bluuebunny/crossref_metadata_2025 huggingface dataset:
Catalytic and Non-Catalytic Combustion of Propane in a Meso-Scale Heat Recirculating Combustor
Authors: Wierzbicki Teresa A. , Lee Ivan C. , Gupta Ashwani K.
Published: November 2014

The results from the observed combustion behavior of propane over platinum and rhodium catalysts in a meso-scale heat recirculating combustor are presented. The extinction limits, conversion, product selectivity/yield, and activation energy using the two catalysts were compared in an effort to determine their performance using a liquid fuel. The extinction limits were also compared to those of non-catalytic combustion in the same reactor. The results showed that the addition of a catalyst greatly expanded the range of stable operating conditions, in respect to both extinction limits and flow rates supported. The Rh catalyst was found to exhibit a higher propane conversion rate, reaching a maximum of 90.4% at stoichiometric conditions (as opposed to the 61.4% offered by the Pt catalyst at lean conditions); however, the Pt catalyst had superior CO2 selectivity for most studied conditions, indicating higher combustion efficiency. The Pt catalyst also had a significantly smaller activation energy (13.8 kJ/mol) than the Rh catalyst (74.7 kJ/mol), except at equivalence ratios richer than Φ = 1.75 (corresponding to catalyst temperatures below 500 °C), where it abruptly changed to 211.4 kJ/mol, signifying a transition from diffusion-limited reactions to kinetically limited reactions at this point. The results reveal that Rh would be a more suitable catalyst for use in a liquid-fueled meso-scale combustor, as fuel conversion has been shown to be a limiting factor for combustion stability in these systems.
Flue Gas Desulfurization Wastewater Treatment for Coal-Fired Power Industry
Authors: Pakzadeh Behrang , Wos Jay , Renew Jay
Published: November 2014

The United States Environmental Protection Agency (USEPA)’s announcement that it will revise the effluent limitation guidelines for steam electric power generating units could affect not only how power plants use water, but also how they discharge it. The revised guidelines may lower discharge limits for various contaminants in flue gas desulfurization (FGD) wastewater including mercury, selenium, arsenic, and nitrate/nitrite. Although the specific details of the guidelines are unknown at present, the power industry is evaluating various technologies that may address the new effluent limitation guidelines and promote water conservation. Moreover, the power industry is looking for avenues to increase water usage efficiency, reuse and recycle throughout its plant processes. Final rule approval is expected by the middle of 2014 and new regulations are expected to be implemented between 2017 and 2022 through 5-year NPDES permit cycles. discharge limits for various contaminants including arsenic, mercury, selenium, and nitrate/nitrite [1]. These pollutant limits may be below the levels achievable today with conventional treatment [2].

A growing interest exists in zero liquid discharge (ZLD) facilities and processes in power plant operations. Potentially stringent discharge limits along with water conservation and reuse efforts are two of the major drivers to achieve ZLD. Potential pollutant levels are so low that ZLD may be the best option, if not an outright requirement [1].

Thermal ZLD systems have been the subject of increased interest and discussion lately. They employ evaporating processes such as ponds, evaporators and crystallizers, or spray dryers to produce a reusable water stream and a solid residue (i.e. waste). Evaporators and crystallizers have been employed in the power industry for a number of years. However, typical A growing interest exists in zero liquid discharge (ZLD) facilities and processes in power plant operations. Potentially stringent discharge limits along with water conservation and reuse efforts are two of the major drivers to achieve ZLD. Potential pollutant levels are so low that ZLD may be the best option, if not an outright requirement. A key disadvantage of thermal ZLD is its high capital cost. One way to reduce this cost is to pre-treat the liquid stream using innovative membrane technologies and reverse osmosis (RO).
Inclusion of a Simple Dynamic Inflow Model in the Blade Element Momentum Theory for Wind Turbine Application
Authors: Chen Xiaomin , Agarwal Ramesh
Published: November 2014

It is well established that the power generated by a Horizontal-Axis Wind Turbine (HAWT) is a function of the number of blades B, the tip speed ratio λr (blade tip speed/wind free-stream velocity) and the lift to drag ratio (CL/CD) of the airfoil sections of the blade. The previous studies have shown that Blade Element Momentum (BEM) theory is capable of evaluating the steady-state performance of wind turbines, in particular it can provide a reasonably good estimate of generated power at a given wind speed. However in more realistic applications, wind turbine operating conditions change from time to time due to variations in wind velocity and the aerodynamic forces change to new steady-state values after the wake settles to a new equilibrium whenever changes in operating conditions occur. The goal of this paper is to modify the quasi-steady BEM theory by including a simple dynamic inflow model to capture the unsteady behavior of wind turbines on a larger time scale. The output power of the wind turbines is calculated using the improved BEM method incorporating the inflow model. The computations are performed for the original NREL Phase II and Phase III turbines and the Risoe turbine all employing the S809 airfoil section for the turbine blades. It is shown by a simple example that the improved BEM theory is capable of evaluating the wind turbine performance in practical situations where operating conditions often vary in time.
Generator Auxiliary Gas System Upgrades
Authors: McPhearson John , Ramirez Gutierrez Blanca
Published: November 2014

Much has been done in recent years to upgrade turbines and improve plant efficiency. Recent years have also seen improvements and upgrades in the hydrogen cooled generator auxiliaries that improve plant efficiency and safety. A summary of upgrades and new products that are available and that have been implemented are presented in this paper.
Wellhead Scaling Problems in Geothermal Power Plants Addressed Using a Needle Valve Derivative
Authors: Atlason Reynir S. , Unnthorsson Runar
Published: November 2014

One of the most frequent problems in geothermal power plants is scaling. If scaling is allowed to build in the wellhead it can hinder the flow from the well. In this study we investigate how exactly that problem was solved at HS Energy in Iceland. We look at the problem, describe it and how it has been successfully solved. The solution, a valve called the Elli valve, which can be regarded a derivative of the Giffard’s injector, is then described. This valve has been shown to allow for a better flow control, less problems with regards to scaling removal and has economical advantages over other control valves. This solution should allow geothermal power plants dealing with scaling problems to use the presented solution to solve it effectively, in a cost efficient manner.
Necessity is the Mother of Invention: The Dawn of Domestic Geothermal Turbine Repairs in Iceland
Authors: Atlason Reynir S. , Gunnarsson Almar , Unnthorsson Runar
Published: November 2014

Even though the Icelandic public relies greatly on geothermal power, to date, intensive maintenance procedures on the geothermal turbines have been conducted by foreign contractors. Such repairs are very time consuming, risky, expensive and leak capital out of the country. This has been discussed greatly within the industry and plans have been made on how the power companies, along with domestic machine shops can address this problem. However, in spring 2013 a turbine failure was observed in a routine quadrennial check at the Nesjavellir geothermal power plant. Corrosion products where found on the last set of the labyrinth packing and the rotor had been worn down approximately 8 mm radius. The backup rotor was also in a non-operational state. The unexpected downtime in power production had to be minimized in order to fulfill contracts. Because of time constraints, foreign service companies were not considered to be feasible due to their waiting queues and the time required for shipping overseas. This scenario initiated collaboration between the power company and domestic machine shops to manufacture spare parts and conduct the overall repair on site. This was due to several reasons such as; currency exchange rate, machines and know-how at the machine shops had improved over the last decade and the fact that the power company was ready to pay for the development cost. This paper presents the problem, how it was solved collaboratively domestically in only a fraction of time that conventional procedures would have taken. The paper investigates the causes of the turbine failure and provides a description the current state of turbine repair facilities in Iceland.
Closed-Form Stress Intensity Factor Solutions for Circumferential Through-Wall Cracks in Cylinder
Authors: Shim Do-Jun , Xu Steven , Lee Darrell
Published: November 2014

The stress intensity factor (SIF) solutions for circumferential through-wall cracks (TWCs) in cylinders are used for various fracture mechanics analyses. For example, it can be used to calculate the crack growth rate for stress corrosion cracking and to calculate the elastic J value which is needed to obtain the total J value for crack stability calculations. Thus, numerous SIF solutions have been published for circumferential TWCs in cylinders under axial tension and global bending. However, recently, it has been indicated that there is a need (e.g., for xLPR software code and ASME BPV Code Case N-513) to expand the solutions to wider ranges of crack lengths and cylinder geometries.

In this paper, solutions from Lacire et al., API 579-1/ASME FFS-1 and Zang (SINTAP) were compared against results from independent finite element (FE) analyses performed by the authors. From these comparisons, it was demonstrated that the Zang (SINTAP) solution provided the most accurate results. Hence, additional FE calculations were performed to expand the Zang (SINTAP) solution to cover Ri/t between 2 and 100 and crack length between 1% and 85% of the cylinder circumference. Furthermore, for practical applications, closed-formed solutions were developed for both axial tension and global bending loads. These new solutions were planned for use in the xLPR software code and ASME BPV Code.
Preliminary Piping Sizing and Pressure Pulsation Evaluation
Authors: Passeri Marco , Generosi Stefano , Bagagli Riccardo , Maggi Carmelo
Published: November 2014

LDPE production developments require processing equipment with increased capacities and existing applications uprating. They include large reciprocating compressors with several cylinders operating at very high pressures. Selection of piping size, as these special components have very long delivery time, including reactors and intercoolers, requires a careful analysis to be performed at an early stage of a project to properly estimate the costs. A preliminary evaluation should be made during the bid stage using compressor data sheet and P&I diagram. A specific pre-study linked to compressor sizing program can be used for preliminary cost estimation.

Prior to piping purchase order issue, based on the first issue of real layout around compressor, the above evaluation has to be confirmed by a preliminary pulsation study.

Once the plant arrangement will be finalized, the final acoustic study will have to be performed. Usually such study will only result in minor adjustments to the design not involving the piping size.
STYLE Project: A Large Scale Ductile Tearing Experiment on a Cladded Ferritic Pipe
Authors: Moinereau Dominique , Le Delliou Patrick , Keim Elisabeth , Nicak Tomas
Published: November 2014

Within the framework of the FP7 European project STYLE, a large scale experiment has been performed at EDF on a cladded ferritic pipe. The objective of such an experiment was to investigate transferability of material properties from small specimens to large scale components.

The large scale experiment involves applying 4-point bending under displacement control at room temperature to a clad ferritic steel pipe with an internal surface crack. The goal of the experiment is to initiate ductile crack growth and track the resulting stable crack growth until the surface flaw fails by producing a through-wall crack.

The test specimen is representative from a surge line consisting of a clad ferritic pipe with an outer diameter of 420 mm, length of 520 mm, and base metal wall thickness of 31 mm, with an internal austenitic stainless steel cladding layer of thickness 5 mm. The base metal is a low alloy 20MnMoNi55 steel (corresponding to the specifications of an SA 508 Grade 3, Class 1 steel), and the necessary extensions are made of a high strength ferritic steel.

A wide range of instrumentation was implemented to provide data for mock-up behavior understanding and detect the ductile tearing initiation during the test.

The test has been conducted with full success on the EDF 4 point bending test facility. After the experiment, samples have been taken from the mock-up for full SEM fractographic examinations of the fracture surface for identification of failure modes.

The present paper describes the large scale experiment and presents the main experimental results and data. A synthesis of SEM fractographic examinations is also presented, to better understand the rupture behavior during the test.
A New Method for the Generation of Representative Time-Domain Turbulence Excitations
Authors: Antunes Jose , Piteau Philippe , Delaune Xavier , Borsoi Laurent
Published: November 2014

In this paper we address the issue of generating, from the spectral and spatial parameters of turbulent flow excitations, time-domain random excitations suitable for performing representative nonlinear numerical simulations of the dynamical responses of flow-excited tubes with multiple clearance supports. The new method proposed in this work, which is anchored in a sound physical basis, can effectively deal with non-uniform turbulent flows, which display significant changes in their spatial excitation properties. Contrary to the classic Shinozuka technique, which generates a large set of correlated physical forces, the proposed method directly generates a set of correlated modal forces. Our approach is particularly effective leading to a much smaller number of generated time-histories than would be needed using physical forces to simulate the turbulence random field. In the case of strongly non-uniform flows, our approach allows for a suitable decomposition of the flow velocity profile, so that the spectral properties of the turbulence excitation are modeled in a consistent manner. The proposed method for simulating turbulence excitations is faster than Shinozuka’s technique by two orders of magnitude. Also, in the framework of our modal computational approach, nonlinear computations are faster, because no modal projection of physical turbulent forces is needed. After presenting the theoretical background and the details of the proposed simulation method, we illustrate it with representative linear and nonlinear computations performed on a multi-supported tube.
A Case Study in Temper Embrittlement of Fluidized Catalytic Cracking Components
Authors: Bowen Matthew , Newell William F. , Penso Jorge
Published: November 2014

As described in API RP 571, temper embrittlement is the reduction in toughness due to a metallurgical change that can occur in some low alloy steels as a result of long term exposure in the temperature range of about 650°F to 1070°F (343°C to 577°C). The loss of toughness is not evident at operating temperatures; however, equipment that is temper embrittled may be susceptible to brittle fracture during start-up and shutdown. 2.25 Chromium 1 Molybdenum steel used in the petrochemical industry is known to be susceptible to temper embrittlement. Most guidance to prevent temper embrittlement is oriented to heavy wall hydroprocessing reactors.

In this work, a case history is presented where Fluidized Catalytic Cracking (FCC) components less than one inch in thickness exposed to temperatures in the 900°F to 1000°F (482°C to 538°C) range experienced temper embrittlement.

Metallurgical analysis that included chemical analysis, microstructure observation, and charpy impact testing at different temperatures before and after heat treatment helped to identify the embrittlement cause.

Several considerations to mitigate the risk in the short term including inspection, definition of minimum metal temperature to prevent brittle fracture, fitness for service, and modification of operational procedures, as well as long term considerations, including pipe component replacement, are described. Additional work regarding the selection of filler metals, welding procedure qualification tests that include step cooling tests, and learning that included bead sequence and heat input controls are also described.

Applicable API RP 934-A [Ref. 6] recommendations were incorporated into the project specification for this work, such as the consideration of chemical restrictions for this alloy, not only for heavy wall applications but also for thinner wall applications working in the temper embrittlement range.
Tests on SENT Specimens to Study Geometry Effects in the Brittle to Ductile Transition
Authors: Le Delliou Patrick , Geniaut Samuel
Published: November 2014

The accurate prediction of ductile fracture behaviour plays an important role in structural integrity assessments of critical engineering structures under fully plastic regime, including nuclear reactors and piping systems. Many structural steels and aluminium alloys generally exhibit significant increases in fracture toughness, characterized by the J-integral, over the first few mm of stable crack extension (Δa), often accompanied by large increases in background plastic deformation. Conventional testing programs to measure crack growth resistance (J–Δa) curves employ three-point bend, SEN(B), or compact, CT. However, laboratory testing of fracture specimens to measure resistance curves (J–Δa) consistently reveals a marked effect of absolute specimen size, geometry, relative crack size (a/W ratio) and loading mode (tension vs. bending) on R-curves. These effects observed in R-curves have enormous practical implications in defect assessments and repair decisions of in-service structures under low constraint conditions. Structural components falling into this category include pressurized piping systems with surface flaws that form during fabrication or during in-service operation.

This paper presents the on-going work to study geometry effects (e.g. triaxiality effects) in the brittle to ductile transition of carbon-manganese steels, the basic idea being to compare the results obtained on these specimens with the results obtained on CT specimens.

A preliminary program was previously conducted at room temperature using deeply notched specimens (Le Delliou, 2012). Finite element computations were made to optimize the specimen shape and to develop the η-factor, the shape factor F (to compute K) and the normalized compliance μ.

For the present program, new specimens have been machined with shallower notches (a/W = 0.4), to get a0/W = 0.5 after fatigue pre cracking. Fatigue pre cracking was conducted in 4-point bending to avoid damaging the back of the notch. Moreover, the specimens have been cut in the TS (Transverse-Short) direction of the plate to get lower toughness properties, and less plasticity during the tests.

Tests at room temperature have been conducted first to validate the revised test procedure. Then, the SENT specimens have been tested at −100°C, −60°C, and −40°C, together with CT specimens.
Fatigue Monitoring Approaches for Power Plants
Authors: Jouan Benoît , Bergholz Steffen , Rudolph Jürgen
Published: November 2014

Modern state-of-the-art fatigue monitoring approaches gain in importance not only as part of the ageing management of nuclear power plant components but also in the context of conventional power plants and renewables such as wind power plants. Consequently, lots of operators have to deal with demanding security requirements to ensure the safe operation of power plants and to cope with plant lifetime extension (PLEX) related issues.

AREVA disposes of a long tradition in the development of fatigue and structural health monitoring solutions. Nuclear and conventional power plant applications require the qualified assessment of measured thermo-mechanical loads. The methodology is transferable to mechanical loading conditions such as those of wind energy plants. The core challenge is the identification and qualified processing of realistic load-time histories. The related methodological requirements will be explained in detail.

In terms of the nuclear industry, the ageing management of power plant components is nowadays a main issue for all actors: states, regulatory agencies, operators, designers or suppliants. As regards fatigue assessment of nuclear components stringent safety standards imply the consideration of new parameters in the framework of the fatigue analysis process:

• new design fatigue curves, consideration of environmental fatigue (EAF) parameters and

• stratification effects.

In this general context AREVA developed the integral approach AREVA Fatigue Calculation (AFC) with new tools and methods in order to live up to operators’ expectations: Simplified Fatigue Estimation (SFE), Fast Fatigue Evaluation (FFE) and Detailed Fatigue Check (DFC). Based on real measured thermal loads and superposed mechanical loads the Fast Fatigue Evaluation (FFE) process allows a highly automated and reliable data processing to evaluate cumulative usage factors of mechanical components. Calculation and management of results are performed within the fatigue assessment software FAMOSi (FAatigue MOnitoring System integrated), thus impact of operating cycles on components in terms of stress and fatigue usage can be taken into account in order to plan optimized decisions relating to the plant operation or maintenance activities.

This paper mainly describes the fatigue and structural health methodologies developed within the AREVA Fatigue Concept (AFC).
Development of Fiber-Optic Probes to Measure Two-Phase Flow Dynamic Parameters in Support of Flow-Induced Vibration Studies
Authors: Pettigrew M. J. , Besner B. , Mureithi N. W. , Lafrance T. , Patrick J. M.
Published: November 2014

Flow-induced vibration in two-phase flows requires the knowledge of flow regime and detailed flow characteristics. This paper outlines the development of fiber-optic probes to measure void fraction, local flow velocity and characteristic size (i.e., bubble diameter) of the two-phase mixture. The principle of operation of such probes is based on the difference in index of refraction between the liquid phase and the gas phase when in contact with a fiber-optic probe supplied with a laser light. The reflected signal levels for the gas phase and the liquid phase are very different thus providing a reliable measure of void fraction.

The paper describes the development of fiber-optic probes for measurements of internal two-phase flow in pipes and of external flow across a tube bundle. The use of double probes allows the measurements of local flow velocity and bubble size. Some detail measurements of flow in the gap between tubes in cross flow are presented. The fabrication of the very small and fragile probes required much development effort. The paper describes the difficulties and the solutions to assure good quality probes. Some data processing and data interpretation issues are also discussed.
Tube Rupture Study of a 300 Bar Heat Exchanger
Authors: Megens Bas
Published: November 2014

From a safety study a concern was raised about the probability of instant tube rupture in 300 bar heat exchangers in LDPE plants. A study has been performed in a multidisciplinary team to determine the potential failure mechanisms. Among the possible potential failure mechanisms those which can cause instant tube rupture were identified. Based on these potential failure mechanisms, non-destructive examinations were performed to investigate if these failure mechanisms were present and online acoustic emission measurements were performed to investigate during which process conditions the damage occurred. Eventually a cooler was dismantled to investigate the root cause of the damage. This paper describes the entire study.
Design-by-Analysis Methods for Asymmetric or Unbalanced Cylindrical Composite Pressure Vessels
Authors: Camilleri Duncan , Ellul Brian , Muscat Martin
Published: November 2014

The combination of fibre volume fraction, fibre orientation and lay-up sequence in composite materials makes it possible to design a multitude of composite pressure vessels and pipes. Analytical models, based on the classical laminate theory and numerical predictive techniques offer a means to optimize the lay-up sequence in order to maximize the strength to weight / cost ratio. This study looks at the validity of using analytical models prescribed in the design by analysis filament wound composite standards and compares the results with realistic test and numerical models. The results show that the classical laminate theory accurately establishes the design load in symmetric and balanced lay-up laminates when appropriate material properties are assigned. However in the case of asymmetric or unbalanced lay-up sequences, the bending and twisting stiffness geometrically strengthens the pipes such that the classical hoop and axial loading conditions based on isotropic material properties, no longer apply. In such instances the analytical solutions can underestimate the design load by more than 33%. An analytical solution that accurately establishes the loading configuration and magnitude is required. On the other hand numerical models gave good agreement with the experimental test results immaterial of the lay-up sequences, when appropriate end coupling, pressure loading and material properties are applied.
Revised η-Factors for 3P SE(B) Fracture Specimens Incorporating 3-D Effects
Authors: de Souza Rodolfo F. , Ruggieri Claudio
Published: November 2014

Standardized procedures to measure cleavage fracture toughness of ferritic steels in the DBT region most commonly employ three-point bend fracture specimens, conventionally termed SE(B) or SENB specimens. The evaluation protocol of fracture toughness for these crack configurations builds upon laboratory records of load and crack mouth opening displacement (CMOD) to relate plastic work with J (or, equivalently, CTOD). The experimental approach employs a plastic η-factor to relate the macroscale crack driving force to the area under the load versus crack mouth opening displacement for cracked configurations. This work provides revised η-factors derived from CMOD records applicable to estimate the J-integral and CTOD in SE(B) specimens with varying crack size and specimen configuration. Non-linear finite element analyses for plane-strain and 3-D models provide the evolution of load with increased CMOD which is required for the estimation procedure. The analysis matrix considers SE(B) specimens with W = 2B and W = B configurations with and without side grooves covering a wide range of specimen thickness, including precracked Charpy (PCVN) specimens. Overall, the present results provide further validation of the J and CTOD evaluation procedure currently adopted by ASTM 1820 while, at the same time, giving improved estimation equations for J incorporating 3-D effects which enter directly into more accurate testing protocols for experimental measurements of fracture toughness values using 3P SE(B) specimens.
Reconsidering the Effect of Stress Biaxiality on Pipe Burst (Effect of Axial Loading on the Onset of Plastic Instability)
Authors: Yoshii Kan , Meshii Toshiyuki
Published: November 2014

Pipe failure under internal pressure loading is understood as due to the onset of plastic instability. Law et al. [1] extended the Considere’s construction [2], which predicts the onset of plastic instability for tensile test specimen, so that it can predict the onset of plastic instability, and thus burst of pipes under internal pressure. They noted that “It is important to note that the reduced stress and strain where instability occurs is not a result of the biaxial stress state, but of the vessel geometry where increased stress comes from both increased inner diameter and reduced wall thickness” [1]. However, they intrinsically assumed that the cylinder plane that experiences instability is in plane strain state. Considering the fact that power plant pipes are often subjected to axial force from sources such as thermal expansion/contraction or fixing, the effect of deviation from the plane strain conditions should be considered.

For this purpose, the onset of plastic instability of the elastic-plastic internally pressurized 1) 2D plane strain pipe, 2) 3D pipe and 3) 3D pipe additionally subjected to axial force, were compared. The results showed that the onset of plastic instability could be monitored at the pressure when pRm−σθt > 0 for all the cases. Here, Rm, σθ, and t are the current mean radius, circumferential stress at mean radius and thickness at pressure p. However, the strain at this instability pressure showed non-negligible change due to presence of axial loading. On this meaning, the biaxiality affected the onset of plastic instability.
Probabilistic Fracture Analysis of Circumferentially Cracked Pipes
Authors: Bhimanadam V. R. , Blom F. J.
Published: November 2014

In the framework of the R6 development programme on leak before break NRG developped a probabilistic fracture-mechanics model for analyzing circumferential through-walled cracked pipe made of Type 304 stainless steel, subjected to bending loads. An elastic-plastic analysis has been carried out using ANSYS for estimating J-integral as a function of moment load. The validity of the J-integral based on the ANSYS calculations was evaluated by comparison with LBB.ENG2 method and Rahman’s calculations.

Probabilistic fracture analysis has been carried out using ANSYS Probabilistic Design System (PDS) module to find out the failure probability of a pipe as a function of applied moment. These results have been compared with LBB.ENG2 probabilistic calculations, which has been developed using MATLAB.

To achieve high efficiency, accuracy and robustness to design structural component with a low probability of failure, Advanced sampling methods (ADIS) have been used for probabilistic calculations. These ADIS results have been compared with Monte Carlo probabilistic results.

The probabilistic method is subsequently extended to a Leak Before Break case (LBB). It is demonstrated that the probability of failure reduces when more probabilistic data for input parameters is added instead of using deterministic safety factors.
Streamwise Fluidelastic Forces in Tube Arrays Subjected to Two-Phase Flows
Authors: Olala Stephen , Mureithi Njuki W. , Sawadogo Teguewinde , Pettigrew Michel J.
Published: November 2014

Detailed unsteady fluid force and phase measurements for a single tube oscillating purely in the streamwise direction in a rotated triangular tube array subjected to air-water two-phase cross-flow have been conducted in this study for homogeneous void fractions between 0% and 90%. Additionally the streamwise steady forces were measured in two-phase flow at a Reynolds number (based on the pitch velocity), Re = 7.2 × 104. The results are compared to those previously obtained for transverse direction oscillations. The measurement results show that the magnitude of the force coefficients for both directions (drag and lift) is comparable both in trend and quantitatively. However, the phase in the drag direction is negative while that for the lift is positive. The range of variation of the phase is also significantly smaller for the drag direction. Noting that negative phase corresponds to positive damping and vice versa, this observation confirms previous findings of lack of instability in the drag direction for a single flexible tube in a rotated triangular tube array. The drag steady fluid force coefficients were found to increase with dimensionless displacement in the flow direction for the entire range of void fractions considered. The derivative of the measured steady fluid force coefficient, which is an important factor in fluidelastic instability study using the quasi-steady model, was found to remain positive in the drag direction. The effect of void fraction on the unsteady fluid force coefficient and other dynamic parameters such as hydrodynamic mass and damping are also discussed.
Breech Lock Exchangers, Obtaining Leak Free Performance
Authors: Reeves David , Clover David
Published: November 2014

High pressure screw plug (also called breech lock) exchangers are arguably the most complicated bolted connection in a refinery. After traveling around the world helping facilities turn these exchangers from chronic leakers (from internal tubesheet and external diaphragm and B style shell leaks) to one of the most reliable heat exchangers in the plant, it is very clear to me that manufacturers, engineers and mechanics struggle to correctly understand the interactions between gaskets, internal pressure, the two circles of external push bolts that are part of A style exchangers and all the internal parts.

Some manufactuers have given up on trying to make these connections operate leak free, and prefer to weld in the tubesheets and diaphragms. This significantly adds to the cost and time needed to open and close these exchangers, as special equipment is needed to machine out the parts and weld them back together again.

There are a handful of equipment manufacturers that build these exchangers, and while there are differences from one manufacturer to the next, once the basic design is understood, the reader should be able understand that they are all basically the same when it comes to the few critical steps that must be followed when opening and closing these exchangers.

In order to obtain reliable leak free performance, all the basic sealing tools must be employed, including:

1. A spreadsheet that will easily analyze the critical variables;

2. Correct gasket selection;

3. Correct assembly procedures that focus on important steps including proper spacing of internal parts and obtaining consistent thread friction;

4. And finally hot torqueing the exchangers after startup.

The goal of this paper to provide the end-user with a good understanding for how parts interact and how the bolted connections function, so that they might also achieve reliable, leak free performance. This paper will explain:

1. How the connections work;

2. Common misunderstanding about screw plug exchangers;

3. Pressure Testing Screw Plug Exchangers;

4. Analyzing the design and calculating the important variables;

5. The key assembly steps that must be included in all assembly procedures;

6. Important design considerations when building new exchangers.
Global Analysis of Shell Key Gasification Equipment Based on Finite Element Method
Authors: Shen Jun
Published: November 2014

Coal gasification is a key technology for clean coal conversion with high efficiency. During the past decade, more than twenty Shell Key Gasification Equipments (SKGE) used in the Shell Coal Gasification Process (SCGP) have been built in coal-to-chemicals industry in China. SKGE comprise the Gasifier and Syngas cooler connected by Transfer duct. The support skirt of the Gasifier base was fixed, while the Syngas cooler side was supported by a constant hanger (floating support). Therefore the design by rule is not applicable to the strength calculation of pressure vessels of the system. In this paper, a FE model of global analysis of the largest SKGE system in China to date was established which considered thirteen loads and twenty-four load combinations. In this model, FEA software ANSYS was used to calculate the global dynamic effect of this 2000-ton system. The whole structural deformation and stress distribution, force and moment on several specified cross sections of SKGE under different load combinations are also determined within this model, which is the prerequisite and foundation for accurate calculation of each key part (e.g. connection between Transfer duct and Gas reversal chamber), and essential safety of SKGE system.
Energy Harvesting Using Vortex-Induced Vibrations of a Hanging Cable
Authors: Grouthier Clément , Michelin Sébastien , Modarres-Sadeghi Yahya , de Langre Emmanuel
Published: November 2014

Many technologies based on fluid-structure interaction mechanisms are being developed to harvest energy from geo-physical flows. The velocity of such flows is low, and so is their energy density. Large systems are therefore required to extract a significant amount of energy. The question of the efficiency of energy harvesting using VIV of cables is addressed in this paper, through the case of a hanging cable with a harvester at its upper extremity. An experimental analysis of the vortex-induced vibrations of a hanging cable with variable tension along its length is first presented. It is shown that standing waves develop and that the extracted mode shapes are self-similar. This self-similar behaviour of the spatial distribution of the vibrations along the hanging string is explained theoretically by performing a linear stability analysis of an adapted wake-oscillator model. The hanging cable is then combined with a localized harvester and its dynamics is measured. An appropriate reduced-order wake-oscillator model is also used to perform parametric studies of the impact of the harvesting parameters on the efficiency. An optimal set of parameters is identified and it is shown that the maximum efficiency is close to the value reached with an elastically-mounted rigid cylinder. The efficiency is found to be essentially driven by the occurrence of traveling wave vibrations.
MAI Benchmark Campaign of International Software for Reactor Pressure Vessel Integrity Assessment
Authors: Dautreme Emilie , Remy Emmanuel , Sueur Roman , Fontes Jean-Philippe , Aubert Karine , Soneda Naoki , Yamamoto Masato , Hardin Tim , Gamble Ron
Published: November 2014

Nuclear Reactor Pressure Vessel (RPV) integrity is a major issue concerning plant safety and this component is one of the few within a Pressurized Water Reactor (PWR) whose replacement is not considered as feasible. To ensure that adequate margins against failure are maintained throughout the vessel service life, research engineers have developed and applied computational tools to study and assess the probability of pressure vessel failure during operating and postulated loads. The Materials Ageing Institute (MAI) sponsored a benchmark study to compare the results from software developed in France, Japan and the United States to compute the probability of flaw initiation in reactor pressure vessels. This benchmark study was performed to assess the similarities and differences in the software and to identify the sources of any differences that were found. Participants in this work included researchers from EDF in France, CRIEPI in Japan and EPRI in the United States, with each organization using the probabilistic software tool that had been developed in their country.

An incremental approach, beginning with deterministic comparisons and ending by assessing Conditional Probability of crack Initiation (CPI), provided confirmation of the good agreement between the results obtained from the software used in this benchmark study. This conclusion strengthens the confidence in these probabilistic fracture mechanics tools and improves understanding of the fundamental computational procedures and algorithms.
Application of Transfer Matrix Method to Dynamic Analysis of Pipes With FSI
Authors: Li Shuaijun , Karney Bryan W. , Liu Gongmin
Published: November 2014

Analytical models of three dimensional pipe systems with fluid structure interaction (FSI) are described and discussed, in which the longitudinal vibration, transverse vibration and torsional vibration were included. The transfer matrix method (TMM) is used for the numerical modeling of both fluidic and structural equations and then applied to the problem of predicting the natural frequencies, modal shapes and frequency responses of pipe systems with various boundary conditions. The main advantage of the present approach is that each pipe section of pipe system can be independently analyzed by a unified matrix expression. Thus the modification of any parameter such as pipe shapes and branch numbers does not involve any change to the solution procedures. This makes a parameterized analysis and further mechanism investigation much easier to perform compared to most existing procedures.
An Analysis of In-Flow Fluidelastic Instability Based on a Physical Insight
Authors: Nakamura Tomomichi
Published: November 2014

Fluidelastic vibration of tube arrays caused by cross-flow has recently been highlighted by a practical event. There have been many studies on fluidelastic instability, but almost all works have been devoted to the tube-vibration in the transverse direction to the flow. For this reason, there are few data on the fluidelastic forces for the in-flow movement of the tubes, although the measured data on the stability boundary has gradually increased.

The most popular method to estimate the fluidelastic force is to measure the force acting on tubes due to the flow, combined with the movement of the tubes. However, this method does not give the physical explanation of the root-cause of fluidelastic instability.

In the work reported here, the in-flow instability is assumed to be a nonlinear phenomenon with a retarded or delayed action between adjacent tubes. The fluid force acting on tubes are estimated, based on the measured data in another paper for the fixed cylinders with distributed pressure sensors on the surface of the cylinders. The fluid force acting on the downstream-cylinder is assumed in this paper to have a delayed time basically based on the distance between the separation point of the upstream-cylinder to the re-attachment point, where the fluid flows with a certain flow velocity.

Two models are considered: a two-cylinder and three–cylinder models, based on the same dimensions as our experimental data to check the critical flow velocity. Both models show the same order of the critical flow velocity and a similar trend for the effect of the pitch-to-diameter ratio of the tube arrays, which indicates this analysis has a potential to explain the in-flow instability if an adequate fluid force is used.
A Method to Quantify Thermal Aging Effect on Fracture Toughness of Cast Stainless Steels Using Small Punch Test
Authors: Jeon Jun-Young , Ryu Dong-Il , Kim Yun-Jae , Lee Mi-Yeon , Kim Jin-Weon
Published: November 2014

In this study, a method to predict fracture toughness of aged cast austenitic stainless steels (CASSs) using small punch (SP) test and finite element (FE) analysis is proposed. Grade CF8M is considered and thermally aged up to 5,000 hours at 400°C. SP tests and fracture toughness test using compact tension (C(T)) specimen are conducted with virgin (unaged) and aged CF8M. FE analyses performed in this study use ductile fracture simulation technique with ‘the multi-axial fracture strain model’. The multi-axial fracture strain model for each aged CF8M are determined from SP test data and FE analyses. Fracture toughness of aged CF8M are predicted by conducting fracture toughness test simulations using FE damage analyses. Predicted fracture toughness results are compared with C(T) data to validate the method suggested in this study. The predicted initiation toughness values are predicted well and fracture toughness values are slightly conservative compared to test data.
Study on a Countermeasure Using Flexible Walls for High Level Sound
Authors: Ishihara Kunihiko
Published: November 2014

Vortices occur when gas flow passes through a duct with a tube bank of heat exchangers, such as a gas heater and/or a boiler. Very high level noise called a “self-sustained tone” occurs due to the interference of the vortices and the sound field in the duct. In general, baffle plates are used to suppress the self-sustained tone. However, it is difficult to use them effectively, because insertion conditions are vague. Then, rubber sheets as flexible walls are installed in both sides of the duct to suppress the self-sustained tone. The reasoning being that the resonant mode of the duct perpendicular to the flow may be suppressed by rubber sheet vibrations when the self-sustained tone occurred. Some experiments were carried out to examine the suppression effect of the installed rubber sheets. As a result, the suppression effect appeared at a certain condition. The purpose of this study is to clarify the effectiveness of the rubber sheet for self-sustained tones.
Investigation on the Intrinsic Plasticity of Gradient Nano-Grained AISI 304 Stainless Steel Treated by Ultrasonic Impact Treatment
Authors: Yang Xinjun , Ling Xiang , Yang Sisheng , Lu Shuhua
Published: November 2014

The gradient nano-grained (GNG) structure was formed on the top layer of AISI 304 with coarse grains (CG) by ultrasonic impact treatment. The impact velocity was 5 m/s and the coverage was changed from 3000% to 15000% to obtain different microstructure GNG /CG materials. The tensile test and small punch test were also performed to investigate the uniaxial and biaxial deformation behaviors of the GNG / CG materials. The results showed that the yield strength σs was enhanced in both uniaxial and biaxial deformation conditions. But the tensile strength σb was not nearly changed. The tensile fracture appeared to be dimple. The size of the dimples changed with gradient from the treated surface to the matrix. The strain localization was effectively suppressed in both conditions. AISI 304 of GNG / CG structure was elastically homogeneous but plastically gradient which offered unusual mechanical responses. So the GNG / CG 304 showed intrinsic plasticity like coarse grain one.
Quantitative Visualization of Unstable, Acoustically Coupled Shear Layers in Deep Axisymmetric Cavities
Authors: Oshkai Peter , Barannyk Oleksandr
Published: November 2014

High-amplitude acoustic pressure fluctuations associated with locked-on, resonant flow states frequently occur in engineering systems that involve internal cavities located in pipelines, such as components of gas transport systems, steam delivery pipelines and jet engines. This paper describes the evolution of fully turbulent, acoustically coupled shear layers that form across deep, axisymmetric cavities. Effects of geometric modifications of the cavity edges on the separated flow structure were investigated using digital particle image velocimetry (PIV). The internal flow was non-intrusively accessed by means of a borescope, which allowed illumination and optical recording of flow tracers inside the cavity. Instantaneous, phase- and time-averaged patterns of velocity and vorticity provided insight into the flow physics during flow tone generation and noise suppression by the geometric modifications. In particular, the first mode of the shear layer oscillations was significantly affected by shallow chamfers located at the upstream and, to a lesser degree, the downstream edges of the cavity. Specifically, the introduction of the chamfers affected the phase and the location of formation of large-scale vortical structures in the shear layer, which is associated with a maximum of the vorticity thickness across the cavity opening. In turn, these changes in the flow structure affected the amplitude of acoustic pressure pulsations.