bluuebunny/crossref_metadata_2025 huggingface dataset:
Difference of Strength Evaluation Approach Between for DBE and for BDBE
Authors: Kasahara Naoto , Sato Takuya
Published: October 2017

Preparation for beyond design basis events (BDBE) becomes important as the lessons learned from the Fukushima Daiichi nuclear accident.

The objective of strength evaluation for design basis events (DBE) is a confirmation to prevent structural failure for assumed events.

For BDBE, main objectives are weak point survey, deterministic and probabilistic risk assessment, and planning of countermeasures including potable equipment and accident management.

According to the above objectives, strength evaluation approach have to be different between for DBE and for BDBE.

(1) DBE

Conservative approach to prevent of failure.

Design by analysis concept is basically adopted

Assumption of hypothetical failure modes to prevent actual failure modes

Stress criteria to bond actual strength

Elastic analyses for conservative loading assumption

Design factor to bound uncertainties

(2) BDBE

Best estimation of failure behavior with uncertainties to plan mitigations

Identification of realistic failure modes to identify failure consequences

Criteria by dominant parameters of failure phenomena

Inelastic analyses for realistic loading prediction

Probabilistic evaluation to quantify uncertainties.

Strength evaluation concept has not yet been established for BDBE. It is necessary to discuss from basic philosophy to make sharable concepts.

Adequate criteria is required to meet above concepts. Instead of stress, strain is one of candidate.

New evaluation technics are desired to satisfy above criteria.

This paper indicates the direction of strength evaluation for BDBE with same examples proposals. Its aims is to promote international discussions and to implement new technologies to actual countermeasures against BDBE.
Stress Analysis of Ellipsoidal Head With Heating Spiral
Authors: Shen Jun , Peng Heng , Tang Yanfang , Liu Xuemei , Liu Yinghua
Published: October 2017

The thermal load is one of important design condition that should be considered carefully in engineering practice. In most instances, the heat source is located inside the vessel, which causes a temperature gradient along the thickness, especially when the thickness is large. In this case, secondary stress should be considered and thermal ratcheting should be checked. In this paper, a thin-walled ellipsoidal head with heating spiral was studied. In this structure, temperature is uniformly distributed along the thickness but changes alternately between hot and cold along the meridional direction. This has a significant effect not only on the head itself but also on the nozzle. For the nozzle, its elastic support condition has been changed and then its stress distribution will also be changed. In this paper, several cases have been calculated and some laws are established. Finally, some useful conclusions and suggestions are proposed for engineering design.
Development of a Novel Test Procedure to Investigate the Impact of Strain Gradients on the Fatigue Endurance of Stainless Steel
Authors: Riley Mohammed-Rafi , Davies Catrin M. , Garwood Stephen
Published: October 2017

In recent years, there has been an increasing need for component specific testing in nuclear power plant (NPP) materials. This has arisen from changes in fatigue design criteria outlined within the ASME Boiler Pressure and Vessel and Pipe Code (BPVC). These are primarily derived from low-cycle fatigue (LCF) testing on idealized small-scale specimens. For the case of stainless steel (SS), testing is performed under membrane loading on traditional uniaxial round-bar specimens according to standards such as ASTM E606. Here, failure is defined as a 25% drop in load, that typically corresponds to a 3 mm deep crack. Real NPP components however, rarely experience such membrane loading due to their complex geometry and in-service loading (combined primary and secondary stresses). For the case of an internally-pressurized pipe subjected to thermal transients, due to temperature fluctuations in the coolant, an additional through-wall stress field gradient is present. This results in fatigue crack initiation and propagation occurring into a decreasing stress field, which may be expected to result in longer fatigue lives than within small specimen testing and, hence, a large degree of inherent over-conservatism may exist in the ASME design data.

This paper describes the development of a novel test procedure able to incorporate the effect of a stress gradient within fatigue endurance testing. A bespoke eight-point bend (8PB) setup has been developed that is capable of performing load-, displacement- and strain-controlled LCF tests. A series of trials have been conducted in all three control modes with the material response validated against finite element analysis (FEA). It is anticipated that this testing procedure can provide a better representation of NPP components under fatigue loading conditions, providing results that would be used to remove over-conservatism within the current design criteria.
Experimental Study of Full-Scale Buckling Restrained Brace With Inspection Windows
Authors: Tsai C. S. , Su Hui-Chen , Chiang T. C.
Published: October 2017

The buckling restrained brace (BRB) has been worldwide accepted as a powerful tool to protect structures from earthquake damage. However, the steel core of the traditional BRB is enclosed by the buckling-restraining unit, it is therefore impossible to observe the condition of the steel core during manufacturing and after earthquakes. Presented in this paper is experimental study on a full-scale buckling restrained brace with inspection windows that allow directly observing the condition of the internal components of the BRB, especially for the steel core. Experimental study in deciding the sizes and locations of the inspection windows to inspect the condition of the steel core during testing without influencing the functionality of the full-scale BRB has been conducted to search for a feasible BRB that is economical and convenient for manufacturing and installation as well as meets testing protocols. Test results of the full-scale BRBs under cyclic loadings showed that the mechanical behavior of the full-scale BRB with inspection windows opened on the buckling-restraining unit was stable and that fracture always occurred at the energy dissipation segments after low cycle fatigue tests. The condition of the steel core can be clearly observed through the inspection windows without dismantling the device during the tests. The test results also indicate that the selected inspection windows on the full-scale BRB have little influence on the strength of the device and that an appropriately designed BRB device with inspection windows can be considered as a stable energy dissipation device. A good indicator to decide the necessity of replacement of the BRB device to prepare for next earthquakes has also been proposed in this study.
Applicability of Hollow Cylindrical Specimens to Environmental Assisted Fatigue Tests
Authors: Asada Seiji , Tsutsumi Kazuya , Fukuta Yuichi , Kanasaki Hiroshi
Published: October 2017

When an environmental assisted fatigue (EAF) test is performed, the surface of a specimen has to contact with simulated LWR water. Autoclave equipment with a solid specimen is a commonly used method for EAF testing. It, however, takes time to setup a specimen into the autoclave and also it is necessary to strive to directly measure the displacement of the specimen. Another EAF testing method, which has been utilized by several research institutes, is to use a hollow cylindrical specimen. The hollow cylindrical specimen does not need the autoclave equipment and can be easily assembled to the fatigue test facility. This paper introduces the EAF test using the hollow cylindrical specimen, comparison between fatigue lives by hollow cylindrical specimens and solid specimens and gives some technical notes to use the hollow cylindrical specimen.
Application of Master Curve Approach to Surveillance Test Data for WWER-1000 Reactor Pressure Vessels
Authors: Revka Volodymyr M. , Chyrko Liudmyla I.
Published: October 2017

An important issue in the safety operation of WWER-1000 type reactor is a decrease in fracture toughness for reactor pressure vessel steels due to neutron irradiation. This effect for RPV metal is known as radiation embrittlement. The radiation induced temperature shift of the fracture toughness transition curve is considered as a measure of the embrittlement rate. The Charpy impact and fracture toughness specimens are included in the surveillance program for an assessment of changes in fracture toughness of RPV materials.

The present analysis is based on a large data set which includes mostly experimental results for pre-cracked Charpy specimens from a WWER-1000 RPV surveillance program. A Master curve approach is applied to analyze the surveillance test data with respect to a shape of the fracture toughness transition curve and a scatter of KJC values.

The RPV base and weld metal in unirradiated, thermally aged and irradiated conditions are considered in this study. The maximum shift in a reference temperature T0 due to irradiation is 107 degree Celsius. It is shown that the Master curve, 5 % and 95 % tolerance bounds describe adequately the temperature dependence and the statistical scatter of KJC values for WWER-1000 RPV steels both in unirradiated condition and after irradiation up to design as well as long term operation neutron fluence. Furthermore, a development of the Weibull plots for considered data sets is shown that the Weibull slope is close to the expected one of 4 on average. Finally, a comparison of the reference temperature T0 and a scatter of KJC values derived from the pre-cracked Charpy and 0,5T C(T) specimens of base and weld metal in unirradiated condition is done. The analysis has shown a significant discrepancy between the T0 values derived from the two different types of specimens for both RPV metals.
Deformation Analysis of Dented Pipeline via Surface Interpolation
Authors: Okoloekwe Chike , Kainat Muntaseer , Langer Doug , Hassanien Sherif , Cheng J. J. Roger , Adeeb Samer
Published: October 2017

Advances in the interpolation techniques of discrete data points and its application to monitoring the displacement of physical infrastructure has led to improved analytical strain evaluation procedures. In order to generate a detailed mathematical model of the strain state of a dented pipeline, it is necessary to decompose the deformation data obtained from monitoring devices into the corresponding radial, longitudinal and circumferential components. In this paper, a technique for analytically evaluating the strains in dented pipelines based on the coordinates of the geometric profile of the dent is investigated and the strains predicted from the said method are benchmarked against the strains predicted from a numerical model generated using nonlinear finite element analysis (FEA) and the codified equations for evaluating strains in dented pipes. This novel technique to strain analysis is an application of the principles of shell theory to a deformed pipeline in order to evaluate the components of the displacements in the cylindrical coordinate system. The coordinates of the deformed profile are obtained from the FEA model and interpolated with B-Splines curves equipped with second order continuity. The resulting strain distribution along the thickness of the pipe wall is evaluated analytically by performing derivatives on the spline functions. The good agreement obtained in the strains predicted by our model and FEA indicates a possibility of conducting in-depth strain analysis of thin-walled structures without the need for the rigorous FEA.
Seismic Response Analysis of Flexible Drain System Into External Floating Roof Storage Tanks
Authors: Bernard Gary , Vera Damien , Lim Weng Kheong
Published: October 2017

Floating roofs are commonly used worldwide on top of cylindrical oil storage tanks as a primary means to prevent formation of vapor above stored products into the storage tanks and should provide a safe and efficient storage of products with minimal risk for the environment.

However, aboveground storage reservoirs built in seismic zones are prone to earthquake damage. Extensive research has been done to enhance performance of the floating roof tanks against damage to ground foundations, fixed and floating roof, tank shells as well as adjacent piping. Indeed, the stored oil sloshing in a cylindrical storage tank is known to have caused damage to the tank shell, tank roof and as well to anti-rotation columns.

One of the possible dangers of liquid sloshing is the resultant damage to in-situ roof drain systems within external floating roof tanks. Indeed, roof drain systems are designed for continuous withdrawal of rainwater from external floating roofs, and if damaged, would result in dysfunction of the systems and irreversible discharge of oil products into the containment dyke. In this regard, a reliable roof drain system should have the capability to withstand liquid sloshing effects, and to a certain degree, ensure resistance in events of displacement of the floating roof.

The aim of this document is to use knowledge of flexible pipe technology and industry recognized dynamic analysis software to analyze the effects of earthquakes on the integrity of a flexible drain pipe system. Analysis of liquid sloshing effects on flexible drain pipe systems using dynamic analysis software will be presented and the effects of structural damages such as loss of anti-rotation columns on the integrity of flexible drain pipe systems will be assessed.

In the end, the document will propose recommendations on how industry can further enhance roof drain systems within external floating roof tanks to ensure performance and functionality after occurrence of earthquakes.
Excellent Resistance to Hydrogen Embrittlement of High-Strength Copper-Based Alloy
Authors: Ogawa Yuhei , Yamabe Junichiro , Matsunaga Hisao , Matsuoka Saburo
Published: October 2017

In order to develop more energy-efficient and safer, hydrogen pre-cooling systems destined for use in hydrogen refueling stations, a metallic material must first be researched and found to possess three excellent material properties: high strength, high thermal conductivity and low susceptibility to hydrogen embrittlement (HE).

This study investigated the hydrogen compatibility of a beryllium-copper alloy 25 (UNS-C17200), fabricated by a solution annealing at 1053 K and via subsequent aging treatment at 588 K. After these thermal processes, the tensile strength exceeded 1200 MPa, due to the precipitation of nano-sized CuBe compounds (γ’ phase). Slow strain rate tensile (SSRT) and tension-compression fatigue tests were performed using this material, in addition to fatigue crack growth and fracture toughness tests, in laboratory air and in gaseous hydrogen with a pressure of 115 MPa at room temperature.

After the SSRT test, the material showed no hydrogen-induced degradation of strength or ductility and, surprisingly, there was also no degradation of fatigue resistance or fracture toughness values in high-pressure gaseous hydrogen. Specifically, it was revealed that the material demonstrated an excellent HE resistance, despite having such a high tensile strength.
Hydrogen-Assisted Degradation of High-Strength Stainless Steel With a Newly Developed Aluminum-Based Coating in High-Pressure Hydrogen Gas Environment
Authors: Yamabe Junichiro , Awane Tohru , Takakuwa Osamu , Matsuoka Saburo
Published: October 2017

The paper presents the hydrogen-entry, tensile, and fatigue properties of a precipitation-hardened martensitic stainless steel, JIS-SUS630, with a newly developed coating, whose thickness ranges from 10 to 20 μm. The newly developed coating consists of alumina, aluminum, and ferroaluminum, and has an excellent resistance to hydrogen entry in 100-MPa hydrogen gas at 270°C. The hydrogen entry in the coated specimen occurred under a diffusion-controlled process and the effective hydrogen diffusivity was approximately one thousandth of that of the base steel. Although the hydrogen diffusivity of JIS-SUS630 was two orders of magnitude larger than that of JIS-SUS304, the effective hydrogen diffusivity of the coated JIS-SUS630 was nearly equal to that of the coated SUS304. In our previous study with secondary-mass ion spectroscopy (SIMS), the coating’s excellent resistance to hydrogen entry was attributed to interfacial hydrogen trapping between the aluminum and ferroaluminum layers. The experimental result obtained in this study suggested that the excellent resistance to hydrogen entry demonstrated by the developed coating can be attributed to the reduction in the permeation area induced by the interfacial trapping of hydrogen. The tensile tests of a smooth, round-bar specimen and fatigue tests of a circumferentially notched specimen with exposure to 100-MPa hydrogen gas at 270°C were performed in air at room temperature (RT). The test results showed that the tensile and fatigue properties of the coated specimens were not degraded by hydrogen exposure, whereas those for the non-coated specimens were significantly degraded. Hydrogen-pressure cycle tests of the coated, tubular specimens with an inner notch were also carried out with 95-MPa hydrogen gas at 85°C, demonstrating that the fatigue life of the tubular specimen was improved by the developed coating.
Benchmark Analysis of Ductile Fracture Simulation for Circumferentially Cracked Pipes Subjected to Bending
Authors: Miura Naoki , Kumagai Tomohisa , Kikuchi Masanori , Takahashi Akiyuki , Kim Yun-Jae , Nagashima Toshio , Wada Yoshitaka
Published: October 2017

In this study, some benchmark problems on fracture tests for circumferentially through-wall/surface cracked pipes were provided. The participants predicted the ductile crack propagation behavior by their own approaches, including nucleation, growth, and coalescence of voids simulated by Gurson model, ductile crack propagation using stress modified fracture strain (SMFS) model, J-integral based ductile crack propagation using XFEM, CTOA based ductile crack propagation using FEM, stress triaxiality and plastic strain (STPS) based ductile crack propagation using FEM, and ductile crack propagation using peridynamics. Among them, GTN, CTOA and STPS models were not applied to surface crack problems. Discrepancies between the experimental maximum loads and calculated maximum loads were within 10% in most cases and 25% in the maximum case. Element size dependency of analysis parameters were considered in SMFS and GTN models while those were determined from independent material tests. Gurson model can predict slanting crack propagation directions. XFEM which did not need analysis fitting parameters cannot analyze beyond the peaks of load-LPD curves. Crack propagation directions were given and fixed in both CTOA and STPS models. Parameters in Gurson model and peridynamics were optimized to reproduce load-LPD curve in one of the benchmark problems.
Research and Development of Three Dimensional Seismic Isolation System Utilized Coned-Disc-Springs With Rubber Bearings
Authors: Miyagawa Takayuki , Watakabe Tomoyoshi , Yamamoto Tomohiko , Fukasawa Tsuyoshi , Okamura Shigeki
Published: October 2017

The seismic isolation system consisting of laminated rubber bearings is applied to development of the Sodium-cooled Fast Reactor (SFR) in Japan. While rubber bearings as horizontal isolation system have been expected to be ensured seismic safety margin of components installed in reactor building against horizontal seismic load, vertical isolation systems have been also studied in order to tolerate to the seismic load which has been increased steadily.

In this paper, the three dimensional seismic isolation system by combining coned disc springs with rubber bearings is proposed as a concept which consists of isolation devices with abundant track record. Analytical study for this system results that the rocking motion can be suppressed by itself without any suppression system and that the mitigation of vertical response can be enough for buckling design of the reactor vessel simultaneously. In particular, it is important that the vertical natural frequency of system is within the range of 3Hz to 5Hz. Besides, layout, size and stacks of coned discs in the unit of system are studied in order to obtain suitable for specification to SFR buildings.
Methods for Uncertainty Quantification and Comparison of Weld Residual Stress Measurements and Predictions
Authors: Lewis John R. , Brooks Dusty , Benson Michael L.
Published: October 2017

Weld residual stress (WRS) is a major driver of primary water stress corrosion cracking (PWSCC) in safety critical components of nuclear power plants. Accurate understanding of WRS is thus crucial for reliable prediction of safety performance of component design throughout the life of the plant. However, measurement uncertainty in WRS is significant, driven by the method and the indirect nature in which WRS must be measured. Likewise, model predictions of WRS vary due to uncertainty induced by individual modeling choices. The uncertainty in WRS measurements and modeling predictions is difficult to quantify and complicates the use of WRS measurements in validating WRS predictions for future use in safety evaluations. This paper describes a methodology for quantifying WRS uncertainty that facilitates the comparison of predictions and measurements and informs design safety evaluations.

WRS is considered as a function through the depth of the weld. To quantify its uncertainty, functional data analysis techniques are utilized to account for the two types of variation observed in functional data: phase and amplitude. Phase variability, also known as horizontal variability, describes the variability in the horizontal direction (i.e., through the depth of the weld). Amplitude variability, also known as vertical variability, describes the variation in the vertical direction (i.e., magnitude of stresses). The uncertainty in both components of variability is quantified using statistical models in principal component space. Statistical confidence/tolerance bounds are constructed using statistical bootstrap (i.e., resampling) techniques applied to these models. These bounds offer a succinct quantification of the uncertainty in both the predictions and measurements as well as a method to quantitatively compare the two. Major findings show that the level of uncertainty among measurements is comparable to that among predictions and further experimental work is recommended to inform a validation effort for prediction models.
Analysis of Environmental Fatigue Crack Growth Behavior of Type 347 Stainless Steels Under Simulated PWR Water Conditions
Authors: Hong Seokmin , Min Ki-Deuk , Jeon Soon-Hyeok , Lee Bong-Sang
Published: October 2017

In this study, the fatigue crack growth behavior of Type 347 stainless steel (SS) used in pressurizer surge line in Korea Standard Nuclear Power Plant was analyzed. Environmental fatigue crack growth rates (FCGRs) were evaluated using pre-cracked compact tension (CT) specimens under the various simulated PWR water conditions; different levels of dissolved oxygen (DO) and loading frequencies. FCGRs of 347SSs were accelerated under PWR water conditions. When DO levels increased and frequency decreased, FCGR of 347SS increased. Under the more corrosive environment at crack tip, FCGRs were accelerated more. FCGRs of 347SSs under PWR water condition were compared with reference FCGR curves of stainless steel in ASME code section XI, ASME Code Case N-809, and JSME based on FCGR data of 304SS and 316SS. In this study, FCGRs of 347SS were slightly faster than reference curves in JSME under PWR environment but slower than that in JSME under BWR environment. Compared to reference FCGR curve in ASME Code Case N-809, FCGRs of 347 stainless steels are similar or slightly higher.
Numerical Analysis of Flow-Induced Vibration of Large Diameter Pipe With Short Elbow
Authors: Takaya Shigeru , Fujisaki Tatsuya , Tanaka Masaaki
Published: October 2017

Japan Atomic Energy Agency is now conducting design study and R&D of an advanced loop-type sodium cooled fast reactor. The cooling system is planned to be simplified by employing a two-loop configuration and shortened piping with less elbows than a prototype fast reactor in Japan, Monju, in order to reduce construction costs and enhance economic performance. The design, however, increases flow velocity in the hot-leg piping and induces large flow turbulence around elbows. Therefore, flow-induced vibration (FIV) of a hot-leg piping is one of main concerns in the design. Numerical simulation is a useful method to deal with such a complex phenomenon. We have been developing numerical analysis models of the hot-leg piping using Unsteady Reynolds Averaged Navier-Stokes simulation with Reynolds stress model. In this study, numerical simulation of a 1/3 scaled-model of the hot-leg piping was conducted. The results such as velocity profiles and power spectral densities (PSD) of pressure fluctuations were compared with experiment ones. The simulated PSD of pressure fluctuation at the recirculation region agreed well with the experiment, but it was found some underestimation at other parts, especially in relatively high frequency range. Eigenvalue vibration analysis was also conducted using a finite element method. Then, stress induced by FIV was evaluated using pressure fluctuation data calculated by URANS simulation. The calculated stress generally agrees well the measurement values, which indicates the importance of precise evaluation of the PSD of pressure fluctuation at the recirculation region for evaluation of FIV of the hot-leg piping with a short elbow.
Seismic Test Results of the Main Steam Safety Relief Valve for Japanese Boiling Water Reactor Nuclear Power Plants
Authors: Nishino Koji , Tsutsumi Yoshitaka , Yonekura Kazuyoshi , Kojima Nobuo , Watanabe Yukio , Kumagai Shin
Published: October 2017

The functional requirements of Main Steam Safety Relief Valves (SRVs) provided in Boiling Water Reactor (BWR) nuclear power plants in Japan 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 seismic operability with respect to high acceleration. In addition, from the viewpoint of equipment fragility in seismic PRA also, it is necessary to determine the practical seismic operability limits.

We used a resonant shaking table in the Central Research Institute of the Electric Power Industry (CRIEPI) [1], which is capable of seismic tests at acceleration levels that have been unachievable until now, and in seismic tests carried out on an SRV, we obtained results confirming that validated seismic operability was possible even at response accelerations as high as 20×9.8 m/s2.

The seismic operability results obtained for this SRV will be applied to a fragility analysis of seismic PRA.
Theoretical Analysis of Free Vibrations Based on a New High Order Shell Theory for Cylindrical Shells Conveying Fluid
Authors: Ji Ming , Inaba Kazuaki
Published: October 2017

The natural frequencies of free vibrations for thick cylindrical shells with clamped-clamped ends conveying fluid are investigated. Equations of motion and boundary conditions are derived by Hamilton’s principle based on the new high order shell theory. The hydrodynamic force is derived from the linearized potential flow theory. Besides, fluid pressure acting on the shell wall is gotten by the assumption of non-penetration condition. The out-of-plane and in-plane vibrations are coupled together due to the existence of fluid-solid-interaction (FSI). Under the assumption of harmonic motion, the dispersion relationships are presented. Using the method of frequency sweeping, the natural frequencies of symmetric modes and asymmetric modes corresponding to each flow velocity are found by satisfying the dispersion relationship equations and boundary conditions. Several numerical examples with different flow velocities and thickness are presented compared with previous thin shell theory and FEM results and show reasonable agreement. The effects of thickness are discussed.
Comparison of Prediction Models for Mechanical Properties of Thermally Aged Cast Austenitic Stainless Steels
Authors: Hirota Takatoshi , Ochi Mayumi , Hojo Kiminobu , Nishi Wataru , Hayashi Shotaro
Published: October 2017

The cast austenitic stainless steel (CASS) is used for the primary loop pipes of some PWR plants. It is known that these stainless steels are susceptible to thermal aging during plant operation. This material degradation decreases the fracture toughness (J-R curve) and increases the tensile strength, which affects the possibility of the fracture of the pipes.

The JPOG prediction models for aged CASS materials were developed based on the CASS material test data for PWR plants in Japan, which was presented in ASME PVP2005-71528. The JPOG prediction models consist of the model to predict the true stress-true strain curve and the model to predict the J-resistance parameters, such as the Js at ductile crack initiation (JIc) and at Δa = 6 mm (J6) in terms of the ferrite contents and aging time. In the US and France, similar degradation models were developed using their own databases or internationally combined one. In this work, three prediction models for thermal aging of CASS were compared and benchmark analyses were performed under Japanese PWR plants operating condition.
Key Technology and Application of Visual Inspection of Buried Polyethylene Pipeline
Authors: Wang Shaojun , Tang Xiaoying , Song Pan , Ren Bin , Qian Yaozhou , Zuo Yantian , Du Yannan
Published: October 2017

Responding to non-conductive, non-magnetic material characteristics of polyethylene (PE) pipe, this paper comes up with the ground penetrating radar (GPR) detection for urban PE gas pipeline visualization research in order to solve the problems of positioning difficulty, and to avoid potential safety hazards caused by undefined positioning of PE pipeline, so that it can provide some experience to the application of position detection technology to locate buried polyethylene pipeline. Responding to the special material properties and welding form and based on the analysis of traditional ultrasonic testing for polyethylene butt-fusion joint, this paper comes up with an ultrasonic phased array dynamic focusing and S scanning imaging technology, to make a testing experiment on polyethylene butt-fusion joint. Results of the phased array ultrasonic testing of cracks in polyethylene butt-fusion joints shows that the testing method is feasible, and verifies the buried polyethylene butt-fusion joints engineering. This research would provide experience to the application of ultrasonic phased array technology in buried polyethylene pipeline inspection.
Stress Analysis and Optimization Research of Cladding Titanium-Steel Tube Sheets in Different Tube Patterns
Authors: Wang Ke , Liu Zunchao , Xu Weifeng , Tan Guofeng , Wang Yongqing , Ma Lu
Published: October 2017

Cladding titanium-steel plate is often used in design of pressure vessel. Using large finite element software, models of cladding titanium-steel tube sheets of tubular heat exchangers are established, to investigate the effect of different tube patterns, including triangle tube pattern and square tube pattern on cladding titanium-steel tube sheets. What is more, stress distribution characteristics of cladding titanium-steel tube sheets in different tube patterns are obtained under different tube diameters. Results show that the effect of tube patterns on cladding titanium-steel tube sheets mainly concentrated in tube layout area. Compared with triangular tube pattern, square tube pattern could effectively improve the phenomenon of stress concentration of cladding titanium-steel tube sheet at the connection of base layer and cladding layer, and then improve performance of cladding titanium-steel tube sheet. However, increase of tube diameters makes an adverse effect on performance of cladding titanium-steel tube sheets in both tube patterns. Through reasonable decrease of tube diameter could enhance the performance of cladding titanium-steel tube sheet. Results provide references to study and design heat exchanger with cladding steel tube sheet.
Study on Dynamic Response of Piping System Induced by Waterhammer Considering Support Characteristics
Authors: Okami Atsushi , Kataoka Shunji , Honda Takuro
Published: October 2017

Waterhammer is the phenomenon which occurs due to rapid valve operation or sudden stop of pumps. When the waterhammer occurs, unbalanced pressure between elbows causes transient load on piping system. In the piping design against the waterhammer, it is necessary to evaluate the strength and the displacement of piping system against the transient load, and required to provide adequate piping supports. In the piping design, dynamic analysis and static analysis with DLF (Dynamic Load Factor) are often conducted to consider dynamic effect of the water hammer load. The piping support often regarded as rigid in the piping system analysis, however, because of support characteristic (flexibility, plastic behavior, sliding friction), the dynamic response of piping system changes from analysis result with rigid support. For this reason, support characteristics shall be considered adequately. Nevertheless, effect of the support characteristics on the piping design has not been discussed sufficiently.

In this paper, to clarify the effect of the support characteristics against the waterhammer load, a series of the nonlinear dynamic analyses were conducted. Based on the analysis results, the response spectra and the ductility charts considering the nonlinearities of the piping system were created. the design approach to properly control the displacement of piping system based on the nonlinear response spectra and ductility charts, is proposed, and the dynamic response against waterhammer load in the piping system of LNG loading line is discussed.
Failure Mode Map of Pipes Under Dynamic Loadings
Authors: Bari Md Abdullah Al , Sakemi Ryota , Kasahara Naoto
Published: October 2017

Preparation for beyond design basis events (BDBE) becomes an important issue as the lessons learned from the Fukushima nuclear accident. IAEA proposed the best estimation approach for strength evaluation under BDBE. It is required to identify dominant failure modes for best estimation approach. Ratcheting, collapse and fatigue are the probable failure modes which can occur due to dynamic loadings like the seismic load. The current studies describe an attempt to clarify occurrence conditions of such failure mode as ratcheting and collapse for pipes. Elbow pipe components have been analyzed by using the inelastic finite element method. Gravity load was the primary loads, while the base acceleration of sinusoidal waveform of different frequencies was considered as pseudo secondary load. The results have been put in a nondimensional stress parameter plot similar to the Bree diagram for thermal ratcheting, paying attention to the similarity between thermal load and dynamic load. From above results, authors have proposed the failure mode map which can evaluate the occurrence conditions of ratcheting and collapse failure mode for pipes under dynamic loadings.
A Remediation of Flaws in Stainless Steel Cladding on Hydroprocessing Reactors
Authors: Tahara Takayasu , Yasutomi Akitada , Sakata Kentaro , Sakata Mikihiro
Published: October 2017

Hydroprocessing reactors are made of heavy wall Cr-Mo steels with stainless steel cladding and installed in the most of oil refineries in the world during past half century. After long time operation, they found several material degradation and/or damages due to high pressure and high temperature hydrogen services. This paper presents typical remediation method of flaws in stainless steel cladding of reactors including flaw sizing, FFS assessment and repair procedures.
On a Plastic Limit Loads of Complex-Cracked Pipes With Weld Overlay Using Finite Element Limit Analyses
Authors: Jeon Da-Som , Huh Nam-Su
Published: October 2017

In the present study, the plastic limit loads of the complex-cracked pipes, which have 360° internal surface crack along the circumference of pipe together with partial through-wall crack, are investigated via detailed 3-dimensional (3-D) finite element (FE) limit analyses. In terms of geometry of the complex-cracked pipe, the Alloys 82/182 butt weld that has welds overlay using the Alloys 52/152 for mitigating primary water stress corrosion cracking (PWSCC) in the nuclear pipe is considered.

In the present FE limit analyses on complex-cracked pipes with welds overlay, the effect of strength mismatch between Alloys 82/182 and Alloys 52/152, depth of 360° internal surface crack and length of partial through-wall crack on plastic limit loads of complex-cracked pipes is systematically evaluated. As for loading conditions, axial tension, global bending and internal pressure are employed.

The resulting FE plastic limit loads of complex-cracked pipes with welds overlay are also compared with the existing solutions, and finally the applicability of simple engineering estimate using the single material property based on the weighted average concept instead of using the properties of Alloys 52/152 and Alloys 82/182 to the prediction of the plastic limit loads of complex-cracked pipes with welds overlay is pursued.
The Formulation of Material Characteristics of Austenitic Stainless Steels at Extremely High Temperature
Authors: Shimomura Kenta , Onizawa Takashi , Kato Shoichi , Ando Masanori , Wakai Takashi
Published: October 2017

This paper describes the formulation of material characteristics of austenitic stainless steels at extremely high temperature which meets in some kinds of severe accidents of nuclear power plants. After the severe accident in Fukushima dai-ichi nuclear power plants, it has been supposed to be very important not only to prevent the occurrence of abnormal conditions, i.e. from the first to the third layer safety, but also to prevent the expansion of the accident conditions, i.e. the fourth layer safety[1] [2]. In order to evaluate the structural integrity under the severe accident condition, material characteristics which can be used in the numerical analyses, such as finite element analysis, were required [3] [4]. However, there were no material characteristics applicable to the structural integrity assessment at extremely high temperature. Therefore, a series of tensile and creep tests was performed for austenitic stainless at extremely high temperature which meets in some kinds of severe accidents of nuclear power plants, namely up to 1000 °C. Based on the acquired data from the tests, monotonic stress-strain equation and creep rupture equation applicable to the structural analysis at extremely high temperature, up to 1000 °C were formulated. As a result, these formulae make it possible to conduct the structural integrity assessment using numerical analysis techniques, such as finite element method.
Introduction of Subsurface Proximity Criteria in the World and Stress Intensity Factors for Transformed Surface Flaws
Authors: Hasegawa Kunio , Li Yinsheng , Katsumata Genshichiro , Dulieu Pierre , Lacroix Valéry
Published: October 2017

Net-section stress at the ligament between component free surface and subsurface flaw increases when the ligament distance is short. It can be easily expected that stress intensity factors increase when the subsurface flaw locates near the free surface. To avoid catastrophic failures caused by ligament failure, fitness-for-service (FFS) codes provide flaw-to-surface proximity rules. The proximity rules are used to determine whether the flaws should be treated as subsurface flaws as-is, or transformed to surface flaws. The stress intensity factor for the transformed surface flaw increases furthermore. The increment of the stress intensity factor before and after transformation depends on the location of the subsurface flaw.

Although the concept of the proximity rules are the same, the specific criteria for the rules on transforming subsurface flaws to surface flaws differ amongst FFS codes. Particularly, the criteria are different amongst the same organizations of ASME (American Society of Mechanical Engineers).

The proximity criteria of the FFS codes in the world were introduced in this paper. In addition, the stress intensity factors based on the different criteria used in the ASME Codes are compared.
CFD Simulation of Supercritical LNG Heat Transfer in a Horizontal Tube of an Intermediate Fluid Vaporizer
Authors: Xu Shuangqing , Chen Xuedong , Fan Zhichao
Published: October 2017

A three-dimensional computational fluid dynamics (CFD) model has been established for the simulations of supercritical LNG heat transfer in a horizontal tube of an intermediate fluid vaporizer (IFV). The influences of inlet pressure and mass flux on heat transfer have been studied. The predictive capabilities of different heat transfer coefficient (HTC) correlations, which is vital for the economic and reliable design of an IFV, have been evaluated. The results indicate that the Jackson correlation gives more accurate HTC predictions for supercritical LNG at the relatively small mass flux, with a maximum deviation of 10% and an average deviation of 6%; while for the cases with larger mass flux, a modification to the Jackson-Hall correlation works well. Detailed flow and heat transfer characteristics and buoyancy effect have also been analyzed. The reported findings would provide insight into the supercritical LNG vaporization process and give guidance to the design optimization of an IFV.
Stress Intensity Factor Interaction of Subsurface Flaws Under Notches
Authors: Hasegawa Kunio , Dulieu Pierre , Lacroix Valery
Published: October 2017

If a single subsurface flaw is detected that is close to the component free surface, a flaw-to-surface proximity rule is used to determine whether the flaw should be treated as a subsurface flaw, or transformed to a surface flaw. The transformation from subsurface to surface flaw is adopted as flaw-to-surface proximity rules in all fitness-for-service (FFS) codes. These proximity rules are used under the condition of the component free surface without stress concentration.

On the other hand, subsurface flaws have been found under the notches, such as roots of bolts, toes in welded joints or geometrical discontinuities of components. The stress intensity factors of the subsurface flaws are affected by the stress concentrations caused by the notches. The interaction of stress intensity factor increases with increasing stress concentration factor and decreasing the ligament distance between the tips of the subsurface flaws and the notches for a given notch width. Such subsurface flaws shall be transformed to surface flaws at far distance of the notch tips for conservative evaluations.

This paper shows the interactions of stress intensity factors of subsurface flaws under stress concentration fields. Based on the interaction, a flaw-to-surface proximity criterion for a circular flaw is proposed under the stress concentration field induced by a notch.
Recent Progress on Interpretation of Tensile Ductility Loss for Various Austenitic Stainless Steels With External and Internal Hydrogen
Authors: Takakuwa Osamu , Yamabe Junichiro , Matsunaga Hisao , Furuya Yoshiyuki , Matsuoka Saburo
Published: October 2017

Slow-strain rate tensile (SSRT) tests on various metals having γ-Fe phase; Type 304 and 316L stainless steels, HP160 high strength stainless steel, and A286 Fe-based super alloy were conducted in external hydrogen and with internal hydrogen. The external hydrogen indicates non-charged specimens tested in high-pressure hydrogen-gas environment, whereas the internal hydrogen indicates hydrogen-charged specimens, with uniform distribution of hydrogen, tested in inert gas. The hydrogen distribution was calculated based on the measured hydrogen diffusivity and solubility. The fracture morphologies were observed by scanning electron microscopy (SEM). For Types 304, 316L, and HP160, the relative reduction in area (RRA) of the steels was successfully reproduced by the nickel equivalent, Nieq, showing the higher Nieq, the lager RRA. Furthermore, at a low Nieq, the RRA of the steel with external hydrogen was nearly equal to that with internal hydrogen. In contrast, at a high Nieq, the RRA of the steel with internal hydrogen was slightly degraded by hydrogen, RRA ≈ 0.8, whereas that in external hydrogen was not degraded, RRA ≈ 1. For A286, despite a high Nieq, the RRA of the alloy with internal hydrogen was significantly degraded by hydrogen, RRA ≈ 0.5. The fracture morphologies were categorized into four types: quasi-cleavage fracture associated with hydrogen-assisted surface cracks; ordinary void formation with no hydrogen effect; small-void formation associated with void sheet enhanced by hydrogen; facet formation induced by hydrogen. These categorized morphologies could be interpreted in terms of hydrogen distribution (internal or external hydrogen), austenitic stability (a low or high Nieq), and microstructure (solution or precipitation-hardened treatment).
Seismic Performance Evaluation for Steel-Frame-Structure Considering Member Fracture
Authors: Shiomi Kensuke
Published: October 2017

Through the 2011 Tohoku Earthquake or the 2016 Kumamoto Earthquake, much larger earthquakes are considered recently in the seismic designs of large steel-frame structures. When structures are exposed by these severe ground motions, partial destructions in the structures, such as damage or fracture of members could happen. Especially, the low cycle fatigue of steel structures because of the repeated load from these long-term ground motions is a serious problem. However, current seismic performance evaluation method based on nonlinear dynamic analysis considers only elastic and plastic deformation of each member, excluding the fracture of members. If this member fracture happens during earthquakes, there is considered to be many effects on the seismic performance, like the changes of the vibration property, the dynamic response and the energy absorbance capacity of structures. Therefore, the fracture of members is preferably taken into account in the seismic performance evaluation for these large earthquakes.

This paper proposes the dynamic analysis method for steel-frame structures which can express the member fracture. Dynamic analyses considering and not considering member fracture under the repeated loads supposing the long-term earthquake are conducted to the FEM model of full-scale structure. By comparing each result, the effects of considering member fracture to the seismic performance such as the dynamic response and the energy absorbance capacity are discussed.
Experimental Determination of Elastic and Plastic LLD Rates During Creep Crack Growth Testing
Authors: Tarnowski K. M. , Davies C. M. , Nikbin K. M. , Dean D. W.
Published: October 2017

Elastic and plastic load line displacement (LLD) rates are often ignored when analyzing Creep Crack Growth (CCG) tests due to difficulties in accurately determining their value for complex crack morphologies typical of creep. Instead, the total LLD rate is assumed to be entirely due to creep. This simplistic approach overestimates the crack tip characterizing parameter C* which is non-conservative.

This paper presents a review of the current method of interpreting CCG test data in ASTM E1457 and proposes an improved approach which accounts for the elastic and plastic LLD rates. Estimations of the elastic and plastic LLD rate are obtained from a partial unload immediately after load-up and a full unload, at the end of the test, prior to final failure. Some finite element validation of this method is presented. Implementing this approach will facilitate more realistic CCG laws.