bluuebunny/crossref_metadata_2025 huggingface dataset:
The Sensitivity of Pressurized Thermal Shock Analysis Results to Alternative Models for Weld Flaw Distributions
Authors: Dickson T. L. , Simonen F. A.
Published: August 2008

The United States Nuclear Regulatory Commission (USNRC) initiated a comprehensive project in 1999 to determine if improved technologies can provide a technical basis to reduce the conservatism in the current regulations for pressurized thermal shock (PTS) while continuing to provide reasonable assurance of adequate protection to public health and safety. A relaxation of PTS regulations could have profound implications for plant license renewal considerations. During the PTS re-evaluation study, an improved risk-informed computational methodology was developed that provides a more realistic characterization of PTS risk. This updated methodology was recently applied to three commercial PWRs. The results of this study provide encouragement that a technical basis can be established to support a relaxation of current PTS regulations. One significant model improvement applied in the PTS re-evaluation study was the development of flaw databases derived from the non-destructive and destructive examinations of material from cancelled reactor pressure vessels (RPV). Empirically-based statistical distributions derived from these databases and expert illicitation were used to postulate the number, size, and location of flaws in welded and base metal (plate and forging) regions of an RPV during probabilistic fracture mechanics (PFM) analyses of RPVs subjected to transient loading conditions such as PTS. However, limitations in the available flaw data have required assumptions to be made to complete the risk-based flaw models. Sensitivity analyses were performed to evaluate the impact of four flaw-related assumptions. Analyses addressed: 1) truncations of distributions to exclude flaws of extreme depth dimensions, 2) vessel-to-vessel differences in flaw data, 3) large flaws observed in weld repair regions, and 4) the basis for estimating the number of surface breaking flaws. None of the four alternate weld flaw models significantly impacted calculated vessel failure frequencies or invalidated the tentative conclusions derived from the USNRC PTS re-evaluation study.
Proposal of Determination Procedure About Fatigue Safety Factors for Arbitrary Best Fit Curves
Authors: Kawasaki Nobuchika
Published: August 2008

Fatigue safety factors cover not only the scattered range of fatigue test results obtained from test specimens, but also the difference in the fatigue lives between the test specimens and vessels / piping in plants. Therefore necessary safety factors have a relation to the accuracy of a best fit curve which is determined by the test results and the component’s conditions. This paper describes a determination procedure of fatigue safety factors for a new best fit curve so that designers can determine adequate safety factors for arbitrary best fit curves and material databases. This determination procedure is explained using a 316FR fatigue database, and the safety factors for new 316FR best fit curve are shown. These safety factors are estimated based on the accuracy of the best fit curve, and are calculated for each surface finish in the designed vessels and piping. Therefore the adoption of accurate best fit curves in limited conditions will result in smaller safety factors than the present code.
Qualification of a Jacketed Vessel Using Finite Element Analysis
Authors: Hari Yogeshwar , Munjal Ram , Obeid Chawki
Published: August 2008

The main objective of this paper is to improve a jacketed vessel. The jacketed vessel is usually chosen to heat the contents of the vessel. The chamber or annulus contains fluid under pressure to heat the inner vessel contents. The initial over-all dimensions of the vessel are based on the capacity of the stored liquid. The design was in accordance with the ASME Boiler & Pressure Vessel Code, Section VIII, Div 1. The jacketed vessel bottom head and jacket bottom head are being improved to withstand internal and external design pressures. Bottom head of the jacket can be reinforced in one of the three ways, namely: (1) rings which are radial (these rings also create flow for the fluid); (2) attachment of the rings to the bottom jacket head with stays, since rings cannot be physically welded to the bottom jacket; or (3) there is a possibility, the new bottom head and jacketed head combination can be cast, but that would not be economically feasible. This leads to the following six configurations considered in this paper and they are: (1) internal pressure of 50 psi, (2) external pressure + vacuum pressure of 65 psi, (3) reinforcement with 5 rings with external pressure of 65 psi, (4) rings welded with the bottom jacket head with external pressure of 65 psi, (5) welded with stays on ring location (stay diameter of 1 inch) with external pressure of 65 psi, and (6) welded with stays on ring location (stay diameter of 1.5 inch) with external pressure of 65 psi. The pattern of stays chosen for this analysis is one of uniform distribution on ring locations, which are radially situated. The design dimensions based on Code sizing are used to recalculate the stresses for the jacket vessel. The dimensional jacketed vessel is modeled using STAAD III Finite Element Analysis (FEA) software. The design is found to be safe for the specific configuration considered herein with stays.
Investigation of Duplex Stainless Steels for Pipeline Repairs
Authors: Fetzner Dave , Ames Nate , Ruschau Greg
Published: August 2008

Hundreds of miles of production pipelines make up the network at the Prudhoe Bay oilfield in Northern Alaska, part of the vast petroleum reserves which feed one million barrels of crude oil per day to the 800-mile Trans Alaska Pipeline System. Part of the inevitable layout on a land-based pipeline of this size is the need to cross roads and undergo similar directional changes. When the pipeline was constructed this hurdle was overcome by burying the pipe for short sections. At present the system has hundreds of buried road crossings. One of the continued high-cost maintenance issues with the pipeline is the corrosion that occurs at the elbows used for direction and elevation changes. The pipelines are constructed primarily out of high tensile strength carbon steels. While carbon steel is sufficient for most of the pipeline, the elbows present new challenges such as the cumulative effects of erosion and pitting corrosion. One proposed solution was to replace the carbon steel with duplex stainless steel in these areas of higher susceptibility. Duplex stainless steel has a high general corrosion resistance and better velocity-assisted corrosion resistance than carbon steel. Coupled with its recent decrease in cost, this solution makes the use of duplex stainless steel a potential candidate for the above application, reducing costs of the repair and inspection for the entire pipeline. Technical issues which are significant in joining carbon steel to duplex stainless steel include the proper selection of the weld metal alloy, weld cooling rates, and corrosion of the carbon steel due to the joining of dissimilar alloys. This paper addresses these issues of welding and corrosion that were investigated for the use of duplex pipe and components in the carbon steel system.
Emergency Assessment and Repairs of a Process Tower Subjected to Corrosion Under Insulation (CUI)
Authors: Rodery Clay D. , Cheta Ayman M.
Published: August 2008

A large process tower in a petroleum refinery was discovered to have severe Corrosion under Insulation (CUI) in two areas. The areas were confined to the vicinity of external rings, but spanned 360 degrees of the tower. The remaining thickness of the shell in these areas ranged from 3 mm to 9 mm (0.13 to 0.35 inches) [original thickness was 23 mm (15/16 inches)]. The tower was assessed for immediate risk of collapse, and emergency stabilizing bracing was installed while options for a permanent repair could be defined and selected. An external automated weld overlay technique was selected as a permanent repair method that restored the corroded areas to original thickness. This paper describes the engineering details taken to assess the immediate risk of collapse of the tower, including the emergency repairs taken to stabilize the tower. The review and selection of longer term repair options and the analysis involved in coordinating the removal of the emergency repairs with the installation of the permanent repairs in such a manner that the tower was returned to service well ahead of schedule are also covered.
Analysis of a Bolted Joint Failure in a Hydraulic Press
Authors: Deadman Jason
Published: August 2008

Micrographic inspection, acceleration tests, Finite Element Analysis and detailed fatigue failure calculations for combined static and dynamic loadings, were used in determining the cause of failure, and an acceptable repair solution, for a critical bolted joint. The bolted joint holds together the piston and ram within a hydraulic press. The press had been in operation for eleven years when the failure occurred. As the press is used in a critical process operation, a repair solution and future maintenance strategy was required that would minimize the possibility of future failures and permit maintenance during planned outages. This paper discusses the method that was followed to arrive at an acceptable solution.
Evaluation of Multiple Crack Propagation Behavior in a Gas Turbine Blade Under Thermal Fatigue Condition
Authors: Morita Akira , Kagawa Hiroyuki , Kubo Shiro
Published: August 2008

Frequent start-stop operation of a gas turbine sometimes causes coating cracks on the surface of the first stage blades. Since the coating cracks tend to propagate into the substrate, accurate prediction of crack propagation behavior is important to make a reasonable judgment for the repair or replacement of blades. This paper describes the development of a crack propagation prediction methodology for first stage blades, which includes evaluation of the stress intensity factor K, and estimation of temperature distribution and stress distribution between the outer surface and the inner cooling hole of blades. Since the coating cracks of blades reveal themselves as multiple parallel cracks with narrow intervals, a primary concern was directed to establish evaluation method of K values of multiple parallel cracks. For this purpose, a series of finite element analyses were performed for multiple edge cracked plate with finite width subjected to a crack face pressure expressed as σ=σn(x/W)n, where x is a distance from the mouth of the crack and σn is the stress at plate surface (x=W). The result was used to make approximate equations for the influence coefficient Gn, defined as K=Gnσn(a/W)n(πa)1/2, where a is a crack length. Temperature distribution was evaluated by observation of microstructure (gamma prime phase) change of a first stage blade used in a power plant for more than 20,000 hrs. Thermal stress distribution was calculated by finite element analysis using the evaluated temperature distribution. These results and the approximate equation of Gn were used to evaluate the crack propagation behavior of the blade surface, together with the fatigue crack propagation data of blade material that had been obtained in other studies.
Life Extension of Bolted Flanged Connections From a Design Peculiarities Point of View
Authors: Efremov Anatoly I.
Published: August 2008

Life extension of Bolted Flanged Connections (BFC) depends directly on early leakage that is a major cause of bolt degradation and failure. Experiments with standard BFC typically used in Nuclear Power Plant equipment and subjected to bolt preload and subsequent internal pressure revealed an influence of the BFC design peculiarities on early leakage. The experimental data became a basis for BFC design improvement.
Approach to Establish Flaw Evaluation Method for Class 2 and 3 Light Water Reactor Pipes
Authors: Miura Naoki , Miyazaki Katsumasa , Hisatsune Masakazu , Hasegawa Kunio , Kashima Koichi
Published: August 2008

To achieve a rational maintenance program for aged Light Water Reactor components, it is important to establish and to improve the flaw evaluation criteria. The current flaw evaluation criteria such as ASME Boiler and Pressure Vessel Code Section XI are focused on Class 1 piping which usually shows relatively higher toughness. On the other hand, flaw evaluation criteria suitable for Class 2, 3 piping with moderate-toughness are also from the viewpoints of in-service inspection request, reduction of operating cost, and systematization of consistent code/standard. In this study, both analytical and experimental studies were conducted to provide the allowable flaw sizes for acceptance standards as well as the evaluation method of fracture loads for acceptance criteria for Class 2, 3 piping. An approach to identify the allowable flaw sizes for acceptance standards was newly proposed using the failure assessment curve, and allowable flaw sizes for Class 2 3 piping were tentatively derived based on the approach. Cracked pipe fracture tests together with finite element analysis and simplified fracture analysis were also conducted using typical moderate-toughness pipe materials. The experimental and analytical results were reduced to the Z-factor to predict fracture loads of Class 2, 3 cracked piping.
Three-Dimensional Identification of Semi-Elliptical Surface Crack by Means of Direct-Current Electrical Potential Difference Method With Multiple-Probe Sensor
Authors: Tada Naoya , Okada Masayoshi , Iwamoto Jun
Published: August 2008

A method of three-dimensional identification of a semi-elliptical surface crack by direct-current electrical potential difference method with a multiple-probe sensor was proposed and its validity was numerically examined. The condition of the surface crack embedded in a conductive plate was specified by the two-dimensional location of the crack center, (yc, zc), length and depth of the crack, c and a, and the surface and inward angles of the crack plane, θsur and θin. Identification was carried out based on the distribution of the electrical potential difference around the crack measured on the surface of the plate with the “multiple-probe sensor” which is composed of many probes aligned in two orthogonal directions. The location, (yc, zc), and surface angle, θsur, were evaluated using the line and point symmetries of the potential difference distribution. The inward angle, θin, was determined by the magnitude of symmetry of potential difference distribution with reference to the evaluated crack line. Finally, length and depth of the crack, c and a, were determined using the exact solution of potential difference for an inclined inner elliptical crack which yields similar potential difference to that of the inclined semi-elliptical surface crack. The validity of the method was numerically confirmed by carrying out the evaluation based on the result obtained by finite element analysis.
Determination of Corrosion Layers and Protective Coatings on Steels and Alloys Used in Simulated Service Environment of Modern Power Plants
Authors: Nickel Hubertus , Quadakkers Willem J. , Singheiser Lorenz
Published: August 2008

The development of modern power generation systems with higher thermal efficiency requires the use of constructional materials of higher strength and improved resistance to the aggressive service atmospheres. In this paper the following examples are discussed: 1) The oxidation behavior of 9% Cr steels in simulated combustion gases: The effects of O2 and H2O content on the oxidation behavior of 9% Cr steels in the temperature range 600–800°C showed that in dry oxygen a protective scale was formed with an oxidation rate controlled by diffusion. In contrast, that in the presence of water vapor, after an incubation period, the scale became non-protective as a result of a change in the oxidation mechanism. 2) The development of NiCrAlY alloys for corrosion resistant coatings and thermal barrier coatings of gas turbine components: The increase of component surface temperature in modern gas turbines leads to an enhanced oxidation attack of the blade coating. Considerable efforts have been made in the improvement of the temperature properties of MCrAlY coatings by the additions of minor elements like yttrium, silicon and titanium. The experimental results show the positive, but different influence of the oxidation behavior of the MCrAlY coatings by the addition of these minor elements. 3) The development of light-weight intermetallics of TiAl-basis: TiAl-based intermetallics are promising materials for future turbine components because of the combination of high temperature strength and low density. These alloys, however, possess poor oxidation resistance at temperatures above 700°C. The experimental results showed that the oxidation behavior of TiAl-based intermetallics can be strongly improved by minor additions of 1–2 at.-% silver. 4) The oxide dispersion strengthened (ODS) alloys provide excellent creep resistance up to much higher temperatures than can be achieved with conventional wrought or cast alloys in combination with suitable high temperature oxidation/corrosion resistance. The growth mechanisms of protective chromia and alumina scales were examined by a two-stage oxidation method with 18O tracer. The distribution of the oxygen isotopes in the oxide scale was determined by SIMS and SNMS. The results show the positive influence of a Y2O3 dispersion on the oxidation resistance of the ODS alloys and its effect on growth mechanisms.
Managing Flow Accelerated Corrosion in Carbon Steel Piping in Nuclear Plants
Authors: Walker Z. H.
Published: August 2008

In 1996, Flow Accelerated Corrosion (FAC) was identified as a degradation mechanism affecting carbon steel outlet feeder pipes in CANDU® (CANadian Deuterium Uranium) reactors. The maximum rate of FAC was estimated to be <0.120 mm/year. In response, wall thickness inspection programs have been implemented to identify and measure the minimum wall thickness in outlet feeder pipes. These data are necessary to ensure fitness-for-service of the feeder pipe. These data, together with the thermalhydraulic and geometric parameters for the measured feeders, are also very useful for developing empirical wall thickness models. Such models can be used to enhance the understanding of feeder wall thinning leading to an improved capability to predict future wall thickness minima and their locations. The determined dependency of the wall-thinning rate on thermalhydraulic conditions can be used to quantify the potential benefits of maintenance activities, such as steam generator cleaning. Activities such as steam generator cleaning are generally viewed as beneficial in recovering lost thermal efficiency, thereby reducing the severity of the thermalhydraulic conditions by reducing the amount of quality (steam phase) exiting the reactor core. Finally, when wall thickness models are applied to data from different plants, there is the potential of identifying operating conditions that can lead to lower rates of wall loss. This paper addresses the aforementioned important issues associated with FAC of ASME PVP Class 1 carbon steel piping.
Extrapolation of Shorter Time Creep Rupture Data Using the Damage Mechanics Approach of Penny
Authors: Furtado Heloisa C. , May Iain Le , de Almeida Luiz Henrique , Peace Robert
Published: August 2008

Recently Penny has extended the use of the continuum damage mechanics approach of Kachanov and Rabotnov to the extrapolation of shorter time creep rupture data to longer times. In this paper the authors review the methodology developed by Penny and have applied it using creep data for 9Cr-1Mo and 2.25Cr-1Mo steels that they have tested, as well as using data from the literature. The method appears to provide a reliable method of extrapolation from isothermal data, and can provide an economical and physically justified approach to the development of longer time creep-rupture data.
Research and Development Issues for Fast Reactor Structural Design Standard (FDS)
Authors: Kasahara Naoto , Ando Masanori , Morishita Masaki , Shibamoto Hiroshi , Tanaka Yoshihiko , Inoue Kazuhiko
Published: August 2008

For the realization of safe and economical fast reactor (FR) plants, the Japan Nuclear Cycle Development Institute (JNC) and Japan Atomic Power Company (JAPC) are cooperating on a research project titled “Feasibility Study on Commercialized FR Cycle Systems.” To certify the design concepts and validate their structural integrity, the research and development of the “Fast Reactor Structural Design Standard (FDS)” is recognized as being an essential theme. FDS considers the general characteristics of FRs and the design requirements for their rationalization. Three main problem areas related to research and development issues were identified by FDS. The first is “refinement of failure criteria,” which takes characteristic design conditions into account. The next is the development of “guidelines for inelastic design analysis” in order to predict the elastic plastic and creep behaviors of high-temperature components. Finally, efforts are being made toward preparing “guidelines for thermal load modeling” for FR component design where thermal loads are dominant. Their research plans and current status are explained.
Cyclic Analysis for High Temperature Design
Authors: Carter Peter , Marriott D. L. , Swindeman M. J.
Published: August 2008

The paper addresses the problem of analysis of cyclic loading for creep and ratcheting. The approach is to use cyclic elastic-plastic analysis to generate shakedown and ratcheting boundaries or reference stresses. These provide bounds to creep damage and strain accumulation, which are independent of time and temperature. Two cases are analyzed, which have different behavior from the Bree problem, which forms a basis for ASME IIINH creep strain design rules.
Simplified Elasto-Plastic Response Analysis Method of Piping
Authors: Otani Akihito , Nakamura Izumi , Takada Hajime
Published: August 2008

When piping systems are subjected to extreme seismic excitation, they undergo a plastic deformation that produces a large damping effect via energy dissipation. Based on our studies of the damping effect of the elasto-plastic response of piping, we have presented a simplified method for predicting the elasto-plastic response of piping in PVP conferences over the last several years. Yet the elasto-plastic response of piping calculated by this method resulted in conservative predictions compared with the results of piping model excitation tests. In the proposed method, we calculate the vibration energy of piping and the dissipation energy with plastic deformation by FEM analysis and obtain the equivalent damping ratio as a ratio between the two. The equivalent damping ratio and response are interdependent and can be calculated as a pair of converged values. In this paper we report simulation results from 3D piping model excitation tests as well as the results from 2D piping model tests. The simulation method is a modified and improved version of the method reported earlier. The results obtained by the revised method more closely matched the results of the excitation tests.
Influences of Fabrication Defects Upon the Strength and Lives of Filament Wound Composite Cylinders
Authors: Takehana Tatsumi , Sano Takeru , Kawahara Masanori
Published: August 2008

Filament wound composite cylinders are much expected as fuel gas containers for hydrogen fuel cell vehicles, hydrogen transportation containers, or pressurizing hydrogen accumulators due to their high performances in strength and lightness. Stress distribution in the cylinder can be controlled by the winding modes of the filaments and the liner thickness design. However, small fabrication defects may sometimes result irregular changes in stress distribution in the composite and liner layers and influences much upon the strength and lives of the composite cylinders. Stress distributions can be analyzed by a finite element method by modeling the mechanical anisotropy in composite layers and elasto-plasticity in the liner layer. The deviation of the position of the hoop layer ends influences much upon the basic performance of the vessel.
Failure of a Second Stage Valve Head on a LDPE Hyper Compressor
Authors: Keltjens Jan , Hendrikx Marcel
Published: August 2008

After 16 years of operation a failure occurred in a 2nd stage valve head of a hyper compressor of a polyethylene plant. The inner cylinder of the shrink-fit assembly ruptured. The fracture was initiated on a fatigue crack starting in the chromium layer on the inner the bore of the valve head. The fatigue crack clearly indicated a large number of arrest lines showing that the failure must have developed over a rather long period of operation. At the location of the crack initiation under normal operation no alternating pressure is present. The paper describes a stress- and fatigue crack growth analysis of the valve head as well as the root cause analysis for the fatigue crack as well as remedial measures taken to prevent future failure.
Stress Analysis and Sealing Performance Evaluation in Non-Circular Flange Connections With Gaskets Subjected to Internal Pressure
Authors: Maezaki Wataru , Sawa Toshiyuki
Published: August 2008

The contact gasket stress distributions of a non-circular flange connection with a compressed asbestos sheet gasket subjected to internal pressure were analyzed taking into account of the hysteresis behaviors of the gasket by using the finite element method (FEM). Leakage tests were also conducted using an actual non-circular flange connection with a compressed asbestos sheet gasket under internal pressure. Using the contact gasket stress distributions and the results of the leakage tests, the new gasket constants were calculated. The difference in the new gasket constants between the values obtained from the present study and those by the PVRC procedure was substantial. In addition, a method to determine the initial clamping bolt force (bolt preload) for a given tightness parameter was demonstrated.
Application of a Knowledge-Based Information System for Life Extension of Steel Making Plant
Authors: Park Y. J. , Choi J. B. , Kim Y. J.
Published: August 2008

In this paper, a knowledge-based information system for the plant operation of steel making company has been proposed. This system, which is named as K-VRS (Knowledge-based Virtual Reality System), provides a connection between ERP PM module and knowledge-based engineering methodologies, and thus, enables network-based highly effective PM process. While the virtual plant is used for the master of K-VRS, there are four expert modules attached; engineering document management module, real time lifetime estimation module, fitness for service module and risk-based inspection module. Each module provides engineering knowledge based evaluation and judgment for more effective PM. K-VRS provides collaborative and concurrent working environment to workers and relevant experts. The developed system is expected to play a great role for plant life extension.
Analytical Study of Flow Regimes for Direct Contact Condensation Based on Parametrical Investigation
Authors: Petrovic Anka
Published: August 2008

Various industrial devices exist where Direct Contact Condensation (DCC) of steam in water takes place. Typical examples are the nuclear reactor coolant systems, steam driven jet pumps and condensers. The modelling of steam condensation is crucial to obtain an appropriate design of such devices. Present models designed for DCC have shown limited agreement with experimental data. Computation of the flow regimes is performed with limited accuracy, due to initial model settings and empirical correlations, which form a main drawback in the computation of DCC related problems. This study, which is a part of a PhD study, presents an investigation of the steam-water interface for various conditions of steam and water, using the computation of balance equations and jump conditions. A simple mathematical model to predict the location of the condensation interface for four different shapes of steam plume at different heat transfer coefficients is presented which will be further developed into an advanced computational model for DCC.
Dynamic Analyses of a Metallic Sample in Sonic Infrared NDE Technique: Experimental and Computational Approach
Authors: P. Saha Chinmoy
Published: August 2008

Sonic IR is an emerging NDE technique being developed at the Wayne State University that has potential crack detectability both in metallic and non-metallic materials. The technique has applications in various sectors of NDE including aerospace, automotive, transportation, pressure vessel, and piping and manufacturing. Although it is established that friction caused by rubbing between the faying surfaces (i.e. tightly closed surfaces of closed surface cracks) or other material flaws under sonic load generates heat, the relationship of the quality and quantity of heat generation mechanics are not yet well known. In this paper a simple aluminum plate sample with generated cracks is studied through both experimentation and finite element (FE) modeling and simulation. The dynamics of Sonic IR for a simple metallic sample are analyzed with LS-DYNA3D finite element program. The FE analysis does support the frictional heat generation due to the rubbing of the faying surfaces of the crack faces. FE analysis also allows visualization of crack faces rubbing mode. The experiments show the infrared signal level as the indication of heat generation, captured in real time video frames. In FE simulation the energy plot at the crack interface is an indicator of heat generation and the energy plots are compared with the infrared signal plot. The results of varying test parameters in experiments as well as FE simulations are also discussed.
Nonlinear Finite Element Analysis of a Threaded Pipe Connection
Authors: Tasbihgoo Farzad , Caffrey John P. , Masri Sami F.
Published: August 2008

For the past several years, USC has been involved in a major research project to study the seismic mitigation measures of nonstructural components in hospitals funded by the Federal Emergency Management Agency (FEMA). It was determined that piping was the one of the most critical components affecting the functionality of a hospital following an earthquake. Consequently, a substantial effort was spent on quantifying the behavior of typical piping components. During the loading of the threaded joint, it was common to hear a loud popping sound, followed by a small water leak. It was assumed that the sound and leakage were due to the sliding of the mating pipe threads. To confirm this theory, and to provide a tool to help understand the failure mode(s) for a wide class of threaded fittings, a detailed nonlinear finite element model was constructed using MSC/NASTRAN, and correlated to the measured failures. In this paper, a simplified model is presented first to demonstrate the modeling procedure and to help understand the sliding phenomenon. Next, a symmetric half 3D model was generated for modeling the physical experiments. It is shown that the finite element analysis (FEA) of the threaded connections captures the dominant mechanism that was observed in the experimental tests.
A New Approach to Predicting Fatigue Crack Propagation
Authors: Jiang Yanyao , Feng Miaolin
Published: August 2008

A new approach was developed for the prediction of fatigue crack growth. Based upon the elastic-plastic stress analysis of a crack component and the application of a general multiaxial fatigue criterion, fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants obtained for crack initiation. The cyclic elastic-plastic stress-strain field near the crack tip was analyzed using the finite element method with the implementation of a robust cyclic plasticity theory. A multiaxial fatigue criterion was employed to determine the fatigue damage. With an incremental form, the multiaxial fatigue criterion can be directly used for assessing fatigue damage near the crack tip. A straightforward method was developed to determine the fatigue crack growth rate. Crack propagation behavior of a material was obtained without any additional assumptions or fitting. Benchmark Mode I fatigue crack growth experiments were conducted using 1070 steel at room temperature. The approach was able to quantitatively capture all the important fatigue crack propagation behaviors including the overload and the R-ratio effects on crack propagation and threshold. The models provide a new perspective for the R-ratio effects. The success of the approach confirms that the fatigue crack initiation and propagation behaviors are governed by the same fatigue damage mechanisms. Crack growth can be treated as a process of continuous crack nucleation. In addition, the sensitivity of the predicted fatigue growth rate to the element size in the finite element model was discussed.
Mechanisms and Modeling Comparing HB7 and A723 High Strength Pressure Vessel Steels
Authors: Troiano E. , Parker A. P. , Underwood J. H. , Mossey C. , Vigilante G. N.
Published: August 2008

HB7, an ultra-clean, high strength pressure vessel steel manufactured in France, is compared to A723 steel. This steel, suggested as an improved pressure vessel material is currently being proposed for critical applications, and will likely be used more frequently as design engineers discover its capabilities. This paper includes comparisons of strength, fracture toughness, fatigue properties and composition of the two steels, followed by an in-depth comparison and modeling of environmental cracking resistance, Bauschinger-modified residual stresses and fatigue lives. Results indicate that in all critical areas, with the exception of Bauschinger-reduced residual stress, the HB7 is superior to the A723 steel. Particularly for small amounts of autofrettage, near-bore residual stresses are reduced for HB7 steel compared to those for A723 steel at the same strength level. The greatest improvement of the HB7 over the A723 is in environmental cracking resistance. The BH7, when tested in concentrated sulfuric acid, exhibits five orders of magnitude longer crack incubation times and three orders of magnitude slower crack growth rates, when compared to A723 steel at the same strength level.
Development of Weight Functions for Modelling Delayed Hydride Cracking Initiation at a Blunt Flaw
Authors: A. Scarth Douglas , Wu Joanna , Smith Ted , Kawa Dennis M.
Published: August 2008

Delayed Hydride Cracking (DHC) in Zr-2.5 Nb alloy material is of interest to the CANDU (Canada Deuterium Uranium) industry in the context of the potential to initiate DHC at a blunt flaw in a CANDU reactor pressure tube. The material is susceptible to DHC when there is diffusion of hydrogen atoms to the flaw, precipitation of hydride platelets, and development of a hydrided region at the flaw tip. The hydrided region can then fracture to the extent that a crack forms, and is able to grow by the DHC crack growth mechanism. An engineering process-zone model for evaluation of DHC initiation at a blunt flaw that takes into account flaw geometry has been developed. The model is based on representing the stress relaxation due to hydride formation, and crack initiation, by an infinitesimally thin process zone. Application of the engineering process-zone model requires calculation of the stress intensity factor, and the crack-mouth opening displacement, for a fictitious crack at the tip of a blunt flaw. In the current model, calculation of these quantities is based on a cubic polynomial fit to represent the stress distribution ahead of the blunt flaw tip, where the stress distribution is generally calculated by finite element analysis. However, the cubic polynomial is not always an optimum fit to the stress distribution for very small root radius flaws, due to the large stress gradients near the flaw tip. Application of the weight function method will enable a more accurate representation of the flaw-tip stress distribution for the calculation of the stress intensity factor and the crack-mouth opening displacement. Weight functions for a crack at the tip of a blunt flaw in a thin wall cylinder have been developed for implementation into the engineering process-zone model. These weight functions are applicable to a wide range of blunt flaw depths and root radii, as well as a wide range of flaw-tip crack depths. The development and verification of the weight functions is described in this paper. The verification calculations are in reasonable agreement with alternate solutions, and have confirmed that the weight functions have reasonable accuracy for engineering applications of the process-zone methodology.
Development of Analytical Evaluation Procedures and Acceptance Criteria for Pipe Wall Thinning in ASME Code Section XI
Authors: Hasegawa Kunio , Wilkowski Gery M. , Goyette Lee F. , Scarth Douglas A.
Published: August 2008

As the worldwide fleet of nuclear power plants ages, the need to address wall thinning in pressure boundary materials becomes more acute. The 2001 ASME Code Case N-597-1, “Requirements for Analytical Evaluation of Pipe Wall Thinning,” provides procedures and criteria for the evaluation of wall thinning that are based on Construction Code design concepts. These procedures and criteria have proven useful for Code Class 2 and 3 piping; but, they provide relatively little flexibility for Class 1 applications. Recent full-scale experiments conducted in Japan and Korea on thinned piping have supported the development of a more contemporary failure strength evaluation methodology applicable to Class 1 piping. The ASME B&PV Code Section XI Working Group on Pipe Flaw Evaluation has undertaken the codification of new Class 1 evaluation methodology, together with the existing Code Case N-597-1 rules for Class 2 and 3 piping, as a non-mandatory Appendix to Section XI. This paper describes the current status of the development of the proposed new Class 1 piping acceptance criteria, along with a brief review of the current Code Case N-597-1 evaluation procedure in general.
A New Approach for Evaluating Radiation Embrittlement of Reactor Pressure Vessel Steels
Authors: Wang J. A. , Rao N. S. V.
Published: August 2008

A new approach is developed to predict the radiation embrittlement of reactor pressure vessel steels. The Charpy transition temperature shift data contained in the Power Reactor Embrittlement Database is used in this study. The results indicate that this new embrittlement predictor achieved about 67.3% and 52.4% reductions respectively, in the uncertainties for General Electric (GE) Boiling Water Reactor plate and weld data compared to Regulatory Guide 1.99, Rev. 2 (RG1.99/R2). The implications of irradiation temperature effects for the development of radiation embrittlement models are then discussed. A new approach for the Charpy trend curve is also developed, which incorporates the chemical compositions into the governing fitting equation. This approach reduces the uncertainty of Charpy data fitting and provides an expedient scheme to link and project the surveillance test results to those for reactor pressure vessel steels.
Benchmark of Plate Forming and Weld Distortion Process
Authors: Gombas James M.
Published: August 2008

A circular flat plate with a perforated central region is to be formed by dies into a dome and then welded onto a cylindrical shell. After welding, the dome must be spherical within a narrow tolerance band. This plate forming and welding is simulated using large deflection theory elastic-plastic finite element analysis. The manufacturing assessment is performed so that the dies may be designed to compensate for plate distortions that occur during various stages of manufacturing, including the effects of weld distortion. The manufacturing simulation benchmarks against measurements taken at several manufacturing stages from existing hardware. The manufacturing simulation process can then be used for future applications of similar geometries.
Computational and Experimental Simulation of Synchronous Generator Ventilation
Authors: Vlach Radek , Grepl Robert , Ondrusek Cestmir
Published: August 2008

This project is concerned with computational simulation of air flow in the individual parts of a synchronous machine. FLUENT6 software was used for computational modeling. A model of a machine fan was built, which was used for calculation of ventilation characteristics. Ventilation characteristics were calculated for three ventilator diameters. The aim was to find the operating point for each fan. A model of the asymmetrical inlet to the machine and the distribution of airflow to the stator and rotor was built, which consisted of inlet to machine, axial stator and rotor channels and ten radial channels in the stator packet. A parametric computational model was developed with three main parameters — size of axial stator and rotor channels and size of radial channels. The results of the computer simulation were compared with experimental measurements, which were accomplished on the synchronous generator using a Pitot tube and digital micro manometer.
Influence of the Cutting Variables on the Surface Roughness of Alloy Steels Machined With Cylindrical Grinding
Authors: Cassier Zulay , Mun˜oz-Escalona Patricia , Tepedino Carlos
Published: August 2008

In machining precision mechanical parts, the prediction and the control of the desired surface roughness is very important. The grinding process requires a good control of the operative variables to guarantee best results. This research analyses the influence of the cutting variables such as workpiece speed, wheels grain size, down feed, and workpiece hardness on the surface finish and it is shown how the surface roughness improves when using low values of workpiece speed, transverse feed and down feed, as well as a small wheel grain size. A mathematical expression for roughness, Ra, as a function of the cutting variables and the mechanical properties, is obtained in order to predict the value of surface roughness. AISI 4140, AISI 4340 and AISI O1 alloy steels under different conditions were used for the experiments.
Influence of Stress on Degradation and Life Prediction of High Strength Ferritic Steels
Authors: Kimura Kazuhiro , Sawada Kota , Kubo Kiyoshi , Kushima Hideaki
Published: August 2008

Influence of stress on creep deformation and degradation behavior has been investigated. Corresponding to inflection of stress vs. time to rupture curve, difference in recovery phenomena, that was homogeneous in short-term and inhomogeneous in long-term, was observed. Inflection of stress vs. time to rupture curve took place at the stress condition corresponding to half of 0.2% offset yield stress at the temperature. Elastic limit stress of Grade 91 steel was evaluated to be 150MPa at 600°C and 100MPa at 650°C, by means of stress abrupt change test. These stresses were found to be almost the same as half of 0.2% offset yield stress at the temperatures. Inflection of stress vs. time to rupture curve is caused by transient of applied stress from higher level than elastic limit to within elastic range. It has been concluded that long-term creep strength of ferritic creep resistant steels should be predicted from the selected creep rupture data under the stresses lower than elastic limit by considering half of 0.2% offset yield stress at the temperature, by means of Larson-Miller parameter with a constant of 20.
Creep Properties of Gr.91 Castings and Forgings With High Residual Elements
Authors: Masuyama F. , Nishimura N. , Ozaki M.
Published: August 2008

Gr.91 castings are used in high temperature valves for main steam lines and elsewhere, while Gr.91 forgings are essential products for power boilers and in turbine construction. However, scrap steel is very often used as a raw material in the manufacturing of Gr.91 castings and forgings, suggesting the inclusion of high levels of residual tramp elements in the products when the quality of the raw material and process is out of control. The influence of residual elements such as P, S, Cu, Sn, and Sb on creep properties is a very important issue from the standpoint of using Gr.91 castings and forgings in high temperature components. This study focuses on the effect of the amount of tramp elements on the creep properties of Gr.91, investigating the creep mechanisms of tempered martensite lath structures with the above-noted elements. As a result, it was found that creep strength increased by either increasing the content of P or S, or by decreasing the amount of Sn or Sb. The Cu content did not affect creep strength at 600°C. At 650°C, the creep rate was unaffected by the tramp elements. Whereas the carbide distribution was hardly influenced by the proportion of the tramp elements, the martensitic lath spacing was observed to be dependent on the content, and was also related to the minimum creep rate obtained in creep testing at 600°C.
Metallurgical Investigation of a Type IV Damage at the Heat Affected Zone of Weld for Tungsten Containing Martensitic Heat Resistant Steels
Authors: Hasegawa Yasushi , Muraki Taro , Ohgami Masahiro
Published: August 2008

Metallographic analyses were carried out to clarify the micro-mechanism of Type IV failure at the outer edge of HAZ for W containing martensitic creep resistant 9 to 12% Cr steels. Microstructure observation and the creep rupture test determined the type IV failure location at fine grain HAZ through the welding thermal cycle simulation. Based on the comparison of three candidate mechanisms, grain size refinement, dislocation sub-structure evolution and precipitation morphology alteration, the microstructure evolution by thermal cycle of welding and PWHT was expected to be the main reason for the failure. TEM analysis of the microstructure elucidated the globular sub-grain microstructure formation by PWHT derived from the low dislocation density of the fine grain martensite with ambiguous lath structure. The precipitation morphology change is also one candidate for type IV failure. The quantification of the influence of V-Wing type MX disappearance at fine grain HAZ on creep rupture strength must be accurately estimated in further research.
Full Size Internal Pressure Creep Test for Welded P91 Hot Reheat Piping
Authors: Nonaka Isamu , Ito Takuya , Takemasa Fumio , Saito Kensuke , Miyachi Yoshikazu , Fujita Akigo
Published: August 2008

In order to establish the life assessment method for the welded modified 9Cr-1Mo steel hot reheat piping, an internal pressure creep test is conducted with a full size test component. As a result, the fracture mode of the component is clarified and the life prediction method is established. Furthermore, the creep damage detection procedures are proposed.
Full Size Internal Pressure Creep Test for Welded P91 Hot Reheat Elbow
Authors: Nonaka Isamu , Ito Takuya , Takemasa Fumio , Saitou Kensuke , Miyachi Yoshikazu , Fujita Akigo
Published: August 2008

In order to establish the life assessment method for the welded modified 9Cr-1Mo steel hot reheat elbow, an internal pressure creep test is conducted with a full size test component. As a result, the fracture mode of the component is clarified and the life prediction method is established. Furthermore, the creep damage detection procedures are proposed.
Phase Transformation and Properties of Gr.91 at Around Critical Temperature
Authors: Masuyama F. , Nishimura N.
Published: August 2008

During the fabrication processes of boiler components, heating, forming and welding processes are commonly applied to the materials used. The effect of heating and strain induced by the these fabrication processes are very important in maintaining the integrity of creep strength enhanced steels, because it is well known that the mechanical properties of normalized and tempered high strength steels are relatively sensitive to thermal and work history. In particular, while Gr.91 steel has been used extensively for boiler and pressure components over the last two decade, the heat treatment and forming procedures for this steel are not fully established based on fundamental transformation and strain behavior. This paper deals with the phase transformation behavior of Gr.91 during tempering at around the Ac1 temperature, and the hardness/creep properties of Gr.91 steel heated at temperatures from just below Ac1 to above Ac3 combined with strain.