bluuebunny/crossref_metadata_2025 huggingface dataset:
A Load Combination Method for Seismic Design of Multiple Supported Piping Systems With Friction Characteristics: Part 1—Generally Correlated Excitations
Authors: Yamauchi Tatsuya , Tsuchikawa Kazumasa , Masuda Arata , Sone Akira
Published: May 2012

A load combination method for seismic response calculation of piping systems with friction characteristics to multiple support excitations is presented. This method has an advantage, such that the cross-correlation among support excitations and “response reduction factor” due to friction are taken into account by use of a stationary random vibration theory approach. Using a simple analytical SDOF piping system with friction characteristics to two support excitations, This method is supplied to various correlation cases of two support excitations and friction characteristics and the maximum responses of piping is calculated. From these calculation results, it is clear that the maximum acceleration responses of nonlinear piping systems can also depend on the cross-correlation among support excitations and can be reduced due to the friction effect. Finally, the conventional equation of the response reduction factor and the maximum response calculated by the proposed method are presented for practical use.
Non Destructive Inspection of Nickel Base Alloys in France
Authors: Champigny F. , Deforge D. , Lemaire E.
Published: May 2012

Nickel base alloys are commonly used in light water reactors because their properties for thermal exchange and also differential thermal expansion with carbon steels are good to very good. Unfortunately, the alloys 600 and 182 / 82 are sensitive to primary water stress corrosion cracking (PWSCC). The effect of the temperature is important and the crack propagation can increase significantly when it is above 320° C. All pressure water reactors use these alloys and most of them have been or are cracked depending of operating conditions, stress level of the materials and other parameters. Due to the fact these alloys are used for important parts of the primary systems for instance like vessel head penetrations or bottom mounted instrumentation, and also particular welds like dissimilar welds, in-service inspection has been developed to be able to detect, characterize and size IGSCC. In France, since the Bugey 3 VH penetration leakage in 1992, periodic reviews have been produced to understand the phenomena and propose adapted ISI. Firstly, on the areas where defects had been seen and secondly, on the other areas where a hazard was identified. The first category reviews the non destructive techniques applied on VH penetrations, BMI, dissimilar welds, SG channel heads. The second one reviews the case of RPV clevis and repaired zones in nozzles.
Structural Integrity Assessment of Notched Components
Authors: Cicero Sergio , Madrazo Virginia , Carrascal Isidro , Laporta Miguel
Published: May 2012

This paper analyzes the notch effect and presents a methodology, based on failure assessment diagrams and the notch analysis approaches based on the theory of critical distances, for the structural integrity assessment of notched components, which allows more accurate structural analyses to be made. The methodology is applied to a set of tests performed on PMMA single edge notched bending (senb) specimens, providing better results than those obtained when the analysis is performed considering that notches behave as cracks.
An Experimental and Numerical Investigation of Residual Stresses in Butt Welding of Two Mild Steel Plates
Authors: Singh Gurdeep , Brar Gurinder Singh
Published: May 2012

Welding is a reliable and efficient joining process in which the coalescence of metals is achieved by fusion. Welding is carried out with a very complex thermal cycle which results in irreversible elastic-plastic deformation and residual stresses in and around fusion zone and heat affected zone (HAZ). A residual stress due to welding arises from the differential heating of the plates due to the weld heat source. Residual stresses may be an advantage or disadvantage in structural components depending on their nature and magnitude. The beneficial effect of these compressive stresses have been widely used in industry as these are believed to increase fatigue strength of the component and reduce stress corrosion cracking and brittle fracture. But due to the presence of residual stresses in and around the weld zone the strength and life of the component is also reduced. To understand the behavior of residual stresses, two 10 mm thick Fe410WC mild steel plates are butt welded using the Metal Active Gas (MAG) process. An experimental method (X-ray diffraction) and numerical analysis (finite element analysis) are carried out to calculate the residual stress values in the welded plates. A three-pass V-butt weld joint is considered in this study. In multi-pass welding operation the residual stress pattern developed in the material changes with each weld pass. In X-ray diffraction method, the residual stresses were derived from the elastic strain measurements using a Young’s modulus value of 210 GPa and Poisson’s ratio of 0.3. Finite element method based, SolidWorks Simulation software is used to develop a coupled thermal-mechanical three dimension finite element model. The finite element model was evaluated for the transient temperatures and residual stresses during welding. Also variations of the physical and mechanical properties of material with the temperature were taken into account. It can also be concluded that when temperature distribution increases then the residual stress in the weldment also increase. The results obtained by finite element method agree well with those from experimental X-ray diffraction method.
Delayed Fracture of an Aluminum Alloy Subjected to Hg LME
Authors: Keller Scott G. , Gordon Ali P.
Published: May 2012

Structural components in a variety of industries are routinely subjected to static and cyclic loadings over an extended period of time; all while exposed to aggressive reactants in the environment. Of critical importance is the interaction between a material discontinuity and its environment. Environmentally assisted cracking (EAC) has been observed in chemical processing, piping and power generation industries to result in the rupture and failure of components. Notably, stress corrosion cracking (SCC) and liquid metal embrittlement (LME) have been extensively researched over the last century; however, there exists uncertainty in the microstructural failure mechanisms. Discrepancies are rooted in theories accounting for some liquid-solid couples but not others subjected to identical conditions. Recently, fracture mechanics experiments have revealed a life-dependency on the level of an initial static stress intensity of a cracked member. Unstable crack growth is observed above a threshold stress intensity value, KILME, or critical stress, σLME, below which rupture does not occur as quickly or at all. Experimental findings suggest that rupture can still occur at a lower stress intensity, provided a favorable microstructural orientation and/or critical stress is achieved that promotes crack initiation. Crack initiation processes are, therefore, the critical limiting factor in assessing the life of a component subjected to corrosive environments. An experimental study implemented Al7075-T651 notched tensile specimens in the study on delayed fracture of specimens subjected to liquid mercury at room temperature. Through varying loads and loading patterns, the stress and strain at the notch root can be evaluated and correlated with time to crack initiation. Life predictions can then be made based on the level of stress experienced in a structural component, even before the existence of a crack is detected.
Tool Interference Issues on ASME B31.3 Listed Flanges
Authors: Reichert Christopher D. , Fedoriw Larissa C.
Published: May 2012

In this paper, the authors investigate situations where flanges listed in ASME B31.3 may cause construction issues, due to interference between the assembly tools and the adjacent nuts. A variety of different tools that may be used for assembly have been considered. ASME B16.47 Series A and B, and AWWA C207 flanges have been evaluated, and tabulated into a series of charts to assist designers in avoiding problem flanges, or to identify situations where designers may need to consider modifying the bolting design to facilitate assembly. Changes between previous and current editions of AWWA C207, which may have exacerbated the problem have been identified, and evaluated, to assist owners and designers in issues that may arise with existing installed flanges, and to highlight several flanges which may have been used satisfactorily in the past, but may cause issues in new construction.
Considerations of Alloy N for Fluoride Salt-Cooled High-Temperature Reactor Applications
Authors: Ren Weiju , Muralidharan Govindarajan , Wilson Dane F. , Holcomb David E.
Published: May 2012

Fluoride Salt-Cooled High-Temperature Reactors (FHRs) are a promising new class of thermal-spectrum nuclear reactors. The reactor structural materials must possess high-temperature strength and chemical compatibility with the liquid fluoride salt as well as with a power cycle fluid such as supercritical water while remaining resistant to residual air within the containment. Alloy N was developed for use with liquid fluoride salts and it possesses adequate strength and chemical compatibility up to about 700°C. A distinctive property of FHRs is that their maximum allowable coolant temperature is restricted by their structural alloy maximum service temperature. As the reactor thermal efficiency directly increases with the maximum coolant temperature, higher temperature resistant alloys are strongly desired. This paper reviews the current status of Alloy N and its relevance to FHRs including its design principles, development history, high temperature strength, environmental resistance, metallurgical stability, component manufacturability, ASME codification status, and reactor service requirements. The review will identify issues and provide guidance for improving the alloy properties or implementing engineering solutions.
Improved J and CTOD Estimation Formulas for C(T) Fracture Specimens Including Overmatched Weldments
Authors: Savioli Rafael G. , Ruggieri Claudio
Published: May 2012

This work focuses on the evaluation procedure to determine the elastic-plastic J-integral and CTOD fracture toughness based upon the η-method for C(T) fracture specimens made of homogeneous and welded steels. The primary objective of this investigation is to enlarge on previous developments of J and CTOD estimation procedures for this crack configuration while, at the same time, addressing effects of strength mismatch on the plastic η-factors. The present analyses enable the introduction of a larger set of factor η for a wide range of crack sizes (as measured by the a/W-ratio) and material properties, including different levels of weld strength mismatch, applicable to structural, pipeline and pressure vessel steels. Very detailed non-linear finite element analyses for plane-strain models of square groove, center cracked C(T) fracture specimens provide the evolution of load with increased crack mouth opening displacement required for the estimation procedure. Overall, the present study, when taken together with previous investigations, provides a fairly extensive body of results to determine parameters J and CTOD for different materials using C(T) specimens with varying overmatch conditions.
Thermomechanical Analysis of a Pressurised Pipe Under Plant Conditions
Authors: Farragher T. P. , O’Dowd N. P. , Scully S. , Leen S. B.
Published: May 2012

This paper is concerned with the development of a methodology for thermo-mechanical analysis of high temperature, steam-pressurised P91 pipes in electrical power generation plant under realistic (measured) temperature and pressure cycles. In particular, these data encompass key thermal events, such as ‘load-following’ temperature variations and sudden, significant fluctuations in steam temperatures associated with attemperation events and ‘trips’ (sudden plant shut-down), likely to induce thermo-mechanical fatigue damage. An anisothermal elastic-plastic-creep material model for cyclic behaviour of P91 is employed in the transient FE model to predict the stress-strain-temperature cycles and the associated strain-rates. The results permit characterisation of the behaviour of pressurised P91 pipes for identification of the thermo-mechanical loading histories relevant to such components, for realistic, customised testing; this type of capability is relevant to design and analysis with respect to the evolving nature of power plant operating cycles, e.g. associated with more flexible use of fossil fuel plant to complement renewable energy sources.
Design of Oil Injection Quills for Hypercompressors Cylinders
Authors: Volterrani Guido , Maggi Carmelo , Manetti Marco
Published: May 2012

Fatigue impacts the life of all components subject to alternating loads, including lube oil injection quills. These occurrences are more frequent if a defect (initial flaw) nucleates in the component due to corrosion, high stress, machining imperfections, etc. The design of components undergoing high fluctuating pressures needs advanced technologies, like autofrettage, and design methods, like FEM or fracture mechanics. This component can be identified as a cylinder with different outside diameters and notches deriving from the geometry variation and threaded connection. The inner diameter is the most stressed area and will require an adequate stress analysis. A sensitivity analysis of the autofrettage pressure can be performed to identify the most appropriate residual stresses on the inner diameter and to obtain a threshold defect larger than the minimum detectable. Fracture mechanics allows the analysis the propagation of an initial defect with materials having different properties and considering different autofrettage pressures. Finite Element Analysis is used to validate the residual stresses predicted by calculation for each autofrettage pressure. An optimized solution of the hypercompressor injection quill can be designed.
Cylinder Valves Reliability and Performance in Booster-Primary Compressors
Authors: Giacomelli Enzo , Schiavone Massimo , Vaglini Claudio
Published: May 2012

The production of LDPE, in addition to the hyper-compressors, requires heavy-duty Booster and Primary compressors. Although operating at lower pressures, Booster-Primary units are complex machines, considering the need of wide operating range and capacity control, due to the different products often required by the plants. They are able to give an appreciable contribution to the operational results. Their cylinder valves, as critical parts need a careful design, that will be important for adequate operation, considering the aspects of Safety, Performance and Reliability. The aim of high efficiency is obtained by the use of methodologies, able to optimize the geometry and positively affecting the energy consumption. Similar advances are used for the strength of the components operating under fatigue stresses, like in the case of seats and rings or plates. The operating results both from energy consumption and mechanical behaviour are consequence of proper simulations. Mathematical models optimize performance and ensure reliable operation, to reach a correct mechanical behaviour with minimum energy consumption of the valves. Also the pulsation can be investigated in case the situation is considered critical for the plant. The selection of the valves, ring or plate type, can be significant as they have a different performance as a function of the lubricating oil quantity and viscosity.
On Identification of Leaky Pipeline Parameters via Monte Carlo Simulation
Authors: Moustafa Kamal A. F. , Emam Samir A. , Haik Yousef S.
Published: May 2012

In this study, a numerical simulation using inverse pipeline analysis is conducted for the localization and quantification of leak using minimum number of measurement points of a leaky pipeline. The friction coefficient and leak cross section area were also identified by window marching technique using only the pressure head at one end of the pipeline and the flow rate measurements at the other end of the pipeline. The Monte Carlo simulation approach is applied to identify the pipeline parameters by minimizing an objective function that represents the mismatch between the measured and numerically modeled pipeline variables. The simulation results are able to identify and localize the leak location as well as the friction coefficient and leak across section area. The effect of additive measurement noise on the leak localization accuracy is also investigated.
Seismic Response Analysis of Multiple Supported Piping System Considering Friction Characteristics of Support
Authors: Sone Akira , Tsuchikawa Kazumasa , Yamauchi Tatsuya , Masuda Arata
Published: May 2012

In this study, a practical method for obtaining the nonlinear seismic maximum response properties of multiple supported piping systems with friction characteristics in industrial plants such as the nuclear power plant and petrochemical plant is presented. In this method, the response reduction effects of friction are effectively considered. The method also facilitates the calculation of maximum nonlinear responses by using those of the linear piping-supporting system. By numerical simulations with a simple 2DOF model, the reduction effect of friction on the maximum acceleration responses of multiple supported piping systems are evaluated in terms of “response reduction factor”. After summarizing the characteristics of the response reduction factor obtained for various system parameters, a practical method for obtained this factor using the maximum linear response of piping system can be introduced. Finally, the maximum response calculated by the proposed method is presented for practical use.
Evaluation of J/CTOD for Clamped SE(T) Specimens With Welds
Authors: Shen Guowu , Tyson William R. , Gianetto James A. , Park Dong-Yeob
Published: May 2012

In BS 7448, Part 2, the stress intensity factor, J-integral and crack tip opening displacement (CTOD) equations developed for evaluation of fracture toughness of a homogeneous material using experimentally measured quantities, such as load-load line displacement, are applied to SE(B) specimens with yield-strength-mismatched welds. The accuracy of this procedure was studied by Gordon and Wang using finite element analysis (FEA). Recently, the so-called “η factor” method for J-integral evaluation of SE(T) specimens with weld-center-line-cracked and yield-strength-mismatched welds was studied by Ruggieri using detailed FEA calculations and the load separation method proposed by Paris et al. For application to strain-based design of pipelines, CANMET has developed equations to evaluate J-integral and CTOD resistance curves for clamped SE(T) specimens of homogeneous materials using experimentally measured load and crack-mouth-opening displacement (CMOD) in a single-specimen procedure similar to that in ASTM E1820. In the present study, the accuracy of using these equations for J-integral evaluation of clamped SE(T) specimens with weld-center-line-cracked and strength-mismatched welds was studied. It was found that the errors in J and CTOD using the equations developed for SE(T) specimens of homogenous materials for these strength-mismatched welds are similar to those for SE(B) specimens with the same weld geometry and mismatch level as reported by Gordon and Wang. It was also found that using the higher of the strength of base and weld metals σY (= (σYS+σTS)/2), (i.e. (σY)w for overmatching and (σY)B for undermatching) in converting J to CTOD gives reasonable and conservative CTOD evaluations for specimens with weld-center-line-cracked and yield-strength-mismatched welds.
Finite Element Based Automated Analysis for Determining Ratchet, Shakedown and Elastic Limits
Authors: Abou-Hanna Jeries , Paluszkiewicz Michael
Published: May 2012

In order to determine the ratchet and shakedown limit curves for even a simple component, such as a tube under a constant pressure load and cyclic thermal load, can be a daunting task when using conventional analysis methods (elasto-plastic cyclic finite element analysis) that require repeated iterative simulations to determine the state of the structure, elastic, shakedown, plastic or ratchet. In some cases, the process is further complicated by the difficulty in interpreting results of the cyclic loading to determine in which regime the structure is. Earlier work by Abou-Hanna and McGreevy was able to demonstrate limit load analysis of a structure whose yield strength is modified based on cyclic load, provided the ratchet limit [1]. The method, called Anisotropic Load Dependent Yield Modification (LDYM), was implemented by using a user subroutine with ABAQUS, a general commercial finite element code. The approach adopted provided ratchet limits for only one individual cyclic load value. The work presented here describes a process for analyzing the structure and determining the elastic, shakedown and ratchet boundaries all in one finite element simulation using only one analysis step. The approach manipulates the structure material behavior that enables the resetting of the material characteristics to their original values in order to be able to analyze the structure for different sets of cyclic and primary load combinations. The process was verified using problems available in the literature, such as the Bree tube and Ponter’s Holed Plate. Additionally, a tubular T-joint was used as an example of the effectiveness of the process for a three dimensional complex geometry. The tubular T-joint results are verified against baseline data from the iterative elastic-plastic simulations used to determine the elastic, shakedown, and ratchet limits. The work presented highlights the advantages and limitations of this numerical approach which requires little interaction with the analyst.
FIV Considerations for BWR Steam Dryers for EPU Operation
Authors: Basavaraju Chakrapani , Manoly Kamal A. , Khanna Meena
Published: May 2012

Steam dryers in Boiling Water Reactors (BWRs), located in the upper steam dome of the reactor pressure vessel, are not pressure retaining components and are not designed and constructed to American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section III safety class. Although the steam dryers in BWRs perform no safety function, they must maintain the structural integrity in order to avoid the generation of loose parts that may adversely impact the capability of other plant equipment to perform their safety functions. The majority of licensees of many operating nuclear plants are applying for extended power uprate (EPU), which increases the thermal power output up to 20% above the original licensed thermal power (OLTP). Nuclear power plant components such as steam dryers can be subjected to strong fluctuating loads and can experience unexpected high cycle fatigue due to adverse flow effects while operating at EPU conditions. However, there are some unique challenges for operation of dryers at EPU conditions requiring special considerations to prevent fatigue damage from the effects of flow induced vibration (FIV). This paper examines the FIV considerations and margin recommendations for fatigue stresses due to many uncertainties in the prediction of the fluctuating pressure loading acting on the steam dryer and the structural analysis of the steam dryer, very limited bench marking of the methods, and operating experience with some dryer failures.
Ratchet Limits for a Crack in a Welded Pipe Subjected to a Cyclic Temperature Load and a Constant Mechanical Load
Authors: Li Tianbai , Chen Haofeng , Chen Weihang , Ure James
Published: May 2012

This paper presents the ratchet limit analysis of a pipe with a symmetric crack in a mismatched weld by using the extended Linear Matching Method (LMM). Two loading conditions are considered: i) a cyclic temperature load and a constant internal pressure; and ii) a cyclic temperature load and a constant axial tension. Individual effects of i) the geometry of the Weld Metal (WM), ii) the size of the crack, iii) the location of the crack and iv) the yield stress of WM on the ratchet limits, maximum temperature ranges to avoid ratchetting and limit loads are investigated. Influence functions of the yield stress of WM on the maximum temperature ranges and limit loads are generated. The results confirm the applicability of the extended LMM to the cracked welded pipe.
Small Punch Testing and Application in Power Generation Industry
Authors: Dogan Bilal
Published: May 2012

The Small Punch (SP) test technique is an innovative, powerful technique based on tests using miniaturized specimens. At present, it is the only existing method capable of providing experimental characterization of service exposed materials of components. It is non invasive and provides direct measured material properties. It provides a significant technology capability that facilitates assessing power plant operating equipment for structural integrity and operational condition. The SP Testing facility supported by the in situ sampling for test specimens provides utility members an attractive option to interrogate equipment for making run/inspect/repair/replace decisions. It is supported by EPRI Software, NDE and Metallography facilities, to define guidelines for components life assessment cross the sector, serving both utilities, and constructors. It addresses the industrial need for personalized material and welds data required for: - lifing of plant, consumed life and residual life of components, - convenience of repairing, replacing, life of the new welds on old components, - cost of component deterioration, cost of normal service, - characterizations and qualifications of blade repairs, of coating materials-methods, - fast determination of new casts strength produced by Electron Beam. The sampling and test facility provides low temperature test data including transition temperature and fracture toughness (KIc, JIc) measurements with minimal empiricism, to a high-temperature material property data including tensile, creep and creep rupture properties. The materials used for components in power generation industry are presented along with the test facility and specific applications in the subject field.
A Multistage Creep Damage Constitutive Model for Isotropic and Transversely-Isotropic Materials With Elastic Damage
Authors: Stewart Calvin M. , Gordon Ali P.
Published: May 2012

In the pressure vessel and piping and power industries, creep deformation has continued to be an important design consideration. Directionally-solidified components have become commonplace. Creep deformation and damage is a common source of component failure. A considerable effort has gone into the study and development of constitutive models to account for such behavior. Creep deformation can be separated into three distinct regimes: primary, secondary, and tertiary. Most creep damage constitutive models are designed to model only one or two of these regimes. In this paper, a multistage creep damage constitutive model is developed and designed to model all three regimes of creep for isotropic materials. A rupture and critical damage prediction method follows. This constitutive model is then extended for transversely-isotropic materials. In all cases, the influence of creep damage on general elasticity (elastic damage) is included. Methods to determine material constants from experimental data are detailed. Finally, the isotropic material model is exercised on tough pitch copper tube and the anisotropic model on a Ni-base superalloy.
A Historical Perspective of HDPE Piping Material Development
Authors: Adams William I.
Published: May 2012

Over more than a century, polyethylene and polyethylene piping materials have been discovered, rediscovered, commercialized and developed. With each new development, field experience and research helped identify and characterize polyethylene material performance, in most cases, leading to improved durability and performance. This paper provides an overview of polyethylene structure, a historical view of significant developments and research, and how ongoing research has provided for continuing development and improvement of polyethylene piping performance.
Analysis of ABWR Containment Pressure-Temperature Loads and Suppression Pool Hydrodynamics Following Loss of Coolant Accidents
Authors: Sawant P. , Khatib-Rahbar M. , Moody F. , Drozd A.
Published: May 2012

This paper focuses on the assessment of Advanced Boiling Water Reactor (ABWR) containment pressure-temperature and suppression pool hydrodynamics under design-basis, loss-of-coolant accident (LOCA) conditions. The paper presents a phenomena identification and ranking table (PIRT) applicable to the ABWR containment response behavior, modeling of pressure-temperature loads using the MELCOR computer code, and analysis of suppression pool hydrodynamics parameters based on a mechanistic one-dimensional hydrodynamics model. A MELCOR 1.8.6 model with detailed nodalization of the ABWR containment is used to perform the containment pressure-temperature calculations following a design basis accident. The best estimate and several sensitivity calculations are performed for the ABWR containment using the suppression pool swell model. The sensitivity calculations demonstrate the influence of key model parameters and assumptions on the suppression pool hydrodynamics response. The comparison of containment pressure-temperature and the suppression pool swell analyses results to those reported in the ABWR licensing calculations showed reasonable agreement.
Redesign of an Adjustable Slope Moving Ground Plane Wind Tunnel
Authors: Boots Matthew T. , Hubbell Meagan L. , Angle Gerald M. , Pertl Emily D. , Smith James E.
Published: May 2012

Ground effect is an aerodynamic phenomenon that occurs when moving bodies come in close proximity to the ground. A “cushion” of air is created underneath the moving body which provides additional lift by increasing the local pressure under the body surface. To experimentally test ground effect vehicles, a unique wind tunnel is currently being redesigned and constructed at West Virginia University. This wind tunnel incorporates a rotating belt as the ground plane and a centrifugal fan that generates the air flow through the test section in the same direction as the belt’s rotation. The combination of a rotating belt and airflow is used to mimic ground effect in that it is representative of a body moving through still air in close proximity to the ground. The test section and fan assembly sit on a platform that is connected to a movable base frame. The base and testing platform connect through a pivot point that is capable of being raised upward to a maximum angle of fifty degrees to account for gravitational vector alignment between modeled and real world conditions. When the platform is raised and the belt is spinning, the structure is less stable and has the potential to create errors in force readings due to these oscillations, as well as the potential to tip in extreme wind conditions. Thus, the evaluation of the original design and the subsequent redesign are addressed in this research effort. To stabilize the wind tunnel, additional structural elements have been added downstream of the test section. Two telescoping poles were added to the end of the platform that will connect onto outriggers attached to the base structure. These poles and outriggers will form an A-shape support system when the platform is raised to any degree between zero and fifty. The width of the outriggers was calculated and then modeled in conjunction with the existing base structure. The final design is presented in this paper.
Utilizing the Turn-of-Nut Method to Stop Gasketed Bolted Joint Leakage
Authors: Brown Warren
Published: May 2012

If a pressure boundary bolted joint leaks during operation, then it is commonplace to re-tighten the joint either during swoop-down (lower pressure) or while the unit is online (full operating pressure). If engineers are involved, and often they are not, then it is common place to specify a torque to which the bolts should be re-tightened. The problem with that approach is that after even just a few days of operation, the nut factor for the bolt is completely unknown and so the torque specified has little relevance to the obtained load. In addition, the break-out torque for an operational stud can be in excess of twice the assembly torque, even at lower loads. To counteract these issues, an alternative approach is to use the Turn-of-Nut method to tighten the joint by a certain amount. This method is similar to that used for structural bolting, but is more complex, as the deflections of the flange and gasket must also be taken into account. This paper gives guidance on the factors that must be considered when determining the amount of nut turn to specify when using Turn-of-Nut and outlines practical guidelines for using the method on standard ASME B16.5 flanges.
Residual Stress Analysis of Bead Welded Low Alloy Steel Plate Specimens Subjected to Post Weld Heat Treatment
Authors: Yanagida Nobuyoshi , Saito Koichi
Published: May 2012

We developed a residual stress analysis method for bead welded low alloy steel JIS SQV2A (equivalent to ASTM A533B cl. 1) plates subjected to post weld heat treatment (PWHT). Two specimens were fabricated; each was a bead welded low alloy steel plate. One was in the as-welded condition (as-welded specimen) and the other was subjected to PWHT at 625°C (PWHT specimen). Strain gauges were used to measure the distributions of the residual stress in these specimens. The measurement data showed that the longitudinal stress at the center of a bead was 0 MPa and that in the heat-affected zone was 100 MPa. The transverse stress at the center of a bead was 200 MPa in the as-welded specimen. The absolute residual stress was decreased to less than 50 MPa for the PWHT specimen. We conducted finite element analyses to predict the distributions of welding residual stress in these specimens. The amount of phase transformation strain in low alloy steel was taken into account in the welding residual stress analysis, and creep strain was taken into account in the stress mitigation analysis. The results from the analyses agree well with the experimental results. These findings prove that welding residual stress can be simulated during a thermal elastic plastic (TEP) analysis by conducting a phase transformation and taking the generation of creep strain in the PWHT samples into consideration can be used to simulate that stress mitigation.
The Limit Load and Safety Assessment of Pressure Pipe With an External Pit Defect at High Temperature
Authors: Wang Bo , Zhou Changyu , He Xiaohua , Xue Jilin
Published: May 2012

Local pit is the common volume defect in high temperature pressure pipe which is widely used in the fields of electric plant, nuclear power station, petrochemical plant and so on. In this paper finite element analysis code ABAQUS was used to simulate limit load of high temperature pressure pipe with an external pit defect which is in service for 105 hours. Four-point bending loading model was applied to calculate the limit load of the pipe. There are three dimensionless factors: relative depth, relative gradient and relative length which characterized the shape of an external pit defect. Orthogonal test of three factors at four different levels was carried out to analyze the sequence of the influence of these three parameters. In present paper when the maximum principal strain reaches 2%, the corresponding load is selected as the limit load. According to this strain criterion and isochronous stress strain data of P91 steel, limit load of high temperature pressure pipe with an external pit was determined by using ABAQUS. Firstly, isochronous stress strain data was generated and was inputted into ABAQUS as equivalent elastic-plastic constitutive relation. Then, sustained load versus cumulative strain curves at high temperature during service was obtained after the simulation. At last, limit loads of high temperature pipe during service time was determined based on 2% total strain criterion. In order to obtain the safety assessment curve of high temperature pipe, five types of limit loads for pressure pipe with an external pit were needed: ultimate limit bending moment, limit internal pressure, limit bending moments at the pressure of 0.25PL,0.5PL and 0.75PL individually. 16 sets of data formed 16 groups of curves which expressed the relationship between the ratio of limit pressure and the ratio of limit bending moment for defective pipe and non-defective pipe. Based on the calculation results of limit load for pipe with 16 kinds of defects, a set of limit load formulae were established through multiple nonlinear regression of relative depth, relative gradient and relative length. So the equations of limit load and safety assessment for pressure pipe with an external pit under combined loading of pressure and bending moment were obtained. The results could provide a reference for safety assessment of high temperature creep pressure pipe with local pit defect.
Non-Probabilistic Failure Assessment Methodology About Titanium Pipes With Cracks
Authors: Dai Qiao , Zhou Changyu , Peng Jian
Published: May 2012

In this paper, the non-probabilistic failure assessment method for a pipe with crack was proposed, and interval model was applied in this assessment method. Compared with the deterministic approach, the assessment parameters were regarded as interval parameters in the non-probabilistic method, which could reflect the uncertainty of data and avoid the unsafety of results caused by the scatter of these parameters. On the other hand, compared with traditional probabilistic method, the non-probabilistic method only needs the range or bound of the parameters rather than detailed statistics information of the parameters which may be uneasy to be obtained from practical engineering. So the new assessment method reduces the request for detailed statistics properties of parameters. In this paper, load, material mechanical properties and the size of crack were treated as interval parameters, and the non-probabilistic failure assessment method was established based on the level 2 normal assessment of the BS 7910:2005. In this case, the assessment point (Lr, Kr) is not a deterministic value, Lr and Kr would vary in a certain interval. As a consequence, the assessment point was changed into a rectangle zone, and the non-probabilistic failure measure for pipe with crack could be obtained by the variation of the rectangle. The non-probabilistic failure measure can be defined as the ratio of the area of failure region to the total area of the rectangle. At last, the non-probabilistic failure assessment method was used to evaluate a titanium pipe, and the analysis results were compared with the results of deterministic method, probabilistic method according to Monte-Carlo and partial safety factors method, respectively. The analysis results sufficiently demonstrated that the new non-probabilistic failure assessment method proposed in this paper was feasible and available.
Thermo-Fluid-Dynamic Design of Reciprocating Compressor Cylinders by Fluid Structure Interaction (FSI)
Authors: Traversari Riccardo , Rossi Alessandro , Faretra Marco
Published: May 2012

Pressure losses at the cylinder valves of reciprocating compressors are generally calculated by the classical equation of the flow through an orifice, with flow coefficient determined in steady conditions. Rotational speed has increased in the last decade to reduce compressor physical dimensions, weight and cost. Cylinder valves and associated gas passages became then more and more critical, as they determine specific consumption and throughput. An advanced approach, based on the new Fluid Structure Interaction (FSI) software, which allows to deal simultaneously with thermodynamic, motion and deformation phenomena, was utilized to simulate the complex situation that occurs in a reciprocating compressor cylinder during the motion of the piston. In particular, the pressure loss through valves, ducts and manifolds was investigated. A 3D CFD Model, simulating a cylinder with suction and discharge valves, was developed and experimentally validated. The analysis was performed in transient and turbulent condition, with compressible fluid, utilizing a deformable mesh. The 3D domain simulating the compression chamber was considered variable with the law of motion of the piston and the valve rings mobile according to the fluid dynamic forces acting on them. This procedure is particularly useful for an accurate valve loss evaluation in case of high speed compressors and heavy gases. Also very high pressure cylinders, including LDPE applications, where the ducts are very small and MW close to the water one, can benefit from the new method.
Microscale Flow Pumping Inspired by Rhythmic Tracheal Compressions in Insects
Authors: Aboelkassem Yasser , Staples Anne E. , Socha John J.
Published: May 2012

Inspired by the physiological network of insects, which have dimensions on the order of micrometers to millimeters, we study the airflow within a single model insect tracheal tube. The tube undergoes localized rhythmic wall contractions. A theoretical analysis is given to model the airflow within the tracheal tube. Since flow motions at the microscale are dominated mainly by viscous effects, and the tube has radius, R, that is much smaller than its length, L, (i.e. δ = R/L ≪ 1), lubrication theory for axisymmetric, viscous, incompressible flows at low Reynolds number (Re ∼ δ) is used to model the problem mathematically. Expressions for the velocity field, pressure gradient, wall shear stress and net flow produced by the driving tube wall contractions are derived. The effect of the contraction amplitudes, time lag, and spacing between two sequences of contractions on the time-averaged net flow over a single cycle of wall motions is investigated. The study presents a new, insect-inspired mechanism for valveless pumping that can guide efforts to fabricate novel microfluidic devices that mimic these physiological systems. A x-ray image that shows the tracheal network of the respiratory system of an insect (Carabid beetle) and the associated locations of these rhythmic contractions are shown in figure (1) to promote this study.
Time History Broadening
Authors: Strzelczyk Andrzej T.
Published: May 2012

Section 6.5.2 of N283.3-10 of the CSA Standard [1] describes analytical methods for seismic qualification of nuclear components. Clause 6.5.2.2 of this Section instructs how to prepare seismic input for the time history method, specifically it states: “Time-histories of support point motion (displacement, velocity, or acceleration) may be used as dynamic inputs to components. To take into account the effects of possible frequency variations of component and structure, the analysis shall be carried out using three different time-history excitations. These time-histories shall be obtained by varying time scale of the original support point time-history by (a) 1.0; (b) 1 - Δfj/fj; and (c) 1 + Δfj/fj, where fj = the dominant structural frequency; Δfj = a parameter defining the frequency variation due to uncertainties in structural soil properties. The most severe effects obtained from these three time history analyses shall be considered in the design of the components. Notes: (1) A value of 15% for Δfj/fj may be used for the time-history analysis specified in this Clause; (2) For structures directly on bedrock, a value of Δfj/fj = 0% may be used”. This paper identifies some ambiguities in the approach described above. It shows, by theory and examples, that significantly different responses are obtained depending on which form of excitation is used (acceleration, velocity or displacement). In a typical acceleration excitation approach, the response may be over or under estimated. To remove this ambiguity, the paper proposes a simple modification of the broadening procedure described in [1]. The problem discussed in this paper may also be meaningful for the broadening time history described in Appendix N of ASME Code [2].
Effect of Velocity Dependence on Sliding Characteristic of Sliding Types of Base Isolation Systems Each With Numerous Sliding Interfaces
Authors: Tsai C. S. , Su H. C. , Chiang T. C.
Published: May 2012

Current structural analysis software programs offer few if any applicable device-specific hysteresis rules or nonlinear elements considering the velocity effect on the mechanical behavior of the multiple friction pendulum system (MFPS) with numerous sliding interfaces. Based on the concept of subsystems, here we propose an equivalent series system that adopts existing nonlinear elements with parameters systematically calculated and mathematically proven through rigorous derivations to take into account the velocity dependence effect on the sliding behavior of the sliding interfaces in the sliding type base isolators. Evaluations of the velocity dependence effect on the features of the sliding motions on numerous sliding interfaces have also been carried out. Results from the given examples demonstrate that the sliding motions of sliding interfaces considering velocity dependence behave quite differently from those excluding the effect of velocity dependence.
Study on In-Flow Vibration of Cylinder Arrays Caused by Cross Flow
Authors: Nakamura Tomomichi , Nishimura Keisuke , Fujita Yoshiaki , Kohara Chihiro
Published: May 2012

The authors have studied the in-flow vibration phenomena of cylinder arrays caused by cross-flow in the low Reynolds number range around Re=800. This Reynolds number range has been studied because it is the range where symmetric vortex shedding occurs. This report is our first trial to study the in-line fluidelastic vibration of cylinder arrays. In initial tests, the flow velocity was increased up to the maximum achievable level by the test equipment. However, it was found that the array’s cantilever tube supports resulted in large static tube deflections due to static drag forces. The cylinder array tube supports have therefore been replaced by thin plates supported at both ends. The cylinders are set to be flexible both in the streamwise direction and the direction transverse to the flow. The obtained results of these two patterns are also compared with previous cantilevered data. The origin of the observed vibrations whether a self-induced mechanism or vortex shedding is discussed in detail.
Revised Guidance on Residual Stresses in BS7910
Authors: Sharples John , Gill Peter , Wei Liwu , Bate Steve
Published: May 2012

A major revision of the British Standard BS7910 on “Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures” is being planned for issue in 2012. This paper provides an overview of the proposed revised guidance in relation to recommended weld residual stress profiles. As such, the paper is focussed on the proposed revised Annex Q of BS7910 which deals with residual stress distributions in as-welded joints.
Linear Friction Damper Consisted of Cylindrical Block and Inclined Lever (Improvement to Avoid Sprag-Slip Problem and Analytical Model to Verify Cause)
Authors: Yamaguchi Hideya , Yoshida Hidehisa
Published: May 2012

For the passive isolation systems, the ordinary friction damper of constant friction force has performance limitations. This is, because the isolation characteristic declines and the displacement remains apart from the equilibrium position after the disturbance disappears, when the friction force is large. It is known that the above drawbacks are improved when the friction force varies depending on the displacement. The authors have proposed a new type of friction damper in our previous paper. This friction damper uses an inclined lever, which contacts the cylindrical block by means of a rotational spring. The angle of inclination of the lever varies together with the displacement of the cylindrical block. Then, the normal and friction forces on the contact surface vary depending on the displacement. However, “Sprag-slip” vibration occurred in some cases in the experiments. This paper investigates the cause of the vibration and a design to prevent it. Then, an analytical model is proposed to simulate the problem and to estimate the effect of improvement.