bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Testing of Hybrid Wet-Dry Cooling Systems: Insights From Numerical Modeling
Authors: Card R. W.
Published: November 2014

A hybrid wet-dry cooling system can reduce water consumption at a power plant while minimizing the performance penalty of an air-cooled condenser (ACC). Automatic allocation of turbine exhaust steam among the wet and dry sections provides robust performance. However, the performance test for the unit must be carefully designed to prove the guarantees for water conservation and thermal performance with minimal uncertainty.

A hybrid wet-dry cooling system of the “parallel” type is modeled based on recently-constructed power plants. Effects of typical off-design test conditions are demonstrated. Techniques are recommended for designing an effective performance test for a hybrid wet-dry cooling system based on the use of existing Performance Test Codes (PTC).
Performance Analysis of Fogging Cooled Gas Turbine With Regeneration and Reheat Under Different Climatic Conditions
Authors: Besharati-Givi Maryam , Li Xianchang
Published: November 2014

One of the most efficient power plants in past decades is the gas turbine. Significant studies have been conducted on the effects of various design and operation parameters on gas turbine performance. However, it is still a challenge to find the optimal operating parameters for the best performance. One of the important parameters is the climate at which the gas turbine operates. The current study is on the performance of gas turbine with fog cooling, focusing on the effect of inlet air humidity and ambient temperature. The overall efficiency will be altered through inlet fog cooling and regenerative heating. Other components such as reheating are accompanied. The fog cooling is also compared to the chiller inlet cooling, in which the performance of coefficient (COP) varies with temperature difference. The analysis is conducted by using Aspen Plus software. The results indicate that a combination of fog cooling and regeneration as well as reheating can substantially improve the system thermal efficiency. Compared to the system with only fog cooling, the efficiency increases by 24.5 % when both regeneration and reheat systems are combined to the fogging cooled system.
Understanding Measurement Uncertainty in DP Flow Devices
Authors: Hering Michael S. , Mesnard David R.
Published: November 2014

This paper examines the concepts and methods involved in the uncertainty analysis of a differential pressure flow measurement, including which variables have the greatest influence on the uncertainty, and how to effectively manage the influence of error sources on the measurement. An uncertainty analysis will provide the user with a good measure of actual and/or potential system performance and can be instrumental in identifying potential areas of improvement in system performance. The wide availability of instruments of all types and levels of performance presents a difficult decision to those who are responsible for project success and budgets. Optimizing the investment in instrumentation is possible when the required performance is known based an appropriate uncertainty analysis.
Experimental and CFD Analyses of Two Bladed Savonius Water Turbine Under Low Velocity Conditions
Authors: Sarma Neelam K. , Biswas Agnimitra , Misra Rahul D.
Published: November 2014

Water is a prime source to all living beings, but for humans it is even more because of its usage to extract power. The idea behind the water turbine is derived from the parental species of wind turbine. The operating fluid properties like density, specific weight of water draw out differences between the two turbine kinds. The objective of the present work is to experimentally investigate the performance of a two bladed Savonius water turbine with an aspect ratio of 1.21 at low water velocity conditions viz. 0.3 m/s, 0.65 m/s and 0.9 m/s. The variation of torque and power with the considered water velocities has been studied. Also a performance study has been conducted with the aid of Computational Fluid Dynamics (CFD) using Ansys 14.0. A detailed study on the flow characteristics has been done that elaborates the factors like torque variation at different angles of rotation of the turbine, revealing high torque generation at 270° position. Also the effect of tip speed ratio (TSR) on performance (Cp) has been studied and found that maximum Cp of 0.343 is obtained for water velocity of 0.65 m/s with a TSR of 0.643. The results obtained through CFD are in agreement with the experimental results.
Solid Fuel to Natural Gas Conversions for Circulating Fluid Bed Boilers
Authors: Gurski Bill , Guarco John , Nunziante Nando
Published: November 2014

Recent discoveries of vast natural gas reserves in the United States have led to increased domestic natural gas production, resulting in lower prices. Utility and large industrial facilities are performing solid fuel conversions on their boilers to natural gas as a cost-effective and efficient fuel solution. Natural gas is not only economically beneficial but also environmentally efficient with cheaper prices and reduced SO2, NOx, and CO2 emissions. The Environmental Protection Agency (EPA) has recently released mandatory requirements that directly affect the cost effective operation of solid fuel boilers, resulting in natural gas becoming a more economically appealing choice of fuel for facility operators.

As more facilities consider boiler fuel conversions, it is important to understand all facets of the conversion, from the thermal evaluation of the boiler, to the complete design, supply and installation of the new firing system. Zeeco will provide specific details and recommended practices from a recent Circulating Fluidized Bed (CFB) Boiler solid fuel conversion to natural gas application designed for 1.3 billion Btu/hr of heat input for the maximum continuous steam rating. The information will detail the boiler conversion from a solid fuel fluid bed to a 100% natural gas fired boiler design. Thermal performance results, design and supply of the complete new gas firing system, and installation conversion assistance for the boiler modifications and firing system installation details are also provided.
Does Online Social Networking Automatically Lead to 21st Century Communities of Practice?
Authors: Hutt Jane A.
Published: November 2014

Online social networking communities can help strengthen professional ties among members of almost any profession. How useful they are to the engineering professions in contributing to the process of intergenerational knowledge transfer depends on the site. Prior to the popularity of online communications and networking tools such as Facebook, Twitter and Linked In, Power Industry engineers have utilized with varying success a number of knowledge transfer facilitation tools, both within their companies and outside them. This paper will discuss the pros and cons of both traditional and emerging methods and present specific examples that address technical issues, learning styles, differences in generational approaches to learning and communication. Issues relating to global needs in the engineering profession, organizational flexibility, the ability of people and organizations to adapt and change, and educational and workforce challenges will also be discussed. Short case studies illustrating various solutions for addressing some of these issues, including development of useful technical content and formation of communities of practice, will also be provided.
Selecting Shell Side Design Temperature for Feedwater Heaters
Authors: Muldoon Kellen J.
Published: November 2014

Operating temperature information was gathered using thermocouples installed on the outside of an existing high pressure feedwater heater (FWH). The operating data was collected to demonstrate the basis for the evaluation of the operational effectiveness of the heater especially during rapid load changes. This information provides insight into the selection of shell side design temperatures of the skirt and shell sections of a feedwater heater. This direct measurement of the temperature was useful in evaluating the appropriateness of both skirt and shell design temperatures selected by standard HEI practice. Also, consideration will be given to upgraded turbines and their impact on the design temperatures and pressures of existing FWH(s).
Transient Simulations of Spouted Fluidized Bed for Coal-Direct Chemical Looping Combustion
Authors: Zhang Zheming , Agarwal Ramesh
Published: November 2014

Chemical-looping combustion holds significant promise as one of the next generation combustion technology for high-efficiency low-cost carbon capture from fossil fuel power plants. For thorough understanding of the chemical-looping combustion process and its successful implementation in CLC based industrial scale power plants, the development of high-fidelity modeling and simulation tools becomes essential for analysis and evaluation of efficient and cost effective designs. In this paper, multiphase flow simulations of coal-direct chemical-looping combustion process are performed using ANSYS Fluent CFD code. The details of solid-gas two-phase hydrodynamics in the CLC process are investigated by employing the Lagrangian particle-tracking approach called the discrete element method (DEM) for the movement and interaction of solid coal particles moving inside the gaseous medium created due to the combustion of coal particles with an oxidizer. The CFD/DEM simulations show excellent agreement with the experimental results obtained in a laboratory scale fuel reactor in cold flow conditions. More importantly, simulations provide important insights for making changes in fuel reactor configuration design that have resulted in significantly enhanced performance.
Copper Deposition in Stator Cooling Water Systems
Authors: Howell A. G.
Published: November 2014

Water cooled steam turbine-generator stator systems are subject to flow restrictions and pluggage by copper that originates from within the stators. Deposition may occur within hollow stator bars or coils, or in filters or screens in the water flow circuit. In extreme cases of deposition, flow restriction can cause the generator to overheat due to reduction of cooling flow, resulting in unit outages and potentially serious equipment damage. Chemistry programs to minimize corrosion and transport of copper within the system include high oxygen, low oxygen, and alkaline (pH elevation). In all cases high purity water is required for the application. Examination of copper deposits can provide clues to the adequacy of the chemistry treatment program for minimizing system corrosion.
Selecting Material Properties for Maximizing Gun Firing Power
Authors: Perry J. , Perl M.
Published: November 2014

The design of gun barrels aims at maximizing its firing power determined by its SMP — the maximal allowed firing pressure, which is considerably enhanced by inducing a favorable residual stress field through the barrel’s wall commonly by the autofrettage process. Presently, there are two distinct processes: hydrostatic and swage autofrettage. In both processes the barrel’s material is fully or partially plastically deformed. Recently, a 3-D code was developed, which finally enables a realistic simulation of both swage and hydraulic autofrettage, using the experimentally measured stress-strain curve, and incorporating the Bauschinger effect. This code enables a detailed analysis of all the factors involving the final SMP of a barrel, and it can be used to establish the optimal process for any gun barrel design. A major outcome of this analysis was the fact that the SMP of an autofrettaged barrel is dictated by the detailed plastic characteristics on the barrel’s material. The main five plastic parameters of the material that have been identified are: the exact (zero offset) value of the yield stress, the universal plastic curve in tension and in compression, the Bauschinger Effect Factor (BEF) curve, and the Elastic-Plastic Transition Range (EPTR). A detailed analysis of these three materials points to the fact that the major parameter determining the barrel’s SMP is the yield stress of the material and that the best way to determine it is by the newly developed “zero offset” method. All these four parameters have a greater influence on the SMP of an hydraulically autofrettaged barrel than on a swaged one.
Creep-Fatigue Crack Initiation Assessments of an Instrument Guide Tube Within a Superheater Header
Authors: Shi Jinhua , Dodia Hassam
Published: November 2014

In order to extend the boiler lives at Advanced Gas-Cooled Reactor (AGR) nuclear power stations in the UK, new temperature measuring instrumentation to monitor reactor gas temperature has been proposed to install on the bore of an intact boiler tube to provide additional boiler operating data to support the station lifetime extension.

This paper details a creep-fatigue crack initiation assessment of the proposed installation of an instrument guide tube within the superheater header using the latest R5 high temperature assessment procedures based on detailed finite element thermal transient stress analysis values for a bounding start-up and shutdown cycle.

The fatigue damage at welds has been calculated based on both weld and parent material properties. The new approach for assessing weldments has been used in this paper. This new approach involves splitting the existing Fatigue Strength Reduction Factor (FSRF) into a Weldment Endurance Reduction (WER), which accounts for reduced fatigue endurance due to weld imperfections, and a Weldment Strain Enhacement Factor (WSEF), which accounts for material mismatch and local geometry.

The creep assessments of the weld material locations have been carried out on both parent and weld material properties including the welding residual stress.

The total creep-fatigue damage is then obtained as the sum of fatigue damage, Df, and creep damage, Dc.
The Combined Effect of a Finite Axial Erosion With Bauschinger Modified Autofrettage on the 3D SIFs of Pressurized Cylinders
Authors: Ma Q. , Levy C. , Perl M.
Published: November 2014

Autofrettage is the process to introduce favorable residual compressive hoop stresses on the bore of a pressurized cylinder to enhance its strength and durability. For certain type of pressurized vessels under certain severe operating conditions, erosions and cracks often occur causing significant reduction in pressure vessel fatigue life. Those erosions and cracks are in general 3D geometrical configurations. The Stress Intensity Factors (SIFs) of the cracks are often the key to estimate the fatigue life. However the SIFs are largely dependent on not only the crack geometrical configurations but also the geometrical configurations of the erosions introduced during its operation. The Bauschinger effect on the SIFs further complicates the analysis. In this study, a closer look is taken at how a finite axial erosion in combination with the Bauschinger modified autofrettage properties affect the 3D SIFs. The problem is solved via the finite element method (FEM). The SIFs are evaluated for a variety of relative crack depth, different crack configurations and erosion geometrical configurations including arc erosion, semi-circular and semi-elliptical erosions. We show that the effective SIFs can be increased significantly by any of these factors but the combined effect often worsens the situation.
Combined Cycle Power Plant Expansion Joint Failure
Authors: Reich Alton
Published: November 2014

Engineers design systems based on the best available information about the design conditions. These design conditions are based on a reasonable understanding about how systems will be operated and the pressures and temperatures expected. This paper focuses on the failure of an expansion joint in a hot water system at a combined cycle power plant. The root cause of the failure can be traced to the way the plant was operated. The operation of the plant produced temperatures and pressures that were well beyond the design basis of the expansion joint and the system in which it was used. This failure highlights some considerations in setting the design temperature and pressure for hot water systems, and for the operation of these systems.
Definition of a Charpy V-Notched Mastercurve to Fit Transition of Ferritic Steels
Authors: Pillot Sylvain , Pacqueau Pascal
Published: November 2014

This paper intends to present the development of a Charpy V-notched (CVN) mastercurve to fit and/or extrapolate the transition curve of ferritic steels (including martensitic, bainitic and ferritic materials).

The purpose of a mastercurve is to define a general mathematical model able to represent the overall behaviour:

• of a material for different test conditions,

• or for a set of materials for given tests conditions.

The role of a mastercurve is then to allow extrapolating or interpolating values from other data on the basis of a robust model, thereby permitting to avoid execution of new tests. It is in general based on practical general observations and research for a common behaviour through a large database of experimental results.

This kind of approach is largely used to fit fracture mechanics data and can also be used in the case of Charpy toughness. Some changes have to be performed in order to take into account specificities of Charpy (such as dependence of transition slope with strength of materials) as well as some verifications linked to statistical distribution of failure probability.

This work is based on the assessment of a very large database collected for years at Industeel’s Research Center (tensile results, Charpy transition curves). This database represents 286 Charpy V-Notched transition curves of ferritic steels. It covers a wide range of materials and applications. Yield strengths of studied materials are ranging from 290 to 1180MPa while ultimate tensile strengths are in the range of 480 to 1690MPa.

The target of this mastercurve is to predict the correct shape of the CVN transition curve with a reasonable safety margin on the basis of a limited amount of data (tensile properties at room temperature at least and when available, few Charpy data).

A brief description of the database used within this study is given in the first part of this contribution as well as a description of the concept and underlying models. Finally, a validation of the work will be given as well as an illustration of its performance in a practical industrial case.
Effect of Pre-Strain on Mechanical Properties of Pressure Vessel Steel Grades: Assessment of Stress Relieving / Post Weld Heat Treatments Efficiency at Regenerating Properties
Authors: Pillot Sylvain , Baudin Carole , Corre Stéphanie , Heritier Deborah , Chauvy Cédric , Coudreuse Lionel , Toussaint Patrick
Published: November 2014

Ensuring mechanical properties of carbon and low alloy steels after deformation is of major concern since the building process of heavy (i.e. thick-walled) pressure vessels may be directly impacted. Indeed, thick plates encounter forming and welding operations that may modify as-delivered properties. From both technical and economical points of view, cold forming is usually preferred. This technique is nowadays widespread and new rolling equipments display sufficient power to handle plates up to at least 250mm thick.

Current limitations are now mainly related to maximum admissible strain in materials and regulation rules resulting from construction codes. The ASME Boilers and Pressure Vessels Construction Code on the American side and the EN 13445 Unfired Pressure Vessels Construction Code on the European side, both allow the use of as-strained material up to maximum 5% plastic (i.e. permanent) strain without any subsequent heat treatment operation.

Above 5% plastic deformation, on one hand the European code requires a full quality treatment (meaning high temperature austenitization treatment, then cooling in air (normalizing – N) or in accelerated conditions (quenching – Q or accelerated cooling – NAC), followed by a Tempering treatment T) and on the other hand the ASME code only requires Tempering that can even be carried out using the mandatory Post Weld Heat Treatment (PWHT) needed by welded zones.

However, it is of high importance to note that thick vessels are always submitted to a final PWHT to insure sufficient toughness in welded zones. This final PWHT is performed whatever the deformation obtained during plate rolling. In practice, there are no thick vessels made out of plates in as-strained conditions.

Avoiding a full quality treatment as demanded per EN 13445 rules is of major interest for fabricators as it allows to decrease the delivery time, the risk of appearance of problematic issues (uncontrolled deformations of the vessel during high temperature treatments…) and significantly reduces the overall fabrication costs.

This paper focuses on the effect of strain on conventional mechanical properties for steel grades widely used for the fabrication of heavy pressure equipments (i.e. tensile properties, hardness, Charpy V toughness) for different strain levels. In particular, it points out and discusses PWHT effects on properties of various pre-strained materials, showing that there is no need for full quality heat treatment.
Surface to Through-Wall Crack Transition Model for Axial Cracks in Pipes
Authors: Shim Do-Jun , Rudland David , Park Jeong-Soon
Published: November 2014

Recent studies have shown that a subcritical surface crack, due to PWSCC, can transition to a through-wall crack with significant differences between the inner diameter and outer diameter crack lengths. This behavior has been observed for both circumferential and axial cracks. Recently, a surface to through-wall crack transition model has been developed for circumferential cracks using existing K and COD solutions for non-idealized circumferential through-wall cracks.

In this paper, a similar crack transition model was developed for axial cracks. As a first step, a study was conducted to define the appropriate crack front shape for non-idealized axial through-wall cracks. Then, elastic finite element analyses were carried out to develop K and COD solutions using these crack front shapes. The newly developed solutions were utilized for the crack transition model. The present crack transition model includes a criterion for transitioning the final surface crack to the initial non-idealized TWC. This criterion determines when the transition should occur (based on surface crack depth) and determines the two crack lengths (at ID and OD surfaces) of the initial non-idealized TWC. Furthermore non-idealized TWC growth can be conducted using the proposed model. Example results (crack length and COD) obtained from the proposed model were compared to those obtained from the natural crack growth simulations. Results presented in this paper demonstrated the applicability of the proposed model for simulating axial crack transition.
Experimental and Numerical Analysis for Fluid-Structure Interaction for an Enclosed Hexagonal Assembly
Authors: Sargentini Lucia , Cariteau Benjamin , Angelucci Morena
Published: November 2014

This paper is related to fluid-structure interaction analysis of sodium cooled fast reactors core (Na-FBR). Sudden liquid evacuation between assemblies could lead to overall core movements (flowering and compaction) causing variations of core reactivity. The comprehension of the structure behavior during the evacuation could improve the knowledge about some SCRAMs for negative reactivity occurred in PHÉNIX reactor and could contribute on the study of the dynamic behavior of a FBR core. An experimental facility (PISE-2c) is designed composed by a Poly-methyl methacrylate hexagonal rods (2D-plan similitude with PHÉNIX assembly) with a very thin gap between assemblies. Another experimental device (PISE-1a) is designed and composed by a single hexagonal rod for testing the dynamic characteristics. Different experiments are envisaged: free vibrations and oscillations during water injection.

A phenomenological analysis is reported showing the flow behavior in the gap and the structure response. Also computational simulations are presented in this paper. An efficient numerical method is used to solve Navier-Stokes equations coupled with structure dynamic equation. The numerical method is verified by the comparison of analytic models and experiments.
Flow Around a Surface-Mounted Finite Square Prism With a Splitter Plate
Authors: Ogunremi Ayodele R. , Sumner David
Published: November 2014

The effect of a wake-mounted splitter plate on the flow around a surface-mounted finite-height square prism was investigated experimentally in a low-speed wind tunnel. Four square prisms of aspect ratios AR = 9, 7, 5 and 3 were tested at a Reynolds number of Re = 7.4×104. The relative thickness of the boundary layer on the ground plane was δ/D = 1.5 (where D is the side length of the prism). The splitter plates were mounted vertically from the ground plane on the wake centreline, with a negligible gap between the leading edge of the plate and rear of the prism. The splitter plate heights were always the same as the heights of prisms, while the splitter plate lengths were varied from L/D = 1 to 7. Measurements of the mean drag force were obtained with a force balance, and measurements of the vortex shedding frequency were obtained with a single-sensor hot-wire probe. Compared to previously published results for an “infinite” square prism, a splitter plate is less effective at drag reduction, but more effective at vortex shedding suppression, when used with a finite-height square prism. Significant reduction in drag was realized only for short prisms (of AR ≤ 5) when long splitter plates (of L/D ≥ 5) were used. In contrast, a splitter plate of length L/D = 3 was sufficient to suppress vortex shedding for all aspect ratios tested. Compared to previous results for finite-height circular cylinders, finite-height square prisms typically need longer splitter plates for vortex shedding suppression.
Influence of Excitation on Junction Coupling at Water Hammer in Piping Systems
Authors: Riedelmeier Stefan , Becker Stefan , Schlücker Eberhard
Published: November 2014

A comprehensive study on junction coupling in two piping system configurations in dependency of the excitation’s condition were performed. The source of the hydraulic excitation is characterized by water hammer produced at various initial mean flow velocities. The resulting forces on the piping system caused bend oscillations. For each system configuration and initial mean flow velocity the support position of the bend was varied. Thus the structural frequency was altered. The pressure inside the pipe, the displacement of the bend, the acceleration at the anchorage and the supports were recorded. Additionally, optical measurement equipment was utilized in order to characterize the structural oscillation more detailed. For both system configurations fluid-structure interaction effects were identified, but two-way effects at the base frequency of water hammer only occurred in one system. The amplitude of excitation had influence on the amplitudes of the pressure, displacement and acceleration and on the number of modes which built up. The results of the measurements pointed out that not only the bend oscillated but also the anchorage and pipe sections behind the bend. In both systems, an energy transfer from the fluid to the anchorage could be observed. Due to the bending of the anchorage, the bends oscillated in multiple directions.
Discussion of Fatigue Data for Austenitic Stainless Steels
Authors: Wilhelm Paul , Steinmann Paul , Rudolph Jürgen
Published: November 2014

The first results of a detailed fatigue model for austenitic stainless steels in general and for the grades 1.4541 and 1.4550 are presented to describe the effect of the light water reactor (LWR) coolant environments on the fatigue life. The statistical evaluations are based on strain (and load) controlled test series from different institutions. The compiled fatigue data include not only results from America (Keller (1971), Conway (1975), Hale (1977), and Argonne National Laboratory (ANL)(1999–2005)), but also from Europe (Solin (2006), Le Duff (2008–2010), De Baglion (2011, 2012), Huin (2013),…) and Japan (Kanasaki (1997)). The fatigue life is defined as the number of cycles necessary for tensile stress to drop 25 percent from its peak value. Fatigue lives defined by other failure criteria are normalized to the load reduction of 25 percent, before the statistical analysis is performed. The fatigue data are expressed in terms of the Langer equation and the parameter “material variability and data scatter” is quantified.

Additionally, fatigue data in air of roughened specimens are compiled and discussed. A reduction factor of 2.5 on number of cycles is derived to cover the maximum allowed surface roughness.

Based on the derived best-fit curves, design-curves in air and, in a second step, environmentally assisted fatigue (EAF) curves for LWR environments, which consider temperature, strain rate, dissolved oxygen content, and hold-time effects, will be incorporated in the detailed fatigue model in the future.
Fluid Hammer and Fatigue Analysis for Oil Transport Pipelines With Peak Points
Authors: Warda Hassan , Haddara Sherif , Wahba Essam
Published: November 2014

The SUMED pipeline is a major oil transport pipeline in the Middle East. It provides an important route for transporting oil from the Arabian Gulf region to Europe and North America. The pipeline was subjected to major damage in the 1990s, which required the replacement of several kilometers at its peak point. Fluid hammer simulations using the method of characteristics show that this damage was due to consecutive shutdown/startup events. Such events led to multiple formation and collapse of vapor cavities at the peak point. Low cycle fatigue analysis confirm the finite lifetime of the pipeline due to the high differential stress resulting from the cavity collapse. Moreover, a safe valve closure operational scheme is computed using fluid hammer analysis that would prevent further formation of cavities and hence ensure safe pipeline operation in the future.
Effect of Warm Pre-Stress on Highly Irradiated Pressure Vessel Steel
Authors: Moinereau Dominique , Landron Caroline , Ait Bachir Malik , Garbay Eric
Published: November 2014

The effect of warm pre-stress (WPS) is well known on cleavage fracture resistance of ferritic steels and has been confirmed on numerous tests on non irradiated materials. Theoretical knowledge let expect that this effect occurs by the same way on irradiated material but has to be demonstrated with experiments in such conditions. An experimental program has been conducted by EDF in Chinon hot cell laboratory on two RPV steels irradiated up to a fluence of 6,5*1019 n/cm2.

The ½ TCT specimens (CT12.5) used in this programme have been irradiated in the capsules of the EDF RPV surveillance program of two PWR reactors. Different types of WPS loading path have been applied to cover typical postulated accidental transients. The results confirmed the effect on WPS on the cleavage fracture resistance of the irradiated materials. No fracture occurred during the cooling phase of the loading path and the fracture toughness values are higher than that measured with conventional isothermal tests.

The analyses of the experiments have been conducted based on use of simplified engineering models and more refined fracture models based on local approach to cleavage fracture. These analyses are in agreement with the experimental results.
Improved Accuracy on Efficiency of PK Hypercompressor Valves
Authors: Maggi Carmelo , Wojnar Jan , Bagagli Riccardo , Tognarelli Leonardo
Published: November 2014

In recent years, also because of the overall contraction of the market, all compressor manufacturers are differentiating their products by offering solutions that optimize/minimize costs while maintaining the same robustness and reliability.

To achieve this goal, the main guidelines are “Power Density” and “Efficiency”.

On hyper compressors for LDPE plants, the absorbed power of the valves has a key role in overall efficiency and, thanks to dedicated development programs aimed to design more and more efficient valves, represents one of the disciplines where it is still possible to improve the performance.

The absorbed power of this type of valves is strictly correlated to their behavior which is challenging to predict because it depends on many factors. The expected macroscopic gas parameters, such as pressure, temperature and gas composition often are not sufficient to properly evaluate valve behavior in the field.

In fact valve operation is highly dependent on local phenomena such as localized pressure losses and presence of vortexes which are in turn influenced by the geometry of the valve and by its behavior.

To better understand all these phenomena it is needed to characterize these valves through experimental tests aimed at defining, with a good precision and accuracy, the valve dimensionless parameters Cd (drag coefficient) and Ks (flow coefficient) as a function of the geometry of the valve itself. If the coefficients Cd and Ks are not accurate, the expected behavior of the valve and, as a consequence the valve losses, may be completely different from the evidence of the field and could not properly explain some unexpected power consumption.

Therefore, through a dedicated characterization of the valves design, it is possible to improve the predictability of the valve, also in terms of power consumption, that contributes to a better evaluation of the total absorbed power by the compressor, which allows designers to reduce their margins of uncertainty.
Study of Safety Margin for Elongated Defect Acceptance Criteria in ASME BPV Code VIII-1/2
Authors: Chen Zhao-he
Published: November 2014

With fracture toughness of carbon/low alloy steels deduced from UG-84 in ASME BPV CODE VIII-1 and table 3.13 in ASME BPV CODE VIII-2 and assessment methods stipulated in Chinese standard GB/T 19624, assessment for safety margin for elongated defect acceptance criteria stipulated in UW-51/52 of ASME Codes shows that the acceptance criteria given could attain safe result for all embedded and surface circumferential elongated defects, except for those located in all highly constrained area. But for some longitudinal elongated defects unsafe results have been found, and some revision suggested for acceptance criteria has been pointed out.
The Influence of Flow Strength and Fracture Toughness on the Computed Reliability of Thermally Aged Grade CF-8M Cast Austenitic Stainless Steel Piping
Authors: Griesbach Timothy J. , Dedhia Dilip , Harris David O. , Cofie Nathaniel G. , Amberge Kyle , Alleshwaram Aparna
Published: November 2014

Thermal aging of cast austenitic stainless steel (CASS) piping is a concern for long-term operation of nuclear power plants. Traditional conservative deterministic fracture mechanics analyses lead to tolerable crack sizes well below the sizes that are readily detectable in these large-grained materials. This is largely due to the conservative treatment of the scatter in material properties and the imposition of multipliers (structural factors) on the applied loads. In order to account for the scatter in the tensile and fracture toughness properties that enter into the analysis, a probabilistic approach is taken. Application of the probabilistic fracture mechanics (PFM) model to representative problems has led to questions regarding the dominant random variables and the influence of the tails of their distributions on computed failure probability. The purpose of this paper is to report the results of a study to identify the important random variables in the PFM model and to investigate the influence of the distribution type on the computed failure probability. Application of the PFM model to a representative piping problem to compute the depth of a part-through part-circumferential crack that will fail with a defined probability (10−6 for example) revealed that the fracture toughness was not a dominant variable and the distribution of the toughness did not strongly affect the results. In contrast to this, the flow strength (which enters into the calculation of the applied crack driving force — J) was important in that low flow strength was controlling the low probability failures in the Monte Carlo simulation. Hence, the low-end tail of the flow strength distribution was influential. Various types of distribution of flow strength consistent with the available data were considered. It was found that the distribution type has a marked, but not overwhelming, effect on the crack depth that would fail with a given probability. From this it is concluded that the PFM model is quite robust, in that it is not highly sensitive to uncertainties in the dominant input distributions.
Fatigue Crack Growth Rates for Nickel Base Alloys in Air
Authors: Nomura Yuichiro , Yamamoto Kenji , Hojo Kiminobu
Published: November 2014

When defects are detected by in-service inspections of the nuclear power plants in Japan, allowable flaws are evaluated according to the Rules on Fitness-for-Service for Nuclear Power Plants of Japan Society of Mechanical Engineers (JSME maintenance rules). The fatigue crack growth analysis is an important part of the flaw acceptance evaluation. However FCGR curves for nickel base alloys in air are not provided in the current JSME maintenance rules.

This paper describes the evaluation of the fatigue tests in air of nickel base alloys and formulation of the FCGR curves for the JSME rules on Fitness-for-Service. From the test results, the temperature and stress ratio are not dominant factors. However, as based on the form of the FCGR curve of NUREG/CR-6721, the proposed curves are shown to be functions of these parameters. Threshold of stress intensity factor is introduced in the curves by taking into account crack closure.
Advanced Analyses of Let-Down Valves to Improve LDPE Plant Performance
Authors: Grassini Ubaldo
Published: November 2014

High pressure plants for LDPE production are characterized by machinery and equipment undergoing severe fatigue, pulsation, vibration and erosion problems.

The collection of data relevant to the performance of compressors and plants has to be properly carried out to help the maintenance engineering team to identify the possible ways of improvement.

The use of advanced laboratory analyses gives a valid contribution to the investigations and the determination of the root causes of the existing problems. While on the compressors the wear and fatigue are generally the reasons for a shut-down, on the plant there are other critical components like the let-down valves, needing careful consideration.

Their periodical actuation implies fatigue and erosion appreciably influencing the MTBF and the availability of the plant.

These valves are real critical components on tubular reactor plants. The analyses carried out at different times have allowed to change material so improving the resistance to wear and the mechanical properties resulting in a higher reliability.
The Impact of Emergency Release in LNG Transfer
Authors: van Bokhorst Evert , Webber Tony , van der Putte Jesper , Smeulers Jan , Remans David
Published: November 2014

This paper describes the results of experimental work and simulations of pressure surges resulting from fast closing valves and activation of an emergency release coupling (ERC) in ship-to-ship LNG transfer. The first part presents the results of an ambient water flow test with a fast closing 4-inch full bore valve in combination with a 4-inch flexible multi-composite hose. High amplitude pressure surges up to 4 times the working pressure occur upstream of the valve. Pressure surge amplitudes strongly depend on valve closing time and flow rate. The propagation speed in the upstream hose is lowered considerably due to the hose flexibility. Furthermore the temporarily deformation of the hose results in loss of energy and acoustic damping of the pressure surge amplitudes.

The measurement results are compared to the results of modeling. Acoustic damping and propagation speed of sound show a non-linear behavior of the hose, due to a varying internal pressure, which is not captured in the present modeling techniques.

The second part of the paper describes the results of a full scale flow test on an 8-inch ERC (KLAW make) for LNG ship-to-ship transfer (Figure 1). The ERC in the test is located downstream of an 8-inch 15-meter long multi-composite flexible hose. The test is intended to investigate operational and mechanical integrity, spill rate and the impact of pressure transients and shock loads on the ERC including upstream hose and downstream piping.

Upon hydraulic activation the ERC separates in two parts, each provided with a fast closing butterfly valve. The complete operation takes about 0.2 s and the actual valve closure duration is about 0.02 s resulting in a negligible spill of less than 0.002 m3. Pressure transients from 34 to 100 bar, over 10 times the operating pressure, occur at the maximum flow rate of 1000 m3/hr, resulting in shock loads and high acceleration levels. The mechanical integrity remains intact even after four successive releases at the maximum flow rate of 1000 m3/hr. The results contribute to the certification of the ERC by Lloyds B.V.

Further development in modeling is necessary to obtain a validated model for the calculation of pressure surges due to emergency shutdown in a LNG transfer.
A Study on Maximum Responses and Their Variances of Elasto-Plastic Structures Subjected to Synthesized Ground Motions
Authors: Sone Akira , Ichihashi Ichiro , Masuda Arata
Published: November 2014

A number of artificial earthquake ground motions compatible with time-frequency characteristics of recorded actual earthquake ground motions as well as the given target response spectrum are generated using wavelet transform. The coefficient of variation (C.O.V..) of maximum displacement on elasto-plastic SDOF systems excited by these artificial ground motions are numerically evaluated.
Stress Analysis of Bulges in Cylindrical and Oval Pressure Vessels
Authors: Samman Mahmod , Samman Mohammad
Published: November 2014

The stress field in and around bulges in cylindrical and oval pressure vessels is examined using linear elastic finite element models. The effects of bulge size and shape on axial and hoop stresses are examined under internal pressure loading. Stress components at the center of the bulge, in the entire bulge, and in the vessel outside the bulge are analyzed both on the inside and outside surfaces of the vessel wall. In addition, the effects of vessel ovality (out-of-roundness) and the location of a bulge relative to ovality on these stress components are studied. This study provides engineers with a detailed look at bulging-induced stresses and the limitations of stress-based fitness-for-service assessment of bulges in pressure vessels such as refinery coke drums.
On-Line Structural Damage Feature Extraction Based on Autoregressive Statistical Pattern of Time Series
Authors: Hu Ming-Hui , Tu Shan-Tung , Xuan Fu-Zhen , Wang Zheng-Dong
Published: November 2014

The main aim of this paper is to demonstrate an autoregressive statistical pattern analysis method for the on-line structural health monitoring based on the damage feature extraction. The strain signals obtained from sensors are modeled as autoregressive moving average (ARMA) time series to extract the damage sensitive features (DSF) to monitor the variations of the selected features. One algebra combination of the first three AR coefficients is defined as damage sensitive feature. Using simple theory of polynomial roots, the relationship between the first three AR coefficient and the roots of the characteristic equation of the transfer function is deduced. Structural damage detection is conducted by comparing the DSF values of the inspected structure. The corresponding damage identification experiment was investigated in X12CrMoWVNbN steel commonly used for rotor of steam turbine in power plants. The feasibility and validity of the proposed method are shown.
A Study on the Normalized Load Function for J-R Curve Testing Using Normalization Method
Authors: Kim Kuk-cheol , Ma Young-wha
Published: November 2014

The purpose of this study is to suggest a more appropriate normalized load G-function for normalization method of J-R curve testing in the ASTM 1820 standard. For leak before break (LBB) design of reactor coolant piping system, J-R curve testing is required to verify the crack stability integration using J-T analysis. The normalization method of J-R curve testing is an excellent candidate testing method for dynamic J-R curve testing. In the normalization function, the load value is normalized by the G-function based on the plastic η factor. The normalized load function, G-function is important because the resultant J-R curve depends on the normalized function type used. However, for existing J-R curve calculation using the G-function in ASME standards, there exists a mismatch of estimated J integral values between the two different J-integral calculation approaches: the standard method in ASTM 1820, and the approach based on a J-integral physical concept with energy release rate. This problem is caused by the G-function type. To set up a more appropriate G-function, finite element (FE) analysis has been performed for compact tension specimens with various a/W and strain hardening index n. Also, application of the newly proposed G-function to J-R curve estimation is discussed.
LBB Nozzle Transition Parameter Variation and Plasticity Influence
Authors: Baas Peter , Blom Frederic
Published: November 2014

In the framework of the R6 development programme on leak before break NRG investigated a circumferential through wall crack in a pipe with nozzle. A range of crack angles (3–180°), radius over wall thickness ratios (Ri/t = 5, 10, 20, 50 and 100) and nozzle divergence angles (0, 5, 10, 20, 30 and 40°) have been investigated in order to investigate parameter sensitivity. The stress intensity factor (KI) and the Crack Opening Area (COA) are compared for the nozzle and pipe models. The nozzle investigation is performed using a longitudinal force (100 MPa).

It can be concluded that with larger nozzle divergence angles, the resulting maximum KI nozzle factors are higher. The larger nozzle divergence angles have a suppressive effect on the crack opening resulting in a lowered COA nozzle factor.

The influence of plasticity has been investigated by a number of analyses including plastic behaviour. The geometry variations are five Ri/t ratios (5, 10, 20, 50 and 100) and eight different crack angles (3, 10, 30, 50, 75, 100, 140 and 180°). A 30° nozzle angle was selected for plastic analyses. The plasticity investigation is performed using longitudinal force (100 MPa).

In general the results for KI are higher with the inclusion of plasticity. However, since the inclusion of plasticity has a stress relieving effect on the pipe/nozzle transition, the resulting maximum KI nozzle factor is lowered. The COA results for the individual analyses are overall higher due to the inclusion of plasticity. The COA nozzle factor is lowered, because the relative influence of plasticity is lower on the stiffer nozzle.
Finite Element Modelling of Welded Austenitic Stainless Steel Plate With 8-Passes
Authors: Patel V. I. , Muránsky O. , Hamelin C. J. , Olson M. D. , Hill M. R. , Edwards L.
Published: November 2014

The current paper presents a finite element analysis of an eight-pass groove weld in a 316L austenitic stainless steel plate. A dedicated welding heat source modelling tool was employed to produce volumetric body power density data for each weld pass, thus simulating weld-induced thermal loads. Thermocouple measurements and cross-weld macrographs taken from a weld specimen were used for heat source calibration. A mechanical finite element analysis was then conducted, using the calibrated thermal loads and a Lemaitre-Chaboche mixed work-hardening model. The predicted post-weld residual stresses were validated using contour method measurements: good agreement between measured and simulated residual stress fields was observed. A sensitivity analysis was also conducted to identify the boundary conditions that best represent a tack-welded I-beam support, which was present on the specimen back-face during the welding.