bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on Ultimate Behavior of Base-Isolated Layer in Nuclear Facility for Cliff-Edges Effect
Authors: Imamura Kouhei , Furuya Osamu , Goda Kengo
Published: October 2017

This study evaluates the ultimate behavior of base-isolated layer in nuclear facility in condition with high surface pressure and huge shear strain of laminated type base isolation device as one of Cliff-Edge effects of safety evaluation by experimental and analytical examination. As the first step of the study, the dynamic properties of laminated base isolation devices were investigated from several loading tests, and then analytical model of the device with strong nonlinearity was examined based on the results of loading tests. Besides, the urethane elastomer was applied to the device that has been newly developed as a base isolation material instead of rubber material. This material has unique characteristics compared with rubber material such as a simple and easy molding, an excellent dynamic property in small deformation, an adjustment of mechanical characteristic by material combination design and so on. In this paper, the evaluation of ultimate behavior of urethane isolation device and the validation of analytical method using finite element method are summarized.
Ultrasonic Testing and Photographic Imaging System for Tube to Tubesheet Weld of Heat Exchanger
Authors: Abe Masamitsu , Murakami Joichi , Shinmura Naoto
Published: October 2017

This paper describes non-destructive testing systems that were constructed to inspect tube-to-tubesheet welds of a heat exchanger operating in a chemical plant such as urea products.

A phased array ultrasonic testing system inserts a testing device into the tube, rotates it and scans the tube-to-tubesheet welds, thereby detecting any weld defects that are not only parallel to a tube axis but also in any direction, and displaying the size and location of the defects on a computer screen using system software. These welds have conventionally been inspected by liquid penetrant testing and visual testing as surface inspections during fabrication at shop and periodic inspection at plant site. This new method, however, provides a practical way to the inspection of weld inside.

In addition, in a photographic imaging system, an imaging device is placed on the tube end to take photos of the inner surface of tube and the outer surface of tube including the tube-to-tubesheet weld. These photos are analyzed any suspected damage area, then displaying the location of the area on a computer screen using system software. In the periodic inspections at site, the presence or absence of a local corrosion dent or other damage are determined by visual testing and finger touch, but it is concerned that hundreds of welds will not be covered by these methods sufficiently. Consequently, this new method enables us to eliminate lacks of inspection and the secular change of each weld will be easily grasped with the suitable records.

The above testing systems perform in a short amount of time and are highly reliable methods with inspection records. For this reason, in particular, the application of the new method to a periodic inspection at site is expected to reduce the period until the plant resumes operations, and also to remove any concerns about emergency shutdown of an operating plant due to damages in the tube-to-tubesheet welds.
The Adsorption Study of Hydrogen on Iron and Vanadium
Authors: He Min , Zhang Zaoxiao , Cheng Guangxu
Published: October 2017

Hydrogenation reactor, a typical equipment in petrochemical industry, usually works in tough condition, such as high temperature, high pressure, with hydrogen gas as medium. 2.25Cr-1Mo is widely used as reactor material. However, with the increase of operating condition, a better material is needed. At present, 2.25Cr-1Mo-0.25V is proved having a better mechanical property in high temperature than that of 2.25Cr-1Mo. Hence, it is very important to study the hydrogen impact on 2.25Cr1Mo0.25V. This paper aims to study the relationship between H atom and metal crystal from microscopic view. Based on the first-principles calculation, the convergence analysis of parameters, the adsorption of H atom on Fe, V and their surfaces have been discussed. The results show that the parameter values of simple crystal surface (110) are less than surface (100), such as energy cutoff, k-point sampling, especially the number of slab layers. Tetrahedral-site is the stable site when H atom exists in bbc Fe, V lattice. And quasi three-ford site is the stable status when atomic H absorption on Fe(110) and V(110).
Coupled Vibration Research for Cylinders in Heat Exchanger Based on Noncontact-Measurement and Acoustic Fluid-Solid Interaction Simulations
Authors: Tan Wei , Wu Hao , Yang Zhihai , Li Zhao , Liu Liyan , Zhu Guorui
Published: October 2017

A cylinder array vibrating in a fluid exhibits multiple coupled frequencies and coupled mode shapes. For a square array of four cylinders with a pitch-to-diameter ratio of 1.25, one cylinder was excited. In order to obtain the coupled modes of the whole array without the influence of exciters, a new method named noncontact-measurement image processing system was used in this paper. This system can guarantee the consistency of the frequencies quantificationally. Due to noncontact-measurement, the flow field around cylinder arrays will not be disturbed and can be measured precisely. Experimental results show that if we want to obtain all the coupled mode shapes, the consistency of cylinder frequencies (within 2%) must be insured and the vibrated cylinder should be chosen with larger amplitude in the coupled mode shapes. Distinct coupled frequencies correspond to symmetric mode shapes, while repeated coupled frequencies correspond to asymmetric ones. Besides, the acoustic fluid-solid interaction numerical method was used to calculate the vibration process of multi objects in still water. The numerical simulation results were in good agreement with experimental ones. It is found that for the same number of cylinders, the bandwidth of coupled frequencies increases with the decrease of pitch-to-diameter ratio, and that for the same pitch-to-diameter ratio, the bandwidth of coupled frequencies increases with the increase of the number of cylinders. Detuning of the cylinder frequencies leads to changes of coupled frequencies and coupled mode shapes.
Relative Influence of Soil Stiffness and Elbow Geometry on Buried Piping Thermal Stresses
Authors: Marohl Michael P. H. , Frazee Glenn R. , Musto Thomas M.
Published: October 2017

The design of buried piping systems requires special considerations. Historically, buried piping was evaluated for thermal expansion and contraction using simple hand calculations considering the piping to be fully-constrained by the surrounding soil. With the development of analytical software, more advanced analysis of buried piping is possible considering detailed piping routing and the stiffness of the surrounding soil and of the piping itself (in cases of more flexible piping materials). Typically, the areas of highest thermal stress occur at changes in direction (i.e. elbows, etc.) due to the applied moments, and the relative stress magnitude is influenced by the stiffness of the surrounding soil.

Due to the relatively high coefficient of thermal expansion of polyethylene, stresses in buried piping due to thermal expansion and contraction are of particular note for high density polyethylene (HDPE) piping. This paper examines the relative influence of the analytical representations of a variety of HDPE piping elbow geometries (e.g. mitered elbows, molded elbows, etc.) and corresponding soil restraint. The study demonstrates that total longitudinal stress calculated in a finite element analysis may be reduced using minor to moderate efforts of refinement.
Research and Development of Viscous Fluid Dampers for Improvement of Seismic Resistance of Thermal Power Plants: Part 1 — Fundamental Analysis and Component Test
Authors: Tanaka Go , Minagawa Keisuke , Aida Kiyoshi , Fujita Satoshi
Published: October 2017

In 2011, Great East Japan Earthquake that is the largest earthquake ever observed occurred. The earthquake had large energy, huge tsunami, long duration time and many aftershocks. Devastated area needed retrieval and revival. However, when electric power was lost, the retrieval delayed. It is necessary to improve seismic proof construction for power plants.

In this paper, authors proposed vibration control by adding dampers for coal-fired power plant and developed it. Fundamental analysis and component test of the damper were conducted.

As the analytical results, characteristic of the damper was searched what kind of performance is more effective for the coal-fired power plants. In the component test, actual scaled prototype of the developed damper was produced and its performance was checked by loading test. As the test results, suitable characteristic of the damper was searched by the analysis. Finally, authors proposed two analytical methods of the developed damper.
A Study on the Influence of Sea Water Convective Heat Transfer Coefficient in Design Verification of Subsea HPHT Equipment
Authors: Sepehri Ali , Harbert Stuart , Holberry Dave
Published: October 2017

As HPHT activity continues to grow and well conditions become more severe, more advanced analysis methods are required. Thermal/heat transfer and structural Finite Element Analyses (FEA) play a fundamental role in the design of subsea equipment for HPHT application.

The objective of this study is to evaluate the effect of seawater convective heat transfer coefficient on design verification of a subsea drilling connector in the HPHT environment (bore pressure more than 15,000 psi, and/or bore temperature more than 300°F). The design verification work contains the elastic-plastic assessments including protection against plastic collapse (global), local failure, hydrotest and ratcheting criteria. The fatigue study is also performed per ASME Boiler & Pressure Vessel Code, Section VIII, Div. 3, Article KD-4 in compliance with API 17TR8. The effect of seawater convective heat transfer coefficient on the global, ratcheting and fatigue criteria is studied/presented. Results show that the higher value of heat transfer coefficient (convection) results in more thermal gradients through assembly causing higher stress and plastic strain deformation in the connector components and lower fatigue life.
Experimental Investigation on Condensation in Corrugated Low Finned Tubes in Presence of Noncondensable Gas
Authors: Ren Bin , Tang Xiaoying , Lu Hongliang , Fu Dongliang , Song Pan , Wang Shaojun , Qian Yaozhou , Zuo Yantian
Published: October 2017

The phenomenon of condensation with noncondensable gas widely exists in many industrial processes. In this paper, the effect of noncondensable gas on condensation heat transfer inside corrugated low finned tubes is investigated experimentally. Air is mixed into steam playing the role of noncondensable gas. The effects of gas mixture inlet conditions and condensation tubes structural parameters are investigated. The results show that the influence mechanism inside corrugated low finned tubes is similar with that inside smooth tubes. The heat transfer coefficient decreases as noncondensable gas fraction increases. However, the decreasing rate is gradually reduced. Increasing inlet mass flux could enhance the heat transfer coefficient especially at small heat transfer rate. And the heat transfer coefficient decreases with the increase of inlet pressure. The heat transfer coefficients inside smaller pitches tubes are higher than that inside larger pitches tubes, and the declining rate is also slightly faster. When the noncondensable gas fraction is large enough, the difference of heat transfer coefficients between different enhanced tubes can be ignored. Tube with the largest protrusion height has the highest heat transfer coefficient. And the gap of heat transfer coefficients between different protrusion heights is larger than that between different pitches. This shows that the protrusion heights have greater influence on condensation compared with pitches.
Effects of Partial Cooling on Tightness of Heat Exchanger Girth Flange
Authors: Takahashi Kyohei , Miyashita Toshikazu , Kataoka Shunji , Uno Yoshiaki , Sato Takuya
Published: October 2017

For the girth flange of heat exchangers, the circumferential temperature distribution of shell and connecting flange due to inside fluid will affect tightness of the girth flange, however this effect is not considered in present design codes. It is important to know the key characteristics of flange tightness to minimize the risk of leakage. In past studies, the effects of circumferential temperature distribution on flange tightness were investigated at high temperature operations. The effects of partial cooling on flange tightness might be severer than circumferential high temperature distribution.

In this paper, the effects of partial cooling on flange tightness were studied. The flange tightness was evaluated by wideness of partially cooled region (liquid level) of heat exchanger and gasket recovery characteristics parametrically. Based on these studies, it was concluded that the gasket contact pressure was decreased by the partial cooling of heat exchanger and the effects of the above mentioned factors were summarized quantitatively.
Numerical Simulation of Temperature Field and Residual Stress in Multi-Pass Welds in 2.25Cr-1Mo-0.25V Steel Plate and Comparison With Experimental Measurements
Authors: Qin Mu , Cheng Guangxu , Zhang Zaoxiao , Li Qing , Zhang Jianxiao
Published: October 2017

The 2.25Cr-1Mo-0.25V steels are widely used in the petroleum chemical industry for the manufacturing of pressure vessels. The multi-pass welding is a critical type of fabrication in hydrogenation reactor. However, very complicated residual stresses could be generated during the multi-pass welding process. The presence of residual stresses could have significant influence on the performance of welded product. In the present work, the transient temperature distribution and residual stress distribution in welding of 2.25Cr-1Mo-0.25V steel are analyzed by using numerical method. An uncoupled thermal-mechanical two-dimensional (2-D) FEM is proposed under the ABAQUS environment. The transient temperature distribution and the residual stress distribution during the welding processes are determined through the finite element method. A group of experiments by using the blind-hole method have been conducted to validate the numerical results. The results of 2-D model agree well with the experiment. The result shows that the maximum welding stress generated at heat affected zone (HAZ) both at the top and bottom surface whether to transverse stress or longitudinal stress.
Allowable Flaw Size of Japanese Cast Stainless Steel Pipe Using Probabilistic Fracture Mechanics Method
Authors: Hayashi Shotaro , Ochi Mayumi , Hojo Kiminobu , Yamane Takahisa , Nishi Wataru
Published: October 2017

The cast austenitic stainless steel (CASS) that is used for the primary loop pipes of nuclear power plants is susceptible to thermal ageing during plant operation. The Japanese JSME rules on fitness-for-service (JSME rules on FFS)[1] for nuclear power plants specify the allowable flaw depths. However, some of these allowable flaw sizes are small compared with the smallest flaw sizes, which can be detected by nondestructive testing. ASME Section XI Code Case N-838[2] recently specified the maximum tolerable flaw depths for CASS pipes determined by probabilistic fracture mechanics (PFM). In a similar way, the allowable flaw depths of CASS pipes were calculated by PFM analysis code “PREFACE”[3] which considers uncertainty of the mechanical properties of Japanese PWR CASS materials. In order to confirm the validity of PREFACE, the allowable flaw depths calculated by PREFACE were compared with the maximum tolerable flaw depths in the technical basis of Code Case N-838. As a result, although the J calculation method and the embrittlement prediction model of CASS are different, these were qualitatively consistent. In addition, the sensitivity of ferrite content to the allowable flaw depths was investigated.
Further Validation of the Weighted Stress Intensity Factor Rate (WKR) Method for Stainless Steel Pressurised Water Reactor Fatigue Crack Growth Calculations
Authors: Emslie Julian , Cruchley Sam , Currie Chris , Wright Keith
Published: October 2017

The reference Fatigue Crack Growth (FCG) rate behaviour for austenitic stainless steel in a deaerated Pressurised Water Reactor (PWR) environment is provided in ASME Boiler and Pressure Vessel Code Section XI Code Case N-809. This FCG law is dependent on temperature, R ratio and environment; the environment effect is defined through a load rise time parameter. The basis for the law is contained within a large dataset of testing of simple waveforms carried out by various industry sources.

In a previous paper, PVP2016-63497, it was demonstrated that the use of load rise time as defined in Code Case N-809 did not provide a good characterisation of FCG rate for complex waveforms where the loading rate varies during the fatigue cycle. For waveforms representative of a thermal shock, the method in Code Case N-809 leads to overly conservative predictions of FCG rate. An improved method was postulated: the Weighted Stress Intensity Factor Rate (WKR) method. This method expresses the FCG law in terms of loading rate; a weighting is then applied to the effect of the loading rate based on its position within the fatigue cycle, according to the exponent on load. This method can be used to provide an effective rise time, which may be used in place of the rise time definition given in Code Case N-809. The WKR method was shown to give excellent correlation with test results for a number of complex waveforms.

This paper provides additional data and discussion related to the WKR method. This includes additional simple waveforms with two different loading rates (2-stage waveforms), several additional waveforms which are representative of PWR plant thermal shock loading and 2-stage waveforms at higher R ratios. Final confirmatory tests are also reported which were carried out at different temperatures and using different grades of stainless steel. These data address the gaps identified in PVP2016-63497. Having analysed the total evidence for the WKR method, the authors consider that there is a sufficiently strong basis for the method to be incorporated into calculations using Code Case N-809.

In order to assist in application of the WKR method, a simple worked example is also provided in this paper.
Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 5 — Non-Linear Analytical Models for Thick Rubber Bearing
Authors: Hirotani Tsutomu , Mori Takahiro , Fukasawa Tsuyoshi , Okamura Shigeki , Yamamoto Tomohiko , Watakabe Tomoyoshi
Published: October 2017

Application of seismic isolation system is essential to reduce the seismic force not only for the horizontal direction but also for vertical direction since the component installed to the Sodium-Cooled-Fast-Reactor (SFR) has thin-walled structures to reduce thermal stress. The authors have performed static loading tests using a half-scale thick rubber bearing to investigate ultimate properties include breaking, and confirmed that the thick rubber bearings have sufficient performance compared to the conventional thin rubber bearings.

The present paper describes the evaluation of analytical models for the thick rubber bearing by following two approaches based on the obtained test results.

a) Spring model

Horizontal and vertical spring models, which are employed to the non-linear seismic response analysis, are compiled to examine applicability of conventional analytical model for thin rubber bearing. In addition, the horizontal and vertical spring models are modified, as a suitable non-linear analytical model for the thick rubber bearing. For the horizontal direction, hysteresis rules composed of multiple lines considering slip effect are modified to correspond to the hysteresis characteristics obtained test results. Hysteresis rules under vertical direction composed of multiple lines in consideration of effect on the shear strain due to horizontal seismic response is constructed.

b) 3D FEM model

The prediction methods of break strain for thin rubber bearings as the conventional rubber bearing have been examined, which have been proposed by the authors as 3D finite element analysis in consideration of the hyper elasticity. To improve suitable the above mentioned methods for the corresponding the restoring force characteristics for thick rubber bearing, 3D FEM model containing a higher-order elements was constructed to express the skeleton curve as restoring force characteristics up to the breaking points. The validity of the constructed 3D FEM model was investigated comparing breaking test results under horizontal and vertical direction. Consequently, the analytical results demonstrated that the skeleton curves up to the horizontal and vertical breaking points can express with constructed 3D FEM model. In addition, this paper describes the criteria with respect to the breaking strain by utilizing the analytical results.
Drop Testing of a Container for the Storage, Transport and Disposal of Intermediate Level Waste
Authors: Quercetti Thomas , Müller Karsten , Johnson Mark , Tait Trevor , Tso Chi-Fung , Izatt Conrad
Published: October 2017

Impact tests were performed, as part of a corresponding container’s substantiation, during design development of a shielded container. The container will be used for storage, transport, and disposal of intermediate level waste in the UK.

The mechanical test program comprised a 9m free drop test onto an unyielding target in a container long lid edge down orientation at ambient conditions. Further, a 0,5m free drop test onto a punch target was performed. Here, the container was orientated with the lid downwards in a way that the punch, a mild steel bar, impacts a filter lid.

The test specimen was instrumented with strain gauges and accelerometers for the drop tests. Transient strains at selected points of the inner and outer container walls, at the shielding lid, as well as at the lid bolts were measured during the container’s impact. Furthermore, decelerations of the container body, container lid, and the skip were measured. The complex geometrical changes of the container due to impact were determined by optical 3d-deformation measures using the projected fringes method in combination with multi-image photogrammetry.

This paper summarizes the performance of the drop tests and various drop test results in context with the design development as well as aspects regarding the associated Finite Element (FE) analyses and post-test evaluation.
Theoretical Analysis and Engineering Implications for the High Order Term Solutions of the Mode II Type Creep Crack
Authors: Dai Yanwei , Liu Yinghua , Chao Yuh J.
Published: October 2017

The high order term (HOT) solutions of crack tip field should be taken into account in engineering applications due to their potential influences on the fracture toughness as well as the crack growth rate. Towards this end, the high order asymptotic analysis of mode II crack in a power-law creeping material under the plane strain condition is presented theoretically in this paper. By comparing among the three order term solution, HRR field and finite element calculations, it can be found that the proposed three order term solution is able to characterize the full field of mode II creep crack tip accurately. The high order term solution of mode II creep crack relies on the creep exponent, which is different from that of mode I crack case. There are two independent terms among these three terms of asymptotic solution for mode II creep crack, which indicates that there exists the constraint effect for the plane strain mode II creep crack though the effect of high order term may not be as significant as the mode I crack case. Based on the theoretical analysis, a modified time-dependent failure assessment diagram (TDFAD) for mode II creep crack is proposed by considering the high order term solution.
Earthquake Resistance Assessment of Contaminated Water Storage Tank and its Reinforcement Basic Design at Fukushima
Authors: Morishige Haruo , Fujita Katsuhisa , Yamashiki Yousuke
Published: October 2017

The core melt accidents at Fukushima Daiichi Units 1-2-3 have occurred due to the tsunami of the Great East Japan Earthquake at March 11, 2011. Now a coolant of approximately 100t is injected into each Reactor Vessel (RPV) in order to cool the fuel debris, and a part of the coolant leaks out from the water. The contaminated water is collected, and it is stored in the contaminated water storage tanks more than approximately 1,000 and the total amounts of coolant exceeds 1,000,000 t. Although the contaminated water is purified by ALPS, it is still in high nuclear pollution density. According to the homepage of Nuclear Regulation Authority (NRA) in Japan, the storage tanks have been placed on the concrete bed without any anchor. Tokyo Electric Company (TEPCO) reported to NRA in 2015 that the design acceleration used for the overturning evaluation of the tanks have 0.3G. At the Fukushima Daiichi Power Station in the Great East Japan Earthquake, the maximum horizontal acceleration was 0.6G, the maximum vertical acceleration was 0.326 G at the time of the Great East Japan Earthquake. Even if an earthquake that is a fraction of this earthquake comes back, there is a possibility that this tank will fall over. The temporary special design guideline is adopted. These tanks have already stored the contaminated water for 6 years. However, it is thought that the more long term countermeasures is necessary for preventing the contaminated water from flowing out into the Pacific Ocean when another great earthquake will attack this area in future. In this paper, we propose a drastic structure to add a foundation without causing ground to the present tank.

In the past, the member fastening the steel plate of the upper structure of the tank and the concrete of the lower structure is a foundation bolt, but this time it is a stud welded to the tank side plate. This made it possible to flexibly design and reinforce the foundation itself even after tank installation.
Investigation of Fracture Toughness of Heat Affected Zone of 2.25Cr-1Mo-0.25V Steel Pressure Equipment
Authors: Wu Weijie , Song Yan , Chai Mengyu , Zhang Zaoxiao , Cheng Guangxu
Published: October 2017

The 2.25Cr-1Mo-0.25V steel, which has excellent thermal mechanical properties under high pressure and temperature, is widely applied in the pressure equipment. Previous researches show that crack generated in the Heat Affected Zone (HAZ) is one of the main failure mechanisms for the high pressure equipment. Consequently, this work aims at investigating the fracture behavior of HAZ by fracture toughness test. A set of specimens was manufactured with the welding current of 580 A, then, specimens were tempered at 705 °C for 32 h. Along with the fracture toughness test, the fracture properties (e.g. crack initiation, propagation and fracture) of specimens were monitored by acoustic emission (AE). Comparing the AE amplitude of each specimen, the crack initiation point was verified by the first peak of AE result, and the analysis of deformation work at the initiation crack point has also been carried out to investigate fracture properties and the fracture toughness of HAZ of the 2.25Cr-1Mo-0.25V steel. Then the relationship between deformation work and crack length has been studied, and the fracture toughness of HAZ could be obtained. Analyzing the fracture characteristics of experiment process and fracture toughness of HAZ has a significant guidance for the further applications of 2.25Cr-1Mo-0.25V steel.
Mode I Ductile Crack Growth of CT Specimen Under Large Cyclic Loading
Authors: Hojo Kiminobu , Kawabata Shinichi
Published: October 2017

Ductile crack growth calculation method under excessive cyclic loading in a fitness for service rule has not been established even in Mode I. The authors simulated ductile crack growth behavior of CT specimens under cyclic loading executed in a committee of the Japan Welding Society. Sensitivity of the used stress-strain curves by monotonic or cyclic loading and the effect of the hardening rule were investigated. For evaluation of the crack growth rate under excessive cyclic loading, the parameter ΔJ was applied and compared with the rate of the JSME rules for FFS.
Numerical Analysis of Transient Temperature Field and Thermal Stress on Coke Drum With 1.25Cr-0.5Mo Steel Based on Iterative Algorithm
Authors: Lu Zhibing , Chen Xuedong , Fan Zhichao , Dong Jie , Zhu Jinhua
Published: October 2017

Coke drum is typical industrial equipment which experiences complex thermal and mechanical cyclic load during its operation, and the thermal stress which is produced by the drastic change of temperature is the main cause of the cracking failure of coke drum. This paper aims at coke drum with 1.25Cr–0.5Mo steel, and is based on iterative algorithm. Then we simulate the process of liquid medium climbing the inner surface of coke drum in the stages of oil filling and water quenching with dynamic thermal boundary, and carry out the numerical calculation of transient temperature field of coke drum in main process stages for one operating cycle. After the comparison of simulated temperature values with the measured temperature data at several locations on the outer surface of coke drum, the appropriate equivalent coefficients of convective heat transfer will be obtained. The variation rules of transient temperature field for the key parts of coke drum are discussed. Based on the simulation results of temperature field, the thermal-structure coupling analysis of coke drum is carried out, and the variation characteristics of thermal stress on coke drum are studied later.
A Simplified Calculation Method for the Wall Temperatures of Pressure Vessels With Insulating Layers
Authors: Ji Fang , Deng Guide , Sun Liang , Suo Hongchao , Yang Junwei
Published: October 2017

Wall temperatures are a necessary part of the design conditions for pressure vessels. Thermal analysis by numerical simulation is widely used to compute the wall temperatures and thermal stresses of the pressure vessels, and insulation layers outside the pressure vessels are normally included in numerical models to predict more accurate results. However, modeling and meshing the insulation layers introduces more work to designers and more cost to enterprises. In this paper, a simplified calculation method for the wall temperatures of the pressure vessels with insulating layers is presented. An equivalent convective heat transfer coefficient between the outside walls of the pressure vessels and circumstances is derived by theoretical analysis, which takes into account the thermal resistances of the insulation layers and the convective heat transfer coefficient between them and the circumstances, then it can be used in numerical models of the pressure vessels without the insulation layers to compute the wall temperatures. Results of comparative analysis show that the wall temperatures of the pressure vessels by the simplified calculation method agree very well with those using the numerical simulation with the insulation layer models.
A Homogenisation Method for a FSI Problem: Application to a Tube Bundle Row
Authors: Artini Gianluca , Broc Daniel
Published: October 2017

A research program is ongoing at CEA in the framework of ASTRID project, for developing and validating tools for the analysis of the mechanical dynamic behaviour of Fast Breeder Reactor (FBR) cores. In this context, Fluid Structure Interaction is a recurring problem, especially in case of tube bundles in nuclear reactor cores or steam generators. The large number of elements makes modelling difficult to perform and any direct numerical simulation at whole core scale unachievable. In order to overcome this limitation, we resort to homogenisation techniques which allow to describe the global dynamic behaviour of the whole fluid-structure system. The purpose of this study is to better understand the effects of the spatial variation of the tube displacement field on the whole bundle dynamics. Thanks to multiple scales, a complete development of the problem is conducted. An analysis of the effects of spatial variations of the long scale displacement field on the tube bundle’s dynamics is led. As a first step we consider the homogenisation of Euler linear equations that gives us the possibility to make a thorough assessment of the problem with the extension to follow to Navier-Stokes equations.
On the Critical Boundary Conditions for Rupture of Buckled Steel Pipelines
Authors: Mohajer Rahbari Nima , Cheng J. J. Roger , Adeeb Samer
Published: October 2017

The environmental contamination due to the leakage of energy pipelines is a serious hazard to the public property and safety. Hence, any premature rupture should be dealt with in the design and the operating mode of steel pipes. A large amount of complexity is involved in the soil-pipe interactions that makes it so challenging to discover the physical boundary conditions (BC) applied to the buried pipelines during differential ground movements. Therefore, the most critical boundary conditions of buried pipes should be conceived based on the probable mechanism of soil-pipe interactions and considered in the experimental and analytical simulations of rupture. The focus of the current research is to address the critical boundary conditions that can trigger the rupture of underground wrinkled pipelines whilst being subjected to a monotonic increase of curvature.

Finite element (FE) simulation of a full-scale bending test on a pressurized X70 line pipe specimen conducted at the University of Alberta is implemented. Cumulative fracture criterion coupled with the equivalent plastic strain to fracture for X70 steel grade is fed into the analysis to predict the ductile crack formation in the pipe’s body. The FE model is verified by the experimental data and is used to study the critical soil-pipe interactions that provoke the rupture of buckled steel pipes on the tensile side of the cross-section under increasing bending curvature. The results of this study suggest that the pipelines which are restricted from axial displacements are extremely vulnerable to experience a rupture along their post-buckling loading path. And so are the pipelines in which tensile axial force is developed due to soil-pipe interactions, e.g. pipelines in arctic regions that are installed during the summer time.
Assessment of Powder Metallurgy-Hot Isostatic Pressed Nozzle-to-Safe End Transition Joints
Authors: Sutton Ben , Gandy David
Published: October 2017

Dissimilar metal nozzle-to-safe end welds represent a complex manufacturing operation for nuclear reactor fabrication. Transitioning from a low alloy steel nozzle to corrosion-resistant reactor coolant system piping systems requires weld buttering, an intermediate heat treatment, and a dissimilar metal weld between the nozzle buttering and safe-end. The process can be both time consuming and costly, and often provides difficulties for inspection of welds in the field. Through the use of powder metallurgy and hot isostatic pressing (PM-HIP), a series of transition joint configurations have been evaluated that could reduce the complexity of nozzle-to-safe end fabrication by eliminating fusion welding from the process.

Test coupons of SA508 low alloy steel have been joined via PM-HIP to either 316L SS or 347NG SS using various powder metal interlayer materials (Alloy 82, Nb-modified Alloy 600 (600M), Alloy 690, and 316L SS). The microstructural evolution and mechanical performance of the joints have been evaluated following a post-HIP solution anneal, quench and temper heat treatment. Particular attention was given to evaluating bond-line regions via Charpy V-notch impact testing, tensile testing, microhardness, optical microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Results demonstrate that multiple transition layer configurations are capable of meeting the acceptable tensile and impact energy specifications of the two parent base material substrates. Interface impact toughness and ductility were dependent upon secondary phase precipitation within the diffusion region of the joints and presence of non-metallic inclusions. This assessment demonstrates that acceptable joint performance is achievable through proper material selection and should be considered for DMW applications in the future.
The Effect of Specimen Size for the P91 Steel at Elevated and High Temperatures
Authors: Stratil Ludek , Siska Filip , Hadraba Hynek , Fintova Stanislava , Mrna Tomas , Dlouhy Ivo
Published: October 2017

The contribution aims to evaluate fracture toughness of the P91 steel in the ductile regime. This steel is broadly used for applications for pressure vessels and piping systems. The J–R curves were obtained using 1T, 0.5T and 0.25T CT specimens at 23 °C and using 0.5T and 0.25T CT specimens up to 600 °C. The energy normalization method for the J–R curve determination according to the ASTM E1820 was used. The resistance to crack propagation shows temperature dependence and the dynamic strain ageing effect with minimum values at 400 °C. Both specimen sizes 0.5T and 0.25T give a similar trend of the temperature dependence of fracture toughness. However, the size effect is observed as fracture toughness decreases with the specimen size. The results obtained are compared with the results of other authors pointing the specimen size effect and the temperature dependence of the steel.
Impact Toughness Deficiencies in ASME SA-350 LF2 Flanges
Authors: Thompson R. M. , Baker K. C.
Published: October 2017

Personnel working on a major capital project experienced a significant issue related to the supply of non-conforming ASME SA-350 LF2 low temperature carbon steel (LTCS) weld neck flanges. Flanges were destructively tested and found to have Charpy impact toughness far below minimum values required by the ASME specification. The scope of this issue involved several thousand flanges, and the nature of this non-conformance could have resulted in the unexpected failure while in service. In all cases, mill certificates supplied for the flanges did not indicate any deviation from the ASME specifications. The investigation revealed that industry standards are not adequate to identify and prevent this potential problem, therefore highlighting the need for changes to be made. This paper details the experience and investigation, and includes suggestions for improvement to the ASME specification.
Development of Process Induced Residual Stress During Flow Forming of Tubular 15-5 Martensitic Stainless Steel
Authors: Khayatzadeh Saber , Moturu Shanmukha Rao , Kelleher Joe F. , Rahimi Salah
Published: October 2017

Flow forming is a near net shape process for manufacturing of dimensionally accurate hollow components such as shaft in gas turbines, that is currently at its development stage for aerospace industry. The process has several advantages such as reducing material wastage, extremely fast manufacturing time, and eliminating extra manufacturing processes such as machining. Due to the nature of this complicated cold deformation process, significant magnitude of residual stress is introduced into the component. Understanding the magnitude and distribution of residual stress is essential to tailor the flow forming process to achieve parts within dimensional tolerances and desired mechanical properties. The present research is aiming to explore the generation and evolution of residual stress at various stages of flow forming process in a tubular component made from martensitic 15Cr-5Ni stainless steel, using different techniques of neutron scattering, x-ray diffraction (XRD) and hole-drilling based on electronic speckle pattern interferometry (ESPI).

Residual stress measurements were carried out in preformed and flow formed components at surface, near-surface and in the bulk of components using XRD, ESPI based hole-drilling and neutron diffraction techniques. These measurements were conducted at different levels of reduction in the thickness of the original part (i.e. after 20% and 40%), by applying identical forming parameters for all samples. The XRD results show significant change in hoop and axial residual stress levels with a reduction in the wall thickness. This is more pronounced for the axial component where the average stress switches from relatively high tensile (∼ 450MPa) in the original part to significant compressive stress (∼ −600MPa) in the formed part, after 20% of reduction. The bulk residual stress components measured in the middle of thickness of the parts, using neutron scattering, show a general increase in the magnitude of residual stress by higher level of deformation (i.e. reduction in the wall thickness). The measured bulk stress components through the thickness were tuned to tensile after reducing the wall thickness by 40%. The results of XRD and neutron diffraction stress measurements suggest that the residual stress along the length of the samples (i.e. axial direction) is consistent with ±800 MPa and ±400 MPa after 20% and 40% reduction by forming process, respectively.

The results of ESPI based hole-drilling show tensile hoop residual stress (≈600 MPa) and an abrupt fluctuation (i.e. tension-compressive-tension) in the axial residual stress near the surface of the part following flow forming. The stresses measured by ESPI based hole-drilling are complementary to the results of the XRD on surface and neutron diffraction in the bulk to reconstruct the residual stress profile form the surface through to the bulk.
Error Norm vs. Uncertainty Metric in Assessing Accuracy of the Finite Element Method
Authors: Marcal Pedro V. , Fong Jeffrey T. , Rainsberger Robert , Ma Li
Published: October 2017

In most finite-element-analysis codes, accuracy is achieved through the use of the hexahedron hexa-20 elements (a node at each of the 8 corners and 12 edges of a brick element). Unfortunately, without an additional node in the center of each of the element’s 6 faces, nor in the center of the hexa, the hexa-20 elements are not fully quadratic such that its truncation error remains at h(0), the same as the error of a hexa-8 element formulation.

To achieve an accuracy with a truncation error of h3(0), we need the fully-quadratic hexa-27 formulation. A competitor of the hexa-27 element in the early days was the so-called serendipity cubic hexa-32 solid elements (see Ahmad, Irons, and Zienkiewicz, Int. J. Numer. Methods in Eng., 2:419-451 (1970) [1]). The hexa-32 elements, unfortunately, also suffer from the same lack of accuracy syndrome as the hexa20’s.

In recent work, we have developed methods to test the errors and the rate of convergence in FEA [2,3,4].

In this paper, we propose a new metric for determining the quality of isoparametric elements a priori. Significance of the highly accurate hexa-27 formulation and a comparison of its results with similar solutions using ABAQUS hexa-20 elements, are presented and discussed. Guidelines are proposed for selection of better elements.
Regulatory Perspectives on Fitness for Service Assessments of CANDU Pressure Boundary Components
Authors: Jin John C. , Carroll Blair
Published: October 2017

Major pressure boundary components such as pressure tubes, feeder pipes and steam generators at some Canadian CANDU nuclear power plants are entering periods of extended operation beyond their initially assumed operating life. The Canadian Nuclear Safety Commission (CNSC) has approved their long term operations based on the assurance of fitness for service of those components which was composed of condition assessments and aging management programs carried out and implemented by the Canadian licensees. The condition assessments were conducted to demonstrate that components would be within their design basis for the period of intended long term operation and the aging management program was implemented to ensure that the conditions of the components would be maintained as evaluated in the condition assessments and to monitor if new degradation mechanisms would become active.

This paper presents the CNSC regulatory practice adopted in the course of technical reviews of fitness for service assessments of major pressure boundary components conducted by Canadian nuclear licensees to demonstrate the safe long term operation of major components can be achieved.
Considerations for the Use of Probabilistic Assessments in Regulatory Decision Making Related to Pressure Boundary Component Aging
Authors: Carroll Blair , Jin John C.
Published: October 2017

Within the current Canadian regulatory framework, the structural integrity of pressure boundary components with detected service-induced degradation must be demonstrated using deterministic evaluation techniques. However, Canadian Nuclear Safety Commission staff has recognized that the inherent conservatism in these deterministic assessment approaches may generate overly conservative conclusions when they are applied to assess the impact of postulated service-induced degradation to establish aging management requirements for nuclear power plant pressure boundary components. This may have the unintended effect of reducing the effectiveness of aging management programs by directing resources towards activities that will have minimal benefit on improving plant safety and could result in unnecessary dose to personnel. With this in mind, CNSC staff has accepted the limited use of probabilistic assessments prepared by licensees to support aging management activities for pressure boundary components. These probabilistic assessments form a part of risk-informed decision making strategies intended to reduce excess conservatism that could arise if decisions are based solely on the results of deterministic assessments.

This paper provides an overview of CNSC staff’s experiences with the review and acceptance of licensee submissions incorporating probabilistic assessments of pressure boundary component aging for risk informed decision making.