bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fragility Analysis of Horizontal Pressure Vessels in the Coupled and Uncoupled Case
Authors: Korndörfer Jonas , Hoffmeister Benno , Feldmann Markus 
Published: December 2016

The European project “INDUSE-2-SAFETY” aims for the development of a quantitative risk assessment methodology for seismic loss prevention of “special risk” petrochemical plants and components. To demonstrate the capabilities of this approach, a representative case study containing typical components is subjected to detailed investigation. Probabilistic seismic models are used to establish a relation between seismic demand and structural performance of the components with respect to relevant limit states. The resulting fragility curves are used as input for the quantitative risk model.
The study at hand focusses on the fragility analysis of a horizontal steel pressure vessel, which represents a common component type in (petrochemical) plants. Prior to performing the fragility analysis, the dynamic characteristics as well as the pushover behaviour of the vessel are investigated in detail. In order to allow for transient dynamic analyses with reasonable computational resources, a simplified model of the pressure vessel is derived. For the probabilistic seismic demand analysis, the so-called cloud method is applied, using 26 seismic records subdivided into three different groups. The influence of different variables, in particular the liquid filling height and the coupling conditions, on the fragility is investigated in greater detail.
Analytical Study on Failure Mode Map for Lower Formed Head of Reactor Pressure Vessel Under BDBE
Authors: Ogawa Hiroshi , Machida Hideo , Kasahara Naoto 
Published: December 2016

Some of the important lessons learned from Fukushima Daiichi nuclear power plant accident are that mitigation of failure consequences and prevention of catastrophic failure are essential to combat severe accidents (SA) and excessive earthquake conditions that correspond to design extension conditions (DEC). To improve mitigation measures and accident management, clarification of failure behaviors depending on locations is premised under DEC such as SA and earthquakes. Design extension conditions induce some failure modes that are different from those in design conditions. The best estimation for these failure modes is necessary in order to prepare countermeasures and management. A prerequisite for conducting best estimation is to clarify the failure modes with the ultimate structural strength under extreme loads due to very high temperatures, pressure, and great earthquakes.
The authors attempt to clarify unclear failure mechanisms caused by extreme loading under DEC using numerical simulation. In this paper, the relationships between failure modes and extreme loading were studied through numerical simulation using the cylinder and half-spherical model that assumes the bottom of the reactor pressure vessel (RPV) (e.g. Lower Formed Head, Instrument Tube, Gide Tube, Nozzle). This bottom structure of RPV is estimated to be under high temperature and pressure conditions due to the relocation of the molten corium. This heat loading causes major deformation of the bottom head due to creep, which leads to RPV failure. On the other hand, there is a possibility that structural discontinuities (e.g. Gide Tube Nozzle) may fail in advance. In order to recognize actual failure modes, the authors had to study the basic relationship between failure modes and load conditions in the failure mode map. This failure mode map is being considered for use as initial simple structural in beyond design basis events (BDBE) and DEC.
Two Different Approaches to Simulate J-Groove Joints
Authors: Terreros Iñigo , Gallee Sébastien , Robin Vincent , Gommez Florence , Lacroix Rémi , Gilles Philippe , Chanussot Jean-Michel 
Published: December 2016

The large thickness of most of the heavy components in Pressurized Water Reactors often lead to use multi-pass welding processes. Distortion tolerance and maximal residual stress requirements if any are difficult to fulfill by simply adjusting welding processes with a trial-and-error procedure. This is the main reason why AREVA has developed a robust methodology to perform welding numerical simulations leading to have a better understanding of the phenomena involved during the process.
The present work details a 3D method successfully used to simulate a peripheral adapter J-Groove attachment weld in a vessel head [1] and compares the results to those obtained with a 3D simplified method.
The first method is the state of the art method use for solving Computational Welding Mechanics problems. It is a transient “step by step” 3D simulation using an equivalent moving heat source as input. The second method is a simplified one. First, an equivalent thermal cycle is obtained from a 3D stationary thermal simulation. This thermal cycle is representative of the welding parameters. This thermal cycle is then prescribed to all nodes in a given sector of the weld. This simplified method is called “prescribed thermal cycle” method.
A comparison between displacements and stresses obtained by both methods is completed in order to validate the hypothesis of the simplified approach. The results show a good agreement between the transient “step by step” method and the simplified one. Furthermore, the simplified method speeds up the calculations by a factor of 10. These performances offer the possibility to simulate a multi-pass welding of Pressurized Water Reactor components in a limited calculation time, providing an efficient decision making tool for engineering purpose.
This work is the result of a fruitful collaboration between AREVA and ESI-FRANCE. All the computations are performed with SYSWELD™ software [3].
Applying Fracture Mechanics to Cracked Components Subjected to Unloading
Authors: Oliver Sam , Pavier Martyn , Mostafavi Mahmoud 
Published: December 2016

The J-integral is widely used as a fracture parameter for elastic-plastic materials. The J-integral describes the intensity of the stress field close to the crack tip in a power-law hardening material under a set of well-known restrictions. This study investigates what happens when one of these restrictions is broken, namely the requirement for no unloading to occur.
In this work, a centre-cracked plate is subjected to a single cycle of load in which unloading occurs. A remote tensile stress is applied, then released, then applied again up to and beyond its initial magnitude. The J-integral at each step of the analysis is calculated using finite element analysis. Its validity as a fracture parameter at each step is discussed with the aid of results from a strip yield analysis of the same problem. The relevance of the results in the context of structural integrity assessment is discussed.
Probabilistic Financial Analysis of Coke Drum Life Cycle Management
Authors: Panzarella Charles H. , Gassama Edrissa , Spring Daniel 
Published: December 2016

The cycle time, and, in particular, the duration of the quenching phase, is known to play an important role in the rate of damage accumulation in a coke drum. A shorter cycle is desirable because it allows for increased production but this comes at the cost of more frequent repairs and a shorter overall life. Therefore, a trade-off decision needs to be made in order to balance these two effects and maximize profitability.
This paper provides guidance for making these sorts of decisions by looking at several different coke drum operating strategies from the perspective of a high level financial analysis, taking into account many cost/benefit factors in order to determine the optimal strategy that maximizes profitability with various levels of confidence. It is shown that the most critical factor is predicting the rate of repairs as the drum ages. This depends on many factors and can only be determined probabilistically due to the many uncertainties involved. One of the most important factors driving the repair rate is the frequency at which fatigue cracks initiate and grow. A probabilistic fatigue model is used to describe this, taking into account the large surface area of the coke drum, which provides more potential nucleation sites for fatigue crack initiation.
It is shown that there is, indeed, an optimal, intermediate cycle time for certain conditions. For other situations running with the shortest possible cycle time is shown to be the best choice.
Development of Acceptance Criteria for Soil-Structure Interaction Solutions Using Linear SSI Techniques
Authors: Costantino Michael C. , Houston Thomas W. , Maham Andrew S. 
Published: December 2016

Seismic analysis and design of high-hazard nuclear facilities requires evaluation of soil-structure interaction (SSI) effects on structure and soil response due to earthquake ground motions. The industry-wide methodology of computing SSI response of buildings is through linear SSI techniques using the computer code SASSI.
Technical issues were identified by users and regulators (Ref. 1) resulting in the U.S. Department of Energy (DOE) commissioning a large scale, multi-year Validation and Verification (V&V) Project for SASSI (Ref. 2). The project was a highly peer reviewed process that included an esteemed Participatory Peer Review Team, DOE oversight, as well as regulatory and stakeholder input.
The project goal was to develop benchmark SSI solutions for the range of SSI problems associated with high-hazard facilities within the DOE complex. As per industry software quality control requirements, an acceptance limit for the benchmark solutions must be provided to define the acceptable accuracy of the results produced by SASSI relative to the benchmark. In order to define this limit, variation in the solution of foundation impedance must be related to an expected level of accuracy in structural design quantities of interest (e.g., response spectra, base shear, etc.). Therefore, extensive parametric analyses were performed for coupled soil-structure systems having a broad range of SSI parameters defined by foundation size, soil properties, building stiffness and mass properties, building height, etc.
Based on the results of the parametric analyses, ASCE 4 code guidance, and engineering judgment of CJC&A and the peer review team, an acceptable level of accuracy in computed foundation impedance was determined for SASSI solutions. This supported the successful qualification of SASSI for use in two large-scale DOE projects.
Critical Plane Search Method for Biaxial and Multiaxial Fatigue Analysis
Authors: Karpanan Kumarswamy 
Published: December 2016

For complex cyclic loadings, stress- or strain-based critical plane search methods are commonly used for fatigue analysis of the structural components. Complex loadings can result in a non-proportional type loading in which it is difficult or impossible to determine the plane with maximum shear stress/strain amplitude. ASME Sec VIII, Div-3 fatigue analysis for non-welded components is a shear stress based fatigue analysis method and, for non-proportional loading, uses the critical plane search method to calculate the plane with maximum shear stress amplitude.
For a two-dimensional non-proportional stress state, analytical stress transformation equations can be used to calculate the shear stress or strain amplitude on any plane at a point. The shear stress range on each plane is the difference between the maximum and minimum shear stress. For a three-dimensional stress state, shear stress amplitude calculations are much more complicated because the shear stress is a vector and both magnitude and direction change during the loading cycle. In ASME VIII-3, the maximum shear stress range among all planes, along with the normal stress on the plane, is used to calculate the stress amplitude. This paper presents a method to calculate the shear stress/strain amplitude using 3D transformation equations. This method can be used for any stress- or strain-based critical plane search method. This paper also discusses ASME proportional and non-proportional fatigue analysis methods in detail.
Thoughts on Improving Confidence in Probabilistic Fracture Mechanics Analyses
Authors: Rudland D. , Kirk M. , Raynaud P. 
Published: December 2016

In the past, the US Nuclear Regulatory Commission (NRC) has typically regulated the use of nuclear structural materials on a deterministic basis. Safety factors, margins, and conservatisms were used to account for model and input uncertainty. However, in the mid-1990s, the NRC issued a policy statement that encouraged the use of Probabilistic Risk Assessments (PRA) to improve safety decision making and improve regulatory efficiency. Since that time, the NRC has made progress in its efforts to implement risk-informed and performance-based approaches into its regulation and continues to revisit and update the approaches on a regular basis.
A major component to the overall safety of nuclear structures is the fracture behavior of the materials. Consensus codes and standards responsible for the design and analysis of such structures, such as ASME Boiler and Pressure Vessel code, typically rely on conservative fracture models with applied safety factors and conservative bounding inputs to account for the numerous uncertainties that may be present. Improving the reliability of such models by truly understanding the impacts of the assumptions and uncertainties becomes difficult because of the conservative nature of the models and inputs and the inadequate documentation of the basis for safety factors.
As a subset of PRA, probabilistic fracture mechanics (PFM) is an analysis technique that allows greater insight into the structural integrity of components than similar deterministic analyses. PFM allows the direct representation of uncertainties through the use of best-estimate models and distributed inputs. This analysis methodology permits determination of the direct impact of uncertainties on the results, which gives the user the ability to determine and possibly refine the specific drivers to the problem. However, PFM analyses can be more complicated and difficult to conduct than deterministic analyses. Determining validated best-estimate models, developing input distributions with limited data, characterizing and propagating input and model uncertainty, and understanding the impacts of problem assumptions on the adequacy of the results, can complicate the development and approval of PFM analyses in a regulatory application.
This paper provides some thoughts on how to improve confidence in structural analyses performed using PFM, by focusing on topics such as solution convergence, input distribution determination, uncertainty analyses, sensitivity analyses (to determine impact of uncertainties on result) and sensitivity studies (to determine impact of mean values on the results). By determining the main drivers to the probabilistic results and investigating the impacts of the assumption made to develop those drivers, the confidence in the overall results can be greatly improved.
Root Cause Analysis and Characterisation of the Doel 3 and Tihange 2 Reactor Pressure Vessel Flaws
Authors: De Vroey Séverine , De Bruycker Evy , De Smet Michel , Stubbe Jacqueline 
Published: December 2016

This paper presents the root cause analysis and characterisation of the indications discovered in two Belgian pressurized water reactor (PWR) pressure vessels (Doel 3 and Tihange 2), during in service inspections performed in 2012.
The only plausible mechanism at the origin of the detected indications is hydrogen flaking during fabrication. Flaking could occur because of the local combination of high hydrogen concentration, stresses and susceptible microstructure.
The phenomenology study performed on several materials including flaked materials provided precious information for the Safety Case: it confirmed the cause of the indications and evidenced that flaking exclusively occurs in segregated zones and that the ligament between flakes is sound.
The paper also briefly addresses the possibility of evolution of the indications during operation: low cycle fatigue during transients is identified as the only mechanism likely to induce flaw growth in operation. A particular attention has been paid to the potential hydrogen effects.
Hardened Pit Lid Design for High Pressure Extreme Temperature Pneumatic Gate Valve Testing
Authors: Wesevich James W. , Dunn Peter E. , Lawver Darell J. , Yeary Taylor J. 
Published: December 2016

This paper discusses the design of a removable hardened test pit lid for conducting high pressure pneumatic testing under extreme temperature variations. The high pressure extreme temperature (HPET) pit configuration requires a robust lid to contain the energy release that could occur through testing a variety of oil services items placed within a frangible thermally insulated enclosure. The insulated and hardened enclosures include an inlet and outlet for airflow. These energetic release scenarios represent postulated test item failures resulting in significant fragment and shock loads within the insulated enclosure. A 618in3 gate valve charged with 20,000psi of compressed nitrogen under a temperature range of −100°F to 600°F was used to produce the worst-case energy release in the event of a catastrophic failure within the test pit.
In order to assess the structural response of the hardened pit lid, two sets of computational fluid dynamics (CFD) analyses were performed. A 2-dimensional axisymmetric CFD model of the gate valve was used to estimate the fragment velocity of its blind flange. A 3-dimensional CFD model of the test pit, insulated enclosure, and blast lid was used to estimate the applied blast loads. The test pit enclosure was assessed using non-linear dynamic finite element analysis using single-integration hexahedral continuum elements. The braces were modeled with layered shell elements and the bolts were explicitly modeled with beam and spring elements. All of the materials are modeled using a plasticity-based piecewise linear hardening constitutive model, with rate dependency and softening, fit to each material yield, tensile, and elongation limit.
Study on Small-Scale Laminated Type Base Isolation Device Using Urethane Elastomer for Practical Application
Authors: Ishihana Kenta , Furuya Osamu , Goda Kengo , Omata Shohei 
Published: December 2016

At the present, base isolation system has been recognized by general earthquake resistant technique since the Great Hanshin Earthquake 1995. The seismic isolation will be aggressively applied to not only architectural and civil structures but also various structures, because the effectiveness on seismic safety had been demonstrated again in the Great East Japan Earthquake. In generally, although the base isolation system is divided into laminated rubber bearing type and friction sliding bearing type. In the case of former type, shape factor, maximum or minimum outer shapes and so on are restricted by the material characteristics in visco-elastic material.
In previous study, the research and development of laminated type base isolation device using urethane elastomer was carried out to upgrade a seismic safety for various structures. The fundamental characteristics was investigated from several loading test by using various experimental devices, and the design formula for the stiffness and equivalent damping coefficient is formulated as an approximate expression of mechanical characteristics until now. The mechanical characteristics based on the loading test up to 500% shear strain using experimental specimen with 100 × 100 mm cross-sectional shape. It was confirmed that urethane elastomer is not hardening up to 500% shear strain. Moreover, the experimental examination for aged deterioration in the urethane material has been continuously carried out. As the results, it was confirmed that the laminated type seismic isolation device using urethane elastomer is possible to develop as a practicable device from the stable mechanical properties as considering in design step.
In this study, the small-scale laminated type base isolation device using urethane elastomer is advanced to the direction of further technical upgrading and of scale down for light-weight structure as a sever rack. The first stage, basic properties of the urethane elastomer has been investigated by loading test. The second stage, the compression creep test with laminated type base isolation device has been investigated to confirm an effect on light-weight mechanical devices.
Impact Toughness for PM HIP 316L at Cryogenic Temperatures
Authors: Berglund Tomas , Östlund Martin 
Published: December 2016

It is well known throughout the PM HIP (Powder Metallurgy Hot Isostatic Pressing) industry that PM HIPed 316L material in general exhibit higher strength than conventional 316L. However, previous studies have shown an uncharacteristic behavior in impact toughness properties at cryogenic temperatures compared to conventional forged material. The uncharacteristic behavior consists of unexpectedly large drop in impact toughness at cryogenic temperatures which is not seen in the same extent in conventional material e.g. forged 316L. With the recent code case approval for PM HIPed 316L material, this behavior can be seen as an uncertainty regarding the performance of the material and its use in nuclear applications can therefore become limited. The behavior and underlying mechanisms is yet to be explained in detail. One possible explanation is that it is caused by oxides in the material, of which a large amount originates from oxygen picked up by the very large surface area of the powder during the manufacturing process. The correlation between impact toughness at room temperature and oxygen content is often referred to.
In this study the non-metallic inclusion content is correlated to the impact properties at −196°C (−321°F), and a suggested explanation for the behavior of PM HIP 316L/316LN vs. conventional 316L is presented. The size and number of inclusions constitutes a major difference between the PM HIPed and conventional material. The results show that the size of the inclusions is significantly smaller in the PM materials compared to the conventional material and as a consequence they are present in larger numbers in the PM materials. Furthermore, the results clearly show the correlation between inclusion content and the impact toughness at cryogenic temperatures. The correlation is not as clear at room temperature where the different materials behave more similar. The suggested explanation is further supported by literature on cryogenic properties of 316L/316LN, 316L weld material and PM HIP 316LN with greatly reduced oxygen content. The impact toughness testing was performed using instrumented test equipment capable of recording load vs. displacement during testing. From this data the crack propagation and crack initiation energy can be estimated.
Furthermore, it is known that grain size can influence mechanical properties. In this study no clear relationship between impact toughness and grain size could be observed. However, a correlation between the grain size and the amount of inclusions in the material was observed. It was found that larger amounts of inclusions in the PM HIPed material are correlated to a finer grain size. The results indicate that the inclusion particles inhibit grain growth during the HIP and heat treatment process by pinning of grain boundaries.