bluuebunny/crossref_metadata_2025 huggingface dataset:
API 579: A Comprehensive Fitness-for-Service Standard
Authors: Osage David A.
Published: August 2008

An overview of API 579 Recommended Practice For Fitness-For-Service [1] is presented in this paper. This document was initially released in January of 2000 and since that time has become the de facto international fitness-for-service standard for the refining and petrochemical industry. Insights into the driving force to create API 579 and the activities of an MPC Joint Industry Project to initiate development of the new FFS technologies included in this publication are discussed. A detailed overview of API 579 is then given that covers applicability of the FFS assessment procedures, overall organization, the general assessment methodology used for all flaw and damage types, options for different assessment levels, remaining life and rerating issues, and the relationship with other existing FFS codes and standards. A discussion of the changes planned for the next release of API 579, efforts to validate the fitness-for-service technology incorporated in API 579, and a discussion of a new API document pertaining to damage mechanisms and the relationship to a fitness-for-service assessment are provided. Plans for a joint API and ASME standard and future directions of the API in-service inspection codes relative to API 579 and equipment integrity are also covered.
A French Guideline for Defect Assessment at Elevated Temperature and Leak Before Break Analysis
Authors: Kayser Y. , Marie S. , Lacire M. H. , Chapuliot S. , Drubay B.
Published: August 2008

A large program is performed in France in order to develop, for the design and operating FBR plants, defect assessment procedures and Leak-Before-Break methods (L.B.B.). The main objective of this A16 guide is to propose analytical solutions at elevated temperature coherent with those proposed at low temperature by the RSE-M (RSE-M, 1997). The main items developed in this A16 guide for laboratory specimen, plates, pipes and elbows are the following: • Evaluation of ductile crack initiation and crack propagation based on the J parameter and material characteristics as JR-Δa curve or Ji / Gfr. Algorithms to evaluate the maximum endurable load under increasing load for through wall cracks or surface cracks are also proposed. • Determination of fatigue or creep-fatigue crack initiation based on the σd approach calculating stress and strain at a characteristic distance d from the crack tip. • Evaluation of fatigue crack growth based on da/dN-ΔKeff relationship with a ΔKeff derived from a simplified estimation of ΔJ for the cyclic load. • Evaluation of creep-fatigue crack growth adding the fatigue crack growth and the creep crack growth during the hold time derived from a simplified evaluation of C*. • Leak-Before-Break procedure. The fracture mechanic parameters determined in the A16 guide (KI, J, C*) are derived from handbooks and formula in accordance with those proposed in the RSE-M document for in service inspection. Those are: • The KI handbook for a large panel of surface and through-wall defects in plates, pipes and elbows. • Elastic stress and reference stress formula. • Analytical Js and Cs* formulations for mechanical and through thickness thermal load. The main part of the formula and assessment methodologies proposed in the A16 guide are included in a software, called MJSAM, developed under the MS Windows environment in support of the document. This allows a simple application of the analysis proposed in the document.
Defect Assessment Procedure for Low to High Temperature Range
Authors: Dogan Bilal , Ainsworth Robert
Published: August 2008

There are many similarities between available procedures used for defect assessment. They have been developed as a result of experience gained from material-specific programs and have often been verified using the same data. One recently updated document covering life assessment procedures under creep and creep/fatigue crack growth conditions is BS 7910. This document takes into account some of the most recent developments in the subject, including some from the British Energy R5 Procedure. Future developments in defect assessment procedures will follow the route of simplified and unified codes covering defect behaviour in the low to high temperature range. In this paper, the relevance of the insignificant creep curves in RCC-MR for defect free structures and the creep exemption criteria in BS7910 are examined. Then, an overview is given of some European developments in defect assessment methods for Fitness-for-Service assessment, based on recent and current projects such as the EC thematic network FITNET.
Probabilistic Predictions for Piping Fatigue Including the Effects of Ultrasonic Examinations
Authors: Simonen F. A.
Published: August 2008

This paper presents a methodology for estimating failure probabilities of piping welds that experience cyclic stresses and that are subject to ultrasonic examinations designed to detect growing fatigue cracks. Fatigue cracks can start as either preexisting fabrication flaws or as cracks initiated after an accumulation of stress cycles. Low levels of cyclic stresses and/or small numbers of cycles produce low failure probabilities, with the failures caused mainly by fabrication flaws. More severe cyclic stress conditions produce higher failure probabilities, with the failures caused mainly by fatigue cracks that initiate during the life of the component. Numerical results are presented to address both crack initiation and crack growth. The calculations cover both stainless and ferritic steels, inservice inspections with different inspection intervals, and stress states with and without high levels of through-wall stress gradients. It is shown that effective inspection programs can significantly reduce failure probabilities, and that such programs require suitable NDE sensitivities and adequate inspection frequencies.
Creep Activation Energy of Electrosleeve™ Nano-Crystalline Nickel–Phosphorous Tube Repair and Ni-200
Authors: Pop Mike G. , Galford James E. , Griffith John C. , Burgess John A.
Published: August 2008

The use of nano-crystalline materials have created a need to reevaluate and/or define basic structural material properties. Electro-deposition of a nano-crystalline material on a pressure retaining structure is an engineering design solution to enhance or restore a valuable component for continued operation. This paper presents an experimental determination of the creep activation energy of an electroformed nano-crystalline nickel phosphorous micro-alloy deposition on PWR steam generator tubes.
The Embedded Flaw Process for Repair of Reactor Vessel Head Penetrations and Its Application at North Anna Unit 2
Authors: Bamford W. H. , Spain L. L. , Gold R. E. , Gahwiller W. R. , Lareau J. P.
Published: August 2008

As a result of an inspection of the reactor vessel upper head penetrations in the fall 2002 outage at North Anna Unit 2, a number of indications were discovered in the attachment welds for the reactor vessel head penetrations. Indications were also found in three penetrations that had been repaired using the Westinghouse embedded flaw weld repair process during the fall outage of 2001. After extensive investigation it was determined that the cracking was mostly in the weld buttering, and that the cracking in the repaired penetrations was the result of inadequate implementation of a qualified repair process. The process was modified slightly as a result of these findings, but the cracking was too extensive to permit a practical repair at North Anna Unit 2. As a result, the head was replaced, and the unit restarted in January of 2003.
Pressure Protection Evaluation Program at Savannah River Site
Authors: Chan James K. , Ramsey John W.
Published: August 2008

This paper describes the current pressure protection program at Savannah River Site (SRS), a Department of Energy chemical processing and nuclear material handling facility in Aiken, South Carolina. It gives a brief description of the design requirements based on ASME, API, CGA, and ASHRAE Codes. Equipment and systems requiring pressure protection at SRS are primarily pressure vessels, steam stations, process chemical systems, refrigerant and cryogenic systems and other air or gas systems. It is understood that any pressure protection program is built on five fundamental areas of responsibility: procurement, verification, registration, inspection, and repair. This paper focuses on the existing process of facility pressure protection evaluation for code compliance followed by identification of failure scenarios and system design requirements, valve selection and sizing, and verification record generation. Improvements to this process are recognized and discussed. They include the development of a computer program to perform pressure protection evaluation and generate verification records. The software would process all applicable pressure protection calculations using improved methodologies. All relevant data required would be accessible within the program. Pressure safety relief device attributes and system parameters would be displayed. The computer program would enhance design consistency, improve quality and plant safety, and make the pressure protection verification process more efficient and cost effective.
A Fracture Mechanics Evaluation of BWR Shroud Mid-Core Horizontal Weld to Justify Continued Operation
Authors: Mehta Hardayal S. , Inch George , Dhar Shashi
Published: August 2008

The Mid-core shroud weld (H4 weld) at a BWR plant was inspected during refueling outages in 1998 (RF06) and 2000 (RF07). A structural margin evaluation considering 2000 inspection results for this weld provided technical justification for continued operation to at least the fuel cycle ending in 2002. IGSCC mitigation measures were implemented during operation through 2002. Therefore, a factor of two improvement in the assumed crack growth rate in the depth direction has been applied for operation between 2002 and 2004. The objectives of this paper are to describe the structural evaluation methodology used and describe the results of the evaluation in support of continued operation of H4 weld to 2004. Structural margins for continued operation of H4 weld to 2004 were evaluated two ways. First, the limit load calculations were conducted for a configuration in which through-wall flaws were assumed in regions where the ID surface fluence in 2004 exceeded 3×1020 n/cm2. Since all of the areas taken credit for had a fluence less than the threshold value of 3×1020 n/cm2, a limit load evaluation constituted a complete structural margin evaluation and no linear elastic fracture mechanics (LEFM) or elastic plastic fracture mechanics (EPFM) evaluations were necessary. Secondly, LEFM and EPFM calculations were conducted for the assumed configuration in which through-wall cracking was assumed where the ID surface fluence exceeded 5×1020 n/cm2. The calculated safety factor for the nominal case was determined to be 4.98, which exceeds the required value of 2.77. To demonstrate structural margin in the LEFM regime, a configuration similar to the limit load nominal case was used except that through-wall cracking was assumed in regions where ID fluence exceeded 5×1020 n/cm2 instead of 3×1020 n/cm2. The calculated value of the highest stress intensity factor was 49.2 ksi√in that is less than the allowable value of 54.2 ksi√in. Additional evaluation with EPFM was also conducted to demonstrate higher available structural margins. The EPFM evaluation was conducted by first determining an equivalent single through-wall flaw to conservatively model the LEFM configuration. The applied J-integral values were calculated using the EPRI ductile fracture handbook. A conservative material J-T curve corresponding to a fluence level of 5×1020 n/cm2 was used in the evaluation. The EPFM evaluation showed the structural margin for this case to be 4.0, which exceeds the required value of 2.77. Based on the results of these limit load, LEFM and EPFM structural margin evaluations, it was concluded that the required structural margins will be maintained at the H4 weld for operation through year 2004.
Allowance for Residual Stresses and Material Interfaces When Calculating J in and Close to Welded Joints
Authors: Beardsmore David W. , Sherry Andrew H.
Published: August 2008

The J-integral is used widely as a measure of crack driving force within structural integrity assessments of engineering structures. The calculation of J in and close to welds using the Equivalent Domain Integral (EDI) found in some finite element (FE) codes can give unreliable, domain-dependent, results. This arises because FE codes typically use simplified, “default” implementations of the EDI which do not allow for the non-uniform strain field, material interface and/or material inhomogeneity which are present as a result of the welding process. This paper provides guidance on the corrections that must be made to restore the domain-independence of the EDI, allowing J to be determined from the far stress field for cracks in and close to welds. Example calculations are presented to illustrate the effect of the modifications. The results are compared with those obtained using the default J post-processor built into a commercial FE code. Calculations are presented for cases where there is a material interface, where there are initial non-uniform strains, and where both of these phenomena occur together. It is shown that the default post-processor results are highly domain dependent, but that independence is restored using the corrected EDI formulation.
Virtual Fabrication Technology Weld Modeling Tool and Its Applications in Distortion Predictions
Authors: Yang Y. P. , Brust F. W. , Cao Z.
Published: August 2008

A virtual fabrication technology (VFT) is introduced in this paper. It is a state-of-the-art cutting and welding simulation tool developed by Battelle and Caterpillar in the past few years. It can model extremely large and complicated structure fabrications. Extensive full-scale experiments have validated the accuracy and predictive power. It can be used to reduce fabrication cost and improve quality by minimizing and controlling distortions. Two application examples are presented to illustrate how to apply this tool in welded structure design and manufacture.
Creep Behavior of a Bimetallic Welded Joint in a Nuclear Piping System
Authors: Yang Y. P. , Brust F. W. , Oh J.
Published: August 2008

The information of the creep behavior of a thick welded joint is very important to secure the safety of high temperature service devices. The creep damage development and behavior are very complex; hence it is time consuming to practice the experiment and theoretical analyses. In this paper a simple accurate model was developed to analyze the creep behavior of weld metal and heat-affected zone on a thick bimetallic welded pipe. The pipe was made by welding an A508-class-2 carbon steel pipe to a 304 stainless steel pipe with a shielded metal arcwelding process using INCONEL 182 electrodes. Virtual fabrication technology weld modeling tools (VFT™) developed jointly by Battelle and Caterpillar was used to obtain welding-induced residual stress. The weld residual stress was read into the creep model as initial stress condition for creep analysis. A temperature 1000°F was applied on the bimetallic weld model with inside pressure and axial loading. The simulation results indicated that creep strains were not uniform through the weld joint due to weld residual stresses, materials creep behavior and geometry changes. Some stress and strain concentrations were found on the A508 steel near buttering region, which results in axial cracks.
Crack Growth Behavior in a Residual Stress Field for Vessel Type Structures
Authors: Dong P. , Rawls G.
Published: August 2008

Detailed residual stress analysis was performed for a multi-pass butt weld, representing the middle butt-girth weld of a storage tank. The analysis procedures addressed welding parameters, joint detail, weld pass deposition sequence, and temperature-dependent properties. The predicted residual stresses were then considered in stress intensity factor calculations using a three-dimensional finite element alternating model (FEAM) for investigating crack growth behavior for both small elliptical surface and through-wall cracks. Two crack orientations were considered: one is parallel to the vessel girth weld and the other is perpendicular to the girth weld. Since the longitudinal (parallel to weld) and transverse (perpendicular to weld) residual stresses exhibit drastically different distributions, a different crack growth behavior is predicted. For a small surface crack parallel to the weld, the crack tends to grow more quickly at the surface along the weld rather than into the thickness. The self-equilibrating nature of the transverse residual stress distribution suggests that a through-wall crack parallel to crack cannot be fully developed solely due to residual stress actions. For a crack that is perpendicular to the weld, a small surface crack exhibit a rapid increase in K at the deepest position, suggesting that a small surface crack has the propensity to become a through-wall crack. Once the through crack is fully developed, a significant re-distribution in longitudinal residual stress can be seen. As a result, in the absence of external loads there exists a limiting crack length beyond which further crack growth is deemed unlikely.
Effect of Plasticity on Fatigue Life of Welded Nuclear Component With Local Brittle Zone
Authors: Kim Jong-Sung , Lee Se-Hwan , Jin Tae-Eun
Published: August 2008

The local brittle zone (LBZ), which has lower tensile properties as well as lower fracture toughness than base metal and weldment, can occur on the heat affected zone (HAZ) of some nuclear components made of low alloy steels due to the carbide coarsening by multi-pass welding and post-weld heat treatment. These variations of material strengths across the welds due to the LBZ can produce strain concentrations when the stress amplitude is large enough to cause cyclic plastic flow. But, it is difficult to find the previous researches about a relation between the fatigue life of LBZ on real nuclear components and plasticity. So, in this study, the microstructures and tensile properties of HAZ on nuclear components are predicted by using the semi-analytical method, and the fatigue lifetimes of welds on nuclear components with the LBZ are evaluated by the finite element method considering the local plasticity and the variations of tensile properties, and the fatigue analysis procedure of ASME B&PV Code Sec.III. Finally, the effect of LBZ on nuclear components on fatigue lifetime is reviewed.
Implementation of an Outer Can Welding System for Savannah River Site Plutonium Processing Facility
Authors: Howard S. , Daugherty W. , Sessions C.
Published: August 2008

This paper details three phases of testing to confirm use of a Gas Tungsten Arc (GTA) system for closure welding the 3013 outer container used for stabilization/storage of plutonium metals and oxides. The outer container/lid closure joint was originally designed for laser welding, but for this application, the gas tungsten arc (GTA) welding process has been adapted. The testing progressed in three phases: (1) system checkout to evaluate system components for operational readiness, (2) troubleshooting to evaluate high weld failure rates and develop corrective techniques, and (3) pre-installation acceptance testing. A total of 190 can/lid welds were made and evaluated. During Phase I, weld failures were common due to pressure buildup and venting through the weld pool. During Phase II, characterization of the electrode contact to the weld pool and weld pool blowouts helped in the development of a corrective technique. During Phase III, a reduction in internal pressure, by controlling the final helium backfill of the can before welding, provided satisfactory weld results. The work described was performed during 2002 pre-installation testing at the Savannah River Technology Center in Aiken, S.C. before installation of an Outer Can Welder (OCW) system at the Savannah River Site (SRS) plutonium processing facility. The first OCW system was originally developed at the SRS to support similar plutonium stabilization/storage efforts at the Hanford Site (operated by Fluor Hanford Corporation).
Repair of a Melter Pour Spout Using an Expanding Ring
Authors: Peacock Harold B. , Imrich Kenneth J. , Lam Poh-Sang , Leader Douglas R. , Iverson Daniel C.
Published: August 2008

An expanding ring was developed that provided remote repair of the pour spout for a radioactive waste vitrification melter. This passive device used gas pressure to expand a metal ring against the irregularly shaped pour spout wall. Laboratory modeling and testing were performed for proof of concept and optimization before final design and field deployment. The ring expanded radially more than 4.8 mm and successfully repaired the melter pour spout allowing continued glass pouring operation.
Experimental Assessment of Material Strength of Two Operating Main Oil Pipelines
Authors: Timashev Sviatoslav A. , Chernyavsky Oleg F. , Rebyakov Yuri N.
Published: August 2008

The paper describes the results of a special experimental study of three types of damaged pipeline steels from two main oil pipelines that had been in operation for 15 years. The experimental study included assessments of the main static characteristics of the steels, parameters of the S-N curve, prognosis of the fatigue limits and assessment of the fracture toughness (FT) and the FT curve. Obtained results permit correct assessments of the pipelines remnant life.
Analytical Solutions of Crack Tip Plasticity Zone Shape for a Semi-Infinite Crack
Authors: Jing Peihua , Khraishi Tariq , Gorbatikh Larissa
Published: August 2008

In this work, closed-form analytical solutions for the plasticity zone shape at the lip of a semi-infinite crack are developed. The material is assumed isotropic with a linear elastic-perfectly plastic constitution. The solutions have been developed for the cases of plane stress and plane strain. The three crack modes, mode I, II and III have been considered. Finally, prediction of the plasticity zone extent has been performed for both the Von Mises and Tresca yield criterion. Significant differences have been found between the plane stress and plane strain conditions, as well as between the three crack modes’ solutions. Also, significant differences have been found when compared to classical plasticity zone calculations using the Irwin approach.
Burst Pressure Predictions of Cracked Pipelines Using a Micromechanics Approach
Authors: Dotta Fernando , Ruggieri Claudio
Published: August 2008

This study extends a micromechanics approach based upon the computational cell methodology to model ductile crack extension of longitudinal crack-like defects in a high strength pipeline steel. Laboratory testing of an API 5L X60 steel at room temperature using standard, deep crack C(T) specimens provide the data needed to measure the crack growth resistance curve for the material. In the computational cell model, ductile crack extension occurs through void growth and coalescence (by cell extinction) within a thin layer of material ahead of crack tip. A simple scheme to calibrate material-specific parameters for the cells is also described. A central focus of the paper is the application of the cell methodology to predict experimentally measured burst pressures for pre-cracked pipe specimens with different crack sizes. The experimental program includes longitudinally precracked 20” (508 mm) O.D. pipe specimens with 15.8 mm thickness containing an internal crack with notch depth (a) and notch length (2c) 7 × 140 mm. Large-scale, full 3-D computations are conducted on detailed finite element models for the pipe specimens to describe crack extension with increased pressure. The numerical simulations demonstrate the effectiveness of the cell approach to describe crack growth response and to predict the burst pressure for the tested pipes.
Damping Effect in Fluid-Structure Interaction: Application to Slamming Problem
Authors: Aquelet N. , Souli M.
Published: August 2008

During a high velocity impact of a structure on an incompressible fluid, impulse loads with high pressure peaks occur. This physical phenomenon called ‘slamming’ is a concern in the shipbuilding industry because of the possibility of hull damage. Shipbuilding companies are carrying out several studies on the slamming modeling using FEM software. This paper presents the prediction of the local high pressure load on a wedge striking a free surface. The fluid-structure interaction is simulated by a fluid-structure coupling algorithm. This method of coupling, which makes it possible to transmit the efforts in pressure from the Eulerian grid to the Lagrangian grid and vice versa, is a relatively recent algorithmic development. It was successfully used in many scientific and industrial applications: the modeling of the bird strike on the fuselage of a Jet for the Boeing Coporation, underwater explosion shaking the oil platforms, and airbag simulation in automotive industry... Predicting the local pressure peak on the structure requires an accurate fluid-structure interaction algorithm. Thus, some penalty coupling enhancements make the slamming modeling possible. The main improvement is a numerical damping factor which permits to smoothing of the pressure signal.
Parallel Computations of the Dynamic Behavior of Bubble Plumes
Authors: Bombardelli Fabia´n A. , Buscaglia Gustavo C. , Garci´a Marcelo H.
Published: August 2008

This paper discusses numerical results obtained with different strategies for modeling air-water flows. Mathematical models for dilute mixtures, derived from the two-fluid model equations, are presented. These models include diverse degrees of complexity, and they handle turbulence via a k-ε model and a Large-Eddy Simulation (LES) approach, in a consistent way. The models are implemented in a parallel code, which is then used to numerically simulate the dynamic behavior of bubble columns in two and three dimensions. The results of the simulations are employed to study the interplay between the turbulence of the carrier and the scales of the wandering motion, and to compare the capability of different models to capture the physics behind the phenomenon.
Study of Burst Conditions of Thin-Walled Pressure Vessels Subjected to Hypervelocity Impact
Authors: Telitchev Igor Ye.
Published: August 2008

The present paper is devoted to analysis of burst conditions of thin-walled cylindrical pressure vessels subjected to hypervelocity impact of space debris particles. Two types of gas-filled pressure vessels onboard the International Space Station were considered: inhabited or laboratory pressurized modules and onboard system vessels with a gas under high pressure. The central concern of this study is to determine the border between simple perforation and catastrophic fracture of gas-filled pressure vessels of both types under hypervelocity impact. Non-linear fracture mechanics techniques were used to analyze and predict whether a vessel perforation will lead to mere leakage of gas, or whether unstable crack propagation will occur that could lead to catastrophic fracture of the vessel. Damage patterns and mechanisms leading to unstable crack growth are discussed. A model of fracture of an impact damaged pressure vessel is presented. A developed model was successfully applied to the simulation of experimental results obtained at Ernst-Mach-Institute (Germany).
Fluidelastic Instability of a U-Bend Tube Array Based on Correlated Unsteady Fluid Force in Two-Phase Flow
Authors: Nakamura Tomomichi , Shimamura Kengo , Iwase Toshihiko , Nishida Seishi
Published: August 2008

The fluidelastic instability threshold of tube arrays can be estimated using measured unsteady fluid force. It is usually assumed that the fluid force is completely correlated along the tube axis; this may be true in single phase flow. However, the flow in the two-phase flow is no longer steady, in space or in time. Thus, the correlation of the fluid force acting along the tube axis should be introduced. There are very few measured data for the correlation of the fluid force in two-phase flow, and it is difficult to deduce from measured time-history fluid data, such as the void fraction or the flow velocity. In this report, the average correlation length is derived from critical flow velocities of U-bend tubes in several two-phase flow conditions, based on an approximate theory for the two-phase flow condition when the unsteady fluid force for a short span model has been measured. As a result, the average correlation length gives the critical flow velocities of each U-bend tube. The result gives a good explanation why the critical factor in the U-bend tube is larger than that in short span models. This method can be a new estimation of the fluidelastic instability of U-bend tubes in two-phase flow conditions.
Dynamics of a Cylinder Wake Under Controlled Excitation
Authors: Mureithi Njuki W. , Goda Syuki , Nakamura Tomomichi
Published: August 2008

This paper presents some results of experimental tests as well as a group theoretic analysis of a 2D cylinder wake under forced excitation. The response of the Karman wake (K mode) to external perturbations is studied. Reflection-symmetric (S mode) perturbations and asymmetric (K1 mode) perturbations are considered. The perturbations are generated by mechanically oscillating the test cylinder. Tests were done in a small wind tunnel. Depending on the excitation to Karman shedding frequency ratio, mode locked states, in the form of spatio-temporally fixed patterns, could be observed. Harmonic asymmetric (mode K1=K) forcing at the Karman frequency strongly enhanced the Karman mode. Superharmonic forcing (with mode K1 ≠ K) had little effect on the Karman mode K. However, a detuning effect was observed. On the other hand, subharmonic (1/2, 1/3) K1 mode forcing significantly affected the K mode, with strong response at K1 mode harmonics. Subharmonic S mode excitation had a damping effect on the K mode. On the other hand harmonic and superharmonic forcing triggered a period-doubling instability, destroying the original K mode. Using a group theoretic approach, the general amplitude equations governing the interaction of the S/K1 modes with the K mode have been derived. A qualitative analysis of the equations helps explains some of the experimental results. For K1/K mode interactions, the symmetrical ‘compatibility’, via common subgroups, explains the strong resonances observed experimentally for 1/1 and 1/3 frequency ratios. For a frequency ratio 1/2, it is shown that K1 and K mode symmetries are incompatible; the two modes do not have a common symmetry subgroup. Consequently, traveling wave solutions, induced by total symmetry breaking, rather than standard steady state modes are expected to be more likely to occur. For S/K mode interaction, an earlier result is reiterated; thus, the Karman mode is shown, theoretically, to be destroyed via a period-doubling instability. This effect occurs for S mode frequencies as high as 3 times the Karman frequency.
Flow-Induced Vibration of Cross-Shaped Tube Bundle: The Effect of Tube Bundle Arrangement
Authors: Inada Fumio , Nishihara Takashi , Yasuo Akira , Morita Ryo , Sakashita Akihiro , Mizutani Jun
Published: August 2008

A cross-shaped tube bundle is proposed for the lower plenum structure in the next-generation LWR. The effect of tube bundle arrangement on the flow-induced vibration characteristics of the cross-shaped tube bundle in cross flow was considered experimentally. Regarding random vibration, the power spectral density of the fluid force of the staggered arrangement as well as the correlation length was measured and those of the normal arrangement were compared with those of the staggered arrangement. Regarding self-excited vibration, vibration response was compared. The trend of the power spectral densities, correlation length, and the critical velocity of the normal arrangement were similar to those of the staggered arrangement.
Improved Flow-Induced Vibration and Work-Rate Measurements of Steam-Generator Tubes
Authors: Janzen V. P. , Smith B. A. W. , Brunet L. , Fernando S. , Fingas D.
Published: August 2008

In the past, the excessive fretting-wear of U-bend tubes observed in some nuclear steam generators has led to increased tube inspections, unexpectedly high numbers of plugged tubes and the prospect of degraded performance if left unchecked. In this paper, recent vibration and work-rate experiments that have attempted to address this problem are summarized, including tests of two-span U-tubes in air-water and straight tubes in two-phase Freon. Tube bundles were subjected to two-phase cross-flow over a wide range of flow conditions, measuring tube vibration, flow characteristics in the bundle, and the dynamic interaction (work-rate) between tubes and supports that gives rise to fretting-wear. Developments in vibration and work-rate instrumentation and software analysis tools are also presented. The result is an improved ability to measure dynamic properties and, thus, to better predict the vibration response and fretting-wear performance of steam generators.
Severed Tubes in Operating Nuclear Steam Generators: Case Analysis — I
Authors: Au-Yang M. K. , Leshnoff Stephen
Published: August 2008

During a routine inspection in October 2001, it was discovered that a plugged tube in one of the steam generators at a nuclear station was completely severed at the upper tubesheet. The severed surface appeared to be fresh, clean, 360-deg. and with no evidence of necking down, ductile failure or visible flaws. Eddy current inspection revealed that the four neighboring tubes downstream of the severed tube each had wedge-shaped wear marks starting from the tubesheet end. However, there was no visible mid-span impact wear marks. Furthermore, the tube was visibly swollen due to over-pressurization. This tube was plugged in 1986 with no indications of flaw or wear marks. It was replugged later. The tube was not stabilized because there was no apparent potential for a circumferential sever to occur anywhere in the tube. Flow-induced vibration based on classic linear theory showed that this tube should have wide margin against fluid-elastic instability, turbulence or vortex-induced fatigue failure. However, it also was found that if for any reason the tube was laterally restrained (clamped) at the support plates, the margin against fluid-elastic instability would be reduced significantly. Still, this tube should have been stable and turbulence or vortex-induced vibration alone, as predicted by the classic linear theory without fluid-structure interaction, should not have caused fatigue failure. This study points out a deficiency in the classic linear turbulence-induced vibration analysis without taking into account the effect of fluid-structure coupling. When the cross-flow gap velocity is near the critical velocity, fluid-structure coupling would greatly increase the vibration amplitude over what is predicted by the classic acceptance integral approach. It is this increase in turbulence-induced vibration that caused this particular tube to fail by fatigue.
A Review of Wear Scar Patterns of Nuclear Power Plant Components
Authors: Ko Pak L. , Lina Agne`s , Ambard Antoine
Published: August 2008

To date, almost all the studies related to component damage have been concerned primarily with dynamic interactions at the interface of contacting components and the subsequent damage due to mechanical wear. Based on the results of examination of a large assortment of photo-micrographs taken from worn reactor components and worn specimens from a broad range of test facilities, it appears that, in many cases, mechanical wear is only a secondary contributing mechanism. With the exception of special cases where severe flow-induced vibration might have occurred, such as in some condensers and primary heat exchangers as well as in the U-bend and inlet regions of some earlier steam generators, resulting in severe component interactions causing substantial wear damage, erosion, corrosion, impacting and perhaps cavitation would seem to be the primary contributing mechanisms.
Probabilistic Assessment of Fretting Wear in Steam Generator Tubes Under Flow Induced Vibrations
Authors: Morandin Greg D. , Sauve´ Richard G.
Published: August 2008

Successful life management of steam generators requires an ongoing operational assessment plan to monitor and address all potential degradation mechanisms. A degradation mechanism of concern is tube fretting as a result of flow-induced vibration. Flow induced vibration predictive methods routinely used for design purposes are based on deterministic nonlinear structural analysis techniques. In previous work, the authors have proposed the application of probabilistic techniques to better understand and assess the risk associated with operating power generating stations that have aging re-circulating steam generators. Probabilistic methods are better suited to address the variability of the parameters in operating steam generators, e.g., flow regime, support clearances, manufacturing tolerances, tube to support interactions, and material properties. In this work, an application of a Monte Carlo simulation to predict the propensity for fretting wear in an operating re-circulation steam generator is described. Tube wear damage is evaluated under steady-state conditions using two wear damage correlation models based on the tube-to-support impact force time histories and work rates obtained from nonlinear flow induced vibration analyses. Review of the tube motion in the supports and the impact/sliding criterion shows that significant tube damage at the U-bend supports is a result of impact wear. The results of this work provide the upper bound predictions of wear damage in the steam generators. The EPRI wear correlations for sliding wear and impact wear indicate good agreement with the observed damage and, given the preponderance of wear sites subject to impact, should form the basis of future predictions.
Chaotic Vibration and Wear Characteristics of a Circular Loosely Supported Tube Subjected to a Fluid Flow
Authors: Fujita Katsuhisa , Nishiumi Hiroyuki , Ito Tomohiro
Published: August 2008

When a circular, loosely supported tube is subjected to fluid forces and vibrates with a large amplitude, the tube may continually collide with support structures and show wear. As a result, the tube is considered to reveal non-linearities such as chaotic behaviors, that depend on the support conditions and the fluid flow conditions. In the present study, a cantilever tube having a loose support at the free end is mathematically modeled based on the FEM. The nonlinear vibration analysis is performed by using the DAE (Differential Algebraic Equation) for the three kinds of excitation forces: (a) harmonic exciting forces, (b) nonlinear fluid forces, such as the Iwan & Blevins wake oscillator model etc., and (c) random fluid forces. The chaotic behavior and the wear damage are investigated for these fluid forces by taking the structural damping ratio and the gap size, for example, as parameters. Moreover, the influences of the chaotic phenomena on the deviation from the deterministically predicted wear volume at the tube support location are discussed.
The Scaling of Pressure Fluctuations From Equal-Tee Piping Components for In-Plant Noise Prediction
Authors: Karczub Denis G. , Catron Fred W. , Fagerlund Allen C.
Published: August 2008

An important element of in-plant noise modeling for high-speed gas flow, in addition to the noise generated by control valves, is the noise due to piping system components such as tees which becomes significant at high mass flow rates. An effective tool for the modeling of noise due to piping system components is non-dimensional pressure fluctuation scaling. The current paper outlines procedures for characterization of the internal noise due to an equal tee with unequal outlet flows using non-dimensional pressure fluctuation scaling. Experimental data is presented demonstrating general collapse of the measured data onto a single characteristic curve for several combinations of flow velocity and gas density under steady-state flow conditions. Flow ratios of 1:2, 1:3, 1:4 and 2:3 between each of the two outlet legs from the equal tee are considered, as well as the affect of gas density over a range of 345kPaG to 1380kPaG.
A Perforated Conical Strainer as an Example of an Acoustic Noise Generator
Authors: Motriuk Roman W.
Published: August 2008

It is customary to insert a perforated conical strainer into the suction piping of the turbo-compressor that boosts the pressure in natural gas transportation systems. Conical strainers prevent foreign objects, left in the pipeline after its construction, from falling into the compressor impellers. In addition, the strainers are believed to be effective permanent scrubbing devices in most services requiring infrequent cleaning, such as dry and sweet natural gas transportation systems. The strainers that ‘substitute’ scrubbers offer remarkable construction and design savings for the pipeline gas operators, hence, they are often installed in today’s gas transportation systems. A conical perforated strainer could be installed as close as few meters from the compressor nozzle or at a distance of ten to fifteen pipe diameters from it. However, the convenience of strainer installation rather than consideration of its acoustic behaviour frequently dictate its location in the piping system. Therefore, the strainers are usually inserted at the flange sets that are installed for a different purpose, for example, at the spool piece flange sets or at the orifice plate flanges. The strainer location is rarely analysed although it frequently contributes to the acoustical fatigue of piping attachments, strainer disintegration, and spectacular noise generation. In this study, a case of noise generation by a conical strainer is illustrated by noise and vibration measurement results, which were carried out at several different locations of the studied piping system. Noise and vibration spectral components are identified and mitigated by the proposed recommendations.
Dynamic Support in Piping Systems: A Novel Design Based on Automotive Shock Absorbers
Authors: Motriuk Roman W. , Mikulcik Edwin
Published: August 2008

Complex vibration fields are observed in piping systems that are mechanically or acoustically interconnected with turbo-machinery. The magnitudes of vibrations in such systems depend on the coupling of the piping response characteristics with the excitations that are present. In cases of high vibration amplitudes, successful mechanical attenuation can be achieved by altering the piping system’s mass or its stiffness, thus detuning the piping response from the excitation. Another approach is to introduce damping into the piping system so that the vibration energy can be efficiently dissipated, hence mitigating unacceptable vibration amplitudes. All of the above principles are used successfully across the industry. This paper describes a novel support design that has been used successfully to solve vibration problems in cases such as those described above. This device was initially conceived as being a very economical solution for simply adding damping to reduce the vibration amplitude. Its economy is derived from being based on the use of standard automotive or truck-type shock absorbers, which were expected to be very effective in providing damping because of their success in automotive applications. The device which was designed is lightweight and therefore very versatile in the manner in which it can be deployed, such that anchoring and attachment requirements can be very simple, thus accommodating space or foundation necessities that could be problematic using more standard approaches. Because of the lack of information existing on the damping properties of such shock absorbers, the first design was implemented on a trial-and-error basis. However, its success motivated further investigations into the characteristics of shock absorbers, so that the initial installation could be evaluated through a more proper analysis and lead to a more general design procedure for other applications. Extensive laboratory tests were done using several different shock absorbers to gain an insight into their characteristics when used in the manner required here. The test procedures and the data from these tests are described in this paper, together with the analysis of the successful installation. It was found, unexpectedly, that the shock absorbers contribute significantly in both damping and stiffness, thus providing a powerful combination of detuning as well as damping when used in this way. This paper demonstrates a general approach to the techniques of testing and the design of similar such systems.
Fluidelastic Instability of Flexible Tubular Cylinders Subjected to Two-Phase Internal Flow
Authors: Monette Christine , Pettigrew Michel J.
Published: August 2008

The fluidelastic instability behaviour of flexible cylinders subjected to internal single-phase (liquid or gas) flows is now reasonably well understood. Although many piping systems operate in two-phase flows, so far very little work has been done to study their dynamic behaviour under such flows. This paper presents the results of a series of experiments to study the fluidelastic instability behaviour of flexible tubular cylinders subjected to two-phase internal flow. Several flexible cylinders of different diameters, lengths and flexural rigidities were tested over a broad range of flow velocities and void fractions in an air-water loop to simulate two-phase flows. Well-defined fluidelastic instabilities were observed in two-phase flows. The existing theory to formulate the fluidelastic behaviour under internal flow was developed further to take into account two-phase flow. The agreement between the experimental results and the modified theory is remarkably good. However, it depends on using an appropriate model to formulate the characteristics of the two-phase flows.
Flow-Induced Vibration of Flexible Disk Subjected to Swirling Fluid Flow
Authors: Watanabe Masahiro , Wakita Nagara , Takahashi Takumi
Published: August 2008

This paper deals with theoretical stability analysis and experimental study of flow-induced vibration of a flexible disk subjected to swirling fluid flow in a confined fluid. The flexible disk subjected to swirling fluid flow undergoes flow-induced vibration when the swirling fluid speed becomes high. The flow-induced vibration occurs due to the interaction between the out-of-plane motion of the flexible disk and swirling fluid flow generated around the disk. In this system, the swirling fluid flow is generated by a rigid disk rotating near the flexible disk. In the theoretical stability analysis, the basic equations of the swirling fluid flow around the flexible disk are based on the Navier-Stokes equations integrated over the gap width between the flexible disk and the rotating rigid disk. The structural equation of the flexible disk is based on the Kirchhoff-Love’s plate model. The equations of the fluid-structure coupling system are derived taking account of the moving boundary conditions of the flexible disk. The equations of the fluid-structure coupling motion are linearized for small out-of-plane motion of the flexible disk near the equilibrium state, and the solutions of the equations are obtained using the multi-modal expansion approximation and the Galerkin’s method. Modal frequencies and modal damping ratios of the system are obtained as a function of the rotational speed of the rotating rigid disk. As a result, it is clarified that unstable vibration occurs in the flexible disk due to the swirling fluid flow. And the critical rotational speed at which the unstable vibration occurs and vibration modes are clarified theoretically and experimentally.