bluuebunny/crossref_metadata_2025 huggingface dataset:
CHF for Uniformly Heated Vertical Tube Under High Pressure Conditions
Authors: Shim W. Jaewoo , Park Joo-Yong
Published: August 2008

In this study, a total of 2,870 high pressure (70 bar ≤ P ≤ 206 bar) data points of critical heat flux (CHF) in uniformly heated round vertical tube for water were collected from 5 different published sources. The data consisted of following parameter ranges: 28.07 ≤ G (mass flux) ≤ 10,565.03 kg/m2s, 1.91 ≤ D (diameter) ≤44.68 mm, 40 ≤L (length) ≤4966 mm, 0.14 ≤qc (CHF) ≤ 9.94 MW/m2, and −0.85 ≤X (exit qualities) ≤ 1.22. With these data a comparative analysis is made on available correlations, and a new correlation is presented. The new high pressure CHF correlation, as in the low and medium pressure cases of earlier studies, comprised of local variables, namely, “true” mass quality, mass flux, tube diameter, and two parameters as a function of pressure only. This study reaffirms our earlier findings that by incorporating “true” mass quality in the local condition hypothesis, the prediction of CHF under these conditions can be obtained quite accurately, overcoming the difficulties of flow instability and buoyancy effects that are inherent in the phenomena. The new correlation predicts the CHF data significantly better than those currently available correlations, with average error 0.12% and rms error 13.52% by the heat balance method.
Numerical Prediction of Flow in a Nuclear Fuel Bundle With Various Turbulence Models
Authors: In Wang Kee , Oh Dong Seok , Chun Tae Hyun
Published: August 2008

The numerical predictions using the standard and RNG k–ε eddy viscosity models, differential stress model (DSM) and algebraic stress model (ASM) are examined for the turbulent flow in a nuclear fuel bundle with the mixing vane. The hybrid (first-order) and curvature-compensated convective transport (CCCT) schemes were used to examine the effect of the differencing scheme for the convection term. The CCCT scheme was found to more accurately predict the characteristics of turbulent flow in the fuel bundle. There is a negligible difference in the prediction performance between the standard and RNG k-ε models. The calculation using ASM failed in meeting the convergence criteria. DSM appeared to more accurately predict the mean flow velocities as well as the turbulence parameters.
Impact of Aircraft Engines Into Reinforced Concrete Walls
Authors: Lawver Darrell , Tennant Darren , Mould John , Levine Howard
Published: August 2008

Major components of storage facilities and nuclear power plants are designed using reinforced concrete walls. Accidental or intentional impact of these structures by aircraft is a concern. The potential for penetration of these facilities by the aircraft or its components and the subsequent damage to the contents and release of toxic substances is a major concern. This paper focuses on analyzing the impact of jet engines into heavily reinforced concrete walls. These engines are among the stiffest and most massive components of an aircraft and the most likely to seriously damage and penetrate the reinforced concrete. We model both the engine and the reinforced concrete deformations using failure models for reinforced concrete and metals. Unlike many projectile impact problems, the impacting engine cannot be considered to be rigid. A large amount of energy is consumed in the plastic deformation and fracture of the engine components. The reinforced concrete is modeled using hexahedral elements for the concrete and beam elements for the rebar reinforcement. An advanced three invariant viscoplastic softening cap constitutive model describes the ductile and brittle rate-dependent characteristics of concrete. The rebar is modeled using a rate dependent, strain hardening von Mises formulation with failure controlled by fracture energy dissipation. A similar constitutive model is employed for the shell elements used to represent the engine components. These failure models are included in the FLEX large deformation finite element code which uses an explicit, central difference solution procedure with subcycling to solve the equations of motion. Element erosion using different criteria for concrete and metals is used to remove severely distorted and failed elements. Procedures used to mitigate the deleterious and unrealistic effects of hourglass control and viscoplasticity in the softening and failure regimes are discussed. The results from the computations are compared with experimental data generated by impacting a TF-30 engine into a two foot thick concrete wall.
Numerical Modeling of Fragmentation Characteristics of Explosive Fragmentation Munitions
Authors: Gold Vladimir M.
Published: August 2008

Numerical simulations of explosive fragmentation munitions presented in this work integrate three-dimensional axisymmetric hydrocode analyses with analytical fragmentation modeling. The developed analytical fragmentation model is based on the Mott’s theory of break-up of cylindrical “ring-bombs” (Mott, 1947), in which the average length of fragments is a function of the radius and velocity of the ring at the moment of break-up, and the mechanical properties of the metal. The fundamental assumption of the model is that the fragmentation occurs instantly throughout the entire body of the shell. Adopting Mott’s critical fracture strain concept (Mott, 1947), the moment of the shell break-up is identified in terms of the high explosive detonation products volume expansions, V/V0. The assumed fragmentation time determined from the high-speed photographic data of Pearson (1990) had been approximately three volume expansions, the fragmentation being defined as the instant at which the detonation products first appear as they emanate from the fractures in the shell. The newly developed computational technique is applied to both the natural and preformed explosive fragmentation munitions problems. Considering relative simplicity of the model, the accuracy of the prediction of fragment spray experimental data is rather remarkable.
Modeling of Munitions Fragmentation and Fragment Interaction With Containment Vessels and Shielding Systems
Authors: Saul W. Venner , Preece Dale S.
Published: August 2008

Design of pressure vessels intended to contain explosive blast and high velocity fragments can present several potential difficulties. The stresses and velocities resulting from explosive events generally result in highly non-linear material behavior, thereby limiting the applicability of standard design techniques. As a result, extensive testing is usually required to verify a containment vessel’s structural integrity. Computer simulation can be utilized to decrease the cost and time associated with vessel development. The Explosive Destruction System (EDS) was created by Sandia National Laboratories to safely dispose of aged chemical weapons. Development of the EDS system has provided a wealth of test data, quite useful for verification and improvement of computer-based predictive capabilities. The computer simulation code AUTODYN (currently being used at Sandia National Laboratories) provides an excellent basis for prediction of munition behavior as a result of explosive effects. Through comparison and refinement, appropriate simulation methods can be determined and integrated into future modeling efforts. Another computer code, CTH, has successfully predicted much of the physical behavior observed in EDS development and testing. Models created in AUTODYN 2-D can be compared with EDS data as well as results of the CTH modeling efforts, further refining the predictive capabilities of AUTODYN.
Single Chain Stochastic Polymer Modeling at High Strain Rates
Authors: Harstad Eric N. , Harlow Francis H. , Schreyer Howard L.
Published: August 2008

Our goal is to develop constitutive relations for the behavior of a solid polymer during high-strain-rate deformations. In contrast to the classic thermodynamic techniques for deriving stress-strain response in static (equilibrium) circumstances, we employ a statistical-mechanics approach, in which we evolve a probability distribution function (PDF) for the velocity fluctuations of the repeating units of the chain. We use a Langevin description for the dynamics of a single repeating unit and a Lioville equation to describe the variations of the PDE Moments of the PDF give the conservation equations for a single polymer chain embedded in other similar chains. To extract single-chain analytical constitutive relations these equations have been solved for representative loading paths. By this process we discover that a measure of non-uniform chain link displacement serves this purpose very well. We then derive an evolution equation for the descriptor function, with the result being a history-dependent constitutive relation.
Yield Pressure Measurements and Analysis for Autofrettaged Cannons
Authors: Underwood John H. , Moak David B. , Audino Michael A. , Parker Anthony P.
Published: August 2008

Yield pressure corresponding to a small permanent OD strain was measured in quasi-static laboratory tests of autofrettaged ASTM A723 steel cannon pressure vessels. Yield pressure was found to be a consistent ratio of the yield strength measured from specimens located in close proximity to the area of observed yielding. Yield pressure measurements for dynamic cannon firing with typically a 5 ms pressure pulse duration gave 14% higher yield pressures, attributed to strain rate effects on plastic deformation. Calculated Von Mises yield pressure for the laboratory test conditions, including the Bauschinger-modified ID residual stress and open-end vessel conditions, agreed with measured yield pressure within 3–5%. Calculated yield pressure was found to be insensitive to the value of axial residual stress, since axial stress is the intermediate value in the Von Mises yield criterion. A description of yield pressure normalized by yield strength was given for autofrettaged A723 open-end pressure vessels over a range of wall ratio and degree of autofrettage, including effects of Bauschinger-modified residual stress. This description of yield pressure is proposed as a design procedure for cannons and other pressure vessels.
Validation of Constraint-Based Methodology in Structural Integrity: Current Issues and Best Practice Handbook
Authors: Nilsson K.-F. , Taylor N. , Bhandari S. , Siegele D. , Lidbury D.
Published: August 2008

The paper presents an assessment of existing constraint-based procedures for as-received and aged nuclear power plant components, which has been performed as part of the European project VOCALIST. Current analytical procedures and gaps in understanding and limitations in constraint-based procedures are summarized and a First Best-Practice Handbook for constraint-based procedures is outlined. This handbook is based on case studies provided by the VOCALIST partners. The cases are selected to provide an overview of the state-of-the art methods include two-parameter and local approach analyses for cleavage and ductile tearing of different structural components.
Validation of Constraint Based Methodology in Structural Integrity – VOCALIST: Experimental Programme
Authors: Bass Richard , Eisele Ulrich , Keim Elisabeth , Keinanen Heikki , Marie Ste´phane , Sherry Andrew
Published: August 2008

The aim of VOCALIST (Validation of Constraint-Based Assessment Methodology in Structural Integrity) is to develop and validate innovative procedures for assessing the level of, and possible changes to, constraint-related safety margins in ageing pressure boundary components [1]. An iterative process of experiment and analysis will address this overall objective. The experimental investigations within VOCALIST are performed on three different materials representing the as new state of materials used for components of nuclear power plants as well as a state representing an in service degraded state of RPV materials. Within the experimental programme fracture mechanics specimens with different constraint situations are tested in order to quantify the influence of the constraint on the specimens failure behaviour as a basis for the advanced components integrity assessment. The investigations are performed on small laboratory specimens as well as on biaxially loaded cruciform specimens and large piping components. Within this contribution the experimental programme of VOCALIST is introduced. The investigated materials are characterized in terms of their mechanical properties. Special consideration is given to results of fracture mechanics specimens highlighting the constraint effect via the shallow crack effect and its contribution to a shift of the master curve.
Overview of NESC-IV Cruciform Specimen Test Results
Authors: Taylor N. , Bass R.
Published: August 2008

NESC-IV is an experimental/analytical program to develop validated analysis methods for transferring fracture toughness data generated on standard test specimens to shallow flaws in reactor pressure vessel welds subject to biaxial loading in the lower-transition temperature region. It is the fourth major project of the Network for Evaluating Structural Components (NESC). The testing program has exploited material removed from a production-quality reactor pressure vessel. In Part A six clad cruciform specimens containing shallow surface-breaking flaws located in weld material were successfully tested. For Part B a further four beam tests were performed using an innovative test piece design with a simulated embedded flaw. Post-test analysis is now in progress. The implications for current best-practice procedures for evaluation of RPV shallow are also being considered.
Local Failure Modes of a Nuclear Reactor Pressure Vessel Nozzle Under Severe Accident Conditions
Authors: Oh Young J. , Jeong Kwang J. , Park Byung G. , Hwang Il S.
Published: August 2008

Most past studies for the creep rupture of a nuclear reactor pressure vessel (RPV) lower head under severe accident conditions, have focused on global deformation and rupture modes. Limited efforts were made on local failure modes associated with penetration nozzles as a part of TMI-2 Vessel Investigation Project (TMI-2 VIP) in 1990’s. However, it was based on an excessively simplified shear deformation model. In the present study, the mode of nozzle failures is investigated using data and nozzle materials from Sandia National Laboratory’s Lower Head Failure Experiment (SNL-LHF). Crack-like separations were revealed at the nozzle weld metal to RPV interfaces indicating the importance of normal stress component rather than the shear stress in the creep rupture. Creep rupture tests were conducted for nozzle and weld metal materials, respectively, at various temperature and stress levels. Stress distribution in the nozzle region is calculated using elastic-viscoplastic finite element analysis (FEA) using the measured properties. Calculation results are compared with earlier results based on the pure shear model of TMI-2 VIE It has been concluded from both LHF-4 nozzle examination and FEA that normal stress at the nozzle/lower head interface is the dominant driving force for the local failure with its likelihood significantly greater than previously assumed.
A New Interaction Integral Method for Mesh-Free Analysis of Cracks in Functionally Graded Materials
Authors: Rao B. N. , Rahman S.
Published: August 2008

This paper presents a Galerkin-based meshless method for calculating stress-intensity factors (SIFs) for a stationary crack in two-dimensional functionally graded materials of arbitrary geometry. The method involves an element-free Galerkin method (EFGM), where the material properties are smooth functions of spatial co-ordinates and two newly developed interaction integrals for mixed-mode fracture analysis. These integrals can also be implemented in conjunction with other numerical methods, such as the finite element method (FEM). Five numerical examples including both mode-I and mixed-mode problems are presented to evaluate the accuracy of SIFs calculated by the proposed EFGM. Comparisons have been made between the SIFs predicted by EFGM and available reference solutions in the literature, generated either analytically or by FEM using various other fracture integrals or analyses. A good agreement is obtained between the results of the proposed meshless method and the reference solutions.
Mesh-Free Simulation in Elastic-Plastic Fracture Mechanics
Authors: Rao B. N. , Rahman S.
Published: August 2008

This paper presents an enriched meshless method for fracture analysis of cracks in homogeneous, isotropic, nonlinear-elastic, two-dimensional solids, subject to mode-I loading conditions. The method involves an element-free Galerkin formulation and two new enriched basis functions (Type I and Type II) to capture the Hutchinson-Rice-Rosengren singularity field in nonlinear fracture mechanics. The Type I enriched basis function can be viewed as a generalized enriched basis function, which degenerates to the linear-elastic basis function when the material hardening exponent is unity. The Type II enriched basis function entails further improvements of the Type I basis function by adding trigonometric functions. Three numerical examples are presented to illustrate the proposed method. The boundary layer analysis indicates that the crack-tip field predicted by using the proposed basis functions matches with the theoretical solution very well in the whole region considered, whether for the near-tip asymptotic field or for the far-tip elastic field. Numerical analyses of standard fracture specimens by the proposed meshless method also yield accurate estimates of the J-integral for the applied load intensities and material properties considered. Furthermore, the meshless results show excellent agreement with the experimental measurements, indicating that the new basis functions are also capable of capturing elastic-plastic deformations at a stress concentration effectively.
The Influence of Thermophysical Properties on a Numerical Model of Solidification
Authors: Stetina Josef , Kavicka Frantisek , Sekanina Bohumil , Heger Jaromir
Published: August 2008

Solidification and cooling of a (con)casting, with the simultaneous heating of the mold, is a case of transient spatial heat and mass transfer. This paper introduces an original and universal numerical model of solidification, cooling and heating, of a one-to-three-dimensional stationary and transient temperature field in a system comprising the casting, the mold and its surroundings. This model simulates both traditional as well as non-traditional technologies of casting conducted in foundries, metallurgical plants, forging operations, heat-treatment processes, etc. The casting process is influenced not only by the thermophysical properties (i.e. heat conductivity, the specific heat capacity and density in the solid and liquid states) of the metallic and non-metallic materials, but also by the precision with which the numerical simulation is conducted. Determining these properties is often more demanding than the actual calculation of the temperature field of the solidifying object. Since the influence of individual properties should be neither under- nor over-estimated, it is necessary to investigate them via a parametric study. It is also necessary to determine the order of these properties in terms of their importance.
Fatigue Crack Propagation Analysis of Nozzle Corner Using the Influence Function Method
Authors: Ochi Mayumi , Hojo Kiminobu , Nagasaki Takeharu
Published: August 2008

A calculation system has been developed in order to evaluate the thermal fatigue crack propagation of a semi-elliptical crack on the corner of a nozzle. One fatigue crack was assumed on the inner surface of the nozzle corner of a representative PWR reactor vessel. The stress intensity factors K were calculated at the deepest and outermost surface points of the crack using the influence function method. A database was prepared for the cracks with a depth of 0.022 t − 0.5 t (t: pressure vessel thickness) and an aspect ratio of 0.1a/c – 1.0 a/c (a: crack depth and c: half surface width). Eight-noded solid elements and the finite element analysis code MARC were used. The calculation system enables the propagation of fatigue cracks at nozzle corners to be carried out in a very short time.
Fatigue Threshold Considerations During Crack Propagation
Authors: Bian Lichun , Lim Jae-Kyoo
Published: August 2008

The angled crack problem has been given special attention in the recent years by fracture mechanics investigators due to its close proximity to realistic conditions in engineering structures. In this paper, an investigation of fatigue crack propagation in steel pipes containing an inclined surface crack is presented. The inclined angle of the crack with respect to the axis of loading varied between 0° and 90°. During the fatigue tests, the growth of the fatigue crack was monitored using the AC potential drop technique. Based on the concept of the effective stress intensity factor range, Δkeff, the rate of fatigue crack propagation, db/dN, is postulated to be a function of the effective strain energy density factor range, ΔSeff. Subsequently, this concept is applied to predict crack growth due to fatigue loads.
Evaluation of Stress-Intensity Factor of Mixed-Mode Crack by Hybrid Speckle Photography
Authors: Machida Kenji
Published: August 2008

The experiment was conducted on the compact normal and shear (CNS) specimens made of homogeneous and dissimilar materials subjected to mixed-mode loading. Many Young’s fringes patterns around the crack tip were taken and analyzed by the image-processing system developed in my laboratory. The displacement obtained by speckle photography is not as smooth as that obtained by the finite element analysis (FEA). Therefore, the displacement data were smoothed by 2 D FFT filtering and least squares method. The intelligent hybrid method proposed by Nishioka et al. was applied to the stress-strain analysis. Consequently, the stress and strain near the crack tip can be evaluated with high accuracy by the present stress-analyzing system. Then, the stress-intensity factor was evaluated by the virtual crack extension method (VCEM) and displacement extrapolation. The accuracy of stress-intensity factor at the free surface was discussed from both viewpoint of experiment and 3 D FEA.
Verification of Alternative Criteria for Shakedown Evaluation Using Flat Head Vessel
Authors: Asada Seiji , Yamashita Norimichi , Okamoto Asao , Nishiguchi Isoharu
Published: August 2008

Alternative stress evaluation criteria suitable for Finite Element Analysis (FEA) proposed by Okamoto et al. [1] have been studied by the Committee on Three Dimensional Finite Element Stress Evaluation (C-TDF) in Japan. Thermal stress ratchet criteria in plastic FEA are now under consideration. Two criteria are proposed: evaluating variations in plastic strain increments and evaluating variations in the elastic core region. To verify the validity of these criteria, calculations were performed for several typical models in C-TDF [2]. This paper shows calculations and evaluation results of a Flat Head Vessel for shakedown. To study shakedown criteria for gross structural discontinuity, a flat head vessel is surveyed. The flat head vessel consists of a stiff flat head and a shell and is subjected internal pressure and thermal cycle. The elastic shakedown area and the plastic area are compared and plastic strain increments are surveyed. A shakedown evaluation method based on distribution of elastic-plastic strain range is proposed.
Evaluation Criteria for Alternating Loads Based on Partial Inelastic Analyses
Authors: Okamoto Asao , Ohtake Yasuhiro , Yamashita Norimichi
Published: August 2008

This paper discusses the evaluation criteria for alternating loads utilizing partial inelastic analyses and free from the stress classification. As finite element analysis becomes popular, it has been noticed by designers that in some cases the conventional stress classification does not work well. The stress classification itself had been engineered as a practical tool to evaluate the integrity of a structure by elastic analyses, which actually could have inelastic behavior. For example, primary stress limits were determined reflecting the stress level at collapse. Therefore, the problem concerning the stress classification can be solved recalling how it had been engineered. In other words, the key to solve the problem is the inelastic evaluation method corresponding to each stress category. From this point of the view, the application of the inelastic analyses becomes widely studied. Consequently, as for primary loads, it has been proven that the collapse load evaluation by Limit or Plastic Analysis is effective and practical for design analyses. On the other hand, as for the alternating loads, it is not sufficiently discussed how the alternative criteria should be without stress classification. In this paper, the following are discussed based on the calculation results in the Committee on Three Dimensional Finite Element Stress Evaluation in JPVRC. 1. Prerequisite of the elastic-plastic analysis for shakedown evaluation, and the evaluation criteria based on plastic strain increment and its distribution. 2. The advantage to use simplified elastic-plastic analysis method than to perform fully elastic-plastic analyses, and the calculation procedure for Ke factors to be used with. The associated code rules are proposed.
Collapse Tests on Externally Pressurised Toroids
Authors: Blachut J.
Published: August 2008

The paper discusses the load carrying capacity of toroidal shells with closed circular cross-section and loaded by static external pressure. Details about the manufacturing, pre-experiment measurements and testing of three, nominally different, steel toroids are provided. Two of them were manufactured from mild steel by spinning two halves and then welding them around the inner and outer equatorial perimeters. The third one has been assembled by welding four 90 deg, stainless elbows. The outer diameter of these models was about 300 mm and the wall thickness varied from 2.0 mm to 3.0 mm. The hoop radius-to-thickness ratio, r/t, varied from about 15 to 30. The experimental collapse pressures were in the range from 4 MPa to 8 MPa. Comparisons with numerical results are also provided.
A Simple Inelastic Constitutive Model for Evaluation of Stable Cyclic Stress Response Under Nonproportional Straining
Authors: Sakane Masao , Itoh Takamoto , Chen Xu
Published: August 2008

This paper proposes a simple two-surface model for cyclic incremental plasticity based on combined Mroz and Ziegler kinematic hardening rules under nonproportional loading. The model has only seven material constants and a nonproportional factor which describes the degree of additional hardening. Cyclic loading experiments with fourteen strain paths were conducted using Type 304 stainless steel. The simulation has shown that the model was precise enough to calculate the stable cyclic stress-strain relationship under nonproportional loadings.
Creep Life Prediction For High Energy Piping Girth Welds Case History: Cholla, Unit 2
Authors: Cohn Marvin J. , Nass Dan
Published: August 2008

Creep damage of high energy piping (HEP) systems in fossil fuel power plants results from operation at creep range temperatures and stresses over many years. Thermal expansion stresses are typically below the yield stress and gradually relax over time. Consequently, the operating stresses in a piping system are typically below the yield stress and become load controlled. Conventional designs of HEP systems use the American Society of Mechanical Engineers B31.1 Power Piping Code. The Code is a general guideline for piping system design. Utilities typically determine examination sites by performing Code piping stress analyses and selecting locations that include the highest sustained longitudinal stress, highest thermal expansion stress, and terminal points. However, the Code does not address weldment properties, redistribution of thermal stresses and time-dependent life consumption due to material creep degradation. As an alternative, a high energy piping life consumption (HEPLC) methodology was used to predict maximum material damage locations. The methodology was used to prioritize expected creep damage locations, considering applicable affects such as weldment properties, field piping displacements, time-dependent operating stresses, and multiaxial piping stresses. This approach was applied to the main steam piping system at Cholla Unit 2. The locations of highest expected creep damage would not have been selected by a conventional site selection approach. Significant creep damage was found at the locations of maximum expected creep damage using the HEPLC methodology.
Results of High Stress Ratio and Low Stress Intensity on Fatigue Crack Growth Rates for 304 Stainless Steel in 288°C Water
Authors: Evans William M. E. , Wire G. L.
Published: August 2008

Fatigue crack growth rate tests were performed on a 304 stainless steel compact tension (CT) specimen in water with 40–60 cc/kg H2. Data in the literature for CT tests show minor environmental effects in hydrogenated water, but higher effects in oxygenated water. However, the PWR data presented by Bernard, et al (1979) were taken at low stress ratios (R = 0.05) and high stress intensity levels (ΔK = 16–41 MPa√m). The purpose of these tests is to explore the crack growth rate characteristics of 304 SS in hydrogenated water at higher R values (0.7 and 0.83) and lower ΔK values (11.0 and 7.7 MPa√m) Each set of R, ΔK conditions were tested at frequencies of 0.1, 0.01 and 0.001 Hz. The results show a pronounced effect on crack growth rates when compared to available literature data on air rates.
Scopes of RTP-1 and Section X, Classes I & II and Design Qualification
Authors: Conlisk Peter J.
Published: August 2008

The ASME does not require design calculations for Section X, Class I vessels. Design qualification is by destructive testing of a prototype vessel. The candidate vessel undergoes repetitive pressure testing up to the design pressure for as many as 100,000 cycles, depending on the type of FRP laminate in the vessel. If the vessel passes the fatigue test, it is then pressurized to six times the design pressure. If it also passes this test, vessels identical to the prototype may be built and receive the code mark. The prototype does not receive a code stamp. Rigorous quality assurance requirements insure that the production vessels are the same as the prototype. The ASME does require design calculations for Class II vessels. It also has stringent quality assurance and inspection requirements. Every Section X Class II vessel must also pass an acoustic emission examination before it receives a code stamp, thereby providing experimental verification of the structural integrity of the vessel. Class I and Class II vessels have different size and pressure scopes. Class I has no geometric limitations. The maximum design pressure for Class I is limited to 150 psig for bag-molded, centrifugally cast, and contact molded vessels, 1500 psig for filament-wound vessels, and 3000 for psig filament-wound vessels with polar boss openings. Class II vessels may be designed by rules or by stress analysis. For vessels designed by rules the diameter must lie between 6 in. and 96 in., and the maximum design pressure is 75 psig. Vessels that are designed by stress analysis must have diameters between 6 in. and 144 in. Their maximum design pressure varies with diameter: from 6 in. to 36 in. the maximum design pressure is 200 psig., and from 36 in. to 144 in. the design pressure is given by P = 7200/D where P is in psi. and D is in inches. RTP-1 has no size restrictions, but design pressure is limited to 15 psig. In both classes of Section X and in RTP-1, external design pressure must be less than 15 psig. Design calculations for FRP differ from calculations for metal vessels because FRP behaves differently from steel and other vessel metals. The material behaviors are compared and the resulting calculation differences are discussed.
Statistical Analyses of In-Air and In-Water Fatigue Test Data of Austenitic Stainless Steels and Ferritic Steels
Authors: Takahashi Yukio , Nakamura Takao
Published: August 2008

Scatter of material properties is always an important factor in the assessment of integrity of structures of any kind. In nuclear power plants, fatigue is one of the major mechanisms which potentially leads to a failure of components. To evaluate scatter of fatigue strength in air and high-temperature water environment for austenitic stainless and ferritic steels (carbon steel and low-alloy steels), statistical analyses were carried out for data packages generated from fatigue test data obtained mainly in Japan. Best-fit equations for in-air data were derived using these data and they were used together with equations developed in Japan for environmental effect to obtain mean property of the materials. Distributions of the ratio of each test data to the mean property, in terms of the number of cycles to failure as well as strain amplitude, were statistically analyzed. In most cases, data scatter obeyed log-normal distribution quite well. Based on the regressions by log-normal distribution function, relations between design factors on them and failure probability were obtained for each material group and environment. It was found that the amounts of scatter of the in-water data were similar to that of the corresponding in-air data. Finally, design factors required to cope with material property variation are discussed.
Consideration of Environmental Fatigue in the ASME Code for Carbon and Low-Alloy Steel Components
Authors: Rosinski Stan T. , Deardorff Arthur F. , Nickell Robert E.
Published: August 2008

The potential impact of reactor water environment on reducing the fatigue life of light water reactor (LWR) piping components has been an area of extensive research. While available data suggest a reduction in fatigue life when laboratory samples are tested under simulated reactor water environments, reconciliation of this data with plant operating experience, plant-specific operating conditions, and established ASME Code design processes is necessary before a conclusion can be reached regarding the need for explicit consideration of reactor water environment in component integrity evaluations. U.S. nuclear industry efforts to better understand this issue and ascertain the impact, if any, on existing ASME Code guidance have been performed through the EPRI Materials Reliability Program (MRP). Based on the MRP activities completed to date there is no need for explicit incorporation of reactor water environmental effects for carbon and low-alloy steel components in the ASME Code. This paper summarizes ongoing MRP activities and presents the technical arguments for resolution of the environmental fatigue issue for carbon and low-alloy steel locations.
Guidelines on Environmental Fatigue Evaluation for LWR Component
Authors: Nakamura Takao , Saito Itaru , Asada Yasuhide
Published: August 2008

Japanese utilities and vendors have taken environmental effects on fatigue (EF) into consideration in the plant life management (PLM) activity of operating plants for several years. In Sep. 2000 MITI notified the utilities to adopt “The Guidelines for Evaluating Fatigue Initiation Life Reduction in LWR Environment (MITI guidelines)” for PLM evaluation of operating plants [1]. In April 2001, the study started to establish detailed procedures for EF evaluation and the committee was organized for developing detailed guidelines at Thermal and Nuclear Power Engineering Society (TENPES). The evaluation guidelines were completed and published as TENPES guidelines [2]. These guidelines proposed several practical options to apply fatigue life reduction factor for environmental effects (Fen) on actual operating plant fatigue evaluation.
Review of Margins Needed to Develop Fatigue Design Curves From Laboratory Test Data
Authors: Van Der Sluys W. A.
Published: August 2008

The PVRC has just completed a review of the effect of LWR (Light Water Reactor) coolant environment on the low cycle fatigue properties of carbon and low alloy steels. The PVRC has made recommendations to the ASME on changes to the boiler and pressure vessel codes to account for the environmental effects. In developing the recommendations, the margins used to produce the design curves from fatigue test results of laboratory specimens, were studied. This paper describes the margins used by the ASME in the development of the current design curves and discusses what margins should be applied when the laboratory fatigue testing includes tests in simulated LWR coolant environments.
Analysis Continuity Considerations and Methods Used in Fatigue Monitoring
Authors: Cranford E. L. , Gray M. A.
Published: August 2008

The integrity of fatigue monitoring results is influenced by the input data stream, and the accurate accounting of continuity between time periods used for data capture and analysis. This paper discusses the treatment of continuity with respect to applied methods of evaluation used in fatigue monitoring. The items discussed here are applicable to various aspects of fatigue monitoring assessment, including the evaluation of reactor water environmental effects. Proper treatment of continuity in the evaluation processes is essential to the accuracy of any monitoring assessment.
Capturing Nuclear Power Plant Design Basis Configuration Through Effective Self Assessments
Authors: Bhavnani Dilip
Published: August 2008

This paper emphasizes the importance of capturing all design basis changes especially in the civil/structural disciplines in a nuclear plant. Constant changes due to plant maintenance activities may lead to a potential loss of configuration, if these changes are not clearly understood and documented. By performing effective self-assessments, benefits gained are substantial and compliance is readily assured. It has been seen from experience that the current configuration control status of design documents such as calculations, procedure adherence, quality of posted changes, tracking aggregate impact, and understanding of the documentation update program by involved personnel is not clearly communicated. Various critical software structural and civil packages, piping specifications, and engineering evaluations, have outstanding changes posted against them as a result of continuing plant operational and maintenance work. Utilities that have nuclear plants also have a tendency to bank calculations, which has the potential to impact configuration control, since all changes that are banked are not supported with adequate backup calculations and justification. This may lead to loss of valuable time, should a plant emergency exist. Often a lack of aggregate impact of outstanding changes to plant design basis calculations continue to increase. Plants have been in operation for many years with reduced staffing levels. Additionally, due to limited resources, the aggregate impact of outstanding changes is not being formally tracked for all calculations. A lack of configuration control is often one of the precursors to safety significance or cost significant events. Increased management attention and allocation of resources is warranted to ensure that corrective actions are implemented. This will ensure that needed improvements are made to the configuration control of design documents. The paper outlines that by performing an in-depth review of changes posted against safety related documents, the potential to impact safety is substantially minimized. An effective self-assessment in the areas where numerous documents such as civil and stress calculations are generated may significantly ease the burden of maintaining adequate configuration.
An Overview of the New ASME Section VIII, Division 2 Pressure Vessel Code
Authors: Osage David A.
Published: August 2008

ASME has decided to undertake a major revision, including significant technical updates, of Section VIII, Division 2 of the Boiler and Pressure Vessel Code. Division 1 will not be affected, but it is anticipated that the revised Division 2 Code will allow significantly more efficient construction for many current Division 1 applications. As a result, it is expected that the revised code will be used for many more applications than the current Division 2.
Observations on the Evolution of Design Rules Considering the Computer
Authors: Becht Charles
Published: August 2008

Many design methods in use today evolved prior to widespread use of computer analysis tools. As the availability of computer analysis has increased some have evolved, and some need to evolve. This discussion lists a few examples.
PVRC Activities Supporting the Development of ASME Codes and Standards
Authors: Koves William J.
Published: August 2008

This panel session provides a forum to discuss the future directions of the ASME Boiler and Pressure Vessel Codes. Historically the Pressure Vessel Research Council (PVRC) has played a strong role in providing the technology base for changes and advancements in the ASME Codes, and any discussion of the future direction of the ASME Codes would be incomplete without mention of PVRC activities. The topic of this discussion is the current structure of PVRC, and its relationship with ASME, and a brief overview of some of the Past, Current and Future projects that have or will impact the ASME Codes.
Pipe Line Security: Design of Pipe to Resist Blast Type Loads
Authors: Stevenson John D.
Published: August 2008

Pipe line security is divided into two categories; pipe line security associated with above ground piping and buried piping. With respect to above ground piping security, the pipe’s ability to resist blast loads which are dynamic and impulsive in nature is required. In this evaluation it is assumed to be dealing with a cratering charges located some distance (feet or meters) from the pipe line. The use of breaching charges which typically consist of plastic explosives in direct contact with the pipe wall or shaped charges which are designed to locally cut or penetrate the pipe wall are not in the scope of this discussion.
The Favorable Effect of Autofrettage on Uniform Arrays of 3-D Unequal-Depth Cracks in a Thick-Walled Cylindrical Pressure Vessel
Authors: Perl M. , Ostraich B.
Published: August 2008

The favorable effect of autofrettage on the mode I stress intensity factor (SIF) distributions along the fronts of radial, semi-elliptical surface cracks pertaining to large uniform arrays of unequal-depth cracks emanating at the bore of a pressurized thick-walled cylinder is studied. The analysis is based on the, previously proposed, “two-crack-depth level model”. SIF values are evaluated by the finite element method (FE) using the ANSYS 6.1 code. In the FE model singular elements are employed along the crack front and an equivalent temperature load simulates the autofrettage residual stress field. The distribution of KIN = KIP + KIA, the combined stress intensity factor due to pressurization and full autofrettage, for numerous uneven array configurations bearing n = n1 + n2 = 8 to 128 cracks, a wide range of crack depth to wall thickness ratios, a1/t = 0.01 to 0.4, and various crack ellipticities, a1/c1 = 0.3 to 1.5, are evaluated for a cylinder of radii ratio Ro/Ri = 2. The accuracy of the evaluated SIFs is increased using an improved displacement extrapolation. The results clearly indicate the favorable effect of the residual stress field on the fracture endurance and the fatigue life of autofrettaged cylindrical pressure vessel bearing uniform arrays of 3-D unequal-depth cracks emanating from its inner bore. This favorable effect is governed by Ψ = σo/p — the ratio of the vessel’s material yield stress to its internal pressure. The higher ψ is the more effective autofrettage becomes. The “interaction range” for the various configurations of uneven crack arrays is evaluated. The range of influence between adjacent cracks on the maximal combined SIF, KNmax, is found to be dependent on the density of the array, as reflected in the inter-crack aspect-ratio, as well as on the cracks’ ellipticity.
Ultrasonic Flexural Torsional Guided Wave Pipe Inspection Potential
Authors: Sun Zongqi , Zhang Li , Gavigan Brian , Hayashi Takahiro , Rose Joseph L.
Published: August 2008

The excitation and propagation characteristics of guided wave torsional flexural mode are exploited in this paper. Theoretical computations and experiments are carried out to show the angular profiles of the torsional flexural modes propagation characteristics and the subsequent natural focusing effects. Because of such inherent advantages as less mode conversion and high sensitivity to axial defects, torsional modes and focusing possibilities have great potential in pipe inspection. By combining longitudinal and torsional modes, defect characterizations including defect size, shape etc. can be determined by truly three-dimensional guided wave pipe inspection.
Characterization of Moon Rock Media With Elastic Waves
Authors: Tittmann Bernhard R.
Published: August 2008

Elastic wave propagation in porous media will be introduced by a discussion of scattering to show the use of broad frequency band pulses in relating the attenuation, velocity and backscattering to information on porosity. Examples will be given for microporosity in castings and powder metal components. This will be followed by a discussion of the influence of volatiles within the pores on the absorption of elastic waves in porous ceramics and rocks. Implications of these findings will be given for ultrasonic device applications and for the interpretation of the lunar seismic experiments carried out as part of the Apollo missions to the moon.
Standardization Related to the Pressure Equipment Directive With a Focus on Bolted Joints
Authors: Ho¨vel Albert , Hecker Peter
Published: August 2008

Standardization related to the European Pressure Equipment Directive 97/23/EC (PED) is of considerable importance. European Member States must permit the placing on the market of pressure equipment and assemblies at the date of application of this Directive since 29 May 2002, and permit such equipment and assemblies to be put into service since this date. The economic significance of the pressure equipment sector for the common European market is made clear by the fact, that approximately every tenth subject presently dealt with by the European Standardization Committee (CEN) is directly or indirectly linked to the PED. On a European level, a total of 19 Technical Committees in CEN and 9 Technical Committees in ECISS (European Committee for Iron and Steel Standardization) are involved in standardization relating to the Directive 97/23/EC. Three committees are dealing with flanges, gaskets, bolts and valves. On a international level two technical committees standardize flanges and bolts.
Distinguishing Ratcheting and Shakedown Conditions in Pressure Vessels
Authors: Reinhardt W.
Published: August 2008

The nature of the boundary between stable cycling and ratcheting is discussed using several illustrative example scenarios. The examples are analyzed in the context of the elastic methods currently in the ASME Code to demonstrate the conservatism of the existing approach that exists in some cases, and the unconservative estimation that exists in others. It is shown that the limit on the linearized primary plus secondary stress range can be related to conditions for elastic shakedown in certain kinematic hardening models of plasticity, while the limits on thermal stress ratchet address only scenarios similar to the Bree problem.