bluuebunny/crossref_metadata_2025 huggingface dataset:
Applicability of a Deterministic Approach to Transfer the Minimum Fracture Toughness Between Different Temperatures in the DBTT Region
Authors: Meshii Toshiyuki , Yamaguchi Teruhiro , Fukinbara Koki
Published: December 2016

In this paper, we demonstrate that a deterministic approach requiring only tensile test data for different temperatures has a possibility to predict the minimum fracture toughness for these temperatures. The material is assumed to be in the Ductile-to-Brittle-Transition Temperature (DBTT) region. The approach was based on one of the authors’ finding that the critical stress σ22c of the modified Ritchie-Knott-Rice criterion is correlated with the minimum fracture toughness and shows very small scatter and is specimen configuration independent. The criterion predicts onset of cleavage fracture of a material in the DBTT transition temperature region, when the crack-opening stress σ22 measured at a distance from the crack-tip equal to four times the crack-tip opening displacement δt exceeds a critical value σ22c. The proposed approach is expected to overcome some inconveniences which recent studies have reported to the Master Curve parameters vary with size and temperature.
Simulation on Propagation and Coalescence of Fatigue Crack by Automatic Three-Dimensional Finite Element Crack Propagation System
Authors: Doi Hiroaki , Azuma Kisaburo
Published: December 2016

Verification analyses of the CRACK-FEM developed to predict the propagation of age-related cracks detected in complicated-shaped components of nuclear power plants are presented. Four fatigue crack propagation tests for plate specimens with one and two initial surface cracks subjected to cyclic tensile and bending load respectively are simulated using the CRACK-FEM, and the analysis results are compared with the experimental data of the tests in literature. For the specimens with one crack, the relation between the number of load cycles and the crack size obtained by the analyses agrees with the experimental data. For the specimens with two cracks, the analysis results until the crack coalescence and the timing of the crack coalescence obtained by the analyses agree with the experimental data. In tensile fatigue test for specimen with two cracks, the relation between the number of load cycles and the crack size after the crack coalescence obtained by the analysis almost agrees with the experimental data, although a little difference of analysis from the experimental data is seen. However, in bending fatigue test for specimen with two cracks, the analysis results for all the number of load cycles show good agreement with the experimental data.
Rationalizing Sampling of Pipe Material Properties for Probabilistic Pipe Fracture Analyses
Authors: Olson Richard , Young Bruce
Published: December 2016

One element of probabilistic pipe fracture analyses is an assessment of the stability of cracks under applied load. If the load at some time step is greater than the cracked section can sustain, the state of the pipe is reported as ruptured. Another element of probabilistic pipe fracture analyses is the calculation of the crack opening displacement (COD) value which is used as an input to a leak rate calculation. Both of these analyses typically require pipe material properties that are sampled from a probabilistic distribution characterized by a mean value and some variance about the mean. Such properties include yield strength, ultimate strength, Ramberg-Osgood stress-strain curve coefficients, and fracture toughness curve parameters such as initiation toughness and tearing parameters.

From a procedural perspective, it is tempting to sample all of the relevant parameters independently. However, in some instances, the assumption of independence leads to nonsensical conditions such as yield being greater than ultimate; yield and ultimate being completely disconnected from the underlying Ramberg-Osgood description of the stress-strain curve; J-R toughness curves that are convex instead of concave; or initiation J values as low as zero.

This paper provides a suggested approach to sampling material properties for probabilistic pipe fracture analyses. The approach maintains consistency between yield, ultimate and the underlying Ramberg-Osgood stress-strain curve, and sets reasonable cutoff limits on the properties that are sampled. Equations for ensuring consistency among the related parameters are given along with justifications for the sampling limits, and an example of application of the proposed methodology.
Analytical and Numerical Solution for a Rigid Liquid-Column Moving in a Pipe With Fluctuating Reservoir-Head and Venting Entrapped-Gas
Authors: Tijsseling Arris S. , Hou Qingzhi , Bozkuş Zafer
Published: December 2016

The motion of liquid filling a pipeline is impeded when the gas ahead of it cannot escape freely. Trapped gas will lead to a significant pressure build-up in front of the liquid column, which slows down the column and eventually bounces it back. This paper is an extension of previous work by the authors in the sense that the trapped gas can escape through a vent. Another addition is that the driving pressure is not kept constant but fluctuating. The obtained analytical and numerical solutions are utilized in parameter variation studies that give deeper insight in the system’s behavior.
Review and Critical Assessment of Hardness Criterion to Avoid Sulfide Stress Cracking in Pipeline Welds
Authors: Kisaka Yuji , Gerlich Adrian P.
Published: December 2016

Although employing high strength steels in pipelines provides many benefits, it is difficult to satisfy all required mechanical properties simultaneously because some are potentially at odds with each other. Additionally, when new natural gas pipelines are constructed for severe sour service, the hardness must be below 248 Vickers to avoid sulfide stress cracking (SSC) regardless of pipe grades, and this has been standardized by NACE and applied for approximately five decades. On the other hand, the relevance of this hardness criterion has been controversial. This paper proposes three possible methods to improve SSC resistance for weld metals; 1) reducing impurities, 2) producing fine and homogeneous microstructure, 3) controlling microstructures that characterize high hydrogen permeability, solubility, and low diffusivity. This paper states that reducing impurities and producing fine and homogeneous microstructure would reduce SSC susceptibility and an acicular ferrite would be the effective microstructure to increase SSC resistance for weld metals.
Evaluation of Thermal and Mechanical Behaviors of Pipe Flange Connections for Low Temperature Fluids by Numerical Analysis and Experiments
Authors: Fukuoka Toshimichi
Published: December 2016

Sealing of contained fluids is the primary criteria required for pipe flange connections. Recently, there is a rapid rate of increase in the use of low temperature fluids, and leakage related accidents are sometimes reported. The leakage mechanism seems to be different from the case in pipe flange connections at elevated temperatures. In this paper, it is examined experimentally how the leakage of low temperature fluids occurs, in which a pipe flange connection is cooled by liquid nitrogen. The variations of bolt temperature and bolt force are continuously measured. Experimental results show that the bolt force is reduced to as low as about 65% of the initial value. Next, a numerical method based on three-dimensional FEM is proposed to simulate the cooling process. Numerical results are in good agreement with those obtained by experiments. Applying the numerical method to the pipe flange connections for LNG, it is found that the bolt force reduces to about 70% of the initial value. The numerical method proposed in this paper is expectantly applied to the cases of different low temperature fluids under various flow conditions.
Introduction of the Scenario of How to Use Low Alloy Steels Safely in High Pressurized Hydrogen Gas
Authors: Fukumoto Hajime , Kobayashi Hiroshi , Shudo Yukoh , Yamamura Toshiyuki , Wada Yoru , Arashima Hironobu , Yanagisawa Yusuke
Published: December 2016

In 2012, the Japanese regulation for selecting SUS316 austenitic stainless steel with a specific Ni equivalent (SUS316 and SUS316L can be used in the temperature ranges between −45 and 250 °C for a Ni equivalent of ≧28.5%, between −10 and 250 °C for a Ni equivalent of ≧ 27.4%, and between 20 and 250 °C for a Ni equivalent of ≧ 26.3%) as an appropriate material available in hydrogen refueling stations (HRSs) that provide 70 MPa fueling to fuel cell vehicles (FCVs) was updated with the support of NEDO (New Energy and Industrial Technology Development Organization) Program Phase 1 [1].
Influences of T-Stress on Constraint Effect in Mismatched Modified Boundary Layer Model for Creep Crack
Authors: Dai Yanwei , Liu Yinghua , Chen Haofeng
Published: December 2016

Constraint effect plays an important role in assessing the stress field and the growth rate of creep crack in components under high temperature. The mismatched modified boundary layer (MMBL) model is extended to creep crack in this paper. For the MMBL model, the Q-parameters for different mismatch factors are studied under different T-stresses. The variation of the dimensionless T-stress in creep zone is given. The variations of open stresses with creep time for different mismatch factors are presented under different T-stresses. The comparisons of Q-parameter between homogeneous material and mismatched materials are made. The influences of mismatch factor on the constraint parameter are discussed. The influence of creep exponent on the open stress is also discussed.
Hydrostatic Testing of Pressure Vessels at Calculated Test Pressure Using ASME Sec.VIII Div.2
Authors: Nawandar Suresh K. , Kasliwal Rashi , Gopalakrishnan Shyam , Mathkar Ameya
Published: December 2016

Pressure vessels designed for the internal pressure are required to be subjected to hydrostatic test after completion of their fabrication. Two methods are provided in the ASME Sec. VIII Div.2 to calculate the minimum test pressure. One method is based on the Maximum Allowable Working Pressure of the vessel or the MAWP and the other is based on the highest permissible pressure of the vessel at the test condition. This latter pressure is also known as the ‘calculated’ test pressure or the pressure based on the Maximum Allowable Pressure in new and cold condition or the MAP. In either case, the induced primary membrane stress, Pm, shall satisfy the below condition Pm≤0.95*Sy where, Sy is the yield strength of the material at the test temperature.

It is common to notice in many User’s Design Specifications (UDS), the requirement to test the vessels at the ‘calculated’ test pressure.

In the year 2007, major changes were made to ASME Sec.VIII Div.2. Some changes that had relevance to the hydrostatic testing were the change in the basis of the allowable stress at room temperature to the yield strength for most materials, increase in the factor on the test pressure basis to 1.43 and the corresponding increase in permissible limits on the induced primary membrane stress to 0.95*Sy.

It is noted in pressure vessels, built with cylindrical shells and(/or) with hemispherical dished heads with materials whose maximum allowable stresses at room temperature were dependent on the yield strength, that the membrane stress induced when subjected to ‘calculated’ test pressure exceeded the Code limit of 0.95*Sy. Increasing the thickness of the shell and(/or) head did not result in containing the stresses below 0.95*Sy as such an increase in thickness resulted in proportional increase in the MAP values and therefore, further increase of the test pressure.

The objective of this paper is to first derive the actual membrane stress induced in the vessel subjected to the ‘calculated’ test pressure and provide an engineering solution to the problem of induced stress exceeding the Code limit in order to achieve Code as well as the UDS compliance.
Case Histories of the Resolution of Bolted Joint Leakage in the Oil and Gas Industry
Authors: Brown Warren , Evans Geoff , Carpenter Lorna
Published: December 2016

Over the course of the past 20 years, methods have been developed for assessing the probability and root cause of bolted joint leakage based on sound engineering assessment techniques. Those methods were incorporated, in part, into ASME PCC-1-2010 Appendix O [7] and provide the only published standard method for establishing bolted joint assembly bolt load. As detailed in previous papers, the method can also be used for troubleshooting joint leakage. This paper addresses a series of actual joint leakage cases, outlines the analysis performed to determine root cause of failure and the actions taken to successfully eliminate future incidents of failure (lessons learned).
Influence of Restraint Stiffness and Preload on Distribution of Reaction Loads
Authors: Johnson Joshua , McKeel Charles , Leduc Daniel
Published: December 2016

With recent advancements in the production of plastic materials the use of woven plastic webbings (Nylon, Polyester, etc) has increased due to decreased cost, increased load rating, greater ease of use over chains, and an increasingly proven history of use. However a common misconception is that chains and plastic webbing can be interchanged as long as the webbing has a sufficient load rating.

Packages in transport are commonly secured by an arrangement of rigid blocks (chock blocks) at the base and chains, cables, or straps to the top. Analysts are apt to evaluate restraint loads by distributing the prescribed shipping loads based on relatively simple free body diagrams, assuming rigid body mechanics. However, due to the lower stiffness of plastic webbing these rigid body assumptions are not always valid, and may lead to incorrect or misleading results.
Considerations for Baseline NDE of Pressure Vessels
Authors: Lu James , Antalffy Leslie P. , Millet Barry , Smythe Dennis
Published: December 2016

ASME B&PV Code, Section VIII “Rules for Construction of Pressure Vessels” do not have requirements for baseline examination by vessel manufacturers. However many Owners require baseline data to establish as-built conditions of pressure vessels. Capturing baseline data at the manufacturing stage in a manner suitable for the Owner’s operations can preclude the need for post installation or preservice examination. Baseline NDE data can be easily referenced and compared to inservice inspection results to determine if any specific damage mechanisms manifest during operation and subsequently develop into damages to the vessel. Baseline NDE data can also provide guidance on inspection scheduling and damage monitoring. Therefore baseline examination in manufacturing phase is important to post-construction inspection and evaluation activities.

This paper discusses baseline NDE considerations based on pressure vessel service conditions and damage mechanisms. It presents a systematic approach to acquire baseline NDE data in Manufacturers’ shops, including Owner’s role, Manufacturer’s responsibilities and design considerations to allow NDE access to all welds. Topics include examination location reference systems and baseline NDE methods, techniques, and tools that facilitate comparison to inservice examination. This paper also provides an example on implementing baseline NDE of a typical pressure vessel.
Alternative Assembly Evaluation for Railcar Pressure Plate Connection
Authors: Bausman Anita R. , Reid Daniel , Benet Stephen
Published: December 2016

Alternative assembly procedures and tool improvements have been developed and validated in order to improve the overall safety and efficiency of bolted flanged joint assembly. This is achieved by reducing both the assembly time and any post assembly leaks. Several alternative procedures are documented in ASME PCC-1 Appendix F [1], and usage of these procedures is becoming more common in the process and power industries. Application of these procedures is valid for other industries as well. A test of an alternative assembly procedure for the transportation industry was conducted at a railcar repair facility in Channelview, TX, USA. The evaluation compared alternative vs. legacy assembly procedures and also compared pneumatic tools vs. more traditional hand tools normally used by the mechanics at this facility. Time and effort to assemble the joint were measured and targeted for reduction while also improving worker safety. Five gaskets were tested using materials common for pressure railcar applications and the pressure plate connection. These gaskets included rings made of flexible graphite with metal foil reinforcement, soft skived glass-filled Polytetrafluoroethylene (PTFE), and expanded PTFE with a tang metal core. Various joint assembly combinations of gasket material, assembly pattern, and tool usage were timed and leak tested. A successful assembly met the normal leak test criteria of the shop: the assembled joint was subjected to pressurized air and leaks detected (or not) using a standard leak detection fluid. This performance evaluation was followed with visual inspection and dimensional measurements of the gaskets after removal from the test fixture.
All-Purpose Packing Cups for Hyper Compressor
Authors: Maggi Carmelo , Wojnar Jan , Tognarelli Leonardo
Published: December 2016

Hyper compressors are designed for LDPE production, compressing ethylene up to 3500bar with only two stages of compression, in order to reach conditions for the polymerization. The high operating and fluctuating pressure strongly impact design and life of all cylinder components.

The packing cups are among the most stressed components of a hyper compressor cylinder. They are particularly subjected to very high pulsating pressures, thus fatigue and wear. Therefore, they are periodically replaced during maintenance and are critical for availability of the hyper compressor.

A typical hyper compressor packing assembly contains 5 to 6 disc shaped packing cups that contain the plunger sealing rings at the internal diameter. The packing cups are provided with lube oil ducts to lubricate the sealing elements. Typically these ducts extend axially through the assembly to the injection points. For that purpose each packing cup could have a different number of lube oil passages. Moreover, at the external diameter are located passages for packing cooling oil. For these reasons each of the packing cups is a unique part with different machining features.

In order to optimize the availability of spare parts and standardize the product, a new design of hyper compressor packing cups has been evaluated, called further “all-purpose packing cup”. The idea was to make the packing cups all equal to each other, and potentially to reduce manufacturing and warehousing costs.

This idea has been realized by introducing in a single all-purpose cup, multiple sectors angularly offset with each other. Each sector contains the oil ducts required for a given cup position in the assembly. By rotating the cup about the plunger axis by e.g. 90° or 180° the desired sector can be activated (put in fluid communication with adjacent lube oil ducts). In this way the “all-purpose packing cup” can be mounted in each of the 5 to 6 different positions in the packing assembly.

The all-purpose cup design has been analyzed by a well validated FEA approach on the high cycle fatigue and flaw propagation safety margins. The analysis was performed considering all multiple possible load combinations where, depending on the assembly configuration, different active lube oil holes (holes that deliver oil to the plunger) were pressurized while all remaining ducts were left unpressurized.
Elastic and Plastic Microscopic Deformation of Polycrystalline Pure Titanium Under Tension
Authors: Tada Naoya , Doi Yuki
Published: December 2016

Commercial pure titanium has been widely used in aerospace, chemical, and biomedical industries for its lightweight, high corrosion resistance, high strength, high heat resistance and good biocompatible properties. Pure titanium takes hexagonal closed-pack structure with anisotropic elasticity and plasticity, and most of the components are polycrystalline aggregate with different crystal orientations. Therefore, inhomogeneous microscopic deformation always occurs by mechanical loading from the elastic condition and the inhomogeneity brings about various damages such as inhomogeneous plastic deformation, microcracking, necking, and so on. It is therefore important to investigate microscopic inhomogeneous deformation under elastic and plastic conditions. However only a few researches deal with the microscopic inhomogeneity because it is not easy to measure a small deformation of crystal grains under elastic condition or very small load. Recently, digital holographic microscope has been developed and a high-speed measurement of surface height of materials became possible with an accuracy of less than a micron meter in a relatively wide area. In this study, a tensile test of a plate specimen of commercial pure titanium was carried out on the stage of digital holographic microscope, and the microscopic deformation of grains was observed and measured under elastic and plastic conditions. During the test, the distribution of height of grains was measured in a fixed area on the specimen surface at each tensile loading step and the height distributions at different loads were correlated. It was found from the measurement results that each grain shows different deformation even under elastic condition with a small load, and the inhomogeneous deformation expanded with increasing the load to plastic condition. Also, a strong correlation was found in the height distributions under elastic and plastic conditions. This fact suggests that the microscopic deformation under plastic condition is predictable from that under elastic condition.
Influence of Notch Geometry on the Notch Vicinity Stress and Strain Responses
Authors: Rice Andrew Robert , Morrison Machel Leigh , Hassan Tasnim
Published: December 2016

The most common method used to determine the crack initiation life of a component containing a stress raiser in the low cycle fatigue regime is to calculate the maximum strain and then to use a strain-life curve. General practice is to base fatigue life estimates on the stabilized strain amplitude and to neglect the effects of transient behavior due to cyclic hardening or softening and ratcheting. For certain structures in which the accumulation of plastic strains may be significant, a separate check may be performed to ensure that these strains remain below a specified level. An objective of this research is to understand the notch tip local strain ratcheting and shakedown through finite element analyses and physical experiments. Towards planning a set of notched flat coupon experiments, this study performed analyses of various notched coupons under force-controlled cyclic loading. A question that will be addressed, what is the notch tip failure mechanism under a force-controlled load cycle with a non-zero mean force? Smooth specimens under such a force-controlled load cycle normally results in strain ratcheting. It is investigated whether notch tip strain responds in a similar manner under a force controlled loading cycle. The analysis results show that the strain ratcheting rate at the notch tip depends on the sharpness of the notch. In case of semi-circular and blunt elliptical notches shakedown of strain ratcheting within 25 cycles is observed, whereas for the sharp elliptical notch strain ratcheting doesn’t shakedown after 300 cycles. A novel observation made from the analysis results is that the mean stress at the notch tip gradually decreases with inelastic cycle while the stress amplitude remains unchanged. These result and future experimental plan on notch specimens are presented in this article.
Hardness and Microstructural Evolution of a JRQ A533 Cl.1 Steel Submitted to Thermal Annealing
Authors: Medina Almazán A. Liliana , Ovando Ramírez Lizandra S. , Auger Thierry
Published: December 2016

For operation of existing nuclear power plants (NPPs) beyond their design lifetime (up to 80 years), one of th7e main issues is the assessment of the performance of its structures, systems and components (SSC) during the period of extended operation. The reactor pressure vessel (RPV) is one of the components that could determine the lifetime of a NPP. Neutron irradiation at the temperature of operation of the nuclear reactors facilitates the chemical equilibrium of the alloying elements of the RPV steels, especially copper, while producing nanoscale precipitates (Cu, Mn-Ni-Si, and ∼M6C carbides) that leads to embrittlement [1–4]; by the other side, neutron irradiation also produces dislocation loops. Both, nanoscale precipitates and dislocation loops, produce loss of toughness and hardness increase. One of the proposals to manage the RPV time life is the thermal annealing, however there are still some concerns about its application, one of them is a possible detrimental effect by the development of new microstructural features that could lead to thermal embrittlement. Thus it is important to have data about the microstructural and hardness evolution of the RPV steels submitted to thermal annealing treatments.

The results of thermal treatments (450°C, 500°C and 550°C) performed in a A533 C1.1 (JRQ) steel during 0.5 to 1000 hours are presented in this work. JRQ steel has a bainitic microstructure, but well separated ferrite and bainite islands are observed at high magnification. The hardness evolution of such islands as a function of the thermal treatment is correlated with the number of precipitates present after thermal treatment as well as with the chemical evolution in these microconstituents. Thermal treatments of JRQ steel at 450, 500 and 550°C promoted the increase of hardness in both, bainite and ferrite. For the thermal treatment at 550°C, it is observed a maximum of the number of precipitates per μm2 in the treatments during 500 hours, which coincides with the depletion of the alloying elements in the bainite matrix and a decrease of Vickers microhardness (HV) in bainite. Cooper rich nanoprecipitates have been observed in the samples treated at 550°C during 500 and 1000 hours. The Cu content in the nanoprecipitates increase according the ageing time.
Direct Observation of Elastic and Plastic Strain Fields During Ductile Tearing of a Ferritic Steel
Authors: Coules Harry E. , Horne Graeme C. M. , Peel Matthew J. , Oliver Sam J. , Van Gelderen Derreck G. A. , Connolley Thomas
Published: December 2016

Residual and thermal stresses have a considerable effect on the process of brittle fracture. In addition to this, the effect of these stresses on elastic-plastic fracture is known to be significant. This is accounted for in structural integrity assessment methodologies such as R6 Rev 4 and BS 7910:2013 by introducing factors representing the interaction between primary and secondary stresses (those that do and do not contribute towards plastic collapse, respectively).

The initiation of ductile tearing in a ferritic pressure vessel steel was studied experimentally. Energy-dispersive X-ray diffraction was used to determine lattice strains in the vicinity of a crack tip in modified compact tension specimens at incremental loading steps until the initiation of ductile tearing. The X-ray diffraction measurements allowed the stress field to be evaluated with a high spatial resolution. At the same time, the pattern of total strain at the surface of the specimen was observed using digital image correlation. Prior to the experiment, two samples were subjected to localised out-of-plane compression ahead of the crack tip to introduce a residual stress field and hence significant crack loading in the absence of external load. Stress and strain field data for cracked specimens, with and without a pre-existing residual stress field, indicated significant differences in the development of plastic strain up to the point of tearing initiation. It is shown that this can only be explained when both residual stress and prior material hardening are taken into account.
Broad Variation in Friction Among Coated Studs
Authors: Worden Kathryn
Published: December 2016

This paper discusses a load cell experiment revealing a broad variation in friction amongst different blue coated studs. The affect of applying lubricant was also investigated. Details include basic coatings research, experimental apparatus, procedure, tabulated results, and observations.
Study on Dynamic Response by Alternating and Static Load
Authors: Otani Akihito , Kai Satoru
Published: December 2016

An inertia force in a seismic response of structure excited by an earthquake generates the seismic force acting on the structure. The handling of seismic forces has been being discussed in terms of how the seismic force on a piping controls the deformation of the piping, load-controlled or displacement-controlled. A seismic design code for nuclear facilities applied in Japan qualifies this kind of seismic forces as primary stress components which shall be limited to prevent any plastic collapse, on the assumption that the seismic force mainly consists of load-controlled loads and the deformation due to earthquakes is caused by the loads. The authors studied about a condition of plastic collapse occurrence by the relationship between response acceleration and displacement of SDOF system. And it was represented in a previous paper that plastic collapse hardly occurred to soft structure due to an inertia force generated from response acceleration tended to oppose a response displacement.

Several elastic plastic response analyses of elastic-perfectly-plastic SDOF model are performed with applying dynamic load and both of dynamic load and static load. By the results of the analyses, three forces, which are inertia force, element force and external force, are investigated the relations against the deformation.
Quality Assurance Guide to B16.20 Spiral Wound Gaskets
Authors: Hamilton Scott , Hantz Benjamin , Felder Kenneth
Published: December 2016

This paper discusses each of the requirements in ASME B16.20 for spiral wound gaskets that a purchaser can check, what they mean, and provides an approach to collect and complete documentation on individual gaskets. This paper will also include other items not mentioned in ASME B16.20 that a purchaser may want to document for reference.
A III+ Generation Pressurizer Stress Analysis and Evaluation
Authors: Zheng Gang , Shen Feng , Peng Yi , Wu Fang , Wang Jundong , Chen Lipei
Published: December 2016

A large scale pressurizer is used in III+ generation Nuclear Power Plant (NPP) which requires a high safety standard. The finite element method was adopted in this study to analyse and evaluate a III+ NPP pressurizer. A 2D integral symmetric model was created for the Upper Head, Lower Head and Shell which comprise the pressurizer. The typical Safety Relief Nozzle was selected to be representative of the nozzles in this analysis. A 3D local model was created for the Safety Relief Nozzle. The pressurizer was loaded under design condition to test its structure integrity and was further evaluated by American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME B&PVC) [1]. Furthermore, a model optimization method was proposed for the 3D nozzle model under ANSYS Workbench. The results showed that the pressurizer stress analysis fully met the ASME B&PVC criteria under design condition. The model optimization method was demonstrated to be valid and could be used for nozzle analysis and evaluation.
Structural Analysis Approach for Risk Assessment Under BDBE
Authors: Kasahara Naoto , Nakamura Izumi , Machida Hideo , Okamoto Koji , Sato Takuya
Published: December 2016

Based on the lessons learned from the Fukushima nuclear power plant accident, it is recognized the importance of the risk assessment and mitigation for failure consequences to avoid catastrophic failure of pressure equipment during severe accidents (SA) and excessive earthquake.

The objectives of structural design (from the first layer to the third layer of the defense-in-depth) is strength confirmation under assumed loading conditions. On the other hand, ones of risk assessment and mitigation (the forth layer of the defense-in-depth) is prediction of realistic failure scenarios.

Through investigation of failure locations and modes of main components under both severe accident and excessive earthquake, different failure modes from DBE(Design Basis Events) were identified for BDBE(Beyond Design Basis Events). To clarify these modes, the failure mechanisms were studied with some strength experiments.

For most of failure modes, their dominant parameters are inelastic strain rather than stress. So that large scale inelastic analysis methods were studied and extended to very high temperature and large strain.

By using above results, this paper has proposed the new structural analysis approach for risk assessment under BDBE. This is the extension of “design by analysis” concept. However it is clearly different from design approach from next viewpoints.

(1) Additional failure modes to design condition

Such additional failure modes induced by excessive loadings are considered for as local failure, creep rupture, creep buckling, ratcheting collapse and so on.

(2) Identification of dominant failure modes

Design codes require conservative evaluation against all of assumed failure modes. On the other hand, risk assessment needs adequate failure scenarios, where failure locations, modes and their order are important. For that reason, dominant failure modes have to be identified. To identify dominant modes, failure mode map concept was proposed.

(3) Best estimation

To estimate realistic accident phenomena, the best estimation is required. Therefore, dominant strength parameters and criteria without safety margins should be adopted. Through strength mechanism investigations, plastic and creep strain are recognized as more dominant parameters than stress for many failure modes. So that realistic inelastic analyses are recommended for BDBE.
Evaluation of Constraint Effect due to Crack Location and Bottom Head Shape
Authors: Choi Shin-Beom , Surh Han-Bum , Kim Jong-Wook
Published: December 2016

The aim of this paper is to evaluate the constraint effect due to the crack location and bottom head shape. To do so, two types of bottom head shape such as a semi-spherical bottom head and semi-elliptical bottom head were considered. In addition, five types of axial crack and two types of circumferential crack, classified by location, were adopted to conduct FE analyses. As a result, the bottom head shape does not affect the stress intensity factor of the circumferential flaw. Moreover, the crack location is not a sensitive parameter of the stress intensity factor for an axial crack located at the semi-spherical bottom head. In contrast, the crack location should be considered when the stress intensity factor of an axial crack located at the semi-elliptical bottom head is calculated. In addition, a heatup curve and cooldown curve were derived from the FE analysis results. As a result, the constraint effect owing to a crack location, except for the transition area, is not shown in the case of a semi-spherical bottom head. In the case of a semi-elliptical bottom head, the difference between each crack location is shown. These results will be helpful to enhance the understanding of the constraint effect and P-T limit curve.
Assessment Method for Complex Cracked Pipe Using Equivalent Pipe Concept
Authors: Bae Kyung-Dong , Ryu Ho-Wan , Kim Seung-Jae , Nam Hyun-Suk , Kim Yun-Jae
Published: December 2016

This paper proposes the assessment method of complex cracked pipes. Complex crack is the form of crack existing through-wall crack and surface crack at the same time [1–2]. Complex crack is mainly caused by PWSCC phenomenon in pipe with overlay maintenance welding. At first, circumferential surface crack is developed by PWSCC phenomenon in the weakest point which is nickel alloy welding point. And this crack propagates to axisymmetric crack in inner surface. After that the crack initiates in not only pipe part but also overlay maintenance welding part, complex crack shape which is main subject in this paper is formed. Unlike through-wall cracked pipes or surface cracked pipes, complex cracked pipes have a complex behavior because of combining through-wall crack behaviors and surface crack behaviors in cracked part. So calculating J-integral and defining amount of crack growth of complex cracked pipes are more difficult than those of through-wall cracked pipes and surface cracked pipes. Therefore, in this paper, the concept using equivalent pipe is proposed for assessment method of complex cracked pipes. To determine equivalent pipe, maximum loads of various through-wall cracked pipes having same circumferential crack size and different thickness are calculated. The reason why through-wall cracked pipe is selected for equivalent pipe is that many researches about J-integral and crack growth of through-wall cracked pipes are already performed and those results are sufficiently validated. In addition, it can be not only directly utilized procedure of leak before break assessment but also compared previous research results using only through-wall cracked part in complex cracked pipes referred to reduced thickness method. Maximum loads of complex cracked pipes and through-wall cracked pipes are calculated using stress-modified fracture strain model in finite element analysis [3–6]. This model is technics removing load bearing capacity in elements which satisfy damage criteria. Damage criteria is determined by using tensile experiment results, fracture toughness experiment results and validated by comparing with real size pipe experiment results. All the experiment results are in pipe fracture encyclopedia published by Battelle [7]. The experiments utilized in the paper are performed in operating temperature 288°C and materials of pipes are stainless steel SA376 TP304 and carbon steel A106 Gr.B. Finally, the results of equivalent through-wall cracked pipe thickness are provided.
Development of Seismic Isolation Systems for Sodium-Cooled Fast Reactors in Japan
Authors: Kawasaki Nobuchika , Watakabe Tomoyoshi , Wakai Takashi , Yamamoto Tomohiko , Fukasawa Tsuyoshi , Okamura Shigeki
Published: December 2016

Sodium-cooled Fast Reactors (SFRs) have components with thinner walls as compared with light water reactors, although Japan is an earthquake-prone country. Thus, seismic isolation systems have been conventionally employed in SFR system design to reduce seismic forces on the systems in Japan.

Implementation of seismic design in the reactor core and buckling design in the reactor vessel requires 8 Hz (or less) vertical frequency’s isolation system being applied. This paper introduces three isolation concepts to achieve the frequency.

The isolation systems, which enable vertical 8 Hz natural frequency, comprise thicker laminated rubber bearings (TRBs). By combining coned disk springs with TRBs, vertical natural frequency is in a range from roughly 3 Hz to 5 Hz. Combining pneumatic springs to RBs and adding the rocking suppression system, vertical natural frequency becomes under 1 Hz. All isolation systems need horizontal damping like oil dampers.

A vertical 8 Hz isolation system with TRBs and oil dampers is under development in Japan as a principal isolation concept. This system was selected because of its simple configuration and fewer issues to be resolved in the development. Since TRBs and oil dampers are basic isolation elements, they can be applied to other isolation systems.

The response acceleration of 5 Hz vertical isolation is 50% of that of 8 Hz based on the analytical survey. A series of static tests of coned disk springs was carried out to confirm design equations. Based on these knowledge, 5 Hz vertical isolation system with TRBs and the coned disk springs can be designed.

The response acceleration of 1 Hz vertical isolation is 10% of that of 8 Hz. A rocking suppression system was studied in the past, and the further simplification of this system is the largest challenge for this concept.

These three isolation concepts are isolation candidates for SFRs in Japan. To obtain enough seismic margins for each plant site, these isolation systems need to be developed.
Measurement of Flow-Induced Forces: Multiple Flexible Tubes in a Triangular-Pitch Bundle Subjected to Two-Phase Cross-Flow
Authors: Deri Enrico , Ries Olivier , Adobes André
Published: December 2016

Flow-induced vibrations of Steam Generator tube bundles are a major concern for the operators of nuclear power plants. In order to predict damages due to such vibrations, EDF has developed the numerical tool GeViBus, which allows one to evaluate safety margins and thereafter to optimize the SG maintenance policy.

The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be assessed by experiment. The database of dimensionless coefficients is progressively updated in order to cover most of existing tube bundle configurations.

Within this framework, a new test rig was presented in a previous conference with the aim of assessing parallel triangular tube arrangement submitted to a two-phase cross-flow. This paper presents the fluid-induced forces measured on a set of flexible tubes placed in a triangular pitch bundle both in the lift and drag directions. Two-phase flow excitation spectra are presented as well.
Identification of the Gradient of Mechanical Properties in Electron Beam Welded Joints of Thick Al6061-T6 Plate
Authors: Rekik W. , Ancelet O. , Gardin C.
Published: December 2016

In this paper, the mechanical behavior of the different metallurgical zones of the Electron Beam welded joint of thick Aluminum alloy 6061-T6 plates was identified by means of a single tensile test on round specimen oriented transversely to the fusion line.

Commonly, the analysis of tensile tests allows a global characterization of the weld joint behavior. However, in this work, specific post processing of results was developed in order to determine in addition to standard findings, the local behavior on each position of the weld joint. The identified behavior laws are then simplified using the Hollomon analytical model. Hence, an evolution of the Hollomon parameters (n, K) along the weld joint is proposed.

To validate the experimental methodology and the analytical approach, the experimental tensile test on crossed tensile specimen was numerically modeled. Experimental results and numerical simulations were in a good agreement which denotes of the reliability of the identified gradient model.

In a second step, for more accurate characterization of the electron beam welded joint, an optimized geometry of tensile specimen was numerically dimensioned and tested.

From these analyses, a relatively large heat affected zone with significant gradients of mechanical properties was highlighted. The fusion zone was qualified as the softest metallurgical zone but with a high strain hardening effect in contrary with the heat affected zone where the fracture occurs.
A Monte Carlo Implementation of the James-Ford-Jivkov Microstructurally Informed Local Approach Applied to Predict Fracture Toughness Across Irradiation Conditions
Authors: Ford Michael , James Peter
Published: December 2016

The need to predict changes in fracture toughness for materials where the tensile properties change through life, such as with irradiation, whilst accounting for geometric constraint effects, such as crack size, are clearly important. Currently one of the most likely approaches by which to develop such ability are through application of local approach models. These approaches appear to be sufficient in predicting lower shelf toughness under high constraint conditions, but may fail when attempting to predict toughness in the transition region, for low constraint geometries or for different irradiation states, when using the same parameters, making reliable predictions impossible. Cleavage toughness predictions in the transition regime are here made with a stochastic, Monte Carlo implementation of the recently proposed James-Ford-Jivkov model. This implementation is based around the creation of individual initiators following the experimentally observed distribution for specific reactor pressure vessel steel, and determining if these initiators form voids or cause cleavage failure using the model’s improved criterion for particle failure. This implementation has been presented previously in PVP2015-45905, where it was successfully applied across different constraint conditions; in the work presented here it is applied across different irradiation conditions for a second type of steel. The model predicts the fracture toughness in a large part of the transition region, demonstrates an ability to predict the irradiation shift and shows a level of scatter similar to that observed experimentally. All results presented, for a given material, are obtained without changes in the model parameters. This suggests that the model can be used predicatively for assessing toughness changes due to constraint-, irradiation- and temperature-driven plasticity changes.
Fatigue Crack Initiation Model of Type 316 Stainless Steel
Authors: Ishizawa Terushi , Nakamura Takao , Kitada Takanori
Published: December 2016

The fatigue tests under different conditions of strain range were conducted in air and the replica observation of fatigue cracks on specimen surface was also conducted. Using data obtained in fatigue tests, statistical dispersion of crack initiation life was quantified and modeled through an application of two-parameter Weibull distribution. The relationship between strain range and two parameters (s, shape parameter and Η, scale parameter) of crack initiation model was discussed. Thereby, the applicability of crack initiation model for arbitrary strain range was shown. Furthermore, the validation of P-curve applied crack initiation model was conducted by the simulation of fatigue life.
Plasticity Correction on the Stress Intensity Factor Evaluation for Underclad Cracks Under Pressurized Thermal Shock Events
Authors: Lu Kai , Katsuyama Jinya , Li Yinsheng
Published: December 2016

When conducting structural integrity assessments for reactor pressure vessels (RPVs) under pressurized thermal shock (PTS) events, the stress intensity factor (SIF) is evaluated for a surface crack which is postulated near the inner surface of RPVs. It is known that cladding made of the stainless steel is a ductile material which is overlay-welded on the inner surface of RPVs for corrosion protection. Therefore, the plasticity of cladding should be considered in the SIF evaluation for a postulated underclad crack. In our previous study, we performed three-dimensional (3D) elastic and elastic-plastic finite element analyses (FEAs) for underclad cracks during PTS transients and discussed the conservatism of a plasticity correction method prescribed in the French code. In this study, additional FEAs were performed to further investigate the plasticity correction on SIF evaluation for underclad cracks. Based on the 3D FEA results, a new plasticity correction method was proposed for Japanese RPVs subjected to PTS events. In addition, the applicability of the new method was verified by studying the effects of the RPV geometry, cladding thickness and loading conditions. Finally, it is concluded that the newly proposed plasticity correction method can provide a more rational evaluation with a margin to some extent on SIFs of underclad cracks in Japanese three-loop RPVs.