bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Welding Simulation of a Vessel Head Adapter: Influence of Modelling Assumptions
Authors: Gallee Sébastien , Robin Vincent , Gommez Florence , Courtin Stéphan , Brosse Alexandre , Lacroix Rémi , Leconte François
Published: December 2016

In nuclear industry, most of heavy components and reactor coolant lines have a large thickness and their manufacturing processes require multi-pass welding. When low-alloy steel components are concerned, the assembly process is often performed in several stages, such as a cladding, a buttering and a Post Weld Heat Treatment (PWHT) before joining two materials without phase transformations. The distortions induced by the welding operation might be an issue and residual stresses could be significant and play a role on the weldability. For these reasons, AREVA has placed a lot of effort to improve the reliability of numerical simulation of its welding processes, in order to have a better understanding of the involved phenomena and also to predict the residual stress state through the structure [1], [2] and [3] because this numerical simulation can be used to select the manufacturing process in the early phase of welded component design.

The aim of the simulations presented in this paper is the investigation of the final residual state of a nozzle placed at the central position of the vessel head. The computations are performed according a robust methodology packaged in AREVA OSS tool [4] which is based on SYSWELD™ Finite Element solver [5]. Two welding configurations are investigated. The first one is a mock-up with an “open” narrow gap, the groove filling being performed by a manual welding process using electrode coatings. The second one is a mock-up with a “closed” narrow gap, the groove filling being performed by an automatic TIG process. After the comparison of these two configurations, a special investigation is performed on the “open” narrow gap mock-up. The influence of the vessel head buttering before the groove filling is investigated, as well as the efficiency of the PWHT performed after the buttering operation.
Effect of Test Frequency on Hydrogen-Enhanced Fatigue Crack Growth in Type 304 Stainless Steel and Ductile Cast Iron
Authors: Matsunaga Hisao , Nakashima Takuya , Yamada Kosei , Matsuo Takashi , Yamabe Junichiro , Matsuoka Saburo
Published: December 2016

The effect of hydrogen gas environment (external hydrogen) and hydrogen-charging (internal hydrogen) on the fatigue crack growth (FCG) in two materials, austenitic stainless steel Type 304 and ductile cast iron, was investigated at various test frequencies. The pressure of hydrogen gas was 0.7 MPa. Both in the tests of external hydrogen and internal hydrogen, ratio of hydrogen-induced FCG acceleration was gradually increased with a decrease in test frequency in the range of 10 ∼ 0.1 Hz, and then peaked out at 0.1 ∼ 0.01 Hz. The frequency at the maximum acceleration was dependent on materials and test types (i.e. external hydrogen or internal hydrogen). It has been pointed out that, in the test of external hydrogen, a small amount of oxygen impurity contained in hydrogen gas, if any, adsorbs on newly-created crack surface, which inhibits hydrogen penetration into the material near crack tip. Lower frequency allows longer time for oxygen adsorption, and consequently, hydrogen-induced acceleration cannot be prominent at very low frequencies (e.g. 0.001 Hz). However, in this study, similar frequency dependence of hydrogen-induced FCG acceleration was also observed in the case of internal hydrogen. The results inferred the presence of another mechanism producing the frequency dependence of hydrogen-induced FCG acceleration, i.e. hydrogen-induced slip localization dominated by the gradient of hydrogen concentration ahead of crack tip.
Application of Stress-Modified Fracture Strain Model to Full-Scale Pipes With a Circumferential Crack in the Center of Welds
Authors: Ryu Ho-Wan , Kim Hune-Tae , Jung Hyun-Woo , Kim Yun-Jae
Published: December 2016

A lot of welded joints are required to connect the junctions of components in the complex piping system. The structural integrity assessment on welded pipes is especially important, because the weldments are susceptible to material discontinuities, flaws and residual stresses. Finite element (FE) damage analysis can be useful and effective method for an accurate assessment on extensive structures. For the case of welded joint, the numerical method is necessarily required to assess complex features because of material discontinuities and flaws. This study provides a simple numerical method to simulate ductile tearing in welded full-scale pipes. Stress-modified fracture strain model is applied to finite element analysis with a stress reduction technique. An element-size-dependent critical damage model is also implemented in the full-scale pipe simulations. From the results of simulation, deformation response and characteristic loads are compared with experimentally measured values to verify the application of damage model on weld material. As a result, the predictions of finite element damage analysis are in good agreement with experiments.
Discussion on the Interference Phenomenon of Multiple Failure Mechanisms and Determination of Dominant Failure Mechanism for Pressure Equipments
Authors: Xuedong Chen , Zhibin Ai , Rongrong Li , Zhichao Fan , Shuangqing Xu , Yanan Zhao
Published: December 2016

For petrochemical pressure vessels subjected to complex media environment, the competition, inhibition, promotion and interference of multiple failure mechanisms have been discussed by several failure case analyses and experimental investigation. The main factors that influence formation of dominant failure mechanism are analyzed and the judgment principles of the dominant failure mechanism are raised in the case of interaction of multiple failure mechanisms. In this paper, relevant mechanisms are also discussed, e.g. intergranular corrosion and intergranular stress corrosion failure mechanisms of austenitic stainless steel, failure mechanisms of austenitic stainless steel when Cl− and alkaline environment exist concurrently and failure mechanism of austenitic stainless steel when medium such as Cl−, CO2, H2S, H2O, etc. exist concurrently.
On the Use of Miniaturized CT Specimens for Fracture Toughness Characterization of RPV Materials
Authors: Chaouadi Rachid , van Walle Eric , Scibetta Marc , Gérard Robert
Published: December 2016

The tendency to reduce specimen size for fracture toughness characterization of structural materials is gaining a spectacular interest in particular for irradiated materials. Indeed, the miniaturized compact tension (mini-CT) with a size of 10×10×4.2 mm is becoming very popular. With such a small volume, a large number of mini-CT specimens can be extracted from broken Charpy impact specimens and therefore makes this geometry very attractive and consequently several round robin exercises are organized to qualify this geometry. SCK•CEN has gained a lot of experience since the first usage of this geometry more than a decade ago. This geometry was qualified and tested in both unirradiated as well as irradiated condition.

This paper overviews the SCK•CEN experience using the mini-CT geometry for fracture toughness characterization. In particular, it discusses the reliability of this geometry in comparison to large specimens such as the precracked Charpy and compares the advantages and limitations of such a geometry to derive some recommendations.
Structural Response From Pressure-Pulse Propagation in Non-Newtonian Slurries With a Void Fraction of Non-Condensable Gas
Authors: Ligon Thomas C. , Schmitt Kyle P. , Minichiello John C.
Published: December 2016

The Hanford Tank Waste Treatment and Immobilization Plant (WTP) will process waste slurries capable of both generating and retaining a dispersed non-condensable gas phase. Given sufficient time, the generated bubbles may coalesce to form pockets of flammable gas. An ignition of the gas pocket may result in a deflagration or detonation that may transmit a pressure pulse into the surrounding gas-liquid slurry. The transmitted pressure pulses will impose structural loads on the pipe and associated supports. This paper describes experiments that generated pressure pulses in a stainless steel pipe filled with a non-Newtonian simulant with various void fractions of non-condensable gas. The focus of this paper is on the measured pipe strains. The details of the propagation of the pressure pulses in the compressible media are described in a separate paper: PVP-2015-45970 [1]. The propagating pressure pulses produced both quasi-static and dynamic excitation of the pipe, and the differences in the nature of the response were determined to be related to the experimental methods used to generate and measure pressure pulses. Finite-element predictions qualitatively reproduced the pipe response characteristics from the experiments.
Liquid Droplets in Contact With Cold Non-Equilibrium Atmospheric Pressure Plasmas
Authors: Vasko Christopher A. , Giannopapa Christina G.
Published: December 2016

Recently, cold, non-equilibrium atmospheric pressure plasmas (CAPs) and their active chemistry have been extensively investigated to the benefit of a wide array of applications such as biomedical and industrial applications mainly in the area of materials processing and chemical synthesis, amongst many others. In general, these plasmas operate at standard conditions (i.e. 1 atm, 300K), are small (∼ cm) and rather simple to operate in comparison to other plasmas. Their complex chemistry gives rise to a wide array of both stable and transient reactive species: such as O3, H2O2, OH and NOx, next to charged species and (V)UV-radiation. This chemistry is the reason for their wide spread application and has already found many industrial applications from waste water treatment, stain free detergents and industrial scale production of oxidants. In recent years, bactericidal effects of CAPs gained increasing attention for applications such as dermatology, disinfection, dentistry and cancer treatment or stimulated blood coagulation. This paper aims to highlight recent research into new biological applications for complex mission scenarios involving humans in remote locations using CAPs for disinfection, bleaching or wound healing. Results using radiofrequency plasma jets for the inactivation of Pseudomonas aeruginosa are summarized, highlighting the importance of liquid plasma interactions. Work with such a CAP paved the way for a promising application in the field of biomedical applications presented here. It involves surface barrier discharges which can be used to treat larger surfaces compared to jets. Their physical construction, using floating or contained electrodes, offer a convenient way of controlling electrical current on a large scale, 3D treatment of both conducting and insulating surfaces with minimal heating. These devices may be tailored to specific skin treatments, allowing fast and effective treatment of larger skin surfaces while following the shape of the skin. This might reduce the need for bactericidal agents and would be a valuable application to assist humans in remote locations. These emerging technologies could be essential both for human health care under extreme conditions, as well as for research itself (sterilisation of tools and large areas, etc.). Especially in the absence of abundant resources (antibiotic agents, disinfectants and the like) alternative approaches to support humans in isolated locations have to be developed. Applications based on a good understanding of plasma chemistry would empower health care under extreme conditions to efficiently use and manage in situ resources. Their low mass, compact size, low power consumption and high reliability could make them essential use under extreme conditions.
Characterizing Successful Robotic Insertion and Removal From a Dry Storage Cask Using Peg-Like Jamming and Wedging Analysis
Authors: McNelly Brendan P. , Leary Robert , Brennan Sean , Reichard Karl
Published: December 2016

This paper describes the derivation and experimental validation of geometric equations that govern insertion and extraction of a robotic inspection system that operates in gaps around vertical dry storage casks. During insertion, a robotic system may become jammed due to unbalanced forces acting on the robot, or wedged due to over-sized robot geometry. The robot must be removable by a tether in the event of power loss. Assuming simplified geometry and a quasi-static approach, the problem is modeled using a two-dimensional representation in which the robot is assumed to be rigid with equal weight distribution and a constant friction coefficient between surfaces. Equilibrium equations are derived from a modified peg-insertion formulation, allowing calculation of the maximum size of the robot and angle of insertion as a function of inspection gap geometry and friction. Experimentation tested the derived relationships using varying robot dimensions in a 1:1 scale mock-up of the overpack-to-canister gap space of a nuclear dry storage container. Experimental data confirmed that the modifications of the typical peg-insertion predicted successful insertion and extraction better than unmodified equations. The error between the model and experimentation had a mean and standard deviation of 4.4 and +/− 0.53 degrees.
Crack Tip Strain Rate Models for Environmentally-Assisted Fatigue Crack Growth in Light Water Reactor Environments
Authors: Eason Ernest , Pathania Raj
Published: December 2016

This paper demonstrates the feasibility of using theoretically-motivated crack tip strain rate (CTSR) models to estimate environmentally-assisted fatigue (EAF) crack growth rate (CGR) in light water reactor (LWR) environments. Four models, each combining one of two CTSR expressions with one of two theoretical derivations from Faraday’s Law, were fitted to measured CGR data under dynamic loadings. The four models were compared with each other and with experimental crack growth data from examples where various austenitic stainless steel base metals and nickel-alloy welds were tested in LWR environments under EAF, periodic partial unloading (PPU) with various hold times, loading gradients with increasing and decreasing stress intensity factor K (±dK/da), and constant K loading. All four models produced good fits to the data on some examples, and the models using the newer derivation performed well on all examples. Default model parameters and an equation for the distance from the crack tip at which strain rate is estimated were successful in simplifying the application of the models. Both variable effects and measured CGR were well modeled. Advantages and issues of theoretically-based CTSR models are presented.
A Wide Range Stress Intensity Factor Solution for Single Edge Notched Tension Specimen With Clamped Ends
Authors: Zhu Xian-Kui
Published: December 2016

Single edge notched tension (SENT) specimen with clamped ends has been accepted in the oil and gas industry as a low-constraint fracture test specimen to directly determine fracture toughness or resistances in low constraint conditions. Different SENT test methods have been developed, including DNV-RP-F108 test practice, CANMET J-resistance curve test procedure, ExxonMobil CTOD test procedure, and others. Based on these methods, a SENT test standard BS 8571 was developed and published in December of 2014. However, the stress intensity factor K used in BS 8571 was a very complicated function and difficult to use. Moreover, the present author found that this complicated K solution is correct only for a/W≤0.6, but incorrect for deep cracks of a/W>0.6. In order to obtain a simple and accurate K solution for the clamped SENT specimen, this paper revisits this topic. Using the crack compliance method, the desired K solution is obtained. Results show that the proposed K solution and its curve fit are very accurate over a wide range of crack sizes, and validated by existing finite element results of K for the SENT specimens.
Characterization of Piezo Electric Wafer Active Sensors After Exposure to High Temperature
Authors: Faisal Haider Mohammad , Lin Bin , Yu Lingyu , Giurgiutiu Victor
Published: December 2016

Piezoelectric wafer active sensors (PWAS) at high temperature with reliable operation are desired for structural health monitoring. The PWAS may be generalized as an electro-mechanical system because of the incorporation of electro-mechanical coupling. The basic principle of SHM method by PWAS is to monitor variation in the electro-mechanical (E/M) impedance/ admittance signature. The operational temperature range of PWAS can be limited by the sensing capability of the piezoelectric material at elevated temperatures. Therefore stability of PWAS at high-temperature environments is of great interest for SHM. In such cases SHM can be done at room temperature or at relatively lower temperature. However, during service permanently bonded PWAS can be exposed to very high temperature. The traditional PWAS use piezoelectric materials Lead Zirconate Titanate (PZT) that have been attracted by researchers due to its enhanced sensing, actuation or both capabilities. This paper discusses properties relevant to sensor applications, including piezoelectric materials that are commercially available. For temperature dependence study PWAS were exposed to 50°C to 250°C with 50°C interval at around 2°C/min heating rate. E/M impedance/ admittance and different material properties such as, dielectric constant, dielectric loss, mechanical quality factor, P-E hysteresis loop, in plane piezoelectric constant were determined experimentally at room temperature after exposure to high temperature. The variation in E/M impedance and admittance signature and different material properties were obtained at each temperature. The piezoelectric material degradation was also investigated by microstructural and crystallographic study.
Summary and Applications of the New Fatigue Rules in Part 14 of API 579-1/ASME FFS-1 and WRC 550
Authors: Stenta Aaron , Gassama Edrissa , Spring Daniel W. , Cochran Jeffrey , Panzarella Charles , Osage David
Published: December 2016

The third edition of API 579-1/ASME FFS-1 Fitness-For-Service includes a new Part 14 covering fatigue assessment procedures for in-service components. This new part provides methods for estimating the time to crack initiation using strain-life approaches, which are important for low-cycle fatigue, and is written as a multi-tiered approach covering screening, current design code methods, and advanced methods that take into account the latest in technology. Cycle counting methods for both welded joint and smooth-bar fatigue methods are included for uniaxial and multiaxial loading histories. In addition, the multiaxial incremental plasticity correction procedure presented in the new Level 3 Assessment represents a significant update to the plasticity correction used previously. Part 14 of API 579-1/ASME FFS-1 is a procedural document that is written for accurate and practical implementation. WRC Bulletin 550 is the basis for Part 14 and provides the background and supporting documentation for its development. This paper summarizes the work that went into developing Part 14, and WRC 550, and provides a specific example of its implementation for a practical problem of interest using software developed by The Equity Engineering Group, Inc. In-depth comparisons, key findings, and limitations of the presented methods are included.
Vessel Design for Unintended Detonation: A Comparison of Alternative Code Rules
Authors: Gross David J. , Ligon Thomas C. , Minichiello John C.
Published: December 2016

The Hanford Tank Waste Treatment and Immobilization Plant (WTP) will process waste slurries that have the potential to generate flammable gases and will utilize a number of atmospheric vessels to store these slurries at various stages of the waste treatment process. Throughout the design process, provisions have been made to ensure that these flammable gasses are vented from these vessels and to eliminate potential sources of ignition. However, Bechtel National, Inc. (BNI) would like to be able to demonstrate that these vessels are capable of withstanding a limited number of unintended detonations.

It is well known that pressure vessels may be designed for internal detonations. However, these loadings tend to cause very brief transients of high stress that can make traditional stress-based design rules to be difficult to meet. In the past decade, a number of strain-based design methodologies have become available, including ASME Boiler and Pressure Vessel Code (BPVC), Section VIII, Division 2, Part 5; ASME Section VIII, Division 3; ASME Section VIII, Division 3 Code Case 2564; and API 579-1 / ASME FFS-1. Each of these sets of rules permits some degree of plasticity in vessel design, but there are key differences in the specific provisions.

In this paper, the use of these different sets of Code rules will be demonstrated in the context of the design of a WTP vessel for a single unintended detonation, and the advantages and disadvantages of these alternative design approaches will be discussed.
Water Freezing Phenomena by Decompression in the Vacuum Vessel
Authors: Watanabe Toshiaki , Shimojima Ken , Nakamura Makoto , Ohta Hiromitsu , Itoh Shigeru
Published: December 2016

Latent heat of vaporization of water is very large compared to the latent heat of vaporization of other fluids. Therefore, when evaporation is promoted by decompressing, water lowers the temperature and freezes finally. We froze without heat exchange by exposure to vacuum the water using a vacuum pump. Despite violent boiling occurs, pressure in the vessel was going down. But, finally, at freeze process, the pressure in the vessel was increased. This pressure rise is caused by that amount of evaporation increases temporarily rapidly. The rapid increase in the amount of evaporation is due to the release of latent heat during freezing. This paper was focused on the pressure temperature change and mass change when the phase change of the water is switched to sublimation from the evaporation. This is likely to provide useful information when considering a phase-change model in a special state.
Effect of Piping Loads on Vessel Support and Foundation Design
Authors: Stefanovic Radoslav , Doctor Christopher , Miller George , Diaz-Barrie May , Sharif Alexander , Ranieri Peter , Pynten Kirsten
Published: December 2016

It is a common challenge for pressure vessel and foundation engineers to determine the effects of piping loads on the foundation and vessel support design and to find out the appropriate design method to be used. Pressure Vessel Codes specify loadings to be considered in the vessel design but limited guidance is provided on the application of piping loads when designing vessel supports. Consideration of piping loads in the design of vessel supports and foundation is left to the engineer’s judgment.

Vessel supports are typically designed to withstand the operating weight of the vessel, seismic and wind loading. Pressure vessel literatures provide well-established methodologies in considering these loads in the design of vessel supports. Civil engineering literature, such as the American Society of Civil Engineers (ASCE) Wind Loads for Petrochemical and Other Industrial Facilities [11] or the ASCE Guidelines for Seismic Evaluation and Design of Petrochemical Facilities [17], provide well documented procedures and guidelines for evaluating wind and seismic loads. However, there is limited literature on how to account for external loads from attached piping.

Typical major project schedules have vessels and their supports/foundations designed well before the development of the piping design that provides calculated actual nozzle and piping loads on the vessel. This paper reviews the type of piping loads, how the piping loads are translated to the vessel support/foundation and provides a proposal for simplified approach analysis on how to apply these piping loads in the design of the vessel support/foundation. There might be cases where the piping loads will cancel out, but that may not always be the case. Ignoring and not considering nozzle loads in the support design/foundation may not be appropriate for all vessels.

The intent of this paper is to also make the Vessel Engineer aware of ways to reduce these loads and to encourage communication with Stress Engineers in regards to flexibilities and other factors used to calculate nozzle/piping loads. In most cases, the vessel shell and nozzles are considered as rigid anchors in the piping stress analysis. By using the proper flexibility at nozzle junctions and the global vessel flexibility, the effect of piping loads in the design of the vessel support can be reduced. There is little or no industry guideline on how to include loads due to the thermal expansion or contraction of piping. Since the thermal loads and calculation of flexibility are the least understood part of the analysis, this paper provides background including examples of how these loads and flexibilities can be calculated.

In short, the intent of the paper is to provide a better understanding of how piping loads are translated to the vessel support and to provide some design guidelines that are not readily available in current literature and are not clearly specified in the industry codes or standards.
The Conservatism of Leak Before Break Analysis in Terms of the Applied Moment at Cracked Section
Authors: Kim Yeji , Oh Young-Jin , Park Heung-Bae
Published: December 2016

In leak before break (LBB) analysis, applied moment at the position of a postulated crack is a key parameter. The current procedures of LBB analysis use the value of design basis loads that are calculated with the assumption that the pipe does not contain a crack and follows the linear elastic behavior. Therefore, this can lead to conservative results of LBB evaluation compared with the case that considers the effect of plastic behavior of cracked pipe on the calculation of the applied moment at the cracked section [2].

This paper aims to quantitatively investigate the conservatism of the existing LBB analysis in terms of the applied moment at the cracked section. The calculation results using the current procedures with linear elastic pipe model without a crack were compared with the results from the cracked pipe analysis. To consider nonlinearity of crack behavior and pipe material, the time history analysis methods that were verified using the simulated seismic pipe system experiment in the IPIRG-2 program were employed.

The comparison results indicated that the applied moment at the cracked section decreases when the effect of crack and nonlinear behavior are considered in the analysis. Therefore, the current procedures of LBB analysis are significantly conservative compared with the elastic-plastic time history analysis. Base on this detailed analysis, the additional safety margin can be secured in the LBB analysis.
Determination of the Creep-Fatigue Interaction Diagram for Alloy 617
Authors: Wright J. K. , Carroll L. J. , Sham T.-L. , Lybeck N. J. , Wright R. N.
Published: December 2016

Alloy 617 is the leading candidate material for an intermediate heat exchanger for the very high temperature reactor (VHTR). As part of evaluating the behavior of this material in the expected service conditions, creep–fatigue testing was performed. The cycles to failure decreased compared to fatigue values when a hold time was added at peak tensile strain. At 850°C, increasing the tensile hold duration continued to degrade the creep–fatigue resistance, at least to the investigated strain–controlled hold time of up to 60 minutes at the 0.3% strain range and 240 minutes at the 1.0% strain range. At 950°C, the creep–fatigue cycles to failure are not further reduced with increasing hold duration, indicating saturation occurs at relatively short hold times. The creep and fatigue damage fractions have been calculated and plotted on a creep–fatigue interaction D–diagram. Test data from creep–fatigue tests at 800 and 1000°C on an additional heat of Alloy 617 are also plotted on the D–diagram.
Three-Dimensional Analysis of Corrosion Surface on Outer Surface of Piping by Use of Fractal Concept
Authors: Yamagiwa Kenta
Published: December 2016

In this study, the three-dimensional geometry of simulated corrosion surface was compared with that of actual corrosion surface by use of fractal concept that was useful to understand the feature of self-similar pattern. To discuss the difference, fractal dimension (Fd) and fractal boundary (λb) are used. The method to make the simulated surface was that the nitric acid was dropped on steel (JIS SB410) plate to make a dimple on it by corrosion. The actual corrosion surface was provided from the piping which used in the actual chemical plant. To calculate Fd and λb of these corrosion surfaces, three-dimensional geometry was measured by the 3D-geometry measurement system (Keyence VR-3000). The measured size was respectively about 90×60mm (4000×3000 pixels). Next, wavelet transform was applied to the three-dimensional geometry. Fd and λb were calculated from the wavelet coefficient instead of the power spectrum. The mother wavelet was the Gabor function that is the combination of sinusoidal wave and Gaussian function.

In the result, the difference of Fd between the simulated surface and the actual surface was obtained. The average Fd of the simulated surface was about 2.2. On the other hand, the average Fd of the actual surface was more than 2.6. It means the actual surface is more complex than the simulated surface. The λb of the actual surfaces was not obtained, because the linier relationship was satisfied in every frequency. However, the λb of the simulated surface was about 1cm. It was similar to the dimple’s diameter. Therefore, there is a difference between the simulated surface and the actual surface by applying the concept of fractal though they look similar by the human observation. The relationship between the burst pressure, Fd and λb will be discussed.
Characterization and Modeling of Time-Dependent Behaviour of Braided Packing Rings
Authors: Kazeminia Mehdi , Bouzid Abdel-Hakim
Published: December 2016

The sealing performance of packed stuffing boxes used in valves and compressors depends on the ability of the structure to maintain a minimum threshold contact pressure through a sufficient period of time. Packing rings exhibit combined creep and relaxation behavior due to internal disordered porous structure and nonlinear material behavior in addition to the interaction with other structural components. A comprehensive understanding of the time-dependent behavior of packing rings is essential for increasing the sealing performance. In this paper, the time-dependent linear viscoelastic behavior of packing material is constitutively simulated. The experimental investigation is carried out in a special test bench which was designed and developed to study the characteristics of the time-dependent behavior of packing rings. The results show that the proposed model can successfully be exploited to determine the time-dependent behavior of packing rings for application in the design of packed stuffing boxes.
A Shaking Table Test for the Evaluation of Floor Response Spectrum of Seismic Isolated NPP Structure
Authors: Kim Min Kyu , Kim Jung Han
Published: December 2016

The development of a floor response spectrum (FRS) is very important for a seismic risk assessment of nuclear power plants. In the case of non-isolated nuclear power plants, the methodology regarding FRS generation has already been developed. But in the case of seismic isolated NPP structure, the methodology for developing floor response spectrum is not been determined yet. Therefore, in this study, shaking table tests for a seismic isolated frame structure were performed for the development of the floor response spectrum. For the shaking table test, a two-story artificial frame structure was manufactured. For the isolation devices, a lead rubber bearing and an EradiQuake system (EQS) were used. An artificial input seismic motion, which was generated for the NRC Reg. guide 1.60 design spectrum, was used but low-frequency range should be cut off for a decrease of the shaking table displacement. One-, two-, and three-dimensional seismic input motions were considered for the assessment of the horizontal bidirectional and vertical directional effects. Through this test, whether a horizontal bi-directional seismic input can make a difference in the floor response, and moreover, whether the vertical input motion can make a change in the horizontal floor response, were investigated.
Elevated Temperature Cyclic Service Evaluation Based on Elastic-Perfectly Plastic Analysis and Integrated Creep-Fatigue Damage
Authors: Sham T.-L. (Sam) , Jetter Robert I. , Wang Yanli
Published: December 2016

The goal of the Elastic-Perfectly Plastic (EPP) combined integrated creep-fatigue damage evaluation approach is to incorporate a Simplified Model Test (SMT) data based approach for creep-fatigue damage evaluation into the EPP methodology to avoid the separate evaluation of creep and fatigue damage and eliminate the requirement for stress classification in current methods; thus greatly simplifying evaluation of elevated temperature cyclic service.

The EPP methodology is based on the idea that creep damage and strain accumulation can be bounded by a properly chosen “pseudo” yield strength used in an elastic-perfectly plastic analysis, thus avoiding the need for stress classification. The original SMT approach is based on the use of elastic analysis. The experimental data, cycles to failure, is correlated using the elastically calculated strain range in the test specimen and the corresponding component strain is also calculated elastically. The advantage of this approach is that it is no longer necessary to use the damage interaction, or D-diagram, because the damage due to the combined effects of creep and fatigue are accounted in the test data by means of a specimen that is designed to replicate or bound the stress and strain redistribution that occurs in actual components when loaded in the creep regime.

The reference approach to combining the two methodologies and the corresponding uncertainties and validation plans are presented. Results from recent key feature tests are discussed to illustrate the applicability of the EPP methodology and the behavior of materials at elevated temperature when undergoing stress and strain redistribution due to plasticity and creep.
Post Weld Heat Treatment and Formation of Untempered Martensite in 410 Steel Welds
Authors: Stone David J. , Alexandrov Boian T. , Penso Jorge A.
Published: December 2016

Martensitic grades of stainless steels are primarily used in applications requiring increased hardenability while maintaining adequate corrosion resistance against halide stress corrosion cracking (SCC), polyphonic acid stress corrosion cracking, oxidation, and sulfur attack at elevated temperatures. Martensitic stainless steels are extensively used in the oil and gas industries where presence of sulfur is elevated in working conditions. A study on the unexpected high hardness and loss of toughness in Type 410 steel weldments experienced in industry has been carried out at the Welding Engineering Laboratory of the Ohio State University. A hypothesis of exceeding the A1 temperature during PWHT in the ASME recommended temperature range was evaluated using thermodynamic software Thermo-Calc™. It was fond that the A1 temperature in Type 410 steel base and weld metal can vary in a temperature range of 686°C to 850°C. A fairly good correlation between the A1 temperatures predicted with Thermo-Calc™ and experimentally validated with Single Sensor Differential Thermal Analysis (SS-DTA) has been found. Based off these results, the PWHT range of 760 to 800°C suggested by ASME B31.3 is likely to be too high for avoiding formation of untempered martensite in the weld metal and heat affected zone of Type 410 steel welds.
Elbow Flexibility Factor Calculations: An Update
Authors: Seipp Trevor G. , Mendoza Gonzalo
Published: December 2016

Widely cited across industry, earlier work by Rodabaugh and Moore, as well as Rodabaugh, Iskander and Moore described the equations to be used during experimental or finite element analysis studies into the flexibility of elbows. The original work was done to determine the flexibility factors commonly used in the piping Codes.

However, these equations were only applicable to 45°, 90°, and 180° elbows with equal length of attached pipe. Recently, the authors had need to calculate the flexibility factors for elbows with non-equal lengths of attached piping and angles different from 45°, 90°, or 180°. This paper presents the expanded set, and hence general case, for the elbow flexibility factors.
Structural Integrity Assessment of Doel 3 and Tihange 2 RPVs Affected by Hydrogen Flakes: Methodology and Results
Authors: Lacroix Valéry , Dulieu Pierre
Published: December 2016

During the 2012 outage at Doel 3 and Tihange 2 Nuclear Power Plants, a large number of quasi-laminar indications were detected in the reactor pressure vessels, mainly in the lower and upper core shells. The observed indications could subsequently be attributed to hydrogen flaking induced during the component manufacturing process.

As a consequence, both units remained core unloaded pending the elaboration of an extensive Safety Case demonstrating that they can be safely operated.

The Structural Integrity Assessment of the RPVs, through the Flaw Acceptability Analysis, aimed at demonstrating that the identified indications do not jeopardize the integrity of the reactor vessel in all operating modes, transients and accident conditions.

This demonstration, presented in this paper, has been done on the basis of a specific innovative methodology inspired by the ASME XI procedure but adapted to the nature and number of indications found in the Doel 3 and Tihange 2 RPVs.
Technical Basis for Code Case N-847: Excavate and Weld Repair (EWR) for SCC Mitigation
Authors: McCracken Steven , Tatman Jonathan , Riccardella Pete
Published: December 2016

Stress corrosion cracking (SCC), though infrequent, is often detected in nuclear power reactor system piping and components. A number of approaches have been developed and successfully deployed for SCC repair and mitigation such as full structural weld overlay (FSWOL), optimized weld overlay (OWOL), and mechanical stress improvement process (MSIP). While these approaches are proven technologies and have served the industry well, a new strategy, excavate and weld repair (EWR), provides yet another option for repair or mitigation of SCC. The EWR approach excavates a portion of the outer part of the butt weld. The excavation is then filled with a weld metal with demonstrated SCC resistance. The EWR approach would require less welding compared to a weld overlay and may be the best option for large bore butt welds where restricted access may make FSWOL, OWOL, or MSIP impractical. For the situation where a flaw is detected and removal or reduction of the flaw to acceptable size is necessary for continued service, the approach would permit a local partial arc EWR where only a portion of the butt weld circumference is removed and repaired. While the partial arc EWR is not a full mitigation, it would provide the needed preparation time for a more permanent repair during a subsequent refueling or maintenance outage. ASME Code Case N-847 was developed to provide examination, design, installation, and preservice/inservice inspection requirements for the EWR repair and mitigation approach. This paper provides a background, description and the technical bases for the EWR case case.
Study on Effects of Non-Isothermal Condition and Strain Holding on Environmentally Assisted Fatigue in PWR Primary Water Environment
Authors: Asada Seiji , Fukuta Yuichi , Ahluwalia Kawaljit , Steininger David
Published: December 2016

To understand the fatigue behavior of austenitic stainless steels in a simulated PWR primary water environment, the patterns were studied. Austenitic stainless steel Type 316 plate was used as the test material.

Regarding non-isothermal testing: isothermal and non-isothermal fatigue tests were carried out for several patterns of temperature change and strain rate change. Typically, fatigue lives for non-isothermal tests with an out-of-phase strain change pattern were longer than those for isothermal tests.

Regarding strain holding testing: multiple groups of strain range cycles were separated by a long hold time and several test cases were carried out. Testing shows there is little difference in fatigue life for strain holding tests with high strain amplitude.
Fundamental Study on Energy Necessary for Tensile Failure
Authors: Minagawa Keisuke , Fujita Satoshi
Published: December 2016

Although, a part of damage of mechanical structures by actual seismic events is caused by cumulative damage, their seismic design is generally carried out by using momentary force or stress, because force and stress are calculated easily. Therefore, damage indicating parameters that can evaluate cumulative damage is necessary, and authors have focused on energy as the parameter. The energy can evaluate fatigue failure because the energy is derived from an integral of a product of force and deformation. In our previous paper, vibration and loading experiments were conducted, and the energy necessary for fatigue failure was reported. However the processes to clarify the energy necessary for failure by fatigue experiments take a long time. The processes will be shortened if the energy is clarified by tensile tests.

This paper deals with the energy necessary for tensile failure. In this paper, tensile tests were carried out, and energy necessary for tensile failure was derived. The tensile tests were conducted with various tensile speeds. As a result, more energy is needed when tensile speed is slow. This relationship is same as the relationship confirmed by vibration and loading experiments in our previous papers.
Bulging Patterns of Coke Drums
Authors: Samman Mahmod
Published: December 2016

One of the most common defects in coke drums is bulging, which is a non-uniform radial growth of the shell. Bulging often leads to cracks that occasionally result in leaks and fires. Drum bulging and cracking often cause unplanned outages, costly repairs, and premature replacement.

Bulging is commonly treated as a single phenomenon that is caused by one failure mechanism. In this study, we examine this assumption using a database of one hundred and eighty four laser scans obtained from operational coke drums that vary in location, metallurgy, age, size, and wall thickness. Based on the study, we identified nine types of bulges and related them to loading mechanisms, design features, operating practices, and fabrication processes that likely contribute to their formation. This new understanding of bulging types and causes should help design, fabricate, and operate coke drums informed manner.
Predicting Evaporator Vessel Base Thicknesses From Inspected Heating Coils
Authors: Fellerman Andy S. , Pyke Caroline K.
Published: December 2016

The Highly Active Liquid Effluent and Storage plant at Sellafield, UK, currently uses three evaporators to reduce the volume of active liquor stored within the facility before being vitrified for long term storage. This liquor is highly corrosive and the lifetime of the evaporators is potentially limited by the corrosion loss from the heating elements, comprising an external jacket and a number of internal coils, all heated by low pressure steam. Inspection of the heating coils inside the evaporators is possible and measurement data is available of their thicknesses by depth at various inspection intervals. This inspection data has been combined with operational data and thermal models for the heating elements. Our theoretical understanding from laboratory measurements suggests that corrosion is related to temperature through an Arrhenius relationship. As such we have been able to develop a predictive model for the thickness profiles and remaining useful life of the uninspected components. This model is a non-linear mixed effects (multilevel) model and has undergone significant developmental work to account for a number of practical data issues. This paper will briefly outline the various components of the model, whilst discussing issues relevant to any statistical model such as complexities of data collection, approaches to handling correlated data, selecting appropriate model formulations and data transformations. The inclusion of uncertainties in prediction via Monte-Carlo simulation will also be discussed.
Critical Strain and Damage Evolution for Crack Growth From a Sharp Notch Tip of High-Strength Steel
Authors: Yu Feng , Jar Ben , Hendry Michael
Published: December 2016

This paper proposes details of an approach that uses expressions of fracture strain and damage evolution as functions of stress triaxiality for notch-free specimens to predict their values for crack growth from a sharp notch tip of a single-edge-notched bend (SENB) specimen. Experimental testing and finite element (FE) modelling are used to determine the basic mechanical properties and deformation behaviour of those specimens, which are needed to calibrate model constants in the proposed approach and to validate prediction from the approach. Three types of mechanical testing were conducted, using standard smooth tensile, short-gauged tensile and standard SENB specimens. The FE modeling is to establish constitutive relationship between stress and strain for notch-free specimens so that the FE modeling can be used to determine parameters such as stress triaxiality and unloading modulus for the prediction of fracture strain and damage evolution at the sharp notch tip of SENB specimen. The study will then examine whether the proposed approach can predict the trend of variation for fracture toughness among three high-strength steels, which is an on-going study and the results will be presented in the conference.
Numerical Analysis of Unsteady Phenomena in Upper Plenum and Hot-Leg Piping System of Advanced Loop-Type Sodium Cooled Fast Reactor
Authors: Takaya Shigeru , Fujisaki Tatsuya , Tanaka Masaaki
Published: December 2016

Japan Atomic Energy Agency is now conducting design study and R&D of an advanced loop-type sodium cooled fast reactor. The cooling system is planned to be simplified by employing a two-loop configuration and shortened piping with less elbows than a prototype fast reactor in Japan, Monju, in order to reduce construction costs and enhance economic performance. The design, however, increases flow velocity in the hot-leg piping and induces large flow turbulence around elbows. Therefore, flow-induced vibration of a hot-leg piping is one of main concerns in the design. The flow field in the hot-leg piping is affected by flow disturbance at the inlet, so it is important to evaluate flow field including the upper plenum. In this study, we analyzed unsteady fluid flow by using an integrated model of the upper plenum and the hot-leg piping system. Unsteady Reynolds averaged Navier-Stokes simulation with Reynolds stress model was used for the numerical simulation. The results were compared with experiment results of 1/3 scaled-model of hot-leg piping with the inlet conditions of rectified, swirling and deflected flows as well as simulation results of 1/3 scaled-model of hot-leg piping with rectified flow. In general, the simulation results obtained by using the integrated model show a similar tendency with the experiment results of deflect flows in the downstream region from the elbow exit. The coupling effect of swirling and deflected flows seems to be not significant although further investigation is needed.