bluuebunny/crossref_metadata_2025 huggingface dataset:
An Effect of Bearing Surface Angle at Bolt Head on the Nut Factor and Contact Area Ratio in Tightening Bolted Joints
Authors: Shirakawa Atsushi , Sawa Toshiyuki
Published: October 2020

Bolted joints are used in many industrial products such as mechanical structures, automobiles, airplanes, chemical plants, and so on. In designing bolted joints, the bolt preload in the joints should be determined appropriately and rationally for preventing accidents due to bolt loosening and fracture. Also, in actual bolt tightening, it is important that the bolts should be fastened with a designed bolt preload range. Several methods for tightening bolts are well known, one of which is the torque clamping method. In this method, the designed bolt preload can be obtained by a controlled tightening torque. The relationship between the tightening torque and bolt preload is assumed to be linear in the elastic range, and the bolt preload is often calculated from the tightening torque using the nut factor. However, in some cases, where the relationship between the tightening torque and the bolt preload is not linear. One of the reasons is the effect of bearing surface angle at bolt head. In this study, the effect of the bearing surface angle at the bolt head on the nut factor is examined experimentally. Also, it is known that the bearing surface angle at the bolt head affects the contact stress at the bearing surface of the joint member. The contact area ratio is newly proposed and obtained. As a result, a method to obtain an appropriate bearing surface angle at the bolt head and tightening torque range is proposed, taking the effect of contact area ratio factor into account.
Utilisation Limits of 1¼Cr½Mo (SA387-11-2) Steel in High Plate Thickness
Authors: Detemple Ingo , Philippi Bastian , Maffert Jörg
Published: October 2020

Technical requirements for petrochemical reactor steels have proliferated in the last decade. The need to increase economic benefits together with higher operating temperatures and pressures are leading to the construction of higher capacity reactors with thicker walls.

Also, more and more severe and sometimes conflicting requirements in these specifications make it difficult, to derivate a steel design, e.g. in terms of chemical composition and processing parameters, for an optimized balance between quality demands and economical aspects.

The design of pressure vessel for petrochemical industry is based on mechanical properties and the design method, which are given by the construction code.
Consideration of Special Effects for the Application of an Optimized Fracture Mechanics Approach for the RPV Assessment: Project CAMERA
Authors: Obermeier Florian , Hein Hieronymus , May Johannes , Kobiela Julia , Kaiser Marco
Published: October 2020

A large database for fracture toughness data according to the standard ASTM E1921 in the brittle and brittle to ductile transition region was generated within the former research programs CARINA and CARISMA for materials used in western pressurized water reactor (PWR) reactor pressure vessels (RPV). These programs confirmed successfully the application of the Master Curve approach for German RPVs. With respect to the RPV proof of safety during plant operation, in particular for integrity assessments considering the event of a Pressurized Thermal Shock (PTS) further relevant issues appeared in terms of the use of suitable fracture toughness curves for components and of the quantification of safety margins for the irradiated material state:

• Validity of fracture toughness curve and Master Curve respectively in the irradiated state at higher test temperatures (ductile material region)

• Verification of the WPS effect (warm pre-stress) in the irradiated state for representative loading paths and materials

• Impact of material inhomogeneities on the fracture toughness

• Transferability of specimen-specific effects on the safety-related RPV integrity assessment

To address these open issues a follow-up project was initiated called CAMERA (Consideration of special effects for the application of an optimized fracture mechanics approach for the RPV safety assessment). One main aspect within this program is to assess the possibility of describing the whole fracture toughness curve including the upper shelf based on empirical T0 correlations and the effect of a load case related warm pre-loading.

Material tests are carried out and evaluated according to ASTM E1820 to get the crack extension resistance as a function of stable crack extension (J-R curves) in the transition to the ductile region and according to ASTM E1921 (WPS) in the lower shelf region and transition region. The least-square fit curves (J-R) as well as the effect of warm pre-stress are determined for several types of irradiated and unirradiated RPV base and weld metals.

The results serve to expand the application window of the Master Curve concept to the ductile region and to complete the fracture toughness curve over the entire temperature range from lower shelf until operating temperature also considering the load scenario based on the effect of warm pre-stress. This paper will summarize and discuss the results of the material tests performed.
Elasto-Visco-Plastic Buckling of Thick Anisotropic Shells: Numerical Buckling Predictions and Experiments
Authors: Jacquet Nicolas , Tardif Nicolas , Elguedj Thomas , Garnier Christophe
Published: October 2020

This work is focused on elasto-visco-plastic (EVP) buckling of thick shell structures. In particular we are interested in predicting accurately the buckling risk of stainless steel components of nuclear fast sodium reactor working under high pressure and at high temperature (around 180 bar and 500 °C). We follow a modeling/experimental approach to solve this problem.

The set-up of relevant experiments at such high temperature being complex, we work with a representative material that shows similar EVP and buckling behavior at room temperature. The representative material is an alloy mostly composed of tin, silver and copper, commonly named Sn 3.0 Ag 0.5 Cu. The elasto-visco-plastic constitutive model of the material was first characterized using tensile tests on notched specimen at room temperature under various strain rates, and the model parameters identified using finite element model updating (FEMU). In a second step we performed in plane compressive buckling tests of thick plates for various displacement rates. Surface 3D displacements were acquired using three cameras and digital image correlation.

It is well known for thick plates that linearized tangent moduli derived from Levy-Mises flow theory does not give accurate elasto-plastic buckling prediction. Linearized tangent moduli derived from Hencky’s deformation theory gives more accurate buckling prediction for thick plates. This numerical phenomenon known as buckling paradox was well correlated to experiments in the literature. This paradox is applied here to thick plates, with EVP constitutive model, in order to predict buckling.

Finally, finite element (FE) modeling of the buckling experiments was performed. Plates are modeled using SHB8PS solid shell elements. Solid shell elements allow direct displacement correlation with experiments and accurate through the thickness behavior with a 3D material model. The numerical modeling includes real plate geometry obtained using post machining measurements, experimental boundary conditions derived from the DIC (Digital Image Correlation) results and the previously identified constitutive material law. Buckling risk is tested at each loading step of the incremental algorithm using the tangent operator derived with the Hencky’s deformation theory.

Numerical results show a very good correlation with the experimental results on load and displacement history as well as buckling critical load and buckling mode.
Implementation of Ductile Damage Models to Determine Constraint Parameters for Ductile Materials: Phase 1 — Generic Constraint Conditions
Authors: Beswick J. , James P. , Sharples J.
Published: October 2020

It has been observed that steels which are operating in the ductile regime demonstrate greater resistance to tearing under conditions of reduced crack-tip constraint. Constraint is influenced by both geometry and load conditions. For example, fracture toughness specimens with shorter cracks relative to wall thickness, or those subjected to tension as opposed to bending, will demonstrate reduced constraint. Constraint may be quantified by an elastic T-Stress or the elastic-plastic Q parameter.

R6, a set of structural integrity guidelines widely used in the nuclear industry, suggests that the effective fracture toughness of a material at reduced constraint may be calculated using a material-specific toughness locus. To define this locus, it is usually necessary to perform laboratory tests on the material at various levels of constraint, which are both expensive and time consuming. For cleavage (low-temperature) fracture, it is also possible to consult look-up tables, which require the calculation of the Weibull stress parameter.

This paper details findings from an investigation into a method to determine the parameters defining failure loci for steels. The work involves the use of finite element analysis and two damage models which consider void growth in ductile materials. The first model is the Rice and Tracey model, which determines void growth based on stress triaxiality and plastic strain, and the second is the GTN local approach, which considers void initiation, growth and coalescence to define a yield surface for the material. The yield surface is governed by numerous parameters which enable the definition of the void volume fraction of the material at the various stages preceding fracture.

Previous work has demonstrated independence of the parameters used to define the toughness loci to the critical void size when defined using the Rice and Tracey approach. The work presented in this paper demonstrates similar behaviour using the GTN model, with independence of the constraint benefit to the governing parameters. The toughness determined using the GTN approach is calculated from J-R type curves obtained by simulating crack growth in idealised constraint scenarios: specifically applying a T-Stress to boundary layer models, where a boundary layer model is an idealised high constraint scenario.

It is shown in this paper that, whilst independence is demonstrated to the GTN parameters, there are discrepancies between the toughness loci derived using the GTN model and those using the Rice and Tracey approach. The reasons for this are discussed and are predicted to be due to load order effects, in that constraint reduces through loading, which may not be captured accurately using the boundary layer model. An introduction to the next phase of work, which does accurately include these effects, is also provided.
Damage Assessment of Similar Martensitic Welds Under Creep, Fatigue and Creep-Fatigue Loading
Authors: Bender Thorben , Klenk Andreas , Weihe Stefan
Published: October 2020

For the assessment of welds under high-temperature conditions in the creep or creep-fatigue regimes, the knowledge on the damage location and its temporal evolution are of high importance. The failure behavior of similar welds of ferritic-martensitic steels in the creep regime is well known. For creep-fatigue loading, the behavior of welds is still subject to research but it seems that the heat affected zone (HAZ) limits the lifetime of welded components as well. This local failure behavior is not reflected in design guidelines using weld reduction factors or in typical assessment approaches. The evaluation of local strains and stresses in the HAZ is unavoidable. For the improvement of design and inspection guidelines, a more detailed consideration of weld behavior is of interest.

In this paper, an overview of current developments in the assessment of welds under creep, fatigue, and creep-fatigue loading conditions is given. An assessment approach for creep damage and failure, including the prediction of rupture time and location, is presented. The assessment is based on numerical analyses considering the different behavior of base material and HAZ represented by three different subzones. The approach is validated with the simulation of a uniaxial cross weld, creep crack, and component tests. Whereas the creep behavior of the HAZ compared to base metal is quite well known, there is only little knowledge of their fatigue behavior. Using a set of fatigue tests on HAZ, base metal specimens and cross weld specimens, the influence of fatigue and creep-fatigue loading on the lifetime and failure location of a weld will be discussed. For the numerical simulations, a viscoplastic material law of Chaboche type is used and an evaluation of the local strains in the HAZ allows an attempt to explain the observed failure locations.
PWHT Exemptions for Carbon Steel in B31.3: An EPC Contractor’s Perspective
Authors: Rensman Jan-Willem , Kraayeveld George
Published: October 2020

In the 2014 edition of the ASME B31.3 Code [1], thick, P-No. 1 carbon steel pipe became exempt from Postweld Heat Treatment (PWHT) under the condition of preheating at 95°C (200°F) and multi-pass welding. The decision whether to apply PWHT or not is left to the designer but no further guideline is provided. The impression is that the need for PWHT is only corrosion/service related, and not beneficial or necessary for the integrity of the piping. Several publications [2][3][4] have addressed these changes and highlighted that this might lead to potentially unsafe situations.

This paper will critically review the arguments used for the justification of the PWHT exemption for carbon steel and show that many arguments are invalid or incomplete. It will discuss the implications for the performance of materials and predict possible failure scenarios. It will then provide estimates of typical PWHT cost eliminated by the current rules. It will provide an EPC contractor’s perspective on the current ASME B31 rules with practical approaches that may be taken to mitigate the risks. Finally, recommendations to the ASME B31 committees involved in PWHT exemption will be provided.
Alternative Design Approach by Finite Element Analysis for High Pressure Equipment
Authors: Trinca Giovan Battista , Ronchi Nicola , Fusari Fausto , Fiordaligi Emanuele
Published: October 2020

Components that are subject to pressure, typical of the pressure vessel industry, can be designed using such calculation methods as “Design by Rule-DBF” or “Design by Analysis-DBA”. DBA, based on the FEM, is used increasingly often because, in addition to providing a reduction in thickness due to the lower uncertainty on the calculation, it helps to verify and study physical phenomena and complex geometry that are otherwise difficult to research while offering a more intuitive usability of the results. In this paper we wish to offer, in an educative and qualitative manner, a general overview of DBA from the creation of the model to obtaining the results, describing the types of analysis that can be carried out according to the constitutive model of the material used and the degree of accuracy that can be achieved. At the end, we cover some case studies in which DBA has been successfully used to verify design or particular conditions (such as heat treatments) for pressure vessels fabrication. The DBA calculation, described in this paper, is used with the same computational methods for high, medium or low pressure components, but it is clear that the most significant reduction in thickness is for high pressure components such as reactors, which is why the DBA calculation is particularly appreciated for this type of equipment. In the context of this paper “high pressure equipment” means when the ratio of the inner diameter to thickness of the walls is < 30.
Advanced Structural Integrity Assessment Tools for Safe Long Term Operation: ATLAS+ Project — Status of the Activities of the WP3 on Modelling in 2020
Authors: Blouin Arnaud , Marie Stéphane , Nicak Tomas , Timperi Antti , Gill Peter
Published: October 2020

The main objective and mission of the ATLAS+ project is to develop advanced structural assessment tools to address the remaining technology gaps for the safe and long term operation of nuclear reactor pressure coolant boundary systems.

ATLAS+ WP3 focuses mainly on ductile tearing prediction for large defect in piping and associated components: Several approaches have been developed to accurately model the ductile tearing process and to take into account phenomena such as triaxiality effects, or the ability to predict large tearing in industrial components. These advanced models include local approach coupled models or advanced energetic approaches. Unfortunately, the application of these tools is currently rather limited to R&D expertise. However, because of the continuous progress in the performance of calculation tools and accumulated knowledge, in particular by members of the ATLAS+ consortium, these models can now be considered as relevant for application in the context of engineering assessments.

WP3 has been planned to:

• Illustrate the implementation of these models for industrial applications through the interpretation of large scale mock-ups (with cracks in weld joints for some of them),

• Make recommendations for the implementation of the advanced models in engineering assessments,

• Correct data from the conventional engineering approach by developing a methodology to produce J-Δa curve suitable case by case, based on local approach models,

• Improve the tools, guidance and procedures for undertaking leak-before-break (LBB) assessments of piping components, particularly in relation to representing structural representative fracture toughness J-Resistance curves and the influence of weld residual stresses.

To achieve these goals, WP3 is divided into 4 sub-WPs and this paper presents the progress of the work performed in each sub-WP after 36 months of activities.
Evaluation by Two-Dimensional Finite Element Analysis of the Effect of Number of Weld Layers on the Residual Stress Profile in Stainless Steel Pipe Welds
Authors: Zumpetta Alexandra K. , Stockdale Andrew W. , Hicks Trevor G. , Mabe William R. , Coughlin Jessica L.
Published: October 2020

Tensile residual stresses associated with stainless steel pipe welds can promote in-service cracking and influence the need for inspections. Previous research via finite element analysis (FEA) [1] and experimental characterization [2] has shown that welds in thick wall pipe can produce compressive residual stresses at the inner diameter (ID) surface. However, research that has evaluated the relationship between the number of weld layers, stemming from different weld bead sizes, and the resulting pipe residual stress profiles is limited. This investigation used two-dimensional (2D) FEA to evaluate the influence of the number of weld layers (resulting from different weld bead sizes) on the ID surface and through-wall residual stress profiles for varying stainless steel pipe radii, thicknesses, and weld joint geometries. The findings herein are compared to previous experimental results [2]. The results demonstrated that for the larger pipe sizes and the welding conditions investigated, increasing the number of weld layers (reducing individual weld bead sizes) reduced the ID surface tensile axial residual stresses. In the larger pipe sizes, the magnitude of the tensile residual stresses extending through (into) the pipe wall is also reduced with an increased number of weld layers. The FEA results show that the weld joint geometry may not affect the residual stress profiles as strongly as do the number of weld layers, based on the similarities in the tensile stress values for the joint geometries that were evaluated.
Probabilistic Creep Modeling of 304 Stainless Steel Using a Modified Wilshire Creep-Damage Model
Authors: Hossain Md. Abir , Cano Jaime A. , Stewart Calvin M.
Published: October 2020

Pressure vessel components subject to high temperature and pressure are susceptible to life-limiting creep and/or creep-induced failure. Traditional continuum damage mechanics (CDM) based creep-damage model are used extensively for the prediction and design against creep in these components. Conventional creep experiments show considerable uncertainty in the creep response of materials where scatter can span decades of creep life. The objective of this paper is to introduce the probabilistic methods into a deterministic creep-damage model in order to predict experimental uncertainty. In this study, a modified Wilshire model capable of creep deformation, damage, and rupture prediction is selected. Creep deformation data for 304 stainless steel is collected from the literature consisting of quintuplicate (five) tests at 600°C with varying stress levels. It is hypothesized that the scatter in creep data is due to: test condition (temperature fluctuations and eccentric loading), initial damage (pre-existing surface and sub-surface defects), and metallurgical (local variation in microstructure) uncertainties. Probability distribution functions (pdfs) and Monte Carlo simulations are applied to introduce the uncertainties into the modified Wilshire equations. The domain of each source of uncertainty must be defined. A systematic calibration approach is followed where the material constant for each creep curve (in the quintuple) are obtained and statistical analysis is performed on the material properties to assess the random distribution associated with each uncertain material parameter. The probabilistic calibration begins with the introduction of test condition randomness (±2°C and ±3.2% MPa of nominal temperature/stress) in accordance with the ASTM standards. Cross calibration of temperature-stress variability proceeds the approximation of initial damage uncertainty which captures the remaining scatter in the data. Deterministic calibration unveils the range of variabilities associated with the material properties. The best-fitted pdfs are assigned to each uncertain parameter and subsequently, the deterministic model is converted into a probabilistic model where reliability is a tunable factor. A large number of Monte Carlo simulation are conducted to generate probabilistic creep deformation, minimum-creep-strain-rate (MCSR), and stress-rupture (SR) predictions. It is demonstrated that the probabilistic model produces quantitatively and qualitatively good fits when compared with experimental data. Future work will be directed towards the inclusion of service condition related uncertainty (power plant, turbine blade, Gen IV nuclear reactor application) into the probabilistic framework where the uncertainties are more robust.
Creep Deformation Property and Creep Life Evaluation of Super304H
Authors: Kimura Kazuhiro , Sawada Kota
Published: October 2020

Creep deformation behavior, creep strength property and microstructural evolution during creep exposure were investigated on Super 304H steel for boiler tube. In the high stress and lower temperature regime, creep rupture strength of Super 304H steel is higher than that of SUS304H steel. The slope of stress vs. time to rupture curve of Super 304H steel, however, becomes steeper with increases in creep exposure time and temperature, and the creep rupture strength of Super 304H steel becomes closer to that of SUS304H steel after the tens of thousands of hours at 700°C (1292°F) and above. In the short-term, at 600°C (1112°F), creep rupture ductility increases with increase in creep rupture life. However, it tends to decrease after showing this maximum value and the creep rupture ductility decreases with increase in temperature. The complex shape of creep rate vs. time curves, with two minima in creep rate, was observed at 600°C (1112°F). Several type precipitates of niobium carbonitride (Nb(C,N)), Z phase (NbCrN), and copper were observed in Super 304H steel, as well as M23C6 carbide and sigma phase observed in SUS304H steel. The change in slope of stress vs. time to rupture curve is caused by disappearance of precipitation strengthening effect during creep exposure. Accuracy of creep rupture life evaluation was improved by stress range splitting method which takes into account the change in slope of stress vs. time to rupture curves was demonstrated.
Investigation of Failure Behavior of Polyethylene Pipe Reinforced by Winding Steel Wires Subject to Inner Pressure and Bending
Authors: Shi Jun , Miao Yuzhuo , Li Xiang , Li Guangzhong , Wan Yu , Lu Panling
Published: October 2020

Polyethylene pipes reinforced by winding steel wires (PSP) have been widely used in many fields such as chemical engineering, pulp conveying, water supply, etc. The combined loads of inner pressure and bending sometimes leads to the failure of PSP, and for engineering projects it is still not proposed that the failure criterion of PSP subject to combined loads. In this paper, full-size finite element models (FEM) of PSP under inner pressure and bending were established to investigate the engineering failure criterion. In the FEM the steel wires and HDPE matrix were modeled separately. The freedom degrees of steel wires and HDPE were coupled together as the interface between these two constituents were considered intact. The investigation contains two parts: firstly, a FEM was established in reference to the details of an existing experiment, including the pipe specimen and relative boundary condition. The validation of the FEM was carried out and the simulation result agreed well with test result indeed. Subsequently, the model was optimized to undertake four-point bending under inner pressure, to analyze the failure behavior of PSP under this kind of condition, with three factors such as varied ratio of diameters to thickness, inner pressure and volume ratio of steel wires. In the end, the curvature of failed PSP was considered as the failure criterion, and the relationship of curvature and the three factors were discussed. This paper is useful for the safety of PSP subject to inner pressure and bending load.
Low Impact Test Results in Carbon Steel Flanges, Fittings and Piping: End User’s View
Authors: Dalal Mitul , Penso Jorge
Published: October 2020

Carbon steel components (Flanges, Fittings and Piping) have been reported with low impact test results. Some have failed during hydrotest and start-up as well as in-service. Steel grades that have shown problems complying with impact test requirements are ASTM/ASME A105, ASTM/ASME A234 Gr. WPB and ASTM/ASME A106. ASTM A350 LF2. These components according to some design-fabrication industry standards are not suitable for use even though they complied with applicable ASTM/ASME materials standards meeting the mechanical properties and chemical composition. Some analyses have led to identify key contributing factors to this low impact test results including Chemistry/Micro-alloying, fabrication approach and use of 100% re-cycle steels. This paper presents summarize findings from numerous reports of failure, testing data and selected approach when screening these materials prior to installation. Based on literature review the need for improvement in the approach for mechanical testing including fracture toughness testing for modern materials was identified.
Investigation of Temperature Dependence of Weibull Parameters of the Beremin Model in Ductile-Brittle Transition Temperature Region
Authors: Hojo Kiminobu , Ogawa Naoki , Yoshimoto Kentaro , Hirota Takatoshi , Nagoshi Yasuto
Published: October 2020

The Beremin model can handle both the plastic constraint effect and data scatter for brittle fracture. Many researchers have been investigating its applicability for more than 30 years and are still discussing the temperature dependence of Weibull parameters used in this model. The authors have already presented the experimental and analytical investigation results for low alloy steel using C(T) specimens in several temperature conditions. The analysis suggested that the Weibull parameters are constant for temperature. In this paper fracture toughness tests of carbon steel using SE(B) specimens at −120°C and −50°C were performed and the Weibull parameters were determined by the test results at −120°C. KJc of the 5% lower bound and the 95% upper bound confidence limit at −50°C were predicted using the Weibull parameters from −120°C. As a result, the predicted 5% lower bound confidence limit was close to the lowest experimental KJc value, whose fracture mode was nearly cleavage fracture. This means there is no temperature dependency of the Weibull parameters and the results are similar to those of low alloy steel. On the other hand the predicted 95% upper bound confidence limit had a large gap when compared with the experimental upper KJc value. One of the reasons of large gap was estimated that the parameter fitting of the GTN model was performed without consideration of the parameters relating to the second void effect and a precise stress-strain field after a large ductile crack growth with several millimeters was not obtained.
Hydrodynamic and Structural Simulations and Measurements in an Explosively Loaded High-Pressure Vessel
Authors: Fehlmann Kevin , Spernjak Dusan , Cardon Devin , Hill Dallas , Yost Nathan , Llobet Anna
Published: October 2020

A containment and confinement pressure vessel system is under development to expand the capability to perform small explosively driven physics experiments at the Proton Radiography facility at Los Alamos National Laboratory (LANL). Two barriers of this vessel system are the Inner Pressure Confinement Vessel (IPCV) and the Outer Pressure Containment Vessel (OPCV).

To achieve high spatial resolution of proton images, radiographic windows (covers) of the Inner Vessel are located extremely close to the experiment containing high explosive (HE). While the Inner Vessel is designed to meet the ASME Boiler and Pressure Vessel Code, Section VIII, Division 3, Code Case 2564 criteria, the small separation between the explosive and the pressure-retaining boundary presents a unique requirement for designing dynamically loaded vessels. We present numerical simulations of HE detonation in the Inner Vessel for several HE configurations. Eularian hydrodynamic code is used to calculate pressure-time history on the inner vessel surface. The pressure-time loading is then imported into a Langrangian structural model, and high-fidelity structural dynamic simulations are performed to obtain stress and strain as functions of time. Simulations are compared against experimental measurements from dynamic testing. Dynamic experiments are conducted in a low-fidelity (LoFi) vessel prototype, to measure the pressure and strain in regions of interest in different vessel locations (body, radiographic windows, covers).
Coupling of Neutron Transport and Probabilistic Fracture Mechanics Codes for Analysis of Embrittled Reactor Pressure Vessels
Authors: Spencer Benjamin W. , Hoffman William M. , Collins Benjamin S. , Henderson Shane C.
Published: October 2020

In light water nuclear reactors, the reactor pressure vessel (RPV) plays the critical role of containing the reactor and coolant and is expected to maintain its integrity under a variety of conditions. The RPV is subjected to high neutron flux and temperature, which lead to material embrittlement and increase its susceptibility to fracture. The degree of embrittlement is highly dependent on the local fluence, so it is critical to accurately characterize the spatial distribution of fluence in the RPV when performing a probabilistic fracture mechanics (PFM) analysis, which individually evaluates the flaws introduced in the manufacturing process. Radiation transport codes typically focus on computing the neutron distribution within the nuclear reactor core to understand phenomena relevant to reactor physics. However, recent developments in the Virtual Environment for Reactor Applications (VERA) allow it to solve for a fuel-pin resolved in-core fission source and use Monte Carlo methods to compute neutron fluence accumulation at locations away from the core, such as within the RPV, with unprecedented accuracy. Grizzly, a PFM code, can read in a 3D map of the fluence computed by VERA, and directly use that in the PFM analysis. This represents a significant advance in the accuracy of the fluence used in PFM calculations. This paper provides an overview of this modeling approach demonstrates its application on PFM analyses of representative RPVs.
Evaluation of Hydrogen Gas Generation and Permeation in the 9979 Type AF Shipping Package
Authors: Flach Joshua P. , Blanton Paul S. , Hoang Don S.
Published: October 2020

The 9979 Type AF Shipping Package is a cost-effective radioactive material packaging designed by Savannah River National Laboratory (SRNL) that consists of two primary components: a foamed outer drum for structural protection and an inner containment drum. The packaging was designed to transport Highly Enriched Uranium (HEU), Low Enriched Uranium (LEU), and other isotopes not exceeding a Type A quantity. These contents have the potential to generate flammable hydrogen gas during transport due to the degradation of hydrogenous materials (e.g. water vapor, plastics, etc) by high-energy alpha radiation. Since 10 CFR 71.43(h) prohibits the incorporation of packaging features explicitly designed for continuous venting, alternative justification was required to demonstrate that the requirements of 10 CFR 71.43(d) for negligible reactions between packaging components and contents were satisfied. An analysis was performed to demonstrate that the potential for hydrogen gas generation over a one-year period was limited by the effects of permeation through the packaging materials. The rate of hydrogen collection was evaluated for both the inner containment drum and the outer structural drum under 10 CFR 71.71 Normal Conditions of Transport (NCT). The analysis concludes that the Lower Flammability Limit (LFL) for hydrogen gas will not be reached in a one-year shipping period assuming a minimum void volume is maintained within the drum.
Quantification of the Material Ductility Effect on Notch Fracture Toughness Using Numerical Damage Analysis Method
Authors: Park Eui-kyun , Youn Gyo-Geun , Kim Yun-Jae , Kamaya Masayuki
Published: October 2020

In this study, the finite element (FE) damage analysis based on the multi-axial fracture strain model was applied to investigate the effect of the material ductility on fracture resistance of notched defect. (The fracture toughness is used only for a cracked specimen and the fracture resistance is used for notched specimens throughout the paper.) To obtain the material property with different ductility, the tensile and fracture toughness tests of the cold-worked SUS316 were used. The damage model was determined from comparing the experimental data with simulated FE analysis results. Then the FE analysis was applied to calculate the fracture resistance according to the notch radius in each material. It shows that the slope of initiation resistance according to the notch radius was related to the material ductility. To quantify this effect of ductility, the relationship between notch fracture resistance and material tensile properties was confirmed.
Research and Development of Three-Dimensional Isolation System for Sodium-Cooled Fast Reactor: Part 5 — Isolation Performance Applied to Reactor Building
Authors: Somaki Takahiro , Fukasawa Tsuyoshi , Okamura Shigeki , Miyagawa Takayuki , Uchita Masato , Yamamoto Tomohiko , Miyazaki Masashi , Fujita Satoshi
Published: October 2020

This paper presents the isolation performance of a three-dimensional base isolated Sodium-cooled Fast Reactor building. The three-dimensional isolation system consists of rubber bearing with the horizontal oil damper for the horizontal isolation system and disc spring units with vertical oil dampers for the vertical one, where the vertical one is set under the horizontal one to be arranged in series.

These elements excepting the horizontal oil damper have been developed for the three-dimensional isolation system through the static or the dynamic loading tests using a full scale or a half scale model. Regarding the horizontal oil damper which is necessary for the three-dimensional isolation system as well as the horizontal isolation system, the details would be described in Part 6.

The authors also have been tackled to create the analytical modeling for each element such as the disc spring units, vertical oil damper and rubber bearing. The previous studies from part 1 to part 4 clarified that the newly analytical model, each of which is defined by the differential equations, could accurately express relationships between the force and displacement of each element.

To demonstrate the reduction effect (performance) of the seismic responses for the three-dimensional isolation system, the seismic response analyses using newly analytical modeling were performed for the Sodium-cooled Fast Reactor building that is modeled into the multi-degree-of-freedom-system. The isolation performance of the three-dimensional isolation system is verified through the floor response spectra evaluated at the position where the primary components are placed, in comparison with those by the conventional 2D horizontally isolation system using the rubber bearing without the vertical elements.
Estimation of the Load Carrying Capacity of the Bellows Compensator for Gas Pipelines in the Areas of Mining Production
Authors: Stryzhalo Volodymyr , Zarazovskii Maksym , Bohdan Andrii , Yaskovets Zakhar , Antonchenko Vitalii
Published: October 2020

The stress state of pipelines in areas of mine production requires obligatory consideration the influence of ground displacements. In this case the rules for design pipelines include the additional actions, such as the wall thickness increasing or U-shaped compensators installation.

The Ukrainian coal mining industry requires the expanding of mine production areas. It leads to the situation where old pipelines, which are not designed for such loads, could rupture due to ground displacements. The principle of “extinguish a fire” is applied in this case. It consists in applying of stress reduction actions before certain stage of mine production (so-called lava), such as digging out long sections, cutting and sanding, which require the involvement of significant human and material resources. But, in some cases, even the large-scale application of these actions does not lead to the stress reduction to the acceptable level (especially for pipelines of diameter less then 200mm). So, to solve this problem the implementation of bellow compensators (BC) is proposed.

The present work consists of:

• experimental investigations of BC which are carried out in order to obtain its bearing capacity and to validate its designed parameters guaranteed by the manufacturer;

• simulation of the BC loading process using FEM with adjusting the way of contact modelling between the BC layers in such manner, to be best correlate with the results of experiments;

• the application of obtained results for modelling of stress state of real pipelines in the areas of coal mine production.

The results of experimental investigation of BC of DN100 is presented. Their include: hydrotest with axial displacements limitation; tension-compression cycles for different values of amplitude with simultaneously loading of the operating value of gas pipeline internal pressure; rupture pressure determination.

Based on the experimental results, numerical modelling and specified domestic software for stress state assessment in pipelines the optimal locations and the required number of BCs is determined for buried gas pipelines. The results of presented works allowed us not only to implement the BCs to gas pipelines DN100 in areas of mine productions, but also the necessary experience for creation of larger diameters BCs is obtained.
Study on Dynamic Pressure Effect of Gas Bearings in Fuel Cell Vehicles
Authors: Zhang Chenxin , Hong Weirong , Zheng Shuiying
Published: October 2020

The dynamic pressure effect can contribute to a better working performance of the gas bearing without changing its overall structure or increase its air supply pressure. To study the dynamic pressure effect of gas bearings, a new method of CFD numerical simulation with self-developed UDF dynamic mesh program was proposed. In this way, values of dynamic characteristics for gas bearings with different fluid fields and under different working conditions can be calculated. Based on the numerical simulation results, the influence law of rotational speed, gas film thickness, and radial eccentricity ratio on the dynamic characteristics (load-carrying capacity, stiffness and damping coefficients, static equilibrium position etc.) were obtained. Afterwards, a bearing’s performance test was conducted on a rotor-bearing system in the high-speed air compressor. Compared to the traditional methods, after the dynamic pressure effect was taken into account, the corresponding rotor dynamic calculation of critical speed is more in accordance with the experimental results, thus proved the credibility of the new CFD numerical simulation method with dynamic mesh.
Regression Analysis of Transition Temperature Shift Database for the Core Region Beltline Welds of WWER-1000 RPVs
Authors: Zarazovskii Maksym , Revka Volodymyr , Chyrko Liudmyla
Published: October 2020

The paper describes the history of application in Ukraine the methods of critical temperature of brittleness (CTB is WWER’s analogue of PWRs ductile to brittle transition temperature) prediction. Also, a current state of chemical factor consideration in radiation embrittlement of PWR and WWER regulatory documentation is briefly presented. It is shown that a chemical factor for WWER RPV have to be defined.

The present paper devoted to the identification of the radiation embrittlement chemical factor for welds only of RPV core region, since it is the most critical zone in terms of RPV resistance against fast fracture. For that, based on the results of WWER-1000 RPV surveillance program of all Ukrainian NPPs, the CTB shift database is created. And it is important to note that database of Ukrainian WWER-1000 reactors is the biggest among other WWER countries.

With using the statistical treatment of CTB shift Database the degree of influence of each chemical element (C, Cr, Cu, Mn, Mo, Ni, P, S and Si) on WWER-1000 RPV weld radiation embrittlement is obtained. It is also found that Silicon and Nickel (in decreasing order) have the greatest impact on the CTB shift. At that, influence of other element separately – is negligible from practical point of view. Nevertheless, due to the literature data (in the radiation material science field) about impact of manganese, additional statistical investigations are performed, which showed us that Nickel and Manganese have synergetic effect which almost the same as level of impact from Silicon element alone. Similar treatments, as with pairs Silicon-Nickel and Silicon-Manganese, as well as Silicon or Nickel with any other element combinations, showed as absence of any other synergetic effect.

Based on the statistical evaluation the general shape of CTB shift trend curve is proposed. Moreover, the recommendations related to the CTB shift trendline prediction are given, which, besides the chemical factor and shape of curve, include the way of considering the CTB shift data scatter.

The obtained results are expected to be the basis in the modern regulatory method for radiation embrittlement assessment of the Ukrainian WWER-1000 RPVs.
Study on Key Parameters of Two-Stage Pressure Reducing Valve for 70MPa Hydrogen Supply System
Authors: Li Chunjie , Zhang Zhixin , Chunpeng Wang , Zheng Shuiying
Published: October 2020

With the increase of endurance mileage, 70MPa hydrogen supply systems are used more and more widely, in which pressure reducing valves are the key component. The flow field and the key parameters of 70MPa two-stage pressure reducing valve for hydrogen are studied in this paper. The two-stage pressure reducing valve with cone and flat valves is simplified to two-dimensional model, which is used in condition of high pressure difference with medium of hydrogen gas. Based on NIST real gas model and state equation of modefied Bennedict-Webb-Rubin (BWR), flow field simulation model is developed. A stepwise initialization method for convergence of calculation is proposed in the paper. The numerical simulations for the flow in two-stage pressure reducing valve are carried out. A set of structural parameters is obtained, which is reasonable for 500km hydrogen fuel cell electric bus.
ASME Sec VIII Div. 3 and API TR 17TR8 Verification and Validation Methodology for Subsea Connectors
Authors: Stewart Barry , Andueza Alejandro
Published: October 2020

Wellhead connectors form a critical part of subsea tree production systems. Their location in the riser load path means that they are subjected to high levels of bending and tension loading in addition to the internal pressure and cyclic loading. As such, they are essential equipment and various industry standards influence their design and qualification requirements. This is particularly true of High Pressure High Temperature (HPHT) equipment where heavier blowout preventers and larger rigs are required to deal with this challenging environment.

Industry standards that cover wellhead connectors include a range of verification techniques based on different base analysis codes each of which uses different factors to determine a design margin. Some of the different methods may therefore lead to different actual design margins on the connector from failure to a safe working load. In order to meet the requirements of the industry and to ensure product integrity a HPHT verification and validation methodology based on API 17TR8 [1] and ASME VIII Div. 3 [2] is presented here for subsea wellhead connector designs. The results from a series of verification and full scale validation tests for a subsea wellhead connector family are presented and discussed. The results prove the design margins of the connectors using this methodology and allow for a full understanding of the limits and true performance of the design.