittle transition curve shifts to lower temperature from high constraint to low constraint specimens.
Corrosion Control for Safety and Integrity of Pipelines
Authors: El Kholy Wael A.
Published: July 2008

Corrosion directly affects our lives by reducing the integrity of possessions. All pipelines, even the best designed and maintained, deteriorate with time. The primary cause of this deterioration is corrosion. Corrosion in metal can be compared to cancer in human body. Both act very slowly without being easily visible and by the time one notices it, serious damage has been done. Owing to corrosion, billions of dollars are wasted in various industries, refineries, petrochemical plants and various underground pipelines and structures in the field of oil, gas, water etc. For the safety and integrity of underground pipelines it is imperative to adopt various methods of corrosion prevention to retard corrosion and thus increase the active working life of pipelines. This paper provides information about various types of corrosion and methods of both inline and outer surface corrosion inspection and monitoring. It also discusses means of pipeline protection, corrosion control and rehabilitation.
Euler-Lagrange Coupling With Deformable Porous Shells
Authors: Aquelet N. , Wang J. , Tutt B. A. , Do I. , Chen H.
Published: July 2008

A newly developed approach for tridimensional fluid-structure interaction with a deformable thin porous media is presented under the framework of the LS-DYNA software. The method presented couples a Arbitrary Lagrange Euler formulation for the fluid dynamics and a updated Lagrangian finite element formulation for the thin porous medium dynamics. The interaction between the fluid and porous medium are handled by a Euler-Lagrange coupling, for which the fluid and structure meshes are superimposed without matching. The coupling force is computed with an anisotropic Ergun porous flow model. As test case, the method is applied to an anchored porous MIL-c-7020 type III fabric placed in an air stream.
Assessment of Ductile Crack Growth Based on a Local Approach
Authors: Lee Tae-Rin , Chang Yoon-Suk , Choi Jae-Boong , Kim Young-Jin
Published: July 2008

The influence of stress triaxiality was a matter of concern on ductile fracture to explain geometry dependent fracture resistance characteristics of specimens and real structures during past two decades. Regarding the issue, recently, interests for local approach and micro-mechanical damage models are increased again in accordance with progress of computational environments. In this paper, the applicability of a local approach is investigated through a series of finite element (FE) analyses incorporating both a modified GTN model and a Rousselier model as well as fracture toughness tests. The ductile crack growth behaviour of SA515 Gr.60 carbon steel is assessed to guarantee transferability of fracture resistance curve from typical specimens with different in-plane and out-of-plane sizes. The material parameters are determined by calibration of test results and corresponding numerical analyses results, and used to simulate the fracture behaviour of CT specimens. Then, a comparison is drawn between the numerically estimated crack resistance curves and experimentally determined ones. Finally, the Rousselier model is applied to estimate J-R curves of circumferential through-wall cracked pipe. The comparison results showed that the two damage models can be used as promising solutions for ductile crack growth simulation.
Interaction of Stress Waves From a Pair of Charge Holes in PMMA
Authors: Matsumoto S. , Nakamura Y. , Itoh S.
Published: July 2008

Fracture control in blasting is very important in underground excavation and demolition of concrete structures. It is valuable to obtain an understanding of the dynamic behavior of stress waves in the blasting process for the development of fracture control method. Experimental visualizations and numerical simulations were performed to observe the propagation and interaction of stress waves between two charge holes in blasting. These are related with control of fracture planes along the line connecting the charge holes in smooth blasting. In model experiments using PMMA plates, the stress waves were generated by initiation of electric detonators at the charge holes and were observed by means of the visualization system. The dynamic behavior of stress waves in the blasting process was also visualized by numerical simulation using the smoothed particle hydrodynamics (SPH) method. The dynamic behavior of stress waves is discussed by means of the experimental results and the simulation results.