bluuebunny/crossref_metadata_2025_split huggingface dataset:
Further Validation of the Technical Basis of Code Case N-838 for Flaw Tolerance Evaluation of CASS Piping
Authors: Griesbach Timothy J. , Dedhia Dilip , Harris David O. , Cofie Nathaniel G. , Alleshwaram Aparna , Amberge Kyle 
Published: November 2015

ASME Code, Section XI Code Case N-838 provides analyses methods that may be used when performing flaw tolerance evaluation of Class 1 and 2 cast austenitic stainless steel (CASS) piping components with ferrite content exceeding 20%. Tolerable flaw sizes are provided in the Code Case that cannot be exceeded during the evaluation period from an initial postulated flaw. The tolerable flaw sizes were determined based on probabilistic fracture mechanics (PFM) techniques employing toughness and flow strength correlations developed at Argonne National Laboratory (ANL) that estimated the crack growth resistance (J-R) curve using material composition with the room temperature Charpy energy as an intermediate variable. Since the publication of the technical basis for this Code Case, additional toughness data have been identified, some of which are significantly lower than the toughness for CASS CF-8M materials considered in the ANL model.
This paper reports the results of evaluations and sensitivity studies performed to examine the additional toughness and tensile data and determine the effects on the Code Case tolerable flaw size tables. The current study directly employs an expanded set of data of actual measured fully saturated high-temperature crack growth resistance curve, thereby bypassing the material composition-to-Charpy-to-toughness correlations in the ANL model. In this study, both deterministic fracture mechanics and PFM analyses were performed using the assembled data of toughness and tensile properties. The results obtained in the current PFM and deterministic analysis which use the actual toughness and tensile data are found to always provide larger tolerable flaw sizes than those obtained from the previous analyses which used ANL material correlations, thereby demonstrating the conservative nature of the technical basis for the Code Case.
Integrity and Life Assessment of Cast Duplex Stainless Steel Elbows of EDF PWR Main Coolant Piping
Authors: Le Delliou Patrick , Saillet Sébastien 
Published: November 2015

Thermal ageing of cast duplex stainless steel elbows is a concern for long-term operation of EDF nuclear power plants. The thermal ageing embrittlement results from the micro-structural evolution of the ferrite phase (spinodal decomposition), and can reduce the fracture toughness properties of the steel. In addition, it is necessary to consider manufacturing quality and the possible occurrence of casting defects such as shrinkage cavities. In a context of life extension, it is important to assess the safety margins to crack initiation and crack propagation instability.
This paper reports the present integrity and life assessment methodologies as carried out by EDF. The approach is based on the in-service inspection and surveillance RSE-M Code and on French regulation requirements for NPPs in operation. This work is supported by an extensive R&D programme on one hand and on field experience analysis on the other hand.
The paper details the three main topics of the life assessment methodology:
- estimation of the fracture toughness of the steel with predictive formulae using the chemical composition and ageing conditions,
- definition of a reference crack size based on an inventory of the manufacturing quality of the elbows,
- fracture mechanics evaluation based on the J parameter, computed either by an engineering estimation method or by a finite element analysis. The calculated J parameter is then compared with the estimated fracture toughness of the material. Partial safety coefficients are included in the calculation process as required by the RSE-M Code.
Introduction of a Research Activity on the Seismic Safety Evaluation of Nuclear Piping Systems Taking the Effect of Elastic-Plastic Behavior Into Account
Authors: Nakamura Izumi , Shiratori Masaki , Otani Akihito , Morishita Masaki , Shibutani Tadahiro , Nakamura Hitoshi 
Published: November 2015

According to investigations of several nuclear power plants (NPPs) hit by actual seismic events and a number of experimental researches on the failure behavior of piping systems under seismic loads, it is recognized that piping systems used in NPPs include a large seismic safety margin until boundary failure and the current code design allowable stresses are very conservative. Since the stress assessment based on the elastic analysis does not reflect actual response of piping systems including plastic region, rational procedures to estimate the elastic-plastic behavior of piping systems under a large seismic load are expected to be developed for piping seismic design applications.
With the aim of establishing a procedure that takes into account the elastic-plastic behavior effect in the seismic safety estimation of nuclear piping systems, a research activity has been planned. Through the activity, the authors intend to establish two kinds of guidelines; 1) a guideline of a standard analysis procedure to evaluate elastic-plastic behavior of piping systems under extreme seismic loads with rational and conservative margins, and 2) a guideline that provide criteria for the seismic safety assessment of piping systems by the standard analysis to evaluate elastic-plastic behavior established by the above guideline. As the first step of making out the analysis guideline, benchmark analyses are conducted for a pipe element test and a piping system test.
In this paper, the outline of the research activity and the preliminary results of benchmark analyses for a pipe element test are described.
A Joint Research Project to the Control of Rapid Temperature Changes in Industrial Components
Authors: Trieglaff Ralf , Rieck Detlef , Schulz Axel 
Published: November 2015

The control of rapid and numerous temperature changes is an urgent requirement in many industrial processes, particularly for thermal power plants in flexible operation.
The paper describes objectives, partners and methodical approaches of the ongoing German research project THERRI.
The project scope is to establish essential Fracture Mechanics basics for an industrial application of a Damage Tolerance concept to thick-walled components of thermal power plants.
One key issue of the stipulated works is to provide an experimental data base for fatigue crack propagation in high-temperature ferritic-martensitic steels in the relevant temperature range from 300°C to 600°C. This will be supplemented by simulation calculations (XFEM) and the further development of ultrasonic measurement techniques.
The research project has been started but not finished yet. Therefore this paper is a snapshot of the ongoing project work and shows — besides the methodological work — first but not final results.
Investigations on Crack Propagation Under Cyclical Isothermal and Thermo-Mechanical Loadings for a Type 304-L Stainless Steel Used for Pressurized Water Reactor
Authors: Gourdin C. , Rossillon F. , Le Delliou P. , Perez G. , Fissolo A. 
Published: November 2015

The integrity of structures exhibiting flaws in Pressurized Water Reactor (PWR) has to be assessed to meet safety criteria. This paper deals with crack-propagation under cyclic thermo-mechanical loadings, as encountered in class I austenitic pipes of PWR’s. To have a conservative and reliable assessment of the crack propagation due to the in-service loading, various codes and standards use simplified method. For example, RSE-M introduces a plastic correction depending on the proportion of the mechanical loading. An improvement of the current method requires additional investigations. Moreover, components loaded with transient or thermal fluctuations are not really in strength-controlled conditions.
To this end, a new device called PROFATH was designed. The specimen is a pre-cracked thick-walled tube undergoing a set of thermal cycles and loaded with a static mechanical force. During the first part of the cycle, a high frequency induction coil heats the external wall. Then, the heating system stops and the specimen is cooled down by running water inside the tube. Finite element calculations show that only a region half-way along the tube should be heated to ensure adequate structural effect. In the heated zone, the machining of a sharp circumferential groove ensures the propagation of a unique crack. An electro-mechanical jack controls the level of the mechanical static load.
To obtain a very precise thermal mapping, a specific specimen with dedicated instrumentation is used: 20 thermocouples are appropriately located on the outer surface and along the wall thickness. During the test, the crack-propagation is estimated through crack-opening measurements (compliance method).
Now, three first tests have been carried out. These tests allow having an evaluation of the pertinence of the correction proposed by the RSE-M for a significant plasticity. Following tests are planned in order to have a confirmation or to propose an extension of the validity domain.
Lateral Influence Coefficients for a Thin Conical Shell Frustum
Authors: Liepins Atis A. , Arnez Javier 
Published: November 2015

Thin conical shell components are often used in vertical process vessels, bins, and water storage tanks. When exposed to the elements, such structures may be subjected to lateral wind forces and seismic accelerations. For calculations of lateral response of such structures with simplified models, in the form of vertical beams, lateral influence coefficients for thin conical frustum shells are useful.
To compute lateral influence coefficient for conical frusta, asymmetric solutions of shell equations for cones are needed. The literature on asymmetric solutions for conical shells is sparse. Hoff [1] derived equations suitable over a limited range of parameters for asymmetric response of conical shells and indicated possible solutions using Fourier and power series. In his discussion of Hoff’s work, Pohle [2] indicated that an asymptotic solution of the equations is useless because of its validity over an impractical range of parameters. Seide [3] derived equations that removed the limitations of Hoff’s equations. Wilson [4] proposed solutions by separation of variables and power series. The slowly converging power series were summed using a computer for a conical panel under distributed loading. Chandrashekhar and Karekar solved the equations for a conical frustum under wind loading by expanding the solution in Fourier series in the circumferential direction, and applying finite differences in the meridional direction. The difference equations were solved using a computer.
Derived here are closed-form expressions for thin conical shell frusta based on the membrane theory of shells. These influence coefficients are compared with finite element results for a conical shell, with specific geometry and material properties, for which wall bending is included.
Creep Crack Incubation in P92 Steel at 650°C in the Presence of Structural Elastic Follow-Up
Authors: Khayatzadeh Saber , Tanner David W. J. , Smith David J. 
Published: November 2015

It is customary to study the creep deformation of materials at high temperatures and the incubation and growth of creep cracks using constant load test machines. However, this highly idealised loading condition does not accurately reflect the practical circumstances that occur when operating high temperature plants. Real loading conditions often lie between load and displacement control and correspond to situations where there is elastic follow-up, with low values relating to near displacement control and high values near to load control.
This paper explains a series of experiments where pre-cracked martensitic P92 steel compact tension specimens are loaded and tested for different values of structural elastic follow-up, ranging from constant load to near fixed displacement. It is found that the degree of elastic follow-up significantly changes the time taken for creep crack incubation. This is a consequence of the relaxation of the load applied to the specimens. Elastic-plastic creep finite element simulations are used to reveal the underlying mechanical behaviour of the specimens. The simulations were confined to 2D analyses for plane stress and plane strain conditions. It is observed, that, irrespective of the initial loading and boundary conditions, the predicted mechanical response for plane stress and plane strain lies either side of the experimental results.
A Comparison of Design by Analysis Techniques for Evaluating Nozzle-to-Shell Junctions per ASME Section VIII Division 2
Authors: Prueter Phillip E. , Brown Robert G. 
Published: November 2015

Part 5 of ASME Section VIII Division 2 offers several design by analysis (DBA) techniques for evaluating pressure retaining equipment for Code compliance using detailed computational stress analysis results. These procedures can be used to check components for protection against multiple failure modes, including plastic collapse, local failure, buckling, and cyclic loading. Furthermore, these procedures provide guidance for establishing consistent loading conditions, selecting material properties, developing post-processing techniques, and comparing analysis results to the appropriate acceptance criteria for a given failure mode. In particular, this study investigates the use of these methods for evaluating nozzle-to-shell junctions subjected to internal pressure and nozzle end loads. Specifically, elastic stress analysis, limit load analysis, and elastic-plastic stress analysis are utilized to check for protection against plastic collapse, and computational results for a given load case are compared. Additionally, the twice elastic slope method for evaluating protection against plastic collapse is utilized as an alternate failure criterion to supplement elastic-plastic analysis results.
The goal of these comparisons is to highlight the difference between elastic stress checks and the non-linear analysis methodologies outlined in ASME Section VIII Division 2; particularly, the conservatism associated with employing the elastic stress criterion for nozzle end loads compared to limit load and elastic-plastic analysis methodologies is discussed. Finally, commentary on the applicability of performing the Code-mandated check for protection against ratcheting for vessels that do not operate in cyclic service is provided. The intent of this paper is to provide a broad comparison of the available DBA techniques for evaluating the acceptability of nozzle-to-shell junctions subjected to different types of loading for protection against plastic collapse. Predicted deformations and stresses are quantified for each technique using linear and non-linear, three-dimensional finite element analysis (FEA) methodologies.
Dynamic Effects on Fracture Toughness for Ferritic Steel in the Ductile-to-Brittle Transition
Authors: Jacquemoud C. , Delvallée-Nunio I. , Balestreri F. 
Published: November 2015

Dynamic loading effects on ferritic steel toughness have been evaluated in the brittle-to-ductile transition, considering loading rates representative of object drops. To verify that the brittle-to-ductile transition curve, initially defined from static tests, tends to shift to higher temperatures due to dynamic effects even in the case of object drops, experiments on 16MND5 steel have been performed.
A three-point bending set-up and a thermal chamber have been designed in order to perform dynamic fracture tests on large Single Edge-notched Bending SE(B) specimen, at very low temperature using a drop-shock machine. In a first step, considering that the reference temperature of the material (according to the master curve concept) is −122 °C, dynamic tests at −120 °C have been performed. These tests have confirmed that the fracture mode is still brittle at this temperature, when an impact speed of 4.85 m/s is used.
Elastic-plastic or viscoplastic dynamic simulations of the tests, compared to classical static analysis, have demonstrated that the effects of inertia and viscosity on fracture toughness are negligible considering the very low values obtained on these tests at −120 °C. These results also confirm the decrease of fracture toughness due to dynamic loading compared to experimental data from static tests. A further step will be to complete this demonstration with dynamic tests at higher temperatures in the brittle-to-ductile transition.
Monitoring Degradation in Nuclear Reactors
Authors: Brumovsky Milan , Kytka Milos 
Published: November 2015

Nuclear reactor materials are affected by many stressors during their operation that result either from the nuclear reactions in the reactor core or by operation conditions (temperature, pressure) and water environment.
Generally, several different methods of monitoring damage in reactor materials are applied, depending on their type, design and conditions:
- Destructive, usually represent by surveillance specimens,
- Semi-destructive, usually performed by cutting small specimens from component surface, e.g. for small punch tests,
- Non-destructive, representing by non-destructive inspection methods applied during in-service inspections, like traditional ultrasonics, optical, dye-penetrant, eddy current etc. and also some new like automated ball indentation, thermoelectric power measurements etc.
The paper summarizes the possibility of application of these methods on main reactor components and shows some typical results and problems.
Validity of Procedure for Plastic Collapse Assessment of a Local Thin Area Near Vessel and Nozzle Intersections Subjected to Internal Pressure and External Loadings
Authors: Oyamada Kenji , Konosu Shinji , Miyashita Tetsuji , Ohno Takashi , Suzuki Hideyuki 
Published: November 2015

There are numerous cases in which a volumetric flaw such as a local thin area (LTA) is found in pressure equipment such as vessels, piping, tanks, and so on. Sometimes it is found near vessel and nozzle intersection. A fitness for service (FFS) rule of such cases was desired, because plastic collapse assessment of LTA near vessel and nozzle intersection usually needed to conduct by numerical analysis such as FEA.
Recently, an FFS assessment rule of plastic collapse assessment of LTA near vessel (run-pipe) and nozzle (branch pipe) intersection subjected to internal pressure and external loadings has been developed and proposed by one of authors of this paper.
In this paper, the proposed plastic collapse assessment rule was verified with results of experiments and FEA for cylindrical vessels with an LTA near vessel and nozzle intersections subjected to internal pressure and external loadings.
Stress Intensity Factor and Elastic COD for Circumferential Through-Wall Cracks in the Interface Between an Elbow and a Straight Pipe Under Internal Pressure
Authors: Jang Youn-Young , Huh Nam-Su , Jeong Jae-Uk , Kim Ki-Seok , Cho Woo-Yeon 
Published: November 2015

Leak-Before-Break (LBB) is one of important approaches applied to nuclear piping design. In the LBB assessment, it is important to evaluate crack instability and to predict leak rate based on a fracture mechanics concept, in which an idealized straight pipes with through-wall cracks (TWCs) are generally considered in the typical LBB analysis. On the other hand, in nuclear piping system, elbows are often connected with straight pipes by welding, in which cracks could occur as well known. Hence, accurate assessment needs to be performed for cracks in weldments joining an elbow and attached straight pipe.
In the previous study, it has been revealed that crack instability of a TWC in the interface between an elbow and a straight pipe under bending moment could be different with that of a straight pipe with a TWC depending on a change of pipe thickness, radius of curvature and crack length. Especially, elbows attached to a pipe were more severe than straight pipes for relatively shorter crack length. Thus, a need of engineering solutions for cracks in the interface between an elbow and a pipe is raised for accurate LBB analysis on nuclear piping system.
In this present study, stress intensity factor (SIF) and crack opening displacement (COD) are estimated via detailed 3-dimensional finite element (FE) elastic analyses for circumferential TWCs in the interface between an elbow and a straight pipe subjected to internal pressure. The geometric variables (pipe thickness, radius of curvature and crack length) affecting SIFs and CODs were systematically considered in order to cover actual ranges of geometric variables. Also, the effect of elbow on elastic fracture parameters was investigated by comparing the present results with the results from the previous straight pipe solution. Moreover, based on the present FE results, the shape factors (F, V) used for calculating SIFs and CODs are proposed for circumferential TWCs in the interface between an elbow and a pipe. The present results can be used to perform the accurate LBB assessment for nuclear piping system including elbows welded to a straight pipe.
On the Effect of Water Film on Flow-Induced Pulsations in Closed Side Branches in Tandem Configuration
Authors: Sanna F. , Golliard J. , Belfroid S. P. C. 
Published: November 2015

Previous studies demonstrate that the presence of liquid strongly influences the pressure pulsation amplitudes of flow induced pulsations. In particular, in case of annular flow (thin liquid film on the walls) the pulsations can be eliminated. The present study aims at evaluating the contribution of the liquid film to the pulsation reduction.
Experiments have been performed in a tandem configuration with two side branches upward oriented. The side branches have the same diameter as the main pipe.
A first set of experiments has been conducted with the injection point located far upstream the upstream side branch. To isolate the sole effect of the film, a second and a third set of experiments have been performed with the injection point located close upstream the T-junction with the injection such that a thin film only was generated.
In the first configuration (far upstream), the pulsation level decreases with increasing liquid rate. The reduction in amplitude compares well with the assumption of added damping in the length between the two side branches.
A similar decrease in pulsation amplitude was obtained in the second configuration. However, the amplitude reduction depends on the local liquid flow pattern at the (upstream) side branch and in particular on whether liquid bypasses the side branch or it interferes with the shear layer.
This indicates that acoustical damping is the main effect and small amounts of liquid do not significantly interfere with the shear layer.