bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Model for Evaluating the Residual Stress Field in an Autofrettaged Spherical Pressure Vessel Incorporating the Bauschinger Effect
Authors: Perl M. , Perry J.
Published: August 2009

Increased strength-to-weight ratio and extended fatigue life are the main objectives in the optimal design of modern pressure vessels. These two goals can mutually be achieved by creating a proper residual stress field in the vessel’s wall, by a process known as autofrettage. Although there are many studies that have investigated the autofrettage problem for cylindrical vessels, only few such studies exist for spherical ones. There are two principal autofrettage processes for pressure vessels: hydrostatic and swage autofrettage, but spherical vessels can only undergo the hydrostatic one. Because of the spherosymmetry of the problem, autofrettage in a spherical pressure vessel is treated as a two-dimensional problem and solved solely in terms of the radial displacement. The mathematical model is based on the idea of solving the elasto-plastic autofrettage problem using the form of the elastic solution. Substituting Hooke’s equations into the equilibrium equation and using the strain-displacement relations, yields a differential equation, which is a function of the plastic strains. The plastic strains are determined using the Prandtl-Reuss flow rule and the differential equation is solved by the explicit finite difference method. The previously developed 2-D computer program, for the evaluation of hydrostatic autofrettage in a thick-walled cylinder, is adapted to handle the problem of spherical autofrettage. The appropriate residual stresses are then evaluated using the new code. The presently obtained residual stress field is then compared to three existing solutions emphasizing the major role the material law plays in determining the autofrettage residual stress field.
PERFECT—Prediction of Irradiation Damage Effects in Reactor Components: Update of Progress in RPV Mechanics Sub-Project
Authors: Lidbury David , Bugat Ste´phane , Diard Olivier , Keim Elisabeth , Marini Bernard , Viehrig Hans-Werner , Planman Tapio , Wallin Kim
Published: August 2009

The EURATOM 6th Framework Integrated Project PERFECT (Prediction of Irradiation Damage Effects in Reactor Components) addresses irradiation damage in RPV materials and components by multi-scale modeling. This approach offers many potential advantages over the conventional empirical methods used in current practice of nuclear plant lifetime management. Launched in January 2004, PERFECT is a 48-month project focusing on two main components of nuclear power plants which are subject to irradiation damage: the ferritic steel reactor pressure vessel (RPV), and the austenitic steel internals. It is the purpose of the present paper to provide an update of progress of work being carried out in the Mechanics Sub-project of PERFECT to predict the fracture behavior of RPVs in PWR and WWER systems.
Use of Analytical and Experimental Monitoring Techniques in Assessing the Performance of a Cold Reheat Steam Line
Authors: Alexander Chris , Frey Joe
Published: August 2009

After a catastrophic failure that occurred in a 30-inch diameter cold reheat (CRH) steam line at the W. A. Parish Plant, Texas Genco requested that Stress Engineering Services, Inc. (SES) assist in determining the cause of the failure. The incident occurred at approximately 12:10 PM on July 15, 2003 and resulted in a catastrophic failure that scattered components around the plant in a radius of 1,200 feet. Reliant Resources and Texas Genco conducted their own failure investigation that involved metallographic examinations, inspection of the fracture surfaces, review of operating conditions at the time of failure, and studies related to the weld profile of the CRH line. Stress Engineering Services’ efforts included studies using computational fluid dynamics (CFD) to address how droplet sizes from the attemperator might impact downstream behavior of the piping system. Follow-on work involved conducting a mock-up testing as well as field monitoring using high temperature strain gages, accelerometers, and thermocouples. The data obtained from the field monitoring efforts, along with process data provided by Texas Genco, were used to perform finite element analyses. The finite element work involved the calculation of static stresses as well as transient stresses generated by cycling of the attemperator (thermal stresses) and vibration of the line (mechanical stresses). Fracture mechanics was used to determine the times required for crack initiation and propagation to failure. The analysis and monitoring efforts clearly demonstrated the operating conditions that were required to produce the failure. Additionally, the failure reinforced the importance of regular inspection of piping systems; even those high energy piping systems such as the cold reheat lines not normally associated with catastrophic failures.
Finite-Element Simulations and Probabilistic Fracture Assessments of the Response of Alternate Rifling Geometries
Authors: Segall A. E. , Carter R.
Published: August 2009

A 3-D finite-element model was used to simulate the severe and localized thermal/pressure transients and the resulting stresses experienced by a rifled ceramic-barrel with a steel outer-liner; the focus of the simulations was on the influence of non-traditional rifling geometries on the thermoelastic- and pressure-stresses generated during a single firing event. In order to minimize computational requirements, a twisted segment of the barrel length based on rotational symmetry was used. Using this simplification, the model utilized uniform heating and pressure across the ID surface via a time-dependent convective coefficient and pressure generated by the propellant gasses. Results indicated that the unique rifling geometries had only a limited influence on the maximum circumferential (hoop) stresses and temperatures when compared with more traditional rifling configurations because of the compressive thermal stresses developed at the heated (and rifled) surface.
IAEA Coordinated Research Project on Master Curve Approach to Monitor Fracture Toughness of RPV Steels: Effect of Loading Rate
Authors: Viehrig Hans-Werner , Lucon Enrico
Published: August 2009

In the final evaluation for the application of the Master Curve in the IAEA Coordinated Research Project Phase 5 (CRP-5), one of the areas which was identified as needing further work concerned the effects of loading rate on the reference temperature To up to impact loading conditions. This subject represents one of the three topic areas within the current CRP-8. The effect of loading rate can be broken down into two distinct aspects: 1) the effect of loading rate on the Master Curve To values for loading rates within the specified in ASTM E1921-05 for quasi-static loading (0.1–2 MPa√m/s); 2) the effect of loading rate on To values for higher loading rates, including impact conditions using instrumented precracked Charpy (PCC) specimens. The new CRP includes both aspects, but primarily focuses on the second element of loading rate effects, i.e. loading rates above 2 MPa√m/s. These issues are investigated within the topic area #2 of CRP-8 (Loading Rate Effect). The mandatory portion of this topic area required participation in a round-robin exercise (RRE) to validate the application of the Master Curve approach to PCC specimens tested in the ductile-to-brittle transition region using an instrumented pendulum (10 tests per participant on the JRQ material). The current status of the RRE is presented in [1]. The non-mandatory portion of this topic area consists in providing Master Curve data obtained at different loading rates on various RPV steels, in order to assess the loading rate dependence of To and compare it with an empirical model proposed by Wallin. Moreover, additional topics will be addressed, such as: • comparison of results from unloading compliance and monotonic loading in the quasi-static range; • estimation of fracture toughness from Charpy V-notch data; • assessment of crack arrest properties from instrumented Charpy results; • effect of irradiation on the relationship between static and dynamic fracture toughness.
Flange Joint Bolt Spacing Requirements
Authors: Koves William J.
Published: August 2009

The bolted flange joint assembly is a complex system. System stresses are dependent on elastic and nonlinear interaction between the bolting, flange and gasket. The ASME Code design rules provides a method for sizing the flange and bolts to be structurally adequate for the specified pressure design conditions and are based on an axi-symmetric analysis of a flange. The ASME rules do not address the circumferential variation in gasket and flange stress due to the discrete bolt loads. Proper bolt spacing is important to maintain leak tightness between bolts and to avoid distorting the flange. This paper provides an analytical solution for the gasket and flange stress variation between bolts. The analytical solution is validated with 3-D Finite Element solutions of standard flange designs.
IAEA Coordinated Research Project on Master Curve Approach to Monitor Fracture Toughness of RPV Steels: Applicability for Highly Embrittled Materials
Authors: Planman Tapio , Onizawa Kunio , Server William , Rosinski Stan
Published: August 2009

In the Master Curve (MC) fracture model, a universal temperature dependence is assumed for ferritic steels, including those used in reactor pressure vessel (RPV) applications. The assumed curve shape also has been observed to be generally valid for highly irradiated or thermally aged materials that exhibit a high value of reference transition temperature, To. Lower than predicted fracture toughness behavior occasionally has been observed, however, in the upper transition range. It has been suggested that this behavior possibly may be associated with a lowered upper shelf toughness due to high irradiation doses. One objective of the present International Atomic Energy Agency (IAEA) Coordinated Research Project 8 (CRP-8) is to clarify the MC shape issue by collecting and analyzing relevant fracture toughness data measured on irradiated (or thermally aged) RPV and corresponding steels. For thermally aged or highly irradiated materials the fracture mode typically tends to gradually change from cleavage to one of intergranular fracture (IGF) which, if the IGF proportion is high, may significantly affect both the scatter and temperature dependence of fracture toughness. The data reviewed to date in this CRP show, in general, a very consistent fracture behavior with the basic Master Curve model that further confirms the applicability of the assumed curve shape. In cases where the basic homogeneity or fracture mode assumptions of the MC model were not satisfied due to high proportions of IGF, correspondence with the measured and predicted behavior could be markedly improved by applying available models developed to address inhomogeneous materials (e.g., SINTAP or the multi-modal model). The onset of upper shelf (TUS) and its correlation with To is presented as a possible approach for characterizing material behavior in the upper transition region when sufficient upper shelf fracture toughness data are available.
Effect of Angle of Attack on Fluidelastic Instability of a Rotated Triangular Tube Bundle
Authors: Khalvatti A. , Mureithi N. W. , Pettigrew M. J.
Published: August 2009

In the operation of shell-and-tube heat exchangers, vibration of the tubes can be induced by fluid flowing over the tube array in cross flow. The region of concern in Steam Generators (SG) is the upper most U-bend region where the flow crosses a large number of tubes which can cause significant hydraulic resistance. This hydraulic resistance forces the flow to change direction. From a fluidelastic instability point of view, the tube bundle is excited by oblique cross flow. The purpose of this paper is to examine the instability phenomena in a rotated triangular tube bundle subjected to oblique single phase cross flow. In this present work tests are conducted in a wind tunnel on a rotated triangle tube array. Fluidelastic instability results are in agreement with what was expected. The results show that fluidelastic instability is strongly dependent on the angle of attack. The results also show that, generally, the elimination of bundle flexibility in the direction transverse to the flow, greatly affects the stability behavior of the array.
The Transition Matrix Formalism for the Scattering of an Alluvium on an Elastic Half-Space
Authors: Liao Wen-I , Teng Tsung-Jen , Wang Shiang-Jung
Published: August 2009

This paper develops the transition matrix formalism for scattering from an three-dimensional alluvium on an elastic half-space. Betti’s third identity is employed to establish orthogonality conditions among basis functions that are Lamb’s singular wave functions. The total displacements and associated tractions exterior and interior to the surface are expanded in a Rayleigh series. The boundary conditions are applied and the T-matrix is derived. A linear transformation is utilized to construct a set of orthogonal basis functions. The transformed T-matrix is related to the scattering matrix and it is shown that the scattering matrix is symmetric and unitary and that the T-matrix is symmetric. Typical numerical results obtained by incident plane waves for verification are presented.
Improved Explicit Method for Time History Analysis
Authors: Chang Shuenn-Yih , Huang Chiu-Li
Published: August 2009

In this paper, an explicit integration method is presented. This method is shown to have the same numerical characteristics as those of the constant average acceleration method for a linear elastic system. This implies that it is unconditionally stable for linear elastic systems. However, it shows very different stability properties for nonlinear systems. In fact, it has conditionally stability for an instantaneous stiffness hardening system while it remains unconditionally stable for an instantaneous stiffness softening system. The conditional stability property is much better than for the Newmark explicit method for instantaneous stiffness hardening systems. Meanwhile, this method involves no iterative procedure in the step-by-step integration. Thus, it is very promising for time history analysis since it is explicit and has improved stability properties.
TIMES: An International Project on Transferability of Fracture Toughness Values for Irradiated RPV Steels
Authors: Huemmer Matthias , Keim Elisabeth , Hoffmann Harald
Published: August 2009

The prediction of specimen or component failure behavior can be attained by the use of local approach (LA) models based on Weibull stresses. Over the last years recent developments have been achieved, and the predictive capabilities of these models have been improved significantly. In this paper a concept, which is based on a LA model, will be proposed for the prediction of fracture toughness for different specimen types made of ferritic base and weld metal in the unirradiated as well as in the irradiated state. The only necessary input parameter will be the yield strength of the material at one temperature (preferably room temperature). The LA model under consideration is tuned for its temperature dependence using a ferritic base material in the unirradiated material state. The outcome of the tuning are the Weibull parameters m, • •u, • •th, • •p,0. The parameters m, • •th, • •p,0 are kept constant over temperature and for variation of materials and fluences. To model the temperature dependence over the transition region, local events like plastic shielding, blunting or arrest of micro cracks have to be considered. These events are modeled via an increase of • •u over temperature. The temperature shift, • •T, in • •u, is obtained by using a correlation between the yield strength of the tuned material and the material under investigation. In order to validate this concept, a large number of computations, which includes different temperatures, specimen types, loading ratios, weld and base metal in unirradiated and irradiated conditions are conducted. They lead to the prediction of a median fracture toughness curve for each material and specimen type. All numerical investigations are compared with experimental results. It could be shown that the predictions made by this approach are in good agreement with the experiments. This is encouraging for further application to other materials and irradiation conditions.
A Qualitative Risk-Based Assessment Procedure for High Temperature Hydrogen Attack of C-1/2Mo Steel
Authors: McLaughlin James E.
Published: August 2009

A qualitative risk-based assessment procedure was developed to determine the relative probability of failure for high temperature hydrogen attack (HTHA) of C-1/2Mo steel. It is well documented that C-1/2Mo possesses a variable resistance to HTHA. Over the years, the Nelson curve limits, as published in API RP 941, Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants, have been significantly reduced since originally published. This has created a need for an assessment procedure to evaluate C-1/2 Mo equipment that was designed many years ago when the Nelson curve was at much higher operating conditions than today. This assessment procedure is based on the current ExxonMobil assignment of C-1/2Mo resistance to HTHA on the Nelson curve and the relative dependence of HTHA on temperature, hydrogen partial pressure and time. We use the Pv relationship that appears in literature to define the relative dependence of HTHA on temperature, hydrogen partial pressure and time. This qualitative assignment of probability levels for HTHA was validated against actual HTHA failures of C-1/2Mo in high temperature hydrogen service that have been reported to the API and other internal Company incidents not reported to API. This assessment procedure is used to qualitatively define the probability of failure consistent with the probability levels defined in the ExxonMobil risk matrix which is used to manage all risk based decisions in the Corporation.
On Abnormal Vibration Generated in Flow Dynamic Conveyer: Understanding of Phenomenon
Authors: Ishihara Kunihiko
Published: August 2009

This paper describes a self-excited vibration of a Flow Dynamic Conveyer (FDC). The FDC is often used in power plants and in iron works because of superiority in noise control compared with a roller type conveyer. The FDC consists of a trough and a belt, and the air is supplied from many holes provided on the trough. A large vibration suddenly occurs when the flow rate becomes the critical value. In this paper, some measurements were performed in order to clarify the phenomenon. As a result, it was found that the phenomenon was the self-excited vibration based on the interference between two vibration systems such as the load • air-spring system and the trough • supporting system.
Further Analysis of Warm Prestressing (WPS) Effects: Role of Local Stress and Strain
Authors: Novak Jiri
Published: August 2009

Effect of WPS in ferritic alloys 15Kh2MFA (CrMoV) and 18MND5 increases with prestress level more rapidly than Chell’s model predicts; this observation had not been understood until now. In this work, experimental data are presented concerning behaviour of steels under simple Load – Unload – Cool – Fracture history. Chell’s model uses as input quantity true fracture toughness and predicts, for simple temperature and loading histories, apparent fracture toughness. A new proposed model based on local approach corrects value of true fracture toughness as an input quantity for Chell’s formulas. Idea of the true fracture toughness increase consists in deactivation of fracture initiation particles during preload. But another interpretation is also possible: Retarding influence of dislocation substructure formed during preload (phase L) on the cleavage microcrack growth at low temperature during loading to fracture (phase F) may cause similar effect. Universal behaviour found in both steels indicates that the second interpretation is more realistic one.
Health Diagnosis of Structural Systems Using a Repetitive Model Updating Approach
Authors: Lin Jeng-Wen , Tsai Chong-Shien , Huang Chih-Wei
Published: August 2009

This paper proposes a statistical confidence interval based model updating approach for the health diagnosis of structural systems subjected to seismic excitations. The proposed model updating approach uses the 95% confidence interval of the estimated structural parameters to determine their statistical significance in a least-squares regression setting. When the parameters’ confidence interval covers the “null” value, it is statistically sustainable to truncate such parameters. The remaining parameters will repetitively undergo such parameter sifting process for model updating until all the parameters’ statistical significance cannot be further improved. This newly developed model updating approach is implemented for the developed series models of multivariable polynomial expansions: the linear, the Taylor series, and the power series model, leading to a more accurate identification as well as a more controllable design for system vibration control.
Identification of Structural Systems Under Tri-Directional Seismic Excitations Using a Statistically Refined Bouc-Wen Model
Authors: Lin Jeng-Wen , Tsai Chong-Shien , Chen Wen-Shin
Published: August 2009

This paper presents the identification of structural systems under tri-directional seismic excitations using a statistically refined Bouc-Wen model of tri-axial interaction. Through limited vibration measurements in the National Center for Research on Earthquake Engineering in Taiwan, the Bouc-Wen model has been statistically and repetitively refined using the 95% confidence interval of the estimated structural parameters so as to determine their statistical significance in a multiple regression setting. The effectiveness of the refined model has been shown considering the effects of the sampling error, of the coupled restoring forces in tri-directions, and of the under-over-parameterization of structural systems. Sifted and estimated parameters such as the stiffness, and its corresponding natural frequency, resulting from the methodology developed in this paper are carefully observed for system vibration control.
Fire Testing of Anti-Sweat Pipe Insulation for Use on Military and Commercial Ships
Authors: Leach David H.
Published: August 2009

This paper presents an overview of the fire and smoke threat to naval vessels and the measures that can be taken to counter the threat. In the confined space of a naval vessel, the damage to men and equipment from the heat, smoke, and toxic gases generated by a fire can occur rapidly. Once the fire has been extinguished, restoring the affected ship systems and cleansing the atmosphere can compromise the mission of the ship. The long-term effect of corrosive gases on electronic equipment adds to the maintenance burden on the ship and the refit facility. This paper will provide suggestions and procedures to reduce the potential for fire damage to naval vessels through the use of improved anti-sweat pipe insulation materials.
Study on Simple Vibration Attenuation System for Light Weight Structure
Authors: Furuya Osamu , Kurabayashi Hiroshi
Published: August 2009

Various vibration attenuation methods such as a base isolation and vibration control are suggested as seismic safety technique for large scale architectural and civil structure, and these methods have been practical used now. In recent years, these vibration reduction technology begins to be applied to a small scale structure. In case that the technology is applied to a small scale structure, specifications and a cost of the device must be examined well. In this study, a vibration attenuation system for light weight structure with low cost and simple mechanizm. This paper describes the effectiveness of the proposed vibration attenuation system which was evaluated from preliminary seismic response analysis.
An Example of Bolted Joints in Pressure Vessels Under Fatigue Conditions
Authors: Le May I. , Pascual R.
Published: August 2009

Flanges in pressure vessels are, in most cases, submitted to non-concentric loading conditions producing bending stresses in the bolts that have to be taken into account for design purposes. The VDI 2230 Guideline [5] provides an excellent tool for the design of bolted joints, especially those in which the bolts are eccentrically loaded, as is commonly the case in pressure vessels. When cyclic loading conditions that can lead to fatigue failure are prevalent, special attention should be paid to the fatigue criteria used in the design. This paper will analyze the general principles of the design of bolted joints, giving particular attention to the use of the VDI 2230 Guideline. The calculation of the stiffness of the joints using this guideline will be introduced and a comparison with the more commonly used approaches will be made. Finally an example of the calculations involved in the design of a bolted flange in a pressure vessel will be shown and a comparison of the different design and fatigue criteria made.
Long-Term Corrosion Potential Behavior of Alloy 22 in Hot 5 m CaCl2 + 5 m Ca(NO3)2 Brines
Authors: Rodri´guez Marti´n A. , Carranza Ricardo M. , Stuart Marshall L. , Rebak Raul B.
Published: August 2009

Alloy 22 is a nickel base alloy highly resistant to all forms of corrosion. In very aggressive conditions (e.g. hot concentrated chloride containing brines) Alloy 22 could suffer localized attack, namely pitting and crevice corrosion. The occurrence of localized corrosion in a given environment is governed by the values of the critical potential (Ecrit) for crevice corrosion and the corrosion potential (Ecorr) that the alloy may establish in the studied environment. If Ecorr is equal or higher than Ecrit, localized corrosion may be expected. This paper discusses the evolution of Ecorr of Alloy 22 specimens in 5 m CaCl2 + 5 m Ca(NO3)2 brines at 100°C and 120°C. Two types of specimens were used, polished as-welded (ASW) creviced and non-creviced specimens and as-welded plus solution heat-treated (ASW+SHT) creviced specimens. The latter contained the black annealing oxide film on the surface. Results show that, for all types of Alloy 22 specimens the Ecorr was higher at 120°C than at 100°C, probably because a more protective film formed at the higher temperature. Specimens with the black oxide film on the surface showed more oscillations in the potential. None of the tested specimens suffered crevice corrosion probably because of the relatively high concentration of nitrate in the electrolyte, R = [NO3]/[Cl] = 1.
The Long-Term Corrosion Test Facility at Lawrence Livermore National Laboratory
Authors: Fix David V. , Rebak Raul B.
Published: August 2009

The long-term corrosion test facility (LTCTF) at the Lawrence Livermore National Laboratory (LLNL) consisted of 22 vessels that housed more than 7,000 corrosion test specimens from carbon steels to highly corrosion resistant materials such Alloy 22 and Ti Grade 7. The specimens from LTCTF range from standard weight-loss coupons to U-bend specimens for testing susceptibility to environmentally assisted cracking. Each vessel contained approximately 1000 liters of concentrated brines at 60°C or 90°C. The LTCTF started its operations in late 1996. Thousands of specimens were removed from the LTCTF in August-September 2006. The specimens are being catalogued and stored for future characterization. Previously removed specimens (e.g. 1 and 5 years) are also archived for further studies.
Proposed FAC Mechanism Using a Macro-Cell Corrosion Model
Authors: Matsumura Masanobu
Published: August 2009

Wall thinning at unusually high rates (0.5∼1 mm y−1) due to FAC (flow accelerated corrosion) may sometimes occur on the walls of carbon steel piping which transports pure, high-temperature water. FAC generally tends to occur in locations where the solution temperature is 140∼150°C, downstream of pipe fittings and flow-meters. It arises quite accidentally: sometimes occurs and sometimes does not in spite of related parameters such as flow velocity and temperature being identical. In addition, the damage may be drastically reduced, when the material of the pipe tube in which unusual wall thinning had occurred is exchanged with low alloyed steel. The macro-cell corrosion mechanism, which is the principle mechanism for galvanic corrosion as well as for cathodic protection with a sacrificial anode, was modified by taking laboratory test results into consideration, and applied to incident cases to successfully explain the generation mechanism of this unusual pipe wall thinning. It explains the characteristic behavior of FAC described above and the anticorrosive effect of chromium. It was concluded that the unusual wall thinning of carbon steel pipe may be attributed to the formation an active/passive macro-cell on the surface. An active/passive macro-cell occurs due to gaps in the distribution of such passivation affecting parameters as the pipe wall temperature and the dissolved oxygen content, so that the basis of prevention amounts to avoidance to these gaps. Thus, it is recommended that stagnation watershed and localized lowering of temperature should be avoided with pipe lines.
Nonlinear Finite Element Analysis of Collapse Loads of Cylindrical Shells Subjected to Combined Thermal Loads and External Pressures
Authors: Sato Takuya , Hirosawa Toshiyuki , Kataoka Shunji
Published: August 2009

The inner tube of the double-tube reactors used in some chemical process units must be designed to resist buckling. When the inner tube is operated at a higher temperature and at a lower pressure and outer tube is operated at a lower temperature and at a higher pressure, the inner tube will be subjected to combined thermal loads and external pressure. ASME Code Sec. VIII Div. 1 provides a design procedure for shells, based on a B-chart, to ensure against buckling under external pressure, however, additional consideration should be made where plastic deformation may occur due to very large longitudinal thermal loads. In this study, nonlinear finite element analyses were performed to investigate the collapse of thick-walled cylindrical shells subjected to combined thermal loads and high external pressures. Two nonlinearities, a material nonlinearity (elastic-plastic behavior) and a geometric nonlinearity (large deformation), were considered in these analyses. The effects of initial imperfection in the shells (out-of-roundness) as well as of thermal loads were studied. The results showed that the longitudinal thermal loads reduce the plastic collapse load especially when the thermal loads are tensile. It was also shown that the loading sequence has a large effect on the collapse load especially when the thermal stress was larger.
The Effect of Residual Stress and Microstructure on Distortion in Thin Welded Steel Plates
Authors: Davies C. M. , Wimpory R. C. , Be´resˇ M. , Lightfoot M. P. , Dye D. , Oliver E. , O’Dowd N. P. , Bruce G. J. , Nikbin K. M.
Published: August 2009

The current trend in ship construction is to reduce the thickness of the ship panels, in order to minimize weight and maximize vessel speed. The ship panels of interest consist of 4 mm thick butt welded plates. This reduction in panel thickness may lead to excessive plate distortion during welding, resulting in significant additional costs during assembly. A ferritic-pearlitic DH-36 steel is used, in which phase transformations during welding may affect the distortion and stress states observed. Two large plates, representative of ship panels, have been butt welded using a metal inert gas (MIG) process. The temperature histories have been recorded during welding and the resulting distortion profile has been obtained using digital photography. Neutron diffraction measurements have been performed to determine the residual stress state in the plates before welding, due to e.g. processing and laser cutting, and after butt welding of the plates. Reference matchsticks from the weld, heat affected zone (HAZ) and parent plate have been taken from similar locations in nominally identical plates and measured to obtain the strain/stress free lattice parameter, α0. A Rietveld analysis has been performed on the diffraction data. Post welding, hardness surveys have indicated the microstructural variation in the weld, parent plate and HAZ. Results from these on-going studies are presented which identify the key factors responsible for thin plate distortion.
Numerical and Experimental Investigation of Nuclear Reactor Core Modeled by a Porous Media
Authors: Ricciardi Guillaume , Bellizzi Sergio , Collard Bruno , Cochelin Bruno
Published: August 2009

This study is about the safety of nuclear reactor core when it is subjected to seismic loading. In order to reduce the uncertainty margin of present day codes, we propose to develop a numerical code including the nonlinear behavior of the structure and the coupling with fluid flow. The challenge of this work is to find out a tractable model taking the structure complexity into account. In this paper we model the nuclear reactor core mechanical behavior including the dynamics of both fuel assemblies and fluid. Each rod bundle is considered as a deformable porous media, so the velocity field of the fluid and the displacement field of the structure are defined in the whole domain space. Fluid part and structure part are first of all considered separately, and secondly, the two parts are coupled. The motion equations of the structure are obtained by a Lagrangian formulation, and to allow fluid structure coupling, the motion equations of the fluid are obtained by an Arbitrary Lagragian Eulerian formulation. The finite elements method is applied to spatially discretize the equations. 2D numerical simulations are compared with experimental data.
Gas Waterhammer
Authors: Goyder Hugh
Published: August 2009

Gas process plant includes pressure relief valves, or pressure safety valves, which enable vessels containing high pressure gas to be emptied quickly into a relief main which takes the gas to a flair stack. The pressure safety valve opens suddenly and sets up acoustic waves, in the manner of a waterhammer, that propagate backwards and forwards in pipework until a steady flow is obtained. Such acoustic waves may set up large forces in pipework that may cause damage. Consequently, an assessment process is required that includes the forces generated by the gas and the resultant stresses in the pipework. One particular problem, investigated here, is the initial conditions for the acoustic waves as the pressure safety valve lifts. The main difficulty with an assessment is the near impossibility of modelling the pipe dynamics adequately. This difficulty is due to the lack of information available concerning pipework support systems and the need to model pipework vibration to high frequencies. A conservative method for assessment based on looking at extremes of support conditions is proposed.
An Application of Computational Fluid Dynamics (CFD) Code to the Design of a Multi-Stage Breakdown Orifice in Support of GSI-191 Evaluations
Authors: Adams J. C. , Ezekoye L. I. , Smith S. M. , Swantner S. R.
Published: August 2009

In September 2004, the Nuclear Regulatory Commission (NRC) issued Generic Letter GL2004-02 “Potential Impact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors” to address Generic Safety Issue 191 (GSI-191) “Assessment of debris accumulation on PWR sump performance.” [1] GL2004-02 requested pressurized water reactor (PWR) licensees to perform a “downstream effects” evaluation of their emergency core cooling (ECCS) and containment spray systems (CSS). GL2004-02 also gave guidance on what analysis had to be completed in order to resolve GSI-191. These evaluations included a wear and plugging assessment of all ECCS and CSS components, including valves. During preliminary “downstream effects” analysis of a plant, it was determined that the positions of ECCS throttle valves could be such that the flow clearances through the valves would be too small to meet the criteria developed for component plugging or wear assessment. This suggested that a modification to the system needs to be made which allows the throttle valves to be more fully opened. In order to allow the throttle valves to be opened more fully, additional hydraulic resistance (i.e. pressure drop at the design flow rate) was added at another location. Several orifice designs were considered to provide the needed resistance. Since the required additional pressure drop was a substantial fraction of the total pressure drop, special design features of the orifice were necessary to preclude system instabilities due to cavitation, degassing and flow swirl. The purpose of this paper is to present a method for assessing the effectiveness of a multi-stage orifice that can be placed in the system to provide the required resistance, thus permitting the throttle valves to be used more efficiently. The paper presents the design aspects of the multi-stage breakdown orifice, CFD modeling used to select the design, and the system condition testing results.
Fatigue Crack Growth Rate Recommended in BS7910 and an Unique Crack Growth Rate Curve Under Different Load Ratios
Authors: Huang Xiaoping
Published: August 2009

It is still difficult to select the proper constants of crack growth rate corresponding to the loading condition for R-ratio has significant effect on crack growth rate. An unique crack growth rate equation, taking equivalent stress intensity factor range (ESIFR) as the driving force, has been examined for steels and as welded joints. An empirical equation of β for structural steels has been presented. The crack growth rate data expressed by ESIFR instead of SIFR (stress intensity factor range) condensing the crack growth data under different R-ratios to the curve corresponding to R = 0. The most commonly tested crack growth rate constants under R = 0∼0.1 are sufficient in fatigue crack growth calculation under different loading condition. Furthermore, the crack growth rate constants for fatigue life calculation under different R-ratios can be obtained directly from the crack growth rate data tested under any given constant R-ratio test conditions according to the relationship between ESIFR and SIFR. This deduction can greatly reduced the requirement of quantity and cost of fatigue tests for determining the constants of crack growth rate. The gape between the curves corresponding to R<0.5 and R≥0.5 respectively in BS7910 can be filled by present model. For fatigue life prediction of as welded joints, the crack growth rate constants corresponding to R = 0 and R = 0.5 can be used.
Lower Bound Net-Section Limit Loads for Circumferential Part-Through Surface Cracked Pipes Under Combined Pressure and Bending
Authors: Oh Chang-Kyun , Kim Yun-Jae , Kim Jong-Sung , Jin Te-Eun
Published: August 2009

This paper provides plastic limit loads of pipes with constant-depth, circumferential part-through surface cracks under combined pressure and bending. A key issue is to postulate discontinuous hoop stress distributions in the net-section. Validity of the proposed limit load solutions are checked against the results from three-dimensional (3-D) finite element (FE) limit analyses using elastic-perfectly plastic material behaviour.
IAEA Coordinated Research Project on Master Curve Approach to Monitor Fracture Toughness of RPV Steels: Effects of Bias, Constraint, and Geometry
Authors: Nanstad Randy K. , Scibetta Marc
Published: August 2009

There is strong interest from the nuclear industry to use the precracked Charpy single-edge notched bend, SE(B), specimen (PCVN) to enable determination of the reference temperature, T0, with reactor pressure vessel surveillance specimens. Unfortunately, for many different ferritic steels, tests with the PCVN specimen (10×10×55 mm) have resulted in T0 temperatures up to 25°C lower than T0 values obtained using data from 25-mm thick compact specimens [1TC(T)]. This difference in T0 reference temperature has often been designated a specimen bias effect, and the primary focus for explaining this effect is loss of constraint in the PCVN specimen. The International Atomic Energy Agency has developed a three-part coordinated research project (CRP) to evaluate various issues associated with the fracture toughness Master Curve for application to light-water reactor pressure vessels. One part of the CRP is focused on the issue of test specimen geometry effects, with emphasis on the PCVN bias. Participating organizations for this part of the CRP are performing fracture toughness testing of various steels, including the reference steel JRQ (A533-B-1) often used for IAEA studies, with various types of specimens under various conditions. Additionally, many of the participants are taking part in a round robin exercise on finite element modeling of the PCVN specimen. Some preliminary results from fracture toughness tests are compared with regard to effects of specimen size and type on the reference temperature T0. In agreement with a number of published results, the results do generally show lower values of T0 from the PCVN specimen compared with the compact and larger bend specimens. They also clearly show higher apparent fracture toughness for the shallow crack compared with the deep crack configuration. Moreover, the SE(B) specimens exhibit a tendency for decreasing T0 with decreasing specimen size (thickness and/or remaining ligament). Additionally, as shown in previous CRPs, the results also exhibit a dependence on test temperature. Following completion of all testing, the results will be evaluated relative to existing proposed models with a view towards developing an understanding of the reasons for the observed differences.
Phased Flow: The Ultimate Initiator Injection System
Authors: Mann Michael D.
Published: August 2009

The Phase pump was designed to eliminate the loss of flow indicative of the standard reciprocating intensifier. This paper will look at the discharge characteristics of the conventional reciprocating pump. Also we will briefly address attempts to minimize the negative effects inherent to the reciprocating pump. This paper will also address how the phase pump corrects the shortcomings of the reciprocating pump. The phase pump also allows other benefits, which will be discussed. Ten years of field data has shown the phase pump to increased production, quality, safety thru predictability.
Determining an Acceptable Value of λc for Multi-Diameter and Multi-Thickness Pressure Vessels
Authors: Bardia Kenhaiya L. , LaBounty Donald G.
Published: August 2009

In Code Case 2286-1, λc, the slenderness factor for column buckling, plays a major role in determining the allowable buckling stress, Fca. For λc > 0.15, consideration of column buckling is required but does not include end forces due to external pressure. A reduction factor, RF, based on λc is calculated to determine the allowable buckling stress. Conversely, for λc ≤ 0.15, consideration of column buckling is not required but axial force due to external pressure is included. In this paper the authors provide a method of determining an acceptable value of λc for multi-diameter and multi-thickness pressure vessels.
An Experimental Investigation Into Fatigue Characterization of Oil Platform Risers Under Variable Amplitude Loading
Authors: Iranpour Mohammad , Taheri Farid
Published: August 2009

One of the many design challenges in offshore industry is the fatigue life estimation of risers due to the loading that is generated by vortex induced vibration (VIV). In deep waters, where the long risers are subjected to sever VIV-induced stresses and may encounter multi-modal vibration, the VIV-induced stresses could be the most significant contributor to the overall damage of the structure. The variable amplitude nature of the stress-time history often creates significant errors in the estimated fatigue life of the structure. The irregularities in the loading scenario could also create a considerable degree of plasticity at the crack tip, thus leading to. variability in material response. The uncertainties in the estimated fatigue damage under such a variable amplitude loading has resulted in the use of large safety factors by industry for establishing the fatigue life of the risers.
Optimization of Environmental Fatigue Evaluation: Step 1
Authors: Nakamura Takao , Iwasaki Masanobu , Asada Seiji
Published: August 2009

In order to introduce environmental effects into fatigue evaluation of design and construction codes, the environmental fatigue evaluation method should not only be established, but the conservativeness of the codes, such as safety factors of design fatigue curve and simplified elastic-plastic analysis method (Ke factor), etc. should also be reviewed. Then plant designers should optimize total system of fatigue evaluation according to the objective of the codes by properly selecting design transient conditions and stress analysis methods used in fatigue evaluations as necessary. In addition, investigation of measures for reducing fatigue should be performed to mitigate possible fatigue initiators and alternative evaluation methods in case that the evaluation result should exceed the criteria specified in the design and construction codes. This paper discusses the present status in the review of these items for the Japanese PWR plants and future prospects to tackle on the application of environmental fatigue evaluation in design stage of plant construction.
Sloshing in a Cylindrical Liquid Storage Tank With a Single-Deck Type Floating Roof Under Seismic Excitation
Authors: Matsui Tetsuya
Published: August 2009

An explicit analytical solution is derived to predict the sloshing response of a cylindrical liquid storage tank with a single-deck type floating roof under seismic excitation. The floating roof is composed of an inner deck which may be idealized as an isotropic elastic plate with uniform thickness and connected to an outer pontoon which can be considered as an elastic curved beam. The contained liquid is assumed to be inviscid, incompressible and irrotational. By expanding the response of the floating roof into free vibration modes in air and applying the Fourier-Bessel expansion technique in cylindrical coordinates, the solution is obtained in an explicit form which is exact within the framework of linear potential theory. Numerical results are presented to investigate the effect of the type (single-deck or double-deck) and stiffness of the floating roof on the sloshing response.