bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Safety Assessment of Marine Operations From a Long-Term Perspective: A Case Study of Offshore Wind Turbine Blade Installation
Authors: Verma Amrit Shankar , Gao Zhen , Jiang Zhiyu , Ren Zhengru , Vedvik Nils Petter
Published: November 2019

A marine operation is a complex non-routine activity of limited duration carried out in offshore environment. Due to safety reasons, these operations are normally performed within specific sea state limits, which are derived from numerical modelling and analysis of hazardous events. In view of the uncertainties in the assessment of structural responses under stochastic environmental conditions, these limiting curves correspond to a target structural failure probability recommended in offshore standards (for example, 10−4 per operation as specified by DNV-GL). However, one of the main limitations is that these curves do not reflect site-specific safety assessment. The current paper presents a novel methodology for assessing the structural safety level of marine operations from a long-term perspective. The methodology includes estimation of extreme response distribution under all possible operational sea states (i.e. the operational domain under the limiting sea states) for a given offshore site and is compared to the response limit to obtain an average failure probability. A case study is also presented for a blade root mating process onto preassembled hub using a jack-up crane vessel and risk of impact between root and hub is considered critical. Global time-domain simulations are performed using multibody dynamics, and extreme value distributions for impact velocities are derived for different wind-wave conditions. The allowable impact velocity between the blade root and the hub is determined by an explicit finite element analysis of the damage at the blade root. Finally, the average failure probabilities considering the operational domain are obtained for four different European offshore sites and are compared to the target level of structural failure probability considered for the limiting sea states.
Nonlinear Analysis of an Oscillating Water Column Wave Energy Device in Frequency Domain via Statistical Linearization
Authors: S. P. da Silva Leandro , Pesce Celso P. , Morishita Helio M. , Gonçalves Rodolfo T.
Published: November 2019

Wave energy converters (WECs) are often subject to large displacements during operating conditions. Hence, nonlinearities present in numerical methods to estimate the performance of WECs must be considered for realistic predictions. These large displacements occur when the device operates on resonant conditions, which results in maximum energy conversion. The system dynamics are usually simulated via time domain models in order to being able to capture nonlinearities. However, a high computational cost is associated with those simulations. Alternatively, the present work treats the nonlinearities in the frequency domain via Statistical Linearization (SL). The SL results are compared to the Power Spectrum Density (PSD) of time domain simulations to verify the reliability of the proposed method. In this regard, the work initiates with the derivation of the governing equations of the air-chamber and the Oscillating Water Column (OWC). Then, the SL technique is presented and applied. The SL results show a satisfactory agreement for the system dynamics, mean surface elevation, mean pressure, and mean power compared to time domain simulations. Also, the SL technique produces a rapid estimation of the response, which is an effective approach for the evaluation of numerous environmental conditions and design, and further optimization procedures.
Gaining Insight in Wind Turbine Drivetrain Dynamics by Means of Automatic Operational Modal Analysis Combined With Machine Learning Algorithms
Authors: Gioia Nicoletta , Daems P. J. , Peeters C. , Guillaume P. , Helsen J. , Medico Roberto , Deschrijver Dirk , Dhaene Tom
Published: November 2019

Detailed knowledge about the modal model is essential to enhance the NVH behavior of (rotating) machines. To have more realistic insight in the modal behavior of the machines, observation of modal parameters must be extended to a significant amount of time, in which all the significant operating conditions of the turbine can be investigated, together with the transition events from one operating condition to another. To allow the processing of a large amount of data, automated OMA techniques are used: once frequency and damping values can be characterized for the important resonances, it becomes possible to gain insights in their changes. This paper will focus on processing experimental data of an offshore wind turbine gearbox and investigate the changes in resonance frequency and damping over time.
Effect of Reynolds Number on Local Scour Around a Monopile in Steady Current
Authors: Lou Xiaofan , Zhang Kaibing , Chen Zhenhong
Published: November 2019

The effect of Reynolds number (Re) on the local scour around a monopile encountering steady current was investigated experimentally in a water flume. The experiment was performed using circular cylinders with different diameters under two different freestream velocities, covering both clear-water and live-bed scours and a Reynolds number range of approximately 9,000–60,000. The time-series of the scour depth was recorded during the whole scour process and the scour pit was scanned after the scour process reached equilibrium. Results are presented in terms of the equilibrium scour depth, the time-scale of the scour process and the three-dimensional scour profile at different Reynolds numbers. For both clear-water and live-bed scours, the time history of the scour process indicate that the time-scale becomes larger as Re increases. It is also found that the normalized equilibrium scour depth, as well as the normalized scour radius, decrease with the increasing Re. An empirical equation of the equilibrium scour depth is derived as a function of Reynolds number based on the experimental results so as to better account for Re effect in the scour design.
Experimental and Numerical Study on the Hydrodynamic Properties of a Simplified Floating Hydrocarbon Storage Facility
Authors: Zhang Chi , Fonseca Nuno , Magee Allan R. , Ren Nianxin
Published: November 2019

A compliant modular floating hydrocarbon storage facility (FHSF) has been proposed for ocean space utilization. The FHSF consists of many floating hydrocarbon storage tanks (FHST) and several surrounding barges. These modules are connected in proximity through soft mooring system which reduces the environmental loads significantly. However, there are concerns on the potential resonance in the narrow gaps and the strong hydrodynamic interactions. This paper focuses on the hydrodynamic properties of a simplified subsystem which qualitatively represents part of the behavior of the entire FHSF but with reduced complexity. This subsystem consists of two FHSTs and a barge frame and is suitable for evaluating numerical analysis tools. Experimental studies on the subsystem and the complete system were performed in the ocean basin in SINTEF Ocean. A series of random, wide-band and realistic random wave tests were carried out to generate benchmark data to verify numerical analysis tools. Empty, partially loaded and fully loaded conditions were tested. The free surface elevations in the narrow gap and in the internal tank were obtained. A frequency domain numerical model of the subsystem was established in WAMIT based on linear potential theory. Higher order boundary element method (HOBEM) has been utilized to improve the accuracy and convergence. The influence of internal liquid (sloshing) inside the tanks is also considered in the linear range. The mooring system is simplified as linear springs. Linearized damping is introduced. The response amplitude operators (RAOs) of 6 degrees of freedom (D.O.F) and free surface elevations from numerical and experimental studies under the head sea conditions are compared. Good agreement on the motion RAOs are found, but significant differences are found on the RAOs of the elevation of the free surface. Finally, the influence of significant gap resonances is used to generate insight into how these problems might be mitigated.
Effect of Special Outermost Module Designs on the Hydrodynamic Responses of a Modular Multi-Purpose Floating Structure System
Authors: Ren Nianxin , Zhang Chi , Magee Allan Ross , Liu Xiao , Hellan Øyvind , Ang Kok Keng
Published: November 2019

The present work investigates the effect of different outermost module designs on the hydrodynamic responses of a modular multi-purpose floating structure (MMFS) system. The MMFS system is initially designed for a mild sea zone. As the entire system consists of more than 20 bodies, a simplified system with seven interconnected standardized modules is proposed for numerical and experimental study. In this simplified system, each module is assumed as a rigid body. Both hydrodynamic interactions and mechanical coupling among modules are taken into consideration in the time-domain numerical analysis. The structural deformation of the MMFS system mainly occurs in the connectors among adjacent modules. The maximum deformation appears at the connectors between outermost modules with the internal modules. To reduce the deformation and improve the concept, two special design, outermost module of deeper draft and outermost module with additional heave plate are proposed and investigated for the MMFS system. The numerical results indicate that the two proposed designs for the outermost module can significantly reduce the hydrodynamic responses of the MMFS system, especially the motion of the outermost module and the vertical bending moment on the connector. The extreme responses of the MMFS system with different outermost module designs are also studied and compared.
How Heuristics and Biases Impact Judgment and Decision Making in Well Integrity Operations
Authors: Teodoriu Catalin , Salehi Saeed
Published: November 2019

The contribution of the human factor in major oil and gas accident events is fully-fledged and admitted. The root cause analysis and incident investigation of these accidents reveal that many of them could have been prevented, with the perception that there was a cascade of failures in human factor elements. This is easy to comprehend, as the human factor has not been accentuated thoroughly in this industry and traditionally the focus has been on personnel knowledge and competence.

A previous paper presented at OMAE 2018 had a brief overview of well integrity, and the pivotal role of cementing operations in well control. The critical role of human and organizational factors in cementing operations and well control was addressed. Furthermore, an outline of the newly implemented SEMS II regulations was also offered, with insight into adjustments that could enhance this program’s modest requirements.

In this paper, the goal is to examine the key heuristics that operational people employ in well integrity procedures. Some of these cognitive biases include status-quo and confirmation biases. Several examples will be discussed to show how underlying biases can lead to improper decisions. Unfortunately, some of these biases have been embedded in companies cultures for several decades now, and are hard to change overnight. Some of these can often lead to tremendous operational costs and not necessary solving the problem. It is highly recommended that training schools consider the problems of psychological biases and start implementing case studies for improvement in judgment and decision making.
Evaluation and Optimization of Trimaran Configurations Using Deep Neural Network
Authors: Yu Dongchi , Wang Lu , Zhong Qian , Yeung Ronald W.
Published: November 2019

To determine the optimal trimaran configuration for best calm-water transportation efficiency, a Deep Neural Network (DNN) is trained with sufficient computational results provided by, as an example, an in-house developed potential-flow code called Multi-hull Simple-source Panel Method (MSPM). Even though the computational method is extremely efficient in accurately establishing the mapping relation between the key design parameters governing the trimaran configuration problem and the resulting calm-water transportation cost, the modeling efforts are non-trivial since the number of geometric and configuration parameters in a typical situation is large. In this work, we demonstrate how the “Big Data” of computational results can be effectively utilized in training a DNN. An optimal trimaran configuration solution within a specified design space, subject to realistic range constraints, can be quickly determined in a minimal amount of time with the DNN. A demonstrative case study is provided for illustration.
B31 J SIF and k-Factor Test of Sweeplus®
Authors: Liu Yuqing , El Jaouhari Ismat , Diwakar Philip , Lin Dan
Published: November 2019

Formerly, an entire catalogue of 90 deg. branch connections called Sweeplus® was developed and accessed to mitigate acoustic induced vibration (AIV) in piping systems exposed to high frequency vibration. Parameters related to cyclic loading was completed on the Sweeplus® fitting to determine the stress intensification factor (SIF) and flexibility factor (k-factor), in accordance with the latest revision of ASME B31J-2017 code and reported in this paper. A Sweeplus® fitting was welded in a Markl test fixture and controlled through LabView software. The testing configuration and equipment were those used in Kahn test reported in WRC 329. K-factor tests were conducted for the in-plane thru both branch and header piping, and the out-of-plane thru branch. SIF tests were performed in the out-of-plane thru branch. The tests confirmed the SIF of Sweeplus® is less than one which means the fatigue life of Sweeplus® is significantly extended, not only under high frequency AIV excitation, but also under low frequency flow induced vibration (FIV) and thermal loading.
Sustained Pressure Test Results for Surface Scratches in PE4710, Cell Classification 445574C High Density Polyethylene Pipe Material
Authors: Hebeisen Jason , Adams Timothy M. , Munson Douglas
Published: November 2019

Mandatory Appendix XXVI of the ASME Boiler and Pressure Vessel Code (BPVC), Section III, Division 1 currently permits the use of high-density polyethylene (HDPE) in buried safety Class 3 piping systems. There have been concerns about how the slow crack growth (SCG) of HDPE emanating from surface scratches that may occur during fabrication or installation. The current allowable scratch depth in Appendix XXVI is 5% of the pipe wall thickness for pipe 4 inch and less in nominal diameter pipe and 0.040 inch (1mm) for pipe greater than 4 inch nominal diameter. This report presents the results of further investigation into the SCG rates by testing of notched PE 4710 HDPE pipes made from PE 4710 cell classification 445574C bimodal resins that meet the requirements of Appendix XXVI. These tests were conducted by first making razor-cut surface scratches in 4 inch, 8 inch, and 16 inch nominal diameter piping made by three different piping manufacturers using three different resins. The pipes were end-capped and pressure-tested at elevated temperature until failure, or until a prescribed number of test hours were reached. The razor cuts were at different depths and lengths so as to result in a variety of stress intensities, net section stresses, and nominal stresses. Following failure, or after the prescribed number of test hours was reached, the pipe specimens were inspected to determine the amount of SCG. This paper presents the results of the testing and recommended ASME BPVC Appendix XXVI changes for allowable crack depth based on the testing are provided.
Dancing Manhole Cover: A Nonlinear Spring-Mass System
Authors: Tijsseling Arris S. , Vasconcelos Jose G. , Hou Qingzhi , Bozkuş Zafer
Published: November 2019

Dancing manhole covers are an intriguing and curious phenomenon but extremely dangerous for road vehicles as well as pedestrians. They are reported worldwide after heavy rainfall in urban environment. Stormwater systems are overloaded with running water containing large entrapped air pockets for which manholes form an escape route. However, heavy lids cover the manholes and they are supposed not to move.

An attempt is made to understand the physics behind dancing manhole covers by means of simple spring-massdashpot modeling. The ingredients are liquid slugs, air pockets, and fluid-structure interaction.
Modification of the MPC Omega Model to Predict Primary and Tertiary Creep
Authors: Haque Mohammad Shafinul
Published: November 2019

The MPC Omega model has become popular in recent years for the prediction of creep deformation. Successful predictions of the tertiary creep for a wide range of materials are available. The Omega model relates the strain as a linear function of the natural logarithm of strain-rate. It is assumed that the primary creep is a short-lived phenomenon and can be neglected. The Omega model is unable to predict the primary creep deformation. Often primary creep is a long-lived phenomenon and cannot be neglected. A mathematical modification can be performed to incorporate the primary creep curve in the Omega model. A common approach is by adding a work hardening function to the original constitutive model. Approaches using power, or exponential, or logarithmic work-hardening function are available. However, it is difficult to discern which function is the best for accurate prediction. In this study, the Omega model is modified to predict the primary and tertiary creep deformation curve by adding a hyperbolic tangent work hardening function. A metamodel incorporating the four modified Omega sub-models (power, exponential, logarithmic and hyperbolic tangent) is developed. The metamodel enables the determination of the most suitable model for a given material and avoids the force fit of a preselected model. Short, medium, and long-term creep deformation data for alloy P91 (pipe) and G91 (plate) at two isotherms of 600°C and 650°C are used to calibrate the metamodel. The data include five stress levels ranging from 70 to 160 MPa including creep life from 233 to 1.1 × 105 hrs. A detail calibration process is provided. A numerical analysis is performed to compare the four submodels. It is observed that the selection of the most suitable function depends on the loading condition and material properties. Based on the analysis, a recommendation to select the suitable work-hardening function to predict the primary and tertiary creep deformation curve is presented.
Repair of B31.1 Fiber Reinforced Polymer Piping System Using Carbon Fiber Reinforced Polymer
Authors: Hebeisen Jason , Adams Timothy M. , Dubovecky Bruce , Jimenez Tomas
Published: November 2019

This paper describes the use of Carbon Fiber Reinforced Polymer (CFRP) for the repair of leaking Fiber Reinforced Polymer (FRP) pipe. The existing piping system, which is used for slurry transport, consisted of straight pipe, reducers, and elbows connected by bell and spigot joints. The piping system was evaluated for pressure, deadweight, and fluid thrust loads in accordance with B31.1 Power Piping Code and ASME BPVC Section III, Code Case N-155. The pipe leaks and joint repairs were in accordance with ASME PCC-2 and ASME BPVC, Section III, Code Case N-155. The CFRP repair was done with Aegion TYFO® Fibrwrap® carbon fiber reinforced fiber wrap (TYFO SCH-41-2X) saturated with epoxy. The repair uses the unidirectional carbon fiber installed in layers 90° to each layer. The circumferential layers are used for hoop pressure stress while the axial layers restrain axial pressure, deadweight, and fluid thrust loadings on the pipe.
Proposal of New Code Case for Alternative UT Flaw Evaluation and Acceptance Criteria of Subsurface Flaw Near Component Surface in Section VIII Division 2 and Division 3
Authors: Terada Susumu
Published: November 2019

The current proximity rules for subsurface flaws near the surfaces of component in Section VIII Division 2 and Division 3 are different from those of Section XI. The current acceptance criteria of Sec. XI were revised in 2008 in order to eliminate the discontinuity of acceptable and unacceptable flaws based on the research work by Dr. K. Hasegawa and Dr. K. Miyazaki el. The fracture mechanics evaluation for the current and proposed alternative acceptance criteria for subsurface flaws near a component’s surfaces based on Section XI have been performed. The stress intensity factors for transformed surface flaws of the current acceptance criteria for subsurface flaws near component’s surfaces are much larger and too conservative compared with the overall acceptance criteria. It is confirmed herein that the proposed alternative converting rules have enough fracture margin. Therefore, the safety level of this proposal is almost the same as that of the current code. The proposed alternative acceptance criteria may avoid unnecessary weld repairs, and eliminate the discontinuity of acceptable and unacceptable flaws in the area near the component’s surface.
A Transfer Matrix Method for Free Vibration Analysis of Tapering Pipe
Authors: Zeng Qingna , Zang Fenggang , Zhang Yixiong , Wang Donghui
Published: November 2019

In this paper, theoretical solutions of free transverse vibration for tapering pipe considering variable cross section have been investigated using Bessel function in low frequency domain. Natural frequency was calculated by transfer matrix method (TMM) based on an accurate theoretical model. The effectiveness and validity of TMM with Bessel function was confirmed in comparison with TMM of discrete uniform pipe and Finite Element Method. Furthermore, dimensionless model was proposed to avoid the singularity, instability and overflow in calculation. The geometry effect, such as tapering ratio, thickness-radius and length-radius ratio influence on the nature frequency was explored. The present study was envisaged to provide useful insights for dynamic analysis of pipeline systems.
Environmentally-Assisted Fatigue Behavior of 316 Stainless Steels in Simulated PWR Primary Environment: Strain Holding, Zn-Addition, and Their Combined Effect
Authors: Lee Hyeon Bae , Kim Ho-Sub , Chen Junjie , Jang Changheui , Kim Tae Soon , Stevens Gary L. , Ahluwalia Kawaljit
Published: November 2019

Low cycle fatigue (LCF) tests of type 316 stainless steel (SS) were conducted in simulated pressurized water reactor (PWR) environments to evaluate the effect of zinc (Zn) content and peak strain holding. The LCF lives of 316 SS increased about 2 to 3 times in PWR environments with Zn addition and peak strain holding (Zn-PWRhold condition). Their combined effect was investigated by using cyclic hardening behavior, dislocation structure analysis, and oxide layer observation. The cyclic behavior in Zn-PWRhold condition showed general primary hardening behavior but quite longer softening behavior than other test conditions. Also, the dislocation density was decreased with Zn addition and increased again with peak strain holding. The Zn penetrates into the oxide layer at the crack tip and modifies the oxide characteristics, which results in improvement of corrosion resistance.
A Residual Lifetime Prediction Method of Aging Polyethylene Gas Pipes in Service
Authors: Wang Yang , Lan Hui-qing , Zhang Hao
Published: November 2019

Polyethylene pipes (PE) have been widely used for various urban gas pipeline transportation engineering. With the increase of service life, the aging of PE pipes has become a safety issue of urban gas pipeline transportation. Therefore, a practical prediction method for predicting the residual lifetime of in-service aging polyethylene pipe is needed. Hitherto, there are a few reports on the aging performance and lifetime prediction of PE pipes under the laboratory research stage, but there are few researches on lifetime prediction methods of in-service aging polyethylene pipes. In this paper, aging PE pipes under different pressures and temperatures were produced by an accelerated aging test which was used by a thermal oxygen aging experimental set-ups PE pipes. Aging PE pipes were respectively tested by a tensile test, DSC and MFR (Melt Mass Flow Rate), and the test’s results of aging PE pipes were analyzed comparatively. Then, a residual lifetime prediction equation of pressured gas PE pipes was proposed by Arrhenius fit of the data which comes from the test’s results. Basing on this equation, a residual lifetime prediction method of aging polyethylene gas pipes in service was proposed, that is, the DSC test data of the particle (about 15 mg) which is cut from the surface of the in-service polyethylene gas pipes can be substituted into the lifetime prediction equation to predict the residual lifetime of aging polyethylene pipes. This residual lifetime prediction method is not only suitable for pressured aging polyethylene gas pipes in service, but also for other pressured plastic pipes in service.
Electric Potential Drop Method for Evaluating Crack Initiation and Crack Propagation: The Help of FE Simulation
Authors: Le Delliou Patrick
Published: November 2019

The electric potential drop (EPD) method is a laboratory technique to monitor the initiation and the propagation of a crack, mainly in the field of fatigue research. It can also be used in fracture experiments, involving plasticity and large deformations. The size of a crack in a metallic member is predicted by applying a constant d.c. (direct current) or a.c. (alternating current) to the member and by measuring an increase in electric resistance due to the crack. Practically, several pairs of probes are attached to the specimen crossing over the crack and the voltage drop is measured periodically along the test. The main difficulty is to correlate the EPD changes to the crack extension.

Thanks to the analogy between the thermal conduction problem and the electrical conduction problem, a classical thermo-mechanical finite element solver can be used to predict the EPD along a crack, given the electrical resistivity of the material, the current intensity and the geometry of the structure and of the crack. This technique works well for fatigue studies, where the structure remains elastic and whose shape is unchanged. However, in fracture experiments, the change in geometry and the possible effect of the plastic strain on electrical resistivity make the problem much more complex.

The paper presents the principle of the EPD method, a work on the effect of the plastic strain on the electrical resistivity, FE computations for the elastic case (for fatigue pre-cracking) and for the plastic case (for ductile tearing experiments). Several practical applications will be presented on various metallic materials.
Analysis of Environmentally Assisted Cracking in S420 Steel by Using the Theory of Critical Distances
Authors: González P. , Cicero S. , Arroyo B. , Álvarez J. A.
Published: November 2019

The behavior of S420 steel under cathodic polarization in low pH aqueous environment is analyzed following the assumptions of the Theory of Critical Distances. This methodology has been successfully applied in fracture and fatigue analysis, but it has not been employed yet under stress corrosion cracking or hydrogen embrittlement conditions. This work focuses on the problem of environmentally assisted cracking by using the Point Method and the Line Method, both of them belonging to the Theory of Critical Distances. Fracture mechanic tests were carried out, using a slow strain rate machine, at two different solicitation rates (6·10−8 m/s and 6·10−9 m/s). The study is based on an experimental program composed of C(T) specimens with notch radii varying from 0 mm up to 2 mm. Cathodic polarization with a 5 mA/cm2 current has been employed and the aqueous aggressive environment was made using the Pressouyre’s method. The study has been completed with finite elements simulation analysis. The results reveal that the Theory of Critical Distances provides accurate predictions of the environmentally assisted cracking behavior of S420 steel in notched conditions.
Augmenting Generic Fatigue Crack Growth Models Using 3D Finite Element Simulations and Gaussian Process Modeling
Authors: Loghin Adrian , Ismonov Shakhrukh
Published: November 2019

Assessing the crack propagation life of components is a critical aspect in evaluating the overall structural integrity of a mechanical structure that poses a risk of failure. Engineers often rely on industry standards and fatigue crack growth tools such as NASGRO [1] and AFGROW [2] to perform life assessment for different structural components. A good understanding of material damage tolerant capabilities, and the component’s loading mission during service conditions are required along with the availability of generic fracture mechanics models implemented in the lifing tools. Three-dimensional (3D) linear elastic fracture mechanics (LEFM) finite element modeling (FEM) is also a viable alternative to simulate crack propagation in a component. This method allows capturing detailed geometry of the component and representative loading conditions which can be crucial to accurately simulate the three dimensionality of the propagating crack shape and further determine the associated loading cycles. In comparison to a generic model, the disadvantage of the 3D FEM is the extended runtime. One feasible way to benefit from 3D modeling is to employ it to understand the crack front evolution and growth path for the representative loading condition. Mode I stress intensity factors (KI) along the predetermined crack growth path can be generated for use in fatigue crack growth tools such as NASGRO.

In the current study, such a 3D FEM lifing process is presented using a classical bolt-nut assembly, components that are commonly used in engineering design. First, KI solutions for a fixed crack aspect ratio a/c = 1 are benchmarked against a similar solution available in NASGRO. Next, a predefined set of crack shapes and sizes are simulated using 3D FEA. A machine learning model Gaussian Process (GP) was trained to predict the KI solutions of the 3D model, which in turn was used in the crack propagation simulation to accelerate the life assessment process. Verification of the implemented procedure is done by correlating the crack growth curves predicted from GP to the results obtained directly from 3D FE crack propagation method.
Optimising the Safe Design of Pressurised Components
Authors: O’Connor Alison N. , Davies Catrin M. , Garwood Stephen J. , Hadley Isabel
Published: November 2019

The structural integrity of pressure vessels (PVs) is controlled by the application of various design and fabrication codes and standards. Within the European single market (ESM) design codes exist at both a European and a national level which can lead to variability in design procedures. The European standard EN 13445 has been updated several times to modify the design curves based on analytical modelling of high strength materials. The design curves in EN 13445 now differ significantly from those presented in the British national code that preceded it, namely PD 5500. As a result higher minimum Charpy test temperatures (T27J) are found using the EN 13445 procedure in comparison to those derived using the PD 5500 procedure. While the PD 5500 design curves have been validated experimentally it is generally accepted that they are overly conservative. This inherent conservatism in PD 5500 may account for some of the differences in the minimum Charpy test temperature, the analytical model used to generate the EN 13445 design curves however was validated with data from high strength steels only (σy ≥ 420 MPa). It is not clear that the results can be applied directly to low/medium strength materials. This work identifies some of the disparities between the EN 13445 and PD 5500 procedures, for low temperature applications. A programme of work, at Imperial College London, is described. This programme of work, currently underway, is aimed at addressing concerns about the robustness of the updated EN 13445 design curves, especially for lower-strength steels in the as-welded condition.
Seismic Test Results of Air-Operated Valve Actuators for Nuclear Power Plants (Air-Operated Butterfly Valve (Direct-Coupled Type))
Authors: Matsubara Yoshinao , Tsutsumi Yoshitaka , Nishino Koji , Kojima Nobuo , Ito Yasuyuki , Kubota Ryo , Suzuki Shigeki
Published: November 2019

The functional requirements of air-operated valves provided in nuclear power plants during an earthquake have been previously evaluated via seismic tests and so forth; however, since the response acceleration has increased in line with a recent reassessment of standard earthquake ground motions, it is necessary to evaluate functional maintenance with respect to high acceleration. It is also necessary to determine practical functionality from the viewpoint of equipment fragility in seismic Probability Risk Assessment (PRA) Here, we used a resonant shaking table (see Ref. [1]) in the Central Research Institute of the Electric Power Industry (CRIEPI), which is capable of seismic tests at acceleration levels that have been unachievable until now. From the results of seismic tests on air-operated valve actuators, the operability of active components used with an existing design was confirmed to be more than 15 × 9.8 m/s2 (horizontal directions (X and Y)) and more than 20 × 9.8 m/s2 (vertical direction (Z)).
Mitigation of Rocking and Sliding Motion of a Free-Standing Structure Subjected to Base Excitation Using Coaxial Circular Cylinders Containing Highly Viscous Liquid in Annular Spaces
Authors: Shintani Atsuhiko , Ito Tomohiro , Nakagawa Chihiro
Published: November 2019

In this study, the effectiveness of coaxial circular cylinders containing a highly viscous liquid in annular spaces for reduction of rocking motion of a free-standing structure is investigated both analytically and experimentally. First, an analytical model of coupled rocking and sliding motions of a free-standing structure, including the coaxial circular cylinders, subjected to seismic input was derived. The free-standing structure was modeled as a free-standing rigid body. The cylinders were attached to the bottom of the rigid body as a damping device.

We then experimentally derived the friction coefficients, inertia moments, and a damping coefficient in the rotating direction.

Furthermore, using these parameters, the effectiveness of this system in suppressing the rocking motion is investigated analytically. The proposed method was determined to be very effective in suppressing the rocking motion of a rigid body subjected to a seismic input by the experiment.
New Developments in PTFE Sheet Gaskets With Engineered Surface Profile
Authors: Drago James
Published: November 2019

This paper presents laboratory performance testing of new technology utilizing a textured raised pattern on filled restructured PTFE (R-PTFE) sheet gasketing. The technology published in PVP2018-84039 and PVP2018-84040 and presented in Prague1,2 examined the load retention attributes of filled PTFE sheet gaskets with hexagonal/honeycomb surface texture in a miniaturized and standard raised face flange joints. This paper will show performance characteristics and comparisons to flat traditional R-PTFE gaskets. Data is presented on leak performance based on DIN-3535-4/6 and EN 13555, deflection under compressive load, bolt load retention and ASTM F36 compression and recovery. The paper gives a summary of results from a study of PTFE gasket users expressing their needs and desires for gasket performance. Examples of current field cases from chemical processors are also be presented.
Quantification of the Conservatisms in the Flaw Acceptability Assessment of Doel 3 and Tihange 2 RPVs Containing Hydrogen Flakes
Authors: Lacroix Valéry , Dulieu Pierre
Published: November 2019

During the 2012 outage at Doel 3 and Tihange 2 Nuclear Power Plants, a large number of quasi-laminar indications were detected in the lower and upper core shells of the reactor pressure vessels (RPVs). The observed indications could subsequently be attributed to hydrogen flaking induced during the component manufacturing process. As a consequence, both units remained core unloaded pending the elaboration of an extensive Safety Case demonstrating that they can be safely operated. One of the most challenging parts of this demonstration was the Flaw Acceptability Assessment, aiming at demonstrating that the identified indications do not jeopardize the integrity of the reactor vessel in all operating modes, transients and accident conditions. This analysis was done by using a methodology: innovative, in line with existing ASME Code Section XI requirements, specific, sufficiently wide to be accepted and, first and foremost, conservative. Through a brief reminder of the Flaw Acceptability Assessment methodology, the paper presents the main hypotheses done for the calculation and quantifies the conservatism related to each of them. This quantification clearly highlights the reliability of final result i.e., the demonstration of the Fitness-for-Service for continued operation of both Doel 3 and Tihange 2 RPVs.
Analysis of a Flanged and Dished Head Assembly Used in a Horizontal Storage Tank
Authors: Zhao Mingxin
Published: November 2019

A nonstandard flanged and dished head is frequently used in the horizontal storage tank for quick and full access to the internal in oil and gas industry. The head is forged into an elliptical shape with a flat edge at its peripheral. The flat edge serves as a flange while the other mating half coming from the tank shell. The flange pair is installed within a C-shaped clamp and secured by compression bolts at its head side. A gasket is sandwiched between the mating surfaces of the flange pair to provide proper seal. While the head can be removed easily by unscrewing the compression bolts, this disintegrated structure does increase the complexity in component design and unique requirement for installation. The bolt compression load not only affects the pressure capacity of the storage tank, but also governs the stresses in flange pair and C-clamp. In this study, the flanged and dished head assembly has been modeled and analyzed by finite element method for stresses and gasket seal performance subject to installation and operation loads. Both elastic and elastic-plastic analysis has been performed. The tightening force of the bolts is examined against component stresses and gasket seal performance. Optimized bolt load is recommended based on acceptance criteria for stresses and leakage prevention.
Shakedown and Limit Analysis of 45-Degree Piping Elbows Under Internal Pressure and Cyclic In-Plane Bending
Authors: Peng Heng , Liu Yinghua
Published: November 2019

This paper carries out the shakedown and limit analysis of 45-degree piping elbows subjected to steady internal pressure and cyclic in-plane closing, opening and reverse bending moments by means of the recently proposed stress compensation method (SCM). Different geometries of the piping elbows and various combinations of these applied loads are investigated to create various shakedown limit and plastic limit load interaction curves. The plastic limit loads for single internal pressure and single bending moment calculated with the SCM are compared to those calculated with the twice-elastic-slope method. Full step-by-step elastic-plastic incremental finite element analyses are utilized to verify the structural cyclic responses on both sides of the curves obtained and further to confirm the correct shakedown limit loads and boundaries. It is shown that the SCM calculates the shakedown limit load accurately and possess more than 40 times the computational efficiency of the step-by-step elastic-plastic incremental method. The effects of the ratios of bending radius to mean radius and mean radius to wall thickness of the piping elbow as well as loading conditions on shakedown limit and plastic limit load interaction curves are presented. The results presented in this work provide a comprehensive understanding of long term response behaviors of the piping elbow under the combined cyclic loading and offer some essential points to be concerned for the design and integrity assessment of piping systems.
ADS-4 Pipe Vibration Evaluation During AP1000® Preoperational Testing
Authors: Nowicki Tim J. , Suddaby David A. , Donovan Joshua J. , Conn Alex , Paharia Madhur
Published: November 2019

Preoperational testing of the first AP1000® pressurized water reactors took place in the fall and winter of 2016. This Hot Functional Testing (HFT) included observation of vibrations throughout the piping systems, and is required to be successfully completed before fuel load.

During HFT, flow through the hot leg passes many piping intersections where instabilities such as vortex shedding create pressure pulsations. Coupling of the vortex shedding frequency and natural acoustic frequency of the piping sidebranch may lead to acoustic resonance of the system. This resonance condition is understood, but difficult to predict; therefore, the HFT plan included screening for such conditions based on ASME Operation and Maintenance of Nuclear Power Plants vibration monitoring group (VMG).

Vibration was observed in the Automatic Depressurization System (ADS) branch off the reactor coolant system hot leg that was potentially in a resonant condition. This paper details the identification, characterization, and analysis of the ADS vibration observed during HFT. Additional instrumentation was employed and data were gathered at varying conditions to determine the nature and extent of the vibrations. Demonstration of acceptable vibration levels in the ADS system was a key engineering accomplishment for AP1000® fuel load.
Tunable EOS Material Model in the Simulation of Pulsed Mercury Spallation Target Vessel
Authors: Lin Lianshan , Winder Drew
Published: November 2019

A pulsed spallation target is subjected to very short (∼1μs) but intense loads from repeated proton pulses. The effect of this pulsed loading on the stainless-steel target module that contains flowing mercury target material is difficult to predict. Different simulation approaches and material models for the mercury have been tried. To date the best matching simulation to the experimental data was obtained by an equation of state (EOS) material model with a specified tensile cutoff pressure, which simulates the cavitation threshold [1]. The inclusion of a threshold to represent cavitation was a key parameter in achieving successful predictions of stress waves triggered by the high energy pulse striking the mercury and vessel. However, recent measurements of strain responses of target modules showed that significant discrepancy between the measured strain and simulated value with the EOS mercury model still exists. These differences grow to irreconcilable values when non-condensable helium gas is intentionally injected into the flowing mercury. A novel EOS mercury model embedded into ABAQUS VUMAT has been investigated in this project, which introduces the concept of proportional, integral, and derivative (PID) control into the mercury EOS model. By tuning the new introduced PID parameters (Kp, Ki and Kd), we replace the specified cutoff pressure with an adjustable spring-damper-like material behavior which may better match the complex dynamics of the mercury and helium mixture. This approach is expected to reduce the gap between measured and simulated vessel strain responses. Primitive application of this tunable EOS mercury model on prototypic shape experimental target has demonstrated its capability and potential of improving mechanical behavior of EOS mercury with cutoff pressure considered.
Thermal Solutions for a Plate With an Arbitrary Temperature Transient on One Surface and Convection on the Other: Direct and Inverse Formulations
Authors: Segall Albert E. , Schoof Craig C. , Yastishock Daniel E.
Published: November 2019

Thick plates that are thermally loaded on one surface with convection on the other are often encountered in engineering practice. Given this wide utility and the limitations of most existing solutions to an adiabatic boundary condition, generalized direct thermal solutions were first derived for an arbitrary surface loading as modeled by a polynomial and its coefficients on the loaded surface with convection on the other. Once formulated, the temperature solutions were then used with elasticity relationships to determine the resulting thermal stresses. Additionally, the Inverse thermal problem was solved using a least-squares determination of the aforementioned polynomial coefficients based on the direct-solution and temperatures measured at the surface with convection. Previously published relationships for a thick-walled cylinder with internal heating/cooling and external convection are also included for comparison. Given the versatility of the polynomial solutions advocated, the method appears well suited for complicated thermal scenarios provided the analysis is restricted to the time interval used to determine the polynomial and the thermophysical properties do not vary with temperature.
Study on Fatigue Crack Growth Behavior of Zr702/TA2/Q345R Composite Plate With a Through-Wall Crack and a Crack Normal to Interface for SENT Specimen
Authors: Zhou Binbin , Zhou Changyu , He Xiaohua
Published: November 2019

In this paper, the fatigue crack growth behavior of Zr702/TA2/Q345R composite plate with a through-wall crack and a crack normal to interface for SENT specimen are studied. For the through-wall crack, the mutual interference in fatigue crack growth rate is found. The crack growth rate of the through-wall crack on both sides in Zr702/TA2/Q345R composite plate depends on the difference of stress intensity factors amplitude caused by the different positions of crack tips on both sides and the crack growth rate in corresponding homogeneous material. For the crack normal to interface, two crack propagation directions are taken into account. When crack initiates from the lower strength material side, the crack growth rate decreases to the minimum before crack penetrates the interface. After crack penetrates the interface, crack growth rate accelerates continuously. When crack initiates from the higher strength material side, the fatigue crack growth rate generally increases with the crack length. For both crack forms, all experiment results demonstrate that the crack growth rate is dependent on the competition of the stress intensity factor amplitude, the crack growth rate in corresponding homogeneous material and the interface strength. Besides, finite element results show that elastic mismatch results in a significantly change in the distribution of stress intensity factor amplitude.