bluuebunny/crossref_metadata_2025 huggingface dataset:
Operating Nuclear Plant License Renewal Program Status and Trends
Authors: Young Garry G.
Published: May 2012

As of February 2011, the NRC has renewed the operating licenses for 62 nuclear units, which will allow for up to 60 years of safe nuclear plant operation. In addition, the NRC has license renewal applications under review for 20 units and nuclear plant owners of more than 17 units have announced plans to submit license renewal applications over the next few years. This brings the total of renewed licenses and announced plans for license renewal to over 95% of the 104 currently operating nuclear units in the U.S. This paper presents the status of the U.S. license renewal process, the positive trend in regulatory stability through 2007, and the negative trend in regulatory stability after 2007. From 2000 through 2007, the NRC was able to complete the license renewal review and issue renewed licenses in 30 months or less for 100% of the license renewal applicants. In fact, approximately 77% of the reviews were completed in 22 months or less. Since 2007, NRC reviews have become much less predictable, with 21% of the reviews exceeding 30 months and only 7% being completed in 22 months or less. In fact, some reviews currently underway have exceeded 60 months and the reviews remain incomplete. One of the main factors leading to the loss of timely regulatory reviews has been the NRC adjudicatory process for license renewal, although the safety and environmental review processes have also become less timely since 2007. The factors that contributed to the positive and the negative trends are presented.
Challenges Associated With License Renewal Fatigue Evaluations for an Older-Vintage BWR Plant: Part 2
Authors: Pace Raymond M. , Mogolesko Fred J. , Herrmann Terry J. , Mileris George , Gustin Harry L. , Novotny Tyler
Published: May 2012

The Pilgrim Nuclear Power Station (PNPS) License Renewal Application (LRA) was submitted to the NRC in January 2006. As a part of the LRA submittal, Entergy committed to manage the aging effects of the reactor coolant environment on fatigue usage during the extended period of operation. As a part of PNPS’s aging management strategy, fatigue analysis was performed for 60-years of operation including EAF. This document provides some background information on the PNPS fatigue analysis, a summary of related information contained in the LRA submitted for NRC review and the specific actions taken to address the LRA commitments. A previous paper (PVP2010-25329) was prepared to provide an example of efforts expended to demonstrate long-term acceptability for license renewal where additional margins are required for PNPS Nuclear Power Station. The intent was to educate the reader on the efforts involved, the vast array of input that is needed and the possible hurdles that may be encountered for the validation and re-evaluation of Class 1 component fatigue for license renewal. The previous PVP paper discussed the foundation aspects necessary to prepare a refined fatigue evaluation with environmental affects for the plant. These include plant history, B31.1 piping analyses, environmental considerations, transient history, design specification and refined nozzle evaluations. The present paper discusses the importance of laying the appropriate foundation in the context of the final results that were obtained. It provides additional background information and actions taken to address the license renewal commitments and summarizes detailed results.
The Design, Analysis, Testing, and Use of a Small Confinement Vessel for Material Shock Physics Experiments
Authors: Valdiviez Robert , Sandoval Peter P. , McNeil Wendy V.
Published: May 2012

This paper describes the design, supporting analyses, fabrication, acceptance testing, and deployment of the Small Experiment Confinement Vessel (SECV). The vessel is used in a radiographic imaging facility for confining shock physics experiments where materials are driven to extreme loading conditions by the detonation of high explosives. The SECV provides an inexpensive means for confining a small shock physics experiment primarily due to its relatively simple design as compared to other confinement vessels. The main function of the SECV is to protect the nearby diagnostic equipment from damage by materials of the dynamic experiment. The vessel has been designed to the criteria of the ASME Boiler and Pressure Vessel Code, Section VIII, Division 3, Code Case 2564, with the exception of the materials of construction. The SECV is intended for reuse, with the total number of firings for any one vessel structure being primarily dependent on the accumulated wall damage. The main body of the SECV is made of pipe material per the American Petroleum Institute standard ANSI/API 5L. Machined end flange weldments are joined to the pipe body to enable the closure covers to be bolted to the body. The closure covers have various devices mounted to them, for example a manually actuated valve for venting the vessel interior of detonation gasses, and feed through devices for sending electrical and optical signals across the pressure boundary.
Isochronous Stress/Strain Curves: Origins, Scope and Applications
Authors: Marriott Douglas L.
Published: May 2012

The isochronous stress/strain curve is a long established method of representing creep data in a manner which, under certain circumstances, provides a quick and often surprisingly accurate approximate solution to time dependent structural problems. Despite criticisms of the foundations of the method, it has survived over the years because it has either been the only method feasible at the time, or it is capable of providing solutions which are often good enough for practical purposes. This paper plans to trace the evolution of structural analysis based on isochronous curves, examining its boundaries of application and the circumstances under which it might be expected to yield plausible answers. Different types of isochronous curves will be described, together with procedures for constructing them from different forms of material data such as constant strain rate tensile tests. Special attention will be given to the representation of tertiary creep in the form of isochronous curves, and how such curves might be used in carrying out simplified analyses of propagating creep damage in complex components. Recent extensions to the original methodology to include variable load and thermal histories will be examined. Possible applications in the emerging field of very high temperature applications, as are expected to be experienced in Gen IV nuclear plant in the future, will be reviewed, with special attention given to the problem of rate dependent short term properties, which looks to become a serious question in development of design allowables for very high temperature applications.
Fatigue Strength Reduction Factors for Socket Welds as a Function of Leg Length
Authors: Hirschberg Paul , Crompton Andrew M. , Couch Robert Dana
Published: May 2012

Socket welds in nuclear power plant piping systems have had a history of failure due to high cycle fatigue. Cyclic bending loads, typically from vibration, have caused cracking either at the weld root or at the toes. A testing program was conducted to measure the effectiveness of proposed changes in socket weld geometry and fabrication [3]. One of the significant results of that testing program was that if the socket weld profile was modified such that the weld leg length along the pipe side is at least double the Code minimum requirement the fatigue life of the weld becomes approximately as good as that of a butt weld. The test results demonstrated that the fatigue strength reduction factor (FSRF) is about 37% smaller for socket welds with the longer weld leg, than for a standard size weld. Many plants have been replacing or building up their socket welds in locations susceptible to vibration to the 2×1 geometry to take advantage of the improved fatigue strength. However, there have been situations where welds were built up from the Code minimum, but inspections determined that the leg length was somewhat less than twice the minimum required and the weld was not accepted as meeting the 2×1 geometry. It is not known how the fatigue strength reduction factor would vary as a function of leg length for intermediate sizes. It is also of interest to determine the effect of increasing the weld leg length on the fitting side. For example, is it possible that increased fatigue resistance can be provided by adding additional leg length on the fitting side instead of the pipe side, or can a greater benefit be achieved if they were provided on both sides?
Development of Tightening Torque for Self Tapping and Thread Rolling Fasteners
Authors: Alkelani Ali , Housari Basil
Published: May 2012

Torque is the most common tightening strategy used to control clamp load when bolts are tightened, since a direct relationship between torque and clamp load exists. For unified and metric fasteners used in non-critical applications, there are torque tables available in the literature that provide a guideline as to what torque level is recommended to be used based on fastener size, thread pitch, and material class. For critical applications, the tightening specification is usually developed based on individual cases. For self tapping and thread rolling screws, the tabulated torque values available for machine threaded screws cannot be used. If the torque spec is not developed carefully for such joints then problems such as stripping the threads or torqueing out before seating the screw may be encountered. This is mainly due to the fact that these types of screws are very sensitive to many variables, such as thread type, hole size, coating, joint surface finish, tapped material thickness, and other factors. For such fasteners, the torque spec should be developed experimentally based on test data for the actual joint. This paper provides an accurate procedure for developing tightening specifications for joints that use self tapping and thread rolling screws. Additionally, it provides a criterion to determine whether the joint design is robust enough for assembly or not.
The Danger of Piping Failure due to Acoustic Induced Fatigue in Infrequent Operations: Two Case Studies
Authors: Al-Muslim Husain Mohammed , Al-Nasri Nadhir Ibrahim , Al-Hashem Mohammad Y.
Published: May 2012

Failure in piping due to acoustic induced fatigue can be considered catastrophic as it could happen only after a few minutes of operation. Acoustic induced fatigue occurs mainly in gas piping systems with high velocity where high energy is dissipated through pressure reducing stations and pipe branch connections. It usually results in pipe through wall longitudinal cracks, pipe detachment from saddle supports and complete shear off of branch connections. There are existing design criteria to avoid acoustic induced fatigue based on comparison of generated power level to an acceptable power level. This criterion is normally used for the design of pressure relief and flare piping where high gas velocity exceeding 50% of the speed of sound (i.e.0.5 Mach) is expected. However, acoustic induced fatigue has been experienced in systems due to intermittent operations. Two case studies are presented in this paper. The first one is during a steam-out operation to clean a newly constructed steam header. During the cleaning operation, an orifice plate was used to control the flow in the steam header. Several pipe vents and drains failed due to fatigue in less than 1 hour. The second case is for drainage of compressed natural gas during process upset condition. Because of the high level buildup in the liquefied gas separator vessel, the drain valve was opened to release the pressurized liquefied gas to the relief system to reduce the level buildup. Wall cracks and several pipe support detachments were found in the system after the upset condition. This paper presents the engineering analysis and material failure analysis conducted to find the root causes of the failures. Moreover, it highlights the recommendations and lessons learned from these two failures.
Meshless Analysis of Ductile Failure
Authors: Li J.
Published: May 2012

We study ductile fracture using Reproducing Kernel Particle Interpolation and the Gurson-Tvergaard-Needleman (GTN) model. The meshless simulations are compared with the available experimental results and previous finite element simulations for crack propagation. The results agree well with experimental results, and it is confirmed that the proposed method provides a convenient and yet accurate means for simulation of ductile fracture.
Type Acceptance Testing of Valves: Petroleum Industry User Experience
Authors: Smart Tony , Cheta Ayman
Published: May 2012

Successful valve testing required by basic industry standards does not guarantee that the valve will continue to function as intended during its normal operation. In the petroleum industry, valve integrity and reliability can make the difference between profit and loss. Type Acceptance Testing of Valves by subjecting the valve to a combination of mechanical, pressure and temperature cycling simulates the actual operating conditions the valve will be subjected to during normal operation. In this paper, the authors share their experience with Type Acceptance Testing of valves.
Review of ASME III Code Case for the Application of Finite Element Based Limit Load Analysis
Authors: Martin Michael , Watson Chris , Wright Keith
Published: May 2012

The use of finite element based limit load analysis for the assessment of the primary load capacity of a pressure vessel is well established and numerous papers on the subject, including experimental results, have been published in the last decade. Finite element based limit load analysis is often used in the context of NB-3228.1 Limit Analysis to demonstrate a margin against ductile burst as an alternative to satisfaction of the NB-3200 limits on general, local and primary membrane plus bending stress intensity. However, although NB-3200 permits the use of ‘limit analysis’, no specific guidance on the use of finite element methods for this purpose is provided. Other pressure vessel codes, including ASME VIII Division 2 and EN13445 contain explicit guidance on the use of finite element methods for limit load analysis. To address this, a Code Case is currently under development to provide technical guidance on the use of finite element based limit load analysis within the context of NB-3200 assessments. The Code Case provides a step-by-step procedure which guides the analyst in the application of limit load analysis and ensures that a valid analysis has been undertaken. The topics of geometric weakening, yield surface selection, tentative wall thickness, element selection and selection of Sm are accounted for in the Code Case and discussed. This paper provides a detailed review of the Code Case and shows how it can be used in practice.
Leakage Analysis of Gasketed Flanged Joints Under Combined Internal Pressure and Thermal Loading
Authors: Abid Muhammad , Khan Kamran Ahmed , Chattha Javed Ahmad , Nash David H.
Published: May 2012

Leakage in Gasketed Flanged Joints (GFJs) has always been a great problem for the process industry. The sealing performance of a GFJ depends on its installation and applied loading conditions. This paper aims to finding the leak rate through ANSI class#150 flange joints using a compressed asbestos sheet (CAS) gasket under combined structural and thermal transient loading conditions using two different leak rate models and two different bolt-up levels. The first model is a Gasket Compressive Strain model in which strains are determined using finite element analysis. The other model is based on Porous Media Theory in which gasket is considered as porous media. Leakage rates are determined using both leak rate models and are compared against appropriate tightness classes and the effectiveness of each approach is presented.
Application of RBI Method to Increase the Efficiency of Furnace B-1201 Belonging to ENAP Aconcagua Refinery, Chile
Authors: Fernandes Isis V. , Segeur Fernando H. , Pelliccioni Orlando J.
Published: May 2012

The Chilean company ENAP has a complex refining system in Conco´n, with important equipments like the furnace B-1201, belonging to the Hydrocracking Plant, and responsible for the partial conversion of vacuum gasoil into lighter products. This equipment works in a temperatures range between 300 and 400°C. During this process, the equipment is exposed to factors causing the decreased in its operative life and catastrophic failures. These results are reported as a decrease in equipment efficiency and significant financial loss. Energy costs represent 80% of operating costs. This paper presents an analysis of risk for furnace B-1201 in the superior limit of design for this equipment, to verify its current load behavior and the possibility of increasing its efficiency by 20% over the security level. Additionally there is the application of a new inspection system. The study applied is based on the RBI methodology, according to the API-580 and API-581, and was used the simulation software HTRI® as a support tool to obtain the maximum temperature of the furnace tube metal B-1201. Results are reported as comparative data analysis of probability of failure in the short and long term, risk matrix, and proposed plans for the various cases in study.
Guidelines for Repair Welding of Pressure Equipment in Refineries and Chemical Plants: Part 4—Weld Repair for Specific Materials - Stainless Steel, Clad Steel and Dissimilar Joints
Authors: Okazaki Tsukasa , Kayano Rinzo , Hoshika Takahisa , Niimoto Shinta
Published: May 2012

It has been recognized that repair welding plays an important role in the long term, safe operation of pressure equipment. In 2009, the Japan Welding Engineering Society (JWES) published guidelines for repair welding of pressure equipment to meet the great need for the safe operation and proper maintenance of aging plants. This paper describes Part 4 of the guideline, which covers repair welding of stainless steel, clad steel, weld overlay and dissimilar joints.
Fabrication Design and Code Requirements for the ITER Vacuum Vessel
Authors: Ahn H. J. , Kim B. C. , Sa J. W. , Lee Y. J. , Hong K. H. , Kim H. S. , Bak J. S. , Jung K. J. , Park K. H. , Kim T. S. , Lee J. S. , Kim Y. K. , Sung H. J. , Ioki K. , Giraud B. , Choi C. H. , Utin Y.
Published: May 2012

The ITER vacuum vessel (VV) is a double walled torus structure and one of the most critical components in the fusion reactor. The design and fabrication of the VV as nuclear equipment shall be consisted with the RCC-MR code based on French fast breeder reactor. The VV is a heavy welded structure with 60 mm thick shells, 40 mm ribs and flexible housing of 275 mm diameter. The welding distortion should be controlled since the total welding length is over 1500 m. To satisfy the design requirement, the electron beam welding (EBW) and narrow gap gas tungsten arc welding (GTAW) techniques are to be applied and developed through the fabrication of mock-ups. The fabrication design has been developed to manufacture the main vessel and port structures in accordance with the RCC-MR code. All fabrication sequences including welding methods are also established to meet the demanding tolerance and inspection requirement by HHI as a supplier.
Study on Stress Intensity Factors of Fatigue Crack in Round Bar Under Rotary Bending
Authors: Maitireyimu Maigefeireti , Kikuchi Masanori , Kitano Hiroko
Published: May 2012

Study on stress intensity factors of surface cracks in round bars under rotary bending is conducted. Superposition FEM is utilized for numerical analysis and Virtual Crack Closure Method is used for stress intensity factor (SIF) calculation. Based on case studies on cracks with different aspect ratio and crack depth, an evaluation method is developed for any rotation angle. And then simulation on single crack has been performed automatically. Results are presented and compared with cyclic loading condition. SIF evaluation method is then extended for two coplanar cracks.
Effect of Local Geometric Imperfections on Axial Buckling of Welded Steel Tanks
Authors: Chen Zhiping , Yu Chulin , Yan Shunjuan , Yang Licai , Cao Guowei
Published: May 2012

Axial buckling critical load of large welded steel tanks is very sensitive to initial circumferential weld geometric imperfections on the tank walls. It is worth noting that some local geometric imperfections are also existed in the following service time. It is meaningful to explore effect of local geometric imperfections on axial buckling of welded steel tanks with circumferential weld imperfections already. FEM was used to learn effect of amplitude and distribution of local geometric imperfections on welded steel tanks with circumferential geometric imperfections. Results showed that the existence of local geometric imperfections give an additional damage to axial buckling critical load and changed axial buckling deformation characteristics of welded steel tanks, while this adverse effect did not vary much with the increasing of amplitude and distribution of local geometric imperfections.
Consideration on Seismic Design Margin of Elbow in Piping
Authors: Otani Akihito , Nakamura Izumi , Takada Hajime , Shiratori Masaki
Published: May 2012

Elbow is an essential element for three dimensionally arranged piping and it is actually used in most kinds of plants. Many great researches on the flexibility and stress intensity regarding elbow elements have been performed. Moreover, we can greatly benefit from the design code where elbow elements are specified. Our research group also started a research on ultimate strength of piping systems containing elbows in 1997 and we have performed several kinds of elbow element tests and shaking table tests. All experimental results have shown that the failure loads are far higher than those described by the design criteria. The authors have confirmed that the seismic design margin is extremely conservative. In this paper, the results of shaking table tests of piping, elbow element experiments and the stress calculation for those experiments based on design code are described, their results are compared with the seismic design criteria, and the margin is discussed. The authors point out the necessity of a new design code on the basis of the detail analysis and strain criteria in order to describe more appropriate and reasonable seismic design margin of the piping.
Ductile Fracture Simulation of Mulitple Surface Flaws
Authors: Suga Kazuhiro , Miyazaki Katsumasa , Senda Ryotaro , Kikuchi Masanori
Published: May 2012

Effect of surface flaw on ductile fracture behavior of non-aligned multiple flaws in plate is studied numerically using Gurson’s constitutive equation. Based on experiments, 2 parallel crack problems are simulated. In experiments and simulation crack coalescence, crack non coalescence and crack interaction was observed. In all cases, ductile fracture processes are obtained and results are compared with experimental ones. In this study, a new alignment rule for the prediction of maximum tensile load or rupture load for multiple cracked plates is compared with the simulation result.
Seismic Isolation of Base-Isolated Vending Machine With Air Dampers
Authors: Mikoshiba Tadashi , Suzuki Toshiya , Sato Takanori , Terai Masakazu , Chiba Toshio
Published: May 2012

By setting the isolation system between the foundation of the house and the foundation ground, it makes it possible to scale back the influence of the earthquake. A sliding isolator, which is compact and has high isolation characteristics, had been developed. This isolation system of the house have found effective and had high performance. This system was applied to the vending machine. Although the sliding isolator has been shown to be effective, it required the wide space around the vending machine. By using the base isolation combined with the air damper, it allowed to use in the narrow space area. It is useful when the vending machine is set in front of the wall. A sliding isolator combined with air damper has high isolation characteristics.
Strength Evaluation for Pressure-Containing Parts of Ultra-High-Pressure Compressor by Using Standards of Ultra-High-Pressure Gas Equipment
Authors: Tanno Yohei , Naruse Tomohiro , Arai Shigeru , Kurita Shinichiro
Published: May 2012

The Japanese standard “KHK-S-0220” (KHK-code) and the American standard “Boiler and Pressure Vessel Code Sec.8 Div.3” (ASME-code) concerning ultra-high-pressure gas equipment were applied to Hitachi’s ultra-high-pressure compressor, and a series of strength evaluations were carried out. Hitachi produces and maintains ultra-high-pressure reciprocating compressors with a design pressure over 200 MPa. In Japan, ultra-high pressure gas equipment over 100 MPa must be designed according to KHK-code established by the High Pressure Gas Safety Institute of Japan. This Japanese standard was applied to an ultra-high-pressure compressor, and design pressure limits, shakedown limits, required absorbed energy of materials, leak-before-break (LBB), and fatigue strength were evaluated. ASME-code was also applied to the compressor, and strength evaluations like the above were carried out. As a result, it was found that KHK-code and ASME-code gave conservative evaluation of fatigue strength for an ultra-high-pressure compressor.
Basic Study on the Seismic Response of the High-Speed Rotational Body Supported by Fluid Film Bearings
Authors: Hatta Masayoshi , Shintani Atsuhiko , Ito Tomohiro
Published: May 2012

In this study, the seismic responses of a disk and a shaft are evaluated analytically. In an analytical model, the disk-shaft system is treated as an elastic shaft with a rigid disk, and the shaft is supported by fluid film bearings. Furthermore, the gyroscopic effect of a disk and the fluid forces due to fluid film bearings are considered. The equations of motion are derived for the translational and rotational motions when the floor is subjected to horizontal and vertical excitations. The displacements of the centers of the disk and the shaft are evaluated by numerical simulations. At first, the response behaviors of a rotating disk without base excitation are evaluated, and at second, the effects of sinusoidal base excitations are investigated. Finally, the response behaviors of this system are subjected to seismic waves of varying frequencies. The results of the different seismic wave input are studied.
XML Related MatDB Tools for Data Exchange and Interoperability
Authors: Over H. H. , Ojala T. , Ha¨hner P. , Austin T.
Published: May 2012

The web-enabled materials properties database MatDB of the European Commission Joint Research Centre (EC-JRC) is a database application for the storage, retrieval and evaluation of experimentally measured materials data coming from European R&D projects. Data exchange and interoperability are important database issues to reduce costs of expensive material tests. Many organizations world-wide are participating in the development of GEN IV reactors. To reduce costs the GEN IV International Forum has agreed to interoperate and exchange data for the screening and qualification of candidate materials. To simplify the complexity of data mapping between differently structured databases, adoption of a standardized XML schema is the favored option. The paper focuses on MatDB XML related tools and items: • Upgrade, extension and implementation of the MatDB XML schema within a planned US/EC cooperation; • European standardization activities for data exchange, interoperability and the development of standard formats for engineering materials data; • MatDB data cite participation.
Numerical Simulation of Coalescence Behavior of Multiple Surface Cracks
Authors: Kikuchi Masanori , Wada Yoshitaka , Suga Kazuhiro , Ohdama Chikako
Published: May 2012

Study on the interaction of multiple cracks during fatigue crack growth processes is important for the integrity evaluation of nuclear structure. By using S-version FEM, this problem has been simulated by authors. In this study, coalescence behavior of 2 surface cracks is simulated using the method. It is assumed that 2 surface cracks exist on the same plane, and grow towards each other by fatigue. As the inner crack tips overlap, coalescence of 2 cracks occurs, and shape of cracks change significantly over very short cycles. This process is simulated in detail, and changes of stress intensity factor distributions along crack front are studied precisely. Three cases of changing crack sizes are simulated and coalescence behaviors are studied. Experimental studies are also conducted and results are compared with those of numerical simulations. Results are compared with conventional evaluation code and discussed.
Investigation on the Characteristic of Residual Stress Distribution in the Dissimilar Metal Welds of a Small Bore Penetration Nozzle by Three-Dimensional Finite Element Analysis
Authors: Seo Joong-Hyun , Kim Jong-Sung
Published: May 2012

In this study, three-dimensional finite element residual stress analysis of a small bore penetration nozzle was performed using the commercial finite element program, ABAQUS. Comparing with the real PWSCC (primary water stress corrosion crack) history, it is identified that the finite element analysis is valid in the viewpoint of PWSCC initiation and growth. Parametric finite element residual stress analysis was systematically implemented in order to investigate effect of the geometric variables including nozzle outer diameter/thickness, buttering thickness, angle between central axes of head & nozzle, etc. on the residual stresses. As a result of the parametric analysis, it is found that effects of the nozzle outer diameter and the angle between central axes of head & nozzle on the maximum residual stress generation location and magnitude are significant while effects of the head thickness, the buttering thickness, the weld depth, and the nozzle thickness to outer diameter are insignificant.
Large Impulsive Loading of Open Ended Rings
Authors: Clayton Alan M. , Booth Rowland
Published: May 2012

A series of tests have been carried out on cast high strength ferritic steel rings 1090 mm internal diameter, with a central 20kg PE4 spherical charge, equivalent to 25 kg TNT. The rings have circular regions in them which have been thinned, some 16 mm wall thickness and some 26 mm thickness. The bulk of the ring undergoes limited cyclic plastic straining as the rings vibrate following the blast impact. The locally thinned regions undergo cyclic plastic strains of up to +/− 4%. The paper describes the experimental arrangements and results. Methods have been developed to measure high strains in the rings and the final plastic displacements of the windows have also been measured. It has proved remarkably difficult to obtain good finite element calculations of the strains measured. After the first blast, the thinned regions had some cracking and the extent of the cracking increased on further blast loads. Within the limits of measured/calculated strains, an assessment has been carried out to the new local tearing rules in ASME VIII Div 2 and 3 and compared to the observed damage.
Design Criteria for a New Weir Surface Repair Method Containing Shock Absorbing Cushions
Authors: Hsu Tse-Shan , Hsieh Yi-Lang
Published: May 2012

Although a weir surface layer is subjected to shocks of the floods with particles of varies sizes, they are generally repaired by covering an abrasion-resistant layer. In the past, based on the knowledge that higher strength materials have higher abrasion resistances, many reports have focused on enhancing the strength of the repair materials. However, the occurrence of brittle fracture and peeling were also significantly increased. These resulted in an awkward situation that the need of repairing becomes more urgent even if the material properties have been greatly improved. In an attempt to break through the traditional methods, the major thrust of this paper is to propose criteria for designing a weir surface containing shock absorbing cushions, and a new method accordingly.. It was then confirmed by in situ tests that such criteria have the capability to lead the above-mentioned shocks to be absorbed. Due to the limited space of this paper, all related test layout and results will be presented on another paper.
Mechanical Behaviour of Alloy 800 Steam Generator Tube With a Circumferential Crack-Like Throughwall Flaw
Authors: Wang Congyue , Duan Xinjian , Jain Mukesh
Published: May 2012

This paper presents an experimental and numerical study of the mechanical behaviour of Alloy 800 tubes with a circumferential crack-like throughwall flaw. The crack-like throughwall flaw was simulated as a slot fabricated by Electron Discharge Machining (EDM). A digital image correlation (DIC) method is employed to measure the distribution of strain and the deformed EDM slot profile during the tension test. A Finite Element Analysis (FEA) model in ANSYS is then developed to predict the mechanical behaviour of Alloy 800 steam generator (SG) tubing in the tension tests. The FEA model with a verified material stress-strain curve and the calibrated failure criterion is applied to simulate the burst test of SG tubing with a circumferential crack-like throughwall flaw. The maximum allowable size for a circumferential throughwall crack is recommended based on FEA simulations.
Time-Domain Modeling of the Random Vibrations of Tubes Subjected to Turbulence-Conveying Flows
Authors: Antunes Jose , Delaune Xavier , Piteau Philippe
Published: May 2012

The vibrations of multi-supported tubes subjected to flow excitation have been the subject of active research for many years, in particular connected with the critical design of heat exchangers and fuel bundles of nuclear power facilities. Because tubes are often loosely supported, their nonlinear dynamics are conveniently addressed through time-domain numerical simulations, for the predictive analysis with respect to wear and fatigue. Turbulence is one of the main excitation mechanisms which drive tube vibrations. We recently revisited the problem of random excitation generation in the time domain, for transverse flows. A new simplified an efficient technique was developed, which properly emulates the spectral and spatial features of the turbulence force field. Results were successfully compared with those from another generation method based on the classical work by Shinozuka and co-workers. In the present paper, we extend our previous work by modeling the time-domain random excitation from flows which display a significant axial velocity component, leading to the convection of turbulence fluctuations. This problem has been addressed by many authors in the past, mainly focusing on linear analysis in the frequency domain, for flow-excited plates, pipes and tubes. Here, for the purpose of nonlinear analysis, we focus on two techniques for generating time-domain turbulence excitations which properly account for the effects of the axial transport term in convective flows. We start by extending our original random force generation method, in order to emulate axial turbulent flows. For the purpose of physical discussion and computational efficiency evaluation, we also implemented an updated version of Shinozuka’s excitation generation technique. We discuss the use of random forces applied at fixed locations, but also investigate the use of axially convected travelling forces. The practical significance of the cross-spectral convection term is evaluated for pure axial and mixed flows. Finally, because time-domain dynamical simulations of practical interest are usually two-dimensional, we discuss the correlation of the orthogonal random forces generated along the motion directions, when simulating two-dimensional turbulence fields.
Recent Developments in Code Case 2235 Applications in the Petrochemical Industry
Authors: Hedden Owen F. , Cowfer C. David
Published: May 2012

Boiler and Pressure Vessel Code Case 2235 linked the elements of UT qualification by performance demonstration and fitness-for-service analysis of weld flaws revealed by NDE. This paper addresses several Boiler and Pressure Vessel Code activities related to these principles.
Expanded Influence of UT Performance Demonstration and Fitness-for-Service Analysis in the Nuclear Power Industry
Authors: Hedden Owen F. , Cowfer C. David
Published: May 2012

This paper addresses recent development and application of ASME Boiler and Pressure Vessel Code and Code Case requirements for weld nondestructive examination (NDE) and for fitness-for-service (FFS) structural analysis of the flaws thus discovered. A brief description of the basis for this development is included. Reviews are presented of additions to the literature addressing applications to nuclear power plant components. Issues regarding application of Code Cases 2235 and N-529 are presented. Concerns regarding the importance of reliable probability of detection (POD) data for different weld categories are addressed. Concerns with appropriate acceptance standards for flaws in different weld categories and materials are also addressed.
Not by Gasket Alone: It Takes a Well Designed and Implemented Flanged Joint
Authors: Neely Clyde C.
Published: May 2012

Because of the wide range of service conditions for which ASME Code vessels are constructed and stamped, there is no economic “one size fits all” gasket style for pressure vessel and heat exchanger flanges generally larger than 24 inches in diameter that have been custom designed in accordance with the ASME Section VIII Division 1, Appendix 2 rules. Based on over 40 years of experience, the 3-ply corrugated gasket that has been designed, purchased and installed as described in this paper will be a performance-upgrade substitute for applications for which either conventional double-jacketed or spiral-wound gaskets are deemed to be suitable for the design service conditions. This is not surprising since the sealing performance operates on the same principle as that of the Kammprofile-style gasket. However, the point is made that this successful sealing performance experience was “not by gasket alone”. Because of the interactions, interdependencies and interrelationships that are inherent in a bolted joint assembly, the performance of a gasket is, as stated in PCC-1-2010, contingent upon, “many selections/activities having been made/performed within a relatively narrow band of acceptable limits.” This includes fabrication of the joint components in accordance with the purchase specifications and properly assembling the joint. Therefore, the joint screening and good practice design considerations upon which the successful experience with the 3-ply corrugated gasket has been established are reviewed in this paper.
A Novel Method for Obtaining the Multiaxiality Constant for Damage Mechanics Which is Appropriate to Crack Tip Conditions
Authors: Hyde C. J. , Sun W. , Hyde T. H.
Published: May 2012

Many engineering components, such as power plant steam pipes, aero-engine turbine discs, etc, operate under severe loading/temperature conditions for the majority of their service life. As a result, cracks can initiate and subsequently propagate over time due to creep. Damage mechanics is a robust method for the prediction of behaviour of components subjected to high temperature creep conditions and in particular, the Liu and Murakami model has proven to be a useful tool for the prediction of creep crack growth under such conditions. Previous methods for obtaining the constant of multiaxiality required for the use of such models, i.e. α, have relied upon the steady load testing of specimens designed to give a specific multiaxial stress-state, such as notched bars, and the failure time obtained. A series of results from finite element (FE) analyses based on the same geometry and loading/temperature conditions as the experiment, each performed with a different α-value, are then interpolated in order to identify the α-value which results in the same failure time, tf, as that of the experimental test. However, the stress-state present within such a specimen geometry (and therefore the α-value obtained) does not reflect the multiaxial severity of the stress state ahead of a crack tip. Therefore, for the application of the Liu and Murakami model to crack tip (i.e., creep crack growth) conditions, it follows that the α-value should be obtained from a multiaxial stress-state of equal severity to that to which it is to be applied, i.e. a crack tip. Therefore compact tension (CT) specimen creep crack growth data has been used in order to obtain the α-value. The process for the α-value determination is similar to that discussed for the notched bar, except that the interpolation of the time to failure is replaced with an interpolation of the time to a given crack length, ta. The resulting FE predictions based on CT and thumbnail crack specimen geometries, for a 316 stainless steel, are shown to be accurate in comparison to experimental results.
Pressure Vessel Burst Directional Effects
Authors: Geng Jihui , Baker Quentin , Thomas Kelly
Published: May 2012

Pressure vessel burst (PVB) is a class of explosion for which there are hazards at virtually all chemical processing facilities. PVBs present both airblast and fragmentation hazards. Blast prediction methods specific to PVBs were first developed in the 1970s and revised blast curves were published in 1995. The published blast curves were developed for spherical vessel bursts, whereas most pressure vessels in use in industry are cylindrical. Blast effects around a bursting cylindrical vessel are not uniform as with a spherical vessel. The blast to the side of a cylindrical vessel is stronger than off the ends, creating non-circular pressure contours. The directional effects diminish with distance as the expanding shock wave approaches a spherical shape. A correlation was developed in the 1970s to account for directional effects using high explosive test data, the best available resource at the time. Like all test programs, pressure transducers extended to limited distances from the explosive charge, yet the data are often extrapolated to a far greater distance. This paper presents the results of recent work on directional effects specific to bursting cylindrical pressure vessels and provides new correlations for blast overpressure and impulse for a range of vessel geometries and burst conditions. The results can be used to predict the airblast hazards from cylindrical PVBs over the range of standoff distances for which directional effects exist.
Mismatch Effect on CT Specimen Mechanical Effect and Consequences on the Weld Toughness Characterization
Authors: Marie S. , Ne´de´lec M.
Published: May 2012

The welded joints are particularly sensitive areas in the structures in terms of harmfulness of defects. Given the complexity of the problem (geometry poorly controlled, multi-material aspect, the potential influence of residual stresses), the tests are conducted based on pessimistic assumptions that can wrap all the uncertainties of the problem. In the case of a defect assessment, the considered toughness is deduced from conventional characterization tests with a crack in the welding, considering the current standards, ISO 12135 [1] or ASTM E-1820 [ 2] which are valid only for an homogeneous specimen. In 2010, a new standard ISO 16563 [3] was published to address the specificity of welded joints. If it covers some of the difficulties, it remains incomplete. In nuclear piping, welds have a mismatch M, ie the ratio between the yield strength of the weld metal and the base metal, usually greater than 1: this avoids any problem of strain localization at the junction and ensure that the stresses in the base metal are also easily supported by the welded joint. In this configuration, it turns out that for a given mechanical loading, a crack in the weld located generally has a solicitation, quantified by the parameter J, less (depending on the size of the junction) to those that would see the same crack located in the base metal. Unfortunately, this phenomenon exists also potentially for a characterization test, which would overestimate the true toughness of the welded joint. Plasticity that develops from the crack tip can quickly reach this interface and be affected. To evaluate this phenomenon, we considered two types of representative welded joint (PWR secondary loop ferritic weld and a 316 stainless steel weld) and performed a F.E. analysis of the multi-material CT specimen mechanical answer and on the η coefficient conventionally used to derive the plastic component of J from the area under the curve force-opening displacement.
Modelling the Tearing Crack Growth in a Ductile Ferritic Steel Using X-FEM Elements
Authors: Simatos A. , Prabel B. , Marie S. , Ne´de´lec M. , Combescure A.
Published: May 2012

eXtended Finite Element Method (X-FEM) is used to model a cracked structure without meshing explicitly the crack. Indeed, the crack is represented by a discontinuity of the displacement field through additional degrees of freedom using Heaviside type function or derived from the Irwin’s singular fields. Initially, the stress integration in the XFEM framework supposed to divide the cut elements into subtriangles that are conform to the crack. This was motivated in order to integrate the behaviour accurately on both sides of the crack in particular at proximity of the crack tip where singular enrichments are present. This strategy induces field projections from the usual Gauss point configuration to a variable new one that depends on the crack position in the element. For ductile fracture modelization, this approach is not applicable, because in presence of large scale yield, the projection of internal variable fields is not conservative, in particular at proximity of the crack tip. In order to circumvent this problem, a new integration strategy was proposed by B. Prabel. It consists in using 64 Gauss points that are placed without regards to the crack position. This simple integration scheme permits to take implicitly into account the crack position and the fields in the element in an accurate and consistent way. This strategy was used in problem calculation for which the plastic radius remained small. It allowed introducing the overintegrated elements in the probable propagation zone, just before plastification. In the case of ductile tearing, the plasticity is not confined near the crack tip and an improvement of the proposed strategy is made. This is then used to model large ductile crack growth in a ductile ferritic steel. To validate the predictions, the modelization is compared to a second F.E. calculation using the node release technique for the crack propagation. It is then shown that the two predictions are strictly equivalents.