bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Material Model for the Crush of Spruce Wood
Authors: Neumann Martin , Eisenacher Germar , Schönfelder Thorsten , Wille Frank
Published: October 2017

Typical transport packages used in Germany are equipped with wooden impact limiting devices. In this paper we give an overview of the latest status regarding the development of a finite element material model for the crush of spruce wood. Although the crush of wood — mainly in longitudinal direction — is a phenomenon governed by macroscopic fracture and failure of wood fibres, we smear fracture and failure mechanisms over the continuous volume. In a first step we altered an existing LS-DYNA material model for foams, which considers an ellipse shaped yield surface written in terms of the first two stress invariants. The evolution of the yield surface in the existing model depends on the volumetric strain only. For the use with spruce wood, we modified the existing material model to consider the deviatoric strain for the evolution of the yield surface as well. This is in accordance with the results of crush tests with spruce wood specimens, where the crushing deformation was rather deviatoric for uniaxial stress states and rather volumetric for multiaxial stress states. We rate the basic idea of this approach to be reasonable, though other problems exist regarding the shape of the yield surface and the assumption of isotropic material properties. Therefore we developed a new transversal isotropic material model with two main directions, which considers different yield curves according to the multiaxiality of the stress state via a multi-surface yield criterion and a non-associated flow rule. The results show the ability to reproduce the basic strength characteristics of spruce wood. Nevertheless, problems with regularization etc. show that additional investigations are necessary.
Current Approaches to Fitness for Service of FRP in Chemical Handling Applications
Authors: Khaladkar Pradip
Published: October 2017

Fiber reinforced Plastics are used extensively and successfully for handling hazardous and corrosive chemicals. Their use stretches back to early 1960s when a series of high performing resins were introduced in the market. Since that time the industry has learned a great deal about the material selection, design, fabrication, repairs and in-service condition assessment and fitness for service as the final objective. The concept of Fitness for Service pioneered by the metals specialist and strongly aided by ASME is driving the same efforts for the use of plastics as well. This paper presents the basic concepts of Fitness for Service for plastics, specifically for composites and presents a couple of case histories which demonstrate its usefulness. It presents a description of on-going joint efforts in the chemical industry and related consortia and concludes with a recommendation for further research.
Design Method of Semi-Active Control Systems Minimizing the Error Between the Controlled Signals of the Semi-Active and its Reference Active Control Systems
Authors: Hiramoto Kazuhiko , Matsuoka Taichi , Sunakoda Katsuaki
Published: October 2017

We propose a semi-active vibration control method of structural systems based on the output emulation approach. In the output emulation approach, the semi-active control law is obtained so that the controlled output signal of the semi-active control system is similar to that of the reference active control system. The reference active control system is a virtual control system employing the actuator for vibration control and achieves the ideal control performance. Because the constraints of the semi-active control comes from the inherent dissipative characteristics of semi-active control devices a certain amount of the error of the controlled output signals between the semi-active and its reference active control system is unavoidable. To realize the semi-active control system based on the output emulation approach, i.e., the semi-active control system whose controlled output signal is similar to that of the reference active control system, the semi-active control law in the present study is obtained for minimizing an error function related to the controlled output. The error function is defined as a quadratic function on the output signal of the error between the semi-active and its reference active control systems and the Lyapunov matrix. The control characteristics of the reference active control law and free parameters in the Lyapunov matrix are searched with a boot-strap optimization algorithm for the optimal semi-active control system. Some simulation results are shown to claim the effectiveness.
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.
Research Progress of High Temperature Naphthenic Acid Corrosion Rules and Prevention Methods in Petrochemical Plants
Authors: Lv Yunrong , Chen Xuedong , Chen Zhiping
Published: October 2017

Naphthenic acid corrosion is a kind of corrosion state that occurs frequently in the high temperature locations of the petroleum distillation and secondary processing units. It is the main factor influencing the long-cycle safe operation of petrochemical plants, and also one of the hottest issues to be solved urgently in the petroleum refining industry. This paper overviewed the research progress related to high temperature naphthenic acid corrosion including the mechanisms, influencing factors, test and controlling methods; analyzed the engineering problems in the processing of high acid crude oil, pointed out the shortcomings of current research methods, and proposed the future research suggestions on the corrosion rules and prevention methods.
Continuity of Environmentally Assisted Fatigue and Stress Corrosion Cracking Based on Short Crack Growth Behavior of 316 Stainless Steel in Simulated PWR Primary Water
Authors: Shim Choongmoo , Takeda Yoichi , Shoji Tetsuo
Published: October 2017

Environmental correction factor (Fen) is one of the parameters to evaluate the effect of a pressurized high temperature water environment. It has been reported that Fen for stainless steel saturates at a very low strain rate. However, the relationship between environmentally assisted fatigue (EAF) and stress corrosion cracking (SCC) is still unclear. The aim of this study is to investigate the short crack growth behavior and possible continuity of EAF and SCC at very low strain rates. Short crack initiation and propagation have similar behaviors, which retard the crack growth between 100–200 μm in depth. We find that the striation spacing correlates well with the maximum crack growth rate (CGR) data. Based on the correlation, it is clarified that the local CGR on an intergranular facet was faster than that on a transgranular facet. Furthermore, the overall maximum and average CGR from the EAF data is well interpreted and compared with the SCC data.
Improvement of Seismic Resistance Performance of Thermal Power Plants by Applying Vibration Control Dampers
Authors: Fushimi Koki , Fujita Satoshi , Minagawa Keisuke
Published: October 2017

Improving earthquake resistance of power plants has been important since Great East Japan earthquake occurred in 2011. In particular, thermal power plants accounted for most of the current Japanese power supply. Thus, improving earthquake resistance of the thermal power plants has been paid attention than other power plants. In current coal-fired power plants, boilers are simply suspended from the top of the support structures. Therefore, boilers easily vibrate. In order to suppress vibration of boilers during earthquakes, stoppers made of steel are installed between a boiler and its support structure. The stoppers dissipate vibration energy by plastic deformation. Therefore, the stoppers are effective in earthquakes with relatively small numbers of repeat counts, but may not effect in earthquakes with relatively large numbers of repeat counts. Then we propose installation vibration control dampers in support structure to suppress more the vibration and perform also in the repetition of earthquakes. In this paper, a seismic response analysis using analytical models of the boiler structure is conducted. In addition, a vibration control damper suitable for installed in the support structure are considered. As a result, a rectangle hysteresis damper is suitable as vibration control damper for the support structure.
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.
Assessment of Aircraft Crash to Containment and its Effects on Reactor Cavity and Major Components
Authors: Sim Jae Min , Chang Yoon-Suk
Published: October 2017

Since a containment serves as the last barrier of NPP (Nuclear Power Plant), high level of safety should be ensured to isolate and protect internal devices against external events such as earthquake, hurricane and aircraft crash. The objective of this study is to assess structural integrity of the reinforced concrete with liner plate of a containment subjected to the aircraft crash, and to examine its effects on an interior structure and major components. In this context, systematic FE (Finite Element) analyses combined with SPH (Smoothed-Particle Hydrodynamics) model for fuel were carried out by taking into account different crash locations and colliding velocities. Damage of the reinforced concrete containment due to crushing and cracking as well as stress and strain of reinforced structure were evaluated. Subsequently, stresses of major components as well as damage of reactor cavity were calculated. As typical results, connector was derived as critical location of the containment with regard to interior components, high stress values occurred at penetration pipes and head fittings, which did not exceed their yield and ultimate strengths respectively.
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.
Thermomechanical Characteristics of Compacted and Non-Compacted Plain Weave Woven Laminated Composites
Authors: Al Kuwaiti Maryam H. , Mourad Abdel-Hamid I.
Published: October 2017

Nowadays, fiber reinforced composites are widely used in variety of industrial applications such as aircraft structures, automotive, pressure vessels and piping, etc. Aircraft standard fabrication process requires certain level of vacuum compaction (debulking) during the lay-up process, and a standard bagging method for curing in an autoclave. Every compacted component cured in an autoclave needs to be vacuum bagged employing edge breathers or bleeders and surface breathers. This process is repetitive and time consuming, and therefore needs further investigation. In this research, the combined effect of the removal of compaction and edge breathing on the thermomechanical behavior of plain weave woven laminated composites is studied. Tests have been conducted on 12 lamina plain weave composite specimens. Results indicated an insignificant difference on the thermomechanical properties between compacted and non-compacted specimens. Tensile, ILSS, flexural and DSC tests confirm that for the 12 lamina specimens compaction and edge breathing are not needed.
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.
Characterization of Additively Manufactured Heat Exchanger Tubing
Authors: Korinko Paul S. , Bobbitt John , McKee Haley , List Frederick , Carver Keith
Published: October 2017

Additive Manufacturing brings unique opportunities to the fabrication world, especially for complex, high value added components that are challenging if not impossible to fabricate using traditional technologies. There are several different technologies that can be used for making metal additive manufactured parts. In this study, selective laser melting (SLM) was used to fabricate conceptual process tubing. Through an evolutionary design and build process coupled with thermal and mechanical modeling, tubing with a unique additive manufacturing compatible geometry has been fabricated. This paper will briefly describe the application, which has a thermal swing from nominally 140°C to −40°C, the evolution of the design, and the characterization conducted to date. Finally, the challenges of designing and printing a coiled segment of this tubing that is 150 cm long will be described. The results will include non-destructive and destructive testing and evaluation. The data from tensile testing the first and second generations of the tubing will be compared. The properties and characterization of the surrogate coil will be described and discussed. Future component development and testing will be discussed for this unique AM process tubing.
Guidelines to the Assessment of Creep Rupture Reliability for 316SS Using the Larson-Miller Time-Temperature Parameter Model
Authors: Ramirez Christopher , Haque Mohammad Shafinul , Stewart Calvin Maurice
Published: October 2017

It is common practice to perform accelerated creep testing (ACT) using time-temperature parameter (TTP) models. The TTP models are calibrated to creep-rupture data at high temperature and/or stress and extrapolate to lower temperature and/or stress where data is not available. The long-term creep rupture behavior (at low temperature and stress) is often not available due to the quantity, duration, and cost of testing. A limited scope of creep-rupture data is often analyzed using the TTP models. When conducting long-term extrapolation, statistical uncertainty becomes an issue. The ability of the TTP models to accurately predict creep-rupture at long life is often limited and the inherent material properties can dramatically influence creep-rupture life. Unfortunately, there is no consensus on the statistic for assessing the quality of TTP extrapolation. This study demonstrates methodology to assessing the uncertainty in creep rupture predictions for 316SS using the Larson Miller parameter. Over 2,000 creep-rupture data points are collected and digitized from the NIMS, ASM, MAPTIS, and ORNL databases; metadata such as the material’s form, thermomechanical processing, and chemical composition are recorded. Statistical uncertainty is measured using the “Z parameter”, which describes the deviation of creep-rupture data to a TTP model. The ability of the TTP models to extrapolate to long life is analyzed via exclusion of data. This is accomplished by: excluding 50% of the data, and by excluding the longest 10% of the data. It is shown that culling data in any way produces more conservative creep rupture predictions. The spread of the dataset will also affect the width of the reliability bands.
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.
Influence of Initial and Welding Residual Stresses on Low Cycle Fatigue and Ratcheting Response Simulations of Elbows
Authors: Islam Nazrul , Hassan Tasnim
Published: October 2017

Earlier studies [1] showed that the ANSYS software package customized with an advanced rate-independent constitutive model was unable to simulate some of the low-cycle fatigue responses of elbow components. Hence, simulations are performed to investigate the influence of manufacturing and welding residual stresses on elbow low-cycle fatigue responses. The sequentially coupled thermo-mechanical finite element analysis is performed to determine the initial residual stress states in elbows due to the elbow manufacturing processes and welding of elbows to straight pipes. Real-time girth-welding processes are taken into account to simulate the welding induced residual stress field. Incorporating these initial residual stresses in the computations, low-cycle fatigue and strain ratcheting responses are simulated by ANSYS. The simulation responses demonstrate that the influence of manufacturing and welding residual stresses in elbows on its low-cycle fatigue responses is negligible. Hence, the question remains what is missing in the simulation models that some of the elbow low-cycle fatigue responses cannot be simulated.
Assessment of Uncertainty Sources in Fatigue Usage in Relation to Deterministic Margins, and Sensitivity Analysis
Authors: Garud Y. S. , Steininger David A.
Published: October 2017

Considerations of environmental effects in fatigue have resulted in proposals to augment the original basis and deterministic methods of fatigue assessment, such as in the ASME Code Subarticles NB-3200 and NB-3600. This process of deterministically combining various elements, each with its own set of safety factors, of the CUF-based assessment has the potential to be overly conservative and restrictive in practice. Furthermore, as in the commonly used deterministic design approaches, fixed safety factors are subjectively assigned; as a result the approach does not provide a logical basis to account for uncertainties or variability, and the resulting level of reliability cannot be assessed quantitatively. Therefore, it is useful and desirable to complement the simplicity of deterministic approach by relating the safety factor to target reliability (or probability of meeting the design criterion) so that an appropriately adequate conservatism can be utilized. The feasibility of such an inter-relation and its underlying probabilistic basis were demonstrated in our recent paper that provided a rational basis to account for the significant uncertainties in assessing the CUF-based fatigue including environmental effects.

The objective of this paper is to provide further assessment of the above basis for uncertainty quantification and its linkage to deterministic safety factor approach, with additional focus on the quantitative sensitivity analysis of varied sources of uncertainty in the CUF estimation. Results of the case studies implementing the proposed approach combining these uncertainties are presented. New expressions for sensitivity assessment are developed. Results of sensitivity analysis are presented with the goal of demonstrating the sensitivity/ranking of significant contributors to the final CUF uncertainty and the resulting deterministic margins in relation to the target (specified) reliability. The overall approach, also summarized in the paper, utilizes the generally accepted concept of propagation of input uncertainties based on the Taylor series method and the framework of the stress-strength interference technique. The utility and limitations of the approach are discussed in defining the acceptable deterministic margins and in quantifying the impact of various elements of conservatism in the current CUF based fatigue evaluations.
Comparisons of CFD and Traditional Solutions for Steam Hammer Events
Authors: Mayes Alex , Gawande Kshitij P. , Williams Dennis K.
Published: October 2017

Sudden pressure changes in the piping system of power plants are inevitable, and thus potential serious damage to large components, piping system, and piping supports is possible. To protect valuable components from such events, abrupt valve closure is employed to restrict the flow and prevent significant incidents and the resulting plant downtime. Unfortunately, when a valve is suddenly closed to prevent damage caused by unexpected events, a pressure wave within the flow is created, which travels upstream and impacts at the pipeline elbows. These events, involving sudden changes in pressure, are known as steam hammer. This steam hammer pressure wave, traveling through the pipe system, is capable of producing significant transient loads and stresses, which can disrupt the piping supports. As such there is a need for further investigation. The pressure wave depends on the characteristics of the flow, valve closure time, the elbow-to-elbow pipe section lengths, and the piping system flexibility. The present study performs a CFD analysis of the fluid experiencing such a sudden pressure change. OpenFOAM is used for this analysis and considers all the flow parameters, valve closure time, and critical length of the straight pipe. The study intends to provide a means of calculating the transient steam hammer loads applied on the pipe elbows, which consequently allows appropriate pipe support selection based upon the resulting peak loads. This computational analysis is compared to analytical methods for peak load determination such as rigid column theory, the Joukowsky method, and the steam hammer method explained by Coccio (1967) and Goodling (1989).
A Statistical Approach to Evaluating Single-Side Inlet vs Dual Inlet Temperature Distributions in Coke Drums
Authors: Penso Jorge , Bedoya Julian J. , Stoller Alex , Boswell Richard S.
Published: October 2017

Slide valves used to unhead coke drums have had a significant impact on the safety and efficiency of the unheading process in these vessels. Therefore, many refiners have changed to the inherently different inlet flow nozzle configurations that the slide valves have introduced. Single-side entry and dual-side entry have been common alternatives used as a result of the implementation of slide valves. Both of these configurations can depart from a centralized flow pattern and can create adverse flow and temperature distributions. Furthermore, these changes manifest themselves throughout the vessel with measureable mechanical integrity consequences in the cone, skirt, shell, and piping. This paper analyzes historic measured skin thermocouple data as a function of elevation of the coke drum. A total of three different refinery sites were included in this study; two of them having dual-side inlets, and one of them having a single-side entry. A statistical comparison was performed using the measurements focusing on the data that causes mechanical integrity problems in coke drums: temperature differences around the circumference and elevations, peak fill and peak quench rates.
Fatigue Modeling of 508 LAS Under Variable Amplitude Loading: A Mechanistic Based Analytical Approach
Authors: Barua Bipul , Mohanty Subhasish , Soppet William K. , Majumdar Saurindranath , Natesan Krishnamurti
Published: October 2017

A Chaboche-based evolutionary cyclic plasticity model is proposed to model the elastic-plastic behavior of 508 Low Alloy Steel (LAS), a commonly used material for Light Water Reactor (LWR), under variable amplitude loading. A novel parameter estimation technique is developed to incorporate the amplitude dependency of the material behavior into the earlier developed time-dependent material models based on constant amplitude fatigue test data. The resulting new material model can be referred as time-dependent-amplitude-independent material models. Variable amplitude fatigue tests under different environmental conditions (in air and pressurized water reactor (PWR) coolant water at 300°C) are analytically/mechanistically modeled. The analytical modeling results show that the time-dependent-amplitude-independent material parameters are able to capture the stress-strain state under variable amplitude fatigue loading. The developed model and reported material parameters can be utilized for more accurate stress analysis of safety-critical reactor components under real-life loading scenarios with variable/random loading transients. Recently a report on related 508 LAS material characterization work has been published by Argonne National Laboratory [1]. In this work a summary of the related work is presented.
Evaluation of Stress-Increase Caused by Geometric Imperfections in Longitudinally-Welded Hot Reheat Steam Piping of Mod. 9Cr-1Mo Steel
Authors: Shigeyama Haruhisa , Takahashi Yukio , Yaguchi Masatsugu
Published: October 2017

In this paper, effect of geometric imperfections on peak stress in softened heat affected zone (HAZ) of longitudinally-welded hot reheat steam piping of mod. 9Cr-1Mo steel was investigated by parametric two-dimensional finite element analyses. Four parameters representing amount of ovalization, amount of flattening, range of flattening and amount of linear misalignment were used in order to express the geometric imperfections of the pipe. The peak stress of a longitudinally-welded pipe with a flattening ratio of about 1% reached about 1.5 times of mean diameter stress. Then, estimation formulas of the stress-increase factor were developed based on the results of finite element analyses. In addition, creep damage distributions were also calculated using three kinds of creep damage models and changes of the creep damage due to the geometric imperfections were compared. The ratios of creep damage increase due to the geometric imperfections were found to be equivalent in the three creep damage models applied.
Phase Characteristics of Vortex Shedding From Tube Banks on Acoustic Resonance
Authors: Hamakawa Hiromitsu , Hino Satoshi , Nishida Eiichi , Kurihara Eru
Published: October 2017

This paper investigates the phase characteristics of vortex shedding from tube banks on acoustic resonance. We measured the time variation of a phase between surface pressures related to the lift force on a tube and acoustic pressure on a side wall related to the acoustic particle velocity when acoustic resonance occurred in in-line tube banks. The measured tube was installed at the second rows in the tube banks. As the peak level of spectrum of surface pressure fluctuations increased, the coherence between vortex shedding and wall acoustic pressure in the tube banks also increased. The phase delay between the lift force and acoustic pressure on the side wall was calculated by using a proposed modeling method. In addition, we discuss the verification of the synchronization feedback for a coupling condition between a sound field and wake oscillator.
An Algorithm for Parameter Identifications of Active Mass Damper and Primary Systems Based on Acceleration Measurements
Authors: Chang Chang-Ching , Wang Jer-Fu , Lin Chi-Chang
Published: October 2017

Active control systems have already been installed in real structures and are able to decrease the wind- and earthquake-induced responses, while the active mass damper (AMD) is one of the most popular types of such systems. In practice, an AMD is generally assembled in-situ along with the construction of a building. In such a case, the AMD and the building is coupled as an entire system. After the construction is completed, the dynamic properties of the AMD subsystem and the primary building itself are unknown and cannot be identified individually to verify their design demands. For this purpose, a methodology is developed to obtain the feedback gain of the AMD controller and the dynamic properties of the primary building based on the complex eigen-parameters of the coupled building-AMD system. By means of the theoretical derivation in state-space, the non-classical damping feature of the system is characterized. This methodology can be combined with any state-space based system identification technique as a procedure to achieve the goal on the basis of the acceleration measurements of the building-AMD system. Results from numerical verifications show that the procedure is capable of extracting parameters and is applicable for AMD implementation practices. In addition, control force execution time delay cannot be avoided in real application of active control. Small delay time can degrade the control performance and may cause system instability. In this study, time delay effect of AMD system is considered in the proposed methodology to obtain the feedback gain of the AMD controller and the dynamic properties of the primary building.
Study on the Mechanism of Fatigue Failure at Branch Connections Caused by Shell Mode Vibration
Authors: Kataoka Shunji
Published: October 2017

Acoustically induced vibration (AIV) is a vibration of piping systems caused by the acoustic loading generated mainly from pressure reducing devices. Recently, the capacities of the pressure reducing systems have been increased and some of the piping systems which are susceptible to acoustic fatigue, such as in flare and depressuring system. Demands on the development of reasonable design method for AIV is increasing. In this paper, the mechanisms of the fatigue failure of branch connection due to AIV were intensively studied. Firstly, the mechanism of the stress concentration was discussed. branch vibration caused by the shell mode vibration was assessed using several branch connection models, massless rigid model, fixed rigid model, and beam model. Next, the relationship between shell-vibration and stress concentrations is studied and re-organized based on acoustic vibration theories. Finally, the risk of the fatigue failure of the branch connection due to acoustic loading was discussed.
Towards Understanding Two-Phase Flow Induced Vibration of Piping Structure With Flow Restricting Orifices
Authors: Bamidele Olufemi E. , Ahmed Wael H. , Hassan Marwan
Published: October 2017

The current work studies air-water flow through a ½-inch flow restricting orifice installed in a 1-inch pipe. Investigation of two phase flow downstream the orifice and its effects on vibration of the piping structure have been carried out. Several flow regimes from bubbly to stratified-wavy flow have been analyzed to evaluate the effects of flow pattern, phase redistribution, bubble frequency, and liquid flow rate on the vibration of the structure. The liquid velocity fields have been obtained using Particle Image Velocimetry (PIV) along with post processing algorithm for phase discrimination. Proximity sensors have been used to capture the pipe response in two orthogonal directions. Also, a capacitance sensor was used to measure the two-phase void fraction. The results show that the magnitude and nature of vibrations of the piping structure is largely affected by the frequency and size of the bubbles upstream, vortex creation by pressure fluctuation downstream, liquid flow rate, and the flow pattern upstream. Slug flow and stratified flow patterns induced significant vibrations in the examined structure. The location of the transition region of slug flow on flow pattern maps, play important role in the dynamic response of the structure to the flow.