bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthetic Esters and Dynamics of Pressure Compensated Proportional Directional Control Valves
Authors: Jakobsen J. H. , Hansen M. R.
Published: November 2018

The purpose of this paper is to help reduce the uncertainty in behavior introduced when changing hydraulic oil from mineral oil (HLP) to biodegradable oil (synthetic esters - HEES) by comparing the behavior of proportional valves with HLP and with HEES at various temperatures.

The focus of this article is on classic proportional valves used in the industry. The study is based on tests and modelling with characterization of dynamic behavior in mind. The characterization is based on tests of two pressure compensated proportional valves, one with closed loop control of the spool position, and one without. The two ester types tested are one based on a saturated, fully synthetic ester and a regular fully synthetic ester.

The tests consist of steps and frequency responses. Both valves are tested at oil temperatures 20°C, 40°C and 60°C.

The adopted models are based on a third order linear model with parameters identified using frequency responses from actual valve tests.

The variation of amplitude and bias has some influence on the resulting frequency response especially at lower temperatures. But the general tendencies are unaffected by amplitude and bias.

As expected a clear tendency for both valves of increasing dampening at decreasing temperatures is seen regardless of oil type, but the increase in dampening is similar for all oil types.

The saturated ester leads to less bandwidth at lower temperatures for both valves, but the overall variations between all oil types stay within 1.66Hz of each other when tested with the same test parameters.

The investigation indicates that the difference in dynamic characteristics at 20°C caused by the different oil types can not be explained with variations in any single one of the classic liquid properties density and viscosity and more investigations are needed to identify the cause.
Supervisory Control for a Switched Mode Hydraulic Transformer
Authors: Lee Sangyoon , Li Perry Y.
Published: November 2018

A supervisory control for a hydraulic transformer is developed. The hydraulic transformer being controlled is configured in a traditional manner where a pair of hydraulic pump/motors are mechanically coupled together. This transformer can be configured in three distinct modes depending on how each port is connected. A supervisory control determines, for the desired output pressure and output flow, the mode and shaft speed that the transformer should operate in order to minimize the power loss. The resulting controller structure ensures that the transformer provides the desired flow while following the desired mode and shaft speed. The supervisory control is further modified to avoid high frequency switching and to achieve bumpless transfer between modes. Experimental results demonstrate the efficacy of the supervisory controller to increase the efficiency of the hydraulic transformer driven system.
Greatly Enhanced Thermal Conductivity of Fully Inert Matrix Dispersion Pellet (IMDP) Produced by Spark Plasma Sintering (SPS) Technique
Authors: Ma Zhaodandan , Liu Tong , Li Rui , Sun Maozhou , Lu Zhiwei
Published: November 2018

In order to improve nuclear reactor’s performance and safety, a new-type fuel, Inert Matrix Dispersion Pellet (IMDP) with greatly enhanced thermal conductivity was studied. In this paper, the pellet was developed by Spark Plasma Sintering Technique (SPS), which brings an improved thermal conductivity compared with normal method and exhibits fully dense SiC matrix with a higher TRISO volume in kernel of pellet. Thermal-physical properties of the IMDP from room temperature to 1400 °C were investigated. The thermal conductivity improved 1100% at room temperature and 974% under 1000°C when TRISO volume is 40%, which behave much better than traditional UO2 fuel. The thermal diffusivity reduced and heat capacity increased at different TRISO volumes, linearly implied stable geometry at high temperature. From CT test we can see an intact structure of uniform TRISO granules. For comparison, modeling thermal conductivity is analyzed by FEM, which shows lower than measured data, indicating an optimized technology of this new method. Advantages of SPS will be discussed as well.
Development of New Design Fatigue Curves in Japan: Discussion of Best-Fit Curves Based on Fatigue Test Data With Small-Scale Test Specimen
Authors: Wang Yun , Hatoh Hisamitsu , Yamamoto Masato , Nakane Motoki , Hirano Akihiko , Hayashi Kentaro
Published: November 2018

Based on the precedent design fatigue curves and recent fatigue data obtained from materials with different mechanical properties, new design fatigue curves with high general versatility in air have been developed by The Japan Welding Engineering Society (JWES). Structural materials with different tensile strength are utilized in fatigue tests to verify the validity of these design fatigue curves and discuss the mean stress effect. The materials employed in this study are austenitic stainless steel (SS) SUS316LTP, carbon steel (CS) STPT370, low-alloy steels (LASs) SQV2A and SCM435H, all of which are used in the structural components of nuclear power plants of Japan. The best-fit curves (BFCs) are formulated by using the parameter of tensile strength to describe the relationship between strain (stress) amplitude and fatigue life [1]. The results of fully reversed axial fatigue tests conducted with small-scale test specimens of those materials in air at ambient temperature show good agreement with the developed BFCs. The results of fatigue tests also indicate that the mean stress effect is remarkable in materials with higher tensile strength. The applicability of Modified Goodman and Smith-Watson-Topper (SWT) approaches to the design fatigue curves is compared and discussed when considering mean stress effect. The correction of mean stress effect with SWT approach shows a good agreement with the developed BFCs.
Shakedown-Ratcheting Analysis of a Spherical Pressure Vessel by Anisotropic Continuum Damage Mechanics
Authors: Nayebi Ali , Surmiri Azam , Rokhgireh Hojjatollah
Published: November 2018

In cyclic loading and when plastic flow occurs, discontinuities grow. In this research, interaction diagram of Bree has been developed when the spherical pressure vessel contains discontinuities such as voids and microcracks. Bree’s diagram is used for ratcheting assessment of pressurized equipment in ASME III NH. Nature of these defects leads to an anisotropic damage. Anisotropic Continuum Damage Mechanics (CDM) is considered to account effects of these discontinuities on the behavior of the structure. Shakedown – ratcheting response of a hollow sphere under constant internal pressure and cyclic thermal loadings are studied by using anisotropic CDM theory coupled with nonlinear kinematic hardening of Armstrong-Frederick m’s model (A-F). Return mapping method is used to solve numerically the developed relations. Elastic, elastic shakedown, plastic shakedown and ratcheting regions are illustrated in the modified Bree’s diagram. Influence of anisotropic damage due to the plastic deformation is studied and it was shown that the plastic shakedown region is diminished because of the developed damage.
Visualization of Thermal Fatigue Damage Distribution With Elastic-Plastic FEA
Authors: Miura Junya , Fujioka Terutaka , Shindo Yasuhiro
Published: November 2018

This paper proposes simplified methods to evaluate fatigue damage in a component subjected to cyclic thermal loading, in order to visualize the distribution of usage factor using a graphical user interface (GUI) incorporated in a widely-used commercial CAE. The objective is to perform the evaluation and visualization using a standard desktop PC. In the previous paper, three simplified methods based on elastic finite-element analysis (FEA) were proposed in place of the method in the procedures employed in ASME Section III Subsection NH. In this paper, the methods have been improved for elastic-plastic FEA. A previously performed thermal fatigue test with a type 304 stainless steel cylinder was simulated. Heat transfer, elastic, and inelastic analyses were conducted. Simultaneously with the analyses performed, the equivalent total strain ranges and fatigue usage factor distributions were calculated using user subroutines developed in this study including three newly proposed simplified and ASME NH-based methods. These distributions can be visualized on a GUI incorporated in a commercial FEA code. The calculation results were consistent with the distribution of cracks observed. In addition, by using these, the analysts can visualize these distributions using their familiar CAE system.
Brittle Fracture Prediction Using Code_Aster: Review of Available Models and Focus on the GP Energy Approach
Authors: Jules Samuel , Métais Thomas , Lorentz Eric , Géniaut Samuel
Published: November 2018

With the life extension of NPPs world-wide, new challenges have emerged in engineering calculations. These challenges often stem from the difficulty to demonstrate an adequate margin for some key components, which have gradually been ageing during the operation of the plant. In particular, the Reactor Pressure Vessel (RPV) is impacted by the irradiation, and the risk of brittle fracture under severe cold shocks must be assessed.

Over the past decades, the RSE-M code [1], which is used in France and internationally for in-service inspection, has been developing methods using a conventional approach to brittle fracture. Analyses are typically performed either using tabulated indices to evaluate analytically the stress intensity factor, or using more advanced approaches which require more complex and time-consuming FEA calculations. Recently, the ongoing trend has been to rely on the latter to demonstrate an adequate margin on the RPV for potential operation beyond 40 years: the question today is whether these existing methods will still provide adequate margins after 50 or 60 years of operation.

In parallel to the conventional approach, a significant amount work has been performed over the past 20 years in France to adapt the historic Griffith energy release-rate approach [2] to engineering space. The work was initiated by Francfort and Marigo [3] who set up a new elastic fracture theory, extended from the Griffith approach.

Within EDF R&D, Lorentz et al. [4] and Wadier et al. [5] have then relied on some of their ideas and applied them to the easier case of the propagation onset of a preexisting crack along a given crack path. Several ingredients are involved in this reduced formulation: the application of an energy minimization principle, the definition of a specific damage model and the use of a notch to represent the crack.

Among other advantages, the Gp method has been developed as a true engineering approach, i.e. not relying on difficult and time-consuming models to set up. It is hence easy to implement in a FE software as a postprocessing of a mechanical calculation. The method has also been applied to various test cases and has shown the potential to increase margins. The drawbacks are that the method is likely restricted to 2D cases for practical reasons.

The paper also provides an overview of the methods implemented in the EDF open source tool code_aster with a specific focus on the Gp approach.
Fast Reactor Cores: Seismic Excitation in the Vertical Direction — Numerical Methods
Authors: Broc Daniel , Artini Gianluca , Cardolaccia Jérome , Martin Laurent
Published: November 2018

In the frame of the GEN IV Forum and of the ASTRID Project, a program is in progress in the CEA (France) 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 (or FA) and Neutronic Shields (or NS) immersed in the primary coolant (sodium), which circulates inside the Fuel Assemblies. The FA and the NS are slender structures, inserted in a grid plate, which may be considered as beams form a mechanical point of view. The dynamic behavior of this system has to be understood, for design and safety studies.

This dynamic behavior of the core is strongly influenced by the sodium and by contacts between the beams at the pads level and at the top. The fluid leads to complex interactions between the structures in the whole core. The contacts between the beams limit the relative displacements.

Two main movements have been considered so far: global horizontal movements under a seismic excitation, and opening of the core.

Physical and numerical methods and tools have been developed to describe and simulate the dynamic behavior. These methods are integrated in CAST3M, general computer code developed at the CEA Saclay. The assemblies are modeled as beams. The impacts at the pads between the assemblies are taken into account by using a nonlinear model. The Fluid Structure Interaction is taken into account by using homogenization methods.

This paper is devoted to the improvement of these methods to take into account the vertical component of a seismic excitation. The key points are:

- the fluid structure coupling in the vertical direction,

- the modification of the description of the impacts to take into account the vertical displacements of the assemblies,

- the modification of the boundary condition at the foot of the assembly, in order to take into account the uplift with a nonlinear model.
Ratcheting Behavior of Pressurized Elbow Pipe After Thermal Aging
Authors: Liu Caiming , Yu Dunji , Chen Xu
Published: November 2018

In the present work, the effect of thermal aging on ratcheting behaviors of three pressurized elbow pipes after different thermal aging periods was experimentally studied under constant internal pressure and reversed in-plane bending. The elbow pipes were thermal aged for 1000 h and 2000 h at the same aging temperature of 500 centigrade degrees. It is indicated that thermal aging period has a significant effect on elbow pipe’s ratcheting deformation. Chen-Jiao-Kim (CJK) kinematic hardening model was employed to evaluate the ratcheting behaviors of pressured elbow pipes affected by thermal aging.
System and Solenoid Valve Interaction Leading to Spurious Opening
Authors: Reich Alton
Published: November 2018

In a pressurized water reactor the high pressure system vent lines from the pressurizer and reactor are routed to a common header that can be emptied to the refueling water storage tank or a drain tank. During plant testing the valves are operated in the following sequence: the pressurizer isolation valve is opened to pressurize the common header, the pressurizer isolation valve is closed, then the drain tank isolation valve is opened. This sequence of valve operation verifies that the valves open and close properly — opening the pressurizer isolation valve allows steam to enter the common header and is verified by pressure indication via a pressure transducer, and opening the drain tank isolation valve decreases the pressure in the common header and verifies that the pressurizer isolation valve closed properly. During this sequence of valve actuation, the other solenoid valves in the system are subject to transient steam pressures. During one test sequence an isolation valve to the refueling water storage tank indicated that it was not closed for a period of several seconds. Since there is only one pressure transducer in the common header, a systemlevel analysis was performed to obtain a more detailed understanding of the transient pressures in the common header, and how that might affect solenoid valve performance.
Application of the T-Scaling Method to Predict Fracture Toughness Under Compressive Residual Stress in the Transition Temperature Region
Authors: Meshii Toshiyuki , Ishihara Kenichi
Published: November 2018

The fracture toughness Jc of a material in the ductile-to-brittle transition temperature region shows a test specimen thickness (TST) effect and temperature dependence, and apparently increases when a compressive residual stress is applied. Many models to explain these phenomena have been proposed that can also consider the large scatter of Jc. On the contrary, the authors have focused on the mean Jc and have demonstrated that the TST effect on Jc and temperature dependence of Jc are due to “the loss of the one-to-one correspondence between J and the crack-tip stress distribution” and that the “scaled” crack-tip stress distribution at fracture is independent of the TST effect on Jc or temperature. The T-scaling method was proposed and validated for this purpose. In this study, the fracture prediction of a specimen with compressive residual stress was performed using the T-scaling method, and its validity was confirmed for high-strength steel of 780-MPa class and 0.45 % carbon steel JIS S45C.
Numerical Fatigue Life Evaluation With Experimental Results for Type III Accumulators
Authors: Kim Sang-Won , Yoshikawa Nobuhiro , Kobayashi Hiroshi , Fujisawa Toshiro , Sano Takeru
Published: November 2018

Composite Reinforced Accumulator (CRA) is widely used in hydrogen stations. A high-cost pressure cycle test is mandatory to ensure the safety of accumulator in present regulations. To reduce the high cost, the aim is to develop a methodology of numerical fatigue life prediction of CRA with results of pressure cycle tests.

An axisymmetric finite element model for the Type III accumulator is created and actual loading process including autofrettage pressure is simulated. Stress amplitude caused by pressure cycle is evaluated based on the instructions in KD-3 of ASME BPVC VIII 3-2015. By comparing stress amplitude distributions with the leak positions after the pressure cycle test, and plotting the results in the design fatigue curve, it could be shown that fatigue life prediction of Type III accumulator can be done by precise finite element analysis of the liner including dome part, where the principal axes of stress change in pressure cycle.
Seismic Test Analysis Evaluation of Motor-Operated Valve Actuators for Nuclear Power Plant
Authors: Kojima Nobuo , Tsutsumi Yoshitaka , Yonekura Kazuyoshi , Nishino Koji , Watanabe Yukio , Kumagai Shin , Kamino Hiroyuki
Published: November 2018

The function of motor-operated valves provided in nuclear power plants during an earthquake has been previously evaluated on the basis of seismic test results; however, since the response acceleration has increased with a recent reassessment of standard earthquake ground motions, it is necessary to evaluate their function during high acceleration earthquakes.

In order to carry out seismic test analysis, we examined the compression characteristics of the gaskets in three kinds of representative valves, in terms of the current load and slide coefficient, by element tests. We created an analysis method using the finite element method which used the gasket’s characteristics, and the result of these analyses could explain the loosing and the amplitude of the bolt connecting force and gasket slipping at the time of excitation to the safety side.

According to the analysis, the actuator connection part of the motor-operated butterfly valve showed a seismic resistance of 20 × 9.8m/s2 and other parts showed a seismic resistance of 30 × 9.8m/s2.
Experimental Research on the Effect of Heating Temperature, Demulsifier Dose and Water Cut on the Oil-Water Separation in Three-Phase Separator
Authors: Li Ang , Bai Jianfeng , Shen Yun , Jin Hang , Wang Wei , Gong Jing , Feng Yaorong
Published: November 2018

The three-phase separator has a wide range of applications in oil production industry. For the purpose of studying the effect of heating temperature, demulsifiers and water content on the separation of oil-water mixture in the three-phase separator, eight kinds of oil samples were taken from different oil transfer stations in Changqing Oilfield and the mixtures were prepared by stirring method. To simulate the two-stage dehydration process, the first stage dehydration experiments without any heating were performed on mixtures at the dose of 100ppm demulsifer at 20°C, and the water cut of these mixtures is the same as that of the gathering pipeline in each oil transfer station. The water cut of the upper crude oil was measured after 40 minutes, and the values of them ranged from 0.5 vol% to 65.2 vol%. No visual stratification was observed for the sample most difficult to separate, so it was selected to conduct the second stage dewatering process. Three bottles of the same mixture were prepared and heated to 30°C, 40°C and 50°C, respectively. The results showed that all of them stratified in 10 minutes, and the water-cut values of the upper oil layer were 1.4 vol%, 0.5 vol% and 0.3 vol%, respectively, compared to 65.2 vol% at 20°C. When the concentration of demulsifier was changed to 200ppm and 300ppm, the results exhibited almost no differences. So it is deduced that the further improvement of heating temperature and demulsifier dose have limited enhancement on oil-water separation. At Last, 35 vol%, 50 vol%, 70 vol% and 85 vol% water cut mixtures of the special oil sample were made to experiment as previously. In consequence, the 35 vol% water-cut emulsions presented a relatively slow rate of oil-water stratification at low heating temperature, and the oil content of the lower separated water was improved by the addition of demulsifier dosage above 100ppm when the water cut was 90 vol%. It is indicated that high heating temperature is necessarry for low water-cut mixtures oil-water separation and can be appropriately reduced to save energy consumption as the water cut continues to rise. The demulsifier dosage is also neccessary be controlled in high water cut period. These experimental data provide the basis for the further optimization operation of the three-phase separator.
Buckling of Corroded Torispherical Shells Under External Pressure
Authors: Błachut J.
Published: November 2018

The current paper examines the effects of corrosion induced wall thinning on buckling of domed closures onto cylindrical vessels. It is assumed that corrosion is axisymmetric and that the wall is corroded on inside, only. The ratio of corroded wall thickness, tc, to the non-corroded thickness, t, is varied between 0.10 ≤ tc/t ≤ 1.0. Both depth of corrosion and its meridional extend are varied during numerical calculations. Three modelling scenarios for placement of corrosion are considered: (i) corrosion confined to the knuckle, (ii) corrosion spanning evenly the knuckle and spherical parts, and (iii) patchtype area positioned at the apex. Numerical results indicate that the following factors influence buckling performance of the dome: (i) meridional position of corroded area, (ii) depth of corrosion itself, and (iii) meridional span of corroded wall. For example, wall thinning of 10 % over 10 % of meridional length causes almost 20 % drop in buckling strength. The largest drop of load carrying capacity is found when the corroded wall is at the knuckle/crown junction. Here it is shown that assessment of strength based on the collapse mechanism is not only wrong but dangerous. For the case of the corroded dome, the collapse pressure overestimates the load carrying capacity associated with asymmetric bifurcation buckling by 40 %.
A Study of Dynamic Pipe Clamp Design
Authors: Wiseman Phillip , Mayes Alex
Published: November 2018

The piping support or restraint design and analysis must meet or exceed requirements of the applicable ASME Codes and standards specified for loading conditions of nuclear power plants such as ASME Boiler and Pressure Vessel Code, Section III, Division 1, Subsection NF. In the piping industry, various restraint types such as shock and energy absorbers, struts, dynamic clamps, etc., are used in the field to provide support between piping and building structures. This work primarily focuses on dynamic clamps, specifically, variations such as traditional 3-bolt dynamic clamps and dynamic yoke clamps. Dynamic yoke clamps have a close fit around the pipe and can be used in more applications than 3-bolt dynamic clamps such as instances of limited space, due to the smaller size of the clamps (distance from center of pipe to center of pin), and connections with larger binding angles. Additionally, finite element analysis is utilized to demonstrate superior performance of the yoke style clamp. Therefore, this study yields results that provide a strong substitute for the 3-bolt clamp. Previously, a 3-bolt clamp was the clamp of choice but the state-of-the-art design of a yoke style clamp makes it a better piping support for the dynamic application.
Dynamic Analysis and Evaluation of Control Rod Device Mechanism Missile Impact on Shielding Plate
Authors: Ye Xianhui , Xiong Furui , Zheng Bin , Jiang Naibin
Published: November 2018

The flying of missile will severely jeopardize the structural integrity in control rod ejection accident. In order to analyze the strength of a new type of shielding plate under control rod drive mechanism (CRDM) missile impact, this article develops the simulation model and conducts the response analysis of the missile under 4 cases. In addition, the strain analysis and evaluation of protection shielding plate at the most dangerous case are performed. The motion analysis of CRDM missile indicates that the fracture at trapezoid thread place as well as the shielding plate rim under impact is most dangerous because the maximum kinetic energy of the impact can be obtained. So only this case should be examined when performing the evaluation of the shielding plate. Stress analysis shows the maximum stress intensity of the shielding plate will exceed the yielding stress and thereby local plasticity will occur. Strain analysis shows that compared with the extension ratio at structural failure, the computed strain still has margin to ensure the shielding plate will not be penetrated. Meanwhile the strain analysis of bolts which fix shielding plate are calculated. The strain level of two bolts are exceed limit and others is relatively low. The shield plate can be firmly fixed. Hence, this new type of the protection shielding plate is capable to prevent the damage of other components by the flying of CRDM missile.
A Study of Self Powered Active Seismic Isolation Floor Device Using Rotational Inertia Mass Damper
Authors: Aoshima Keita , Miura Nanako , Sone Akira
Published: November 2018

In recent years, active seismic isolations have been developed actively, but they have a problem of running when external power supply is cut off. To solve this problem, we proposed a self-powered active seismic isolation floor device based on the idea of electric power regeneration. This device can control using regenerated vibration energy from earthquakes, and doesn’t require external energy to produce control force. However, when long-period earthquakes occur, this device can’t regenerate enough electric power to decrease vibration of equipment. The aim of this paper is to propose a new model using a rotating inertia mass damper (inerter) which can decrease vibration of equipment and regenerate electric power more effectively than the previous model. The inerter is a mechanical element corresponding to capacitor in electrical circuits. In this paper, we compared the response and amount of energy regeneration of previous model with those of the new model adding inerter to the previous model. By using its characteristic of rotation of the spindle, the effect of electric power regeneration can be improved for long-period earthquakes. We discuss the usefulness of inerter in self-powered active isolation floor device for long-period earthquakes.
A Proposal of Cladding Materials for Coke Drum Based on Fatigue Tests
Authors: Nabeshima Hiroshi , Shishido Yasuhiko , Kouno Nobuhisa , Murakami Takushi
Published: November 2018

Coke drums undergo cyclic operations typically in temperatures ranging from the ambient temperature to about 500°C. Generally, coke drums are fabricated from clad plates consisting of chromium-molybdenum low alloy steel as the base metal and ferritic stainless steel typically Type 410S stainless steel (TP.410S) as cladding material. TP.410S cladding material is used for protection against sulfide corrosion.

Coke drums frequently display major cracking on the inside surface of their circumferential weld along the fusion line between restoration weld and the TP.410S cladding. Moreover, an array of cracks commonly referred to as “elephant skin” are typically observed proximity to the major cracks. These cracks have been reported by multiple papers, particularly in the API Technical Report 934-G, up to the present and primarily attributed to the thermal fatigue which occurs from the repeated thermal loads experienced during each operating cycle. When the existence of severe cracks is recognized, users are forced to schedule extensive repairs.

The authors conducted fatigue tests employing coupons made from two kinds of cladding material, TP.410S and Alloy 625, which simulate the circumferential weld seam of coke drums. The paper summarizes the essential properties for the cladding material in order to delay cracking on the inside surface and proposes new common cladding materials which could be employed for coke drums based on test results.
A Probabilistic Approach for the Assessment of LOC Events in Steel Storage Tanks Under Seismic Loading
Authors: Paolacci Fabrizio , Corritore Daniele , Caputo Antonio C. , Bursi Oreste S. , Kalemi Bledar
Published: November 2018

The damage states in a storage tank subjected to seismic loading can induce loss of containment (LOC) with possible consequences (fire, explosion, etc..) both for the surrounding units and people. This aspect is particularly crucial for the Quantitative Risk Analysis (QRA) of industrial plants subjected to earthquakes. Classical QRA methodologies are based on standard LOC conditions whose frequency of occurrence is mainly related to technological accident rather than natural events and are thus useless. Therefore, it is evident the necessity of establishing new procedures for the evaluation of the frequencies of occurrence of LOC events in storage tanks when subjected to an earthquake.

Consequently, in this work a simple procedure founded on a probabilistic linear regression-based model is proposed, which uses simplified numerical models typically adopted for the seismic response of above ground storage tanks. Based on a set of predetermined LOC events (e.g. damage in the pipes, damage in the nozzles, etc..), whose probabilistic relationship with the local response (stress level, etc..) derives from experimental tests, the probabilistic relationship of selected response parameters with the seismic intensity measure (IM) is established. As result, for each LOC event, the cloud analysis method is used to derive the related fragility curve.
Vibration Reduction Mechanism and NPPs Seismic Safety of TMD Shield Building for AP1000 NPPs
Authors: Zheng Gang , Shen Feng , Chen Yaodong , Hou Gangling
Published: November 2018

Without additional mass, the tuned mass damping (TMD) shield building for AP1000 Nuclear Power Plants (NPPs) was achieved easily by changing the stiffness and damper between parts of shield building. Meanwhile, the new TMD structure combined the structural features of the shield building with TMD technology. The optimal model for the new structure was built and the optimal stiffness and damper of TMD bearing were given on the dynamic characters of the shield building and its parts. The vibration mitigation mechanism and reduction effect were clearly stated by using base shear force transfer function. By comparing with the seismic responses of the traditional model and the base isolation model, the influence factors of the new TMD structure, such as the mechanism of TMD bearing, the gravity liquid tank mass, and the earthquake waves under different sites were studied. The new TMD structure is tested to satisfy the NPPs seismic safety requirements, stable reduction efficiency, anti-seismic robust characteristics and adaptive site.
Improvement of J Estimation Schemes Based on Reference Stress for Linear Hardening Behavior
Authors: Gilles Philippe
Published: November 2018

In Elastic-Plastic Fracture Mechanics, several J-estimation schemes are based on the reference stress approach. This approach has been developed initially for creep analyses and later on for elasto-plastic fracture assessments in 1984, then included in the R6 rule. Much later, other methods, based on the reference stress concept, were derived for 3D applications like the Js method introduced in the French RSE-M code in 1997 and the Enhanced Reference Stress (ERS) method in Korea around 2001. However, these developments are based on the J2 deformation plasticity theory and well established for a pure power hardening law. Js and ERS schemes propose some corrections for recorded behavior laws which cannot be fitted by a power law. Nevertheless, their application to materials governed by a bilinear hardening law has been called into question by several studies. One of these, carried out by M. T. Kirk and R. H. Dodds [1, 2] is of great interest since addressing the practical case of a surface cracked plate.
Study on Ultimate State of Filament Winding FRP Pipes Under Bending Force
Authors: Shiogama Yuzo , Kumagai Nobuaki , Ando Yutaka , Kuribayashi Toshiyuki
Published: November 2018

To investigate of ultimate state of filament winding FRP pipe against bending force caused by earthquake, we perform four-point bending test of the FRP pipes with 1.4MPa inner water pressure. Twelve pipes with four different proportions are applied to the test. The test results show that the damaged form and strength depends on the proportion of the pipe. It is considered reasonable to set the allowable bending capacities according to size of the pipes.
Appropriate Damping on Seismic Design Analysis for Inelastic Response Assessment of Piping
Authors: Watakabe Tomoyoshi , Morishita Masaki
Published: November 2018

The current seismic design rule on piping assumes elastic analysis without the effect of response reduction due to plasticity, although some degree of plasticity is allowed in its allowable limits. Damping for the seismic design analysis is conservatively determined depending on the number of supports and thermal insulation conditions. These conservative assumptions lead to large amount of design margin. Based on such recognition, to provide a more rational seismic design method, a new Code Case for seismic design of piping is now under development in the framework of JSME Nuclear Codes and Standards as an alternative rule to the current design rule. The Code Case provides detailed inelastic analysis with using shell or solid FEA models as a more rational method. Simplified analysis with an additional damping taking the response reduction due to plasticity into account is now under consideration to incorporate the convenience in design. In this study, a series of analysis was made to see the adequacy of the simplified inelastic analysis. Design margins contained in the current design analysis method composed of response spectrum analysis and stress factors was quantitatively assessed in the view point of additional damping.
Root Cause and FFS Analysis of a Dent in a 22mm Thick Elliptical Head
Authors: Schreurs Pascal , Kusters Stan
Published: November 2018

This paper describes the failure of a jacketed vessel. The product pressure is 16 barg (inner vessel; D = 2200 mm) and is heated with thermal oil in the jacket (operated at 4barg). The jacket is split up in different zones which can be opened and closed separately. After a shut down, several valves were not opened properly. This resulted in blocking-in of the jacket on the top head of the vessel during the start-up and operation of the vessel. The vessel was heated to the operating temperature (±250°C), causing a pressure increase of the blocked-in thermal oil. The jacket has a wall thickness of 10 mm, and the vessel head has a wall thickness of 22 mm. Because of the pressure increase, failure occurred at a nozzle weld on the inner pressure vessel shell. This resulted in a leakage of thermal oil into the vessel. The jacket itself deformed but did not fail.

Based on a detailed FE analysis, it has been concluded that failure occurred as a result of (local) buckling of the 22mm thick elliptical head (diameter of ±2.200mm). This paper describes the failure that occurred and the assessments performed to determine and validate the root cause of the failure. A level 3 assessment according to ASME VIII div 2 Part 5 (1) was used to determine if the vessel is still safe for operation.
Research and Development of Viscous Fluid Dampers for Improvement of Seismic Resistance of Thermal Power Plants: Part 6 — Influence of Damper Properties on Vibration Control Performance
Authors: Minagawa Keisuke , Aida Kiyoshi , Tanaka Go , Fujita Satoshi
Published: November 2018

Coal-fired thermal power generation became a very important power source in Japan after Great East Japan Earthquake [1]. Therefore improvement of seismic reliability of the coal-fired thermal power plants is required, because occurrence of very large earthquakes is expected in Japan. Boilers of coal-fired power plants are usually suspended from the upper end of support structures in order to allow thermal expansion of the boilers [2], so boilers easily sway during earthquakes. In order to suppress the vibration, stoppers made of steel are generally installed between boilers and their support structures. Although stoppers made of steel are effective for vibration suppression, further countermeasure for earthquakes having long duration and many aftershocks is required. Authors have developed a vibration control damper for coal-fired power plants. The damper is set instead of conventional stopper. Construction of the damper is similar to oil dampers, but inner fluid is viscous fluid. In PVP2017, the basic performance of the proposed damper was presented [3–5]. In this paper, damper properties were adjusted in order to improve vibration control performance of the damper. Influence of damper properties on the performance was investigated by sensitivity analyses. In addition, influence of dispersion of damper properties was also investigated. Long period and long duration earthquake waves were considered in the analyses.
Long-Term Operation of BWR RPV and its Internals
Authors: Cronvall Otso
Published: November 2018

This study concerns the long-term operation (LTO) of a boiling water reactor (BWR) reactor pressure vessel (RPV) and its internals. The main parts of this study are: survey on susceptibility to degradation mechanisms, and computational time limited ageing analyses (TLAAs).

The ageing of nuclear power plants (NPPs) emphasises the need to anticipate the possible degradation mechanisms. The BWR survey on susceptibility to these uses the OL1/OL2 RPVs and significant internals as a pilot project.

It is not necessary to carry out the TLAAs for all components. Some components were excluded from the TLAAs with a screening process. To do this, it was necessary to determine the component specific load induced stresses, strains and temperature distributions as well as cumulative usage factor (CUF) values.

For the screened-in components, the TLAAs covered all significant time dependent degradation mechanisms. These include (but are not limited to):

• irradiation embrittlement,

• fatigue,

• stress corrosion cracking (SCC), and

• irradiation accelerated SCC (IASCC).

For the components that were screened-in, the potential to brittle, ductile or other degradation was determined. Only some of the most significant cases and results are presented. According to the analysis results, the operational lifetime of the OL1/OL2 RPVs and internals can safely be extended from 40 to 60 years.
Repair and FFS of Vacuum Column for Corrosion Under Insulation
Authors: Adusumilli Yeswanth Kumar , Chiluvuri Siva Kumar , Cheta Ayman
Published: November 2018

One of the vacuum column made of Carbon steel (SA 285 Gr. C) was found with severe corrosion under insulation during turnaround inspection. The equipment was in service for the past 46 years. The corrosion was around the full circumference of the column at a location immediately above the stiffener ring. The wall loss was extensive, which mandated a welded full circumferential patch to encapsulate the corroded region. A full circumferential lap patch with reinforcement plug welds was designed as per ASME PCC-2 [2], fabricated and installed at site. During the dye penetrant examination of the patch plate welds, fine cracks were noted at the toe of the fillet welds. A subsequent PAUT (Phased Array Ultrasonic Testing) of patch plate welds, showed that the cracks were in column shell (base material) surface initiating from toe of the fillet weld of the patch and beneath the fillet weld.

The cracks found in first few sections of welds were ground and re-welded with appropriate pre-heating and post-heating. However, some cracks were still observed in base material, although with reduced magnitude compared to previous welding. Despite proper controls in place during the welding, the challenge was, some minor cracks were re-occurring at the base material surface below fillet welds. A multi discipline review was carried out to understand the potential root cause for the cracks, detailed assessment of risks and impact due to the cracks. A risk based approach was followed, in evaluating cracks for acceptance based on API 579-1/ASME FFS-1 [1], for continued service of the column and to minimise the extension of turn around duration. Later, a long-term plan was made to replace the equipment.
Research and Development of Viscous Fluid Dampers for Improvement of Seismic Resistance of Thermal Power Plants: Part 4 — Experimental Study on Environmental Applicability and Durability of Damper
Authors: Tanaka Go , Minagawa Keisuke , Aida Kiyoshi , Fujita Satoshi
Published: November 2018

A purpose of this study is an improvement of seismic proof construction for power plants to supply power stably at an emergency. At present, the most common type of power generation in Japan is thermal. In particular, coal-fire becomes base load power. A proposal of this study is that boiler structure is applied vibration control. The way is that a damper used viscous fluid is set instead of stopper between the boiler and the support structure. However, inside temperature of the boiler structure is higher than the environment of the general because it uses burning of coal and steam. Therefore, this paper shows that the damper has applicability for the environment of the boiler structure.

Then it is necessary for structures to endure earthquake with long duration and long period component in Japan. The 2011 off the Pacific coast of Tohoku Earthquake had the largest energy in history of Japan with them. The damage occurred not only in Tohoku but also in far Tokyo and Osaka. Moreover, it is predicted that large earthquakes with them at the south Pacific coast of Japan occur. This paper shows that the developed damper is effective in earthquake with these characteristics by analyses and component tests.
Long-Term Performance of Elastomer Seals: From Aging Tests to Lifetime Estimations
Authors: Jaunich Matthias , Kömmling Anja , Horn Jutta , Völzke Holger , Wolff Dietmar
Published: November 2018

Elastomers show a high versatility which makes them ideal materials for sealing applications in various fields. Especially under changing application conditions the high recovery potential of this class of material is beneficial to compensate temperature or pressure fluctuation, and geometrical changes resulting from mechanical loads in e.g. accident conditions. Out of these reasons elastomers are also used in containers for low and intermediate level radioactive waste and for spent fuel transportation casks. In casks designed for low and intermediate level waste elastomer seals can act as primary seal responsible for the containment function whereas in spent fuel storage and transportation casks (dual purpose casks (DPC)) elastomer seals are used as auxiliary seals to allow leakage rate measurements of metal barrier seals. An inherent prerequisite for this kind of application is the long time-scale of operation without or with limited possibility of seal replacement. In Germany an interim storage license for DPC’s is typically issued for 40 years, a timeframe which might increase in the future due to challenges of the final repository siting procedure. For low and intermediate level waste, also long time periods are required before final disposal can be achieved. Therefore, the performance of elastomer seals over extended time periods is, as for other applications, of high importance.

A typical approach to ensure long-term functionality is to perform accelerated aging tests to calculate an estimated lifetime by assuming e.g. Arrhenius like equations for the timetemperature relationship. This approach requires a suitable end of life criterion considering the application of interest. This often can represent a challenge on its own.

As BAM is involved in most of the cask licensing procedures and especially responsible for the evaluation of cask-related long-term safety issues we initiated several test programs for investigating the behavior of elastomer seals. Experiments concerning the low temperature performance down to −40 °C and the influence of gamma irradiation have been started first. Currently the thermal aging behavior of elastomer seals, which is the topic of this contribution, is examined.

For our aging investigations we use a broad approach to first determine the property changes in different elastomer materials due to thermo-oxidative aging at elevated temperatures and secondly, we test how the typical methods of lifetime extrapolation can be applied to these results. This approach enables us to detect and exclude undesired side effects which very often influence lifetime estimations. In this contribution, our recent results are extended. The results show that lifetime estimation based on single material properties can be misleading and therefore a combination of several methods is recommended.
An Iterative Method for Solving Static Piping Analysis Including Friction Between Pipes and Support
Authors: Anderegg Martin
Published: November 2018

We present an iterative method to solve static piping analysis including Coulomb friction between pipes and supports. It is known that the most stable method to find the solution of this problem is to look for the correct stiffness to add in the plane orthogonal to the direction of the restraints for the resulting forces to be of correct intensity. The naivest way to pick the stiffnesses at each step is to choose the ones that would give the correct forces intensities if the displacements were correct. It is very effective in term of precision, but sometimes slow in term of execution. The penalty comes from the fact that the stiffness matrix is different at each iteration and thus that it must be factorized again. In this article we propose a way to increase the speed of convergence: selecting a subset of supports among the ones where convergence is the worst, and introducing sub-iterations focusing only on those supports can reduce the number of main iterations. Those sub-iterations can be calculated at a much lesser cost than the main ones by using the generalized Sherman-Morrison formula.

This algorithm was successfully implemented into the piping analysis software PIPESTRESS version 3.9.1 developed by DST Computer Services SA (the version number is temporary, the release date is Q3/Q4 of 2018).