bluuebunny/crossref_metadata_2025 huggingface dataset:
Experiment and Simulation on Pressure Pulsation Accompanied by Acoustic Resonance and Piping Vibration
Authors: Tsuji Takashi , Maekawa Akira , Takahashi Tsuneo , Noda Michiyasu , Kato Minoru , Fujita Katsuhisa
Published: May 2012

To improve condition-based maintenance (CBM) techniques for operating plants, it is necessary to investigate, by experiments and numerical simulations, on the behavior of fluid inside piping system in detail. This study was conducted using the full-scale piping system under conditions that could seriously threaten the plant operation, by matching pressure pulsation, acoustic resonance and piping natural frequency. Although piping vibration is reported to influence fluid pressure pulsation, there were few examples of such influence in the conditions of this experiment. Knowing that the opening ratio of the pressure control valve affects the boundary condition for acoustic resonance, the experiment and numerical simulation at different opening ratios were conducted. It was suggested that there are cases in which a valve partially open at 25% or less shouldn’t be taken as a closed end. This finding conflicts with widespread design assumption.
Mechanistic Formulation of PWSCC Growth Rates of Ni-Base Alloys and Weld Metals
Authors: Lu Zhanpeng , Shoji Tetsuo , Xue He , Fu Chaoyang
Published: May 2012

Several Ni-base alloys and their weld metals such as Alloy 600 and Alloy 82/182 suffered from stress corrosion cracking in pressurized water reactor primary water environments. Materials Reliability Program (MRP) proposed a CGR disposition curve in a report MRP 55 for PWSCC of thick-section Alloy 600 materials. This deterministic CGR equation has been adopted by Section XI Nonmandatory Appendix O of the ASME Boiler and Pressure Code for flaw evaluation. MRP also proposed a CGR disposition curve in MRP report 115 for PWSCC of Alloy 82/182/132 weld metals. In the same fashion, JSME and JNES also provided CGR disposition curves in the flaw evaluation procedure in structural integrity analysis. Stress intensity factor (K), temperature and thermal activation energy are included in both MRP 55 and MRP 115 reports. Both MRP 55 and MRP 115 are engineering-based rather than mechanism-based. The fundamental correlations such as crack growth rate vs. K are quantified based on the theoretical model and screened experimental data, which are compared to the reported disposition curves and used for improving the prediction.
Numerical Simulation on Hydrogen Dispersion in Automobiles due to Storage Cylinder Failure
Authors: Liu Yan-Lei , Zheng Jin-Yang , Han Shu-Xin , Zhao Yong-Zhi
Published: May 2012

A numerical model for dispersion of hydrogen in hydrogen powered automobiles was established basing on finite element method with species transport and reaction module of FLUENT. And corresponding numerical simulations were done in order to analysis the dispersion of hydrogen due to leakage from different position of the storage cylinder on the automobiles. Also, the distribution of the hazard region due to hydrogen dispersion was obtained. The simulation results show that the baffle above the cylinder can accumulate the hydrogen. Therefore, the high concentration region of hydrogen exists near the baffle. The study can provide reference for hydrogen sensor placement and safety design of hydrogen powered automobiles.
Study on Generation Mechanisms of Abnormal Vibrations of Flow Dynamic Conveyers
Authors: Ishihara Kunihiko
Published: May 2012

The FDC (Flow Dynamics Conveyer) has often been used in power plants and iron works because of its superiority in quietness compared with a roller type conveyer. Moreover, it is excellent in low noise and low power. The FDC consists of a trough and a belt, and the air is supplied from numerous holes provided on the trough. However, large vibrations occur when the flow rate reaches a certain value. This abnormal vibration is defined to be a self-excited vibration caused by leakage flow. It is well known that abnormal vibrations occur when the flow channel spreads out at the edges. The purpose of this study is to clarify the generation mechanism of the abnormal vibration. The experimental setup is made of steel. The trough is made of a thick plate and the belt is made of a thin plate with a thickness of 1.2mm. The air is supplied by a blower and the flow rate is adjusted by a ball valve. The flow rate is measured by a venturi tube and a liquid manometer. The loads are given by piling thick steels one by one with a weight of 1kg. The vibration of the belt center is measured by a laser displacement meter and the data are processed by a FFT analyzer. The experiment was carried out to examine the effects of various parameters such as the taper angle θ, the floating amount H generated by loads and flow rates on abnormal vibrations. Firstly, vibrations of the belt were obtained by changing loads and flow rates. When the flow rate is constant, the taper angle θ increases and the floating height of the belt H decreases with increasing loads. The area of abnormal vibrations could be obtained in the θ—H plane. Secondarily, the damping coefficients were obtained based on the free vibration method by changing loads and flow rates when abnormal vibrations did not occur. As a result, it was found that the damping ability decreases with an increase in the taper angle and a decrease in the floating height. Furthermore it was clarified that the abnormal vibrations occur for θ > αH (α: constant value).
Local Ratcheting by Elastic-Plastic FEA: Criteria and Code Based Approaches
Authors: Rudolph Ju¨rgen , Kalnins Arturs , Go¨tz Andreas , Hilpert Roland
Published: May 2012

Emanating from a discussion of local ratcheting effects and appropriate limiting criteria this paper examines existing ratcheting rules based on local (or material) response that are currently in Section III of the ASME B&PV Code, German KTA rules, and other design codes. The objective is to offer clarification of the rules that may be useful to the designer, their bases and practical application. Among these rules, different ratcheting checks are required that use different ratcheting measures. The paper considers only the rules for which the ratcheting checks can be evaluated by a direct cycle-by-cycle elastic-plastic FEA. Examples are provided to illustrate the procedures.
Structural Modification of a Pipe Under Harmonic Excitation Using an Hybrid Numerical/Experimental Method
Authors: Bodel Charles
Published: May 2012

Vibrations generated by centrifugal pumps are difficult to predict at the design stage, for it is hardly possible to accurately determine the natural frequencies of pipes and to avoid coincidences with the blade pass frequency of the pump and its harmonics. One is often led to modify the existing structure, by adding stiffness, mass or damping. This paper illustrates this point on a pipe connected to a pump in a nuclear power plant operated by EDF (E´lectricite´ de France). In October 2010, abnormal vibrations were measured on a thin pipe at the outlet of a pump in a powerplant in France. The French nuclear regulatory commission asked EDF to perform a diagnosis and to define solutions within a few months. EDF/R&D division has used an original method developed in 2004 based on hybrid data, and called LMME-SDM (for Local Model Mode-shapes Expansion Structural Dynamic Modification). The main objective is to define a structure modification able to remove all natural frequencies close to the harmonic excitation. For the purpose of the study, we need a numerical model, which should be fairly correct from a static point of view, but which is not necessarily updated from a dynamic point of view, and an experimental modal analysis carried out under real conditions on the pipe. During the experimental modal analysis, a test of added mass has been carried out so that the method can be validated by comparing the predicted and the observed frequency. This method has already been used in industrial cases in former studies [3], however the study presented here has reached a higher level in complexity. Even if this method is able to give reasonable results compared to measurements, it is close to its limits.
Study of the Crack Propagation Behaviour of 304L Austenitic Stainless Steel Under Thermal Fatigue
Authors: Bouin Pauline , Fissolo Antoine , Gourdin Ce´dric
Published: May 2012

Thermal fatigue phenomena are long term deterioration mechanisms which become more and more important as the life-time of nuclear power plant increases. Some incidents as the incident of Civaux I and some works in thermal fatigue have disproved current methodologies and usual criteria to predict propagation of thermal fatigue cracks in nuclear power plants. This paper presents the results of the thermal fatigue tests, Fat3D, which are conducted on 304L austenitic stainless steel pipes. This experiment has been designed to study the problem of closure effect and fatigue crack growth under thermal fatigue conditions on quasi-structure specimens. The importance of the initiation and the propagation phases on a notched specimen and the evolution of the stress intensity factor according to the propagation are investigated as well. The use of different non destructive techniques to detect and follow crack propagation is also assessed. In parallel, a numerical interpretation is developed based on a material characterisation and using finite element analyses with the French Cast3M code. This combined experimental and numerical study enables to assess improvements of classical methods to accurately predict the crack growth propagation under thermal loads and to understand the influence of the main parameters concerning crack propagation in such components.
Experimental Demonstration of Shakedown in a Vessel Submitted to Impulsive Loading
Authors: Simoens B. , Lefebvre M. H. , Nickell R. E. , Minami F.
Published: May 2012

Vessels subjected to internal impulsive loadings, such as those used for controlled-detonation chambers, can be designed for a single impulsive load application or for multiple impulsive loads. Design of a single-use vessel may take advantage of the capability of the vessel material to absorb energy through elastic-plastic behavior, provided that the public health and safety is protected, even though the owner’s investment in the vessel may be compromised because of severe distortion and potential loss of containment functionality. However, when the vessel is designed to contain multiple internal impulse loads, the usual design practice is to require completely elastic response or, at most, very localized elastic-plastic behavior. A recently-approved ASME Boiler & Pressure Vessel Code, Section VIII, Division 3 action (Code Case 2564-2) provides limits for the accumulated plastic strains in such vessels, including a limit on the accumulated plastic strain averaged across the wall thickness of the vessel, that are sufficiently conservative to permit the design of vessels for both single-impulse and for multiple-impulse applications. Analytical or experimental demonstration to meet the Code Case 2564-2 strain limits is straightforward for the single-impulse vessel design, and is relatively straightforward for multiple-impulse vessel designs when the vessel response to any of the individual impulsive loads is nearly elastic. However, when the design-basis impulsive loading for a multiple-impulse vessel design leads to significant plastic straining, the demonstration of design adequacy becomes extremely complex, raising issues of impulsive loading sequences (since elastic-plastic response is load-path dependent, what is the temporal order of the impulse loadings?) and demonstration of shakedown to elastic or near-elastic behavior. In such cases, an analytical demonstration of design adequacy may be impractical, while an experimental demonstration may be both practical and illuminating, especially if the demonstration is carried out at a scale that is both economical and convincing. Here, a one-seventh-scale model of a controlled detonation vessel is used as the basis for demonstrating the effect of shakedown to essentially elastic behavior, with no further accumulation of plastic straining, along with the satisfaction of ASME Code Section VIII, Division 3, local ductility exhaustion requirements. The experiments on a scale model vessel have proved that the phenomenon of shakedown can be demonstrated experimentally, for internal detonation loadings that initially led to plastic strains up to 0.7%.
Fast Computational Residual Stress Analysis for Welded Pipe Joint Based on Iterative Substructure Method
Authors: Maekawa Akira , Takahashi Shigeru , Serizawa Hisashi , Murakawa Hidekazu
Published: May 2012

An efficient and reliable method for welding residual stress analysis is reported in this paper. The analysis method to calculate the residual stress using the iterative substructure method was developed and compared with a conventional one using a commercial finite element analysis code; comparisons were made for the analysis accuracy and the computational speed of the residual stress in a welded pipe joint. The residual stress distributions obtained by the both methods agreed well with each other. Moreover, it was clarified that the developed method could calculate the residual stress in a shorter computing time and could calculate the residual stress distribution much faster with nearly the same accuracy as the conventional method when the size of the welding structure was large.
Effects of Interface Wedge Angle in Metal Side on Bonding Strength in Ceramic to Metal Joint
Authors: Tateno Masayoshi , Yokoi Eiichirou
Published: May 2012

This study was performed to clarify dependences of bonding strength on the interface wedge angle in the metal side of ceramic-to-metal joint. Each plate Si3N4 and Ni used for this experiment is produced by wire electric discharge machining. The geometric interface shape at the edge of the interface is characterized by wedge angle on both side of the ceramic and metal defined as a configuration angle between the free surface of each material and the interface. As the wedge angle of Si3N4 is a right angle, the wedge angle of Ni is set from 30° to 180°. Joint specimens were bonded at high temperature using braze metal of 0.05mm thickness under vacuum and cooled slowly. The tensile bonding strength of the ceramic-to-metal joint was evaluated to determine the optimum interface shape. The highest bonding strength appeared under identical interface conditions where the fracture pattern changed. This study provided a useful geometric interface shape to improve the tensile bonding strength of ceramic-to-metal joint.
A Critical Evaluation of Methods for Computing Small Failure Probabilities for Ductile Piping Components
Authors: Varfolomeev Igor , Ivanov Denys , Siegele Dieter
Published: May 2012

This paper focuses on the application of the failure assessment diagram (FAD) approach to accomplish robust and reliable calculations of small failure probabilities, as required for safety relevant nuclear components. Specifically, the first- and second-order reliability methods (FORM, SORM) as well as different sampling algorithms are investigated as to their performance and numerical stability. In particular, computational problems are noticed in the assessment range corresponding to the transition from ductile fracture to plastic collapse which is a typical operating regime for ferritic piping. Numerical errors are found to result due to the occurrence of multiple design points in the FORM procedure, thus leading to an underestimation of failure probabilities. Subsequent benchmark calculations reveal a high efficiency of the improved numerical algorithms within a very broad range of failure probabilities. Another aspect considered in the paper is the application of FORM/SORM to the assessment of crack instability taking into account the scatter in crack resistance curves. Finally, the methods and computer tools developed within the framework of this research are applied for evaluating some pipe burst tests described in the literature.
Seismic Safety Margin of Cylindrical Liquid Storage Tanks in Nuclear Power Plants
Authors: Maekawa Akira , Takahashi Tsuneo , Fujita Katsuhisa
Published: May 2012

In Japanese nuclear power plants, quantitative evaluation for seismic safety margin of the equipment is an important issue. In this study, the seismic safety margin of cylindrical liquid storage tanks used in nuclear power plants was investigated experimentally and analytically using test tanks with water inside. The buckling load of the tanks was examined because buckling was their dominant damage mode. The test tanks were reduced-scale models similar to the large-scale liquid storage tanks used in nuclear power plants. The experimental buckling load was compared with the design value. Furthermore, dynamic and static elastic-plastic buckling simulations by finite element analysis using a three-dimensional model were made and then the simulation results were compared with the experimental and design values. The simulated and experimental results agreed well, showing the values were the nearly-true buckling load, that is, proof stress. The design value was lower than the other values, indicating the difference was the seismic safety margin. The above results illustrated that existing actual tanks would have a bigger seismic safety margin.
Numerical Simulation of a Single Bead on Plate and Three Pass Slot Welds in Austenitic Stainless Steel
Authors: Xu Jijin , Gilles Philippe
Published: May 2012

This paper provides the numerical simulations of two welding benchmark cases defined in the frame of the European Network on Neutron Techniques Standardization for Structural Integrity. The network involves over 35 organizations from industry and promotes the application of modern experimental and numerical techniques to problems related to the determination of residual stress and distortion in components. The first case issued by Task Group 1, addresses the estimation of residual stress fields around a single weld bead deposited on an austenitic stainless steel plate. The second case issued by Task Group 4, deals with the estimation of residual stress fields in a three-pass slot weld in an austenitic stainless steel plate. In both cases, the welding processes and types of material are same: tungsten-inert-gas welding and AISI 316 stainless steel. It is therefore of interest to compare these two studies in terms of differences between calculated / measured and in terms of the influences of the number of welding pass and heat input.
Further Understanding on Deformation-Oxidation Model in Stress Corrosion Cracking Tip Based on Meso-Scale Mechanical Field
Authors: Xue He , Li Zhijun , Xue Xiaofeng , Lu Zhanpeng , Shoji Tetsuo
Published: May 2012

Stress corrosion cracking (SCC) is a common failure in stainless steel and nickel based alloys in high-temperature oxygenated aqueous systems. Because the propagating mode and morphology is particular at the SCC tip, it is necessary to investigate and understand in detail the mechanical state close to the SCC tip for improving the prediction accuracy of SCC growth rate in stainless steel and nickel based alloys in the nuclear pressure vessels and piping. By using a sub-model technique in commercial finite element analysis code, the meso-scale stress and strain field in the SCC tip constituted by the oxide film and base metal is simulated and analyzed in this study. And reasonable and operational mechanical parameters in the prediction method of SCC growth rate based on the slip-oxidation model are also discussed. The results of the investigation provide a new insight into the quantitative prediction of SCC growth rate in nuclear structural materials in high temperature water environments.
Development of 7%Ni-TMCP Steel Plate for LNG Storage Tanks
Authors: Ando Ryuichi , Arimochi Kazushige , Kawabata Tomoya , Onishi Kazushi , Kamo Takahiro , Yamashita Maki , Iwahashi Hiroshi , Kubo Naoshige , Fuchimoto Yoichi , Takata Masanori , Sakato Naokazu , Mitsumoto Masahiko , Hirai Shuichi , Hirose Hitoshi , Hagihara Yukito
Published: May 2012

Demand of natural gas continues to increase in the recent years due to the rise of environmental issue and the drastic increase of crude oil price. These events led to the increase of constructions of Liquefied Natural Gas (LNG) storage tanks worldwide. The inner tank material for above ground LNG storage tanks have mostly been made of a 9% nickel steel plate over the last 50 years as it has excellent mechanical properties under the cryogenic temperature of −160deg-C. During this period, the LNG storage tanks made of 9%Ni steel plate have been operated safely at the many LNG export and import terminals in the world. Meanwhile, technologies of steel making, refinement, design, analysis, welding and inspection have been improved significantly and enabled enlarging volumetric capacity of the tank 2–3 times. There was a tendency for nickel price to increase in recent years. In such a circumstance lowering Ni content has focused attention on the 9%Ni steel as nickel is an expensive and valuable rare metal and a 7%Ni steel plate was eventually researched and developed by optimizing the chemical compositions and applying Thermo-Mechanical Controlled Process (TMCP). As a result, it was demonstrated that 7%Ni-TMCP steel plate had excellent physical and mechanical properties equivalent to those of 9%Ni steel plate. In order to evaluate fitness of the 7%Ni-TMCP steel plate and its weld for LNG storage tanks a series of testing was conducted. Several different plate thicknesses, i.e. 6,10,25,40 and 50 mm, were chosen to run large scale fracture toughness tests including duplex ESSO tests, cruciform wide plate tests as well as small scale tests. It was concluded that the 7%Ni-TMCP steel plate warrants serious consideration for use in LNG storage tanks. This paper reports details of the research and development of the 7%Ni-TMCP steel plate.
Stochastic Floor Response Spectra for an Actively-Controlled Secondary System
Authors: Mochio Takashi
Published: May 2012

The purpose of this paper is to propose a newly floor response spectra (FRS) in order to evaluate simply the structural response of the actively-controlled secondary system subjected to earthquake. This paper adopts a linear single-degree-of-freedom system as a main structure and an active mass damper (AMD) system as the active control technology. Also, the earthquake wave is modeled as product of a non-stationary envelope function and a stationary Gaussian random process of which power spectral density is equal to the Kanai-Tajimi spectrum. The control design is executed by using linear quadratic Gaussian control strategy against an enlarged state space system. Finally, the response amplification factor is given by the combination of the obtained statistical response values and the extreme value theory. Analytical results are compared with numerical simulations, and both show a good agreement. As a result, it seems that the validity of the proposed technique is confirmed.
Blast Testing a High Strength Steel Containment Vessel
Authors: Clayton Alan M. , Wallace Stuart , Rushton Nicholas
Published: May 2012

An extensive series of tests have been carried out on an explosive containment vessel. The vessel geometry and the blast and overload tests are described, covering the experimental set up and instrumentation. Strains in the vessel are compared to calculated values using the AUTODYN explicit finite element software, showing good correlation over the first few cycles and generally good prediction of maximum strains. Leakage measurements using a carbon monoxide detector have shown that in all these tests the glass encapsulated DG O’Brien electrical penetrations through the vessel inner closure performed well. A modified version of this penetration to allow exhaust gases through the wall has also performed well and offers an alternative to NPT tapered thread connections.
High Strain Rate Fracture Properties of High Strength Steels and Their Application
Authors: Clayton Alan M. , Dabinett John
Published: May 2012

The evaluation of fracture of ferritic steels using the methods in ASME Code Case 2564 for impulsively loaded vessels requires the static reference temperature T0 and the upper shelf toughness, and these are used together with the Master Curve to define the transition temperature curve. The effect of high rates of strain on the ductile-brittle transition is determined in the code case using a correlation due to Wallin. Two steels used for impulsively loaded vessels, welded steel similar to HY80 plate and a cast steel similar to HY100 have been evaluated to obtain their static fracture and strength properties. Additional instrumented pre-cracked Charpy testing using a draft ISO standard has determined the shift in T0 with high strain rates and the results have been compared to the Wallin correlation. The strain rate correlation is used to evaluate the fracture response of vessels made of these steels when subjected to internal blast. By using the instantaneous strain rates of the vessel wall vibration considerable gains in critical crack size can be obtained compared to using the highest rate throughout the whole of the transient.
Differences in the Assessment of Plastic Collapse in BS 7910:2005 and R6/FITNET FFS Procedures
Authors: Eren S¸efika Elvin , Hadley Isabel , Nikbin Kamran
Published: May 2012

At present within the fracture assessment routes of different codes and standards, two different options for the assessment of plastic collapse, Lr, are available, namely reference stress and limit load approaches. Recent comparative studies have shown significant differences in the assessment of plastic collapse depending on whether the reference stress solutions in BS 7910:2005 or the limit load solutions in R6/FITNET are used for the calculation of Lr. In this paper, differences with respect to the choice of solutions and boundary conditions will be illustrated and observations regarding the route that the Codes should take with respect to a unified assessment will be discussed.
Development of a Numerical Model to Represent Two-Phase Flow Configurations in a Tube Bundle
Authors: Senez Hubert , E´tienne Ste´phane
Published: May 2012

Two-phase cross-flow exists in many shell-and-tube heat exchangers. Flow-induced vibration excitation forces can cause tube motion that will result in long-term fretting wear or fatigue. Studies on the subject, providing results on turbulence-induced displacement, fluid-elastic instabilities, and flow patterns have already been performed. It has been shown that the flow configuration plays an important role in the vibrations excitation mechanism. Previous studies showed the existence of unexpected quasi-periodic forces acting on a tube bundle subjected to two-phase cross-flow. The present work aims to understand the physical origin of these forces. A simple numerical model was developed to simulate two-phase cross-flow acting on a tube bundle. This model considers a continuous liquid potential flow across a tube bundle, with virtual bubbles being introduced in the flow. Three kinds of forces act on the bubbles: buoyancy forces, drag forces, and impact forces. These forces take place between two bubbles, or between a bubble and a cylinder. Two bubbles may coalesce if they hit each other, and conversely a bubble may split into two bubbles if the shear flow is strong enough. These local considerations on bubbles have global consequences on the flow configuration. Preliminary results show similarities between the numerical flow configuration and the experiments.
Provisional Results for an Experimental Investigation Into the Effect of Combined Primary and Secondary Stresses When Considering the Approaches of R6 and the Recently Developed g() Method
Authors: James Peter , Hutchinson Paul , Madew Colin
Published: May 2012

Engineering components, particularly those containing weldments, may contain small crack-like defects that experience combinations of primary and secondary stresses during service. A new function, g(), has been introduced previously to quantify the influence of plasticity interaction under combined primary and secondary loading on a components crack driving force. This paper compares g() with experiments performed to consider g() over a range of plasticity values. This experimental programme was performed on scalloped notch three point bend specimens that had experienced a pre-compression to induce a residual stress field before being tested to failure over a range of temperatures (−150, −90 and −50 °C). Samples which did not undergo a pre-compression were also tested to provide an estimate of the materials fracture toughness at the temperature in question. Through analysing the experimental results it is clear that further material characterisation is required. This paper, therefore, only presents the initial results at this stage. However, as a pessimistic interpretation of the results has been made, and since both the existing R6 and the g() plasticity interaction parameters are acceptable, the experiments provide useful validation to both methods.
Finite Element Analysis of Industrial Steel Elbows Under Strong Cyclic Loading
Authors: Varelis George E. , Pappa Patricia , Karamanos Spyros A.
Published: May 2012

Steel elbows are used in petrochemical facilities and power plants. In the case of an earthquake event, in addition to other service loads, they are subjected to strong repeated cyclic structural loading that may lead to failure due to cyclic accumulation of plastic strain or collapse. Furthermore, due to their flexibility, significant non-linearities occur and the elbow cross-section shape distorts as cyclic loading takes place resulting at an oval or flatten shape at the end of the loading sequence. Accumulation of plastic strains takes place at the most stressed parts of the elbow, associated with extensive bulging of the cross-section which is more pronounced in the presence of internal pressure. The present study is numerical, based on a finite element simulation of the elbow, and examines elbow behavior subjected to strong cyclic bending in the presence of internal pressure. The material constitutive model has a dominant effect on describing the elbow response, and this is shown through the employment of three different classical plasticity models.
J and CTOD Estimation Procedure for Circumferentially Cracked Pipes Under Combined Bending and Internal Pressure
Authors: Parise Lui´s F. S. , Ruggieri Claudio
Published: May 2012

This work provides an estimation procedure to determine the J-integral and CTOD for pipes with circumferential surface cracks subjected to combined bending load and internal pressure for a wide range of crack geometries and material (hardening) based upon fully-plastic solutions. The present investigation broadens the applicability of current evaluation procedures for J and CTOD which enter directly into structural integrity analyses and flaw tolerance criteria. Extensive 3-D nonlinear analyses of circumferentially cracked pipes with surface flaws having different crack depth (a) over pipe wall thickness (t) ratios and varying crack length for different strain hardening properties provide the dimensionless parameters relating the elastic-plastic crack-tip driving forces with the applied (remote) bending moment and internal pressure. The investigation provides a fairly comprehensive body of numerical solutions for J and CTOD in circumferentially cracked pipes subjected to biaxial loading.
An Experimental Study of the Phase Lag Causing Fluidelastic Instability in Tube Bundles
Authors: Khalifa Ahmed , Weaver David , Ziada Samir
Published: May 2012

The phenomenon of fluidelastic instability forms a major limitation on the performance of tube and shell heat exchangers. It is believed that fluidelastic instability is attributed to two main mechanisms; the first is called the “Damping Mechanism”, while the second is called the “Stiffness Mechanism”. It is established in the literature that in order to model the damping controlled fluidelastic instability, a finite time delay between tube vibration and fluid response has to be introduced. Experimental investigation of the time delay between structural motion and the induced fluid forces is detailed in the present study. A parallel triangular tube array consisting of seven rows and six columns of aluminum tubes is built with a pitch ratio of 1.54. Hot-wire measurements of the interstitial flow perturbations are recorded while monitoring the tube vibrations in the lift and drag directions. Pressure transducers are installed inside the instrumented tubes to monitor the fluid forces. The phase lag between tube vibration and flow perturbation is obtained at different locations in the array. The effect of tube frequency, turbulence level, location of measurements, and mean gap velocity on the relative phase values is investigated. It is found that there are two well-defined regions of phase trends along the flow channel. It is concluded from this study that the time delay between tube vibration and downstream flow perturbation is associated with the vorticity convection downstream, while the time delay for upstream perturbations is associated with the effect of flow separation and vorticity generation which is propagated upstream from the vibrating tube.
Effects of Soil-Pipe Interaction on the Global Buckling Response of Submarine Pipelines
Authors: Teixeira Paulo , Gonzalez Marco , Lorenzo Nicolas
Published: May 2012

At the moment, in eastern Venezuela several projects involving design, fabrication and installation of submarine pipelines from offshore platforms to onshore plants are being developed. These pipelines will be subjected to high pressure–high temperature conditions, which will cause relevant compressive forces in the pipeline as a consequence of restricted thermal expansion, generating that pipelines can suffer a global buckling. One of the most important factors in this buckling situation is the soil–pipe interaction. In this work, a numerical study of soil–pipe interaction and its effect on the global buckling response for a specific Venezuelan submarine pipeline using the Finite Element Method is presented. A 3D pipe–soil model using shell elements with contact elements for pipe-soil interface for three different pipelines cases is applied. This model has considered nonlinear behaviour for pipe material, loads and contact zones. The main results indicate that global buckling response of a pipeline under axial compressive load depends mainly of pipe-soil interaction, being the main variables: friction factor and submerged weight of pipe.
Analysis of Cured-in-Place Piping for a Nuclear Plant Application
Authors: Reich Alton , Newman Victor , Di Salvo Roberto , Charest John
Published: May 2012

Cured-in-place piping (CIPP) is used to repair existing pressure pipe that has compromised structural integrity and is no longer capable of holding operating pressure without leaking. It is often used to repair buried piping where digging the piping up to replace it would be inconvenient and/or cost prohibitive. CIPP is routinely used to repair water and sewer lines, and an ASTM specification exists to guide the design of the pipe repair for these applications. CIPP can also be used as a repair technique for piping at nuclear power plants; however, such use must be approved on a case-by-case basis. This paper discusses some of the design challenges associated with designing the CIPP for a nuclear plant application. It presents an overview of the analytical approach and the results.
Effects of Weld Geometry on Stress Intensity Factor Solutions for Laser Welds in Lap-Shear Specimens
Authors: Sripichai Kulthida , Asim Kamran , Pan Jwo
Published: May 2012

In this paper, the effects of weld geometry on the stress intensity factor solutions for laser welds in lap-shear specimens are investigated. Analytical stress intensity factor solutions for laser welded lap-shear specimens based on the beam bending theory are derived and compared with the analytical solutions for two semi-infinite solids with connection. Finite element analyses of laser welded lap-shear specimens with different weld widths were also conducted to obtain the stress intensity factor solutions. Approximate closed-form stress intensity factor solutions based on the results of the finite element analyses in combination with the analytical solutions based on the beam bending theory and Westergaard stress function for a full range of the normalized weld widths are developed for use with the stress intensity factor solutions for kinked cracks to correlate and estimate fatigue lives of laser welded lap-shear specimens. The effects of the weld protrusion on the stress intensity factor solutions for the pre-existing cracks in lap-shear specimens are also investigated. The presence of the weld protrusion decreases the stress intensity factor solutions for the pre-existing crack near the weld protrusion for the load carrying sheets and the lower stress intensity factor solutions can be used to explain more favorable conditions for kinked fatigue crack propagation from the other pre-existing crack tip and to estimate fatigue lives of laser welded lap-shear specimens under high cycle loading conditions as observed in experiments.
Modeling of Subcritical Crack Growth due to Stress Corrosion Cracking: Transition From Surface Crack to Through-Wall Crack
Authors: Shim Do-Jun , Rudland David , Harris David
Published: May 2012

Recent work conducted using the Advanced Finite Element Analysis (AFEA) method to simulate the ‘natural’ crack growth of a circumferential PWSCC demonstrated that a subcritical surface crack can transition to a through-wall crack with significant differences between the inner diameter and outer diameter crack lengths. In the current version of the xLPR (Extremely Low Probability of Rupture) code, once the surface crack penetrates the wall thickness, an idealized through-wall crack (which has an equivalent area as the final surface crack) is formed. This type of crack transition was selected since no general stress intensity factor (K) solutions were available for crack shapes that would form during the transitioning stages, i.e., non-idealized or slanted through-wall cracks. However, during the pilot study of the xLPR code, it has been identified that this crack transition method may provide non-conservative results in terms of leak-rate calculations. In this paper, in order to compare the ‘natural’ versus ‘idealized’ crack transition behavior, limited example cases were considered where both crack transitions were simulated using 3D finite element analyses. In addition, leak-rate calculations were performed to study how the two different crack transition methods can affect the leak-rates. The results of the present study demonstrate that the ‘idealized’ transition from surface to through-wall crack can significantly affect the leak-rate calculations.
A Microstructural Study of Compressive Plastic Pre-Strain Effects on Creep Damage Behaviour of Type 316H Stainless Steel
Authors: Mehmanparast Ali N. , Davies Catrin M. , Ardakani Mahmoud , Nikbin Kamran M.
Published: May 2012

Compressive plastic pre-strain induced at room temperature in type 316H stainless steel, significantly influences the tensile, creep deformation and crack growth behaviour of the material. It is known that the material is hardened after pre-strain to 8% plastic strain and thus exhibits little or no plasticity during loading of uniaxial or creep crack growth (CCG) tests. In addition pre-compression (PC) has been found to reduce the creep rupture time, creep ductility and accelerate creep crack growth rates compared to as-received (AR) (i.e. uncompressed) material. In order to understand pre-straining effects on mechanical behaviour of 316H, optical and scanning electron microscopy (SEM) studies have been performed on uncompressed and 8% pre-compressed material. Samples have been examined in three orientations (i.e. parallel and perpendicular to the pre-compression direction). Furthermore, the influence of cold pre-compression on local creep damage formation ahead of the crack tip on interrupted CCG tests on AR and PC material has been studied. The results are discussed in terms of intergranular and transgranular damage caused by the compression process and the importance of microstructural changes on the mechanical behaviour of the material in long term tests.
Quantification of Residual Stresses Induced by Prior Loading at High Temperatures
Authors: Mehmanparast Ali N. , Davies Catrin M. , Wimpory Robert C. , Nikbin Kamran M.
Published: May 2012

High temperature components generally undergo cyclic loading conditions. Prior tensile/compressive loading of a fracture specimen can induce compressive/tensile residual stress fields at the crack tip. These residual stresses will influence the subsequent fracture behaviour of the cracked body. This work forms part of a project to examine the influence of creep induced damage at a crack tip on subsequent fatigue crack growth and fracture toughness properties of austenitic type 316H stainless steel. Creep damage is introduced local to the crack tip of a fracture specimen by interrupting a creep crack growth test, performed at 550 °C. Prior to testing, the material was pre-compressed in order to strain harden the material. The compact tension, C(T), specimen geometry has been considered in this work. Since residual stresses are known to influence fatigue and fracture toughness properties of a cracked body, it is important that the residual stress levels at the crack tip are quantified. Neutron diffraction (ND) measurements have therefore been performed to quantify the extent of residual stress in these samples after initial loading, and compared to finite element model predictions. Two specimens have been considered with the crack plane orientated in parallel and perpendicular to the pre-compression direction. Compressive residual stresses of around 100 MPa have been measured directly ahead of the crack tip. Reasonable predictions of the principal residual stress distributions have been obtained by the simplified FE analysis. Though the tensile properties differ significantly in for specimens orientated parallel and perpendicular to the pre-compression direction, no significant differences in the residual stress field are predicted in the C(T) specimens orientated in both directions.
Probabilistic Models of Reliability of Cast Austenitic Stainless Steel Piping
Authors: Qian Haiyang , Harris David , Griesbach Timothy J.
Published: May 2012

Thermal embrittlement of cast austenitic stainless steel piping is of growing concern as nuclear power plants age. The difficulty of inspecting these components adds to the concerns regarding their reliability, and an added concern is the presence of known defects introduced during the casting fabrication process. The possible presence of defects and difficulty of inspection complicate the development of programs to manage the risk contributed by these embrittled components. Much work has been done in the past to characterize changes in tensile properties and fracture toughness as functions of time, temperature, composition, and delta ferrite content, but this work has shown a great deal of scatter in relationships between the important variables. The scatter in material correlations, difficulty of inspection and presence of initial defects calls for a probabilistic approach to the problem. The purpose of this study is to describe a probabilistic fracture mechanics analysis of the maximum allowable flaw sizes in cast austenitic stainless steel piping in commercial power reactors. Attention is focused on fully embrittled CF8M material, and the probability of failure for a given crack size, load and composition is predicted considering scatter in tensile properties and fracture toughness (fracture toughness is expressed as a crack growth resistance relation in terms of J-Δa). Random loads can also be included in the analysis, with results generated by Monte Carlo simulation. This paper presents preliminary results for CF8M to demonstrate the sensitivity of key input variables. The outcome of this study is the flaw sizes (length and depth) that will fail with a given probability when a given load is applied.
Creep Constitutive Law of Packing Materials Based on Relaxation Tests
Authors: Diany Mohammed , Bouzid Abdel-Hakim
Published: May 2012

The tightness of valves, compressors and pumps is ensured by superposed braided rings installed in a system of stuffing-box. The nature of the packings material and structure, which is like a rectangular braided cord, influences the proper stuffing-box assembly behavior. During installation, a minimum compressive load is required to ensure a minimum level of tightness. A fairly large percentage of this axial compression load is transferred to the radial direction to generate the contact pressures at the packing-stem and packing-housing interfaces necessary for sealing. The packing is considered in several studies as a viscoelastic material with its creep-relaxation behavior assumed as one-dimensional rheological model. In the present work, relaxation tests in a test-bunch containing all the components of the packed stuffing-box, are carried out to define a creep constitutive law for packing braids of different materials. Based on three-dimensional compression tests the developed method is applied to three different packing materials.
Sealing Performance and FE Analysis of Pipe Flange Connection With Gasket Under Cyclic Thermal Condition
Authors: Omiya Yuya , Takagi Yoshio , Sawa Toshiyuki , Torii Hiroyasu
Published: May 2012

Pipe flange connections with gaskets have been widely used in mechanical structures such as nuclear plants, petroleum refining plants and chemical plants and so on. Those connections are usually exposed to elevated temperature with internal pressure. Thus some investigations on the mechanical behavior of pipe flange connections with gaskets under thermal condition such as the sealing performance, the contact stress at the interfaces and a variation in the axial bolt force, have been performed. However, it is important to investigate the sealing performance of pipe connections under long term thermal exposure for using them safely. In this study, the effects of cyclic thermal condition on the sealing performance and mechanical behavior in pipe flange connection will be discussed based on the experimental leakage tests of pipe flange connections with gasket and FEM analyses.
Use of NUREG/CR-6909 Environmentally-Assisted Fatigue Rules for a Nuclear Plant License Renewal Application
Authors: Weitze William F. , Walter Matthew C. , Evon Keith R.
Published: May 2012

As part of the process of renewing the operating license for an additional 20 years after the original 40-year design life, nuclear plant owners in the United States (US) are required to show that they are managing the effects of aging of systems, structures, and components. US Nuclear Regulatory Commission (NRC) report NUREG-1801, the “Generic Aging Lessons Learned (GALL) Report,” identifies acceptable aging management programs, including programs for fatigue and cyclic operation. This includes fatigue usage analyses that account for reduced fatigue life for components in a reactor water environment. Earlier revisions of the GALL report required plants to perform environmentally-assisted fatigue (EAF) analyses using the rules in reports NUREG/CR-6583 (for carbon and low alloy steels) and NUREG/CR-5704 (for austenitic stainless steels), which were developed in 1998 and 1999, respectively. However, GALL Revision 2, issued in December 2010, requires that the rules in NUREG/CR-6909, issued in 2007, be used for nickel alloy materials, and allows it to be used for carbon, low-alloy and stainless steels as an alternative to those in the previous reports. This paper presents an application of the NUREG/CR-6909 rules, and makes several observations about the differences between using the newer and older rules. The analyses presented were performed for a sample set of boiling water reactor (BWR) locations.