bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress Intensity Factor Interaction of Subsurface Flaws Under Notches
Authors: Hasegawa Kunio , Dulieu Pierre , Lacroix Valery 
Published: October 2017

If a single subsurface flaw is detected that is close to the component free surface, a flaw-to-surface proximity rule is used to determine whether the flaw should be treated as a subsurface flaw, or transformed to a surface flaw. The transformation from subsurface to surface flaw is adopted as flaw-to-surface proximity rules in all fitness-for-service (FFS) codes. These proximity rules are used under the condition of the component free surface without stress concentration.
On the other hand, subsurface flaws have been found under the notches, such as roots of bolts, toes in welded joints or geometrical discontinuities of components. The stress intensity factors of the subsurface flaws are affected by the stress concentrations caused by the notches. The interaction of stress intensity factor increases with increasing stress concentration factor and decreasing the ligament distance between the tips of the subsurface flaws and the notches for a given notch width. Such subsurface flaws shall be transformed to surface flaws at far distance of the notch tips for conservative evaluations.
This paper shows the interactions of stress intensity factors of subsurface flaws under stress concentration fields. Based on the interaction, a flaw-to-surface proximity criterion for a circular flaw is proposed under the stress concentration field induced by a notch.
Seismic Performance Evaluation for Steel-Frame-Structure Considering Member Fracture
Authors: Shiomi Kensuke 
Published: October 2017

Through the 2011 Tohoku Earthquake or the 2016 Kumamoto Earthquake, much larger earthquakes are considered recently in the seismic designs of large steel-frame structures. When structures are exposed by these severe ground motions, partial destructions in the structures, such as damage or fracture of members could happen. Especially, the low cycle fatigue of steel structures because of the repeated load from these long-term ground motions is a serious problem. However, current seismic performance evaluation method based on nonlinear dynamic analysis considers only elastic and plastic deformation of each member, excluding the fracture of members. If this member fracture happens during earthquakes, there is considered to be many effects on the seismic performance, like the changes of the vibration property, the dynamic response and the energy absorbance capacity of structures. Therefore, the fracture of members is preferably taken into account in the seismic performance evaluation for these large earthquakes.
This paper proposes the dynamic analysis method for steel-frame structures which can express the member fracture. Dynamic analyses considering and not considering member fracture under the repeated loads supposing the long-term earthquake are conducted to the FEM model of full-scale structure. By comparing each result, the effects of considering member fracture to the seismic performance such as the dynamic response and the energy absorbance capacity are discussed.
Experimental Determination of Elastic and Plastic LLD Rates During Creep Crack Growth Testing
Authors: Tarnowski K. M. , Davies C. M. , Nikbin K. M. , Dean D. W. 
Published: October 2017

Elastic and plastic load line displacement (LLD) rates are often ignored when analyzing Creep Crack Growth (CCG) tests due to difficulties in accurately determining their value for complex crack morphologies typical of creep. Instead, the total LLD rate is assumed to be entirely due to creep. This simplistic approach overestimates the crack tip characterizing parameter C* which is non-conservative.
This paper presents a review of the current method of interpreting CCG test data in ASTM E1457 and proposes an improved approach which accounts for the elastic and plastic LLD rates. Estimations of the elastic and plastic LLD rate are obtained from a partial unload immediately after load-up and a full unload, at the end of the test, prior to final failure. Some finite element validation of this method is presented. Implementing this approach will facilitate more realistic CCG laws.
Gap Effect on the Random and Fluid-Elastic Forces Acting in the Vibration of a Loosely Supported Tube Under Cross-Flow
Authors: Borsoi Laurent , Piteau Philippe , Delaune Xavier , Antunes Jose 
Published: October 2017

In degraded situations of heat-exchangers, tubes may become loosely supported while subjected to intense crossflow which generates both turbulent and fluid-elastic forces. The vibro-impacting regimes that result have been studied by the authors during these last few years, based on analytical experiments and numerical simulations. Taking advantage of this material, the paper aims at showing some dynamic effects that have been observed and drawing lessons concerning the vibration of tubes under cross-flow when they are linearly unstable.
If the fluid-elastic damping drops until the total damping becomes negative when the flow reduced velocity increases, a non-linear gap-system escapes from instability by reinforcing the sequence of impacts and its apparent frequency. On the other hand, the turbulent excitation is characterized by broadband PSDs that decrease with frequency. Thus the vibro-impacting response of the tubes results from a competition between the turbulent and fluid-elastic forces, according to a process that depends on the gap size. The fluid-elastic coupling forces may be either stabilizing (positive damping) or destabilizing (negative one), and, in a more amazing way, the random forces may be dissipative.
The paper illustrates the previous points from the tested experimental configuration which was mainly 1-DOF. Dimensionless results are given for this configuration. Extensions to more realistic tubes are discussed from numerical simulations of a straight beam with three loosely supports. The starting point of simulations is though experiments where the fluid-elastic forces would act, but not the turbulent ones, which would produce limit cycles in the phase space. Turbulence is then considered as perturbation of limit cycles, and as shown below by notably introducing a dimensionless “gap-turbulence” parameter, smaller the gap sizes are, larger the relative weight of turbulence is. The Rice frequency and the mean impact force are indicators of this relative weight and the competition between the fluid-forces.
From this general understanding, and using preliminary results with the beam model, a few guidelines are finally evoked for determining allowable gaps sizes in degraded situations. But a lot of work has to be done with more sophisticated models to concretize these ideas.
Fluid Structure Interaction for Tubes Bundles: Presentation of a Linear Equivalent Model
Authors: Broc Daniel , Artini Gianluca 
Published: October 2017

ASTRID is a project for an industrial prototype of a 600 MWe sodium cooled Fast Reactor, led by CEA. An important program is in progress for the development and the validation of numerical tools for the simulation of the dynamic mechanical behavior of the Fast Reactor cores, with both experimental and numerical parts. The cores are constituted of Fuel Assemblies (of FA) and Neutronic Shields (or NS) immersed in the primary coolant (sodium), which circulates inside the Fluid Assemblies. The FA and the NS are slender structures, which may be considered as beams, form a mechanical point of view.
The analysis of the dynamic behavior of tubes bundles immersed in a dense fluid is a major challenge in the nuclear industry (reactor cores, steam generators). In some cases, the excitation is given by the fluid flow, with a complex behavior which may lead to instabilities. The paper only considers the case of an external excitation (earthquake or shock). The fluid leads to two main effects: “inertial effects” with lower vibration frequencies and “dissipative effects” with a higher damping.
In the general case the fluid has to be described by the Navier-Stokes equations. It is possible to use the Euler linear equations in the case of vibrations of the tubes in a globally stagnant fluid. In all cases the modeling of the system could lead to huge numerical problems if each tube is described explicitly. Homogenization technics allow to limit the size of the problem.
Homogenization methods taking into account the Euler equations for the fluid have been developed, and widely used for analyses of the dynamic behavior of reactor cores. Only the inertial effects are theoretically described but the dissipative effects may be roughly taken into account by using a Rayleigh damping.
The paper presents an improvement of the method, allowing a better description of the dissipative effects, with a more general form of the expression of the forces exchanged between the fluid and the tubes. The theoretical basis of the numerical model are presented, as well as illustrations of the interest of the method: a better physical description is obtained for the dynamic behavior of the tubes bundle, particularly in the case of interactions with free fluid, without tubes.
Transient Impact of Valve Closure Times: Disagreements Between Design and Application
Authors: Telci Ilker T. , Koirala Shesh R. 
Published: October 2017

Many pressurized liquid systems require emergency shut down procedures in order to prevent damage to the piping and components, environmental contamination and fire hazard. The emergency shutdowns (ESDs) are facilitated by fast closing on-off valves installed at various locations along the piping system. When these valves close they create transient pressure waves traveling through the pipe network. These waves can be reflected at the dead-ends or closed valves. At locations where the pressure decreases below the vapor pressure, liquid column separation followed by a rejoining can cause creation of new transient pressure waves. As these waves travel, they may meet and superpose. These complex surge pressure wave behaviors require modeling of the pipe network and simulation of the transient event as the first step of a transient analysis. The second step of the transient analysis is to pin point the problems such as excessive surge pressures and dynamic loads that may occur in the system. The third step is to provide recommendations to prevent undesired transient consequences. One of the most important components of these recommendations include valve closure times during ESDs. Recent field measurements on the valve closure rates showed that the valve closure times recommended by the transient analysis were not accurately implemented. One reason for this disagreement between the designed closure rates and the applied closure rates is that the actuators of the valves introduce a time lag between the shutdown signal and start of valve closure. Another reason comes from the decision taken by the operator adjusting the actuator timing. Some operators may adjust the actuators such that the valves close within the prescribed time including the lag time which may result in very fast valve closures depending on the lag of the actuators. Other operators may choose to close the valves within the prescribed time including the lag time or even slower than the recommended rates. This may impair the orchestrate of the valve closure events designed in the transient analysis resulting in excessive surge pressures or dynamic loads.
This study investigates (i) the discrepancies between the recommendations from transient study made early in the design stage and (ii) the transient impact due to the deviation and/or misinterpretation of those recommendations. Specifically, in this study, these problems are demonstrated in a case study from LNG - Ship loading systems. The results indicated that transient analysis is the essential tool in finding critical components of the system in the field conditions providing a variety of solutions such as valve closure rate adjustments, flow rate reduction at the beginning of ESDs via pump trips and pipe size increase at dead legs. This study showed that the pressure piping systems can deviate from initial design under dynamic field conditions and frequent inspections of the ESD valves are crucial for safe operations of these systems.
Influence of Impact Angle and Real Target Properties on Drop Test Results of Cubic Containers
Authors: Zencker Uwe , Qiao Linan , Völzke Holger 
Published: October 2017

Drop test scenarios with cubic containers without impact limiters at interim storage sites or in a final repository have been investigated by numerical simulations. An ideally flat drop is impossible to conduct as a free fall of a container even under laboratory conditions. Dynamic stresses and strains inside the container structure are sensitive to the impact angle. Even very small impact angles cause remarkable changes in the experimental or numerical results when a flat bottom or wall of a container hits a flat target.
For drop tests with transport packages the International Atomic Energy Agency (IAEA) regulations define an essentially unyielding target. In contrast, potential accident scenarios for storage containers are derived from site-specific safety analyses or acceptance criteria in Germany. Each interim storage site or repository has a yielding or so-called real target with individual structural and material properties. The real target acts as a kind of impact limiter. A more conservative container design is required if the impact limiting effect of the target is not considered.
Seismic Design of Free Standing Racks in Japanese Nuclear Power Plants
Authors: Takaki Yu , Taniguchi Katsuhiko , Kishimoto Junichi , Iwasaki Akihisa , Nekomoto Yoshitsugu , Kuga Tohru , Kameyama Masashi 
Published: October 2017

The free standing racks are spent fuel storage racks with self-sustained structure without fixation to the pit floor or pit walls. If a free standing rack receives a force to move it due to an earthquake, the force acting on each member of the rack is reduced in compared to the floor-anchored racks owing to sliding of the free standing rack. Now it is planned to exchange the existing floor-anchored racks with the free standing racks to secure higher seismic resistance.
In previous studies, efforts were made to establish a behavior analysis model that allows for evaluation of sliding and rocking behaviors of free standing racks and to make out a seismic design method based on an evaluation technique to evaluate, in a conservative manner, vibration test results of full-scale free standing racks.
The free standing racks which consist of connected eight racks are designed with this seismic design method. It was confirmed that the free standing racks have enough seismic resistance by performing evaluation using the basic seismic motion and making an analysis on beyond the design event.
Cylinder Axial Crack Reference Stress Comparison Using Elastic-Plastic FEA 3D Crack Mesh J-Integral Values
Authors: Thorwald Greg , Vargas Pedro 
Published: October 2017

The reference stress for axial (longitudinal) surface cracks in cylinders is compared using equations from the 2016 API 579-1/ASME FFS-1 and BS 7910:2013 engineering standards, and by using J-integral values from elastic-plastic Finite Element Analysis of three-dimensional crack meshes to compute crack front reference stress. The cylinder axial surface crack reference stress solutions from the two standards differ, and further examination and comparison is desired.
To evaluate if a crack is unstable and may cause catastrophic structural failure, the Failure Assessment Diagram method provides an evaluation using two ratios: brittle fracture and plastic collapse. The FAD vertical axis gives the Kr stress intensity to toughness ratio, and the FAD horizontal axis gives the Lr reference stress to yield strength ratio. The details of the FAD method are described in both standards, along with stress intensity and reference stress solutions for various geometries and crack shapes. Since the cylinder axial surface crack reference stress solutions from API 579 and BS 7910 differ, J-integral values are used to compute reference stress trends that provide additional insight and reveal if there is agreement with one or the other or neither standard.
Computing reference stress from crack front J-integral results is described in API 579 Annex 9G Section 9G.4. A 3D crack mesh is created for each crack and cylinder size. Along the crack front the focused mesh pattern uses initially coincident groups of nodes at each crack front position. The group of nodes at each location on the crack front are initially coincident and can separate to help model the blunting at the crack front as the loading increases and local plasticity occurs. Post processing calculations use the J-integral versus load trend and the material specific Kr at Lr = 1 ratio to determine the reference stress geometry factor. The reference stress is computed at each crack front node to find the maximum crack front reference stress value for comparison to the engineering standards’ reference stress solutions.
A range of surface crack sizes in thin to thick wall cylinders with internal pressure are used to examine reference stress trends. Standard pipe sizes and typical pipeline steel material is used in the analysis.
The difference in reference stress solutions was found during an engineering critical assessment, so the J-integral approach was used to improve the solution to reduce conservatism and allow the component to remain in service.
Determining Accuracy and Repeatability of Torque Through Powered Equipment
Authors: Hamilton Scott , Hantz Benjamin F. , Wright Jason 
Published: October 2017

This paper explores torque wrench accuracy, one source of the overall inaccuracy associated with bolted flange joint assembly. The accuracy and repeatability of various pneumatic torque wrenches were tested and analyzed. Pneumatic torque wrenches were benchmarked against a hydraulic wrench which has a lower perceived bolt load scatter. The testing was performed on two mock-up flanges, NPS 8 Class 150 and NPS 16 Class 300 raised-face flanges with spiral-wound gaskets. The analysis compares the accuracy and repeatability of the following: each tool versus its manufacturer’s claims; duplicate models of the same tool; and overall tool type (pneumatic or hydraulic) versus another tool type. Because accuracy is closely related to tool calibration, torque wrench calibration method and frequency are also discussed.
There are several methods of applying axial load through torque that have been used within the industrial assembly of Bolted Flanged Joint Assemblies (BFJA’s). The most common tool used within the industry is the manual torque “clicker” wrench which traditionally allows an assembler to reach 600ft/lbs. While companies make wrenches that achieve higher amounts of torque, they are harder on the assembler to use so other tools, such as hydraulic and pneumatic torque wrenches (Powered Equipment), that require less physical strength are used instead. This paper will discuss the accuracy and repeatability of pneumatic and hydraulic wrenches and compare them to the manufacturer’s/industry standards.
Hot Tap Fittings: To Extrude or Fabricate
Authors: McKone Tommy , Cooper Grant 
Published: October 2017

A common means of accessing a pipeline for such operations as diversions, new connections, maintenance, etc. is to use a hot tap. Hot taps are widely accepted in the industry and offer several advantages over shutting down the pipeline such as reducing production downtime, eliminating the loss of pipeline product and preventing unwanted carbon emissions.
Split tee fittings (Fig. 1) are the most effective way to complete a hot tap and are designed in such a way that they can be left in place on the pipeline safely while minimizing future integrity risks and impact to operations. There are two ways in which these fittings can be manufactured; one is to use a welding fabrication method whereby a branch connection is welded to a run1 with associated opening. The second is to use an extrusion technique that forms heated plate or cylindrical shell into a tee shape. Techniques used in extrusion must be tightly controlled to ensure correct wall thickness, material homogeneity, mechanical properties, and geometric conformity. Fabricated fittings must have rigidly controlled rolling, cutting, welding, and heat treatment when applicable.
This paper will present the advantages and challenges of both techniques and how modern analysis methods (Finite Element Analysis) helped in the development of a new extrusion process to overcome the issues associated with this method. The paper will also highlight what operators need to consider when choosing between an extruded or fabricated fitting.
Determination of Temperature Limits for Heat Exchanger Joint Assembled of Solid Stainless Tubesheet With Girth Flanges
Authors: Mohamed Bassel Y. , Hamdy Mohamed A. , Eid Tamer I. 
Published: October 2017

Although heat exchangers are built according to international codes and proved to be leak tight by hydrotesting at ambient temperature, leak of stainless steel heat exchangers girth flanges at the tubesheet gaskets likely occurs during startup and operation at high temperatures. Accordingly, evaluation of the design to assure leak free operation considering anticipated thermal events is required.
WRC 510 bulletin [4] introduces a simplified analytical method to address this issue and provides safe guarding against leakage.
This study is performed on solid 300 series stainless stationary tubesheet flanged with girth flanges having the same or different material of construction.
A thermal finite element analysis is performed to obtain the transient temperature distribution through a girth flanges and stationary tubesheet assembly of a heat exchanger using SOLIDWORKS® SIMULATION [7]. The model of the flanged joint consists of two girth flanges with a tubesheet and gaskets in between. Thermal time dependent transient analysis of the above model is conducted to compute the temperature distribution in the flanged joint assembly for different time steps.
Further, these temperature distributions are used to compute the expansion, deflection and rotation for the flanged joint parts using WRC 510 bulletin [4] equations.
The study determines both the permissible heating rates during startup and the temperature limits, for the example studied, which are suitable for using solid 300 series stainless tubesheet for both material types of the girth flanges to have the most leak tight & economical assembly when the minimum design metal temperature allows these materials.