bluuebunny/crossref_metadata_2025 huggingface dataset:
Validity of Successive Inspections to the Piping With Multiple Circumferential Stress Corrosion Cracks
Authors: Machida Hideo
Published: July 2010

This paper describes the validity of successive inspections in a chain of the integrity assessment applying Fitness-For-Service (FFS) Codes to piping with stress corrosion cracks. Integrity assessment of primary recirculation system (PLR) piping with stress corrosion cracks is one of the recent interests in Japanese boiling water reactor (BWR) plants. Girth weld joints with detected stress corrosion cracks are required to secure the integrity during subsequent 5 years operation and to conduct three times of successive inspections for PLR piping. If the safety factor included in FFS Codes works effectively, this, like frequent successive inspections are deemed unnecessary. However, since there is some uncertainty in the measurement of crack size and in crack growth estimation in the integrity assessment of piping with stress corrosion cracks, a possibility of failure cannot be denied when not conducting successive inspections to confirm the validity of the integrity assessment. In this study, piping failure probability when conducting and not conducting successive inspections using a probabilistic fracture mechanics (PFM) code, and the validity of successive inspections were examined quantitatively from the failure probabilities. The effect of crack sizing accuracy, which has great influence on the validity of inspections, was also examined. The validity of successive inspections was examined for 12, 16, and 24 inch pipes which were employed in PLR piping of BWR-5. It became clear that successive inspections were very effective in decreasing failure in 12 and 24 inch pipes, but not as effective in decreasing failure in 16 inch pipes. The reason is suggested that the crack growth rate in a 16 inch pipe is high compared with the other two sized pipes and opportunity of renewal of crack growth estimation at successive inspections is few. When successive inspections are carried out, there are several times of opportunity for improvement of underestimated crack growth behavior unless a crack size is measured smaller than the actual size in all successive inspections. Consequently, the influence of the crack sizing error on failure probability of pipes becomes very small.
Coupled EFGM and F2LFEM for Fracture Analysis of Cracks
Authors: Rajesh K. N. , Rao B. N.
Published: July 2010

This paper presents a coupling technique for integrating the element–free Galerkin method (EFGM) with fractal two-level finite element method (F2LFEM) for analyzing homogeneous, isotropic, and two dimensional linear–elastic cracked structures subjected to mixed–mode (modes I and II) loading conditions. F2LFEM is adopted for discretization of domain close to the crack tip and EFGM is adopted in the rest of the domain. In the transition region interface elements are employed. The shape functions within interface elements which comprises both the element–free Galerkin and the finite element shape functions, satisfies the consistency condition thus ensuring convergence of the proposed method. The proposed method combines the best features of EFGM and F2LFEM, in the sense that no structured mesh or special enriched basis functions are necessary and no post–processing (employing any path independent integrals) is needed to determine fracture parameters such as stress–intensity factors (SIFs) and T–stress. The numerical results show that SIFs and T–stress obtained using the proposed method are in excellent agreement with the reference solutions for the structural and crack geometries considered in this study. Also a parametric study is carried out to examine the effects of the similarity ratio, and the number of transformation terms on the quality of the numerical solutions.
Extrapolation of Tearing Resistance Curves
Authors: Wallin Kim R. W.
Published: July 2010

Due to the measuring capacity limitation in normal test specimens, it is often necessary to extrapolate the tearing resistance curves beyond the measuring limit of the specimen. There are theoretically two possible limits for extrapolation. A conservative estimate, sometimes used in e.g. the British R6 failure assessment method is to assume crack growth at a constant J, equal to the limiting value. A more realistic, but possibly un-conservative estimate of the tearing resistance is based on the assumption that crack growth will continue with the same slope at the limiting value. The true behavior is likely to lie somewhere between these two extremes. Conservative extrapolation beyond a limiting crack growth can be performed by considering the change in tearing resistance with crack growth. Two possible methods are in this presentation highlighted through a simple hypothetic example. The realism of the two methods is then tested on actual tearing resistance data going to large crack growths.
Lower and Upper Bound Shakedown Analysis of Structures With Temperature-Dependent Yield Stress
Authors: Chen Haofeng
Published: July 2010

Based upon the kinematic theorem of Koiter, the Linear Matching Method (LMM) procedure has been proved to produce very accurate upper bound shakedown limits. This paper presents a recently developed LMM lower bound procedure for shakedown analysis of structures with temperature-dependent yield stress, which is implemented into ABAQUS using the same procedure as for upper bounds. According to the Melan’s theorem, a direct algorithm has been carried out to determine the lower bound of shakedown limit using the best residual stress field calculated during the LMM upper bound procedure with displacement-based finite elements. By checking the yield condition at every integration point, the lower bound is calculated by the obtained static field at each iteration, with the upper bound given by the obtained kinematic field. A number of numerical examples confirm the applicability of this procedure and ensure that the upper and lower bounds are expected to converge to the theoretical solution after a number of iterations.
The Implementation of Hot Isostatically Pressed Powder Type 316L/304L Pressure Boundary Components in a PWR Plant
Authors: Burdett W. Barry , Hookham Ian D.
Published: July 2010

Hot Isostatic Pressing (HIP) has been used since the 1980s to consolidate porosity in cast metal shapes and improve mechanical properties in conventional forgings and wrought components. The availability of high quality metal powders has made it possible to produce Near Net Shape (NNS) items and more complex geometry components that are fully dense and offer an attractive set of properties at reduced cost. Powder HIP manufacturing reduces initial material usage and subsequent machining costs. Metal powder production and HIP processing are automated methods, which also provide protection against forging route obsolescence. Setup costs are lower and batch sizes smaller. HIPped powder microstructures are isotropic and equiaxed, with fine grain sizes not normally achieved in heavy section components, which facilitates ultrasonic NDE examination. Inclusion contents are lower and of more benign geometry, easing fracture and safety case development. Although widely used in the off-shore oil industry in high integrity applications, particularly to reduce welded connections, in the nuclear industry interest has been limited. The quality of HIPped powder items can provide through life cost savings since there is greater assurance of structural integrity compared to welded or wrought components. In an extensive programme of testing, it was established that HIPped powder 316L and 304L components, in items up to several tons in weight, have equivalent or slightly better strength, toughness and corrosion resistance. HIPped powder items are now in service as pressure retaining components in PWR plant. Effort is now directed at widening the range of components for which the HIP process is appropriate focusing on reducing welds in the plant construction sequence. This is particularly relevant to pipework manufacture and assembly. The benefits of facilitating an ASME Code Case for Powder HIP are also being considered.
Feasibility of an Explosive End-Projector for Conducting Shock Loading Experiments
Authors: Kleiser Geremy , Steinberg Michael , Chhabildas Lalit
Published: July 2010

This paper focuses on examining the feasibility of using an explosive end-projector device to conduct shock loading experiments. The concept employs an explosive end-projector to accelerate a bonded bimetallic impactor toward a stationary target material in order to conduct complex shock loading experiments. A high-impedance material, tantalum, was specifically selected to generate high stresses in targets. The driver plate materials were varied to create an impedance spectrum from 2 to 4 which would encompass materials from aluminum to zirconium. Techniques for launching single density metal plates exist. [1] The objective of this paper is to further refine an existing explosive technique to launch bimetallic plates which would generate complex shock/reshock or shock/release waves when used as a impactor. Although a bimetallic impactor will generate complex wave loading within a target material upon impact, it must first survive intact the explosive shock acceleration stress history imposed during launch in order to obtain the terminal velocity for use as an impactor. Initial computational studies using the Lagrangian finite element code EPIC were promising. [2] Based on the concern of the plate spallation during launch [2], an air gap between explosive and the backside of the bimetallic plate was modeled to reduce the magnitude of the initial shock resulting from direct explosive-metal interaction and to further gain insight into its effects on pressure, terminal velocity, and planarity of the plate. Initially, a single, homogenous plate of aluminum was modeled to examine the effects of the air gap without the complication of bimetallic wave reverberation. The air gap did reduce the intensity of pressure by 30% with only a 4% loss in terminal velocity. Planarity was exacerbated by the air gap leading to increased warping. With the introduction of bimetallic plates and the corresponding wave reverberation pressure reductions ranged between 20% to 30% with corresponding losses in terminal velocity of between 5% to 7%. Planarity was improved for the configurations in which the high density material, tantalum, was on the free surface or impacting side of the impactor but warping increased when the order was reversed. This results from the low-impedance material serving as a buffer to allow quasi-isentropic and monotonic increase in loading of the tantalum plate. However, when the high density material was placed on the back side of the impactor, the loading history was reversed and the low density material was subjected to high pressures. Overall, the technique appears to be a feasible alternative for conducting shock loading experiments. The air gap reduces pressure with only a minimal loss in terminal velocity, and the air gap in conjunction with plate geometry changes appears to mitigate spall. The air gap does not improve planarity with the explosive end-projector design used in this investigation but optimized designs would improve the flexibility of the technique.
Correlation of Gaseous Mass Leak Rates Through Micro and Nano-Porous Gaskets
Authors: Grine Lotfi , Bouzid Abdel-Hakim
Published: July 2010

The present work deals with theoretical and experimental studies of gaseous flow through tight gasket. The paper presents an innovative approach to accurately predict and correlate leak rates of several gases through nano-porous gaskets. The new approach is based on the calculation of the gasket porosity parameters (DH, N) using a model based on a first order slip flow regime. The model assumes the flow to be continuum but employs a slip boundary condition on the channel wall. Experimental measured gas flow rates were performed on gaskets with a microscopic flow rate range and isothermal steady conditions. The flow rate is accurately measured using multi-gas mass spectrometers. The gasket porosity parameters in the developed leakage rate formula were obtained experimentally for a reference gas (helium) for each stress level. In the presence of these statistical properties of a porous media the leak rates for different gases can be predicted with reasonable accuracy. It was found that the approach that considers the slip flow with the first order combined to the molecular flow covers the prediction of flow rates at the microscopy level and down to 10−8 mg/s very well.
A Robust Method to Determine Statistical Parameters for Cleavage Fracture Evaluation
Authors: Ko Han-Ok , Choi Jae-Boong , Kim Young-Jin
Published: July 2010

During the last couple of decades, several design guidelines and codes relating to major nuclear components have been introduced and revised for risk-based design and evaluation. It is an important process to determine statistical parameters in practice, for instance, by using the traditional method of moments and Maximum Likelihood Method (MLM). Since appropriate estimation of the parameters is not easy due to mathematical complexity, a robust method adopting concepts of both Chi-Square test and genetic algorithm (GA) is proposed in this paper. The Chi-Square test is a useful technique to get the goodness-of-fit of distributions, which is represented in terms of error between observed frequencies and frequencies calculated by assumed probability density function (PDF) of certain statistical distribution. The GA is an efficient optimization algorithm to solve nonlinear optimum problems. Using the Chi-Square test, statistical parameters can be determined and transferred to an optimum problem, and then solved by the GA employing proper nonlinear objective function. Reliability of the proposed method is verified against fracture toughness test data sets of SA508 reactor pressure vessel material obtained from PCVN specimens at various temperatures. The large scatter of experimental data is examined in use of a distribution reported by Neville and Kennedy, Burr type III and XII distributions by Nadarajah and Kortz as well as well-known Weibull distribution. A systematic assessment is carried out by using the new method and its results are compared with corresponding ones derived from the traditional method. Pros and corns of the alternative distributions as well as technical findings from the statistical assessment are fully discussed to show applicability of them.
Buckling Design of Confined Steel Cylinders Under External Pressure
Authors: Vasilikis Daniel , Karamanos Spyros A.
Published: July 2010

Thin-walled steel cylinders surrounded by an elastic medium, when subjected to uniform external pressure may buckle. In the present paper, using a two dimensional model with nonlinear finite elements, which accounts for both geometric and material nonlinearities, the structural response of those cylinders is investigated, towards developing relevant design guidelines. Special emphasis is given on the response of the confined cylinders in terms of initial imperfections; those are considered in the form of initial out-of-roundness of the cylinder and as an initial gap between the cylinder and the medium. Furthermore, the effects of the deformability of the surrounding medium are examined. The results indicate significant imperfection sensitivity and a strong dependency on the medium stiffness. The numerical results are employed to develop a simple and efficient design methodology, which is compatible with the recent general provisions of European design recommendations for shell buckling, and could be used for design purposes.
Design Evaluation Method for Random Fatigue Based on Spectrum Characteristics
Authors: Sakai Shinsuke , Okajima Satoshi , Izumi Satoshi , Kasahara Naoto
Published: July 2010

This paper shows the new design approach for random fatigue evaluation based on spectral characteristics. Fatigue damage under random loading is usually evaluated according to the following steps: 1. decomposition of random wave to stress amplitude using the rainflow cycle counting method (RFC) 2. evaluation of fatigue damage using Palmgren-Miner’s linear summation rule. In design process, the fluctuation of load is usually characterized through power spectral density (PSD). Therefore, the design process is expected to be generalized if the fatigue damage is directly evaluated from the PSD together with S-N diagram of the material. In fact many properties related to fatigue damage, such as distribution of extreme values, can be derived theoretically from geometrical properties of PSD. However, concerning the distribution of stress amplitude counted by RFC, it is rather difficult to derive it theoretically due to its complicated procedure. In this paper, upper bound of stress amplitude distribution is confirmed for many random waves generated by numerical simulation for many types of PSD. Expressing the upper bound distribution by closed form function using PSD characteristics leads us to the direct evaluation of fatigue damage with safety margin if the fatigue damage by particular stress amplitude is approximated using some series expansion form. Simple approximation procedure of high cycle fatigue damage for austenitic stainless steel and ferritic steel will be proposed in the paper. Finally, design evaluation procedure for the fatigue damage evaluation from PSD together with S-N diagram is summarized.
Mathematical Model for Metal Dusting on Low Alloy Steels
Authors: Chen Cheng , Zhou Changyu , Hu Guiming , Lei Na
Published: July 2010

Metal dusting is a kind of catastrophic corrosion phenomenon that can be observed in a wide range of petrochemical industry, it occurs in high-temperature equipments and tubes that exposed to hydrocarbon atmosphere and involves the disintegration of metals or alloys into graphitic carbon, fine metal or carbide particles. It is generally considered that the process of metal dusting can be divided into three stages: carburization, precipitation of carbides and decomposition of carbides, the precipitated carbides may include one or several kinds of formation such as Fe3C, Fe5C2 and Fe2C. The experiment was carried out on the dusting of low alloy steel Cr5Mo in CO-H2 gas mixture at 600 °C, the experimental results proved that the process of metal dusting for this kind of low alloy steels could be seen as uniform corrosion. By X-ray diffraction analysis, the formations of corrosion samples from exterior surface to interior matrix were: brittle layer of Fe5C2, intermediate layer of Fe3C plus Fe, inner metallic matrix. To describe the process of metal dusting in Cr5Mo, the mathematical model for the three stages of metal dusting was offered respectively: 1st stage, based on correlative theories on metal carburization, the distribution of carbon concentration in initial stage could be simulated by finite difference method; 2nd stage, based on 3-D diffusion theories of metal solid solution, Fick’s diffusion equation and jump mass balance equation was applied at interface. Reaction of metal dusting was simplified to be the proceeding of carbon diffusing into metallic matrix through Fe5C2 and Fe3C+Fe layers, then the growing rate equation of corrosion layer was represented. 3rd stage, based on the reaction rate equation, the carbides products were considered to be decomposed thoroughly to calculate the rate of disintegration reaction. Using the model with 3 stages mentioned above, the depth of corrosion samples for simplified 1-D plate of Cr5Mo steel was calculated. Compared with the actual measured corrosion depth of Cr5Mo samples subject to carburizing atmosphere after different exposure time, the calculated result showed a good agreement for the experimental result, so this model could be applied for the description of metal dusting in low alloy steels, and the method for calculating corrosion rate might offer some theoretical supports for further research such as life prediction of chemical process equipment subject to attack of metal dusting.
Z-Factors for Feeder Bends With Planar Axial Flaws
Authors: Wasiluk Bogdan S. , Scarth Douglas A.
Published: July 2010

Article C-6000 of Appendix C of ASME Section XI includes Z-factor load multipliers for straight pipes with circumferential flaws. Application of this article is limited to straight pipes with nominal pipe size (NPS) larger than 4 and materials with fracture toughness JIc higher than 105 kJ/m2. Section XI of the ASME B&PV Code does not provide Z-factors for pipes with axial flaws, even for pipes with NPS≥4. Feeders are small diameter pipes (NPS≤2.5) used in a primary heat transport system in the CANDU nuclear reactors. Developments of Z-factor load multipliers for warm-bent feeder bends with axial flaws under pressure are presented in this paper. An empirical approach was adopted using experimental results from the Feeder Bend Testing Program founded by the CANDU Owners Group. The elastic-plastic fracture mechanics stress has been defined by failure stress from the experiments. Limit load solutions for elbow/bends recently published by Kim et al. were discussed. Additionally, lower bound limit load simulations were performed using finite element models implemented for ANSYS. The results from straight pipe models exhibited good correlation with analytical solution. Numerical simulations for elbows/bends showed analogous trends for limit load of elbow/bends with axial cracks as reported by Kim et al.
Numerical Analyses of Residual Stress Fields in Welded Components
Authors: Siegele Dieter , Brand Marcus , Varfolomeev Igor , Hohe Jo¨rg
Published: July 2010

Residual stresses in welded components can influence the lifetime significantly. Besides experimental methods of residual stress measurements numerical methods of welding simulation are an important tool to determine the whole residual stress field in a component as a basis for lifetime prediction. As examples, the residual stresses in a core shroud of a boiling water reactor (BWR) and in a cladded plate have been investigated. In case of the core shroud postulated cracks in the residual stress field of the weld have been assessed with respect to possible crack corrosion cracking. For the cladded plate, the numerical simulation of the cladding and heat treatment process was accompanied by measurements of temperature, distortions and residual stresses. In the analysis, the temperature dependent material properties as well as the transformation behavior of the ferritic base metal were taken into account. The calculated residual stresses show tensile stresses in the cladding followed by compressive stresses in the base metal that are in agreement with measurements with X-ray diffraction technique.
Thermo-Mechanical Design of Brazed Plate-Fins Heat Exchanger Based on Finite Element Modeling Using Homogenization Techniques
Authors: Dib Johan , Lewon Ivan , Martin Boris
Published: July 2010

Using classical Finite Element (FE) tools to model heat exchangers emphasizes the need to elaborate specific methods to reduce the size of the numerical problem. Among these methods, homogenization techniques can be adapted and used for Brazed Aluminum Plate-Fins Heat Exchangers (BAHX) including layers of periodic structures. Actually the core is formed by stacking single layers consisting of periodic corrugated fins, side-bar and parting sheets which are all made of aluminum base metals, and brazed in a furnace. So in this paper a global methodology of BAHX modeling and design is presented. It integrates homogenization techniques to perform FE calculation and localization techniques to allow applying the appropriate design criteria. Finally, to validate this methodology, results are then compared on a basic heat exchanger modeled both by classical FE tools and a dedicated software tool encapsulating both homogenization and localization techniques.
Experimental Investigation of Flow Over a Backward-Facing Step in Proximity to a Flexible Wall
Authors: Velikorodny A. , Duck G. , Oshkai P.
Published: July 2010

Turbulent flow between a flexible wall and a solid surface containing a backward-facing step (BFS) was investigated using digital particle image velocimetry (PIV) and high-speed photography. Motivation for this study stems from paper manufacturing industry, where high-speed, wall-bounded jets of air are employed in air clamp devices to precisely position moving sheets of paper at the specified locations with respect to other equipment. In the current investigation, stationary sheet of paper under tension was positioned in proximity to the BFS. The incoming air flow emerged from a planar nozzle that was located in the solid wall upstream of the BFS. Curvature of the nozzle wall resulted in a favorable pressure gradient condition. As a result, the flow upstream of the BFS was attached to the solid wall due to the Coanda effect. Flows corresponding to two values of the Reynolds number (3000 and 3600) based on the step height and the maximum flow velocity at the step location were characterized in terms of patterns of instantaneous and time-averaged velocity, out-of-plane vorticity, streamline topology, and turbulence statistics. In addition, paper sheet oscillation was characterized using high-speed photography. Frequencies of the natural vibration modes of the flexible wall (paper sheet) were well separated from the hydrodynamic frequencies corresponding to the oscillations of the shear layer downstream of the BFS, which resulted in the absence of resonance in the system and low characteristic amplitudes of the paper sheet oscillation. In the time-averaged sense, interaction between the separated flow downstream of the BFS and the flexible wall (paper sheet) resulted in deformation of the paper sheet and formation of diverging channel geometry between the sheet and the solid wall. As the inflow velocity increased, the paper sheet was pulled closer to the surface of the air clamp, which resulted in increased confinement of the incoming Coanda jet. The flow reattachment length calculated on the basis of time-averaged flow patterns increased with the increasing Reynolds number.
Engineering Procedure for Calculation of Elastic Stress Concentration Factors of Bearing Pad Fretting Flaws
Authors: Wasiluk Bogdan S. , Scarth Douglas A.
Published: July 2010

Procedures to evaluate volumetric bearing pad fretting flaws for crack initiation are in the Canadian Standard N285.8 for in-service evaluation of CANDU® pressure tubes. The crack initiation evaluation procedures use equations for calculating the elastic stress concentration factors. Newly developed engineering procedure for calculation of the elastic stress concentration factor for bearing pad fretting flaws is presented. The procedure is based on adapting a theoretical equation for the elastic stress concentration factor for an elliptical hole to the geometry of a bearing pad fretting flaw, and fitting the equation to the results from elastic finite element stress analyses. Non-dimensional flaw parameters a/w, a/c and a/ρ were used to characterize the elastic stress concentration factor, where w is wall thickness of a pressure tube, a is depth, c is half axial length, and ρ is root radius of the bearing pad fretting flaw. The engineering equations for 3-D round and flat bottom bearing pad fretting flaws were examined by calculation of the elastic stress concentration factor for each case in the matrix of source finite element cases. For the round bottom bearing pad fretting flaw, the fitted equation for the elastic stress concentration factor agrees with the finite element results within ±3.7% over the valid range of flaw geometries. For the flat bottom bearing pad fretting flaw, the fitted equation agrees with the finite element results within ±4.0% over the valid range of flaw geometries. The equations for the elastic stress concentration factor have been verified over the valid range of flaw geometries to ensure accurate results with no anomalous behavior. This included comparison against results from independent finite element calculations.
Cross Comparison of European and American Pressure Vessel Standards in the Design of the Main Pressure Vessel Components
Authors: Lidonnici Fernando
Published: July 2010

A comparison among the different Pressure Vessel standards is a difficult exercise. In fact consideration should be given not only to the differences in the resulting thicknesses, but also to the fabrication, testing and inspection procedures, which sometimes are a substantial part of the final cost of a vessel. Moreover, each national standard should be used with its national material specifications, that sometimes have a remarkable influence on the calculation formulae or on the nominal design stresses. The purpose of this paper is to consider only the design and calculation aspects, comparing the minimum thicknesses obtained with the most important American and European Pressure Vessel standards for the most common shapes used in Pressure Vessel fabrication (Cylinders, Spheres, Cones, Flanges, Tubesheets, etc.). Tables and graphs will be provided, with the intention to understand the reasons of the differences, and giving a particular attention to the more modern standards, ASME Section VIII division 2 - 2007 for the United States and EN 13445 - 2009 for the European Union.
Using Fuzzy Inference System to the Analysis of Debris Flow Hazard
Authors: Lin Pao H. , Chen K. H.
Published: July 2010

In this study 11 factors influential to the evolvement of debris flows are identified via literature review and a thorough comparison among previous studies. Aided by MATLAB software and the concept of property in Fuzzy logic theory, an evaluation system for debris flow hazard is developed. Also, the proposed inference system is facilitated with Graphic User Interface Design Environment, so that observers or researchers may easily become familiar with system operation and utilize the system’s estimation as references for hazard judgment. Validation results with simulated cases of three different degrees of hazard severity evidenced that the present evaluation system on debris flows was effective with debris flows of high, low, and median hazards, as well as acceptable feasibility. Further, based on data gathered from rivers subject to debris flow and several actual cases in Taiwan, this proposed system was proved to achieve acceptable precision on the hazard evaluation of debris flow.
Warm Pre-Stressing Tests for WWER 440 Reactor Pressure Vessel Material
Authors: Lauerova Dana , Pistora Vladislav , Brumovsky Milan , Kytka Milos
Published: July 2010

During years 2006 – 2008, warm pre-stressing tests on small (Charpy size) and 1T CT specimens were performed at NRI Rez. The specimens were made from WWER 440 reactor pressure vessel material in as-received, thermally treated (artificially aged) and irradiated conditions, the last two conditions simulating the end of life state of the RPV. In this paper, only results of tests performed for this material in as-received and irradiated conditions are presented. Evaluation of WPS tests was performed with using Chell and Wallin predictive models. The attention was paid to 5% probability level fracture predictions, since this level of probability is important for WPS application in pressurized thermal shock evaluation performed within the RPV integrity assessment. From point of view of this 5% probability fracture prediction, both Chell and Wallin models appeared not to be sufficiently conservative for LCF regime (prediction of “Case 2”); for other regimes (LUCF, LPUCF, LTUF and LPTUF) they appeared to be sufficiently conservative (in almost all cases). Based on the results of the tests, Wallin model was selected for implementation into the RPV integrity evaluation procedure, but simultaneously a decision was adopted to decrease its predictions when the “Case 2” is predicted: instead of predicting some surplus (15% of virgin KIC) above the value of KWPS, only value of KWPS (without any surplus) is predicted. This measure enhances conservativeness of the Wallin model to a sufficient level: the performed WPS experiments then well confirm the Wallin model predictions decreased in this manner. Taking 90% of the value of KWPS represents an additional margin implemented currently in the WPS methodology.
Determination of Ductile Tearing Resistance Curve in Weld Joints
Authors: Marie S. , Gilles P. , Ould P.
Published: July 2010

Steels present in the ductile domain a tearing resistance which increase with the crack propagation up to the failure. This ductile tearing resistance is in general characterised with curves giving the variation of a global parameter (opening displacement at the crack tip δ, integral J) versus the crack extension Δa. These global approaches depend more or less on the specimen geometry and on the type of the imposed loading. Local approaches based on the description of the ductile tearing mechanisms provide reliable solution to the transferability problem (from the lab specimen to the component) but are complex and costly to use and are not codified. These problems get worse in the case of a weld joint where no standard is available for the measurement of their ductile tearing resistance. But the welded joints are often the weak point of the structure because of greater risk of defects, the heterogeneity of the microstructure of the weld, deformation along the interface between two materials with different yield stress (mismatch).... After briefly recalling the problems of transferability of the ductile tearing resistance curves obtained on lab specimen to the case of components, this article identifies the factors complicating the determination of the toughness in the welded joints and gives recommendations for the experimental determination of ductile tearing resistance curves of welded joints.
Prediction of Cleavage Fracture From Non-Sharp Defects Using the Weibull Stress Based Toughness Scaling Model
Authors: Horn Anthony J. , Sherry Andrew H.
Published: July 2010

Non-sharp defects exhibit a higher resistance to cleavage fracture than sharp cracks. This study uses the Weibull stress based toughness scaling model to predict cleavage fracture initiation in Single Edge Notch Bend SE(B) specimens with notches of varying root radii. Numerical predictions are compared with the results of an experimental study of SE(B) specimens with similar notches. The predictions correlate well with the test results, indicating that the Weibull stress approach and toughness scaling model can be successfully applied to predict cleavage fracture initiation from non-sharp defects. However, care needs to be taken to ensure that calibration of the Weibull parameters references fracture toughness data from constraint levels that span the defect of interest. This ensures the model interpolates between the constraint states used for calibration, rather than extrapolating outside the range of applicability.
Application of Simulation Based Reliability Analysis on the Dimensioning of Viscous Dampers GERB
Authors: Pecinka Ladislav , Svrcek Miroslav , Zeman Petr , Reinsch Karl-Heinz
Published: July 2010

GERB pipework dampers are highly effective viscous – elastic elements applied in many conventional and nuclear power plants. The best approximation for the seismic analyses of safety related pipeworks is the application of double Maxwell model represented by spring stiffnesses k1, k2 and damping coefficients b1, b2. These parameters represent damper capacity CN. Each damper is designed and manufactured for given operating temperature t0 and experimentally obtained curves of pseudostiffnesses and damping coefficients as the function of frequency in the range of 〈0; 35〉 Hz. Two parameters influence reliability of damper under seismic event: Overloading of nominal capacity in kN and conservation of minimal gap between piston and damper housing. The probabilities of exceeding of related allowable values may be assessed using Simulation Based Reliability Analysis. The needed input parameters are capacity and actual loadings and displacement of a piston in horizontal direction. General theory and numerical example are presented.
Dynamic Response of the WWER 1000/320 Reactor on the Pressure Pulsations Generated by Main Circulation Pumps
Authors: Pecinka Ladislav , Stulik Petr , Zeman Vladimir
Published: July 2010

Dynamic response of all PWR reactors is generated by the turbulent pressure pulsations (TPP) in the boundary layer on the surface of core barrel and acoustic pressure pulsations (APP) generated by main circulation pumps (MCP). While TPP have character of the white noise in the frequency range 〈0; 35〉 Hz, APP generate discrete set of frequencies called revolution and blade frequencies. The rotor revolutions of individual MCPs are slightly different and are changing as the operation conditions are changing. It results in the varying beat character of reactor vibrations. Results of numerical simulations and experimental measurements are presented.
Assessment of the Integrity of the Channel Shelter of the Experimental Nuclear Reactor LVR 15
Authors: Svrcek Miroslav , Krasny Ivan , Lestina Jan
Published: July 2010

The experimental reactor LVR 15 is operated in Nuclear Research Institute Rez. A pressurized experimental channel forming a field tube is installed in the reactor core. The operating parameters of the channel water are 16MPa and 290°C. From the point of view of operation (neutron absorption) the channel is located in a quadratic shelter 68×68mm with internal diameter 65mm (see Fig. 2). Based on the recommendation of IAEA INSAR mission, the integrity of the shelter must be conserved if a through wall crack in the outer channel tube is postulated, moreover the stability of the through wall crack must be guaranteed. Solutions of both situations are presented in the paper.
Effective Materials Property Information Management for the 21st Century
Authors: Ren Weiju , Cebon David , Arnold Steven M.
Published: July 2010

This paper discusses key principles for the development of materials property information management software systems. There are growing needs for automated materials information management in various organizations. In part these are fuelled by the demands for higher efficiency in material testing, product design and engineering analysis. But equally important, organizations are being driven by the need for consistency, quality and traceability of data, as well as control of access to sensitive information such as proprietary data. Further, the use of increasingly sophisticated nonlinear, anisotropic and multi-scale engineering analyses requires both processing of large volumes of test data for development of constitutive models and complex materials data input for Computer-Aided Engineering (CAE) software. And finally, the globalization of economy often generates great needs for sharing a single “gold source” of materials information between members of global engineering teams in extended supply-chains. Fortunately, material property management systems have kept pace with the growing user demands and evolved to versatile data management systems that can be customized to specific user needs. The more sophisticated of these provide facilities for: (i) data management functions such as access, version, and quality controls; (ii) a wide range of data import, export and analysis capabilities; (iii) data “pedigree” traceability mechanisms; (iv) data searching, reporting and viewing tools; and (v) access to the information via a wide range of interfaces. In this paper the important requirements for advanced material data management systems, future challenges and opportunities such as automated error checking, data quality characterization, identification of gaps in datasets, as well as functionalities and business models to fuel database growth and maintenance are discussed.
Overview of Seismic Issues in Design Certification and Combined License Application Reviews
Authors: Xu Jim , Samaddar Sujit
Published: July 2010

The U.S. Nuclear Regulatory Commission (NRC) established a new process for licensing nuclear power plants under Title 10 of the Code of Federal Regulations (10 CFR) Part 52, “Licenses, Certifications, and Approvals for Nuclear Power Plants,” which provides requirements for early site permits (ESPs), standard design certifications (DCs), and combined license (COL) applications. In this process, an application for a COL may incorporate by reference a DC, an ESP, both, or neither. This approach allows for early resolution of safety and environmental issues. The COL review will not reconsider the safety issues resolved by the DC and ESP processes. However, a COL application that incorporates a DC by reference needs to demonstrate that pertinent site-specific parameters are confined within the safety envelopes established by the DC. This paper provides an overview of site parameters related to seismic designs and associated seismic issues encountered in DC and COL application reviews using the 10 CFR Part 52 process. Since DCs treat the seismic design and analysis of nuclear power plant (NPP) structures, systems, and components (SSC) as bounding to future potential sites, the design ground motions and associated site parameters are often conservatively specified, representing envelopes of site-specific seismic hazards and parameters. For a COL applicant to incorporate a DC by reference, it needs to demonstrate that the site-specific hazard in terms of ground motion response spectra (GMRS) is enveloped by the certified design response spectra of the DC. It also needs to demonstrate that the site-specific seismic parameters, such as foundation-bearing capacities, soil profiles, and the like, are confined within the site parameter envelopes established by the DC. For the noncertified portion of the plant SSCs, the COL applicant should perform the seismic design and analysis with respect to the site-specific GMRS and associated site parameters. This paper discusses the seismic issues encountered in the safety reviews of DC and COL applications. Practical issues dealing with comparing site-specific features to the standard designs and lessons learned are also discussed.
An Analytical Evaluation of the Effect of Weld Sequencing on Residual Stresses Produced by Full Structural Weld Overlays on Pressurized Water Reactor Primary Cooling Piping
Authors: Fredette L. F. , Scott Paul M. , Brust F. W. , Csontos A.
Published: July 2010

Full Structural Weld Overlay (FSWOL) has been used successfully to mitigate intergranular stress corrosion cracking in boiling water reactor (BWR) welded stainless steel piping for many years. The FSWOL technique adds structural reinforcement, can add crack resistant material, and can create compressive residual stresses at the inside surface of the welded joint which reduces the possibility of further stress corrosion cracking. Recently, the FSWOL has been applied as a preemptive measure to prevent primary water stress corrosion cracking (PWSCC) in pressurized water reactors (PWR) on susceptible welded pipes with dissimilar metal welds common to PWR primary cooling piping. This study uses finite element models to evaluate the likely residual and operating stress profiles remaining after FSWOL for typical dissimilar metal weld configurations and describes the results of sensitivity studies which were performed to examine the effect of weld sequencing on the residual stresses produced in common configurations of PWR primary cooling system piping.
Considerations of Stricter TOFD Acceptance Criteria for Severe Refinery Services
Authors: Shargay Cathleen , Smythe Dennis , Antalffy Les
Published: July 2010

ASME Code Case 2235 and the new adoption of this Code Case into ASME Code Section VIII, Div. 2 has acceptance criteria which were based on predicted flaws and fracture mechanics modeled after the nuclear industry. These criteria were developed in response to a query about how to apply the acceptance criteria of ASME Article 4, Appendix 12 when using non-amplitude based ultrasonic methods such as phased array and time-of-flight diffraction. Since the traditional acceptance criteria were based on amplitude, they could not be applied for these alternative methods. The Code committees responded with a flaw size acceptance criteria based on the fracture mechanics properties of the materials and service conditions found in the nuclear industry. This was a major improvement and added a technical basis for the criteria lacking in past standards, however, there are no limitations or qualifications in CC 2235 on its applicability to other materials or service conditions. This is a concern for some oil refining and other plant services, especially those leading to embrittlement, various types of hydrogen-induced damage or high cycle fatigue cracking. The CC 2235 criteria were also not adequate for the recent major industry problem with reheat cracking in 2 1/4 Cr-1 Mo-V reactor fabrication. This paper summarizes the basis for CC 2235, describes the concerns with applying the acceptance criteria without consideration of material or service conditions, and suggests how to approach the issue from a better informed perspective and in some cases, establish stricter maximum flaw sizes.
Effects of Temperature and Thermal Cycling on the Threshold Stress Intensity Factor for Delayed Hydride Cracking in Zr-2.5Nb Pressure Tubes
Authors: Shek Gordon K. , Cui Jun
Published: July 2010

CANDU™ reactor uses Zr-2.5 Nb alloy pressure tubes as the primary coolant containment. The pressure tubes are susceptible to a crack initiation and growth mechanism known as Delayed Hydride Cracking (DHC), which is a repetitive process that involves hydrogen diffusion, hydride precipitation, hydrided region formation and fracture at a crack-tip. The threshold stress intensity factor for DHC initiation from a crack, KIH, is an important material parameter for assessing DHC initiation from crack-like or blunt flaws in the pressure tubes. Tests were performed on compact tension samples machined from hydrided unirradiated pressure tubes over the temperature range of 105°C and 286°C to determine the effect of test temperature on KIH. The results indicated that KIH values increased by about 10% from 105°C to 200°C. From 200°C to 286°C, a larger increase in the order of 30% was observed. The crack-tip hydrides when KIH was reached at different test temperatures were examined by metallography which showed that the hydrides had a taper shape and increased in both thickness and length with increasing test temperature. The test results were discussed in terms of the temperature dependence of material properties of the zirconium matrix and zirconium hydrides, as well as the hydride formation process. Implication of the experimental observations on the hydride fracture criteria was discussed. Another set of KIH tests was performed on C-shape hydrided unirradiated pressure tube samples to obtain KIH values under thermal cycling conditions. The test results were compared to KIH values obtained under isothermal condition at a test temperature of 200°C. The results indicated that the difference in KIH values was small and can be accounted for by the dependence of KIH on temperature.