bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational Fluid Dynamics Investigation of a High Temperature Waste Heat Exchanger Tube Sheet Assembly
Authors: Porter Michael A. , Martens Dennis H. , Duffy Thomas , McGuffie Sean
Published: August 2008

Many modern Sulfur Recovery Unit (SRU) process waste heat recovery exchangers operate in high temperature environments. These exchangers are associated with the thermal reactor system where the tubesheet/tube/ferrule assemblies are exposed to gasses at temperatures approaching 3000°F. Because sulfur compounds are present in the process gas, the carbon steel tubesheet and tubes in the assembly will be deteriorated by sulfidation as the operating metal temperature rises above 600°F. Ferrule systems are used to protect the carbon steel from exposure to excessive temperatures. The temperature distribution in the steel tubesheet/tube/ferrule system is affected by process gas flow and heat transfer through the assembly. Rather than depend upon “assumed” heat transfer coefficients and fluid flow distribution, a Computational Fluid Dynamics (CFD) investigation was conducted to study the flow fields and heat transfer in the tubesheet assembly. It was found that the configuration of the ferrule installation has a large influence on the temperature distribution in the steel materials and, therefore, the possible sulfidation of the carbon steel parts.
Repair of Class 1 Control Rod Drive and In-Core Housing Bottom Head Penetrations in BWRs
Authors: Harttraft Greg , Corieri Roy , Ranganath Sam , Wolfe Ken , McCurdy H. William , Corchon Fernando
Published: August 2008

The ASME Section XI committee is developing a code case to permit repair of leakage on Boiling Water Reactor (BWR) bottom head penetrations with a mechanical roll expansion process. This technology has been successfully utilized for this application over the last two decades to address leakage due to Control Rod Drive (CRD) stub tube cracking. The code case defines the technical and administrative requirements for use of the mechanical roll expansion process for repair of Class 1 Control Rod Drive and Incore housing penetrations in the bottom head of BWRs. The code case specifies the process qualification, essential variables, process application, examination and pressure testing requirements for this process. The technical basis of the proposed code case includes detailed fracture mechanics analysis to evaluate the structural consequences of the cracking, metallurgical assessment and extensive testing to determine the load capability of the roll repair joint. Based on this assessment, the successful BWR field experience and the inspections/ qualifications required under the code case, the mechanical roll expansion repair can be used as a permanent repair option for addressing leakage in BWR CRD and In-core housing penetrations, The application of this code case will provide significant reduction in facility down time and will offer a reduction in personnel radiation exposure as compared to welded repair options.
Recommended List of “Known” Materials for Hydrogen Service
Authors: Joseph Thomas
Published: August 2008

The paper will address commonly used materials in Hydrogen service and their limitations as the service conditions (like pressure) get into more challenging areas. For example, Aluminum has good history of use in hydrogen applications upto 3000 psig. It’s compatible with Hydrogen even at pressures higher than 15,000 psig. However, are we comfortable in continued use of Aluminum and similar low melting point materials at higher pressures for containing Hydrogen? The paper is expected to provide basis for a discussion on this safety issue. In addition, the paper will include a discussion around pressure vs stress level limits for common materials. A user friendly material selection chart will be presented for the benefit of the audience.
Subsea Manifolds: An Alternate Fabrication Strategy Using HIP PM Near Net Shapes
Authors: Hjorth Carl-Gustaf , Hebeisen John C.
Published: August 2008

The fabrication of near net shape powder metal (PM) components by hot isostatic pressing (HIP) has been an important manufacturing technology for steel and stainless steel alloys since about 1985. The manufacturing process involves inert gas atomization of powder, 3D CAD capsule design, sheet metal capsule fabrication and densification by HIP in very large pressure vessels. Since 1985, several thousand tonnes of parts have been produced. The major applications are found in the oil and gas industry especially in offshore applications, the industrial power generation industry, the pulp and paper industry and in pharmaceuticals and traditional engineering industries. Typically, the components replace castings, forgings and fabricated parts and are produced in grades such as martensitic steels, austenitic and duplex (ferritic/austenitic) stainless steels and nickel- based superalloys. The application of HIP PM near net shapes to manifolds for medium to high pressure use has a number of advantages compared to the traditional forging and welding approach. First, the need for machining of the components is reduced to a minimum and welding during final assembly is reduced substantially. Manifolds by HIP design reduce the necessary welding by 70–90%. Mechanical properties of the HIP PM part are isotropic and equal to the best forged properties in the flow direction as is demonstrated below. This derives from the fine uniform microstructure of the PM parts. The PM parts are significantly lighter in weight because of the need to stiffen the forged component at the location of the weldment for the intersecting passageway — the PM parts can be smoothly blended into the intersection without need for welding. Furthermore, the PM HIP components can be made with significantly reduced manufacturing lead-time, greater design flexibility and improved cost for the final component. The PM HIP near net shape route has received approval from both ASTM [1,2,3] and NACE [4] for specific steel, stainless steel and nickel base alloys. This paper reviews the manufacturing sequence for PM near net shapes and discusses the details of several successful applications. The application of the HIP PM process to subsea manifolds is highlighted.
Two-Phase Flow-Induced Vibration of Parallel Triangular Tube Arrays With Asymmetric Support Stiffness
Authors: Feenstra Paul , Weaver David S. , Nakamura Tomomichi
Published: August 2008

Laboratory experiments were conducted to determine the flow-induced vibration response and fluidelastic instability threshold of a model heat exchanger tube bundle subjected to a cross-flow of refrigerant 11. Tube bundles were specially built with cantilevered tubes mounted on asymmetric supports so that the stiffness in the streamwise direction was about double that of the transverse direction. This was designed to simulate the tube dynamics in the U-bend region of a recirculating-type nuclear steam generator. Three model tube bundles were tested, one with a pitch ratio of 1.49 and two with a smaller pitch ratio of 1.33. The primary intent of the research was to improve our understanding of the flow-induced vibrations of heat exchanger tube arrays subjected to two-phase cross-flow. Of particular concern was to compare the effect of the asymmetric support stiffness on the fluidelastic stability threshold with that of symmetric stiffness arrays tested most prominently in the literature. The experimental results are analysed and compared with existing data from the literature using various definitions of two-phase fluid parameters. The fluidelastic stability thresholds of the present study agree well with results from previous studies for single phase flow. In two-phase flow, the comparison of the stability data depends upon the definition of two-phase flow velocity.
Simplified Analysis of the Tightening Process of Bolted Joint With a Bolt Heater
Authors: Fukuoka Toshimichi , Takaki Tomohiro
Published: August 2008

A bolt heater is frequently used when tightening large bolts that cannot be tightened with other methods. Although the tightening process inherently needs a fair amount of working hours, a bolt heater is less expensive than the other tightening tools and it can be applied to the tightening operation in a narrow space. In this paper, an elementary method is proposed to evaluate the tightening process with a bolt heater, aiming at its broader use for middle-sized bolts. One-dimensional finite difference method is employed to analyze the heating process with taking the effects of heat transfer through small gaps into consideration, by which the corresponding bolt elongation is calculated for the specified heating period. The equation relating the bolt elongation and axial bolt force is also proposed, in which the effects of interface stiffness due to surface roughness are incorporated for better estimation of the axial bolt force. The effectiveness of the elementary method proposed here is demonstrated by experiments.
Study on the Seismic Load Coupling Effects Due to Horizontal and Vertical Excitation for the Newly Developed 3-Dimensional Base Isolation System
Authors: Ito Tomohiro , Fujita Katsuhisa , Ohkubo Takeshi
Published: August 2008

Recently, many huge earthquakes occurred in many places, such as Hyogo-ken Nambu earthquake in 1995, Kocaeli earthquake and Chi-Chi earthquake in 1999 and Niigata Chuetsu earthquake in 2004 etc., and huge earthquakes are also considered to occur in near future. Therefore, many horizontal isolation structures have been proposed and constructed. In addition to the horizontal isolation, 3-dimensional isolation systems are under development as well. For these reasons, the authors also have developed a new 3-dimensional base isolation system and evaluated the effectiveness of the system. This isolation system employs sliding pads and laminated rubber bearings for horizontal isolation as some other isolation systems do. Thus, the vibration response of the upper structure depends on the friction force between sliding pads and the floor. In the actual seismic events, these sliding type isolation systems suffer from both horizontal and vertical seismic excitations simultaneously. For these reasons, the friction force in the horizontal direction has two components; one depends on the self weight and the other depends on the vertical seismic response. The latter will change time-dependently. Therefore, it can be said that the coupling effects between the horizontal and vertical seismic excitations become predominant. In this study, the coupling effects of the horizontal and vertical seismic excitations are investigated analytically as for the rocking motion, response displacement and response acceleration for the various seismic wave inputs. The effects of the phase difference between the horizontal and vertical seismic input and the amplitude of the vertical excitation are clarified and the design guide lines for the sliding type base isolation systems exposed to the horizontal and vertical simultaneous seismic excitations are proposed.
Investigation of Flow and Forces on a Strongly Accelerated Circular Cylinder
Authors: Melot Vincent , Auvity Bruno , Peerhossaini Hassan
Published: August 2008

The present paper exposes the current research work carried out at LABORATOIRE DE THERMOCINE´TIQUE de NANTES within the framework of a collaborative research with DCN PROPULSION concerning the design of nuclear structures subjected to dynamic loading. The case under study consists of a cylinder strongly accelerated from rest in an infinite fluid medium. The main aim of the study is to predict forces acting on the cylinder and to provide a clear description of the flow phenomena. The duration of the mechanical impulse imposed on the cylinder is extremely short (of the order 15 milliseconds). The level of acceleration is 30 times the gravitational acceleration. These operating conditions are representative of a typical shock encountered in the environment of a military ship. This work is composed of a numerical and an experimental part. The numerical modeling is developed in a finite volume formulation. The cylinder is moved inside the computational domain using the ALE formulation for the moving mesh grid. Well-documented experiments on a cylinder impulsively started from rest are simulated to test the numerical procedure and validate our code. Then shocks with sinusoidal acceleration are simulated and compared with the theoretical model of Stokes. The experimental part presents the set-up currently under construction in the laboratory. The cylinder is put in motion by a hydraulic accelerator connected to a power hydraulic station and driven by a computer-controlled servo-valve. The metallic bar holding the cylinder is equipped with strain gauges measuring the integral forces acting on the cylinder.
Warm Pre-Stress Effect Measured at Irradiated RPV Weld Material
Authors: Keim Elisabeth , Langer Reinhard , Schnabel Hilmar , Bartsch Reinhard
Published: August 2008

The recently initiated German project CARISMA (Crack Initiation and Arrest of Irradiated Steel Materials) will create a data base on pre-irradiated original materials of the four generations of German nuclear pressurized water reactors, which allows the examination of the consequences if the Master Curve instead of the RTNDT concept is applied. Several original materials of the four generations of German nuclear power plants (typical for KWO, KKS - Biblis A, Biblis B, KKU - KKG, KWG, KKP2, KBR - KKE, KK12, GKN2) will be investigated. They have been irradiated in six large scale irradiation capsules in a German research reactor (the VAK plant) at corresponding plant conditions. The capsules contain regular tensile and Charpy impact specimens as well as Pellini and fracture toughness wedge opening load specimens up to a specimen thickness of 100 mm. The first fracture toughness tests have been performed on a weld metal NiCrMo1 UP(mod.)/LW320, LW340 (1. generation, lower bound of the weld materials)—with a fluence Φ = 2,12E19 cm−2 (E > 1 MeV). This weld has a Cu-content of 0.22 wgt.% and it was therefore supposed to show a large transition temperature shift. Some fracture toughness tests in the irradiated material condition were already available and during this project four 100 mm thick wedge opening load (WOL) specimens were tested. At one of the specimens brittle failure could not be achieved during the test, because the load capacity of the test machine was exceeded. Therefore the specimen was loaded by a load-unload-cool-fracture load path to demonstrate the warm pre-stress effect of this highly irradiated specimen. At the final fracture of the specimen at a lower temperature, the failure load was significantly higher than the original one (factor 3 higher), which clearly indicates that the benefit of warm pre-stressing will not be eroded with irradiation.
Section XII Transport Tank Code Preview: Cargo Tanks
Authors: Paulick Nick , Rogers Tom
Published: August 2008

ASME Section XII Transport Tank Code will have an impact on the regulations related to the construction and continued service of highway cargo tanks used in the transportation of dangerous goods. Modal Appendix 1 of this code specifically addresses these transport tanks, and is intended to replace a large portion of the DOT regulations currently governing how they are built and serviced. This paper presents a preview of Modal Appendix 1, one of the mandatory appendices related to cargo tanks, and how these changes will affect manufacturers and repair shops.
J and COD Estimation for Throughwall Circumferentially Cracked Elbow Under Closing Moment: Analytical Scheme and Experimental Validation
Authors: Chattopadhyay J. , Tomar A. K. S. , Dutta B. K. , Kushwaha H. S.
Published: August 2008

Leak-before-break (LBB) assessment of primary heat transport piping of nuclear reactors involves detailed fracture assessment of pipes and elbows with postulated throughwall cracks. Fracture assessment requires the calculation of elastic-plastic J-integral and crack opening displacement (COD) for these piping components. Analytical estimation schemes to evaluate elastic-plastic J-integral and COD simplify the calculations. These types of estimation schemes are available for pipes with various crack configurations subjected to different types of loading. However, no such schemes are available for throughwall circumferentially cracked elbow (or pipe bend), an important component for LBB analysis. In this paper, simple J and COD estimation schemes are proposed for throughwall circumferentially cracked elbow subjected to closing bending moment. The ovalisation of elbow cross section has a significant bearing on its fracture behavior. Therefore, unlike conventional deformation theory plasticity analysis, incremental flow theory is adopted considering both material and geometric non-linearities in the development of the proposed estimation schemes. Although it violates Ilyushin’s theorem, it has been shown that the resulting estimation schemes is still reasonably accurate for engineering purposes. Finally, experimental/numerical validation has been provided by comparing the J-integral and COD between numerical/test data and predictions of the proposed estimation schemes.
An Experimental Study on Active Control of Leakage-Flow-Induced Vibrations: Experiments for Translational One-Degree-of-Freedom System
Authors: Watanabe Masahiro , Yamauchi Ayako
Published: August 2008

This paper describes the active feedback control of leakage-flow-induced vibrations in translational one-degree-of-freedom system. In this paper, suppression of the leakage-flow-induced vibrations by the active feedback control technique is demonstrated experimentally. A rigid plate, as a controlled object, is elastically supported in a narrow tapered passage by using two flat-springs. The leakage-flow-induced vibrations occur to the plate in the translational motion due to the fluid flow in the narrow passage. The leakage-flow-induced vibrations are suppressed by the active feedback to the injection (and drawing) of the fluid at the inlet or outlet of the passage. The critical flow rate under controlled condition is examined with varying the controller gain and phase-shift between the injection (and drawing) of the fluid and the vibration strain (displacement) signal of the plate. As a result, it is indicated experimentally that the active feedback control technique increases the critical flow rate, and suppress the leakage-flow-induced vibrations effectively. Further, the control performance is examined and stabilization mechanism by the active feedback control is discussed.
Modeling of Delamination in Composites
Authors: Cheng Wing , Itoh Shigeru
Published: August 2008

Stacking sequence, number of plies, and geometry of the composite structure have significant impact on the strength and reliability of the structure. The most detrimental failure mode in composite structures is delamination. Modeling of delamination failure is, therefore, a very important technique for predicting the reliability of composite structures. A modified crack closure technique was used in determining the driving force for crack propagation and branching of laminated composites at the interfaces. Mixed mode fracture parameters, GI for the opening mode, GII for the shear mode, were calculated using the technique for two typical composite structures; namely a composite laminate subjected to tensile loading, and a curved composite laminate subjected to bending. Results of these analyses give a better understanding on the crack growth behavior of these structures, and therefore, provide insight in the composite construction for improved design of the structures.
Numerical Simulation of a Non Linear Coupled Fluid-Structure Problem by Explicit Finite Element-Finite Volume Coupling
Authors: Sigrist Jean-Franc¸ois , Laine Christian , Peseux Bernard
Published: August 2008

The present paper deals with the numerical simulation of a coupled non linear fluid-structure problem by explicit coupling between a finite element structure code and a finite volume fluid code. This numerical study is carried out in order to develop robust and general coupling with FE and CFD commercial code for industrial applications. A geometrically simple non linear coupled problem is presented in order to validate the numerical approach. The structure non linear problem is solved with a finite element technique, using a iterative implicit algorithm for time integration. The fluid problem is solved using standard numerical techniques (finite volume approach, implicit splitting operator scheme). The whole coupled problem is solved with a commercial CFD code: a dedicated FE structure code is developed in the CFD code together with coupling (in time, in space) procedures. The proposed method is validated in the case of a incompressible inviscid fluid, for which the coupled problem is solved with an analytical solution. The present study gives a reference test case for a full scale fluid-structure model. Industrial applications can now be considered by coupling commercial FE and FV codes with general coupling code.
SMILE: A European R&D Program for the Inclusion of Warm Pre-Stress in RPV Assessment
Authors: Moinereau Dominique
Published: August 2008

The Reactor Pressure Vessel (RPV) is an essential component liable to limit the lifetime duration of PWR plants. The assessment of defects in RPV subjected to PTS transients made at an European level generally do not take necessary into account the beneficial effect of load history (warm pre-stress WPS). A 3-year Research & Development program — SMILE — has been started in January 2002 as part of the Fifth Framework of the European Atomic Energy Community (EURATOM). The SMILE project (“Structural Margin Improvements in aged-embrittled RPV with Load history Effects”) is one of a “cluster” of Fifth Framework projects in the area of Plant Life Management. It aims to give sufficient elements to demonstrate, to model and to validate the beneficial WPS effect in a RPV integrity assessment. Finally, this project aims to harmonize the different approaches in the European Codes and Standards regarding the inclusion of the WPS effect in a RPV structural integrity assessment. Within the framework of the project, an important experimental work has been conducted including WPS type experiments on CT specimens and also a PTS type transient experiment on a large component. The experimental results on CT specimens confirm the beneficial effect of warm pre-stress, with an effective significant increase of the material resistance regarding the risk of brittle failure. The WPS type experiment on the cylinder has been successfully conducted, with a final brittle failure during the reloading. The present paper describes the aims and objectives of the SMILE project, the main experimental results, and the corresponding analyses based on engineering methods, finite element elastic and elastic-plastic computations, and local approach to fracture.
Design for Leakage in Flange Joints Under External Loads
Authors: Koves William J.
Published: August 2008

This paper uses an analytical model based on the Pressure Vessel Research Council (PVRC) ROTT test gasket constants to compute leakage in gasketed flange joints subjected to internal pressure and external bending moments. The model results are compared with test data and design recommendations are made, consistent with the ASME/PVRC tightness based methodology.
A Fatigue Failure Mechanism of Welded Piping Joints
Authors: Hassan Tasnim , Lu Xiangyang
Published: August 2008

Fatigue failures of small bore piping systems have historically occurred in nuclear power plants, resulting in unanticipated plant downtime and substantial financial loss. If the failures were not caused by defects, the reasons of the initiation of fatigue cracks were not clear in many cases. This paper presented a set of weld fatigue response data which pointed to the strain ratcheting response as a probable reason for weld fatigue failure. A systematic set of low-cycle fatigue tests on butt- and socket welded piping joints in the cantilever set up is conducted. A new observation made in these tests is that the recorded strains near the weld toe ratchet continuously, which results in the initiation of fatigue crack(s). Comparison of these ratcheting responses with those from the cyclic bending of straight pipe and ratcheting experiments at the material level indicates that the residual stresses at welded joints may induce the ratcheting responses. This observation is further supported by the symmetric strain response (no ratcheting) at the mid-pipe length, which is located away from the welded joint. At this location, there are no residual stresses to induce ratcheting. It is observed that the fatigue cracks in all experiments occurred at the weld toe location where the ratcheting strain is the largest. The experimental data indicate that the fatigue life of materials is reduced in the presence of ratcheting. It is also observed that the ratcheting is influenced by the welding sequence. One interesting aspect of the weld fatigue data developed is that the ratcheting at the weld joints occurred under a displacement-controlled loading cycle. This study with its limited time and resource could not explore this issue. A plausible reason could be due to material heterogeneity at the welded joints.
Stress State Detection Based on Metal Magnetic Memory Theory
Authors: Xing HaiYan , Wang RiXin , Xu MinQiang , Zhang JiaZhong
Published: August 2008

The metal magnetic memory (MMM) technology, a new nondestructive evaluation (NDE) method, is an effective means for early damage prediction. However, there is so much work to do, such as the relationship between the magnetic field density and stress state. This paper aims at finding out MMM signal characteristics of critical damage stress state by tension experiments. Comparisons between MMM testing and traditional NDE method are presented. The principle of MMM testing is investigated. Different materials, low carbon steal X70 and medium carbon Q235B, are detected on-line and off-line respectively. It is found that MMM signal rules are gradually increasing up to fluctuating on the verge of yield and sharp changing of magnetic polarity on the verge of fracture. With the increase in material strength, magnetic field density of low carbon steel X70 is lower than that of medium carbon steel Q235B. This offers fundamental study for the quantitative MMM testing of critical damage stress state.
Reinforcement Analysis of a Slab Tank
Authors: Hari Yogeshwar
Published: August 2008

The objective of this paper is to reduce the stresses and deflection of an existing slab tank [2]. The slab tank is to store various criticality liquids used in today’s industry. The preliminary overall dimensions of the slab tank are determined from the capacity of the stored liquids. The slab tank design is broken up into (a) two long side members, (b) two short side members, (c) top head, and (d) bottom head. The slab tank is supported from the bottom at a height by a rectangular plate enclosure. The deflection of the linear space is a critical requirement. The deflection is controlled by providing external supports from the bottom at a height by adjustable bolts. The analysis of the slab tank showed excessive stresses at the concentrated supports. The slab tank was modified by providing reinforcement on the long side members. Several reinforcement arrangements were considered. The slab tank is subjected to two conditions. First, vacuum condition, the long side plates will deflect inwards. Second, internal pressure condition the design pressure consists of working internal pressure plus static head pressure. For this the long side plates will deflect outwards. The heads are designed for internal pressure at the bottom where the pressure is the maximum. The vacuum pressure is not critical. The dimensioned slab tank is modeled using STAAD III finite element software. The slab tank showed excessive stresses. The concentrated supports were removed. The long side member was reinforced by a Channel section. The slab tank analysis was simplified by modeling a single long side member and three cases of Channel section reinforcement were considered. The reinforced arrangement was analyzed by STAAD III finite element software. Further analysis by changing the Channel section by plate reinforcement was found to be better.
Governing Equations of Motion of Walking Behavior of Unanchored Flat-Bottom Cylindrical Shell Tanks During Free Rocking Motion
Authors: Taniguchi Tomoyo , Imai Koji
Published: August 2008

The governing equations of motion of the walking phenomena of the unanchored flat-bottom cylindrical shell tanks are examined. This paper considers that the walking phenomena is followed by the rocking motion of the tanks, since the rocking motion induces the reduction of self-weight and consequently reduces friction force between the tank and the foundation. The equations of motion are derived through variational approach. The physical quantities related to the walking phenomena are the mass of tank itself, tank content, the effective mass of liquid for bulging motion, for rocking motion and for rocking-bulging interaction motion, and friction force including self-weight reduction effects. The roles of every physical quantity related to the walking motion are clearly identified. The time history of the walking motion of the model tank induced by the initial enforced uplift angle and then gently released is well computed by the proposed procedure.
Controlled Initiation of Short Fatigue Cracks in 316L Steel
Authors: Stefanescu D. , Marrow J. , Preuss M. , Sherry A.
Published: August 2008

Validation of models for short crack behavior requires accurate measurement of crack opening displacement and crack tip strain fields. Development of reliable measurement procedures, using new techniques such as Image Correlation (IC), requires specimens containing cracks with a well defined geometry. In this paper, results of an experimental study concerning controlled initiation of short fatigue cracks at positive R-ratio in laboratory specimens made from 316L stainless steel are presented. Experimental techniques, including hardness testing and X-ray diffraction were employed in order to investigate the effect of surface preparation on the surface mechanical properties and residual stresses. Crack nucleation is difficult in smooth specimens of 316L austenitic stainless steel at positive R-ratio due to the high fatigue limit and low tensile strength. Specimens with a thin ligament were therefore developed to enable nucleation of a single short fatigue crack. An experimental study of the crack growth aspect ratio evolution was then carried out using a beach marking technique. The technique described in this paper enables single short fatigue cracks of well defined geometry to be nucleated under tensile cyclic loading. Stress corrosion cracks can be developed using the same specimen geometry. Miniature tensile specimens can then be extracted to perform in-situ measurements of the crack opening displacement and crack tip strain field by Image Correlation from Scanning Electron Microscopy observations.
Assessment of Limit Loads for Circumferential Cracks in Steam Generator Tube Considering Constraining Effect of Tube Support
Authors: Kim Hyun Su , Kim Jong Sung , Jin Tae Eun , Kim Hong Deok , Chung Han Sub
Published: August 2008

The steam generator in a nuclear power plant is a large heat exchanger that uses heat from reactor to generate steam to drive the turbine generators. Rupture of a steam generator tube can result in release of fission products to environment. Therefore, an accurate integrity assessment of the steam generator tubes with cracks is of great importance for maintaining safety of a nuclear power plant. The steam generator tubes are supported at periodic intervals by support plates and rotations of the tubes are constrained. Although it was reported that the limit load for a circumferential crack was significantly affected by boundary condition of the tube, existing limit load solutions do not include the constraining effect of tube supports. This paper provides detailed limit load solutions for circumferential cracks in steam generator tubes considering the actual boundary conditions to simulate the constraining effect of the tube supports. Such solutions are developed based on three dimensional (3D) finite element analyses. The resulting limit load solutions are given in a polynomial form, and thus can be simply used in practical integrity assessment of the steam generator tubes.
Residual Stress Analysis of Tube Attachment Weld in Pressure Vessel Forging: Baseline FE Analysis and Sensitivity Studies
Authors: Leggatt N. A. , Dennis R. J. , Hurrell P. R.
Published: August 2008

Full two and three-dimensional single or multi-pass weld simulations are now feasible and practical given the development of improved analysis tools (e.g. ABAQUS), and significantly greater computer power. This paper describes a finite element analysis undertaken to predict the as-welded residual stress field following the welding of a tube attachment weld inside a thick pressure vessel (PV) forging. The coupled thermal-mechanical analysis was performed using the finite element (FE) code ABAQUS, A heat source modelling tool was employed to calculate welding fluxes, which were read into ABAQUS via a user subroutine. The ‘block’ dumped approach was utilised in the 2D thermal analysis such that complete weld rings are deposited instantaneously. Heat inputs were based on the actual weld parameters and bead sizes. The predicted fusion depths matched well with those found in sectioned weld test pieces. 2D FE sensitivity studies were performed examining the effect of variations in a number of parameters (bead sequence, hardening law, inter-pass temperature and annealing temperature). The hardening law was changed from isotropic to kinematic to investigate the effect of material behaviour. Large weld residual tensile stresses were calculated with significant compressive stresses in the adjacent vessel wall. Stress results were generally insensitive in the tube and forging, indicating that the vessel constraint dominates over local welding conditions. Weld hoop stresses were overestimated partly due to the ‘tourniquet’ effect of depositing rings of weld metal and the isotropic hardening law assumed.
Effect of Secondary Stresses on Pipe Fracture
Authors: Wilkowski Gery , Scott Paul , Olson Richard , Rudland Dave
Published: August 2008

This paper presents experimental results from pipe-system tests from the International Piping Integrity Research Group (IPIRG) and Battelle Integrity of Nuclear Piping (BINP) programs where the magnitudes of the thermal expansion (secondary) stresses were different in two pipe-system experiments with identical circumferential surface cracks in the same material. The pipe systems were loaded with a single-frequency dynamic forcing function to provide inertial and seismic anchor motion (SAM) moments. In the first tests, the hydraulic ram at the dynamic loading point was locked in place during the heating, so that the natural thermal expansion stresses developed. In the second test, the hydraulic ram at the dynamic loading point was statically offset after the heating to simulate a higher thermal expansion stress. The magnitude of the thermal expansion stress for both cases was within the ASME Section III limits. The results showed that the same total moment was reached in both tests, but the magnitude of the inertial moments at failure was reduced in the second test by the increase of the moment from the thermal expansion stresses. The reason for this effect is that the crack was relatively large, so the failure stress due to the crack was below yield of the uncracked pipe in the pipe system. In this case, the plasticity at the surface crack causes small displacements of the pipe compared to the overall elastic displacements of the pipe system; therefore, the yielding at the crack plane did not relieve the secondary stress, causing them to behave as a primary stress. This behavior is consistent with the B31.1 and ASME Section III Class 2 and 3 piping paragraphs on “Local Overstrain”. The implication from this work is that the safety factor on secondary stresses in the ASME Section XI Code pipe flaw evaluation procedures should be a function of the failure stress. Furthermore, secondary stresses should be included for all piping materials (including wrought stainless steels), and have the same safety factor as the primary stresses for stresses below the yield strength of the material.
Analytical Method and Its Experimental Verification for Seismic Reduction of Story-Increased Structures Under Earthquake
Authors: Li Hong-Nan , Zhao Yan-Gang , Li Chen , Yin Yong-Wei
Published: August 2008

Structural passive control devices have widely used in various engineering projects for resisting the wind load or earthquake excitation until now. The friction damper and sand isolation technology among them are of many advantages, such as easy installation, less cost and less maintenance fee. In this paper, a new type of energy-dissipated structural system for the reconstructive building with the story-increased frame is presented and investigated, in which the sliding-friction layer with sand between the lowest increased floor of outer frame structure and roof of original building is applied, and friction energy-dissipated dampers are used for the connections between the columns of outer frame and each floor of original building. A simplified analytical model of this system is proposed. For more appropriate theoretical analysis, the non-classical damping approach is introduced to calculation. The shaking table test is performed on the model of system to verify the effectiveness of the above seismic reduction system and proposed method. The results show that friction and energy-dissipated devices are very effective in reducing the seismic response and dissipating the input energy of model structure.
Influence of the Interaction on Stress Intensity Factor of Semi-Elliptical Surface Cracks
Authors: Kamaya Masayuki
Published: August 2008

The interaction between multiple surface cracks is an important consideration in the cracking behavior due to thermal fatigue and stress corrosion cracking. However, it is difficult to evaluate the intensity of the interaction quantitatively because there are many factors such as the relative position, size and geometry of the cracks. Furthermore, the influence of the interaction differs with the crack tip position along the front. In this study, in order to investigate the intensity of interaction, the stress intensity factor (SIF) of interacting semi-elliptical surface cracks was evaluated by the finite element method and finite element alternating method. These methods enable us to evaluate the SIF of interacting cracks for various conditions. The analysis results reveal that the change in the averaged SIF along the crack front caused by coalescence of two cracks can be estimated from the change in the area size. The maximum interaction can be estimated by simple addition of the area size of two cracks regardless of the loading condition and relative crack size. To exclude the conservativeness caused by the current combination rule, new criteria are shown.
Development of Three-Dimensional Seismic Isolation Technology for Next Generation Nuclear Power Plant Applications
Authors: Takahashi K. , Inoue K. , Morishita M. , Fujita T.
Published: August 2008

Seismic isolation technology plays an important role in the area of architect engineering, especially in Japan where earthquake comes so often. This technology also makes the nuclear power plant rationalized. The horizontal base isolation with laminated rubber bearings has already been proven its effectiveness. These days, seismic isolation technology is expected to mitigate even the vertical load, which affects the structural design of primary components. Seismic isolation system has possibility to improve the economical situation for the nuclear power plant. From these points of view, a research project has been proceeded to realize practical three dimensional seismic isolation systems from 2000 to 2005 under the sponsorship of the Ministry of Economy, Trade and Industry of the Japanese government. The isolation system is developed for the supposed “Fast Breeder Reactor (abbreviated FBR)” of the next generation. Two types of seismic isolation systems are developed in the R&D project. One is a three-dimensional base isolation for a reactor building (abbreviated 3D SIS) and the other is a vertical isolation for main components with horizontal base isolation of the reactor building (abbreviated V. +2D SIS). At first step of the R&D, requirements and targets of development for the seismic isolation system were identified. Seismic condition for R&D was discussed based on the real seismic response. Vertical natural frequency and damping ratio required to the system were introduced from the response to the seismic movement. As for 3D SIS, several system concepts were proposed to satisfy the requirements and targets. Through discussions and tests on performance, reliability, applicability, maintainability, “Rolling seal type air spring system with hydraulic anti-rocking devices” was decided to be developed. Verification shaking tests with the 1/7 scale model of the system and analysis for applicability to the real plant are conducted. The result shows that the system is able to support the reactor building, to suppress the rocking motion and to mitigate the vertical seismic load. As for V.+2D SIS, coned disk spring device was selected at the beginning of R&D. Performance tests of the elements, which include common deck movement, were conducted and the system applicability to the plant is confirmed. Verification tests were conducted with 1/8 scale model of the system and the result proves the applicability to the real plant.
Determination of Modification Factor R for Seismic Design of Pressure Vessels Using ASME and Eurocodes
Authors: Kokavesis N. , Botsis Ch.
Published: August 2008

The design of pressurized equipment such as columns, towers and reactors, heaters subjected to external loads is important from a safety point of view. Pressure vessel design codes provide guidelines for the combination of membrane stresses due to external loads and hoop stress. Customarily the seismic loads imposed by pressure vessel design codes are functions of allowable stress. The factor R is a modification factor of the design response spectrum. Its numerical value is based the capacity of a structural system to resist seismic actions in the nonlinear range. It generally reduces the seismic design forces to be smaller than those corresponding to a linear elastic response. The Uniform Building Code (UBC) has been used extensively for the seismic design of pressure vessels. With the advent of EUROCODES [2], the values proposed by UBC for factor R (usually 3 or 4) are not automatically accepted by local authorities. The pressure vessel mechanical designer must select a factor R that satisfies both the requirements of the pressure vessel code and the structural design code (local code) where the vessel is installed. This problem has also been acknowledged by several collogues in the past PVP conferences. In this paper the factor R is examined using ASME [10] codes and the guidelines provided by EUROCODES. A common basis for the selection of the factor R that satisfies both allowable stress design philosophies and structural design codes is established.
Predicting Gasket Leak Rates Using a Laminar-Molecular Flow Model
Authors: Marchand Luc , Derenne Michel , Masi Vincent
Published: August 2008

The tightness characterization of gaskets used in static seal applications, such as bolted flanged connections, is achieved by performing leakage tests with a single fluid, usually a gas like helium. Attempts made in the past to predict gasket leakage with other gases had limited success unless the leak flow regime through the gasket was predominately laminar, which is not the case with most of the gaskets. In this work, a new gasket leak flow model that combines both molecular and laminar flow regimes is developed to predict the gasket leak rate under different pressures and with different gases. The Laminar-Molecular Flow (LMF) model is first constructed around a reference pressure for which the fraction of the total leakage that occurs through laminar flow channels is established. This fraction is computed using a simple leakage test performed with one gas and at least two different pressures. The model is then tested against experimental leak data obtained from two different gaskets and four gases and is shown to produce accurate predictions.
Limit Load Analysis of Pipe Bend Using the R-Node Method
Authors: Fanous Ihab F. Z. , Adibi-Asl R. , Seshadri R.
Published: August 2008

The R-Node method has been developed earlier as a technique to find the limit load using the Elastic Modulus Adjustment Procedures (EMAP). It utilizes the systematic redistribution of the stress to find the load controlled locations in a component to estimate the collapse load. In this paper, the method is shown to be applicable for multiple loads. A simple cantilever beam is analyzed using the R-Node method subjected to both bending force and moment. The results compare well with the closed form solution of the problem. The method is then used to estimate the limit load for an elbow subjected to in-plane and out-of-plane moment. The results compare well with the elastic-plastic analysis.
Application of Surface Stress Improvement Technologies to Nuclear Power Plant Components
Authors: Payne Ronald J. , Levesque Stephen
Published: August 2008

The susceptibility of Alloy 600 to Primary Water Stress Corrosion Cracking (PWSCC) has proven detrimental to several nuclear power plant components. Repair, modification or replacement of the components to mitigate the effects of PWSCC on Alloy 600 has been deemed necessary. In some cases, repair or replacement of plant components can be exorbitantly expensive; therefore, modification of the components is necessary to keep the plant operable. A form of modification is surface stress improvement, which alters the stress state of the material. Changing the stress state of the material eliminates one of the contributing factors required for the propagation of PWSCC. This paper discusses the application of surface stress improvement technologies to commercial nuclear power plant components and provides insight to where these technologies can be employed in the future.
Study on Isolation Device for Decrease of Displacement by Using Control of Friction
Authors: Shintani Masanori , Hattori Yuichi , Kotera Tadashi
Published: August 2008

This paper deals with an isolation device by using friction force. An isolation device decreases response acceleration and external force. Therefore, earthquake damage is reduced. However, an isolation device has a demerit for large relative displacement. A low horizontal natural frequency decreases the response acceleration. Therefore, in this research, a soft spring is attached to the base of the structure. The purpose of this research is to decrease the relative displacement by using the friction force. Then, an analytical model in consideration of the friction force is proposed, and a simulation is analyzed with well-known earthquake waves. Consequently, as the friction force increases, the results show that the relative displacement decreases. However, it is found that the response acceleration increases. But it is thought that optimal friction force exists, and this force decreases both the response acceleration and the relative displacement. This is considered to change with the properties of earthquake waves. Therefore, it is thought that the response acceleration and the relative displacement are decreased by changing the friction force to the most suitable value for earthquakes. This isolation device is examined with simulation analysis. An experimental device is made under the same conditions as the proposed analytical model. The analytical results are compared with the experimental results, and the validity of an analytical program is examined.