bluuebunny/crossref_metadata_2025 huggingface dataset:
Burst Cause Analysis of the High Temperature Steam Pipe in Heavy Oil Well
Authors: Liu Qiang , Song Sheng-yin , Feng Yao-rong , Duan Bo
Published: November 2014

The high temperature steam pipe used in one heavy oil well in China burst. This failure pipe was investigated and analyzed by macroscopic analysis, material tests (including chemical composition, metallurgical analysis & mechanical property) and fracture surface scanning electronic microscopy (SEM) analysis. Then it can be concluded that the mechanical properties of the burst pipe accord with related standards, and that the fracture surface is a typical brittle fracture. The herringbone stripes were found on the fracture surfaces and pointed to a fracture source where there were over 1.6mm deep mechanical damages on the pipe surface. After micro hardness testing near mechanical damage area and the nearby substrate, it was found that the toughness of mechanical damage area was low. The expanding diameter of the burst pipe was also investigated. Because the residual water in the pipe was pushed by high temperature steam when the steam was turned on, the speed of water was very fast, and the stress caused by water hammer were higher than yield pressure of the pipe, which is the internal pressure in the pipe and which could produces a maximum hoop stress in the pipe equal to the yield strength of the pipe material, the pipe would be expanded.

The fracture surface is a typical brittle fracture. There are two mechanical damages on the fracture source, and the pipe burst because of the mechanical damages and huge impact of water hammer.
Project STYLE: Post-Test Analysis of Mock-Up3
Authors: Nicak Tomas , Schendzielorz Herbert , Keim Elisabeth , Meier Gottfried , Moinereau Dominique , Le Delliou Patrick
Published: November 2014

The safety and reliability of all systems has to be maintained throughout the lifetime of a nuclear power plant. Continuous R&D work is needed in targeted areas to meet the challenges of long term operation of existing and new plants designs. The European project STYLE aims to develop and validate advanced methods of structural integrity assessment applicable in the ageing and lifetime management of primary circuit components.

There are three large scale mock-up tests in STYLE each of them dedicated to investigate specific effects. This paper presents the work related to Mock-up3, which is dedicated to investigate influence of cladding on the crack initiation and propagation as well as the transferability of material properties from small scale specimens to a large scale component.

The performed post-test analyses focus on both the further understanding and interpretation of the Mock-up3 test and on the effect of cladding on structural integrity and LBB behavior of reactor coolant pressure boundary components.
Environmental Fatigue Evaluation for Class 1 Components of an Advanced PWR
Authors: Asada Seiji , Tatsuno Kunimitsu , Toyoda Masanori , Takayama Yoshihiro , Hirota Naoaki , Takayama Yasushi , Tajima Masakazu
Published: November 2014

Environmentally assisted fatigue (EAF) evaluations for Class 1 components of an advanced PWR have been performed to comply with Regulatory Guide 1.207 and NUREG/CR-6909. The procedure consists of 3 steps. Step 1 is to use the maximum Fen values, Step 2 is to use the Modified Rate Approach and Step 3 is to use elastic-plastic Finite Element (FE) analysis with the Modified Rate Approach. This procedure can efficiently proceed with the evaluation. Also, the Class 1 components of an advanced PWR have satisfied with the code qualification requirement for EAF evaluation required by RG 1.207.
Ratchet Analysis of Structures Under a Generalised Cyclic Load History
Authors: Lytwyn Michael , Chen Haofeng , Martin Michael
Published: November 2014

This paper introduces a new approach based upon the Linear Matching Method in order to obtain the ratchet limit of structures subjected to an arbitrary thermo-mechanical load history. This method varies from the traditional Linear Matching Method ratchet analysis, where the cyclic load history is decomposed into cyclic and constant components, instead calculating the ratchet limit with respect to a proportional cyclic load variation, as opposed to an additional constant load. The shakedown and limit load boundaries are initially obtained for the given structure, followed by the utilisation of a bisection procedure in order to calculate an approximate ratchet boundary based upon a predefined magnitude of ratchet strain per cycle. The method also yields the total and plastic strain ranges based upon perfect plasticity, for low-cycle fatigue post-processing considerations. The effects of analysing the ratcheting mechanism of structures undergoing a cyclic primary load that varies proportionally with a cyclic secondary load can be seen to lead to modified and less conservative ratchet boundaries compared to the traditional Bree solution in which the thermal ratcheting requirement (NB-3222.5) of ASME III is based upon. This paper introduces the theory, numerical implementation and verification of the proposed method via a series of example problems.
Biaxial Residual Stress Mapping for a Dissimilar Metal Welded Nozzle
Authors: Hill Michael R. , Olson Mitchell D. , DeWald Adrian T.
Published: November 2014

This paper describes a sequence of residual stress measurements made to determine a two-dimensional map of biaxial residual stress in a nozzle mockup having two welds, one a dissimilar metal (DM) weld and the other a stainless steel (SS) weld. The mockup is cylindrical, designed to represent a pressurizer surge nozzle of a nuclear pressurized water reactor (PWR), and was fabricated for Phase 2a of the NRC/EPRI welding residual stress round robin. The mockup has a nickel alloy DM weld joining a SS safe end to a low-alloy steel cylinder and stiffening ring, as well as a SS weld joining the safe end to a section of pipe. The biaxial mapping experiments follow the approach described earlier, in PVP2012-78885 and PVP2013-97246, and comprise a series of experimental steps and a computation to determine a two-dimensional map of biaxial (axial and hoop) residual stress near the SS and DM welds. Specifically, the biaxial stresses are a combination of a contour measurement of hoop stress in the cylinder, slitting measurements of axial stress in thin slices removed from the cylinder wall, and a computation that determines the axial stress induced by measured hoop stress. At the DM weld, hoop stress is tensile near the OD (240 MPa) and compressive at the ID (−320 MPa), and axial stress is tensile near the OD (370 MPa) and compressive near the mid-thickness (−230 MPa) and ID (−250 MPa). At the SS weld, hoop stress is tensile near the OD (330 MPa) and compressive near the ID (−210 MPa), and axial stress is tensile at the OD (220 MPa) and compressive near mid-thickness (−225 MPa) and ID (−30 MPa). The measured stresses are found to be consistent with earlier work in similar configurations.
Dynamics of a Pipe Conveying Fluid Flexibly Supported at the Ends
Authors: Kheiri Mojtaba , Païdoussis Michael P. , Costa del Pozo Giorgio
Published: November 2014

The subject of this paper is the study of dynamics and stability of a pipe flexibly supported at its ends and conveying fluid. First, the equation of motion of the system is derived via the extended form of Hamilton’s principle for open systems. In the derivation, the effect of flexible supports, modelled as linear translational and rotational springs, is appropriately considered in the equation of motion rather than in the boundary conditions. The resulting equation of motion is then discretized via the Galerkin method in which the eigenfunctions of a free-free Euler-Bernoulli beam are utilized. Thus, a general set of second-order ordinary differential equations emerge, in which, by setting the stiffness of the end-springs suitably, one can readily investigate the dynamics of various systems with either classical or non-classical boundary conditions.
Application of Seismic Isolation Systems to High-Raised Houses in Lowland Regions
Authors: Su H.-C. , Tsai C. S.
Published: November 2014

According to the statistics of the World Bank between years 1970–2010, most economy losses caused by disasters in rich countries were due to floods and earthquakes. The East Asia was the most disastrous area in terms of the death toll caused by earthquakes, which proved that the earthquake is unpredictable. To cope with the crisis of the rise of the sea level, the concept of Marine Cities has been proposed. The most famous one among these concepts is the Dutch amphibious house. People living in earthquake and flood prone areas should be aware of the threat from oceans. Therefore, Ministry of Interior in Taiwan passed the rule 4 No. 2 in the chapter of the design and construction regulations to allow the use of high-raised buildings for reducing life and property loss. Furthermore, the most threatening natural hazards we are facing over a long period of time are floods and earthquakes. When are focusing on the flood resistant buildings in flood-prone areas, we should also aim at the prevention of earthquake disasters.

The purpose of this study is to simulate the seismic behavior of the high-raised structures with different water levels, which are capable of flood resistance. We also propose a new seismic isolation system for these structures and study its efficiency in protecting these types of structures from earthquake damage. It appears from experimental results that the seismic responses of high-raised houses have been significantly reduced by the proposed device. Experimental results also disclosed that the proposed concept in this study is feasible for protecting structures in lowlands from damage resulting from floods as well as earthquakes.
Technical Basis for Proposed Fourth Revision to ASME Code Case N-513
Authors: McGill Robert O. , DeBoo Guy , Cipolla Russell C. , Houston Eric J.
Published: November 2014

Code Case N-513 provides evaluation rules and criteria for temporary acceptance of flaws, including through-wall flaws, in moderate energy piping. The application of the Code Case is restricted to moderate energy, Class 2 and 3 systems, so that safety issues regarding short-term, degraded system operation are minimized. The first version of the Code Case was published in 1997. Since then, there have been three revisions to augment and clarify the evaluation requirements and acceptance criteria of the Code Case that have been published by ASME. The technical bases for the original version of the Code Case and the three revisions have been previously published.

There is currently work underway to incorporate additional changes to the Code Case and this paper provides the technical basis for the changes proposed in a fourth revision. These changes include addressing the current condition on the Code Case acceptance by the US Nuclear Regulatory Commission (NRC), clarification of the Code Case applicability limits and expansion of Code Case scope to additional piping components. New flaw evaluation procedures are given for through-wall flaws in elbows, bent pipe, reducers, expanders and branch tees. These procedures evaluate flaws in the piping components as if in straight pipe by adjusting hoop and axial stresses to account for the geometry differences. These changes and their technical bases are described in this paper.
Large-Eddy Simulations of Turbulence-Induced Vibrations in Annular Pipe Flow
Authors: De Ridder Jeroen , Degroote Joris , Vierendeels Jan , Van Tichelen Katrien , Schuurmans Paul
Published: November 2014

This paper investigates the turbulence-induced vibration of a circular beam in annular pipe flow. Vibrations induced by turbulence are one of the causes of fatigue and fretting wear in process environments. Although the small-scale vibrations are normally not leading to immediate failure of structural components, they typically result in long term damage.

To predict the amplitude of these subcritical vibrations, current methods require an accurate description of the incident pressure field. However, measurements of cross-spectral pressure fields in annular geometries are rare. Models to describe the pressure field have a tendency to provide only descriptive information, after a series of experiments have been performed. Therefore this paper aims to predict the pressure field numerically, by means of wall-resolved large-eddy simulations.

In order to validate this approach the flow field of an experiment available in literature is computed. In the conditions simulated, water is flowing at 10 m/s in an annulus with a hydraulic diameter of 1.27cm. Pressure correlations obtained from the computations are compared to descriptive models such as the Corcos and Chase models. The numerical power spectra are also compared to experimental spectra.
A Novel High Cycle Fatigue Assessment of Small-Bore Side Branches: Tailor-Made Acceptable Vibration Levels Based on the Remaining Life of Existing Structures
Authors: van Beek Pieter , Pijpers Richard , Macdonald Kenneth , Maljaars Johan , Lunde Knud , Korst Harry , Hansen Frode
Published: November 2014

In the process systems of offshore installations, welded small-bore side branches can prove vulnerable to high-cycle fatigue failure due to vibrations. This is especially the case for welded connections at tie-in points to the main pipe which are often critical details. International standards and guidelines therefore provide maximum acceptable vibration levels to ensure long term safe operation. In some guidelines, however, these acceptable vibration levels are phrased in terms of screening levels and in practice can be unduly conservative. Process pipework might then unjustly be regarded as unsafe based on measured vibrations in the field. This is especially true for offshore systems, which are characterized by low mechanical damping in the structure. This may result in overdesigned piping or over-conservative operational limits in order to keep vibration levels within the acceptable range. Furthermore, the screening methods and any detailed fatigue assessments typically use established stress-life (S-N) based fatigue design methods where uncertainty exists in the very high-cycle regime.

This paper describes a novel and advanced tailor-made fatigue assessment method whereby acceptable vibration levels are based on maximum acceptable stress ranges for individual side branches. The acceptable stress ranges for each critical welded connection are based on a fracture mechanics analysis of fatigue crack growth. This method also minimizes the cantilevered (overhung) mass of small-bore side branches, whilst remaining safe for long-term operation.

To illustrate the strength of the assessment methodology in practice, this paper describes the application of the procedure to a 2″ side branch connected to a main piping system. A fracture mechanics model and a detailed 3D finite element model are made. By comparing the stress ranges from the fracture mechanics model with the normalized stress ranges obtained from the dynamic FE analysis, maximum acceptable vibration levels for this particular side branch have been derived. The method is validated with experimental modal analysis and strain gauge measurements.
Study on Viscous-Friction Hybrid Damper Installed in Industrial Plants
Authors: Enomoto Yu , Fujita Satoshi , Minagawa Keisuke
Published: November 2014

Every year, many earthquakes happen in Japan. Many high rise structures which are in a long distance from the hypocenter of the earthquake resonate with the long period ground motion. In industrial plants, there are structures which have a long natural period such as boiler system, and there is a risk of resonating by long period ground motion. Recently, many industrial plants require countermeasure for long period ground motion. Various viscous dampers have been developed and applied to actual structures to suppress vibration response. However, the vibration control performance decreases with the long duration time of earthquake because of a temperature rise of the viscous material. Therefore, there is concern that these viscous dampers can not suppress vibration response in case of long period ground motion. In order to solve this problem, a viscous-friction damper in series is proposed in this study. Then, in this hybrid damper, the friction damper can absorb vibration energy as well in case of the long period ground motion. In this paper, seismic response analysis is conducted to confirm performance of hybrid damper. We propose using genetic algorithm to select parameters of the hybrid damper.
Numerical Modeling of Turbulent Cavitation Flows in Safety Relief Valves
Authors: Couzinet Anthony , Gros Laurent , Pinho Jorge , Chabane Said , Pierrat Daniel
Published: November 2014

Safety relief valve (SRV) is still the ultimate security component of pressure vessels or piping equipment. It does not take the place of a regulating or control valve but it aims to protect devices and people by preventing damage due to overpressure in the system. This is ensured by discharging an amount of fluid when excessive rising pressure occurs. For the incompressible flows, the discharge coefficient of the relief valve can be modified by cavitation development under specific operating conditions. Then, the sizing of the valve doesn’t correspond to the flow discharged resulting in severe damage.

This study aims to demonstrate the capability of numerical modeling to predict the evolution of discharge coefficient under cavitation conditions. URANS simulations have been performed with ANSYS CFX 13.0 using Shear Stress Transport modeling. A Rayleigh-Plessey model is used to predict the development of cavitation in the relief valve. A modification of the saturation vapor pressure is proposed in the cavitation model to take into account the turbulent effects on the cavitation development.

Additionally a Plexiglas mock-up has been built for flow visualization and two valve discs are used to measure the discharge coefficient or the flow force acting on the valve. Numerical and experimental approaches are compared first by analyzing qualitative results through flow visualization and also by evaluating hydraulic characteristics of the SRV.
Design and Maintenance in an IAEA Technical Guidelines on Fluid-Structure Interaction
Authors: Inada Fumio , Nakamura Tomomichi , Nishihara Takashi , Kaneko Shigehiko , Kim Manwoong , Ainsworth Robert A. , Takahashi Shiro
Published: November 2014

In nuclear power plants, fluid structure interactions (FSI) occurring in component systems can cause excessive forces or stresses to the structures resulting in mechanical damages that may eventually threaten the structural integrity. FSI in the guidelines includes flow-induced vibration, water hammer, and pipewhip. It can also include movement, deformation, or fracture of equipments by tsunami etc. They can be issues of design and maintenance. Authors cannot find complete guidelines to correspond to the FSI phenomena which can be important in the design and maintenance of nuclear power plants. Based on the background, International Atomic Energy Agency (IAEA) has drafted guidelines on FSI. This paper summarizes general description of FSI as well as design and maintenance against FSI.
Fluid-Loaded Vibration due to a Non-Homogeneous Turbulent Boundary Layer
Authors: Tomko Jason R. , Morris Scott C.
Published: November 2014

Flow-induced structural acoustics involves the study of the vibration of a structure induced by a fluid flow as well as the resulting sound generated and radiated by the motion of the structure. A thin rectangular, structure, non-fluid-loaded was excited by turbulent boundary layer flow. A method called magnitude-phase identification (MPI) is derived to measure modal information from a structure using only two-point measurements. Using MPI, the mode shapes and the auto-spectral density of vibration of each mode was measured and found to agree well with the theoretical values. When the non-fluid-loaded structure was excited with a spatially non-homogeneous wall pressure field or fluid-loaded structure was excited with a spatially homogeneous wall pressure field, the measured mode shapes were found to be the same as those predicted by theory. When a fluid-loaded structure was excited with a spatially non-homogeneous wall pressure field, the mode shapes were found to change. This suggests that standard modal analysis may not be sufficient to predict the vibration of fluid-loaded structures, as such theory assumes that the mode shapes of the structure are independent of the method by which the structure is excited.
Additional Data Concerning French PWR RPV Steel to Evaluate the Relevance of a Size Effect Correction on Toughness in the Ductile-to-Brittle Transition
Authors: Jacquemoud C. , Delvallée-Nunio I. , Nédélec M. , Balestreri F.
Published: November 2014

In the ductile-to-brittle transition range of ferritic steels, fracture toughness exhibits a size effect. Up to now, in the safety demonstration of the French Reactor Pressure Vessel (RPV) integrity, a size effect correction has been considered by the operator to take into account fracture toughness variation of ferritic steels with crack length. The correction consists in increasing the toughness estimated on the RCC-M curve by a factor which depends on a reference length and on the crack length considered.

IRSN has already examined the relevance of this correction through statistical analysis of toughness results coming from two ferritic steel databases. To complete its evaluation on French RPV steel, IRSN has supported a large experimental campaign on 16MND5 steel at different temperatures in the ductile-to-brittle transition (from −150°C to −50°C), including tests on various Compact Tension (CT) specimen geometries. Specimens with semi-elliptical crack have been also considered.

The results confirm the observations made in its previous study: a size effect exists on mean or median toughness, for the latter more or less in accordance with Beremin theory. Nevertheless, the minimum toughness appears to be independent of the specimen geometry. This indicates that the use of a size effect correction on minimum toughness is not relevant.
Benchmark Evaluations to Compare R6 Calculations to European Engineering Assessment and Leak-Before-Break Methods Based on STYLE Mock-Up Experiments
Authors: Madew Colin , Sharples John , Budden Peter , Lauerova Dana
Published: November 2014

As part of the recent STYLE European project, three large scale mock-up experiments (Mock-up 1, Mock-up 2 and Mock-up 3) were performed. The Mock-ups were representative of nuclear power plant locations containing welds or cladding and contained an initial defect, either through-wall or surface breaking, and were loaded under four point bending conditions.

Benchmarks based on each of these experiments were launched to investigate current Engineering Assessment Methods (EAMs) and Leak-before-Break (LbB) procedures used throughout Europe and how the application of these methods compare to each other and to the experimental data. Parameters that were specified for the benchmark participants to evaluate included crack opening displacement (COD), critical crack size, limit load, and load vs various amounts of ductile tearing.

This paper presents and compares the results of the calculations performed by the participants in the benchmark. It focuses on the AMEC calculations using R6 and draws conclusions regarding its relative conservatism compared with each of the other methods and through comparison with the results of the Mock-up experiments.
Reference Stress-Based J Estimation of Circumferential Through-Wall Cracked Elbow With Unequal Thickness Under Bending
Authors: Bae Kyung-Dong , Kim Chul-Goo , Murni Zalikha , Kim Seung-Jae , Kim Yun-Jae
Published: November 2014

In large plant facilities, elbow and straight pipe have large potion in whole piping system. When the cracks are initiated in pipe, the cracks have to be evaluated using fracture mechanics parameter such as J-integral. Unlike calculating J-integral of straight pipes, estimation J-integral of elbow using finite element analysis is not easy. Because the effect of geometries for crack behavior of elbow are more complex than straight pipes. Also, there is another difference between elbow and straight pipe. That is unequal thickness in intrados and extrados. Unequal thickness of elbow pipes generally occurs by the manufacturing process. Thickness in intrados is getting thicker than nominal thickness but thickness in extrados is getting thinner than nominal thickness. So first, this paper provides a reference stress-based J-integral estimation of circumferential through-wall cracked elbow with equal thickness. And this paper provides also a reference stress-based J-integral estimation of circumferential through-wall cracked elbow with unequal thickness. To find the reference stress-based approximate J-integral, various ratio of thickness (t), pipe radius (r), pipe bend radius (R) and crack length (θ) are considered. And three-dimensional finite element analyses using elastic property for elastic crack behavior and elastic–perfectly plastic property for limit load are performed. Finally Results in this research are presented in the failure assessment diagram (FAD) space.
Evaluation of Fracture Toughness Behavior of Polyethylene Pipe Materials
Authors: El-Bagory Tarek M. A. A. , Sallam Hossam E. M. , Younan Maher Y. A.
Published: November 2014

The main purpose of the present paper is to investigate the effect of strain rate, specimen thickness and welding on the fracture toughness. The material of the investigated pipe is a high-density polyethylene, (HDPE) which is commonly used in natural gas piping systems. The welding technique used in this study is butt fusion (BF) welding technique. The crosshead speed ranged from 5 to 500 mm/min and specimen thickness ranged from 9 to 45mm for both welded and unwelded specimens at room temperature, Ta equal 20 °C. Curved three point bend (CTPB) specimens were used to determine KQ. Furthermore, the results of fracture toughness, KQ, will be compared with the plane strain fracture toughness, JIC, for welded and unwelded specimens. The experimental results revealed that KQ increases with increasing the crosshead speed, while KQ decreases as the specimen thickness increases. The investigation reveals that the apparent fracture toughness, KQ, for HDPE pipe of unwelded specimen is greater than that of corresponding value for welded specimen. The same trend was observed for the plane strain fracture toughness, JIc. At lower crosshead speeds there is a minimum deviation in KQ between welded and unwelded specimens, while the deviation becomes larger with increasing crosshead speed.
Improving Creep-Fatigue Design Methodology for Advanced Ferritic-Martensitic Steels
Authors: Li Meimei , Soppet William K. , Majumdar Saurin , Natesan Ken
Published: November 2014

Advanced materials are a critical element in the development of advanced sodium-cooled fast reactors. High temperature design methodology of advanced materials is an enabling reactor technology. Removal of unnecessary conservatism in design rules could lead to more flexibility in construction and operation of advanced sodium-cooled fast reactors. Developing mechanistic understanding and predictive models for long-term degradation phenomena such as creep-fatigue are essential to the extrapolation of accelerated laboratory data to reactor environments with high confidence, and to improve the American Society of Mechanical Engineers (ASME) code rules. This paper examines the cyclic softening and stress relaxation responses and associated plastic damage accumulation for Grade 91 ferritic-martensitic steel. Creep-fatigue experiments were conducted at 550°C in strain-controlled mode under various types of creep-fatigue loading conditions. Constitutive models were developed to describe the creep-fatigue interaction in G91.
Study of Crack Propagation Under Fatigue Equibiaxial Loading
Authors: Bradaï S. , Gourdin C. , Gardin C.
Published: November 2014

In some nuclear power plant components, the fatigue loading may be equibiaxial because of thermal fatigue. As a consequence, the potential impact of multiaxial loading on the fatigue life of components is a major concern. However, few experimental data are available about austenitic stainless steels. It is essential to improve the fatigue assessment methodologies taking into account the potential equibiaxial fatigue damage. It implies obtaining experimental data on the considered material, with a strain tensor corresponding to equibiaxial tension. Many multiaxial criteria, based on thermal fatigue tests or uniaxial fatigue tests, were proposed by Von Mises, Zamrik and other researchers [cited in 1]. Yet, additional thermal fatigue tests and isothermal equibiaxial fatigue tests must be carried out. In this context, a new experimental fatigue device FABIME2 [cited in 2] is developed, in the LISN, in collaboration with EDF and AREVA, in order to characterize accurately the possible equibiaxiality effect on the fatigue behavior of the 316L austenitic stainless steel.

This paper is focused on the identification of a new criterion in order to be able to take into account the possible effect to the equibiaxial loading on fatigue life. It will be identified by a comparison of experimental results and numerical predictions. In this aim, a test campaign with several experiments was realized on the new FABIME2 device, in order to determine the crack growth rate from an equibiaxial fatigue loading. Propagation tests were carried out on 316L austenitic stainless steel CT specimens, at room temperature, in order to obtain the Paris law [cited in 3]: (crack growth rate da/dN versus the applied stress intensity factor range ΔK). The crack growth is followed throughout equibiaxial test. This allows obtaining, the da/dN evolution, and the corresponding ΔK values. A finite element modeling done with CASTEM®, will be proposed to simulate the crack propagation in the FABIME2 specimen using a 3-dimensional approach, considering a semi-elliptical crack shape.
Cleavage Crack Path Prediction in a PWR Vessel Steel
Authors: Yang Xiaoyu , Marie Stéphane , Jacquemoud Clémentine
Published: November 2014

Cleavage crack propagation has been tested for three different geometries of Compact Tensile (CT) specimens: CT25, CT50 and extended CT25 (CT25 with CT50 width) (Figure 3). The experimental results show that the crack paths are straight for CT25 and CT50, but they are unstable and curved for extended CT specimens (Figure 5 to 7).

Numerical computation had been performed by extended finite element method (XFEM) in CAST3M software. 2D modeling was used in order to predict the crack path. The analysis was based on a local non-linear dynamic approach with a RKR fracture stress criterion depending on temperature and strain rate.

In order to simulate the curvature of the cracks path, a statistical effect was introduced in the model to take into account the spatial distribution of cleavage initiators, which is the characteristic of cleavage fracture. At each step of propagation during the modeling, the direction was randomly chosen, according to a uniform defects distribution.

The numerical results show a good agreement with experience. The different crack paths were curved in extended CT25, but remained almost straight in CT25 and CT50 specimens, despite of the instability introduced in the modeling in the propagation direction. These results show that the statistics of micro-defects can induce, jointly with the geometry of specimen, a large scatter of crack propagation paths.
Process Optimization of Ultrasonic Shot Peening by Realistic Modeling of Beads Motion
Authors: Brosse Alexandre , Le Moal Simon , Lacroix Rémi , Mourgue Philippe , Robin Vincent , Gilles Philippe
Published: November 2014

In the nuclear industry surface mechanical treatments are used in order to improve the surface integrity of the component, which increases their lifetime regarding corrosion and fatigue damages. A good understanding of these processes and their consequences is required to ensure the efficiency and perpetuity of such mitigation treatment.

This study focuses on the ultrasonic shot peening process. It consists in shooting at high speed small steel beads on the part to be treated by using a high frequency vibration device. Parameters such as the number and the size of beads, the input frequency and the dimensions of the chamber can induce large ranges of impact velocity and coverage. In order to help manufacturers to control the treatment applied on their components, a numerical model has been developed. It accounts for the shocks of the beads against the walls of the chamber, the peening head and between beads, describing their motions accurately.

In this paper, we will introduce the numerical model developed to simulate the motions of beads in the peening chamber. Special attention will be taken to the determination of the restitution rates related to the different materials. Results of the model will be shown for different process parameter (e.g. the number of beads), and a thorough analysis of their effects on the workpiece will be presented, including a comparison with some experimental results.
Main Steam Line Break Loads on BWR and ABWR Steam Dryer
Authors: Faal-Amiri Asgar , Salehzadeh Amir , Shoulders Jacky , Yuan Peng
Published: November 2014

In a boiling water reactor (BWR) and advanced boiling water reactor (ABWR) a main steam line pipe rupture in the main steam piping system, hereafter called main steam (MS) line, will create a decompression wave and a pressure disturbance that moves through the MS line toward the reactor pressure vessel (RPV). It expands into a large region transmitting a compression wave at acoustic speed and spreads as an acoustic wave over the adjacent dryer plate. The initial acoustic pressure force on the dryer is expected to spread from an origin at the steam line attachment. It reflects back toward the RPV wall and again to the dryer until it dissipates. This is expected in a space that is not of uniform spacing because the dryer surface is nearly flat and the vessel wall is a curved surface. The acoustic load region is bounded by the steam dryer outer surface and RPV inner wall surfaces. In this paper, simplified, conservative modeling is applied in this approach to obtain reasonable bounding loads. The method is compared against the result of a detailed fine-structure Computation Fluid Dynamic (CFD) analysis using the same input data. Therefore, the simplified method may be used to quickly estimate conservative decompression forces on a dryer surface.
The Effect of Aspect Ratio and Angle of Attack on the Transition Regions of the Inverted Flag Instability
Authors: Cossé Julia , Sader John , Kim Daegyoum , Cerdeira Cecilia Huertas , Gharib Morteza
Published: November 2014

The fluttering flag instability has been thoroughly studied through experimental, computational and theoretical means. However, each of these studies only considers the boundary conditions where a flagpole or other tethering mechanism precedes the plate in the fluid flow. Under the inverse condition, where the so-called flag is fixed by its downstream edge in the fluid flow, three regions of behavior exist: straight, flapping, and bent back. This paper expands on these findings by closely examining the transition regions between straight and flapping and flapping and bent back. The onset mechanism of the instability and the terminating mechanism are shown to be dependent on different factors. The region of flapping occurs within a narrow range of non-dimensional bending stiffness, with the region boundaries depending on the aspect ratio and angle of attack of the plate.
Proposed Modifications to API 579-1/ASME FFS-1 2007 Fitness-for-Service
Authors: Osage David A. , Macejko Brian , Brown Robert G.
Published: November 2014

The first edition of API 579 Recommended Practice for Fitness-For-Service was published in 2000, and subsequently recognized as the de facto international fitness-for-Service standard in the refining and petrochemical industry. The second edition of this document, API 579-1/ASME FFS-1 Fitness-For-Service, was published in 2007 as a joint standard of the American Petroleum Institute (API) and the American Society of Mechanical Engineers (ASME). The second edition included fitness-for-service assessment procedures applicable to other industries including fossil utility and pulp and paper. Work on the third edition of API 579-1/ASME FFS-1 has begun with many planned technical improvements to further address industry needs. These improvements include the edition of a new part on fatigue evaluation, updates to the assessment procedures for crack-like flaws and remaining life assessments for components operating at elevated temperatures, and a rewrite of residual stress solutions for use in the evaluation of crack-like flaws based on the latest state-of-the-art approaches. In addition, the third edition will be reorganized where by technical information currently placed in separate annexes that currently appear after all of the parts will be re-deployed as annexes to specific parts with a similar topic. This new organization will facilitate use and also simplify future updates to the document. An overview of proposed improvements to fitness-for-service technologies is provided along with a description of the new organization of API 579-1/ASME FFS-1.
Development of a Numerical Model for Quasi-Periodic Forces of Two-Phase Cross Flow in Tube Bundles
Authors: Zoghlami Sarra , Béguin Cédric , Étienne Stéphane
Published: November 2014

To reduce the damage caused by induced vibrations due to two-phase cross flow on tube bundles in heat exchangers, a deep understanding of the different sources of this phenomenon is required. For this purpose, a numerical model was previously developed to simulate the quasi periodic forces on the tube bundle due to two-phase cross flow. An Euler-Lagrange approach is adopted to describe the flow. The Euler approach describes the continuous phase (liquid) using potential flow. The dispersed phase is assumed to have no interaction on liquid flow. Based on visual observation, static vortices behind the tube are introduced. The Lagrange approach describes the dispersed phase (gas). The model allows bubbles to split up or to coalesce. The forces taken into account acting on the bubbles are the buoyancy, the drag and induced drag, the added mass and induced added mass and impact force (bubble-bubble and bubble-tube). Forces taken into account acting on the tubes are impact forces and induced drag and added mass forces. This model allows us to obtain quasi periodic force on tube induced by two-phase cross flow of relative good magnitude and frequency contains. The model still needs improvement to bring us closer to experimental data of force, for example by introducing a dependency between the void ratio and the intensity of the vortex and by taking into account the bubbles deformation.
Predicting Fluidelastic Instability in Tube Array With Potential Theory
Authors: Plagnard T. , Béguin C. , Étienne S.
Published: November 2014

This paper studies the possibility to use potential theory to predict fluidelastic instability critical velocity in tube bundles. Potential flow is calculated semi analytically using Laurent expansions with the addition of discrete vortices behind the tube. The only experimental criterion used in this approach is the location of vortices behind the tubes. Using the linearized unsteady Bernoulli theorem we are able to model fluid forces as added mass, damping and stiffness effects. Fluid forces include coupling terms; that is the force on another tube induced by tube acceleration, velocity and location. The tube array is then described by a mass, damping and stiffness. The fluidelastic instability critical velocity becomes the solution of a linear eigenvalue problem. This approach has been compared with several experimental values of mass, damping and stiffness measurements, as well as the critical velocity. Mass matrix is in a very good agreement with experimental values, however damping and stiffness models still need some improvement. In the end, the model is able to predict the critical velocity within 20% of experimental values. This approach does not need stiffness experimental values (stability derivative) nor time delay as the stiffness, damping and mass matrices are calculated independently. The main purpose of this work is to understand the effect of induced forces involved in the fluidelastic instability.
Internal Crack Growth Simulation Using S-Version FEM
Authors: Kikuchi Masanori , Yamada Shinya , Serizawa Ryosuke , Yulong Li
Published: November 2014

In nuclear power plant, there is a proximity rule to evaluate multiple inner cracks [1]. Inner cracks are generated inside of the structure in different manners. There are many parameters which affects the growing processes of inner cracks. They are; locations, slant angles, aspect ratio of each inner crack and distances between adjacent inner cracks. When multiple inner cracks are detected, proximity rules are proposed. But due to the complexity of the problem, it is necessary to verify proposed proximity rules. But experimental study is very difficult due to existence of many parameters, and crack growth occurs inside of the structure. Numerical simulation is needed for this purpose.

This problem is simulated using S-version FEM [2]. Using S-FEM, inner crack is modeled independently from global structure, and crack growth is easily simulated. In maintenance code of nuclear power plant, initial defects are modeled as elliptical cracks in a normal plane to tension loading direction, and growth rate is estimated on this plane. But by using S-FEM, realistic defect shape is modeled, and crack growth by fatigue is simulated. Usually, such small defects are subjected to multi-axial loading, and crack growth behaviors are very complicated. Finally, detect shape becomes elliptical or circular crack in a plane normal to tension loading direction in the structure. Fatigue cycles for these growing processes are calculated, and conservativeness of this maintenance code is discussed. Parametric studies are conducted for this problem, and proximity rules are verified with numerical results.
Water Hammer (With FSI): Exact Solution — Parallelization and Application
Authors: Loh Kelvin , Tijsseling Arris S.
Published: November 2014

The 1D fully coupled Fluid-Structure Interaction (FSI) model can adequately describe the water hammer effect on the fluid, and the structural behaviour of the pipe. This paper attempts to increase the capability of using an exact solution of the 1D FSI problem applied to a straight pipe with a valve. The work builds upon a simple recursion algorithm to obtain exact solutions. This paper describes the attempts to parallelize the time-consuming algorithm and presents an optimization case study. The algorithm has been parallelized using a Master-Slave MPI model for scalability. The applicability of this all has been explored by an optimization case study, which seeks the optimal damping coefficient of a dashpot connected to the valve to reduce the structural stresses in the pipe wall and the pressure in the fluid. Thus, an external damper is used to mitigate internal fluid transients.
Cluster Analysis of Acoustic Emission Signals During Carbon Steel Pitting Corrosion Process
Authors: Zhang Zhongzheng , Ye Cheng , Jiang Jun
Published: November 2014

In order to study acoustic emission (AE) signals characteristics of pitting corrosion on carbon steel, Pitting corrosion process on carbon steel in 6% ferric chloride solution was monitored by AE technology. K-mean cluster algorithm was used to classify the monitored AE signals, in which the duration, counts, amplitude, absolute energy and peak frequency were analyzed as the AE signals characteristics, and different types AE sources were identified. The results showed that there were mainly three type AE sources during carbon steel pitting corrosion process in ferric chloride solution, and the different types AE sources could be classified by cluster analysis. The research results have some certain significance for AE monitoring of pitting corrosion on carbon steel.
Detection of Defects in Pipes and Elbows Using Guided Waves
Authors: Zhang Pugen , Zhou Shaoping , Lv Wenchao
Published: November 2014

This paper deals with the detection of circumferential cracks of different areas in elbow pipes using the guided waves in mode of L(0,2) which are excited by a piezoelectric transducer. The experimental results show that the circumferential cracks can be located in axial position for bend straight side by the reflected echo of defects in the pipes. The detection sensitivity depends on the location of the cracks in bend areas of the pipes. It is easier to detect cracks in the extradose of elbow while harder to detect those in the other locations of the bend. There is a relationship between the detection sensitivity and the frequency of guided waves. The signal-to-noise ratio when detecting the crack before and beyond elbows is highest for the frequency ranges from 120kHz to 130kHz; the crack on the intradose of elbow can be inspected more effectively when using frequencies near 80kHz. Therefore, the combination of high-frequency and low-frequency is used to inspect elbows. The propagation behaviors in elbows are investigated by using numerical simulation. The results of simulation intuitively explain the experimental phenomenon.
Material Damage Analysis and Life Prediction of Cr5Mo Used as Furnace Tubing
Authors: Xu Feng , Ye Yufeng , Xia Li
Published: November 2014

Cr5Mo furnace tubes have served in a coking furnace nearly 15 years. For the purpose of risk reduction and to assure a safe long term stable operation of the furnace, these tubes have been investigated by measns of macrographic observation, chemical composition analysis, mechanical property analysis, hardness and metallurgical structure analysis, etc. The experiment results shows that after a long period serve at high temperature, the hardness of the tube has decreased in 15 years. However, the hardness of inner wall is higher than the others, from which we can infer that the inner wall of the tubes is carburized. Taking GB9948-2006 as a reference standard, the yield stress of the furnace tube in normal temperature has decreased by 16%, and the yield stress in high temperature is also failed to fit the standard. Metallographic analysis shows that the grain fineness is 6 grade and the nodulizing grade is 3.5 grade, pearlite spheroidization is getting severer and it will reduce the creep limit and creep rupture strength. Based on the result of high temperature endurance test, isotherm method and L-M extrapolation are adopted to predict the remaining life of furnace tubes, assessment shows that these furnace tubes are able to serve for another cycle under the operating temperature of 650°C and the stress of 18MPa.